Synchrotron Microscopic Fourier Transform Infrared Spectroscopy Analyses of Biogenic Guanine Crystals Along Axes of Easy Magnetization

Our previous study remained a question why biogenic guanine crystals that cause magnetic orientation under magnetic fields scattered light so intensively. In addition, the magnetic orientation analyses indicated that the crystal plate has primal and second axes of easy magnetization by diamagnetism, by which two-stage orientation of the crystal is caused. This paper aims to reveal the molecule arrangement inside the guanine crystal, which is related to optical and magnetic anisotropy. A transient light scattering increase from the guanine crystals that occurs with increasing and decreasing magnetic fields between 0 and 0.5 T was measured. The results indicate that the biogenic guanine crystal plates have a specific direction to scatter the light incidence. In the next, molecular vibrations in a single-crystal plate were investigated by utilizing the synchrotron microscopic Fourier transform infrared (FTIR) spectroscopy, and the obtained spectrum compared with that in magnetically oriented guanine crystal. The FTIR and attenuated total reflectance measurements reproducibly observed the IR absorbance spectrum peak appearance and disappearance when the polarization direction was set parallel and perpendicular to the morphological length of a biogenic guanine crystal. It is speculated that spectrum peak appearance and disappearance were caused by vibration of C = O bonds and N-H bonds in guanine crystal for polarization direction. In conclusion, we revealed that the surface and inside of biogenic guanine crystal possessed the anisotropy for molecule orientation related to optical and magnetic property.