DAVYDOV SPLITTING AND RIGID-LAYER MODES IN INS CRYSTAL

Polarized infrared reflection spectra of InS layer crystal have been measured. Both components of the Davydov doublets caused by the splitting of intralayer vibrations due to the interlayer interactions are active in i.r. spectra. Doublet frequencies have been used to calculate the rigid-layer mode frequencies which are correlated with the experimental ones. It has been established that in InS crystal the frequencies of rigid-layer modes are much higher than those of ordinary layer crystals. Atomic displacements have been found at i.r.-active normal modes

Beyond Terrestrial Biology: Charting the Chemical Universe of α-Amino Acid Structures

Abstract: α-Amino acids are fundamental to biochemistry as the monomeric building blocks with which cells construct proteins according to genetic instructions. However, the 20 amino acids of the standard genetic code represent a tiny fraction of the number of α-amino acid chemical structures that could plausibly play such a role, both from the perspective of natural processes by which life emerged and evolved, and from the perspective of human-engineered genetically coded proteins. Until now, efforts to describe the structures comprising this broader set, or even estimate their number, have been hampered by the complex combinatorial properties of organic molecules. Here, we use computer software based on graph theory and constructive combinatorics in order to conduct an efficient and exhaustive search of the chemical structures implied by two careful and precise definitions of the α-amino acids relevant to coded biological proteins. Our results include two virtual libraries of α-amino acid structures corresponding to these different approaches, comprising 121 044 and 3 846 structures, respectively, and suggest a simple approach to exploring much larger, as yet uncomputed, libraries of interest