TY - JOUR A1 - Adelsberger, Joseph A1 - Bivigou Koumba, Achille Mayelle A1 - Miasnikova, Anna A1 - Busch, Peter A1 - Laschewsky, André A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Polystyrene-block-poly (methoxy diethylene glycol acrylate)-block-polystyrene triblock copolymers in aqueous solution-a SANS study of the temperature-induced switching behavior JF - Colloid and polymer science : official journal of the Kolloid-Gesellschaft N2 - A concentrated solution of a symmetric triblock copolymer with a thermoresponsive poly(methoxy diethylene glycol acrylate) (PMDEGA) middle block and short hydrophobic, fully deuterated polystyrene end blocks is investigated in D2O where it undergoes a lower critical solution temperature-type phase transition at ca. 36 A degrees C. Small-angle neutron scattering (SANS) in a wide temperature range (15-50 A degrees C) is used to characterize the size and inner structure of the micelles as well as the correlation between the micelles and the formation of aggregates by the micelles above the cloud point (CP). A model featuring spherical core-shell micelles, which are correlated by a hard-sphere potential or a sticky hard-sphere potential together with a Guinier form factor describing aggregates formed by the micelles above the CP, fits the SANS curves well in the entire temperature range. The thickness of the thermoresponsive micellar PMDEGA shell as well as the hard-sphere radius increase slightly already below the cloud point. Whereas the thickness of the thermoresponsive micellar shell hardly shrinks when heating through the CP and up to 50 A degrees C, the hard-sphere radius decreases within 3.5 K at the CP. The volume fraction decreases already significantly below the CP, which may be at the origin of the previously observed gel-sol transition far below the CP (Miasnikova et al., Langmuir 28: 4479-4490, 2012). Above the CP, small, and at higher temperatures, large aggregates are formed by the micelles. KW - Hydrogel KW - Thermoresponsive KW - LCST behavior KW - SANS Y1 - 2015 U6 - https://doi.org/10.1007/s00396-015-3535-6 SN - 0303-402X SN - 1435-1536 VL - 293 IS - 5 SP - 1515 EP - 1523 PB - Springer CY - New York ER - TY - THES A1 - Ambrogi, Martina T1 - Application of Poly(Ionic Liquid)s for the synthesis of functional carbons Y1 - 2015 ER - TY - JOUR A1 - Attenberger, Bianca A1 - Moussa, Mehdi El Sayed A1 - Brietzke, Thomas Martin A1 - Vreshch, Volodimir A1 - Holdt, Hans-Jürgen A1 - Lescop, Christophe A1 - Scheer, Manfred T1 - Discrete Polymetallic Arrangements of Ag-I and Cu-I Ions Based on Multiple Bridging Phosphane Ligands and pi-pi Interactions JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - A simple and straightforward approach to new polymetallic Ag-I and Cu-I supramolecules is presented. The reaction of N,P,N,P,N ligand 2 with Ag-I ions affords a trimetallic complex bearing a triangular Ag-3 core; metallophilic interactions are stabilized by ligands that display a multiple bridging coordination mode as 10-electron donors. Heteroleptic polymetallic Ag-I and Cu-I complexes based on ligand 2 and the 1,12-diazaperylene (dape) ligand are obtained by an alternative molecular organization of the polymetallic arrays compared to that in homoleptic complexes of ligand 2. KW - Heterocycles KW - N KW - P ligands KW - Pi interactions KW - Polyaromatic fragments KW - Supramolecular chemistry Y1 - 2015 U6 - https://doi.org/10.1002/ejic.201500445 SN - 1434-1948 SN - 1099-0682 IS - 18 SP - 2934 EP - 2938 PB - Wiley-VCH CY - Weinheim ER - TY - THES A1 - Baier, Heiko T1 - Palladium(II)-Komplexe mit 4,5-Dicyanoimidazol-2-ylidenen BT - Synthese, Charakterisierung und Anwendung in der Mizoroki-Heck- und der Suzuki-Miyaura-Reaktion Y1 - 2015 ER - TY - JOUR A1 - Baier, Heiko A1 - Kelling, Alexandra A1 - Holdt, Hans-Jürgen T1 - PEPPSI-Effect on Suzuki-Miyaura Reactions Using 4,5-Dicyano-1,3-dimesitylimidazol-2-ylidene-Palladium Complexes: A Comparison between trans-Ligands JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - The PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12-15 with the structure [PdCl2{(CN)(2)IMes}(3-R-py)] (12: R = H; 13: R = Cl; 14: R = Br; 15: R = CN) bearing the maleonitrile-based N-heterocyclic carbene (NHC) (CN)(2)IMes ({(CN)(2)IMes}: 4,5-dicyano-1,3-dimesitylimidazol-2-ylidene) were prepared. Solid state structures of 14 and 15 were obtained. Complexes 14 and 15 adopt a slightly distorted square-planar coordination geometry in the solid state with the substituted pyridine ligand trans to the NHC. Catalytic activities of precatalysts 12-15 were studied and subsequently compared to complexes [PdCl2{(CN)(2)IMes}(PPh3)] (4) and [PdCl(dmba){(CN)(2)IMes}] (5) recently reported by our group in the Suzuki-Miyaura reaction of various aryl halides and phenylboronic acid. Reactions using previously reported [PdCl2(IMes)(py)] (IMes: 1,3-dimesitylimidazol-2-ylidene) (1) were also carried out and their results contrasted to those involving 12-15, 4 and 5. Differences in initiation rates and the catalytically active species related to the seven complexes in regards to the throw away ligand were investigated. Poisoning experiments with mercury show that palladium nanoparticles are responsible for the catalytic activity. KW - Carbene ligands KW - Palladium KW - Cross-coupling KW - Arenes Y1 - 2015 U6 - https://doi.org/10.1002/ejic.201500010 SN - 1434-1948 SN - 1099-0682 IS - 11 SP - 1950 EP - 1957 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Banerjee, Shiladitya A1 - Stueker, Tony A1 - Saalfrank, Peter T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp(2)/sp(3) hybrid species with CQC double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp02615f SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 29 SP - 19656 EP - 19669 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Banerjee, Shiladitya A1 - Stüker, Tony A1 - Saalfrank, Peter T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp2/sp3 hybrid species with C[double bond, length as m-dash]C double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 211 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-86826 ER - TY - JOUR A1 - Banerjee, Shiladitya A1 - Stüker, Tony A1 - Saalfrank, Peter T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp2/sp3 hybrid species with C[double bond, length as m-dash]C double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP02615F SN - 1463-9084 SN - 1463-9076 VL - 17 IS - 29 SP - 19656 EP - 19669 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Bartoloni, Marco A1 - Jin, Xian A1 - Marcaida, Maria José A1 - Banha, Joao A1 - Dibonaventura, Ivan A1 - Bongoni, Swathi A1 - Bartho, Kathrin A1 - Gräbner, Olivia A1 - Sefkow, Michael A1 - Darbre, Tamis A1 - Reymond, Jean-Louis T1 - Bridged bicyclic peptides as potential drug scaffolds BT - synthesis, structure, protein binding and stability JF - Chemical Science N2 - Double cyclization of short linear peptides obtained by solid phase peptide synthesis was used to prepare bridged bicyclic peptides (BBPs) corresponding to the topology of bridged bicyclic alkanes such as norbornane. Diastereomeric norbornapeptides were investigated by 1H-NMR, X-ray crystallography and CD spectroscopy and found to represent rigid globular scaffolds stabilized by intramolecular backbone hydrogen bonds with scaffold geometries determined by the chirality of amino acid residues and sharing structural features of β-turns and α-helices. Proteome profiling by capture compound mass spectrometry (CCMS) led to the discovery of the norbornapeptide 27c binding selectively to calmodulin as an example of a BBP protein binder. This and other BBPs showed high stability towards proteolytic degradation in serum. Y1 - 2015 U6 - https://doi.org/10.1039/C5SC01699A SN - 2041-6520 SN - 2041-6539 VL - 10 IS - 6 SP - 5473 EP - 5490 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Bartoloni, Marco A1 - Jin, Xian A1 - Marcaida, Maria José A1 - Banha, Joao A1 - Dibonaventura, Ivan A1 - Bongoni, Swathi A1 - Bartho, Kathrin A1 - Gräbner, Olivia A1 - Sefkow, Michael A1 - Darbre, Tamis A1 - Reymond, Jean-Louis T1 - Bridged bicyclic peptides as potential drug scaffolds BT - synthesis, structure, protein binding and stability N2 - Double cyclization of short linear peptides obtained by solid phase peptide synthesis was used to prepare bridged bicyclic peptides (BBPs) corresponding to the topology of bridged bicyclic alkanes such as norbornane. Diastereomeric norbornapeptides were investigated by 1H-NMR, X-ray crystallography and CD spectroscopy and found to represent rigid globular scaffolds stabilized by intramolecular backbone hydrogen bonds with scaffold geometries determined by the chirality of amino acid residues and sharing structural features of β-turns and α-helices. Proteome profiling by capture compound mass spectrometry (CCMS) led to the discovery of the norbornapeptide 27c binding selectively to calmodulin as an example of a BBP protein binder. This and other BBPs showed high stability towards proteolytic degradation in serum. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 197 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81239 ER - TY - JOUR A1 - Bauer, Monika A1 - Hartmann, Lutz A1 - Kleinpeter, Erich A1 - Kuschel, Frank A1 - Pithart, Cornelia A1 - Weissflog, Wolfgang T1 - Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power JF - Molecular crystals and liquid crystals N2 - Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature H-1 NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C-N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy. KW - ephedrine/pseudoephedrine KW - Chiral dopants KW - ATR-FTIR KW - molecular structure KW - dielectric spectroscopy KW - H-1 NMR Y1 - 2015 U6 - https://doi.org/10.1080/15421406.2014.949592 SN - 1542-1406 SN - 1563-5287 VL - 608 IS - 1 SP - 14 EP - 24 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Behrens, Karsten A1 - Mondal, Suvendu Selchar A1 - Nöske, Robert A1 - Baburin, Igor A. A1 - Leoni, Stefano A1 - Günter, Christina A1 - Weber, Jens A1 - Holdt, Hans-Jürgen T1 - Microwave-Assisted Synthesis of Defects Metal-Imidazolate-Amide-Imidate Frameworks and Improved CO2 Capture JF - Inorganic chemistry N2 - In this work, we report three isostructural 3D frameworks, named IFP-11 (R = Cl), IFP-12 (R = Br), and IFP-13 (R = Et) (IFP = Imidazolate Framework Potsdam) based on a cobalt(II) center and the chelating linker 2-substituted imidazolate-4-amide-5-imidate. These chelating ligands were generated in situ by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under microwave (MW)-assisted conditions in DMF. Structure determination of these IFPs was investigated by IR spectroscopy and a combination of powder X-ray diffraction (PXRD) with structure modeling. The structural models were initially built up from the single-crystal X-ray structure determination of IFP-5 (a cobalt center and 2-methylimidazolate-4-amide-5-imidate linker based framework) and were optimized by using density functional theory calculations. Substitution on position 2 of the linker (R = Cl, Br, and Et) in the isostructural IFP-11, -12, and -13 allowed variation of the potential pore window in 1D hexagonal channels (3.8 to 1.7 angstrom A). The potential of the materials to undergo specific interactions with CO2 was measured by the isosteric heat adsorption. Further, we resynthesized zinc based IFPs, namely IFP-1 = Me), IFP-2 (R = Cl), IFP-3 (R = Br), and IFP-4 (R = Et), and cobalt based IFP-5 under MW-assisted conditions with higher yield. The transition from a nucleation phase to the pure crystalline material of IFP-1 in MW-assisted synthesis depends on reaction time. IFP-1, -3, and -5, which are synthesized by MW-assisted conditions, showed an enhancement of N-2 and CO2, compared to the analogous conventional electrical (CE) heating method based materials due to crystal defects. Y1 - 2015 U6 - https://doi.org/10.1021/acs.inorgchem.5b01952 SN - 0020-1669 SN - 1520-510X VL - 54 IS - 20 SP - 10073 EP - 10080 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Beisebekov, Madiar Maratovich A1 - Serikpayeva, Saniya B. A1 - Zhumagalieva, Shynar Nurlanovna A1 - Beisebekov, Marat Kianovich A1 - Abilov, Zharylkasyn Abduachitovich A1 - Kosmella, Sabine A1 - Koetz, Joachim T1 - Interactions of bentonite clay in composite gels of non-ionic polymers with cationic surfactants and heavy metal ions JF - Colloid and polymer science : official journal of the Kolloid-Gesellschaft N2 - Chemically cross-linked composite gels based on bentonite clay from Manyrak deposit (Kazakhstan Republic) and nonionic polymers, i.e., poly(hydroxyethylacrylate) and poly(acrylamide), were polymerized in situ after preliminary intercalation of monomers in an aqueous suspension of bentonite clay. By means of cryo-scanning electron microscopy, it was shown that bentonite clay is well incorporated into the gel network structure with pore sizes up to 1.5 mu m. The intercalated bentonite clay can adsorb cationic surfactants as well as heavy metal ions due to electrostatic interactions. Conductometric and surface tension measurements indicate not only the adsorption of surfactants and heavy metals inside the hydrogel, but also the displacement of the critical micellization concentration (CMC) of the surfactants. KW - Bentonite clay KW - Cationic surfactants KW - Heavy metal ions KW - Composite hydrogels Y1 - 2015 U6 - https://doi.org/10.1007/s00396-014-3463-x SN - 0303-402X SN - 1435-1536 VL - 293 IS - 2 SP - 633 EP - 639 PB - Springer CY - New York ER - TY - JOUR A1 - Bodrova, Anna A1 - Chechkin, Aleksei V. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Quantifying non-ergodic dynamics of force-free granular gases JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - Brownianmotion is ergodic in the Boltzmann–Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann– Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat—depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions—both a constant and a velocity-dependent (viscoelastic) restitution coefficient e. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of e on the impact velocity of particles. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP02824H SN - 1463-9084 IS - 17 SP - 21791 EP - 21798 ER - TY - GEN A1 - Bodrova, Anna A1 - Chechkin, Aleksei V. A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Quantifying non-ergodic dynamics of force-free granular gases N2 - Brownianmotion is ergodic in the Boltzmann–Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat—depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions—both a constant and a velocity-dependent (viscoelastic) restitution coefficient e. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of e on the impact velocity of particles. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 206 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-85200 ER - TY - JOUR A1 - Boese, Adrian Daniel T1 - Density Functional Theory and Hydrogen Bonds: Are We There Yet? JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - Density functional theory (DFT) has become more successful at introducing dispersion interactions, and can be thus applied to a wide range of systems. Amongst these are systems that contain hydrogen bonds, which are extremely important for the biological regime. Here, the description of hydrogen-bonded interactions by DFT with and without dispersion corrections is investigated. For small complexes, for which electrostatics are the determining factor in the intermolecular interactions, the inclusion of dispersion with most functionals yields large errors. Only for larger systems, in which van der Waals interactions are more important, do dispersion corrections improve the performance of DFT for hydrogen-bonded systems. None of the studied functionals, including double hybrid functionals (with the exception of DSD-PBEP86 without dispersion corrections), are more accurate than MP2 for the investigated species. KW - ab initio calculations KW - basis sets KW - density functional calculations KW - hydrogen bonds KW - intermolecular interactions Y1 - 2015 U6 - https://doi.org/10.1002/cphc.201402786 SN - 1439-4235 SN - 1439-7641 VL - 16 IS - 5 SP - 978 EP - 985 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Boese, Adrian Daniel T1 - Basis set limit coupled-cluster studies of hydrogen-bonded systems JF - Molecular physics N2 - As hydrogen-bonded systems are of utmost importance in especially biological and chemical systems, a new set of highly accurate reference dissociation energies, denoted HB49, is devised. For the molecules in this set, the basis set convergence of post-Hartree-Fock methods, including F12 methods, is investigated. Using combined Moller-Plesset perturbation theory (MP2) and CCSD(T) approaches for energies and MP2 and QCISD(T) for gradients, we achieve CCSD(T) accuracy, which has been determined before to yield an accuracy of 0.2 kJ/mol for a subset of HB49. Both conventional extrapolation techniques and F12 techniques are competitive with each other. By using MP2+Delta CCSD(T), a rather fast basis set convergence is obtained when both basis sets are carefully chosen. KW - coupled-cluster KW - hydrogen bonds KW - ab initio KW - F12 methods Y1 - 2015 U6 - https://doi.org/10.1080/00268976.2014.1001806 SN - 0026-8976 SN - 1362-3028 VL - 113 IS - 13-14 SP - 1618 EP - 1629 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Boese, Adrian Daniel A1 - Boese, Roland T1 - Tetrahydrothiophene and Tetrahydrofuran, Computational and X-ray Studies in the Crystalline Phase JF - Crystal growth & design : integrating the fields of crystal engineering and crystal growth for the synthesis and applications of new materials N2 - Calculations at various levels of theory with different methods and respective evaluations confirm that the twist conformation (C-2) is preferred for tetrahydrothiophene (THT) in the gas phase. In the crystalline phase, achieved by a laser assisted crystallization device, THT has C-1 symmetry (slightly distorted C-2 symmetry) in the chiral space group P2(1)2(1)2(1). This is obviously a packing effect caused by the nonsymmetrical arrangement of neighboring molecules. The distortion from C-2 symmetry costs very little energy as confirmed by computational methods in the gas phase. Only one enantiomer of the chiral THT is found in the cell which requires spontaneous crystallization, which results in a racemic mixture of crystals, or a racemization occurs prior to/during nucleation or in the embryonic state. The racemization happens by a mechanism that can be described as a partial pseudo rotation within a five-membered mono-heterocycle with a C-2-C-S-C-2' transition (C-2 and C-2' are enantiomers) maintaining the heteroatom residing within the symmetry elements. While THT has the molecular symmetry of the gas phase almost also in the crystalline phase, THF has an envelope conformation (CS). This was also established by calculations at various levels of theory which agrees well with the previously experimentally found conformation by electron diffraction. However, in the X-ray crystal structure, previously determined by Luger & Buschmann, THF has C-2 symmetry in the centrosymmetric space group C2/c with the oxygen atom situated on the crystallographic C-2 polar axis, requesting a racemic crystal for the twisted conformers of the enantiomers. No solid-state phase transitions were detected within the experimental ranges for THT and THF. Following the stabilization by molecular clustering, and ending at the crystal lattice, we stepwise increased the number of molecules by calculation of the respective monomers, dimers, trimers, and tetramers for THF and THT. The starting point was taken from the arrangements as found in the respective crystal structures. Both conformational enantiomers are equal in energy. In such cases, a crystal may contain either a racemate of conformers or one of the conformational enantiomers only. The first case is observed in THF, the latter one in THT. It is quite likely that the selection of one enantiomeric conformer of THT from an equilibrium of conformers at the early stage of nucleation (embryonic stage) is responsible for the spontaneous crystallization. In order to check if THF could form a polymorph with the molecular packing of THT and vice versa, we first calculated THF and THT in their respective crystal lattices as determined by X-ray diffraction. Exchanging the compounds in the THT and THF crystal lattices (i.e., replacing O against S and vice versa) results in significantly worse lattice energies indicating that such a polymorph is not a probable option. Y1 - 2015 U6 - https://doi.org/10.1021/cg501228w SN - 1528-7483 SN - 1528-7505 VL - 15 IS - 3 SP - 1073 EP - 1081 PB - American Chemical Society CY - Washington ER - TY - THES A1 - Brietzke, Thomas Martin T1 - Mono- und dinukleare Metallkomplexe mit dem neuen Bis(a,a'-diimin)-Brückenliganden 1,6,7,12-Tetraazaperylen Y1 - 2015 ER - TY - JOUR A1 - Brosnan, Sarah M. A1 - Schlaad, Helmut A1 - Antonietti, Markus T1 - Aqueous Self-Assembly of Purely Hydrophilic Block Copolymers into Giant Vesicles JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - Self-assembly of macromolecules is fundamental to life itself, and historically, these systems have been primitively mimicked by the development of amphiphilic systems, driven by the hydrophobic effect. Herein, we demonstrate that self-assembly of purely hydrophilic systems can be readily achieved with similar ease and success. We have synthesized double hydrophilic block copolymers from polysaccharides and poly(ethylene oxide) or poly(sarcosine) to yield high molar mass diblock copolymers through oxime chemistry. These hydrophilic materials can easily assemble into nanosized (<500nm) and microsized (>5m) polymeric vesicles depending on concentration and diblock composition. Because of the solely hydrophilic nature of these materials, we expect them to be extraordinarily water permeable systems that would be well suited for use as cellular mimics. KW - block copolymers KW - polymersomes KW - polysaccharides KW - self-assembly KW - vesicles Y1 - 2015 U6 - https://doi.org/10.1002/anie.201502100 SN - 1433-7851 SN - 1521-3773 VL - 54 IS - 33 SP - 9715 EP - 9718 PB - Wiley-VCH CY - Weinheim ER -