We observed low-frequency Raman spectra of tetragonal lysozyme crystals and DNA films, with varying water content of the samples. The spectra are fitted well by sums of relaxation modes and damped harmonic oscillators in the region from approximately 1 cm(-1) to 250 cm(-1). The relaxation modes are due to crystal water, and the distribution of relaxation times is determined. In wet samples, the relaxation time of a small part of the water molecules is a little longer than that of bulk water. The relaxation time of a considerable part of the crystal water, which belongs mainly to the secondary hydration shell, is an order of magnitude longer than that of bulk water. Furthermore, the relaxation time of some water molecules in the primary hydration shell of semidry samples is shorter than we expected. Thus we have shown that low-frequency Raman measurements combined with properly oriented samples can give specific information on the dynamics of hydration water in the ps range. On the other hand, we concluded, based on polarized Raman spectra of lysozyme crystals, that the damped oscillators correspond to essentially intramolecular vibrational modes.
SynopsisThe Raman spectra of poly(L-lysine) with various structures, ionized poly(L-glutamic acid), and deuterated N-methylacetamides have been observed using visible and the 257.3-nm laser lines as the light source. Most of the Raman bands with significantly enhanced intensities in the uv-excited spectra of the polymers have been assigned to the vibrations associated with the C=O and C-N stretching modes, the amide I, 11, 111, 1', 11', and 111', with reference to the results obtained for simple amide molecules including the deuterated N-methylacetamides. Several amide frequencies have been newly identified and the structures of the polymers have been discussed through the comparison of the Raman and ir amide frequencies.
Relative humidity induces the reversible crystal transition of guanosine between the dihydrate and the anhydrous state. The characteristics of the transition was investigated by means of X-ray powder diffraction analysis and high-resolution solid-state 13C NMR spectroscopy. Adsorption-desorption hysteresis was observed. Guanosine dihydrate (the H-state) which is crystallized from an aqueous solution rapidly loses crystal water below 10% relative humidity (rh), and is anhydrous at 0% rh (the A-state). The crystals gradually recover the H-state at approximate 20% rh. In the adsorption process between 10-20% rh, there exists one intermediate state, M, with 1.2-1.3 moles water per mole guanosine. The lattice of the M-state was determined to be orthorhombic with the cell parameters of a = 16.248(1), b = 11.603(1), and c = 13.643(2) A. The base-stacking structure is retained throughout the transition. On the other hand, conformational changes of the riboses and break of the hydrogen-bonding network between the bases would be induced in the A-state in conformity with lack of crystal water.
Two new thermally irreversible photochromic
(R)-binaphthol-condensed indolylfulgides (with a
1-(1,2-dimethyl-3-indolyl)-2-methylpropylidene group and with a
1-(1,2-dimethyl-3-indolyl)butylidene group, 6 and
7,
respectively) were synthesized. Because of rapid thermal
equilibration between the conformational isomers of
7E
at room temperature, photocyclization of a substantial portion of
7E occurred through (P)-7Eα to give
(9aS)-7C
selectively. On the other hand, as thermal equilibration requires
a long time for 6E at room temperature, its
photochromic interconversion occurs only between
(P)-6Eα and (9aS)-6C, and
the photocyclization-inert 6E remained
unchanged. The thermal stability and fatigue resistivity toward
the iterative photochromic interconversion of 7
have
been proved to be excellent among the fulgide derivatives. The
photochromic reactions were accompanied by large
changes of specific rotation values. The X-ray crystallographic
analysis of a visible-light-sensitive colored form,
(9aS)-6C, was carried out.
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