Abstract. DFT quantum-chemical calculations were carried out for the cationic, zwitterionic and anionic form of the L-Alanyl-L-Alanine di-peptide that can be experimentally accessed at different pH. The N NMR chemical shielding tensor of the amide nitrogen was used for theoretical modeling of the cross-correlated relaxations. In particular, effective chemical shielding anisotropies (effective C...

Title of Dissertation: Dynamics and Chemical Shielding in a Small Protein from NMR Spin Relaxation Experiments Jennifer Blake Hall, Doctor of Philosophy, 2006 Directed By: Prof. David Fushman Department of Chemistry and Biochemistry NMR spin relaxation spectroscopy is a proven method for characterization of the timescales and amplitudes of intramolecular motions in proteins. In a typical NMR re...

The long-held “shielding cone” model of the through-space NMR shielding effect of a carbon-carbon double bond predicts only the effect of the magnetic anisotropy of the double bond; it ignores other important contributors to the overall shielding. GIAO-SCF and GIAO-MP2 calculations have been performed on a simple model system, methane moved sequentially above ethene or 2-methylpropene. These ca...

Gas-phase multinuclear magnetic resonance (MR) spectra allow the total elimination of intermolecular effects from magnetic shielding in molecules. Consequently, the resonance frequencies of isolated atoms and molecules are also available for reading from MR spectra. Following the connectivity between nuclear magnetic moments, resonance frequencies of two different nuclei in the same MR experime...

Ring currents can exert a large effect upon the chemical shielding of NMR resonances. The analytical expression developed by Waugh and Fessenden (Waugh, J. S.; Fessenden, R. W. J. Am. Chem. Soc. 1957, 79, 846) and Johnson and Bovey (Johnson, C. E.; Bovey, F. A. J. Chem. Phys. 1957, 29, 1012) only quantifies the contribution of ring currents to the isotropic component of the shielding tensor. In...

A gradient expansion of the electronic current in the electron density is used to obtain expressions for the magnetic susceptibity and chemical shielding. The first term in the expansion is the Thomas Fermi expression. All succeeding terms diverge for both properties. A renormalized functional is used which removes the divergences and gives asymptotic diamagnetism. A single parameter which depe...

Periodic-boundary and cluster calculations of the magnetic-shielding tensors of (119)Sn sites in various co-ordination and stereochemical environments are reported. The results indicate a significant difference between the predicted NMR chemical shifts for tin(ii) sites that exhibit stereochemically-active lone pairs and tin(iv) sites that do not have stereochemically-active lone pairs. The pre...

In this research, Quantum-mechanical calculations were performed at the HF method with the 6-31+G*basis set and at the B3LYP method with the 6-31+G* basis set in the gas phase and five solvents such as water, DMSO, methanol, ethanol and dichloromethane at six temperatures. According to these theoretical results of IR, we extracted thermo chemical parameters such as enthalpy (∆H Kcal/mol), Gibbs...

This paper presents a new method to calculate solid-state effects on NMR chemical shifts. Using full crystal potentials, this new method (CPPCh) eliminates the need to arbitrarily select the point charges that are included in the calculations of the NMR chemical shieldings to take into account intermolecular effects. By eliminating the arbitrary selection of the point charges, the method provid...

Chemical shift requires the knowledge of both the sample and a reference magnetic shielding. In few cases as nitrogen (15N), the standard experimental reference corresponds to its liquid phase. Theoretical estimate of NMR magnetic shielding parameters of compounds in their liquid phase is then mandatory but usually replaced by an easily-get gas phase value, forbidding direct comparisons with ex...