Orientation of tensorial interactions determined from two-dimensional NMR powder spectra

Abstract

Methods are described for determining the mutual orientation of molecular interaction tensors based on twodimensional NMR powder spectra. Necessary conditions are derived under which this determination can be made, procedures for the computation and analysis of 2D powder spectra are indicated, and a technique for the construction of ridge plots is worked out. Chemical shift resolved dipolar powder spectra provide an easily interpreted representation of the mutual orientation of chemical shielding and dipolar coupling tensors. The various features and practical applications of such spectra are demonstrated with 2D powder spectra of benzene, lead formate. and methyl formate.It is sufficient to consider a system of two nuclear species, I and S, including Zeeman, dipolar, and possibly quadrupolar interactions. The general Hamiltonian of the system is 1C =JC OI + JC ZI +·JC II + JC IS + JC ss +·JC zs +JCos with the two quadrupolar interaction terms the Zeeman terms and the three dipolar interaction terms

Phosphorus-31 solid-state nuclear magnetic resonance study of monophosphazenes

“…If the magnitude of the latter interaction is on the order of the 1 4~ Zeeman interaction, the high-field approximation breaks down and the Zeeman spin functions mix, introducing distortions in the nmr lineshape calculated from eq. [8]. Stoll et al (29) have shown that provided the ratio of the 14N Larmor frequency, vN = yNBo/2.rr, to the 14N quadrupolar coupling constant, X, is greater than 4, the high-field approximation results in relatively small errors when calculating the lineshape.…”

“…Recently, however, there have been several reports of determination of the orientation of the shielding tensor from a single experiment (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). This has been accomplished by studying an isolated spin pair where dipolar coupling exists between the two nuclei.…”

A 13C and 15N nuclear magnetic resonance study of solid ammonium thiocyanate

“…The principal challenge in powder nrnr is to extract these observables from a powder spectrum or to devise ingenious experiments that allow one to separate these interactions so that they can be observed individually (1)(2)(3)(4)(5)(6)(7)(8)(9)(10).…”

Orientational constraints as three‐dimensional structural constraints from chemical shift anisotropy: The polypeptide backbone of gramicidin A in a lipid bilayer

“…Therefore, the tensors from single crystals of model compounds could provide only an approximate (k5-10") orientation of the tensor with respect to the molecular frame. With the advent of relating the chemical shift tensor to a dipolar interaction that has a unique axis fixed in the molecular frame (Linder et al, 1980) it is possible to consider a determination of the chemical shift tensor orientation for specific sites in the molecule of interest. This was first achieved with "N backbone sites in gramicidin in 1989 (Teng & Cross, 1989), and other tensors have been determined since Wang et al, 1992).…”