Theoretical ¹³C chemical shift, ¹⁴N, and ²H quadrupole coupling‐ constant studies of hydrogen bonding in L‐alanylglycine dipeptide

Abstract

(13)C chemical shieldings and (14)N and (2)H electric field gradient (EFG) tensors of L-alanylglycine (L-alagly) dipeptide were calculated at RHF/6-31 + + G** and B3LYP/6-31 + + G** levels of theory respectively. For these calculations a crystal structure of this dipeptide obtained from X-ray crystallography was used. Atomic coordinates of different clusters containing several L-alagly molecules were used as input files for calculations. These clusters consist of central and surrounding L-alagly molecules, the latter forming short, strong, hydrogen bonds with the central molecule. Since the calculations did not converge for these clusters, the surrounding L-alagly molecules were replaced by glycine molecules. In order to improve the accuracy of calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs), different geometry-optimization strategies were applied for hydrogen nuclei. Agreement between calculated and experimental data confirms that our optimized coordinates for hydrogen nuclei are more accurate than those obtained by X-ray diffraction.

Density functional theory study of nitrogen‐14 nuclear quadrupole coupling parameters of L‐histidine: hydrogen‐bonded system

“…The values of χ and η increase considerably. This had also been demonstrated in theoretical studies of α‐glycylglycine and L ‐alanylglycine clusters . The quadrupole coupling constant values are in fair agreement with experiment.…”

“…This had also been demonstrated in theoretical studies of a-glycylglycine [63] and L-alanylglycine clusters. [64] The quadrupole coupling constant values are in fair agreement with experiment. However, much larger deviation is observed in the asymmetry parameter,.…”

Sulfur hexafluoride plasma surface modification of Gly-Ala and Ala-Gly as Bombyx mori silk model compounds: Mechanism investigations

“…The simplest model consistent with the X-ray scattering pattern is Gly-Ala or Ala-Gly [8]. Although these structures were solved earlier by Tranter et al and Naganathan and Venkatesan [10][11][12][13][14][15][16], the Gly-Ala structure is polymorphic, indicating the flexibility and the potential of possible alternate structures.…”

NMR spin–spin coupling constants in hydrogen‐bonded glycine clusters

“…Since H‐bonded interactions affect the electron density of the participating atoms, SSCCs can be useful in the detection and analysis of the nature of hydrogen bonds. A significant progress regarding the calculation of the SSCCs for H‐bonded molecular systems has been made in last few years …”

“…A significant progress regarding the calculation of the SSCCs for H-bonded molecular systems has been made in last few years. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Several highly sophisticated correlation-consistent wavefunctions-based methods like the multiconfigurational self-consistent field (MCSCF) theory, [35][36][37][38] second-order polarization propagator approach (SOPPA), [39][40][41][42] Equation of motion coupled cluster with single and double excitation (EOM-CCSD), [43][44][45] iterative approximate coupled cluster singles, doubles, and triples (CC3) model [46][47][48] have been developed, in last few decades, to study the electronic structure of molecular systems. These first-principle correlation-consistent methods, although predict the SSCCs quite accurately, they are generally costly from the computational point of view.…”