Highly effective antimicrobial nanocomposites based on hydrogel matrix and silver nanoparticles: long-lasting bactericidal and bacteriostatic effects.

Antimicrobial nanocomposites (NCs) are being used as an alternative antibacterial therapy for killing antibiotic-resistant pathogenic bacteria. The NCs are made of Ag nanoparticles (AgNPs) inside biocompatible hydrogel matrixes. The NCs were synthesized by the absorption of AgNO3 solution into a hydrogel matrix, followed by UV light irradiation, without using additional toxic reactants. The hydrogels used as matrixes are based on N-isopropylacrylamide (NIPAM) and copolymers with different functional groups: 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-hydroxyethylacrylamide (HEAA) and (3-acrylamidepropil)trimethylammonium chloride (APTMAC). Neutral, anionic and cationic groups were added to the matrixes in order to study their effects on the release of antibacterial species. The NCs were characterized by UV-visible spectroscopy and transmission electronic microscopy. The kinetics of the release of Ag+ ions from the NCs were followed by UV-visible spectroscopy at 300 nm. Biological experiments were based on the plate count method and agar diffusion testing against Pseudomonas aeruginosa. The bacterial death rate using the NCs is higher than when PNIPAM and nanoparticles in solution are used and seems to be related to the large amount of AgNPs contained inside the gels. In all cases, inhibition and diffusion halos were observed upon the exposure of bacterial cultures on agar to NC discs. The presence of both halos confirmed the bactericidal and bacteriostatic effects of the NCs. The reusability (prolonged use) of the materials was demonstrated until the Ag-NP content was exhausted. The NCs with a higher antibacterial capacity are based on a PNIPAM-co-6%APTMAC matrix. It was demonstrated that these NC materials have the capacity to maintain an aseptic/antiseptic zone for 7 to 15 days.

Triplet state quenching of phenosafranine dye by indolic compounds studied by transient absorption spectroscopy.

The interaction of the triplet state of the synthetic dye phenosafranine (3,7-diamino-5-phenylphenazinium chloride) with indolic compounds of biological relevance was investigated in water by means of laser flash photolysis. The rate constants for the triplet quenching were determined. The quenching process may be explained by an electron transfer from the indole to the dye in its triplet state. The rate constants present a typical dependence of an electron transfer process with the one-electron oxidation potential of the indole. Indole-3-acetic acid and its homologous indole propionic and indole butyric acids are the most effective quenchers with rate constants reaching the diffusion limit. Rate constants for indole itself, tryptophan and indole-3 carboxylic acid are one order of magnitude lower. The electron transfer nature of the quenching reaction is further confirmed by the detection of the semi-reduced form of the dye by its transient absorption. The absorption coefficients of the transient species were estimated, and the quantum yield of the charge separation process was determined. The efficiency of formation of radical species is between 60 and 90% of the triplets intercepted.

Biointerfacial behavior of stallion spermatozoa adhered to hydrogel surfaces: Impact of the hydrogel chemical composition and the culture medium.

Novel soft materials based on hydrogel are proposed to enhance the selection of high-quality stallion sperm based on their adhesion capacity. The hydrogel surfaces are derived from polyacrylamide (PAAm), which is copolymerized with neutral and ionic co-monomers to modify the interfacial properties. The hydrogels undergo characterization through FTIR spectroscopy, assessment of swelling capacity, and wettability under various experimental conditions. Sperm adhesion capacity on the hydrogels is examined through several parameters including the percentage of bound sperm (%Sp) to hydrogels, tail oscillation intensity and flagellar movement. The biointerfacial properties of sperm-hydrogel systems vary based on the chemical composition of hydrogel as well as the components present in the culture medium. High %Sp and excellent metabolic activity of the spermatozoa are observed on hydrogel surfaces that possess moderate hydrophilicity. Specifically, a cationic hydrogel in BGM3 culture medium and a neutral surface in BGM3 medium supplemented with BSA exhibit favorable outcomes. Scanning Electron Microscopy (SEM) reveals the normal morphology of the head and tail in spermatozoa adhered to the hydrogel. Therefore, these hydrogel surfaces are potential materials for selecting stallion sperm with high quality, and their application could be extended to the study of other mammalian reproductive cells.

Proton and electron transfer in the excited state quenching of phenosafranine by aliphatic amines.

The quenching of the excited singlet and triplet states of phenosafranine by aliphatic amines was investigated in acetonitrile and methanol. The rate constants for the quenching of the excited singlet state depend on the one-electron redox potential of the amine suggesting a charge transfer process. However, for the triplet state, quenching dependence on the redox potential either is opposite to the expectation or there is not dependence at all. Moreover, in MeOH the first-order rate constant for the decay of the triplet state, k(obs) presents a downward curvature as a function of the amine concentration. This behavior was interpreted in terms of the reversible formation of an intermediate excited complex, and from a kinetic analysis the equilibrium constant K(exc) could be extracted. The log K(exc) shows a linear relationship with the pKb of the amine. On the other hand, for the triplet state quenching in acetonitrile k(obs) varies linearly with the amine concentration. Nevertheless, the quenching rate constants correlate satisfactorily with pKb and not with the redox potential. The results were interpreted in terms of a proton transfer quenching, reversible in the case of MeOH and irreversible in MeCN. This was further confirmed by the transient absorption spectra obtained by laser flash photolysis. The transient absorption immediately after the triplet state quenching could be assigned to the unprotonated form of the dye. At later times the spectrum matches the semireduced form of the dye. The overall process corresponds to a one-electron reduction of the dye mediated by the deprotonated triplet state.