@article{GharabekyanKoetzPoghosyan2021, author = {Gharabekyan, Hrant H. and Koetz, Joachim and Poghosyan, Armen H.}, title = {A protonated L-cysteine adsorption on gold surface}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {629}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2021.127452}, pages = {7}, year = {2021}, abstract = {The adsorption of protonated L-cysteine onto Au(111) surface was studied via molecular dynamics method. The detailed examination of trajectories reveals that a couple of picoseconds need to be strongly adsorbed at the gold surface via L-cysteine's sulfur and oxygen atoms. The average distances of L-cysteine's adsorbed sulfur and oxygen from gold plane are-2.7 angstrom and-3.2 angstrom, correspondingly. We found that the adsorption of L-cysteine takes place preferentially at bridge site with possibility of-82\%. Discussing the conformation features of protonated L-cysteine, we consider that the most stable conformation of protonated L-cysteine is "reverse boat" position, where sulfur and oxygen pointed down to the gold surface, while the amino group is far from the gold surface.}, language = {en} } @article{DebatinBehrensWeberetal.2012, author = {Debatin, Franziska and Behrens, Karsten and Weber, Jens and Baburin, Igor A. and Thomas, Arne and Schmidt, Johannes and Senkovska, Irena and Kaskel, Stefan and Kelling, Alexandra and Hedin, Niklas and Bacsik, Zoltan and Leoni, Stefano and Seifert, Gotthard and J{\"a}ger, Christian and G{\"u}nter, Christina and Schilde, Uwe and Friedrich, Alwin and Holdt, Hans-J{\"u}rgen}, title = {An isoreticular family of microporous metal-organic frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate Syntheses, structures and properties}, series = {Chemistry - a European journal}, volume = {18}, journal = {Chemistry - a European journal}, number = {37}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201200889}, pages = {11630 -- 11640}, year = {2012}, abstract = {We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-14, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.01.7 angstrom), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and 1H MAS and 13C CP-MAS NMR spectroscopy. All IFPs showed high thermal stability (345400?degrees C); IFP-1 and IFP-4 were stable in boiling water for 7 d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO2 was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH4 (at 298 K), CO2 (at 298 K) and H2 (at 77 K) at high pressure were also investigated. In situ IR spectroscopy showed that CO2 is physisorbed on IFP-14 under dry conditions and that both CO2 and H2O are physisorbed on IFP-1 under moist conditions.}, language = {en} } @article{OtterMondalAlrefaietal.2021, author = {Otter, Dirk and Mondal, Suvendu Sekhar and Alrefai, Anas and Kr{\"a}tz, Lorenz and Holdt, Hans-J{\"u}rgen and Bart, Hans-J{\"o}rg}, title = {Characterization of an isostructural MOF series of Imidazolate Frameworks Potsdam by means of sorption experiments with water vapor}, series = {Nanomaterials}, volume = {11}, journal = {Nanomaterials}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2079-4991}, doi = {10.3390/nano11061400}, pages = {20}, year = {2021}, abstract = {Sorption measurements of water vapor on an isoreticular series of Imidazolate Frameworks Potsdam (IFP), based on penta-coordinated metal centers with secondary building units (SBUs) connected by multidentate amido-imidate-imidazolate linkers, have been carried out at 303.15 K. The isotherm shapes were analyzed in order to gain insight into material properties and compared to sorption experiments with nitrogen at 77.4 K and carbon dioxide at 273.15 K. Results show that water vapor sorption measurements are strongly influenced by the pore size distribution while having a distinct hysteresis loop between the adsorption and desorption branch in common. Thus, IFP-4 and -8, which solely contain micropores, exhibit H4 (type I) isotherm shapes, while those of IFP-1, -2 and -5, which also contain mesopores, are of H3 (type IV) shape with three inflection points. The choice of the used linker substituents and transition metals employed in the framework has a tremendous effect on the material properties and functionality. The water uptake capacities of the examined IFPs are ranging 0.48 mmol g(-1) (IFP-4) to 6.99 mmol g(-1) (IFP-5) and comparable to those documented for ZIFs. The water vapor stability of IFPs is high, with the exception of IFP-8.}, language = {en} } @phdthesis{Gutjahr2007, author = {Gutjahr, Petra}, title = {Conformations of semiflexible polymers and filaments}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-15918}, school = {Universit{\"a}t Potsdam}, year = {2007}, abstract = {The biological function and the technological applications of semiflexible polymers, such as DNA, actin filaments and carbon nanotubes, strongly depend on their rigidity. Semiflexible polymers are characterized by their persistence length, the definition of which is the subject of the first part of this thesis. Attractive interactions, that arise e.g.~in the adsorption, the condensation and the bundling of filaments, can change the conformation of a semiflexible polymer. The conformation depends on the relative magnitude of the material parameters and can be influenced by them in a systematic manner. In particular, the morphologies of semiflexible polymer rings, such as circular nanotubes or DNA, which are adsorbed onto substrates with three types of structures, are studied: (i) A topographical channel, (ii) a chemically modified stripe and (iii) a periodic pattern of topographical steps. The results are compared with the condensation of rings by attractive interactions. Furthermore, the bundling of two individual actin filaments, whose ends are anchored, is analyzed. This system geometry is shown to provide a systematic and quantitative method to extract the magnitude of the attraction between the filaments from experimentally observable conformations of the filaments.}, language = {en} } @article{Cherstvy2012, author = {Cherstvy, Andrey G.}, title = {Critical polyelectrolyte adsorption under confinement Planar slit, cylindrical pore, and spherical cavity}, series = {Biopolymers}, volume = {97}, journal = {Biopolymers}, number = {5}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0006-3525}, doi = {10.1002/bip.22023}, pages = {311 -- 317}, year = {2012}, abstract = {We explore the properties of adsorption of flexible polyelectrolyte chains in confined spaces between the oppositely charged surfaces in three basic geometries. A method of approximate uniformly valid solutions for the Green function equation for the eigenfunctions of polymer density distributions is developed to rationalize the critical adsorption conditions. The same approach was implemented in our recent study for the inverse problem of polyelectrolyte adsorption onto a planar surface, and on the outer surface of rod-like and spherical obstacles. For the three adsorption geometries investigated, the theory yields simple scaling relations for the minimal surface charge density that triggers the chain adsorption, as a function of the Debye screening length and surface curvature. The encapsulation of polyelectrolytes is governed by interplay of the electrostatic attraction energy toward the adsorbing surface and entropic repulsion of the chain squeezed into a thin slit or small cavities. Under the conditions of surface-mediated confinement, substantially larger polymer linear charge densities are required to adsorb a polyelectrolyte inside a charged spherical cavity, relative to a cylindrical pore and to a planar slit (at the same interfacial surface charge density). Possible biological implications are discussed briefly in the end.}, language = {en} } @misc{MondalBhuniaBaburinetal.2013, author = {Mondal, Suvendu Sekhar and Bhunia, Asamanjoy and Baburin, Igor A. and J{\"a}ger, Christian and Kelling, Alexandra and Schilde, Uwe and Seifert, Gotthard and Janiak, Christoph and Holdt, Hans-J{\"u}rgen}, title = {Gate effects in a hexagonal zinc-imidazolate-4-amide-5-imidate framework with flexible methoxy substituents and CO2 selectivity}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94341}, pages = {7599 -- 7601}, year = {2013}, abstract = {A new imidazolate-4-amide-5-imidate based MOF, IFP-7, is generated, having flexible methoxy groups, which act as molecular gates for guest molecules. This allows highly selective CO2 sorption over N2 and CH4 gases.}, language = {en} } @article{OmorogieBabalolaUnuabonahetal.2014, author = {Omorogie, Martins O. and Babalola, Jonathan Oyebamiji and Unuabonah, Emmanuel Iyayi and Gong, Jian R.}, title = {Hybrid materials from agro-waste and nanoparticles: implications on the kinetics of the adsorption of inorganic pollutants}, series = {Environmental technology}, volume = {35}, journal = {Environmental technology}, number = {5}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0959-3330}, doi = {10.1080/09593330.2013.839747}, pages = {611 -- 619}, year = {2014}, abstract = {This study is a first-hand report of the immobilization of Nauclea diderrichii seed waste biomass (ND) (an agro-waste) with eco-friendly mesoporous silica (MS) and graphene oxide-MS (GO+MS ) nanoparticles, producing two new hybrid materials namely: MND adsorbent for agro-waste modified with MS and GND adsorbent for agro-waste modified with GO+MS nanoparticles showed improved surface area, pore size and pore volume over those of the agro-waste. The abstractive potential of the new hybrid materials was explored for uptake of Cr(III) and Pb(II) ions. Analysis of experimental data from these new hybrid materials showed increased initial sorption rate of Cr(III) and Pb(II) ions uptake. The amounts of Cr(III) and Pb(II) ions adsorbed by MND and GND adsorbents were greater than those of ND. Modification of N. diderrichii seed waste significantly improved its rate of adsorption and diffusion coefficient for Cr(III) and Pb(II) more than its adsorption capacity. The rate of adsorption of the heavy metal ions was higher with GO+MS nanoparticles than for other adsorbents. Kinetic data were found to fit well the pseudo-second-order and the diffusion-chemisorption kinetic models suggesting that the adsorption of Cr(III) and Pb(II) onto these adsorbents is mainly through chemisorption mechanism. Analysis of kinetic data with the homogeneous particle diffusion kinetic model suggests that particle diffusion (diffusion of ions through the adsorbent) is the rate-limiting step for the adsorption process.}, language = {en} } @phdthesis{Haluska2004, author = {Haluska, Christopher K.}, title = {Interactions of functionalized vesicles in the presence of Europium (III) Chloride}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-2482}, school = {Universit{\"a}t Potsdam}, year = {2004}, abstract = {We incorporate amphiphilic receptors bearing ß-diketone functional units into large (LUV's) and giant unilamellar vesicles (GUV's). Electrolyte solutions containing di- and trivalent ions were used to induce inter-membrane interactions. Measurements performed with isothermal titration calorimetry (ITC) revealed that interaction between EuCl3 and ß-diketone receptors was characterized by a molar enthalpy 126 ± 5 kcal/mole and an equilibrium binding constant 26 ± 4 mM-1. The results indicate a molecular complex formed binding two ß-diketone receptors to one Eu3+ ion. Dynamic light scattering (DLS) was used to follow changes in LUV diameter indicated in an increase in vesicle size distribution of on average 20 \%. Optical microscopy was employed to visualize the inter-membrane interaction measured using DLS and ITC. Depending on membrane composition of the functionalized vesicles we found that local injections of micromolar EuCl¬3 induced membrane pore formation and membrane fusion. Our collection of results leads to the conclusion that formation of intra-molecular ligand receptor complexes leads to pore formation and inter-membrane complex formation leads to membrane fusion. Detailed characterization of the fusion process shows that irreversible opening of the fusion pore can be extrapolated to times below 50 µsec. We have found that formation of membrane bound ligand (Eu3+)-receptor complexes provides versatility to the function of vesicle membranes.}, subject = {Biophysik}, language = {de} } @article{PerovicAloniMastaietal.2020, author = {Perovic, Milena and Aloni, Sapir Shekef and Mastai, Yitzhak and Oschatz, Martin}, title = {Mesoporous carbon materials with enantioselective surface obtained by nanocasting for selective adsorption of chiral molecules from solution and the gas phase}, series = {Carbon}, volume = {170}, journal = {Carbon}, publisher = {Elsevier}, address = {Oxford}, issn = {0008-6223}, doi = {10.1016/j.carbon.2020.08.010}, pages = {550 -- 557}, year = {2020}, abstract = {Separation of enantiomers is an everlasting challenge in chemistry, catalysis, and synthesis of pharmaceuticals. The design and fabrication of chiral adsorbent materials is a promising way to increase the surface area of chiral information, as well as to maximize the available surface for the adsorption of one enantiomer. Porous materials such as silica or metal-organic-frameworks are established compounds in this field, due to their well-defined surface structure and ease of functionalization with chiral groups. As another class of porous materials, carbons provide the advantages of high thermal and chemical stability, resistance against moisture, electrical conductivity, and widely tunable pore size. Although they are well established in many adsorption-related applications, carbons received far less attention in enantioselective adsorption processes because the controlled functionalization of their surface is rather difficult due to the chemically heterogeneous atoms in the network. A suitable approach to overcome this limitation is the synthesis of chiral carbons directly from chiral precursors. So far, chiral carbons synthesized from chiral precursors used salt-templating as a way of introducing porosity, which resulted in mainly microporous materials or materials with broad pore size distribution. In the present study, the possibility of combining nanocasting as an alternative templating approach with chiral ionic liquids as a carbon precursor is demonstrated. Chiral recognition is measured in the gas phase, by adsorption of chiral gas, as well as in the solution, by using isothermal titration calorimetry. (C) 2020 Elsevier Ltd. All rights reserved.}, language = {en} } @phdthesis{Haase2011, author = {Haase, Martin F.}, title = {Modification of nanoparticle surfaces for emulsion stabilization and encapsulation of active molecules for anti-corrosive coatings}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-55413}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Within this work, three physicochemical methods for the hydrophobization of initially hydrophilic solid particles are investigated. The modified particles are then used for the stabilization of oil-in-water (o/w) emulsions. For all introduced methods electrostatic interactions between strongly or weakly charged groups in the system are es-sential. (i) Short chain alkylammonium bromides (C4 - C12) adsorb on oppositely charged solid particles. Macroscopic contact angle measurements of water droplets under air and hexane on flat silica surfaces in dependency of the surface charge density and alkylchain-length allow the calculation of the surface energy and give insights into the emulsification properties of solid particles modified with alkyltrimethylammonium bromides. The measure-ments show an increase of the contact angle with increasing surface charge density, due to the enhanced adsorp-tion of the oppositely charged alkylammonium bromides. Contact angles are higher for longer alkylchain lengths. The surface energy calculations show that in particular the surface-hexane or surface-air interfacial en-ergy is being lowered upon alkylammonium adsorption, while a significant increase of the surface-water interfa-cial energy occurs only at long alkyl chain lengths and high surface charge densities. (ii) The thickness and the charge density of an adsorbed weak polyelectrolyte layer (e.g. PMAA, PAH) influence the wettability of nanoparticles (e.g. alumina, silica, see Scheme 1(b)). Furthermore, the isoelectric point and the pH range of colloidal stability of particle-polyelectrolyte composites depend on the thickness of the weak polye-lectrolyte layer. Silica nanoparticles with adsorbed PAH and alumina nanoparticles with adsorbed PMAA be-come interfacially active and thus able to stabilize o/w emulsions when the degree of dissociation of the polye-lectrolyte layer is below 80 \%. The average droplet size after emulsification of dodecane in water depends on the thickness and the degree of dissociation of the adsorbed PE-layer. The visualization of the particle-stabilized o/w emulsions by cryogenic SEM shows that for colloidally stable alumina-PMAA composites the oil-water interface is covered with a closely packed monolayer of particles, while for the colloidally unstable case closely packed aggregated particles deposit on the interface. (iii) By emulsifying a mixture of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) and styrene with silica nanoparticles a highly stable o/w emulsion can be obtained in a narrow pH window. The amphoteric character of 8-HQ enables a pH dependent electrostatic interaction with silica nanoparticles, which can render them interfa-cially active. Depending on the concentration and the degree of dissociation of 8-HQ the adsorption onto silica results from electrostatic or aromatic interactions between 8-HQ and the particle-surface. At intermediate amounts of adsorbed 8-HQ the oil wettability of the particles becomes sufficient for stabilizing o/w emulsions. Cryogenic SEM visualization shows that the particles arrange then in a closely packed shell consisting of partly of aggregated domains on the droplet interface. For further increasing amounts of adsorbed 8-HQ the oil wet-tability is reduced again and the particles ability to stabilize emulsions decreases. By the addition of hexadecane to the oil phase the size of the droplets can be reduced down to 200 nm by in-creasing the silica mass fraction. Subsequent polymerization produces corrosion inhibitor filled (20 wt-\%) poly-styrene-silica composite particles. The measurement of the release of 8-hydroxyquinoline shows a rapid increase of 8-hydroxyquinoline in a stirred aqueous solution indicating the release of the total content in less than 5 min-utes. The method is extended for the encapsulation of other organic corrosion inhibitors. The silica-polymer-inhibitor composite particles are then dispersed in a water based alkyd emulsion, and the dispersion is used to coat flat aluminium substrates. After drying and cross-linking the polmer-film Confocal Laser Scanning Micros-copy is employed revealing a homogeneous distribution of the particles in the film. Electrochemical Impedance Spectroscopy in aqueous electrolyte solutions shows that films with aggregated particle domains degrade with time and don't provide long-term corrosion protection of the substrate. However, films with highly dispersed particles have high barrier properties for corrosive species. The comparison of films containing silica-polystyrene composite particles with and without 8-hydroxyquinoline shows higher electrochemical impedances when the inhibitor is present in the film. By applying the Scanning Vibrating Electrode Technique the localized corrosion rate in the fractured area of scratched polymer films containing the silica-polymer-inhibitor composite particles is studied. Electrochemical corrosion cannot be suppressed but the rate is lowered when inhibitor filled composite particles are present in the film. By depositing six polyelectrolyte layers on particle stabilized emulsion droplets their surface morphology changes significantly as shown by SEM visualization. When the oil wettability of the outer polyelectrolyte layer increases, the polyelectrolyte coated droplets can act as emulsion stabilizers themselves by attaching onto bigger oil droplets in a closely packed arrangement. In the presence of 3 mM LaCl3 8-HQ hydrophobized silica particles aggregate strongly on the oil-water inter-face. The application of an ultrasonic field can remove two dimensional shell-compartments from the droplet surface, which are then found in the aqueous bulk phase. Their size ranges up to 1/4th of the spherical particle shell.}, language = {en} }