Hisako Urabe

Internal modes and local symmetry of PO4 tetrahedrons in KH2PO4 by Raman scattering

Abstract The internal mode Raman spectra of crystalline KH 2 PO 4 (KDP) have been observed above the transition temperature T c , and the local and momentary site symmetry of PO 4 tetrahedrons has been analysed to be C 2 , which is the symmetry of the tetrahedrons below T c . From this result, the mechanism of phase transition in this crystal has been concluded to be of the order-disorder type of distorted PO 4 tetrahedrons. It was a long-pending problem in KDP why the low-lying broad transverse mode (⪅ 150 cm -1 ) appears above T c in the x ( yx ) y spectrum. This has been assigned to the libration mode of the tetrahedrons observed owing to the broken selection rule due to the disordered structure.

Collective vibrational modes in molecular assembly of DNA and its application to biological systems. Low frequency Raman spectroscopy

The origin of low frequency modes in a molecular assembly of DNA has been investigated by changing the assembly conditions of DNA molecules. The ∼85 cm−1 broadband in B form DNA was found to be insensitive of the assembly condition, and was ascribed mainly to motions of base pairs bound with hydrogen bonds. The lowest frequency mode was found, on the contrary, to be sensitive to the assembly condition and therefore considered to include motions of backbone chains. Through the observation of the lowest frequency mode in B‐form DNA in biological systems such as lambda phage, chromatin and nucleosome core, we have concluded that from the dynamical point of view the DNA molecules in biological systems is more likely in a solid state than in an aqueous solution state.

Experimental evidence of collective vibrations in DNA double helix (Raman spectroscopy)

The collective vibrational motions in the solid DNA fiber have been found from the wave vector dependence of the low frequency Raman spectra. The main part of the low frequency modes have been assigned to the αxz(αyz) component of the Raman tensor from the polarized Raman spectroscopy.

Coupled dynamics between DNA double helix and hydrated water by low frequency Raman spectroscopy

Low frequency Raman spectra (±50 cm−1) of DNA gels from 0 to −140 °C have been obtained. A drastic spectral change near −20 °C has been observed, and this is well explained by the model of coupled dynamics between the collective vibrational mode of the DNA and the relaxational mode of the secondary hydration shell. The obtained relaxation time of the secondary hydration shell at 0 °C is τ≈4×10−12 s which is the same order as that of bulk water.

Raman spectral of low-lying longitudinal mode of KH2PO4 and KD2PO4 in ferroelectric phase

Abstract The origin of the low-lying modes of KH 2 PO 4 and KD 2 PO 4 in the ferroelectric phase has been clarified by the z(xy)z Raman scattering experiments. The “ S -mode”, which has been usually assigned to the proton tunneling mode in KH 2 PO 4 at T T c , has been found in the z(xy)z spectrum of KD 2 PO 4 in contrast to the x(xy)y spectrum. It has been found that the frequency of the “ S -mode” of KD 2 PO 4 is higher than that of KH 2 PO 4 . These results have shown that the “ S -mode” is far from the proton tunneling mode nor the proton/deuteron mode at all. From the present Raman spectroscopy, it is concluded that the “ S -mode” is assigned to the libration mode of the PO 4 tertahedrons.

Low Frequency Raman Spectra of DNA

The low frequency collective modes of DNA in aqueous solution have been observed by Raman spectroscopy. The broad response at ∼85 cm -1 disappears when DNA is thermally denatured. This fact indicates the existence of characteristic motion of the DNA double helix.

Counterion dependence of water of hydration in DNA gel

The cooling process of DNA gel (20 wt./wt.%–40 wt./wt.%) with various counterions has been investigated by low frequency Raman spectroscopy and differential scanning calorimetry (DSC). We have found that the dynamics of water of hydration is different among counterion species below 0 °C. For K‐, Rb‐, Sr‐, and Ba‐DNA gels, a part of nonfreezing water slowly changes its dynamical structure, when the gel is kept at ∼−30 °C after cooling below −50 °C. This relaxation process can be monitored both by the frequency increment of the lowest Raman band from ∼17 to ∼20 cm−1 and by the intensity increment of an extra endothermic peak in DSC heating curves. We propose that this relaxation process corresponds to the crystallization of a part of nonfreezing water and is caused by the rearrangement of the secondary hydrated water including counterions when the temperature is held at ∼−30 °C. This relaxation process cannot be observed for NH4‐ and Li‐DNA gels. For Na‐, Mg‐, and Ca‐DNA gels, this phenomenon is more compli...

Low-Lying B2(LO) Raman Spectra in Paraelectric KH2PO4

The temperature dependence of the low-lying pure longitudinal optical phonon mode of B 2 ( z ) symmetry in KDP has been observed by the backward Raman scattering. These B 2 (LO) spectra have the under-damped phonon peaks at about 110 cm -1 , which are almost temperature independent. This result strongly suggests that the low-lying broad response of y ( x y ) x Raman spectrum below ∼110 cm -1 is primarily the transverse optical phonon excitation.

Raman spectra and lattice dynamics of KH2PO4

Abstract The low-lying plateau response of the pure E (TO) Raman spectra in KH2PO4 (KDP) have been well explained by a simple coupled oscillator model, where the low-lying two TO phonon modes are coupled with highly damped O-H O motions of the hydrogen bonds. The low-lying pure B2 (LO) spectra have under-damped phonon peaks at about 110cm−1, which shows the existence of the pure TO phonon excitation below ∼110cm−1. The very low frequency Raman response of the B2 (TO) mode (≲20cm−1) has been found to increase drastically near the transition temperature. This central component of the Raman spectrum which had been neglected in the previous analyses plays the important role on the ferroelectric phase transition.

Raman‐active torsional vibrations in DNA molecule

Raman active torsional frequencies are calculated using the elastic constants of mitter et al..1 (AIP)