International Journal of Molecular Sciences

157 KiB

Open AccessArticle

Self-energy Effects on Nuclear Magnetic Resonance Parameters within Quantum Electrodynamics Perturbation Theory

by Rodolfo H. Romero and Gustavo A. Aucar

Int. J. Mol. Sci. 2002, 3(8), 914-930; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080914 - 31 Aug 2002

Cited by 15 | Viewed by 6588

A theory for the calculation of self-energy corrections to the nuclear magnetic parameters is given in this paper. It is based on the S-matrix formulation of bound-state quantum electrodynamics (QED). Explicit expressions for the various terms of the S-matrix are given. The interpretation [...] Read more.

A theory for the calculation of self-energy corrections to the nuclear magnetic parameters is given in this paper. It is based on the S-matrix formulation of bound-state quantum electrodynamics (QED). Explicit expressions for the various terms of the S-matrix are given. The interpretation of the self-energy, one- and two-vertex terms and some perspective for possible future developments are discussed. Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

197 KiB

Open AccessArticle

Proton NMR Chemical Shift Behavior of Hydrogen-Bonded Amide Proton of Glycine-Containing Peptides and Polypeptides as Studied by ab initio MO Calculation

by S. Hori, K. Yamauchi, S. Kuroki and I. Ando

Int. J. Mol. Sci. 2002, 3(8), 907-913; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080907 - 31 Aug 2002

Cited by 25 | Viewed by 11843

Abstract

NMR chemical shifts of the amide proton of a supermolecule, an Nmethylacetamide hydrogen-bonded with a formamide, were calculated as functions of hydrogen-bond length RN…O and hydrogen-bond angles by FPT-GIAO method within the framework of HF/STO 6-31⁺⁺G(d,p) ab initio MO method. The [...] Read more.

NMR chemical shifts of the amide proton of a supermolecule, an Nmethylacetamide hydrogen-bonded with a formamide, were calculated as functions of hydrogen-bond length RN…O and hydrogen-bond angles by FPT-GIAO method within the framework of HF/STO 6-31⁺⁺G(d,p) ab initio MO method. The calculations explained reasonably the experimental data reported previously that the isotropic proton chemical shifts move downfield with a decrease in R_N…O. Further, the behavior of proton chemical shift tensor components depending on the hydrogen-bond length and hydrogen-bond angle was discussed. Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

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329 KiB

Open AccessArticle

Ab Initio Calculations of 31P NMR Chemical Shielding Anisotropy Tensors in Phosphates: Variations Due to Ring Formation

by Todd M. Alam

Int. J. Mol. Sci. 2002, 3(8), 888-906; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080888 - 31 Aug 2002

Cited by 19 | Viewed by 10038

Abstract

Ring formation in phosphate systems is expected to influence both the magnitude and orientation of the phosphorus (³¹P) nuclear magnetic resonance (NMR) chemical shielding anisotropy (CSA) tensor. Ab initio calculations of the ³¹P CSA tensor in both cyclic and acyclic [...] Read more.

Ring formation in phosphate systems is expected to influence both the magnitude and orientation of the phosphorus (³¹P) nuclear magnetic resonance (NMR) chemical shielding anisotropy (CSA) tensor. Ab initio calculations of the ³¹P CSA tensor in both cyclic and acyclic phosphate clusters were performed as a function of the number of phosphate tetrahedral in the system. The calculation of the ³¹P CSA tensors employed the GAUSSIAN 98 implementation of the gauge-including atomic orbital (GIAO) method at the Hartree-Fock (HF) level. It is shown that both the ³¹P CSA tensor anisotropy, and the isotropic chemical shielding can be used for the identification of cyclic phosphates. The differences between the ³¹P CSA tensor in acyclic and cyclic phosphate systems become less pronounced with increasing number of phosphate groups within the ring. The orientation of the principal components for the ³¹P CSA tensor shows some variation due to cyclization, most notably with the smaller, highly strained ring systems. Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

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174 KiB

Open AccessArticle

Ab Initio Calculations of Co Shielding in Model Complexes

by Elaine A. Moore

Int. J. Mol. Sci. 2002, 3(8), 873-887; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080873 - 31 Aug 2002

Cited by 2 | Viewed by 6957

Abstract

Recent ab initio calculations of cobalt NMR shielding show that DFT-GIAO calculations using hybrid functionals are found to reproduce experimental values well. This method is used to calculate the variation of the cobalt NMR shielding tensor of sqaure pyramidal nitrosyl complexes with respect [...] Read more.

Recent ab initio calculations of cobalt NMR shielding show that DFT-GIAO calculations using hybrid functionals are found to reproduce experimental values well. This method is used to calculate the variation of the cobalt NMR shielding tensor of sqaure pyramidal nitrosyl complexes with respect to the CoNO geometry and to differing basal ligands. The isotropic shielding is shown to have a large negative derivative with respect to CoX distance where X is a ligating atom.; the derivative with respect to NO distance is smaller but still significant. The zz component where z is along the CoN(NO) bond is more sensitive to the basal ligands but the other two principal components are sensitive to the CoNO geometry. Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

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82 KiB

Open AccessArticle

¹⁵N Chemical Shifts in Energetic Materials: CP/MAS and ab Initio Studies of Aminonitropyridines, Aminonitropyrimidines, and Their N-Oxides

by Karen L. Anderson, Lawrence H. Merwin, William S. Wilson and Julio C. Facelli

Int. J. Mol. Sci. 2002, 3(8), 858-872; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080858 - 31 Aug 2002

Cited by 25 | Viewed by 11161

Abstract

Solid state ¹⁵N NMR chemical shift measurements have been performed on a series of nitro- and amino-substituted nitrogen-containing heterocycles that are of interest as potential new insensitive explosives. Due to low solubilities, many of these compounds are not amenable to study by [...] Read more.

Solid state ¹⁵N NMR chemical shift measurements have been performed on a series of nitro- and amino-substituted nitrogen-containing heterocycles that are of interest as potential new insensitive explosives. Due to low solubilities, many of these compounds are not amenable to study by solution state methods. Theoretical calculations of 15N chemical shift parameters have been performed on the structures of interest and are reported herein. The calculated and experimental values are in good agreement. The use of a model that includes intermolecular effects and allows the proton positions of the nearest neighbors to be optimized leads to the best agreement between calculated and experimental values. The theoretical models accurately predict the effects of nitro and amino substituents on ringnitrogen chemical shifts, explaining a seeming reversal in trend that is noted in the pyridine and pyridine-1-oxide chemical shifts of the highly substituted compounds. Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

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15 KiB

Open AccessEditorial

Special Issue on Recent Advances in Nuclear Magnetic Shielding Theory

by Marta B. Ferraro

Int. J. Mol. Sci. 2002, 3(8), 856-857; https://0-doi-org.brum.beds.ac.uk/10.3390/i3080856 - 31 Aug 2002

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Abstract

Nuclear Magnetic Resonance Spectroscopy (NMR) is one of the most important tools to elucidate structure and environment.[...] Full article

(This article belongs to the Special Issue Recent Advances in Nuclear Magnetic Shielding Theory)

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Int. J. Mol. Sci., Volume 3, Issue 8 (August 2002) – 6 articles , Pages 856-930

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