This article is published as part of a themed issue of Photochemical & Photobiological Sciences in honour of The contribution of Japanese scientists to photochemistry

Guest edited by Cornelia Bohne and Tadashi Mori

Published in issue 9, 2011

Communications

Enantiospecific 6π-photocyclization of atropisomeric α-substituted acrylanilides in the solid-state, A. J.-L.

Ayitou, N. Vallavoju, A. Ugrinov and J. Sivaguru, Photochem. Photobiol. Sci., 2011, 10, 1380

Applications of hydrogen-bond-acceptor templates to direct „in-phase‟ reactivity of a diene diacid in the solid state, M. B. J. Atkinson, A. N. Sokolov, D.-K. Bučar, S. V. S. Mariappan, M. T. Mwangi, M. C. Tiedman and L. R. MacGillivray, Photochem. Photobiol. Sci., 2011, 10, 1384

Asymmetric photocycloaddition of naphthamide with a diene using the provisional molecular chirality in a chiral crystal, M. Sakamoto, F. Yagishita, A. Saito, S. Kobaru, A. Unosawa, T. Mino and T. Fujita, Photochem. Photobiol. Sci., 2011, 10, 1387

Role of entropy in supramolecular photochirogenesis, R. Maeda, T. Wada, A. Kusaka, T. Mori, M. Iwamoto and Y. Inoue, Photochem. Photobiol. Sci., 2011, 10, 1390

Papers

Supramolecular architecture of tetrathiafulvalene-bridged bis(β-cyclodextrin) with porphyrin and its electron transfer behaviors, Y.-M. Zhang, Y. Chen, R.-J. Zhuang and Y. Liu, Photochem. Photobiol. Sci., 2011, 10, 1393

Microphotochemistry: a reactor comparison study using the photosensitized addition of isopropanol to furanones as a model reaction, O. Shvydkiv, A. Yavorskyy, S. B. Tan, K. Nolan, N. Hoffmann, A. Youssef and M. Oelgemöller, Photochem. Photobiol. Sci., 2011, 10, 1399

Competitive photocyclization/rearrangement of 4-aryl-1,1-dicyanobutenes controlled by intramolecular charge-transfer interaction, T. Ito, E. Nishiuchi, G. Fukuhara, Y. Inoue and T. Mori, Photochem. Photobiol. Sci., 2011, 10, 1405

A new photo-switchable “on-off” host–guest system, Y. Kim, Y. H. Ko, M. Jung, N. Selvapalam and K. Kim, Photochem. Photobiol. Sci., 2011, 10, 1415

Effect of sodium chloride on the binding of polyaromatic hydrocarbon guests with sodium cholate aggregates, D. Fuentealba, K. Thurber, E. Bovero, T. C. S. Pace and C. Bohne, Photochem. Photobiol. Sci., 2011, 10, 1420

Sweet chiral porphyrins as singlet oxygen sensitizers for asymmetric Type II photooxygenation, A. G. Griesbeck, M. A. Miranda and J. Uhlig, Photochem. Photobiol. Sci., 2011, 10, 1431

Enhancement of vibrational coherence by femtosecond degenerate four-wave-mixing for a chromophore in 1-propanol glass, Y. Nagasawa, S. Ito, M. Muramatsu and H. Miyasaka, Photochem. Photobiol. Sci., 2011, 10, 1436

Efficient and selective photodimerization of 2-naphthalenecarbonitrile mediated by cucurbit[8]uril in an aqueous solution, B. Chen, S.-F. Cheng, G.-H. Liao, X.-W. Li, L.-P. Zhang, C.-H. Tung and L.-Z. Wu, Photochem. Photobiol. Sci., 2011, 10, 1441

Hydrogen-bonding directed, regioselective photocycloaddition reactions of cyanonaphthalenes with furanmethanols, H. Maeda, K. Chiyonobu and K. Mizuno, Photochem. Photobiol. Sci., 2011, 10, 1445

Photochemistry of 2-diphenylmethoxyacetophenone, A. K. Sundaresan, S. Jockusch and N. J. Turro, Photochem. Photobiol. Sci., 2011, 10, 1450

Role of free space and weak interactions on geometric isomerization of stilbenes held in a molecular container, A. Parthasarathy and V. Ramamurthy, Photochem. Photobiol. Sci., 2011, 10, 1455

Chirogenic [3 + 2]-photocycloaddition reactions of 2-substituted naphthoquinones with cyclic alkenes, C. Müller, A. Bauer and T. Bach, Photochem. Photobiol. Sci., 2011, 10, 1463

Hydroxy-group effect on the regioselectivity in a photochemical oxetane formation reaction (the Paternò-Büchi Reaction) of geraniol derivatives, K.

Hisamoto, Y. Hiraga and M. Abe, Photochem. Photobiol. Sci., 2011, 10, 1469

Photochemical and photophysical properties of dibenzoylmethane derivatives within protein, M. Marin, V. Lhiaubet-Vallet, C. Paris, M. Yamaji and M. A. Miranda, Photochem. Photobiol. Sci., 2011, 10, 1474

The synthesis and stereospecific solid-state photodecarbonylation of hexasubstituted meso- and d,l-ketones, S. Shiraki, A. Natarajan and M. A. Garcia-Garibay, Photochem. Photobiol. Sci., 2011, 10, 1480

Kinetic studies on visible-light-switchable photochromic fluorophores based on diarylethenes, B. Seefeldt, K. Altenhöner, O. Tosic, T. Geisler, M. Sauer and J. Mattay, Photochem. Photobiol. Sci., 2011, 10, 1488

Regiospecific [2 + 2] photocyclodimerization of trans-4-styrylpyridines templated by cucurbit[8]uril, A. Nakamura, H. Irie, S. Hara, M. Sugawara and S. Yamada, Photochem. Photobiol. Sci., 2011, 10, 1496

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online / Journal Homepage / Table of Contents for this issue

Photochemical &Photobiological Sciences

Dynamic Article Links

Cite this: Photochem. Photobiol. Sci., 2011, 10, 1474

www.rsc.org/pps PAPER

Photochemical and photophysical properties of dibenzoylmethane derivativeswithin protein†

Mireia Marin,a Virginie Lhiaubet-Vallet,a Cecilia Paris,a Minoru Yamaji*b and Miguel Angel Miranda*a

Received 15th February 2011, Accepted 3rd April 2011DOI: 10.1039/c1pp05072a

In the present work, three dibenzoylmethane derivatives in their b-diketo form have been selected toinvestigate their photophysical and photochemical behavior upon interaction with human serumalbumin (HSA). In organic solvents, absorption and phosphorescence emission spectra of the a-bromoderivative of avobenzone (BrAB) were similar to those of the a-methylated and a-propyl analogs(MeAB and PrAB). However, laser flash photolysis experiments revealed a different transient speciescentered at 350 nm, assigned to the radical obtained from a singlet excited state dehalogenation process.Interestingly, the transient absorption spectrum of BrAB within HSA showed the typical features of theb-diketone triplet excited state. In the case of MeAB and PrAB derivatives, binding to HSA wasassociated with a significant increase of their triplet lifetimes as compared to acetonitrile. Finally, theNorrish type II process has been considered as a model to evaluate the influence of the proteinmicroenvironment on the photoreactivity. In this context, photodegradation of PrAB in aeratedsolutions, to give avobenzone (AB), has been monitored by UV spectroscopy. Interestingly, the quantumyields of AB formation were markedly dependent on the reaction medium (1.4 ¥ 10-2 in acetonitrile and3.9 ¥ 10-2 within albumin medium); by contrast, chemical yields of ca. 50% were obtained in both cases.

Introduction

Supramolecular photochemistry is an important research field.In this context, organized assemblies have been demonstrated toenhance the efficiency and selectivity of numerous photochemicalreactions.1–10 During the last decade, special emphasis has beenplaced on serum albumins as host molecules, because of theirability to bind a large variety of compounds.11–18 The chiral envi-ronment provided by protein cavities has been exploited to achievestereoselective photoprocesses, such as the photodegradation of1,1¢-binaphthol, ketoprofen and carprofen,12–13,19 or the bimolec-ular [4 + 4] photodimerization of 2-anthracene carboxylate.15–18

More recently, studies on 9-anthraceneacetic acid encapsulatedwithin serum albumins have shown that proteins provide animportant protection towards photooxidation.11 Interestingly, inthe photo-Fries rearrangement of naphthyl esters it has been foundthat the quantum yield of product formation depends not only onthe serum albumin species but also on the binding site location ofthe substrate.14

aInstituto de Tecnologıa Quımica UPV-CSIC, Universidad Politecnica deValencia, Consejo Superior de Investigacion Cientificas, Avda de LosNaranjos, s/n, 46022, Valencia, Spain. E-mail: mmiranda@qim.upv.es;Fax: +34 963877807; Tel: +34 963877809bDepartment of Chemistry and Chemical Biology, Graduate Schoolof Engineering, Gunma University, Kiryu, Gunma, 376-8515, Japan.E-mail: yamaji@gunma-u.ac.jp; Fax: +81-277-301212; Tel: +81-277-301212† This article is published as part of a themed issue in honour of YoshihisaInoue’s research accomplishments on the occasion of his 60th birthday.

It is well established that the photophysics and photochemistryof b-dicarbonyl compounds are governed by keto-enol tautomer-ization, with the chelated enol form predominating in solution.Typical examples of this family are 1,3-dibenzoylmethane (DBM)derivatives. Strong UVA absorption of the enol tautomer has beenexploited in the field of solar protection with avobenzone (AB, 4-tert-butyl-4¢-methoxydibenzoylmethane), which is recognized asone of the most representative UVA filters. Nevertheless, ABexhibits an important drawback; under UVA-irradiation extensivephotoisomerization to the b-diketone takes place (Scheme 1).Indeed, this tautomer is photoactive giving rise to irreversible

Scheme 1 Structures of avobenzone (AB) and its a-methyl (MeAB),a-propyl (PrAB) and a-bromo (BrAB) derivatives.

1474 | Photochem. Photobiol. Sci., 2011, 10, 1474–1479 This journal is © The Royal Society of Chemistry and Owner Societies 2011

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online

photodegradation by fragmentation and oxidation, and as aconsequence the protoprotecting properties are lost.

We have previously investigated the photobehavior of twoa-alkylated AB derivatives exhibiting the typical spectroscopicproperties of the DBM in their b-diketonic forms, namely 1,1-(4-tert-butylbenzoyl)-(4¢-methoxybenzoyl)ethane and 1,1-(4-tert-butylbenzoyl)-(4¢-methoxybenzoyl)butane (MeAB and PrAB, re-spectively, Scheme 1).20–21 The former has been demonstrated to bea good model of the AB b-diketo form, not only for photophysicalcharacterization of the triplet excited state, but also for the studyof its reactivity towards biological targets like 2¢-deoxyguanosine,thymidine, tyrosine or tryptophan.20 As regards the latter, its mostinteresting feature is the ability to generate AB upon irradiationby a Norrish II reaction, behaving therefore as a pro-UV filter.21

In the present study, interest has shifted to the influence ofhuman serum albumin on the photochemical and photophysicalproperties of b-diketones. For this purpose, we have selected assubstrates MeAB, PrAB and the a-bromo AB derivative (4-tert-butyl-4¢-methoxydibenzoylbromomethane; BrAB, Scheme 1). Inprinciple, this compound is also expected to be in the keto-formin the ground state, and could undergo C–Br bond dissociationin the excited states, resulting in radical formation. Therefore,in a first stage, spectroscopic study of BrAB in solution will bepresented. Then, the influence of human serum albumin (HSA) onthe photobehavior of the three AB derivatives will be discussed.

Experimental

Chemicals

Avobenzone (4-tert-butyl-4¢-methoxydibenzoylmethane, AB)>99% purity was purchased from Fluka, and purified byrecrystallizations from ethanol before use. Methylavobenzone(MeAB) was prepared and purified according to thepreviously reported procedure.20 Bromoavobenzone (BrAB)was prepared according to the procedure reported fordibenzoylbromomethane.22 N-Methyldiphenylamine (MDPA)from Tokyo Kasei (TCI) was distilled under reduced pressurefor purification before the use. Acetonitrile (ACN) was distilledfor purification. Ethanol (EtOH, spectroscopy grade) fromKishida, methylcyclohexane (MCH, Spectrosol) from Dojinand isopentane (IP, for UV-spectroscopy) from Fluka were usedwithout further purification. Solutions of phosphate-bufferedsaline (PBS) (0.01 M, pH 7.4) were prepared by dissolvingphosphate-buffered saline tablets (Sigma) in deionized water.

Absorption and emission spectroscopy

Absorption spectra were recorded on a U-best 50 (JASCO)or a Cary 300 spectrophotometer, while emission spectra weremeasured on a Hitachi F-4010 fluorescence spectrophotometer.All the samples for transient absorption measurements wereprepared in the dark, and Ar-purged or degassed in a quartz cellwith a 1 cm path length by several freeze-pump-thaw cycles on ahigh vacuum line.

Laser flash photolysis

Two laser flash photolysis systems were employed for the presentstudies. The first one was based on a pulsed Xe/HCl Excimer

Laser (LEXTRA50 Lambda Physik LaserTechnik), using 308 nmas excitation wavelength (40 mJ per pulse, 10 ns per pulse). A Lo255Oriel xenon lamp was employed as detecting light source. The laserflash photolysis apparatus consisted of a pulsed laser, a Xe lamp,a monochromator (Oriel, model 77200), a photomultiplier (Oriel,model 70705) system and a TDS-640A Tektronix oscilloscope.The output signal from the oscilloscope was transferred to apersonal computer. The concentration of BrAB was adjusted toan absorbance of ~0.3 at the excitation wavelength. Solutions ofHSA/AB derivatives (1/1 molar ratio) were prepared in PBS andequilibrated in the dark for 1 h.

The second system was used to record a transient absorptionspectrum of BrAB in EtOH at 77 K. The excitation laser lightsource was obtained from the fourth harmonics (266 nm) of aNd3+:YAG laser (JK Lasers HY-500; pulse width 8 ns). Furtherdetails of the detection system for the time profiles of thetransient absorption have been reported elsewhere.23 The transientabsorption spectra were taken with a USP-554 system fromUnisoku, which can provide a transient absorption spectrum withone laser pulse.

Quenching of xanthone triplet excited state by BrAB

An argon bubbled acetonitrile solution of xanthone was preparedwith absorbance of ~0.3 at lexc = 308 nm (Xe/HCl laser). A stocksolution of BrAB was used so that it was only necessary to addmicrolitre volumes to the sample cell in order to obtain appropriateconcentrations of the quencher (from 0 to 1.6 ¥ 10-5 M). A rateconstant for the reaction of the triplet excited state of xanthonewith BrAB was obtained from Stern–Volmer plots, following eqn(1).

kobs = ko + kq[Q] (1)

where kobs and ko are the triplet decay rate constants in the presenceand in the absence of quencher, kq is the quenching rate constantand [Q] is the quencher concentration in mol L-1.

Photoirradiation systems

Steady-state photolysis was carried out by using monochromaticirradiation at 305 nm with a Microbeam system (model L-201),including a 150 W xenon lamp coupled with a monochromator(model 101).

Kinetics of PrAB photodegradation

Aerated solutions of PrAB in ACN (2.85 ¥ 10-5 M) or in PBSin the presence of HSA (1/1 molar ratio) were prepared in 10mm ¥ 10 mm quartz cuvettes. Irradiation was carried out at themonochromatic wavelength of 305 nm with slit bandwidth of 2.5nm. Kinetics of photoproduct formation was obtained by plottingabsorbance at 357 nm versus irradiation time. Molar absorptioncoefficients of AB were determined to be 32 200 and 18 500 M-1

cm-1 for acetonitrile and HSA solutions, respectively.The photon flux at 305 nm was determined by using MDPA

in aerated MCH as a chemical actinometer. The quantum yieldfor the formation of N-methylcarbazole from MDPA has beenestablished as 0.42.24 The procedure for determining quantumyields from absorption changes was the same as that described

This journal is © The Royal Society of Chemistry and Owner Societies 2011 Photochem. Photobiol. Sci., 2011, 10, 1474–1479 | 1475

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online

Table 1 Photophysical properties of AB derivatives

Compound lmax/nm (e/M-1 cm-1) ET/kcal mol-1

MeAB 260 (21000)a ,b 70.7a ,b

PrAB 269 (26900)b 70.7b

BrAB 270 (22100) 68.3

a Data from ref. 20. b Data from ref. 21.

in the literature.25 All the samples were prepared in a quartz cellwith a 1 cm path length in the dark.

Results and discussion

Absorption and emission properties of BrAB

As shown in Fig. 1, BrAB exhibits the typical absorption bandof the b-diketo form of DBM at 260–270 nm.20 No fluorescenceemission was observed in ACN at 295 K. The phosphorescencespectrum obtained in EtOH at 77 K shows an emission centeredat 440 nm, with vibrational structures due to the carbonylprogression. Moreover, the excitation spectrum of this emissionagrees well with BrAB absorption. The energy level of the lowesttriplet (T1) state was determined to be 68.3 kcal mol-1 fromthe 0–0 origin of the phosphorescence spectrum. Thus, BrABspectroscopic data were very similar to those previously reportedfor MeAB and PrAB (Table 1).20–21

Fig. 1 Absorption and phosphorescence spectra of BrAB in ACN at 295K and in EtOH at 77 K, respectively.

Laser flash photolysis study of BrAB

To investigate the reaction intermediates generated by photolysisof BrAB in solution, laser flash photolysis was performed at308 nm, with a pulsed excimer Xe/Cl laser. In ACN at 295 K,a transient absorption with maximum at 350 nm was observed(Fig. 2A). The corresponding decay showed a first order kineticswith a lifetime of 70 ms under nitrogen. This transient absorptionspectrum must be due to an avobenzone radical (ABR) producedby excited state debromination of BrAB.

In order to further characterize the BrAB excited species, xan-thone was used as triplet sensitizer. As shown in Fig. 2B, xanthonetriplet excited state was efficiently quenched by BrAB (kq ca. 2 ¥1010 M-1 s-1). However, no new transient species was detected.Different explanations could be given as a very short lifetimeand/or a low molar absorption coefficient of 3BrAB transient. It is

Fig. 2 (A)Transient absorption spectrum obtained upon 308 nm laserflash photolysis at 295 K of BrAB in deaerated ACN, 3 ms after thelaser pulse. (B) Kinetic traces of the triplet–triplet absorption of xanthonemonitored at 612 nm, in the presence of increasing amounts of BrAB (from0 to 1.6 ¥ 10-5 M). (C) Transient absorption spectrum of BrAB at 100 ns,obtained upon 266 nm laser pulsing in EtOH solution at 77 K.

noteworthy that the long-lived transient with maximum at 350 nmwas not observed under triplet state photosensitization conditions,thus suggesting that dehalogenation leading to ABR radical is asinglet excited state mediated process. Next, low temperature 266-nm laser photolysis of BrAB was run in EtOH matrix at 77 K.A transient absorption spectrum with a maximum at ca. 400 nmwas obtained and assigned to 3BrAB by comparison with the T-Tabsorption of other b-diketo derivatives (Fig. 2C).

Interaction between MeAB, PrAB or BrAB and HSA

Aerated solutions of MeAB, PrAB or BrAB in the presence ofHSA (1/1 molar ratio) were submitted to laser flash photolysis

1476 | Photochem. Photobiol. Sci., 2011, 10, 1474–1479 This journal is © The Royal Society of Chemistry and Owner Societies 2011

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online

at 308 nm. At this wavelength, the protein alone did not give riseto any absorption band. Moreover, due to the limited solubilityof the three compounds in PBS, the photobehavior of the HSAcontaining systems was compared to that of the AB derivatives inaerated ACN solutions.

Similar transient absorption spectra were obtained for MeABand PrAB in the presence and in the absence of HSA. In both cases,the detected species was the triplet excited state of the b-diketoform (see Fig. 3A and B). Moreover, as previously observed inbulk solution, 3PrAB gave rise to formation of an absorption bandcentered at 350 nm, which was ascribed to AB formation through

Fig. 3 Transient absorption spectra of MeAB (2.8 ¥ 10-4 M, A), PrAB(2.5 ¥ 10-4 M, B) and BrAB (3.8 ¥ 10-5 M, C) in aerated PBS, in the presenceof HSA (1/1 molar ratio) after 308 nm laser pulse. Inset: Correspondingdecays monitored at 400 nm.

a Norrish type II reaction. By contrast, both 3MeAB and 3BrABdecayed without generation of new detectable intermediates. Animportant observation was the decay kinetics of these transients,which was markedly slower within the protein (Fig. 3, insets).Thus, 3MeAB lifetime increased from 0.13 ms to 2.4 ms (18 times),whereas a 40-fold enhancement was noticed in the case of 3PrAB(t = 0.14 and 6.0 ms in ACN and HSA media, respectively). Theseresults are in agreement with the reported protecting effect of HSAfrom self-quenching or from attack by oxygen.12–13,26

Interestingly, different species were observed for BrAB in thebulk solution and complexed within HSA. In this latter case, atransient with maximum at ca. 400 nm and a lifetime of 0.3 ms,corresponding to BrAB triplet–triplet absorption spectrum, wasdetected (Fig. 3C). It is worth noting that this species was onlyobserved during the laser flash photolysis of BrAB in EtOH glass(Fig. 2C) at 77 K, but not at room temperature. Thus, the confinedmicroenvironment provided by the protein produces similar effectsas the rigid matrix supplied by the low temperature glass.

Photochemistry of protein-bound PrAB

After investigating the photophysical behavior of AB derivativeswithin HSA, the influence of the protein cavities on the photore-activities was considered. For this purpose, the Norrish II reactionof PrAB was selected as model reaction, because it was clean (ascompared to the photodegradation of MeAB and BrAB) and easyto monitor by UV-spectral changes.

Thus, monochromatic irradiation (l = 305 nm) was performedfor aerated solutions of PrAB in ACN or PBS/HSA, and thecourse of the reaction was followed by UV spectroscopy. As shownin Fig. 4A, the decrease of PrAB absorption band at 260 nm inboth media gave rise to a new band centered at 357 nm, assignedto AB enol.21 When the kinetics of AB formation was compared(Fig. 4B), the reaction was found to be significantly slower in thepresence of HSA. This is consistent with the quantum yields (fR)of AB formation, determined using N-methyldiphenylamine asactinometer, which were 2.8 times lower in protein than in ACN (fR

= 1.4 ¥ 10-2 and 3.9 ¥ 10-2, respectively). This correlates well withthe increase of 3PrAB lifetime when complexed with the protein(see above). Therefore, it appears that the conformation requiredfor intramolecular abstraction of the g-hydrogen by the excitedcarbonyl is disfavored within the confined microenvironmentprovided by HSA. Interestingly, after long irradiation times theyields of AB formation (ca. 50%) were very similar in both media.

Conclusions

In this work, three dibenzoylmethane derivatives have been con-sidered to investigate the influence of HSA on their photobehavior.From a photophysical point of view, the increase of tripletexcited state lifetime of PrAB and MeAB reflects the protectiveeffect provided by the protein cavity. Another interesting resultis detection of the triplet excited state of BrAB, a species that,in the absence of HSA, is only observed in low temperaturematrixes. Thus, the confined environment supplied by the proteinis similar to the matrix effect. From the photochemical viewpoint,the most remarkable result is the modified photoreactivity of PrABin the Norrish type II reaction, probably due to conformationalrestrictions.

This journal is © The Royal Society of Chemistry and Owner Societies 2011 Photochem. Photobiol. Sci., 2011, 10, 1474–1479 | 1477

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online

Fig. 4 (A) Norrish type II photoreaction of PrAB (2.85 ¥ 10-5 M) in ACNunder UVB irradiation (monochromatic light at 305 nm), followed by UVabsorption spectroscopy (at 357 nm). Inset: Experiment performed underthe same conditions for PrAB in PBS, in the presence of HSA (1/1 molarratio); for a better clarity the initial spectrum of PrAB/HSA solutionshas been subtracted (B) Yields of AB formation, determined from theabsorption changes (followed at 357 nm) after monochromatic irradiationof PrAB in ACN or PBS, in the presence of HSA (1/1 molar ratio).

Acknowledgements

Spanish Government (CTQ2009-13699 project, Ramon y Cajalcontract to V.L.-V. and JAE pre-doc contract to M. M.), General-itat Valenciana (Prometeo Program 2008/090 and GV/2009/051projects) and Universidad Politecnica de Valencia (PAID 06-08project) are gratefully acknowledged for financial support. M.Y. is grateful for a financial support, Grant-in-Aid for ScientificResearch (KAKENHI) from JSPS.

Notes and references

1 S. Arumugam, D. R. Vutukuri, S. Thayumanavan and V. Ramamurthy,Amphiphilic homopolymer as a reaction medium in water: productselectivity within polymeric nanopockets, J. Am. Chem. Soc., 2005,127, 13200–13206.

2 T. Bach, H. Bergmann, B. Grosch and K. Harms, Highly enantioselec-tive intra- and intermolecular [2 + 2] photocycloaddition reactions of2-quinolones mediated by a chiral lactam host: host–guest interactions,product configuration, and the origin of the stereoselectivity in solution,J. Am. Chem. Soc., 2002, 124, 7982–7990.

3 D. F. Cauble, V. Lynch and M. J. Krische, Studies on the enan-tioselective catalysis of photochemically promoted transformations:

“sensitizing receptors” as chiral catalysts, J. Org. Chem., 2003, 68, 15–21.

4 T. J. Dickerson, M. R. Tremblay, T. Z. Hoffman, D. I. Ruiz and K.D. Janda, Catalysis of the photo-Fries reaction: antibody-mediatedstabilization of high energy states, J. Am. Chem. Soc., 2003, 125, 15395–15401.

5 L. S. Kaanumalle, C. L. D. Gibb, B. C. Gibb and V. Ramamurthy,Photo-Fries reaction in water made selective with a capsule, Org.Biomol. Chem., 2007, 5, 236–238.

6 L. S. Kaanumalle, J. Nithyanandhan, M. Pattabiraman, N. Jayaramanand V. Ramamurthy, Water-soluble dendrimers as photochemicalreaction media: chemical behavior of singlet and triplet radical pairsinside dendritic reaction cavities, J. Am. Chem. Soc., 2004, 126, 8999–9006.

7 Y. Kawanami, T. C. S. Pace, J.-i. Mizoguchi, T. Yanagi, M. Nishi-jima, T. Mori, T. Wada, C. Bohne and Y. Inoue, Supramolecu-lar complexation and enantiodifferentiating photocyclodimerizationof 2-anthracenecarboxylic acid with 4-aminoprolinol derivatives aschiral hydrogen-bonding templates, J. Org. Chem., 2009, 74, 7908–7921.

8 S. Saphier, Y. Hu, S. C. Sinha, K. N. Houk and E. Keinan, Origin ofselectivity in the antibody 20F10-catalyzed Yang cyclization, J. Am.Chem. Soc., 2005, 127, 132–145.

9 S. Saphier, R. Piran and E. Keinan, Photoenzymes and photoabzymes,in Catalytic antibodies, ed. E. Keinan, Wiley-VCH, 2005, pp. 350–369.

10 S. Saphier, S. C. Sinha and E. Keinan, Antibody-catalyzed enantios-elective Norrish type II cyclization, Angew. Chem., Int. Ed., 2003, 42,1378–1381.

11 R. Alonso, M. Yamaji, M. C. Jimenez and M. A. Miranda, Enhancedphotostability of the anthracene chromophore in aqueous mediumupon protein encapsulation, J. Phys. Chem. B, 2010, 114, 11363–11369.

12 V. Lhiaubet-Vallet, F. Bosca and M. A. Miranda, Stereodifferentiatingdrug-biomolecule interactions in the triplet excited state: studieson supramolecular carprofen/protein systems and on carprofen-tryptophan model dyads, J. Phys. Chem. B, 2007, 111, 423–431.

13 V. Lhiaubet-Vallet, Z. Sarabia, F. Bosca and M. A. Miranda, Humanserum albumin-mediated stereodifferentiation in the triplet state behav-ior of (S)- and (R)-carprofen, J. Am. Chem. Soc., 2004, 126, 9538–9539.

14 M. Marin, V. Lhiaubet-Vallet and M. A. Miranda, Site-dependentphoto-Fries rearrangement within serum albumins, J. Phys. Chem. B,2011, 115, 2910–2915.

15 M. Nishijima, T. C. S. Pace, A. Nakamura, T. Mori, T. Wada,C. Bohne and Y. Inoue, Supramolecular photochirogenesis withbiomolecules. Mechanistic studies on the enantiodifferentiation forthe photocyclodimerization of 2-anthracenecarboxylate mediated bybovine serum albumin, J. Org. Chem., 2007, 72, 2707–2715.

16 M. Nishijima, T. Wada, T. Mori, T. C. S. Pace, C. Bohne and Y. Inoue,Highly enantiomeric supramolecular [4 + 4] photocyclodimerization of2-anthracenecarboxylate mediated by human serum albumin, J. Am.Chem. Soc., 2007, 129, 3478–3479.

17 T. C. S. Pace, M. Nishijima, T. Wada, Y. Inoue and C. Bohne,Photophysical studies on the supramolecular photochirogenesis forthe photocyclodimerization of 2-anthracenecarboxylate within serumalbumins, J. Phys. Chem. B, 2009, 113, 10445–10453.

18 T. Wada, M. Nishijima, T. Fujisawa, N. Sugahara, T. Mori, A.Nakamura and Y. Inoue, Bovine serum albumin-mediated enantiod-ifferentiating photocyclodimerization of 2-anthracenecarboxylate, J.Am. Chem. Soc., 2003, 125, 7492–7493.

19 A. Ouchi, G. Zandomeneghi and M. Zandomeneghi, Complexationwith albumins of chiral aromatic substrates and their chemistry inground and excited states. Catalytic and chirality recognition propertiesof the protein in the cases of binaphthol, its photoisomers, andketoprofen, Chirality, 2002, 14, 1–11.

20 C. Paris, V. Lhiaubet-Vallet, O. Jimenez, C. Trullas and M. A. Miranda,A blocked diketo form of avobenzone: photostability, photosensitizingproperties and triplet quenching by a triazine-derived UVB-filter,Photochem. Photobiol., 2009, 85, 178–184.

21 M. Yamaji, C. Paris and M. A. Miranda, Steady state and laserflash photolysis studies on photochemical formation of 4-tert-butyl-4¢-methoxydibenzoylmethane from its derivative via the Norrish typeII reaction in solution, J. Photochem. Photobiol., A, 2010, 209, 153–157.

22 J. Kosmrlj, M. Kocevar and S. Polanc, A new convenient brominationwith KBrO3/KBr/DowexR, Synth. Commun., 1996, 26, 3583–3592.

1478 | Photochem. Photobiol. Sci., 2011, 10, 1474–1479 This journal is © The Royal Society of Chemistry and Owner Societies 2011

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online

23 M. Yamaji, Y. Aihara, T. Itoh, S. Tobita and H. Shizuka, Thermo-chemical profiles on hydrogen atom transfer from triplet naphthol andproton-induced electron transfer from triplet methoxynaphthalene tobenzophenone via triplet exciplexes studied by laser flash photolysis, J.Phys. Chem., 1994, 98, 7014–7021.

24 E. W. Forster, K. H. Grellmann and H. Linschitz, Reaction patternsand kinetics of the photoconversion of N-methyldiphenylamine to N-methylcarbazole, J. Am. Chem. Soc., 1973, 95, 3108–3115.

25 M. Hoshino and M. Koizumi, Order of quencher partici-pation in photochemistry. I. Proton, transfer from the ex-cited p-hydroxybenzophenone in mixed solvents of cyclohex-ane and alcohols, Bull. Chem. Soc. Jpn., 1972, 45, 2731–2736.

26 I. Vaya, C. J. Bueno, M. C. Jimenez and M. A. Miranda, Use of tripletExcited states for the study of drug binding to human and bovine serumalbumins, ChemMedChem, 2006, 1, 1015–1020.

This journal is © The Royal Society of Chemistry and Owner Societies 2011 Photochem. Photobiol. Sci., 2011, 10, 1474–1479 | 1479

Publ

ishe

d on

05

May

201

1. D

ownl

oade

d by

Sta

te U

nive

rsity

of

New

Yor

k at

Sto

ny B

rook

on

28/1

0/20

14 0

5:37

:47.

View Article Online