Effects of structural differences on the NMR chemical shifts in isostructural dipeptides.
Related Articles Effects of structural differences on the NMR chemical shifts in isostructural dipeptides.
J Phys Chem A. 2014 Apr 10;118(14):2618-28
Authors: Altheimer BD, Mehta MA
Abstract
Porous crystalline dipeptides have gained recent attention for their potential as gas-storage materials. Within this large class is a group of dipeptides containing alanine, valine, and isoleucine with very similar crystal structures. We report the (13)C (carbonyl and C?) and (15)N (amine and amide) solid-state NMR isotropic chemical shifts in a series of seven such isostructural porous dipeptides as well as shift tensor data for the carbonyl and amide sites. Using their known crystal structures and aided by ab initio quantum chemical calculations for the resonance assignments, we elucidate trends relating local structure, hydrogen-bonding patterns, and chemical shift. We find good correlation between the backbone dihedral angles and the C?1 and C?2 shifts. For the C1 shift tensor, the ?11 value shifts downfield as the hydrogen-bond distance increases, ?22 shifts upfield, and ?33 shows little variation. The C2 shift tensor shows no appreciable correlation with structural parameters. For the N2 tensor, ?11 shows little dependence on the hydrogen-bond length, whereas ?22 and ?33 both show a decrease in shielding as the hydrogen bond shortens. Our analysis teases apart some, but not all, structural contributors to the observed differences the solid-state NMR chemical shifts.
PMID: 24654604 [PubMed - indexed for MEDLINE]
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