Mechanism of TBD-catalyzed hydrolysis of acetonitrile

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) has recently been shown to be an effective organocatalyst for the hydrolysis reaction of acetonitrile. This reaction involves the acetamide-forming reaction of acetonitrile hydrolysis and the further hydrolysis of acetamide to form acetic acid and NH₃. Density functional theory (DFT) and Hartree–Fock (HF) methods were employed to comprehensively investigate these two hydrolysis steps to elucidate the TBD-catalyzation mechanism. Structures and energies of the reactants, intermediates, transition states and products along the reaction path were presented. Charge population and bond orders were given by natural bond orbital (NBO) analysis to clarify the computed atomic and molecular behaviors. The results showed that compared with the noncatalyzed reaction, the TBD-catalyzed process had significantly lower energy barriers in both the hydration steps and the isomerization steps. As a result, the whole reaction process could be accelerated and the TBD-catalyzation mechanism was clarified.     

Comparative studies on hydrolysis of bis(p-nitrophenyl) phosphate catalyzed by short- and long-alkyl-multiamine metallomicelles

Four short- and long-alkyl-multiamine ligands L¹–L⁴ have been synthesized and characterized. The catalytic efficiency of complex CuL¹ and functional metallomicelles CuL²–CuL⁴ were comparatively investigated for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in buffered solution at 30 °C. The ternary kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k^′_N, K_T and pK_a were obtained. The results indicated that the complexes with 1:1 ratio of ligands L²–L⁴ to copper(II) ion were the kinetic active catalysts, and the deprotonized Cu(II) complex formed by activated water molecule was the real active species for BNPP catalytic hydrolysis. The real rate constant of the reaction catalyzed by CuL¹–CuL⁴ was 4.00 × 10⁻⁶, 7.44 × 10⁻⁵, 1.42 × 10⁻⁴ and 4.10 × 10⁻⁴ s⁻¹, respectively. The effects of ligand and microenvironment on the hydrolytic reaction of BNPP have been discussed in detail.     

Accelerated hydrolysis of esters catalyzed by receptors, I nonenzymatic cleavage ofp-nitrophenyl acetate by polypeptides

The hydrolysis kinetics ofp-nitrophenyl acetate by basic polypeptides with a variety of amino acid residues were analyzed. The results suggest that the tertiary structure of microenvironment brought about by random coil assembly is more important as a binding site than the number of basic residues (catalytic sites).     

抗体酶催化的不对称反应

本文综述了抗体酶催化的不对称反应, 并讨论了抗体酶的应用前景。     

Formal DNA hydrolysis by mono- and dinuclear iron complexes

The complexes CpFe(CO)(2)Ph and [CpFe(CO)(2)](2) cleave DNA in the presence of H2O2 or organic peroxides to give products resulting from the formal hydrolysis of the phosphodiester groups.     

Specific hydrolysis of DNA by Ce~(4+) -ODN hybrid

The cerium complex bound to the derivative of oligoDNA has been synthesized successfully that can hydrolyze DNA with sequence-specificity. The synthesized derivative of oligoDNA, 5'-EDTA-P-10 mers ODN, was demonstrated by HPLC. The fluorescence spectrum of Tb3+ was detected after its interaction with the hybrid of 10-mers ODN and 26-mers ODN and the results show that the artificial endo-enzyme can recognize and combine firmly with the substrate DNA. The electrophorogram shows that the cerium-oligoDNA hybrid can specifically hydrolyze its substrate DNA and the cleavage site of this hydrolysis reaction is also discussed. This artificial nuclease can be widely used in molecular biology and genetic engineering as one kind of endo-enzyme.     

Phosphate diester and DNA hydrolysis by a multivalent, nanoparticle-based catalyst

2-nm gold nanoclusters coated with Zn(II) complexes bearing auxiliary hydrogen bond donors act as multivalent catalysts capable of promoting the hydrolysis of model phosphate diesters with exceptional activity and inducing DNA double strand cleavage.     

Site-selective DNA hydrolysis induced by a metal-free peptide nucleic acid-cyclen conjugate

A metal-free artificial restriction DNA cutter which is composed of cyclen and classical peptide nucleic acid (PNA) was synthesized. Analysis of DNA cleavage products indicates the site-selective hydrolysis.     

通过快速定点突变表征人源含硒单链抗体酶的底物结合部位

为了对人源含硒单链抗体酶Se-scFv-B3的底物结合部位和催化基团进行研究, 在理论预测的基础上, 通过快速定点突变法分别在2个理论预测的底物结合部位(位点1和位点2)内选定Ala180和Ala44定点突变为丝氨酸(Ser). 2个突变体蛋白经化学修饰将Ser转变成谷胱甘肽过氧化物酶(GPX)的催化基团硒代半胱氨酸(Sec)后, 前者的GPX活力达到了Se-scFv-B3的2倍多, 而后者的GPX活力没有明显提高, 这表明位点1可能是主要的底物结合部位, 与理论预测的结果一致.     

Dynamic Kinetic Resolution of 2-(Quinolin-8-yl)Benzaldehydes: Atroposelective Iridium-Catalyzed Transfer Hydrogenative Allylation

An atroposelective Ir-catalyzed dynamic kinetic resolution (DKR) of 2-(quinolin-8-yl)benzaldehydes/1-naphthaldehydes by transfer hydrogenative coupling of allyl acetate is disclosed. The allylation reaction takes place with simultaneous installation of central and axial chirality, reaching high diastereoselectivities and excellent enantiomeric excesses when ortho-cyclometalated iridium-DM-BINAP is used as the catalyst. The racemization of the substrates occurs through a designed transient Lewis acid-base interaction between the quinoline nitrogen atom and the aldehyde carbonyl group.     

Synthesis of N-Glycosides by Silver-Assisted Gold Catalysis

The synthesis of N-glycosides from stable glycosyl donors in a catalytic fashion is still challenging, though they exist ubiquitously in DNA, RNA, glycoproteins, and other biological molecules. Herein, silver-assisted gold-catalyzed activation of alkynyl glycosyl carbonate donors is shown to be a versatile approach for the synthesis of purine and pyrimidine nucleosides, asparagine glycosides and quinolin-2-one N-glycosides. Thus synthesized nucleosides were subjected to the oxidation–reduction sequence for the conversion of Ribf- into Araf- nucleosides, giving access to nucleosides that are otherwise difficult to synthesize. Furthermore, the protocol is demonstrated to be suitable for the synthesis of 2’-modified nucleosides in a facile manner. Direct attachment of an asparagine-containing dipeptide to the glucopyranose and subsequent extrapolation to afford the dipeptide disaccharide unit of chloroviruses is yet another facet of this endeavor.     

Catalysis by Molecular Metal Clusters

Molecular metal clusters form a very large and diverse family. They present the opportunity of modeling the intermediates involved in surface mediated catalytic reactions, of providing a source of very reactive mononuclear metal fragments, and of effecting catalytic cycles in which the cluster remains intact. The last mentioned aspect is the subject of this review article. The state-of-the-art of cluster catalysis is critically analyzed. The possibilities offered by molecular metal catalysts of performing catalytic reactions at multimetal atom sites are also discussed.     

Double-strand hydrolysis of plasmid DNA by dicerium complexes at 37 degrees C.

Significant effort has been made to develop synthetic metal complexes that hydrolyze DNA. Here we report a new dicerium complex, Ce(2)(HXTA) (HXTA = 5-methyl-2-hydroxy-1,3-xylene-alpha,alpha-diamine-N,N,N',N'-tetraacetic acid), which can hydrolyze DNA at pH 8 and 37 degrees C. This complex hydrolyzes DNA restriction fragments to give products with high regioselectivity, affording >90% 5'-OPO(3) and 3'-OH ends, like the products of DNA hydrolyzing enzymes. Ce(2)(HXTA) also hydrolyzes Litmus 29 plasmid DNA to afford both nicked and linear DNA. Analysis of the relative amounts of supercoiled, nicked, and linear DNA present show that there is one double-strand cleavage per ten single-strand cleavages, indicating that the linear DNA formed cannot be the result of two random single-strand cleavage events. The kinetics of nicked and linear DNA formation are comparable, both being associated with apparent first-order rate constants of approximately 1 x 10(-)(4) s(-)(1) for complex concentrations of 10(-)(5)-10(-)(4) M. These observations suggest that similar factors affect the hydrolysis of the first and second DNA strands and that cleaving the phosphodiester bond is likely the rate determining step in both cases. This is the first detailed study of a metal complex shown to mimic DNA hydrolases in their capability to effect double-strand DNA hydrolysis regioselectively at the 3'-O-P bond.     

SO_4~(2-)/ZrO_2-TiO_2-SiO_2固体酸催化苯乙烯选择氧化反应的研究

制备了一种 SO2 -4 促进的金属氧化物固体酸 SO2 -4 / Zr O2 - Ti O2 - Si O2 ,并将其用于催化C6H5C2 H3的选择氧化反应 ,发现该新型固体酸具有较高的活性和选择性 ,C6H5C2 H3转化率达 1 0 .73% ,C6H5C2 H3O选择性达 2 0 .73%。随着 Ti含量的增大 ,催化活性提高 ;用共沉淀法比用浸渍法能更有效地在固体酸中形成选择氧化活性结构。用 IR,XRD等方法进行的表征表明 ,反应的选择氧化活性位可能含有 Zr,Si,O,Ti等成分。     

Turning on Asymmetric Catalysis of Achiral Metal-Organic Frameworks by Imparting Chiral Microenvironment

The development of heterogeneous asymmetric catalysts has attracted increasing interest in synthetic chemistry but mostly relies on the immobilization of homogeneous chiral catalysts. Herein, a series of chiral metal–organic frameworks (MOFs) have been fabricated by anchoring similar chiral hydroxylated molecules (catalytically inactive) with different lengths onto Zr-oxo clusters in achiral PCN-222(Cu). The resulting chiral MOFs exhibit regulated enantioselectivity up to 83 % ee in the asymmetric ring-opening of cyclohexene oxide. The chiral molecules furnished onto the catalytic Lewis sites in the MOF create multilevel microenvironment, including the hydrogen interaction between the substrate and the chiral −OH group, the steric hindrance endowed by the benzene ring on the chiral molecules, and the proximity between the catalytic sites and chiral molecules confined in the MOF pores, which play crucial roles and synergistically promote chiral catalysis. This work nicely achieves heterogeneous enantioselective catalysis by chiral microenvironment modulation around Lewis acid sites.     

The counterion influence on the CH-activation of methane by palladium(II) biscarbene complexes - structures, reactivity and DFT calculations

Novel bridged palladium(II) biscarbene complexes with different counterions are reported: 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium(II) bischloride (1) and bis(trifluoroacetate) (2) have been synthesized in good yields. Both complexes are active in the catalytic conversion of methane to methanol and show comparable activities to previously published NHC-catalysts. The results of the single-crystal X-ray structure determination of 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium(II) bischloride (1) and 1,1^′-dimethyl-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene palladium (II) bis(trifluoro-acetate) 2 confirmed the structural similarity to the known corresponding palladium bromide and iodide complexes. Since free 1,1^′-dimethyl-R-3,3^′-methylene-4-diimidazolin-2,2^′-diylidene are only available in low yields these compounds have been synthesized via the bromide complex, exchanging the counterion by AgCF₃COO or by exchanging the counterion of the imidazolium salt by NH₄PF₆.     

Photochemical Desaturation and Epoxidation with Oxygen by Sequential Flavin Catalysis

Catalytic desaturations are important strategies for the functionalization of organic molecules. In nature, flavoenzymes mediate the formation of α,β-unsaturated carbonyl compounds by concomitant cofactor reduction. Contrary to many laboratory methods for these reactions, such as the Saegusa-Ito oxidation, no transition metal reagents or catalysts are required. However, a molecular flavin-mediated variant has not been reported so far. We disclose a photochemical approach for silyl enol ether oxidation, which leads to α,β-unsaturated ketones (13 examples) in very good yields. The flavin catalysts are stable throughout the desaturation reaction, and we successfully applied them in a subsequent aerobic epoxidation by simply changing the reaction conditions. This protocol allowed us to directly convert silyl enol ethers into α,β-epoxyketones in a one-pot fashion (12 examples). Sequential flavin catalysis is not limited to one specific reactivity combination and can, inter alia, couple the photochemical oxidation with radical additions. We anticipate that flavin-catalyzed desaturation will be applicable to other substrate classes and that its sequential catalytic activity will enable rapid substrate diversification.     

Catalytic hydrolysis of carboxylic acid esters by Cu(II) and Zn(II) complexes containing a tetracoordinate macrocyclic Schiff base ligand in Brij35 micellar solution

The macrocyclic Schiff base complexes of Cu(II) and Zn(II) in Brij35 micellar solution are investigated kinetically for the catalytic hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl picolinate (PNPP) at 30 °C. The results indicate that different mechanisms are operative for the two complexes in the hydrolysis of PNPA and PNPP. The Cu(II) complex can only catalyze the hydrolysis of PNPP by the mechanism which involves the nucleophilic attack of external hydroxide ion on the carbonyl, while the Zn(II) complex can accelerate the hydrolysis of both PNPP and PNPA, by way of the intramolecular nucleophilic attack of zinc-bound hydroxide ion on carbonyl for PNPP and the less effective intermolecular nucleophilic attack of zinc-bound hydroxide ion on carbonyl for PNPA, respectively. The catalytic activity of Zn(II) complex is close to or even higher than that of Cu(II) complex. The reason is discussed in details.     

中国催化三十年进展:理论和技术的创新

中国的催化科学与技术始于20世纪初,经过先辈的努力使其经历了发展初期和稳定发展阶段,在历史上由于人为因素的严重破坏使其处于停滞并失去了宝贵的十余年大好发展时机.20世纪80年代,中国催化事业进入了快速发展时期.在这一历史时期,迅速恢复和建立了以中科院、高校和产业部门研究院组成的三个方面军的研究队伍.开展了以形式动力学为主要方法和手段的研究,基础研究方面提炼出新催化材料、新催化表征方法和新催化反应为主要研究方向.表面科学、纳米科学的出现大大促进和深化了催化的基础探索,催化正从艺术走向科学…….在应用催化研究方面,在不同历史时期结合国家重大需求,在煤、石油、天然气优化利用,先进材料,环境,人类健康等领域做出了重大贡献.当前的中国已成为催化大国并正在走向催化强国.     

The preparation and resolution of 2-(2-pyridyl)- and 2-(2-pyrazinyl)-Quinazolinap and their application in palladium-catalysed allylic substitution

The preparation and resolution of two new axially chiral quinazoline-containing phosphinamine ligands, 2-(2-pyridyl)-Quinazolinap and 2-(2-pyrazinyl)-Quinazolinap, is described. The ligands were synthesised in good yield over eight steps and included two Pd-catalysed reactions, a Suzuki coupling to form the biaryl linkage and the introduction of the diphenylphosphino group, as the key transformations. The racemic ligands were resolved via the fractional crystallisation of diastereomeric palladacycles derived from (+)-di-μ-chlorobis{(R)-dimethyl[1-(1-naphthyl)ethyl]aminato-C₂,N}dipalladium (II) X-ray crystal structures of the (S,R)-2-pyridyl- and (S,R)-2-pyrazinyl-palladacycles are included. Displacement of the resolving agent by reaction with 1,2-bis(diphenylphosphino)ethane gave enantiopure 2-(2-pyridyl)-Quinazolinap and 2-(2-pyrazinyl)-Quinazolinap, new atropisomeric phosphinamine ligands for asymmetric catalysis. These ligands were applied in the palladium-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate resulting in moderate conversions and enantioselectivities of up to 81%.