应用原子-键电负性均衡方法预测超氧化物歧化酶催化反应的活性部位

应用原子-键电负性均衡方法计算了超氧化物歧化酶的电荷分布和Fukui函数. 结果表明, 超氧化物歧化酶活性中心与超氧阴离子自由基作用时, 金属离子电荷转移在0.1 e～0.3 e之间, 而配体原子等的电荷转移却很小; 同时金属离子的Fukui函数大于配位原子的Fukui函数. 超氧化物歧化酶活性中心与抑制剂作用失活后, 金属离子的Fukui函数小于抑制剂中配位原子的Fukui函数. 电荷转移和Fukui函数表明, Mn, Fe和Cu离子分别是含锰、铁和铜锌超氧化物歧化酶的活性中心部位, 该预测不仅与量子化学理论计算一致, 而且与实验现象相吻合.     

浅析对血红素氧合过程认识的几个争议

血红蛋白是高等动物体内广泛存在的一种载氧蛋白,其活性中心是血红素,氧分子可与血红素中的铁可逆结合实现载氧。虽然人们对血红蛋白运载氧气的生物化学作用机制已有系统的认识,但由于研究方法的限制与分析数据的差异和分歧,对于血红素中心铁离子与氧分子配位的键合结构及相关性质变化仍存在诸多争议。本文就目前教学中存在的部分争议进行梳理总结,同时结合相关研究进展,对几种血红素氧合过程的结构模型进行合理性分析。     

BC 1s

单原子催化剂凭借其超高的原子利用率及在某些反应中表现出的出色催化效果,被认为是最有前途的电催化剂之一,引起了研究人员的极大热情和兴趣.制备高金属含量的单原子催化剂是基础研究和实际应用的前提和关键.然而,由于原子表面自由能随着尺寸的减小而急剧增加,在制备和催化过程中,单原子催化剂的金属原子很容易聚集成团簇甚至颗粒,因此如何制备高负载量的单原子催化剂仍然是一个不小的挑战.在众多单原子催化剂中,非贵金属中铁基单原子被认为是燃料电池中的Pt催化剂的有效替代品.在燃料电池的核心反应–电化学氧还原反应中, Fe-Nx被证明是铁单原子催化剂中的主要活性中心.因此,为了获得更好的氧还原性能,提高铁单原子催化剂中Fe-Nx的含量就显得非常关键.前期已报道了一些关于制备高Fe含量的铁单原子催化剂材料的策略,例如空间限域策略和配位合成策略.其中卟啉和葡萄糖作为配位剂,双氰胺和三聚氰胺可热解成氮掺杂碳材料以捕获金属原子,形成M-Nx.同时,具有高比表面积的富氧碳载体可以通过掺杂氮来作为固定金属原子的位点.我们开发了一种简单直接的方法,通过碳辅助金属配合物热解法制备高金属含量的Fe-N4单原子催化剂,即在最佳碳化温度800°C、三聚氰胺存在下对氮掺杂多孔碳辅助分散铁邻苯二胺配合物进行热解.在该方法中,氮掺杂多孔碳是一种具有丰富氮缺陷,高表面积(1267 m2?g–1)和良好分散性的多孔生物质碳材料.邻苯二胺作为含两个氨基的二齿配体,可以很容易地与过渡金属配位,形成稳定的平面四配位络合物.此外,由于在高温条件下过渡金属的催化作用,邻苯二胺也被用作氮掺杂碳的前体.因此,氮掺杂多孔碳和邻苯二胺是合成高金属含量铁单原子催化剂的关键前驱体.通过X射线光电子能谱,大角度环形暗场扫描透射电子显微镜和X射线吸收精细结构光谱表征,发现所制备的铁单原子催化剂中铁原子以单个原子的形式锚固在碳载体上,并与碳基质的四个掺杂氮原子配位,得到Fe-N4的构型.通过调节Fe前驱体量,铁单原子催化剂中Fe的最高负载量达到7.5 wt%,在目前已经报道的铁单原子催化剂中排第四.电化学氧还原测试表明,在0.10 MKOH溶液中,随着铁含量的增加,铁单原子催化剂的氧还原性能逐渐提高.其中250Fe-SA/NPC-800样品表现出最高起始电位0.97 V和最正的半波电位0.85 V,可与市售的40%Pt/C催化剂相媲美.和已报道的铁单原子催化剂相比,由于我们制得的催化剂的比表面积较低,只有247 m2?g–1,所以制约了催化剂的性能.在混合动力学势域中,根据Koutecky-Levich方程计算得出的电子转移数约为3.6,表明250Fe-SA/NPC-800主要催化四电子转移过程,这可以归因于以Fe-N4活性中心降低了四电子过程中关键中间体的形成能垒及过程的自由能变化.此外,250Fe-SA/NPC-800展现了较高的电化学稳定性.连续工作6 h后, 250Fe-SA/NPC-800保留了超过87%的电流密度,而Pt/C表现出明显的衰减,仅保留了49%.     

茂基铱络合物中Ir–H键解离能的理论预测及其形变-结合能分析

铱氢络合物是诸多铱催化反应中的催化剂和关键中间体,Ir–H键的断裂与生成在这些反应中往往起到至关重要的作用.本文利用密度泛函方法(DFT)对多种茂基配位的铱氢络合物的铱氢键均裂能和异裂能(负氢解离)进行了系统研究.计算发现,铱中心贫电子有利于Ir–H键的均裂,而吸电子基团以及强p电子受体有利于减弱Ir中心电子密度.刚性螯环以及大位阻取代基可以通过释放空间位阻进一步减小其键能.而如2-苯基吡啶、联吡啶配体等配位的铱氢化合物,由于Ir中心d轨道可以与这些配体的芳香体系形成大p键,因此降低了这些物种的H~-解离焓.烯烃配体有利于均裂过程,却不利于异裂的H~-解离.膦配体对均裂过程影响不大,但是可以大大减小H~-解离焓.贫电子的B原子,有利于均裂,因会形成Ir–H–B的氢桥键,不利于解离H~-.Si原子相对富电子,对这两个过程均不利.     

亚胺配体协同氮杂环卡宾钯配合物催化碳碳偶联反应的作用机制

在氮杂环卡宾-钯(NHC-Pd)配合物催化的碳-碳偶联反应中,配体结构对催化反应起到关键作用.为了实现更好的催化效果,不仅要对NHC配体进行结构优化,还需要第二配体的协同作用.然而,由于第二配体配位能力大大弱于NHC配体,其在催化反应中的协同作用往往被忽视.合成出了3种由相同结构NHC配体以及不同结构亚胺配体组成的NHC-Pd配合物来催化Suzuki-Miyaura交叉偶联反应.实验结果表明,在相同的反应条件下,3种亚胺配体协同的NHC-Pd配合物表现出了明显不同的催化效果.进一步采用理论计算来深入研究亚胺配体协同的NHC-Pd配合物在催化反应中的作用机制.通过完整催化循环过程的计算,发现虽然亚胺配体并没有参与到催化循环过程中,但亚胺配体与氯苯会形成竞争配位,它们与NHC-Pd(0)的配位能力差异直接导致实际参与催化循环的有效活性中心的浓度的差异,计算表明大位阻缺电子的亚胺配体更有利于反应的进行.通过研究,更好地阐明了亚胺配体在催化碳-碳偶联反应中的作用机制,并为NHC-Pd配合物的结构调控提供了新策略.     

[Cu(HIm)_2(PPh_3)_2](BF_4)的合成与晶体结构

铜?配合物以结构多样化、生物和医药活性和独特的光谱性能而成为活跃的研究领域,其合成、结构以及性能的研究已受到日益广泛的重视,它们与普通配体的分子设计和结构测定涉及生物无机化学,无机合成和金属基药物设计等内容犤１,２犦。咪唑衍生物是常见的生物配体,对生物功能起重要的作用,咪唑氮原子与金属离子配位成键,形成各种金属生物分子的活性中心,通过了解金属与咪唑氮原子配位的结构特点,建立生物活性结构模型配合物,可以达到研究金属酶活性中心结构与物性关系的目的犤３,４犦。生物体中大部分铜与两种以上配体形成混配配合…     

聚铝氨烷-铂合物的制备及其催化加氢和氧化性能的研究

近十几年来,已有很多关于高分子金属络合物催化剂的文献报导,但几乎全都是属于有机高分子金属络合物催化剂的研究.在这些催化剂中,配位体的配位原子如氮、硫和磷都是与碳原子直接相连接的.最近,我们研制了一种新的无机高分子催化剂,即二氧化硅为载体的聚铝氨烧-铂络合物.在这个络合物中,配位氮原子是与铝原子相键连的. 二氧化硅为载体的聚铝氨烧-铂络合物(简称为Al-N-Pt)的合成方法如下:     

烯烃聚合钯催化剂研究进展

综述了烯烃聚合钯催化剂的研究进展,烯烃聚合钯催化剂的配体类型有膦配体、氮配体、碳配体、氧配体、氮-氧配体、膦-氧配体、氮-膦配体等。与齐格勒-纳塔催化剂和茂金属催化剂相比,烯烃聚合钯催化剂具有高催化活性、单活性中心和良好的分子剪裁性等优点,可在分子层次上实现烯烃聚合的分子设计与组装;与铁、钴、镍等后过渡金属催化剂相比,烯烃聚合钯催化剂具有反应条件较温和、催化活性和立体选择性较高的优势。     

稀土烟酸与8-羟基喹啉三元配合物的合成、表征及荧光光谱

合成了 4种稀土烟酸 (HL)与 8 羟基喹啉 (Hhq)的三元固体配合物 ,对它们进行元素分析 ,确定其通式为REL2 ·hq·2H2 O (RE =La ,Eu ,Tb ,Dy) ,用摩尔电导、TG DTA分析、IR、UV和荧光光谱等研究了配合物的有关性质。结果表明 ,烟酸脱掉羧酸上的质子以酸根的形式与稀土离子呈双齿配位 ,而吡啶环上的氮原子未参加配位。hq- 的羟基氧和杂氮原子与RE3+ 离子配位。配体与稀土配位后 ,配合物中稠环数目增多 ,π键共轭程度增大。配合物中所含的水可能为配位水。荧光光谱研究发现 ,La和Dy的配合物的荧光表现为配体的荧光 ,Eu配合物中心离子的特征荧光峰表现不明显 ,而Tb配合物中配体能有效地将吸收的能量传递给Tb3+ ,敏化Tb3+ 的发光 ,发射较强荧光     

几种生物碱铂(Ⅱ)络合物的1H、13C-NMR研究

本文测定了具有抗癌活性的咖啡咽铂、茶碱铂、可可碱铂络合物的~1H和~(13)C-NMR谱,考察了络合前后生物碱配体~1H和~(13)C化学位移的变化,结合氢-铂、碳-铂偶合常数的测定,确定了各生物碱配位原子为咪唑环上双键氮,应用核磁共振技术搞清了与一般抗癌铂类络合物结构不同的咖啡咽铂等络合物的结构,并用异核选择去偶双共振技术对全部~(13)C和~1H谱线进行了归属。     

Theoretical density functional theory studies on interactions of small biologically active molecules with isolated heme group

We present ab-initio density functional theory studies on the interactions of small biologically active molecules, namely NO, CO, O(2), H(2)O, and NO(2) (-) with the full-size heme group. Our results show that the small molecule-iron bond is the strongest in carbonyl and the weakest in nitrite system. Trans influence induced by NO binding to the five-coordinate heme complex is shown. Nitric oxide in the resulting complex might be described as NO(-). The differences among the small ligands of XO type (CO, NO, O(2)), and their distant chemical behavior from H(2)O and NO(2) (-) ligands in binding to the Fe(II) ion, are shown. Moreover, the role of the heme ring as a reservoir of electrons in the studied complexes is invoked. The analysis of the parameters defining the iron-histidine bond indicates that this bond is longer and weaker in nitrosyl and carbonyl complexes than in the other systems. Our findings support the proposed mechanism of soluble guanylate cyclase (sGC) activation and suggest that the first step of sGC activation by CO may be the same as during the activation by NO. Obtained results are then compared with the data concerning smaller model of the heme, the porphyrin complexes, available in the literature.     

Alkylamine-ligated H93G myoglobin cavity mutant: a model system for endogenous lysine and terminal amine ligation in heme proteins such as nitrite reductase and cytochrome f

His93Gly sperm whale myoglobin (H93G Mb) has the proximal histidine ligand removed to create a cavity for exogenous ligand binding, providing a remarkably versatile template for the preparation of model heme complexes. The investigation of model heme adducts is an important way to probe the relationship between coordination structure and catalytic function in heme enzymes. In this study, we have successfully generated and spectroscopically characterized the H93G Mb cavity mutant ligated with less common alkylamine ligands (models for Lys or the amine group of N-terminal amino acids) in numerous heme iron states. All complexes have been characterized by electronic absorption and magnetic circular dichroism spectroscopy in comparison with data for parallel imidazole-ligated H93G heme iron moieties. This is the first systematic spectral study of models for alkylamine- or terminal amine-ligated heme centers in proteins. High-spin mono- and low-spin bis-amine-ligated ferrous and ferric H93G Mb adducts have been prepared together with mixed-ligand ferric heme complexes with alkylamine trans to nitrite or imidazole as heme coordination models for cytochrome c nitrite reductase or cytochrome f, respectively. Six-coordinate ferrous H93G Mb derivatives with CO, NO, and O(2) trans to the alkylamine have also been successfully formed, the latter for the first time. Finally, a novel high-valent ferryl species has been generated. The data in this study represent the first thorough investigation of the spectroscopic properties of alkylamine-ligated heme iron systems as models for naturally occurring heme proteins ligated by Lys or terminal amines.     

pH controls the rate and mechanism of nitrosylation of water-soluble FeIII porphyrin complexes

In-depth kinetic and mechanistic studies on the reversible binding of NO to water-soluble iron(III) porphyrins as a function of pH revealed unexpected reaction kinetics for monohydroxo-ligated (P)Fe(III)(OH) species formed by deprotonation of coordinated water in diaqua-ligated (P)Fe(III)(H(2)O)(2). The observed significant decrease in the rate of NO binding to (P)Fe(OH) as compared to that of (P)Fe(H(2)O)(2) does not conform with expectations based on previous mechanistic work on NO-heme interactions, which would point to a diffusion-limited reaction for the five-coordinate Fe(III) center in (P)Fe(OH). The decrease in rate and an associatively activated mode of NO binding observed at high pH is ascribed to an increase in the activation barrier related to spin state and structural changes accompanying NO coordination to the high-spin (P)Fe(III)(OH) complex. The existence of such a barrier has previously been observed in the reactions of five-coordinate iron(II) hemes with CO and is evidenced for the first time for the process involving coordination of NO to the iron heme complex. The observed reactivity pattern, relevant in the context of studies on NO interactions with synthetic and biologically important hemes (in particular, hemoproteins), is reported here for an example of a simple water-soluble iron(III) porphyrin [meso-tetrakis(sulfonatomesityl)porphinato]-iron(III), (TMPS)Fe(III).     

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria,ionic conductivities,and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.     

茂铁基稀土铈配合物的合成与结构

本文利用单羧基二茂铁Fc-COOH和1，1′-二羧基二茂铁HOOC-Fc-COOH作为配体分别合成了双核铈配合物Ce₂(FcCOO)₆ (1)和二维层状配位聚合物Ce₂(OOC-Fc-COO)₃(2)，测定了两种配合物的晶体结构。配合物1中的金属铈离子为九配位结构，分别与周围的羧基二茂铁上的氧原子和作为辅助配体的水分子配位，茂铁间的π-π相互作用将配合物1的二聚体单元连结在一起形成二维的网状结构。配合物2中的金属铈离子亦为九配位结构，分别与周围的羧基二茂铁上的氧原子，作为辅助配体的水分子和甲醇配位形成类似于配合物1的二聚体单元，1，1′-二羧基二茂铁HOOC-Fc-COOH作为桥基配体将二聚体单元连结在一起，形成二维网状的配位聚合物。     

4,5-二氮芴-9-酮Cu(II),Zn(II)配合物的合成、晶体结构、热分析及理论计算

合成了 4,5 二氮芴 9 酮 (dafo)的Cu(II) ,Zn(II)配合物 [Cu(dafo) 2 (H2 O) 2 ] (NO3 ) 2 和 [Zn(dafo) 2 (H2 O) 2 ] (NO3 ) 2 ,通过单晶X射线衍射法确定了它们的结构 .晶体结构分析表明 ,配合物分子中Cu(II) ,Zn(II)分别和来自两配体的四个氮原子及两个水分子中的氧原子配位 ,处于六配位的配位环境中 ,两配体基本处于同一平面 ,两水分子垂直于两配体所在平面 ,Cu(II)处于畸变八面体中心 ,Zn(II)处于正常八面体中心 ,对两种配合物进行了元素分析、红外和热分析表征 ,在实验的基础上 ,采用Gaussian 98w中的DFT B3LYP/LANL2DZ对两种配合物进行了全几何优化以及后续计算     

The H93G myoglobin cavity mutant as a versatile template for modeling heme proteins: ferrous, ferric, and ferryl mixed-ligand complexes with imidazole in the cavity

One of the difficulties in preparing accurate ambient-temperature model complexes for heme proteins, particularly in the ferric state, has been the generation of mixed-ligand adducts: complexes with different ligands on either side of the heme. The difference in the accessibility of the two sides of the heme in the H93G cavity mutant of myoglobin (Mb) provides a potential general solution to this problem. To demonstrate the versatility of H93G Mb for the preparation of heme protein models, numerous mixed-ligand adducts of ferrous, ferric, and ferryl imidazole-ligated H93G (H93G(Im) Mb) have been prepared. The complexes have been characterized by electronic absorption and magnetic circular dichroism (MCD) spectroscopy in comparison to analogous derivatives of wild type Mb. The starting ferric H93G(Im) Mb state spectroscopically resembles wild-type ferric Mb as expected for a complex containing a single imidazole in the proximal cavity and water bound on the distal side. Addition of a sixth ligand to ferric H93G(Im) Mb, whether charge neutral (imidazole) or anionic (cyanide and azide), results in formation of six-coordinate low-spin complexes with MCD characteristics similar to those of parallel derivatives of wild-type ferric Mb. Reduction of ferric H93G(Im) Mb and subsequent exposure to either CO, NO, or O2 produces ferrous complexes (deoxy, CO, NO, and O2) that consistently exhibit MCD spectra similar to the analogous ferrous species of wild-type ferrous Mb. Most interestingly, reaction of ferric H93G(Im) Mb with H2O2 results in the formation of a stable high-valent oxoferryl complex with MCD characteristics that are essentially identical to those of oxoferryl wild-type Mb. The generation of such a wide array of mixed-ligand heme complexes demonstrates the efficacy of the H93G Mb cavity mutant as a template for the preparation of heme protein model complexes.     

Density Functional Theory Study on La Complex with Schiff-base as Building Block

1 INTRODUCTION Recently, there has been a growing interest[1~5] inlanthanon complexes because of their abundant stru-ctural characters and important biologic activities.The complexes are extensively used as coordinationand stabilization agents[6, 7] for the measures of me-tallic ions, antibacterial and anticancer drugs[8], cata-lysts for vitamin B6 in amination and oxidation re-actions[9], biological models of N2, O2 carriers andaminophenol asymmertry synthesis and preparationof nonprote…     

Iron hemiporphycene as a functional prosthetic group for myoglobin

The iron complex of hemiporphycene, a molecular hybrid of porphyrin with porphycene, was incorporated into the apomyoglobin pocket to examine ligand binding ability of the iron atom in the novel porphyrinoid. Apomyoglobin was successfully coupled with a stoichiometric amount of ferric hemiporphycene to afford the reconstituted myoglobin equipped with the iron coordination structure of native protein. Cyanide, imidazole, and fluoride coordinated to the ferric protein with affinities comparable with those for native myoglobin. The ferrous myoglobin was functionally active to bind O(2) and CO reversibly at pH 7.4 and 20 degrees C. The O(2) affinity is 12-fold higher than that of native myoglobin while the CO affinity is slightly lower, suggesting decreased discrimination between O(2) and CO in the heme pocket. The functional anomaly was interpreted to reflect increased sigma-bonding character in the Fe(II)-O(2) bond. In contrast with 6-coordinate native NO protein, the NO myoglobin containing ferrous hemiporphycene is in a mixed 5- and 6-coordinate state. This observation suggests that the in-plane configuration of the iron atom in hemiporphycene is destabilized by NO. Influence of the core deformation was also detected with both the infrared absorption for the ferrous CO derivative and electron paramagnetic resonance for ferric imidazole complex. Anomalies in the ferric and ferrous derivatives were ascribed to the modified iron-N(pyrrole) interactions in the asymmetric metallo core of hemiporphycene.