Hydrogen Bonding Effects on the ¹³ C NMR Chemical Shift Tensors of Some Amino Acids in the Solid State

Abstract

The influence of hydrogen bonding (HB) on the 13C chemical shift tensors in four solid amino acids was studied by the ab initio gauge-included atomic orbital (GIAO) approach. The results of the present calculations were compared with those predicted previously and with the experimentally observed shieldings. The RMS error (without HB) found on comparing the calculated and observed principal components of the shielding tensor for the four carboxyl carbons is 35.3 ppm, whereas when the HB effects are included, the RMS error is reduced to 19.6 ppm. This clearly demonstrates the importance of including HB effects in the calculation of the 13C shieldings for the carboxyl carbons, especially for the δ22 component; this also agrees with published experimental results. © 1997 by John Wiley & Sons, Ltd.