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Showing papers in "Chemical Reviews in 2000"


Journal ArticleDOI
Masahiro Irie1

3,623 citations


Journal ArticleDOI
TL;DR: When considering new sensory technologies one should look to nature for guidance, as living organisms have developed the ultimate chemical sensors.
Abstract: When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

3,464 citations


Journal ArticleDOI
TL;DR: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to make organic preparations.
Abstract: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to

3,373 citations





Journal ArticleDOI
TL;DR: Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.
Abstract: One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

1,719 citations


Journal ArticleDOI

1,612 citations




Journal ArticleDOI
TL;DR: A detailed molecular mechanism has been proposed for IPNS based on spectroscopic and crystallographic studies and the role of cosubstrate ascorbate is proposed to reduce the toxic peroxo byproduct to water.
Abstract: ion step follows the decarboxylation, which is consistent with the deuterium isotopic effects observed for thymine 7-hydroxylase which indicate that an irreversible step (or steps) occurs prior to the C-H bond breaking.395 It has also been shown for prolyl 4-hydroxylase that a substrate-derived radical is generated in the reaction, which is consistent with a rebound mechanism.437 It is important to point out that no oxygen intermediate (i.e., bridged superoxo or oxo-ferryl) has been observed for any R-KGdependent enzyme. This warrants future theoretical and experimental study. A detailed molecular mechanism has been proposed for IPNS based on spectroscopic and crystallographic studies.422 Resting IPNS/FeII is also 6C and thus relatively stable toward dioxygen. Substrate ACV binds directly to FeII IPNS through its thiolate group, providing an open coordination position at the FeII. O2 can then react to form an FeIII-superoxo intermediate. This intermediate is suggested422 to perform the first hydrogen-atom abstraction step and close the â-lactam ring, resulting in the formation of the first water molecule and generating an FeIVdO-II intermediate, which completes the second ringclosure process by hydrogen-atom abstraction forming a thiazolidine ring. Previously proposed mechanisms of ACCO involved direct binding of cosubstrate ascorbate to the iron before O2 as part of the oxygen activation process.438,439 The EPR and ESEEM studies of the NO complex of ACCO suggested a quite different molecular mechanism for ACCO.435 An FeIII-superoxo intermediate is proposed. Whether it is preceded by a 6C f 5C process with substrate binding is presently under study.440 This intermediate is thought to initiate a radical process by single hydrogen-atom abstraction or electron-coupled proton transfer (PT)ion or electron-coupled proton transfer (PT) from the bound amino group. The resulting substrate radical may undergo spontaneous conversion into products. The role of cosubstrate ascorbate is proposed to reduce the toxic peroxo byproduct to water. Alternatively, the two-electron reduction of FeIIIsuperoxo by the cosubstrate ascorbate could result in an FeIVdO-II intermediate which initiates the radical reaction.435 4. Rieske-Type Dioxygenases Biochemical Characterization. The Rieske ironsulfur center is a two iron-two sulfur cluster ([2Fe2S]) which has a 2His (on one iron), 2Cys (on the other iron) coordination environment, instead of the 4Cys present in plant ferredoxins. It plays a key role in the electron transport pathway in membranebound cytochrome complexes as well as in some dioxygenases.441 The latter are mainly comprised of two protein components: a reductase containing flavin and a ferredoxin [2Fe-2S], and a terminal oxygenase containing a Rieske [2Fe-2S] cluster and a non-heme iron active site.442 Except for the recently reported alkene monooxygenase that has a binuclear iron site in its terminal oxygenase,10 most of the Rieske-type oxygenases have a mononuclear iron site, which is believed to be the site of dioxygen activation and substrate oxygenation.442,443 The majority of the Rieske-type mononuclear non-heme oxygenases form a family of enzymes which are aromatic-ring-hydroxylating dioxygenases. These catalyze the regioand stereospecific cis-dihydroxylation of an aromatic ring using dioxygen and NAD(P)H (Table 1). Examples include benzene dioxygenase (BDO, EC 1.14.12.3),444 phthalate dioxygenase (PDO, EC 1.14.12.7),445 toluene dioxygenase (EC 1.14.12.11),446 and naphthalene 1,2-dioxygenase (NDO, EC 1.14.12.12),447 which initiate the aerobic degradation of aromatic compounds in the soil bacteria and are targets for bioengineering in bioremediation. This step is the first step in the pathway that ultimately leads to ring cleavage by the intraand extradiol dioxygenases (sections II.B.2 and II.C.1).443 Besides these bacterial dioxygenases, other Rieske-type mononuclear non-heme oxygenases include anthranilate 1,2-dioxygenase (EC 1.14.12.1),448 which deaminates and decarboxylates the substrate to produce catechol; chlorophenylacetate 3,4-dioxygenase (EC 1.14.2.13),449 which converts substrate to catechol with chloride elimination; and 4-methoxybenzoate O-demethylase (putidamonooxin),450 which catalyzes the conversion of 4-methoxybenzoic acid to 4-hydroxybenzoic acid and formaldehyde. The reductase component is usually a monomer (MW ) 12-15 kDa) and utilizes flavin to mediate ET from the two-electron donor NAD(P)H to the oneelectron acceptor [2Fe-2S] cluster and is specific to each terminal oxygenase; other electron donors do not support efficient oxygenation.442 The crystal structure of phthalate dioxygenase reductase is available.451 The terminal oxygenases are large protein aggregates (MW ) 150-200 kDa) containing either multiples of R subunits (BDO R2, PDO R4) or an equimolar combination of R and â subunits (toluene dioxygenase R2â2, NDO R3â3). The R subunits contain a Rieske [2Fe-2S] cluster and a catalytic non-heme FeII center. â subunits do not seem to be involved in the catalytic function (vide infra). Kinetics. Steady-state kinetic studies coupled with various rapid reaction studies of the partial reactions of PDO allowed Ballou et al. to propose a kinetic scheme (Scheme 15).443 On the basis of steady state 278 Chemical Reviews, 2000, Vol. 100, No. 1 Solomon et al.







Journal ArticleDOI
TL;DR: Conventional approaches to chemical sensors have traditionally made use of a “lock-and-key” design, wherein a specific receptor is synthesized in order to strongly and highly selectively bind the analyte of interest.
Abstract: Conventional approaches to chemical sensors have traditionally made use of a “lock-and-key” design, wherein a specific receptor is synthesized in order to strongly and highly selectively bind the analyte of interest.1-6 A related approach involves exploiting a general physicochemical effect selectively toward a single analyte, such as the use of the ionic effect in the construction of a pH electrode. In the first approach, selectivity is achieved through recognition of the analyte at the receptor site, and in the second, selectivity is achieved through the transduction process in which the method of detection dictates which species are sensed. Such approaches are appropriate when a specific target compound is to be identified in the presence of controlled backgrounds and interferences. However, this type of approach requires the synthesis of a separate, highly selective sensor for each analyte to be detected. In addition, this type of approach is not particularly useful for analyzing, classifying, or assigning human value judgments to the composition of complex vapor mixtures such as perfumes, beers, foods, mixtures of solvents, etc.







Journal ArticleDOI
TL;DR: A synthetic method for the synthesis of polysubstituted benzenes and, compared to the following transition metal-catalyzed methods, these approaches have some drawbacks from the viewpoint of atom economy or environmental concern.
Abstract: method for the synthesis of polysubstituted benzenes. However, high regioselectivity (and yield) can only be achieved by the careful choice of the reagents and synthetic route. Furthermore, it is usually necessary to convert and/or protect-deprotect the substituents properly. Directed ortho metalation is another synthetic method which has been studied extensively, and this approach is a useful method for the introduction of a substituent at the ortho position.2 However, the scope of this reaction is clearly restricted by its nature. Compared to the following transition metal-catalyzed methods, these approaches have some drawbacks from the viewpoint of atom economy3 or environmental concern. In 1948, Reppe et al. discovered the transitionmetal-catalyzed [2+2+2] cyclotrimerization of alkynes,4 and this new synthetic method was applied to the synthesis of substituted benzenes (eq 2). In this



Journal ArticleDOI
TL;DR: The history of “ligand effects” in catalysis, a range of reactions for which a notable effect has been observed, and some of the established examples of bite angle effects involve diphosphine ligands.
Abstract: phinoethane) seemed mainly to stabilize intermediates, and often the catalytic reactions were slower when dppe was used instead of the most common monodentate triphenylphosphine. We will briefly review the history of “ligand effects” in catalysis before discussing a range of reactions for which a notable effect has been observed. It has taken quite some time before the positive effect that bidentates can have on selectivities and rates of catalytic reactions was fully recognized. Most of the established examples of bite angle effects involve diphosphine ligands. Therefore, many important catalysts containing a chelate ligand such as bipyridine and diimine will fall outside the scope of this review. The connecting bridge in these bidentates does play a dominant role in the performance of these catalysts, but systematic studies have not been published. The effects of phosphine ligands in catalysis have been known for quite some time. One of the first reports involves the use of triphenylphosphine in the “Reppe” chemistry, the reactions of alkynes, alcohols, and carbon monoxide.1 It was found that formation of acrylic esters was much more efficient using NiBr2(PPh3)2 than NiBr2 without ligand. In the commercial system, though, a phosphine-free catalyst is used. While the reaction was not yet understood mechanistically, the use of phosphines in catalysis attracted the attention of the petrochemical industry worldwide. An early example of a phosphine ligand modified catalytic process is the Shell process for alkene hydroformylation using a cobalt catalyst containing a trialkylphoshine.2 The reaction requires higher temperatures, but it leads to more linear product as compared to the unmodified catalyst. The general mechanism of the hydroformylation reaction has been known for a long time.3 Hydrocyanation as used by Du Pont is another early example of an industrially applied catalytic reaction employing ligands.4 It is a nickel-catalyzed reaction in which aryl phosphite ligands are used for the production of adiponitrile. The development of this process has played a key role in the introduction of the now very common study of “ligand effects” in the field of homogeneous catalysis by organometallic complexes.5 While several industries were working on new homogeneous catalysts, important contributions to the new field were made in academia in the early 1960s with the appearance of the first phosphinemodified hydrogenation catalysts. An early example of a phosphine-free ruthenium catalyst was published by Halpern.6 Triphenylphosphine-modified platinumtin catalysts for the hydrogenation of alkenes were reported by Cramer from Du Pont in 1963.7 In the same year Breslow (Hercules) included a few phosFigure 1. Bite angle: The ligand-metal-ligand angle of bidentate ligands. 2741 Chem. Rev. 2000, 100, 2741−2769

Journal ArticleDOI
TL;DR: One of the most challenging targets is the controlled copolymerization of simple olefins with polar functional monomers, which would mark a quantum advance in polyolefin field.
Abstract: Transition-metal catalysts long ago made it from the laboratory bench to the polymerization reactor. Indeed, they are being used around the world to make more than 70 million tons of polyethylene and polypropylene a year. Transition-metal catalysts give polyolefin producers unprecedented flexibility in process and polymer design. However, there are still new worlds for catalysts to conquer. One of the most challenging targets is the controlled copolymerization of simple olefins with polar functional monomers. Success in this area would mark a quantum advance in polyolefin field.