Metal Fluorides as Analogues for Studies on Phosphoryl Transfer Enzymes

The 1994 structure of a transition‐state analogue with AlF₄⁻ and GDP complexed to G1α, a small G protein, heralded a new field of research into the structure and mechanism of enzymes that manipulate the transfer of phosphoryl (PO₃⁻) groups. The number of enzyme structures in the PDB containing metal fluorides (MF_x) as ligands that imitate either a phosphoryl or a phosphate group was 357 at the end of 2016. They fall into three distinct geometrical classes: 1) Tetrahedral complexes based on BeF₃⁻ that mimic ground‐state phosphates; 2) octahedral complexes, primarily based on AlF₄⁻, which mimic “in‐line” anionic transition states for phosphoryl transfer; and 3) trigonal bipyramidal complexes, represented by MgF₃⁻ and putative AlF₃⁰ moieties, which mimic the geometry of the transition state. The interpretation of these structures provides a deeper mechanistic understanding into the behavior and manipulation of phosphate monoesters in molecular biology. This Review provides a comprehensive overview of these structures, their uses, and their computational development.     

Phosphoryl and Thiophosphoryl Transfer Reactions: Stereochemical Imperatives for Metaphosphate and Thiometaphosphate

Abstract

The stereochemical courses of phosphoryl transfer reactions in aprotic solvents and thiophosphoryl transfer reactions in protic solvent have been determined. The extensive racemisation observed in both instances is discussed in terms of metaphosphate and thiometaphosphate intermediates of significant life-times.     

The Twin-Excited State as a Probe for the Transition State in Concerted Unimolecular Reactions: The Semibullvalene Rearrangement

A twin of the transition state , which can be investigated spectroscopically and can thus supply information about the structure of the transition state, has now been characterized for the Cope rearrangement of semibullvalene (shown below). It involves an excited state with B₂ symmetry and results from a linear combination of the ground-state wave functions of (mirror-image) reactant and product.     

Active Site Model for Phosphoryl Transfer Enzymes Via Hexacoordination

Previous work has demonstrated the ease with which phosphorus can increase its coordination geometry. The present study has more closely modeled active sites of phosphoryl transfer enzymes by the inclusion of anionic phosphorus, which allows for oxygen atom donor coordination at phosphorus in the presence of a hydrogen bonding network. The resulting increase in phosphorus-oxygen donor coordination compared to analogous systems containing neutral phosphorus compounds serves as a model applicable to proposed mechanisms at active sites of phosphoryl transfer enzymes.     

The Guanidinium Unit in the Catalysis of Phosphoryl Transfer Reactions: From Molecular Spacers to Nanostructured Supports

Examples of guanidinium‐based artificial phosphodiesterases are illustrated in this review article. A wide set of collected catalytic systems are presented, from the early examples to the most recent developments of the use of this unit in the design of supramolecular catalysts. Special attention is dedicated to illustrate the operating catalytic mechanism and the role of guanidine/ium units in the catalysis. One or more of these units can act by themselves or in conjunction with other active units. The analogy with the mechanism of enzymatic systems is presented and discussed. In the last part of this overview, recent examples of guanidinophosphodiesterases based on nanostructured supports are reported, namely gold‐monolayer‐protected clusters and polymer brushes grafted to silica nanoparticles. The issue of the dependence of the catalytic performance on the preorganization of the spacer is tackled and discussed in terms of effective molarity, a parameter that can be taken as a quantitative measurement of this preorganization for both conventional molecular linker and nanosized supports.     

Intermolecular Phosphoryl Transfer Between Serine and Histidine Residues

A novel intermolecular phosphoryl transfer from O-trimethylsilyl-N-(O, O-diisopropyl)phosphoryl serine trimethylsilyl ester to N, N‘-bis(trimethylsilyl) histidine trimethylsilyl ester wasstudied through electrospray ionization mass spectrometry (ESI-MS). It was proposed that thetransfer reaction went through penta-coordinated phosphorus intermediate.     

Cyano Analogues of 7‐Azaindole: Probing Excited‐State Charge‐Coupled Proton Transfer Reactions in Protic Solvents

The interplay between excited‐state charge and proton transfer reactions in protic solvents is investigated in a series of 7‐azaindole (7AI) derivatives: 3‐cyano‐7‐azaindole (3CNAI), 5‐cyano‐7‐azaindole (5CNAI), 3,5‐dicyano‐7‐azaindole (3,5CNAI) and dicyanoethenyl‐7‐azaindole (DiCNAI). Similar to 7AI, 3CNAI and 3,5CNAI undergo methanol catalyzed excited‐state double proton transfer (ESDPT), resulting in dual (normal and proton transfer) emission. Conversely, ESDPT is prohibited for 5CNAI and DiCNAI in methanol, as supported by a unique normal emission with high quantum efficiency. Instead, the normal emission undergoes prominent solvatochromism. Detailed relaxation dynamics and temperature dependent studies are carried out. The results conclude that significant excited‐state charge transfer (ESCT) takes place for both 5CNAI and DiCNAI. The charge‐transfer specie possesses a different dipole moment from that of the proton‐transfer tautomer species. Upon reaching the equilibrium polarization, there exists a solvent‐polarity induced barrier during the proton‐transfer tautomerization, and ESDPT is prohibited for 5CNAI and DiCNAI during the excited‐state lifespan. The result is remarkably different from 7AI, which is also unique among most excited‐state charge/proton transfer coupled systems studied to date.     

B(C6F5)3 as a Highly Effective Catalyst for the Phosphoryl Transfer Reaction

The phosphoryl transfer reactions of diphenyl chlorophosphate with a wide range of alcohols were catalyzed by tris(pentafluorophenyl)boron [B(C₆F₅)₃], giving the corresponding phosphate esters in excellent yields. This methodology has advantages over older ones because it employs the easily handled B(C₆F₅)₃, avoids the side reaction, and has shorter reaction time.     

Synthesis of Unsaturated Aminopyranosides as Possible Transition State Mimics for Glycosidases

Four unsaturated aminopyranosides have been prepared as possible transition‐state mimics targeted towards carbohydrate processing enzymes. The conformations of the protonated aminosugars have been investigated by molecular modelling and their ability to inhibit α‐ and β‐glucosidases and an α‐mannosidase have been probed. Two targets proved moderate inhibitors of α‐glucosidases from Brewer's yeast and Bacillus stearothermophilus.     

Aryl Compounds of Pentavalent Antimony: Syntheses,Reactions, and Structures

Russian Journal of Coordination Chemistry - The synthesis methods, some reactions, and specific features of the structures of aryl compounds of pentavalent antimony and examples of their possible...     

Computational Insights into the Excited State Intramolecular Proton Transfer Reactions in Ortho-hydroxylated Oxazolines

Excited-state intramolecular proton transfer(ESIPT) reactions of three ortho-hydroxylated oxazolines, 2-(4,4-dimethyl-4,5-dihydro-oxazol-2-yl)-phenol(DDOP), 4-(4,4-dimethyl-4,5-dihydro-oxazol-2-yl)-[1,1?-biphenyl]-3-ol(DDOP-C_6H_5) and 4-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-3-hydroxy-benzonitrile(DDOP-CN), have been systematically explored by density functional theory(DFT) and time-dependent density functional theory(TDDFT) methods. Two stable configurations(enol and keto forms) are found in the ground states(S_0) for all the compounds while the enol form only exists in the first excited states(S_1) for the compound modified with electron donating group(-C_6H_5). In addition, the calculated absorption and emission spectra of the compounds are in good agreements with the experiments. Infrared vibrational spectra at the hydrogen bond groups demonstrate that the intramolecular hydrogen bond O(1)-H(2)···N(3) in DDOP-C_6H_5 is strengthened in the S_1 states, while the frontier molecular orbitals further reveal that the ESIPT reactions are more likely to occur in the S_1 states for all the compounds. Besides, the proton transfer potential energy curves show that the enol forms can barely convert into keto forms in the S_0 states because of the high energy barriers. Meanwhile, intramolecular proton transfer of all the compounds could occur in S_1 states. The ESIPT reactions of the ortho-hydroxylated oxazolines are barrierless processes for unsubstituted DDOP and electron withdrawing substituted DDOP-CN, while the electron donating substituted DDOP-C_6H_5 has a small barrier, so the electron donating is unfavorable to the ESIPT reactions of ortho-hydroxylated oxazolines.     

单电子转移反应

本文对重要有机反应之一的单电子转移过程作了综述。单电子转移反应与极性反应的根本区别在于,前者每次只发生一个电子的转移,而后者通常每次发生一对电子的转移。影响这二种历程的主要因素是反应物的立体因素,电子结构及氧化还原能力。单电子转移按其反应方式又被细分(?)inner-sphere ET (?) outer-sphere ET 二种历程。一些典型的单电子转移反应已被分类介绍。     

General Kinetic Equation for Solid State Reactions

A general kinetic equation is suggested in order to describe solid state decompositions or, more generally, solid state reactions and transformations on the basis of some existing general equations. This differential equation can be expressed as: dα/dt=k[(1-α)^q]^x{[1-(1-α)^1−q]/(1-q)}^y, where α represents the degree of conversion, k is the rate constant while q, x and y are characteristic parameters for a given mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

N-羟基邻苯二甲酰亚胺及其类似物催化下的分子氧氧化反应

本文综述了近年来N-羟基邻苯二甲酰亚胺（NHPI）及其类似物催化下分子氧氧化的各种反应,并对它们的催化机理作了简要介绍。NHPI与过渡金属离子组成的催化体系能高效的催化乙烷氧化为乙酸、环烷烃氧化为二元羧酸、甲苯氧化为苯甲酸、烯烃氧化为环氧化物、炔烃氧化为炔酮、酰胺氧化为酰亚胺;NHPI单独使用能催化金刚烷发生氧化羰基化反应、催化氧化醇制取过氧化氢;NHPI与有机助催化剂如：偶氮二异丁腈、溴化季铵盐、蒽醌、醇等也能催化分子氧氧化反应。