Development of high performance photoelastic modulator and its application to measurements of solid-state circular dichroism

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(1)Improvement of photoelastic modulator (PEM) driverPEM driver, which is optimized to have highest driving efficiency by means of phase-locked loop technique, was improved to have a wide range of driving frequency.(2)Development of thin PEM headsNovel thin PEM heads were made to minimize residual birefringence in the optical element of PEM head which results in artifact signals in solid-state CD measurements. The thickness of the conventional PEM head had been 6.4 mm from the birth of Schnattery type PEM. The thicknesses of novel PEM heads are 2, 3, and 4 mm. The values of R in the electrical equivalent circuit of PEM head are quite low compared with conventional ones.(3)In situ measurement of CD of DNA adsorbing onto a solid surfaceThe adsorption process of DNA dissolved in aqueous solutions onto the surface of polyethyleneimine (PEI) has been examined by the observation of in situ CD, including time-resolved measurements, to elucidate the conformation of DNA at the liquid/solid interface. The adsorption process can be characterized by two stages that are characterized in terms of CD. In the first stage, time (t) <700s, a slight change in the time-resolved CD spectra of DNA is observed, whereas in the second stage, t>700s, where no further adsorption occurs, a change in the induced CD as well as in the CD of DNA is observed.(4)Structural investigation of Poly(ε-lysine) (PL)by solid state-CD measurements.The conformation of microbial PL was estimated by means of solid-state CD measurements. The CD measurements were done by using artifact-free technique for the PL films obtained by casting the aqueous solution with various pH onto a glass plate.