Photonics Research Institute (PRI) of the National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, has achieved the world-first success in putting CD measurement for determining 3D structures of bio-polymers such as protein and its constituents, amino acids, into practical application in the region of vacuum ultraviolet (VUV) of wavelengths shorter than 140nm ( 1nm = a billionth of meter) in collaboration with Kobe University. This is an epoch-making accomplishment based on synchrotron radiation from AIST’s original AC modulated polarizing undulator.
The new technique has made it possible to measure CD in the VUV region, and is expected to contribute to determination of 3D structures of bio-polymers and acceleration of the development of chiral medical drug to eliminate drug-induced suffering.
Circular Dichroism for 3D Structure Analysis of Bio-Polymers
Circular dichroism is an optical measuring technique based on difference in polarization responses among different bio-polymer species. CD is caused by difference in response to left- and right-handed circular polarization depending on molecular structures, and exhibits spectra highly sensitive to 3D structure of bio-polymers. The CD and the X-ray crystallography constitute important means for non-empirical determination of bio-polymer structures.
In practice, 3D structures of many bio-polymers have been determined by CD. At present, CD is applicable only to infrared, visible and ultraviolet regions. If the coverage could be extended to vacuum ultraviolet region, more detailed structures of bio-polymer would be revealed, and structural information hitherto unavailable would be obtained.
High Sensitivity CD Analysis Extended to VUV Region Shorter than 140nm
Commercially available CD spectropolarimeter using mercury or xenon lamp as light source have a coverage to 190nm wavelength. Recently, efforts have been paid to the extension of CD measurement to vacuum ultraviolet through the combination of synchrotron radiation with polarizing modulator, and SOR facilities in the world have embarked on the race for developing CD technology in VUV.
The conventional method using transmission type calcium fluoride or magnesium fluoride as polarizing modulator could not measure at wavelengths shorter than 120nm in principle, and 140nm in practice.
The PRI-AIST has developed CD measuring technique by polarization modulation at the source, without using transmission type polarizing modulator, to extend the coverage to wavelengths shorter than 140nm.
VUV CD Spectrum at Wavelengths beyond Previous Limit with AC Modulated Undulator
AIST developed in 1986 AC modulated polarizing undulator (SOR device) by using a small-sized electron storage ring, TERAS based on an original concept. With this SOR device, the PRI-AIST developed CD technique for identifying 3D structure of amino acids. This technique enabled to extend the coverage to 130nm without using transmission type modulator. Since the TERAS can produce AC-modulated polarized radiation of wavelength as short as 40nm, it is expected to have CD measurement extended to 40nm.
VUV CD Promising 3D Structure and Reaction Process Analysis for Bio-Polymers, as well as Development of Chiral Medical Drugs
In order to fully understand the effectiveness of a medical drug, it is necessary to identify 3D structure of target molecule and that of drug molecule. The X-ray crystallography, mainstay method for structural analysis of bio-polymers requires preparing single crystal specimen and enormous computing time as the molecular size grows. On the other hand, the VUV CD method takes much less labor and time than the former. Moreover, the time course of changes in CD intensity at a particular wavelength may make it possible to trace the mechanism of drug action. In this way, the new technique is expected to contribute to elimination of drug-induced troubles and development of chiral medical drugs.
The present work was carried out at the AIST on the basis of assessment by the Atomic Energy Board and supported by the Test and Research Fund for Atomic Energy, Ministry of Education, Culture, Sports, Science and Technology (MEXT).