th  - 1988 - 51st ENC Conference

- - 206
THE WORLD AND WONDERS OF 3H NMR SPECTROSCOPY: Philip G.
/i.lliam:s. ,* National Tritium Labeling Facility, Lawrence Berkeley Laboratory 75-123,
mverslty of California, Berkeley, California 94720.
The NTLF is a national User Facility, funded by the National Institutes of Health. The Facility combines
e availability of high levels of carrier free tritium gas, extensive radiochemical purification resources, and an
n-house NMR instrument dedicated to tritium NMR spectroscopy. The NTLF combines its User service
unction with core and collaborative research based on the use of hydrogen isotopes.
Tritium is an excellent nucleus for NMR observation, but NMR applications in the chemical and biological
ciences have been very limited in number. "Onepulse" tritium measurements can quickly and cleanly give the
hemical shift and relative abundance of tritons in a sample, and in combination with other physical methods
an rapidly assure quality control in labelling experiments. In catalysis hydrogen isotope exchange is readily
nonitored, with the relative incorporation at each position of a substrate yielding specificity rules for the
atalyst as well as mechanistic detail.
Hydrogenation and halogen replacement reactions are the cornerstone of high level tritium labelling
procedures. Little is known about concomitant side-reactions, but these are extremely important when specific
abelling is required. Observation of tritium NMR peaks from supposedly "unlabelled" positions obviates
hese extra mechanisms, and allows the choice of appropriate precursors and reaction conditions for the
lesired tritiation.
As one example, allylic methyl exchange in the hydrogenation of I]-methyl styrene to yield n-
,ropylbenzene is readily detected, and the full range of isotopomers can be distinguished by J-resolved
pectroscopy. Secondly, tritio-dehalogenation of 2-chloro-2'-deoxyadenosine with pure T2 does not give
,roduct with the theoretical specific activity, and factors influencing this "dilution" may be followed.
Important and developing uses of tritium NMR spectroscopy include monitoring of the conversion of
ntermediates in biological systems, studies of substrate binding, and as an aid in spectral elucidation of proton
~VMR spectra. The use of modern multipulse techniques in concert with simple and elegant older sequences
aas the potential for giving a great deal of conformational and coupling information, through the interaction of
I-H and 1-H atoms. NMR work at the Tritium Facility is intent on establishing the benefits and problems
tssociated with tritium NMR spectroscopy of many diverse substrates - from simple organics to solids and
nacromolecules.
202