PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy.
J Org Chem. 2017 Dec 1;82(23):12162-12172. doi: 10.1021/acs.joc.7b01963. Epub 2017 Nov 20.
Irradiation of the three isomeric chlorobenzylphophonic acids in aqueous buffer led to a pH-dependent photochemistry. Under acidic conditions (pH = 2.5), photocleavage of the Ar-Cl bond occurred and a phenyl cation chemistry resulted. Under basic conditions (pH = 11), a photoinduced release of the chloride anion followed by the detachment of the metaphosphate anion gave α,n-didehydrotoluene diradicals (α,n-DHTs), potential DNA cleaving intermediates. At a physiological pH (pH = 7.2), both a cationic and a diradical reactivity took place depending on the phosphonic acid used. It is noteworthy that the complexation exerted by a monosaccharide (glucose or methylglucopyranoside) present in solution induced an exclusive formation of α,n-DHTs. The mechanistic scenario of the different photoreactivities occurring when changing the pH of the solution and the role of the various intermediates (phenyl cations, diradicals, etc.) in the process was studied by computational analysis.
三种氯苄膦酸异构体在水缓冲液中的辐照导致了一种依赖于 pH 值的光化学反应。在酸性条件下（pH = 2.5），Ar-Cl 键发生光解，生成苯阳离子化学物质。在碱性条件下（pH = 11），氯离子阴离子光诱导释放，随后亚磷酸盐阴离子脱离，生成α,n-去氢甲苯自由基（α,n-DHTs），这是潜在的 DNA 断裂中间体。在生理 pH 值（pH = 7.2）下，根据所用膦酸的不同，同时存在阳离子和自由基反应。值得注意的是，溶液中存在的单糖（葡萄糖或甲基吡喃葡萄糖苷）的络合作用导致仅形成α,n-DHTs。通过计算分析研究了改变溶液 pH 值时发生的不同光反应的机制情景以及各种中间体（苯阳离子、自由基等）在该过程中的作用。
