We present a novel procedure for vibrationally resolved sum-frequency generation (SFG) in which a broad-bandwidth IR pulse is mixed with a narrow-bandwidth visible pulse. The resultant SFG spectrum is dispersed with a spectrograph and detected in parallel with a scientific-grade CCD detector, permitting rapid and high signal-to-noise ratio data acquisition over a 400-cm(-1) spectral region without scanning the IR frequency. Application to the study of a self-assembled monolayer of octadecanethiol is discussed.

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Surface second-harmonic generation (SHG) is recognized as a second-order non-linear laser-based spectroscopy offering good surface sensitivity and selectivity. With the goal of developing optical methods to study chiral surfaces, a way to detect dichroic behaviour in SHG in analogy to circular dichroism (CD) spectroscopy has been elucidated. The SHG efficiency from a monolayer of oriented chiral molecules [(R)or (S)-2,2'-dihydroxy-1,l'-binaphthyl (BN)] has a strong dependence upon whether the excitation beam has left-or right-handed circular polarization. The relative differential SHG signal is much larger than in ordinary CD spectroscopy.The large chiroptical effects in SHG are attributed not to R, the rotational strength responsible for traditional C D (R = Im p * m), but to the electric dipole-allowed second-order non-linear tensor, f 2 ) . There is a chiral element of x('), ;cxyz, that must be included in descriptions of the SHG

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The novel nonlinear optical method of second harmonic generation-circular dichroism (SHG-CD) has been used to follow the adsorption and redox properties of a peripheral membrane protein, horse heart cytochrome c, adsorbed at several model membrane surfaces. The SHG-CD response is shown to be affected by the oxidation state of the heme within surface-adsorbed cytochrome c, as is consistent with the sensitivity of SHG to the chirality of the heme. SHG-CD measurements show that adsorbed cytochrome c is reducible by ascorbate at alkanethiol surfaces, but not at phospholipid/alkanethiol hybrid bilayer membranes (HBMs). The adsorption of cytochrome c at the model membrane surfaces was verified by surface plasmon resonance. Surface-enhanced resonance Raman measurements show that cytochrome c adsorbed on a hybrid bilayer membrane retains the Fe-heme conformation associated with solution-phase cytochrome c and is reducible by applying potential to the supporting electrode. The inability of ascorbic acid to reduce cytochrome c associated with the HBM is attributed not to a change in its redox potential, but rather to the nature of the interaction of cytochrome c with the HBM.

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