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On the photoreactivity of vitamin K compounds
Author(s) -
Swartz Angela M.,
Patton Valerie,
Heppleston Marianne J.,
Barra Mónica
Publication year - 2008
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20356
Subject(s) - chemistry , quinone , reaction rate constant , quenching (fluorescence) , reactivity (psychology) , alkyl , naphthoquinone , photochemistry , moiety , electron affinity (data page) , medicinal chemistry , organic chemistry , kinetics , molecule , fluorescence , medicine , physics , alternative medicine , pathology , quantum mechanics
Abstract Rate constants for conversion of vitamin K 1 ‐and K 2 ‐derived 1,3‐quinone methides into 1,2‐quinone methides have been measured in CH 3 CN solutions in the presence of Brönsted acids and bases. Second‐order rate constants approach the diffusion‐controlled limit and are essentially independent of the (acid or base) strength of the catalyst. On the other hand, rate constants for triplet quenching of 2‐methyl‐3‐undecyl‐1,4‐naphthoquinone, used as model compound, are presented and compared with data for 1,4‐naphthoquinone and 2‐methyl‐1,4‐naphthoquinone. A significant decrease in reactivity is observed as the number of alkyl substituents in the quinoid moiety increases, which is attributed to the concomitant increase in triplet π,π* character. Correlation of rate constants for physical quenching, by aromatic hydrocarbons and dimethylsulfoxide, with the electron affinity of the (ground state) quinone and ionization potential of the quenchers suggests quenching by charge‐transfer interactions. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 839–844, 2008