芳香氨基酸光敏化瞬态产物的光谱学及动力学表征

运用KrF激光闪光光解瞬态吸收光谱 ,以丙酮为光敏剂 ,研究了水溶液中芳香氨基酸的光化学反应 .通过动力学分析和猝灭实验 ,鉴别了光化学反应过程中的瞬态产物 ,获取了激发三重态的瞬态吸收光谱及动力学参数 .在丙酮存在下 ,色氨酸(Trp)和酪氨酸 (Tyr)的水溶液光解 ,分别观察到Trp激发三重态、N中心色氨酸自由基 (Trp/N·)和酪氨酸的酚氧自由基 (Tyr/O·) ,阐述了二者是丙酮三重态与Trp ,Tyr分别通过三重态 三重态 (T T)激发能转移和电子转移生成 ;苯丙氨酸 (Phe)不能与丙酮三重态进行激发能转移和电子转移 .进一步 ,在色氨酰酪氨酸 (Trp Tyr)敏化光解过程中 ,观察到分子内的电子转移 ,即Trp/N· Tyr→Trp Tyr/O·自由基的生成过程 .     

甲基萘醌光敏化单电子氧化多聚鸟苷酸的动态研究

用248 nm激光光解瞬态吸收光谱研究了乙腈-水混合溶液中甲基萘醌(MQ)激发三重态(3MQ^*)单电子氧化多聚鸟苷酸(polyG)的原初过程, 应用解析瞬态吸收谱方法分别获取了MQ阴离子自由基(MQ^-·)及polyG阳离子自由基(polyG^+·)的瞬态吸收谱, 进而分别测定了MQ^-·及polyG^+·的生成速率常数及3MQ^*的衰减速率常数. 结果表明, 3MQ^*与polyG的反应速率常数非常接近于3MQ^*与dGMP反应的速率常数.     

丙酮三重态与含芳香氨基酸肽的物理化学过程

用激光闪光光解瞬态吸收光谱研究了水溶液中含芳香氨基酸残基肽的光敏化反应过程.结果表明,在丙酮存在的含色氨酸残基肽(Trp-Gly,n-f-Met-Trp,Trp-Phe)体系的光解,丙酮三重态与Trp分别通过三重态-三重态(T-T)激发能转移和电子转移生成Trp激发三重态和N中心自由基(Trp/N^·);丙酮三重态仅与含酪氨酸残基肽(Phe-Tyr)通过电子转移生成Tyr酚氧自由基(Tyr/O^·).在色氨酰酪氨酸(Trp-Tyr)与丙酮的光解体系中,观察到分子内的电子转移,即由Trp/N^·-Tyr→Trp-Tyr/O^·自由基的生成过程     

VP-16抗癌机理的脉冲辐解

运用脉冲辐解技术, 对用于肿瘤治疗的依托泊甙(VP-16)的抗癌机理进行探讨. 首次对过硫酸根氧化VP-16的过程进行了研究, 测得其绝对反应速率常数为4.04×10⁹ dm³·mol^-1·s^-1, 同时观测到VP-16与酪氨酸之间的电子转移, 两者绝对反应速率常数为1.1×10⁸ dm³·mol^-1·s^-1. 为医学工作者进一步了解、探讨VP-16的抗肿瘤机理提供科学的参考.     

稀土金属离子及pH诱导牛血清白蛋白构象变化的同步荧光光谱研究

用同步荧光法并辅以普通荧光法对不同浓度稀土离子及pH诱导的牛血清白蛋白(BSA)构象变化进行了详细研究, 发现稀土离子使色氨酸(Trp)残基的荧光蓝移, 荧光强度降低; 酪氨酸(Tyr)残基荧光峰位置不变, 稀土离子浓度较低时, 荧光峰强度降低, 而当浓度较高时, Tyr残基荧光峰强度反而增强. 据此推断了稀土离子与BSA结合反应中Trp残基微环境和Tyr残基微环境及构象的变化并与pH引起的变化进行了比较.     

CCl3OO· 槲皮素、芦丁、EGCG的分子反应机理

采用脉冲辐解时间分辨吸收光谱技术,研究了在近中性条件下槲皮素、芦丁、没食子儿茶素没食子酸酯(EGCG) 3种天然抗氧化剂清除CCl₃OO^· 自由基的反应机理,提出 CCl₃OO^·自由基与芦丁、EGCG反应均为单电子转移反应,而与槲皮素的反应可能存在单电子转移和加成两种机理,并测定了它们的反应速率常数,证明槲皮素、芦丁清除CCl₃OO^·自由基的能力比EGCG强得多.     

维生素K3的激发三重态与色氨酸、酪氨酸电子转移氧化反应的激光闪光光解研究

利用时间分辨的激光闪光光解技术研究了乙腈-水混合溶液(1:1,V/V)中2-甲基萘醌(通常称为维生素K3)的激发三重态对色氨酸、酪氨酸的光敏氧化机理.通过瞬态吸收光谱的变化可以推断维生素K3的激发三重态可以与色氨酸、酪氨酸发生电子转移反应,反应形成的维生素K3阴离子自由基的吸收峰可以直接从瞬态吸收谱图中观察到.维生素K3与色氨酸、酪氨酸的电子转移反应的速率分别为1.1×109和0.6×109L·mol-1·s-1.吉布斯自由能(ΔG)的计算结果表明维生素K3的激发三重态与色氨酸、酪氨酸电子转移反应在热力学上是可行的.     

酪氨酸与色氨酸间电子转移——氧化还原活性及电子跃迁能的从头算研究

在HF/6-31G和GASSCF/6-31G水平上对色氨酸和酪氨酸间的电子转移进行了理论 研究。用类导体屏蔽模型考察体系的溶剂效应。通过对给、受体几何构型的优化， 计算了孤立的给、受体之间电子转移反应的内重组能和反应能差。分别用 Koopmans定理和CASSCF/6-31G方法计算了色氨酸和酪氨酸的电离能。计算了此两种 氨基酸从基态到最低激发态的跃迁能。理论计算结果很好地解释了N_3~·高选择性 地氧化色氨酸残基，并诱发电子从酪氨酸残基向色氨酸残基转移的实验现象。     

草酰氯氯解离(ClCO)2→2Cl·+ 2CO通道的量子化学研究

对草酰氯分子的多键解离方式进行了从头算研究. 计算表明: 草酰氯分子基态(S₀)解离C—Cl键不经过过渡态; 吸收一个光子后, 分子在第一电子激发态(S₁)解离生成高能态Cl^·和ClCOCO^·*自由基, 此时体系很容易放出能量Q, 变成基态的Cl^·和ClCOCO^·自由基, 放出的Q能量足以使ClCOCO^·自由基进一步热解为ClCO^·和CO, 并能使ClCO^·再进一步热解为CO和Cl^·自由基而发生串级解离反应. 这与Kong报道的光解草酰氯的实验结果相一致.     

稀有三环核苷衍生物单电子氧化反应的脉冲辐解研究

运用纳秒级脉冲辐解技术研究了稀有三环核苷衍生物6-甲基三环鸟苷(dYt)与一些单电子氧化性自由基的反应, 表征了反应过程中产生的阳离子自由基dYt^•+及其脱质子中性自由基dYt(-H)^• 的瞬态吸收光谱及pKa, 并首次得到该化合物与^• OH自由基及单电子氧化性自由基SO₄^•-, CO₃^•-, N₃^•反应的动力学速率常数, 揭示了反应机理, 为进一步了解该类化合物的氧化反应提供了一定的证据.     

苝醌/富勒烯C60超分子与电子给体的电子转移作用

利用紫外-可见吸收光谱、瞬态吸收光谱及X射线衍射等方法研究了苝醌染料竹红菌素镁离子配合物(Mg2+-HA)与富勒烯C60的相互作用. 结果表明, Mg2+-HA与C60在溶液和固体状态下都能够形成稳定的超分子. Mg2+-HA存在条件下, C60能够溶于多种极性溶剂, 在二甲基亚砜(DMSO)中的溶解度能够达到1×10^-4 mol·L^-1. 作为超分子体系中的光捕获分子, Mg2+-HA能显著地提高C60与N,N-二甲基苯胺(DMA)的光诱导电子转移反应效率, 生成的C60负离子自由基的电子自旋共振光谱(ESR)信号强度比未加入Mg2+-HA时增强了9倍左右.     

孔雀石绿与牛血清白蛋白的相互作用

运用荧光光谱和紫外-可见吸收光谱研究了在缓冲溶液中不同温度下孔雀石绿(MG)与牛血清白蛋白(BSA)之间的相互作用. 实验结果表明, MG对BSA的内源荧光猝灭为静态猝灭过程. 测定了该反应在不同温度下的结合常数KA, KA分别为7.69×10⁴ L·mol-1(10 ℃)、5.31×10⁴ L·mol-1(20 ℃)和4.85×10⁴ L·mol-1(37 ℃), MG与BSA以摩尔比1:1结合. 根据Forster非辐射能量转移理论, 求出了37 ℃时给体(MG)和受体(BSA)之间能量转移效率和结合距离分别为E=0.1635 和r=2.30 nm. 计算出的热力学参数表明, MG 和BSA之间的作用力主要是通过氢键和范德华力相互作用.     

Comparison of intermediates of tryptophan, tyrosine and their dipeptide induced by UV light and SO. 4 –

The chemical processes of tryptophan (Trp), tyrosine (Tyr) and a dipeptide Trp-Tyr, which are induced by UV radiation and one-electron oxidation of SO^. ₄ ^–, have been investigated in aqueous solution by KrF (248 nm) laser flash photolysis. On the basis of optical studies, the photoionization of Trp and Tyr produces the tryptophan indolyl radical and tyrosine phenoxyl radical, respectively, and these are different from the intermediates resulting from interaction of Trp and Tyr with SO^. ₄ ^–. In the case of Trp, SO^. ₄ ^– would attack the indole moiety to produce a C(2)-yl sulphate radical adduct, and Tyr is oxidized to produce mainly the corresponding one-electron oxidized radical, which deprotonates rapidly to form the phenoxyl radical in neutral solution, and a possible sulphate radical adduct. From transient absorption spectra of photoionization of Trp-Tyr, an intramolecular electron transfer, Trp/N^.-Tyr Trp-Tyr/O^., has been observed, but there was no observation of the process of one-electron oxidation of Trp-Tyr by SO^. ₄ ^–.     

5-氟尿嘧啶与牛血清白蛋白的相互作用

根据合理的假设和Langmuir结合理论, 在298.15 K下, 以等温滴定微量热(ITC)实验数据为依据, 应用非线性最小方差拟合方法确定了抗肿瘤药物配5-氟尿嘧啶(5-FU)与牛血清白蛋白(BSA)相互作用的热力学性质的改变. 研究结果表明, 牛血清白蛋白(BSA)与5-氟尿嘧啶相互作用存在两类结合位点. 第一类结合, N=(54.0 0.3), ⊿H⁰=(30.0±0.4) kJ·mol^-1 (吸热), ⊿S⁰=(196.0±2.6) J·mol-1·K-1(熵增), ⊿G⁰=(-28.4±0.3) kJ·mol^-1; 第二类结合, N=(77.0±0.4), ⊿H⁰=(-20.0±0.4) kJ·mol^-1 (放热), ⊿S⁰=(28.6±0.3) J·mol^-1·K^-1 (熵增), ⊿G⁰=(-28.5±0.2) kJ·mol^-1. 结合体系的圆二色谱(CD)分析结果说明, 抗肿瘤药物5-氟尿嘧啶与BSA的相互作用诱导蛋白质(BSA)二级结构单元的相对含量发生了一定程度的变化.     

磁性壳聚糖微球对牛血清白蛋白的吸附性能

在微乳液体系中, 以戊二醛为交联剂制备了磁性壳聚糖纳米粒子(Fe₂O₃-CS). 采用透射电子显微镜(TEM)、红外光谱(IR)、振动样品磁强计(VSM)等手段对纳米粒子进行表征. 结果表明, 纳米粒子的粒径在40 nm左右, 分散性良好, 具有较好的磁响应性能. 以碳二亚胺(EDC)为活化剂, 研究了Fe₂O₃-CS纳米粒子对牛血清白蛋白(BSA)分子的吸附性能, 并使用原子力显微镜(AFM)、紫外分光光度计(UV)进行表征. Fe₂O₃-CS粒子对BSA 的吸附大致符合Langmuir吸附模型, 298 K时饱和吸附量约为250 mg·g^-1, 吸附常数为0.007 L·mg^-1. 将BSA-粒子分散在不同pH的缓冲溶液中, 研究BSA-粒子复合物的稳定性. 用聚丙烯酰氨凝胶电泳(SDS-PAGE)对结果进行表征, 发现在碱性条件下BSA分子能从磁性粒子表面脱附下来.     

A laser flash photolysis study of amino acids and dipeptides using 4-nitroquinoline 1-oxide as a photosensitizer: The pH dependence

The pH effects on the photochemical reaction of amino acids and related dipeptides with 4-nitroquinoline 1-oxide (4NQO) as a photosensitizer have been investigated by laser flash photolysis. The obtained kinetic parameters show that the electron transfer from Tryptophan (Trp), Tyrosine (Tyr) as well as dipeptides containing Trp and/or Tyr residue to triplet 4NQO (^T4NQO) are efficient, but inefficient from methionine (Met) and dipeptides containing neither Trp nor Tyr. The result was supported by the calculated values of the free energy change from measured oxidation potentials for the electron transfer. It was demonstrated that Trp and Tyr residues are initial reaction sites with ^T4NQO, while Tyr/O^? radical may be final species for Trp-Tyr dipeptide. In acidic aqueous solutions, the self-quenching rate constants of ^T4NQO and the rate constants of electron transfer from amino acids to ^T4NQO decrease with decreasing pH. In alkaline solutions, amino acids are easily oxidized by 4NQO under irradiation of laser pulse, and no transient absorption signal was observed.     

LASER FLASH PHOTOLYSIS AND PHOTOINACTIVATION OF SUBTILISIN BPN'

Abstract— Laser flash photolysis of subtilisin BPN'at 265 nm has shown that photoionization of tryptophanyl (Trp) and tyrosinyl (Tyr) residues are the principal initial photochemical reactions. The initial products are the corresponding oxidized radicals. Trp and Tyr, and hydrated electrons (e_aq) which react with the enzyme at: k (e_aq+ subt. BPN') = 2.1 × 10¹⁰ M⁻¹ s⁻¹. The photoionization quantum yield was 0.032 ± 0.005 at 265 nm, which was enhanced 3.5-fold by simultaneous excitation at 265 and 530 nm. The photoionization yields were unchanged by 3 M bromide ion and 8 M urea. which did affect the enzyme fluorescence excited at 265 and 295 nm. A similar lack of correlation between the effects of perturbants on the photionization yields and fluorescence yields was found for subtilisin Carlsherg. The results indicate that the monophotonic and biphotonic ionization of the Trp residues does not involve the thermally-equilibrated. lowest excited singlet state and that singlet energy transfer from Tyr to Trp does not contribute to Trp photoionization. The photoinactivation quantum yield was 0.014 for 265 nm laser excitation. which was not changed by simultaneous 530 nm excitation. The corresponding quantum yield was 0.009 for low intensity 254 nm radiation, indicative of a biphotonic contribution to photoinactivation. The results are explained by postulating that photolysis of Trp-113 leads to disruption of hydrogen bonding to Asn-117 and a shift in the primary chain sequence associated with the aromatic substrate binding sites. The photoionization quantum yields in subtilisin BPN'and subtilisin Carlsberg agree with a model based on the assumption that exposed Trp and Tyr residues contribute independently at intrinsic photoionization efficiencies characteristic of the chromophores.     

对乙酰基偶氮胂光度法测定粮食中的钙

粮食中钙的测定一般采用EDTA滴定法和原子吸收法。前者难应用于微量分析,后者则需要贵重的仪器。变色酸双偶氮衍生物光度法可以克服二者的缺点。这方面的研究已见报导。但仍有一些干扰离子的问题须待解决。我们曾研究过对溴偶氮胂在强碱性条件下测定土壤中的钙,避免了镁离子的干扰。本文报导对乙酞基偶氮肿在强碱性条件下测定粮食中的钙,Mg²⁺和许多重金属离子无干扰,不需分离操作,方法简捷。     

Intermolecular vs. intramolecular photoinduced electron transfer from nucleotides in DNA to acridinium ion derivatives in relation with DNA cleavage

Photoirradiation of various 10-methylacridinium ions (AcrR⁺, R = H, ⁱPr, and Ph) intercalated in DNA results in ultrafast intramolecular electron transfer, followed by rapid back electron transfer between AcrR⁺ and nucleotides in DNA. The electron-transfer dynamics in DNA were monitored by femtosecond time-resolved transient absorption spectroscopy. Both acridinyl radical and nucleotide radical cations, formed in the photoinduced electron transfer in DNA, were successfully detected in an aqueous solution. These transient absorption spectra were assigned by the comparison with those of DNA nucleotide radical cations, which were obtained by the intermolecular electron-transfer oxidation of nucleotides with the electron-transfer state of 9-mesityl-10-methylacridinium ion (Acr–Mes⁺) produced upon photoexcitation of Acr⁺–Mes. Photoinduced cleavage of DNA with various acridinium ions (AcrR⁺, R = H, ⁱPr, Ph, and Mes) has also been examined by agarose gel electrophoresis, which indicates that the rapid intramolecular back electron transfer between acridinyl radical and nucleotide radical cation in DNA suppresses the DNA cleavage as compared with the intermolecular electron-transfer oxidation of nucleotides with Acr–Mes⁺.