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Isotropic nuclear shielding constants at the equilibrium molecular structure σeq and zero-point vibrational corrections (ZPVCs) to σeq are evaluated using the B3LYP/aug-cc-pVTZ level of theory, as well as the KT2/aug-cc-pVTZ level of theory. Various scaling factors and systematic corrections are obtained by linear regression to experimental shielding constants. Comparisons of the scaled and systematically corrected equilibrium and vibrationally averaged shielding constants reveal that, at the 99% confidence level, the ZPVCs via second-order perturbation theory do not improve the agreement of B3LYP/aug-cc-pVTZ and KT2/aug-cc-pVTZ calculated shielding constants with experiment. This holds true when the same analysis is applied to CCSD(T)/aug-cc-pCV[TQ]Z calculated σeq of Teale et al. [ Journal of Chemical Physics 2013, 138, 024111]. In addition, at the 99% confidence level, B3LYP/aug-cc-pVTZ and KT2/aug-cc-pVTZ scaled and systematically corrected shielding constants are found to be statistically no different from CCSD(T)/aug-cc-pCV[TQ]Z calculated σeq. The use of scaling factors and systematic corrections could thus provide a cheaper but yet reasonably accurate alternative for the study of nuclear shielding constants of larger systems. [ABSTRACT FROM AUTHOR]

The article reports that researchers have modeled the initial stage of the Maillard reaction , which involves the formation of a Schiff base between the amino group of an amino acid or protein and the carbonyl group of a sugar. The mechanism for Schiff base formation was used for the modeling of the Maillard reaction.