A new optical parametric amplifier based on lithium thioindate used for sum frequency generation vibrational spectroscopic studies of the amide I mode of an interfacial model peptide.
We describe a new optical parametric amplifier (OPA) that employs lithium thioindate, LiInS2 (LIS), to create tunable infrared light between 1500 cm(-1) and 2000 cm(-1). The OPA based on LIS described within provides intense infrared light with a good beam profile relative to similar OPAs built on silver gallium sulfide, AgGaS2 (AGS), or silver gallium selenide, AgGaSe2 (AGSe). We have used the new LIS OPA to perform surface-specific sum frequency generation (SFG) vibrational spectroscopy of the amide I vibrational mode of a model peptide at the hydrophobic deuterated polystyrene (d8-PS)-phosphate buffered saline interface. This model polypeptide (which is known to be an alpha-helix in the bulk solution under the high ionic strength conditions employed here) contains hydrophobic leucyl (L) residues and hydrophilic lysyl (K) residues, with sequence Ac-LKKLLKLLKKLLKL-NH2. The amide I mode at the d8-PS-buffer interface was found to be centered around 1655 cm(-1). This can be interpreted as the peptide having maintained its alpha-helical structure when adsorbed on the hydrophobic surface, although other interpretations are discussed.
York
Roger L
RL
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, USA.
Holinga
George J
GJ
Guyer
Dean R
DR
McCrea
Keith R
KR
Ward
Robert S
RS
Somorjai
Gabor A
GA
D000577:Amides / Q000737:chemistry*; D000669:Amplifiers, Electronic; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008094:Lithium / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D013057:Spectrum Analysis / Q000295:instrumentation*; D014732:Vibration
D000577:Amides; D010455:Peptides; D008094:Lithium