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Visible-Light-Mediated Photodynamic Water Disinfection @ Bimetallic-Doped Hybrid Clay Nanocomposites
(2019)
This study reports a new class of photocatalytic hybrid clay nanocomposites prepared from low-cost sources (kaolinite clay and Carica papaya seeds) doped with Zn and Cu salts via a solvothermal process. X-ray diffraction analysis suggests that Cu-doping and Cu/Zn-doping introduce new phases into the crystalline structure of Kaolinite clay, which is linked to the reduced band gap of kaolinite from typically between 4.9 and 8.2 eV to 2.69 eV for Cu-doped and 1.5 eV for Cu/Zn hybrid clay nanocomposites (Nisar, J.; Arhammar, C.; Jamstorp, E.; Ahuja, R. Phys. Rev. B 2011, 84, 075120). In the presence of solar light irradiation, Cu- and Cu/Zn-doped nanocomposites facilitate the electron hole pair separation. This promotes the generation of singlet oxygen which in turn improves the water disinfection efficiencies of these novel nanocomposite materials. The nanocomposite materials were further characterized using high-resolution scanning electron microscopy, fluorimetry, therrnogravimetric analysis, and Raman spectroscopy. The breakthrough times of the nanocomposites for a fixed bed mode of disinfection of water contaminated with 2.32 x 10(7) cfu/mL E. coli ATCC 25922 under solar light irradiation are 25 h for Zn-doped, 30 h for Cu-doped, and 35 h for Cu/Zn-doped nanocomposites. In the presence of multidrug and multimetal resistant strains of E. coli, the breakthrough time decreases significantly. Zn-only doped nanocomposites are not photocatalytically active. In the absence of light, the nanocomposites are still effective in decontaminating water, although less efficient than under solar light irradiation. Electrostatic interaction, metal toxicity, and release of singlet oxygen (only in the Cu-doped and Cu/Zn-doped nanocomposites) are the three disinfection mechanisms by which these nanocomposites disinfect water. A regrowth study indicates the absence of any living E. coli cells in treated water even after 4 days. These data and the long hydraulic times (under gravity) exhibited by these nanocomposites during photodisinfection of water indicate an unusually high potential of these nanocomposites as efficient, affordable, and sustainable point-of-use systems for the disinfection of water in developing countries.
Diamondoids are hydrogen-saturated molecular motifs cut out of diamond, forming a class of materials with tunable optoelectronic properties. In this work, we extend previous work on neutral, closed-shell diamondoids by computing with hybrid density functional theory and time-dependent correlation functions vibrationally broadened absorption spectra of cations and radicals derived from the simplest diamondoid, adamantane, namely, the neutral 1- and 2-adamantyl radicals (C10H15), the 1- and 2-adamantyl cations (C10H15+), and the adamantane radical cation (C10H16+). For selected cases, we also report vibrationally broadened emission, photoelectron, and resonance Raman spectra. Furthermore, the effect of the damping factor on the vibrational fine-structure is studied. The following trends are found: (1) Low-energy absorptions of the adamantyl radicals and cations, and of the adamantane cation, are all strongly red-shifted with respect to adamantane; (2) also, emission spectra are strongly red-shifted, whereas photoelectron spectra are less affected for the cases studied; (3) vibrational fine-structures are reduced compared to those of adamantane; (4) the spectroscopic signals of 1- and 2-adamantyl species are significantly different from each other; and (5) reducing the damping factor has only a limited effect on the vibrational fine-structure in most cases. This suggests that removing hydrogen atoms and/or electrons from adamantane leads to new optoelectronic properties, which should be detectable by vibronic spectroscopy.
High Harmonic Generation (HHG) is a nonlinear optical process that provides a tunable source for high-energy photons and ultrashort laser pulses. Recent experiments demonstrated that HHG spectroscopy may also be used as an analytical tool to discriminate between randomly oriented configurational isomers of polyatomic organic molecules, namely, between the cis- and trans-forms of 1,2-dichloroethene (DCE) [M. C. H. Wong et al., Phys. Rev. A 84, 051403 (2011)]. Here, we suggest as an economic and at the same time a reasonably accurate method to compute HHG spectra for polyatomic species, Time-Dependent Configuration Interaction Singles (TD-CIS) theory in combination with extended atomic orbital bases and different models to account for ionization losses. The HHG spectra are computed for aligned and unaligned cis- and trans-DCE. For the unaligned case, a coherent averaging over possible rotational orientations is introduced. Furthermore, using TD-CIS, possible differences between the HHG spectra of cis- and trans-DCE are studied. For aligned molecules, spectral differences between cis and trans emerge, which can be related to their different point group symmetries. For unaligned, randomly oriented molecules, we also find distinct HHG spectra in partial agreement with experiment. In addition to HHG response in the frequency space, we compute time-frequency HHG spectra to gain insight into which harmonics are emitted at which time. Further differences between the two isomers emerge, suggesting time-frequency HHG as another tool to discriminate configurational isomers.
Background: While incidences of cancer are continuously increasing, drug resistance of malignant cells is observed towards almost all pharmaceuticals. Several isoflavonoids and flavonoids are known for their cytotoxicity towards various cancer cells. Methods: The cytotoxicity of compounds was determined based on the resazurin reduction assay. Caspases activation was evaluated using the caspase-Glo assay. Flow cytometry was used to analyze the cell cycle (propodium iodide (PI) staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP) (JC-1) and reactive oxygen species (ROS) (H2DCFH-DA). CCRF-CEM leukemia cells were used as model cells for mechanistic studies. Results: Compounds 1, 2 and 4 displayed IC50 values below 20 mu M towards CCRF-CEM and CEM/ADR5000 leukemia cells, and were further tested towards a panel of 7 carcinoma cells. The IC50 values of the compounds against carcinoma cells varied from 16.90 mu M (in resistant U87MG.Delta EGFR glioblastoma cells) to 48.67 mu M (against HepG2 hepatocarcinoma cells) for 1, from 7.85 mu M (in U87MG.Delta EGFR cells) to 14.44 mu M (in resistant MDA-MB231/BCRP breast adenocarcinoma cells) for 2, from 4.96 mu M (towards U87MG.Delta EGFRcells) to 7.76 mu M (against MDA-MB231/BCRP cells) for 4, and from 0.07 mu M (against MDA-MB231 cells) to 2.15 mu M (against HepG2 cells) for doxorubicin. Compounds 2 and 4 induced apoptosis in CCRF-CEM cells mediated by MMP alteration and increased ROS production. Conclusion: The present report indicates that isoflavones and biflavonoids from Ormocarpum kirkii are cytotoxic compounds with the potential of being exploited in cancer chemotherapy. Compounds 2 and 4 deserve further studies to develop new anticancer drugs to fight sensitive and resistant cancer cell lines.
By varying reaction parameters for the syntheses of the hydrogen-bonded metal-imidazolate frameworks (HIF) HIF-1 and HIF-2 (featuring 14 Zn and 14 Co atoms, respectively) to increase their yields and crystallinity, we found that HIF-1 is generated in two different frameworks, named as HIF-1a and HIF-1b. HIF-1b is isostructural to HIF-2. We determined the gas sorption and magnetic properties of HIF-2. In comparison to HIF-1a (Brunauer-Emmett-Teller (BET) surface area of 471m(2) g(-1)), HIF-2 possesses overall very low gas sorption uptake capacities [BET(CO2) surface area=85m(2) g(-1)]. Variable temperature magnetic susceptibility measurement of HIF-2 showed antiferromagnetic exchange interactions between the cobalt(II) high-spin centres at lower temperature. Theoretical analysis by density functional theory confirmed this finding. The UV/Vis-reflection spectra of HIF-1 (mixture of HIF-1a and b), HIF-2 and HIF-3 (with 14 Cd atoms) were measured and showed a characteristic absorption band centered at 340nm, which was indicative for differences in the imidazolate framework.
We report a new synthetic route to a series of a-carboxynitrobenzyl photocaged L-aspartates for application in time-resolved structural biology. The resulting compounds were characterised in terms of UV/Vis absorption properties, aqueous solubility and stability, and photocleavage rates (tau = ms to ms) and quantum yields (phi = 0.05 to 0.14).
Qualifying X-ray and Stimulated Raman Spectromicroscopy for Mapping Cutaneous Drug Penetration
(2019)
Research on topical drug delivery relies on reconstructed human skin (RHS) in addition to ex vivo human and animal skin, each with specific physiological features. Here, we compared the penetration of dexamethasone from an ethanolic hydroxyethyl cellulose gel into ex vivo human skin, murine skin, and RHS. For comprehensive insights into skin morphology and penetration enhancing mechanisms, scanning transmission X-ray microscopy (STXM), liquid chromatography tandem mass spectrometry (LC-MS/MS), and stimulated Raman spectromicroscopy (SRS) were combined. STXM offers high spatial resolution with label-free drug detection and is therefore sensitive to tissue damage. Despite differences in sample preparation and data analysis, the amounts of dexamethasone in RHS, detected and quantified by STXM and LC-MS/MS, were very similar and increased during the first 100 min of exposure. SRS revealed interactions between the gel and the stratum corneum or, more specifically, its protein and lipid structures. Similar to both types of ex vivo skin, higher protein-to-lipid ratios within the stratum corneum of RHS indicated reduced lipid amounts after 30 min of ethanol exposure. Extended ethanol exposure led to a continued reduction of lipids in the ex vivo matrixes, while protein integrity appeared to be compromised in RHS, which led to declining protein signals. In conclusion, LC-MS/MS proved the predictive capability of STXM for label-free drug detection. Combining STXM with SRS precisely dissected the penetration enhancing effects of ethanol. Further studies on topical drug delivery should consider the potential of these complementary techniques.
We investigate light-induced irreversible structuring of surface topographies in poly(3-sulfopropyl methacrylate/potassium salt) (PSPMK) brushes on flat solid substrates prepared by surface-initiated atom transfer radical polymerization. The brushes have been loaded with azobenzene-based surfactant comprised of positively charged headgroups and hydrophobic tail. The surfactant exhibits photoresponsive properties through photoisomerization from the trans to cis states leading to significant changes in physicochemical properties of grafted polymer chains. The azobenzene surfactant enables photoresponsive behavior without introducing irreversible changes to chemical composition of the parent polymer brush. Exposing these photosensitive brushes to irradiation with UV interference beams causes the polymer brush to form surface relief grating (SRG) patterns. The cationic surfactant penetrates only similar to 25% of the upper portion of the PSPMK brush, resulting in the formation of two sections within the brush: a photoresponsive upper layer and nonfunctional buried layer, which is not affected by the UV irradiation. Using nano-FTIR spectroscopy, we characterize locally the chemical composition of the polymer brush and confirm partial penetration of the surfactant within the film. Strong optomechanical stresses take place only within the upper layer of the brush that is impregnated with the surfactants and causes surface topography alternation due to a local rupture of grafted polymer chains. The cleaved polymer chains are then removed from the surface by using a good solvent, leaving behind topographical grating on top of the nonfunctional brush layer. We demonstrate that photostructured polymer brush can be used for reversible switching of brush topography by varying external humidity.
Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm-3(+) or Er-3(+) as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < lambda(em) < 480 nm (for Tm-3(+), three and four photon induced emission) or 525 nm < lambda(em) < 545 nm (for Er-3(+), two photon induced emission), respectively. Especially for UCNPs containing Tm-3(+) a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (lambda(ex) = 976 nm) in the presence of the Tm-3(+)-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR.
Glycan-protein interactions are essential biological processes with many disease-related modulations and variations. One of the key proteins involved in tumor progression and metastasis is galectin-3 (Gal-3). A lot of effort is put into the development of Gal-3 inhibitors as new therapeutic agents. The avidity of glycan-protein interactions is strongly enhanced by multivalent ligand presentation. Multivalent presentation of glycans can be accomplished by utilizing glycopolymers, which are polymers with pendent glycan groups. For the production of glycopolymers, glycomonomers are synthesized by a regioselective, microwave-assisted approach starting from lactose. The resulting methacrylamide derivatives are polymerized by RAFT and immobilized on gold surfaces using the trithiocarbonate group of the chain transfer agent. Surface plasmon resonance spectroscopy enables the label free kinetic characterization of Gal-3 binding to these multivalent glycopolymers. The measurements indicate oligomerization of Gal-3 upon exposure to multivalent environments and reveal strong specific interaction with the immobilized polymers.
Water can adsorb molecularly or dissociatively onto different sites of metal oxide surfaces. These adsorption sites can be disentangled using surface-sensitive vibrational spectroscopy. Here, we model Vibrational Sum Frequency (VSF) spectra for various forms of dissociated, deuterated water on a reconstructed, Al-terminated α-Al2O3(0001) surface at submonolayer coverages (the so-called 1-2, 1-4, and 1-4′ modes). Using an efficient scheme based on velocity-velocity autocorrelation functions, we go beyond previous normal mode analyses by including anharmonicity, mode coupling, and thermal surface motion in the framework of ab initio molecular dynamics. In this way, we calculate vibrational density of states curves, infrared, and VSF spectra. Comparing computed VSF spectra with measured ones, we find that relative frequencies of resonances are in quite good agreement and linewidths are reasonably well represented, while VSF intensities coincide not well. We argue that intensities are sensitively affected by local interactions and thermal fluctuations, even at such low coverage, while absolute peak positions strongly depend on the choice of the electronic structure method and on the appropriate inclusion of anharmonicity.
Background signals from in situ-formed amorphous carbon, despite not being fully understood, are known to be a common issue in few-molecule surface-enhanced Raman scattering (SERS). Here, discrete gold and silver nanoparticle aggregates assembled by DNA origami were used to study the conditions for the formation of amorphous carbon during SERS measurements. Gold and silver dimers were exposed to laser light of varied power densities and wavelengths. Amorphous carbon prevalently formed on silver aggregates and at high power densities. Time-resolved measurements enabled us to follow the formation of amorphous carbon. Silver nanolenses consisting of three differently-sized silver nanoparticles were used to follow the generation of amorphous carbon at the single-nanostructure level. This allowed observation of the many sharp peaks that constitute the broad amorphous carbon signal found in ensemble measurements. In conclusion, we highlight strategies to prevent amorphous carbon formation, especially for DNA-assembled SERS substrates.
Thermal treatment of hexaazatriphenylene-hexacarbonitrile (HAT-CN) in the temperature range from 500 degrees C to 700 degrees C leads to precise control over the degree of condensation, and thus atomic construction and porosity of the resulting C2N-type materials. Depending on the condensation temperature of HAT-CN, nitrogen contents of more than 30 at% can be reached. In general, these carbons show adsorption properties which are comparable to those known for zeolites but their pore size can be adjusted over a wider range. At condensation temperatures of 525 degrees C and below, the uptake of nitrogen gas remains negligible due to size exclusion, but the internal pores are large and polarizing enough that CO2 can still adsorb on part of the internal surface. This leads to surprisingly high CO2 adsorption capacities and isosteric heat of adsorption of up to 52 kJ mol(-1). Theoretical calculations show that this high binding enthalpy arises from collective stabilization effects from the nitrogen atoms in the C2N layers surrounding the carbon atom in the CO2 molecule and from the electron acceptor properties of the carbon atoms from C2N which are in close proximity to the oxygen atoms in CO2. A true CO2 molecular sieving effect is achieved for the first time in such a metal-free organic material with zeolite-like properties, showing an IAST CO2/N-2 selectivity of up to 121 at 298 K and a N-2/CO2 ratio of 90/10 without notable changes in the CO2 adsorption properities over 80 cycles.
Methylmercury (MeHg), an abundant environmental pollutant, has long been known to adversely affect neurodevelopment in both animals and humans. Several reports from epidemiological studies, as well as experimental data indicate sex-specific susceptibility to this neurotoxicant; however, the molecular bases of this process are still not clear. In the present study, we used Caenorhabditis elegans (C. elegans), to investigate sex differences in response to MeHg toxicity during development. Worms at different developmental stage (L1, L4, and adult) were treated with MeHg for 1h. Lethality assays revealed that male worms exhibited significantly higher resistance to MeHg than hermaphrodites, when at L4 stage or adults. However, the number of worms with degenerated neurons was unaffected by MeHg, both in males and hermaphrodites. Lower susceptibility of males was not related to changes in mercury (Hg) accumulation, which was analogous for both wild-type (wt) and male-rich him-8 strain. Total glutathione (GSH) levels decreased upon MeHg in him-8, but not in wt. Moreover, the sex-dependent response of the cytoplasmic thioredoxin system was observedmales exhibited significantly higher expression of thioredoxin TRX-1, and thioredoxin reductase TRXR-1 expression was downregulated upon MeHg treatment only in hermaphrodites. These outcomes indicate that the redox status is an important contributor to sex-specific sensitivity to MeHg in C. elegans.
Thermoresponsive films of poly(N-isopropyl methacrylamide) (PNIPMAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) are compared with respect to their hydration and dehydration kinetics using in situ neutron reflectivity. Both as-prepared films present a homogeneous single-layer structure and have similar transition temperatures of the lower critical solution temperature type (TT, PNIPMAM 38 degrees C and PMDEGA 41 degrees C). After hydration in unsaturated D2O vapor at 23 degrees C, a D2O enrichment layer is observed in PNIPMAM films adjacent to the Si substrate. In contrast, two enrichment layers are present in PMDEGA films (close to the vapor interface and the Si substrate). PNIPMAM films exhibit a higher hydration capability, ascribed to having both donor (N-H) and acceptor (C=O) units for hydrogen bonds. "While the swelling of the PMDEGA films is mainly caused by the increase of the enrichment layers, the thickness of the entire PNIPMAM films increases with time. The observed longer relaxation time for swelling of PNIPMAM films is attributed to the much higher glass transition temperature of PNIPMAM. When dehydrating both films by increasing the temperature above the TT, they react with a complex response consisting of three stages (shrinkage, rearrangement, and reswelling). PNIPMAM films respond faster than PMDEGA films. After dehydration, both films still contain a large amount of D2O, and no completely dry film state is reached for a temperature above their TTs.
All-in-One "Schizophrenic" self-assembly of orthogonally tuned thermoresponsive diblock copolymers
(2019)
Smart, fully orthogonal switching was realized in a highly biocompatible diblock copolymer system with variable trigger-induced aqueous self-assembly. The polymers are composed of nonionic and zwitterionic blocks featuring lower and upper critical solution temperatures (LCSTs and UCSTs). In the system investigated, diblock copolymers from poly(N-isopropyl methacrylamide) (PNIPMAM) and a poly(sulfobetaine methacrylamide), systematic variation of the molar mass of the latter block allowed for shifting the UCST of the latter above the LCST of the PNIPMAM block in a salt-free condition. Thus, successive thermal switching results in "schizophrenic" micellization, in which the roles of the hydrophobic core block and the hydrophilic shell block are interchanged depending on the temperature. Furthermore, by virtue of the strong electrolyte-sensitivity of the zwitterionic polysulfobetaine block, we succeeded to shift its UCST below the LCST of the PNIPMAM block by adding small amounts of an electrolyte, thus inverting the pathway of switching. This superimposed orthogonal switching by electrolyte addition enabled us to control the switching scenarios between the two types of micelles (i) via an insoluble state, if the LCST-type cloud point is below the UCST-type cloud point, which is the case at low salt concentrations or (ii) via a molecularly dissolved state, if the LCST-type cloud point is above the UCST-type cloud point, which is the case at high salt concentrations. Systematic variation of the block lengths allowed for verifying the anticipated behavior and identifying the molecular architecture needed. The versatile and tunable self-assembly offers manifold opportunities, for example, for smart emulsifiers or for sophisticated carrier systems.
The humidity-induced swelling and exchange behavior of a block copolymer thin film, which consists of a zwitterionic poly(sulfobetaine) [poly(N,N-dimethyl-N-(3-(methacrylamido)propyl)ammoniopropanesulfonate) (PSPP)] block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block, are investigated by time-of-flight neutron reflectometry (TOF-NR). We monitor in situ the swelling in the H2O atmosphere, followed by an exchange with D2O. In the reverse experiment, swelling in the D2O atmosphere and the subsequent exchange with H2O are studied. Both, static and kinetic TOF-NR measurements indicate significant differences in the interactions between the PSPP80-b-PNIPAM(130) thin film and H2O or D2O, which we attribute to the different H- and D-bonds between water and the polymer. Changes in the chain conformation and hydrogen bonding are probed with Fourier transform infrared spectroscopy during the kinetics of the swelling and exchange processes, which reveals the key roles of the ionic SO3- group in the PSPP block and of the polar amide groups of both blocks during water uptake and exchange.
Core-shell nanoparticles stabilized by a cationic surfactant are prepared from the poly(2,2,6,6-tetra-methylpiperidinyloxy-4-yl methacrylate) redox polymer. The nanoparticles are further self-assembled with negatively charged reduced graphene oxide nanosheets and negatively charged mull-walled carbon nanotubes. This results in the formation of a free-standing cathode with a layered nanostructure and a high content of redox polymer that exhibits 100% utilization of the active substance with a measured capacity as high as 105 mAh/g based on the whole weight of the electrode.
MoS2, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS2-carbon was successfully synthesized through an L-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m(2) g(-1), a total pore volume of 0.677 cm(3) g(-1), and fairly small mesopores (approximate to 5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g(-1) (0.12 F cm(-2)) at a constant current density of 0.1 Ag-1; thus suggesting that hollow carbon-MoS2 carbon nanoplates are promising candidate materials for supercapacitors.
A facile and novel method for the fabrication of core-shell nanoparticles (PTMA@SiO2) based on a poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) core and a porous SiO2 shell is reported. The core-shell nanoparticles are further self-assembled with negatively charged multi-walled carbon nanotubes (MWCNTs), which results in the formation of a free-standing cathode electrode. The porous SiO2 shell not only effectively improves the stability of the linear PTMA redox polymer with low molar mass in organic electrolytes but also leads to the uniform dispersion of PTMA active units in the MWCNTs conductive network. The PTMA@SiO2@MWCNT composite electrode exhibits a specific capacity as high as 73.8 mAh g at 1 C and only 0.11% capacity loss per cycle at a rate of 2 C.
HighlightsFacile electrodeposition for fabricating active Ni nanodots (NiNDs) on Ni foam (NF) is shown.Binder- and heteroatom-free recyclable NiO/NiNDs@NF electrodes are efficiently made.NiO/NiNDs@NF bifunctional catalytic electrodes are used for water splitting. AbstractIn past decades, Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for water splitting. With increasing demands for Ni worldwide, simplifying the fabrication process, increasing Ni recycling, and reducing waste are tangible sustainability goals. Here, binder-free, heteroatom-free, and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method. Typically, active Ni nanodot (NiND) clusters are electrodeposited on Ni foam (NF) in Ni(NO3)(2) acetonitrile solution. After drying in air, NiO/NiND composites are obtained, leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode. The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials ((10)(HER)=119mV and (50)(OER)=360mV) and can promote water catalysis at 1.70V@10mAcm(-2). More importantly, the recovery of raw materials (NF and Ni(NO3)(2)) is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes. Additionally, a large-sized (S similar to 70cm(2)) NiO/NiNDs@NF catalytic electrode with high durability has also been constructed. This method provides a simple and fast technology to construct high-performance, low-cost, and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of typical N-heterocyclic carbenes NHCs, r-NHCs, a-NHCs and MICs have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. Prior to that both structures and 13C chemical shifts were calculated and in case of isolated carbenes the computed δ(13C)/ppm values compared (as a quality criterion for obtained structures) with the experimental ones. The TSNMRS values of the studied carbenes, which are in mesomeric equilibrium with zwitterionic (ylide/betaine/mesoionic) resonance contributors, are employed to qualify and quantify the present electronic structure and if the term carbene is still justified to denote the compounds studied. The results, thus obtained from spatial magnetic properties (TSNMRS), are compared with the geometry of the compounds, the corresponding WIBERG's bond index values, and the 13C chemical shifts especially of the carbene electron-deficient centre.
The numerical prediction of radiative transport is a challenging task due to the complexity of the radiative transport equation. We apply the lattice Boltzmann method (LBM), originally developed for fluid flow problems, to solve the radiative transport in volume. One model (meso RTLBM) is derived directly from a discretization of the radiative transport equation, yielding in a precise but numerical costly scheme. The second model (macro RTLBM) solves the Helmholtz equation, which is a proper approximation for highly scattering volumes. Both numerical algorithms are validated against Monte-Carlo data for a set of 35 optical parameters, which correspond to radiative transport ranging from ballistic to diffuse regimes. Together with a set of four benchmark simulations, the comprehensive validation concludes the overall quality and detects asymptotic trends for radiative transport LBM. Furthermore, an accuracy map is presented, which summarizes the error for all parameters. This graph allows to determine the validity range for both radiative transport LBM at a glance. Finally, comprehensive guidelines are formulated to facilitate the choice of the radiative transport LBM model.
A new micro/mesoporous hybrid clay nanocomposite prepared from kaolinite clay, Carica papaya seeds, and ZnCl2 via calcination in an inert atmosphere is presented. Regardless of the synthesis temperature, the specific surface area of the nanocomposite material is between approximate to 150 and 300 m(2)/g. The material contains both micro- and mesopores in roughly equal amounts. X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy suggest the formation of several new bonds in the materials upon reaction of the precursors, thus confirming the formation of a new hybrid material. Thermogravimetric analysis/differential thermal analysis and elemental analysis confirm the presence of carbonaceous matter. The new composite is stable up to 900 degrees C and is an efficient adsorbent for the removal of a water micropollutant, 4-nitrophenol, and a pathogen, E. coli, from an aqueous medium, suggesting applications in water remediation are feasible.
Photoisomerization in some azobenzene-containing polymers (azopolymers) results in reversible solid-to-liquid transitions because trans- and cis-azopolymers have different glass transition temperatures. This property enables photoinduced healing and processing of azopolymers with high spatiotemporal resolution. However, a general lack of knowledge about the influence of the polymer structure on photoinduced reversible solid-to-liquid transitions hinders the design of such novel polymers. Herein, the synthesis and photoresponsive behavior of new azopolymers with different lengths of spacers between the polymer backbone and the azobenzene group on the side chain are reported. Azopolymers with no and 20 methylene spacers did not show photoinduced solid-to-liquid transitions. Azopolymers with 6 or 12 methylene spacers showed photoinduced solid-to-liquid transitions. This study demonstrates that spacers are essential for azopolymers with photoinduced reversible solid-to-liquid transitions, and thus, gives an insight into how to design azopolymers for photoinduced healing and processing.
Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3), we reveal the band dispersion in two high-symmetry directions and identify the global valence band maxima. With these benchmark data, we construct "standard" photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature for determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.
Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric-plasmonic circuits. It is crucial though, to control the distance of the wire to a supporting substrate, to another metal layer or to active materials with sub-nanometer precision. A dielectric coating can be utilized for distance control, but it must not degrade the plasmonic properties. In this paper, we introduce a controlled synthesis and coating approach for silver nanowires to fulfill these demands. We synthesize and characterize silver nanowires of around 70 nm in diameter. These nanowires are coated with nm-sized silica shells using a modified Stober method to achieve a homogeneous and smooth surface quality. We use transmission electron microscopy, dark-field microscopy and electron-energy loss spectroscopy to study morphology and plasmonic resonances of individual nanowires and quantify the influence of the silica coating. Thorough numerical simulations support the experimental findings showing that the coating does not deteriorate the plasmonic properties and thus introduce silver nanowires as usable building blocks for integrated hybrid plasmonic systems.
Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag⁺ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption.
Decoupling of optical properties appears challenging, but vital to get better insight of the relationship between light and fruit attributes. In this study, nine solid phantoms capturing the ranges of absorption (μa) and reduced scattering (μs’) coefficients in fruit were analysed non-destructively using laser-induced backscattering imaging (LLBI) at 1060 nm. Data analysis of LLBI was carried out on the diffuse reflectance, attenuation profile obtained by means of Farrell’s diffusion theory either calculating μa [cm−1] and μs’ [cm−1] in one fitting step or fitting only one optical variable and providing the other one from a destructive analysis. The nondestructive approach was approved when calculating one unknown coefficient non-destructively, while no ability of the method was found to analysis both, μa and μs’, non-destructively. Setting μs’ according to destructive photon density wave (PDW) spectroscopy and fitting μa resulted in root mean square error (rmse) of 18.7% in comparison to fitting μs’ resulting in rmse of 2.6%, pointing to decreased measuring uncertainty, when the highly variable μa was known.
The approach was tested on European pear, utilizing destructive PDW spectroscopy for setting one variable, while LLBI was applied for calculating the remaining coefficient. Results indicated that the optical properties of pear obtained from PDW spectroscopy as well as LLBI changed concurrently in correspondence to water content mainly. A destructive batch-wise analysis of μs’ and online analysis of μa may be considered in future developments for improved fruit sorting results, when considering fruit with high variability of μs’.
The lack of soil data, which are relevant, reliable, affordable, immediately available, and sufficiently detailed, is still a significant challenge in precision agriculture. A promising technology for the spatial assessment of the distribution of chemical elements within fields, without sample preparation is laser-induced breakdown spectroscopy (LIBS). Its advantages are contrasted by a strong matrix dependence of the LIBS signal which necessitates careful data evaluation. In this work, different calibration approaches for soil LIBS data are presented. The data were obtained from 139 soil samples collected on two neighboring agricultural fields in a quaternary landscape of northeast Germany with very variable soils. Reference analysis was carried out by inductively coupled plasma optical emission spectroscopy after wet digestion. The major nutrients Ca and Mg and the minor nutrient Fe were investigated. Three calibration strategies were compared. The first method was based on univariate calibration by standard addition using just one soil sample and applying the derived calibration model to the LIBS data of both fields. The second univariate model derived the calibration from the reference analytics of all samples from one field. The prediction is validated by LIBS data of the second field. The third method is a multivariate calibration approach based on partial least squares regression (PLSR). The LIBS spectra of the first field are used for training. Validation was carried out by 20-fold cross-validation using the LIBS data of the first field and independently on the second field data. The second univariate method yielded better calibration and prediction results compared to the first method, since matrix effects were better accounted for. PLSR did not strongly improve the prediction in comparison to the second univariate method.
Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures).
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzyne 1 and analogues (benzene 2, 1,2,3-cyclohexatriene 3, cyclohexen-3-yne 4, cyclohexen-4-yne 5, cyclohexyne 6) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values could be employed to compare the diatropic ring current effects of benzene and benzyne, and, when compared with the spatial magnetic properties of the analogues, to answer the question whether the benzyne electronic structure is more acetylene- or cumulene-like, supported by structural data and delta(C-13)/ppm values. (C) 2019 Published by Elsevier Ltd.
To synthesize functionalized Mannich bases that can serve two different types of ortho-quinone methide (o-QM) intermediates, 2-naphthol and 6-hydroxyquinoline were reacted with salicylic aldehyde in the presence of morpholine. The Mannich bases that can form o-QM and aza-o-QM were also synthesized by mixing 2-naphthol, 2-nitrobenzaldehyde, and morpholine followed by reduction of the nitro group. The highly functionalized aminonaphthol derivatives were then tested in [4+2] cycloaddition with different cyclic imines. The reaction proved to be both regio- and diastereoselective. In all cases, only one reaction product was obtained. Detailed structural analyses of the new polyheterocycles as well as conformational studies including DFT modelling were performed. The relative stability of o-QMs/aza-o-QM were also calculated, and the regioselectivity of the reactions could be explained only when the cycloaddition started from aminodiol 4. It was summarized that starting from diaminonaphthol 25, the regioselectivity of the reaction is driven by the higher nucleophilicity of the amino group compared with the hydroxy group. 12H-benzo[a]xanthen-12-one (11), formed via o-QM formation, was isolated as a side product. The proton NMR spectrum of 11 proved to be very unique from NMR point of view. The reason for the extreme low-field position of proton H-1 could be accounted for by theoretical calculation of structure and spatial magnetic properties of the compound in combination of ring current effects of the aromatic moieties and steric compression within the heavily hindered H(1)-C(1)-C(12b)-C(12a)-C(12)=O structural fragment.
1-Methylthio-1-phenyl-1-silacyclohexane 1, the first silacyclohexane with the sulfur atom at silicon, was synthesized and its molecular structure and conformational preferences studied by gas-phase electron diffraction (GED) and low temperature C-13 and Si-29 NMR spectroscopy (LT NMR). Quantum-chemical calculations were carried out both for the isolated species and solvate complexes in gas and in polar medium. The predominance of the 1-MeSaxPheq conformer in gas phase (1-Ph-eq :1-Ph-ax = 55:45, Delta G degrees = 0.13 kcal/mol) determined from GED is consistent with that measured in the freon solution by LT NMR (1-Ph-eq:1-Ph-ax = 65:35, Delta G degrees = 0.12 kcal/mol), the experimentally measured ratios being close to that estimated by quantum chemical calculations at both the DFT and MP2 levels of theory. (C) 2019 Elsevier Ltd. All rights reserved.
The DFT and MP2 theoretical conformational analysis of the recently synthesized (1,1-phenyl-1,1-silacyclohex-1-yl)disiloxane has revealed the energetic preference of the Ph-ax,Ph-ax conformer. The Ph-ax,Ph-ax: Ph-ax,Ph-eq: Ph-eq,Ph-eq conformers ratio has been estimated as of 46.6: 33.1: 20.3 from the M062X/6-311G(d,p) free energy simulation, suggesting the possibility of detecting individual conformers experimentally, e.g., by low-temperature H-1 and C-13 NMR spectroscopy. However, only the presence of several conformers has been detected by means of H-1 NMR spectroscopy at 113 K; determination of the (Hz) and G(#) (kcal/mol) parameters for the 6-membered ring interconversion has been impossible due to the signals broadening at low temperature, signal temperature shifts, and extremely low barrier of ring inversion at T-c < 113 K.
Benzenium Ion
(2019)
The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of the benzenium cation (C6H7+) 1 and of +/- I/M-substituted analogues C6H6X+ 3-8 [X = -Me, -CF3, -NH2, -NO2, -NO, -SiH3] have been calculated using the gauge-independent atomic orbital perturbation method employing the nucleus-independent chemical shift concept, and iso-chemical-shielding surfaces of various sizes and directions have been observed. The TSNMRS values were employed to compare the spatial magnetic properties (TSNMRS) of benzene and the benzenium ion 1 and then further compared with analogues 3-8, to answer the question whether the electronic structures of 1 and 3-8 are still similar to those of aromatic species or somewhat similar to the antiaromatic cyclopentadienyl cation 2, supported by structural data and delta(C-13)/ppm values.
A novel and efficient metal- and solvent-free regioselective para-C-H cyanation of hydroxy-, alkoxy-, and benzyloxyarene derivatives has been introduced, using nontoxic potassium thiocyanate as a cyanating reagent in the presence of silica sulfuric acid (SSA). The desired products are obtained in good to high yields without any toxic byproducts.