scispace - formally typeset
Search or ask a question
Author

Pierre Kennepohl

Other affiliations: Concordia University, University of Calgary, Harvard University  ...read more
Bio: Pierre Kennepohl is an academic researcher from University of British Columbia. The author has contributed to research in topics: Ligand & Halogen bond. The author has an hindex of 25, co-authored 65 publications receiving 5065 citations. Previous affiliations of Pierre Kennepohl include Concordia University & University of Calgary.


Papers
More filters
Journal ArticleDOI
TL;DR: The authors present here a classification and structure/function analysis of native metal sites based on these functions, and the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized.
Abstract: For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

2,242 citations

Journal ArticleDOI
TL;DR: In this article, the 1s → 3d pre-edge features of high-spin ferrous and ferric model complexes in octahedral, tetrahedral, and square pyramidal environments were investigated and the allowable many-electron excited states were determined using ligand field theory.
Abstract: X-ray absorption Fe−K edge data on ferrous and ferric model complexes have been studied to establish a detailed understanding of the 1s → 3d pre-edge feature and its sensitivity to the electronic structure of the iron site. The energy position and splitting, and intensity distribution, of the pre-edge feature were found to vary systematically with spin state, oxidation state, geometry, and bridging ligation (for binuclear complexes). A methodology for interpreting the energy splitting and intensity distribution of the 1s → 3d pre-edge features was developed for high-spin ferrous and ferric complexes in octahedral, tetrahedral, and square pyramidal environments and low-spin ferrous and ferric complexes in octahedral environments. In each case, the allowable many-electron excited states were determined using ligand field theory. The energies of the excited states were calculated and compared to the energy splitting in the 1s → 3d pre-edge features. The relative intensities of electric quadrupole transitions...

1,181 citations

Journal ArticleDOI
TL;DR: A new approach to alkyl fluorination has been developed that utilizes the reagent N-fluorobenzenesulfonimide as a fluorine transfer agent to alKYl radicals, and calculations reveal that fluorine-containing ionic reagents are likely candidates for further expansion of this approach to polar reaction media.
Abstract: The development of new synthetic technologies for the selective fluorination of organic compounds has increased with the escalating importance of fluorine-containing pharmaceuticals. Traditional methods potentially applicable to drug synthesis rely on the use of ionic forms of fluorine (F– or F+). Radical methods, while potentially attractive as a complementary approach, are hindered by a paucity of safe sources of atomic fluorine (F•). A new approach to alkyl fluorination has been developed that utilizes the reagent N-fluorobenzenesulfonimide as a fluorine transfer agent to alkyl radicals. This approach is successful for a broad range of alkyl radicals, including primary, secondary, tertiary, benzylic, and heteroatom-stabilized radicals. Furthermore, calculations reveal that fluorine-containing ionic reagents are likely candidates for further expansion of this approach to polar reaction media. The use of these reagents in alkyl radical fluorination has the potential to enable powerful new transformations...

255 citations

Journal ArticleDOI
TL;DR: The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described and the degree of covalency is similar to that which is observed in transition metal coordinate covalent bonds.
Abstract: The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described. The XB acyclic receptor displays selectivity for acetate over halides with enhanced anion recognition properties compared to the analogous hydrogen-bonding (HB) acyclic receptor. A reversal in halide selectivity is observed in the XB [2]catenane, in comparison to the acyclic XB receptor, due to the interlocked host’s unique three-dimensional binding cavity, and no binding is observed for oxoanions. Notable halide anion association constant values determined for the [2]catenane in competitive organic–aqueous solvent mixtures demonstrate considerable enhancement of anion recognition as compared to the HB catenane analogue. X-ray crystallographic analysis of a series of halide catenane complexes reveal strong XB interactions in the solid state. These interactions were studied using Cl and Br K-edge X-ray Absorption Spectroscopy (XAS) indicat...

184 citations

Journal ArticleDOI
TL;DR: A protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion as discussed by the authors.
Abstract: For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

134 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this paper, the development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed.
Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

3,305 citations

Journal ArticleDOI
TL;DR: This review presents an overview of silver nanoparticles (Ag NPs) preparation by green synthesis approaches that have advantages over conventional methods involving chemical agents associated with environmental toxicity.

3,290 citations

Journal ArticleDOI
TL;DR: An overview of the field of semiconductor photocatalysis can be found in this paper, where a brief examination of its roots, achievements and possible future is presented, and the semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work.
Abstract: The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

3,245 citations

Journal ArticleDOI
TL;DR: Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers.
Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.

3,241 citations