No abstract

Antitumor antibiotics like bleomycin or neocarzinostatin induce damage of the DNA strand mainly by H-abstraction of the 4'and/or S'-position of a deoxyribose unit.1 2Recently we have shown that a single-stranded 4'-oligonucleotide radical like 2 can be generated by photoinduced C-Se bond cleavage of the modified oligonucleotide l.2a In the absence of added traps the 4'-deoxyribosyl radical 2 yields oligonucleotide phosphates 3 and 4 as main products. The reaction starts with a heterolytic cleavage of the secondary phosphate group at C-3'. This leads to oligonucleotide fragment 4 and radical cation 6, which reacts with H20 and generates radical 7. Now the slower C-O bond cleavage of the primary phosphate group26 at C-5' can occur, which leads to fragment 3. The presence of the intermediate radicals 2 and 7 could be proven by trapping experiments with glutathione that yielded oligonucleotides 5 and 8 as further reaction products (Scheme 1).

No abstract

A new nucleation method to form diamond by chemically pretreating silicon (111) surfaces is reported. The nucleation consists of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Then low-pressure diamond growth was performed for 2 h via microwave plasma CVD in a tubular deposition system. The resulting diamond layers presented a good cristallinity and the Raman spectra showed a single very sharp peak at 1331 cm(-1), indicating high-quality diamonds.