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Andrés H. Thomas - One of the best experts on this subject based on the ideXlab platform.
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photo oxidation of unilamellar vesicles by a lipophilic pterin deciphering biomembrane photodamage
Langmuir, 2018Co-Authors: Mariana Vignoni, María Noel Urrutia, Alexander Greer, Helena Couto Junqueira, Ana Reis, Mauricio S Baptista, Rosangela Itri, Andrés H. ThomasAbstract:Pterins are natural products that can photosensitize the oxidation of DNA, proteins, and phospholipids. Recently, a new series of decyl-chain (i.e., lipophilic) pterins were synthesized and their photophysical properties were investigated. These decyl-pterins led to efficient intercalation in large unilamellar vesicles and produced, under UVA irradiation, singlet molecular oxygen, a highly oxidative species that react with polyunsaturated fatty acids (PUFAs) to form hydroperoxides. Here, we demonstrate that the association of 4-(decyloxy)pteridin-2-amine (O-decyl-Ptr) to lipid membranes is key to its ability to trigger phospholipid oxidation in unilamellar vesicles of phosphatidylcholine rich in PUFAs used as model biomembranes. Our results show that O-decyl-Ptr is at least 1 order of magnitude more efficient photosensitizer of lipids than pterin (Ptr), the unsubstituted derivative of the pterin family, which is more hydrophilic and freely passes across lipid membranes. Lipid peroxidation photosensitized ...
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lipophilic decyl chain pterin conjugates with sensitizer properties
Molecular Pharmaceutics, 2017Co-Authors: Mariana Vignoni, Niluksha Walalawela, Alexander Greer, Sergio M Bonesi, Andrés H. ThomasAbstract:A new series of decyl chain [−(CH2)9CH3] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the pterins, a nucleophilic substitution (SN2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N3 site. However, the O-alkylated pterin converts to N3-alkylated pterin under basic conditions, pointing to a kinetic product in the former and a thermodynamic product in the latter. Two additional adducts were also obtained from an N-amine condensation of DMF solvent molecule as byproducts. In comparison to the natural product pterin, the alkyl chain pterins possess reduced fluorescence quantum yields (ΦF) and increased singlet oxygen quantum yields (ΦΔ). It is shown that the DMF-condensed pterins were more photostable compared to the N3- and O-alkylated pterins bearing a free amine group. The alkyl chain pterins efficiently intercalate in large unilamellar vesicles, which is a good i...
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photooxidation of tryptophan and tyrosine residues in human serum albumin sensitized by pterin a model for globular protein photodamage in skin
Biochemistry, 2016Co-Authors: Lara O Reid, Andrés H. Thomas, Ernesto A Roman, Laura M DantolaAbstract:Human serum albumin (HSA) is the most abundant protein in the circulatory system. Oxidized albumin was identified in the skin of patients suffering from vitiligo, a depigmentation disorder in which the protection against ultraviolet (UV) radiation fails because of the lack of melanin. Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin affected by vitiligo. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to induce structural and chemical changes in HSA under UV-A irradiation. Our results showed that Ptr is able to photoinduce oxidation of the protein in at least two amino acid residues: tryptophan (Trp) and tyrosine (Tyr). HSA undergoes oligomerization, yielding protein structures whose molecular weight increases with irradiation time. The protein cross-linking, due to the formation of dimers of Tyr, does not significantly affect the secondary and tertiary structures of HSA. Trp is consumed in the photosensitized process, and N-formylkynurenine was identified as one of its oxidation products. The photosensitization of HSA takes place via a purely dynamic process, which involves the triplet excited state of Ptr. The results presented in this work suggest that protein photodamage mediated by endogenous photosensitizers can significantly contribute to the harmful effects of UV-A radiation on the human skin.
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photooxidation of tryptophan and tyrosine residues in human serum albumin sensitized by pterin a model for globular protein photodamage in skin
Biochemistry, 2016Co-Authors: Lara O Reid, Andrés H. Thomas, Ernesto A Roman, M. Laura DántolaAbstract:Human serum albumin (HSA) is the most abundant protein in the circulatory system. Oxidized albumin was identified in the skin of patients suffering from vitiligo, a depigmentation disorder in which the protection against ultraviolet (UV) radiation fails because of the lack of melanin. Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin affected by vitiligo. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to induce structural and chemical changes in HSA under UV-A irradiation. Our results showed that Ptr is able to photoinduce oxidation of the protein in at least two amino acid residues: tryptophan (Trp) and tyrosine (Tyr). HSA undergoes oligomerization, yielding protein structures whose molecular weight increases with irradiation time. The protein cross-linking, due to the formation of dimers of Tyr, does not significantly affect the secondary and tertiary structures of HSA. Trp is consumed in the photosensiti...
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Mariana Vignoni, Patricia Vicendo, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
Mariana Vignoni - One of the best experts on this subject based on the ideXlab platform.
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photo oxidation of unilamellar vesicles by a lipophilic pterin deciphering biomembrane photodamage
Langmuir, 2018Co-Authors: Mariana Vignoni, María Noel Urrutia, Alexander Greer, Helena Couto Junqueira, Ana Reis, Mauricio S Baptista, Rosangela Itri, Andrés H. ThomasAbstract:Pterins are natural products that can photosensitize the oxidation of DNA, proteins, and phospholipids. Recently, a new series of decyl-chain (i.e., lipophilic) pterins were synthesized and their photophysical properties were investigated. These decyl-pterins led to efficient intercalation in large unilamellar vesicles and produced, under UVA irradiation, singlet molecular oxygen, a highly oxidative species that react with polyunsaturated fatty acids (PUFAs) to form hydroperoxides. Here, we demonstrate that the association of 4-(decyloxy)pteridin-2-amine (O-decyl-Ptr) to lipid membranes is key to its ability to trigger phospholipid oxidation in unilamellar vesicles of phosphatidylcholine rich in PUFAs used as model biomembranes. Our results show that O-decyl-Ptr is at least 1 order of magnitude more efficient photosensitizer of lipids than pterin (Ptr), the unsubstituted derivative of the pterin family, which is more hydrophilic and freely passes across lipid membranes. Lipid peroxidation photosensitized ...
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lipophilic decyl chain pterin conjugates with sensitizer properties
Molecular Pharmaceutics, 2017Co-Authors: Mariana Vignoni, Niluksha Walalawela, Alexander Greer, Sergio M Bonesi, Andrés H. ThomasAbstract:A new series of decyl chain [−(CH2)9CH3] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the pterins, a nucleophilic substitution (SN2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N3 site. However, the O-alkylated pterin converts to N3-alkylated pterin under basic conditions, pointing to a kinetic product in the former and a thermodynamic product in the latter. Two additional adducts were also obtained from an N-amine condensation of DMF solvent molecule as byproducts. In comparison to the natural product pterin, the alkyl chain pterins possess reduced fluorescence quantum yields (ΦF) and increased singlet oxygen quantum yields (ΦΔ). It is shown that the DMF-condensed pterins were more photostable compared to the N3- and O-alkylated pterins bearing a free amine group. The alkyl chain pterins efficiently intercalate in large unilamellar vesicles, which is a good i...
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Mariana Vignoni, Patricia Vicendo, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
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soybean phosphatidylcholine liposomes as model membranes to study lipid peroxidation photoinduced by pterin
Biochimica et Biophysica Acta, 2016Co-Authors: Andrés H. Thomas, Angel Catala, Mariana VignoniAbstract:Oxidized pterins, efficient photosensitizers under UVA irradiation, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. Soybean phosphatidylcholine (SoyPC) liposomes were employed as model membranes to investigate if pterin (Ptr), the parent compound of oxidized pterins, is able to photoinduced lipid peroxidation. Size exclusion chromatography and dialysis experiments showed that Ptr is not encapsulated inside the liposomes and the lipid membrane is permeable to this compound. The formation of conjugated dienes and trienes, upon UVA irradiation, was followed by absorption at 234 and 270 nm, respectively. The photoproducts were characterized by mass spectrometry and oxygenation of SoyPC was demonstrated. In addition, analysis of MS/MS spectra suggested the formation hydroperoxides. Finally, the biological implications of the findings are discussed.
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Production and quenching of reactive oxygen species by pterin derivatives, an intriguing class of biomolecules
Pure and Applied Chemistry, 2010Co-Authors: Esther Oliveros, M. Laura Dántola, Mariana Vignoni, Andrés H. Thomas, Carolina LorenteAbstract:Pterins, a family of heterocyclic compounds derived from 2-aminopteridin-4(1H)- one, are widespread in living systems and participate in important biological functions, such as metabolic redox processes. Under UV-A excitation (320-400 nm), aromatic pterins (Pt) can generate reactive oxygen species (ROS), as a consequence of both energy- and electron- transfer processes from their triplet excited state. Quantum yields of singlet oxygen ( 1 O 2 ) production depend largely on the nature of the substituents on the pterin moiety and on the pH. Formation of the superoxide anion by electron transfer between the pterin radical anion and molecular oxygen leads to the production of significant amounts of hydrogen peroxide (H 2 O 2 ) by disproportionation. Dihydropterins (H 2 Pt) do not produce 1 O 2 but are oxidized by this species with high rate constants yielding pterins as well as H 2 O 2 . In contrast to aromatic derivatives, H 2 Pt are oxidized by H 2 O 2 , and rates and products strongly depend on the na- ture of the substituents on the H 2 Pt moiety. Aromatic pterins have been found in vivo under pathological conditions, e.g., biopterin or 6-carboxypterin are present in the skin of patients affected by vitiligo, a depigmentation disorder. The biomedical implications of the produc- tion of ROS by pterin derivatives and their reactivity with these species are discussed.
Carolina Lorente - One of the best experts on this subject based on the ideXlab platform.
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Mariana Vignoni, Patricia Vicendo, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
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unraveling the degradation mechanism of purine nucleotides photosensitized by pterins the role of charge transfer steps
ChemPhysChem, 2015Co-Authors: Mariana P. Serrano, Claudio Darío Borsarelli, Carolina Lorente, Andrés H. ThomasAbstract:: Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen ((1) O2 ) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O2 to proceed, therefore the reaction is classified as (1) O2 -mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2'-deoxyguanosine 5'-monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring (1) O2 photosensitizers, takes place through an electron-transfer-initiated process (type I mechanism), whereas the contribution of the (1) O2 -mediated oxidation is almost negligible.
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Photosensitizing properties of biopterin and its photoproducts using 2'-deoxyguanosine 5'-monophosphate as an oxidizable target.
Physical chemistry chemical physics : PCCP, 2012Co-Authors: Mariana P. Serrano, Claudio Darío Borsarelli, Carolina Lorente, Faustino E. Morán Vieyra, Andrés H. ThomasAbstract:UV-A radiation (320–400 nm) induces damage to the DNA molecule and its components through photosensitized reactions. Biopterin (Bip) and its photoproducts 6-formylpterin (Fop) and 6-carboxypterin (Cap) accumulate in the skin of human beings suffering from vitiligo, a depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. This study was aimed to evaluate the photosensitizing properties of oxidized pterins present in the skin and to elucidate the mechanisms involved in the photosensitized oxidation of purine nucleotides by pterins in vitro. For this purpose, steady-state and time-resolved experiments in acidic (pH 5.0–5.8) aqueous solution were performed using Bip, Fop and Cap as photosensitizers and the nucleotide 2′-deoxyguanosine 5′-monophosphate (dGMP) as an oxidizable target. The three pterin derivatives are able to photosensitize dGMP, being Fop the most efficient sensitizer. The reactions proceed through two competing pathways: (1) electron transfer from dGMP to triplet excited-state of pterins (type I mechanism) and (2) reaction of dGMP with 1O2 produced by pterins (type II mechanism). Kinetic analysis revealed that the electron transfer pathway is the main mechanism and the interaction of dGMP with the triplet excited-state of pterins and the formation of the corresponding dGMP radicals were demonstrated by laser flash photolysis experiments. The biological implications of the results obtained are also discussed.
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Production and quenching of reactive oxygen species by pterin derivatives, an intriguing class of biomolecules
Pure and Applied Chemistry, 2010Co-Authors: Esther Oliveros, M. Laura Dántola, Mariana Vignoni, Andrés H. Thomas, Carolina LorenteAbstract:Pterins, a family of heterocyclic compounds derived from 2-aminopteridin-4(1H)- one, are widespread in living systems and participate in important biological functions, such as metabolic redox processes. Under UV-A excitation (320-400 nm), aromatic pterins (Pt) can generate reactive oxygen species (ROS), as a consequence of both energy- and electron- transfer processes from their triplet excited state. Quantum yields of singlet oxygen ( 1 O 2 ) production depend largely on the nature of the substituents on the pterin moiety and on the pH. Formation of the superoxide anion by electron transfer between the pterin radical anion and molecular oxygen leads to the production of significant amounts of hydrogen peroxide (H 2 O 2 ) by disproportionation. Dihydropterins (H 2 Pt) do not produce 1 O 2 but are oxidized by this species with high rate constants yielding pterins as well as H 2 O 2 . In contrast to aromatic derivatives, H 2 Pt are oxidized by H 2 O 2 , and rates and products strongly depend on the na- ture of the substituents on the H 2 Pt moiety. Aromatic pterins have been found in vivo under pathological conditions, e.g., biopterin or 6-carboxypterin are present in the skin of patients affected by vitiligo, a depigmentation disorder. The biomedical implications of the produc- tion of ROS by pterin derivatives and their reactivity with these species are discussed.
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electron transfer processes induced by the triplet state of pterins in aqueous solutions
Free Radical Biology and Medicine, 2010Co-Authors: Laura M Dantola, Mariana Vignoni, Patricia Vicendo, Constanza Gonzalez, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Vis spectrophotometry, HPLC, and an enzymatic method for H2O2 determination. The formation of the superoxide anion (O2•−) was investigated by electron paramagnetic resonance–spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state. The resulting radical anion (Pt•−) reacts with dissolved O2 to yield O2•−, regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt•− and EDTA•+, yielding the corresponding stable dihydroderivatives H2Pt. The effects of EDTA and dissolved O2 concentrations on the efficiencies of the different competing pathways were analyzed.
Esther Oliveros - One of the best experts on this subject based on the ideXlab platform.
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Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.
Free Radical Biology and Medicine, 2016Co-Authors: Mariana P. Serrano, Mariana Vignoni, Patricia Vicendo, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract UV-A radiation (320–400 nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5′-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties.
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Production and quenching of reactive oxygen species by pterin derivatives, an intriguing class of biomolecules
Pure and Applied Chemistry, 2010Co-Authors: Esther Oliveros, M. Laura Dántola, Mariana Vignoni, Andrés H. Thomas, Carolina LorenteAbstract:Pterins, a family of heterocyclic compounds derived from 2-aminopteridin-4(1H)- one, are widespread in living systems and participate in important biological functions, such as metabolic redox processes. Under UV-A excitation (320-400 nm), aromatic pterins (Pt) can generate reactive oxygen species (ROS), as a consequence of both energy- and electron- transfer processes from their triplet excited state. Quantum yields of singlet oxygen ( 1 O 2 ) production depend largely on the nature of the substituents on the pterin moiety and on the pH. Formation of the superoxide anion by electron transfer between the pterin radical anion and molecular oxygen leads to the production of significant amounts of hydrogen peroxide (H 2 O 2 ) by disproportionation. Dihydropterins (H 2 Pt) do not produce 1 O 2 but are oxidized by this species with high rate constants yielding pterins as well as H 2 O 2 . In contrast to aromatic derivatives, H 2 Pt are oxidized by H 2 O 2 , and rates and products strongly depend on the na- ture of the substituents on the H 2 Pt moiety. Aromatic pterins have been found in vivo under pathological conditions, e.g., biopterin or 6-carboxypterin are present in the skin of patients affected by vitiligo, a depigmentation disorder. The biomedical implications of the produc- tion of ROS by pterin derivatives and their reactivity with these species are discussed.
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electron transfer processes induced by the triplet state of pterins in aqueous solutions
Free Radical Biology and Medicine, 2010Co-Authors: Laura M Dantola, Mariana Vignoni, Patricia Vicendo, Constanza Gonzalez, Esther Oliveros, Carolina Lorente, Andrés H. ThomasAbstract:Abstract Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Vis spectrophotometry, HPLC, and an enzymatic method for H2O2 determination. The formation of the superoxide anion (O2•−) was investigated by electron paramagnetic resonance–spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state. The resulting radical anion (Pt•−) reacts with dissolved O2 to yield O2•−, regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt•− and EDTA•+, yielding the corresponding stable dihydroderivatives H2Pt. The effects of EDTA and dissolved O2 concentrations on the efficiencies of the different competing pathways were analyzed.
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photosensitization of 2 deoxyadenosine 5 monophosphate by pterin
Organic and Biomolecular Chemistry, 2007Co-Authors: Gabriela Petroselli, André M. Braun, Alberto L Capparelli, Esther Oliveros, Carolina Lorente, Franco M. Cabrerizo, Rosa Errabalsells, Andrés H. ThomasAbstract:UV-A radiation (320–400 nm) induces damages to the DNA molecule and its components through photosensitized reactions. Pterins, heterocyclic compounds widespread in biological systems, participate in relevant biological processes and are able to act as photosensitizers. We have investigated the photosensitization of 2′-deoxyadenosine-5′-monophosphate (dAMP) by pterin (PT) in aqueous solution under UV-A radiation. The effect of pH was evaluated, the participation of oxygen was investigated and the products analyzed. Kinetic studies revealed that the reactivity of dAMP towards singlet oxygen (1O2) is very low and that this reactive oxygen species does not participate in the mechanism of photosensitization, although it is produced by PT upon UV-A excitation. In contrast, analysis of irradiated solutions by means of electrospray ionization mass spectrometry strongly suggested that 8-oxo-7,8-dihydro-2′-deoxyadenosine-5′-monophosphate (8-oxo-dAMP) was produced, indicating that the photosensitized oxidation takes place via a type I mechanism (electron transfer).
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substituent effects on the photophysical properties of pterin derivatives in acidic and alkaline aqueous solutions
Photochemistry and Photobiology, 2005Co-Authors: Franco M. Cabrerizo, Gabriela Petroselli, André M. Braun, Alberto L Capparelli, Andrés H. Thomas, Carolina Lorente, Esther OliverosAbstract:Pterins are heterocyclic compounds with important biological functions, and most of them may exist in two acid-base forms in the pH range between 3 and 13 in aqueous solution. In this work, the photophysical properties of acid and basic forms of six compounds of the pterin family (6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT], N-methylfolic acid [MFA], and pteroic acid [PA]) have been studied. The effects of the chemical nature of the substituents at position 6 of the pterin moiety and the effects of the pH on the absorption and emission properties are analyzed. The fluorescence characteristics (spectra, quantum yields, lifetimes) of these compounds have been investigated using the single-photon-counting technique. Results obtained for pterin derivatives containing small substituents with 1 carbon atom (HPT, MPT, DPT) and short hydrocarbon chain (4 carbon atoms) (RPT) are different from those found for pterin derivatives containing a p-aminobenzoic acid (PABA) moiety in the substituent (MFA and PA). Fluorescence quantum yields (Phi(F)) of the first group of compounds are relatively high (>/=0.4), whereas MFA and PA exhibit very small Phi(F) values (
Libing Zhang - One of the best experts on this subject based on the ideXlab platform.
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phylogeny and systematics of the brake fern genus Pteris pteridaceae based on molecular plastid and nuclear and morphological evidence
Molecular Phylogenetics and Evolution, 2018Co-Authors: Liang Zhang, Libing ZhangAbstract:Abstract The brake fern genus Pteris belongs to Pteridaceae subfamily Pteridoideae. It is one of the largest fern genera and has been estimated to contain 200–250 species distributed on all continents except Antarctica. Previous studies were either based on plastid data only or based on both plastid and nuclear data but the sampling was small. In addition, an infrageneric classification of Pteris based on morphological and molecular evidence has not been available yet. In the present study, based on molecular data of eight plastid markers and one nuclear marker (gapCp) of 256 accessions representing ca. 178 species of Pteris, we reconstruct a global phylogeny of Pteris. The 15 major clades identified earlier are recovered here and we further identified a new major clade. Our nuclear phylogeny recovered 11 of these 16 major clades, seven of which are strongly supported. The inclusion of Schizostege in Pteris is confirmed for the first time. Based on the newly reconstructed phylogeny and evidence from morphology, distribution and/or ecology, we classify Pteris into three subgenera: P. subg. Pteris, P. subg. Campteria, and P. subg. Platyzoma. The former two are further divided into three and 12 sections, respectively.
