Book of Abstracts: Albany 2003
June 17-21 2003
Phosphorus Nuclear Spin Relaxation Results on Nuclec Acids and Phosphlipids Obtained with a Field Shuttling Device Attached to a Shared Commercial NMR
Our shuttler is complete and working. It is a device that allows us to measure the relaxation rate (1/T1) at any field lower than the center field, yet accesses the full capability of the spectrometer for preparation and readout. It pokes into the top of Brandeis' Varian 500 and can pull a standard-sized NMR tube to any field down to 0.1 T, and back, in around 200 ms. We will describe our system very briefly and then describe our 1D results on 31P relaxation on the octamer d(GGAATTCC)2 and on various phospholipid somicated unilamelar vesicles (SUV's). In both cases we see a roughly constant R1 rate centered around a minimum rate at around 4T, due to chemical shift anisotropy (CSA) averaged over fast internal motion and mediated by overall rotational diffusion and an order parameter that is somewhat residue-specific for DNA; and we see an increased contribution to the rate proportional to the square of the field , at high field. At lower field we see an increase in rate, leveling off below 0.2 T, which must be due to dipolar relaxation by protons near to the phosphorus. For the DNA (at 22C, 50 mM NaCl, 50 mM phosphate pH~7) this measures an overall rotational correlation time of around 4 ns. The vesicles show a similar-looking increase implying a correlation time in the same range; this must be due to a low-frequency motion of many lipid side-chain, previously see by others. The SUV dynamics are strongly influenced by the nature of the polar chain, and by added cholesterol, and phospholipase C, in interesting ways. AGR hopes to have a 31P field cycling run in tRNA, if possible, in honor of Kees. With Elan Eisenmesser and Dorothee Kern we have also obtained 2D 15N relaxation measurements in cyclophilin, proving that 2D shuttling spectroscopy is feasible Supported primarily by the Petroleum Research Fund of the A. C. S.
Mary F. Roberts1