Spiral Structure And The Theory Of Optical Activity Of Biological Chiral Molecules

The property of material should be determined by their structure. They will have optical rotation if molecules include helix structures. In this paper we have investigated the relations between the helix structures and their optical rotations by using theoretical calculation. Another, we also study the effect of different chiral C* of the same molecule to the optical rotation.The rotatory direction determined under different conditions will be change for some optically active molecules because their conformations have been changed under different conditions. The change of the helical direction in molecular structure results in change of the rotatory direction. This does not disagree with the rule of helix theory. When the changes of conditions applied to determine can not have influence on the conformation in molecular structure, the rotatory direction will not change, optical rotation of molecule is mostly determined by predominance C * when there are two C * in molecule.By using the helix theory and analyzing the stereostructure of optically active substances can be connected with the value of their mole rotation. A range of more rotation of optically active compounds can be deduced from the structure. Thereby the fundamental theory of stereochemistry is further improvedOn the basis of these theories, we have investigated the relations between the structure parameters, the optical rotations, helix structures of some conformer of lactic acid using density functional theory. The ten conformers of natural lactic acid have been determined in the gaseous phase, using B3LYP/6-311++G(2d, 2p). Then we calculated the specific optical rotations at sodium D line. By analyzing the affection of the changes of dihedral angle of each conformer on the optical rotation and helical structure of the molecule conformers, we made a conclusion that optical rotation depend on the helix greatly. What's more, we have found helices in lactic acid in a new way.Gas stationary conformers of lactic acid and its derivatives (F, Cl, Br and CN replace OH)have been optimized at the B3LYP/6-311++G(2d, 2p) level of DFT. We have analyzed the conformers of lactic acid and its derivatives (F, Cl, Br and CN replace OH) and given out thedefinition of the helical structure in chiral molecules. We find that the molar rotation values and the formula K r~2S/4π~2r~2+S~2 have the direct proportions [M]_D=K r~2S/4π~2r~2+S~2On the same computational level, we also studied the conformers of cyclo(L-Pro-Gly), cyclo(L-Ala-L-Ala), and cyclo(L-Pro-Ala). we also discuss the effect of different chiral C* of the same molecule to the optical rotation. optical rotation of molecule is mostly determined by predominance C * when there are two C * in molecule, and further indicated that the helix is the essential cause of the optical rotations.