Nuclear magnetic moment of 57Cu ground state

The nuclear magnetic moment of the ground state of ⁵⁷Cu(I^π = 3/2^-, T_1/2 = 196.3 ms) has been measured to be |μ(⁵⁷Cu)| = (2.00 ±0.05) μ_N using the β-NMR technique. Together with the known magnetic moment of the mirror partner ⁵⁷Ni, the spin expectation value was extracted as = -0.78 ± 0.13. Discrepancy between present results and shell model calculations in the full fp shell implies significant shell breaking at ⁵⁶Ni with the neutron number N = 28.     

15N chemical shifts in concentrated aqueous solutions of ammonium salts

¹⁵N n.m.r. spectra have been recorded from salts of ¹⁵N enriched ammonium ions in aqueous solution. Shifts of the resonance frequency have been attributed to direct interaction between the ammonium and its counter ion in solution.     

NMR chemical shifts in copper (I) chalcogen compounds

NMR chemical shifts of ⁶³Cu have been determined in the three binary Cu(I) chalcogenides and in six ternary Cu(I) chalcopyrites. In all compounds studied, a decrease of chemical shift is observed with decreasing atomic number of the chalcogen. This downshift is discussed, and accounted for by p-d hybridization of the copper chalcogen bonds.     

Nuclear magnetic moment of the 57Cu ground state

The nuclear magnetic moment of the ground state of (57)Cu(Iota(pi) = 3/2(-), T(1/2) = 196.3 ms) has been measured to be /mu((57)Cu)/ = (2.00 +/- 0.05)mu(N) using the beta-NMR technique. Together with the known magnetic moment of the mirror partner (57)Ni, the spin expectation value was extracted as = -0.078 +/- 0.13. This is the heaviest isospin mirror T = 1/2 pair above the (40)Ca region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full f p shell giving mu((57)Cu) approximately 2.4mu(N) and approximately 0.5 implies significant shell breaking at (56)Ni with the neutron number N = 28.     

NMR chemical shifts in amino acids: effects of environments in the condensed phase

We present calculations of NMR chemical shifts in crystalline phases of some representative amino acids such as glycine, alanine, and alanyl-alanine. We explore the effects of environment on the chemical shifts in selected glycine geometries ranging from the crystalline phase to completely isolated molecules. In the crystalline and dilute molecular limits, the calculated distinct NMR chemical shifts are attributed to intermolecular hydrogen-bonds and dipole electric field effects, respectively.     

Assigning solid-state NMR spectra of aligned proteins using isotropic chemical shifts

A method for assigning solid-state NMR spectra of membrane proteins aligned in phospholipid bicelles that makes use of isotropic chemical shift frequencies and assignments is demonstrated. The resonance assignments are based on comparisons of 15N chemical shift differences in spectra obtained from samples with their bilayer normals aligned perpendicular and parallel to the direction of the applied magnetic field.     

93Nb and 17O NMR chemical shifts of niobiophosphate compounds

Niobiophosphate compounds with a large range of niobium and oxygen environments were studied with (93)Nb and (17)O solid-state NMR. (93)Nb isotropic chemical shift of pure niobate Nb(ONb)(6), pure phosphate Nb(OP)(6) and mixed phosphate-niobate Nb(OP)(x)(ONb)((6-x)) (1相似文献   

A polarised neutron study of magnetic moment density in Cu2MnAl

A polarised neutron study of the ferromagnetic Heusler alloy Cu₂Mn_0.863Al_1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn²⁺ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of the Cu atoms. No appreciable conduction electron polarisation is found.     

Ab initio predictions of zeolite structures and Si NMR chemical shifts

A recent shell-model potential parameterized on ab initio data is used for predicting the all-silica structures of zeolites MFI, MEI, MTW, TON, FAU and of α-quartz. Cluster models are defined around each site and the ²⁹Si NMR shielding constants are calculated by ab initio techniques (GIAO-HF). Good agreement with observed ²⁹Si NMR chemical shifts is found. Comparison is made with shifts calculated for observed structures. The structures predicted by the ab initio shell-model potential prove as accurate as the observed ones when judged on the quality of the calculated ²⁹Si NMR spectra.     

Further conventions for NMR shielding and chemical shifts IUPAC recommendations 2008

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the ¹H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS).

This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating ¹³C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.     

NMR chemical shifts of129Xe dissolved in liquid haloalkanes and their mixtures

Xenon-129 NMR spectra have been measured for solutions containing Xe dissolved in a variety of linear 1-haloalkanes, α, ω-dihaloalkanes, and their mixtures. The data are found to be linearly related to solvent composition expressed as volume fraction of the constituent methyl groups, methylene groups, and halogen atoms. This behavior is consistent with a model in which the large dispersion force contributions to the chemical shift of¹²⁹Xe result from pair interactions between dissolved Xe atoms and the methyl, and methylene groups, and the halogen atom, from which the solvent molecules are composed.     

NMR frequency and magnetic dipole moment of (3)He nucleus

We present new gas-phase NMR spectra which relate the resonance frequency of (3)He nucleus to the resonance frequency of the proton in tetramethylsilane (TMS). We discuss the dependence of (3)He resonance frequency on the density of the solvent gas, and we consider in detail the absolute shielding scales of both nuclei. Finally, we analyse the accuracy of the results, using the relationship between the resonance frequencies, absolute shielding constants and magnetic dipole moments of (1)H and (3)He nuclei.     

Modeling NMR chemical shifts: a comparison of charge models for solid state effects on N chemical shift tensors

This paper presents results from applying different point charge models to take into account intermolecular interactions to model the solid state effects on the ¹⁵N NMR chemical shifts tensors. The DFT approach with the BLYP gradient corrected exchange correlation functional has been used because it can include electron correlation effects at a reasonable cost and is able to reproduce ¹⁵N NMR chemical shifts with reasonable accuracy. The results obtained with the point charge models are compared with the experimental data and with results obtained using the cluster model, which includes explicitly neighboring molecular fragments. The results show that the point charge models can take into account solid state effects at a cost much lower than the cluster methods.