Study of the degradation performance (TOC, BOD, and toxicity) of bisphenol A by the photo-Fenton process

Degradation of bisphenol A (BPA, 0.5 L, 30 mg L^-1) was studied by photo-Fenton treatment, while Fenton reagents were variables. The efficiency of the degradation process was evaluated by the reduction of total organic carbon (TOC), the biochemical oxygen demand (BOD), and toxicity. For toxicity analysis, bacterial methods were found infeasible, but the in vitro assay of VERO cells culture was successfully applied. Experiments according to a 2² design of experiments (DOE) with star points and three center points for statistical validity allowed selecting those process conditions (Fe(II) and H₂O₂ load) that maximized the process performance. Photo-Fenton process effectively eliminated BPA and partly degraded its by-products (residual TOC <15 %) under substoichiometric H₂O₂ dose (100.62 mg L^-1) and at least 4 mg L^-1 Fe(II), after a 90-min treatment. All treated samples were at least partially biodegradable. The cytotoxic concentration (LD₅₀) of BPA for VERO cells was 7 mg L^-1. With small H₂O₂ amount (15.24 mg L^-1), only low BPA mineralization (TOC = 92 %) was attained. Toxicity was also detected to 50 % of cellular mortality even at long reaction times. However, 40.25 mg L^-1 of H₂O₂ decreased residual TOC to 70 % while cell mortality decreased down to 25 %. With more H₂O₂, the residual TOC decreased down to 15 % but cell mortality remained within the 20-25 % level. Photo-Fenton increased the biodegradability and reduced the toxicity of the studied sample.

Biocompatibility and drug release behavior of scaffolds prepared by coaxial electrospinning of poly(butylene succinate) and polyethylene glycol

Scaffolds constituted by electrospun microfibers of poly(ethylene glycol) (PEG) and poly(butylene succinate) (PBS) were studied. Specifically, coaxial microfibers having different core-shell distributions and compositions were considered as well as uniaxial micro/nanofibers prepared from mixtures of both polymers. Processing conditions were optimized for all geometries and compositions and resulting morphologies (i.e. diameter and surface texture) characterized by scanning electron microscopy. Chemical composition, molecular interactions and thermal properties were evaluated by FTIR, NMR, XPS and differential scanning calorimetry. The PEG component of electrospun fibers could be solubilized by immersion of scaffolds in aqueous medium, giving rise to high porosity and hydrophobic samples. Nevertheless, a small amount of PEG was retained in the PBS matrix, suggesting some degree of mixing. Solubilization was slightly dependent on fiber structure; specifically, the distribution of PEG in the core or shell of coaxial fibers led to higher or lower retention levels, respectively. Scaffolds could be effectively loaded with hydrophobic drugs having antibacterial and anticarcinogenic activities like triclosan and curcumin, respectively. Their release was highly dependent on their chemical structure and medium composition. Thus, low and high release rates were observed in phosphate buffer saline (SS) and SS/ethanol (30:70 v/v), respectively. Slight differences in the release of triclosan were found depending on fiber distribution and composition. Antibacterial activity and biocompatibility were evaluated for both loaded and unloaded scaffolds.

Restricted puckering of mineralized RNA-like riboses

The pseudorotational motions of highly hydroxylated pentafuranose sugars in the free state and tethered to hydroxyapatite have been compared. The conformation pentafuranose ring remains restricted at the North region of the pseudorotational wheel, which is the one typically observed for nucleosides and nucleotides in the double helix A-RNA, when the phosphate-bearing sugar is anchored to the mineral surface. Results indicate that the severe restrictions imposed by the mineral are responsible of the double helix preservation when DNA and RNA are encapsulated in crystalline nanorods.

Analysis of quinolone-resistance in commensal and diarrheagenic Escherichia coli isolates from infants in Lima, Peru

BACKGROUND

Antibiotic resistance is an increasing problem, particularly in countries where antibiotic use is frequently not controlled. The aim of this study was to analyse the prevalence of the molecular mechanisms of quinolone-resistance in E. coli isolated from faeces of healthy Peruvian children or those presenting diarrhoea.

METHODS

The presence of target mutations, transferable quinolone-resistance mechanisms and the role of Phe-Arg-β-Naphtylamyde inhibitible efflux pumps were studied in 96 Escherichia coli (46 diarrheogenic and 50 non-diarrheogenic) isolates exhibiting resistance or diminished susceptibility to quinolones.

RESULTS

The most resistant phenotype, Nal(R) and Cip(R), was most frequently present in isolates of healthy children. The distribution of quinolone resistance mechanisms between diarrheogenic (DEC) and commensal (non DEC) isolates was equitable, although the aac(6')Ib-cr gene was mainly detected in DEC isolates: 17 (34%) vs non DEC isolates nine (20%). QnrB was present in five (10%) DEC vs three (6%) non DEC isolates.

CONCLUSIONS

Point mutations in gyrA and parC genes play a relevant role in quinolone resistance acquisition and highlight the role of efflux pumps also. This study provides knowledge about the molecular mechanisms involved in quinolone resistance in isolates in a non exposed population under high community antibiotic pressure.

Specific isomerization of rhodopsin-bound 11-cis-retinal to all-trans-retinal under thermal denaturation

The natural ligand of the retinal photoreceptor rhodopsin, 11-cis-retinal, is isomerized to its all-trans configuration as a consequence of light absorption in the first step of the visual phototransduction process. Here we show, by means of difference spectroscopy and high-performance liquid chromatography analysis, that thermal denaturation of rhodopsin induces the same type of isomerization. This effect is likely due to thermally induced conformational rearrangements of amino acid residues in the retinal-binding pocket--possibly implying helical movements--and highlights the tight coupling between 11-cis-retinal and opsin. This effect could have implications in the instability and functional changes seen for certain mutations in rhodopsin associated with retinal disease, and in the stability of the different conformers induced by mutations in other G protein-coupled receptors.

Cleavage and development in cultured preimplantation mouse embryos exposed to lidocaine

Two-cell preimplantation mouse embryos were exposed in vitro to lidocaine (0 to 1,000 micrograms/mL) for 72 h to determine the effects of this anesthetic on subsequent cleavage and development during prolonged exposures. Embryonic development was monitored each 24 h for 3 d. Lidocaine adversely affected the in vitro development of the mouse embryos, altering the distribution of the development stages at the evaluated culture times. The percentage of two-cell embryos that cleaved and developed to more advanced stages was decreased by the exposure to lidocaine. After 24 h of culture, two-cell embryos were arrested before completion of cellular division; this occurred in 30% of the embryos at concentrations of 10 to 100 micrograms/mL and in 73.2% of the embryos with 1,000 micrograms/mL. After 48 h the blastomeres of the arrested embryos began to degenerate, showing lysis or fragmentation. At the lowest concentration, 14.9% of the arrested embryos exhibited the capacity to recover. These embryos continued their cleavage and normal development towards blastocyst formation. The cytotoxic effect and arrest at the two-cell stage were observed in a dose-dependent manner after 72 h of culture. We conclude that sensitivity to lidocaine embryotoxicity occurs during a window at the two-cell stage.

Prolonged exposure to lidocaine disturbs preimplantation mouse embryo development

OBJECTIVE

To determine the in vitro and in vivo effects of lidocaine on preimplantation mouse embryo development during prolonged exposure.

STUDY DESIGN

In vitro experiments: Two-cell mouse embryos were exposed to lidocaine doses of 0, 10, 100, and 1000 micrograms/mL for 72 h. In vivo experiments, female mice were exposed to lidocaine doses of 0, 0.3, 1.7, and 3.3 mg/kg body weight on days 1, 2, 3, and 4 of pregnancy. Early development, cell number, mitotic index, and micronuclei frequency were examined.

RESULTS

Development to the blastocyst stage was inhibited by all the doses tested in vitro and in vivo. Most of the affected embryos showed arrest and degeneration. The cell number was decreased, but not the mitotic index. Furthermore, clastogenic damage was observed in vitro.

CONCLUSIONS

Lidocaine adversely affects preimplantation mouse embryo development in vitro and in vivo.