Photodegradation of nimodipine and felodipine in microheterogeneous systems

Indexación: Web of Science; ScieloThe photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072012000300025&nrm=is

Spiropyran-based reversible, light-modulated sensing with reduced photofatigue

Switchable materials have tremendous potential for application in sensor development that could be applied to many fields. We are focusing on emerging area of wireless sensor networks due to the potential impact of this concept in society. Spiropyran-based sensors are probably the most studied type of photoswitchable sensing devices. They suffer from many issues but photofatigue, insufficient selectivity and lack of sensitivity are probably the most important characteristics that hinder their wider application. Here, we are address these issues and demonstrate that covalent attachment of modified spiropyran into a polymeric film significantly reduces photodegradation. The observed signal loss after 12th cycle of switching between the spiropyran and merocyanine forms is only about 27% compared to the loss of 57% of the initial signal in an equivalent experiment based on non-immobilized spiropyran. This has enabled us to demonstrate at least five reversible cycles of detection of an ion of interest (in our case H+) with minimal signal loss. Furthermore, we demonstrate that the sensitivity can be increased by incorporation of additional binding groups in the parent spiropyran molecule. Using molecular modelling to calculate the relevant bond lengths as a measure of interaction between MC and H+, the calculated increase of H-bond strength is approximately an order of magnitude for a derivative containing a methoxy group incorporated in the o-position of the parent spiropyran in comparison to the equivalent unsubstituted phenol. This theoretical result was found to correspond very well with experimental observation. As a result, we have increased the sensitivity to H+ by approximately one order of magnitude

A combined photolytic–electrolytic system for the simultaneous recovery of copper and degradation of phenol or 4-chlorophenol in mixed solutions

The effects of the presence of copper on the photooxidation of phenol and 4-chlorophenol and of the presence of the phenols on the recovery of copper by electrodeposition are studied in three systems: a photolytic cell in the presence and absence of TiO2 as a catalyst or H2O2 as an oxidant; an electrolytic cell and a combined photolytic – electrolytic system. The optimum system for the simultaneous removal of copper and destruction of the phenols which overcomes the effects of copper-phenol reactions is a combined system with concentrator electrode technology incorporated into the electrolytic cell. This combined system achieves > 99% removal of copper and destruction of phenol or 4-chlorophenol in an 8 h period.EPSRC/Environmental Technology Best Practice Programme (ETBPP) and Fluid Dynamic International Ltd. for a grant under the Link (WMR03) programme

Oxygen doping of P3HT:PCBM blends: Influence on trap states, charge carrier mobility and solar cell performance

We investigated the influence of oxygen on the performance of P3HT:PCBM (poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester) solar cells by current--voltage, thermally stimulated current (TSC) and charge extraction by linearly increasing voltage (CELIV) measurement techniques. The exposure to oxygen leads to an enhanced charge carrier concentration and a decreased charge carrier mobility. Further, an enhanced formation of deeper traps was observed, although the overall density of traps was found to be unaffected upon oxygen exposure. With the aid of macroscopic simulations, based on solving the differential equation system of Poisson, continuity and drift-diffusion equations in one dimension, we demonstrate the influence of a reduced charge carrier mobility and an increased charge carrier density on the main solar cell parameters, consistent with experimental findings

Characterizing the removal of antibiotics in algal wastewater treatment ponds : a case study on tetracycline in HRAPs: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering at Massey University, Turitea Campus, Palmerston, New Zealand

Antibiotics are ubiquitous pollutants in wastewater, owing to their usefulness in both animal and human treatment. Antibiotic pollution is a growing concern because of the risk of encouraging antibiotic resistance in wastewater treatment (WWT) systems and downstream of effluent discharge. The aim of this thesis was to investigate the fate of antibiotics in algal WWT ponds, which have unique ecological and environmental characteristics (e.g. presence of algae; diurnal variation in pH, dissolved oxygen, and temperature) compared with conventional biological WWT. The research in this thesis focused on a case study of the fate of tetracycline (TET, an antibiotic) in high rate algal ponds (HRAP). Indoor lab scale HRAP studies were used to investigate the fate of TET under several operating conditions. Outdoor pilot scale studies (900 L and 180 L HRAPs) under Oceanic and Mediterranean climates were used to validate the lab scale findings. Results showed that high removal (85% to >98%) of TET was possible in the lab and pilot scale HRAPs with HRTs of 4 and 7 days. Sorption was consistently a low contributor (3-10% removal by sorption) during continuous HRAP studies, based on the amount of TET extracted from biomass. Batch experimentation was used to further distinguish mechanisms of TET removal. The majority of TET removal was caused by photodegradation. Indirect photodegradation of TET was dominant over direct photolysis, with 3-7 times higher photodegradation observed in wastewater effluent than for photodegradation in purified water during batch tests incubated in sunlight. Under dark conditions sorption was the dominant removal mechanism, and biodegradation was negligible in batch tests since aqueous TET removed was recovered (± 10%) by extraction of sorbed TET from the biomass. Irreversible abiotic hydrolysis was not observed during TET removal batch tests in purified (MQ) water. A kinetic model was developed and used to predict TET removal in the pilot HRAPs, based on parameters derived from batch experiments. The model predictions for aqueous TET concentrations were successfully validated against initial TET pulse tests in the 180 L pilot scale HRAP. However TET removal decreased in subsequent pulse tests in the pilot HRAP, resulting in over-prediction of TET removal by the kinetic model. This decrease in TET removal was associated with decrease in pH, dissolved oxygen concentrations, and biomass settleability, but causal relationships between TET removal and these variables could not be quantified. Until the predictive kinetic model is developed further, this model may serve as a preliminary estimate of TET fate in algal WWT ponds of different design and operation. Future research should also investigate the potential formation and toxicity (including antibiotic efficiency) of TET degradation products, but this was outside the scope of this thesis. Predictions from the model were sensitive to the daily light intensity, suggesting that TET removal would be reduced in the winter months