大分子拥挤条件下光诱导辣根过氧化物酶还原的光谱研究

稀溶液中光诱导辣根过氧化物酶(Horseradish Peroxidase, HRP)能够发生还原反应,但这一研究忽略了生物体细胞内因存在各种分子而高度拥挤的真实环境。本文采用紫外可见、荧光、同步荧光及圆二色光谱法,研究了大分子拥挤环境中光诱导HRP的还原过程及外界环境对其光还原的影响。UV-Vis光谱和同步荧光光谱结果表明,采用403 nm单色光照射时,HRP在拥挤试剂葡聚糖70(Dextran70)中还原程度较好,而HRP在聚蔗糖70(Ficoll70)拥挤环境下不发生光还原反应;采用280 nm单色光照射时,在拥挤试剂Dextran70和Ficoll70中HRP光还原反应程度增加,且HRP的光还原程度在Ficoll70溶液中远高于在Dextran70溶液中;光诱导HRP还原的最适温度在Dextran70和Ficoll70环境中分别为4 ℃和24 ℃;HRP在Dextran70溶液中的最佳光还原浓度是100 g/L,在Ficoll70环境中HRP还原程度随着Ficoll70浓度的增加而增大;CD光谱结果表明拥挤环境中HRP被光还原后,蛋白的二级结构基本没有变化。     

游离芳香氨基酸和半胱氨酸对光诱导高铁肌红蛋白还原的影响

肌红蛋白(Myoglobin,Mb)中血红素辅基不仅具有储氧功能,也能吸收特定波长的光而影响蛋白功能表达。实验发现,部分游离的氨基酸对光诱导高铁肌红蛋白(metM b,Fe(III)-Mb)的还原过程及还原程度都有重要作用,因此,本文采用紫外-可见吸收光谱、圆二色谱、三维荧光光谱法,在光照体系中加入拥挤试剂来模拟细胞内拥挤环境,研究芳香氨基酸[色氨酸(Trp)、苯丙氨酸(Phe)、酪氨酸(Tyr)、半胱氨酸(Cys)]对metM b还原的影响。结果表明,含-OH或-SH的氨基酸(Tyr、Cys)能使metM b发生较好的光还原,无-OH或-SH基团的氨基酸(Trp、Phe)对metM b的光还原作用较弱,氨基酸促进metM b光还原的整个过程可能是分子间电子转移的过程。metM b在拥挤环境聚蔗糖70(Ficoll 70)中的光诱导还原程度比在稀溶液中高,拥挤试剂Ficoll70对蛋白的二级结构起保护作用,能够稳定血红素微环境。     

细胞色素C与NO的反应机制

细胞色素C(Cytochrome C,Cyt C)与NO(由NO供体药物proliNONOate提供)之间的反应已在电化学和医疗方面受到重视,而直接与NO气体作用尚未得到关注;且前者主要是从Q带进行分析的,Soret带未提及。本文采用紫外-可见(UV-Vis)吸收光谱、电子顺磁共振(EPR)光谱、紫外可见时间过程光谱以及同步荧光光谱等方法同时分析了其Soret带与Q带的变化,探讨了不同价态的Cyt C与NO气体结合及解离反应的过程。结果表明:Cyt C与NO相互作用时,无论是高铁细胞色素C(ferric cytochrome C,Fe(Ⅲ)-Cyt C)还是亚铁细胞色素C(ferrous cytochrome C,Fe(Ⅱ)-Cyt C),反应产物都是细胞色素C配合物(Cyt C-NO);Fe(Ⅱ)-Cyt C先被NO氧化生成Fe(Ⅲ)-Cyt C,之后再与NO结合生成Cyt C-NO,Fe(Ⅲ)-Cyt C则直接与NO结合生成Cyt C-NO。Cyt C-NO是一种不稳定的配合物,当通入少量NO时Cyt C-NO很快解离生成Fe(Ⅲ)-Cyt C,其解离速率为(0.005 07±0.001) s^-1,是与供体药物结合所形成配合物解离速率的十分之一;NO过量时,生成的Cyt C-NO不会再发生解离。对实验结果分析,得出Cyt C与NO配位反应机制为溶液中的NO进入Heme腔内,Fe-S断裂,Fe-N间形成新的配位键,NO气体可以直接与Cyt C反应,生成的配合物比供体药物稳定,同时Soret带具有明显变化。这对于利用NO来缓解细胞内的氧化压以及利用NO检测细胞内呼吸类酶的变化,进而检测细胞凋亡具有重要意义。     

酸诱导拥挤条件下肌红蛋白及突变体去折叠过程

采用紫外-可见吸收光谱、同步荧光光谱和圆二色(CD)光谱法研究拥挤试剂葡聚糖70 (Dextran70)和聚蔗糖70 (Ficoll70)存在条件下, 酸诱导野生型肌红蛋白Mb(WT)及其突变体Mb(D60K)的去折叠过程. 结果显示: 在Dextran70 和Ficoll70 两种拥挤环境下, Mb(WT)的变性中点pH值由4.25 分别降低到3.78 与3.76, 拥挤试剂加入后增强了Mb(WT)的耐酸能力; 肌红蛋白60位天冬氨酸(Asp)突变为赖氨酸(Lys)后, 变性中点pH值由4.25 降低到4.19, 耐酸性比野生型肌红蛋白有所增强, Mb(D60K)在Dextran70 和Ficoll70 两种拥挤环境下变性中点pH值由4.19 分别降至3.74 和3.12. 以上实验说明肌红蛋白表面氨基酸突变和拥挤试剂的添加起到了稳定血红素微环境、芳香族氨基酸及二级结构和保护蛋白天然状态的作用.     

表面活性剂对细胞色素C的作用及光诱导还原的影响

通过UV-Vis吸收光谱、普通荧光和同步荧光光谱、圆二色(CD)光谱等技术研究了表面活性剂(阴离子表面活性剂-琥珀酸二辛酯磺酸钠AOT、阳离子表面活性剂-十六烷基三甲基溴化铵、两性离子表面活性剂-3[(3-胆固醇氨丙基)二甲基氨基]-1-丙磺酸CHAPS)对细胞色素C(Cytochrome c,Cyt c)的相互作用及光诱导Cyt c还原的影响。结果显示:表面活性剂能够与Cyt c相互作用,进而影响Cyt c蛋白的结构及功能的表达。阴离子型表面活性剂AOT与Cyt c发生直接相互作用;阳离子型表面活性剂DTAB与Cyt c不发生作用或作用很小;两性离子型表面活性剂CHAPS是通过静电作用与Cyt c发生相互作用,作用强度很弱,远远低于AOT与Cyt c之间的相互作用。表面活性剂的加入改变Cyt c中Tyr和Trp残基微环境。AOT浓度达到1.25×10~(-3)mol·L~(-1)时Cyt c变性。并且研究结果表明,表面活性剂的存在抑制光诱导细胞色素C的还原,且抑制能力DTABCHAPSAOT。     

吸附色素蛋白与纳米银粒子间的光诱导电子传递

采用表面增强拉曼光谱研究了吸附态微过氧化物酶和细胞色素c的光诱导还原.结果表明,吸附于粗糙银电极表面的过氧化物酶和细胞色素c在413nm激光连续照射下被部分还原.光诱导还原可归因于电极表面纳米银粒子的定域表面等离子体吸收使得自由电子受激,受激电子进而转移进入吸附分子空轨道,导致吸附蛋白质的还原.     

细胞色素c在植物凝胶-离子液体复合膜修饰电极上的直接电化学

用植物凝胶（GG）和亲水性离子液体（ILs）氯化1-庚基-3-甲基咪唑（[HMIM]Cl）制得一种有效的复合膜（GG-ILs）.将细胞色素c（Cyt c）包埋在该复合膜中并修饰于玻碳电极（GCE）表面,构置了细胞色素c修饰玻碳电极（GG-Cyt c-ILs/GCE）.紫外-可见光谱表明,复合膜内的Cyt c仍保持其原始...     

纳米金三明治结构调制细胞色素c电子传递特性的分子机理研究

以细胞色素c(Cyt c)为模型蛋白,采用表面增强红外吸收光谱监测了三明治结构所吸附的纳米金对氧化还原诱导的Cyt c表面增强红外差谱的改变.研究表明,在单层Cyt c分子表面组装纳米金,使得血红素的红外差谱特征峰明显增强,这归因于纳米金和血红素之间的电子传递.纳米金与Cyt c氧化还原活性中心血红素的相互作用加速了蛋白质的电子传递.这为实现并优化表面吸附蛋白质的直接电化学提供了一种新技术.     

细胞色素c在微-液/液界面上电化学行为的研究

本文采用电化学技术,研究了细胞色素c（Cyt c）在玻璃微米管尖端处形成的微-水/1,2-二氯乙烷（W/DCE）界面上的电化学行为.选用四丁基铵四苯硼（TBAT-PB）、四丁基铵四氯代苯硼（TBATPBCl）以及四丁基铵四氟代苯硼（TBATPBF）三种不同的有机相支持电解质来研究Cyt c在W/DCE界面上的反应.在电势窗较窄的含TBATPB体系中只能够观察到吸附过程;在电势窗较宽的含TBATPBCl和TBATPBF的体系中,可以同时观察到吸附与离子转移过程.当Cyt c浓度较低时,两种过程都可以观察到;当Cyt c浓度较高时,主要是吸附.文中对这些过程的机理进行了探讨.     

电化学研究聚乙二醇单甲醚接枝壳聚糖的pH敏感性及对细胞色素c的控制释放

采用电化学沉积法在Au电极上制备了聚乙二醇单甲醚接枝壳聚糖（mPEG-g-CS）电沉积膜及其与细胞色素c（Cyt c）复合膜。 循环伏安（CV）和交流阻抗（EIS）等电化学手段研究表明,mPEG-g-CS膜具有良好的pH敏感性,通过调节溶液的pH值,可以改变电化学探针[Fe(CN)6]3-/4-在电极表面的电子转移速率;Cyt c在mPEG-g-CS膜内可以实现直接电子转移,该复合膜电极对H2O2的响应快速而灵敏,说明mPEG-g-CS能较好的保持Cyt c的生物活性。 通过控制溶液的pH值,实现了Cyt c在mPEG-g-CS膜内的可逆释放和关闭。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.