44307-07-5Relevant articles and documents
Kinetics, Mechanism, and Thermodynamics of Glyoxal-S(IV) Adduct Formation
Olson Terese M.,Hoffmann, Michael R.
, p. 533 - 540 (1988)
The reversible addition of glyoxal (ethanedial) and S(IV) to form glyoxal monobisulfite (GMBS) was studied spectrophotometrically over the pH range of 0.7-3.3.Far from equilibrium, the rate of GMBS formation is given by d/dt = (k1,appα1) + k2,appα2), where = + + , = + -> + 2->, α1 = ->/, and α2 = 2->/.The apparent rate constants, k1,app = 0.13 M-1 s-1 and k2,app = 2.08E3 M-1 s-1, are pH independent functions of the dehydration equilibrium constants of (CH(OH)2)2 and CHOCH(OH)2, and intrinsic rate constants for the reaction of HSO3- and SO32- with unhydrated and singly hydrated glyoxal.Glyoxal dibisulfite (GDBS) and GMBS were shown to dissociate with a rate given by d/dt = -1 + k"-1KD3 + (k'-2K'a2 + k"-2K"a2KD3)/+>>t + -3 + k-4Ka3/+>>t, where k-1 and k-2 correspond to the release of bisulfite and sulfite, respectively, from unhydrated and hydrated GMBS species; k-3 and k-4 correspond to the release of bisulfite and sulfite from GDBS; KD3 is the dehydration constant for GMBS; K'a2, K"a2, and Ka3 are acid dissociation constants.Stability constants for the formation of GMBS and GDBS were determined to be cK1 = ->/(-) = 2.81E4 M-1 and cK2 = -)2>/(->->) = 1.45E4 M-1 at 25 deg C and μ = 0.2 M.
Photochemistry of 2-azido-1-methylimidazole in aqueous solutions. Observation of the 1-methyl-2-imidazolylnitrenium ion
Gadosy, Timothy A.,McClelland, Robert A.
, p. 1459 - 1465 (2007/10/03)
Irradiation of 2-azido-1-methylimidazole (12) in aqueous solution gives products from two reaction channels. One pathway involves a ring opening typical of azidoheterocycles. The observed products are glyoxal bis-hydrate, the methylammonium ion, and cyanamide; a glyoxal bis-oxime is presumed to be the intermediate initially formed in the ring opening. The other pathway leads to products that retain the five-membered ring, the 2-amino-4,5-dihydro-4,5-dihydroxy-1-methylimidazolium ion 3, its monophosphate ester 6 when the irradiation is carried out in phosphate buffer, and glutathione adducts 7 and 8 when glutathione (GSH) is present. These products have been previously observed in the reactions of 2-hydroxylamino-1-methylimidazole in aqueous solution, and arise from reaction of the 1-methyl-2-imidazolylnitrenium ion (2+) with water, phosphate, and GSH. This pathway is therefore proposed to involve formation of the cation 2+ via protonation of the singlet 1-methyl-2-imidazolylnitrene 13 formed upon irradiation of the azide. A single transient species undergoing exponential decay with λmax at 230-235 nm is observed with flash photolysis. This transient is assigned to 2+ on the basis of the pH dependence of the yields of products, and especially because of the correspondence of k2(GS-):ks ratios measured directly with flash photolysis and by competition kinetics starting from the hydroxylaminoimidazole. The cation 2+ has a lifetime in water of 100 ms, and shows a high selectivity for GSH with k2(GS-) = 3 × 107 M-1 s-1. There is evidence that this class of nitrenium ion is formed upon reductive metabolism of 2-nitroimidazoles. Thus this class of drugs is capable of producing a relatively long-lived electrophile in biological systems.
