• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Time-Resolved Chemically Induced Dynamic Nuclear Polarization Studies of Structure and Reactivity of Methionine Radical Cations in Aqueous Solution as a Function of pH
【24h】

Time-Resolved Chemically Induced Dynamic Nuclear Polarization Studies of Structure and Reactivity of Methionine Radical Cations in Aqueous Solution as a Function of pH

机译：时间分辨化学诱导的动态核极化研究水溶液中蛋氨酸自由基阳离子的结构和反应性与pH的关系

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Using time-resolved chemically induced dynamic nuclear polarization (CIDNP) techniques,we have studied the mechanism of the photoreactions of triplet excited 4-carboxybenzophenone (CBP) with L-methionine (Met) and 3-(methylthio)propylamine (MTPA) in aqueous solution and the details of the formation of CIDNP at pH from 6.7 to 13.6.At a pH below the pK_a of the nitrogen atom of Met,the CIDNP is strongly affected by degenerate electron exchange between the S-S cationic radical dimer and the zwitterionic form of Met with the rate constant k_(ex)=3.4 x 10~8 s~(-1) providing an exhaustive explanation of the pH dependence of steady-state CIDNP that was previously interpreted as a manifestation of fast interconversion among three different methionine radical species (Goez,M.;Rozwadowski,J.J.Phys.Chem.A 1998,102,7945-7953).By analyzing the polarization of different protons formed in geminate recombination as a function of the pH,we obtained the branching ratio between two reaction pathways for oxidative quenching of ~TCBP via electron transfer from the sulfur and nitrogen atoms of Met and MTPA.Nuclear spin-lattice relaxation times were determined in the dimeric cation radical of Met (T_(1,s)=8.5 mus).In the cyclic radical cation of MTPA with a three-electron two-center S-N bond,the estimated paramagnetic relaxation is comparatively slow for all protons.Fast deprotonation of the primary aminium radical cation of MTPA and Met in strongly basic solution takes place on the submicrosecond time scale leading to efficient formation of CIDNP in the neutral aminyl radical.
机译：利用时间分辨化学诱导动态核极化（CIDNP）技术，研究了三重激发的4-羧基二苯甲酮（CBP）与L-蛋氨酸（Met）和3-（甲硫基）丙胺（MTPA）的光反应机理。 pH值从6.7到13.6的溶液以及CIDNP的形成细节。在低于Met氮原子的pK_a的pH值下，CIDNP受SS阳离子自由基二聚体和Met的两性离子形式之间简并电子交换的影响速率常数k_（ex）= 3.4 x 10〜8 s〜（-1）详尽地解释了稳态CIDNP的pH依赖性，该常数先前被解释为三种不同蛋氨酸基团之间快速相互转化的表现（ Goez，M。; Rozwadowski，JJPhys.Chem.A 1998,102,7945-7953）。通过分析在发芽重组中形成的不同质子的极化随pH的变化，我们获得了两个反应路径之间的支化比。通过从Met和MTPA的硫和氮原子转移电子而完成〜TCBP的氧化猝灭。在Met的二聚阳离子自由基（T_（1，s）= 8.5 mus）中确定了核自旋晶格弛豫时间。带有三电子二中心SN键的MTPA阳离子，估计所有质子的顺磁弛豫都相对较慢.MTPA和Met的主要铝自由基阳离子在强碱性溶液中快速去质子化，其亚微秒级导致在中性氨基自由基中有效形成CIDNP。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号