title: Theoretical investigation of hydrogen bonding effects on oxygen, nitrogen, and hydrogen chemical shielding and electric field gradient tensors of chitosan/HI salt.
abstract: A density functional theory study has been carried out to calculate the (17)O, (15)N, (13)C, and (1)H chemical shielding as well as (17)O, (14)N, and (2)H electric field gradient tensors of chitosan/HI type I salt. These calculations were performed using the B3LYP functional and 6-311++G (d,p) and 6-31++G (d,p) basis sets. Calculated EFG and chemical shielding tensors were used to evaluate the (17)O, (14)N, and (2)H nuclear quadruple resonance, NQR, and (17)O, (15)N, (13)C, and (1)H nuclear magnetic resonance, NMR, parameters in the cluster model, which are in good agreement with the available experimental data. The difference in the isotropic shielding (sigma(iso)) and quadrupole coupling constant (C(Q)) between monomer and target molecule in the cluster was analyzed in detail. It was shown that both EFG and CS tensors are sensitive to hydrogen-bonding interactions, and calculating both tensors is an advantage. A different influence of various hydrogen bond types, N-Hcdots, three dots, centeredI, O-Hcdots, three dots, centeredI, and N-Hcdots, three dots, centeredO was observed on the calculated CS and EFG tensors. On the basis of this study, nitrogen and O-6 are the most important nuclei to confirm crystalline structure of chitosan/HI. These nuclei have large change in their CS and EFG tensors because of forming intermolecular hydrogen bonds. Moreover, the quantum chemical calculations indicated that the intermolecular hydrogen-bonding interactions play an essential role in determining the relative orientation of CS and EFG tensors of O-6 and nitrogen atoms in the molecular frame axes.
authors: Department of Chemistry, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran.
authors: Sajjad
authors: S
authors: Khodaei
authors: Nasser L
authors: NL
authors: Hadipour
authors: Mohammad Reza
authors: MR
authors: Kasaai
mesh_terms: D002241:Carbohydrates / Q000737:chemistry; D048271:Chitosan / Q000737:chemistry*; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D007454:Iodides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D012492:Salts / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D007454:Iodides; D012492:Salts; D006859:Hydrogen; D048271:Chitosan; D009584:Nitrogen; D010100:Oxygen