Takakazu Nakabayashi

The liquid structure of acetic acid was studied experimentally and theoretically. Experimentally, the Raman spectra of acetic acid at various temperatures between 287 and 348 K were measured in the region 15−3700 cm-1. Theoretically, ab initio molecular orbital calculations were performed on the Raman activities of seven cluster species of acetic acid molecules. The Raman spectrum (in R(ν̄) representation) of crystalline acetic acid at 287 K shows six distinct bands in the 15−300 cm-1 region. Th

We have studied physiological parameters in a living cell using fluorescence lifetime imaging of endogenous chromophores. In this study, pH dependence of the fluorescence lifetime of flavin adenine dinucleotide (FAD), that is a significant cofactor exhibiting autofluorescence, has been investigated in buffer solution and in cells. The fluorescence lifetime of FAD remained unchanged with pH 5 to 9 in solution. However, the fluorescence lifetime in HeLa cells was found to decrease with increasing

Liquid-liquid phase separation (LLPS) plays an important role in a variety of biological processes and is also associated with protein aggregation in neurodegenerative diseases. Quantification of LLPS is necessary to elucidate the mechanism of LLPS and the subsequent aggregation process. In this study, we showed that ataxin-3, which is associated with Machado-Joseph disease, exhibits LLPS in an intracellular crowding environment mimicked by biopolymers, and proposed that a single droplet formed

We propose a label-free method for measuring intracellular temperature using a Raman image of a cell in the O-H stretching band. Raman spectra of cultured cells and the medium were first measured at various temperatures using a Raman microscope and the intensity ratio of the two regions of the O-H stretching band was calculated. The intensity ratio varies linearly with temperature in both the medium and cells, and the resulting calibration lines allow simultaneous visualization of both intracell

The vibrational relaxation process of trans-stilbene in the lowest electronically excited singlet state after photoexcitation has been studied by picosecond time-resolved anti-Stokes Raman spectroscopy using several pump and probe wavelengths. Measurements of pump wavelength dependency have shown that, when the molecules are excited by pump photons with a high excess vibrational energy (∼5200 cm-1), part of the excess vibrational energy remains localized in the olefinic CC stretching (ν7) and th

External electric field effects on state energy and photoexcitation dynamics have been examined for para-substituted and unsubstituted all-trans-diphenylpolyenes doped in a film, based on the steady-state and picosecond time-resolved measurements of the field effects on absorption and fluorescence. The substitution dependence of the electroabsorption spectra shows that the dipole moment of the substituted stilbene in the Franck-Condon excited state becomes larger with increasing difference betwe

Fluorescence decays of flavin adenine dinucleotide (FAD) that is a typical autofluorescent species in cells and tissues have been measured in a mixture of alcohol and water in the femtosecond and nanosecond time range. The fluorescence lifetimes of both the stacked conformation between the isoalloxazine and adenine moieties in close proximity and the extended open conformation in water are affected by the addition of alcohol. The nanosecond fluorescence lifetime of the open conformation increase

The local structures of acetic acid in protic and aprotic polar solvents have been studied by Raman spectroscopy and ab initio calculations with the self-consistent reaction field (SCRF) method. As acetic acid is diluted in water, the CO stretching Raman band of acetic acid becomes broader and shows a higher wavenumber shift from 1666 to 1710 cm-1, which arises from the generation of acetic acid microphases. In the region of 0.001 ≤ χA (acetic acid mole fraction) ≤ 0.2, both the peak position an

The vibrational relaxation process in the ground electronic state (S0) of canthaxanthin after internal conversion from the lowest excited electronic state (S1) to the S0 state is studied by picosecond time-resolved anti-Stokes Raman spectroscopy. The pump-induced intensities of two strong anti-Stokes Raman bands reach their maxima at delay time ∼12 ps from the pump pulse, and decay with a time constant of 15−20 ps. The peak position of the transient “in-phase” CC stretching anti-Stokes Raman ban

The effects of hydration on the dimerization energies and structures of acetic acid dimers are studied by the reference interaction site model self-consistent-field (RISM-SCF) method. Comparisons of the RISM-SCF results are also made with those obtained from the self-consistent reaction field (SCRF) methods to examine the dielectric effects of the solvent. The RISM-SCF method predicts the marked stabilization due to solvation in the dimer structures with large dipole moments. From the decomposit

Liquid-liquid phase separation (LLPS) is an important phenomenon in biology, and it is desirable to develop quantitative methods to analyze protein droplets generated by LLPS. This study quantified the change in protein concentration in a droplet in label-free and single-droplet conditions using Raman imaging and the Raman band of water as an intensity standard. Small changes in the protein concentration with variations in pH and salt concentration were observed, and it was shown that the concen

The picosecond anti-Stokes Raman spectra of trans-stilbene in the S1 state have been observed by using several probe wavelengths (580−670 nm) and a fixed pump wavelength giving a sufficient excess vibrational energy (≈5200 cm-1). The probe-wavelength dependency of the ratio of the anti-Stokes Raman-band intensity at 1180 cm-1 due to the C−Ph stretching (ν15) to that at 1570 cm-1 due to the olefinic CC stretching (ν7) is analyzed by assuming a model based on the Franck−Condon mechanism. It has be