含氮不饱和大环铈配合物催化磷酸二酯降解的研究

本文利用含氮不饱和大环铈配合物催化BNPP水解。通过改变温度、pH等方法测定含氮大环铈配合物催化对硝基苯酚磷酸二酯的反应速率。整个实验过程保持含氮大环铈配合物浓度高于底物浓度10倍以上,以使反应为一级反应。结果表明:其水解反应的最佳温度在45℃左右,最佳pH在8.0左右。     

一种新型水解明胶铈配合物的抑菌活性研究

报道了用水相法合成水解明胶铈配合物,采用红外光谱证明了水解明胶与铈的配合反应.用厚平板洞穴法对真菌为芽孢菌、金黄色葡萄球菌和大肠杆菌的抑菌活性进行了测定,结果表明,配合物对芽孢菌、金黄色葡萄球菌和大肠杆菌的抑制能力较同浓度铈增强,且随着铈浓度的增加,抑菌活性增强.     

带有苯酚侧臂的四氮大环Zn（Ⅱ）配合物催化羟酸酯水解研究

合成并表征了在大环侧臂引入取代苯酚作为功能基团的新型四氮大环配体（Ｌ１，Ｌ２和Ｌ３）对配体Ｌ３的质子化过程及其与Ｚｎ（Ⅱ）的配位过程的研究表明，配体中的酚羟基与四氮大环环中的质子之间存在较强的氢键，测得配体及配合物中配合羟基的ＰＫdisplay status     

双环八氮杂大环双核铜配合物催化羧酸酯水解研究

合成了一类新的双环二氧大环四胺双核铜配合物，其组成经元素分析、热重/差热分析、摩尔比法及等物质的量连续变化法所确证。在水溶液中，详细研究了其催化2-吡啶甲酸对硝基苯酚酯(PNPP)水解的动力学和机理，并与相应的单核铜配合物进行了对比。结果表明，此双核铜配合物能有效地催化PNPP的水解；两个金属中心之间具有明显的协同作用，较好的模拟了某些天然水解金属酶的“双功能催化机理”。     

铈(Ⅲ)-巴比妥钠配合物催化双(对硝基苯基)磷酸酯水解性能

研究了Ce(Ⅲ)离子与巴比妥钠形成的配合物对双(对硝基苯基)磷酸酯(BNPP)的催化水解作用。 结果表明, Ce(Ⅲ)与巴比妥钠形成的配合物对BNPP的水解具有很高的催化活性,可使BNPP水解速率提高至自发水解时的1.52×10⁸倍。 体系的pH值和温度对催化水解反应的影响,发现在温度为25 ℃和pH值为8.50的条件下,催化效果最佳。     

La(Ⅲ)配合物催化磷酸酯水解动力学研究

实验合成了单核镧和异双核的铜镧配合物,并研究了35℃时在50%二甲亚砜水溶液中催化磷酸二酯（bis(p-nitropheny1 phosphate)(BNPP))水解的动力学。结果表明,这两种配合物均能有效地催化BNPP的水解,得到的pH~速率曲线图呈钟形;但不同的配合物表现出不同的催化活性,单核的La(Ⅲ)配合物比异双核的Cu(Ⅱ)La(Ⅱ)配合物能更有效地催化BNPP的水解,这很可能是由于底物对催化剂的空间需要不同造成的。本文运用相应的动力学模型处理得到了相关的动力学和热学参数。     

多功能臂大环多胺La(Ⅲ)配合物的合成及其对PNPP催化水解研究

本文合成了一个多功能臂大环多胺La(Ⅲ)配合物,通过光谱法研究了pH值、温度以及表面活性剂对α-吡啶甲酸对硝基苯酚酯(PNPP)催化水解反应的影响。结果表明非离子表面活性剂Brij35胶束体系的催化活性比阳离子表面活性剂CTAB胶束体系高。前者加速催化,后者则禁阻催化。     

环四烯四胺-Ce（Ⅲ）金属配合物催化水解双（对硝基苯酚）磷酸酯

研究金属离子在金属酶中的作用机理以及用双核金属配合物模拟酶的催化中心和协同作用的研究倍受关注。镧系金属离子由于其特殊的化学结构对磷酸酯的水解有促进作用，本文研究发现环四烯四胺-Ce(Ⅲ)金属配合物对BNPP有显著的催化水解作用。     

互为立体异构的大环多胺铜(Ⅱ)配合物催化羧酸酯水解的比较研究

合成并表征了互为立体异构的四氮杂大环多胺配体及其铜(Ⅱ)配合物。在B rij35胶束溶液中,比较研究了配合物催化羧酸酯(2-吡啶甲酸对硝基苯酚酯PNPP)水解的动力学,探讨了导致其催化活性差异的可能原因,提出了可能的催化反应的机理。     

环四烯四胺-Ce(Ⅲ)金属配合物催化水解双(对硝基苯酚)磷酸酯研究

研究金属离子在金属酶中的作用机理以及用双核金属配合物模拟酶的催化中心和协同作用的研究倍受关注[1].     

Effective Homogeneous Hydrolysis of Phosphodiester and DNA Cleavage by Chitosan‐copper Complex

We aimed to explore the role of chitosan‐based metal complexes in catalyzing the hydrolysis of phosphodiesters. To this end, we performed detailed studies on the kinetics of the chitosan copper complex (CSCu)‐catalyzed hydrolysis of bis(4‐nitrophenol) phosphate (BNPP) in Tris‐H⁺ buffer and in an organic solvent. A significant enhancement in the rate of reaction (up to 3×10⁵‐fold acceleration) was observed at pH 8.0 (25°C). The pH dependence of BNPP hydrolysis at pH 5.5–9.5 and the UV spectra revealed that the copper‐bounded water molecules underwent deprotonation to form the active catalytic species CSCu‐OH. The kinetic behavior of BNPP catalytic hydrolysis in the Tris‐H⁺ buffer was consistent with that predicted by the Michaelis‐Menten kinetics model. An intramolecular nucleophilic attack by the copper‐bonded hydroxide group on the same activated phosphodiester substrate was proposed as the catalytic mechanism for CSCu‐catalyzed reaction system. The results of DNA binding and cleavage experiments indicated electrostatic binding mode of CSCu to DNA as well as the strong capability of CSCu to disturb the supercoiled strand of DNA and cleave it to nicked circular form.     

Kinetic Study of the Hydrolysis of BNPP by the Cerium(III) Complex

5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane (L) was synthesized and characterized. The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the catalytic system containing macrocyclic ligand and cerium(III) was investigated. This catalytic system show high catalytic activity and better reproducibility and stability than other similar systems in the range of pH of around 5.6–7.2. The stoichiometry and spectral analysis showed that the real active species is the macrocyclic complex of cerium(III). Based on the analytical results of the specific absorption spectra, an intramolecular nucleophilic substitution mechanism for the catalytic hydrolysis of BNPP is proposed, a correlative kinetic mathematical model is established, and the corresponding thermodynamic and kinetic constants are calculated.     

Alkene Isomerisation Catalysed by a Ruthenium PNN Pincer Complex

The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2‐di‐tert‐butylphosphinomethyl‐6‐diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable‐temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side‐arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal–hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru⁰ coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined.     

Mechanistic Investigation of the Reaction of Epoxides with Heterocumulenes Catalysed by a Bimetallic Aluminium Salen Complex

The bimetallic aluminium(salen) complex [(Al(salen))₂O] is known to catalyse the reaction between epoxides and heterocumulenes (carbon dioxide, carbon disulfide and isocyanates) leading to five‐membered ring heterocycles. Despite their apparent similarities, these three reactions have very different mechanistic features, and a kinetic study of oxazolidinone synthesis combined with previous kinetic work on cyclic carbonate and cyclic dithiocarbonate synthesis showed that all three reactions follow different rate equations. An NMR study of [Al(salen)]₂O and phenylisocyanate provided evidence for an interaction between them, consistent with the rate equation data. A variable‐temperature kinetics study on all three reactions showed that cyclic carbonate synthesis had a lower enthalpy of activation and a more negative entropy of activation than the other two heterocycle syntheses. The kinetic study was extended to oxazolidinone synthesis catalysed by the monometallic complex Al(salen)Cl, and this reaction was found to have a much less negative entropy of activation than any reaction catalysed by [Al(salen)]₂O, a result that can be explained by the partial dissociation of an oligomeric Al(salen)Cl complex. A mechanistic rationale for all of the results is presented in terms of [Al(salen)]₂O being able to function as a Lewis acid and/or a Lewis base, depending upon the susceptibility of the heterocumulene to reaction with nucleophiles.     

The Metallomicelle of Lanthanide Metal (Ce,La) Aza-Macrocyclic Complexes with a Carboxyl Branch: The Catalytic Activity and Mechanism in the Hydrolysis of a Phosphate Diester

Journal of Solution Chemistry - An aza-macrocyclic ligand, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-N/- acetic acid (L), was synthesized and characterized. The chemical...     

Hydrolysis of Hydrophobic Esters in a Bicontinuous Microemulsion Catalysed by Lipase B from Candida antarctica

Selective enzyme‐catalysed biotransformations offer great potential in organic chemistry. However, special requirements are needed to achieve optimum enzyme activity and stability. A bicontinuous microemulsion is proposed as reaction medium because of its large connected interface between oil and water domains at which a lipase can adsorb and convert substrates in the oil phase of the microemulsion. Herein, a microemulsion consisting of buffer–n‐octane–nonionic surfactant C_iE_j was used to investigate the key factors that determine hydrolyses of p‐nitrophenyl esters catalysed by the lipase B from Candida antarctica (CalB). The highest CalB activity was found around 44 °C in the absence of NaCl and substrates with larger alkyl chains were better hydrolysed than their short‐chained homologues. The CalB activity was determined using two different co‐surfactants, namely the phospholipid 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) and the sugar surfactant decyl β‐D ‐glucopyranoside (β‐C₁₀G₁). The results show the CalB activity as linear function of both enzyme and substrate concentration with an enhanced activity when the sugar surfactant is used as co‐surfactant.     

Benzonitrile Hydrolysis Catalyzed by a Ruthenium(II) Complex

The rate constant for the basic hydrolysis of benzonitrile (PhCN) to benzamide (PhCONH₂) in the [Ru^II(tpy)(bpy)] moiety (tpy = 2,2' : 6',2"-terpyridine, bpy = 2,2'-bipyridine) (k_OH = 3.7 2 10^-2 M^-1s^-1) is 5 2 10³ times higher than that of the free ligand and two times higher than that corresponding to the analogous acetonitrile complex. This effect is unusual for a transition metal in the (II) oxidation state, and can be attributed to the π-electron acceptor properties of both the polypyridyl ligands and the phenyl group. Since amides, being poor π-acceptor ligands, are rapidly released from the coordination sphere of ruthenium(II), the final product of this process is the [Ru(tpy)(bpy)(OH)]⁺ complex. The activation parameters for this nitrile hydrolysis have been determined and compare reasonably well with other values for similar reactions.     

Synthesis and Crystal Structure of a Tetravalent Cerium Complex with a Bridging Triphenolate Ligand

Reaction of(NH4)2 Ce(NO3)6 first with NaOtBu in a 1:6 molar ratio in THF, then with an equivalent of 2-bis(salicylidieneamino)methylphenol(H3 salmp) affords the(salmp)2 Ce2-(O)Na4(OtBu)4(THF)4 ·2C6 H6 complex. It crystallizes in monoclinic, space group C2/c with a = 16.5218(14), b = 23.992(2), c = 21.9454(18), β = 97.470(1)°, V = 8625.1(12)3, Z = 4, Mr = 1811.96, Dc = 1.395 g/cm3, μ = 1.126 mm-1, F(000) = 3736, S = 1.061, R = 0.0405 and wR = 0.0932(I 2σ(I)).     

Hydroboration of Alkenes Catalysed by a Nickel N-Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects

The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η⁵-C₅Me₅)Cl(IMes)] (IMes=1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in the presence of a catalytic amount of potassium tert-butoxide, and joins the very exclusive club of nickel catalysts for this important transformation. Interestingly, the regioselectivity can be reversed in some cases by using pinacolborane instead of catecholborane. Mechanistic investigations involving control experiments, ¹H and ¹¹B NMR spectroscopy, cyclic voltammetry, piezometric measurements and DFT calculations suggest an initial reduction of the Ni^II precursor to a Ni^I active species with the concomitant release of H₂. The crucial role of the alkoxo-catecholato-borohydride species resulting from the reaction of potassium tert-butoxide with catecholborane in the formation of an intermediate nickel-hydride species that would then be reduced to the Ni^I active species, is highlighted.