杯[4]吡咯在不同溶液中的分子动力学模拟研究

运用分子动力学(MD)模拟方法对杯[4]吡咯与不同溶剂之间的相互作用能、杯[4]吡咯在不同溶液中的构象变化以及杯[4]吡咯与溶剂分子之间的氢键相互作用进行了计算研究.模拟发现,杯[4]吡咯与不同溶剂间的相互作用能受溶剂分子偶极矩和杯[4]吡咯-溶剂分子间氢键相互作用影响.杯[4]吡咯在不同溶液中的构象发生翻转的主导因素是杯[4]吡咯与溶剂分子间形成氢键相互作用,溶剂分子的偶极矩不是杯[4]吡咯发生构象转化的主要因素.     

3,4,5-三羟基苯甲酸二聚体氢键结构性质

分子间相互作用在生物和材料等科学中发挥着关键作用,研究分子间相互作用的本质意义重大。氢键是分子间相互作用的一种主要形式,在确定分子构象和晶体结构以及生物分子尤其是核酸和蛋白质的结构功能中起着重要作用[1-3]。苯甲酸衍生物广泛存在于生物大分子内,与生物活性离子通过氢键作用等改变生物活性分子的活性功能,研究苯甲酸衍生物分子间氢键相互作用对于了解生物体内的化学现象具有重要意义。研究表明菱角的抗肿瘤作用明显,实验上已经从菱角中成功提取了活性单体化合物:3,4,5-三羟基苯甲酸二聚体[4],理论研究标题化合物的氢键结构与氢…     

表面等离子体子共振技术实时研究蛋白质在修饰表面的静电吸附行为

研究蛋白质在固相表面的静电吸附特性,进而控制蛋白质在修饰表面的静电吸附尤为重要,表面等离子体子共振可以检测金属表面吸附物质厚度和折射率的变化^[1]。这种技术已在研究生物分子相互作用^[2]和考察自组装单层的形成^[3]及蛋白质在固体表面吸附行为^[9-11]等方面得到广泛的应用。对蛋白质在固体表面吸附行为的研究多为考察不同的蛋白质在不同的修饰表面的吸附行为。然而,对蛋白质在修饰表面静电吸附的本质影响因素的研究却少有报道^[4]。本文使用表面等离子体子共振技术实时研究了蛋白质在甲羧基化葡聚糖修饰表面的静电吸附与溶液pH值及离子强度的依赖关系。     

水介质钯卟啉室温磷光探针与小牛胸腺DNA作用的光谱特性

研究水溶性卟啉及其金属配合物与生物大分子 ,特别是核酸的相互作用方式对获得 DNA的碱基序列和识别 DNA的结构进而设计新型药物尤其是抗癌药物具有重要意义 [1] .近年来 ,采用电子吸收光谱、荧光光谱法和电化学技术研究卟啉与 DNA的相互作用多有报道 [2～ 4 ] ,磷光探针 [5]已成为探索有机介质中微环境性质或生物大分子如核酸和蛋白质的构型变化以及它们与药物作用机理的有力工具 .由于磷光具有更高的选择性 ,且与体系氧浓度密切相关 ,而生物分子在接近红外的长波长区几乎没有室温磷光发射 ,因此 ,寻找或合成一种在这一波段具有室温磷…     

邻香兰素氨基酸Schiff碱化合物的合成及构象研究

Schiff碱是指含有亚甲氨基－PC＝N－的化合物,这类化合物因Schiff于1864年首先发现而得名。一些Schiff碱及其过渡金属配合物对肿瘤和病菌有一定的抑制作用^[1-3]。1970年,Hodnett^[4,5]制得几种Schiff碱,实验发现它们对老鼠肌肉内的Walker206瘤有抑制生长的作用,它们和某些金属形成的螯合物效果更好。Schiff碱配体可以作为螯合剂、生物活性剂、分析试剂和催化剂等,在科学研究和化工生产中有着广泛应用^[6,7]。本文报道一类新型的Schiff碱－邻香兰素氨基酸化合物的合成和构象研究,采用分子动力学模拟退火搜索方法对4人邻香兰素Schiff碱化合物的不同构型分子进行了构象研究,在搜索出的系列低能构象中分别找出全局最低能量构象,以此为初始构象进行了PM3量子化学计算。4个化合物的分子骨架结构如图1所示。     

表面活性剂中DNA构象变化的研究

以荧光探针法研究了表面活性剂与小牛胸腺DNA的相互作用，结果表明：阳离子表面活性剂主要通过静电引力和疏水方式与DNA作用；阴离子表面活性剂与DNA之间存在静电排斥力，两者之间的相互作用不太明显；而非离子表面活性剂与DNA的相互作用类似于有机溶剂对DNA的影响，即通过溶液的极性、粘度和介电常数来影响DNA的构象，表面活性剂使得DNA构象发生较大的变化，预示了它可能使DNA的生物功能发生较大的变化。     

识别手性六螺烯分子的计算机模拟

手性拆分分子与手性分子间的短程相互作用会形成非对映异构体的接触对,从而导致的立体选择作用很难传统实验方法进行研究^[1]。蛋白质－核酸识别机理和研究表明,计算机模拟可以很好地研究这个问题^[2]。用高分子分离性分子的计算机模拟尚未见报道。     

2－（1，11－十一亚甲基）－5－取代亚胺基－△^3-1,3,4-噻二唑啉的构象

用NMR分子力学计算和单晶X射线衍射的方法对2-(1，11-十一亚甲基)-5-取代 亚胺基-△^3-1，3，4-噻二唑啉（1）的构象进行了分析，结果表明，标题化合物 1的十二员环采取D4对称的[3333]构象，噻二唑啉环与十二员环近似平面几乎垂直 构成螺环，位于[3333]构象的一个角碳，亚胺基上的取代基对母体十二员环内架的 构象及^13C NMR化学位移影响极小。     

杯[4]吡咯-阴离子体系相互作用的理论研究——杯[4]吡咯-卤素阴离子体系的密度泛函研究

用密度泛函B3LYP/LANL2DZ方法对自由杯[4]吡咯的最低能量构象和卤素阴离子-杯[4]吡咯复合物进行了计算研究.结果表明,杯[4]吡咯与卤素离子能通过彼此间的相互作用形成复合物,并且这种相互作用在本质上应为分子间的氢键相互作用;杯[4]吡咯与卤素阴离子形成的复合物在构型变化、电荷转移、前线轨道及其作用方式、成键布居以及能量和热力学参数等方面均按元素周期律有规律地变化,杯[4]吡咯与卤素阴离子间的相互作用沿元素周期依次减少.     

Complexes of cadmium ion with guanine bases detected by electrospray ionization mass spectrometry

The complexations of cadmium ion with guanine bases were detected by electrospray ionization mass spectrometry (ESI-MS). In order to explore the toxicity of cadmium, such as oxidative stress to DNA and carcinogenesis, it is very important to determine the interactions between the cadmium ion and nucleotide. The analysis of mixed cadmium ion-guanosine aqueous solution (molar ratio 1 : 9) using ESI-MS (cone voltage 20 V) showed the presence of various cadmium complex ions, such as [n (guanosine) + Cd](2+) (n = 3-8), [2guanine + Cd](2+), [guanosine + guanine + Cd](2+) and [guanosine + 2guanine + Cd](2+). The observed [2guanine + Cd](2+), [guanosine + guanine + Cd](2+) and [guanosine + guanine + Cd](2+) ions are formed through the dissociation of the N-glycoside bond at the interface of ESI-MS. For deoxyguanosine and ethylguanine, similar cadmium complexes were observed. However, the complexes between the cadmium ion and 8-hydroxydeoxyguanosine were not detected. Furthermore, when a higher molar ratio (Cd : guanosine) or cone voltage were used, more of the monovalent ion peaks, such as [Cd(guanine - H)(2) + H](+) and [Cd(guanosine - H)(2) + H](+), were observed and a decrease in the abundance of the divalent ions, such as [n(guanosine)+Cd](2+), occurred.     

In situ evaluation of heavy metal-DNA interactions using an electrochemical DNA biosensor

Heavy metal ions, lead, cadmium and nickel, are well known carcinogens with natural different origins and their direct mode of action is still not fully understood. A dsDNA-electrochemical biosensor, employing differential pulse voltammetry, was used for the in situ evaluation of Pb2+, Cd2+ and Ni2+ interaction with dsDNA. The results confirm that Pb2+, Cd2+ and Ni2+ bind to dsDNA, and that this interaction leads to different modifications in the dsDNA structure. These modifications were electrochemically recognized as changes in the oxidation peaks of guanosine and adenosine bases. Using homopolynucleotides of guanine and adenine it has been proved that the interaction between Pb2+ and DNA causes oxidative damage and preferentially takes place at adenine-containing segments, with the formation of 2,8-dihydroxyadenine, the oxidation product of adenine residues and a biomarker of DNA oxidative damage. The Pb2+ bound to dsDNA can still undergo oxidation. The interaction of Cd2+ and Ni2+ causes conformational changes, destabilizing the double helix, which can enable the action of other oxidative agents on DNA.     

Cd2+和Ni2+在粉煤灰上的吸附特性

考察了粉煤灰对Cd2+和Ni2+的单组分吸附和双组分吸附性能。结果表明,粉煤灰可有效吸附水溶液中的Cd2+和Ni2+,去除率随pH升高而增加。吸附约60min后趋于平衡。粉煤灰对Ni2+的吸附容量高于Cd2+。单组分吸附平衡符合Freundlich模型和Redlich Peterson (R P)模型。双组分吸附时,Ni2+和Cd2+之间存在明显的竞争吸附效应;随干扰离子浓度升高,竞争吸附效应增强。不同模型拟合结果表明,双组分吸附平衡符合Freundlich竞争吸附模型。脱附实验表明,Cd2+比Ni2+易于脱附;0.1mol/L HCl、0.1mol/L HNO3 和0.05mol/L H2SO4的脱附效果接近,对Cd2+脱附率>60%,对Ni2+脱附率>35%。     

工程化蛋白质纳米孔实时监测镉离子与谷胱甘肽的单分子反应

本研究利用合成的全-6-季铵基-β-环糊精(Per-6-quaternary ammonium-β-cyclodextrin,p-QABCD)装备基因工程化的α-溶血素(α-Hemolysin,αHL)蛋白质纳米孔(M113R)7,构建全新的单分子纳米孔反应器,在单分子水平实现对谷胱甘肽(GSH)和镉离子(Cd2+)的络合反应的实时原位监测,并辨认络合反应的不同路径、反应中间产物和最终产物.结果表明,溶液的pH值显著影响GSH与Cd2+络合产物的络合比例.pH=7.4时,GSH与Cd2+络合反应的最终产物为Cd(GSH)2;pH=9.0时,最终产物为Cd(GSH)2和Cd2(GSH)2.其中,Cd2(GSH)2的形成遵循两种路径:(1)一个Cd2+首先结合两个GSH分子的巯基形成Cd(GSH)2,然后,第二个Cd2+结合去质子化的氨基形成Cd2(GSH)2;(2)两个Cd2+分别结合同一个GSH分子的巯基和去质子化的氨基形成Cd2(GSH)1,然后,第二个GSH分子的巯基和去质子化的氨基结合Cd2(GSH)1的Cd2+形成Cd2(GSH)2.本研究实现了在单分子水平无标记和无化学修饰研究金属离子和生物小分子的反应,对理解细胞内重金属的解毒机理和拓展纳米孔单分子技术的研究领域具有重要意义.     

Roles of anionic and cationic template components in biomineralization of CdS nanorods using self-assembled DNA-membrane complexes

Complexes of anionic DNA and cationic liposomes self-assemble into a multilamellar structure where two-dimensional lipid sheets confine a periodic one-dimensional lattice of parallel DNA chains, between which Cd(2+) ions can condense, and be subsequently reacted with H(2)S to form CdS nanorods. In this work, we identify the synergistic roles of the anionic and cationic components within the DNA-membrane template; DNA is highly anionic and condenses the Cd(2+) ions, while the cationic membrane modulates the concentration of condensed Cd(2+) ions to control the final CdS nanorod dimensions. Due to the strong electrostatic interactions between the DNA sugar-phosphate backbone and the Cd(2+) ions, crystallographic control of CdS nanostructures is possible using these simple DNA-membrane templates, which we demonstrate using nanobeam electron diffraction experiments on individual templated CdS nanorods.     

THE THEORETICAL STUDY OF ADSORPTION OF METAL IONS ON CHITOSAN

The interactions between metal ions such as Zn2+, Pb2+, Mn2+, Hg2+, Cd2+, Ni2+ and chitosan have been investigated using the model cluster model method and density functional method. Full optimization and frequency analysis of all cluster models have been performed employing B3LYP hybrid method at 3-21G basis set level except metal ions which were invoked to use effective core potential (ECP) method. The energy changes, and the main structural parameters have been obtained during the theoretical study of the adsorption of metal ions on the chitosan. The calculations showed that the coordination modes of metal ions with chitosan models were different, the geometries of Mn2+, Zn2+, Cd2+, Hg2+, Pb2+ ions coordinated with two nitrogen atoms and two oxygen atoms were distorted tetrahedral, while the square planar structure of Ni2+ coordinated two nitrogen atoms and two oxygen atoms was observed. The heat of reaction between six metal ions and chitosan models showed the order: Mn2+ ＞Ni2+ ＞Zn2+ ＞Pb2+ ＞Hg2+ ＞Cd2+, this suggested that the coordination strength of Mn2+ ＞Ni2+ ＞Zn2+ ＞Pb2+ ＞Hg2+ ＞Cd2+.     

Ni2+和Cd2+跨人红细胞膜的比较研究

以往对金属离子跨红细胞膜转运多集中在体内的宏量金属离子, 如Na+, K+, Ca2+, Mg2+及某些必需的重金属元素Fe2+, Cu2+, Zn2+等[1～3], 对其它重金属离子的跨膜转运研究较少. 我们曾研究了具有不同电荷的Co(Ⅲ)配合物的红细胞摄入动力学及机理[4]. 在此基础上进一步选择离子电荷数相同, 但电子组态不同的两个金属离子Ni2+和Cd2+为研究对象. Ni2+为d8组态, 动力学上是惰性的, 为体内必需的微量元素; 而Cd2+为d10组态, 动力学上是活性的, 却为有毒重金属, 本研究比较了它们跨人红细胞膜传递的动力学以及其与人红细胞作用的差异性.     

Effect of operating conditions on the removal of Pb2+ by microporous titanosilicate ETS-10 in a fixed-bed column

The breakthrough behavior of Pb2+ in an ETS-10 fixed bed was experimentally examined at various operating conditions. Results showed that the adsorption amount of Pb2+ ions per unit mass of ETS-10 particles in a column is about 1.68 mmol/g under the experimental conditions. This amount was not markedly affected by the operating conditions because of the rapid adsorption rate of Pb2+ ions on ETS-10. In the presence of competitive metal ions, the amount of Pb2+ adsorbed on ETS-10 was slightly reduced. An overshoot of the effluent concentrations of competitive metal ions Cu2+ and Cd2+ was observed in the adsorption systems of binary and ternary solutions. This is ascribed to the replacement of pre-adsorbed Cu2+ and Cd2+ ions by Pb2+ ions. The ETS-10 column broken up by Pb2+ ions can be regenerated by using an EDTA-Na2 solution and the regenerated column can be reused.     

Determination of cadmium in river water samples by flame AAS after on-line preconcentration in mini-column packed with 2-aminothiazole-modified silica gel.

A rapid and sensitive method was developed to determine trace levels of Cd2+ ions in an aqueous medium by flame atomic absorption spectrometry, using on-line preconcentration in a mini-column packed with 100 mg of 2-aminothiazol modified silica gel (SiAT). The Cd2+ ions were sorbed at pH 5.0. The preconcentrated Cd2+ ions were directly eluted from the column to the spectrometer's nebulizer-burner system using 100 microL of 2 mol L(-1) hydrochloric acid. A retention efficiency of over 95% was achieved. The enrichment factor (calculated as the ratio of slopes of the calibration graphs) obtained with preconcentrations in a mini-column packed with SiAT (A = -1.3 x 10(-3) + 1.8 x 10(-3)[Cd2+]) and without preconcentrations (A = 4 x 10(-5) + 3.5 x 10(-5)[Cd2+]), was 51 and the detection limit calculated was 0.38 microg L(-1). The preconcentration procedure was applied to determine trace levels of Cd in river water samples. The optimum preconcentration conditions are discussed herein.     

Crystal structures of the NO and N2O4 sorption complexes of fully dehydrated fully Cd2+-exchanged zeolite X (FAU): coordination of neutral NO and N2O4 to Cd2+

The structures of the nitric oxide and dinitrogen tetroxide sorption complexes of dehydrated fully Cd2+-exchanged zeolite X (FAU) have been determined using single-crystal X-ray diffraction in the cubic space group Fdm at 21(1) degrees C. Ion exchange was accomplished by allowing an aqueous stream 0.05 M in Cd2+ to flow past each crystal for 5 days. Each crystal was then dehydrated at 500 degrees C and 2 x 10(-6) Torr for 2 days, followed by exposure to 100 Torr of zeolitically dry NO or NO2/N2O4 gas. The structures were determined in these atmospheres. The unit cell constants at 21(1) degrees C are 24.877(2) A for the dark-yellow NO complex, |Cd46(NO)16|[Si100Al92O384]-FAU, and 24.735(2) A for the black N2O4 complex, |Cd46(N2O4)25.5|[Si100Al92O384]-FAU. The structure of the NO complex was refined to R1 = 0.072 and wR2 = 0.134. In this structure, Cd2+ ions occupy four crystallographic sites. Fifteen Cd2+ ions occupy site I (at the centers of the double 6-rings (D6Rs)), and one occupies site I' (in the sodalite cavity opposite a D6R). The remaining 30 Cd2+ ions occupy two different sites II (near 6-rings in the supercages): 16 coordinate to nitric oxide molecules and 14 do not. Sixteen NO molecules lie in the supercage where each interacts weakly with a Cd2+ ion: Cd-N = 2.57(22) A. The observed N-O bond distance is 1.28(25) A and Cd-N-O is 118(10) degrees. The structure of the N2O4 complex was refined to R1 = 0.084 and wR2 = 0.216. In this structure, Cd2+ ions occupy only three crystallographic sites. The 16 D6Rs per unit cell are filled with 11.5 Cd2+ ions at site I and 9 Cd2+ ions at site I': 11.5 + 9/2 = 16. The remaining 25.5 Cd2+ ions occupy site II where each coordinates at 2.43(8) A to a nitrogen atom of a N2O4 molecule. At the coordinating nitrogen atom, O-N-O is 147(10) degrees and the N-O bond lengths are 1.07(9) and 1.23(10) A. At the second nitrogen atom, O-N-O is 140(10) degrees, and the N-O bond lengths are 1.03(13) and 1.42(12) A. The imprecisely determined N-N bond length, 2.74(17) A, appears to be very much lengthened by coordination to Cd2+. The Cd-N-N angle is 144(10) degrees. This appears to be the first crystallographic report of the coordination of N2O4 to a cation.