Conformational space reduction

The reasons for DKPs being more stable than their linear dipeptides are as follows (1) breakdown of a peptide chain proceeds most easily starting at C- or N-end groups. Therefore, the lack of a free terminal COOH or NH2 will increase stability (2) rigidity of the peptide backbone and (3) reduction of conformational space. Thus in DKPs, degradation is slower and the biological activity is more sustained. ... 

Out of the six amino acid residues in the loop segment, which undergo conformation upon reduction, the only residue whose solvent accessibility to the intermembrane space changes is Asp 51. In the fully oxidized state. 

The side chain at C-3 undergoes profound redox-dependent alterations in its chemical properties. The electron orbitals of the carboxamide in NAD are not delocalized into the pyridine ring. On reduction, however, the side chain becomes effectively a vinylogous urea. It shows strong resonance delocalization into the double bonds, with the carbonyl coplanar [although skewed conformations at 150° also represent local minima in the torsional conformation space... 

Table II contains a rough comparison of execution times for the generation of one data point 6x10 random conformations of chains of 100 mass-points were placed each at 100 equally spaced radial positions of a pore with Aq=0.8. It is obvious that the increase in performance, i.e., a reduction in execution time to 20%, is an excellent return on the investment required to change five lines of a FORTRAN program. We fear, however, that this is a relatively rare situation.

Initially Klepeis et al. allowed the dihedral angles to vary over the entire [—7T, 7r] domain. It was found, however, that the problem required intensive computational effort (Androulakis et al., 1997). A reduction of the domain space was therefore proposed by setting limits based on the actual distributions of the dihedral angles. Obviously, for the algorithm to be successful, these reductions could not exclude the region of the global minimum conformation. 

To the best of our knowledge, the first paper devoted to symmetry reduction of the 57/(2) Yang-Mills equations in Minkowski space has been published by Fushchych and Shtelen [27] (see also Ref. 21). They use two conformally invariant ansatzes in order to perform reduction of Eqs. (1) to systems of ordinary differential equations. Integrating the latter yields several exact solutions of Yang-Mills equations (1). 

The face-selectivity of hydride reductions of the conformationally-rigid ketone series (100) has been examined for pure axial and equatorial isomers with four different R groups, viz. Me, Cl, OMe, and SMe.162 The reactivities show Taft correlations with the inductive effects of the substituents. Only through-bond and -space electrostatic interactions are used to explain the results neither Cieplak nor Anh antiperiplanar effects are invoked. 

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