Alkylation converts riboflavin into an efficient photosensitizer of phospholipid membranes.

A new decyl chain [-(CH2)9CH3] riboflavin conjugate has been synthesized and investigated. A nucleophilic substitution (SN2) reaction was used for coupling the alkyl chain to riboflavin (Rf), a model natural photosensitizer. As expected, the alkylated compound (decyl-Rf) is significantly more lipophilic than its precursor and efficiently intercalates within phospholipid bilayers, increasing its fluorescence quantum yield. The oxidative damage to lipid membranes photoinduced by decyl-Rf was investigated in large and giant unilamellar vesicles (LUVs and GUVs, respectively) composed of different phospholipids. Using a fluorogenic probe, fast radical formation and singlet oxygen generation was demonstrated upon UVA irradiation in vesicles containing decyl-Rf. Photosensitized formation of conjugated dienes and hydroperoxides, and membrane leakage in LUVs rich in poly-unsaturated fatty acids were also investigated. The overall assessment of the results shows that decyl-Rf is a significantly more efficient photosensitizer of lipids than its unsubstituted precursor and that the association to lipid membranes is key to trigger phospholipid oxidation. Alkylation of hydrophilic photosensitizers as a simple and general synthetic tool to obtain efficient photosensitizers of biomembranes, with potential applications, is discussed.

Synthesis, Characterization and Photocleavage of Bis-decyl Pteroic Acid: A Folate Derivative with Affinity to Biomembranes†.

Here, we provide mechanistic insight to the photocleavage of a compound in the folate family, namely pteroic acid. A bis-decyl chain derivative of pteroic acid was synthesized, structurally characterized and photochemically investigated. We showed that, like folic acid, pteroic acid and the decylated derivative undergo a photocleavage reaction in the presence of H2 O, while no reaction was observed in methanol solution. Furthermore, density functional theory calculations were carried out to predict relative stabilities of hypothetical mono-, bis- and tris-decylated pteroic acid derivatives to help rationalize the regioselectivity of the bis-decyl pteroic acid product. Additionally, the lipophilicity of the bis-decyl pteroic acid appears to confer a hydrophobic property enabling an interaction with biomembranes.

Antibacterial activity against enterovirulent Escherichia coli strains from Bacillus amyloliquefaciens B31 and Bacillus subtilis subsp. subtilis C4: MALDI-TOF MS profiling and MALDI TOF/TOF MS structural analysis on lipopeptides mixtures.

In this work, two Bacillus strains isolated from honey (Bacillus subtilis subsp. subtilis C4; access code HQ828992) and from a waste of an artisanal tannery (Bacillus amyloliquefaciens B31; access code KP893752) were evaluated in order to determine their antibacterial activity against five enteropathogenic Escherichia coli strains. The number of viable cultivable cells of the different strains of E. coli analyzed was determined by plate count. The crude cell-free supernatants of both Bacillus strains exerted anti-E. coli activities, whereas only the lipopeptide fraction of B31 had significant E. coli inhibition. The lipopeptides produced by the Bacillus were analyzed using matrix-assisted laser desorption-ionization mass spectrometry (MALDI MS). The analysis was conducted combining the profiles (fingerprints) of the lipopeptides mixture and the individual lipopeptide fragmentation (tandem mass spectrometry [MS/MS] mode), both obtained from the same lipopeptides mixture sample, for higher output. Data obtained from C4 and B31 revealed that surfactin homologues were the most abundant lipopeptides produced by both strains studied. Additionally, kurstakin, iturin, and fengycin homologues were detected. Using the MS/MS mode, it was demonstrated that isobar compounds belonging to different families were produced by each Bacillus strain (e.g., C-16 bacillomycin D was detected in B31 samples, meanwhile C-15 iturin C was detected in C4). MS/MS analysis contributed with relevant information about the type of lipopeptides synthesized by Bacillus strains studied in this work.

Antibacterial activity of Bacillus licheniformis B6 against viability and biofilm formation of foodborne pathogens of health importance.

We studied a strain of Bacillus isolated from an artisanal tannery in Salta, Argentina. It was identified as Bacillus licheniformis B6 by 16 S phylogenetic analysis and MALDI TOF (GenBank accession code No. KP776730). The synthesis of lipopeptides by B6 and their antibacterial activity against clinical pathogenic strains was analyzed both in the cell-free supernatant (CFS) and in the crude fraction of lipopeptides (LF). Overall, the CFS did not significantly reduce the viability of the studied strains (Staphylococcus aureus 269 and ATCC 43,300, Escherichia coli 4591 and 25,922, Klebsiella sp. 1087 and 1101). However, LF at 9 mg/mL reduced the viability of those pathogenic strains by 2 and 3 log orders compared to those of the control. When the effects of LF and ampicillin were compared, they showed different sensitivity against pathogenic strains. For example, E. coli 4591 was the strain most resistant to ampicillin, requiring 250 mg/mL of antibiotic to achieve the same inhibitory effect as 9 mg/mL of B6 LF. SEM observations of the effect of LF on biofilm formation by E. coli 4591 and Klebsiella sp. 1087 clearly showed that biofilm structures were destabilized, these strains turning into weak biofilm formers. Signals in the CFS and LF corresponding to kurstakin and iturin were identified by MALDI TOF. Interestingly, surfactin was detected, rather than lichenysin, the expected lipopeptide in B. licheniformis species. Signals of bacitracin and fengycins were also found, the latter with a higher number of homologues and relative intensity in the LF than the other lipopeptides. These results show that the lipopeptides synthesized by B. licheniformis B6 have both potential antibacterial and anti-biofilm activity against pathogenic bacteria of health importance.

Antioxidant and cytoprotective effect of peptides produced by hydrolysis of whey protein concentrate with trypsin.

Whey protein is one of the most relevant co-products manufactured by the dairy industry and it is a powerful environmental pollutant. Therefore, the enzymatic hydrolysis of whey protein concentrate (WPC 35) to produce antioxidant peptides is an innovative approach which can provide added value to whey. The WPC 35 hydrolysis with trypsin was carried out for 4.31 h at 41.1 °C with an enzyme/substrate ratio of 0.017. Under such hydrolysis conditions, the peptides produced have the highest radical scavenging activity and cytoprotector effect. The WPC hydrolysate and a permeate ≤3 kDa were characterized by SDS-page, RP-HPLC and MALDI-TOF-MS. Furthermore, O2•- and HO• scavenging activity and the cytoprotective effect against a stress agent in epithelial cells of the rat ileum (IEC-18) were determined. In this study, strong antioxidant and cytoprotective peptides were obtained from a low-cost dairy industry product, which could improve consumers' health when used as functional ingredients.

Chemical Modifications of Globular Proteins Phototriggered by an Endogenous Photosensitizer.

The main goal of the present work was to investigate the damages photoinduced by pterin (Ptr), an endogenous photosensitizer present in human skin under pathological conditions, on a globular protein such as ubiquitin (Ub). Particular attention has been paid on the formation of covalent adducts between Ptr and the protein that can behave as photoantigen and provoke an immune system response. Here, a multifaceted approach including UV-visible spectrophotometry, fluorescence spectroscopy, electrophoresis, size exclusion chromatography, and mass spectrometry is used to establish the Ub changes triggered by UV-A irradiation in the presence of Ptr. Under anaerobic conditions, the only reaction corresponds to the formation of a covalently bound Ptr-Ub adduct that retains the spectroscopic properties of the free photosensitizer. A more complex scheme is observed in air-equilibrated solutions with the occurrence of three different processes, that is, formation of a Ptr-Ub adduct, dimerization, and fragmentation of the protein.

Aphicidal activity of Bacillus amyloliquefaciens strains in the peach-potato aphid (Myzus persicae).

Myzus persicae Sulzer (Hemiptera: Aphididae), is a generalist cosmopolitan insect that infests more than 400 plant species of 40 different families and is one of the major pests infesting potato crops. It causes direct damage and also spread plant viruses. The intensive use of synthetic insecticide to control aphids has led to resistant populations. Therefore, there is a need to develop biopesticides for effective control that minimizes environmental hazards. The bacteria Bacillus amyloliquefaciens is recognized as a producer of a variety of bioactive compounds. The aim here was to evaluate the aphicidal effect of B. amyloliquefaciens strains, CBMDDrag3, PGPBacCA2, and CBMDLO3, and their metabolites on the mortality and fecundity of M. persicae. Cells suspensions, heat-killed cell suspensions, cell-free supernatants, or isolated lipopeptide fractions from B. amyloliquefaciens strains were offered to aphids through artificial diets. The isolated lipopeptide fractions composed mainly of kurstakins, surfactins, iturins, and fengycins, when were administrated through diets, had no aphicidal effect against M. persicae. However, aphids fed on diets with whole cell suspensions and its cell-free supernatant of all three bacteria strains resulted in 100% mortality of adult aphids and nymphs. Specially, B. amyloliquefaciens CBMDLO3, has an effective aphicidal effect on M. persicae, used both bacterial cells and their metabolites. Moreover, heat-killed cells of B. amyloliquefaciens CBMDLO3 also had aphicidal action, although the aphid mortality was lower than on diet with living bacteria. Therefore, these results propose that B. amyloliquefaciens, could function as a novel eco-friendly biopesticide for the control of M. persicae.

Synthesis, characterization and chemical degradation of poly(ester-triazole)s derived from d-galactose.

α-Azide-ω-alkynyl ester monomers were designed and synthesized in order to obtain hydrolytically degradable polymers. The monomers were prepared from d-galactose, as a renewable resource. Environmentally benign azido-alkyne cycloaddition polymerizations were conducted to afford poly(ester-triazole)s, with complete atom economy. Although polymer formation prevailed under optimized polymerization conditions, variable proportions of cyclic oligomer byproducts were detected. The Cu-catalyzed click polymerization led regioselectively to 1,4-disubstituted triazole linkages, while the thermal, metal-free polymerization produced a random distribution of 1,4- and 1,5-disubstituted triazoles in the polymer backbone. The poly(ester-triazole)s exhibited high molecular weights (M w in the range 35-85 kDa). They were soluble in organic solvents but highly insoluble in water, thus removal of the Cu(i) catalyst was simplified. The polymers were stable up to 300 °C, and had T g values in the range 90-100 °C. The materials were hydrolysed under either basic or strong acid conditions, and the degradation products have been characterized.

MALDI- and LDI-MS saponin fingerprint of leaves and stick components of commercial yerba mate (Ilex paraguariensis).

Yerba mate (YM) is massively produced and consumed as an infusion in South America and spreading all over the world. This product is obtained from dried leaves of Ilex paraguariensis Saint Hilaire, mixed with fragments of dried branches (sticks). For its commercialization, YM must have a minimum percentage of leaves because its presence determines YM quality and price. Till today, a mechanical methodology to determine the relative amount of components (sticks, leaves, and powder) is used. There is not any modern analytical method that provides information for quick characterization of the YM components. Typical saponin fingerprints for leaves and sticks were found by using ultraviolet matrix-assisted laser desorption ionization and ultraviolet laser desorption ionization mass spectrometry. Then, their possible application as useful tools for quick characterization of components of commercial YM (leaves and sticks) is presented. Furthermore, fingerprints obtained from authentic samples of Ilex paraguariensis and Ilex dumosa are also included and discussed. Each Ilex show typical saponin fingerprints for leaves and sticks.

Identification of an intermediate for 1,8-dihydroxynaphthalene-melanin synthesis in a race-2 isolate of Fulvia fulva (syn. Cladosporium fulvum).

Fulvia fulva (syn. Cladosporium fulvum, Mycosphaerellaceae) is a dematiaceous fungus that causes tomato leaf mould. It is characterized by its biotrophic lifestyle and the synthesis of the bianthraquinone secondary metabolite, cladofulvin. The aim of the study was to characterize the dark pigment photochemically synthesized by F. fulva and to elucidate its biochemical pathway. We isolated a black pigment from in vitro cultures of the fungus. We determined the pigment to be 1,8-dihydroxynaphthalene (DHN)-melanin based on its chemical and photochemical characteristics, as well as the presence of flaviolin, when fungal reductases were inhibited by tricyclazole. Furthermore, the pks1 gene involved in pigment synthesis has a KS domain already associated with DHN-melanin. Our findings support the relevance of studying melanization in F. fulva.

Biocontrol of Sclerotinia sclerotiorum (Lib.) de Bary on common bean by native lipopeptide-producer Bacillus strains.

Bacillus sp. B19, Bacillus sp. P12 and B. amyloliquefaciens B14 were isolated from soils of Salta province, and PGPR properties on the common bean (Phaseolus vulgaris L.) cv. Alubia and antagonistic activity against Sclerotinia sclerotiorum were studied. It was determined that B19 and P12 increased crop germination potential (GP) from the common bean by 14.5% compared to control seeds; these strains also increased root length (10.4 and 15%, respectively) and stem length (20.2 and 30%, respectively) compared to the control; however, as for the B14 strain, no increases in growth parameters were detected. In addition, all the treatments that combined two bacilli: B14 + B19, B14 + P12 and B19 + P12, generated beneficial effects on GP and seedling growth compared to control seeds, but not compared to a single inoculant. B19 and P12 strains synthesized auxins at concentrations of 5.71 and 4.90 mg/mL, respectively, and it was qualitatively determined that they synthesize siderophores. In addition, previous studies have determined that B14 produces auxins in a concentration of 10.10 mg/mL, and qualitatively synthesizes siderophores. The phytosanitary state of the white bean cv. Alubia control seeds revealed bacterial contamination in 87% of all the evaluated seeds and different fungi such as Cladosporium sp., Fusarium sp., and Rhizopus sp. Bean seeds treated with B14, B19 or P12 showed no growth of contaminating bacteria or of pathogenic fungi; in fact, bacilli inoculum development was observed in all seeds. Additionally, B19, P12 and B14 strains inhibited in vitro the development of 9 native S. sclerotiorum strains isolated from the Salta region, with FI ranging between 60 and 100%. The three Bacillus strains synthesized different isoforms of the lipopeptides: surfactin, iturin, and fengycin in the presence of S. sclerotiorum, as determined by MALDI-TOF. In the in vivo trials, when common bean seeds were grown in soils contaminated with S. sclerotiorum, an incidence of 100% was determined when the seeds were not treated with any Bacillus. Seeds treated with the chemical fungicide and sown in S. sclerotiorum-infested soil did not produce seed emergence, while the inoculation of the seeds with B14 + P12, B14 + B19 or B19 + P12 reduced the effect of the pathogen by 46, 43 and 25%, respectively. Disease progression in B14 + P12 and B14 + B19 treatments was significantly lower than in the remaining treatments, with an AUDPC of 873.75 and 1071, respectively.

MALDI-MS argininyl bufadienolide esters fingerprint from parotoid gland secretions of Rhinella arenarum: Age, gender, and seasonal variation.

In many amphibians, the granular glands can be grouped in special regions forming macroglands. This is the case of toads, characterized by the presence of a pair of parotoid macroglands, strategically located to give protection by poison release in case of attacks. The product secreted consists of a wide variety of chemical compounds including proteins, peptides, biogenic amines, toxic steroidal bufadienolides, and various alkaloids, depending on the species. In this work, using Rhinella arenarum, we have performed, for the first time, the matrix assisted-ultraviolet laser desorption/ionization mass spectrometry and tandem mass spectrometry characterization of the components of the secretion used as crude material, just suspended in MeOH (or MeCN). The crude sample as a whole (whole suspension) was spotted on the matrix assisted-ultraviolet laser desorption plate for analysis. Electrospray ionization-Orbitrap was used for cross-checking experiments. The pattern of signals obtained at m/z ranges 600 to 800 and 1200 to 1600 could be assigned as the argininyl bufadienolide esters fingerprint characteristic of female and male. Variation patterns for gender (female, male), age (non-reproductive, reproductive), and season (non-reproductive, reproductive) are described.

Biospectroscopy, biospectrometry and imaging of Ilex paraguariensis. Basis for non-destructive quality evaluation using artificial vision.

Yerba mate (YM) is massively produced and consumed as an infusion in South America and is gaining popularity all over the world. This product is obtained from the dried leaves of Ilex paraguariensis Saint Hilaire, mixed with fragments of its dried branches. For its commercialization YM must have a minimum percentage of leaves according to a standard classification. Until now, composition quantification has been mechanically performed, thus development of new methods is still pending. In this work a quantification method using solid-phase molecular fluorescence, alternately diffuse reflectance spectroscopy and an imaging technique using a scanner have been proposed. Strong differences between the spectroscopic properties of leaves and sticks were observed and in all the cases linear correlations between the processed signals and composition were observed. Interesting differences in chemical composition of YM leaves and sticks were additionally obtained in this work by means of total phenol content quantification, ultraviolet matrix assisted laser-desorption ionization mass spectrometry and ultraviolet laser-desorption ionization mass spectrometry.

Norharmane rhenium(I) polypyridyl complexes: synthesis, structural and spectroscopic characterization.

Two novel Re(i) complexes with the general formula fac-[Re(CO)3(L)(nHo)]CF3SO3, where L = 2,2'-bipyridine (bpy) or 1,10 phenanthroline (phen) and nHo (9H-pyrido[3,4-b]indole; norharmane) have been synthesized. The Re(i)-nHo complexes were characterized by structural X-ray diffraction, (1)H and (13)C NMR, UV-vis absorption and FT-IR spectroscopy, and by a combination of two mass spectrometry techniques, namely ESI-MS and UV-MALDI-MS. All characterizations showed that nHo is coordinated to the metal atom by the pyridine nitrogen of the molecule. X-ray structural analysis revealed that the crystal lattices for both complexes are further stabilized by a strong >N-HO bond between the pyrrole NH group of the pyridoindole ligand and one oxygen atom of the trifluoromethanesulfonate counter-ion. Ground state geometry optimization by DFT calculations showed that in fluid solution the nHo ligand may rotate freely. The nature of the electronic transitions of Re(CO)3(bpy)(nHo)(+) were established by TD-DFT calculations. The set of the most important electronic transitions present in this complex are comprised of π→π* electronic transitions centered on bpy and nHo moieties, LLCTnHo→COs, MLLCTRe(CO)3→bpy and LLCTnHo→bpy transitions. Additionally, TD-DFT calculations predict the existence of another two intense MLLCTRe(CO)3→nHo electronic transitions. Calculated UV-vis absorption spectra are in good agreement with the corresponding experimental data for the bpy-containing complex.

In situ analysis of soybeans and nuts by probe electrospray ionization mass spectrometry.

The probe electrospray ionization (PESI) is an ESI-based ionization technique that generates electrospray from the tip of a solid metal needle. In the present work, we describe the PESI mass spectra obtained by in situ measurement of soybeans and several nuts (peanuts, walnuts, cashew nuts, macadamia nuts and almonds) using different solid needles as sampling probes. It was found that PESI-MS is a valuable approach for in situ lipid analysis of these seeds. The phospholipid and triacylglycerol PESI spectra of different nuts and soybean were compared by principal component analysis (PCA). PCA shows significant differences among the data of each family of seeds. Methanolic extracts of nuts and soybean were exposed to air and sunlight for several days. PESI mass spectra were recorded before and after the treatment. Along the aging of the oil (rancidification), the formation of oxidated species with variable number of hydroperoxide groups could be observed in the PESI spectra. The relative intensity of oxidated triacylglycerols signals increased with days of exposition. Monitoring sensitivity of PESI-MS was high. This method provides a fast, simple and sensitive technique for the analysis (detection and characterization) of lipids in seed tissue and degree of oxidation of the oil samples.

Photoacoustic and luminescence characterization of nitrogen heterocyclic aromatic UV-MALDI matrices in solution.

A group of nitrogen heterocyclic aromatic compounds used, among others, as UV-MALDI matrices was studied. By using spectroscopic, luminescence and photoacoustic techniques, as well as time resolved phosphorescence for singlet oxygen production determination, the behaviour of 9-aminoacridine (9AA), 3-aminoquinoline (3AQ), 2-(2-aminoethylamino)-5-nitropyridine (AAN) and 3,4-dihydro-7-methoxy-1-methyl-9H-pyrido[3,4-b] indole (harmaline, HLA) in acetonitrile solutions is described. The results show that for these compounds radiationless processes that release prompt heat to the media are a quite important deactivation mechanism.

Mass spectrometry of rhenium complexes: a comparative study by using LDI-MS, MALDI-MS, PESI-MS and ESI-MS.

A group of rhenium (I) complexes including in their structure ligands such as CF(3)SO(3)-, CH(3)CO(2)-, CO, 2,2'-bipyridine, dipyridil[3,2-a:2'3'-c]phenazine, naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and 1,10-phenanthroline have been studied for the first time by mass spectrometry. The probe electrospray ionization (PESI) is a technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid metal needle. In this work, mass spectra for organometallic complexes obtained by PESI were compared with those obtained by classical ESI and high flow rate electrospray ionization assisted by corona discharge (HF-ESI-CD), an ideal method to avoid decomposition of the complexes and to induce their oxidation to yield intact molecular cation radicals in gas state [M](+·) and to produce their reduction yielding the gas species [M](-·). It was found that both techniques showed in general the intact molecular ions of the organometallics studied and provided additional structure characteristic diagnostic fragments. As the rhenium complexes studied in the present work showed strong absorption in the UV-visible region, particularly at 355 nm, laser desorption ionization (LDI) mass spectrometry experiments could be conducted. Although intact molecular ions could be detected in a few cases, LDI mass spectra showed diagnostic fragments for characterization of the complexes structure. Furthermore, matrix-assisted laser desorption ionization (MALDI) mass spectra were obtained. Nor-harmane, a compound with basic character, was used as matrix, and the intact molecular ions were detected in two examples, in negative ion mode as the [M](-·) species. Results obtained with 2-[(2E)-3-(4-tert-buthylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) as matrix are also described. LDI experiments provided more information about the rhenium complex structures than did the MALDI ones.

α-Rhamnosyl-ß-glucosidase-catalyzed reactions for analysis and biotransformations of plant-based foods.

Most aroma compounds exist in vegetal tissues as disaccharide conjugates, rutinose being an abundant sugar moiety in grapes. The availability of aroma precursors would facilitate analytical analysis of plant-based foods. The diglycosidase α-rhamnosyl-ß-glucosidase from Acremonium sp. DSM 24697 efficiently transglycosylated the rutinose moiety from hesperidin to 2-phenylethanol, geraniol, and nerol in an aqueous-organic biphasic system. 2-Phenethyl rutinoside was synthesized up to millimolar level with an 80% conversion regarding the donor hesperidin. The hydrolysis of the synthesized aroma precursors was not detected in an aqueous medium. However, in the presence of ethanol as a sugar acceptor, the enzyme was able to transfer the disaccharide residue forming the alkyl-rutinoside. The aroma precursors were significantly hydrolyzed (up to 3-4% in 2 h at 30 °C), which indicated the potential use of the enzyme for biotechnological applications, for example, in aroma modulation of fermented foods.

Quenching of the fluorescence of aromatic pterins by deoxynucleotides.

Steady-state and time-resolved studies of the fluorescence of four aromatic unconjugated pterins (pterin (Ptr), 6-(hydroxymethyl)pterin (Hmp), 6-methylpterin (Mep), and 6,7-dimethylpterin (Dmp)) in aqueous solutions in the presence of different nucleotides (2'-deoxyguanosine 5'-monophosphate (dGMP), 2'-deoxyadenosine 5'-monophosphate (dAMP), and 2'-deoxycytosine 5'-monophosphate (dCMP)) have been performed using the single-photon counting technique. The singlet excited states of acid forms of pterins are deactivated by purine nucleotides (dGMP and dAMP) via a combination of dynamic and static processes. The efficiency of the dynamic quenching is high, independently of the nature of the purine base of the nucleotide and of the chemical structure of the substituents linked to the pterin moiety. Analysis of the static quenching indicates that ground-state association between pterins and purine nucleotides takes place, but the formation of the corresponding complexes is significant only at relatively high reactant concentrations. The quenching of the fluorescence of acid forms of pterin derivatives by dCMP, a pyrimidine nucleotide, is slightly less efficient than the quenching by purine nucleotides and is purely dynamic. In alkaline media, the fluorescence quenching is much less efficient than in acidic media, the deactivation by purine nucleotides being purely dynamic, whereas quenching by dCMP is negligible. Possible mechanisms for the quenching of fluorescence of pterin derivatives by the different nucleotides are discussed.

Oxidation of 2'-deoxyguanosine 5'-monophosphate photoinduced by pterin: type I versus type II mechanism.

UV-A radiation (320-400 nm) induces damage to the DNA molecule and its components through different photosensitized reactions. Among these processes, photosensitized oxidations may occur through electron transfer or hydrogen abstraction (type I) and/or the production of singlet molecular oxygen ((1)O2) (type II). Pterins, heterocyclic compounds widespread in biological systems, participate in relevant biological processes and are able to act as photosensitizers. We have investigated the photosensitized oxidation of 2'-deoxyguanosine 5'-monophosphate (dGMP) by pterin (PT) in aqueous solution under UV-A irrradiation. Kinetic analysis was employed to evaluate the participation of both types of mechanism under different pH conditions. The rate constant of (1)O2 total quenching (k(t)) by dGMP was determined by steady-state analysis of the (1)O2 NIR luminescence, whereas the rate constant of the chemical reaction between (1)O2 and dGMP (k(r)) was evaluated from kinetic analysis of concentration profiles obtained by HPLC. The results show that the oxidation of dGMP photosensitized by PT occurs through two competing mechanisms that contribute in different proportions depending on the pH. The dominant mechanism in alkaline media involves the reaction of dGMP with (1)O2 produced by energy transfer from the PT triplet state to molecular oxygen (type II). In contrast, under acidic pH conditions, where PT and the guanine moiety of dGMP are not ionized, the main pathway for dGMP oxidation involves an initial electron transfer between dGMP and the PT triplet state (type I mechanism). The biological implications of the results obtained are also discussed.