64Cu enrichment using the Szilard-Chalmers effect - The influence of γ-dose.

Cu is an important trace metal which plays a role in many biological processes. The radioisotope 64Cu is often used to study such processes. Furthermore, 64Cu finds applications in cancer diagnostics as well as therapy. For all of these applications 64Cu having high specific activity is needed. 64Cu can be produced in cyclotrons or in nuclear reactors. In this paper we study the effect of gamma dose on the production of 64Cu according to the Szilard-Chalmers reaction using Cu(II)-phthalocyanine as a target. For this purpose, irradiations were performed in the nuclear reactor of the Delft University of Technology using a novel irradiation facility helping to limit the dose produced by gammas present in the reactor pool. The obtained 64Cu activity yield was in general above 60% in accordance to the theoretical expected value. An increase in gamma dose has no significant influence on the obtained activity yield but increases the loss of Cu from Cu(II)-phthalocyanine up to 0.9% and hence decreases the specific activity that can be obtained. However, without optimisation, when reducing the gamma dose specific activities in the order of 30 TBq/g can be achieved.

The role of the imidazolyl nitrogen atoms of histidine-12 in ribonuclease S.

S-peptide (residues 1--14) analogues in which the active histidine-12 residue is replaced by Npi-methyl-L-histidine, Ntau-methyl-L-histidine and beta-(pyrid-3-yl)-L-alanine were synthesized and tested for their capacity to bind to S-protein and to activate it. The results show that both imidazolyl nitrogen atoms are required for optimal catalytic functioning, Ntau being essential to the catalytic reaction itself, Npi playing a role in keeping the imidazole ring in the correct position.

An improved synthesis of tert-butyloxycarbonyl-L-histidine.

In our investigations on the effect of replacement of histidine by homohistidine (1) on the biological activity of some peptide-hormones, relatively large quantities of Boc-homohistidine were required. Homohistidine being difficult to synthesize, it was essential to find an effective way of introducing the Boc-group. In the past, many syntheses of Boc-histidine were reported (2-6), none of which proved to be quite satisfactory. However, by modifying the procedure of Flouret et al. (6) a convenient method resulting in a high yield of Boc-histidine and Boc-homohistidine was found.