Photo-Modification of Melanin by a Mid-infrared Free-electron Laser.

Melanin is rigidly constructed by several nitrogen-containing aromatic rings, and its excess accumulation in skin tissue is closely associated with melanosis. Although visible lasers (wavelength: 600-1000 nm) are conventionally used for the photo-thermolysis of melanocyte, several pigmented nevi are difficult to be treated. Here, we propose an alternate method for targeting the molecular structure of melanin using an infrared free-electron laser (FEL) tuned to 5.8 µm that corresponds to the stretching vibrational mode of carboxylate group. A drastic morphological change on the black-colored surface of melanin powder was observed after the pulse irradiation with power energy of 500 mJ cm-2 , and the minimum irradiation time for damage to the morphology was 1.4 s. Analyses by mass spectroscopy, infrared spectroscopy, and 13 C-nuclear magnetic resonance implied that a pyrrole group was removed by the FEL irradiation. In addition, the FEL irradiation dispersed almost all of the melanoma cells from a culture solution without any influence on other ingredients in the medium, and one-cell analysis by infrared microscopy showed that the structure of melanoma could be substantially damaged by the irradiation. This study proposes the potency of intense mid-infrared laser as novel alternative way to reduce melanin.

Deuterium NMR study of molecular dynamics and phase transition in acetonitrile crystal.

The molecular dynamics and local structure in the alpha and beta phases of CD(3)CN were studied by (2)H NMR spectroscopy. From the (2)H NMR spin-lattice relaxation time (T(1)), the activation energies of the rotation of the CD(3) group about the C(3) axis in both phases were found to be 6.2 and 11 kJ mol(-1), respectively. These activation energy values suggest that the packing between CD(3)CN molecules in the alpha phase is weaker than that in the beta phase. The slow structural change of the crystal due to the alpha-beta phase transition was investigated using the (2)H NMR spectra and T(1). A jump of CH(3)CN between two neighboring sites in the hydrogen-bond network accompanying the molecular reorientation was observed by the (2)H NMR 2D exchange spectra and the stimulated-echo method in the alpha phase. Vacancy diffusion occurred in the one-dimensional hydrogen-bond network in the alpha phase.

Molecular dynamics in paramagnetic materials as studied by magic-angle spinning 2H NMR spectra.

A magic-angle spinning (MAS) 2H NMR experiment was applied to study the molecular motion in paramagnetic compounds. The temperature dependences of 2H MAS NMR spectra were measured for paramagnetic [M(H2O)6][SiF6] (M=Ni2+, Mn2+, Co2+) and diamagnetic [Zn(H2O)6][SiF6]. The paramagnetic compounds exhibited an asymmetric line shape in 2H MAS NMR spectra because of the electron-nuclear dipolar coupling. The drastic changes in the shape of spinning sideband patterns and in the line width of spinning sidebands due to the 180 degrees flip of water molecules and the reorientation of [M(H2O)6]2+ about its C3 axis were observed. In the paramagnetic compounds, paramagnetic spin-spin relaxation and anisotropic g-factor result in additional linebroadening of each of the spinning sidebands. The spectral simulation of MAS 2H NMR, including the effects of paramagnetic shift and anisotropic spin-spin relaxation due to electron-nuclear dipolar coupling and anisotropic g-factor, was performed for several molecular motions. Information about molecular motions in the dynamic range of 10(2) s(-1)