UV-absorbing Molecules Research Articles

Substituent effects in 2-hydroxybenzophenone-based ultraviolet absorbers

2-Hydroxybenzophenone is the simplest molecule among benzophenone-based UV absorbers. Changing the position and type of substituents affects the strength of intramolecular hydrogen bonding and thus modulates the UV absorption properties. In this work, 132 2-hydroxybenzophenone-based UV absorbers with different substituent positions and species were designed to investigate the substituent effect in their UV absorption properties. The results show that when the substituent positions are the same, the characteristic peaks of the compounds containing substituents of the same group of atoms or homologous groups correspond to similar wavelengths. When the substituent groups are the same, the wavelength redshift of the characteristic peaks of the UV absorption spectra of the compounds of the NX and NZ classes is more pronounced than that of the remaining species, and the substituent group containing N atoms causes the molecule to have a more pronounced wavelength redshift. The redshift of the characteristic absorption peaks corresponding to the wavelengths decreases with the increase of the energy level difference. Atoms-in-molecules (AIM) analysis showed that the electron-absorbing group in the compound enhances the hydrogen bond strength to a lesser extent than the electron-donating group. Natural Bond Orbital (NBO) analysis further revealed that the type and position of the substituent groups in the molecular structure influenced the strength of the intramolecular hydrogen bonding by affecting the distribution of the charges among individual atoms in the 2-hydroxybenzophenone molecules. This work aims to reveal the effect of substituents on the UV absorption properties of 2-hydroxybenzophenone-based molecules and to provide theoretical guidance for the design of such UV absorber molecules absorbing UV light at specific wavelengths.

Spectra and photorelaxation of tris-biphenyl-triazine-type UV absorbers: from monomers to nanoparticles

Water-insoluble organic UV filters like tris-biphenyl-triazine (TBPT) can be prepared as aqueous dispersions of nanoparticles. The particles consist of the respective UV absorber molecules and show strong UV absorbance. Since there is a certain solubility of such UV absorbers in organic solvents, it is possible to measure the absorbance spectrum also in solution, for instance in ethanol or dioxane. The UV spectrum of the aqueous dispersion shows a slight hypsochromic shift of the original band with an additional shoulder at longer wavelengths. For the understanding of the observed changes of UV–Vis spectra of this UV absorber, either dissolved in an organic solvent or dispersed as nanoparticles in water, DFT calculations were carried out with the respective monomer and aggregates of TBPT molecules in the different media. The calculated UV–Vis spectra of isolated, that means dissolved, TBPT molecules in ethanol and in dioxane agree well with experimentally observed ones. The observed changes in the shape of experimental UV–Vis spectra in aqueous dispersion cannot be explained with a solvent effect only. It was found that the studied molecules could form stable energetically favorable π-stacked aggregates, which show UV–Vis spectra in reasonable agreement with those experimentally observed in aqueous dispersion. Such aggregates of TBPT are most likely the reason for the observed additional shoulder in the UV/vis absorbance spectrum. In addition, the mechanism of the photochemical deactivation of excited TBPT molecules was studied in detail with TD DFT in dioxane and in water.Graphical abstract

Shielding from UV Photodamage: Implications for Surficial Origins of Life Chemistry on the Early Earth.

UV light has been invoked as a source of energy for driving prebiotic chemistry, but such high energy photons are also known to cause damage to biomolecules and their precursors. One potential mechanism for increasing the lifetime of UV-photounstable molecules is to invoke a protection or shielding mechanism. UV shielding could either occur by the molecule in question itself (self-shielding) or by the presence of other UV-absorbing molecules. We investigate and illustrate these two shielding mechanisms as means of increasing the lifetime of 2-aminooxazole (AO), a prebiotic precursor molecule moderately susceptible to UV photodamage, with an expected half-life of 7 h on the surface of the early Earth. AO can be protected by being present in high concentrations, such that it self-shields. AO can similarly be protected by the presence of UV-absorbing nucleosides; the degree of protection depends on the concentration and identity of the nucleoside. The purine nucleosides (A, G, and I) confer more protection than the pyrimidines (C and U). We find that 0.1 mM purine ribonucleosides affords AO about the same protection as 1 mM AO self-shielding, corresponding to a lifetime enhancement of 2–3×. This suggests that only a modest yield of nucleosides can potentially allow for protection of UV photounstable molecules, and therefore this could be a plausible mechanism for protecting sensitive molecules while prebiotic synthesis is occurring simultaneously. Our findings suggest that both synthetic and degradative reactions can proceed at the same time, given various degrees of shielding.

Effect of UV Irradiation on Storage of Riviera Olive Oil in Glass Bottles Coated with BNNSs/PVB Multilayer Thin Film

UV absorbers are used to reduce the harmful effects of UV rays and to ensure that the properties of the materials are adequately protected. To protect against UV rays, one of the UV absorber molecules can reduce the combined energy of radiation to thermal energy that provides less energy in a photophysical process. Inorganic materials such as metal oxide semiconductors can effectively absorb UV irradiation and exhibit good heat-resistance properties. TiO2, CeO2, and ZnO are inorganic compounds with UV protective properties. Since some of these compounds are colored, their use is limited. Boron nitride nanosheets (BNNSs) are alternative UV inhibitors to these inorganic compounds. In this study BNNSs/PVB multilayer thin films were produced for the protection of glass packages using the dip-coating method. Riviera olive oil (RO-oil) samples in the both coated and uncoated bottle were exposed to UV irradiation for different times (75, 170, 360 and 720 hours). After the UV irradiation at different times, the total phenol and antioxidant contents in RO-oil were determined by Folin Ciacalteu and DPPH methods. The color change of RO-oil after UV irradiation was determined by UV visible spectrophotometer. Specific absorption coefficients K232 and K270 in the ultraviolet region were measured to determine the oxidation degree of RO-oil after degradation. Free fatty acid (FFA) of RO-oil after UV irradiation was determined by the titration method. According to the results of the analysis, the acidity values of RO-oil were preserved 20 times compared to the uncoated glass bottle after 720 hours UV. BNNSs/PVB coating was also effective in preserving total phenol, antioxidant contents and oxidation state of RO-oils under long term UV irradiation.

Synergistic effects of binary oil mixtures on the solubility of sunscreen UV absorbers

Sunscreens for the photoprotection of human skin often are prepared as emulsions, containing organic UV-absorber molecules dissolved in the oil phase. The solubility of such oil-soluble UV-absorbers can be a limiting factor when aiming for high protection against UV-radiation. Possible synergistic effects of combinations of oil components toward UV-absorber solubility are therefore of great interest. Since a multitude of different combinations of oil components are possible, it would be desirable to predict synergistic effects by computational methods. As a model system, the solubility of a hydroxyphenyl triazine type UV-absorber was studied in several binary oil mixtures, experimentally and also by using a computational procedure based on density functional theory (DFT) and the continuum solvation model COSMO-RS. We have found good agreement of experimental and computational results. Computational methods may thus be employed to predict synergistic behaviour of solubility for systems containing two or more solvents.

Spectra and Photorelaxation of Hydroxyphenyl-benzotriazole-Type UV Absorbers: From Monomers to Nanoparticles.

Water-insoluble organic UV filters such as 2,2'-methylene-bis-(6-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol) (MBBT) can be prepared as aqueous dispersions of nanoparticles. The particles consist of the respective UV absorber molecules and show strong UV absorbance. Because there is a certain solubility of such UV absorbers in organic solvents, it is possible to measure the absorbance spectrum in solution also, for instance, in ethanol or dioxane. The UV spectrum of the aqueous dispersion shows a significant bathochromic shift of the long-wavelength band with an additional shoulder. For the understanding of the observed changes of UV-vis spectra of this UV absorber, either dissolved in an organic solvent or dispersed as nanoparticles in water, density functional theory (DFT) calculations were carried out with the respective monomer and aggregates of MBBT molecules in different media. The calculated UV-vis spectra of isolated, that means dissolved, MBBT molecules in ethanol and in dioxane agree well with the experimentally observed ones. The observed changes in the shape and position of experimental UV-vis spectra in aqueous dispersion cannot be explained with the solvent effect alone. It was found that the studied molecules could form stable energetically favorable π-stacked dimers, which show UV-vis spectra in reasonable agreement with those experimentally observed in aqueous dispersion. Such aggregates of MBBT are most likely the reason for the observed bathochromic shift in the UV-vis absorption spectrum. In addition, the mechanism of the photochemical deactivation of the excited MBBT molecules was studied in detail with time-dependent DFT in dioxane and in water. The energetically most favorable pathway for the deactivation of absorbed energy by MBBT occurs through intramolecular enol-keto tautomerization in the first excited singlet state.

Impact of the Interaction between Aquatic Humic Substances and Algal Organic Matter on the Fouling of a Ceramic Microfiltration Membrane.

The influence of the interaction between aquatic humic substances and the algal organic matter (AOM) derived from Microcystis aeruginosa on the fouling of a ceramic microfiltration (MF) membrane was studied. AOM alone resulted in a significantly greater flux decline compared with Suwannee River humic acid (HA), and fulvic acid (FA). The mixture of AOM with HA and FA exhibited a similar flux pattern as the AOM alone in the single-cycle filtration tests, indicating the flux decline may be predominantly controlled by the AOM in the early filtration cycles. The mixtures resulted in a marked increase in irreversible fouling resistance compared with all individual feed solutions. An increase in zeta potential was observed for the mixtures (becoming more negatively charged), which was in accordance with the increased reversible fouling resistance resulting from enhanced electrostatic repulsion between the organic compounds and the negatively-charged ceramic membrane. Dynamic light scattering (DLS) and size exclusion chromatography analyses showed an apparent increase in molecular size for the AOM-humics mixtures, and some UV-absorbing molecules in the humics appeared to participate in the formation of larger aggregates with the AOM, which led to greater extent of pore plugging and hence resulted in higher irreversible fouling resistance.

Smart self-assembled microgel films as encapsulating carriers for UV-absorbing molecules

This article reports the ability of oligo(ethylene glycol)-based stimuli-responsive microgels to spontaneously form self-assembled microgel films under different conditions such as the presence or absence of water soluble polymers (WSP, formed during the microgel synthesis) and the type and/or amount of salt in the microgel dispersion.

Liposomogenic UV Absorbers are Water-Resistant on Pig Skin—A Model Study With Relevance for Sunscreens

An important property of sunscreens is their water resistance after the application on human skin. In this work, the hypothesis that UV absorber molecules which are able to form liposomes, so-called liposomogenic UV absorbers, show better water resistance on a pig skin model than UV-absorbing molecules lacking this ability was tested. The assumption behind is that molecules which can form liposomes are able to integrate into the stratum corneum lipids of the skin. Three different liposomogenic UV absorbers were synthesized and their behavior investigated, leading to the confirmation of the hypothesis. With one of the liposomogenic UV absorbers, it was possible to show the integration of the UV absorber molecules into the bilayers of another liposome consisting of phosphatidylcholine, supporting the assumption that liposomogenic UV absorbers exhibit improved water resistance because they integrate into the skin lipids.

Functionalization of Silica Surface with UV-Active Molecules by Multivalent Organosilicon Spacer

Immobilization of active molecules by attachment onto solid surfaces is a well-established practice in many processes and applications. Silica micro- and nano-particles are attractive candidates as support for active molecules as a result of a combination of desirable properties. The present study deals with grafting of a functional UV active molecule onto silica surfaces via hydrosilylation reactions using multivalent organosilicon spacers. Different types of organosilicon precursors based on dimethylsiloxysilanes containing multiple SiH groups were used as spacers between vinyl-modified silica surface and the benzotriazole UV-absorber (UVA). Firstly, the surface of silica was modified with vinyltrimetoxsisilane coupling agent. The UVA molecules were attached to the silica-vinyl by a two-step procedure involving hydrosilylation reaction. The successful grafting was confirmed by FTIR, TGA and UV-Vis characterization. More than fivefold increase in UVA loading was found for the MH30 multifunctional spacer, which contains approximately 75 SiH groups per molecule, when compared to a four-functional spacer. Furthermore a branched, bulky six-functional spacer is preferred over a linear spacer of the same functionality. UV activity of functionalized silica was studied by UV-Vis spectroscopy, indicating that the immobilization of UVA onto silica surface has not altered its UV absorbance properties.

Mangiferin and naringenin affect the photostability and phototoxicity of sunscreens containing avobenzone

Efficient UV-absorbing molecules are designed to protect against UV-light exposure. However, the development of photostable sunscreens is important to preserve the photoprotective efficacy and to prevent the formation of reactive oxygen species (ROS) and photodegradation products, which can promote phototoxic or photoallergic contact dermatitis. The aim of this study was to evaluate the effects of mangiferin and naringenin on the photostability and phototoxicity of sunscreens containing avobenzone. Cosmetic sunscreen formulations containing octocrylene (OCT), octyl methoxycinnamate (OMC) and avobenzone (AVO) were prepared and supplemented or not with mangiferin, naringenin, or with both compounds in combination. For photostability studies, samples of the formulations were spread onto glass plates, exposed to UVA radiation and then analyzed by high performance liquid chromatography (HPLC) to determine UV filters and the antioxidants recovery. The phototoxicity of the UV filters and antioxidants was evaluated using 3T3 fibroblast cultures that were subjected (or not) to irradiation according to OECD TG 432. The photostability studies demonstrated that AVO and naringenin showed the highest photodegradation when present in formulation FN (containing octocrylene, avobenzone, octyl methoxycinnamate and naringenin). The addition of mangiferin to this combination (FMN) resulted in an improved photostability of both substances compared to FN. The in vitro phototoxicity test showed that only avobenzone was considered phototoxic. The combination containing AVO/naringenin exhibited phototoxic potential; however, this was reduced by the addition of mangiferin (combination CMN). The results of this study are promising because it was demonstrated that mangiferin could increase the photostability and reduce the phototoxic potential of the combination of naringenin and AVO.

Chemical characterization and photoprotective activity measurement of extracts from the red macroalga Solieria chordalis

Abstract The photoadaptive responses of macroalgal communities to abiotic stresses have been studied, and a number of UV-absorbing molecules have been identified. Among these compounds, photoprotective compounds such as mycosporine-like amino acids and carotenoids have been isolated from various red macroalgal species. However, several substances still need to be characterized. We describe the preparation of photoprotective extracts obtained from Solieria chordalis. Two solvents, 2-octyl dodecanol and octyldodecyl ester of l-pyrrolidone carboxylic acid, were selected based on their cosmetic functions for performing an ultrasound-assisted extraction. The efficiency of extraction was monitored by spectrophotometry and in vitro photoprotective activity measurements. 2-Octyl dodecanol and octyldodecyl ester of l-pyrrolidone carboxylic acid extracts showed maximum absorption wavelengths ranging from 280 to 340 nm and 270 to 350 nm, respectively. The anti UV-B capacity for protecting a synthetic chlorophyll solution was assessed by measuring its pseudo first-order degradation kinetics at room temperature. Under irradiation at 312 nm, chlorophyll introduced in the 2-octyl dodecanol S. chordalis extract showed the slowest degradation kinetics with a half-life t1/2 of 121.0 min. Several compounds were detected in the seaweed extract by high-performance liquid chromatography. Among them, the mycosporine-like amino acid, palythenic acid, was detected in the algal extract.

A NanoDrop-based method for rapid determination of viability decline in suspension cultures of animal cells

We describe a rapid method for monitoring the cell growth and decline phases in suspension cultures of animal cells. During the cell growth phase, ultraviolet (UV)-absorbing components in the medium are consumed, but at later times as cells begin to die, UV-absorbing molecules such as proteins are released into the medium. Measuring the absorbance at 280nm (A280) with a NanoDrop spectrophotometer, an inverse correlation between the onset of the cell decline phase and A280 was observed. This simple method can be applied to quickly determine the beginning of the decline phase of cultures of mammalian and insect cells in suspension.

Anti-ultraviolet radiation effects of Coptis chinensis and Phellodendron amurense glycans by immunomodulating and inhibiting oxidative injury

HPLC analysis proved that Coptis chinensis glycan contained Ara, Man, and Gal. The monosaccharide constituents of Phellodendron amurense glycan were determined by HPLC analysis. HPLC analysis proved that P. amurense glycan contained Ara, Xyl, Glu, and Gal. FT-IR spectrum of C. chinensis glycan and P. amurense glycan showed the characteristic absorption peaks of carbohydrate polymers. Exposure of the human skin to ultraviolet radiation (UVR) leads to depletion of cutaneous antioxidants, regulation of gene expression and ultimately to the development of skin diseases. In the present study, free radical scavenging activity of C. chinensis and P. amurense glycan were evaluated. The photoprotective effect of C. chinensis and P. amurense glycan against UV-induced oxidative damage was also investigated in skin. At the concentration range employed, the two glycans showed strong free radical scavenging activity. Ultraviolet radiation reduced skin antioxidant enzyme and immunity activities in animals. Administration of C. chinensis and P. amurense glycans dose-dependently significantly increased skin antioxidant enzyme and immunity activities in animals. In conclusion, C. chinensis and P. amurense glycans present photoprotective properties, which can be attributed to molecules, such as flavonoids and carotenoids, which act as UV-absorbing molecules and as antioxidants, as well as stimulate immunity activities in animals.

Application of ATR-UV Spectroscopy for Monitoring the Crystallisation of UV Absorbing and Nonabsorbing Molecules

In the pharmaceutical industry, controlling the crystallization process of active pharmaceutical ingredients (API) is crucial to ensure chemical quality and physical properties. Process analytical technologies (PAT) provide a large number of tools that provide information in real-time to allow mastery of the final solid chain. In this paper is described how attenuated total reflection ultraviolet (ATR-UV) spectroscopy can be used to monitor concentration. Besides its classical application to UV-absorbing molecules, it will be shown how, in principle, it may be applied to molecules that do not absorb at UV wavelengths.

Sunscreens: the impervious path from theory to practice

The preparation of commercial products able to protect the skin against damage from solar radiation requires safe and photo-stable stable UV-absorbing molecules with high extinction coefficients, prepared with solvents of the appropriate polarities and polarizabilities in formulas which allow the uniform spreading of the UV-absorbing substances. The products should also maintain the ingredients on the top of the skin and provide efficient scavenging activities against singlet oxygen and other directly or indirectly generated reactive oxygen species. Because of the high doses of UV used to test high SPF, simple and reproducible methods are needed to estimate the protection afforded by the product before risking the induction of severe burns to the volunteers, as can occur when the value of the product's SPF is smaller than the expected one. This paper describes several aspects of the preparation of commercial sunscreens. It also points out several of the hidden hypotheses which, when not tested, might lead to the overestimation of the protection factor of a product.

Photostability and retention of UV absorber molecules in sol–gel hybrid UV-protective coatings

Highly efficient UV-protecting coatings were prepared, consisting on UV absorber molecules embedded in transparent sol–gel phenyl-functionalized silica thin-films. The photostability and retention of the molecules in the films depend strongly on parameters such as the composition of the hybrid host matrix, the UV-absorber loading in the matrix and the sol–gel preparation conditions. The amount of the modifying phenyl group was found to affect strongly the retention of the UV absorber molecules in the matrix. The retention of the molecules incorporated in the thin-films showed an increase of 21 times as the amount of the phenyl groups is reduced by a factor of 4. On the other hand, the incorporation of increasing amounts of Ph groups lead to a slight decrease of the photostability of the UV absorber molecules. The ability to control the parameters affecting the durability of the UV absorber molecules in the sol–gel matrices allows us increase the effectiveness of the UV-protective films and hence their potential usage in both, indoors and outdoors applications.

Evaluation of Soyscreen in an Oil-Based Formulation for UV Protection of <I>Beauveria bassiana</I> Conidia

Soyscreen oil was studied as a formulation ingredient to protect Beauveria bassiana (Balsamo) Vuillemin conidia from UV degradation. Feruloylated soy glycerides, referred to as Soyscreen oil, are biobased UV-absorbing molecules made by combining molecules of soybean oil with ferulic acid. Conidia stored in Soyscreen oil for 28 wk at 25, 30, and 35 degrees C retained viability as well as conidia stored in sunflower oil, demonstrating that Soyscreen did not adversely affect viability with prolonged storage. For samples applied to glass and exposed to simulated sunlight (xenon light), conidia in sunflower oil with or without sunscreens (Soyscreen or oxyl methoxycinnimate) had similar conidia viability after exposure. These oil formulations retained conidia viability better than conidia applied as an aqueous treatment. However, the 10% Soyscreen oil formulation applied to field grown cabbage (Brassica oleracea L.) and bean (Phaseolus vulgaris L.) plants, did not improve residual insecticidal activity compared with aqueous applications of unformulated conidia or two commercial formulations when assayed against Trichoplusia ni (Hübner) larvae. Our results suggest that the oil applications lose UV protection because the oil was absorbed by the leaf. This conclusion was supported in subsequent laboratory exposures of conidia in oil-based formulations with UV screens applied to cabbage leaves or balsa wood, which lost protection as measured by decreased viability of conidia when exposed to simulated sunlight. As a result, additional formulation techniques such as encapsulation to prevent separation of the protective oil from the conidia may be required to extend protection when oil formulations are applied in the field.

Protective effects of three extracts from Antarctic plants against ultraviolet radiation in several biological models

The photoprotective effect of the methanolic extracts of three Antarctic plant species – Deschampsia antarctica Desv., Colobanthus quitensis (Kunth) Bartl., and Polytrichum juniperinum Hedw. against UV-induced DNA damage was investigated in hamster lung fibroblasts (V79 cells) and in a biomonitor organism Helix aspersas, using comet assay. The protective, mutagenic, and antimutagenic profiles of these extracts were also evaluated using haploid strains of the simple eukaryote Saccharomyces cerevisiae, and antioxidant activity were investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay, as well as the hypoxanthine/xanthine oxidase assay. At the concentration range employed, the extracts were not cytotoxic or mutagenic to S. cerevisiae. In addition, the treatment with these extracts enhanced survival, and decreased induced reverse, frameshift, and forward mutations in a dose-response manner in all UVC doses employed. The plants extracts did not generate DNA strand breaks in V79 cells, and the treatment significantly decreased DNA damage induced by UVC. Extracts significantly decreased UVC-induced lipid peroxidation in V79 cells , showing a clear antioxidant property. Moreover, results of comet assay in V79 cells, employing Fpg, Endo III, and Endo V enzymes, demonstrated significant reduction of UVC-induced DNA damage after pre-incubation with these extracts. The treatment with all tested extracts were much less efficient against UVC-induced cytotoxicity in the yeast strain defective in photolyase as compared to the wild type strain, suggesting that this DNA repair pathway is stimulated by substances present in the extracts. All extracts showed a significant inhibitory effect in the hypoxanthine/xanthine oxidase assay, and they had the ability to scavenge DPPH. In H. aspersas, the treatment was able to protect against UVC-induced damage. In conclusion, D. antarctica, C. quitensis, and P. juniperinum extracts present photoprotective properties, which can be attributed to molecules, such as flavonoids and carotenoids, which act as UV-absorbing molecules and as antioxidants, as well as stimulate DNA-repair processes.

Composition and properties of flaxseed phenolic oligomers

An extract from flaxseed containing oligomeric structures of the phenolic glucosides secoisolariciresinol diglucoside (SDG), p-coumaric acid glucoside and ferulic acid glucoside was fractionated into three oligomeric fractions (F50, F60 and F70) by reversed phase liquid chromatography and further subfractionated by Sepharose CL-6B. The F50 fraction, which had the highest proportion of hydroxycinnamic acid glucosides, was also fractionated on Sephadex LH-20 according to hydrophobicity and size. The different separations resulted in complex profiles of UV-absorbing molecules. HPLC analyses indicated that reversed-phase chromatography separated the oligomers according to composition of the phenolic glucosides, while the subfractionation revealed that other structural features of the oligomers were also important. Using the DPPH radical, SDG and oligomeric fractions showed similar hydrogen-donating abilities comparable to ferulic acid but higher than α-tocopherol, which suggests that SDG was the only active antioxidant.