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Dark field scattering microscopy can create large hyperspectral data sets that contain a wealth of information on the properties and the molecular environment of noble metal nanoparticles.
For a quick screening of samples of microscopic dimensions that contain many different types of plasmonic nanostructures, we propose a multivariate analysis of data sets of thousands to several hundreds of thousands of scattering spectra.
By using non-negative matrix factorization for decomposing the spectra, components are identified that represent individual plasmon resonances and relative contributions of these resonances to particular microscopic focal volumes in the mapping data sets. Using data from silver and gold nanoparticles in the presence of different molecules, including gold nanoparticle-protein agglomerates or silver nanoparticles forming aggregates in the presence of acrylamide, plasmonic properties are observed that differ from those of the original nanoparticles.
For the case of acrylamide, we show that the plasmon resonances of the silver nanoparticles are ideally suited to support surface enhanced Raman scattering (SERS) and the two-photon excited process of surface enhanced hyper Raman scattering (SEHRS). Both vibrational tools give complementary information on the in situ formed polyacrylamide and the molecular composition at the nanoparticle surface.
Enzymatic hydrolysis holds great promise for plastic waste recycling and upcycling.
The interfacial catalysis mode, and the variability of polymer specimen properties under different degradation conditions, add to the complexity and difficulty of understanding polymer cleavage and engineering better biocatalysts.
We present a systemic approach to studying the enzyme-catalyzed surface erosion of poly(ethylene terephthalate) (PET) while monitoring/controlling operating conditions in real time with simultaneous detection of mass loss and changes in viscoelastic behavior.
PET nanofilms placed on water showed a porous morphology and a thicknessdependent glass transition temperature (T-g) between 40 degrees C and 44 degrees C, which is >20 degrees C lower than the T-g of bulk amorphous PET.
Hydrolysis by a dual-enzyme system containing thermostabilized variants of Ideonella sakaiensis PETase and MHETase resulted in a maximum depolymerization of 70% in 1 h at 50 degrees C.
We demonstrate that increased accessible surface area, amorphization, and T-g reduction speed up PET degradation while simultaneously lowering the threshold for degradation-induced crystallization.
Hybrid nanophotonic elements, fabricated by organic and inorganic materials, are going to be key components of modern devices.
Coupled systems of photoemitters with a plasmonic waveguide serve the demand for nanoscopic frequency converters.
However, processes like the degradation of the photoemitters via photobleaching occur and need to be monitored and controlled, to realize future successful devices.
We introduce a hybrid perylene-diimide / silver nanowire as plasmon frequency converter. A versatile method is presented to monitor and analyze the bleaching process. It is based on a time series of photoluminescence images, during the operation of a single converter.
An analytical model is applied on the data and unveils that the photobleaching rate is constant and independent of the operation of the plasmon converter.
Lanthanide based ceria nanomaterials are important practical materials due to the redox properties that are useful in the avenues pertaining to technology and life sciences. Sub 10 nm spherical and highly monodisperse Ce1−xYbxO2−y (0.04 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition, annealed separately at 773 K and 1273 K for 2 hours and characterized. Elemental mapping for Yb3+ doped ceria nanoparticles shows homogeneous distribution of Yb3+ atoms in the ceria with low Yb3+ content annealed at 773 K and 1273 K for 2 hours. However, clusters are observed for 773 K annealed ceria samples with high concentration of Yb3+. These clusters are not detected in 1273 K annealed nanomaterials. Introducing small amounts of Yb3+ ions into the ceria lattice as spectroscopic probes can provide detailed information about the atomic structure and local environments allowing the monitoring of small structural changes, such as clustering. The emission spectra observed at room temperature and at 4 K have a manifold of bands that corresponds to the 2F5/2 → 2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern depending on the sample and the annealing conditions. The deconvolution by PARAFAC analysis yielded luminescence decay kinetics as well as the associated luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high concentration of Yb3+ annealed at the two temperatures showed only one species with lower decay times as compared to the low Yb3+ doped ceria samples.
Photo-iniferter (PI)-RAFT polymerization, the direct activation of chain transfer agents via light, is a fascinating polymerization technique, as it overcomes some restriction of conventional RAFT polymerization.
As such, we elucidated the role of reversible deactivation in this context using a monomer-CTA pair with low chain transfer capabilities.
Tests with varying targeted degrees of polymerization (DP) or monomer concentrations revealed no significant improvement of polymerization control using the PI-process. Control can however be achieved via slow monomer addition, increasing the number of activation/deactivation events per monomer addition.
More importantly, the livingness of the polymerization was found to be extraordinarily high, enabling the straightforward and rapid synthesis of multiblock copolymers with up to 20 blocks and a high number of repeating units per block (DP = 25-100) maintaining an overall excellent definition (M-n = 90 300 g mol(-1), D = 1.29).
This study highlights the enormous potential of PI-RAFT polymerization for the synthesis of polymeric materials.
Mechanism comics as a task in a written exam in organic chemistry for pre-service chemistry teachers
(2022)
In this paper, we describe and evaluate a study on the use of mechanism comics for writing solutions to a task in a written exam for the course "Organic Chemistry I for Pre-Service Chemistry Teachers."
The students had to design a reaction mechanism for a reaction that was unknown to them and write captions explaining every step of their reaction mechanism.
The students' work was evaluated using the method of qualitative content analysis in four rounds by both authors. The majority of the captions were coded as "descriptive" and only a minority as "causal."
This means that the students mostly described "what" happened, but seldom "why" this happened. Implicit electron movement was also described more often than explicit electron movement. The majority of the captions were technically correct. In summary, the students were capable of designing and describing a reaction mechanism for a previously unknown reaction.
The quality of their reasoning could be improved, however. In the new course, the quality of students' mechanistic reasoning and then especially their explanations of "why" mechanistic steps occur will be given much clearer emphasis.
Azobenzene is a prototypical molecular photoswitch, widely used to trigger a variety of transformations at different length scales.
In systems like self-assembled monolayers or micelles, azobenzene chromophores may interact with each other, which gives rise to the emergence of exciton states.
Here, using first-principles calculations, we investigate how conformational disorder (induced, e.g., by thermal fluctuations) affects localization of these states, on an example of an H-type azobenzene tetramer.
We find that conformational disorder leads to (partial) exciton localization on a single-geometry level, whereas ensemble-averaging results in a delocalized picture. The pi pi* and n pi* excitons at high and low temperatures are discussed.
The regioselectivity of two mechanistically distinct alkenylation reactions catalyzed by in situ-formed cationic transition metal complexes was studied using
N-allyl-N-phenylethenesulfonamide as a model compound.
Orthogonal selectivity was observed for the Ru-catalyzed C-H-activating alkenylation with acetanilides, which occurs preferentially at the electron deficient double bond, and for a Pd-catalyzed Heck-type coupling with arene diazonium salts, which occurs preferentially at the more electron rich double bond of the N-allyl substituent.
The quantification and identification of aerosols in industry plays a key role in process monitoring and control and lays the foundation for process automation aspired by the industry 4.0 initiative.
However, measuring particulate matter's mass and number concentrations in harsh environments poses great analytical constraints.
The presented approach comprises a comprehensive set of light-and imaging-based techniques, all contactless, in-line, and real-time. It includes, but is not limited to, stroboscopic imaging, laser-induced breakdown spectroscopy (LIBS) and laser-induced incandescence (LII). Stroboscopic imaging confirmed the particles sphericity and was used to measure the particle number density. A phase-selective LIBS setup with low fluence and 500 Hz repetition rate was used to classify each particle with a single-pulse and in real time. Simultaneously, the created plasma was captured by CCD imaging to determine the detection volume and hit rate of the LIBS setup.
Both data sets combined were converted to a particle number density, which was consistent with the particle number density of the stroboscopic measurements. Furthermore, using a photodiode and microphone in parallel to the LIBS setup allowed for the photoacoustic normalization of the spectral line intensity at the laser repetition rate of 500 Hz.
This was done as a partial photoacoustic normalization method with the cut-off based on the coefficient of variation (CV), reducing it by 25%. Aside from that photodiode and microphone were proven to be valuable event counting with the advantage of the less spatially constricted. A second laser setup was used for laser -induced incandescence (LII) making it possible to classify the particles based on their incandescence tendency. Given its larger probing volume, LII could be employed at very low particle number densities.
With respect to the current literature, this is the first approach of using LII as an in-line, real-time analytical technique for the compositional classification of metal-bearing aerosols.
We report on the triplet sensitization of the intramolecular Photo-Dehydro-Diels-Alder (PDDA) reaction of two diaryl suberates bearing methyl propiolate chromophors. Compared with the non-sensitized irradiation, considerably increased yields could be observed.
Moreover, it is possible to use the more efficient UVA lamps instead of UVB lamps.
Among three investigated sensitizers (xanthone, benzophenone, thioxanthone) xanthone gave the best results.
Low-energy (5-20 eV) electron-induced single and double strand breaks in well-defined DNA sequences
(2022)
Ionizing radiation is used in cancer radiation therapy to effectively damage the DNA of tumors. The main damage is due to generation of highly reactive secondary species such as low-energy electrons (LEEs). The accurate quantification of DNA radiation damage of well-defined DNA target sequences in terms of absolute cross sections for LEE-induced DNA strand breaks is possible by the DNA origami technique; however, to date, it is possible only for DNA single strands. In the present work DNA double strand breaks in the DNA sequence 5 '-d(CAC)4/5 ' d(GTG)4 are compared with DNA single strand breaks in the oligonucleotides 5 '-d(CAC)4 and 5 '-d(GTG)4 upon irradiation with LEEs in the energy range from 5 to 20 eV. A maximum of strand break cross section was found around 7 and 10 eV independent of the DNA sequence, indicating that dissociative electron attachment is the underlying mechanism of strand breakage and confirming previous studies using plasmid DNA.
During the last decades, therapeutical proteins have risen to great significance in the pharmaceutical industry. As non-human proteins that are introduced into the human body cause a distinct immune system reaction that triggers their rapid clearance, most newly approved protein pharmaceuticals are shielded by modification with synthetic polymers to significantly improve their blood circulation time. All such clinically approved protein-polymer conjugates contain polyethylene glycol (PEG) and its conjugation is denoted as PEGylation. However, many patients develop anti-PEG antibodies which cause a rapid clearance of PEGylated molecules upon repeated administration. Therefore, the search for alternative polymers that can replace PEG in therapeutic applications has become important. In addition, although the blood circulation time is significantly prolonged, the therapeutic activity of some conjugates is decreased compared to the unmodified protein. The reason is that these conjugates are formed by the traditional conjugation method that addresses the protein's lysine side chains. As proteins have many solvent exposed lysines, this results in a somewhat uncontrolled attachment of polymer chains, leading to a mixture of regioisomers, with some of them eventually affecting the therapeutic performance.
This thesis investigates a novel method for ligating macromolecules in a site-specific manner, using enzymatic catalysis. Sortase A is used as the enzyme: It is a well-studied transpeptidase which is able to catalyze the intermolecular ligation of two peptides. This process is commonly referred to as sortase-mediated ligation (SML). SML constitutes an equilibrium reaction, which limits product yield. Two previously reported methods to overcome this major limitation were tested with polymers without using an excessive amount of one reactant.
Specific C- or N-terminal peptide sequences (recognition sequence and nucleophile) as part of the protein are required for SML. The complementary peptide was located at the polymer chain end. Grafting-to was used to avoid damaging the protein during polymerization. To be able to investigate all possible combinations (protein-recognition sequence and nucleophile-protein as well as polymer-recognition sequence and nucleophile-polymer) all necessary building blocks were synthesized. Polymerization via reversible deactivation radical polymerization (RDRP) was used to achieve a narrow molecular weight distribution of the polymers, which is required for therapeutic use.
The synthesis of the polymeric building blocks was started by synthesizing the peptide via automated solid-phase peptide synthesis (SPPS) to avoid post-polymerization attachment and to enable easy adaptation of changes in the peptide sequence. To account for the different functionalities (free N- or C-terminus) required for SML, different linker molecules between resin and peptide were used.
To facilitate purification, the chain transfer agent (CTA) for reversible addition-fragmentation chain-transfer (RAFT) polymerization was coupled to the resin-immobilized recognition sequence peptide. The acrylamide and acrylate-based monomers used in this thesis were chosen for their potential to replace PEG.
Following that, surface-initiated (SI) ATRP and RAFT polymerization were attempted, but failed. As a result, the newly developed method of xanthate-supported photo-iniferter (XPI) RAFT polymerization in solution was used successfully to obtain a library of various peptide-polymer conjugates with different chain lengths and narrow molar mass distributions.
After peptide side chain deprotection, these constructs were used first to ligate two polymers via SML, which was successful but revealed a limit in polymer chain length (max. 100 repeat units). When utilizing equimolar amounts of reactants, the use of Ni2+ ions in combination with a histidine after the recognition sequence to remove the cleaved peptide from the equilibrium maximized product formation with conversions of up to 70 %.
Finally, a model protein and a nanobody with promising properties for therapeutical use were biotechnologically modified to contain the peptide sequences required for SML. Using the model protein for C- or N-terminal SML with various polymers did not result in protein-polymer conjugates. The reason is most likely the lack of accessibility of the protein termini to the enzyme. Using the nanobody for C-terminal SML, on the other hand, was successful. However, a similar polymer chain length limit was observed as in polymer-polymer SML. Furthermore, in case of the synthesis of protein-polymer conjugates, it was more effective to shift the SML equilibrium by using an excess of polymer than by employing the Ni2+ ion strategy.
Overall, the experimental data from this work provides a good foundation for future research in this promising field; however, more research is required to fully understand the potential and limitations of using SML for protein-polymer synthesis. In future, the method explored in this dissertation could prove to be a very versatile pathway to obtain therapeutic protein-polymer conjugates that exhibit high activities and long blood circulation times.
In precision agriculture, the estimation of soil parameters via sensors and the creation of nutrient maps are a prerequisite for farmers to take targeted measures such as spatially resolved fertilization. In this work, 68 soil samples uniformly distributed over a field near Bonn are investigated using laser-induced breakdown spectroscopy (LIBS). These investigations include the determination of the total contents of macro- and micronutrients as well as further soil parameters such as soil pH, soil organic matter (SOM) content, and soil texture. The applied LIBS instruments are a handheld and a platform spectrometer, which potentially allows for the single-point measurement and scanning of whole fields, respectively. Their results are compared with a high-resolution lab spectrometer. The prediction of soil parameters was based on multivariate methods. Different feature selection methods and regression methods like PLS, PCR, SVM, Lasso, and Gaussian processes were tested and compared. While good predictions were obtained for Ca, Mg, P, Mn, Cu, and silt content, excellent predictions were obtained for K, Fe, and clay content. The comparison of the three different spectrometers showed that although the lab spectrometer gives the best results, measurements with both field spectrometers also yield good results. This allows for a method transfer to the in-field measurements.
Efficient Removal of Tetracycline and Bisphenol A from Water with a New Hybrid Clay/TiO2 Composite
(2023)
New TiO2 hybrid composites were prepared fromkaolinclay, predried and carbonized biomass, and titanium tetraisopropoxideand explored for tetracycline (TET) and bisphenol A (BPA) removalfrom water. Overall, the removal rate is 84% for TET and 51% for BPA.The maximum adsorption capacities (q (m))are 30 and 23 mg/g for TET and BPA, respectively. These capacitiesare far greater than those obtained for unmodified TiO2. Increasing the ionic strength of the solution does not change theadsorption capacity of the adsorbent. pH changes only slightly changeBPA adsorption, while a pH > 7 significantly reduces the adsorptionof TET on the material. The Brouers-Sotolongo fractal modelbest describes the kinetic data for both TET and BPA adsorption, predictingthat the adsorption process occurs via a complex mechanism involvingvarious forces of attraction. Temkin and Freundlich isotherms, whichbest fit the equilibrium adsorption data for TET and BPA, respectively,suggest that adsorption sites are heterogeneous in nature. Overall,the composite materials are much more effective for TET removal fromaqueous solution than for BPA. This phenomenon is assigned to a differencein the TET/adsorbent interactions vs the BPA/adsorbent interactions:the decisive factor appears to be favorable electrostatic interactionsfor TET yielding a more effective TET removal.
Graphene is well-knownfor its unique combination of electricaland mechanical properties. However, its vanishing band gap limitsthe use of graphene in microelectronics. Covalent functionalizationof graphene has been a common approach to address this critical issueand introduce a band gap. In this Article, we systematically analyzethe functionalization of single-layer graphene (SLG) and bilayer graphene(BLG) with methyl (CH3) using periodic density functionaltheory (DFT) at the PBE+D3 level of theory. We also include a comparisonof methylated single-layer and bilayer graphene, as well as a discussionof different methylation options (radicalic, cationic, and anionic).For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e.,the fully methylated analogue of graphane) are considered. We findthat up to a coverage theta of 1/2, graphene readily accepts CH3, with neighbor CH3 groups preferring trans positions. Above theta = 1/2, the tendency to accept further CH3 weakens and the lattice constant increases. The band gapbehaves less regularly, but overall it increases with increasing methylcoverage. Thus, methylated graphene shows potential for developingband gap-tuned microelectronics devices and may offer further functionalizationoptions. To guide in the interpretation of methylation experiments,vibrational signatures of various species are characterized by normal-modeanalysis (NMA), their vibrational density of states (VDOS), and infrared(IR) spectra, the latter two are obtained from ab initio moleculardynamics (AIMD) in combination with a velocity-velocity autocorrelationfunction (VVAF) approach.
Geometry, 11B, 13C chemical shifts and the spatial magnetic properties (Through-Space NMR Shieldings -TSNMRS) of both cations and anions of boron-trapped N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) and of the corresponding diborane/diborene/diboryne dis-carbene adducts have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept; the TSNMRS results are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The ICSS of the TSNMRS (actually the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the present multiple bond character of the Carbene-Boron bond in the trapped NHCs and CAACs. Results are confirmed by bond length and 11B/13C chemical shift variations. Thus the partial multiple bond character of the Carbene-Boron bond cannot be expressed by the arrow of weak, much longer dative bonds and should be omitted as in other covalent lone pair-it or triel bonds. & COPY; 2023 Elsevier Ltd. All rights reserved.
High-solid-content polystyrene and polyvinyl acetate dispersions of polymer particles with a 50 nm to 500 nm mean particle diameter and 12-55% (w/w) solid content have been produced via emulsion polymerization and characterized regarding their optical and physical properties. Both systems have been analyzed with common particle-size-measuring techniques like dynamic light scattering (DLS) and static light scattering (SLS) and compared to inline particle size distribution (PSD) measurements via photon density wave (PDW) spectroscopy in undiluted samples. It is shown that particle size measurements of undiluted polystyrene dispersions are in good agreement between analysis methods. However, for polyvinyl acetate particles, size determination is challenging due to bound water in the produced polymer. For the first time, water-swelling factors were determined via an iterative approach of PDW spectroscopy error (X-2) minimization. It is shown that water-swollen particles can be analyzed in high-solid-content solutions and their physical properties can be assumed to determine the refractive index, density, and volume fraction in dispersion. It was found that assumed water swelling improved the reduced scattering coefficient fit by PDW spectroscopy by up to ten times and particle size determination was refined and enabled. Particle size analysis of the water-swollen particles agreed well with offline-based state-of-the-art techniques.
In recent years, due to its great promise in boosting the energy density of lithium batteries for future energy storage, research on the Li metal anode, as an alternative to the graphite anode in Li-ion batteries, has gained significant momentum. However, the practical use of Li metal anodes has been plagued by unstable Li (re)deposition and poor cyclability. Although tremendous efforts have been devoted to the stabilization of Li metal anodes, the mechanisms of electrochemical (re-)deposition/dissolution of Li and solid-electrolyte-interphase (SEI) formation remain elusive. This article highlights the recent mechanistic understandings and observations of Li deposition/dissolution and SEI formation achieved from advanced characterization techniques and simulation methods, and discusses major limitations and open questions in these processes. In particular, the authors provide their perspectives on advanced and emerging/potential methods for obtaining new insights into these questions. In addition, they give an outlook into cutting-edge interdisciplinary research topics for Li metal anodes. It pushes beyond the current knowledge and is expected to accelerate development toward a more in-depth and comprehensive understanding, in order to guide future research on Li metal anodes toward practical application.
Die vorliegende Arbeit thematisiert die Synthese und die Polymerisation von Monomeren auf der Basis nachwachsender Rohstoffe wie zum Beispiel in Gewürzen und ätherischen Ölen enthaltenen kommerziell verfügbaren Phenylpropanoiden (Eugenol, Isoeugenol, Zimtalkohol, Anethol und Estragol) und des Terpenoids Myrtenol sowie ausgehend von der Rinde einer Birke (Betula pendula) und der Korkeiche (Quercus suber). Ausgewählte Phenylpropanoide (Eugenol, Isoeugenol und Zimtalkohol) und das Terpenoid Myrtenol wurden zunächst in den jeweiligen Laurylester überführt und anschließend das olefinische Strukturelement epoxidiert, wobei 4 neue (2-Methoxy-4-(oxiran-2-ylmethyl)phenyldodecanoat, 2-Methoxy-4-(3-methyl-oxiran-2-yl)phenyldodecanoat, (3-Phenyloxiran-2-yl)methyldodecanoat, (7,7-Dimethyl-3-oxatricyclo[4.1.1.02,4]octan-2-yl)methyldodecanoat) und 2 bereits bekannte monofunktionelle Epoxide (2-(4-Methoxybenzyl)oxiran und 2-(4-Methoxyphenyl)-3-methyloxiran) erhalten wurden, die mittels 1H-NMR-, 13C-NMR- und FT-IR-Spektroskopie sowie mit DSC untersucht wurden. Die Photo-DSC Untersuchung der Epoxidmonomere in einer kationischen Photopolymerisation bei 40 °C ergab die maximale Polymerisationsgeschwindigkeit (Rpmax: 0,005 s-1 bis 0,038 s-1) sowie die Zeit (tmax: 13 s bis 26 s) bis zum Erreichen des Rpmax-Wertes und führte zu flüssigen Oligomeren, deren zahlenmittlerer Polymerisationsgrad mit 3 bis 6 mittels GPC bestimmt wurde. Die Umsetzung von 2-Methoxy-4-(oxiran-2-ylmethyl)phenyldodecanoat mit Methacrylsäure ergab ein Isomerengemisch (2-Methoxy-4-(2-hydroxy-3-(methacryloyloxy)propyl)phenyldodecanoat und 2-Methoxy-4-(2-(methacryl-oyloxy)-3-hydroxypropyl)phenyldodecanoat), das mittels Photo-DSC in einer freien radikalischen Photopolymerisation untersucht wurde (Rpmax: 0,105 s-1 und tmax: 5 s), die zu festen in Chloroform unlöslichen Polymeren führte.
Aus Korkpulver und gemahlener Birkenrinde wurden selektiv 2 kristalline ω-Hydroxyfettsäuren (9,10-Epoxy-18-hydroxyoctadecansäure und 22-Hydroxydocosansäure) isoliert. Die kationische Photopolymerisation der 9,10-Epoxy-18-hydroxyoctadecansäure ergab einen nahezu farblosen transparenten und bei Raumtemperatur elastischen Film, welcher ein Anwendungspotential für Oberflächenbeschichtungen hat. Aus der Reaktion von 9,10-Epoxy-18-hydroxyoctadecansäure mit Methacrylsäure wurde ein bei Raumtemperatur flüssiges Gemisch aus zwei Konstitutionsisomeren (9,18-Dihydroxy-10-(methacryloyloxy)octadecansäure und 9-(Methacryloyloxy)-10,18-dihydroxyoctadecansäure) erhalten (Tg: -60 °C). Die radikalische Photopolymerisation dieser Konstitutionsisomere wurde ebenfalls mittels Photo-DSC untersucht (Rpmax: 0,098 s-1 und tmax: 3,8 s). Die Reaktion von 22-Hydroxydocosansäure mit Methacryloylchlorid ergab die kristalline 22-(Methacryloyloxy)docosansäure, welche ebenfalls in einer radikalischen Photopolymerisation mittels Photo-DSC untersucht wurde (Rpmax: 0,023 s-1 und tmax: 9,6 s).
Die mittels AIBN in Dimethylsulfoxid initiierte Homopolymerisation der 22-(Methacryloyloxy)docosansäure und der Isomerengemische bestehend aus 2-Methoxy-4-(2-hydroxy-3-(methacryloyloxy)propyl)phenyldodecanoat und 2-Methoxy-4-(2-(methacryl-oyloxy)-3-hydroxypropyl)phenyldodecanoat sowie aus 9,18-Dihydroxy-10-(methacryloy-loxy)octadecansäure und 9-(Methacryloyloxy)-10,18-dihydroxyoctadecansäure ergab feste lösliche Polymere, die mittels 1H-NMR- und FT-IR-Spektroskopie, GPC (Poly(2-methoxy-4-(2-hydroxy-3-(methacryloyloxy)propyl)phenyldodecanoat / 2-methoxy-4-(2-(methacryloyloxy)-3-hydroxypropyl)phenyldodecanoat): Pn = 94) und DSC (Poly(2-methoxy-4-(2-hydroxy-3-(methacryloyloxy)propyl)phenyldodecanoat / 2-methoxy-4-(2-(methacryloyloxy)-3-hydroxypropyl)phenyldodecanoat): Tg: 52 °C; Poly(9,18-dihydroxy-10-(methacryloyloxy)-octadecansäure / 9-(methacryloyloxy)-10,18-dihydroxyoctadecansäure): Tg: 10 °C; Poly(22-(methacryloyloxy)docosansäure): Tm: 74,1 °C, wobei der Schmelzpunkt mit dem des Photopolymers (Tm = 76,8 °C) vergleichbar ist) charakterisiert wurden.
Das bereits bekannte Monomer 4-(4-Methacryloyloxyphenyl)butan-2-on wurde ausgehend von 4-(4-Hydroxyphenyl)butan-2-on hergestellt, welches aus Birkenrinde gewonnen werden kann, und unter identischen Bedingungen für einen Vergleich mit den neuen Monomeren polymerisiert. Die freie radikalische Polymerisation führte zu Poly(4-(4-methacryloyloxyphenyl)butan-2-on) (Pn: 214 und Tg: 83 °C). Neben der Homopolymerisation wurde eine statistische Copolymerisation des Isomerengemisches 2-Methoxy-4-(2-hydroxy-3-(methacryl-oyloxy)propyl)phenyldodecanoat / 2-Methoxy-4-(2-(methacryloyloxy)-3-hydroxypropyl)-phenyldodecanoat mit 4-(4-Methacryloyloxyphenyl)butan-2-on untersucht, wobei ein äquimolarer Einsatz der Ausgangsmonomere zu einem Anstieg der Ausbeute, der Molmassenverteilung und der Dispersität des Copolymers (Tg: 44 °C) führte. Die unter Verwendung von Diethylcarbonat als „grünes“ Lösungsmittel mittels AIBN initiierten freien radikalischen Homopolymerisationen von 4-(4-Methacryloyloxyphenyl)butan-2-on und von Laurylmethacrylat ergaben vergleichbare Polymerisationsgrade der Homopolymere (Pn: 150), welche jedoch aufgrund ihrer Strukturunterschiede deutlich unterschiedliche Glasübergangstemperaturen hatten (Poly(4-(4-methacryloyloxyphenyl)butan-2-on): Tg: 70 °C, Poly(laurylmethacrylat) Tg: -49 °C. Eine statistische Copolymerisation äquimolarer Stoffmengen der beiden Monomere in Diethylcarbonat führte bei einer Polymerisationszeit von 60 Minuten zu einem leicht bevorzugten Einbau des 4-(4-Methacryloyloxyphenyl)butan-2-on in das Copolymer (Tg: 17 °C). Copolymerisationsdiagramme für die freien radikalischen Copolymerisationen von 4-(4-Methacryloyloxyphenyl)butan-2-on mit n-Butylmethacrylat beziehungsweise 2-(Dimethylamino)ethylmethacrylat (t: 20 min bis 60 min; Molenbrüche (X) für 4-(4-Methacryloyloxyphenyl)butan-2-on: 0,2; 0,4; 0,6 und 0,8) zeigten ein nahezu ideales azeotropes Copolymerisationsverhalten, obwohl ein leicht bevorzugter Einbau von 4-(4-Methacryloyloxyphenyl)butan-2-on in das jeweilige Copolymer beobachtet wurde. Dabei korreliert ein Anstieg der Ausbeute und der Glasübergangstemperatur der erhaltenen Copolymere mit einem zunehmenden Gehalt an 4-(4-Methacryloyloxyphenyl)butan-2-on im Reaktionsgemisch. Die unter Einsatz der modifizierten Gibbs-DiMarzio-Gleichung berechneten Glasübergangstemperaturen der Copolymere stimmten mit den gemessenen Werten gut überein. Das ist eine gute Ausgangsbasis für die Bestimmung der Glasübergangstemperatur eines Copolymers mit einer beliebigen Zusammensetzung.
Self-assembly of plasmonic nanoantenna-waveguide structures for subdiffractional chiral sensing
(2021)
Spin-momentum locking is a peculiar effect in the near-field of guided optical or plasmonic modes. It can be utilized to map the spinning or handedness of electromagnetic fields onto the propagation direction. This motivates a method to probe the circular dichroism of an illuminated chiral object. In this work, we demonstrate local, subdiffraction limited chiral coupling of light and propagating surface plasmon polaritons in a self-assembled system of a gold nanoantenna and a silver nanowire. A thin silica shell around the nanowire provides precise distance control and also serves as a host for fluorescent molecules, which indicate the direction of plasmon propagation. We characterize our nanoantenna-nanowire systems comprehensively through correlated electron microscopy, energy-dispersive X-ray spectroscopy, dark-field, and fluorescence imaging. Three-dimensional numerical simulations support the experimental findings. Besides our measurement of far-field polarization, we estimate sensing capabilities and derive not only a sensitivity of 1 mdeg for the ellipticity of the light field, but also find 10(3) deg cm(2)/dmol for the circular dichroism of an analyte locally introduced in the hot spot of the antenna-wire system. Thorough modeling of a prototypical design predicts on-chip sensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffraction limit.
Herein, the concept of constructing binder- and carbon additive-free organosulfur cathode was proved based on thiol-containing conducting polymer poly(4-(thiophene-3-yl) benzenethiol) (PTBT). The PTBT featured the polythiophene-structure main chain as a highly conducting framework and the benzenethiol side chain to copolymerize with sulfur and form a crosslinked organosulfur polymer (namely S/PTBT). Meanwhile, it could be in-situ deposited on the current collector by electro-polymerization, making it a binder-free and free-standing cathode for Li-S batteries. The S/PTBT cathode exhibited a reversible capacity of around 870 mAh g(-1) at 0.1 C and improved cycling performance compared to the physically mixed cathode (namely S&PTBT). This multifunction cathode eliminated the influence of the additives (carbon/binder), making it suitable to be applied as a model electrode for operando analysis. Operando X-ray imaging revealed the remarkable effect in the suppression of polysulfides shuttle via introducing covalent bonds, paving the way for the study of the intrinsic mechanisms in Li-S batteries.
In vitro thrombogenicity test systems require co-cultivation of endothelial cells and platelets under blood flow-like conditions. Here, a commercially available perfusion system is explored using plasma-treated cyclic olefin copolymer (COC) as a substrate for the endothelial cell layer. COC was characterized prior to endothelialization and co-cultivation with platelets under static or flow conditions. COC exhibits a low roughness and a moderate hydrophilicity. Flow promoted endothelial cell growth and prevented platelet adherence. These findings show the suitability of COC as substrate and the importance of blood flow-like conditions for the assessment of the thrombogenic risk of drugs or cardiovascular implant materials.
Recent advances in organic solar cell performance have been mainly driven forward by combining high-performance p-type donor-acceptor copolymers (e.g.PM6) and non-fullerene small molecule acceptors (e.g.Y6) as bulk-heterojunction layers. A general observation in such devices is that the device performance, e.g., the open-circuit voltage, is strongly dependent on the processing solvent. While the morphology is a typically named key parameter, the energetics of donor-acceptor blends are equally important, but less straightforward to access in the active multicomponent layer. Here, we propose to use spectral onsets during electrochemical cycling in a systematic spectroelectrochemical study of blend films to access the redox behavior and the frontier orbital energy levels of the individual compounds. Our study reveals that the highest occupied molecular orbital offset (Delta E-HOMO) in PM6:Y6 blends is similar to 0.3 eV, which is comparable to the binding energy of Y6 excitons and therefore implies a nearly zero driving force for the dissociation of Y6 excitons. Switching the PM6 orientation in the blend films from face-on to edge-on in bulk has only a minor influence on the positions of the energy levels, but shows significant differences in the open circuit voltage of the device. We explain this phenomenon by the different interfacial molecular orientations, which are known to affect the non-radiative decay rate of the charge-transfer state. We compare our results to ultraviolet photoelectron spectroscopy data, which shows distinct differences in the HOMO offsets in the PM6:Y6 blend compared to neat films. This highlights the necessity to measure the energy levels of the individual compounds in device-relevant blend films.
Structure, mechanical properties and degradation behavior of electrospun PEEU fiber meshes and films
(2021)
The capability of a degradable implant to provide mechanical support depends on its degradation behavior. Hydrolytic degradation was studied for a polyesteretherurethane (PEEU70), which consists of poly(p-dioxanone) (PPDO) and poly(epsilon-caprolactone) (PCL) segments with a weight ratio of 70:30 linked by diurethane junction units. PEEU70 samples prepared in the form of meshes with average fiber diameters of 1.5 mu m (mesh1.5) and 1.2 mu m (mesh1.2), and films were sterilized and incubated in PBS at 37 degrees C with 5 vol% CO2 supply for 1 to 6 weeks. Degradation features, such as cracks or wrinkles, became apparent from week 4 for all samples. Mass loss was found to be 11 wt%, 6 wt%, and 4 wt% for mesh1.2, mesh1.5, and films at week 6. The elongation at break decreased to under 20% in two weeks for mesh1.2. In case of the other two samples, this level of degradation was achieved after 4 weeks. The weight average molecular weight of both PEEU70 mesh and film samples decreased to below 30 kg/mol when elongation at break dropped below 20%. The time period of sustained mechanical stability of PEEU70-based meshes depends on the fiber diameter and molecular weight.
Plasmon-driven dehalogenation of brominated purines has been recently explored as a model system to understand fundamental aspects of plasmon-assisted chemical reactions. Here, it is shown that divalent Ca2+ ions strongly bridge the adsorption of bromoadenine (Br-Ade) to Ag surfaces.
Such ion-mediated binding increases the molecule's adsorption energy leading to an overlap of the metal energy states and the molecular states, enabling the chemical interface damping (CID) of the plasmon modes of the Ag nanostructures (i.e., direct electron transfer from the metal to Br-Ade).
Consequently, the conversion of Br-Ade to adenine almost doubles following the addition of Ca2+.
These experimental results, supported by theoretical calculations of the local density of states of the Ag/Br-Ade complex, indicate a change of the charge transfer pathway driving the dehalogenation reaction, from Landau damping (in the lack of Ca2+ ions) to CID (after the addition of Ca2+).
The results show that the surface dynamics of chemical species (including water molecules) play an essential role in charge transfer at plasmonic interfaces and cannot be ignored. It is envisioned that these results will help in designing more efficient nanoreactors, harnessing the full potential of plasmon-assisted chemistry.
Informatische Bildung spielt eine immer zentralere Rolle in der Bildung einer Gesellschaft des 21. Jahrhunderts. Für den Chemieunterricht ergeben sich daraus zwei Aspekte: Einerseits können Konzepte der informatischen Bildung dabei helfen, chemie- und naturwissenschaftsspezifische Denk- und Arbeitsweisen zu fördern. Andererseits kann der Chemieunterricht einen Beitrag für die informatische Bildung leisten. Dieser Artikel geht auf beide Aspekte ein und versucht die gegenseitigen Vorteile der informatischen Bildung und der naturwissenschaftlichen Bildung im Chemieunterricht darzustellen.
In this study, the kinetics of the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been intensively investigated, as molecular doping is known to play a crucial role in organic electronic devices. Based on the results obtained from UV-visible (vis)-near-infrared (NIR) absorption spectroscopy, cryogenic transmission electron microscopy, scanning nanobeam electron diffraction, and electron energy loss spectroscopy, a two-step interaction kinetics has been proposed for the Ag NPs and F(4)TCNQ molecules, which includes the first step of electron transfer from Ag NPs to F(4)TCNQ indicated by the ionization of F(4)TCNQ and the second step of the formation of a Ag-F(4)TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F(4)TCNQ molecules on the interaction between Ag NPs and F(4)TCNQ molecules in an organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs manifests that the charge transfer at the surface between Ag NPs and F(4)TCNQ molecules is prohibited by a silica layer of 18 nm.
Sulfated biomolecules are known to influence numerous biological processes in all living organisms. Particularly, they contribute to prevent and inhibit the hypercoagulation condition. The failure of polymeric implants and blood contacting devices is often related to hypercoagulation and microbial contamination. Here, bioactive sulfated biomacromolecules are mimicked by sulfation of poly(glycerol glycidyl ether) (polyGGE) films. Autoclaving, gamma-ray irradiation and ethylene oxide (EtO) gas sterilization techniques were applied to functionalized materials. The sulfate group density and hydrophilicity of sulfated polymers were decreased while chain mobility and thermal degradation were enhanced post autoclaving when compared to those after EtO sterilization. These results suggest that a quality control after sterilization is mandatory to ensure the amount and functionality of functionalized groups are retained.
This thesis presents a comprehensive exploration of the application of DNA origami nanofork antennas (DONAs) in the field of spectroscopy, with a particular focus on the structural analysis of Cytochrome C (CytC) at the single-molecule level. The research encapsulates the design, optimization, and application of DONAs in enhancing the sensitivity and specificity of Raman spectroscopy, thereby offering new insights into protein structures and interactions.
The initial phase of the study involved the meticulous optimization of DNA origami structures. This process was pivotal in developing nanoscale tools that could significantly enhance the capabilities of Raman spectroscopy. The optimized DNA origami nanoforks, in both dimer and aggregate forms, demonstrated an enhanced ability to detect and analyze molecular vibrations, contributing to a more nuanced understanding of protein dynamics.
A key aspect of this research was the comparative analysis between the dimer and aggregate forms of DONAs. This comparison revealed that while both configurations effectively identified oxidation and spin states of CytC, the aggregate form offered a broader range of detectable molecular states due to its prolonged signal emission and increased number of molecules. This extended duration of signal emission in the aggregates was attributed to the collective hotspot area, enhancing overall signal stability and sensitivity.
Furthermore, the study delved into the analysis of the Amide III band using the DONA system. Observations included a transient shift in the Amide III band's frequency, suggesting dynamic alterations in the secondary structure of CytC. These shifts, indicative of transitions between different protein structures, were crucial in understanding the protein’s functional mechanisms and interactions.
The research presented in this thesis not only contributes significantly to the field of spectroscopy but also illustrates the potential of interdisciplinary approaches in biosensing. The use of DNA origami-based systems in spectroscopy has opened new avenues for research, offering a detailed and comprehensive understanding of protein structures and interactions. The insights gained from this research are expected to have lasting implications in scientific fields ranging from drug development to the study of complex biochemical pathways. This thesis thus stands as a testament to the power of integrating nanotechnology, biochemistry, and spectroscopic techniques in addressing complex scientific questions.
Manganese (Mn) as well as iron (Fe) are essential trace elements (TE) important for the maintenance of physiological functions including fetal development. However, in the case of Mn, evidence suggests that excess levels of intrauterine Mn are associated with adverse pregnancy outcomes. Although Mn is known to cross the placenta, the fundamentals of Mn transfer kinetics and mechanisms are largely unknown. Moreover, exposure to combinations of TEs should be considered in mechanistic transfer studies, in particular for TEs expected to share similar transfer pathways. Here, we performed a mechanistic in vitro study on the placental transfer of Mn across a BeWo b30 trophoblast layer. Our data revealed distinct differences in the placental transfer of Mn and Fe. While placental permeability to Fe showed a clear inverse dose-dependency, Mn transfer was largely independent of the applied doses. Concurrent exposure of Mn and Fe revealed transfer interactions of Fe and Mn, indicating that they share common transfer mechanisms. In general, mRNA and protein expression of discussed transporters like DMT1, TfR, or FPN were only marginally altered in BeWo cells despite the different exposure scenarios highlighting that Mn transfer across the trophoblast layer likely involves a combination of active and passive transport processes.
Numerous phosphorus-rich metal phosphides containing both P-P bonds and metal-P bonds are known from the solid-state chemistry literature. A method to grow these materials in thin-film form would be desirable, as thin films are required in many applications and they are an ideal platform for high-throughput studies. In addition, the high density and smooth surfaces achievable in thin films are a significant advantage for characterization of transport and optical properties. Despite these benefits, there is hardly any published work on even the simplest binary phosphorus-rich phosphide films. Here, we demonstrate growth of single-phase CuP2 films by a two-step process involving reactive sputtering of amorphous CuP2+x and rapid annealing in an inert atmosphere. At the crystallization temperature, CuP2 is thermodynamically unstable with respect to Cu3P and P-4. However, CuP2 can be stabilized if the amorphous precursors are mixed on the atomic scale and are sufficiently close to the desired composition (neither too P poor nor too P rich). Fast formation of polycrystalline CuP2, combined with a short annealing time, makes it possible to bypass the diffusion processes responsible for decomposition. We find that thin-film CuP2 is a 1.5 eV band gap semiconductor with interesting properties, such as a high optical absorption coefficient (above 10(5) cm(-1)), low thermal conductivity (1.1 W/(K m)), and composition-insensitive electrical conductivity (around 1 S/cm). We anticipate that our processing route can be extended to other phosphorus-rich phosphides that are still awaiting thin-film synthesis and will lead to a more complete understanding of these materials and of their potential applications.
Guidance of postinfarct myocardial remodeling processes by an epicardial patch system may alleviate the consequences of ischemic heart disease. As macrophages are highly relevant in balancing immune response and regenerative processes their suitable instruction would ensure therapeutic success. A polymeric mesh capable of attracting and instructing monocytes by purely physical cues and accelerating implant degradation at the cell/implant interface is designed. In a murine model for myocardial infarction the meshes are compared to those either coated with extracellular matrix or loaded with induced cardiomyocyte progenitor cells. All implants promote macrophage infiltration and polarization in the epicardium, which is verified by in vitro experiments. 6 weeks post-MI, especially the implantation of the mesh attenuates left ventricular adverse remodeling processes as shown by reduced infarct size (14.7% vs 28-32%) and increased wall thickness (854 mu m vs 400-600 mu m), enhanced angiogenesis/arteriogenesis (more than 50% increase compared to controls and other groups), and improved heart function (ejection fraction = 36.8% compared to 12.7-31.3%). Upscaling as well as process controls is comprehensively considered in the presented mesh fabrication scheme to warrant further progression from bench to bedside.
Binary III-V nitrides such as AlN, GaN and InN in the wurtzite-type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower-symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non-existence of compounds crystallizing in Pmc2(1), formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
Applications of advanced cathode materials with well-designed chemical components and/or optimized nanostructures promoting the sulfur redox kinetics and suppressing the shuttle effect of polysulfides are highly valued. However, in the case of actual lithium-sulfur (Li-S) batteries under practical working conditions, one long-term obstacle still exists, which is mainly due to the difficulties in massive synthesis of such nanomaterials with low cost and ease of control on the nanostructure. Herein, we develop a facile synthesis of carbon coated Ti4O7 hollow nanoparticles (Ti4O7) using spherical polymer electrolyte brush as soft template, which is scalable via utilizing a minipilot reactor. The C Ti4O7 hollow nanoparticles provide strong chemical adsorption to polysulfides through the large polar surface and additional physical confinement by rich micro- & mesopores and have successfully been employed as an efficient sulfur host for multilayer pouch cells. Besides, the sluggish kinetics of the sulfur and lithium sulfide redox mechanism can be improved by the highly conductive Ti4O7 via catalyzation of the conversion of polysulfides. Consequently, the C-Ti4O7 based pouch cell endows a high discharge capacity of 1003 mAhg(-1) at 0.05 C, a high-capacity retention of 83.7% after 100 cycles at 0.1 C, and a high Coulombic efficiency of 97.5% at the 100th cycle. This work proposes an effective approach to transfer the synthesis of hollow Ti4O7 nanoparticles from lab- to large-scale production, paving the way to explore a wide range of advanced nanomaterials for multilayer Li-S pouch cells.
Electrochemical reduction stands as an alternative to revalorize CO2. Among the different alternatives, Ni single atoms supported on carbonaceous materials are an appealing catalytic solution due to the low cost and versatility of the support and the optimal usage of Ni and its predicted selectivity and efficiency (ca. 100% towards CO). Herein, we have used noble carbonaceous support derived from cytosine to load Ni subnanometric sites. The large heteroatom content of the support allows the stabilization of up to 11 wt% of Ni without the formation of nanoparticles through a simple impregnation plus calcination approach, where nickel promotes the stabilization of C3NOx frameworks and the oxidative support promotes a high oxidation state of nickel. EXAFS analysis points at nickel single atoms or subnanometric clusters coordinated by oxygen in the material surface. Unlike the wellknown N-coordinated Ni single sites selectivity towards CO2 reduction, O-coordinated-Ni single sites (ca. 7 wt% of Ni) reduced CO2 to CO, but subnanometric clusters (11 wt% of Ni) foster the unprecedented formation of HCOOH with 27% Faradaic efficiency at - 1.4 V. Larger Ni amounts ended up on the formation of NiO nanoparticles and almost 100% selectivity towards hydrogen evolution.
Quenching mechanism of uranyl(VI) by chloride and bromide in aqueous and non-aqueous solutions
(2021)
A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl-halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X-2(center dot-) and the formed uranyl(V) into fully solvated ions, thereby "reigniting" U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.
Colloidal metal sulfide nanoparticles for high performance electrochemical energy storage systems
(2022)
Transition metal sulfides have emerged as excellent replacement candidates of traditional insertion electrode materials based on their conversion or alloying mechanisms, facilitating high specific capacity and rate ability. However, parasitic reactions such as massive volume change during the discharge/ charge processes, intermediate polysulfide dissolution, and passivating solid electrolyte interface formation have led to poor cyclability, hindering their feasibility and applicability in energy storage systems. Colloidal metal sulfide nanoparticles, a special class that integrates the intrinsic chemical properties of metal sulfides and their specified structural features, have fairly enlarged their contribution due to the synergistic effect. This review highlights the latest synthetic approaches based on colloidal process. Their corresponding electrochemical outcomes will also be discussed, which are thoroughly updated along with their insight scientific standpoints.
Effect of magnesium salts with chaotropic anions on the swelling behavior of PNIPMAM thin films
(2023)
Poly(N-isopropylmethacrylamide) (PNIPMAM) is a stimuli responsive polymer, which in thin film geometry exhibits a volume-phase transition upon temperature increase in water vapor. The swelling behavior of PNIPMAM thin films containing magnesium salts in water vapor is investigated in view of their potential application as nanodevices. Both the extent and the kinetics of the swelling ratio as well as the water content are probed with in situ time-of-flight neutron reflectometry. Additionally, in situ Fourier-transform infrared (FTIR) spectroscopy provides information about the local solvation of the specific functional groups, while two-dimensional FTIR correlation analysis further elucidates the temporal sequence of solvation events. The addition of Mg(ClO4)2 or Mg(NO3)2 enhances the sensitivity of the polymer and therefore the responsiveness of switches and sensors based on PNIPMAM thin films. It is found that Mg(NO3)2 leads to a higher relative water uptake and therefore achieves the highest thickness gain in the swollen state.
Halide perovskites
(2021)
FicucariconeD (1) and its 4 '-demethyl congener 2 are isoflavones isolated from fruits of Ficus carica that share a 5,7-dimethoxy-6-prenyl-substituted A-ring. Both naturalproducts were, for the first time, obtained by chemical synthesisin six steps, starting from 2,4,6-trihydroxyacetophenone. Key stepsare a microwave-promoted tandem sequence of Claisen- and Cope-rearrangementsto install the 6-prenyl substituent and a Suzuki-Miyaura crosscoupling for installing the B-ring. By using various boronic acids,non-natural analogues become conveniently available. All compoundswere tested for cytotoxicity against drug-sensitive and drug-resistanthuman leukemia cell lines, but were found to be inactive. The compoundswere also tested for antimicrobial activities against a panel of eightGram-negative and two Gram-positive bacterial strains. Addition ofthe efflux pump inhibitor phenylalanine-arginine-beta-naphthylamide(PA beta N) significantly improved the antibiotic activity in mostcases, with MIC values as low as 2.5 mu M and activity improvementfactors as high as 128-fold.
To systematically add functionality to nanoscale polymer switches, an understanding of their responsive behavior is crucial. Herein, solvent vapor stimuli are applied to thin films of a diblock copolymer consisting of a short poly(methyl methacrylate) (PMMA) block and a long poly(N-isopropylmethacrylamide) (PNIPMAM) block for realizing ternary nanoswitches. Three significantly distinct film states are successfully implemented by the combination of amphiphilicity and co-nonsolvency effect. The exposure of the thin films to nitrogen, pure water vapor, and mixed water/acetone (90 vol%/10 vol%) vapor switches the films from a dried to a hydrated (solvated and swollen) and a water/acetone-exchanged (solvated and contracted) equilibrium state. These three states have distinctly different film thicknesses and solvent contents, which act as switch positions "off," "on," and "standby." For understanding the switching process, time-of-flight neutron reflectometry (ToF-NR) and spectral reflectance (SR) studies of the swelling and dehydration process are complemented by information on the local solvation of functional groups probed with Fourier-transform infrared (FTIR) spectroscopy. An accelerated responsive behavior beyond a minimum hydration/solvation level is attributed to the fast build-up and depletion of the hydration shell of PNIPMAM, caused by its hydrophobic moieties promoting a cooperative hydration character.
Vibrational relaxation of adsorbates is a sensitive tool to probe energy transfer at gas/solid and liquid/solid interfaces. The most direct way to study relaxation dynamics uses time-resolved spectroscopy. Here we report on a non-equilibrium ab initio molecular dynamics (NE-AIMD) methodology to model vibrational relaxation of OH vibrations on a hydroxylated, water-covered alpha-Al2O3(0001) surface. In our NE-AIMD approach, after exciting selected O-H bonds their coupling to surface phonons and to the water adlayer is analyzed in detail, by following both the energy flow in time, as well as the time-evolution of Vibrational Density of States (VDOS) curves. The latter are obtained from Time-dependent Correlation Functions (TCFs) and serve as prototypical, generic representatives of time-resolved vibrational spectra. As most important results, (i) we find a few-picosecond lifetime of the excited modes and (ii) identify both hydrogen-bonded aluminols and water molecules in the adsorbed water layer as main dissipative channels, while the direct coupling to Al2O3 surface phonons is of minor importance on the timescales of interest. Our NE-AIMD/TCF methodology is powerful for complex adsorbate systems, in principle even reacting ones, and opens a way towards time-resolved vibrational spectroscopy.
Elucidation of the reaction mechanism for the synthesis of ZnGeN2 through Zn2GeO4 ammonolysis
(2021)
Ternary II-IV-N-2 materials have been considered as a promising class of materials that combine photovoltaic performance with earth-abundance and low toxicity. When switching from binary III-V materials to ternary II-IV-N-2 materials, further structural complexity is added to the system that may influence its optoelectronic properties. Herein, we present a systematic study of the reaction of Zn2GeO4 with NH3 that produces zinc germanium oxide nitrides, and ultimately approach stoichiometric ZnGeN2, using a combination of chemical analyses, X-ray powder diffraction and DFT calculations. Elucidating the reaction mechanism as being dominated by Zn and O extrusion at the later reaction stages, we give an insight into studying structure-property relationships in this emerging class of materials.
This study deals with the facile synthesis of Fe1-xS nanoparticle-containing nitrogen-doped porous carbon membranes (denoted as Fe1-xS/N-PCMs) via vacuum carbonization of hybrid porous poly(ionic liquid) (PIL) membranes, and their successful use as a sulfur host material to mitigate the shuttle effect in lithium-sulfur (Li-S) batteries. The hybrid porous PIL membranes as the sacrificial template were prepared via ionic crosslinking of a cationic PIL with base-neutralized 1,1 '-ferrocenedicarboxylic acid, so that the iron source was molecularly incorporated into the template. The carbonization process was investigated in detail at different temperatures, and the chemical and porous structures of the carbon products were comprehensively analyzed. The Fe1-xS/N-PCMs prepared at 900 degrees C have a multimodal pore size distribution with a satisfactorily high surface area and well-dispersed iron sulfide nanoparticles to physically and chemically confine the LiPSs. The sulfur/Fe1-xS/N-PCM composites were then tested as electrodes in Li-S batteries, showing much improved capacity, rate performance and cycle stability, in comparison to iron sulfide-free, nitrogen-doped porous carbon membranes.
Toll-like receptor (TLR) can trigger an immune response against virus including SARS-CoV-2. TLR expression/distribution is varying in mesenchymal stromal cells (MSCs) depending on their culture environments. Here, to explore the effect of periodic thermomechanical cues on TLRs, thermally controlled shape-memory polymer sheets with programmable actuation capacity were created. The proportion of MSCs expressing SARS-CoV-2-associated TLRs was increased upon stimulation. The TLR4/7 colocalization was promoted and retained in the endoplasmic reticula. The TLR redistribution was driven by myosin-mediated F-actin assembly. These results highlight the potential of boosting the immunity for combating COVID-19 via thermomechanical preconditioning of MSCs.
This paper is focused on the temperature-dependent synthesis of gold nanotriangles in a vesicular template phase, containing phosphatidylcholine and AOT, by adding the strongly alternating polyampholyte PalPhBisCarb.
UV-vis absorption spectra in combination with TEM micrographs show that flat gold nanoplatelets are formed predominantly in the presence of the polyampholyte at 45°C. The formation of triangular and hexagonal nanoplatelets can be directly influenced by the kinetic approach, i.e., by varying the polyampholyte dosage rate at 45°C. Corresponding zeta potential measurements indicate that a temperature-dependent adsorption of the polyampholyte on the {111} faces will induce the symmetry breaking effect, which is responsible for the kinetically controlled hindered vertical and preferred lateral growth of the nanoplatelets.
Rapid migration of mesenchymal stem cells (MSCs) on device surfaces could support in vivo tissue integration and might facilitate in vitro organoid formation. Here, polydopamine (PDA) is explored as a biofunctional coating to effectively promote MSC motility. It is hypothesized that PDA stimulates fibronectin deposition and in this way enhances integrin-mediated migration capability. The random and directional cell migration was investigated by time-lapse microscopy and gap closure assay respectively, and analysed with softwares as computational tools. A higher amount of deposited fibronectin was observed on PDA substrate, compared to the non-coated substrate. The integrin beta 1 activation and focal adhesion kinase (FAK) phosphorylation at Y397 were enhanced on PDA substrate, but the F-actin cytoskeleton was not altered, suggesting MSC migration on PDA was regulated by integrin initiated FAK signalling. This study strengthens the biofunctionality of PDA coating for regulating stem cells and offering a way of facilitating tissue integration of devices.
Copolyesterurethanes (PDLCLs) based on oligo(epsilon-caprolactone) (OCL) and oligo(omega-pentadecalactone) (OPDL) segments are biodegradable thermoplastic temperature-memory polymers. The temperature-memory capability in these polymers with crystallizable control units is implemented by a thermomechanical programming process causing alterations in the crystallite arrangement and chain organization. These morphological changes can potentially affect degradation. Initial observations on the macroscopic level inspire the hypothesis that switching of the controlling units causes an accelerated degradation of the material, resulting in programmable degradation by sequential coupling of functions. Hence, detailed degradation studies on Langmuir films of a PDLCL with 40 wt% OPDL content are carried out under enzymatic catalysis. The temperature-memory creation procedure is mimicked by compression at different temperatures. The evolution of the chain organization and mechanical properties during the degradation process is investigated by means of polarization-modulated infrared reflection absorption spectroscopy, interfacial rheology and to some extend by X-ray reflectivity. The experiments on PDLCL Langmuir films imply that degradability is not enhanced by thermal switching, as the former depends on the temperature during cold programming. Nevertheless, the thin film experiments show that the leaching of OCL segments does not induce further crystallization of the OPDL segments, which is beneficial for a controlled and predictable degradation.
The synthesis and the crystal structure of the double cluster compound [Nb6Cl14(MeCN)(4)][Nb6Cl14(pyz)(4)]middot6CH(3)CN are described. The synthesis is based on a partial ligand exchange reaction, which proceeds upon dissolving [Nb6Cl14(pyz)(4)]middot2CH(2)Cl(2) in acetonitrile. The compound is built up of two discrete neutral cluster units, which consist of octahedra of Nb-6 atoms coordinated by 12 edge-bridging chlorido and two terminal chlorido ligands, and four acetonitrile ligands on one and four pyrazine ligands on the other cluster unit. Co-crystallized acetonitrile molecules are also present. The single-crystal structure determination has revealed a cluster arrangement in which the [Nb6Cl14(pyz)(4)] units are connected by (halogen) lone-pair-(pyrazine) pi interactions. These lead to chains of [Nb6Cl14(pyz)(4)] clusters. These chains are further connected to cluster layers by (nitrile-halogen) dipole-dipole interactions, in which the [Nb6Cl14(MeCN)(4)] and co-crystallized MeCN molecules are also involved. These cluster layers are arranged parallel to the crystallographic {011} plane.
The water vapor-induced swelling, as well as subsequent phase-transition kinetics, of thin films of a diblock copolymer (DBC) loaded with different amounts of the salt NaBr, is investigated in situ. In dilute aqueous solution, the DBC features an orthogonally thermoresponsive behavior. It consists of a zwitterionic poly(sulfobetaine) block, namely, poly(4-(N-(3'-methacrylamidopropyl)-N, N-dimethylammonio) butane-1-sulfonate) (PSBP), showing an upper critical solution temperature, and a nonionic block, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), exhibiting a lower critical solution temperature. The swelling kinetics in D2O vapor at 15 degrees C and the phase transition kinetics upon heating the swollen film to 60 degrees C and cooling back to 15 degrees C are followed with simultaneous time-of-flight neutron reflectometry and spectral reflectance measurements. These are complemented by Fourier transform infrared spectroscopy. The collapse temperature of PNIPMAM and the swelling temperature of PSBP are found at lower temperatures than in aqueous solution, which is attributed to the high polymer concentration in the thin-film geometry. Upon inclusion of sub-stoichiometric amounts (relative to the monomer units) of NaBr in the films, the water incorporation is significantly increased. This increase is mainly attributed to a salting-in effect on the zwitterionic PSBP block. Whereas the addition of NaBr notably shifts the swelling temperature of PSBP to lower temperatures, the collapse temperature of PNIPMAM remains unaffected by the presence of salt in the films.
The understanding of bidimensional materials dynamics and its electrolyte interface equilibrium, such as graphene oxide (GO), is critical for the development of a capacitive biosensing platform. The interfacial capacitance (C-i) of graphene-based materials may be tuned by experimental conditions such as pH optimization and cation size playing key roles at the enhancement of their capacitive properties allowing their application as novel capacitive biosensors. Here we reported a systematic study of C-i of multilayer GO films in different aqueous electrolytes employing electrochemical impedance spectroscopy for the application in a capacitive detection system. We demonstrated that the presence of ionizable oxygen-containing functional groups within multilayer GO film favors the interactions and the accumulation of cations in the structure of the electrodes enhancing the GO C-i in aqueous solutions, where at pH 7.0 (the best condition) the C-i was 340 mu F mg(-1) at -0.01 V vs Ag/AgCl. We also established that the hydrated cation radius affects the mobility and interaction with GO functional groups and it plays a critical role in the Ci, as demonstrated in the presence of different cations Na+=640 mu F mg(-1), Li+=575 mu F mg(-1) and TMA(+)=477 mu F mg(-1). As a proof-of-concept, the capacitive behaviour of GO was explored as biosensing platform for standard streptavidin-biotin systems. For this system, the C-i varied linearly with the log of the concentration of the targeting analyte in the range from 10 pg mL(-1) to 100 ng mL(-1), showing the promising applicability of capacitive GO based sensors for label-free biosensing.
Carbon nitride semiconductors: properties and application as photocatalysts in organic synthesis
(2023)
Graphitic carbon nitrides (g-CNs) are represented by melon-type g-CN, poly(heptazine imides) (PHIs), triazine-based g-CN and poly(triazine imide) with intercalated LiCl (PTI/Li+Cl‒). These materials are composed of sp2-hybridized carbon and nitrogen atoms; C:N ratio is close to 3:4; the building unit is 1,3,5-triazine or tri-s-triazine; the building units are interconnected covalently via sp2-hybridized nitrogen atoms or NH-moieties; the layers are assembled into a stack via weak van der Waals forces as in graphite. Due to medium band gap (~2.7 eV) g-CNs, such as melon-type g-CN and PHIs, are excited by photons with wavelength ≤ 460 nm. Since 2009 g-CNs have been actively studied as photocatalysts in evolution of hydrogen and oxygen – two half-reactions of full water splitting, by employing corresponding sacrificial agents. At the same time application of g-CNs as photocatalysts in organic synthesis has been remaining limited to few reactions only. Cumulative Habilitation summarizes research work conducted by the group ‘Innovative Heterogeneous Photocatalysis’ between 2017-2023 in the field of carbon nitride organic photocatalysis, which is led by Dr. Oleksandr Savatieiev.
g-CN photocatalysts activate molecules, i.e. generate their more reactive open-shell intermediates, via three modes: i) Photoinduced electron transfer (PET); ii) Excited state proton-coupled electron transfer (ES-PCET) or direct hydrogen atom transfer (dHAT); iii) Energy transfer (EnT). The scope of reactions that proceed via oxidative PET, i.e. one-electron oxidation of a substrate to the corresponding radical cation, are represented by synthesis of sulfonylchlorides from S-acetylthiophenols. The scope of reactions that proceed via reductive PET, i.e. one-electron reduction of a substrate to the corresponding radical anion, are represented by synthesis of γ,γ-dichloroketones from the enones and chloroform.
Due to abundance of sp2-hybridized nitrogen atoms in the structure of g-CN materials, they are able to cleave X-H bonds in organic molecules and store temporary hydrogen atom. ES-PCET or dHAT mode of organic molecules activation to the corresponding radicals is implemented for substrates featuring relatively acidic X-H bonds and those that are characterized by low bond dissociation energy, such as C-H bond next to the heteroelements. On the other hand, reductively quenched g-CN carrying hydrogen atom reduces a carbonyl compound to the ketyl radical via PCET that is thermodynamically more favorable pathway compared to the electron transfer. The scope of these reactions is represented by cyclodimerization of α,β-unsaturated ketones to cyclopentanoles.
g-CN excited state demonstrates complex dynamics with the initial formation of singlet excited state, which upon intersystem crossing produces triplet excited state that is characterized by the lifetime > 2 μs. Due to long lifetime, g-CN activate organic molecules via EnT. For example, g-CN sensitizes singlet oxygen, which is the key intermediate in the dehydrogenation of aldoximes to nitrileoxides. The transient nitrileoxide undergoes [3+2]-cycloaddition to nitriles and gives oxadiazoles-1,2,4.
PET, ES-PCET and EnT are fundamental phenomena that are applied beyond organic photocatalysis. Hybrid composite is formed by combining conductive polymers, such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with potassium poly(heptazine imide) (K-PHI). Upon PET, K-PHI modulated population of polarons and therefore conductivity of PEDOT:PSS. The initial state of PEDOT:PSS is recovered upon material exposure to O2. K-PHI:PEDOT:PSS may be applied in O2 sensing.
In the presence of electron donors, such as tertiary amines and alcohols, and irradiation with light, K-PHI undergoes photocharging – the g-CN material accumulates electrons and charge-compensating cations. Such photocharged state is stable under anaerobic conditions for weeks, but at the same time it is a strong reductant. This feature allows decoupling in time light harvesting and energy storage in the form of electron-proton couples from utilization in organic synthesis. The photocharged state of K-PHI reduces nitrobenzene to aniline, and enables dimerization of α,β-unsaturated ketones to hexadienones in dark.
Poly(N,N-bis(2-methoxyethyl)acrylamide) (PbMOEAm) featuring two classical chemical motifs from non-ionic water-soluble polymers, namely, the amide and ethyleneglycolether moieties, was synthesized by reversible addition fragmentation transfer (RAFT) polymerization. This tertiary polyacrylamide is thermoresponsive exhibiting a lower critical solution temperature (LCST)-type phase transition. A series of homo- and block copolymers with varying molar masses but low dispersities and different end groups were prepared. Their thermoresponsive behavior in aqueous solution was analyzed via turbidimetry and dynamic light scattering (DLS). The cloud points (CP) increased with increasing molar masses, converging to 46 degrees C for 1 wt% solutions. This rise is attributed to the polymers' hydrophobic end groups incorporated via the RAFT agents. When a surfactant-like strongly hydrophobic end group was attached using a functional RAFT agent, CP was lowered to 42 degrees C, i.e., closer to human body temperature. Also, the effect of added salts, in particular, the role of the Hofmeister series, on the phase transition of PbMOEAm was investigated, exemplified for the kosmotropic fluoride, intermediate chloride, and chaotropic thiocyanate anions. A pronounced shift of the cloud point of about 10 degrees C to lower or higher temperatures was observed for 0.2 M fluoride and thiocyanate, respectively. When PbMOEAm was attached to a long hydrophilic block of poly(N,N-dimethylacrylamide) (PDMAm), the cloud points of these block copolymers were strongly shifted towards higher temperatures. While no phase transition was observed for PDMAm-b-pbMOEAm with short thermoresponsive blocks, block copolymers with about equally sized PbMOEAm and PDMAm blocks underwent the coil-to-globule transition around 60 degrees C.
Global warming, driven primarily by the excessive emission of greenhouse gases such as carbon dioxide into the atmosphere, has led to severe and detrimental environmental impacts. Rising global temperatures have triggered a cascade of adverse effects, including melting glaciers and polar ice caps, more frequent and intense heat waves disrupted weather patterns, and the acidification of oceans. These changes adversely affect ecosystems, biodiversity, and human societies, threatening food security, water availability, and livelihoods. One promising solution to mitigate the harmful effects of global warming is the widespread adoption of solar cells, also known as photovoltaic cells. Solar cells harness sunlight to generate electricity without emitting greenhouse gases or other pollutants. By replacing fossil fuel-based energy sources, solar cells can significantly reduce CO2 emissions, a significant contributor to global warming. This transition to clean, renewable energy can help curb the increasing concentration of greenhouse gases in the atmosphere, thereby slowing down the rate of global temperature rise.
Solar energy’s positive impact extends beyond emission reduction. As solar panels become more efficient and affordable, they empower individuals, communities, and even entire nations to generate electricity and become less dependent on fossil fuels. This decentralized energy generation can enhance resilience in the face of climate-related challenges. Moreover, implementing solar cells creates green jobs and stimulates technological innovation, further promoting sustainable economic growth. As solar technology advances, its integration with energy storage systems and smart grids can ensure a stable and reliable energy supply, reducing the need for backup fossil fuel power plants that exacerbate environmental degradation.
The market-dominant solar cell technology is silicon-based, highly matured technology with a highly systematic production procedure. However, it suffers from several drawbacks, such as: 1) Cost: still relatively high due to high energy consumption due to the need to melt and purify silicon, and the use of silver as an electrode, which hinders their widespread availability, especially in low-income countries. 2) Efficiency: theoretically, it should deliver around 29%; however, the efficiency of most of the commercially available silicon-based solar cells ranges from 18 – 22%. 3) Temperature sensitivity: The efficiency decreases with the increase in the temperature, affecting their output. 4) Resource constraints: silicon as a raw material is unavailable in all countries, creating supply chain challenges.
Perovskite solar cells arose in 2011 and matured very rapidly in the last decade as a highly efficient and versatile solar cell technology. With an efficiency of 26%, high absorption coefficients, solution processability, and tunable band gap, it attracted the attention of the solar cells community. It represented a hope for cheap, efficient, and easily processable next-generation solar cells. However, lead toxicity might be the block stone hindering perovskite solar cells’ market reach. Lead is a heavy and bioavailable element that makes perovskite solar cells environmentally unfriendly technology. As a result, scientists try to replace lead with a more environmentally friendly element. Among several possible alternatives, tin was the most suitable element due to its electronic and atomic structure similarity to lead.
Tin perovskites were developed to alleviate the challenge of lead toxicity. Theoretically, it shows very high absorption coefficients, an optimum band gap of 1.35 eV for FASnI3, and a very high short circuit current, which nominates it to deliver the highest possible efficiency of a single junction solar cell, which is around 30.1% according to Schockly-Quisser limit. However, tin perovskites’ efficiency still lags below 15% and is irreproducible, especially from lab to lab. This humble performance could be attributed to three reasons: 1) Tin (II) oxidation to tin (IV), which would happen due to oxygen, water, or even by the effect of the solvent, as was discovered recently. 2) fast crystallization dynamics, which occurs due to the lateral exposure of the P-orbitals of the tin atom, which enhances its reactivity and increases the crystallization pace. 3) Energy band misalignment: The energy bands at the interfaces between the perovskite absorber material and the charge selective layers are not aligned, leading to high interfacial charge recombination, which devastates the photovoltaic performance. To solve these issues, we implemented several techniques and approaches that enhanced the efficiency of tin halide perovskites, providing new chemically safe solvents and antisolvents. In addition, we studied the energy band alignment between the charge transport layers and the tin perovskite absorber.
Recent research has shown that the principal source of tin oxidation is the solvent known as dimethylsulfoxide, which also happens to be one of the most effective solvents for processing perovskite. The search for a stable solvent might prove to be the factor that makes all the difference in the stability of tin-based perovskites. We started with a database of over 2,000 solvents and narrowed it down to a series of 12 new solvents that are suitable for processing FASnI3 experimentally. This was accomplished by looking into 1) the solubility of the precursor chemicals FAI and SnI2, 2) the thermal stability of the precursor solution, and 3) the potential to form perovskite. Finally, we show that it is possible to manufacture solar cells using a novel solvent system that outperforms those produced using DMSO. The results of our research give some suggestions that may be used in the search for novel solvents or mixes of solvents that can be used to manufacture stable tin-based perovskites.
Due to the quick crystallization of tin, it is more difficult to deposit tin-based perovskite films from a solution than manufacturing lead-based perovskite films since lead perovskite is more often utilized. The most efficient way to get high efficiencies is to deposit perovskite from dimethyl sulfoxide (DMSO), which slows down the quick construction of the tin-iodine network that is responsible for perovskite synthesis. This is the most successful approach for achieving high efficiencies. Dimethyl sulfoxide, which is used in the processing, is responsible for the oxidation of tin, which is a disadvantage of this method. This research presents a potentially fruitful alternative in which 4-(tert-butyl) pyridine can substitute dimethyl sulfoxide in the process of regulating crystallization without causing tin oxidation to take place. Perovskite films that have been formed from pyridine have been shown to have a much-reduced defect density. This has resulted in increased charge mobility and better photovoltaic performance, making pyridine a desirable alternative for use in the deposition of tin perovskite films.
The precise control of perovskite precursor crystallization inside a thin film is of utmost importance for optimizing the efficiency and manufacturing of solar cells. The deposition process of tin-based perovskite films from a solution presents difficulties due to the quick crystallization of tin compared to the more often employed lead perovskite. The optimal approach for attaining elevated efficiencies entails using dimethyl sulfoxide (DMSO) as a medium for depositing perovskite. This choice of solvent impedes the tin-iodine network’s fast aggregation, which plays a crucial role in the production of perovskite. Nevertheless, this methodology is limited since the utilization of dimethyl sulfoxide leads to the oxidation of tin throughout the processing stage. In this thesis, we present a potentially advantageous alternative approach wherein 4-(tert-butyl) pyridine is proposed as a substitute for dimethyl sulfoxide in regulating crystallization processes while avoiding the undesired consequence of tin oxidation. Films of perovskite formed using pyridine as a solvent have a notably reduced density of defects, resulting in higher mobility of charges and improved performance in solar applications. Consequently, the utilization of pyridine for the deposition of tin perovskite films is considered advantageous.
Tin perovskites are suffering from an apparent energy band misalignment. However, the band diagrams published in the current body of research display contradictions, resulting in a dearth of unanimity. Moreover, comprehensive information about the dynamics connected with charge extraction is lacking. This thesis aims to ascertain the energy band locations of tin perovskites by employing the kelvin probe and Photoelectron yield spectroscopy methods. This thesis aims to construct a precise band diagram for the often-utilized device stack. Moreover, a comprehensive analysis is performed to assess the energy deficits inherent in the current energetic structure of tin halide perovskites. In addition, we investigate the influence of BCP on the improvement of electron extraction in C60/BCP systems, with a specific emphasis on the energy factors involved. Furthermore, transient surface photovoltage was utilized to investigate the charge extraction kinetics of frequently studied charge transport layers, such as NiOx and PEDOT as hole transport layers and C60, ICBA, and PCBM as electron transport layers. The Hall effect, KP, and TRPL approaches accurately ascertain the p-doping concentration in FASnI3. The results consistently demonstrated a value of 1.5 * 1017 cm-3. Our research findings highlight the imperative nature of autonomously constructing the charge extraction layers for tin halide perovskites, apart from those used for lead perovskites.
The crystallization of perovskite precursors relies mainly on the utilization of two solvents. The first one dissolves the perovskite powder to form the precursor solution, usually called the solvent. The second one precipitates the perovskite precursor, forming the wet film, which is a supersaturated solution of perovskite precursor and in the remains of the solvent and the antisolvent. Later, this wet film crystallizes upon annealing into a full perovskite crystallized film. In our research context, we proposed new solvents to dissolve FASnI3, but when we tried to form a film, most of them did not crystallize. This is attributed to the high coordination strength between the metal halide and the solvent molecules, which is unbreakable by the traditionally used antisolvents such as Toluene and Chlorobenzene. To solve this issue, we introduce a high-throughput antisolvent screening in which we screened around 73 selected antisolvents against 15 solvents that can form a 1M FASnI3 solution. We used for the first time in tin perovskites machine learning algorithm to understand and predict the effect of an antisolvent on the crystallization of a precursor solution in a particular solvent. We relied on film darkness as a primary criterion to judge the efficacy of a solvent-antisolvent pair. We found that the relative polarity between solvent and antisolvent is the primary factor that affects the solvent-antisolvent interaction. Based on our findings, we prepared several high-quality tin perovskite films free from DMSO and achieved an efficiency of 9%, which is the highest DMSO tin perovskite device so far.
The water swelling and subsequent solvent exchange including co-nonsolvency behavior of thin films of a doubly thermo-responsive diblock copolymer (DBC) are studied viaspectral reflectance, time-of-flight neutron reflectometry, and Fourier transform infrared spectroscopy.
The DBC consists of a thermo-responsive zwitterionic (poly(4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate)) (PSBP) block, featuring an upper critical solution temperature transition in aqueous media but being insoluble in acetone, and a nonionic poly(N-isopropylmethacrylamide) (PNIPMAM) block, featuring a lower critical solution temperature transition in water, while being soluble in acetone.
Homogeneous DBC films of 50-100 nm thickness are first swollen in saturated water vapor (H2OorD2O), before they are subjected to a contraction process by exposure to mixed saturated water/acetone vapor (H2OorD2O/acetone-d6 = 9:1 v/v).
The affinity of the DBC film toward H2O is stronger than for D2O, as inferred from the higher film thickness in the swollen state and the higher absorbed water content, thus revealing a pronounced isotope sensitivity.
During the co-solvent-induced switching by mixed water/acetone vapor, a two-step film contraction is observed, which is attributed to the delayed expulsion of water molecules and uptake of acetone molecules.
The swelling kinetics are compared for both mixed vapors (H2O/acetone-d6 and D2O/acetone-d6) and with those of the related homopolymer films.
Moreover, the concomitant variations of the local environment around the hydrophilic groups located in the PSBP and PNIPMAM blocks are followed.
The first contraction step turns out to be dominated by the behavior of the PSBP block, where as the second one is dominated by the PNIPMAM block.
The unusual swelling and contraction behavior of the latter block is attributed to its co-nonsolvency behavior.
Furthermore, we observe cooperative hydration effects in the DBC films, that is, both polymer blocks influence each other's solvation behavior.
Thermally stable photoswitches that are driven with low-energy light are rare, yet crucial for extending the applicability of photoresponsive molecules and materials towards, e.g., living systems. Combined ortho-fluorination and -amination couples high visible light absorptivity of o-aminoazobenzenes with the extraordinary bistability of o-fluoroazobenzenes. Herein, we report a library of easily accessible o-aminofluoroazobenzenes and establish structure-property relationships regarding spectral qualities, visible light isomerization efficiency and thermal stability of the cis-isomer with respect to the degree of o-substitution and choice of amino substituent. We rationalize the experimental results with quantum chemical calculations, revealing the nature of low-lying excited states and providing insight into thermal isomerization. The synthesized azobenzenes absorb at up to 600 nm and their thermal cis-lifetimes range from milliseconds to months. The most unique example can be driven from trans to cis with any wavelength from UV up to 595 nm, while still exhibiting a thermal cis-lifetime of 81 days. <br /> [GRAPHICS] <br /> .
Poly(ionic liquid)s (PIL) are common precursors for heteroatom-doped carbon materials. Despite a relatively higher carbonization yield, the PIL-to-carbon conversion process faces challenges in preserving morphological and structural motifs on the nanoscale. Assisted by a thin polydopamine coating route and ion exchange, imidazoliumbased PIL nanovesicles were successfully applied in morphology-maintaining carbonization to prepare carbon composite nanocapsules. Extending this strategy further to their composites, we demonstrate the synthesis of carbon composite nanocapsules functionalized with iron nitride nanoparticles of an ultrafine, uniform size of 3-5 nm (termed "FexN@C "). Due to its unique nanostructure, the sulfur-loaded FexN@C electrode was tested to efficiently mitigate the notorious shuttle effect of lithium polysulfides (LiPSs) in Li-S batteries. The cavity of the carbon nanocapsules was spotted to better the loading content of sulfur. The well-dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li2S, owing to their high electronic conductivity and strong binding power to LiPSs. Benefiting from this well-crafted composite nanostructure, the constructed FexN@C/S cathode demonstrated a fairly high discharge capacity of 1085 mAh g(-1) at 0.5 C initially, and a remaining value of 930 mAh g(-1 )after 200 cycles. In addition, it exhibits an excellent rate capability with a high initial discharge capacity of 889.8 mAh g(-1) at 2 C. This facile PIL-to-nanocarbon synthetic approach is applicable for the exquisite design of complex hybrid carbon nanostructures with potential use in electrochemical energy storage and conversion.
Shape-memory hydrogels (SMH) are multifunctional, actively-moving polymers of interest in biomedicine. In loosely crosslinked polymer networks, gelatin chains may form triple helices, which can act as temporary net points in SMH, depending on the presence of salts. Here, we show programming and initiation of the shape-memory effect of such networks based on a thermomechanical process compatible with the physiological environment. The SMH were synthesized by reaction of glycidylmethacrylated gelatin with oligo(ethylene glycol) (OEG) alpha,omega-dithiols of varying crosslinker length and amount. Triple helicalization of gelatin chains is shown directly by wide-angle X-ray scattering and indirectly via the mechanical behavior at different temperatures. The ability to form triple helices increased with the molar mass of the crosslinker. Hydrogels had storage moduli of 0.27-23 kPa and Young's moduli of 215-360 kPa at 4 degrees C. The hydrogels were hydrolytically degradable, with full degradation to water-soluble products within one week at 37 degrees C and pH = 7.4. A thermally-induced shape-memory effect is demonstrated in bending as well as in compression tests, in which shape recovery with excellent shape-recovery rates R-r close to 100% were observed. In the future, the material presented here could be applied, e.g., as self-anchoring devices mechanically resembling the extracellular matrix.
The nanoscale combination of a conductive carbon and a carbon-based material with abundant heteroatoms for battery electrodes is a method to overcome the limitation that the latter has high affinity to alkali metal ions but low electronic conductivity. The synthetic protocol and the individual ratios and structures are important aspects influencing the properties of such multifunctional compounds. Their interplay is, herein, investigated by infiltration of a porous ZnO-templated carbon (ZTC) with nitrogen-rich carbon obtained by condensation of hexaazatriphenylene-hexacarbonitrile (HAT-CN) at 550-1000 degrees C. The density of lithiophilic sites can be controlled by HAT-CN content and condensation temperature. Lithium storage properties are significantly improved in comparison with those of the individual compounds and their physical mixtures. Depending on the uniformity of the formed composite, loading ratio and condensation temperature have different influence. Most stable operation at high capacity per used monomer is achieved with a slowly dried composite with an HAT-CN:ZTC mass ratio of 4:1, condensed at 550 degrees C, providing more than 400 mAh g(-1) discharge capacity at 0.1 A g(-1) and a capacity retention of 72% after 100 cycles of operation at 0.5 A g(-1) due to the homogeneity of the composite and high content of lithiophilic sites.
Advanced catalysis triggered by photothermal conversion effects has aroused increasing interest due to its huge potential in environmental purification.
In this work, we developed a novel approach to the fast degradation of 4-nitrophenol (4-Nip) using porous MoS2 nanoparticles as catalysts, which integrate the intrinsic catalytic property of MoS2 with its photothermal conversion capability.
Using assembled polystyrene-b-poly(2-vinylpyridine) block copolymers as soft templates, various MoS 2 particles were prepared, which exhibited tailored morphologies (e.g., pomegranate-like, hollow, and open porous structures).
The photothermal conversion performance of these featured particles was compared under near-infrared (NIR) light irradiation.
Intriguingly, when these porous MoS2 particles were further employed as catalysts for the reduction of 4-Nip, the reaction rate constant was increased by a factor of 1.5 under NIR illumination.
We attribute this catalytic enhancement to the open porous architecture and light-to-heat conversion performance of the MoS2 particles. This contribution offers new opportunities for efficient photothermal-assisted catalysis.
Bimetallic nanostructures comprising plasmonic and catalytic components have recently emerged as a promising approach to generate a new type of photo-enhanced nanoreactors. Most designs however concentrate on plasmon-induced charge separation, leaving photo-generated heat as a side product.
This work presents a photoreactor based on Au-Pd nanorods with an optimized photothermal conversion, which aims to effectively utilize the photo-generated heat to increase the rate of Pd-catalyzed reactions. Dumbbell-shaped Au nanorods were fabricated via a seed-mediated growth method using binary surfactants. Pd clusters were selectively grown at the tips of the Au nanorods, using the zeta potential as a new synthetic parameter to indicate the surfactant remaining on the nanorod surface.
The photothermal conversion of the Au-Pd nanorods was improved with a thin layer of polydopamine (PDA) or TiO2.
As a result, a 60% higher temperature increment of the dispersion compared to that for bare Au rods at the same light intensity and particle density could be achieved.
The catalytic performance of the coated particles was then tested using the reduction of 4-nitrophenol as the model reaction. Under light, the PDA-coated Au-Pd nanorods exhibited an improved catalytic activity, increasing the reaction rate by a factor 3.
An analysis of the activation energy confirmed the photoheating effect to be the dominant mechanism accelerating the reaction. Thus, the increased photothermal heating is responsible for the reaction acceleration.
Interestingly, the same analysis shows a roughly 10% higher reaction rate for particles under illumination compared to under dark heating, possibly implying a crucial role of localized heat gradients at the particle surface.
Finally, the coating thickness was identified as an essential parameter determining the photothermal conversion efficiency and the reaction acceleration.
The influence of polymer architecture of polycations on their ability to transfect mammalian cells is probed. Polymer bottle brushes with grafts made from partially hydrolysed poly(2-ethyl-2-oxazoline) are used while varying the length of the polymer backbone as well as the degree of hydrolysis (cationic charge content). Polyplex formation is investigated via gel electrophoresis, dye-displacement and dynamic light scattering. Bottle brushes show a superior ability to complex pDNA when compared to linear copolymers. Also, nucleic acid release was found to be improved by a graft architecture. Polyplexes based on bottle brush copolymers showed an elongated shape in transmission electron microscopy images. The cytotoxicity against mammalian cells is drastically reduced when a graft architecture is used instead of linear copolymers. Moreover, the best-performing bottle brush copolymer showed a transfection ability comparable with that of linear poly(ethylenimine), the gold standard of polymeric transfection agents, which is used as positive control. In combination with their markedly lowered cytotoxicity, cationic bottle brush copolymers are therefore shown to be a highly promising class of gene delivery vectors.
The catalytic activity of metal nanoparticles (NPs) supported on porous supports can be controlled by various factors, such as NPs size, shape, or dispersivity, as well as their interaction with the support or the properties of the support material itself. However, these intrinsic properties are not solely responsible for the catalytic behavior of the overall reaction system, as the local environment and surface coverage of the catalyst with reactants, products, intermediates and other invloved species often play a crucial role in catalytic processes as well. Their contribution can be particularly critical in liquid-phase reactions with gaseous reactants that often suffer from low solubiltiy. One example is (D)-glucose oxidation with molecular oxygen over gold nanoparticles supported on porous carbons. The possibility to promote oxygen delivery in such aqueous phase oxidation reactions via the immobilization of heterogenous catalysts onto the interface of perfluorocarbon emulsion droplets is reported here. Gold-on-carbon catalyst particles can stabilize perfluorocarbon droplets in the aqueous phase and the local concentration of the oxidant in the surroundings of the gold nanoparticles accelerates the rate-limiting step of the reaction. Consequently, the reaction rate of a system with the optimal volume fraction of fluorocarbon is higher than a reference emulsion system without fluorocarbon, and the effect is observed even without additional oxygen supply.
Advances in characteristics improvement of polymeric membranes/separators for zinc-air batteries
(2022)
Zinc-air batteries (ZABs) are gaining popularity for a wide range of applications due to their high energy density, excellent safety, and environmental friendliness. A membrane/separator is a critical component of ZABs, with substantial implications for battery performance and stability, particularly in the case of a battery in solid state format, which has captured increased attention in recent years. In this review, recent advances as well as insight into the architecture of polymeric membrane/separators for ZABs including porous polymer separators (PPSs), gel polymer electrolytes (GPEs), solid polymer electrolytes (SPEs) and anion exchange membranes (AEMs) are discussed. The paper puts forward strategies to enhance stability, ionic conductivity, ionic selectivity, electrolyte storage capacity and mechanical properties for each type of polymeric membrane. In addition, the remaining major obstacles as well as the most potential avenues for future research are examined in detail.
Mycotoxins and pesticides regularly co-occur in agricultural products worldwide. Thus, humans can be exposed to both toxic contaminants and pesticides simultaneously, and multi-methods assessing the occurrence of various food contaminants and residues in a single method are necessary. A two-dimensional high performance liquid chromatography tandem mass spectrometry method for the analysis of 40 (modified) mycotoxins, two plant growth regulators, two tropane alkaloids, and 334 pesticides in cereals was developed. After an acetonitrile/water/formic acid (79:20:1, v/v/v) multi-analyte extraction procedure, extracts were injected into the two-dimensional setup, and an online clean-up was performed. The method was validated according to Commission Decision (EC) no. 657/2002 and document N° SANTE/12682/2019. Good linearity (R2 > 0.96), recovery data between 70-120%, repeatability and reproducibility values < 20%, and expanded measurement uncertainties < 50% were obtained for a wide range of analytes, including very polar substances like deoxynivalenol-3-glucoside and methamidophos. However, results for fumonisins, zearalenone-14,16-disulfate, acid-labile pesticides, and carbamates were unsatisfying. Limits of quantification meeting maximum (residue) limits were achieved for most analytes. Matrix effects varied highly (−85 to +1574%) and were mainly observed for analytes eluting in the first dimension and early-eluting analytes in the second dimension. The application of the method demonstrated the co-occurrence of different types of cereals with 28 toxins and pesticides. Overall, 86% of the samples showed positive findings with at least one mycotoxin, plant growth regulator, or pesticide.
The use of organic materials with reversible redox activity holds enormous potential for next-generation Li-ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox-active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g(-1) at 0.1 A g(-1) and low capacity fading, retaining approximately 80% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone-catecholate redox mechanism responsible for the high capacity of tannic acid is confirmed by electrochemical characterization of a model compound similar to tannic acid but without catecholic groups.
Electrical actuation of coated and composite fibers based on poly[ethylene-co-(vinyl acetate)]
(2020)
Robots are typically controlled by electrical signals. Resistive heating is an option to electrically trigger actuation in thermosensitive polymer systems. In this study electrically triggerable poly[ethylene-co-(vinyl acetate)] (PEVA)-based fiber actuators are realized as composite fibers as well as polymer fibers with conductive coatings. In the coated fibers, the core consists of crosslinked PEVA (cPEVA), while the conductive coating shell is achieved via a dip coating procedure with a coating thickness between 10 and 140 mu m. The conductivity of coated fibers sigma = 300-550 S m(-1) is much higher than that of the composite fibers sigma = 5.5 S m(-1). A voltage (U) of 110 V is required to heat 30 cm of coated fiber to a targeted temperature of approximate to 65 degrees C for switching in less than a minute. Cyclic electrical actuation investigations reveal epsilon '(rev) = 5 +/- 1% reversible change in length for coated fibers. The fabrication of such electro-conductive polymeric actuators is suitable for upscaling so that their application potential as artificial muscles can be explored in future studies.
We present a comparative study of the gas-phase UV spectra of uracil and its thionated counterparts (2-thiouracil, 4-thiouracil and 2,4-dithiouracil), closely supported by time-dependent density functional theory calculations to assign the transitions observed. We systematically discuss pure gas-phase spectra for the (thio)uracils in the range of 200-400 nm (similar to 3.2-6.4 eV), and examine the spectra of all four species with a single theoretical approach. We note that specific vibrational modelling is needed to accurately determine the spectra across the examined wavelength range, and systematically model the transitions that appear at wavelengths shorter than 250 nm. Additionally, we find in the cases of 2-thiouracil and 2,4-dithiouracil, that the gas-phase spectra deviate significantly from some previously published solution-phase spectra, especially those collected in basic environments.
Polypropylene as one of the world's top commodity polymers is also widely used in the textile industry. However, its non-polar nature and partially crystalline structure significantly complicate the process of industrial coloring of polypropylene. Currently, textiles made of polypropylene or with a significant proportion of polypropylene are dyed under quite harsh conditions, including the use of high pressures and temperatures, which makes this process energy intensive. This research presents a three-step synthesis of coloring agents, capable of adhering onto synthetic polypropylene yarns without harsh energy-consuming conditions. This is possible by encapsulation of organic pigments using trimethoxyphenylsilane, introduction of surface double bonds via modification of the silica shell with trimethoxysilylpropylmethacrylate and final attachment of highly adhesive anchor peptides using thiol-ene chemistry. We demonstrate the applicability of this approach by dyeing polypropylene yarns in a simple process under ambient conditions after giving a step-by-step guide for the synthesis of these new dyeing agents. Finally, the successful dyeing of the yarns is visualized, and its practicability is discussed.
Polypropylene as one of the world's top commodity polymers is also widely used in the textile industry. However, its non-polar nature and partially crystalline structure significantly complicate the process of industrial coloring of polypropylene. Currently, textiles made of polypropylene or with a significant proportion of polypropylene are dyed under quite harsh conditions, including the use of high pressures and temperatures, which makes this process energy intensive. This research presents a three-step synthesis of coloring agents, capable of adhering onto synthetic polypropylene yarns without harsh energy-consuming conditions. This is possible by encapsulation of organic pigments using trimethoxyphenylsilane, introduction of surface double bonds via modification of the silica shell with trimethoxysilylpropylmethacrylate and final attachment of highly adhesive anchor peptides using thiol-ene chemistry. We demonstrate the applicability of this approach by dyeing polypropylene yarns in a simple process under ambient conditions after giving a step-by-step guide for the synthesis of these new dyeing agents. Finally, the successful dyeing of the yarns is visualized, and its practicability is discussed.
The replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S-4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein, we demonstrate that the replacement of less than four sulfur atoms (S-1-DBD, 1,2-S-2-DBD, and 1,4-S-2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S-1- and S-2-DBD dyes is improved, compared with S-4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).
Enzyme degradable polymersomes from chitosan-g-[poly-l-lysine-block-epsilon-caprolactone] copolymer
(2020)
The scope of this study includes the synthesis of chitosan-g-[peptide-poly-epsilon-caprolactone] and its self-assembly into polymeric vesicles employing the solvent shift method. In this way, well-defined core-shell structures suitable for encapsulation of drugs are generated. The hydrophobic polycaprolactone side-chain and the hydrophilic chitosan backbone are linked via an enzyme-cleavable peptide. The synthetic route involves the functionalization of chitosan with maleimide groups and the preparation of polycaprolactone with alkyne end-groups. A peptide functionalized with a thiol group on one side and an azide group on the other side is prepared. Thiol-ene click-chemistry and azide-alkyne Huisgen cycloaddition are then used to link the chitosan and poly-epsilon-caprolactone chains, respectively, with this peptide. For a preliminary study, poly-l-lysin is a readily available and cleavable peptide that is introduced to investigate the feasibility of the system. The size and shape of the polymersomes are studied by dynamic light scattering and cryo-scanning electron microscopy. Furthermore, degradability is studied by incubating the polymersomes with two enzymes, trypsin and chitosanase. A dispersion of polymersomes is used to coat titanium plates and to further test the stability against enzymatic degradation.
This opinion article describes recent approaches to use the "biorefinery" concept to lower the carbon footprint of typical mass polymers, by replacing parts of the fossil monomers with similar or even the same monomer made from regrowing dendritic biomass. Herein, the new and green catalytic synthetic routes are for lactic acid (LA), isosorbide (IS), 2,5-furandicarboxylic acid (FDCA), and p-xylene (pXL). Furthermore, the synthesis of two unconventional lignocellulosic biomass derivable monomers, i.e., alpha-methylene-gamma-valerolactone (MeGVL) and levoglucosenol (LG), are presented. All those have the potential to enter in a cost-effective way, also the mass market and thereby recover lost areas for polymer materials. The differences of catalytic unit operations of the biorefinery are also discussed and the challenges that must be addressed along the synthesis path of each monomers.
A method for the fabrication of well-defined metallic nanostructures is presented here in a simple and straightforward fashion. As an alternative to lithographic techniques, this routine employs microcontact printing utilizing wrinkled stamps, which are prepared from polydimethylsiloxane (PDMS), and includes the formation of hydrophobic stripe patterns on a substrate via the transfer of oligomeric PDMS. Subsequent backfilling of the interspaces between these stripes with a hydroxyl-functional poly(2-vinyl pyridine) then provides the basic pattern for the deposition of citrate-stabilized gold nanoparticles promoted by electrostatic interaction. The resulting metallic nanostripes can be further customized by peeling off particles in a second microcontact printing step, which employs poly(ethylene imine) surface-decorated wrinkled stamps, to form nanolattices. Due to the independent adjustability of the period dimensions of the wrinkled stamps and stamp orientation with respect to the substrate, particle arrays on the (sub)micro-scale with various kinds of geometries are accessible in a straightforward fashion. This work provides an alternative, cost-effective, and scalable surface-patterning technique to fabricate nanolattice structures applicable to multiple types of functional nanoparticles. Being a top-down method, this process could be readily implemented into, e.g., the fabrication of optical and sensing devices on a large scale.
Lithium-ion batteries have revolutionized battery technology. However, the scarcity of lithium in nature is driving the search for alternatives. For that reason, sodium-ion batteries have attracted increasing attention in recent years. The main obstacle to their development is the anode as, unlike for lithium-ion batteries, graphite cannot be used due to the inability to form stoichiometrically useful intercalation compounds with sodium. A promising candidate for sodium storage is hard carbon a form of nongraphitisable carbon, that can be synthesized from various precursor materials. Processing of hard carbons is often done by using mechanochemical treatments. Although it is generally accepted and often observed that they can influence the porosity of hard carbons, their effect on battery performance not well understood. Here, the changes in porosity occurring during ball milling are elucidated and related to the properties of hard carbons in sodium storage. Analysis by combined gas physisorption and small angle X-ray scattering shows that porosity changes during ball milling with a significant increase of the open porosity, unsuitable for reversible sodium storage, and decrease of the closed porosity, suitable for reversible sodium storage. While pristine hard carbon can store 58.5 mAh g(-1) in the closed pores, upon 5 h of mechanical treatment in a ball mill it can only store 35.5 mAh g(-1). The obtained results are furthermore pointing towards the disputed "intercalation-adsorption" mechanism.
Point-of-care and in-vivo bio-diagnostic tools are the current need for the present critical scenarios in the healthcare industry. The past few decades have seen a surge in research activities related to solving the challenges associated with precise on-site bio-sensing. Cutting-edge fiber optic technology enables the interaction of light with functionalized fiber surfaces at remote locations to develop a novel, miniaturized and cost-effective lab on fiber technology for bio-sensing applications. The recent remarkable developments in the field of nanotechnology provide innumerable functionalization methodologies to develop selective bio-recognition elements for label free biosensors. These exceptional methods may be easily integrated with fiber surfaces to provide highly selective light-matter interaction depending on various transduction mechanisms. In the present review, an overview of optical fiber-based biosensors has been provided with focus on physical principles used, along with the functionalization protocols for the detection of various biological analytes to diagnose the disease. The design and performance of these biosensors in terms of operating range, selectivity, response time and limit of detection have been discussed. In the concluding remarks, the challenges associated with these biosensors and the improvement required to develop handheld devices to enable direct target detection have been highlighted.
The CH2Cl2/MeOH (1:1) extract of Zanthoxylum holstzianum stem bark showed good antiplasmodial activity (IC50 2.5 +/- 0.3 and 2.6 +/- 0.3 mu g/mL against the W2 and D6 strains of Plasmodium falciparum, respectively). From the extract five benzophenanthridine alkaloids [8-acetonyldihydrochelerythrine (1), nitidine (2), dihydrochelerythine (3), norchelerythrine (5), arnottianamide (8)]; a 2-quinolone alkaloid [N-methylflindersine (4)]; a lignan [4,4 '-dihydroxy-3,3 '-dimethoxylignan-9,9 '-diyl diacetate (7)] and a dimer of a benzophenanthridine and 2-quinoline [holstzianoquinoline (6)] were isolated. The CH2Cl2/MeOH (1:1) extract of the root bark afforded 1, 3-6, 8, chelerythridimerine (9) and 9-demethyloxychelerythrine (10). Holstzianoquinoline (6) is new, and is the second dimer linked by a C-C bond of a benzophenanthridine and a 2-quinoline reported thus far. The compounds were identified based on spectroscopic evidence. Amongst five compounds (1-5) tested against two strains of P. falciparum, nitidine (IC50 0.11 +/- 0.01 mu g/mL against W2 and D6 strains) and norchelerythrine (IC50 value of 0.15 +/- 0.01 mu g/mL against D6 strain) were the most active.
The swelling and co-nonsolvency behaviors in pure H2O and in a mixed H2O/CH3OH vapor atmosphere of two different polar, water-soluble polymers in thin film geometry are studied in situ. Films of a zwitterionic poly(sulfobetaine), namely, poly[3-((2-(methacryloyloxy)ethyl)dimethylammonio) propane-1-sulfonate] (PSPE), and a polar nonionic polymer, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), are investigated in real time by spectral reflectance (SR) measurements and Fourier transform infrared (FTIR) spectroscopy. Whereas PSPE is insoluble in methanol, PNIPMAM is soluble but exhibits cononsolvency behavior in water/methanol mixtures. First, the swelling of PSPE and PNIPMAM thin films in H2O vapor is followed. Subsequently, CH3OH is added to the vapor atmosphere, and its contracting effect on the water-swollen films is monitored, revealing a co-nonsolvency-type behavior for PNIPMAM and PSPE. SR measurements indicate that PSPE and PNIPMAM behave significantly different during the H2O swelling and subsequent exposure to CH3OH, not only with respect to the amounts of absorbed water and CH3OH, but also to the cosolvent-induced contraction mechanisms. While PSPE thin films exhibit an abrupt one-step contraction, the contraction of PNIPMAM thin films occurs in two steps. FTIR studies corroborate these findings on a molecular scale and reveal the role of the specific functional groups, both during the swelling and the cosolvent-induced switching of the solvation state.
We search for homovalent alternatives for A, B, and X-ions in ABX(3) type inorganic halide perovskites suitable for tandem solar cell applications. We replace the conventional A-site organic cation CH3NH3, by 3 inorganic cations, Cs, K, and Rb, and the B site consists of metals; Cd, Hg, Ge, Pb, and Sn This work is built on our previous high throughput screening of hybrid perovskite materials (Kar et al 2018 J. Chem. Phys. 149, 214701). By performing a systematic screening study using Density Functional Theory (DFT) methods, we found 11 suitable candidates; 2 Cs-based, 3 K-based and 6 Rb-based that are suitable for tandem solar cell applications.
Stem cells are capable of sensing and processing environmental inputs, converting this information to output a specific cell lineage through signaling cascades. Despite the combinatorial nature of mechanical, thermal, and biochemical signals, these stimuli have typically been decoupled and applied independently, requiring continuous regulation by controlling units. We employ a programmable polymer actuator sheet to autonomously synchronize thermal and mechanical signals applied to mesenchymal stem cells (MSC5). Using a grid on its underside, the shape change of polymer sheet, as well as cell morphology, calcium (Ca2+) influx, and focal adhesion assembly, could be visualized and quantified. This paper gives compelling evidence that the temperature sensing and mechanosensing of MSC5 are interconnected via intracellular Ca2+. Up-regulated Ca2+ levels lead to a remarkable alteration of histone H3K9 acetylation and activation of osteogenic related genes. The interplay of physical, thermal, and biochemical signaling was utilized to accelerate the cell differentiation toward osteogenic lineage. The approach of programmable bioinstructivity provides a fundamental principle for functional biomaterials exhibiting multifaceted stimuli on differentiation programs. Technological impact is expected in the tissue engineering of periosteum for treating bone defects.
Stem cells are capable of sensing and processing environmental inputs, converting this information to output a specific cell lineage through signaling cascades. Despite the combinatorial nature of mechanical, thermal, and biochemical signals, these stimuli have typically been decoupled and applied independently, requiring continuous regulation by controlling units. We employ a programmable polymer actuator sheet to autonomously synchronize thermal and mechanical signals applied to mesenchymal stem cells (MSC5). Using a grid on its underside, the shape change of polymer sheet, as well as cell morphology, calcium (Ca2+) influx, and focal adhesion assembly, could be visualized and quantified. This paper gives compelling evidence that the temperature sensing and mechanosensing of MSC5 are interconnected via intracellular Ca2+. Up-regulated Ca2+ levels lead to a remarkable alteration of histone H3K9 acetylation and activation of osteogenic related genes. The interplay of physical, thermal, and biochemical signaling was utilized to accelerate the cell differentiation toward osteogenic lineage. The approach of programmable bioinstructivity provides a fundamental principle for functional biomaterials exhibiting multifaceted stimuli on differentiation programs. Technological impact is expected in the tissue engineering of periosteum for treating bone defects.
The potential of using crystallinity as morphological parameter to control polyester degradation in acidic environments is explored in ultrathin films by Langmuir technique. Films of hydroxy or methacrylate end-capped oligo(epsilon-caprolactone) (OCL) are prepared at the air-water interface as a function of mean molecular area (MMA). The obtained amorphous, partially crystalline or highly crystalline ultrathin films of OCL are hydrolytically degraded at pH similar to 1.2 on water surface or on silicon surface as-transferred films. A high crystallinity reduces the hydrolytic degradation rate of the films on both water and solid surfaces. Different acceleration rates of hydrolytic degradation of semi-crystalline films are achieved either by crystals complete melting, partially melting, or by heating them below their melting temperatures. Semi-crystalline OCL films transferred via water onto a solid surface retain their crystalline morphology, degrade in a controlled manner, and are of interest as thermoswitchable coatings for cell substrates and medical devices.
The alpha-Al2O3(0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al-I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the alpha- Al2O3(0001)/H2O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al-OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated alpha-Al2O3(0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al-I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the alpha-Al2O3(0001)/liquid water interface -different preparation methods may create surfaces that do not interconvert-and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.
The production and consumption of commodity polymers have been an indispensable part of the development of our modern society. Owing to their adjustable properties and variety of functions, polymer-based materials will continue playing important roles in achieving the Sustainable Development Goals (SDG)s, defined by the United Nations, in key areas such as healthcare, transport, food preservation, construction, electronics, and water management. Considering the serious environmental crisis, generated by increasing consumption of plastics, leading-edge polymers need to incorporate two types of functions: Those that directly arise from the demands of the application (e.g. selective gas and liquid permeation, actuation or charge transport) and those that enable minimization of environmental harm, e.g., through prolongation of the functional lifetime, minimization of material usage, or through predictable disintegration into non-toxic fragments. Here, we give examples of how the incorporation of a thoughtful combination of properties/functions can enhance the sustainability of plastics ranging from material design to waste management. We focus on tools to measure and reduce the negative impacts of plastics on the environment throughout their life cycle, the use of renewable sources for their synthesis, the design of biodegradable and/or recyclable materials, and the use of biotechnological strategies for enzymatic recycling of plastics that fits into a circular bioeconomy. Finally, we discuss future applications for sustainable plastics with the aim to achieve the SDGs through international cooperation. <br /> Leading-edge polymer-based materials for consumer and advanced applications are necessary to achieve sustainable development at a global scale. It is essential to understand how sustainability can be incorporated in these materials via green chemistry, the integration of bio-based building blocks from biorefineries, circular bioeconomy strategies, and combined smart and functional capabilities.
Identification of patterns in chemical reaction pathways aids in the effective design of molecules for specific applications. Here, we report on model reactions with a water-soluble single thiol-thioester exchange (TTE) reaction substrate, which was designed taking in view biological and medical applications. This substrate consists of the thio-depsipeptide, Ac-Pro-Leu-Gly-SLeu-Leu-Gly-NEtSH (TDP) and does not yield foul-smelling thiol exchange products when compared with aromatic thiol containing single TTE substrates. TDP generates an alpha,omega-dithiol crosslinker in situ in a 'pseudo intramolecular' TTE. Competitive intermolecular TTE of TDP with externally added "basic" thiols increased the crosslinker concentration whilst "acidic" thiols decreased its concentration. TDP could potentially enable in situ bioconjugation and crosslinking applications.
The low temperature (95 K) NMR study of 1-Ph-1-t-Bu-silacyclohexane (1) showed the conformational equilibrium to be extremely one-sided toward thePh(ax),t-Bueq conformer. The barrier to interconversion has been measured (4.2-4.6 kcal/mol) and the conformational equilibrium [Delta nu = 1990.64 ppm (Si-29), 618.9 ppm (C-13), 1-Ph-ax:1-Pheq = (95.6-96.6%):(3.4-4.4%), K = 25 +/- 3, Delta G degrees = -RT ln K = 0.58-0.63 kcal/mol] analyzed. The assignment and quantification of the NMR signals is supported by MP2 and DFT calculations.
The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a alpha-Al2O3 (0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree-Fock and local Moller-Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72 eV): the correction to the frozen core-approximation of 0.06 eV and the CCSD(T) correction of 0.07 eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3.
The remarkable antifouling properties of zwitterionic polymers in controlled environments are often counteracted by their delicate mechanical stability. In order to improve the mechanical stabilities of zwitterionic hydrogels, the effect of increased crosslinker densities was thus explored. In a first approach, terpolymers of zwitterionic monomer 3-[N -2(methacryloyloxy)ethyl-N,N-dimethyl]ammonio propane-1-sulfonate (SPE), hydrophobic monomer butyl methacrylate (BMA), and photo-crosslinker 2-(4-benzoylphenoxy)ethyl methacrylate (BPEMA) were synthesized. Thin hydrogel coatings of the copolymers were then produced and photo-crosslinked. Studies of the swollen hydrogel films showed that not only the mechanical stability but also, unexpectedly, the antifouling properties were improved by the presence of hydrophobic BMA units in the terpolymers.
Based on the positive results shown by the amphiphilic terpolymers and in order to further test the impact that hydrophobicity has on both the antifouling properties of zwitterionic hydrogels and on their mechanical stability, a new amphiphilic zwitterionic methacrylic monomer, 3-((2-(methacryloyloxy)hexyl)dimethylammonio)propane-1-sulfonate (M1), was synthesized in good yields in a multistep synthesis. Homopolymers of M1 were obtained by free-radical polymerization. Similarly, terpolymers of M1, zwitterionic monomer SPE, and photo-crosslinker BPEMA were synthesized by free-radical copolymerization and thoroughly characterized, including its solubilities in selected solvents.
Also, a new family of vinyl amide zwitterionic monomomers, namely 3-(dimethyl(2-(N -vinylacetamido)ethyl)ammonio)propane-1-sulfonate (M2), 4-(dimethyl(2-(N-vinylacetamido)ethyl)ammonio)butane-1-sulfonate (M3), and 3-(dimethyl(2-(N-vinylacetamido)ethyl)ammonio)propyl sulfate (M4), together with the new photo-crosslinker 4-benzoyl-N-vinylbenzamide (M5) that is well-suited for copolymerization with vinylamides, are introduced within the scope of the present work. The monomers are synthesized with good yields developing a multistep synthesis. Homopolymers of the new vinyl amide zwitterionic monomers are obtained by free-radical polymerization and thoroughly characterized. From the solubility tests, it is remarkable that the homopolymers produced are fully soluble in water, evidence of their high hydrophilicity. Copolymerization of the vinyl amide zwitterionic monomers, M2, M3, and M4 with the vinyl amide photo-crosslinker M5 proved to require very specific polymerization conditions. Nevertheless, copolymers were successfully obtained by free-radical copolymerization under appropriate conditions.
Moreover, in an attempt to mitigate the intrinsic hydrophobicity introduced in the copolymers by the photo-crosslinkers, and based on the proven affinity of quaternized diallylamines to copolymerize with vinyl amides, a new quaternized diallylamine sulfobetaine photo-crosslinker 3-(diallyl(2-(4-benzoylphenoxy)ethyl)ammonio)propane-1-sulfonate (M6) is synthesized. However, despite a priori promising copolymerization suitability, copolymerization with the vinyl amide zwitterionic monomers could not be achieved.
The widespread use of antimicrobial agents to treat infectious diseases has led to the emergence of antibiotic resistant pathogens. Plants have played a central role in combating many ailments in humans, and Parinari curatellifolia has been used for medicinal purposes. Seven extracts from P. curatellifolia leaves were prepared using serial exhaustive extraction of nonpolar to polar solvents. The microbroth dilution method was used to evaluate antimicrobial bioactivities of extracts. Five of the extracts were significantly active against at least one test microbe. Mycobacterium smegmatis was the most susceptible to most extracts. The methanol and ethanol extracts were the most active against M. smegmatis with an MIC of 25 mu g/mL. The hexane extract was the most active against Candida krusei with an MIC of 25 mu g/mL. None of the extracts significantly inhibited growth of Klebsiella pneumoniae and Staphylococcus aureus. Active extracts were selected for fractionation and isolation of pure compounds using gradient elution column chromatography. TLC analyses was carried out for pooling fractions of similar profiles. A total of 43 pools were obtained from 428 fractions. Pools 7 and 10 were selected for further isolation of single compounds. Four compounds, Pc4963r, Pc4962w, Pc6978p, and Pc6978o, were isolated. Evaluation of antimicrobial activities of Pc4963r, Pc4962w, and Pc6978p showed that the compounds were most active against C. krusei with MFC values ranging from 50 to 100 mu g/mL. Only Pc6978p was shown to be pure. Using spectroscopic analyses, the structure of Pc6978p was determined to be beta-sitosterol. The antifungal effects of beta-sitosterol were evaluated against C. krusei in vitro and on fabrics. Results showed that beta-sitosterol reduced the growth of C. krusei attached to Mendy fabric by 83%. Therefore, P. curatellifolia can be a source of lead compounds for prospective development of novel antimicrobial agents. Further work needs to be done to improve the antifungal activity of the isolated compound using quantitative structure-activity relationships.
We report on the multiple response of microgels triggered by a single optical stimulus. Under irradiation, the volume of the microgels is reversibly switched by more than 20 times. The irradiation initiates two different processes: photo-isomerization of the photo-sensitive surfactant, which forms a complex with the anionic microgel, rendering it photo-responsive; and local heating due to a thermo-plasmonic effect within the structured gold layer on which the microgel is deposited. The photo-responsivity is related to the reversible accommodation/release of the photo-sensitive surfactant depending on its photo-isomerization state, while the thermo-sensitivity is intrinsically built in. We show that under exposure to green light, the thermo-plasmonic effect generates a local hot spot in the gold layer, resulting in the shrinkage of the microgel. This process competes with the simultaneous photo-induced swelling. Depending on the position of the laser spot, the spatiotemporal control of reversible particle shrinking/swelling with a predefined extent on a per-second base can be implemented.
The degradation of polymers is described by mathematical models based on bond cleavage statistics including the decreasing probability of chain cuts with decreasing average chain length. We derive equations for the degradation of chains under a random chain cut and a chain end cut mechanism, which are compared to existing models. The results are used to predict the influence of internal molecular parameters. It is shown that both chain cut mechanisms lead to a similar shape of the mass or molecular mass loss curve. A characteristic time is derived, which can be used to extract the maximum length of soluble fragments l of the polymer. We show that the complete description is needed to extract the degradation rate constant k from the molecular mass loss curve and that l can be used to design polymers that lose less mechanical stability before entering the mass loss phase.
Functionalization of gelatin with glycidylmethacrylate (GMA-gelatin) enables network formation employing the double bond, so that the reaction is orthogonal to the inherent functional groups in the biomacromolecule. Here, network formation by crosslinking of GMA-gelatin with hexane 1,6-dithiol or nonane 1,9-dithiol to tailor properties and enable a shape-memory effect is shown by H-1 NMR and FT-IR spectroscopy. Hydrogel swelling (460-1900 vol%) and mechanical properties (Young's modulus E = 59-512 kPa, elongation at break epsilon(b) = 44-127%) depended on the molecular composition of the networks and temperature. Increased crosslinker length, thiol:methacrylate molar ratio, and precursor concentrations led to denser networks. Change of properties with temperature suggested adoption of triple helices by gelatin chains, forming physical netpoints at lower temperatures (< 20 degrees C). However, the limited freedom of the gelatin chains to move allowed only a minimal extent of triple helices formation, as it became apparent from the related signal in wide-angle X-ray scattering and the thermal transition associated to triple helices in some networks by DSC. The presented strategy is likely transferable to other biomacromolecules, and the results suggest that too short crosslinkers may result in a significant amount of grafting rather than network formation.
Effect of endothelial culture medium composition on platelet responses to polymeric biomaterials
(2021)
Near-physiological in vitro thrombogenicity test systems for the evaluation of blood-contacting endothelialized biomaterials requires co-cultivation with platelets (PLT). However, the addition of PLT has led to unphysiological endothelial cell (EC) detachment in such in vitro systems. A possible cause for this phenomenon may be PLT activation triggered by the applied endothelial cell medium, which typically consists of basal medium (BM) and nine different supplements. To verify this hypothesis, the influence of BM and its supplements was systematically analyzed regarding PLT responses. For this, human platelet rich plasma (PRP) was mixed with BM, BM containing one of nine supplements, or with BM containing all supplements together. PLT adherence analysis was carried out in six-channel slides with plasma-treated cyclic olefin copolymer (COC) and poly(tetrafluoro ethylene) (PTFE, as a positive control) substrates as part of the six-channel slides in the absence of EC and under static conditions. PLT activation and aggregation were analyzed using light transmission aggregometry and flow cytometry (CD62P). Medium supplements had no effect on PLT activation and aggregation. In contrast, supplements differentially affected PLT adherence, however, in a polymer- and donor-dependent manner. Thus, the use of standard endothelial growth medium (BM + all supplements) maintains functionality of PLT under EC compatible conditions without masking the differences of PLT adherence on different polymeric substrates. These findings are important prerequisites for the establishment of a near-physiological in vitro thrombogenicity test system assessing polymer-based cardiovascular implant materials in contact with EC and PLT.
Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.
Hydrogels with a hierarchical structure were prepared from a new highly water-soluble crosslinker N,N,N',N'-tetramethyl-N,N'-bis(2-ethylmethacrylate)-propyl-1,3-diammonium dibromide and from the sulfobetaine monomer 2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate. The free radical polymerization of the two compounds is rapid and yields near-transparent hydrogels with sizes up to 5 cm in diameter. Rheology shows a clear correlation between the monomer-to-crosslinker ratio and the storage and loss moduli of the hydrogels. Cryo-scanning electron microscopy, low-field nuclear magnetic resonance (NMR) spectroscopy, and small-angle X-ray scattering show that the gels have a hierarchical structure with features spanning the nanometer to the sub-millimeter scale. The NMR study is challenged by the marked inhomogeneity of the gels and the complex chemical structure of the sulfobetaine monomer. NMR spectroscopy shows how these complications can be addressed via a novel fitting approach that considers the mobility gradient along the side chain of methacrylate-based monomers.
In vivo endothelialization of polymer-based cardiovascular implant materials is a promising strategy to reduce the risk of platelet adherence and the subsequent thrombus formation and implant failure. However, endothelial cells from elderly patients are likely to exhibit a senescent phenotype that may counteract endothelialization. The senescence status of cells should therefore be investigated prior to implantation of devices designed to be integrated in the blood vessel wall. Here, human umbilical vein endothelial cells (HUVEC) were cultivated up to passage (P) 4, 10 and 26/27 to determine the population doubling time and the senescence status by four different methods. Determination of the senescence-associated beta-galactosidase activity (SA-beta-Gal) was carried out by colorimetric staining and microscopy (i), as well as by photometric quantification (ii), and the expression of senescence-associated nuclear proteins p16 and p21 as well as the proliferation marker Ki67 was assessed by immunostaining (iii), and by flow cytometry (iv). The population doubling time of P27-cells was remarkably greater (103 +/- 65 h) compared to P4-cells (24 +/- 3 h) and P10-cell (37 +/- 15 h). Among the four different methods tested, the photometric SA-beta-Gal activity assay and the flow cytometric determination of p16 and Ki67 were most effective in discriminating P27-cells from P4- and P10-cells. These methods combined with functional endothelial cell analyses might aid predictions on the performance of implant endothelialization in vivo.