Shift reagents natural abundance

The study of nucleic acid bases by NMR has been reported in a number of monographs (/), but very little data is available on the, 3C and, 5N NMR chemical shift tensors in these compounds. The low sensitivity of NMR spectroscopy and the long relaxation times exhibited by many of these compounds have posed the main impediments for these studies. The use of sample doping with free radical relaxation reagents, to reduce the relaxation times facilitating 2D multiple pulse experiment (2, 3), enables one to measure and analyze the principal values of the chemical shift tensors in natural abundance samples. In previous papers from this laboratory we have presented, 5N NMR chemical shift principal values for adenine, guanine, cytosine, thymine and uracil (4, 5). 

NMR technique. NMR-active metal ions entrapped in the liposome can be differentiated from those outside by the addition of shift reagents such as Dy(III) or Gd(III) to the external phase. Then metal concentrations inside and outside the liposome can be determined directly. This is attractive for 7Li+, 23Na+, and 39K+ ions because of high sensitivities and natural abundances. The direct determination of the metal ion concentrations are attractive but limited only for slow kinetics. When the rate becomes faster, line shape analysis or magnetization-inversion transfer techniques are employed. The latter method has been successfully applied to gramicidin channels,143 144 but not to artificial ion channels. 

Conformational analysis of perhydroazocine (3) was accomplished using a novel cobalt(III) porphyrin shift reagent (see Structures (3a) and (3b)) <90MRC343>. The structure of the AT-benzyl derivative of perhydroazocine was elucidated by C NMR <8lAJC2307>. Natural abundance of 0 NMR data for 30 lactones and 36 lactams in acetonitrile at 75°C was reported <89H(29)30i, 89H(29)307>. 

Geology, Geochemistry, and Natural Abundances of the Rare Earth Elements Lanthanide Complexes with Mul-tidentate Ligands Lanthanides Luminescence Applications Lanthanide Shift Reagents. 

Lanthanide shift reagents used in NMR studies at natural abundance become routine Sievers, NMR Shift Reagents, Academic Press... 

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