## 4 Conclusions  
Various substituents and, thus, different analytical and physicochemical properties of hybrid molecules containing an \(N\)-(substituted phenyl)-/\(N\)-diphenylmethylpiperazine privilegeed scaffold allowed for the modulation of their in vitro activity against several tuberculous and nontuberculous mycobacteria as well as a particular cancer cell line (HepG2). The absorption intensity increased slightly for the compounds containing bulky substituents with strong EW properties (**6e** and **6f**) as well as the molecule with a bulky diphenylmethyl moiety (**6g**). This behavior strongly influenced the increase in efficiency against both \(Mtb\) H\({}_{37}\)R\({}_{a}\) (\(r\) = 0.7909) and \(MS\) (\(r\) = 0.7798). The increased lipophilicity of analyzed salts led to higher efficiency against \(MM\) (\(r\) = 0.9128), \(MS\) (\(r\) = 0.8650), and \(MK\)_DSM_ (\(r\) = 0.8411) as well as \(Mtb\) H\({}_{37}\)R\({}_{a}\) (\(r\) = 0.8199). Higher lipophilicity of **6a-g** provided their stronger ability to reduce the in vitro viability of HepG2 cell populations to 50% of its maximum viability (\(r\) = 0.8320). The efficient anti-\(Mtb\) H\({}_{37}\)R\({}_{a}\) and anti-\(MM\) compounds (**6e** and **6g**) reduced in vitro the viability of given cells most effectively (IC\({}_{50}\) = 22.18 and 29.39 uM, respectively). The cytotoxic properties of all tested hybrid molecules were not connected significantly with their activity against \(MS\) (\(r\) = 0.5820) or \(MK\)_DSM_ (\(r\) = 0.5209). The calculated selectivity index (SI) values for the entire **6a-g** set (SI \(<\) 10.00) might be considered direct proof that eventual treatment of patients suffering from mycobacterial infections with the analyzed compounds or structurally similar drugs has to be conducted with care. These SI parameters clearly prevented the conclusion that the synthesized molecules, **6a-g**, were safe. In addition, current calculations indicated that risk of tachycardia or QT interval prolongation due to the activity of a basic form of **6g** could not be completely excluded. The proper selection of the substituents attached to the fundamental structural framework of screened substances will be decisive for the development of effective antimicrobial derivatives with a (notably) weakened ability to reduce the survival and growth of cancer cells or efficient anticancer agents. The following are available online at [[https://www.mdpi.com/article/10.3390/app12010300/s1](https://www.mdpi.com/article/10.3390/app12010300/s1)]([https://www.mdpi.com/article/10.3390/app12010300/s1](https://www.mdpi.com/article/10.3390/app12010300/s1)), Table S1: Retention times \(t_{\rm r}\) and lipophilicity indices log \(k\) (RP-HPLC) of **6a-g** determined in the mobile phases with a various volume ratio (\(v/v\)) of a methanol (MeOH) organic modifier and water, i.e., from 60:40 to 70:30; Table S2: Retention times \(t_{\rm r}\) and lipophilicity indices log \(k\) (RP-HPLC) of **6a-g** determined in the mobile phases with a various volume ratio (\(v/v\)) of a methanol (MeOH) organic modifier and water, i.e., from 75:25 to 90:10; Table S3: The prediction of probability for the bases (**5a-g**) to act as general pump inhibitors (\(I_{\rm GPI}\)) and membrane permeability inhibitors (\(I_{\rm MPI}\)) as well as drugs for the treatment of cancer-associated diseases (\(I_{\rm CADT}\)). The calculation of probability that these molecules might cause bradycardia (\(I_{\rm B}\)), palpitation (\(I_{\rm P}\)), tachycardia (\(I_{\rm T}\)), and prolongation of a QT interval (\(I_{\rm QTP}\)); Table S4: The selectivity index (SI) values of in vitro evaluated compounds **6a-g**, which were calculated as SI = IC\({}_{50}\) (in uM units)/MIC (in uM units). The IC\({}_{50}\)s indicated toxicity in human liver hepatocellular carcinoma (HepG2) cells, the MICs were determined against \(M\). _tuberculosis_ H\({}_{37}\)R\({}_{a}\) ATCC 25177 (\(Mtb\) H\({}_{37}\)R\({}_{a}\)), \(M\). _kansasii_ DSM 44162 (\(MK\) DSM), \(M\). _smegnatis_ ATCC 700084 (\(MS\)), and \(M\).