**6. Biological, cytotoxic and antibacterial activities**

All the synthesized benzimidazolium salts (**4a**-**4j**) and their corresponding Ag(I) complexes (**5a**-**5j**) were investigated for antibacterial against the gram (+)/(−) bacteria. The DMSO did not exhibit any antimicrobial activity as reported earlier [61–73].

All tested compounds exhibited antibacterial activities against all bacteria strains. Compound **5i** was found the most effective in inhibiting the growth of the *Micrococcus luteus* LB 14110. Also, for compounds **5c**, **5 h** and **5f** showed excellent activities against the same bacteria strain. Moreover, NHC precursors (**4a–j**) were less active than corresponding silver complexes (**5a-5j**) against all bacteria strains. The complexes showed an increased antibacterial activity due to the synergistic effect that increases the lipophilicity of the complexes, which facilitates the penetration of the complexes through the cell's membrane.

#### **6.1 MIC determination**

The MIC values of tested silver complexes and their starting material against *Listeria monocytogenes* ATCC 19117, *Salmonella* Typhimurium ATCC 14028 and *M. luteus* are presented in **Table 4**.

The antimicrobial activity of compounds **4h**, **4i** and **5f** was also reported in terms of the MIC values, defined as the lowest concentration of an antimicrobial that visibly inhibits the growth of the bacteria after overnight incubation.

*Novel N-Heterocyclic Carbene Silver (I) Complexes: Synthesis, Structural Characterization… DOI: http://dx.doi.org/10.5772/intechopen.101950*


#### **Table 4.**

*Minimal bacterial inhibitory concentration (MIC) of benzimidazoles salts and Ag(I) complexes [27–31].*

As shown in **Table 4**, Silver complex **5f** showed better activity than ampicillin against *L. monocytogenes*, *Salmonella Typhimurium* and *M. luteus* with an MIC of 0.0058, 0.0034, and 0.0034 mg mL − 1, respectively. The NHC precursor **4i** gave a good result with an MIC of 0.041 mgmL−1 against *Salmonella Typhimurium.* The other compound performed poorly.
