Chiral Dualism as an Instrument of Hierarchical Structure Formation in Molecular Biology

The origin of chiral asymmetry in biology has attracted the attention of the research community throughout the years. In this paper we discuss the role of chirality and chirality sign alternation (L–D–L–D in proteins and D–L–D–L in DNA) in promoting self-organization in biology, starting at the level of single molecules and continuing to the level of supramolecular assemblies. In addition, we also discuss chiral assemblies in solutions of homochiral organic molecules. Sign-alternating chiral hierarchies created by proteins and nucleic acids are suggested to create the structural basis for the existence of selected mechanical degrees of freedom required for conformational dynamics in enzymes and macromolecular machines.

Analysis of the NMR Spectrum of Phenylethane-1,2-Dithiol

The NMR spectrum of phenylethane-1,2-dithiol has been analyzed completely (except for the aromatic protons) by Reilly's new computer program MARIPI which is based on the Swalen and Reilly programs NMRIT and NMRENI. The geminal coupling constant, J34, was assumed to be negative in accord with the recent theoretical and experimental evidence on the signs of (H,H) coupling constants. The magnitudes of the two vicinal H-C-C-H coupling constants, J35 and J45, indicate that the molecule exists primarily in the two forms with gauche-trans arrangement of the hydrogen atoms on these carbon atoms The H-C-S-H coupling constants, J13, J14, and J25, can be either positive or negative in sign; however, a positive sign is favored in line with the –, +, – pattern of sign-alternation for (H,H) coupling across 2, 3, and 4 bonds. The long-range coupling constants, J15, J23, and J24, are small and probably negative. The very long-range coupling between the S-H protons, J12, is too small to be determined