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The performance of Poly(lactic acid) (PLA) composites reinforced with functionalized titanium dioxide (TiO2) nanoparticles in rutile and anatase crystalline phases were systematically investigated. The results underline that the incorporation of TiO2, regardless of its crystalline structure, significantly enhances PLA's crystallinity by 85%. Notably, rutile TiO2, when functionalized with higher glutaric acid concentrations, was an effective crystallinity booster by 95%, passing from 20.39% to 39.58% crystallinity for the PLA/TiO2 R20 + 10% system. Furthermore, this research elucidates that the selection between anatase and rutile phases plays a vital role in the photostabilization. Functionalized Rutile TiO2 exhibited exceptional UV resistance, effectively inhibiting photodegradation; for example, after 15 days of exposure, the functionalized systems exhibited a 497.6% improvement for PLA/TiO2 R10 + 5% (22.1 ± 2.5 MPa), while the PLA/TiO2 R10 + 5% showed an 85.1% increase in composite stiffness (35.5 ± 3.5 MPa) after 7 days of degradation, in comparison with pristine PLA (19.2 ± 2.9 MPa). Anatase, conversely, displayed varying effects depending on concentration, acting as a stabilizer at lower levels and a promoter of degradation at higher concentrations. This knowledge enables the precise modifying of PLA composites for specific applications, balancing crystallinity, mechanical properties, and UV resistance for a diverse array of applications. Highlights: TiO2 enhances photostability in PLA confirming its potential as a UV stabilizer.Comparing anatase and rutile phase: Unveiling PLA composite dynamics.Glutaric acid on TiO2 enhances PLA composite strength significantly.Optimal acid concentration key to composite performance.Tailored PLA composites balance crystallinity, mechanics, and UV resistance. [ABSTRACT FROM AUTHOR]

The performance of Poly(lactic acid) (PLA) composites reinforced with functionalized titanium dioxide (TiO2) nanoparticles in rutile and anatase crystalline phases were systematically investigated. The results underline that the incorporation of TiO2, regardless of its crystalline structure, significantly enhances PLA's crystallinity by 85%. Notably, rutile TiO2, when functionalized with higher glutaric acid concentrations, was an effective crystallinity booster by 95%, passing from 20.39% to 39.58% crystallinity for the PLA/TiO2 R20 + 10% system. Furthermore, this research elucidates that the selection between anatase and rutile phases plays a vital role in the photostabilization. Functionalized Rutile TiO2 exhibited exceptional UV resistance, effectively inhibiting photodegradation; for example, after 15 days of exposure, the functionalized systems exhibited a 497.6% improvement for PLA/TiO2 R10 + 5% (22.1 ± 2.5 MPa), while the PLA/TiO2 R10 + 5% showed an 85.1% increase in composite stiffness (35.5 ± 3.5 MPa) after 7 days of degradation, in comparison with pristine PLA (19.2 ± 2.9 MPa). Anatase, conversely, displayed varying effects depending on concentration, acting as a stabilizer at lower levels and a promoter of degradation at higher concentrations. This knowledge enables the precise modifying of PLA composites for specific applications, balancing crystallinity, mechanical properties, and UV resistance for a diverse array of applications. Highlights: TiO2 enhances photostability in PLA confirming its potential as a UV stabilizer.Comparing anatase and rutile phase: Unveiling PLA composite dynamics.Glutaric acid on TiO2 enhances PLA composite strength significantly.Optimal acid concentration key to composite performance.Tailored PLA composites balance crystallinity, mechanics, and UV resistance. [ABSTRACT FROM AUTHOR]

Extractives, which naturally evolve as fundamental defense mechanisms in wood against environmental stresses, hold an essential place in the field of wood conservation science. Despite their low content in woody substrates, extractives are chemically complex and can be extracted accurately by solvents with different polarities, covering key components such as aliphatic, terpenoid, and phenolic compounds. The application of solvent extraction allows for the effective recovery of these extracts from forestry waste, thereby creating new opportunities for their reuse in wood modification and enhancing the economic value and potential applications of forestry waste. In the wood industry, extractives not only act as efficient preservatives and photo-stabilizers, significantly improving the decay resistance and photodegradation resistance of wood, but also serve as ideal dyes for fast-growing wood due to their abundant natural colors, which lend the product a distinct aesthetic appeal. The aim of this paper is to provide a comprehensive review of the origin and distribution characteristics of wood extractives and to examine the impact of solvent selection on extraction efficiency. At the same time, the mechanism of extractives in enhancing wood decay resistance and slowing down photodegradation is deeply analyzed. In addition, specific examples are presented to illustrate their wide utilization in the wood industry. This is intended to provide references for research and practice in related fields. [ABSTRACT FROM AUTHOR]

This work involved the successful synthesis of three new Schiff base complexes, including Ni(II), Mn(II), and Cu(II) complexes. The Schiff base ligand was created by reacting the malonyldihydrazide molecule with naphthaldehyde, and the final step involved reacting the ligand with the corresponding metallic chloride yielding pure target complexes. FTIR, 1 H NMR, 13 C NMR, mass, and UV/Vis spectroscopies were used to comprehensively characterize the produced complexes. These substances have been employed in this study to photo-stabilize polystyrene (PS) and lessen the photo-degradation of its polymeric chains. Several methods, including FTIR, weight loss, viscosity average molecular weight, light and atomic force microscopy, and energy dispersive X-ray (EDX) mapping, were used to assess the effectiveness of produced complexes as photo-stabilizers. These experiments supported one another and showed how well novel complexes stabilize PS photos. Hence, after 300 h of exposure to UV light with a wavelength of 313 nm, they lessen the photo-degradation of PS films containing these complexes compared to blank PS. Also, it has shown that the copper(II) complex works well as a photo-stabilizer. This is due to the highly conjugated systems in these compounds. The findings of this study have significant implications for reducing PS usage globally, which poses a serious danger to the environment, particularly the marine eco-system as a result of plastic trash. [ABSTRACT FROM AUTHOR]

Several developments and research methods are ongoing in drug technology and chemistry research to elicit effectiveness regarding the therapeutic activity of drugs along with photoprotection for their molecular integrity. The detrimental effect of UV light induces damaged cells and DNA, which leads to skin cancer and other phototoxic effects. The application of sunscreen shields to the skin is important, along with recommended UV filters. Avobenzone is widely used as a UVA filter for skin photoprotection in sunscreen formulations. However, keto-enol tautomerism propagates photodegradation into it, which further channelizes the phototoxic and photoirradiation effects, further limiting its use. Several approaches have been used to counter these issues, including encapsulation, antioxidants, photostabilizers, and quenchers. To seek the gold standard approach for photoprotection in photosensitive drugs, combinations of strategies have been implemented to identify effective and safe sunscreen agents. The stringent regulatory guidelines for sunscreen formulations, along with the availability of limited FDA-approved UV filters, have led many researchers to develop perfect photostabilization strategies for available photostable UV filters, such as avobenzone. From this perspective, the objective of the current review is to summarize the recent literature on drug delivery strategies implemented for the photostabilization of avobenzone that could be useful to frame industrially oriented potential strategies on a large scale to circumvent all possible photounstable issues of avobenzone. [ABSTRACT FROM AUTHOR]

The synthesis of novel copolymer acrylicacid-Co-N-(substitutedphenyl-1,3,4thiadiazole acryl methylamine copolymer into three steps was achieved by the reaction benzoic acid derivatives with thiosemicarbazide presence of phosphorous oxychloride(pocl3) to from compound 2-Amino-5-(substitutedphenyl)-1,3,4-thiadiazole. The purified products were reacted with allyll chloride to from compounds 2-N-(allyl amino)-5-(substituted phenyl)-1,3,4-thiadiazole). Finally the copolymers were synthesized by the free radical of compounds (B1-B5) with acrylic acid by using AIBN as initiator. All the prepared compounds (A1 - A5), and (B1 - B5) have been characterized based on(FT-IR), and (p1 - p5,) based on (FT-IR, ¹HNMR, GPC, TGA,) techniques. The polymers were used as additives to PVC in calculated percentages and composites were irradiated with UV light for 300h and found to be good Photostabilization. The adhesion strength for the polymers were evaluated by using single-lapshear method. The Solubility of the polymers where ested against some solvents the polymers were soluble in some of them. [ABSTRACT FROM AUTHOR]

Poly(vinyl chloride) (PVC) was prepared and the photo-stabilization of polymer films was studied using ultraviolet (UV) light. The efficiency of the synthesized polymer complex of ibuprofen-tin which is the photo-stabilizer in this study afterward of 300 hours of irradiation were evaluated by calculate the constant of PVC degradation rate. The outcome of this research has shown that the additives (ibuprofen-tin complexes) effect significantly on the decreased degradation constant compare to blank PVC, without additives the rate of degradation constant of PVC is greater than when the additives are added. The surface morphologies of the irradiated polymer film with additives were researches utilizing Field Emission Scanning Electron Microscope (FESEM). It can be seen that the polymer film with added additives is less roughness than the irradiated PVC (blank). The organotin complexes behave in this study as a photostabilizer to maintain the PVC from any decomposition by absorbing the incident light and convert it over the time as a heat to the polymeric chain.

Bis-ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT) was previously shown to efficiently quench the excited state of Butyl Methoxydibenzoylmethane (BMDBM) and to prevent its photodegradation. However, little is known on the consequences for the quenching molecule in this process. In this study we examined the impact of BMDBM on the photokinetics of the quencher BEMT by HPLC measurements and determination of the rate constant. We extended the investigation to Ethylhexyl Triazone (EHT) and Diethylhexyl Butamido Triazone (DBT), two 1,3,5-Triazine filters that became standardly used UVB filters in systems with BMDBM and without Octocrylene (OCR). We performed DFT computations on each studied UV filter to identify possible photostabilization mechanisms within the binary systems. Additionally, we evaluated the number of free radicals formed in formulations containing the studied mixtures. The same investigation was carried out with Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB) as an alternative UVA filter to BMDBM. Our experiments showed that EHT and DBT own no capability in photostabilizing BMDBM but confirmed the photostabilization effect of BEMT on BMDBM. At the same time, our work revealed a photodestabilization effect of BMDBM on BEMT, EHT and DBT as well as an increased UV-induced number of free radicals in the formulations containing the binary mixture of the 1,3,5-Triazine UV filters and BMDBM. This is hypothesized to be the consequence of chain reactions following the production of free radicals of destabilized BMDBM. In contrary to BMDBM, DHHB photostabilized the three 1,3,5-Triazine filters BEMT, EHT and DBT completely. Corresponding results of quantum computations predicted efficient triplet-triplet energy transfer to DHHB. No free radicals could be detected after UV exposure in the formulations containing the binary combination of BEMT, EHT, DBT with DHHB in contrast to formulations containing binary combinations with BMDBM.

One of the main disadvantages of the use of synthetic or semi-synthetic polymeric materials is their degradation and aging. The purpose of this study was to use artificial neural networks (ANN) and multiple linear regressions (MLR) to predict the carbonyl, hydroxyl, and polyene indices (ICO, IOH, and IOP), and viscosity average molecular weight (MV) of poly(vinyl chloride), polystyrene, and poly(methyl methacrylate). These physicochemical properties are considered fundamental during the study of photostabilization of polymers. From the five repeating units of monomers, the structure of the polymer studied is shown. Quantitative structure-property relationship (QSPR) models obtained by using relevant descriptors showed good predictability. Internal validation {R2, RMSE, and Q2LOO}, external validation {R2, RMSE, Q2pred, rm2, Δrm2, k, and k’}, and applicability domain were used to validate these models. The comparison of the results shows that the ANN models are more efficient than those of the MLR models. Accordingly, the QSPR model developed in this study provides excellent predictions, and can be used to predict ICO, IOH, IOP, and MV of polymers, particularly for those that have not been tested.

Poly(vinyl chloride) photodecomposition films that contains melamine Schiff base (0.5% by weight) as photostabilizers upon preservation with an ultraviolet light (UV) was investigated. The photodecomposition rate constant was reduced significantly in existence of melamine Schiff base compared to PVC (blank). The Schiff base 1 was found to most effective additive in PVC photostabilization films. Photodecomposition rate content for PVC films containing Schiff base 1 was found to be 5 × 10-3 sec-1 compared to 8.7 × 10-3 sec-1 for blank film. Ultraviolet radiation aging behaviors of PVC films were studied through leaching test by measuring the degree of migration. The surface morphology of PVC films was inspected by scanning electron microscope.

In Part I of this two‐part series the most important aspects of antioxidants (primary and secondary), processing aids, metal deactivators and some light stabilizers were described and highlighted together with their mechanisms, problems, and interactions. Emphasis was placed on synergism and antagonism in performances and color problems with a special insight regarding PVC. Part 2 of this article presents in a similar way general perspective on the type, mode of action, properties, uses, problems (and circumvention) of light stabilizers and of some important fillers and pigments. Montmorillonites, silica, carbon blacks, and titanium dioxide will be the main features with an emphasis on structure, activity, and formulations in polymer systems. Additive interactions between stabilizers and fillers/pigments is a major controlling factor in the end use performance from a physical, esthetic, structural, mechanical, and chemical point of view. Indeed, with filled polymers one enters an overly complex world of interactions giving rise to some extreme synergistic and often antagonistic problems which can in many cases destroy or even enhance the activity of functional processing additives. Several of these will be highlighted to provide the technologist with at least some experience such that one can be alert to any potential issues in formulating more complex packages where not just color but high performance is also required. [ABSTRACT FROM AUTHOR]

Poly(vinyl chloride) (PVC) is commonly used in many industrial applications. Ultraviolet (UV) radiation causes undesirable changes to PVC properties. Therefore, PVC should be protected from radiation to increase its lifetime for outdoor applications. Here, new organotin complexes containing captopril were synthesized for use as low‐concentration additives to enhance PVC photostability. Reacting captopril with the appropriate organotin chloride or dibutyltin oxide gave the corresponding organotin complex in 63% to 89% yield. Captopril tin complexes (0.5 wt%) were added to PVC solution and thin films were produced. The films were irradiated with UV light for 300 hours. The formation of specific functional groups and reduction in weight and molecular weight were monitored during irradiation. In addition, the surface morphology was checked pre before and after irradiation. The results confirmed that undesirable changes in the PVC films occurred to a lower extent in the presence of captopril tin complexes. These additives function as UV absorbers, scavengers for hydrogen chloride, and decomposers for peroxide and coordinate well with the PVC chains. The triphenyltin complex was the best inhibitor of PVC photodegradation, which is likely due to its high aromatic content. [ABSTRACT FROM AUTHOR]

Cyanocobalamin (B12) is a photosensitive vitamin, and its photodegradation to hydroxocobalamin (B12b) in liposomes has been investigated. The values of apparent first‐order rate constants (kobs) for the photodegradation of B12 in liposomes (nine preparations) are in the range of (0.52‐2.24) × 10–3 min–1, compared to 3.21 × 10–3 min–1 for B12 in aqueous solution (pH 5.0). The entrapment efficiency of B12 in liposomes is 26.4‐38.8%. The values of kobs show a linear relation with phosphatidylcholine (PC) content in liposomes, indicating the influence of PC in inhibiting the rate of photolysis of B12. The value of the bimolecular rate constant for photochemical interaction of B12 and PC is 0.32 M–1 min–1, indicating the stabilizing effect of PC on the photolysis of B12. The ratio of B12 stabilization in liposomal preparations is in the range 2‐6 compared to that of the unentrapped vitamin The stabilization of B12 is mediated by a photoinduced charge‐transfer B12‐PC complex that leads to the reduction of B12 to B12r, which is then oxidized to B12b that has low susceptibility to photolysis. The extent of stabilization of B12 probably depends on the degree of interaction between the two compounds under the reaction conditions, indicated by the loss of B12 fluorescence. [ABSTRACT FROM AUTHOR]

The present work is concerned with the photodegradation and photostabilization of poly(3-hydroxybutyrate) (PHB) biopolymer. Two commercial grades of PHB were investigated, containing of 4.0% and 6.2% of hydroxyvalerate (HV) comonomer, named PHB1 and PHB2, respectively. Injection moulded specimens were exposed to ultraviolet radiation (UV-A) in the laboratory for periods of up to 12 weeks and then characterized by tensile testing, surface appearance, size exclusion chromatography (SEC), and scanning electron microscopy (SEM). The exposure to UV radiation caused great damaged on the surface color, reduction of molecular size and mechanical properties. The effects were more pronounced on PHB2, probably due a lighter surface color and less packed macromolecular structure which facilitates the transmission of light throughout the samples. Specimens of PHB1 were also injected with the addition of a UV absorber and antioxidant, resulting in a higher UV stability of PHB, as shown by a low reduction in molar mass and better mechanical properties.

Graphene, the newest member of the carbon’s family, has proven its efficiency in improving polymers’ resistance against photodegradation, even at low loadings equal to 1 wt% or lower. This protective role involves a multitude of complementary mechanisms associated with graphene’s unique geometry and chemistry. In this review, these mechanisms, taking place during both the initiation and propagation steps of photodegradation, are discussed concerning graphene and graphene derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO). In particular, graphene displays important UV absorption, free radical scavenging, and quenching capabilities thanks to the abundant π-bonds and sp2 carbon sites in its hexagonal lattice structure. The free radical scavenging effect is also partially linked with functional hydroxyl groups on the surface. However, the sp2 sites remain the predominant player, which makes graphene’s antioxidant effect potentially stronger than rGO and GO. Besides, UV screening and oxygen barriers are active protective mechanisms attributed to graphene’s high surface area and 2D geometry. Moreover, the way that graphene, as a nucleating agent, can improve the photostability of polymers, have been explored as well. These include the potential effect of graphene on increasing polymer’s glass transition temperature and crystallinity.

The weathering performance of wood coated with a combination of rutile TiO2 hierarchical nanostructures and a sol-gel deposit of alkoxysilanes was determined by exposing three sets of specimens to UV light and water spray. The first set consisted of specimens coated with a mixture of methyltrimethoxysilane (MTMOS) and hexadecyltrimethoxysilane (HDTMOS). The second set consisted of specimens coated with nanostructural TiO2 followed by a mixture of MTMOS and HDTMOS. The third set consisted of uncoated control specimens. The wood coated with TiO2 followed by a mixture of MTDMOS and HDTMOS exhibited significantly less surface color change and weight loss as a result of UV light-induced degradation and erosion from water spray in comparison with the other groups. However, the coated surfaces were gradually transformed from hydrophobic to hydrophilic. Despite this apparent weakness, the MTMOS/HDTMOS/TiO2 coating, with superior photostabilization properties and resistance to surface erosion, may be useful for improving the weathering performance of wood coated with semi-transparent wood stains.

Purpose Several active compounds are sensitive to light, especially to the ultraviolet radiation (UV-R) leading to their degradation or modification, with lost or decrease of their biological activity. The aim of this study was to perform a systematic review regarding photostabilization strategies used on health products and perform a critical appraisal of their effectiveness. Results The bibliographic search identified 2261 results and merely 40 studies met the selection criteria. Of these, 85% referred to encapsulation strategies, 10% to antioxidants and 5% to the use of solar filters. Cyclodextrins (CD’s) were the most used encapsulation systems (32.5%) followed by liposomes and lipid nanoparticles (each 17.5%), microparticles (15%) and polymeric nanoparticles (10%). The most effective were found to be liposomes and lipid nanoparticles. However, the different methodological conditions used limit the true relevance of this finding. Conclusions A gold standard strategy suitable for all compounds cannot be proposed. Instead, case-by-case evaluation, supported on the photodegradation mechanism is recommended. Systematic studies that compare different photostabilization strategies undertaken with the same irradiation conditions are also needed. [ABSTRACT FROM AUTHOR]

Five Schiff bases derived from melamine have been used as efficient additives to reduce the process of photodegradation of poly(vinyl chloride) films. The performance of Schiff bases has been investigated using various techniques. Poly(vinyl chloride) films containing Schiff bases were irradiated with ultraviolet light and any changes in their infrared spectra, weight, and the viscosity of their average molecular weight were investigated. In addition, the surface morphology of the films was inspected using a light microscope, atomic force microscopy, and a scanning electron micrograph. The additives enhanced the films resistance against irradiation and the polymeric surface was much smoother in the presence of the Schiff bases compared with the blank film. Schiff bases containing an ortho-hydroxyl group on the aryl rings showed the greatest photostabilization effect, which may possibly have been due to the direct absorption of ultraviolet light. This phenomenon seems to involve the transfer of a proton as well as several intersystem crossing processes.

The 1,4-dihydropyridine (DHP) drugs are nowadays the most used drugs in the treatment of hypertension. However, all the structures in this series present a significant sensitivity to light, leading to the complete loss of pharmacological activity. This degradation is particularly evident in aqueous solution, so much so that almost all DHP drugs on the market are formulated in solid preparations, especially tablets. The first and main process of photodegradation consists in the aromatization of the dihydropyridine ring, after which secondary processes can take place on the various substituents. A potential danger can result from the formation of single oxygen and superoxide species that can in turn trigger phototoxic reactions. Several strategies for the photostabilisation of DHP drugs have been proposed in recent years, in particular with the aim to formulate these drugs in liquid preparations, as well as to limit any toxicity problems related to light degradation. This review summarizes and describes the main aspects of the studies conducted in recent years to obtain photostable formulations of DHP drugs.

A study on the character of influence of organic derivatives of quinquevalent phosphorus (cyclohexyl phosphonic acid and its nickel salts) on photodegradation of high-density polyethylene is performed. It is established that organophosphorus compounds demonstrate both photostabilizing and photocatalytic degradation effects toward polyethylene. [ABSTRACT FROM AUTHOR]

Five metal complexes containing Ni(II), Cu(II), Zn(II), Cd(II) and Sn (II) metals and 4-amino-5-(pyridine-4-yl)-4 H -1,2,4-triazole-3-thiol have been prepared for use as polystyrene photostabilizers. The additives (0.5% by weight) were mixed with polystyrene in chloroform to produce modified PS using the casting method. PS films were irradiated (λ = 250–380 nm) with a light absorption intensity of 6.02 × 10 −9 ein dm −3 s −1 at room temperature. The photostabilization activity of the films was determined by monitoring various changes, such as the carbonyl index, hydroxyl index, weight loss, viscosity average molecular weight, surface morphology and quantum yield of the chain scission. [ABSTRACT FROM AUTHOR]

The photostabilization of poly(vinyl chloride) (PVC) films in the presence of 2-(4-isobutylphenyl)propanoate metal complexes (0.5 wt%) was investigated at room temperature under ultraviolet radiation ( $$\lambda = 320 \hbox { nm}$$ ) for 300 h. The changes in various functional groups indices, viscosity average molecular weight and quantum yield of the chain scission of PVC films were monitored upon irradiation. The metal complexes used showed decreases in PVC films photodegradation. The quantum yield for the chain scission was measured exhibiting a range of $$2.054 \times 10^{-6}$$ and $$1.005 \times 10^{-7}$$ . The photostabilization of poly(vinyl chloride) in the presence of metal complexes was in the order $$\hbox {ZnL}_{2} (\hbox {H}_{2}\hbox {O})_{2}< \hbox {CdL}_{2} (\hbox {H}_{2}\hbox {O})_{2}<\hbox {CuL}_{2}< \hbox {SnL}_{2} (\hbox {H}_{2}\hbox {O})_{2}<\hbox {NiL}_{2} (\hbox {H}_{2}\hbox {O})_{2}$$ . The metal complexes can act as hydrogen chloride scavengers, UV absorbers, peroxide decomposers and also as radical scavengers to enhance PVC photostability. [ABSTRACT FROM AUTHOR]

2-Nitrobenzaldehyde was found to efficiently block singlet oxygen generation in a series of different test samples upon exposure to UV and visible light under aerobic conditions. The effect of quenching singlet oxygen formation was monitored in the presence of 1, 4-diazabicyclo [2.2.2] octane (DABCO) acting as a well-known singlet oxygen scavenger. A comparison of different nitrobenzaldehyde isomers with other highly effective synthetic antioxidants used in the food industry such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ) revealed that the protection of materials from singlet oxygen decreases in the order of 2-nitrobenzaldehyde > DABCO > TBHQ > 3-nitrobenzaldehyde > BHA > 4-nitrobenzaldehyde > BHT. Upon addition of 2-nitrobenzaldehyde, the oxidation of fatty acids and the degradation of photosensitizers was found to be considerably diminished, which indicates that the presence of 2-nitrobenzaldehyde has a significant protective influence by restricting the singlet oxygen generation and photodegradation of dyes. Moreover, the compound turned out to display its highly suppressing effects on typical singlet oxygen-dependent reactions, such as fatty acid photooxidation and dye photosensitizer degradation, in a rather broad spectral region covering wavelengths from 300 nm (UV-B) to 575 nm (close to the maximum of ambient solar radiation).

Series of 4-(4-substituted benzylideneamino)-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thiols were synthesized and their structures were confirmed. The synthesized Schiff bases were used as photostabilizers for polystyrene against photodegradation. Polystyrene polymeric films containing synthesized Schiff bases (0.5% by weight) were irradiated (λmax = 365 nm and light intensity = 6.43 × 10-9 ein.dm-3.s-1) at room temperature. The photostabilization effect of 1,2,4-triazole-3-thiols Schiff bases was determined using various methods. All the additives used enhanced the photostability of polystyrene films against irradiation compared with the result obtained in the absence of Schiff base. The Schiff bases can act as photostabilizers for polystyrene through the direct absorption of UV radiation and/or radical scavengers. [ABSTRACT FROM AUTHOR]

The paper describes coating properties (pencil hardness, adhesion, flexibility, solvent resistance) of a flexible biobased polyepoxide network from diglycidyl ether of bisphenol A crosslinked with castor oil maleate. Curing kinetics, electrical and photochemical behaviour were described. The structure was confirmed by Fourier transform infrared spectroscopy (FTIR). Global kinetic curing parameters values were determined via differential scanning calorimetry (DSC), by applying the Ozawa, Kissinger and non-linear regression methods. Kinetic parameters of each individual stage, obtained through multivariate non–linear regression method, indicated a three stage curing mechanism. A good correlation was found between experimental data and that simulated by the applied software. The material was further characterized by DSC and dielectric measurements. Crosslinking density and Shore hardness were determined from swelling and mechanical tests. 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol photostabilizer was added and photochemical behaviour was assessed at two different wavelengths. [ABSTRACT FROM AUTHOR]

1,4-dihydropyridine antihypertensives (DHPs) are almost all dispensed in solid pharmaceutical formulations for their easy lability when exposed to light. This paper reports a study on the photoprotective effect of containers in different glassy or polymeric matrices with regard to four known DHPs when in solutions. The samples were subjected to forced degradation by means of a Xenon lamp, in accordance with the international rules on drug stability evaluation. The simultaneous determination of the drugs and their photoproducts was carried out by applying the multivariate curve resolution (MCR) methodology to the spectral data recorded along the irradiation test. This technique was able to determine the kinetic parameters and resolve the spectra of the photoproducts. The time required to reduce by 10% the concentration of the drug ( t 0.1 ) was adopted as a criterion to compare the protective ability of the containers. A significant photoprotection for all drugs tested was obtained by the use of polyethylene terephthalate (PET) containers. The best result was achieved for the felodipine solution in blue PET transparent bottle of 0.6 mm thickness, reaching an almost complete stabilization up to six hours under stressing irradiation. In contrast, the glass containers, whether or not coloured, did not provide a satisfactory photoprotection of the drugs, showing in any case t 0.1 values under 24 min. These results can be a good opportunity to design new photoprotective pharmaceutical packaging for DHPs in liquid dosage form. [ABSTRACT FROM AUTHOR]

The weathering performance of wood coated with a combination of rutile TiO2 hierarchical nanostructures and a sol-gel deposit of alkoxysilanes was determined by exposing three sets of specimens to UV light and water spray. The first set consisted of specimens coated with a mixture of methyltrimethoxysilane (MTMOS) and hexadecyltrimethoxysilane (HDTMOS). The second set consisted of specimens coated with nanostructural TiO2 followed by a mixture of MTMOS and HDTMOS. The third set consisted of uncoated control specimens. The wood coated with TiO2 followed by a mixture of MTDMOS and HDTMOS exhibited significantly less surface color change and weight loss as a result of UV lightinduced degradation and erosion from water spray in comparison with the other groups. However, the coated surfaces were gradually transformed from hydrophobic to hydrophilic. Despite this apparent weakness, the MTMOS/HDTMOS/TiO2 coating, with superior photostabilization properties and resistance to surface erosion, may be useful for improving the weathering performance of wood coated with semi-transparent wood stains. [ABSTRACT FROM AUTHOR]

Photostability studies were performed on topical formulations containing diclofenac (DC). Niosomal gels were designed as photostabilization systems and ascorbic acid was also added to the new topical formulations because of its antioxidant property. Photodegradation tests were applied on commercial formulations containing DC and novel prepared gels, according to the ICH rules. The experiments were monitored by spectrophotometry and the data processed by multivariate curve resolution analysis to estimate the spectra and concentration profiles of evolved components. Characterization of niosomes was evaluated by size and distribution measurement, morphological analysis and encapsulation efficiency. Permeation experiments were performed across rabbit ear skin up to 24 h. Photodegradation rate of DC was found very fast in commercial formulation, with a residual content of 90% after only 4.38 min under a radiant exposure of 450 W/m 2 . Photostability resulted increased significantly when the drug was entrapped in niosomal systems. The best results were obtained by reaching a 10% degradation after 50.00 min of light exposure after incorporation of DC in niosomes in presence of 5% ascorbic acid. Moreover, niosomal gel also influenced the permeation capability of DC by enhancing the transdermal delivery of the drug. The cumulative dose permeated of DC from niosomal gel was about three times that obtained with the commercial gel. [ABSTRACT FROM AUTHOR]

Here, we report a durable and ultraviolet (UV) resistant nanocomposite membrane of chitosan (CS) with effective photostabilization ascribed to Zinc oxide (ZnO) nanoparticles. Zinc oxide nanoparticles were successfully dispersed in the solution of chitosan polymer. The nanocomposite films with the homogenous dispersion of ZnO nanoparticles in the chitosan matrix were obtained by solution casting method and the influence of ZnO nanoparticles as a photostabilizer was studied. The nanocomposite membranes were photoirradiated by polychromatic radiations with λ > 300 nm using mercury vapour lamps in SEPAP instrument. The resulting nanocomposite material exhibited excellent UV-resistance in very low percentages of ZnO nanoparticles. The chitosan membranes showed fast degradation attributes than the nanocomposite membranes. ZnO nanoparticles effectively absorbed UV radiations, thus protecting polymer from radiation degradation. The neat and irradiated nanocomposites of chitosan and ZnO nanoparticles (CS/ZnO) were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) spectroscopy for the chemical changes/degradation taking place. Chitosan nanocomposites were further characterized for tensile properties, contact angle measurements and surface morphology. [ABSTRACT FROM AUTHOR]

Light fastness of thermochromic colorants, which shows reversible changes in color with temperature, is of great importance for different textile and non-textile application. Light fastness of commercial thermochromic colorants was determined by measuring the color strength (K/S) of cotton fabric dyed with thermochromic colorants at regular intervals after exposure in Xenon Arc Light fastness tester and found to be poor for any application. An attempt to improve the light fastness of thermochromic colorant was made by using two ultraviolet absorbers (UVA) and two Hindered Amine Light Stabilizer (HALS) individually and in combination as additives in dye-bath formulation. UV absorbers showed better performance than HALS in terms of photostabilization. Significant improvement of photostability was observed when UV absorber and HALS were used in combination. [ABSTRACT FROM AUTHOR]

Distinct differences have been observed between L -tryptophan and D -tryptophan containing contryphan-Ar1131 in oxidative folding, trypsin binding, and photostabilization activity on avobenzone. [W5] contryphan-Ar1131 and [w5] contryphan-Ar1131 were chemically synthesized and characterized using RP-HPLC and mass spectrometry. Structural differences due to the change of configuration of tryptophan were evident from the optimized structures of contryphan-Ar1131 using density functional theory (DFT). The comparison of early events of oxidative folding has revealed the role of D -tryptophan in accelerating the formation of a disulfide bond. The optimized structures of the reduced form of peptides revealed the occurrence of aromatic-aromatic and aromatic-proline interactions in [w5] contryphan-Ar1131 which may be critical in aiding the oxidative folding reaction. The presence of the Lys6-Pro7 peptide bond indicates that contryphan-Ar1131 is resistant but may bind to trypsin allowing to assign the binding affinity of peptides to the protein surface. Competitive binding studies and molecular docking along with molecular dynamic (MD) simulations have revealed that [w5] contryphan-Ar1131 has more affinity for the active site of trypsin. Given tryptophan is a photostabilizer of FDA-approved chemical UV-A filter avobenzone, the report has compared the photostabilization activity of [W5]/ [w5] contryphan-Ar1131 on avobenzone under natural sunlight. [w5] contryphan-Ar1131 has better photostabilization activity than that of [W5] contryphan-Ar1131 and also individual D -tryptophan and L -tryptophan amino acids. These biochemical studies have highlighted the significance of D -tryptophan in contryphan-Ar1131 and its photostabilization activity on avobenzone may find applications in cosmetics. [Display omitted] • Contryphan contains unusual posttranslational modification of reversal from L- to D -configuration of tryptophan residue. • Biochemical studies were carried out using synthetic peptides to unravel the significance of D -Trp-5 in contryphan-Ar1131. • D -Trp-5 induces structural changes in reduced forms and assists in the oxidative folding of the peptide. • Altered orientation of tryptophan in 3D structure of [w5] contryphan-Ar1131 enhances its binding affinity to the trypsin. • The native [w5] contryphan-Ar1131 exhibits pronounced photostabilization activity on UV-A filter avobenzone. [ABSTRACT FROM AUTHOR]

Abstract: Topical commercial formulations containing diclofenac (DC) were submitted to photostability tests, according to the international rules, showing a clear degradation of the drug. The degradation process was monitored by applying the multivariate curve resolution technique to the UV spectral data from samples exposed to stressing irradiation. This method was able to estimate the number of components evolved as well as to draw their spectra and concentration profiles. Three photoproducts (PhPs) were resolved by the analysis of photodegradation kinetics, according to two consecutive reactions with a mechanism postulated as DC>PhP1 >PhP2 and PhP3. Photodegradation rate of DC in gel was found to be very fast, with a residual content of 90% only after 3.90min under a radiant exposure of 450Wm−2. Because of a very slow skin uptake of DC, a prolonged time of exposure to light could lead to a significant decrease of drug available or the uptake of undesired photoproducts. New gel formulations were designed to increase the photostability of DC by incorporating chemical light-absorbers or entrapping the drug into cyclodextrin. Drug photostability resulted increased significantly in comparison with that of the commercial formulations. The gel containing the light-absorbers such as octisilate, octyl methoxycinnamate and a combination thereof showed a residual DC of 90% up to 12.22min, 13.75min and 15.71min, respectively, under the same irradiation power. The best results were obtained by incorporating the drug in β-cyclodextrin with a degradation of 10% after 25.01min of light exposure. [Copyright &y& Elsevier]

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The weathering behavior of polystyrene (PS) and PS/montmorillonite nanocomposite with and without addition of ultraviolet (UV) absorber and/or antioxidant was investigated. Samples were exposed to UV radiation in the laboratory for periods of up to approximately 12 weeks. The samples were exposed for various irradiation intervals, and their tensile and impact strength was monitored through a factorial experimental design 24. The molecular weight, yellowness, and fracture surface were also monitored. The results generated by analysis of variance (ANOVA) Table showed that UV absorber and exposure time had the most important effects positive and negative, respectively. These results could be seen for neat PS and PS/MMT nanocomposite. The presence of antioxidant alone did not have any significant effect but when mixed with UV absorber presented a small synergism. These results corroborate with molecular weight, yellowing and fracture surface of tensile and impact samples. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

The effects of solvent [acetonitrile, methanol, and acetonitrile/water mixture (20:80, v/ v)], buffer concentration (phosphate buffer, pH 7.5), ionic strength and commonly employed adjuvants on the photodegradation of betamethasone-17 valerate in cream and gel formulations have been studied on exposure to UV light (300-400 nm). A validated high-performance liquid chromatography method has been used to determine the parent compound and its photodegraded products. The photodegradation data in the studied solvents showed greater decomposition of the drug in solvents with a lower dielectric constant. A comparatively higher rate of photodegradation was observed in the cream formulation compared to that for the gel formulation. The kinetic treatment of the photodegradation data revealed that the degradation of the drug follows first-order kinetics and the apparent first-order rate constants for the photodegradation reactions, in the media studied, range from 1.62 to 11.30 × 10 min. The values of the rate constants decrease with increasing phosphate concentration and ionic strength which could be due to the deactivation of the excited state and radical quenching. The second-order rate constant ( k′) for the phosphate ion-inhibited reactions at pH 7.5 has been found to be 5.22 × 10 M s. An effective photostabilization of the drug has been achieved in cream and gel formulations with titanium dioxide (33.5-42.5%), vanillin (21.6-28.7%), and butyl hydroxytoluene (18.2-21.6%). [ABSTRACT FROM AUTHOR]

The textiles for protection against harmful UV radiation have become the focus of great interest in the present time. However, not all apparel is well-protected against UV light. Therefore, the application and improvement of UV absorbers for sun protective fabrics is being sought.In this study, various benzophenone UV absorbers containing benzotoriazolyl groups were prepared, and the Ultraviolet Protection Factors (UPF) and improving the light fastness of dyes was examined. A series of hydroxybenzophenones bearing a built-in benzotriazole moiety showed a very high UPF, and played a very important role in the improvement of light fastness of dyes. It was found that 2,2’,4,4’-tetrahydroxy-5,5’-dibenzotriazolylbenzophenonesulfonic acid or the methyl derivative shows very high UPF, and plays an important role in improving the light fastness of dyes. It was further demonstrated that the combined use of these UV absorbers and singlet oxygen quencher, NTS (Nickel p-toluenesulfonate), can be applied as effective stabilizers against the photofading of dyes. [ABSTRACT FROM PUBLISHER]

Abstract: β-carotene, the most abundant carotenoid in nature and a natural antioxidant, has been added at a concentration of 2 × 10−4 g per mL of polymer film forming solution to three biopolyester matrices, poly(lactic acid) (PLA), polycaprolactone (PCL) and polyhydroxybutyrate-co-valerate (PHBV). The dispersion and stability of the antioxidant within the films was studied using confocal Raman imaging spectroscopy, colorimetry and UV/visible spectrophotometry. The films were characterized in terms of thermal and mechanical properties in comparison with control films without β-carotene. Addition of β-carotene to the three biopolyesters studied resulted in significant increases in the deformation at break and lower Young modulus. This antioxidant is thought to act as a plasticizer in the biopolyesters, thus increasing their free volume and causing a change in their thermal properties. Moreover, when exposed to UV light the mechanical properties of the films with β-carotene were less affected displaying, in general, higher modulus and similar ultimate tensile strength while keeping the films more ductile than the pure films. Therefore, β-carotene can be potentially used as a natural additive to increase the UV stability of the biopolyesters. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of complex formation with triethanolamine (TEA) alone and in combination with hydroxypropyl-β-cyclodextrin (HP-β-CD) on the photostability of ascorbic acid was evaluated for exposure to artificial and diffuse daylight. The first-order rate constants for the photodegradation reactions were determined. The data obtained showed that these complexes strongly reduced the photodegradation process with an 11- and 35-fold increase in the photostability of ascorbic acid, depending of the ligand concentration and the irradiation source. The multicomponent complex gave a significantly better stabilization for exposure to light than TEA alone. Due to the fact that the complexation extended the exposure of ascorbic acid to light (without molecular changes), UV spectrophotometric and reversed phase high performance liquid chromatographic (HPLC) methods were developed for the quantitative determination of the vitamin in pure form and in pharmaceutical preparations. These methods were statistically validated, all the validation parameters were found to be within the acceptance range. These results demonstrate that the proposed methods are suitable for the quality control of ascorbic acid, providing simple, rapid, precise, accurate and convenient approaches for routine analysis of bulk drug and pharmaceutical formulations. [Copyright &y& Elsevier]

A new cyclic, hindered amine light stabilizer (HALS) was prepared by the addition polymerization of a diepoxide and 4-amino-2,2,6,6-tetramethylpiperidine, and its photostabilizing effects on styrenic polymers were examined. The chemical structure of cyclic HALS was characterized by MALDI-TOF mass spectrometry. The prepared cyclic HALS had a moderate molecular weight ( $$ \overline M _w $$ = 900∼1,100) and high thermal stability ( T d ≈ 300 °C) that were compatible with styrenic polymers, such as polystyrene and styrene-butadiene rubber. The photostabilization effect of cyclic HALS was similar to or better than that of Tinuvin 770, a commercially available polymeric HALS. A synergistic effect between cyclic HALS and a UV absorber on the inhibition of photo-oxidation was observed. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the photostabilization of rotenone when exposed to ultraviolet light (UV) in the presence of some photoprotectants. Rotenone with and without photoprotectants in methanol were applied onto the surface of glass slides. The remaining concentration of rotenone was analyzed by HPLC at particular intervals. The dissipation half-life values for the degradation of rotenone under ultraviolet radiation were obtained by first-order kinetic equation. It indicated that the addition of UV531, UV326, Photo-stabilizer 770, Photo-stabilizer 622, Vitamin C, Antioxidant 168, Antioxidant 1010 and Antioxidant 1098 provided moderate degree of photostabilization of rotenone and that addition of UV-P provided the best photostabilization, which due to the competitive energy absorption of UV photons by the photoprotectants. The dissipation half-life values of rotenone after irradiation under UV suggested that the addition of UV-P (in 1:1 mol ratio) could provide better photostabilization of rotenone molecule. [Copyright &y& Elsevier]

Polystyrene is a common thermoplastic and is produced in different shapes and forms. The scale of manufacture of polystyrene has grown over the years because of its numerous applications and low cost of production. However, it is flammable, brittle, has low resistance to chemicals, and is susceptible to photodegradation on exposure to ultraviolet radiation. There is therefore scope to improve the properties of polystyrene and to extend its useful lifetime. The current work reports the synthesis of organometallic complexes and investigates their use as photostabilizers for polystyrene. The reaction of excess ibuprofen sodium salt and appropriate metal chlorides in boiling methanol gave the corresponding complexes excellent yields. The organometallic complexes (0.5% by weight) were added to polystyrene and homogenous thin films were made. The polystyrene films blended with metal complexes were irradiated with ultraviolet light for extended periods of time and the stabilizing effects of the additives were assessed. The infrared spectroscopy, weight loss, depression in molecular weight, and surface morphology of the irradiated blends containing organometallic complexes were investigated. All the synthesized organometallic complexes acted as photostabilizers for polystyrene. The damage (e.g., formation of small polymeric fragments, decrease in weight and molecular weight, and irregularities in the surface) that took place in the polystyrene blends was much lower in comparison to the pure polystyrene film. The manganese-containing complex was very effective in stabilizing polystyrene and was superior to cobalt and nickel complexes. [ABSTRACT FROM AUTHOR]