Time-resolved infrared spectral measurements were made successfully for studying the microscopic mechanism of water-induced solid-state phase transitions of poly(ethylene imine) (PEI) in the hydration process at room temperature. The initial sample, obtained by cooling the melt under a dry atmosphere, showed the infrared spectra characteristic of the anhydrate phase consisting of doubly stranded helices. When this sample was exposed into an atmosphere of 100% relative humidity, the infrared spectra were found to change in a multistage mode from anhydrate to hemihydrate (molar ratio of ethylene imine unit/water ) 1/0.5) to sesquihydrate (1/1.5) and to dihydrate (1/2), where the molecular chains in the latter three phases take the planar-zigzag all-trans conformation and form the complexes with water through the hydrogen bonds. The spectral measurements were made also for heavy water (D 2O) as well as light water (H2O), and the quantitative analysis could be made more successfully for the former case, because the overlap of the polymer bands with water bands could be avoided due to the shift of the broad absorption bands of water molecules. A comparison was made for the strength of hydrogen bonds between PEI and PEI, PEI and water, and water and water. The infrared bands characteristic of the amorphous region could be detected in the frequency region of 1800-2500 cm -1 , the intensities of which were found to decrease in parallel to the crystal phase transition, indicating that some parts of the amorphous region can also crystallize into the hydrates in the hydration process.

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Thymine derivativeshaving long alkyl chain showed a very high photoreactivity in a single crystal and gave only one isomer of photodimer while the photodimerization in solution gave the four isomers. The crystal structure determined by X-ray diffraction method suggested the formation of the traps-syn or cis-anti photodimer.The photodimer obtained, however, was identified as the trans-anti isomer from the NMR spectrum. It was concluded that the trans-anti photodimer was formed by disrotatory motion of the thymine in the crystal.

Oligonucleotide-based DNA microarrays are becoming increasingly useful tools for the analysis of gene expression and single nucleotide polymorphisms (SNPs). Here, we present a method that permits the manufacture of microarrays from non-modified oligonucleotides on a poly carbodiimide-coated glass surface by UV-irradiation. The use of UV-irradiation facilitates an increase in the level of signal intensity, but it does not affect signal discrimination by the oligonucleotides immobilized on the surface. The signal intensity obtained for an array fabricated using non-modified oligonucleotides with UV-irradiation is approximately 7-fold greater than that without UV-irradiation. The detection of SNPs was tested to ascertain whether this technique could discriminate specific hybridization signals without causing significant UV-irradiation-induced damage to the immobilized oligonucleotides. We found that this immobilization method provides greater hybridization signals and a better match/mismatch ratio of SNPs than do the established aminosilane techniques. Application of this technology to manufacturing DNA microarrays for sequence analysis is discussed.

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