Multiple Quantum Coherence NMR Research Articles

Multiple Quantum Nuclear Coherences in Pulsed ENDOR Spectroscopy

AbstractExperimental and theoretical aspects of multiple quantum (MQ) NMR coherence phenomena for paramagnetically coupled nuclei are presented. The spin interactions responsible for MQ NMR coherences observed in pulsed EPR and pulsed ENDOR (Electron Nuclear Double Resonance) are contrasted with those responsible for MQ coherences in pulsed NMR spectroscopy. MQ NMR coherences in pulsed ENDOR spectroscopy are demonstrated experimentally and described using an operator formalism approach. Detailed discussions of the phase incrementation technique for detecting MQ NMR coherences in ENDOR spectroscopy, different microwave excitation schemes for the preparation of nuclear spin order, off‐resonance excitation, and the evolution of MQ coherences under free precession are presented. Experimental results on a single crystal of irradiated malonic acid and on the conjugated polyene polymer poly acetylene are presented.

Nuclear magnetic resonance studies of N–H bonds in platinum anticancer complexes: detection of reaction intermediates and hydrogen bonding in guanosine 5′-monophosphate adducts of [PtCl2(NH3)2

Reactions between 15N-labelled cis-[PtCl2(NH3)2] and guanosine 5′-monophosphate (GMP) have been studied in aqueous solutions at millimolar concentrations using 15N-edited one-dimensional 1H NMR spectroscopy, and two-dimensional [1H, 15N] heteronuclear multiple quantum coherence NMR spectroscopy; the reactive species [PtCl(H2O)(NH3)2]+ was detected, as well as hydrogen bonding in the product [Pt(GMP-N7)2(NH3)2]2+.

Identification and localization of bound internal water in the solution structure of interleukin 1.beta. by heteronuclear three-dimensional proton rotating-fram Overhauser nitrogen-15-proton multiple quantum coherence NMR spectroscopy

The presence and location of bound internal water molecules in the solution structure of interleukin 1 beta have been investigated by means of three-dimensional 1H rotating-frame Overhauser 1H-15N multiple quantum coherence spectroscopy (ROESY-HMQC). In this experiment through-space rotating-frame Overhauser (ROE) interactions between NH protons and bound water separated by less than or equal to 3.5 A are clearly distinguished from chemical exchange effects, as the cross-peaks for these two processes are of opposite sign. The identification of ROEs between NH protons and water is rendered simple by spreading out the spectrum into a third dimension according to the 15N chemical shift of the directly bonded nitrogen atoms. By this means, the problems that prevent, in all but a very few limited cases, the interpretation, identification, and assignment of ROE peaks between NH protons and water in a 2D 1H-1H ROESY spectrum of a large protein such as interleukin 1 beta, namely, extensive NH chemical shift degeneracy and ROE peaks obscured by much stronger chemical exchange peaks, are completely circumvented. We demonstrate the existence of 15 NH protons that are close to bound water molecules. From an examination of the crystal structure of interleukin 1 beta [Finzel, B. C., Clancy, L. L., Holland, D. R., Muchmore, S. W., Watenpaugh, K. D., & Einspahr, H. M. (1989) J. Mol. Biol. 209, 779-791], the results can be attributed to 11 water molecules that are involved in interactions bridging hydrogen-bonding interactions with backbone amide and carbonyl groups which stabilize the 3-fold pseudosymmetric topology of interleukin 1 beta and thus constitute an integral part of the protein structure in solution.

Multiple Quantum NMR Study of Hydrogen Clustering in Amorphous Silicon

ABSTRACTBecause Multiple Quantum NMR coherences occur only between spins which are coupled together by the dipole interaction, this technique has been used to study the clustering of hydrogen in amorphous silicon. The clustered hydrogen was found to be associated with the broad line of the single quantum NMR spectra. For device quality films, the average cluster size is approximately six protons. The concentration of these five to seven atom defects increases with increasing hydrogen content until, at very high hydrogen content, the clusters are replaced by a continuous network of silicon-hydrogen bonds.