1. Department of Chemistry Seminar Announcement Date/Time/VenueTitle/Speaker 27 Jan (Thu) 11am – 12nn @ S8 Level 3 Executive Classroom Effect of Highly Fluorinated Amino Acids on Secondary Structure Stability Assoc Professor Richard Ping Cheng National Taiwan University, Taiwan Host : Assoc Prof Tan Choon Hong About the Speaker All are Welcome Assoc Professor Richard Ping Cheng obtained his B.S. degree in chemistry from National Taiwan University in 1992. He then continued his graduate studies with Barbara Imperiali and Harry Gray at the California Institute of Technology and obtained his Ph.D. degree in 1998. He carried out his postdoctoral research as an NIH postdoctoral fellow at University of Pennsylvania School of Medicine with William DeGrado (1998-2002) and DuPont Central Research & Development with Mark Scialdone (1998 - 1999). He started his Abstract Highly fluorinated amino acids have been used to stabilize helical proteins, with limited studies on sheet-containing proteins. Here we will present the effect of these highly fluorinated amino acids on two protein secondary structures: alpha-helix and beta-sheet. Furthermore, we will present a three-step chemoenzymatic stereoselective gram-scale synthesis of fluorinated leucines. We will also show the effect of introducing fluorines on the hydrophobicity of the amino acids. The helix propensity was measured using Ala-based peptides, whereas the effect on beta-sheet stability was measured using protein G B1 domain (GB1). Various amino acids were studied including 5,5,5,5’,5’,5’-hexafluroleucine, 5,5,5’,5’-tetrafluoroleucine, pentafluorophenylalanine, leucine, phenylalanine, and alanine. The peptides and proteins were synthesized by solid phase peptide synthesis. The hydrophobicity of the amino acids were measured by thin layer chromatography under neutral and acidic conditions. The Rf values were used to derive the logarithm of the partition coefficient (logP) as a gauge for hydrophobicity. The circular dichroism spectra of the Ala-based peptides were used to derive the helix propensity. Thermal denaturation of GB1 derivatives were monitored by circular dichroism spectroscopy and used to explore the effect on sheet stability. In general, complete fluorination of the methyl or phenyl groups resulted in increase in hydrophobicity; partial fluorination of these groups led to decrease in hydrophobicity. Helix propensity decreased significantly upon fluorination. In contrast, sheet stability increased upon introducing the fluorines. Therefore, highly fluorinated amino acids may be more suitable for stabilizing beta- sheets in sheet-containing proteins compared to helical proteins. independent career as the Jere Solo Assistant Professor of Medicinal and Organic Chemistry at the State University of New York at Buffalo in 2002. In 2008, he moved to the Department of Chemistry, National Taiwan University, as an Associate Professor. His research interests include the synthesis, characteristics, and application of non-natural amino acids.