## Results and Discussion
### Proton Dissociation Processes  
As expected, compounds **6a-h** have a poor aqueous solubility, according to UV-visible spectrophotometric titrations. This fact means that lower concentrations had to be used to monitor their proton dissociation processes, thus titrations were done under highly diluted conditions (10 \(\upmu\)M) in aqueous solution (containing 1% (_v/v_) EtOH). Compounds displayed absorption bands in the UV region mostly due to \(\uppi\)-\(\uppi^{*}\) transitions of the benzene ring and the pyrazole moiety. Representative UV spectra for **6a** are shown in Figure 2a. Deprotonation of the compounds resulted in characteristic spectral changes, namely the \(\uplambda_{\text{max}}\) was increased (Table 2) and the absorbance decreased upon this process. Notably, precipitate appeared while increasing the pH (from pH \(>\) 5) in all cases except the nitro derivative **6h** (pH \(>\) 3.5). Thus, spectra recorded in the pH range 1.8-5 (or 3.5) were used for the calculations. The changes revealed one deprotonation step in the studied pH range. Computed molar spectra for the HL\({}^{+}\) and L ligand species of 6a are shown in Figure 2b.  
Proton dissociation constants (pK\({}_{\text{a}}\)) were determined by the deconvolution of the measured spectra and are collected in Table 2. The determined pK\({}_{\text{a}}\) values are attributed to the pyrazole N\({}_{2}\)H\({}^{+}\) moiety, and its deprotonation results in the formation of the neutral L form with fairly limited solubility. The pK\({}_{\text{a}}\) values vary by the different substituents of the benzene ring. The methoxy (**6b**), methyl (**6c**), and fluorine groups (**6d**) resulted in similar or somewhat lower pK\({}_{\text{a}}\) value of the pyrazole nitrogen (Table 2, entries 2-4) compared with that of the reference compound **6a** (entry 1). On the other hand, the presence of the chloro (**6e**), promo (**6f**), cyano (**6g**) and nitro substituents (**6h**) decreased the pK\({}_{\text{a}}\) value significantly due to their strong electron-withdrawing effect (Table 2, entries 5-8).  
In summary, all steroidal heterocycles (**6a-h**) are neutral (L) at pH 7.4 based on the determined pK\({}_{\text{a}}\) values. Moreover, they are highly lipophilic and characterized by a poor water solubility. The lipophilic character and membrane permeability are important drug properties as they strongly affect the passage through biological membranes. Thus, we attempted to determine the logD\({}_{7.4}\) and permeability values by the traditional shake-flask method in _n_-octanol/H\({}_{2}\)O (buffered aqueous solution, pH 7.40) and by the parallel artificial membrane permeability assay (PAMPA), respectively. All these compounds were found to be so lipophilic that logD\({}_{7.4}\) and permeability data could not be obtained experimentally, since practically the total quantity of the compounds remained in the _n_-octanol phase after the partitioning, which hindered the concentration determination in the aqueous phase. Therefore, logD\({}_{7.4}\) values were estimated for the compounds by the means of the MarvinSketch software [31] (Table 2). The predicted logD\({}_{7.4}\) values indicated that the aforementioned compounds are strongly lipophilic, which should be accompanied by very good membrane permeability.