Mercaptoethanol, formation constants

Formation Constants of Mercaptoethanol with Metal Ions of Medical and Biomedical Interest0... 

Therefore, the kinetics and the product yields of isomerization and thiol adduct formation for a variety of Z- and ii-monounsaturated fatty acid (MUFA) esters were studied. The reactions were initiated by continuous °Co y-irradiation of N20-saturated f rf-butanol solutions containing -mercaptoethanol and MUFA esters. The time-dependent isomerizations and thiol additions were analyzed on the basis of the radiation chemical yields of radicals and established rate data. The rate constants for the reversible RS addition, within experimental error, do not depend on the double bond position in the alkyl chains vide Table 6). 

Reduction with dithiothreitol (DTT). The use of DTT, in place of mercaptoethanol, has gained wide acceptance. The reduction proceeds essentially to completion at low levels of DTT, because of the thermodynamically favored formation of a 6-membered ring. The equilibrium constant at pH 7 and 25°C for the reduction of cystine by DTT is 10", as compared to approximately 1 for mercaptoethanol (Konigsberg 1972). 

Like their amine analogues (Section 20.4.2.1) thiol-substituted alcohols may act as bidentates with chelation often leading to polymeric products. The stability constants of the Cd" complexes of both 2-mercaptoethanol (mel) and 3-mercapto-1,2-propanediol (mpd) have been determined, with polymeric structures being concluded similar to those of the previously determined Ni and Zn compounds. Similar data for the Pb" complexes showed polymer formation with mpd and gave evidence for Pb-mel species with at least five different metal ligand ratios. Reaction of the pertechnetate(VII) ion [Tc04] with sodium dithionite and 2-mercaptoethanol results in the... 

The kinetics and mechanism have been elucidated for the reduction of cobalt(II) 4,4, 4",4" -tetrasulfophthalocyanine by 2-mercaptoethanol. A rate constant of 228 3.8 s was obtained for the rate-limiting electron transfer in the formation of the 2-hydroxyethyl disulfide. The reduction of Cr(VI) by glutathione has been examined by visible spectroscopy (A ax = nm) and by... 

Rate constants on the order of several 10 M s and 10 -10 s for the forward and back reactions, respectively, yield equilibrium constants of lO -lO" M [39-41], Although this indicates reasonable stability for the thioperoxyl radical it may nevertheless easily escape detection. In air saturated solutions ([O2] ca. 2.5 X lO M), for example, formation of thioperoxyl radicals occurs with r,/2 ca. 1 ps, which is of the same magnitude as the halflife of its decay. This is of particular significance when a distinction between the reactions of RS and RSOO is at stake, and wrong assignments may be made unless absolute kinetic and thermodynamic data are known and taken into account. Two of the still small number of systems for which accurate measurements are available deal with the respective thiyl and thioperoxyl radicals of mercaptoethanol and glutathione. At least in case of the mercaptoethanol derived thioperoxyl radical, investigations have been facilitated by a weak but distinct optical absorption of RSOO with near 550 nm (c ca. 200-400 M cm ) [37,42]. 

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