ヘテロダイン検出キラル和周波発生による界面におけるたんぱく質の二次構造の解明

科学研究費助成事業 研究成果報告書：若手研究(B)2015-2016課題番号 : 15K1780

Chirality Discriminated by Heterodyne-Detected Vibrational Sum Frequency Generation

We first demonstrated chiral vibrational sum frequency generation (VSFG) in the heterodyne detection, which enables us to uniquely determine chiral second-order nonlinear susceptibility consisting of phase and amplitude and distinguish molecular chirality with high sensitivity. Liquid limonene was measured to evaluate the heterodyne-detected chiral VSFG developed in this study. <i>R</i>-(+)- and <i>S</i>-(−)-limonene showed clearly opposite signs in the complex spectra of the second-order nonlinear susceptibility in the CH stretching region. This is the first report of the chiral distinction by VSFG without any a priori knowledge about chiral and achiral spectral response. Furthermore, from the phase of the chiral VSFG field measured in the heterodyne detection, the origin of the chiral signal was ascribed to the bulk limonene. The heterodyne detection also improves detection limits significantly, allowing us to observe weak chiral signals in reflection. The heterodyne-detected chiral VSFG can provide information on absolute molecular configuration

Heterodyne-Detected Achiral and Chiral Vibrational Sum Frequency Generation of Proteins at Air/Water Interface

We present complex achiral and chiral vibrational sum frequency generation (VSFG) spectra at the air/water interface of protein solutions by using heterodyne-detected VSFG. Bovine serum albumin, pepsin, concanavalin A, and α-chymotrypsin were measured as model proteins. The obtained achiral Im­[χ⁽²⁾] spectra gave us insights into the molecular orientation of protein molecules and water at the interface. From the chiral Im­[χ⁽²⁾] spectra in the NH stretching and amide I regions, the secondary structures of the interfacial proteins were deduced. We attributed the chiral signals in the amide I and NH stretching regions to the interface on the basis of the phase of the signals. All the achiral and chiral spectra in each region showed the same sign despite different secondary-structure contents of the examined proteins. Real-time observation of the spectral change of α-chymotrypsin was also performed by heterodyne-detected chiral VSFG. The signal intensity of the chiral Im­[χ⁽²⁾] spectra in the NH stretching and amide I regions decreased on the scale of 10 min, originating from the decrease of the portion of antiparallel β-sheet conformation in the molecule. The conformational change occurred not in the bulk but at the interface. Heterodyne-detected achiral and chiral VSFG are capable of addressing the molecular orientation and conformation of proteins at air/water interfaces

Sensitive and Quantitative Probe of Molecular Chirality with Heterodyne-Detected Doubly Resonant Sum Frequency Generation Spectroscopy

Heterodyne-detected vibrationally electronically doubly resonant chiral sum frequency generation (HD-DR chiral SFG) spectroscopy has been developed for the study of chiral molecules with chromophores. The method enables us to detect and distinguish chiral molecules with high sensitivity and to obtain information on molecular vibrations. Strong enhancement due to the electronic resonance improves the sensitivity, and heterodyne detection ensures that the signal intensity is linear to the sample concentration. Detection of HD-DR chiral SFG signal from a dilute solution of binaphthol with 20 mM concentration and tens of nanometers thickness was demonstrated. Taking advantage of the enantiomer-dependent sign and linearity of the signal to the concentration, molecular concentrations and enantiomeric excesses were accurately evaluated. HD-DR chiral SFG is expected to have widespread application in the study of molecular chirality of thin films or samples of a very small quantity

Hyperspectral coherent Raman imaging – principle, theory, instrumentation, and applications to life sciences

International audienceCoherent Raman scattering microscopy such as coherent anti-Stokes Raman scattering and stimulated Raman scattering microscopy boosts the weak Raman signal and enables us to perform label-free visualization of the molecular distribution and its dynamical behavior in living cells and tissues with high speed. In comparison with fluorescence imaging, cells and tissues can be visualized without specifying the target molecule. In this review, we describe the characteristics of a hyperspectral coherent Raman imaging method, which is capable of acquiring both spectra and images simultaneously, and review applications to life sciences. Copyright © 2015 John Wiley & Sons, Ltd