Solvents on conformation

The extent to which this kind of calculation is able to predict the effect of the solvent on conformational properties of carbohydrates has been thoroughly tested on 2-substituted oxane derivatives, D-glucopyranose, and methyl a- and y -D-glucopyranoside. In the model applied, the cavity term in Eq. 7 is based on an expression taken from the Scaled Particle Theory, and the electrostatic term is calculated according to the reaction held theory. The dispersion term takes into account both attractive and repulsive nonbonding interactions by using a combination of Lx)ndon dispersion energy and Bom-type repulsion. ... 

Table 4-4. Influence of Solvent on Conformation of meso-2,4-Pentanediol at 40° C...

In the present report we summarize the results of experiments aimed at ascertaining the effect of some organic solvents (mainly monohydric alcohols) on the functional stability of two proteins (human hemoglobin and calf liver 3 galactosidase) and on the helix--coil transition of calf thymus DNA. Aim of this report is to give a comprehensive picture of the work we have been performing on the role played by the solvent on conformational and functional stability of biological macromolecules. 

In a study of the conformational statistics of PS, Yoon, Sundararajan and Flory (YSF) included solvent effects in the analysis [47]. The influence of solvent on conformational energy is important because the distance between chemical groups separated by four bonds is large enough for solvent molecules to penetrate the space between them and provide additional interactions. These results are in complete agreement with the experimental studies of PS conformational structure. For example, YSF found the g rotational states to be insignificant due to severe steric interactions. In addition, the inclusion of solvent effects led to the conclusion that the tt conformation is not the ground state of the meso dyad. 

Yun-Yu S, W Lu and W F van Gunsteren 1988. On the Approximation of Solvent Effects on Conformation and Dynamics of Cyclosporin A by Stochastic Dynamics Simulation Teclmiqi Molecular Simulation 1 369-383. 

The influence of the solvent on the oxidation of film under conformational relaxation control is illustrated in Fig. 47, which shows chronoamperograms obtained by steps from -2000 to 300 mV vs. SCE at room temperature (25°C) over 50 s in 0.1 M LiC104 solutions of different solvents acetonitrile, acetone, propylene carbonate, (PC), dimethyl sulfoxide (DMSO), and sulfolane. Films were reduced over 120 s in the corresponding background solution. Despite the large differences observed in the relative shape of the curves obtained in different solvents, shifts in the times for the current maxima (/max) are not important. This fact points to a low influence of the solvent on the rate at which confor-... 

Foresman et al.175 applied the DFT(B3LYP)/SCRF calculations to obtain the polar solvent effect on conformational equilibria in furfuraldehyde and on the C-C rotational barrier of (2-nitrovinyl)amine. The authors demonstrated that the poor results obtained using either spherical or ellipsoidal cavities can be significantly improved upon performing the SCRF calculations for the cavity of molecular shape. 

There are many different solubility criteria available in order to establish the solubility of a certain molecule in a given solvent. Hansen (2007) and Hansen and Smith (2004) have made extensive review of such criteria. For simplicity of the mathematical treatment we prefer to follow the criteria proposed by Van Krevelen (1990) for the solubility of a polymer in a solvent. The first point is that we assume that C60 and C70 are polymeric forms of elemental carbon and treat them on these terms. To predict the solubility according to Van Krevelen (1990), the difference in the solubility parameters between solute and solvent should conform to the following equation ... 

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

The characteristics that discourage the use of RPLC for preparative isolation of bioactive proteins favor its use as an analytical tool for studying protein conformation. Chromatographic profiles can provide information on conformational stability of a protein and the kinetics of folding and unfolding processes. Information about solvent exposure of certain amino acid residues (e.g., tryptophan) as a function of the folding state can be obtained by on-line spectral analysis using diode array UV-vis detection or fluorescence detection. 

Srinivasan, G. and Muller, K., Influence of solvents on the conformational order of C-18 alkyl modified silica gels, J. Chromatogr. A, 1110, 102, 2006. 

The principal tumor-localizing component of Hematoporphyrin Derivative (HPD) has been demonstrated to be dimeric and trimeric hematoporphyrins (HP) interconnected with ester groups. Synthetic analogs as well as model compounds are used in our study to conclude that the reaction conditions employed in the traditional HPD preparation promote a nucleophilic substitution of the acetate group of one HP-acetate molecule by an propionate anion of another HP molecule. The effect of solvent on the stability and structural conformation of the diporphyrin esters have also been examined by spectroscopic methods. 

The influence of the solvent on chiroptical properties of synthetic polymers is dramatically illustrated in the case of poly (propylene oxide). Price and Osgan had already shown, in their first article, that this polymer presents optical activity of opposite sign when dissolved in CHCI3 or in benzene (78). The hypothesis of a conformational transition similar to the helix-coil transition of polypeptides was rejected because the optical activity varies linearly with the content of the two components in the mixture of solvents. Chiellini observed that the ORD curves in several solvents show a maximum around 235 nm, which should not be attributed to a Cotton effect and which was interpreted by a two-term Drude equation. He emphasized the influence of solvation on the position of the conformational equilibrium (383). In turn, Furakawa, as the result of an investigation in 35 different solvents, focused on the polarizability change of methyl and methylene groups in the polymer due to the formation of a contact complex with aromatic solvents (384). 

Vitalis, A., Wang, X., Pappu, R.V. Atomistic simulations of the effects of polyglutamine chain length and solvent quality on conformational equilibria and spontaneous homodimerization. J. Mol. Biol. 2008, 384, 279-97. 

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