JMR, Kuchel, 23Na and 133Cs NMR as probes of alignment in macromolecules

Apparatus for rapid adjustment of the degree of alignment of NMR samples in aqueous media: Verification with residual quadrupolar splittings in Na and Cs spectra

Philip W. Kuchel, Bogdan E. Chapman, Norbert Müller, William A. Bubb, David J. Philp and Allan M. Torres

Journal of Magnetic Resonance
Volume 180, Issue 2 , June 2006, Pages 256-265

aSchool of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia
bInstitut für Chemie, Johannes Kepler Universität A-4040 Linz, Austria

Abstract

NMR spectra of 23Na+ and 133Cs+ in gelatine in a silicone rubber tube that was stretched to various extents showed remarkably reproducible resonance multiplicity. The relative intensities of the components of the split peaks had ratios, 3:4:3, and 7:12:15:16:15:12:7, respectively, that conformed with those predicted using a Mathematica program. The silicone-rubber tube was sealed at its lower end by a small rubber stopper and placed inside a thick-walled glass tube. Gelatine was injected in solution into the silicone tube and ‘set’ by cooling below 30 °C. A plastic thumb-screw held the silicone tube at various degrees of extension, up to not, vert, similar2-fold. After constituting the gel in buffers containing NaCl and CsCl, both 23Na and 133Cs NMR spectroscopy revealed that after stretching the initial single Lorentzian line was split into a well-resolved triplet and a heptet, respectively. This was interpreted as being due to coupling between the electric quadrupoles of the nuclei and the average electric field gradient tensor of the collagen molecules of gelatine; these molecules became progressively more aligned in the direction of the main magnetic field, B0, of the vertical bore magnet, as the gel was stretched. This apparatus provides a simple way of demonstrating fundamental physical characteristics of quadrupolar cations, some characteristics of gelatine under stretching, and a way to invoke static distortion of red blood cells. It should be useful with these and other cell types, for studies of metabolic and membrane transport characteristics that may change when the cells are distorted, and possibly for structural studies of macromolecules.

Keywords: Alignment tensor; Electric field tensor; Quadrupolar splitting; Gelatine; Gel; Erythrocytes; 133-Caesium; 23-Sodium