SCANNING TUNNELING MICROSCOPY STUDIES OF THE SYNTHETIC POLYPEPTIDE POLY (GAMMA-BENZYL-L-GLUTAMATE)

Scanning tunneling microscopy (STM) studies of the synthetic polypeptide poly(gamma-benzyl-L-glutamate) (PBLG) [-NH-CHR-CO-]n where R = CH2CH2COOCH2C6H5, are reported. These experiments are performed in air, and the molecules are imaged in the form of a thin liquid crystalline film cast from a dilute N,N-dimethylformamide (DMF) solution onto highly ordered pyrolytic graphite (HOPG). The images reported reveal both the helical molecular structure of the PBLG molecules and the highly organized nature of these films due to the strong hydrogen-bonding interactions between the biopolymers. Direct correlation of the image features observed with the STM and the three-dimensional structure of PBLG molecules is made using the molecular modeling program MacroModel and data from reported X-ray diffraction studies. Implications of the observed STM image features for future molecular imaging experiments are discussed.