Antimicrobial V-Shaped Copper(II) Pentaiodide: Insights to Bonding Pattern and Susceptibility

Abstract

Antimicrobial resistance (AMR) is a major concern for the survival of mankind. COVID-19 accelerated another silent pandemic of AMR through the uncontrolled use of antibiotics and biocides. New generations of antimicrobial agents are needed to combat resistant pathogens. Crown ethers can be used as models for drug action because they are similar to antibiotics. Iodine is a well-known microbicide but is characterized by instability and short-term effectivity. Iodine can be stabilized in the form of polyiodides that have a rich topology but are dependent on their immediate surroundings. In addition, copper has been successfully used since the beginning of history as a biocidal agent. We, therefore, combined iodine and copper with the highly selective crown ether 1,4,7,10-tetraoxacyclododecane (12-crown-4). The morphology and composition of the new pentaiodide [Cu(12-crown-4)2]I5 was investigated. Its antimicrobial activities against a selection of 10 pathogens were studied. It was found that C. albicans WDCM 00054 is highly susceptible to [Cu(12-crown-4)2]I5. Additionally, the compound has good to intermediate antimicrobial activity against Gram-positive and Gram-negative bacilli. The chain-like pentaiodide structure is V-shaped and consists of iodine molecules with very short covalent bonds connected to triiodides by halogen bonding. The single crystal structure is arranged across the lattice fringes in the form of ribbons or honeycombs. The susceptibility of microorganisms towards polyiodides depends on polyiodide bonding patterns with halogen-, covalent-, and non-covalent bonding.

Thymol, a Monoterpenoid within Polymeric Iodophor Formulations and Their Antimicrobial Activities

“…The Raman examination of the formulation AV-PVP-Thymol-I2 depicted in Figure 5 validates the existence of polyiodide groups. The Raman spectrum is consistent with our earlier investigations [42,43,45,46,48,51]. The high-intensity absorption peak observed at 112 cm −1 signifies the presence of smart, linear, symmetric I3 − units accompanied by a minority of nonlinear, asymmetric triiodide ions.…”

“…However, the Raman spectrum reveals no indication of other iodine moieties. The absence of prominent absorption bands between 140 and 175 cm −1 , along with the lack of absorption around 166 cm −1 , definitively confirms the absence of I 5 − ions in AV-PVP-Thymol-I 2 like in the previous formulation AV-PVP-Thyme-I 2 (Figure 5, Table 1) [42,43,45,46,48]. Additionally, the Raman spectrum further validates the purity of the title compound.…”

“…The high-intensity absorption peak observed at 112 cm −1 signifies the presence of smart, linear, symmetric I 3 − units accompanied by a minority of nonlinear, asymmetric triiodide ions. The latter moieties are verified by a broad band between 141 and 148 cm −1 (Figure 5, Table 1) [20,29,38,42,43,45,46,48,51,83].…”

“…Within various molecular structures, iodine forms diverse moieties, including molecular iodine, iodide ions, triiodide, and higher polyiodide anions like pentaiodides and heptaiodides [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. Our previous investigations dealt with some of those polyiodide units within different molecular environments like 12-crown-4 or PVP, which impact their stability and antimicrobial activities [42][43][44][45][46][47][48][49][50][51][52][53]. Although triiodides [I 3 − ] are deemed the most stable form of polyiodides, they display several different structural subtypes with different stability [25,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]45,46,…”

“…AMR could be mitigated by utilizing combinations of plant bioactive compounds with or without diverse nanoparticles (NPs). Our research team explored iodine-based formulations comprising silver nanoparticles (AgNPs) and/or plant extracts previously [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. Among the materials employed in our investigations were iodophors with Aloe vera (AV) in combination with either Salvia officinalis L. (Sage), Cinnamomum zeylanicum (Cinn), or Thymus vulgaris L. (Thyme) [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56].…”