Thioester, absorption spectrum

The formula of the intermediate may be recognized as that of a thioester formed from lactic acid and GSH. Its ultraviolet absorption spectrum is characterized by a maximum at 235 m/i. This maximum absorption as well as its stability properties are characteristics manifested by other thioesters such as acetyl-CoA. The intermediate should also yield the hydroxamic acid derivative of lactic acid upon treatment with neutral hydroxylamine. The fact that it is a thioester suggests, by analogy with acetyl-CoA, that it is a high-energy compound. 

In this section we focus on the analysis of the solvent effect and coumaryl tail on the absorption spectrum of some p-coumaric derivatives acid (pCA ), thioacid (pCTA ), methyl ester (pCMe ) and methyl thioester (pCTMe ), see Scheme 5.4. The comparison of the behavior of these systems permits to analyze the modifications introduced by the substitution of a sulfur by an oxygen atom and the influence of the methyl group. As we will show the presence of the sulfur modulates the solvent effect, as a consequence the first two excited states become practically degenerated for pCA- and pCMe- but moderately well separated for pCTA- and pCTMe-. 

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