ISBN: 978-83-60043-10-3 - eurobic9

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Eurobic9, 2-6 September, 2008, Wrocław, Poland P167. DNA-based Catalysis: Mechanism and Applications F. Rosati, A.J. Boersma, J. Klijn, B.L. Feringa and G. Roelfes Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands e-mail: F.Rosati@rug.nl, http:// roelfes.fmns.rug.nl DNA’s characteristic right-handed helical structure is one of the most elegant examples of chirality in nature. Due to its unique chiral architecture, it is an ideal scaffold for asymmetric catalysis. Previously, we have demonstrated that DNA can induce enantiomeric excess in the product of a reaction, i.e. a Diels-Alder reaction between an aza-chalcone and cyclopentadiene, by non-covalent binding of a catalytically active metal complex [1, 2]. A key aim is to gain insight into the structure of the active site generated by the DNA-bound complexes. Our current research efforts are directed towards the development of a tentative stereochemical model of this active site and a mechanistic study was performed with the aid of CD spectroscopy, in combination with other spectroscopic techniques (UV, EPR).The effect of DNA on the reaction rate was investigated, as well as the effect of different DNA sequences on the enantioselectivity. Additionally we are currently exploring other reactions using this novel catalytic concept. For example, incorporation of DNA-based catalysts into micellar aggregates has been investigated. References: [1] G. Roelfes & B.L. Feringa Angew. Chem. Int. Ed. 2005, 44, 3230-3232. [2] G. Roelfes, A.J. Boersma, B.L. Feringa Chem. Commun. 2006, 635-637. _____________________________________________________________________ 286
Eurobic9, 2-6 September, 2008, Wrocław, Poland P168. A Versatile Electronic Hole in One-electron Oxidized Ni II bissalicylidene Phenylenediamine Complexes O. Rotthaus a , O. Jarjayes a , C. Perez Del Valle b , C. Philouze a , F. Thomas a a Département de Chimie Moléculaire - Chimie Inorganique Redox Biomimétique (CIRE) – UMR-5250, Université Joseph Fourier, Grenoble, France e-mail: Fabrice.Thomas@ujf-grenoble.fr; Olivier.Jarjayes@ujf-grenoble.fr b Département de Chimie Moléculaire - Chimie Théorique – UMR-5250, Université Joseph Fourier, Grenoble, France. Phenoxyl radicals coordinated to divalent or trivalent metal ions are the focus of a considerable interest since the discovery of a Cu II -tyrosyl radical entity in the active site of Galactose Oxidase. Several Cu II -coordinated phenoxyl radicals have been characterized during the last decade in order to mimic the enzyme active site. Recently, nickel complexes of pro-phenoxyl ligands (the phenolate moiety is substituted by electron-donating groups) have emerged in literature. Compared to Cu II -phenoxyl complexes, they exhibit ligand and metal redox active orbitals closer in energy. Consequently, either Ni II -phenoxyl or Ni III -phenolate redox state are expected to be reached upon one-electron oxidation, making these compounds particularly interesting. We present in this poster a series of one-electron oxidized nickel salen complexes that exhibit a radical character with partial delocalization of the spin density onto the orbital of the nickel ion. We show that the degree of delocalization could be modulated by the electron-donating properties of phenolate para substituent R (Fig. 1-3). In addition, we found that it greatly influences the affinity of exogenous ligands for the metal, and thus the ability of the complexes to exhibit valence tautomerism properties (tetracoordinated Ni II -phenoxyl to octahedral Ni III - phenolate transformation in the presence of exogenous ligands). N Ni R O O R N R = t-Bu: 1 R = OMe: 2 R = NMe 2: 3 (R = NHMe 2 + : 3H2 2+ ) Figure 1 Formula of the neutral phenolate-nickel complexes dX'' dB 1 + 2 + 3 + g = 2.034 g = 2.017 g = 2.006 320 325 330 335 340 345 B / mT Figure 3 X-Band EPR spectra of CH2Cl2 solutions (anhydrous + 0.1 M TBAP) of 1 + (1mM), 2 + (0.5 mM) and 3 + (1 mM) at 233 K. Microwave Freq : 9.42 GHz, power: 20 mW, Mod. Freq: <strong>10</strong>0 KHz, Amp. 0.4 mT (1 + ), 0.05 mT (2 + , 3 + ). Figure 2 Optimized structures and calculated SOMO for 1 + , 2 + and 3 + ; The Mulliken contribution of the nickel orbitals (mainly the dyz) to the total spin density is indicated. _____________________________________________________________________ 287
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ISBN: 978-83-60043-10-3 - eurobic9

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