**3. Biological activities**

It is known that the number of silver centers plays an important role in biological activity. The competence of the biological potential of silver (I) complexes is essentially influenced by the type of ligands bound to the metal centre. The presence of lipophilic groups such as alkyl chains on the NHC ligand enhances the lipophilic nature of the silver complex, which helps it penetrate the cell wall easily. The complexes have shown antibacterial activity to different extents, according to the type of ligand.

Benzimidazolium salts (**2a-j**) and Ag(I) complexes (**3a-j**) were tested against bacterial strains both Gram-positive and negative bacterial. As it was reported in the literatures [50–52], the DMSO did not exhibit any antimicrobial activity. The results are reported [27–31] in **Table 1**. Generally, all the Ag(I) complexes exhibited antibacterial activity against all bacterial strains except, the two compounds **3a** and **3i** were not active against Listeria monocytogenes. While all the benzimidazolium salts (**2a–j**) performed a good antibacterial potential against the test Gram-negative and positive strains and showed bacterial inhibition in the range 14 ± 0.5–36 ± 0.2 mm. There was rarely a difference in the antibacterial activity of benzimidazolium salts (**2a-j**) and Ag(I) complexes (**3a-j**) between all bacterial strains, except that with *Micrococcus luteus* strains, the tested compounds showed better antibacterial potential than others. The observed antibacterial activity of tested complexes is


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

#### **Table 1.**

*Zone of bacterial inhibition measured in mm of the synthesized salts and silver complexes [27–31].*


#### **Table 2.**

*Minimal bacterial inhibitory concentration measured in mg/mL of benzimidazoles salts and Ag(I) complexes [27–31].*

comparable to that of our previous silver complexes [53–55]. The MIC values of tested Ag(I) complexes and their starting material against *L. monocytogenes* ATCC 19117, *Salmonella Typhimurium* ATCC 14,028 and *M. luteus* are presented in **Table 2**.
