同型半胱氨酸硫内酯和α-甲基同型半胱氨酸硫内酯与水合电子（e-(aq)）和羟基自由基（OH-）的反应活性：脉冲辐解研究
Reactivity of homocysteine-thiolactone and alpha-methylhomocysteine-thiolactone with e-(aq) and OH-radical: a pulse radiolysis study.
作者信息
Getoff N, Solar S, Lubec G
机构信息
Institute for Theoretical Chemistry and Radiation Chemistry, The University of Vienna, Austria.
出版信息
Life Sci. 1998;63(16):1469-84. doi: 10.1016/s0024-3205(98)00414-7.
The efficient radiation protecting agents homocysteine-thiolactone x HCl (HCTL x HCl) and its alpha-alkylated derivative (alpha-methyl-homocysteine, alpha-MHCTL x HCl) have been investigated in respect to the identification of the primarily formed species after absorption of ionizing radiation using pulse radiolysis technique.The reaction of e-(aq) with the unprotonated form of HCTL (k = 2.1 x 10(9) dm3 mol(-1) s(-1)) is leading to the formation of a radical anion having two absorption bands: at 275 nm (epsilon = 2500 dm3 mol(-1) cm(-1)) and 510 nm (epsilon = 930 dm3 mol(-1) cm(-1)), which decay with 2k = 2.3 x 10(9) dm3 mol(-1) s(-1). The protonated form of HCTL reacts with e-(aq) with k = 4.0 x 10(10) dm3 mol(-1) s(-1). The OH-radicals react with HCTL with k = 1.95 x 10(9) dm 3 mol(-1) x s(-1) resulting in a transient spectrum with lambda(max) = 265 nm (epsilon =2000 dm3 mol(-1) cm(-1)). The transients disappear with 2k = 2.1 x 10(9) dm3 mol(-1) s(-1). The reactivity of e-(aq) with alpha-MHCTL was determined for both forms: for the protonated, k = 1.25 x 10(10) dm3 mol(-1) s(-1) and for the unprotonated, k = 2.6 x 10(9) dm3 mol(-1) s(-1). The transient absorption spectrum at pH = 8.4 shows two absorption bands: lambda = 275 nm (epsilon = 3500 dm3 x mol(-1) x cm(-1)) and 490 nm (epsilon = 1160 dm3 x mol(-1) x cm(-1)). The transients disappear with 2k = 2.2 x 10(9) dm3 x mol(-1) x s(-1). The reaction of OH with alpha-MHCTL x HCl,k = 8.4 x 10(9) dm3 x mol(-1) x s(-1) (pH = 8.6) is resulting in an absorption spectrum with lambda(max) < 260 nm and an absorption band at 350 nm (epsilon = 510 dm3 x mol(-1) x cm(-1)). Up to 50 micros after pulse the transients decay with 2k = 5.5 x 10(9) dm3 x mol(-1) x s(-1) and thereafter by a k = 8.4 x 10(9) dm3 x mol(-1) x s(-1) (pH = 8.6) is resulting in an absorption spectrum with lambda(max) < 260 nm and an absorption band at 350 nm (epsilon = 510 dm3 x mol(-1) x cm(-1)). Up to 50 micros after pulse the transients decay with 2k = 5.5 x 10(9) dm3 x mol(-1) x s(-1) and thereafter by a first order reaction. In addition, the formation of some products was also studied. The yield of ammonia resulting from alpha-MHCTL x HCl strongly depends on pH, e.g. at pH = 5.1 Gi (NH3) = 0.95, whereas at pH = 9.15 it increases to Gi = 3.1. Hydrogen sulphide is formed in airfree solutions, Gi (H2S) = 0.29, whereas in the presence of N2O it is reduced to Gi (H2S) = 0.10. Some probable reaction mechanisms are presented.
已使用脉冲辐解技术对高效辐射防护剂同型半胱氨酸硫内酯盐酸盐（HCTL·HCl）及其α-烷基化衍生物（α-甲基同型半胱氨酸，α-MHCTL·HCl）进行了研究，以确定电离辐射吸收后最初形成的物种。水合电子（e-(aq)）与未质子化形式的HCTL反应（k = 2.1×10⁹ dm³ mol⁻¹ s⁻¹）会导致形成一种具有两个吸收带的自由基阴离子：在275 nm（ε = 2500 dm³ mol⁻¹ cm⁻¹）和510 nm（ε = 930 dm³ mol⁻¹ cm⁻¹）处，其以2k = 2.3×10⁹ dm³ mol⁻¹ s⁻¹的速率衰减。质子化形式的HCTL与e-(aq)反应，k = 4.0×10¹⁰ dm³ mol⁻¹ s⁻¹。羟基自由基（OH·）与HCTL反应，k = 1.95×10⁹ dm³ mol⁻¹ s⁻¹，产生一个λ(max) = 265 nm（ε = 2000 dm³ mol⁻¹ cm⁻¹）的瞬态光谱。这些瞬态以2k = 2.1×10⁹ dm³ mol⁻¹ s⁻¹的速率消失。测定了e-(aq)与α-MHCTL两种形式的反应活性：对于质子化形式，k = 1.25×10¹⁰ dm³ mol⁻¹ s⁻¹；对于未质子化形式，k = 2.6×10⁹ dm³ mol⁻¹ s⁻¹。pH = 8.4时的瞬态吸收光谱显示两个吸收带：λ = 275 nm（ε = 3500 dm³ mol⁻¹ cm⁻¹）和490 nm（ε = 1160 dm³ mol⁻¹ cm⁻¹）。这些瞬态以2k = 2.2×10⁹ dm³ mol⁻¹ s⁻¹的速率消失。OH与α-MHCTL·HCl的反应，k = 8.4×10⁹ dm³ mol⁻¹ s⁻¹（pH = 8.6），产生一个λ(max) < 260 nm的吸收光谱和一个在350 nm处的吸收带（ε = 510 dm³ mol⁻¹ cm⁻¹）。在脉冲后高达50微秒内，瞬态以2k = 所给内容有误，应是5.5×10⁹ dm³ mol⁻¹ s⁻¹的速率衰减，此后按一级反应衰减。此外，还研究了一些产物的形成。由α-MHCTL·HCl产生的氨的产率强烈依赖于pH，例如在pH = 5.1时，Gi(NH₃) = 0.95，而在pH = 9.15时，它增加到Gi = 3.1。在无空气的溶液中形成硫化氢，Gi(H₂S) = 0.29，而在存在N₂O的情况下，它降低到Gi(H₂S) = 0.10。还提出了一些可能的反应机制。 （注：原文中“Up to 50 micros after pulse the transients decay with 2k = 5.5 x 10(9) dm3 x mol(-1) x s(-1) and thereafter by a k = 8.4 x 10(9) dm3 x mol(-1) x s(-1)”存在表述问题，推测可能是想表达“Up to 50 micros after pulse the transients decay with 2k = 5.5 x 10⁹ dm³ mol⁻¹ s⁻¹ and thereafter by a first order reaction”，译文按此推测进行了修正。）
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