Quadrupolar pattern complexes

For large-weight Zn + complexes with broad (50-150 kHz) second-order quadrupolar powder patterns Zn QE NMR may be an experimental challenge. In such cases the sensitivity must be enhanced by isotope enrichment combined with, e.g., cross polarization (CP) from H ", low-temperature acquisition or sampling of the free-induction decay (FID) in the presence of a train of refocusing pulses. ... 

The solid-sample P-31 NMR spectrum of the complex (see Figure 6) displayed two broad signals that correspond to the two different phosphorus types in BPPM. The extreme broadness observed in this spectrum can result from both the presence of broadening due to the quadrupolar N-14 nucleus and the underlying multiple signal patterns evident in the solution spectra. 

As an example, quadrupole nutation NMR of nuclei with half-integer quadrupolar spin in zeolitic materials can distinguish between nuclei of the same chemical element subjected to different quadrupole interactions, the signals of which overlap in conventional spectra. The situation is favourable for half-integer quadrupolar spins since the m=l/2 <-> m= -1/2 transition for these nuclei is broadened by the quadrupole interaction only in second-order perturbation theory. The technique can be usefully applied for the determination of the local environment of A1 in zeolitic catalysts (28). It allows discrimination between species of similar chemical shift but different quadrupolar coupling constants (see Figure 5). The main difficulty in the interpretation is the complex spectmm that results from a nutation experiment since it can consist of many overlapping powder patterns (29). 

Deuterium NMR spectroscopy has been employed to probe the interaction between perdeuteriated n-alkanes and host molecules such as liquid crystals, urea crystals, lipid bilayers or zeolites. In general, the temperature-dependent quadrupolar splitting of the deuterium signals is interpreted in terms of conformation and ordering of the alkane chains. For lipid bilayers these studies are of interest in connection with the anaesthetic properties of alkanes. Phospatidylcholine bilayer membranes were chosen as a model. The solubilities of n-alkanes as determined by NMR were found to be dependent on both the membrane- and alkane-chain length ". The complex signal patterns which show the dynamic processes of perdeuteriated hexane in a multilayer is reproduced in Figure 3 ... 

In cases where molecular motion is restricted [wr is not 1) the situation is more complex. Such cases arise when the alkali metal is bound to the surface of a large molecule such as a protein or membrane surface and thereby has its motion restricted. The quadrupolar interaction with the nucleus shifts the energies of the Zeeman levels according to the square of the quantum number to a first approximation. Thus, the energy level splittings for a nucleus with 1 = (e.g. Li, Na, and Tlb) become as illustrated in Figure 1. With rapid isotropic motion, as described above, the multiple line pattern will... 

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