Giessner-Prettre C, Cung M T, Marraud M
Eur J Biochem. 1987 Feb 16;163(1):79-87. doi: 10.1111/j.1432-1033.1987.tb10739.x.
The variation of the nuclear magnetic shielding constant of the different protons and carbons of trans HCO-L-Pro-NH2 with the value of the angle psi is calculated by a non-empirical method for three conformations of the proline ring. The results concerning the CH protons show that the chemical shift of the alpha, beta and gamma endo hydrogens can vary by more than 1 ppm when psi goes from -30 degrees to 180 degrees. The theoretical variation of the chemical shift difference between alpha and gamma or beta and gamma carbons is found to be sensitive to the puckering of the proline ring. For the second of these differences the theoretical results are in agreement with Siemion's relation only for a limited range of molecular conformations. Additional calculations show that the variations of the proton shifts with the value of psi are due to the magnetic anisotropy of the proline carbonyl group and to the polarization of the CH bonds by the multipolar charge distribution carried by this carbonyl. The results are discussed in relation to experiment and the possibility of using 1H and 13C chemical shifts for the determination of the value of the torsion angle about the C alpha C' bond.
采用非经验方法，针对脯氨酸环的三种构象，计算了反式HCO-L-脯氨酰胺中不同质子和碳的核磁屏蔽常数随ψ角值的变化。关于CH质子的结果表明，当ψ从-30°变化到180°时，α、β和γ内氢的化学位移变化可超过1 ppm。发现α与γ或β与γ碳之间化学位移差的理论变化对脯氨酸环的褶皱敏感。对于这些差异中的第二个，理论结果仅在有限的分子构象范围内与西缅恩关系一致。额外的计算表明，质子位移随ψ值的变化是由于脯氨酸羰基的磁各向异性以及该羰基携带的多极电荷分布对CH键的极化。结合实验对结果进行了讨论，并探讨了利用1H和13C化学位移确定围绕Cα-C'键的扭转角值的可能性。
