title: Probing water and biomolecules at the air-water interface with a broad bandwidth vibrational sum frequency generation spectrometer from 3800 to 900 cm(-1).
abstract: We have built a broad bandwidth vibrational sum frequency generation (VSFG) spectrometer that can provide high-quality spectra over the range of 3800 to 900 cm(-1). The spectrometer contains a commercial Ti:sapphire based 6 W regenerative amplifier as the master light source, a home-built pulse shaper to produce a narrow bandwidth 800 nm beam, a commercial optical parametric amplifier to generate a broad bandwidth femtosecond infrared (IR) pulse, and a detection system with a monochromator and a charge-coupled device (CCD). We applied this spectrometer to obtain VSFG spectra of a lipid monolayer at the air-water interface in the O-H stretching region (3800-3000 cm(-1)), the C-H stretching region (3100-2700 cm(-1)), the C-D stretching region (2300-2000 cm(-1)), the C=O stretching region (1800-1700 cm(-1)), and the PO(2)(-) symmetric stretching region (1200-1000 cm(-1)). We also obtained the VSFG spectrum of neat water in the O-H stretching region (3800-3000 cm(-1)) and the VSFG spectrum of a protein, alpha-synuclein, in the amide I region (1700-1600 cm(-1)) at the air-water interface. The spectrometer can provide a VSFG spectrum in the O-H stretching region (3800-3000 cm(-1)) without scanning the IR frequency. This feature will be useful in probing water dynamics at interfaces because the free OH and H-bonded OH can be investigated simultaneously. We have also provided instrumental details and discussed further improvements that should be beneficial to other researchers interested in setting up VSFG instrumentation.
authors.affiliation: Department of Chemistry, Yale University, New Haven, CT 06520, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Ma
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.forename: Li
authors.initials: L
authors.lastname: Fu
authors.forename: Elsa C Y
authors.initials: EC
authors.lastname: Yan
mesh_terms: D000388:Air; D002138:Calibration; D004867:Equipment Design; D008055:Lipids / Q000032:analysis*; D013055:Spectrophotometry, Infrared / Q000295:instrumentation* / Q000379:methods*; D013499:Surface Properties; D014732:Vibration; D014867:Water / Q000032:analysis*; D051844:alpha-Synuclein / Q000032:analysis*
chemical_list: D008055:Lipids; D051844:alpha-Synuclein; D014867:Water