engleski

Secondary Structure Dependence of Chemical Shift Anisotropy in Model Peptides by Quantum Chemical Simulations

Density Functional Theory (DFT) calculations were used to quantitatively predict the influence of secondary structure (phi and psi angles) on CSA tensors as a prerequisite to structural interpretation of experimental CSA values. The Gaussian98 program package was used employing implemented methods, basis sets and approaches (e.g., the 6 311G(d, p) basis set for geometry optimization, as well as frequency calculation and 6 311++G(3df, 3pd) basis set for NMR parameters calculation). The Becke's three parameter hybrid functional with the Lee, Yang and Parr correlation functional (B3LYP) was employed in DFT calculation. The gauge independence requirement for NMR parameter calculation was treated with the Gauge Invariant Atomic Orbital (GIAO) approach. Molecular models used in simulation of secondary structure elements and CSA calculations were capped alanine dipeptide and octapeptide. The results of DFT simulations of 1H, 13C and 15N CSA showing dependence on secondary protein structure will be demonstrated by way of Ramachandran-CSA diagrams for the dipeptide model. A chain length and hydrogen bonding influence on CSA in alpha-helices were tested with the octapeptide model.

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