Antimicrobial Hexaaquacopper(II) Complexes with Novel Polyiodide Chains

Abstract

The non-toxic inorganic antimicrobial agents iodine (I2) and copper (Cu) are interesting alternatives for biocidal applications. Iodine is broad-spectrum antimicrobial agent but its use is overshadowed by compound instability, uncontrolled iodine release and short-term effectiveness. These disadvantages can be reduced by forming complex-stabilized, polymeric polyiodides. In a facile, in-vitro synthesis we prepared the copper-pentaiodide complex [Cu(H2O)6(12-crown-4)5]I6 ´ 2I2, investigated its structure and antimicrobial properties. The chemical structure of the compound has been verified. We used agar well and disc-diffusion method assays against nine microbial reference strains in comparison to common antibiotics. The stable complex revealed excellent inhibition zones against C. albicans WDCM 00054, and strong antibacterial activities against several pathogens. [Cu(H2O)6(12-crown-4)5]I6 ´ 2I2 is a strong antimicrobial agent with an interesting crystal structure consisting of complexes located on an inversion center and surrounded by six 12-crown-4 molecules forming a cationic substructure. The six 12-crown-4 molecules form hydrogen bonds with the central Cu(H2O)6 . The anionic substructure is a halogen bonded polymer which is formed by formal I5− repetition units. The topology of this chain-type polyiodide is unique. The I5− repetition units can be understood as a triodide anion connected to two iodine molecules.

Facile Synthesis of Bio-Antimicrobials with “Smart” Triiodides

“…This results in the formation of PVP-I3 − complexes within the biohybrid: The two biohybrids AV-PVP-Sage and AV-PVP-Sage-I 2 absorb in the range between 200 to 450 nm (Figure 3). The iodinated formulation is dominated by absorption peaks of smart triiodides at 291 and 359 nm in compliance with our previous investigations (Figure 3a,b) [31,56,[59][60][61][62][63]72].…”

“…The very weak absorbance by iodine moieties in the UV-vis spectroscopic analysis confirms the same results (Figure 5, Table 2). Pentaiodide units are not available in our title compound because they usually appear around 137 to 147 cm −1 and 167 cm −1 [59,78,79]. Free iodine absorbs usually at 172 cm −1 , but is not available in free form in our biohybrid AV-PVP-Sage-I 2 (Figure 5, Table 2) [53,59,80,81].…”

“…Figure S1: Raman analysis full spectrum, Figure S2: FTIR spectrum of PVPI, Figure S3: FTIR spectrum of AV, Table S1. FTIR analysis [cm -1 ] AV-PVP-Sage-I 2 (1), AV-PVP-Sage (2), Sage extract [14], AV-PVP-I 2 (3) [31], AV-PVP-NaI (4) [31], PVP pure (5) [59,74] (cm −1 ).…”

“…This allows use of iodine in lower concentrations and eradicates the disadvantages of skin discoloration, skin irritation and uncontrolled iodine release [46][47][48]56]. The polyiodide structure also strongly depends on the surrounding atoms and can be stabilized by complexation [58][59][60][61][62][63][64]. Crown ether molecules like 12-crown-4 render stable polyiodide-structures, which can be used for antimicrobial applications [59][60][61][62][63].…”

“…The polyiodide structure also strongly depends on the surrounding atoms and can be stabilized by complexation [58][59][60][61][62][63][64]. Crown ether molecules like 12-crown-4 render stable polyiodide-structures, which can be used for antimicrobial applications [59][60][61][62][63]. Polymeriodine complexes are another alternative with many antimicrobial applications [47,[64][65][66][67][68][69][70][71][72].…”