Hydrogen Bond Formation (hydrogen + bond_formation)

Distribution by Scientific Domains

Selected Abstracts

Layer-by-Layer Hydrogen-Bonded Polymer Films: From Fundamentals to Applications

Eugenia Kharlampieva
Abstract Recent years have seen increasing interest in the construction of nanoscopically layered materials involving aqueous-based sequential assembly of polymers on solid substrates. In the booming research area of layer-by-layer (LbL) assembly of oppositely charged polymers, self-assembly driven by hydrogen bond formation emerges as a powerful technique. Hydrogen-bonded (HB) LbL materials open new opportunities for LbL films, which are more difficult to produce than their electrostatically assembled counterparts. Specifically, the new properties associated with HB assembly include: 1) the ease of producing films responsive to environmental pH at mild pH values, 2) numerous possibilities for converting HB films into single- or two-component ultrathin hydrogel materials, and 3) the inclusion of polymers with low glass transition temperatures (e.g., poly(ethylene oxide)) within ultrathin films. These properties can lead to new applications for HB LbL films, such as pH- and/or temperature-responsive drug delivery systems, materials with tunable mechanical properties, release films dissolvable under physiological conditions, and proton-exchange membranes for fuel cells. In this report, we discuss the recent developments in the synthesis of LbL materials based on HB assembly, the study of their structure,property relationships, and the prospective applications of HB LbL constructs in biotechnology and biomedicine. [source]

Characteristics of hydrogen bond formation between sugar and polymer in freeze-dried mixtures under different rehumidification conditions and its impact on the glass transition temperature

Koreyoshi Imamura
Abstract The characteristics of hydrogen bond formation between trehalose and polyvinylpyrrolidone (PVP) in amorphous mixtures at different hydration states were quantitatively investigated. Amorphous trehalose,PVP mixtures were prepared by freeze-drying and equilibrated at different relative humidities (RH). Infrared (IR) spectra of the trehalose,PVP mixtures were obtained by Fourier transform IR spectroscopy,(FTIR) and the IR band corresponding to CO groups of PVP was deconvolved into the component bands responsible for CO groups that were free and restricted by hydrogen bonds, to estimate the degree of the trehalose,PVP interactions. The FTIR analysis indicated that approximately 80% of the CO groups of PVP formed hydrogen bonds with trehalose in the presence of more than 3 g of trehalose per gramme of PVP, independent of the RH. IR analysis of the OH stretching vibration of the sugar demonstrated that the presence of PVP lead to an increase in the free hydroxyl groups of trehalose that did not form hydrogen bonds at RH 0%. On the other hand, the water sorption behavior of the trehalose,PVP mixtures suggested that rehumidification diminished the effect of PVP on increasing the free OH groups. Thus a peculiar relationship may exist between Tg, RH and the composition of the mixture: The presence of PVP increased Tg at RHs 0 and above 23% but decreased Tg at 11%. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1301,1312, 2008 [source]

Fourier transform Raman and Fourier transform infrared spectra of cross-linked polyurethaneurea films synthesized from solutions

Valentina Romanova
Cross-linked polyurethaneurea films based on polyoxytetramethylene glycol and polyoxypropylene glycol with toluene diisocyanate and 3,3,-dichloro-4,4,-diaminodiphenylmethane were synthesized in a solution where the solvent evaporates during the polymerization. FT-Raman and FTIR spectra were analysed and intermolecular force constants of hydrogen bonds were calculated. On the basis of the intensity of the Raman and IR spectral lines, which reflects hydrogen bond formation, the optimum structure of hydrogen bonds and the conformations of macromolecules of polyurethaneurea were observed for the solvent ethyl acetate. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Reactive Blending of Polyamides with Different Carbonyl Containing Olefin Polymers

David Sémeril
Abstract In this paper the blending of polyamides nylon 6 and nylon 12, with a perfectly alternating ethylene/CO copolymer containing 50 mol-% carbonyl groups (polyketone) is investigated in comparison to blends of the same polyamides with polyolefins containing varying degrees of carbonyl group incorporation. These include a poly[ethylene- co -(methyl acrylate)] copolymer containing 1.9 mol-% methyl ester groups and poly[ethylene- co -(ethyl undecylenate)] copolymers with between 0.20 and 1.25 mol-% ester incorporation. Blends were obtained of polyamides and the polyolefins in compositions between 20/80 and 80/20 in solution and in a Brabender mixer. SEM studies together with TGA, DSC and FTIR measurements show excellent compatibilization for both polyketone and poly[ethylene- co -(methyl acrylate)] copolymers with the nylons. The poly[ethylene- co -(ethyl undecylenate)] polymers displayed much less compatibilization although they still performed significantly better compared to pure polyethylene. The difference in compatibilization is discussed with respect to the importance of both the number of interactive groups present in the polyolefin and the steric requirements of hydrogen bond formation. SEM micrograph of the fracture surface of the blend nylon 6/polyethylene 70:30. [source]

Solution Structure of a DNA Duplex Containing a Biphenyl Pair

Zeena Johar
Abstract Hydrogen-bonding and stacking interactions between nucleobases are considered to be the major noncovalent interactions that stabilize the DNA and RNA double helices. In recent work we found that one or multiple biphenyl pairs, devoid of any potential for hydrogen bond formation, can be introduced into a DNA double helix without loss of duplex stability. We hypothesized that interstrand stacking interactions of the biphenyl residues maintain duplex stability. Here we present an NMR structure of the decamer duplex d(GTGACXGCAG), d(CTGCYGTCAC) that contains one such X/Y biaryl pair. X represents a 3,,,5,,-dinitrobiphenyl- and Y a 3,,,4,,-dimethoxybiphenyl C -nucleoside unit. The experimentally determined solution structure shows a B-DNA duplex with a slight kink at the site of modification. The biphenyl groups are intercalated side by side as a pair between the natural base pairs and are stacked head to tail in van der Waals contact with each other. The first phenyl rings of the biphenyl units each show tight intrastrand stacking to their natural base neighbors on the 3,-side, thus strongly favoring one of two possible interstrand intercalation structures. In order to accommodate the biphenyl units in the duplex the helical pitch is widened while the helical twist at the site of modification is reduced. Interestingly, the biphenyl rings are not static in the duplex but are in dynamic motion even at 294,K. [source]

Nonempirical calculations of nonlinear optical properties of p -nitroaniline in acetone: Comparison of supermolecule and semicontinuum approaches

Marina Yu.
Abstract The comparison of the conventional continuum, supermolecule, and semicontinuum models for the description of solvent effect on the (hyper)polarizability of p -nitroaniline (PNA) in acetone is performed. The supermolecule approach is used for the clusters containing PNA and one or two acetone molecules. The account of the specific solute,solvent interactions via the hydrogen bonds formation is shown to result in the enhancement of (hyper)polarizability values. The continuum approach exploited in the framework of polarizable continuum model (PCM) was shown to describe mainly the solvent effect on (hyper)polarizability. The semicontinuum approach, accounting explicitly the interaction between PNA and solvent molecules and treating the rest of the solvent as a continuum, results in a moderate increase of the (hyper)polarizability values compared to those obtained within the conventional PCM approach. All the calculations of (hyper)polarizabilities are performed at the Hartree,Fock level in the aug-cc-pVDZ' Dunning basis set. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]