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Research discusses the effect of proline puckering on the stability of the collagen triple helix by quantum mechanical and molecular mechanical analysis of the (proline-proline-glycine)(sub)n polypeptides. Results indicate that inclusion of interresidue interactions do not lead to significant stabilization of the peptides .

The importance of local (intraresidue) effects in determining the stability of the collagen triple helix has been investigated with special reference to the role played by hydroxyproline. The dipeptide analogues of L-proline (ProDA), 4(R)-hydroxy-L-proline (HypDA), and 4(R)-fluoro-L-proline (FlpDA) have been studied by means of quantum mechanical initio calculations, taking into account solvent effects by the polarizable continuum model (PCM).

The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining 13C NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The molecular biaxiality order parameter is found to be small and essentially constant with temperature, giving further support to the common assumption of effective uniaxiality for these probes [ABSTRACT FROM AUTHOR]

High-level ab initio g and A tensor components have been calculated for PD-tempone and tempo-palmitate (TP) radical spin probes dissolved in n-pentyl and n-hexyl cyanobiphenyl liquid crystals. Solvent effects have been included in the proposed approach by means of the polarizable continuum model, allowing for solvent anisotropy. An in-depth analysis of the electronic structure of probes was performed to choose a suitable model for TP and make the calculations more accessible. Computed magnetic tensor components have been compared with corresponding values measured in the rigid limit. The quality of the results suggests the use of quantum-mechanical data to determine the order parameter of the nematic from experimental electron-spin resonance measurements. [ABSTRACT FROM AUTHOR]

The development of a stochastic model for the interpretation of the emission fluorescence of 4-(N,N-dimethylamino)benzonitrile (DMABN) in polar environment is reported. The model allows to estimate the emission fluorescence by numerically solving the diffusion/sink/source equation for the stationary population of excited state.

A combined theoretical and experimental procedure to evaluate the order parameters of solutes in liquid crystals is developed. The ordering properties of an anisotropic liquid crystal can be studied by recording (super 13)C NMR spectra at different temperatures for a number of rigid solutes.

We discuss an interpretation of the emission signal of a class of dimethylaminobenzonitrile (DMABN) derivatives, based on a stochastic model approach. This study is prompted by the interest in building relatively simple theoretical tools for understanding the static and dynamic properties of metal chelation-controlled fluorescent molecular systems with internal flexibility and solvation effects, which can be used as fluorescent sensors of metal ions. We proceed by extending a stochastic modeling approach, previously used for DMABN, in which internal degrees of freedom are coupled to an effective solvent relaxation variable. The model is based on an integrated approach that combines stochastic methods and QM calculations. The static and dynamic properties of the molecule are obtained by a combination of a continuum treatment and a detailed solute dynamics. Simple computational approximations lead to a semianalytical treatment of the resulting equations, which reproduce correctly the static spectra at room temperature of 4-(1-aza-4,7,10-trioxacyclododecyl) benzonitrile (DMABN-Crown4) and 4-(1-aza-4,7,10,13-tetraoxacyclododecyl) benzonitrile (DMABN-Crown5) in solvents with different polarity. A qualitative analysis of the dynamic spectra of the DMABN-Crown4 is also presented. A discussion is finally provided on how combined quantum and classical methods can be used to define a general robust and reliable computational approach for predicting fluorescence properties of organic molecules in solution. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Examines the importance of vicinal and long-range interresidue effects in determining collagen stability. Elucidation of collagen structure; Conformational behavior of the collagen triple helix; Influence of the proline puckering on the stability of helix.

The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining (13)C NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The molecular biaxiality order parameter is found to be small and essentially constant with temperature, giving further support to the common assumption of effective uniaxiality for these probes.