Orientation and conformation of amino acids in monolayers adsorbed at an oil/water interface as determined by vibrational sum-frequency spectroscopy

Vibrational sum-frequency spectroscopy has been employed to acquire vibrational spectra in the C-H stretching region of a variety of monolayers of amino acids adsorbed at the CCl4/aqueous interface. Analysis of the spectra combined with surface tension measurements has been utilized to determine orientational and conformational characteristics of the L-forms of phenylalanine, lysine, leucine, isoleucine, methionine, tryptophan, threonine, and tyrosine and the aromatic acid L-mandelic acid in monolayers at this interface. Spectra have been acquired under different polarization schemes to allow extraction of orientational and conformational information from spectral fits. The results demonstrate the ability to monitor the orientation of particular side chains in more complex molecules.