Quantification of sunscreen 2-phenylbenzimidazole-5-sulfonic acid in cosmetic products and water samples by HPTLC/densitometry with fluorescent detection

The water-soluble sunscreen 2-phenylbenzimidazole-5-sulfonic acid (PBS) was quantified in a sun-care product and water samples by thin layer chromatography followed by densitometric scanning in fluorescence mode (cut-off filter 370 nm, wavelength of excitation — 300 nm). Normal phase TLC was performed on silica gel 60 as stationary phase. Mobile phase used was ethyl acetate-ethanol-water 70:35:30 (v/v/v). The limit of detection (LOD) was 0.0004 μg spot-1, and the limit of quantification (LOQ) was — 0.001 μg spot^?1 without any sample pre-concentration.      

Phase behavior of aqueous mixtures of 2-phenylbenzimidazole-5-sulfonic acid and cetyltrimethylammonium bromide: hydrogels, vesicles, tubules, and ribbons

We studied the phase behavior and aggregation in mixed aqueous solutions of the anionic UV-absorber 2-phenylbenzimidazole-5-sulfonic acid sodium salt, PhBSA (Na salt), and the cationic surfactant cetyltrimethylammonium bromide, CTAB. The mixtures of the two components behave similarly to catanionic surfactant mixtures. The samples on the PhBSA-rich side have low viscosity and are turbid. The turbidity, due to uni- and multilamellar vesicles (SUVs and MLVs), increases with the mole ratio of CTAB. The interbilayer distance inside the MLV changes with the mole ratio of the two components from a few 10 nm for the 7:3 (molar ratio of PhBSA, Na salt, to CTAB) system to practically zero for the 5:5 mixture. The latter mixture forms a precipitate within less than 1 h. With the exception of the 5:5 mixture, all samples on the PhBSA-rich side are stable for many days. After that period, within one more day, the turbid vesicle phases are transformed into more or less clear hydrogels. We found that the gelation is due to the formation of very long stiff tubules about 14 nm in diameter, which is independent of the mixing ratio of the samples. The hydrogels and the tubules melt around 45 degrees C. On the CTAB-rich side, the 4:6 sample behaves like the 6:4 sample, whereas at 3:7 a precipitate was found to form shortly after mixing. At still smaller PhBSA (Na salt) to CTAB ratios, only clear, viscoelastic solutions are found that do not change with time. We determined the micellar structures in the samples by cryo-TEM and by SAXS. The rheological properties of the hydrogels and of the viscoelastic samples were characterized by oscillating rheological measurements. DSC measurements indicated that the tubules are in a semicrystalline state and melt at around 45 degrees C. The semicrystalline bilayer of the tubules seems to have a 1:1 composition of PhBSA to CTAB. The excess PhBSA seems to be adsorbed on the tubules. It is assumed that the stiffness of the bilayer of the vesicles and the stiffness of the tubules are due to the stiffness of the PhBSA molecule.     

Photophysical and photochemical studies of thifensulfuron-methyl herbicide in aqueous solution

The photophysical and photochemical studies of a sulfonylurea herbicide, thifensulfuron-methyl (THM), have been investigated in a buffered aqueous solution. In the first part, the influence of pH on the spectroscopic properties was studied. This allowed the determination of the ground and excited state acidity constants, pK_a = 4 and 4.4, respectively, thus exhibiting the potential existence of a photoinduced protonation in the singlet state. In the second part, the photolysis kinetics was studied at different pH and varying oxygen concentrations, using an HPK 125 W lamp and followed up by the identification of photoproducts formed under continuous photo-irradiation. The kinetics results suggest that the photolysis process is faster in acidic (k = 3 × 10^?4 s^?1) than in basic medium (k = 9.8 × 10^?5 s^?1). The photolysis products were identified by high performance liquid chromatography HPLC-DAD, HPLC–MS and HPLC–MS–MS. In order to obtain a better understanding of the photodegradation mechanism, a laser flash photolysis study was performed. By comparing the quenching rate constant (k_q = 9.64 × 10⁸ mol^?1 l s^?1) obtained from triplet state quenching by molecular oxygen and from the Stern–Volmer relation (k_q = 0.41 × 10⁸ mol^?1 l s^?1), the role of the singlet state in the photodegradation process was demonstrated. The photoproducts originating from both singlet and triplet excited states have been identified and hypothetical photodegradation pathways of the thifensulfuron-methyl in aqueous solution are proposed.     

Complexes of barium ions with quercetin-5′-sulfonic acid and sodium salt of morin-5′-sulfonic acid

Complex formation of Ba²⁺ ions with quercetin-5′-sulfonic acid and sodium salt of morin-5′-sulfonic acid was studied by potentiomety. Solid complexes were obtained, and their composition and physicochemical properties were studied.     

Photophysical and photochemical effects of dye binding

Abstract— A discussion is given of the photophysical and photochemical consequences of the binding of dyes and of pigments of biological importance to polymeric substrates. The modification of the photochemical properties induced by dye binding can in large part be ascribed to the known changes in photophysical properties of dyes engendered by such interactions. Principally, these involve enhanced formation of metastable species of dye molecules and decreased opportunity for self-quenching. In photochemical terms, dye binding thus enhances susceptibility to photoreduction, causes an increase in the quantum yield of photoreduction with increasing concentration of bound dye, and induces enhanced ability to act as a sensi-tizer in photoreduction. Paradoxically, dye binding decreases the ability of the bound dye to act as a sensitizer in photoxidation.     

超分子体系中的光物理和光化学过程

总结了我们组近几年来对超分子体系中的光物理和光化学过程所做的工作,包括三个部分：(1)微反应器控制的有机光化学反应的选择性,(2)疏水、疏脂作用对光物理和光化学过程的影响,(3)超分子体系中的电子转移、能量传递和光化学转换。     

Chemical and photoluminescence properties of purified poly(2-methoxyaniline-5-sulfonic acid) and oligomer

Both the chemical and the electrochemical synthesis of poly(2-methoxyaniline-5-sulfonate) (PMAS) in aqueous media have been found to give two distinct polymer fractions with molecular weights of approximately 8-10 and 2 kDa, respectively. It is now possible to isolate the pure high molecular weight (HMWT) PMAS and low molecular weight (LMWT) PMAS oligomer and to study their individual and combined photochemistry and redox chemistry. The HMWT PMAS fraction was confirmed to be an emeraldine salt by its characteristic redox and pH switching behavior, in contrast to the oligomeric LMWT PMAS, which was inert under the same conditions. Mixtures of these two fractions exhibit photoluminescence arising from the oligomeric LMWT PMAS fraction. The observed LMWT PMAS emission was modulated by the presence of the conducting HMWT PMAS emeraldine salt via a static resonant energy transfer arising from quenching at 460 nm when excited at 355 nm. The nonlinear fluorophore-quencher behavior suggests that the two PMAS fractions are strongly associated. The behavior fitted the static Perrin quenching model in which the oligomeric LMWT PMAS fluorophore is diffusionally restricted by the presence of HMWT PMAS quencher.     

Photophysical, photochemical, and thermodynamic properties of shikimic acid derivatives: calycin and rhizocarpic acid (lichens)

Photophysical and photochemical parameters of the lichen metabolites calycin and rhizocarpic acid were determined. Experiments were carried out in micellar solutions of 3% Brij 35, at pH 2 and 12, and in acetonitrile. Both metabolites absorb in the UV-A and UV-B regions, and emit fluorescence in the visible region of the solar spectrum. Shifts were not observed in the absorption spectra, at pH 2 and 12. The low phi(c), between 10(-5) and 10(-2), shows that both compounds are photostable in the experimental conditions. For rhizocarpic acid, two values of pK(a) were obtained: 5.1 corresponding to the hydroxyl group, and 9.0 corresponding to the protonated nitrogen. Calycin presents only one value of pK(a): 4.9, that is attributed to the hydroxyl group. L-(+)-Gluconic-gamma-lactonic acid was used as a reference model; the compound showed greater photoinstability, demonstrating that the photodegradation observed occurs mainly in the oxolane carbonylic ring.     

Complex formation and Fluorescence : Complexes of 8-hydroxyquinoline-5-sulfonic acid

The fluorescence of solutions of cation complexes with 8-hydroxyquinoline-5-sulfonic acid has been studied. The complexes formed with transition elements do not fluoresce. The additivity of the fluorescence at certain pH values has been used to indicate new generally applicable analytical method for mixtures of cations which have similar reactions. The method is especially applicable to small or very dilute samples.     

Photophysical and photochemical properties of lignin chromophores in aqueous systems

The results are given of an investigation of the changes in the physicochemical properties of the chromophores of lignin substances of effluents by photopotential, luminescence, and ESR spectroscopy and the polarographic determination of oxygen as a function of the number of quanta of incident energy in the interval from 300 to 600 nm. It has been established that under the action of light a change in the redox properties, an increase in the rate of consumption of oxygen, the formation of radical intermediate products, and the appearance of excited triplet states of the lignin chromophores take place in the lignin substances. Action spectra of the photopotential, of the yield of EPCs of free radicals, and of the consumption of oxygen by the lignin substances in the interval from 300 to 600 nm have been obtained.Siberian Scientific-Research Institute of Cellulose and Board Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 269–274, March–April, 1987.     

Photochemical studies on a phenolic phenylcoumarone lignin model molecule in relation to the photodegradation of lignocellulosic materials. Part 2. Photophysical and photochemical studies

The structure of the photoproducts obtained by irradiation of a phenylcoumarone molecule PCO, model of the photodegradation of lignin, being established, the mechanism of their formation was approached by fluorescence and flash photolysis techniques, low temperature absorption spectroscopy in rigid matrix, and continuous irradiation in solution and in the solid state. Some evidence was given for the formation of a phenoxy radical leading either by oxidoreductive processes to the formation of a catechol IR3, or by coupling with the starting phenol to the generation of a cyclobutane radical dimer, prone to be transformed into stilbene phenoxy radical by retro “2π+2π” reaction. It was proposed that the oxidation of the latter could give the very coloured quinone methide IR1 or the α-carbonylstilbenol IR2. The singlet manifold appears to be the main pathway of the production of IR1, IR2 and IR3 which are formed in the presence of ground state oxygen.     

Substitution reactions of 5-nitropyridine-2-sulfonic acid. A new pathway to 2,5-disubstituted pyridines

We have investigated reactions of 5-nitropyridine-2-sulfonic acid and its potassium salt in which substitution of the sulfonate group by oxygen, nitrogen and halogen nucleophiles has been attempted. By this approach, 2-methoxy- (95% yield), 2-ethoxy- (97%), 2-isopropoxy- (65%), 2-amino- (92%), 2-butylamino- (76%), 2-diethylamino- (62%), 2-ethylamino- (32%), 2-benzylamino- (77%), 2-(R-1-phenylethylamino)- (71%) and 2-chloro-5-nitropyridine (87%) have been obtained. No reactions were observed with phenols or anilines. With t-BuOH, 2-hydroxy-5-nitropyridine was formed together with 2-methylpropene.     

A novel photoaddition of 2-phenylbenzimidazole

Irradiation of 2-phenylbenzimidazole ( 3 ) in the presence of methyl acrylate (20 equivalents) using a medium pressure mercury lamp gives methyl 2-(2-phenylbenzimidazol-1-yl)propionate ( 4 ) (75%) whose structure has been confirmed by an X-ray analysis. A similar reaction using acrylonitrile gave only a low yield (1%) of the corresponding propionitrile derivative 5 . A mechanism involving photoexcitation of 2-phenylbenzimidazole ( 3 ) followed by sequential single electron transfer, proton transfer and radical coupling is proposed to account for the formation of the novel photoadducts 4 and 5 .     

Tautomeric structure of 1-Oxy-2-phenylbenzimidazole

The synthesis of 3-methyl-2-phenylbenzimidazole-1-oxide (VIII) has been accomplished. Consequently, it has been possible to establish the tautomeric structure of I as 1-hydroxy-2-phenylbenzimidazole (Ia). Contrary to recent observations on the parent 1-oxybenzimidazole (IV), I shows no tendency to exist as an N-oxide (Ib) in aqueous solution.     

Indirect fluorescent determination of selected nitro-aromatic and pharmaceutical compounds via UV-photolysis of 2-phenylbenzimidazole-5-sulfonate

An indirect fluorescence (FL) detection method via the reactivity of UV-photolyzed 2-phenylbenzimidazole-5-sulfonate (PBSA) has been developed for non-fluorescent aromatic compounds. At high pH with UV photolysis, PBSA in the excited state is known to be quenched by reaction with oxygen species and analyte compounds that are reactive toward these oxygen species produced during photolysis can lessen the loss of PBSA FL. After off-line photolysis of PBSA in the presence of various nitro-aromatic test compounds, the increase in PBSA FL is clearly evident. A flow injection (FI) instrument using a PBSA mobile phase propelled through a Teflon coil wrapped around a Hg lamp is optimized and modified for use for liquid chromatography (LC). For the on-line FI determination of the non-fluorescent nitro-aromatic compounds such as 4-nitroaniline, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, and -nitronaphthalene, a positive linear response for PBSA FL from about 0.5 to 15 μM and detection limits generally between 0.2 and 1 μM (4–20 pmol) are found. Linear responses and detection limits of selected pharmaceutical compounds such as the antibacterial nitrofurantoin, antihistamines chlorpheniramine and brompheniramine, and other compounds were similar. In general, detection limits using UV detection at about 214 nm were not as good in the 1–2 μM range but linearity extended up to 100 μM. The amino acid phenylalanine and small peptides containing this aromatic amino acid were also determined using this method. Application of this detection method for the liquid chromatography determination of 4-nitroaniline, 2-nitrophenol, nitrofurantoin, and salicylate is shown.     

Enhancement and quenching of fluorescence of metal chelates of 8-hydroxyquinoline-5-sulfonic acid

Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents. Al is extraordinarily amenable to both types of fluorescence enhancement, an order of magnitude to two order of magnitude enhancement of fluorescence intensity has been observed with aqueous hexadecyltrimethylammonium chloride (HTAC) and certain mixed aqueous-organic solvents. Fe(III) appears to be an unusually powerful fluorescence quencher in these systems — the effect is noticeable in low micromolar concentrations and is greatly amplified by cationic surfactants such as HTAC.     

Crystal structure of 2-aminopyridine-5-sulfonic acid and its 2D coordination polymer [Ag(C5H5N2O3S)] n

The crystal structure of an organosulfonate ligand 2-aminopyridine-5-sulfonic acid is reported here. Reaction of AgNO₃ and the 2-aminopyridine-5-sulfonic acid in basic ethanol/aqueous solution gave [Ag(C₅H₅N₂O₃S)] _n (1). X-ray crystallographic study reveals that 1 is a 2D network structure constructed by strong Ag-pyridine, Ag–NH₂ interactions and weaker Ag-sulfonate interactions. The replacement of the benzene ring by the pyridine ring causes the coordination modes of the sulfonate group to change from μ ³ to μ². Its TG/DSC property is also discussed.