Thermodynamic study on conformation change of carbonic anhydrase

The effect of pHs on structural stability of the zinc-containing metalloenzyme carbonic anhydrase has been studied by means of differential scanning calorimetry. The rule of the conformational change for the enzyme with pH change has been found by thermodynamic analysis. The experimental results also provide valuable information: in the pH range from 5.26 to 9.04, two independent endothermal peaks were observed on DSC thermogram. It shows the existence of two structural domains in the molecule. The transition temperature and enthalpy of the two domains are different.     

呋塞米对碳酸酐酶的抑制效应再研究

呋塞米是一种高效利尿剂,本实验主要探究其对碳酸酐酶的抑制效应.相比较乙酰唑胺而言,呋塞米在其浓度接近碳酸酐酶浓度时能使该酶基本失活.研究发现,呋塞米对碳酸酐酶的抑制效应表现为非竞争性抑制,其IC50为0.759μM,KI为0.61μM,乙酰唑胺的IC50为0.199μM,KI为0.099μM,表现为竞争性抑制.     

不同环境条件下水稻叶片中叶绿体内碳酸酐酶活性的变化

以水稻(Oryza．Sativa L．)为材料,在不同光照、高盐、高温及缺N、K培养等条件下研究碳酸酐酶活性的变化。结果表明;在16μmolES^-2-64μmolES^-2。光强范围内,随着光照的增加,碳酸酐酶活性并无明显的变化．在高盐逆境条件下碳酸酐酶活性降低2-3倍,在高温逆境条件下碳酸酐酶活性降低了2～4倍,在缺N培养条件下碳酸酐酶活性降低了7-8倍,在缺K的培养条件下碳酸酐酶活性降低了2—3倍。     

CIONO2与Br反应机理的密度泛函理论研究

用密度泛函理论方法（B3LYP），在6-31G＊水平上对CION02与Br反应进行了研究，计算了反应中各驻点物种的平衡构型、振动频率、总能量和零点能（ZPE）．计算得到各可能反应途径的过渡态．并经过内禀反应坐标分析加以证实．研究表明，存在如下三种可能的反应途径：Br＋CIONO2→BrCI＋N03，Br＋CIONO2→C10＋BrONO，Br＋CIONO2→BrOCI＋NO2，其中第一个反应捅措韵后廊涪化能垒最低，为2.33kJ/mol，是主反应通道。     

高浓度CO_2对小新月菱形藻胞外碳酸酐酶活性和光合作用的影响

以赤潮硅藻小新月菱形藻(Nitzschia closterium var.minutissima)为实验材料,研究了短期内(12 h)高浓度CO2(5%CO2)对其胞外碳酸酐酶活性和光合作用的影响,结果显示,高浓度CO2培养导致小新月菱形藻胞外碳酸酐酶活性、叶绿素a和叶绿素c含量明显下降.与通空气培养(0.035%CO2)相比,在短期内(12 h)胞外碳酸酐酶活性下降了75.4%,叶绿素a、c含量分别降低了5.6%和7.3%;高浓度CO2培养下最大光化学效率(Fv/Fm)、实际光化学效率(Yield)和光化学淬灭系数(qP)下降,但非光化学淬灭系数(gN)升高.研究结果表明,高浓度CO2对胞外碳酸酐酶活性具有明显的抑制作用,小新月菱形藻通过调整光系统Ⅱ的能量流动和能量利用效率以适应高浓度CO2的环境.     

单硫代次膦酸异构体及质子转移异构化反应的理论研究

采用量子化学密度泛函B3LYP方法, 在6-311 G**基组水平上全优化得到了硫代次磷酸的硫酮式和硫醇式两种构型异构体以及相应的对映异构体, 同时对分子内质子转移异构化反应微观机理进行了理论分析. 研究结果表明,硫酮式H2P(S)OH比硫醇式H2P(O)SH的能量低26.2 kJ/mol;质子转移异构化过程中形成一个四员环过渡态结构, 与迁移原子H6无直接键连关系的其他构型参数在异构化过程几乎保持不变.     

测定醋酸质子转移平衡常数的方法

介绍了三种测定醋酸质子转移常数的方法,通过实验对三种方法进行了验证,并针对三种测定方法的优缺点,对实验的开设提供了建议.结果表明：三种方法测定的结果精确度均较高.pH法原理简单,但是操作复杂,需要准确标定醋酸溶液的浓度,比较适合于分析化学实验课程开设.缓冲溶液法原理简单,不需要准确标定醋酸的浓度,可以作为非化学专业开设普通化学实验内容.电导法仪器先进,操作方法简单,实验综合性较强,适合于物理化学实验开设.     

C2+C2H2→C4H2反应机理的密度泛函研究

在密度泛函理论B3LYP/6-31 G水平上研究C2分子自由基与C2H2分子的反应机理。优化计算得到可能反应途径上的反应物、中间产物、过渡态和产物的几何结构,并通过频率振动分析对过渡态和中间产物进行了确认。结果表明,反应C2 C2H2→C4H2是多步骤的强放热反应。     

C3H7/NH2/Fe+体系反应活性的密度泛函研究

采用B3LYP密度泛函理论对C3H7/NH2／Fe^＋体系生成乙烯和丙烯的反应路径进行了研究。在B3LYP／6-31＋G＊＊水平上，优化了4重态势能面上的极小值和过渡态的几何构型，计算了它们的能量和频率等参数，得到了该反应的势能面以及反应基元过程的详细信息。     

苯分子的溴代反应研究

应用量子化学密度泛函理论在UB3LYP/6-31G（d）水平上, 结合MP4和AM1方法研究了苯的溴代反应过程. 计算结果表明, 这是包括一个过渡态和两个中间态的多步反应, 反应过程中Br⁺所带的正电荷经正离子中间体［C₆H₆Br］⁺转移给H, 是电子转移过程.     

Changes of dipole moment in intramolecular proton transfer process of perylenequinone

Semiempirical quantum chemistry method AM1 was employed to calculate dipole moment of perylenequinone (PQ) in intramolecular proton transfer (IPT) process. It was found that there existed a maximum of dipole moment in all IPT process except PQ anion (PQ) which possessed a minimum. Moreover, almost all states of PQ except ground state had high changes in dipole moment. All of these laid foundations to clarify solvent effects in IPT of PQ.     

虹鳟假鳃组织中的碳酸酐酶免疫细胞化学定位

研究目的：假腮的功能早已引起科学家兴趣,但还有待阐明。本文通过研究硬骨鱼类品种虹鳟鱼（Oncorhynchusmykiss）的假腮碳酸酐酶的免疫定位,来探讨假腮碳酸酐酶的生理功能。研究方法：免疫组织化学染色技术。重要结论：免疫组化结果显示碳酸酐酶分布在假腮细胞中,更精确地说是在其细胞顶端分布。细胞基底端、管状系统、毛细血管和柱细胞均无免疫染色。免疫细胞化学定位进一步验证了这些结果,并显示一部分是细胞质碳酸酐酶,其余的与细胞膜结构连接。此外,腔隙层未显示出免疫过氧化物酶的活性。本研究揭示了假腮碳酸酐酶的功能与细胞外介质有关,碳酸酐酶能干预传入神经纤维刺激机制。     

氢键加强引起的链式激发态多质子转移的动力学研究进展

作为自然界中最广泛存在的基本反应过程之一,质子转移(proton transfer,PT)一直是动力学研究中的一个重要话题.而沿着一系列氢键进行的多质子转移过程,更是由于绿色荧光蛋白的发现及广泛应用,成为了近年来的热门课题.我们使用密度泛函理论(DFT)对新兴的链式激发态多质子转移过程进行了系统的理论研究.我们以赵广久与韩克利研究员建立的激发态氢键加强理论为基础,对6-hydroxyquinoline(6HQ)光酸分子及其阳离子形式6HQc的激发态质子转移反应,给出了新的解释及机理:(1)在一个体系中,氢键加强与氢键减弱可能会同时存在,归结其原因,主要取决于激发态分子的电荷再分布;(2)单个或者少数的水分子是很难从酸性分子上夺得质子的,只有当水分子形成更大的团簇(即氢键更多)时,其夺质子能力会大大加强;(3)链式激发态多质子转移(即多质子转移机理)并不单纯的是分步机理或者是协同机理,也有可能是分步与协同相结合的进行,是一种复杂多变的反应.     

Mechanism of skeletal reorganization of 1,6-enynes catalyzed by GaCl<Subscript>3</Subscript>

The mechanism of skeletal reorganization of 1,6-enynes catalyzed by GaCI3 has been studied with the density functional method at the B3LYP/6-31G* level. The structures and energies of the stationary points were calcu-lated to identify the activation barriers. The transition stateswere testified with vibration analysis and IRC calculations.The results of calculation show that the conversion of 1,6-enynes is a step-wise reaction. The whole reaction process is formation and migration of three-membered cycle involvinga three-center and two-electron (3c-2e) bond. High stereose-lectivity of the reaction is in good agreement with experimental results.     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

咪唑型离子液体催化Diels-Alder反应的理论研究

采用量子化学从头计算和密度泛函理论方法,研究了咪唑类离子液体催化Diels-Alder反应(环戊二烯和丙烯酸甲酯反应)的反应机理.在HF/6-31 G*和B3LYP/6-31 G*方法水平上,考察了反应的endo/exo(内型/外型)选择性、活化能等.研究结果表明,离子液体主要借助阳离子参与来催化该反应.阳离子的参与能够大大的降低反应过渡态的能垒,增大反应的endo选择性.     

Density functional theory study of the reaction paths of reactions of CH_3C(O)O_2 radicals with HO_2 in the gas phase

Acetyl peroxyradicals play a major roleinthe at-mospheric degradation of organic compounds .In pol-luted atmospheres ,the reaction between CH3C(O)O2radical and NO2forms the well-known PAN(peroxy-acetyl nitrate , CH3C(O)OONO2) ,an i mportant or-ganic contributor to photochemical smog.Inless pol-luted atmospheres ,the reactions between CH3C(O)O2and HO2radicals become critical as NOxlevels maybe low[1 ,2]. Niki et al . were the first to examine thereactions of CH3C(O)O2with HO2radic…     

氢键系统中质子传递的孤子特性

用庞小峰先生提出的氢键系统的非线性激发与质子传递的新理论并采用四阶Runge-Kutta数值分析方法,通过计算机模拟,研究了冰晶体中质子传递孤子的动力学特征.研究表明,该孤子在传递过程中状态一直保持稳定,能够较好的实验结果符合.从而自数值模拟角度证明了新理论的可利用性.     

Water as dual functional cocatalyst: A theoretical study on the mechanism of direct aldol reaction on water catalyzed by a leucine derivative

The role of water and stereoselectivity in the direct syn-aldol reaction involving 3-pentanone and 4-nitrobenzaldehyde catalyzed by amino acid derivatives on water has been investigated by density functional theory. Calculations indicate that the formation of intermediate enamine is the rate determining step via a three-step process with activation enthalpies of 50 kcal/mol in the gas phase and 21 kcal/mol in the presence of water. The subsequent nucleophilic addition of enamine to aldehyde is relatively easier with activation enthalpies below 10 kcal/mol both in the gas phase and in the presence of water. The diastereoselective formation of syn- and anti-aldol products results from the preferential formation of Z-enamine to E-enamine, kinetically and thermodynamically. The enantioselectivity of both syn- and anti-products is controlled by the steric repulsive interactions between the amino alcohol moiety of catalyst and the phenyl ring of aldehyde. Calculations show that water molecule can act as a proton shuttle in the proton-transport catalytic processes. The water-assisted proton-transfer is very efficient to reduce the activation barriers via protonation and deprotonation in the formation of C–N and C–C bonds, dehydration, and β-elimination processes by inhibiting the generation of zwitterionic transition states. The theoretical discoveries indicate that in the present proton-transport assistance, the amino alcohol moiety of the catalyst plays a critical role as hydrogen bond donor to anchor substrates with carbonyl group close to the amine or enamine moiety so that the water molecule can bridge the NH of amine and the oxygen of carbonyl by hydrogen bonding interaction around the reactive site to activate the reactants and promote the reaction effectively.     

2-硝基丙烯热解反应机理和电子密度拓扑研究

采用密度泛函DFT（B3LYP）方法,在6311G＊＊,6—311＋＋G＊＊以及cc-pvtz基组水平上,计算了2-硝基丙烯在热解反应过程中反应物、过渡态和中间体的几何结构,研究了各反应沿极小能量途径反应分子几何构型的变化,并通过电子密度拓扑分析,讨论了反应过程中化学键断裂、生成的变化规律．结果表明,2-硝基丙烯的热解反应存在2种反应机理,一是甲基上的H原子进攻硝基上的O原子直接生成CH2CCH2和HNO2,反应位垒为199．6kJ/mol;二是O原子进攻亚甲基C原子首先生成四元环状中间体,住垒为200．3kJ／mol,环状中间体进一步发生C—C键和N-0断裂生成CH2CNO和CH2O,此反应是一个一步反应,位垒为144．7M／mol,所得环状中间体的分解反应机理与现有的AM1的研究结果不同．