Conformational behavior

For 1,3-dithiolanes the ring is flexible and only small energy differences are observed between the diastereoisomeric 2,4-dialkyl derivatives. The 1,3-oxathiolane ring is less mobile and pseudoaxial 2- or 5-alkyl groups possess conformational energy differences (cf. 113 114) see also the discussion of conformational behavior in Section 4.01.4.3. 

Chirooptical properties give more subtle information on the conformational behavior of biopolymers and peptides in solution. In early experiments, optical rotation and optical rotatory dispersion (ORD) have been recognized as valuable techniques, followed more recently by significant progress and refinements in the equipment which have resulted in the routine measurements of applied circular dichroism (CD). 

Farmer RS, Kiick KL (2005) Conformational behavior of chemically reactive alanine-rich repetitive protein polymers. Biomacromolecules 6 1531-1539... 

Some pharmacologically important properties such as pKj, tautomeric equihbrium, conformational behavior, solubihty and partitioning are temperature and solvent dependent... 

Conversely, in a membrane model, acetylcholine showed mean log P values very similar to those exhibited in water. This was due to the compound remaining in the vicinity of the polar phospholipid heads, but the disappearance of extended forms decreased the average log P value somewhat. This suggests that an anisotropic environment can heavily modify the conformational profile of a solute, thus selecting the conformational clusters more suitable for optimal interactions. In other words, isotropic media select the conformers, whereas anisotropic media select the conformational clusters. The difference in conformational behavior in isotropic versus anisotropic environments can be explained considering that the physicochemical effects induced by an isotropic medium are homogeneously uniform around the solute so that all conformers are equally influenced by them. In contrast, the physicochemical effects induced by an anisotropic medium are not homogeneously distributed and only some conformational clusters can adapt to them. 

Fig. 1.8 The conformational behavior of the two amino acyl residues of carnosine (1 2 versus plot) as simulated for 5 ns in water (in blue) or when bound to carnosinase (in...

Stepanian, S. G., Reva, D., Radchenko, E. D., Adamowicz, L., 1998b, Conformational Behavior of Alanine. Matrix-Isolation Infrared and Theoretical DFT and ab Initio Study , J. Phys. Chem. A, 102, 4623. 

Barone, V., C. Adamo, and F. Lelj. 1995. Conformational behavior of gaseous glycine by a density functional approach. J. Chem. Phys. 102, 364. 

Chiu, N. S., H. L. Sellers, L. Schafer, and K. Kohata. 1979. Molecular Orbital Constrained Electron Diffraction Studies. Conformational Behavior of 1,2-Dimethylhydrazine. J. Am. Chem. Soc. 101, 5883-5889. 

The aspects of synthesis, chemical properties, and conformational behavior considered above are very useful for a discussion of the properties of compounds containing P—C—N and P—C—O—B fragments. They may be also applied in the more complicated field of coordination compounds of cyclic functionally substituted phosphines. 

A concept of amphiphilicity, as applied to single monomer units of designed water-soluble polymers, is presented in the third chapter by Okhapkin, Makhaeva, and Khokhlov. The concept is relevant to biomolecular structures and assemblies in aqueous solution. The authors consider the substantial body of information obtained experimentally and theoretically on surface molecular chemical structures, including those that are prospective for surface catalysis. Unusual conformational behaviors of single amphiphilic polymers recently observed in simulations are also discussed in detail. 

Methylenecyclohex-l-ene (Table 19) is not planar and the MW data do not allow any detailed discussion on the distances because of the conformational behavior, which is consistent with a high barrier to ring conversion159. No X-ray structures... 

The 3H chemical shifts, coupling constants, temperature coefficients, exchange rates and inter-residual ROEs of the hydroxyl protons of various synthetic type II trisaccharides, analogues of (3-D-Galp-(l - 4)-p-D-GlcpNAc-(l - 2)-a-D-Man-(l - 0)(CH2)7CH3, were reported and interpreted,8 assisted with molecular dynamic simulations, to deduce key information on the conformational behavior of these important molecules in aqueous solution. 

The conformational behavior of Ai-mcthyl-pi peri dine (6) had been extensively studied. Most researchers now agree that the Me-equatorial conformer is favored by about... 

An extensive study of the conformational behavior of perhydroazepine 66 was carried out by Espinosa and coworkers105. This pure force field based analysis, with no reference to experiment or other theoretical methods, was part of a series of studies on cycloheptane, cycloheptene and some of their oxygen, sulfur and nitrogen heterocyclic analogs. MM2... 

Dynamic NMR spectroscopic measurements indicate, that the free enthalpies of activation of 57 and 59 are 10.2 kcal/mol and 11.9 kcal/mol, respectively. Similar conformational behavior is exhibited by the [2.2](2,5)heterophanes 43, 61, and 62. The thiophene-containing hetero-phanes 61 and 62 8b82) are conformationally rigid up to 200 °C and are not subject to ring inversion, whereas the furanophane 43 is conforma-... 

The characteristic properties of peptides result from the presence of a chain of several or many amide bonds. A first problem is that of numbering, and here Fig. 6.1 taken from the IUPAC-IUB rules may help. A second and major aspect of the structure of peptides is their conformational behavior. Three torsion angles exist in the backbone (Fig. 6.2). The dihedral angle co (omega) describes rotation about C-N,

rotation about N-C , and ip (psi) describes rotation about C -C. Fig. 6.2 represents a peptide in a fully extended conformation where these angles have a value of 180°. 

Increased occurrence of d.v-peptide bonds and differences in conformational behavior ... 

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