The energetics of the oxidative additive of 12 to [Ir(/.t-L)(CO)2]2 [L = t-buthylthiolate (S'Bu),... more The energetics of the oxidative additive of 12 to [Ir(/.t-L)(CO)2]2 [L = t-buthylthiolate (S'Bu), 3,5-dimethylpyrazolate (3,5-Me2pz), and 7-azaindolate (7-aza)] complexes was investigated by using the results of reaction-solution calorimetric measurements, X-ray structure determinations, and extended HiJckel (EH) molecular orbital calculations. The addition of I mol of iodine to 1 mol of [Ir(/~-L)(CO)2]2, in toluene, leads to [Ir(/z-L)(l)(CO),.]2, with the formation of two Ir--I bonds and one Ir--lr bond. The following enthalpies of reaction were obtained for this process: -125.8 __ 4.9 kJ mol -I (L = S'Bu), -152.0 +_ 3.8 kJ mol -I (L = 3,5-Me2pz), and -205.9 4-9.9 kJ mol -~ (L = 7-aza). These results are consistent with a possible decrease of the strain associated with the formation of three-, four-, and five-membered rings, respectively, in the corresponding products, as suggested by the results of EH calculations. The calculations also indicate a slightly stronger Ir--Ir bond for L = 3,5-Me,_pz than for L = S'Bu despite the fact that the Ir--Ir bond lengths are identical for both complexes. The reaction of l mol of [Ir(p,-S'Bu)(CO)2] 2 with 2 mol of iodine to yield [Ir(tt-S'Bu)(I)2(CO)2]2 was also studied. In this process four Ir--I bonds are formed, and from the corresponding enthalpy of reaction (-186.4 _ 2.7 kJ tool -~) a solution phase Ir--I mean bond dissociation enthalpy in [Ir(p,-S'Bu)(I)2(CO)2]2, DH~ln(Ir--I) = 122.2 _ 0.7 kJ mol -t, was derived. This value is lower than most D--H, in values reported for octahedral mononuclear Ir m complexes. New large-scale syntheses of the [Ir(/z-L)(CO)2]2 complexes, with yields up to 90%, using [Ir(acac)(CO)2] as starting material, are also reported. The X-ray structures of [Ir(#-L)(I)(CO)2]2 (L = S'Bu and 3,5-MeEpz) complexes have been determined. For L = S'Bu the crystals are monoclinic, space group P2dc, a = 10.741(2) ,~, b = 11.282(3) ,4,, c = 1.8.308(3) ,~,,/3 = 96.71(1) ~ and Z = 4. Crystals of the/.t-3,5-MeEpz derivative are monoclinic, space group P2t/n, a = 14.002(3) A., b = 10.686(1) ,~, c = 15.627(3) tk, t3 = 112.406(8) ~ and Z = 4.
... The concentration of anthocyanin was in the range 0.1−1 mΜ in the voltammetric measurements a... more ... The concentration of anthocyanin was in the range 0.1−1 mΜ in the voltammetric measurements and the protocatechuic acid was 10 mM. ... Theoretical calculations were carried out on a personal computer using HyperChem version 5.0 software from Hypercube. ...
The fluorescence decays of a stereoregular head-to-tail RR-HT poly(3-hexylthiophene), P3HT, in me... more The fluorescence decays of a stereoregular head-to-tail RR-HT poly(3-hexylthiophene), P3HT, in methylcyclohexane (MCH) are described by sums of three or four exponential terms, respectively above and below -10 °C. In the high-temperature region, the polymer lifetime (ca. 500 ps) is accompanied by two shorter decay times (ca. 20 and 120 ps), which are assigned to intrachain energy transfer from high to lower energy excitons on the basis of temperature and wavelength dependence of the fluorescence decays. The absence of conformational (torsional) relaxation is attributed to the small dihedral angle between monomers that is predicted for the stereoregular polymer in the ground state. Below -10 °C, the polymer forms excimer-like aggregates, showing vibrational structured absorption and emission bands similar to those observed in thin films. The vibrational structure is attributed to a deep minimum in the ground-state energy surface of the dimer or aggregate. Below -40 °C, the fluorescence measured at the aggregate emission wavelength (670 nm) basically results from direct excitation of the aggregate and decays with a sum of three exponential terms (decay times of ca. 0.14, 0.6, and 1.5 ns, with similar weights). Because the spectral similarities between film and aggregates indicate similar electronic first singlet excited states (and oscillator strengths), the much shorter decay times (0.05, 0.15, and 0.43 ns) and lower fluorescence quantum yield of P3HT in films are assigned to efficient exciton dissociation and/or phonon-induced internal conversion competing with radiative decay (>1 ns).
The red flavylium cations of anthocyanins form ground-state charge-transfer complexes with severa... more The red flavylium cations of anthocyanins form ground-state charge-transfer complexes with several naturally occurring electron-donor copigments, such as hydroxylated flavones and hydroxycinnamic or benzoic acids. Excitation of the 7-methoxy-4-methyl-flavylium-protocatechuic acid complex results in ultrafast (240 fs) internal conversion to the ground state of the complex by way of a low-lying charge-transfer state. Thus, both uncomplexed anthocyanins, whose excited state decays by fast (5-20 ps) excited-state proton transfer, and anthocyanin-copigment complexes have highly efficient mechanisms of deactivation that are consistent with the proposed protective role of anthocyanins against excess solar radiation in the vegetative tissues of plants.
Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate ... more Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate constant for proton transfer to water in the excited state as high as 1.5 x 10(11) s(-1). The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) has an additional carboxyl group at the 4-position of the flavylium cation that deprotonates in the ground state at a lower pH (pK(a1) = 0.73; AH2+ --> Z) than the 7-hydroxy group (pK(a2) = 4.84; Z --> A-). Ground-state deprotonation of the carboxyl group of the acid (AH2+) to form the zwitterion (Z) is too fast to be detected by nanosecond laser flash perturbation of the ground-state equilibrium, while deprotonation of the hydroxyl group of Z to form the anionic base (A-) occurs in the microsecond time range (k(d2) = 0.6 x 10(6) s(-1) and k(p2) = 4.2 x 10(10) M(-1) x s(-1)). In the excited state, the cationic form (AH2+) deprotonates in approximately 9 ps, resulting in the excited neutral base form (AH), which is unstable in the ground state. Deprotonation of Z occurs in 30 ps (k(d2) = 2.9 x 10(10) s(-1)), to form excited A-, which either reprotonates (k(p3)* = 3.7 x 10(10) M(-1) x s(-1)) or decays in 149 ps, and shows an important contribution from geminate recombination to give the excited neutral base (AH). Predominant reprotonation of A- at the carboxylate group reflects both the presence of the negative charge on the carboxylate and the increase in the excited-state pK(a) of the carboxyl group. Thus, while the hydroxyl pK(a) decreases by approximately 5 units upon going from the ground state (pK(a) = 4.84) to the excited state (pK(a) = -0.2), that of the carboxyl group increases by at least this much. Consequently, the excited state of the Z form of CHMF acts as a molecular proton transporter in the picosecond time range.
Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmenta... more Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E red ≈ -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA Anthoc -IP Cop , the difference between the electron affinity of the anthocyanin, EA Anthoc , and the ionization potential of the copigment, IP Cop . Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.
Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV ra... more Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV radiation and are effective antioxidants and scavengers of active oxygen species. In plant leaves, one of the functional roles proposed for anthocyanins is protection of the photo synthetic apparatus from the effects of excess incident visible or UV-B radiation and photo oxidative stress. In essence, a photoprotective role requires that the excited singlet states of both complexed and uncomplexed anthocyanins deactivate back to the ground state so quickly that intersystem crossing, photoreaction, and diffusion-controlled quenching processes cannot compete. Studies of the photochemical properties of synthetic analogs of anthocyanins and of several naturally occurring anthocyanins show that this is indeed the case, uncomplexed anthocyanins decaying back to the ground state via fast (subnanosecond) excited-state proton transfer (ESPT) and anthocyanin-copigment complexes by fast (subpicosecond) charge-transfer-mediated internal conversion.
The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed... more The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed to probe some of the fundamental features of proton transfer reactions at the surface of anionic sodium dodecyl sulfate (SDS) and cationic hexadecyltrimethylammonium chloride (CTAC) micelles. In contrast to most ordinary flavylium salts, HHMF is insoluble in water, but readily incorporates into SDS and CTAC micelles. In the ground state, the rate constant for deprotonation of the acid form (AH + ) of HHMF decreases 100-fold upon going from CTAC (k d ) 3.0 × 10 6 s -1 ) to SDS (k d ) 1.4 × 10 4 s -1 ), consistent with the presence of an activation barrier for proton transfer in the ground state and reflecting, respectively, stabilization or destabilization of the AH + cation by the micelle. Reprotonation of A is diffusion-controlled in both micelles (k p (SDS) ) (2.1 × 10 11 )[H + ] aq s -1 and k p (CTAC) ) (3.7 × 10 8 )[H + ] aq s -1 ), the difference reflecting the rate of proton entry into the micelles. In the excited singlet state, the rate constants for deprotonation of the AH + * form of HHMF are similar in the two micelles (2.4 × 10 10 s -1 ), consistent with activationless proton transfer. Reprotonation of the excited A* is dominated by fast geminate recombination of the photogenerated (A*-H + ) pair at the micelle surface (k rec (SDS) ) 6.1 × 10 9 s -1 and k rec (CTAC) ) 3.4 × 10 10 s -1 ) and the net efficiencies of geminate recombination are quite similar in SDS (0.89) and CTAC (0.86).
Keywords: Alkyl side chain / Hydrophobic flavylium salts / Micelles / Photochromism / Ultrafast p... more Keywords: Alkyl side chain / Hydrophobic flavylium salts / Micelles / Photochromism / Ultrafast proton transfer A one-step preparation of several flavylium salts containing alkyl side chains in their 3-, 4Ј-, 5-or 6-positions is described. Flavylium salts with alkyl side chains in positions 3 or 4Ј were isolated from reactions between 2,4-dihydroxybenzaldehyde and decanophenone, dodecanophenone and 4Ј-hexyl-or 4Јdodecylacetophenone. Flavylium salts with alkyl side chains in positions 5 or 6 were prepared through reactions between benzoylacetone and 4-hexyl-, 4-dodecyl-or 5-pentylresorcinol. The new compounds are insoluble or sparingly soluble [a]
This article describes the results of a coupled photophysical and photobiological study aimed at ... more This article describes the results of a coupled photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs amodiaquine (AQ), primaquine (PQ) and chloroquine (CQ). Photophysical experiments were carried out in aqueous solutions by steady-state and time-resolved spectrometric techniques to obtain information on the different decay pathways of the excited states of the drugs and on the transient species formed upon laser irradiation. The results showed that all three drugs possess very low fluorescence quantum yields (10 )2 -10 )4 ). Laser flash photolysis experiments proved the occurrence of photoionization processes leading to the formation of a radical cation in all three systems. In the case of AQ the lowest triplet state was also detected. Together with the photophysical properties the photobiological properties of the antimalarial drugs were investigated under UV irradiation, on various biological targets through a series of in vitro assays. Phototoxicity on mouse 3T3 fibroblast and human keratinocyte cell lines NCTC-2544 was detected for PQ and CQ but not for AQ. In particular, PQ-and CQ-induced apoptosis was revealed by the externalization of phosphatidylserine. Furthermore, upon UV irradiation, the drugs caused significant variations of the mitochondrial potential (Dw mt ) measured by flow cytometry. The photodamages produced by the drugs were also evaluated on proteins, lipids and DNA. The combined approaches were useful in understanding the mechanism of phototoxicity induced by these antimalarial drugs.
The energetics of the oxidative additive of 12 to [Ir(/.t-L)(CO)2]2 [L = t-buthylthiolate (S'Bu),... more The energetics of the oxidative additive of 12 to [Ir(/.t-L)(CO)2]2 [L = t-buthylthiolate (S'Bu), 3,5-dimethylpyrazolate (3,5-Me2pz), and 7-azaindolate (7-aza)] complexes was investigated by using the results of reaction-solution calorimetric measurements, X-ray structure determinations, and extended HiJckel (EH) molecular orbital calculations. The addition of I mol of iodine to 1 mol of [Ir(/~-L)(CO)2]2, in toluene, leads to [Ir(/z-L)(l)(CO),.]2, with the formation of two Ir--I bonds and one Ir--lr bond. The following enthalpies of reaction were obtained for this process: -125.8 __ 4.9 kJ mol -I (L = S'Bu), -152.0 +_ 3.8 kJ mol -I (L = 3,5-Me2pz), and -205.9 4-9.9 kJ mol -~ (L = 7-aza). These results are consistent with a possible decrease of the strain associated with the formation of three-, four-, and five-membered rings, respectively, in the corresponding products, as suggested by the results of EH calculations. The calculations also indicate a slightly stronger Ir--Ir bond for L = 3,5-Me,_pz than for L = S'Bu despite the fact that the Ir--Ir bond lengths are identical for both complexes. The reaction of l mol of [Ir(p,-S'Bu)(CO)2] 2 with 2 mol of iodine to yield [Ir(tt-S'Bu)(I)2(CO)2]2 was also studied. In this process four Ir--I bonds are formed, and from the corresponding enthalpy of reaction (-186.4 _ 2.7 kJ tool -~) a solution phase Ir--I mean bond dissociation enthalpy in [Ir(p,-S'Bu)(I)2(CO)2]2, DH~ln(Ir--I) = 122.2 _ 0.7 kJ mol -t, was derived. This value is lower than most D--H, in values reported for octahedral mononuclear Ir m complexes. New large-scale syntheses of the [Ir(/z-L)(CO)2]2 complexes, with yields up to 90%, using [Ir(acac)(CO)2] as starting material, are also reported. The X-ray structures of [Ir(#-L)(I)(CO)2]2 (L = S'Bu and 3,5-MeEpz) complexes have been determined. For L = S'Bu the crystals are monoclinic, space group P2dc, a = 10.741(2) ,~, b = 11.282(3) ,4,, c = 1.8.308(3) ,~,,/3 = 96.71(1) ~ and Z = 4. Crystals of the/.t-3,5-MeEpz derivative are monoclinic, space group P2t/n, a = 14.002(3) A., b = 10.686(1) ,~, c = 15.627(3) tk, t3 = 112.406(8) ~ and Z = 4.
... The concentration of anthocyanin was in the range 0.1−1 mΜ in the voltammetric measurements a... more ... The concentration of anthocyanin was in the range 0.1−1 mΜ in the voltammetric measurements and the protocatechuic acid was 10 mM. ... Theoretical calculations were carried out on a personal computer using HyperChem version 5.0 software from Hypercube. ...
The fluorescence decays of a stereoregular head-to-tail RR-HT poly(3-hexylthiophene), P3HT, in me... more The fluorescence decays of a stereoregular head-to-tail RR-HT poly(3-hexylthiophene), P3HT, in methylcyclohexane (MCH) are described by sums of three or four exponential terms, respectively above and below -10 °C. In the high-temperature region, the polymer lifetime (ca. 500 ps) is accompanied by two shorter decay times (ca. 20 and 120 ps), which are assigned to intrachain energy transfer from high to lower energy excitons on the basis of temperature and wavelength dependence of the fluorescence decays. The absence of conformational (torsional) relaxation is attributed to the small dihedral angle between monomers that is predicted for the stereoregular polymer in the ground state. Below -10 °C, the polymer forms excimer-like aggregates, showing vibrational structured absorption and emission bands similar to those observed in thin films. The vibrational structure is attributed to a deep minimum in the ground-state energy surface of the dimer or aggregate. Below -40 °C, the fluorescence measured at the aggregate emission wavelength (670 nm) basically results from direct excitation of the aggregate and decays with a sum of three exponential terms (decay times of ca. 0.14, 0.6, and 1.5 ns, with similar weights). Because the spectral similarities between film and aggregates indicate similar electronic first singlet excited states (and oscillator strengths), the much shorter decay times (0.05, 0.15, and 0.43 ns) and lower fluorescence quantum yield of P3HT in films are assigned to efficient exciton dissociation and/or phonon-induced internal conversion competing with radiative decay (>1 ns).
The red flavylium cations of anthocyanins form ground-state charge-transfer complexes with severa... more The red flavylium cations of anthocyanins form ground-state charge-transfer complexes with several naturally occurring electron-donor copigments, such as hydroxylated flavones and hydroxycinnamic or benzoic acids. Excitation of the 7-methoxy-4-methyl-flavylium-protocatechuic acid complex results in ultrafast (240 fs) internal conversion to the ground state of the complex by way of a low-lying charge-transfer state. Thus, both uncomplexed anthocyanins, whose excited state decays by fast (5-20 ps) excited-state proton transfer, and anthocyanin-copigment complexes have highly efficient mechanisms of deactivation that are consistent with the proposed protective role of anthocyanins against excess solar radiation in the vegetative tissues of plants.
Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate ... more Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate constant for proton transfer to water in the excited state as high as 1.5 x 10(11) s(-1). The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) has an additional carboxyl group at the 4-position of the flavylium cation that deprotonates in the ground state at a lower pH (pK(a1) = 0.73; AH2+ --> Z) than the 7-hydroxy group (pK(a2) = 4.84; Z --> A-). Ground-state deprotonation of the carboxyl group of the acid (AH2+) to form the zwitterion (Z) is too fast to be detected by nanosecond laser flash perturbation of the ground-state equilibrium, while deprotonation of the hydroxyl group of Z to form the anionic base (A-) occurs in the microsecond time range (k(d2) = 0.6 x 10(6) s(-1) and k(p2) = 4.2 x 10(10) M(-1) x s(-1)). In the excited state, the cationic form (AH2+) deprotonates in approximately 9 ps, resulting in the excited neutral base form (AH), which is unstable in the ground state. Deprotonation of Z occurs in 30 ps (k(d2) = 2.9 x 10(10) s(-1)), to form excited A-, which either reprotonates (k(p3)* = 3.7 x 10(10) M(-1) x s(-1)) or decays in 149 ps, and shows an important contribution from geminate recombination to give the excited neutral base (AH). Predominant reprotonation of A- at the carboxylate group reflects both the presence of the negative charge on the carboxylate and the increase in the excited-state pK(a) of the carboxyl group. Thus, while the hydroxyl pK(a) decreases by approximately 5 units upon going from the ground state (pK(a) = 4.84) to the excited state (pK(a) = -0.2), that of the carboxyl group increases by at least this much. Consequently, the excited state of the Z form of CHMF acts as a molecular proton transporter in the picosecond time range.
Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmenta... more Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E red ≈ -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA Anthoc -IP Cop , the difference between the electron affinity of the anthocyanin, EA Anthoc , and the ionization potential of the copigment, IP Cop . Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.
Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV ra... more Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV radiation and are effective antioxidants and scavengers of active oxygen species. In plant leaves, one of the functional roles proposed for anthocyanins is protection of the photo synthetic apparatus from the effects of excess incident visible or UV-B radiation and photo oxidative stress. In essence, a photoprotective role requires that the excited singlet states of both complexed and uncomplexed anthocyanins deactivate back to the ground state so quickly that intersystem crossing, photoreaction, and diffusion-controlled quenching processes cannot compete. Studies of the photochemical properties of synthetic analogs of anthocyanins and of several naturally occurring anthocyanins show that this is indeed the case, uncomplexed anthocyanins decaying back to the ground state via fast (subnanosecond) excited-state proton transfer (ESPT) and anthocyanin-copigment complexes by fast (subpicosecond) charge-transfer-mediated internal conversion.
The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed... more The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed to probe some of the fundamental features of proton transfer reactions at the surface of anionic sodium dodecyl sulfate (SDS) and cationic hexadecyltrimethylammonium chloride (CTAC) micelles. In contrast to most ordinary flavylium salts, HHMF is insoluble in water, but readily incorporates into SDS and CTAC micelles. In the ground state, the rate constant for deprotonation of the acid form (AH + ) of HHMF decreases 100-fold upon going from CTAC (k d ) 3.0 × 10 6 s -1 ) to SDS (k d ) 1.4 × 10 4 s -1 ), consistent with the presence of an activation barrier for proton transfer in the ground state and reflecting, respectively, stabilization or destabilization of the AH + cation by the micelle. Reprotonation of A is diffusion-controlled in both micelles (k p (SDS) ) (2.1 × 10 11 )[H + ] aq s -1 and k p (CTAC) ) (3.7 × 10 8 )[H + ] aq s -1 ), the difference reflecting the rate of proton entry into the micelles. In the excited singlet state, the rate constants for deprotonation of the AH + * form of HHMF are similar in the two micelles (2.4 × 10 10 s -1 ), consistent with activationless proton transfer. Reprotonation of the excited A* is dominated by fast geminate recombination of the photogenerated (A*-H + ) pair at the micelle surface (k rec (SDS) ) 6.1 × 10 9 s -1 and k rec (CTAC) ) 3.4 × 10 10 s -1 ) and the net efficiencies of geminate recombination are quite similar in SDS (0.89) and CTAC (0.86).
Keywords: Alkyl side chain / Hydrophobic flavylium salts / Micelles / Photochromism / Ultrafast p... more Keywords: Alkyl side chain / Hydrophobic flavylium salts / Micelles / Photochromism / Ultrafast proton transfer A one-step preparation of several flavylium salts containing alkyl side chains in their 3-, 4Ј-, 5-or 6-positions is described. Flavylium salts with alkyl side chains in positions 3 or 4Ј were isolated from reactions between 2,4-dihydroxybenzaldehyde and decanophenone, dodecanophenone and 4Ј-hexyl-or 4Јdodecylacetophenone. Flavylium salts with alkyl side chains in positions 5 or 6 were prepared through reactions between benzoylacetone and 4-hexyl-, 4-dodecyl-or 5-pentylresorcinol. The new compounds are insoluble or sparingly soluble [a]
This article describes the results of a coupled photophysical and photobiological study aimed at ... more This article describes the results of a coupled photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs amodiaquine (AQ), primaquine (PQ) and chloroquine (CQ). Photophysical experiments were carried out in aqueous solutions by steady-state and time-resolved spectrometric techniques to obtain information on the different decay pathways of the excited states of the drugs and on the transient species formed upon laser irradiation. The results showed that all three drugs possess very low fluorescence quantum yields (10 )2 -10 )4 ). Laser flash photolysis experiments proved the occurrence of photoionization processes leading to the formation of a radical cation in all three systems. In the case of AQ the lowest triplet state was also detected. Together with the photophysical properties the photobiological properties of the antimalarial drugs were investigated under UV irradiation, on various biological targets through a series of in vitro assays. Phototoxicity on mouse 3T3 fibroblast and human keratinocyte cell lines NCTC-2544 was detected for PQ and CQ but not for AQ. In particular, PQ-and CQ-induced apoptosis was revealed by the externalization of phosphatidylserine. Furthermore, upon UV irradiation, the drugs caused significant variations of the mitochondrial potential (Dw mt ) measured by flow cytometry. The photodamages produced by the drugs were also evaluated on proteins, lipids and DNA. The combined approaches were useful in understanding the mechanism of phototoxicity induced by these antimalarial drugs.
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