Fusae Kaneko

Natural Circular Dichroism Spectra of Alanine and Valine Films in Vacuum Ultraviolet Region

Natural circular dichroism (CD) of alanine (Ala) and valine (Val) films were measured in vacuum ultraviolet region using a polarizing undulator as a circularly polarized light source. Compared with absorption spectra, CD spectra showed clear differences between Ala and Val films. In order to explain these differences, a time-dependent density functional theory was applied to calculated CD spectra. The calculated CD spectra showed good agreement with the experimental CD spectra.

Chiroptical study of α-aliphatic amino acid films in the vacuum ultraviolet region.

A series of natural circular dichroism (CD) and absorption spectra for films of α-aliphatic amino acids--such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine, and isoleucine--in the vacuum ultraviolet (VUV) region were observed with the absolute values of optical constants at the undulator-based CD beamline TERAS BL5. Preliminary predictions of some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra were found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain--such as valine, leucine, and isoleucine--exhibit strong negative CD peaks in this energy region. In contrast, the corresponding CD peaks were weak or absent in the spectra of amino acids with straight alkyl groups. Our simple calculation, and the absorption spectra of alkanes, suggest that this difference partly originates from the contribution of the alkyl group. Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed; this is probably caused by the different molecular structures in each state. Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules.

Vacuum ultraviolet circular dichroism spectroscopy using an ac-modulated polarizing undulator

To obtain vacuum ultraviolet (VUV) circular dichroism (CD) measurements, an Onuki-type crossed undulator in an electron storage ring (TERAS) at the National Institute of Advanced Industrial Science and Technology (AIST) was used as a light source and a polarization modulator was used instead of a photoelastic modulator (PEM). Polarization modification through the beam-line optics was theoretically considered and experimentally examined by polarization analysis. The modulation frequency of 2Hz was chosen to optimize the signal-to-noise ratio. On this basis, VUV-CD spectra of alanine films were measured and calibrated. The resulting CD spectra were consistent with other data obtained that was measured by a conventional CD spectropolarimeter (JASCO, J720WI) at a wavelength range of 190–210nm. The spectra of L- and D-alanine films showed an obvious symmetry with respect to the baseline at a wavelength range of 120–210nm. These results proved that the true CD of the samples was measured. The present technique ...

First observation of natural circular dichroism spectra in the extreme ultraviolet region using a polarizing undulator-based optical system and its polarization characteristics.

Natural circular dichroism (CD) spectra in the extreme ultraviolet (EUV) region down to a wavelength of 80 nm have been observed for the first time, using an alanine thin film deposited on sodium salicylate coated glass as a sample. Calibrated EUV-CD spectra of L-alanine exhibited a large negative peak at around 120 nm and a positive CD signal below 90 nm, which were roughly predicted by theoretical calculations. A CD measurement system with an Onuki-type polarizing undulator was used to obtain the EUV-CD spectra. This CD system, the development of which took five years, can be used to observe even weak natural CD spectra. The polarization characteristics of this system were also evaluated in order to calibrate the recorded CD spectra.

Recent progress in vacuum-ultraviolet polarization modulation spectroscopy using polarizing undulator at the TERAS BL5 beamline

Polarization modulation spectroscopy using an Onuki-type undulator is a useful technique for circular dichroism study in the vacuum-ultraviolet region. We have been developing the vacuum-ultraviolet circular dichroism (vuv-CD) spectroscopy in TERAS BL5 beamline at AIST. This paper describes recent improvements in our instrumentation and methods of analysis to achieve precise and absolute measurements. The CD signal is usually accompanied by experimental artifacts, and elimination of all possible artifacts is the key issue for making reliable measurements. After improving beamline optical system, light flux monitor, and undulator operation method, the base line shift of the CD spectrum is suppressed less than 3x10(-4). Sample manipulation and data processing procedures are also described and absolute CD spectrum can be obtained even for linear anisotropic sample. These progresses lead to more quantitative comparison of experimental with calculation on vuv-CD spectrum.

Compact optical cell system for vacuum ultraviolet absorption and circular dichroism spectroscopy and its application to aqueous solution sample

We have designed a compact optical cell for studying the absorption and circular dichroism (CD) of a solution sample in the vacuum ultraviolet (VUV) region using a temperature control unit. The cell size was 34 mm in diameter and 14 mm in length. Such compactness was obtained by coating the VUV scintillator onto the outside of the back window. Because this scintillator converts the transmitted VUV light to visible light, the outside of this cell is operated under atmospheric pressure. The temperature of the sample solution was maintained in the range of 5 degrees C to 80 degrees C using a temperature control unit with a Peltier thermoelectric element. Changes in the sample temperature were observed by monitoring the absorption intensity of water. Through the study of VUV-CD spectra of ammonium camphor-10-sulfonate aqueous solutions and the transmitted spectrum of an empty cell, it was concluded that this cell unit has sufficient performance for use in VUV spectroscopy.