ИСТИНА

Water plays a huge role in the functioning of biological systems and can be classified as a bulk and bound water [1]. Strongly or weakly bound water, as well as free (unbound) water, makes valuable but different contribution to the THz response of biological objects. The reason for the change in the THz response in biological samples is the transition of part of water from free to bound state and back. To interpret the results, we need to know precisely spectrum of bound water. Our measurements were performed using two THz-TDS spectrometers described previously [2, 3]. We measured the THz spectra of dry and wet glucose pressed into tablets. Then we added some water to these tablets and again measured the THz spectra. Water concentrations in glucose were varied from 0% to 30% (v/v). THz signal of free water starts to appear after 14-16% v/v water concentrations in glucose. Till 30% water concentrations glucose, free water and crystals coexists in this mixture, even phonon resonances are detectable. In THz absorption spectra we can recognize the contribution both free water (by strong dispersion below 0.2 THz) as well as glucose crystals with its own phonon spectra above 1.4 THz. We confirmed that the absorption of bound water is an order of magnitude less than that of free water.