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.

Geometric and Electronic Structure/Function Correlations in Non-Heme Iron Enzymes

1 Review 1.1 Overview 1.2 Solid-phase organic synthesis (SPOS) 1.3 Beyond conventional solid-phase organic synthesis 1.4 The review 1.5 Some definitions 1.6 Solid-supported reagents and scavengers 1.7 Multi-step use of solid-supported reagents and scavenging reagents 1.8 Conclusions and future perspective 2 Introduction to the tables 2.1 Organisation of tables (reagent and catalyst section) 2.2 Representative data entry (reagent and catalyst section) 2.3 Organisation of tables (scavenging agents section) 2.4 Representative data entry (scavenging agents section) 3 Tables of reagents and catalysts 4 Tables of scavengers 5 Other relevant reviews 5.1 Insoluble polymers 5.1.1 Structure and physical properties (insoluble polymers) 5.1.2 General (insoluble polymers) 5.1.3 Reactions (insoluble polymers) 5.1.4 Miscellaneous (insoluble polymers) 5.2 Soluble polymers 5.2.1 General (soluble polymers) 5.2.2 Reactions (soluble polymers) 5.3 Inorganic solids 5.3.1 Structure and physical properties (inorganic solids) 5.3.2 General (inorganic solids) 5.3.3 Reactions (inorganic solids) 5.3.4 Miscellaneous (inorganic solids) 5.4 Miscellaneous supports 5.4.1 Structure and physical properties (miscellaneous supports) 5.4.2 General (miscellaneous supports) 5.4.3 Reactions (miscellaneous supports) 5.4.4 Miscellaneous (miscellaneous supports) 5.5 Purification strategies 5.5.1 Various supports (purification strategies) 5.5.2 Insoluble polymers (purification strategies) 6 Acknowledgements 7 Abbreviations 8 References 1 Review

Multi-step organic synthesis using solid-supported reagents and scavengers: a new paradigm in chemical library generation

Curved pi-conjugation, aromaticity, and the related chemistry of small fullerenes (< C60) and single-walled carbon nanotubes.

In the first part, the theory of molecules in a magnetic field is reviewed with special attention to chemical shifts. The central role of the current density is pointed out. The gauge origin problem and its solution by means of the IGLO method is explained. Various methods for the calculation of chemical shifts are compared and the IGLO method is presented in detail both as far as computations and interpretation of the result are concerned.

The IGLO-Method: Ab-initio Calculation and Interpretation of NMR Chemical Shifts and Magnetic Susceptibilities

Use of solid catalysts in Friedel-Crafts acylation reactions.

Bridgehead adamantyl, diamantyl, and related cations and dications

Stable carbocations. 273. [1.1.1.1]- and [2.2.1.1]Pagodane dications: frozen two-electron Woodward-Hoffmann transition-state models

La transposition de Fries est etudiee a partir de benzoate de phenyle et p-tolyle de p-toluate de phenyle et p-tolyle et de chloro-3 benzoate de phenyle et de p-tolyle

V. V. Krishnamurthy

Papers

Bridgehead adamantyl, diamantyl, and related cations and dications

Stable carbocations. 273. [1.1.1.1]- and [2.2.1.1]Pagodane dications: frozen two-electron Woodward-Hoffmann transition-state models

Heterogeneous catalysis by solid superacids. 17. Polymeric perfluorinated resin sulfonic acid (Nafion-H) catalyzed Fries rearrangement of aryl esters

Stable carbocations. Part 267. Pagodane dication, a unique 2.pi.-aromatic cyclobutanoid system

Stable carbocations. 266. Study of carbon-13-carbon-13 NMR coupling constants in .alpha.-cyanodiarylmethyl and 1,1-diaryl-2-butynyl cations