Showing papers in "Chemical Reviews in 1993"
3,257 citations
1,986 citations
TL;DR: In this article, the authors review the applications of free energy calculations employing molecular dynamics or Monte Carlo methods to a variety of chemical and biochemical phenomena, including molecular solvation, molecular association, macromolecular stability, and enzyme catalysis.
Abstract: The author will review the applications of free energy calculations employing molecular dynamics or Monte Carlo methods to a variety of chemical and biochemical phenomena. The focus is on the applications of such calculations to molecular solvation, molecular association, macromolecular stability, and enzyme catalysis. The molecules discussed range from monovalent ions and small molecules to proteins and nucleic acids.
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TL;DR: In this article, a review of catalysis by metal clusters and colloids is presented, covering the period from 1980 to mid-1992, with a focus on the use of the terms colloid and cluster.
Abstract: This review covers catalysis by metal clusters and colloids. Any system that is a continuous phase is considered. Specifically not covered will be supported catalysts or heterogeneous catalysts except as they serve as comparative examples. Polymer-stabilized clusters and colloids are considered if they are soluble. The review will roughly cover the period from 1980 to mid-1992. Essential to this review is the establishment of definitions for the terms cluster and colloid. There are certain intuitive definitions for cluster and colloid. Recent work discussed below shows that the terms cluster and colloid are not clearly distinguishable. This review uses cluster and colloid interchangeably. However, several studies describe methods for distinguishing homogeneous from heterogeneous catalysts where heterogeneous catalysts may include colloids. For purposes of this review, a heterogeneous catalyst is defined as one where the catalyst is a separate phase, usually a filterable solid from a liquid phase. The distinction between mononuclear or low nuclearity clusters and large clusters or colloids does not necessarily distinguish homogeneous from heterogeneous catalysts. Methods for distinguishing whether a reaction is catalyzed by a mononuclear species or one where metal-metal bonds are present are described. The paper discusses the following: structure of large clusters and small colloids;more » onset to metallic properties; mononuclear vs. cluster catalysis; hydrogenation; CO activation; hydroformylation; H-H and C-H activation; hydrosilylation; isomerization; oligomerization; redox reactions; photocatalysis; water activation; oxidation; electrochemistry and electroless metal deposition; and ammonia synthesis and related nitrogen chemistry. 402 refs.« less
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TL;DR: In the last decade, there has been increasing recognition that organic reactions carried out in aqueous media may offer advantages over those occurring in organic solvents as discussed by the authors, which is the essence of organic synthesis.
Abstract: Carbon-carbon bond formation is the essence of organic synthesis. Although the well-known Kolbe synthesis was discovered in 1849Ia (the first observation wasmadein 1834byFaraday),'bformorethanacentury, carbon-carbon bond formation in aqueous media has been limited mainly to electrochemical processes and aldol condensation reactions. This is in contrast to the many enzymatic processes that by necessity must occur in an aqueous environment. In the last decade, there has been increasing recognition that organic reactions carried out in aqueous media may offer advantages over those occurring in organic solvents. For example, protection and deprotection processes in organic synthesis can possibly be simplified. This review will survey this area, concentrating mainly on the last decade. The review is organized into three main portions: nonorganometallic reactions, organometallic reactions, and transition-metal-catalyzed organic reactions in aqueous media. The conventional aldol-type and related reactions, stabilized carbanion alkylation reactions, electrochemical reactions as well as bioorganic reactions involving aqueous media and leading to carbon-carbon bond formation will not be included.
TL;DR: Simulation of Enzyme Reactions Using Valence Bond Force Fields and Other Hybrid Quantum/Classical Approaches as mentioned in this paper is an example of a hybrid approach that combines classical and quantum approaches.
Abstract: Simulation of Enzyme Reactions Using Valence Bond Force Fields and Other Hybrid Quantum/Classical Approaches
TL;DR: In this article, a review of the reaction chemistry occurring in solution routes to multicomponent metal oxides from metal-organic precursors is presented, with specific attention on those reports where mechanistic insight is presented.
Abstract: The goal of this article is to review the reaction chemistry occurring in solution routes to multicomponent metal oxides (i.e. containing two or more metals) from metal-organic precursors. In this context, the metal-organic precursor is usually a metal alkoxide, metal [beta]-diketonate or metal carboxylate compound. In the preparation of multicomponent metal oxide compounds, a number of key issues should be addressed which relate to the structure, properties, and performance of the final ceramic material. These issues pertain to control over the stoichiometry, homogeneity, phase, and crystallinity, which relate directly to the structure and reactivity of the metal-organic precursors in homogeneous solutions and their fate in subsequent processing steps. Perovskite-phase multicomponent mixed-metal oxides have been chosen as the material to which these questions are addressed in this review. The discussion is organized in the following manner. The relevant properties of perovskite-phase materials are reviewed and the requirements for the materials produced from metal-organic precursors are identified. The synthesis of perovskite-phase materials is reviewed with specific attention on those reports where mechanistic insight is presented. Recent advances in relevant structural and reaction chemistry of metal-organic precursors necessary to interpret these observations is then presented, and finally, conclusions are drawn and directions formore » future work are discussed.« less
TL;DR: This review discusses the coordination chemistry that forms the basis for nuclear medicine applications of the FDA-approved radiopharmaceuticals that are in clinical use, and of the most promising diagnostic and therapeutic radiophARMaceuticals That are in various stages of development.
Abstract: Radiopharmaceuticals, drugs containing a radionuclide, are used routinely in nuclear medicine departments for the diagnosis of disease and are under investigation for use in the treatment of disease. Nuclear medicine takes advantage of both the nuclear properties of the radionuclide and the pharmacological properties of the radiopharmaceutical. Herein lies the real strength of nuclear medicine, the ability to monitor biochemical and physiological functions in vivo. This review discusses the coordination chemistry that forms the basis for nuclear medicine applications of the FDA-approved radiopharmaceuticals that are in clinical use, and of the most promising diagnostic and therapeutic radiopharmaceuticals that are in various stages of development. 232 refs.
TL;DR: A comprehensive review of the synthesis, characterization, structure, and reactivity of dihydrogen complexes can be found in this paper, where the authors present a detailed analysis of the most commonly used methods to synthesize dihydrogens.
Abstract: At the present time more than 170 dihydrogen complexes have been reported. The very rapid development of this field is remarkable. This review summarizes in a comprehensive fashion the synthesis, characterization, structure, and reactivity of dihydrogen complexes. Coverage of the literature is up to the end of 1992. The paper begins with dihydrogen synthesis methods: reaction with hydrogen, protonation of hydride complexes, and synthesis under reducing conditions. After a section on computational studies, the paper describes the characterization of dihydrogen complexes by diffraction, solid state NMR, vibrational spectroscopy, and solution NMR methods (H-D coupling, relaxation time measurements, and correlation of H-H distance with J[sub H-D]). The section on reactivity includes a review of the kinetics and thermodynamics of H[sub 2] binding and displacement, dihydrogen/dihydride interconversion, acidity of coordinated dihydrogen, and hydrogenation and reduction reactions. 153 references.
TL;DR: In this article, the authors take a kineticist perspective in answering the question, what is a ''sufficiently accurate`` prediction of an enthalpy of formation, i.e., the difference between, say, 90% and 64% reaction yield.
Abstract: In the present manuscript describing traditional, macroscopic thermochemical properties, the authors` language will be that of molecular structure. Enthalpies (or heats of formation) are the subject of this article, and since the most important practical application of enthalpies is to explore reactivities and/or equilibria, they take a kineticist`s perspective in answering the question, what is a ``sufficiently accurate`` prediction of an enthalpy of formation. In a general reaction, A + B {yields} C + D, a shift in {Delta}{sub r}H (enthalpy of reaction) of 1 kcal/mol will generally result in a change in the equilibrium constant, K{sub eq}, of exp({minus}500/T) where T is the temperature in Kelvins. At room temperature, this means a factor of over 5 in K{sub eq}; the difference between, say, 90% and 64% reaction yield. Or, in terms of the time required for reaction completion, it could also mean an increase of a factor of 5. This factor of 5 is the same whether the total enthalpy of reaction is 5 kcal/mol or 500 kcal/mol. Thus, while theoreticians have struggled to attain the stage where they can with pride calculate enthalpy quantities with 2--4 kcal/mol uncertainty, they are not solving the practical problems at hand.