Macromolecule/Polymer-Iodine Complexes: An Update

Abstract

The great chemical affinity of molecular iodine towards several macromolecules and innumerable polymers allows the formation of macromolecule/polymer-iodine complexes, usually commensurate with the desired uses and applications. In many instances, the formation of such complexes occurs through a charge-transfer mechanism. The strength of the ensued complex is more accentuated by the presence of heteroatoms (nitrogen, oxygen, sulfur) and the π-conjugation induced moieties within the chemical structure of the polymer. A wide range of polymers with high specific surface areas and large total pore volumes are excellent candidates for iodine adsorption, suggesting their use in the removal of radioactive iodine in nuclear power plants. The recent results of iodine uptake by polysaccharides such as starch, chitin, chitosan, alginate, and cellulose are but novelties. Complexing vinyl polymers such as poly(N-vinyl-2-pyrrolidone), poly(vinyl pyridine), poly(vinyl alcohol), poly(vinyl chloride), poly(acrylonitrile), and polyacrylics, with molecular iodine revealed special chemistry, giving rise to polyiodide ions (In -) as the actual complexing agents. Carbon allotropes (graphene, graphene oxide, carbon nanotubes, amorphous carbons) and polyhydrocarbons are prone to interact with molecular iodine. The treatment of a broad set of polymers and macromolecules with molecular iodine is but a doping process that ends up with useful materials of enhanced properties such conductivity (electrical, ionic, thermal); in some cases, the obtained materials were of engineering applications. Complexation and doping materials with iodine are also aimed at ensuring the antimicrobial activity, particularly, for those intended for medical uses. In several cases, the impact of the iodine doping of polymer is the alteration of its morphology, as is the case of the disruption of the graphitic morphology of the graphene or graphene oxide.

Facile Synthesis of Bio-Antimicrobials with “Smart” Triiodides

“…with absorptions at 290, 305 and 359 nm in agreement with previous investigations [31,64]. The complexed triiodide ions are purely halogen bonded [I-I-I]-units within the polymer PVP-framework.…”

“…The region after 284 nm shows lower absorption in the three-day-old AV-PVP-Sage-I 2 sample compared to the same fresh sample (Figure 3b, Table 1). This result suggests the continued encapsulation of the triiodide moieties by hydrogen bonding through electrostatic attraction to the carbonyl groups of PVP according to Equation (1) [31,47,[64][65][66][67][68][69][70][71][72]…”

“…The release starts, when electrostatic interactions between the cell membrane of microorganisms lead to deformations of the complex, polymer compound [31,56,61]. The formula PVP-I 2 can be used interchangeably with PVP-I 3 − [31,47,[64][65][66][67][68][69][70][71][72]. The UV-vis spectrum of AV-PVP-Sage-I 2 shows absorption peaks of molecular iodine at around 205 nm [31,75,76].…”

“…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].…”

“…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]. Povidone-iodine, a combination between iodine and polyvinylpyrrolidone (PVP), is an example of a popular microbicide with anti-pathogenic effects even against resistant microorganisms [47,66,67].…”