Calculation of the Effective Chemical Shielding Anisotropy in L-Alanyl-L-Alanine, Conformational and Charge Dependence Study

Abstract. DFT quantum-chemical calculations were carried out for the cationic, zwitterionic and anionic form of the L-Alanyl-L-Alanine di-peptide that can be experimentally accessed at different pH. The N NMR chemical shielding tensor of the amide nitrogen was used for theoretical modeling of the cross-correlated relaxations. In particular, effective chemical shielding anisotropies (effective CSA, ∆σ) were calculated in dependence on two major structural descriptors of the peptide backbone, the torsion angles φ and ψ. Proposed calibration of Karplus-like curves can be used for structural interpretation of the cross-correlated relaxation rates in peptides. The variation of modeled effective CSA’s upon pH was discussed.