Special Issue "Biomimetic Catalysts"

Guest Editor
Prof. Dr. Armando Córdova
1 Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91 Stockholm, Sweden
2 Mid Sweden University, Department of Natural Sciences, Engineering and Mathematics, 851 70 Sundsvall, Sweden
Website: http://www.organ.su.se/Forskning/ac.php
E-Mail: acordova@organ.su.se
Phone: +46 8 162479
Fax: +46 8 154908
Interests: asymmetric catalysis; biomimetic catalysis; organocatalysis; biocatalysis; vombination of organo- and transition metal catalysis; domino, tandem cascade reactions; development of environmentally friendly catalytic reactions; catalytic modification of cellulose and polysaccharides; asymmetric synthesis; diversity oriented synthesis

Dear Colleagues,

Nature has always been a great inspiration for synthetic chemists in finding new ways of preparing their molecules and reactions. Catalysis is arguably one of the most efficient, economic and environmentally benign ways of assemble useful molecules and materials for the betterment of human health. In fact, it is the foundation for the perfectly evolved biochemical pathways of the cell and consequently life. Thus, lessons from how natural catalysts operate can therefore be very important for the design of the next generation of catalysts and chemical processes. In this special issue, some of the state of the art in the broad field of “biomimetic catalysis” is presented.

Prof. Dr. Armando Córdova
Guest Editor

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• biomimetic catalysis/catalyze
• mimic biological system
• biosynthesis
• metalloporphyrin (Porphyrin)
• cytochrome P-450

Type of Paper: Article
Title: Enzyme-Catalyzed Transetherification of Alkoxysilanes
Authors: Vincenzo Abbate ¹, Kurt F. Brandstadt ², Peter G. Taylor ¹ and Alan R. Bassindale ¹
Affiliation:¹ Department of Chemistry and Analytical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
² Dow Corning Corporation, Dow Corning Corp, 2200 W Salzburg Rd, Midland, MI 48686 USA; E-mail addresses: a.bassindale@open.ac.uk
Abstract: We report the first evidence of an enzyme-catalyzed transetherification of model alkoxysilanes. A biphasic-aqueous organic systems employed during the alkoxysilane studies consisted of 1-octanol saturated with tris-buffered water. In addition to the enzyme-catalyzed hydrolysis and condensation of alkoxysilanes, the formation of the octylsilyl ethers during transetherification and/or silanol-alcohol condensation was observed in this solvent as opposed to negative control reactions. The reactions were formulated with approximately 5:1 reactant to enzyme weight ratio in wet 1-octanol (5:1 solvent to reactant weight ratio) and conducted in inert glass vials. After 24 hours with stirring at room temperature, the reactions were filtered and analyzed by GC-FID. In order to chromatographically quantify the trimethyloctyloxysilane and phenyldimethyloctiloxysilane products, the compounds had to be synthesized, as they are not commercially available. The synthetic procedures are detailed in the Experimental Section (not shown here). In general, the appropriate chlorosilane was refluxed with 1-octanol in THF in the presence of triethylamine. The products were subsequently purified by vacuum distillation, characterized and used as standard references in the gas-chromatography analyses. Selected enzymes were observed to catalyze the formation of the octyltrimethyl silylether and/or the octylphenyldimethylsilyl ether after 24 hours at room temperature, while no condensation was observed in the negative control reactions. Interestingly, the extensive enzymatic screening conducted during the hydrolysis and condensation study of monoalkoxysilanes in wet tert-butanol did not lead to any tert-butyl silylether product formation. This may be due to the steric hindrance of tert-butyl groups, as opposed to the longer but more flexible octyl chains, which may be more accessible to the enzyme cavities. Notably, ROL was observed to catalyze both octyl ether formations. Lipases normally interact with long-chain alcohols and/or carboxylic acids as natural substrates. Our results show that ROL catalyzes the formation of octyl-silyl ethers. Conversely, the lipase was not able to catalyze the formation of tert-butyl silyl ethers. This is in agreement with the natural substrate-selectivity of the ROL, and suggests the involvement of the active site during the catalysis. To our knowledge, this represents the first case of enzymatic transetherification of alkoxysilanes. Although it is only a preliminary study, the results clearly show the advantage of utilizing mild biocatalysts during the synthesis of novel alkoxysilanes in comparison with chemical methods, which employ the use of caustic chemicals and high temperatures.

Type of Paper: Review
Title: Enzymatic Catalysis in Miniemulsion – Heterophase Systems as Substrates for Enzymatic Action
Authors: Clemens K. Weiss and Katharina Landfester
Affiliation: Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
Abstract: Some essential enzyme catalyzed processes, as e.g. the digestion of fat, are proceeding only at the interface of two immiscible phases. Typically, these systems consist of an organic substrate, dispersed in an aqueous continuous phase, with a specialized enzyme (e.g. a lipase) capable of working at the interface. For adopting such a system for efficient organic synthesis, a stable heterophase system with a large interfacial area is required. These prerequisites can be found in so-called miniemulsions. These liquid-liquid heterophase systems feature droplets with sizes smaller than 500 nm and, more important, in contrast to other heterophase systems diffusional degradation, the so-called Ostwald ripening, is suppressed in miniemulsions. Consequently, the droplets show long term stability even when reactions are conducted in the droplets. In this review, we will briefly discuss the physicochemical background of miniemulsions, provide a comprehensive overview over the enzymatically catalyzed reactions conducted in miniemulsion, and compare the most important features to conventional systems, as reverse micoremulsions, (macro)emulsions and solvent based systems.

Type of Paper: Article
Title: Biomimetic Catalysts for Oxidation of Lignin-like Compounds
Authors: Gustavo González-Riopedre, M. Isabel Fernández-García, Esther Gómez-Fórneas and Marcelino Maneiro
Affiliation: Departamento de Química Inorgánica, Facultade de Ciencias, Universidade de Santiago de Compostela, Lugo 27002, Spain
Abstract: Kraft pulp has to be bleached to eliminate the chromophoric structures which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for industry. Herein we report the synthesis and characterization of six manganese(III) complexes 1-6, incorporating dianionic hexadentate Schiff base ligands (H2L1-H2L4) and different anions. Complex 4, Mn2L22(H2O)2(DCA)2 was crystallographically characterised. Complexes 1-4 behave as more efficient mimics of peroxidase in contrast with 5-6. The catalytic studies for the use of these complexes as oxygen activators for the degradation of the lignin model compound veratrylalcohol have been studied. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratrylalcohol conversion to veratrylaldehyde have been achieved at room temperature in presence of air flow using 0.5 % of catalyst.

Type of Paper: Article
Title: Protein Dynamics as a function of Enzyme Kinetics probed by Spectro-Electrochemistry: Cytochrome c Oxidase from R. sphaeroides
Author: Renate Naumann
Affiliation: AIT （Austrian Institute of Technology） GmbH，1190 Vienna, Austria
Abstract: Electronic wiring of multi-redox center membrane proteins such as the cytochrome c oxidase (CcO) has been achieved by oriented immobilization on a conducting surface via his-tag technology. Immobilization is followed by reconstitution a protein-tethered bilayer lipid membrane. Electrochemical and FTIR spectroscopic investigations have been performed to investigate electron transfer kinetics into these proteins. Electrons are transferred to the first electron acceptor, CuA. A kinetic model has been established, which accounts for sequential electron exchange between redox centers of the CcO including protonation in the absence and presence of oxygen. On the basis of these model calculations, a mechanism of proton transport coupled to redox transitions is proposed. Moreover, fast-scan voltammetry data are analyzed as well as time-resolved Surface-Enhanced IR-Absorption Spectra (tr-SEIRAS) of the CcO.

Type of Paper: Article
Title: Lewis acid Properties of Cr, Fe and Co Porphyrin Analogues Embedded in Graphene—The 18 Electron Rule Revisited
Author: Itai Panas and Michael Busch
Affiliation: Department of Chemistry and Biotechnology, Chalmers University of Technology, Gothenburg, Sweden
Abstract: Graphene promises to serve as technological platform in electronic industry. This effort concerns potential utilization of this platform e.g., as a gas sensor or as an electrocatalyst. In both cases a necessary prerequisite, besides the innate nearly ideal conductivity, is the integration of catalytic sites with the graphene structure. Two ways may be thought of. One is to achieve this during synthesis, and the second is by post-treatment, which in turn would involve several steps. Firstly, one would create well-defined vacancies by effectively removing acetylide units, leaving behind tetradendate sites. This could be achieved by careful oxidation e.g., by H2O2(aq) producing epoxides, which upon subsequent heating would detach as CO(g). The resulting site displays high affinity even to N2. By repeating the soft oxidation and subsequent nitrogenation, it would in principle be possible to nucleate the nitrogens at tetradentate sites thus arriving at the porphyrin structural analog. The affinities of these sites to neutral Cr, Fe, and Co atoms are quantified. The Lewis acid properties of the resulting metal sites are arrived at by analyzing the metal associated LUMO:s as SOMO:s, as well as by adsorbing CO and NO. The results are rationalized in terms of the well-known 18 electron rule.

pe of Paper: Article

Title: Lewis acid Properties of Cr, Fe and Co Porphyrin Analogues Embedded in Graphene—The 18 Electron Rule Revisited

Author: Itai Panas and Michael Busch

Affiliation: Department of Chemistry and Biotechnology, Chalmers University of Technology, Gothenburg, Sweden

Abstract: Graphene promises to serve as technological platform in electronic industry. This effort concerns potential utilization of this platform e.g., as a gas sensor or as an electrocatalyst. In both cases a necessary prerequisite, besides the innate nearly ideal conductivity, is the integration of catalytic sites with the graphene structure. Two ways may be thought of. One is to achieve this during synthesis, and the second is by post-treatment, which in turn would involve several steps. Firstly, one would create well-defined vacancies by effectively removing acetylide units, leaving behind tetradendate sites. This could be achieved by careful oxidation e.g., by H2O2(aq) producing epoxides, which upon subsequent heating would detach as CO(g). The resulting site displays high affinity even to N2. By repeating the soft oxidation and subsequent nitrogenation, it would in principle be possible to nucleate the nitrogens at tetradentate sites thus arriving at the porphyrin structural analog. The affinities of these sites to neutral Cr, Fe, and Co atoms are quantified. The Lewis acid properties of the resulting metal sites are arrived at by analyzing the metal associated LUMO:s as SOMO:s, as well as by adsorbing CO and NO. The results are rationalized in terms of the well-known 18 electron rule.