期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 138, 期 43, 页码 14250-14256出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.6b05299
关键词
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资金
- Austrian Science Fund (FWF) [P-28892]
- U.S. National Science Foundation [CHE-1464584]
- Austrian Science Fund (FWF) [P28892] Funding Source: Austrian Science Fund (FWF)
- Direct For Mathematical & Physical Scien [1464584] Funding Source: National Science Foundation
- Division Of Chemistry [1464584] Funding Source: National Science Foundation
Cobalamins are of widespread importance in biology. Both of the cofactors essential for human metabolism, the organocobalamins coenzyme B-12 and methylcobalamin, are highly photolabile, as are other alkylcobalamins. The alkynylcobalamin phenylethynylcobalamin (PhEtyCbl) and the arylcobalamin 4-ethylphenylcobalamin (EtPhCbl) with atypical Co-C-bonds to unsaturated carbons, were recently designed as metabolically inert cobalamins, classified as antivitamins B-12. The further development of an ideal light-activated or conditional antivitamin B-12 would require it to be readily converted by light into an active B-12 vitamin form. Very photolabile antivitamins B-12 would also represent particularly useful scaffolds for therapeutic light-activated reagents. Here, the photoactive arylcobalamin EtPhCbl and the remarkably photostable alkynylcobalamin PhEtyCbl are examined using femtosecond to picosecond UV-visible transient absorption spectroscopy. PhEtyCbl undergoes internal conversion to the ground state with near unit quantum yield on a time scale < 100 ps and an activation energy of 12.6 +/- 1.4 kJ/mol. The arylcobalamin EtPhCbl forms an excited state with a ca. 247 ps lifetime. This excited state branches between internal conversion to the ground state and formation of a long-lived base-off species with a quantum yield of similar to 9%. Anaerobic steady state photolysis of light-sensitive EtPhCbl results in the formation of co(II)alamin, but only with quantum yield <1%. Hence, our studies suggest that suitably modified arylcobalamins may be a rational basis for the design of photoresponsive antivitamins B-12.
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