Salvatore Sortino | University of Catania (original) (raw)
Papers by Salvatore Sortino
Photochemistry and photobiology, 1998
The photosensitizing activity of enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- ... more The photosensitizing activity of enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- 1,8-naphthyridine-3-carboxilic acid (ENX), toward membranes and DNA has been studied, taking into account human erythrocyte photohemolysis, unilamellar liposome alterations and plasmid pBR322 DNA photocleavage. Hydroxyl radicals and an aromatic carbene generated from ENX photodefluorination seem to be the active intermediates involved in the photosensitization process. The steady-state photolysis products do not participate in the process. The mechanism of photosensitization responsible for the membrane damage depends on the oxygen concentration and follows a different path with respect to that operative for DNA cleavage. Between oxygenated radicals, the hydroxyl seems the species mainly responsible for membrane damage, whereas DNA cleavage is mainly produced by the carbene intermediate. A molecular mechanism of the photosensitization induced by ENX is proposed.
Journal of The American Chemical Society, 2003
We report the first example of a molecular switch of multifunctional dipolar ruthenium(III/II) pe... more We report the first example of a molecular switch of multifunctional dipolar ruthenium(III/II) pentaammine-N-methyl-(4,4'-bipyridinium) complexes, exclusively driven by light. This is achieved by using a two-phase (water/benzene) system in which RuIII/II complexes are soluble only in the water phase. The reversible redox switching is triggered by the selective irradiation of the water and the benzene compartments with 254 and 528 nm light, respectively.
Journal of the Chemical Society, Faraday Transactions, 1997
ABSTRACT
Biomaterials, 2002
In the present work, the preparation and characterization of hydrogels based on α,β-polyaspartylh... more In the present work, the preparation and characterization of hydrogels based on α,β-polyaspartylhydrazide (PAHy) chemically crosslinked with ethyleneglycol diglycidylether (EGDGE) containing Tolmetin sodium salt, are reported. In particular, these samples have been prepared both as water swellable microparticles and as gels at two different crosslinking degrees. The incorporation of Tolmetin sodium salt in PAHy–EGDGE microparticles has been performed after the
Photochemistry and Photobiology, 1999
The photophysical properties of doxacin, 9-fluoro-2,3dihydro-l0-(4-methyl-l-pyrazinyl)-7-0~0-7-H-... more The photophysical properties of doxacin, 9-fluoro-2,3dihydro-l0-(4-methyl-l-pyrazinyl)-7-0~0-7-H-pyrido[l,2,3-de]-1,4-benzothiazin-6-carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steadystate and time-resolved emission, triplet-state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long-lived state (af = 0.075, Tf = 4.5 ns)
New Journal of Chemistry, 1998
The photochemistry of 2-(3-benzoylphenyl) propionic acid (Ketoprofen) has been studied in the β-c... more The photochemistry of 2-(3-benzoylphenyl) propionic acid (Ketoprofen) has been studied in the β-cyclodextrin cavity by stationary and time-resolved (picosecond and nanosecond) spectroscopic techniques. Conformational calculations of the inclusion complex were ...
Journal of Inorganic Biochemistry, 1995
Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with... more Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with UVC (254 nm) and UVB (300 nm) light. The irradiation provoked lipid peroxidation and liposome lysis with release of entrapped glucose-6-phosphate. At the same intensity of absorbed light, the photochemical effect at 254 nm is higher than at 300 nm. The addition of copper(II) and manganese(II) reduced both the
New Journal of Chemistry - NEW J CHEM, 2003
The effects of a novel cationic amphiphilic cyclodextrin (SC6CDNH2) on the photoprocesses of the ... more The effects of a novel cationic amphiphilic cyclodextrin (SC6CDNH2) on the photoprocesses of the phototoxic non-steroidal anti-inflammatory drug diflunisal (DF) have been investigated in aqueous medium. Association between DF and SC6CDNH2 was indicated by steady-...
New Journal of Chemistry - NEW J CHEM, 2008
... Mariarita Barone, Angela Mascali and Salvatore Sortino*. Dipartimento di Scienze Chimiche, Un... more ... Mariarita Barone, Angela Mascali and Salvatore Sortino*. Dipartimento di Scienze Chimiche, Università di Catania, Viale Andrea Doria 8, I-95125, Catania, Italy. E-mail: ssortino@unict.it. ... 14, See, for example: AC Templeton, WP Wuelfing and RW Murray, Acc. Chem. ...
The Journal of Physical Chemistry B, 2006
This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin d... more This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin dimers (1) in Langmuir-Schäfer (LS) thin films by combining scanning force microscopy (SFM) with film balance, UV-vis absorption, fluorescence, and nanosecond laser flash photolysis measurements. Results show that depending on the surface pressure the Langmuir films of pure 1 can be arranged in two different condensed phases, whereas SFM of the LS films shows characteristic fractal networks constituted by nanoscopic aggregates. The spectral findings agree with a picture in which 1 is apparently present in the anti conformation but aggregated in a sort of H-type structure whose optical features resemble those of the syn conformer. This type of structure is not responsive to light stimuli. By diluting 1 in arachidic acid the porphyrin aggregation is significantly minimized with 1 exhibiting almost exclusively the anti conformation. As a result the LS films become photoresponsive, showing fluorescence emission and triplet-triplet transient absorption.
The Journal of Physical Chemistry A, 2000
Surface Science, 2004
The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the... more The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the airwater interface. The molecular organization of floating films of pure 1 and its mixture with amphiphilic substances, such as arachidic acid and n-octadecylamine, was ...
Physical Chemistry Chemical Physics, 2005
A combined approach using global analysis of circular dichroism multiwavelength data and time res... more A combined approach using global analysis of circular dichroism multiwavelength data and time resolved fluorescence was applied to investigate the interaction of R-(À)-and S-(þ)-ketoprofen with bovine serum albumin in buffer solution at neutral pH. A characterization of the most stable drug : protein adducts of 1 : 1 and 2 : 1 stoichiometry, as individual chemical species, was obtained. The stability constants and the absolute circular dichroism spectra of the diastereomeric complexes were determined. The spectra of the 1 : 1 conjugates are opposite in sign, those of the 2 : 1 complexes are both negative, but different in shape from each other (peaks at 358 and 342 nm for S-(þ)-and R-(À)-ketoprofen, respectively). A tryptophan residue was shown to be involved in the binding of the drug, in the primary site for the R-(À) and in the secondary site for the S-(þ) enantiomer, thereby showing that chiral recognition by the protein causes the site of highest affinity being not the same for both optical antipodes.
Photochemistry and Photobiology, 1998
The spectroscopic and photochemical behavior of Enoxacin (ENX), l-ethyl-6-fluoro-1,4-dihydro-4-ox... more The spectroscopic and photochemical behavior of Enoxacin (ENX), l-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(l-piperazinyl)-1,8-naphthyridine-3-carboxylic acid, has been investigated in aqueous solutions between pH 3.5 and pH 12. The absorption and emission properties of ENX are strongly affected by pH. The fluorescence quantum yield, 4 x 1O-j at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH. The photodegradation quantum yield also depends on pH, being maximum in neutral conditions (ca 0.04). Nanosecond flash photolysis experiments confirm that the yield of absorbing transients is maximum at neutral pH while it decreases to zero at acid and alkaline pH. These results indicate that both the dissociation of the carboxylic group and the protonation of the piperazinyl residues are key steps for the formation of the photochemically active form of ENX. Loss of F-by heterolytic cleavage of the C-F bond is proposed to occur from the triplet state of the zwitterion with formation of a carbocation. A path for the evolution of this intermediate to the final product is also proposed.
Photochemistry and Photobiology, 2007
The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP Ϫ ) was ... more The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP Ϫ ) was studied in water and in 0.1 M phosphate buffer solutions in the pH range 5.7-11.0 by laser-induced optoacoustic spectroscopy (LIOAS, T range 9.5-31.6؇C). Upon exciting KP Ϫ with 355 nm laser pulses under anaerobic conditions, two components in the LIOAS signals with well-separated lifetimes were found ( 1 Ͻ 20 ns; 250 Ͻ 2 Ͻ 500 ns) in the whole pH range, whereas a long-lived third component (4 Ͻ 3 Ͻ 10 s) was only detected at pH Յ 6.1. The heat and structural volume changes accompanying the first step did not depend on pH or on the presence of buffer. The carbanion resulting from prompt decarboxylation within the nanosecond pulse (Ͻ10 ns) drastically reduces its molar volume ([Ϫ18.9 ؎ 2.0] cm 3 /mol) with respect to KP Ϫ and its enthalpy content is (256 ؎ 10) kJ/ mol. At acid pH (ca 6), a species is formed with a lifetime in the hundreds of ns. The enthalpy and structural volume change for this species with respect to KP Ϫ are (181 ؎ 15) kJ/mol and (؉0.6 ؎ 2.0) cm 3 /mol, respectively. This species is most likely a neutral biradical formed by protonation of the decarboxylated carbanion, and decays to the final product 3-ethylbenzophenone in several s. At basic pH (ca 11), direct formation of 3-ethylbenzophenone occurs in hundreds of ns involving a reaction with the solvent. The global decarboxylation reaction is endothermic ([45 ؎ 15] kJ/mol) and shows an expansion of (؉14.5 ؎ 0.5) cm 3 /mol with respect to KP Ϫ . At low pH, the presence of buffer strongly affects the magnitude of the structural volume changes associated with the intermolecular proton-transfer processes of the long-lived species due to reactions of the buffer anion with the decarboxylated ketoprofen anion. ¶Posted on the web on 24 May 2000.
Photochemistry and Photobiology, 1998
The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a f... more The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a function of the temperature, the concentration and the presence of oxygen by steady-state and time-resolved photochemical techniques. The process is characterized by an activation energy of 9-10 kcaYmol, the precursor state being the lowest triplet which is of m,m* nature. The reactivity of the drug was also studied in the p-cyclodextrin inclusion complex and an additional photoreaction involving the macrocycle as reactive species was observed. Representative NMR and circular dichroism measurements were performed. Singlet molecular oxygen formation was also investigated.
Photochemistry and Photobiology, 2006
The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumi... more 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.
Photochemistry and Photobiology, 1999
The UVA irradiation of 9-fluoro-2,3-dihydro-lO-4'-methyl-1 ' -piperazinyl-7-0~0-7H-pyrido[ 1,2,3-... more The UVA irradiation of 9-fluoro-2,3-dihydro-lO-4'-methyl-1 ' -piperazinyl-7-0~0-7H-pyrido[ 1,2,3-de]-1,4-benzothiazine-6-carboxylic acid, rufloxacin, a fluoroquinolone antibacterial that shows photosensitizing properties toward biological substrates, leads to formation of two main steady photoproducts characterized by a decarboxylation process and an opening of the piperazinyl ring, respectively. The deprotonation of the 10-piperazinyl group and the dissociation of the 6-carboxyl group of rufloxacin are strictly pH dependent. The photosensitizing activity was tested toward membranes as biological targets. Red blood cell hemolysis and lipid peroxidation were considered as markers of photosensitization. Ultraviolet A-induced damage is strongly influenced by the presence of oxygen, it is triggered by transient species, such as singlet oxygen and free radicals, photogenerated via rufloxacin irradiation, whereas no drug photoproduct is involved in the photosensitization process.
Photochemistry and Photobiology, 1999
The effects of P-cyclodextrin complexation on the photochemical and photosensitizing properties o... more The effects of P-cyclodextrin complexation on the photochemical and photosensitizing properties of tohetin have been investigated. Absorption, emission, circular dichroism and NMR measurements were used to characterize the host-guest complex. Nanosecond laser flash photolysis and steady-state photolysis experiments were performed to clarify the photoreactivity of the drug in the macrocycle. The decarboxylation of the drug is markedly reduced upon inclusion and the rate constants of the decay of the transient intermediates involved in tolmetin photodecomposition were slowed down due to their incorporation in the hydrophobic cavity. This also influenced the distribution of the stable photoproducts. A remarkable cyclodextrin-mediated protection against the tohetin-photoinduced damage on biological substrates was observed. A rationale for these biological effects is provided.
Photochemistry and Photobiology, 2007
The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)... more The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide, in homogeneous media and in the -cyclodextrin (-CD) cavity has been investigated. The photoreactivity of the free molecule has been rationalized on the basis of an intramolecular nitro to nitrite rearrangement followed by cleavage of the nitrite intermediate. The twisted geometry of the nitro group with respect to the aromatic plane plays a key role in triggering such a photoprocess. Incorporation of FM in the -CD cavity leads to dramatic effects on both the efficiency and the nature of the photochemical deactivation pathways of the guest molecule. A 20-fold increase in the FM photodecomposition quantum yield and the formation of photoproducts originated by both reduction of the nitro group and cleavage of the amide bond were observed in the presence of the macrocycle. Such a behavior cannot be attributed exclusively to the micropolarity of -CD and/or to its role as a reactant. The induced circular dichroism spectra and the nature of the photoproducts formed in these experimental conditions provide indications that the photoreactivity in the -CD microenvironment could likely be mediated by structural changes of FM upon complexation.
Photochemistry and photobiology, 1998
The photosensitizing activity of enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- ... more The photosensitizing activity of enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)- 1,8-naphthyridine-3-carboxilic acid (ENX), toward membranes and DNA has been studied, taking into account human erythrocyte photohemolysis, unilamellar liposome alterations and plasmid pBR322 DNA photocleavage. Hydroxyl radicals and an aromatic carbene generated from ENX photodefluorination seem to be the active intermediates involved in the photosensitization process. The steady-state photolysis products do not participate in the process. The mechanism of photosensitization responsible for the membrane damage depends on the oxygen concentration and follows a different path with respect to that operative for DNA cleavage. Between oxygenated radicals, the hydroxyl seems the species mainly responsible for membrane damage, whereas DNA cleavage is mainly produced by the carbene intermediate. A molecular mechanism of the photosensitization induced by ENX is proposed.
Journal of The American Chemical Society, 2003
We report the first example of a molecular switch of multifunctional dipolar ruthenium(III/II) pe... more We report the first example of a molecular switch of multifunctional dipolar ruthenium(III/II) pentaammine-N-methyl-(4,4'-bipyridinium) complexes, exclusively driven by light. This is achieved by using a two-phase (water/benzene) system in which RuIII/II complexes are soluble only in the water phase. The reversible redox switching is triggered by the selective irradiation of the water and the benzene compartments with 254 and 528 nm light, respectively.
Journal of the Chemical Society, Faraday Transactions, 1997
ABSTRACT
Biomaterials, 2002
In the present work, the preparation and characterization of hydrogels based on α,β-polyaspartylh... more In the present work, the preparation and characterization of hydrogels based on α,β-polyaspartylhydrazide (PAHy) chemically crosslinked with ethyleneglycol diglycidylether (EGDGE) containing Tolmetin sodium salt, are reported. In particular, these samples have been prepared both as water swellable microparticles and as gels at two different crosslinking degrees. The incorporation of Tolmetin sodium salt in PAHy–EGDGE microparticles has been performed after the
Photochemistry and Photobiology, 1999
The photophysical properties of doxacin, 9-fluoro-2,3dihydro-l0-(4-methyl-l-pyrazinyl)-7-0~0-7-H-... more The photophysical properties of doxacin, 9-fluoro-2,3dihydro-l0-(4-methyl-l-pyrazinyl)-7-0~0-7-H-pyrido[l,2,3-de]-1,4-benzothiazin-6-carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steadystate and time-resolved emission, triplet-state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long-lived state (af = 0.075, Tf = 4.5 ns)
New Journal of Chemistry, 1998
The photochemistry of 2-(3-benzoylphenyl) propionic acid (Ketoprofen) has been studied in the β-c... more The photochemistry of 2-(3-benzoylphenyl) propionic acid (Ketoprofen) has been studied in the β-cyclodextrin cavity by stationary and time-resolved (picosecond and nanosecond) spectroscopic techniques. Conformational calculations of the inclusion complex were ...
Journal of Inorganic Biochemistry, 1995
Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with... more Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with UVC (254 nm) and UVB (300 nm) light. The irradiation provoked lipid peroxidation and liposome lysis with release of entrapped glucose-6-phosphate. At the same intensity of absorbed light, the photochemical effect at 254 nm is higher than at 300 nm. The addition of copper(II) and manganese(II) reduced both the
New Journal of Chemistry - NEW J CHEM, 2003
The effects of a novel cationic amphiphilic cyclodextrin (SC6CDNH2) on the photoprocesses of the ... more The effects of a novel cationic amphiphilic cyclodextrin (SC6CDNH2) on the photoprocesses of the phototoxic non-steroidal anti-inflammatory drug diflunisal (DF) have been investigated in aqueous medium. Association between DF and SC6CDNH2 was indicated by steady-...
New Journal of Chemistry - NEW J CHEM, 2008
... Mariarita Barone, Angela Mascali and Salvatore Sortino*. Dipartimento di Scienze Chimiche, Un... more ... Mariarita Barone, Angela Mascali and Salvatore Sortino*. Dipartimento di Scienze Chimiche, Università di Catania, Viale Andrea Doria 8, I-95125, Catania, Italy. E-mail: ssortino@unict.it. ... 14, See, for example: AC Templeton, WP Wuelfing and RW Murray, Acc. Chem. ...
The Journal of Physical Chemistry B, 2006
This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin d... more This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin dimers (1) in Langmuir-Schäfer (LS) thin films by combining scanning force microscopy (SFM) with film balance, UV-vis absorption, fluorescence, and nanosecond laser flash photolysis measurements. Results show that depending on the surface pressure the Langmuir films of pure 1 can be arranged in two different condensed phases, whereas SFM of the LS films shows characteristic fractal networks constituted by nanoscopic aggregates. The spectral findings agree with a picture in which 1 is apparently present in the anti conformation but aggregated in a sort of H-type structure whose optical features resemble those of the syn conformer. This type of structure is not responsive to light stimuli. By diluting 1 in arachidic acid the porphyrin aggregation is significantly minimized with 1 exhibiting almost exclusively the anti conformation. As a result the LS films become photoresponsive, showing fluorescence emission and triplet-triplet transient absorption.
The Journal of Physical Chemistry A, 2000
Surface Science, 2004
The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the... more The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the airwater interface. The molecular organization of floating films of pure 1 and its mixture with amphiphilic substances, such as arachidic acid and n-octadecylamine, was ...
Physical Chemistry Chemical Physics, 2005
A combined approach using global analysis of circular dichroism multiwavelength data and time res... more A combined approach using global analysis of circular dichroism multiwavelength data and time resolved fluorescence was applied to investigate the interaction of R-(À)-and S-(þ)-ketoprofen with bovine serum albumin in buffer solution at neutral pH. A characterization of the most stable drug : protein adducts of 1 : 1 and 2 : 1 stoichiometry, as individual chemical species, was obtained. The stability constants and the absolute circular dichroism spectra of the diastereomeric complexes were determined. The spectra of the 1 : 1 conjugates are opposite in sign, those of the 2 : 1 complexes are both negative, but different in shape from each other (peaks at 358 and 342 nm for S-(þ)-and R-(À)-ketoprofen, respectively). A tryptophan residue was shown to be involved in the binding of the drug, in the primary site for the R-(À) and in the secondary site for the S-(þ) enantiomer, thereby showing that chiral recognition by the protein causes the site of highest affinity being not the same for both optical antipodes.
Photochemistry and Photobiology, 1998
The spectroscopic and photochemical behavior of Enoxacin (ENX), l-ethyl-6-fluoro-1,4-dihydro-4-ox... more The spectroscopic and photochemical behavior of Enoxacin (ENX), l-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(l-piperazinyl)-1,8-naphthyridine-3-carboxylic acid, has been investigated in aqueous solutions between pH 3.5 and pH 12. The absorption and emission properties of ENX are strongly affected by pH. The fluorescence quantum yield, 4 x 1O-j at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH. The photodegradation quantum yield also depends on pH, being maximum in neutral conditions (ca 0.04). Nanosecond flash photolysis experiments confirm that the yield of absorbing transients is maximum at neutral pH while it decreases to zero at acid and alkaline pH. These results indicate that both the dissociation of the carboxylic group and the protonation of the piperazinyl residues are key steps for the formation of the photochemically active form of ENX. Loss of F-by heterolytic cleavage of the C-F bond is proposed to occur from the triplet state of the zwitterion with formation of a carbocation. A path for the evolution of this intermediate to the final product is also proposed.
Photochemistry and Photobiology, 2007
The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP Ϫ ) was ... more The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP Ϫ ) was studied in water and in 0.1 M phosphate buffer solutions in the pH range 5.7-11.0 by laser-induced optoacoustic spectroscopy (LIOAS, T range 9.5-31.6؇C). Upon exciting KP Ϫ with 355 nm laser pulses under anaerobic conditions, two components in the LIOAS signals with well-separated lifetimes were found ( 1 Ͻ 20 ns; 250 Ͻ 2 Ͻ 500 ns) in the whole pH range, whereas a long-lived third component (4 Ͻ 3 Ͻ 10 s) was only detected at pH Յ 6.1. The heat and structural volume changes accompanying the first step did not depend on pH or on the presence of buffer. The carbanion resulting from prompt decarboxylation within the nanosecond pulse (Ͻ10 ns) drastically reduces its molar volume ([Ϫ18.9 ؎ 2.0] cm 3 /mol) with respect to KP Ϫ and its enthalpy content is (256 ؎ 10) kJ/ mol. At acid pH (ca 6), a species is formed with a lifetime in the hundreds of ns. The enthalpy and structural volume change for this species with respect to KP Ϫ are (181 ؎ 15) kJ/mol and (؉0.6 ؎ 2.0) cm 3 /mol, respectively. This species is most likely a neutral biradical formed by protonation of the decarboxylated carbanion, and decays to the final product 3-ethylbenzophenone in several s. At basic pH (ca 11), direct formation of 3-ethylbenzophenone occurs in hundreds of ns involving a reaction with the solvent. The global decarboxylation reaction is endothermic ([45 ؎ 15] kJ/mol) and shows an expansion of (؉14.5 ؎ 0.5) cm 3 /mol with respect to KP Ϫ . At low pH, the presence of buffer strongly affects the magnitude of the structural volume changes associated with the intermolecular proton-transfer processes of the long-lived species due to reactions of the buffer anion with the decarboxylated ketoprofen anion. ¶Posted on the web on 24 May 2000.
Photochemistry and Photobiology, 1998
The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a f... more The photodecarboxylation of suprofen in the carboxylate form was studied in aqueous medium as a function of the temperature, the concentration and the presence of oxygen by steady-state and time-resolved photochemical techniques. The process is characterized by an activation energy of 9-10 kcaYmol, the precursor state being the lowest triplet which is of m,m* nature. The reactivity of the drug was also studied in the p-cyclodextrin inclusion complex and an additional photoreaction involving the macrocycle as reactive species was observed. Representative NMR and circular dichroism measurements were performed. Singlet molecular oxygen formation was also investigated.
Photochemistry and Photobiology, 2006
The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumi... more 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.
Photochemistry and Photobiology, 1999
The UVA irradiation of 9-fluoro-2,3-dihydro-lO-4'-methyl-1 ' -piperazinyl-7-0~0-7H-pyrido[ 1,2,3-... more The UVA irradiation of 9-fluoro-2,3-dihydro-lO-4'-methyl-1 ' -piperazinyl-7-0~0-7H-pyrido[ 1,2,3-de]-1,4-benzothiazine-6-carboxylic acid, rufloxacin, a fluoroquinolone antibacterial that shows photosensitizing properties toward biological substrates, leads to formation of two main steady photoproducts characterized by a decarboxylation process and an opening of the piperazinyl ring, respectively. The deprotonation of the 10-piperazinyl group and the dissociation of the 6-carboxyl group of rufloxacin are strictly pH dependent. The photosensitizing activity was tested toward membranes as biological targets. Red blood cell hemolysis and lipid peroxidation were considered as markers of photosensitization. Ultraviolet A-induced damage is strongly influenced by the presence of oxygen, it is triggered by transient species, such as singlet oxygen and free radicals, photogenerated via rufloxacin irradiation, whereas no drug photoproduct is involved in the photosensitization process.
Photochemistry and Photobiology, 1999
The effects of P-cyclodextrin complexation on the photochemical and photosensitizing properties o... more The effects of P-cyclodextrin complexation on the photochemical and photosensitizing properties of tohetin have been investigated. Absorption, emission, circular dichroism and NMR measurements were used to characterize the host-guest complex. Nanosecond laser flash photolysis and steady-state photolysis experiments were performed to clarify the photoreactivity of the drug in the macrocycle. The decarboxylation of the drug is markedly reduced upon inclusion and the rate constants of the decay of the transient intermediates involved in tolmetin photodecomposition were slowed down due to their incorporation in the hydrophobic cavity. This also influenced the distribution of the stable photoproducts. A remarkable cyclodextrin-mediated protection against the tohetin-photoinduced damage on biological substrates was observed. A rationale for these biological effects is provided.
Photochemistry and Photobiology, 2007
The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)... more The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide, in homogeneous media and in the -cyclodextrin (-CD) cavity has been investigated. The photoreactivity of the free molecule has been rationalized on the basis of an intramolecular nitro to nitrite rearrangement followed by cleavage of the nitrite intermediate. The twisted geometry of the nitro group with respect to the aromatic plane plays a key role in triggering such a photoprocess. Incorporation of FM in the -CD cavity leads to dramatic effects on both the efficiency and the nature of the photochemical deactivation pathways of the guest molecule. A 20-fold increase in the FM photodecomposition quantum yield and the formation of photoproducts originated by both reduction of the nitro group and cleavage of the amide bond were observed in the presence of the macrocycle. Such a behavior cannot be attributed exclusively to the micropolarity of -CD and/or to its role as a reactant. The induced circular dichroism spectra and the nature of the photoproducts formed in these experimental conditions provide indications that the photoreactivity in the -CD microenvironment could likely be mediated by structural changes of FM upon complexation.