The objective of the proposed research is to study the conditions under which tritium labeled compounds such as unsaturates, polypeptides, proteins, and biomolecules, can be obtained with high specific activity and minimum degradation. The use of energy transfer agents, catalytic surfaces and graded tritium energies to increase the selectivity of tritium labeling by active species of tritium will be studied. The short duration of exposure, mild conditions, minimum radiation degradation and high specific activity can be obtained make excitation labeling the method of choice for complex molecules and biomelecules. Adsorbed or chemisorbed tritium on supported metal catalysts will be used for tritium labeling. Adsorbed tritium is the mildest tritium exchange agent and can label compounds with hydrogen sensitive groups without causing their reduction or substitution. The method can be improved to increase the amount of tritium adsorbed or chemisorbed on the catalyst so that curie amount of tritium is available for tritation of biological molecules. The use of surfaces to complex and stabilize the peptide bond and the N- and C-terminal residues in peptide molecules to minimize degradation will be investigated and, particularly, the reactions of protected and non-protected small peptides with tritium to determine how polypeptides such as interferons and insulin can be routinely labeled with high specific activity. The dehalogenation reactions, i.e., T-for-I and T-for-Br reactions are particularly useful for introducing tritium into specific positions in a molecule in the absence of hydrogen transfer catalyst and will be investigated. Dehalogenation in the presence of metal catalyst may result in tritium exchange and is undesirable. Tritium NMR spectroscopy of some of these labeled compounds will be performed by Dr. Yang of Lawrence Berkeley Laboratory.
