			Home About us Contact

Internuclear Distances (internuclear + distance)

Distribution by Scientific Domains

Chemistry	62%

Selected Abstracts

Theoretical study of NMR chemical shift induced by H/D isotope effect

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010
Kimikazu Sugimori
Abstract The isotope effect induced by deuterium substituted species is observed in molecular properties, such as geometry, kinetics, and electronic state, of the molecules through nuclear-electron interaction. Theoretical considerations and experimental alignments have been studied by ab initio molecular orbital, density functional theory, and other empirical strategies. The Born-Oppenheimer approximation with nuclear vibrational wavefunction can treat isotope effect because nuclear mass effect account for the average distance of vibrational motion. In this study, we introduce Morse anharmonic oscillator model to calculate average internuclear distance of diatomic molecules having X-H bonding and X-D bonding. Morse parameters are determined by fitting to potential energy surface of molecular orbital and/or density functional calculations, and then the average distance are obtained as the expectation value of the analytical Morse vibrational wavefunction. Nuclear magnetic resonance shielding constants of the H/D isotopomer are calculated again on the average distance by using GIAO with B3LYP and CCSD calculation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

High-precision measurement of internuclear distances using solid-state NMR

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2008
Jae-Seung Lee
Abstract Today, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high-resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two-dimensional single-echo scheme, enhanced with adiabatic cross-polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high-precision crystallographic technique, complementing the X-ray, and neutron-scattering methods. Experimental examples are presented for intramolecular CN and CC distances in ,-crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56,67, 2008. [source]

Structural information from quadrupolar nuclei in solid state NMR

CONCEPTS IN MAGNETIC RESONANCE, Issue 3 2006
Sharon E. Ashbrook
Abstract Solid-state NMR has become the method of choice for determining details of molecular-level structure in heterogeneous systems. Though spin-1/2 nuclei still form the core of most such studies, quadrupolar nuclei are increasingly being used. This review assesses what is currently possible, from achieving high-resolution spectra for quadrupolar nuclei (a prerequisite for most structure determination work), to forming correlation spectra which give qualitative details of spatial proximity of nuclei and the determination of internuclear distances, between quadrupolar spins and quadrupolar and spin-1/2 nuclei. Examples are given of each method discussed, and the advantages and disadvantages of the various experiments for different possible applications are assessed. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 183,248, 2006. [source]

Design and preparation of polyphenyl distance markers for solid-state 19F NMR

ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2000
Kenji Monde
With 13C-labeled samples, it is possible to measure internuclear distances up to 7 Å by solid-state NMR, thus providing a powerful tool for probing ligand,receptor interactions. However, limitations in measurable distances and appreciable natural abundant 13C background signals present problems in solid-state 13C NMR. In order to overcome these disadvantages, a set of reference compounds with known F,F distances, namely, quinolinol, p -biphenyl, and p -terphenyl-bearing trifluoromethyl and trifluoromethylthio groups, have been synthesized. The preparation of these reference compounds and means for diluting these references in solid-state NMR are described. [source]

Structures and Vibrational Spectra of the Sulfur-Rich Oxides SnO (n = 4,9): The Importance of ,,, Interactions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007
Wah Wong Prof.
Abstract The structures of a large number of isomers of the sulfur oxides SnO with n = 4,9 have been calculated at the G3X(MP2) level of theory. In most cases, homocyclic molecules with exocyclic oxygen atoms in an axial position are the global minimum structures. Perfect agreement is obtained with experimentally determined structures of S7O and S8O. The most stable S4O isomer as well as some less stable isomers of S5O and S6O are characterized by a strong ,*,,* interaction between SO and SS groups, which results in relatively long SS bonds with internuclear distances of 244,262,pm. Heterocyclic isomers are less stable than the global minimum structures, and this energy difference approximately increases with the ring size: 17 (S4O), 40 (S5O), 32 (S6O), 28 (S7O), 45 (S8O), and 54,kJ,mol,1 (S9O). Owing to a favorable ,*,,* interaction, preference for an axial (or endo) conformation is calculated for the global energy minima of S7O, S8O, and S9O. Vapor-phase decomposition of SnO molecules to SO2 and S8 is strongly exothermic, whereas the formation of S2O and S8 is exothermic if n<7, but slightly endothermic for S7O, S8O, and S9O. The calculated vibrational spectra of the most stable isomers of S6O, S7O, and S8O are in excellent agreement with the observed data. [source]

X-ray Diffraction and Solid-State NMR Studies of a Germanium Binuclear Complex

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006
Luís Mafra
Abstract A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2],4,H2O (where pmida4,=N -(phosphonomethyl)iminodiacetate and C4H12N22+=piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2, complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H,X(13C,31P) heteronuclear correlation (HETCOR) and 1H,1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee,Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic,organic hybrids. We assigned the NMR resonances with the help of C,,,H and P,,,H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry). [source]

Backbone-Only Protein Solution Structures with a Combination of Classical and Paramagnetism-Based Constraints: A Method that Can Be Scaled to Large Molecules

CHEMPHYSCHEM, Issue 6 2004
Renato Barbieri Dr.
Abstract Herein, it is shown that a medium-resolution solution structure of a protein can be obtained with the sole assignment of the protein backbone and backbone-related constraints if a derivative with a firmly bound paramagnetic metal is available. The proof-of-concept is provided on calbindin D9k, a calcium binding protein in which one of the two calcium ions can be selectively substituted by a paramagnetic lanthanide ion. The constraints used are HN (and H,) nuclear Overhauser effects (NOEs), hydrogen bonds, dihedral angle constraints from chemical shifts, and the following paramagnetism-based constraints: 1) pseudocontact shifts, acquired by substituting one (or more) lanthanide(s) in the C-terminal calcium binding site; 2) NHN residual dipolar couplings due to self-orientation induced by the paramagnetic lanthanide(s); 3) cross-correlations between the Curie and internuclear dipole,dipole interactions; and 4) paramagnetism-induced relaxation rate enhancements. An upper distance limit for internuclear distances between any two backbone atoms was also given according to the molecular weight of the protein. For this purpose, the paramagnetism-based constraints were collectively implemented in the program CYANA for solution structure determinations, similarly to what was previously done for the program DYANA. The method is intrinsically suitable for large molecular weight proteins. [source]