TRANSIENT PHENOMENA IN THE PULSE RADIOLYSIS OF RETINYL POLYENES—7. RADICAL ANIONS OF VITAMIN A AND ITS DERIVATIVES
TRANSIENT PHENOMENA IN THE PULSE RADIOLYSIS OF RETINYL POLYENES—7. RADICAL ANIONS OF VITAMIN A AND ITS DERIVATIVES
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维生素A及其衍生物的自由基阴离子脉冲辐射分解的瞬态现象
DOI：
10.1111/j.1751-1097.1988.tb02697.x
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
P. Das
中科院分区：
文献类型：
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作者：
K. Bhattacharyya;K. Bobrowski;S. Rajadurai;P. Das
全反式视黄醇(ROH)和视黄基甲醚(ROMA)在非质子性溶剂中经电子脉冲辐照后，形成瞬时物种(τ=0.5-7μS，λmax=5 75-5 90 nm)，可鉴定为自由基阴离子。在N，N-二甲基苯胺存在于乙腈中的情况下，这些视黄酸衍生物的激光脉冲光激发也形成了类似的物种。相反，电子转移或连接到全反式视黄酸乙酯(ROAc)和棕榈酸酯(ROPA)会导致电子加合物中的羧酸阴离子从电子加合物中瞬间损失，从而产生视黄甲基自由基(R-，λmax=395 nm，τk>；100μ，S)；这些情况下的自由基阴离子寿命太短，无法通过纳秒脉冲辐解检测到。ROH和ROMA的自由基寿命对水和醇非常敏感(如Kq=107M~(-1)S~(-1)，用甲醇作为四氢呋喃中ROH~-的猝灭剂)。根据这些发现，ROH和ROAc在醇和水胶束中的单电子还原产物的光谱差异可以解释为在ROH的情况下，质子化的自由基阴离子(RH(OH)，τ1/2，>；100μS，λmax=370-375 nm)的快速形成，以及在ROAc的情况下，通过从自由基中失去ACO-而产生的视黄甲基自由基。在四氢呋喃中，ROH-与Na+和Bu4N+等阳离子的络合作用影响其主要衰变模式的相对重要性，即质子化和脱羟化，后者的作用因Na+的存在而显著增强。
Abstract— Upon e‐‐pulse irradiation in nonprotic solvents, all‐trans retinol (ROH) and retinylmethyl ether (ROMe) form transient species (τ= 0.5–7μs, λmax=575–590 nm) identifiable as radical anions. Similar species are also formed upon laser pulse photoexcitation of these retinyl derivatives in the presence of N,N‐dimethylaniline in acetonitrile. In contrast, electron transfer or attachment to all‐trans retinyl acetate (ROAc) and palmitate (ROPa) results in ‘instantaneous’ loss of carboxylate anions from electron adducts giving the retinylmethyl radical (R‐, λmax= 395 nm, τk > 100 μ,s); the radical anions in these cases are too short‐lived to be detected by nanosecond pulse radiolysis. The lifetimes of radical anions of ROH and ROMe are very sensitive to water and alcohols (e.g. kq= 107M‐1 s‐1 with methanol as quencher for ROH‐ in tetrahydrofuran). Based on these findings, the spectral dissimilarity of the one‐electron reduction products from ROH and ROAc in alcohols and aqueous micelles becomes explainable in terms of fast formation of protonated radical anions (RH(OH), τ1/2, > 100 μs, λmax=370–375 nm) in the case of ROH and of retinylmethyl radical via loss of AcO‐ from radical anion in the case of ROAc. In tetrahydrofuran, the complexation of ROH‐ with cations such as Na+ and Bu4N+ affects the relative importance of its major decay modes, namely, protonation and dehydroxylation, the latter process being significantly enhanced by the presence of Na+.