Drug Delivery Strategies for Avobenzone: A Case Study of Photostabilization.

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.

Significance of D- tryptophan in Contryphan-Ar1131 Conus peptide: Oxidative folding, trypsin binding, and photostabilization activity.

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.

Fabrication of Highly Photostable Polystyrene Films Embedded with Organometallic Complexes.

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.

Tin Complexes of 4-(Benzylideneamino)benzenesulfonamide: Synthesis, Structure Elucidation and Their Efficiency as PVC Photostabilizers.

Poly(vinyl chloride) (PVC) suffers from photo-oxidation and photodegradation when exposed to harsh conditions. Application of PVC thus relies on the development of ever more efficient photostabilizers. The current research reports the synthesis of new complexes of tin and their assessment as poly(vinyl chloride) photostabilizers. The three new complexes were obtained in high yields from reaction of 4-(benzylideneamino)benzenesulfonamide and tin chlorides. Their structures were elucidated using different tools. The complexes were mixed with poly(vinyl chloride) at a very low concentration and thin films were made from the blends. The effectiveness of the tin complexes as photostabilizers has been established using a variety of methods. The new tin complexes led to a decrease in weight loss, formation of small residues, molecular weight depression, and surface alteration of poly(vinyl chloride) after irradiation. The additives act by absorption of ultraviolet light, removal the active chlorine produced through a dehydrochlorination process, decomposition of peroxides, and coordination with the polymeric chains. The triphenyltin complex showed the greatest stabilizing effect against PVC photodegradation as a result of its high aromaticity.

Characterization of Fluorescent Proteins with Intramolecular Photostabilization*.

Genetically encodable fluorescent proteins have revolutionized biological imaging in vivo and in vitro. Despite their importance, their photophysical properties, i. e., brightness, count-rate and photostability, are relatively poor compared to synthetic organic fluorophores or quantum dots. Intramolecular photostabilizers were recently rediscovered as an effective approach to improve photophysical properties of organic fluorophores. Here, direct conjugation of triplet-state quenchers or redox-active substances creates high local concentrations of photostabilizer around the fluorophore. In this paper, we screen for effects of covalently linked photostabilizers on fluorescent proteins. We produced a double cysteine mutant (A206C/L221C) of α-GFP for attachment of photostabilizer-maleimides on the ß-barrel near the chromophore. Whereas labelling with photostabilizers such as trolox, a nitrophenyl group, and cyclooctatetraene, which are often used for organic fluorophores, had no effect on α-GFP-photostability, a substantial increase of photostability was found upon conjugation to azobenzene. Although the mechanism of the photostabilizing effects remains to be elucidated, we speculate that the higher triplet-energy of azobenzene might be crucial for triplet-quenching of fluorophores in the blue spectral range. Our study paves the way for the development of fluorescent proteins with photostabilizers in the protein barrel by methods such as unnatural amino acid incorporation.

Tin Complexes Containing an Atenolol Moiety as Photostabilizers for Poly(Vinyl Chloride).

The lifetime of poly(vinyl chloride) (PVC) can be increased through the addition of additives to provide protection against irradiation. Therefore, several new tin complexes containing atenolol moieties were synthesized and their photostabilizing effect on PVC was investigated. Reacting atenolol with a number of tin reagents in boiling methanol provided high yields of tin complexes. PVC was then mixed with the tin complexes at a low concentration, producing polymeric thins films. The films were irradiated with ultraviolet light and the resulting damage was assessed using different analytical and surface morphology techniques. Infrared spectroscopy and weight loss determination indicated that the films incorporating tin complexes incurred less damage and less surface changes compared to the blank film. In particular, the triphenyltin complex was very effective in enhancing the photostability of PVC, and this is due to its high aromaticity (three phenyl rings) compared to other complexes. Such an additive acts as a hydrogen chloride scavenger, radical absorber, and hydroperoxide decomposer.

Dissolution of amorphous nifedipine from micelle-forming carboxymethylcellulose derivatives.

We show that a novel amphiphilic graft copolymer combining the biodegradability and biocompatibility of oxidized carboxymethylcellulose (CMC) with that of hydrophilic poly(ethylene glycol) (PEG), and hydrophobic dodecylamine (DDA), improves the solubility and dissolution performance of nifedipine (NIF), considered as a model hydrophobic drug. The hydrophobic components of the graft copolymer have the multiple effect of favouring micelle formation and loading. At the same time, the interaction between the hydrophobic core and NIF has the secondary effect to suppress drug crystallization, favouring its dissolution, and to increase photostability. Oxidized CMC-g-PEG-DDA micelles reached values of drug concentration, loading capacity and encapsulation efficiency as high as 340 µg mL-1, 6.4 % and 34.1 %, respectively. Loaded micelles showed a good stability with a limited release profile at pH 1.2, whereas at pH 7.4 the swollen cores enable much higher and progressive release, that reaches 3.4 and 6.6 % after 3 and 5 h, respectively, corresponding to very competitive concentration of 34 and 66 µg mL-1.

Photoprotective Effects of Selected Amino Acids on Naproxen Photodegradation in Aqueous Media.

It is important to develop a photostabilization strategy to ensure the quality of photosensitive compounds, including pharmaceuticals. This study focused on the protective effects of 20 amino acids on the photodegradation of naproxen (NX), a photosensitive pharmaceutical, to clarify the important nature of a good photostabilizer. Our previous report indicated the photodegradability of NX and the protective effects of some antioxidants on its photodegradation, therefore, this compound was used as a model compound. The degradation of NX in aqueous media during ultraviolet light (UV) irradiation and the protective effects of selected amino acids were monitored through high-performance liquid chromatography (HPLC), equipped with a reverse-phase column. Addition of cysteine, tryptophan, and tyrosine induced the significant suppression of NX photodegradation after UV irradiation for 3 h (residual amount of NX; 15.35%, 6.82%, and 15.64%, respectively). Evaluation of the antioxidative activity and UV absorption spectrum showed that cysteine suppressed NX degradation through its antioxidative ability, while tryptophan and tyrosine suppressed it through their UV filtering ability. Furthermore, three amino acids at higher concentrations (more than 100 µmol/L) showed more protective effects on NX photodegradation. For 10 mmol/L, residual amounts of NX with cysteine, tryptophan, and tyrosine were 58.51%, 69.34%, and 82.40%, respectively. These results showed the importance of both photoprotective potencies (antioxidative potency and UV filtering potency) and stability to UV irradiation for a good photostabilizer of photosensitive pharmaceuticals.

Influence of Polyphosphates on the Physicochemical Properties of Poly (Vinyl Chloride) after Irradiation with Ultraviolet Light.

Three new polyphosphates were synthesized in good yields by reacting diethylenetriamine with the appropriate phosphate ester in ethanol under acidic conditions. The polyphosphate structures were determined using FT-IR and 1H-NMR spectroscopies, and their elemental compositions were confirmed by EDX spectroscopy. Polyphosphates were added to poly(vinyl chloride) (PVC) at low concentrations to fabricate thin films. The PVC films were irradiated with ultraviolet light for long periods, and the effect of polyphosphates as the photostabilizer was investigated by determining changes in the infrared spectra (intensity of specific functional group peaks), reduction in molecular weight, weight loss, and surface morphology. Minimal changes were seen for PVC films containing polyphosphate compared to that for the blank film. In addition, optical, scanning electron, and atomic force microscopies were used to inspect the surface morphology of films. Undesirable changes due to photodegradation were negligible in PVC films containing additives compared to films containing no additives. In addition, the surfaces were smoother and more homogeneous. Polyphosphates, and in particular ones that contain an ortho-geometry, act as efficient photostabilizers to reduce the rate of photodegradation. Polyphosphates absorb ultraviolet light, chelate with polymeric chains, scavenge radical moieties, and decompose peroxide residues.

The Morphology and Performance of Poly(Vinyl Chloride) Containing Melamine Schiff Bases against Ultraviolet Light.

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.

1,4-Dihydropyridine Antihypertensive Drugs: Recent Advances in Photostabilization Strategies.

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.

Suppressing Effect of 2-Nitrobenzaldehyde on Singlet Oxygen Generation, Fatty Acid Photooxidation, and Dye-Sensitizer Degradation.

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).

Photostabilization strategies of photosensitive drugs.

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.

Photostability and Performance of Polystyrene Films Containing 1,2,4-Triazole-3-thiol Ring System Schiff Bases.

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.

Photostabilization studies of antihypertensive 1,4-dihydropyridines using polymeric containers.

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 (t0.1) 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 0.6mm 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 t0.1 values under 24min. These results can be a good opportunity to design new photoprotective pharmaceutical packaging for DHPs in liquid dosage form.

Photostability and ex-vivo permeation studies on diclofenac in topical niosomal formulations.

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.

Preparation and characterization of self-photostabilizing UV-durable bionanocomposite membranes for outdoor applications.

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>300nm 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.

The difficulties for a photolabile drug in topical formulations: the case of diclofenac.

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 3.90 min under a radiant exposure of 450 Wm(-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 12.22 min, 13.75 min and 15.71 min, respectively, under the same irradiation power. The best results were obtained by incorporating the drug in ß-cyclodextrin with a degradation of 10% after 25.01 min of light exposure.

The Power of Two: Covalent Coupling of Photostabilizers for Fluorescence Applications.

Fluorescence is a versatile tool for spectroscopic investigations and imaging of dynamic processes and structures across various scientific disciplines. The photophysical performance, that is, signal stability and signal duration, of the employed fluorophores is a major limiting factor. In this Letter, we propose a general concept to covalently link molecules, which are known for their positive effect in photostabilization, to form a combined photostabilizer with new properties. The direct linkage of two (or more) photostabilizers will allow one to obtain combined or synergetic effects in fluorophore stabilization and can simplify the preparation of imaging buffers that would otherwise require a mixture of photostabilizers for optimal performance. This concept was explored by synthesizing a molecule with a reducing and oxidizing moiety that is referred to as internal ROXS or "iROXS". Using single-molecule fluorescence microscopy, inter- and intramolecular healing of iROXS was observed, that is, strongly reduced blinking and increased photostability of the cyanine fluorophore Cy5. Moreover, it is shown that a covalently coupled photostabilizer can replace a mixture of molecules needed to make a functional photostabilizing ROXS buffer and might hence represent the new standard for defined and reproducible imaging conditions in single-molecule experiments. In self-healing fluorophores with intramolecular triplet-state quenching, an unprecedented photostability increase of >100-fold was obtained when using iROXS, which is even competitive with solution-based healing. Control experiments show that the oxidizing part of the iROXS molecule, an aromatic nitro group, dominates the healing process. The suggested synthetic concept and the proof-of-concept experiments represent the starting point for the quest to identify optimal combinations of linked photostabilizers for various fluorescence applications.

Estabilización de disoluciones acuosas de riboflavina por solapamiento espectral / Stabilization of aqueous solution of Riboflavin by spectral overlapping

Se evaluó la fotoestabilización de la riboflavina en disolución acuosa a través de solapamiento espectral. En estudios previos se determinó que la longitud de onda a 445 nm promueve la degradación de la riboflavina, por eso se escogieron los colorantes que mejor eficiencia de absorción presentaran a esta longitud de onda. El estudio de fotoprotección consistió en determinar y comparar las constantes de velocidad (k0) de las reacciones de fotodegradación de la riboflavina en disoluciones (80 µM) en presencia y ausencia de colorantes a diferentes concentraciones: tartrazina (40, 58, 71 y 187 µM), amarillo ocaso (80, 160, 442 y 1 600 µM) y amarillo de quinoleína (80,133, 160 y 1 600 µM). Las cinéticas se realizaron irradiando las muestras en una cámara de simulación solar a 250 W.m-2, a diferentes tiempos y cuantificando la riboflavina residual, mediante cromatografía líquida de alta resolución. Las constantes de velocidad (k0) se determinaron mediante el método integral. En ausencia de colorantes la fotodegradación de la riboflavina obedece a una cinética de orden cero (k0= 0,0012 mg.mL-1×min-1) con un 79,9 por ciento de degradación tras 20 min de exposición a la luz. En presencia de colorantes la estabilidad de la riboflavina mejora significativamente con el aumento de la concentración del colorante empleado; sin embargo, se encontró que el amarillo de quinoleína a bajas concentraciones (< 160 µM) incrementó la degradación de la riboflavina, mientras que en la concentración más alta estudiada, redujo 6 veces la k0, lo cual sugiere que interacciones químicas se están llevando a cabo. La mayor fotoprotección se obtuvo con el amarillo ocaso a la concentración legal permitida, donde la concentración de la riboflavina se mantuvo inalterada tras 30 min de irradiación. El estudio muestra que debido a la alta capacidad fotosensibilizante de la riboflavina, la técnica de fotoprotección por solapamiento espectral no se pueda usar de forma genérica, pues no solo se puede esperar un efecto fisicoquímico de solapamiento sino que pueden generarse interacciones fotoquímicas.

The photostabilization of Riboflavin (RF) in aqueous solution was evaluated through spectral overlap. Previous studies established that wavelength at 445nm promoted RF degradation; hence dyes that exhibited high absorption performance at 445 nm were selected. The photoprotection study consisted in determining and comparing the rate constants (k0) of the RF photodegradation reactions in solutions (80 µM), both in presence and absence of dyes at different concentrations: tartrazine (40, 58, 71 y 187 µM), sunset yellow (80, 160, 442 y 1 600 µM) and quinoline yellow (80, 133, 160 y 1600 µM).The kinetics were estimated by irradiating the samples in a solar simulation chamber at 250 W×m-2 and at different times; then the residual RF was quantified by HPLC method. The rate constants (k0) were determined by the integral method. When dyes are absent, the RF photodegradation is due to zero order kinetics (k0= 0.0012 mg×mL-1×min-1) with 79.9 percent degradation after 20 min of exposure to light. When dyes are present, the RF stability improves significantly with increasing concentration of the dye; however, it was found that quinoline yellow at low concentrations (<160 µM) increased the EF degradation, whereas at the highest studied concentration, k0 was reduced 6 times, suggesting that chemical interactions occurred. Most photoprotection was obtained from the sunset yellow at allowable concentration where RF concentration was unchanged after 30 min of irradiation. The study showed that the high photosensitizing capacity of riboflavin hindered the generic use of photoprotective technique through spectral overlapping, because physical-chemical effect of overlapping may be expected in addition to occurrence of photochemical interactions.