Function Of Light Exposure Time Research Articles

Promethazine-montmorillonite inclusion complex to enhance drug photostability.

The capability of montmorillonite as a matrix (MONT) to improve the photostability of photolabile drugs has been recently reported. Herein promethazine (PRO), which was chosen as a model drug because of its photodegradation mechanism, was intercalated into this inorganic matrix, and the effects on drug photoprotection were evaluated as well. The hybrid material (MONT-PRO) was successfully prepared with high drug loading and then was characterized by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and FTIR spectroscopy. The spectrophotometric measurements as a function of light exposure time showed that PRO intercalation into montmorillonite markedly improved the drug photostability because a 5-fold-slower degradation rate was determined compared to that measured for PRO in homogeneous solutions; nanosecond transient absorption measurements highlighted that the interaction with the inorganic matrix made negligible the photoionization process of the drug, and its efficiency in producing singlet oxygen was strongly reduced. The MONT-PRO intercalation compound could be easily formulated in gel or ointment media without losing its photostability.

Switchable photovoltaic effect in bilayer graphene/BiFeO3/Pt heterostructures

We report the switchable photovoltaic effects in graphene/BiFeO3/Pt heterostructures. Pure phase polycrystalline BiFeO3 films were deposited on Pt/TiO2/SiO2/Si substrates by pulse laser deposition. A bilayer graphene was transferred onto the BiFeO3 film which serves as transparent conducting electrodes. The heterostructures showed switchable photovoltaic effect depending on ferroelectric polarization directions indicating depolarization field induced separation of photo-generated carriers. The open circuit voltage (VOC) and short circuit current density (JSC) were measured to be ∼110 mV, ∼92 μA/cm2 in positive polarity and similar values were obtained when the polarity was reversed. The JSC and VOC also showed rapid response (<100 ms) as a function of light exposure time.

Montmorillonite as an agent for drug photostability

Among the large number of applications of montmorillonite and halloysite, low attention has been devoted to the photostabilization effect of these matrices on photounstable agents and no studies have been performed concerning their employment for drug photostability improvement. Herein we report the preparation of novel hybrids of these inorganic matrices and piroxicam (PX), which was chosen as a model drug due to its instability to light. The hybrid materials were successfully prepared with high drug loading and then were characterized by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and FT-IR spectroscopy. Finally, in order to investigate the matrix effects on piroxicam photostability, the hybrids were subjected to spectrophotometric analysis as a function of light exposure time. The results highlighted that PX intercalation into montmorillonite markedly improves the drug photostability and that this matrix can be proposed as an excipient for drug photostability enhancement.

Investigation of the structural, optical and electrical transport properties of n-doped CdSethin films

Thin films of (CdSe)90(In2O3)10, (CdSe)90(SnO2)10 and (CdSe)90(ZnO)10 have been grown on glass substrates by the electron beam evaporationtechnique. It has been found that undoped and Sn or In doped CdSefilms have two direct transitions corresponding to the energy gapsEg and Eg+Δ due to spin–orbit splitting of the valence band. The electrical resistivity for n-doped CdSethin films as a function of light exposure time has been studied. The influence of doping onthe structural, optical and electrical characteristics of In doped CdSe films hasbeen investigated in detail. The lattice parameters, grain size and dislocationwere determined from x-ray diffraction patterns. The optical transmittance andband gap of these films were determined using a double beam spectrophotometer.The DC conductivity of the films was measured in vacuum using a two-probetechnique.

Involvement of Singlet Oxygen in 5-Aminolevulinic Acid-Induced Photodynamic Damage of Cucumber (Cucumis sativus L.) Chloroplasts

Cucumber (Cucumis sativus L., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem II activity was reduced by 50%. The singlet oxygen ((1)O(2)) scavengers, histidine and sodium azide (NaN(3)) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of (1)O(2) monitored as N,N-dimethyl p-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the (1)O(2) quencher, NaN(3). Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN(3) and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type II photosensitizer.

UV‐stabilization of ABS with sterically hindered amines. Results of an ESR‐study

AbstractABS polymers have been limited in outdoor applications due to their poor weathering characteristics. On exposure to light the polybutadiene phase on the exposed side of the sample is photooxidized resulting in loss of impact strength and discoloration. We have found that the combination of a hindered amine light stabilizer (HALS) and a benzotriazole UV absorber dramatically outperforms either component alone. This L‐S blend provides a level of impact strength retention many times that of unstabilized ABS and also protects the polymer from discoloration. The present study describes the results of an E.S.R. investigation intented to explain the synergistic effect between HALS and benzotriazole UV absorber. Since the photostabilizing effect of HALS is associated with the reaction of the nitroxide radicals formed upon irradiation, the concentration of these radicals, as a function of light exposure time, was determined. Two types of . radicals were found. First, a broad . signal with an anisotropic hyperfine nitrogen interaction, was detected. This signal is characteristic of the . radicals localized in the SAN matrix. Second, a narrow . signal with an isotropic hyperfine nitrogen interaction, corresponding to nitroxide radicals localized in the polybutadiene phase, was also found. The . concentration in the SAN matrix and in the polybutadiene phase could, therefore, be determined separetely, as a function of light exposure time.In both phases, a maximum of . is observed after approximately 50 hours exposures. However, the maximum . concentration is ten times higher in the polybutadiene phase of ABS stabilized with a blend 0,5% HALS/0,5% UV Absorber than in the BR phase of an ABS containing only 0,5% HALS. On the other hand, there is only a slight increase of . radicals in the SAN phase when 0,5% UV absorber is added on top of 0,5% HALS. A comparable effect is observed in the polybutadiene phase when 8% titanium dioxide is added to an ABS stabilized with 0,5% HALS.Since the polybutadiene phase is the most sensitive toward photooxidative degradation, these results rationalize the observed synergistic effect of the combinations of HALS/Benzotriazole UV absorber.

Long-term, light-induced changes in dark conductivity of Kapton

The light-induced increase in dark conductivity of Kapton in space and simulated space environments has been investigated. It was found that a long-term increase in conductivity is caused by an accumulation of electrically active centers generated by solar radiation in the bulk of the material if maintained in vacuum. An analysis of the increase in conductivity as a function of light exposure time indicates that the dark conductivity of Kapton can be raised to a level at which the film can become sufficiently conductive to be antistatic simply by exposing it to solar radiation in orbit.