Photolytic Activity Research Articles

Fabrication of a peptide–AuNP–TiO2 nanocomposite and its application as a VOC sensor

AbstractWe fabricated a volatile organic compound (VOC) sensor with a peptide–Au nanoparticle (AuNP)–TiO2 nanocomposite in which AuNPs were linked with TiO2-coated conductive peptide nanowires. The conductive peptide nanowires were formed between the AuNPs via self-assembly through the complexation of amphiphilic peptides, LESEHEKLKSKHKSKLKEHESEL, and Co(II). Furthermore, TiO2 mineralization on the surface of the peptide nanowires yielded mixed crystals of rutile and anatase, which exhibited highly effective photolytic activity. In particular, the obtained TiO2 exhibited three times greater photodecomposition activity in the unsintered state toward organic matter than did commercially available TiO2. Next, we constructed a VOC sensor by immobilizing peptide–AuNP–TiO2 nanocomposites on a comb electrode. The electrochemical properties of the nanocomposite changed drastically under light irradiation in the presence of VOCs, indicating transport of the VOC-decomposition-generated photoexcited electrons of TiO2 to AuNPs through conductive peptide nanowires, which prevented electron–hole recombination. The obtained sensor exhibited a sensing range of 2–100 ppm for dichloromethane, which was used as a representative VOC. Therefore, nanocomposites made of AuNPs linked with conductive TiO2 nanotubes may be highly effective for TiO2-driven VOC decomposition. Moreover, we believe that this nanocomposite has high sensitivity for sensing VOCs.

Discovery of a novel photosensitizer based on the enediyne antibiotic N1999A2 and its application as a glutathione-activatable theranostic agent

Abstract The 2-naphthol derivative 2, which corresponds to the aromatic moiety of the enediyne antibiotic N1999A2, was found to degrade protein under irradiation with long-wavelength UV light in the absence of any additives. Structure–activity relationship studies of 2 indicated that 3, in which the primary hydroxyl group at the C5 position of 2 is modified with a t-butyldiphenylsilyl group, has strong protein photodegradation ability. Furthermore, the theranostic molecule 5 was designed and synthesized. Compound 5 comprises a disulfide moiety linked to the hydroxyl group at the C2 position of 3 and to the fluorescent molecule dicyanomethylene-4H-pyran (DCM) chromophore derivative 6. The disulfide moiety is cleaved in the presence of glutathione (GSH), 5 showed significantly reduced photolytic activity and fluorescence compared to 3 and 6, but produced 3 and 6 when reacted with GSH. 5 showed selective fluorescence and photocytotoxicity against cancer cells that highly express GSH.

Fabricating mesoporous titanium nanocomposites with high adsorption and photolysis performance by using rice husk ash as a renewable support source

Rice husk (RH) is a valuable and renewable source of bioenergy. Once RH has been burned to produce thermal energy, RH ash (RHA) remains, and this ash can be used as a sustainable resource to improve the circular economy. In this study, we used RHA as a silicon source to fabricate RH-SBA-15. Incipient wetness impregnation was then employed to directly incorporate TiO2 nanocrystals into the mesopores of the RH-SBA-15. XRD and TEM confirmed the successful integration of TiO2 into the framework of RH-SBA-15, with the hexagonal array and ordered mesostructure of RH-SBA-15 being unchanged. FTIR and XPS revealed the formation of Ti–O–Si bonds on the surface of RH-SBA-15, which enhanced the activity of TiO2. The pore volume and surface area of TiO2/RH-SBA-15 were 0.292–0.604 cm3/g and 170–366 m2/g. Photocatalytic tests were conducted to examine the catalysts used in the degradation of Reactive Blue 4 (RB4). The results indicated that TiO2/RH-SBA-15 exhibited 63% higher catalytic efficiency than that did bare TiO2. The surface adsorption of RH-SBA-15 and the high photolytic activity of TiO2 resulted in an improvement in RB4 degradation. The photoactivity increased with decreasing solution pH and calcination temperature and increasing catalyst mass. A TiO2 ratio of 25% resulted in the highest photoactivity, yielding a composite that completely eliminated RB4 within 5 h. The catalyst composites had high stability and photoactivity after four cycles. Overall, the method used in this study for fabricating mesoporous photocatalysts from recycled RHA is valuable for bio-waste disposal and wastewater purification.

Constructing carbon-vacancy introduced g-C3N4 coating ZIF-8 with strong adsorption performance and internal electric field for enhanced photodegradation

Graphitic carbon nitride (g-C3N4) is limited in photocatalytic degradation efficiency owing to its weak adsorption capacity and finite charge utilization. In this work, carbon-vacancy defective g-C3N4 (CNP) wrapped around Zeolitic-imidazolate-framework-8 (ZIF-8) photocatalysts (ZCNP) were designed to overcome these drawbacks. ZCNP exhibits strong antibiotic adsorption effect due to π-π interactions and intermolecular forces. Benefitting from abundant carbon-vacancy coordination sites on CNP, ZIF-8 tightly binds to CNP, forming a built-in electric field at the contact interface and efficiently promoting electron-hole separation. Considering the strong adsorption performance combined with efficient electron-hole separation, ZCNP illustrates superhigh photolytic antibiotic activity (6.2 times higher than that of the pristine g-C3N4, 5.0 times higher than that of pure ZIF-8) and can degrade 98 % Doxycycline, 98 % Tetracycline and 61 % Ofloxacin within 30 min. ZCNP also maintains good efficiency in surface water and ground water. Moreover, the radical trapping experiments demonstrate that h+, 1O2 and •O2− have significant effects on the photocatalytic process, while h+ and 1O2 have great effects on the adsorption process. This work will provide novel insights for the design and development of efficient hybrid photocatalysts with high absorption capacity and photolytic activity.

Characterization of submicro-sized Ag/ZnO particles generated using the spray pyrolysis method

Environmental issues caused by the rapid industrialization and urbanization of modern society are a serious problem. For example, conventional wastewater treatment technologies such as adsorption, coagulation, and filtration are expensive and cannot completely treat the discharge of organic pollutants in industrial wastewater. A promising alternative is the decomposition treatment of organic pollutants using an eco-friendly metal oxide photocatalyst. However, the rapid recombination of excited electron-holes limits the photolytic activity of semiconductor photocatalysts. This study investigates the inhibition of electron-hole recombination by supporting Ag nanoparticles on a ZnO photocatalyst. Ag/ZnO particles are generated under various conditions using ultrasonic spray pyrolysis. XRD analysis confirms the presence of Ag and ZnO crystal peaks in the generated particles. EDX mapping and STEM images show that Ag nanoparticles are well dispersed in ZnO. The photolysis rate of organic dye (rhodamine-B) is faster than that of ZnO in all Ag/ZnO particles, and particles with a 0.2 mass% silver nitrate supported on ZnO particles exhibit twice the photolysis activity of P25. Additionally, the optimal photolysis activity in 100 mL of 5 mg/L rhodamine-B aqueous solution with 10 mg of Ag/ZnO particles are confirmed and had excellent persistence and stability even during 7 reuses.

Drug loaded essential oil microemulsions enhance photostability and evaluation of in vitro efficacy.

Loss of stability of pharmaceutical APIs (Active Pharmaceutical Ingredient) due to photolytic activity has been a major concern in the pharmaceutical industry as it leads to loss of activity of API and excipients, the formation of toxic by-products, change in color and flavor. Itraconazole (ITZ) bulk drug was exposed to UVC (254 nm) irradiation in an environmental chamber (37 °C, 75 %RH) and its photoprotection by cinnamon, clove, eugenol, and oregano based microemulsion was analyzed. No significant change in the spectra was observed at various time points, confirming the photo-protective activity of microemulsions, unlike the bulk drug. FTIR spectra illustrate the fundamental peaks of the functional groups of ITZ and ITZ loaded MEs. The overlaid spectra showed that there was a minor change in peaks of UV exposed ITZ bulk drug but the ITZ loaded microemulsions were able to protect all the major functional groups. The in vitro anti-microbial assay against C. albicans demonstrated no significant change in the activity of ITZ loaded microemulsion between untreated, 7th day and 15th day while the activity of bulk drug was reduced drastically in the UVC exposed sample. It was concluded that microemulsions can be used as an effective photo-protective drug delivery vehicle for light-sensitive compounds.

Modeling the OEC with Two New Biomimetic Models: Preparations, Structural Characterization, and Water Photolysis Studies of a Ba–Mn Box Type Complex and a Mn4N6 Planar-Diamond Cluster

The oxygen-evolving complex (OEC) is the native enzyme that catalyzes the oxidation of water in natural photosynthesis. Two new classes of manganese cluster complexes of formula Ba2Mn2L12(H3L1)2(CH3OH)4 1 and Mn4L26Cl2 2 were prepared (H4L1 = N,N′-(ethane-1,2-diyl)bis(2-hydroxybenzamide); L2 = methyl picolinimidate) and characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. X-ray diffraction studies of these complexes revealed (i) a box-type structure for 1 formed by two redox-active manganese(III) ions and two barium(II) ions connected by two bridging bisamido-bisphenoxy ligand molecules; and (ii) a planar-diamond array for Mn4N6 cluster 2 where the picolinimidates act as chelating ligands through the two nitrogen atoms. The ability of 1 and 2 to split water has been studied by means of water photolysis experiments. In these experiments, the oxygen evolution was measured in aqueous media in the presence of p-benzoquinone (acting as the hydrogen acceptor), the reduction of which was followed by UV-spectroscopy. The relevant photolytic activity found for 1 is in contrast to the inactivity of 2 in the photolytic experiments. This different behavior is discussed on the basis of the structure of the biomimetic models and the proposed reaction mechanism for this process supported by DFT calculations.

Morphology control of ZnO microstructures by varying hexamethylenetetramine and trisodium citrate concentration and their photocatalytic activity

The morphologies of ZnO with various microstructures synthesized by a facile solution-phase method using different molar ratios of zinc nitrate hexahydrate (Zn(NO3)2) to hexamethylenetetramine (HMTA) and trisodium citrate were investigated. It revealed that the molar ratio of Zn(NO3)2 to HMTA plays a significant role in the formation of hollow ZnO microstructures. Meanwhile ZnO with rod-like, flower-like or spherical-like microstructures can be nicely tailored by varying the molar ratio of Zn(NO3)2 to HMTA and trisodium citrate during growth process. In addition, the photocatalytic decolourization of aqueous solution of methyl orange in the presence of various morphological ZnO powder was investigated under ultraviolet light irradiation. The results showed that hollow ZnO microstructures had extremely high photocatalytic activities compared with those of solid ZnO samples. This remarkable photolytic activity is mainly due to their unique hollow structures, which resulting in larger surface area to volume ratio.

Aminophthalocyanine-Mediated Photodynamic Inactivation of Leishmania tropica.

Photodynamic inactivation ofLeishmaniaspp. requires the cellular uptake of photosensitizers, e.g., endocytosis of silicon(IV)-phthalocyanines (PC) axially substituted with bulky ligands. We report here that when substituted with amino-containing ligands, the PCs (PC1 and PC2) were endocytosed and displayed improved potency againstLeishmania tropicapromastigotes and axenic amastigotesin vitro The uptake of these PCs by bothLeishmaniastages followed saturation kinetics, as expected. Sensitive assays were developed for assessing the photodynamic inactivation ofLeishmaniaspp. by rendering them fluorescent in two ways: transfecting promastigotes to express green fluorescent protein (GFP) and loading them with carboxyfluorescein succinimidyl ester (CFSE). PC-sensitizedLeishmania tropicastrains were seen microscopically to lose their motility, structural integrity, and GFP/CFSE fluorescence after exposure to red light (wavelength, ∼650 nm) at a fluence of 1 to 2 J cm(-2) Quantitative fluorescence assays based on the loss of GFP/CFSE from liveLeishmania tropicashowed that PC1 and PC2 dose dependently sensitized both stages for photoinactivation, consistent with the results of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay.Leishmania tropicastrains are >100 times more sensitive than their host cells or macrophages to PC1- and PC2-mediated photoinactivation, judging from the estimated 50% effective concentrations (EC50s) of these cells. Axial substitution of the PC with amino groups instead of other ligands appears to increase its leishmanial photolytic activity by up to 40-fold. PC1 and PC2 are thus potentially useful for photodynamic therapy of leishmaniasis and for oxidative photoinactivation ofLeishmaniaspp. for use as vaccines or vaccine carriers.

Possibility of Secondary Sub-micron Aerosol Mass Concentrations Forecasting: A Case Study Toward the Possibility of A Future Nowcasting Approach

Particulate Matter (PM) pollution represents a global concern, due to its adverse effect both on environment and on human health. European Environmental Protection Agency data reveal that one of the most exposed regions is Northern Italy. The attention has been focused on a metropolitan city within this area, Torino (NW Italy), and studied the relation between sub-micron particles and their precursor gases under real atmospheric conditions, considering that fine particles have the most relevant adverse health effects. A photolytic computation model developed using an environmental chamber has been adapted and tested for real environmental conditions. The obtained algorithm can constitute the basic building-block for an effective PM1 nowcasting method. Testing it through the use of 2008-2011 summertime data (during the summer the photolytic activity is greater), selected considering only the days with stable fine weather conditions, we found that there is a strong stable dependence between the concentrations of sub-micron particles and its precursor gases, NO in particular. This fact will allow to calculate separately the dependence of PM1 mass concentration values (that represent 65% of PM10) on generation, respect to transport and scavenging phenomena. Finally, this result makes clear that an active policy on NO emission reduction should have effects also on PM pollution in the atmosphere.

Synthesis, characterization and photolytic degradation activity of poly-o-toluidine–thorium(IV)molybdophosphate cation exchanger: Analytical application in metal ion treatment

A new hybrid cation exchanger poly-o-toluidine–thorium(IV)molybdophosphate (POT-TMP) has been synthesized using sol–gel method by the incorporation of inorganic precipitates of thorium(IV)molybdophosphate into the matrices of organic poly-o-toluidine. The product formation was optimized by varying the synthesis conditions at pH of 1.0. Ion exchange capacity, pH titration, effect of calcinations, chemical stability and distribution behavior of the exchanger were also studied. Activation energy calculated from Arrhenius plot using Broido equation was found to be 7.94KJmol−1 at 50°C. The distribution coefficient values of metal ions determined in different solvent media show the selectivity of the hybrid exchanger for Hg2+ and Pb2+ ions. The analytically important separations of metal ions have been successfully achieved using columns packed with this exchanger. The practical utility of the material was shown by qualitative as well as quantitative determination of Pb2+ and Hg2+ in the synthetic mixtures and industrial effluents. The limit of detection (LOD) evaluated for Pb2+ and Hg2+ was found to be 1.53 and 0.72μgL−1 respectively. The photocatalytic degradation of Congo red dye using the composite under natural sunlight shows that about 74% of Congo red dye was degraded within 8h of photo irradiation.

The photolytic activity of poly-arginine cell penetrating peptides conjugated to carboxy-tetramethylrhodamine is modulated by arginine residue content and fluorophore conjugation site.

Upon light irradiation, Fluorophore-cell-penetrating peptide (Fl-CPP) conjugates can disrupt the integrity of biological membranes. This activity can in turn be used to photoinduce the disruption of endocytic organelles and promote the delivery of entrapped macromolecules such as proteins or RNAs into live cells. Recent mechanistic studies have shown that ROS production by the fluorophore and a latent lytic ability of CPPs act in synergy to elicit photolysis. However, how the structure of fluorophore-CPP conjugates impacts this synergistic activity remains unclear. Herein, using red blood cells (RBCs) as a model of biological membranes, we show that the number of arginine residues in a CPP as well as the position of fluorophore with respect to the CPP dramatically affect the photolytic activity of a fluorophore-CPP conjugate. These factors should therefore be considered for the development of effective photoinducible delivery agents.

First principles calculations on structural, elastic, acoustic and optical properties of fluorite phase TiO2 under pressure

The electronic, elastic, acoustic and optical properties of fluorite phase TiO 2 are calculated by using the first principles method. Different exchange-correlation functionals are used with the ultrasoft plane wave pseudopotential method under pressure from 0 GPa to 90 GPa. The calculated values of the lattice constant, cell volume, bandgap, bulk modulus and the pressure derivative of bulk modulus are in agreement with the prior published results. The calculated elastic parameters show that the fluorite structure is mechanically stable, the ratio of bulk to shear modulus [Formula: see text] indicates that it is brittle, and pressure derivative of the bulk modulus shows that it is not a super hard material, but a hard material. The longitudinal and transverse acoustic velocities in the direction [100], [110] and [111] are computed by using prior determined data. Besides, the optical properties are also studied under the aforementioned range of pressure, and the results show more photolytic activity over the other phases.

Overview of Pathogenic Micro-Organisms Destruction in Contaminated Water by Oxide Photocatalysis

The titanium dioxide (TiO2) is a semiconductor oxide photocatalys, which is chemically and biologically inert but exhibits excellent photolytic activity in the ultraviolet (UV) region. Progress in photocatalytic water disinfection requires understanding both concepts of TiO2 semiconductor as well the biochemistry of microorganisms. The advantage and disadvantage for current water purifications are discussed. Finally, the photocatalytic reactions to water disinfection and detoxification using solar energy.

Synergy Between Cell‐Penetrating Peptides and Singlet Oxygen Generators Leads to Efficient Photolysis of Membranes

Cell-penetrating peptides such as TAT or R9 labeled with small organic fluorophores can lyse endosomes upon light irradiation. The photoendosomolytic activity of these compounds can in turn be used to deliver proteins and nucleic acids to the cytosol of live cells with spatial and temporal control. In this report, we examine the mechanisms by which such fluorescent peptides exert a photolytic activity using red blood cells as a membrane model. We show that the peptides TAT and R9 labeled with tetramethylrhodamine photolyze red blood cells by promoting the formation of singlet oxygen in the vicinity of the cells' membranes. In addition, unlabeled TAT and R9 accelerate the photolytic activity of the membrane-bound photosensitizer Rose bengal in trans, suggesting that the cell-penetrating peptides participate in the destabilization of photo-oxidized membranes. Peptides and singlet oxygen generators therefore act in synergy to destroy membranes upon irradiation.

Intracellular Targeting Specificity of Novel Phthalocyanines Assessed in a Host-Parasite Model for Developing Potential Photodynamic Medicine

Photodynamic therapy, unlikely to elicit drug-resistance, deserves attention as a strategy to counter this outstanding problem common to the chemotherapy of all diseases. Previously, we have broadened the applicability of this modality to photodynamic vaccination by exploiting the unusual properties of the trypanosomatid protozoa, Leishmania, i.e., their innate ability of homing to the phagolysosomes of the antigen-presenting cells and their selective photolysis therein, using transgenic mutants endogenously inducible for porphyrin accumulation. Here, we extended the utility of this host-parasite model for in vitro photodynamic therapy and vaccination by exploring exogenously supplied photosensitizers. Seventeen novel phthalocyanines (Pcs) were screened in vitro for their photolytic activity against cultured Leishmania. Pcs rendered cationic and soluble (csPcs) for cellular uptake were phototoxic to both parasite and host cells, i.e., macrophages and dendritic cells. The csPcs that targeted to mitochondria were more photolytic than those restricted to the endocytic compartments. Treatment of infected cells with endocytic csPcs resulted in their accumulation in Leishmania-containing phagolysosomes, indicative of reaching their target for photodynamic therapy, although their parasite versus host specificity is limited to a narrow range of csPc concentrations. In contrast, Leishmania pre-loaded with csPc were selectively photolyzed intracellularly, leaving host cells viable. Pre-illumination of such csPc-loaded Leishmania did not hinder their infectivity, but ensured their intracellular lysis. Ovalbumin (OVA) so delivered by photo-inactivated OVA transfectants to mouse macrophages and dendritic cells were co-presented with MHC Class I molecules by these antigen presenting cells to activate OVA epitope-specific CD8+T cells. The in vitro evidence presented here demonstrates for the first time not only the potential of endocytic csPcs for effective photodynamic therapy against Leishmania but also their utility in photo-inactivation of Leishmania to produce a safe carrier to express and deliver a defined antigen with enhanced cell-mediated immunity.

Photoselective excited state dynamics in ZnO–Au nanocomposites and their implications in photocatalysis and dye-sensitized solar cells

Improving the performance of photoactive solid-state devices begins with systematic studies of the metal-semiconductor nanocomposites (NCs) upon which such devices are based. Here, we report the photo-dependent excitonic mechanism and the charge migration kinetics in a colloidal ZnO-Au NC system. By using a picosecond-resolved Förster resonance energy transfer (FRET) technique, we have demonstrated that excited ZnO nanoparticles (NPs) resonantly transfer visible optical radiation to the Au NPs, and the quenching of defect-mediated visible emission depends solely on the excitation level of the semiconductor. The role of the gold layer in promoting photolytic charge transfer, the activity of which is dependent upon the degree of excitation, was probed using methylene blue (MB) reduction at the semiconductor interface. Incident photon-to-current efficiency measurements show improved charge injection from a sensitizing dye to a semiconductor electrode in the presence of gold in the visible region. Furthermore, the short-circuit current density and the energy conversion efficiency of the ZnO-Au NP based dye-sensitized solar cell (DSSC) are much higher than those of a DSSC comprised of only ZnO NP. Our results represent a new paradigm for understanding the mechanism of defect-state passivation and photolytic activity of the metal component in metal-semiconductor nanocomposite systems.

Comparative analysis of structural and functional characteristics of soleus muscle in rats and mongolian gerbils during gravitational unloading of different duration

A comparative investigation of the dynamics of contractile properties of the whole soleus muscle and its fibers during 3- and 12-day-long hind limb suspension of Wistar rats and Mongolian gerbils (Meriones unguiculatus) has been performed. The data obtained indicate that the structural and functional changes caused by hypogravity in gerbils are slowed down compared with rats. A very intensive drop in water containment in gerbils was found, which can cause shifts in the ionic strength of the intracellular space of the muscle fiber. As a result, the photolytic activity of different enzymes may change, which can induce a less pronounced reduction in Z-disc and M-line stiffness and contractile capabilities in gerbils compared to rats.

Electron-accepting potential of solvents determines photolysis rates of polycyclic aromatic hydrocarbons: Experimental and density functional theory study

Photochemical behaviour of polycyclic aromatic hydrocarbons (PAHs) is strongly dependent on the physical and chemical nature of the media in/on which they exist. To understand the media effects, the photolysis of phenanthrene (PHE) and benzo[a]pyrene (BaP) in several solvents was investigated. Distinct photolysis rate constants for PHE and BaP in the different solvents were observed. Some theoretical parameters reflecting the solvent properties were computed and employed to explain the solvent effects. Acetone competitively absorbed light with PHE and BaP, and the excited acetone molecules played different roles for the photodegradation of PHE and BaP. The photolysis rate constants of PHE and BaP in hexane, isopropanol, ethanol, methanol, acetonitrile and dichloromethane were observed to correlate with the electron-accepting potential of the solvent molecules. Absolute electronegativity of the solvents linearly correlated with the photolytic activity (log k) of the PAHs significantly. The results are important for better understanding the photodegradation mechanism of PAHs in different media.

Important role of reaction field in photodegradation of deca-bromodiphenyl ether: Theoretical and experimental investigations of solvent effects

Photolysis of deca-bromodiphenyl ether (BDE-209) was investigated in tetrahydrofuran, dichloromethane, isopropanol, acetone, ethanol, methanol, acetonitrile and dimethylsulfoxide. Noticeable differences of the photolytic rates and quantum yields were found in the diverse solvents. Different to the previous deductions, hydrogen donating efficiency and electron donating efficiency of solvents were not the decisive factors for the photolytic rate in this study, which was proved by the fast photolysis of BDE-209 in CCl 4, a solvent without hydrogen and difficult to donate electrons. Besides hydrogen addition process, intermolecular polymerization might occur during the photolysis. Density functional theory (DFT) calculation was performed to understand the molecular properties of BDE-209 in different solvents. The lowest singlet vertical excitation energy ( E ex) and the average formal charge on Br ( q Br + ) of BDE-209, reflecting the difficulty for the excitation of BDE-209 and for the departing of Br atom, respectively, were changed by the reaction fields formed by the different solvents. E ex and q Br + linearly correlated with the photolytic activity (log k). This study is helpful to better understand the photolytic behavior of BDE-209 in different media.