Paramagnetic metal “probe” addition

Zhang et have studied the heme environment and ligand binding properties of two large membrane proteins (quinol oxidases) containing multiple paramagnetic metal centers. Perturbations of hyperfine-shifted proton resonances were used to probe the chemical changes induced by oxidation-reduction reactions and cyanide addition. 

While nitroxides have been used most frequently in SDSL, other types of spin labels have also been employed to study nucleic acids. One class of such spin probes is paramagnetic metal ions. For example, the paramagnetic Mn ion, which is capable of substituting the Mg " " ion to support RNA folding and catalysis, has been used to investigate structure and catalysis of ribozymes. In addition, chelated Gd " " ions... 

The interaction of nitric oxide (NO) with metal ions in zeolites has been one of the major subjects in catalysis and environmental science and the first topic was concerned with NO adsorbed on zeolites. NO is an odd-electron molecule with one unpaired electron and can be used here as a paramagnetic probe to characterize the catalytic activity. In the first topic focus was on a mono NO-Na" complex formed in a Na -LTA type zeolite. The experimental ESR spectrum was characterized by a large -tensor anisotropy. By means of multi-frequency ESR spectroscopies the g tensor components could be well resolved. The N and Na hyperfine tensor components were accurately evaluated by ENDOR spectroscopy. Based on these experimentally obtained ESR parameters the electronic and geometrical structures of the NO-Na complex were discussed. In addition to the mono NO-Na complex the triplet state (NO)2 bi-radical is formed in the zeolite and dominates the ESR spectrum at higher NO concentration. The structure of the bi-radicai was discussed based on the ESR parameters derived from the X- and Q-band spectra. Furthermore the dynamical ESR studies on nitrogen dioxides (NO2) on various zeolites were briefly presented. 

Nucleotides, in many cases as their metal ion complexes, are involved in a great variety of enzymatic reactions either as substrates or as cofactors. In addition they may be viewed as the monomers of DNA and RNA. Lanthanide complexes of nucleotides have been extensively studied by R.J.P. Williams and his coworkers at Oxford. The interest in these complexes is two fold. The nucleotide conformation in solution can be elucidated by NMR from lanthanide induced chemical shifts and line-broadenings, (Barry et al., 1971). Lanthanide-nucleotide complexes may act as competitive inhibitors in enzymatic reactions, (Tanswell et al., 1974), and can be used as paramagnetic probes in the mapping of their binding site on the enzyme, (Tanswell et al., 1976). 

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