Spectral assignments based on the 13C NMR spectra of mixed liquid crystals of opposite diamagnetic anisotropies

The proton-decoupled 13C NMR spectra of mixtures of liquid crystals with opposite diamagnetic anisotropies have been studied in the natural abundance of 13C. A new method to assign the spectral lines to specific carbons in the liquid crystalline phase has been developed. For this purpose, the assignments of lines in the isotropic media are required, and they were obtained from two-dimensional hetero-COSY experiments. From the spectra in the �critical� mixtures where both the orientations of the liquid crystal directors, with the alignments along and perpendicular to the direction of the magnetic field, �coexist,� the 13C chemical-shift anisotropies have been determined, assuming uniaxial symmetry.

The Design and Construction of Synthetic Protein Mimics

A strategy for the modular construction of synthetic protein mimics based on the ability non-protein amino acids to act as stereochemical directors of polypeptide chain folding, is described. The use of alpha-aminoisobutyric acid (Aib) to construct stereochemically rigid helices has been exemplified by crystallographic and spectroscopic studies of several apolar peptides, ranging in length from seven to sixteen residues. The problem of linker design in elaborating alpha,alpha motifs has been considered. Analysis of protein crystal structure data provides a guide to choosing linking sequences. Attempts at constructing linked helical motifs using linking Gly-Pro segments have been described. The use of flexible linkers, like epsilon-aminocaproic acid has been examined and the crystallographic and solution state analysis of a linked helix motif has been presented. The use of bulky sidechain modifications on a helical scaffold, as a means of generating putative binding sites has been exemplified by a crystal structure of a peptide packed in a parallel zipper arrangement.