Increasing antimicrobial and non-hemotoxic characteristics of polymers bearing thiazole and triazole groups by the appropriate selection of spacer and quaternization groups.
Two series of antimicrobial polymethacrylates (PMTAs) bearing mono and bis-cationic quaternary ammonium cations (QUATs) were prepared by controlled N-alkylation of 1,3-thiazole and 1,2,3-triazole pendant groups with butyl iodide (PMTAs-BuI). The degree of quaternization (DQ) of the azole heterocycles was monitored by (1)H NMR spectroscopy over a wide range of reaction times. Spectra analysis of the (1)H NMR aromatic region allowed to characterize and quantify the different species involved and, therefore, to control the chemical composition distribution of the amphiphilic polycations. The polymer charge density and the hydrodynamic sizes were measured by zeta potential and dynamic light scattering (DLS), respectively. Consequently, the relationship between structure and antibacterial properties and toxicity was studied. Interestingly, these polyelectrolytes present excellent selective toxicity against bacteria being nonhemolytic even at low values of DQ. Furthermore, they were also evaluated for their microbial time-killing efficiency, presenting a 3 log-reduction in only 15 min. Additionally, the bacteria cell morphology treated with PMTAs-BuI was analyzed.
A variety of cycloheptapyrane derivatives were prepared via Ni-catalyzed formal [8+3] cycloaddition of tropones with 1,1-cyclopropanediesters. The asymmetric version of the process can be achieved using either an enantiomerically enriched cyclopropane as the starting material or a racemic cyclopropane and a chiral Lewis acid.
Amphiphilic polymers are tunable systems to construct supramolecular hierarchically self-assembled structures. Six families of heterocyclic polymethacrylates (PMTAs) bearing 1,3-thiazole and 1,2,3-triazole pendant groups with alkyl and succinate spacers were chemically modified by quaternization reaction of the azole heterocycles with five alkylating agents (methyl, butyl, octyl, dodecyl, and hexadecyl iodide) leading to a library of 30 different amphiphilic poly(ionic liquid)s (PMTAs-RI). These polymers have been characterized in bulk by small-and wideangle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). Quaternization induces a dramatic effect (increase) on the glasstransition temperature T g , being strongest for methyl iodide members. Increasing the length of the quaternizing agent, plasticization is first observed, followed by a further increase of T g . This effect, together with evidence of a second T g and crystallization for the members with the longest quaternizing agents, could be attributed to the presence of well-developed alkyl nanodomains evidenced by the structural investigation. WAXS and SAXS results have been consistently interpreted by assuming nanostructuration driven by the amphiphilicity balance of poly(ionic liquid)s. The different morphologies revealed by SAXS have been characterized, assigning a plausible chemical nature to the phases involved in each case. The nonpolar fraction has been considered as the control parameter defining the main features of the achieved morphology. By increasing this parameter, structures ranging from hexagonally packed nonpolar cylinders in a polar matrix to the inverse situation have been found, passing through lamellar phases. Under some conditions, within the polar lamellae a third phase formed by cylinders of heterocycles has even been determined. We have checked the validity of the scenario proposed by comparing the sizes deduced from the SAXS analysis with the expected characteristic lengths of the associated moieties, inferring thereby how alkyl side groups arrange within the nanodomains. On the basis of the complete picture achieved, the type of nanostructures formed by this class of polymers can be predicted, if the chemical composition including the quaternization degree is known.
An efficient Cu(I)-catalyzed asymmetric [3 + 2] cycloaddition of N-(2-pyridylmethyl) imines has been developed. In the presence of a Cu(CH(3)CN)(4)PF(6)/bisoxazoline catalyst system, high levels of enantioselectivity (up to 97% ee) and moderate to high exo selectivity were achieved with a wide variety of substituted dipolarophiles, including maleimides, fumarates, fumarodinitrile, enones, and nitroalkenes. The reaction with unsymmetrically substituted dipolarophiles is completely regioselective.
Abstract:The aim of this work is the preparation of contact active antimicrobial films by blending copolymers with quaternary ammonium salts and polyacrylonitrile as matrix material. A series of copolymers based on acrylonitrile and methacrylic monomers with quaternizable groups were designed with the purpose of investigating the influence of their chemical and structural characteristics on the antimicrobial activity of these surfaces. The biocide activity of these systems was studied against different microorganisms, such as the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Pseudomona aeruginosa and the yeast Candida parapsilosis. The results confirmed that parameters such as flexibility and polarity of the antimicrobial polymers immobilized on the surfaces strongly affect the efficiency against microorganisms. In contrast to the behavior of copolymers in water solution, when they are tethered to the surface, the active cationic groups are less accessible and then, the mobility of the side chain is critical for a good contact with the microorganism. Blend films composed of copolymers with high positive charge density and chain mobility present up to a more than 99.999% killing efficiency against the studied microorganisms.
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