## 4 Discussion
From the approach proposed for the analysis of terahertz spectra, a number of parameters were obtained (Table 1), and for some of them the HD Abs to IFN-\(\gamma\) statistically significantly differs from the control solutions. This fact indicates the high sensitivity and informative value of the proposed THz-TDS-based approach for analyzing this class of solutions. In order to give an interpretation of the differences shown in this study, consideration should be given to the meaning of each band included into model (3). The relaxation band in the spectra reflects the Debye relaxation of water molecules in solution. This band is described by two parameters: relaxation time \(\tau\) and amplitude \(\Delta\varepsilon\). The parameter \(\tau\) determines specific time of finding a water molecule in the bound state between the moments of hydrogen bond disruption and molecule reorientation. The parameter \(\Delta\varepsilon\) reflects the contribution of the relaxation process to the total dielectric response. In this study, only \(\Delta\varepsilon\), and not the parameter \(\tau\) (it was fixed), was calculated in the fitting procedure. An increase of \(\tau\) (a shift of the band maximum to the low-frequency region of the spectrum) in the terahertz region was registered similarly to a decrease in the amplitude of \(\Delta\varepsilon\). In the investigated spectral range, both trends (an increase of \(\tau\) and a decrease of \(\Delta\varepsilon\)) are indistinguishable and indicate the same phenomenon: intensification of depolarization of water molecules in the solution, i.e., their enhanced binding. Therefore, in our model, the parameter \(\Delta\varepsilon\) alone is sufficient for describing the depolarization processes. The data in Table 1 show a statistically significant decrease in \(\Delta\varepsilon\) for the HD Abs to IFN-\(\gamma\) in comparison to both controls, suggesting an increased binding of water molecules in this solution. This conclusion is also supported by a statistically significant reduction in the frequency \(2\
u_{\max}\) obtained by IR spectroscopy in the HD Abs to IFN-\(\gamma\) as compared to both controls (Table 2). As is known [57], a decrease in the frequency of intramolecular stretching vibrations indicates an increase in the intermolecular binding of water molecules in the solution. A statistically significant decrease was observed in the resonant frequency of translational oscillations \(\omega_{1}\) in the spectrum of the solution of lactose saturated with the HD Abs to IFN-\(\gamma\) (Table 1) as compared to both controls. The indicated difference in \(\omega_{1}\), when considered separately, can be interpreted as weakening of bonds between water molecules in the studied solution and, at first sight, this conclusion is in contradiction with the previous assumption. However, this apparent contradiction is resolved by taking into consideration the established differences in the parameters of the widths of the transmission bands \(\gamma_{1}\) and \(\gamma_{2}\), which will be described below. A statistically significant increase in the values of \(\gamma_{1}\), \(\gamma_{2}\) in the HD Abs to IFN-\(\gamma\), as compared to both controls, indicates a broadening of energy distributions of intermolecular (hydrogen) bonds in this solution. Importantly, the parallelism of this broadening tendency in the two transmission bands strengthens the reliability of this conclusion. Regarding the apparent contradiction between the two conclusions mentioned above, in HD Abs to IFN-\(\gamma\), intermolecular hydrogen bonds are strengthened, as evidenced by the decrease in \(\Delta\varepsilon\); moreover. The weakening of intermolecular hydrogen bonds can also be recorded which is indicated by a decrease in \(\omega_{1}\). This issue is resolved when taking into account the registered broadening of energy distributions of intermolecular hydrogen bonds in the HD Abs to IFN-\(\gamma\).