Gian Gaetano Aloisi - Academia.edu (original) (raw)

Papers by Gian Gaetano Aloisi

Research paper thumbnail of Cis-trans photoisomerization of 1,2-diarylethylenes: Effect of charge transfer interactions

Journal of Chemical Sciences, 1993

This paper describes the results of an extensive study of trans-,cis photoisomerization of variou... more This paper describes the results of an extensive study of trans-,cis photoisomerization of various 1,2-diarylethylenes (DAE). The structure effect on the competitive radiative and reactive deactivations and on the isomerization mechanism (singlet/triplet, diabatic/adiabatic) is discussed. The effect of charge-transfer (CT) interactions of DAE with electron donors and acceptors are then presented. Triplet-induced isomerization is generally the common effect in non-polar solvents, and is particularly efficient when a heavy atom is involved. Typical examples of CT-induced triplet photoisomerizafion of DAE by electron donors and acceptors are llustrated. New results on some fluorescent cis compounds are also reported. Prevalent radical ion formation in polar solvents is shown to generally quench isomerization from trans to cis but to induce isomerization from cis to the more stable trans radical ion.

Research paper thumbnail of Photochemical and photophysical studies of organic molecules included within zeolites

Accounts of Chemical Research, 1992

the primary step of eq 12. For the adsorbed phase, the secondary product C2H4 along with CO is ob... more the primary step of eq 12. For the adsorbed phase, the secondary product C2H4 along with CO is observed.77 Acetylene photochemistry by 185 nm produces the radicals H and C2H' in the gas phase and a number of secondary pr0du~t.s.~~ The adsorbed-phase reaction 13 is by contrast remarkably clean, with hydrogen exchange among isotopomers the only evidence for chem-istryYs Finally, 185-nm gas-phase photochemistry of SO2 produces SO and 0 and secondary reactions generate However no reaction for this system occurs in the adsorbed phaseY9 It is likely that the arrangementa of the excited adsorbed species play a crucial role in the resulting photo~hemistry.'~ While the mechanisms of adsorbed-phase photochemistry on dielectric substrates have been explored for LiF(lOO):g* we view the understanding of simple adsorbed-phase reactions like those in eqs 12-14 to be essentially lacking. Finally, we turn our attention to the most poorly understood (but likely most important) energy pro-(76) Okabe, H.

Research paper thumbnail of DNA Cleavage Induced by Photoexcited Antimalarial Drugs: A Photophysical and Photobiological Study

Photochemistry and Photobiology, 2007

The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), meflo... more The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), mefloquine (MQ) and quinacrine (QC) toward DNA was studied. Evidences obtained by absorption and emission spectroscopy and by linear dichroism measurements indicate that these derivatives bind the macromolecule with a high affinity (binding constants K a $ 10 5 M)1). The absorption characteristics of the drugs changed markedly by addition of DNA and their fluorescence was quenched with rate constants higher than that of diffusion. The geometry of binding involves predominantly the intercalation into the double helix. The DNA photocleavage properties of antimalarials was investigated using plasmid DNA as a model, at different [drug] ⁄ [DNA] ratios. The results indicate that mainly MQ and Q are able to induce significant photodamage to DNA. In particular the marked effect of the former drug is evidenced after treatment of photosensitized DNA by two base excision repair enzymes, formamydo-pyrimidine glycosilase (Fpg) and Endonuclease III (Endo III). From a mechanistic point of view, experiments carried out in different experimental conditions indicate that these drugs photoinduce DNA damage through singlet oxygen and ⁄ or radical cation production. These findings are further supported by the determination of two photoproducts of 2¢-deoxyguanosine, which are diagnostic for Type I and Type II pathways, namely 2,2-diamino(2-deoxy-b-D D-erythro-pentofuranosyl)-4-amino-5(2H)-oxazolone and (R,S)4-hydroxy-8-oxo-4,8-dihydro-2¢-deoxyguanosine (4-OH-8-oxo-dGuo). Laser flash photolysis experiments carried out in the presence of DNA indicates that the excitation produces mainly the triplet state for Q and the triplet and radical cation for QC. Moreover the singlet and triplet states and radical cations of the drugs are quenched by 2¢-deoxyguanosine monophosphate. The absorbances of these transients decrease with increasing DNA concentration.

Research paper thumbnail of Cis-trans photoisomerization of 1,2-diarylethylenes: Effect of charge transfer interactions

Journal of Chemical Sciences, 1993

This paper describes the results of an extensive study of trans-,cis photoisomerization of variou... more This paper describes the results of an extensive study of trans-,cis photoisomerization of various 1,2-diarylethylenes (DAE). The structure effect on the competitive radiative and reactive deactivations and on the isomerization mechanism (singlet/triplet, diabatic/adiabatic) is discussed. The effect of charge-transfer (CT) interactions of DAE with electron donors and acceptors are then presented. Triplet-induced isomerization is generally the common effect in non-polar solvents, and is particularly efficient when a heavy atom is involved. Typical examples of CT-induced triplet photoisomerizafion of DAE by electron donors and acceptors are llustrated. New results on some fluorescent cis compounds are also reported. Prevalent radical ion formation in polar solvents is shown to generally quench isomerization from trans to cis but to induce isomerization from cis to the more stable trans radical ion.

Research paper thumbnail of Photochemical and photophysical studies of organic molecules included within zeolites

Accounts of Chemical Research, 1992

the primary step of eq 12. For the adsorbed phase, the secondary product C2H4 along with CO is ob... more the primary step of eq 12. For the adsorbed phase, the secondary product C2H4 along with CO is observed.77 Acetylene photochemistry by 185 nm produces the radicals H and C2H' in the gas phase and a number of secondary pr0du~t.s.~~ The adsorbed-phase reaction 13 is by contrast remarkably clean, with hydrogen exchange among isotopomers the only evidence for chem-istryYs Finally, 185-nm gas-phase photochemistry of SO2 produces SO and 0 and secondary reactions generate However no reaction for this system occurs in the adsorbed phaseY9 It is likely that the arrangementa of the excited adsorbed species play a crucial role in the resulting photo~hemistry.'~ While the mechanisms of adsorbed-phase photochemistry on dielectric substrates have been explored for LiF(lOO):g* we view the understanding of simple adsorbed-phase reactions like those in eqs 12-14 to be essentially lacking. Finally, we turn our attention to the most poorly understood (but likely most important) energy pro-(76) Okabe, H.

Research paper thumbnail of DNA Cleavage Induced by Photoexcited Antimalarial Drugs: A Photophysical and Photobiological Study

Photochemistry and Photobiology, 2007

The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), meflo... more The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), mefloquine (MQ) and quinacrine (QC) toward DNA was studied. Evidences obtained by absorption and emission spectroscopy and by linear dichroism measurements indicate that these derivatives bind the macromolecule with a high affinity (binding constants K a $ 10 5 M)1). The absorption characteristics of the drugs changed markedly by addition of DNA and their fluorescence was quenched with rate constants higher than that of diffusion. The geometry of binding involves predominantly the intercalation into the double helix. The DNA photocleavage properties of antimalarials was investigated using plasmid DNA as a model, at different [drug] ⁄ [DNA] ratios. The results indicate that mainly MQ and Q are able to induce significant photodamage to DNA. In particular the marked effect of the former drug is evidenced after treatment of photosensitized DNA by two base excision repair enzymes, formamydo-pyrimidine glycosilase (Fpg) and Endonuclease III (Endo III). From a mechanistic point of view, experiments carried out in different experimental conditions indicate that these drugs photoinduce DNA damage through singlet oxygen and ⁄ or radical cation production. These findings are further supported by the determination of two photoproducts of 2¢-deoxyguanosine, which are diagnostic for Type I and Type II pathways, namely 2,2-diamino(2-deoxy-b-D D-erythro-pentofuranosyl)-4-amino-5(2H)-oxazolone and (R,S)4-hydroxy-8-oxo-4,8-dihydro-2¢-deoxyguanosine (4-OH-8-oxo-dGuo). Laser flash photolysis experiments carried out in the presence of DNA indicates that the excitation produces mainly the triplet state for Q and the triplet and radical cation for QC. Moreover the singlet and triplet states and radical cations of the drugs are quenched by 2¢-deoxyguanosine monophosphate. The absorbances of these transients decrease with increasing DNA concentration.