Efficient photosensitized degradation of 4-chlorophenol over immobilized aluminum tetrasulfophthalocyanine in the presence of hydrogen peroxide

The photosensitized degradation of 4-chlorophenol (4-CP) under visible light (lambda > or = 450 nm) irradiation in an aerated aqueous medium at pH 12 was studied using an immobilized photosensitizer, aluminum tetrasulfophthalocyanine, on a commercial resin Amberlite IRA 400. The catalyst exhibited strong adsorption toward 4-CP, but the adsorption led to an exponential decrease in both the initial rate and the apparent first-order rate constant, as measured by 4-CP loss in the bulk solution. Several intermediates were formed from 4-CP oxidation, including fumaric acid, benzoquinone, and hydroquinone, which were adsorbed strongly on the catalyst and lowered the photosensitized reaction. Addition of H2O2 was found to be an efficient way to eliminate the colored intermediates and consequently recover the catalyst activity. The immobilized sensitizer was stable and could be used repeatedly in the presence of H2O2. The optimal loading of the photosensitizer in the catalyst was about 1.0 wt %.     

Photoinduced degradation of orange II on different iron (hydr)oxides in aqueous suspension: rate enhancement on addition of hydrogen peroxide, silver nitrate, and sodium fluoride

Photoinduced organic oxidation with iron (hydr)oxides in aqueous suspension has been argued with respect to two principal mechanisms: (a) photoinduced ligand-to-metal charge transfer within a surface complex and (b) semiconductor photocatalysis. In this work, the photodegradation of azo dye orange II with UV light (lambda > or = 320 nm) in the aerated aqueous suspensions of haematite, maghemite, magnetite, goethite, lepidocrocite, and feroxyhite at an initial pH of 6.5 has been examined. The results showed that (1) all of the catalysts were effective at initiating dye photodegradation but the iron oxides appeared to be more active than the iron hydroxides; (2) the photodissolution of different iron phases and the dye photolysis in the dissolved iron solutions were very slow; (3) the initial rate of dye loss was proportional to the initial amount of adsorption, implying dye photodegradation on the catalyst surface; and (4) upon addition of H2O2, AgNO3, and NaF to the suspension, the rate of dye photodegradation was significantly enhanced with all the catalysts. In the presence of H2O2, less than 50% of the total rate enhancement was ascribed to the photo-Fenton reaction in solution and the dark Fenton reactions in solution and on the catalyst. In the presence of AgNO3, about 1 mole of silver particles was produced by consuming 3 moles of the dye substrate. In the presence of NaF, hydroxyl radicals were detected by an ethanol scavenger, whereas such radicals were not found in the absence of NaF. Moreover, under visible-light irradiation (lambda > or = 450 nm), the dye degradation was much slower than that under UV irradiation, but the reaction was also accelerated by the addition of NaF and AgNO3. The results suggest that mechanism b, not mechanism a, is operative for dye photodegradation occurring on the iron (hydr)oxides. A detailed discussion of all possible pathways is given in the text.     

Formation and characterization of the gallium and indium subhydride molecules Ga2H2 and In2H2: a matrix isolation study

Ga2 reacts spontaneously with H2 in solid Ar matrixes at 12 K to form the cyclic molecule Ga(mu-H)2Ga. In2 does not react with H2 under similar conditions, but irradiation at wavelengths near 365 nm induces the formation of the corresponding indium hydride, In(mu-H)2In. The molecules have been identified and characterized by the IR spectra displayed by matrixes containing the metal and H2, D2, HD, or H2 + D2; they each have planar, dihydrido-bridged structures with D2h symmetry, as endorsed by comparison of the measured spectra (i) with the properties forecast by quantum chemical calculations and (ii) with the spectra of known gallium and indium hydrides. Both are photolabile under visible light (lambda > 450 nm): green light (lambda = ca. 546 nm) causes Ga(mu-H)2Ga to isomerize to a mixture of HGaGaH and H2GaGa, whereas broad-band visible irradiation (lambda > 450 nm) of In(mu-H)2In gives rise to the isomer HInInH, together with InH. The isomerization can be reversed by UV photolysis (lambda = ca. 365 nm) of HGaGaH, H2GaGa, and HInInH or by near-IR photolysis (lambda > 700 nm) of HGaGaH and H2GaGa.     

Visible-light-induced photocatalytic degradation of 4-chlorophenol and phenolic compounds in aqueous suspension of pure titania: demonstrating the existence of a surface-complex-mediated path

The visible-light-induced degradation reaction of 4-chlorophenol (4-CP) was investigated in aqueous suspension of pure TiO2. Contrary to common expectations, 4-CP could be degraded under visible illumination (lambda > 420 nm), generating chlorides and CO2 concomitantly. The observed visible reactivity was not due to the presence of trace UV light since the visible-light-induced reactions exhibited behaviors distinguished from those of UV-induced reactions. Dichloroacetate could not be degraded under visible light, whereas it degraded with a much faster rate than 4-CP under UV irradiation. The addition of tert-butyl alcohol, a common OH radical scavenger, did not affect the visible reactivity of 4-CP, which indicates that OH radicals are not involved. Other phenolic compounds such as phenol and 2,4-dichlorophenol were similarly degraded under visible light. The surface complexation between phenolic compounds and TiO2 appears to be responsible for the visible light reactivity. Diffuse reflectance UV-vis spectra showed that 4-CP adsorbed on TiO2 powder induced visible light absorption. The visible light reactivity among several TiO2 samples was apparently correlated with the surface area of TiO2. The visible-light-induced photocurrents on a TiO2 electrode could be obtained only in the presence of 4-CP. It is proposed that a direct electron transfer from surface-complexed phenol to the conduction band of TiO2 upon absorbing visible light (through ligand-to-metal charge transfer) initiates the oxidative degradation of phenolic compounds. When the surface complex formation was hindered by surface fluorination, surface platinization, and high pH, the visible-light-induced degradation of 4-CP was inhibited. The evidence of visible-light-induced reactions and the experimental conditions affecting the visible reactivity were discussed in detail.     

Access to the naphthylcarbene rearrangement manifold via isomeric benzodiazocycloheptatrienes

Irradiation (lambda = 670 or >613 nm) of 4,5-benzodiazocycloheptatriene (15), matrix isolated in argon at 10 K, produces primarily 2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene (9) accompanied by small amounts of triplet 4,5-benzocycloheptatrienylidene (2) and 2-naphthylcarbene (10). A reversible photoequilibrium is established in which 9 is converted to 10 at lambda = 290 nm and then regenerated at lambda = 360 nm. Similarly, matrix-isolated 2,3-benzodiazocycloheptatriene (16) produces 4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene (11) at lambda = 670 or >613 nm, but without detection of 2,3-benzocycloheptatrienylidene (4). Irradiation of 11 at lambda = 290 nm induces ring opening to triplet 1-naphthylcarbene (12), which, in turn, cyclizes back to 11 at lambda = 342 or >497 nm. The diazo compounds and photoproducts are characterized by IR, UV/visible, and ESR spectroscopy, where appropriate, and by comparison of the experimental and B3LYP/6-31G calculated IR spectra for each species. Alternate rearrangement products such as allenes 6, 7, and 8 are not detected in the photolysis of either diazo compound.     

Application of a "black body" like reactor for measurements of quantum yields of photochemical reactions in heterogeneous systems

We report for the first time an experimental application of the concept of a "black body" like reactor to measure quantum yields (Phi) of photochemical reactions in liquid-solid heterogeneous systems. A major advantage of this new method is its simplicity since the fractions of reflected and transmitted light are negligible due to reactor geometry and high optical density of the heterogeneous systems. The average quantum yield of a test reaction (phenol photodegradation) over TiO(2) (Degussa P25) as determined by this method was 0.14, identical to the quantum yield measured earlier for this same reaction under similar conditions by Salinaro and Serpone. We also report the quantum yield of phenol photodegradation over N-doped TiO(2) during photoexcitation at the fundamental absorption band (lambda = 365 nm; Phi = 0.12) and at the N-doping induced extrinsic absorption band (lambda = 436 nm; Phi = 0.08) of the photocatalyst.     

Characterization of an LED based photoreactor to degrade 4-chlorophenol in an aqueous medium using coumarin (C-343) sensitized TiO2

A detailed performance evaluation of a simple high intensity LED based photoreactor exploiting a narrow wavelength range of the LED to match the spectrum of a dye in a photocatalysis system is reported. A dye sensitized (coumarin-343, lambda max = 446 nm) TiO 2 photocatalyst was used for the degradation of 4-chlorophenol (4-CP) in an aqueous medium using the 436 nm LED based photoreactor. The LED reactor performed competitively with a conventional multilamp reactor and sunlight in the degradation of 4-CP. Light intensities entering the reaction vessel were measured by conventional ferrioxalate actinometry. The results can be fitted by approximate first order kinetic behavior in this system. Hydroxyl radicals were detected by spin trapping EPR, and effects of OH radical quenchers on kinetics suggest that the reaction is initiated by these radicals or their equivalents. LEDs operating at competitive intensities offer a number of advantages to the photochemist or the environmental engineer via long life, efficient current to light conversion, narrow bandwidth, forward directed output, and direct current power for remote operation. Matching light source spectrum to chromophore is a key.     

Photodynamics of the bacteriochlorophyll-carotenoid system. 1. Bacteriochlorophyll-photosensitized oxygenation of beta-carotene in acetone.

Carotenoids are well-known physical quenchers of chlorophyll excited states and reactive oxygen species both in vivo and in vitro. They may also be involved in chemical quenching undergoing, e.g. isomerizations or oxidations. We have found that beta-carotene (Car) in aerobic acetone is rapidly oxygenated under strong illumination with red light (lambda exc > or = 630 nm) in the presence of bacteriopheophytin a. At the same time the photosensitizer undergoes only slight (< 10%) photodegradation. By preparative high-performance liquid chromatography as many as seven major products of oxygen attachment to Car have been isolated. Their molecular masses show that Car sequentially accumulates up to six oxygen atoms while its C40-skeleton remains intact.     

Photosensitization of crystalline and amorphous titanium dioxide by platinum(IV) chloride surface complexes

Anatase, rutile, and amorphous titania powders were surface-modified by grinding with PtCl4 and H2[PtCl6]. Only the anatase modification afforded hybrid photocatalysts capable of degradation of 4-chlorophenol (4-CP) with visible light, with sufficient stability towards decomplexation. Grinding with K2[PtCl4] produced materials of only low photocatalytic activity. Most efficient photocatalysts contained up to 2 wt% of PtIV. At higher surface loading the excess fraction of the complex is desorbed into the aqueous solution. Scavenging experiments with benzoic acid and tetranitromethane revealed that hydroxyl radicals are produced by the primary reduction of oxygen by conduction band electrons generated through electron injection from a postulated surface platinum(III) complex. It is proposed that the latter is formed from a charge-transfer ligand-to-metal (CTLM) excited state through homolysis of the Pt-Cl bond. Accordingly. the primary oxidation of 4-CP may occur by adsorbed chlorine atoms, the intermediary existence of which was demonstrated by scavenging experiments with phenol.     

Organogermanium reactive intermediates. The direct detection and characterization of transient germylenes and digermenes in solution

Diphenylgermylene (Ph2Ge) and its Ge=Ge doubly bonded dimer, tetraphenyldigermene (6a), have been characterized directly in solution for the first time by laser flash photolysis methods. The germylene is formed via (formal) cheletropic photocycloreversion of 3,4-dimethyl-1,1-diphenylgermacyclopent-3-ene (4a), which is shown to proceed in high chemical (>95%) and quantum yield (phi = 0.62) by steady-state trapping experiments with methanol, acetic acid, isoprene, and triethylsilane. Flash photolysis of 4a in dry deoxygenated hexane at 23 degrees C leads to the prompt formation of a transient assigned to Ph2Ge (lambda(max) = 500 nm; epsilon(max) = 1650 M(-1) cm(-1)), which decays with second-order kinetics (tau approximately 3 micros), with the concomitant growth of a second transient species that is assigned to digermene 6a (tau approximately 40 micros; lambda(max) = 440 nm). Analogous results are obtained from 1,1-dimesityl- and 1,1-dimethyl-3,4-dimethylgermacyclopent-3-ene (4b and 4c, respectively), which afford Mes2Ge (tau approximately 20 micros; lambda(max) = 560 nm) and Me2Ge (tau approximately 2 micros; lambda(max) = 480 nm), respectively, as well as the corresponding digermenes, tetramesityl- (6b; lambda(max) = 410 nm) and tetramethyldigermene (6c; lambda(max) = 370 nm). The results for the mesityl compound are compared to the analogous ones from laser flash photolysis of the known Mes2Ge/6b precursor, hexamesitylcyclotrigermane. The spectra of the three germylenes and two of the digermenes are in excellent agreement with calculated spectra, derived from time-dependent DFT calculations. Absolute rate constants for dimerization of Ph2Ge and Mes2Ge and for their reaction with n-butylamine and acetic acid in hexane at 23 degrees C are also reported.     

Isomerizations between nitrosyl halides X-N=O and isonitrosyl halides X-O-N: a matrix-spectroscopic study

Irradiation of nitrosyl bromide BrNO (4) with light of the wavelength lambda = 248 nm and nitrosyl chloride CINO (6) with lambda = 193 nm in an argon matrix at 10 K leads to the corresponding isomers isonitrosyl bromide BrON (5) and isonitrosyl chloride CION (7). Both new compounds 5 and 7 have been identified by comparison of the experimental and calculated (BLYP/6-311 + G*) IR spectra. Nitrosyl fluoride FNO (8) could not be transferred into isonitrosyl fluoride FON (9). The back reactions 5-->4 and 7-->6 can be initiated by UV (lambda > 310 nm), visible or IR light. The retransformation also occurs spontaneously in the matrix at 10 K under exclusion of any UV/Vis or IR radiation. Surprisingly, the reaction rates of these spontaneous back reactions are temperature independent between 8.5 and 25 K. The mechanism of these processes is discussed.     

Enhancement of metal-metal coupling at a considerable distance by using 4-pyridinealdazine as a bridging ligand in polynuclear complexes of rhenium and ruthenium

Novel polynuclear complexes of rhenium and ruthenium containing PCA (PCA = 4-pyridinecarboxaldehyde azine or 4-pyridinealdazine or 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) as a bridging ligand have been synthesized as PF(6-) salts and characterized by spectroscopic, electrochemical, and photophysical techniques. The precursor mononuclear complex, of formula [Re(Me(2)bpy)(CO)(3)(PCA)](+) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), does not emit at room temperature in CH(3)CN, and the transient spectrum found by flash photolysis at lambda(exc) = 355 nm can be assigned to a MLCT (metal-to-ligand charge transfer) excited state [(Me(2)bpy)(CO)(3)Re(II)(PCA(-))](+), with lambda(max) = 460 nm and tau < 10 ns. The spectral properties of the related complexes [[Re(Me(2)bpy)(CO)(3)}(2)(PCA)](2+), [Re(CO)(3)(PCA)(2)Cl], and [Re(CO)(3)Cl](3)(PCA)(4) confirm the existence of this low-energy MLCT state. The dinuclear complex, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(II)(NH(3))(5)](3+), presents an intense absorption in the visible spectrum that can be assigned to a MLCT d(pi)(Ru) --> pi(PCA); in CH(3)CN, the value of lambda (max) = 560 nm is intermediate between those determined for [Ru(NH(3))(5)(PCA)](2+) (lambda(max) = 536 nm) and [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](4+) (lambda(max) = 574 nm), indicating a significant decrease in the energy of the pi-orbital of PCA. The mixed-valent species, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(III)(NH(3))(5)](4+), was obtained in CH(3)CN solution, by bromine oxidation or by controlled-potential electrolysis at 0.8 V in a OTTLE cell of the [Re(I),Ru(II)] precursor; the band at lambda(max) = 560 nm disappears completely, and a new band appears at lambda(max) = 483 nm, assignable to a MMCT band (metal-to-metal charge transfer) Re(I) --> Ru(III). By using the Marcus-Hush formalism, both the electronic coupling (H(AB)) and the reorganization energy (lambda) for the metal-to-metal intramolecular electron transfer have been calculated. Despite the considerable distance between both metal centers (approximately 15.0 Angstroms), there is a moderate coupling that, together with the comproportionation constant of the mixed-valent species [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](5+) (K(c) approximately 10(2), in CH(3)CN), puts into evidence an unusual enhancement of the metal-metal coupling in the bridged PCA complexes. This effect can be accounted for by the large extent of "metal-ligand interface", as shown by DFT calculations on free PCA. Moreover, lambda is lower than the driving force -DeltaG degrees for the recombination charge reaction [Re(II),Ru(II)] --> [Re(I),Ru(III)] that follows light excitation of the mixed-valent species. It is then predicted that this reverse reaction falls in the Marcus inverted region, making the heterodinuclear [Re(I),Ru(III)] complex a promising model for controlling the efficiency of charge-separation processes.     

Synthesis of new visible light active photocatalysts of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M' = Nb, Ta): a band gap engineering strategy based on electronegativity of a metal component

We have synthesized new, efficient, visible light active photocatalysts through the incorporation of highly electronegative non-transition metal Pb or Sn ions into the perovskite lattice of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M = Sn, Pb; M' = Nb, Ta). X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that tetravalent Pb or Sn ions exist in the B-site of the perovskite lattice, along with In and Nb/Ta ions. According to diffuse UV-vis spectroscopic analysis, the Pb-containing quaternary metal oxides Ba(In(1/3)Pb(1/3)M'(1/3))O3 possess a much narrower band gap (E(g) approximately 1.48-1.50 eV) when compared to the ternary oxides Ba(In(1/2)M'(1/2))O3 (E(g) approximately 2.97-3.30 eV) and the Sn-containing Ba(In(1/3)Sn(1/3)M'(1/3))O3 derivatives (E(g) approximately 2.85-3.00 eV). Such a variation of band gap energy upon the substitution is attributable to the broadening of the conduction band caused by the dissimilar electronegativities of the B-site cations. In contrast to the ternary or the Sn-substituted quaternary compounds showing photocatalytic activity under UV-vis irradiation, the Ba(In(1/3)Pb(1/3)M'(1/3))O3 compounds induce an efficient photodegradation of 4-chlorophenol under visible light irradiation (lambda > 420 nm). The present results highlight that the substitution of electronegative non-transition metal cations can provide a very powerful way of developing efficient visible light harvesting photocatalysts through tuning of the band structure of a semiconductive metal oxide.     

185 nm UV降解水中4-CP、4-NP和Rh B的研究

本文以对氯苯酚(4-CP)、对硝基苯酚(4-NP)和罗丹明B(Rh B)为模型有机物(以4-CP和4-NP为小分子模型有机物,以Rh B为大分子模型有机物),分别研究了185 nm UV对水中这3种模型有机物的降解规律、性能和效果.研究结果表明,185 nm UV直接对水中4-CP、4-NP和Rh B有很好的降解效果.研究内容包括:185 nm UV降解模型有机物的浓度、TOC(Total organic carbon)浓度、185 nm UV降解模型有机物过程中溶液pH及电导率变化、以及降解模型有机物过程中产生的无机离子等几个方面.     

Photoproducts formed from photofrin II in cells

Fluorescence and absorption spectra of light-exposed cells containing the tumour-localizing porphyrin preparation Photofrin II (PII) have been studied. Light exposure results in spectral changes that may be due to a photoinduced modification of the porphyrins without breakage of the porphyrin macrocycle and/or to a photoinduced displacement of the porphyrins in the cells. Photochemical reaction involving breakage of the porphyrin macrocycle also occur as can be seen from the loss of absorbance within the Soret band region during light exposure. Singlet oxygen may be involved in the photodegradation of PII in cells since the process is slowed down on bubbling N2 through the samples and is slightly faster in suspensions in Dulbecco's phosphate buffered saline (PBS) made of D2O compared with suspensions in PBS made of H2O. During light exposure a fluorescent product is formed in the cells with fluorescence excitation and emission characteristics similar to those of the "age pigment" lipofuscin (lambda exc = 350 nm, lambda em = 440 nm).     

Study of acetone photodissociation over the wavelength range 248-330 nm: evidence of a mechanism involving both the singlet and triplet excited states

Measurements of the acetyl yield from acetone photolysis have been made using laser flash photolysis/laser induced fluorescence. Phi(total)(lambda,p,T) was determined over the ranges: 266 < or = lambda/nm < or = 327.5, 0.3 < or = p/Torr < or = 400 and 218 < or = T/K < or = 295. The acetyl yield was determined relative to that at 248 nm by conversion to OH by reaction with O2. Linear Stern-Volmer plots (1/[OH] vs [M]) describe the data for lambda < 300 nm, but for lambda > 300 nm, nonlinear Stern-Volmer plots were observed. This behavior is interpreted as evidence for dissociation from two excited states of acetone: S1 when the Stern-Volmer plots are linear and both S1 and T1 when Stern-Volmer plots are nonlinear. A model for acetone photolysis is proposed that can adequately describe both the present and literature data. Barriers to dissociation are invoked in order to explain the dependence of pressure quenching of the acetone photolysis yields as a function of wavelength and temperature. This pressure quenching was observed to become more efficient with increasing wavelength, but it was only above approximately 300 nm that a significant T dependence was observed, which became more pronounced at longer wavelengths. This is the first study to observe a T-dependent phi(total)(lambda,p,T). A parametrized expression for phi(total)(lambda,p,T) has been developed and is compared against the recommended literature data by running box model simulations of the atmosphere. These simulations show that acetone photolysis occurs more slowly at the top of the troposphere.     

Photodegradation of Rhodamine B over unexcited semiconductor compounds of BiOCl and BiOBr

This study reported, for the first time systematically, photodegradation of Rhodamine B (RhB) in aqueous solution over BiOCl and BiOBr semiconductors. Under visible light irradiation (λ>400 nm, λ>420 nm and λ=550±15 nm), RhB adsorbed on the surface of BiOCl and BiOBr was photosensitized and decomposed effectively over unexcited BiOCl and BiOBr. The degradation of Methyl Orange (MO) and Methylene Blue (MB) over BiOCl and BiOBr was investigated as well, and the results were compared with RhB photodegradation. It was found that MB molecules having the lowest LUMO could not be degraded by this process. Utilizing the quantum chemical calculation (Gaussian 03 program), the relationship between frontier orbital energy of selected dye molecules and photodegradation rate was established for the first time in this study.     

Computational modeling of the adsorption and photodegradation of 4-chlorophenol on anatase TiO2 particles

In the present work, the adsorption and photodegradation of 4-chlorophenol (4-CP) on the (100) surface of TiO₂ anatase with semiempirical SCF MO method MSINDO has been investigated. The (100) surface is modeled with free clusters (TiO₂)_n, where n = 20–80. The surface lattice titanium atoms, which are Lewis acid sites, are considered as adsorption sites. Molecular dynamics (MD) simulations have been used for the investigation of 4-CP adsorption conformations and the surface reaction mechanism studies. The 4-CP molecule has revealed parallel adsorption upon optimization, whereas under excitation conditions the perpendicular configuration is dominant. The aromatic ring cleavage by atomic oxygen has been studied computationally and accordingly, the relevant mechanism was suggested. By comparison with experimental and other theoretical calculations, it is shown that MSINDO can reproduce literature data with acceptable accuracy.     

Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

Summary The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV >290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.Presented at the 5th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region, Blanes, Spain, 2–6 October, 1989.     

Diastereoselectivity and site dependency in the photochemistry of ketoprofen in the bovine serum albumin matrix

The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumin matrix was studied by steady-state photolysis with the use of lambda(irr) > 320 nm and transient absorption spectroscopy with lambda(exc) = 355 nm, at 1/1 and 2/1 KP/BSA molar ratios. R(-)-KP was found to be more labile than S(+). Triplet ketoprofen species were evidenced with lifetimes of 400 ns for S(+) and 600 ns for R(-)-KP. Further longer-lived transients with lifetimes of 2.6 and 6.0 mus for S(+) and R(-), respectively, were detected. On the basis of the binding constants of the drug enantiomers to the two main binding sites of the protein, obtained from circular dichroism experiments, the individual disappearance quantum yields of the 1:1 and 2:1 diastereomeric KP:BSA complexes could be estimated. The photoreactivity in the BSA matrix was rationalized on the basis of diastereoselective photodecarboxylation in the two main protein sites.