## 4 Discussion
Apparently, different parameters of the bands of terahertz spectra exhibit various sensitivity to the strengthening and weakening of intermolecular bonds. When the energy distributions of intermolecular bonds are broadened, more molecules emerge both with stronger and weaker intermolecular bonds. In this case, the amplitude \(\Delta\varepsilon\) as well as the frequency \(2\
u_{\max}\) show a stronger response to an increase in the energy of intermolecular bonds. Parameter \(\omega_{1}\), on the contrary, is to a higher extent contributed to by molecules with weakened intermolecular energy. Thus, the previously used different spectral parameters allow analyzing the process of structural changes in solutions from different perspectives. Various levels of sensitivity of these parameters to the strengthening and weakening of hydrogen bonds may be related to the difference in the transition dipole moments in different types of vibrations (intramolecular and intermolecular). This issue deserves a separate thorough study within the framework of the theory of vibrational spectroscopy; however, this aspect is beyond the scope of the present investigation. Regarding the parameters \(\Delta\epsilon\), \(\gamma_{1}\), \(\gamma_{2}\) and \(2\
u_{\rm max}\), for which statistically significant differences between the HD Abs to IFN-\(\gamma\) and the control solutions were found, no statistically significant differences between the control solutions were observed, which in general increases the validity of the techniques used for sample testing. At the same time, the parameter \(\omega_{1}\), which also differed between the control solutions, may be sensitive to minor changes in the solution state, i.e., a statistically significant difference in \(\omega_{2}\) between the controls may indicate a certain physicochemical modification of the control lactose sample after saturation with water-alcohol solution which is likely mediated by technological reasons. Considering this, it can be concluded that the THz-TDS method is capable of tracking even minor differences in lactose samples and, after establishing proper standards, can be used to control the quality of manufactured drugs based on highly diluted substances. It should be mentioned separately that the mathematical model for analysis of terahertz spectra proposed in this paper is not the only and ultimate one. It can be expanded and extended. For instance, other spectral bands from within the studied frequency range or beyond can be added for consideration, thereby expanding the set of parameters characterizing the analyzed system. Further developing this approach, one can add to the consideration the librational absorption band with a maximum of about 600 cm\({}^{-1}\)[47], reflecting the rotational vibrations of water molecules bound by hydrogen bonds. Also, more recently, attention has been paid to another relaxation band of about 20 cm\({}^{-1}\)[22; 54; 58], which can be considered as well. It is important to maintain a balance between the number of parameters taken into account and the stability of the fitting procedure, since too many parameters can, firstly, complicate calculations, and secondly, lead to ambiguities in the results obtained and difficulties in interpreting them. Using the described approach, we demonstrate that the THz-TDS method has advantages over the IR spectroscopy method traditionally used to analyze structural properties of water solutions [59; 60]. Terahertz spectroscopy, taking into account its location on the frequency scale, contains data on intermolecular dynamics in aqueous solutions. IR spectroscopy contains data on the intramolecular dynamics. At the same time, the intramolecular vibrations of the water molecule depend on the intermolecular binding of these molecules. This underlies an approach that allows us to evaluate the binding of water in various systems using IR spectra. That is, we can say that THz spectroscopy analyzes intermolecular characteristics directly, and IR spectroscopy does it indirectly.