Department of Chemistry Seminar Announcement

Date/Time/Venue

Title/Speaker

20 Jan (Thu)10am – 11am

@ S8 Level 3 Executive Classroom

Directed Assembly of CDirected Assembly of C44-Symmetric -Symmetric Vanadate-Centered Quadruplexes: Vanadate-Centered Quadruplexes: Synergistic Ion-specific Transport Synergistic Ion-specific Transport and Asymmetric Catalysisand Asymmetric Catalysis

Professor Chen Chien-TienNational Tsing Hua University, TaiwanHost : Asst Prof Huynh Han Vinh

About the Speaker Professor Chen Chien-Tien, b 1964 in Taipei, Taiwan. National Tsing-Hua Univ. (BS 1986; MS 1988), Univ. of Illinois at Urbana-Champaign (Ph.D. 1994, Prof. S. Denmark), Scripps Research Institute (Postdoc. 1995, Prof. B. Sharpless) Associate Prof. (1995), Professor (2000-), Research Chair of NTNU (2008-2009), Distinguished Professor of NTHU (2010-). Research filed: (synergistic) asymmetric catalysis, organic optoelectronic materials and LC-based optical switches, DNA photocleavages, and nanoparticle-encapsulated dendritic probes, directed assembly for synergistic ion-specific transport.

Abstract

All are Welcome

We have developed a series of N-Salicylidene-based L-a-amino acids as chiral auxiliaries for chiral vanadyl(V) methoxide complex synthesis. These configurationally well-defined complexes have been examined for kinetic resolution of 2o alcohols. They serve as efficient and highly enantioselective catalysts for asymmetric aerobic oxidation of a-hydroxy acid, phosphonic acid, and ketone derivatives at ambient temperature. The asymmetric inductions of the oxidation process are in the range of 50 - > 500 in terms of selectivity factors (krel) in most instances. X-ray crystallographic analysis of an adduct between N-benzyl-mandelamide and the catalyst allows for probing the origin of the nearly exclusive asymmetric control in the oxidation process. In the case of the 3,5-di-tert-butyl and 3,5-dihalo- substituted analogs, pentanuclear C4-symmetric complexes were formed when potassium salts were employed instead of the corresponding sodium salts. The complexes work synergistically in the asymmetric aerobic oxidations of various racemic a-hydroxy acid and ketone derivatives with excellent selectivity factors. A directed assembly process to form C4-symmetric, vanadate-centered helical quadruplexes, for the first time, from a given chiral oxidovanadium(V) complex allows for highly efficient K+-, Ag+, Ba2+, Pb2+, Hg2+, and (chiral) ammonium ion-specific transports from aqueous phase into organic solvents, reminiscent of the K+ specific transport exerted by four homochiral glycine residues of the opening site in KcsA membrane protein.

References:

(a) Weng, S.-S.; Shen, M.-W.; Kao, J.-Q.; Munot, Y. S.; Chen, C.-T. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 3522. (b) Pawar, V. D.; Weng, S.-S.; Bettigeri, S.; Kao, J.-Q.; Chen, C.-T. J. Am. Chem. Soc. 2006, 128, 6308. (c) Chen, C.-T. and Lee, W.-Z. J. Org. Chem. 2007, 72, 8175. (d) Chen, C.-T.; Lin, Y.-H.; Kuo, T.-S. J. Am. Chem. Soc. 2008, 130, 12843. (e) Lee, W.-Z. and Chen, C.-T. et al. Organometallics 2009, 28, 652. (f) C.-T. Chen, J.-Q. Kao, S. B. Salunke, Y.-H. Lin; Organic Lett. 2010, 12, on web (Dec. 6).