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Time-resolved absorption and resonance Raman studies of free radicals in model biochemical systems.

机译：模型生化系统中自由基的时间分辨吸收和共振拉曼研究。

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This dissertation presents a detailed investigation of the spectroscopic and kinetic properties of a number of short-lived radicals which are models for systems of biochemical relevance. Focus is on radicals produced in the oxidation and reduction of 4-hydroxy- and 4-amino-benzoic acids, isonicotinic acid and its amide and riboflavin. Experimental data on reaction rate constants and absorption and vibrational characteristics of the radicals are presented, and their formation and decay mechanisms are discussed.; The radicals were prepared under controlled conditions by electron pulse irradiation of appropriate chemical precursors in aqueous solutions. Time-resolved optical absorption and resonance Raman spectroscopic methods were used for their detection. Studies were performed in very acidic to highly basic solutions to examine the structural and kinetic behavior of intermediates in their different states of protonation.; The work on 4-hydroxybenzoic acid (a substrate of the enzyme 4-hydroxybenzoate hydroxylase) clarifies the mechanism of the base catalyzed water elimination from the OH-adducts of phenols (dihydroxycyclohexadienyl radicals). First, H{dollar}sp+{dollar} is lost by reaction with base, followed by intramolecular electron transfer and OH{dollar}sp-{dollar} elimination, and phenoxyl radical is formed. The OH{dollar}cdot{dollar}O{dollar}sp-cdot{dollar} radicals react with phenoxide ions by addition, and not by electron transfer. In a related study on 4-aminobenzoic acid, adduct radicals have been observed to decay into aniline cation (pKa {dollar}sim{dollar} 6.8), which deprotonates in basic solution to form anilino radical.; In the study of reduction of isonicotinic acid and its amide, the anionic form of the electron adduct in the latter system has been observed for the first time. Proton ionization involves amide N-H (pKa {dollar}sim{dollar} 13.5) and not ring N-H. It has been also found that the hydrogen atom bonds exclusively to the isonicotinamide ring N site if it is not protonated. In acidic solutions, where the ring N is protonated, {dollar}sim{dollar}29% of hydrogen atoms add to amide CO and rest to ring carbons. Thus, the protonation state of the pyridine ring affects the chemistry.; The resonance Raman studies of riboflavin (vitamin {dollar}rm{lcub}Bsb2{rcub}{dollar}) semiquinone radicals have provided, for the first time, reference vibrational frequencies for probing protein interactions.
机译：本文对许多短寿命自由基的光谱和动力学性质进行了详细的研究，这些自由基是生物化学相关系统的模型。重点是在4-羟基-和4-氨基-苯甲酸，异烟酸及其酰胺和核黄素的氧化和还原中产生的自由基。给出了反应速率常数，自由基的吸收和振动特征的实验数据，并讨论了它们的形成和衰变机理。通过在水溶液中通过适当的化学前体的电子脉冲辐射在受控条件下制备自由基。使用时间分辨的光吸收和共振拉曼光谱法进行检测。在非常酸性至高度碱性的溶液中进行了研究，以检查处于不同质子化状态的中间体的结构和动力学行为。对4-羟基苯甲酸（4-羟基苯甲酸羟化酶的底物）的研究阐明了从酚（二羟基环己二烯基）的OH加合物中除去碱催化的水的机理。首先，H {dollar} sp + {dollar}通过与碱反应而损失，然后进行分子内电子转移和OH {dollar} sp- {dollar}消除，形成苯氧基。 OH {dollar} cdot {dollar} O {dollar} sp-cdot {dollar}自由基通过加成而不是通过电子转移与酚盐离子反应。在有关4-氨基苯甲酸的一项相关研究中，已观察到加成基团会降解为苯胺阳离子（pKa {dol} sim {dollar} 6.8），后者在碱性溶液中会去质子化，形成苯胺基。在还原异烟酸及其酰胺的研究中，首次观察到后者体系中电子加合物的阴离子形式。质子电离涉及酰胺N-H（pKa {dol} sim {dollar} 13.5），而不是环N-H。还发现如果氢不被质子化，则氢原子仅与异烟酰胺环的N位键合。在环N为质子化的酸性溶液中，29％的氢原子加到酰胺CO中，并保留在环碳上。因此，吡啶环的质子化状态影响化学反应。核黄素（维生素{rm} {rm} {lcub} Bsb2 {rcub} {dollar}）半醌基的共振拉曼研究首次为检测蛋白质相互作用提供了参考振动频率。

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