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A polymeric photosensitizer was synthesized through covalent attachment of the natural photosensitizer 6-carboxypterin (Cap) to a poly(allylamine hydrochloride) (PAH) polymer. The optimization of the functionalization steps and purification procedure is described. The overall yield of the functionalization reaction was 67% to generate the modified polymer (PAH-Cap), featuring a Cap substitution degree of approximately 1% and advantageous spectroscopic properties. Photosensitizing properties of PAH-Cap were observed to occur via both photooxidation mechanisms, i.e., type I and type II. This feature was demonstrated using a biologically relevant target molecule, 2'-deoxyguanosine (dG). The spectroscopic, photophysical, and photochemical behaviors in aqueous environments were studied and compared to Cap. To explore possible further relevant biological applications, experiments with PAH-Cap and dG were carried out at physiological pH. PAH-Cap can generate singlet molecular oxygen and initiate an electron transfer process at pH 7 in air-saturated solutions upon UVA irradiation. Moreover, based on its spectroscopic features, visible light can be used to initiate the photooxidation of biological compounds in water, with many interesting advantages compared to free Cap and other related pteridines. These advantages include an enhancement of the photosensitizing effect at physiological pH and the potential of PAH-Cap for its use as a building block in supramolecular assemblies. The functionalization strategy hereby described can be employed for the preparation of robust photoactive polymers with great potential for its application in photodynamic therapy (PDT) and disinfection technologies.

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We hereby present a novel "grafting-to"-like approach for the covalent attachment of plasmonic nanoparticles (PNPs) onto whispering gallery mode (WGM) silica microresonators. Mechanically stable optoplasmonic microresonators were employed for sensing single-particle and single-molecule interactions in real time, allowing for the differentiation between binding and non-binding events. An approximated value of the activation energy for the silanization reaction occurring during the "grafting-to" approach was obtained using the Arrhenius equation; the results agree with available values from both bulk experiments and ab initio calculations. The "grafting-to" method combined with the functionalization of the plasmonic nanoparticle with appropriate receptors, such as single-stranded DNA, provides a robust platform for probing specific single-molecule interactions under biologically relevant conditions.

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Background: Gastric cancer (GC) is the fourth most common cause of cancer deaths around the world and the first cause of cancer deaths in Peru; however, there are no prospective trials for adjuvant chemotherapy in GC after curative gastrectomy in this country. The objective of this study was to evaluate the effectiveness of adjuvant chemotherapy in stage II-III gastric cancer patients who underwent D2 gastrectomy. Methods: We included patients with stage II-III gastric cancer who underwent radical gastrectomy and D2 dissection between 2014 and 2016 at our institution. Patients received 3-week cycles of capecitabine (1,000 mg/m2 twice daily on days 1-14) plus oxaliplatin (130 mg/m2 on day 1) for 6 months. Survival curves were estimated with the Kaplan-Meier method, and the Cox proportional hazards model was used to identify prognostic factors for survival. Results: In total, 173 patients were included: 100 (57.8%) patients received adjuvant chemotherapy and surgery (AChS) and 73 (42.2%) surgery alone (SA). Three-year disease-free survival (DFS) was higher in the AChS groups (69%) than in the SA group (52.6%) (p = 0.034). Regarding overall survival (OS), 31 patients (31%) died in the AChS group compared with 34 (46.6%) in the SA group (p = 0.027). In the multivariate analysis, adjuvant chemotherapy was an independent prognostic factor for DFS (HR = 0.60; 95% CI = 0.37-0.97; p = 0.036) and OS (HR = 0.58; 95% CI = 0.36-0.95; p = 0.029). ACh showed consistent benefit in DFS and OS for patients with albumin >3.5 g/dL, lymphovascular and perineural invasion, pT4, pN2-3, pathologic stage (PS) IIIA and IIIB and lymph node ratio (LNR) > 13.1. Conclusion: These data suggest that adjuvant capecitabine and oxaliplatin reduce the recurrence and mortality in patients with stage II-III gastric cancer who underwent D2 gastrectomy. PS IIIA and IIIB and LNR > 13.1 benefited more from receiving adjuvant chemotherapy and poorly cohesive gastric carcinoma did not significantly reduce the rates of survival.

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BACKGROUND: Ampullary adenocarcinoma (AAC) is a rare neoplasm that accounts for only 0.2% of all gastrointestinal cancers. Its incidence rate is lower than 6 cases per million people. Different prognostic factors have been described for AAC and are associated with a wide range of survival rates. However, these studies have been exclusively conducted in patients originating from Asian, European, and North American countries. AIM: To evaluate the histopathologic predictors of overall survival (OS) in South American patients with AAC treated with curative pancreaticoduodenectomy (PD). METHODS: We analyzed retrospective data from 83 AAC patients who underwent curative (R0) PD at the National Cancer Institute of Peru between January 2010 and October 2020 to identify histopathologic predictors of OS. RESULTS: Sixty-nine percent of patients had developed intestinal-type AAC (69%), 23% had pancreatobiliary-type AAC, and 8% had other subtypes. Forty-one percent of patients were classified as Stage I, according to the AJCC 8th Edition. Recurrence occurred primarily in the liver (n = 8), peritoneum (n = 4), and lung (n = 4). Statistical analyses indicated that T3 tumour stage [hazard ratio (HR) of 6.4, 95% confidence interval (CI) of 2.5-16.3, P < 0.001], lymph node metastasis (HR: 4.5, 95%CI: 1.8-11.3, P = 0.001), and pancreatobiliary type (HR: 2.7, 95%CI: 1.2-6.2, P = 0.025) were independent predictors of OS. CONCLUSION: Extended tumour stage (T3), pancreatobiliary type, and positive lymph node metastasis represent independent predictors of a lower OS rate in South American AAC patients who underwent curative PD.

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Introducción: El presente artículo resume el proceso de elaboración de la Guía de Práctica Clínica (GPC) para el manejo de dolor en pacientes oncológicos. Este proceso se llevó a cabo con la participación de un equipo multidisciplinario de médicos asistenciales, metodólogos y diversos revisores externos (especialistas con dominio en la metodología y el tema). La priorización de preguntas PICO fue realizada por el Grupo Elaborador de la GPC (GEG), acordando trabajar cinco preguntas PICO. Para dar respuesta a las preguntas se realizó una búsqueda sistemática de GPC, revisiones sistemáticas y estudios primarios. Se utilizó la metodología GRADE y los lineamientos de la normativa nacional para la formulación de recomendaciones. Se formularon 12 recomendaciones (10 fuertes y 2 débiles), 5 puntos de buena práctica clínica y 4 cuadros consensuados sobre el manejo de dolor oncológico. Los temas que abarcaron las recomendaciones para el manejo de dolor en pacientes oncológicos fueron: intervención temprana de tratamiento, terapia analgésica en dolor leve a moderado y en dolor moderado a severo, dolor neuropático e intervenciones no farmacológicas.

Background: The article summarizes the process of elaboration of the Clinical Practice Guide (CPG) for the management of cancer patients. The elaboration process was carried out with the participation of a multidisciplinary team of assisting physicians, methodologists and various external reviewers (specialists with mastery in the methodology and the subject). The prioritization of PICO questions was carried out by the GPC Elaboration Group (GEG), after which 05 PICO questions were concluded. To answer the questions, a systematic search of CPGs, systematic reviews and primary studies was carried out. The "GRADE" methodology and the guidelines of national regulations were used to formulate recommendations. Twelve recommendations were made (ten strong and two weak),5 points of good clinical practice,04 consensus tables on the management of cancer pain. The topics that covered the recommendations for pain management in cancer patients were: early treatment intervention, analgesic therapy in mild to moderate pain and moderate to severe pain, neuropathic pain and non-pharmacological interventions

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Tyrosine is an amino acid related to crucial physiological events and its oxidation, that produce beneficial or detrimental effects on biological systems, has been extensively studied. Degradation of tyrosine often begins with the loss of an electron in an electron transfer reaction in the presence of a suitable electron acceptor. The reaction is facilitated by excited states of the acceptor in photosensitized processes. Several products of tyrosine oxidation have been described, the main ones being 3,4-dihydroxy-l-phenylalanine (commonly known as DOPA) and tyrosine dimers. Here, we report tyrosine recovery from tyrosyl radical, after one-electron oxidation, in the presence of DOPA. We propose that under high oxidative stress the oxidation of tyrosine may be controlled, in part, by one of its oxidation products. Also, we present strong evidence of antioxidant action of DOPA by preventing tyrosine dimerization, one of the most serious oxidative protein modifications, and the origin of structural modifications leading to the loss of protein functionality.

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Over the past few years, the interest in Resveratrol (3,4',5,-trihydroxystilbene, RSV) has increased due to the evidence found of its antioxidant action that protects biomolecules and cells from oxidative damage. The interest has been further exacerbated by the natural presence of RSV in some fruits and derivatives, especially in red wine. In this paper we present evidence of RSV capacity in protecting a deoxynucleotide, an essential constituent of DNA, from one-electron oxidation. This article evaluates the mechanism responsible for the antioxidant action of RSV, after one-electron oxidation of 2'-deoxyguanosine 5'-monophosphate (dGMP), by kinetic analysis during steady-state irradiation and laser flash photolysis experiments. Results showed that RSV protects dGMP by recovering the nucleotide from its radical, which is formed after the reaction of dGMP with the triplet excited state of the photosensitizer. In the absence of RSV, dGMP is irremediably oxidized, and if the damage occurs in dGMP located in DNA molecules, the consequences can be as serious as mutations and subsequent carcinogenic lesions.

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DNA - bioinspired polyelectrolytes poly[vinylbenzylthymine (VBT)-4-vinylbenzyltriethylammonium chloride (VBA)] and poly[vinylbenzylthymine (VBT)-4-vinylphenylsufonate (VPS)] were used for the preparation of hollow microcapsules (HMC) using the layer-by-layer method and CaCO3 microspheres as removable molds. Stable aqueous suspensions of spherical-shaped HMCs with a shell composed of six layers of VBA-based polyelectrolytes were obtained, of approximately (7.0±1.5) µm diameter and a shell thickness of 1 µm. Ultraviolet-B irradiation of the HMC suspensions induces an efficient crosslinking between adjacent polyelectrolyte chains through the formation of thymine photodimers, such as the cyclobutane pyrimidine dimer (CPD) and the (6-4) pyrimidine-pyrimidone photoproduct (6-4PP). This process resulted in a reduction of the average interstitial mesh size of the HMC shells, modulating their permeability properties and increasing the mechanical stability of the HMC without a noticeable modification of size and shape. Thus, the DNA-bioinspired polyelectrolytes are promising materials for the preparation of UVB-responsive HMCs.

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Unconjugated oxidized pterins accumulate in the skin of patients suffering from vitiligo and, under UVA irradiation, photosensitize the oxidation of amino acids. In this work, we study the interaction of the singlet and triplet excited states of pterin (Ptr), the parent compound of oxidized pterins, with four oxidizable amino acids: tryptophan (Trp), tyrosine (Tyr), histidine (His) and methionine (Met). Steady-state and time-resolved fluorescence measurements and laser flash photolysis experiments were performed to investigate the quenching of the Ptr excited states by the amino acids in aqueous solution. The singlet excited states of Ptr are quenched by Met mainly via a dynamic process and by Trp via a combination of dynamic and static processes. His does not quench singlet excited states of Ptr, and quenching by Tyr could not be investigated due to the low solubility of this amino acid. The triplet excited states of Ptr are quenched by the four studied amino acids, and the corresponding bimolecular quenching rate constants are in the range of diffusion controlled limit. The assessment of the results in the context of the Ptr-photosensitization of amino acids suggests that triplet excited state of Ptr is the species that initiates the photochemical processes.

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Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1 O2 ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.

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OBJECTIVE: To determine the clinical and histological characteristics and prognostic factors of cervical cancer (CC) in young Peruvian patients. MATERIALS AND METHODS: Retrospective analysis of patients younger than 35 years old diagnosed with CC between 2008 and 2012 in the Instituto Nacional de Enfermedades Neoplásicas. RESULTS: 449 patients had epithelial neoplasms. The main histological types were: squamous cell carcinoma (84.9%), adenocarcinoma (11.0%) and adenosquamous carcinoma (2.4%). The average tumor size was 4.98 cm. Anemia (55.7%), elevated creatinine (21.2%) and hydronephrosis (13.8%) were also identified. 82.3% of the patients presented locally advanced disease. Stages IIB (47.4%) and IIIB (25.8%) were the most common. Overall 5-year survival was 59.5% (I, 90.9%; II, 57.5%; III, 42.7% and IV, 13.3%). Elevated creatinine, anemia, tumor size, parametrial involvement and hydronephrosis were factors that affected survival. No significant relation was found between histological type and survival. The presence of anemia (adjusted hazard ratio [aHR]: 2.5; 95% confidence interval [CI 95%]: 1.6-4.0) and hydronephrosis (aHR: 1.6; CI 95%: 1.0-4.0) were independently associated with survival; likewise, the parametrial commitment with (aHR: 3.3; CI 95%: 1.5-7.2) or without (aRH: 2.6; CI 95%: 1.3-5.3) extension to the pelvic bone. CONCLUSIONS: Cervical cancer in young Peruvians is diagnosed in advanced stages. Overall survival in each stage is similar to the reported in older patients. The importance of conventional prognosis- related factors was confirmed. Anemia was an important independent prognostic factor requiring further investigations.

OBJETIVOS: Determinar las características clínicas, histológicas y los factores pronósticos del cáncer cervical (CC) en pacientes jóvenes peruanas. MATERIALES Y MÉTODOS: Análisis retrospectivo de pacientes de 35 años de edad o menos diagnosticadas con CC entre el 2008 y el 2012 en el Instituto Nacional de Enfermedades Neoplásicas. RESULTADOS: 449 pacientes tenían neoplasias epiteliales. Los tipos histológicos principales fueron: carcinoma de células escamosas (84,9%), adenocarcinoma (11,0%) y carcinoma adenoescamoso (2,4%). El tamaño tumoral promedio fue 4,98 cm. También se identificó anemia (55,7%), creatinina elevada (21,2%) e hidronefrosis (13,8%). El 82,3% de los pacientes presentaron enfermedad localmente avanzada. Los estadios IIB (47,4%) y IIIB (25,8%) fueron los más comunes. La supervivencia global a 5 años fue de 59,5% (I, 90,9%; II, 57,5%; III, 42,7% y IV, 13,3%). La creatinina elevada, la anemia, el tamaño tumoral, el compromiso parametrial y la hidronefrosis fueron factores que afectaron la supervivencia. No se encontró relación significativa entre el tipo histológico y la supervivencia. La presencia de anemia (Hazard Ratio ajustado [HRa]: 2,5; intervalo de confianza al 95% [IC 95%]: 1,6-4,0) y la hidronefrosis (HRa: 1,6; IC 95%: 1,0-4,0) estuvieron independientemente asociados con la supervivencia; asimismo, el compromiso parametrial con (HRa: 3,3; IC 95%: 1,5-7,2) o sin (HRa: 2,6; IC 95%: 1,3-5,3) extensión al hueso pélvico. CONCLUSIONES: El cáncer cervical en jóvenes peruanas es diagnosticado en estadios avanzados. La supervivencia global en cada estadio es similar a la reportada en pacientes mayores. Se confirmó la importancia de los factores convencionales relacionados con el pronóstico. La anemia fue un factor de pronóstico independiente importante que requiere mayores investigaciones.

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RESUMEN Objetivos Determinar las características clínicas, histológicas y los factores pronósticos del cáncer cervical (CC) en pacientes jóvenes peruanas. Materiales y métodos Análisis retrospectivo de pacientes de 35 años de edad o menos diagnosticadas con CC entre el 2008 y el 2012 en el Instituto Nacional de Enfermedades Neoplásicas. Resultados 449 pacientes tenían neoplasias epiteliales. Los tipos histológicos principales fueron: carcinoma de células escamosas (84,9%), adenocarcinoma (11,0%) y carcinoma adenoescamoso (2,4%). El tamaño tumoral promedio fue 4,98 cm. También se identificó anemia (55,7%), creatinina elevada (21,2%) e hidronefrosis (13,8%). El 82,3% de los pacientes presentaron enfermedad localmente avanzada. Los estadios IIB (47,4%) y IIIB (25,8%) fueron los más comunes. La supervivencia global a 5 años fue de 59,5% (I, 90,9%; II, 57,5%; III, 42,7% y IV, 13,3%). La creatinina elevada, la anemia, el tamaño tumoral, el compromiso parametrial y la hidronefrosis fueron factores que afectaron la supervivencia. No se encontró relación significativa entre el tipo histológico y la supervivencia. La presencia de anemia (Hazard Ratio ajustado [HRa]: 2,5; intervalo de confianza al 95% [IC 95%]: 1,6-4,0) y la hidronefrosis (HRa: 1,6; IC 95%: 1,0-4,0) estuvieron independientemente asociados con la supervivencia; asimismo, el compromiso parametrial con (HRa: 3,3; IC 95%: 1,5-7,2) o sin (HRa: 2,6; IC 95%: 1,3-5,3) extensión al hueso pélvico. Conclusiones El cáncer cervical en jóvenes peruanas es diagnosticado en estadios avanzados. La supervivencia global en cada estadio es similar a la reportada en pacientes mayores. Se confirmó la importancia de los factores convencionales relacionados con el pronóstico. La anemia fue un factor de pronóstico independiente importante que requiere mayores investigaciones.

ABSTRACT Objective To determine the clinical and histological characteristics and prognostic factors of cervical cancer (CC) in young Peruvian patients. Materials and methods Retrospective analysis of patients younger than 35 years old diagnosed with CC between 2008 and 2012 in the Instituto Nacional de Enfermedades Neoplásicas. Results 449 patients had epithelial neoplasms. The main histological types were: squamous cell carcinoma (84.9%), adenocarcinoma (11.0%) and adenosquamous carcinoma (2.4%). The average tumor size was 4.98 cm. Anemia (55.7%), elevated creatinine (21.2%) and hydronephrosis (13.8%) were also identified. 82.3% of the patients presented locally advanced disease. Stages IIB (47.4%) and IIIB (25.8%) were the most common. Overall 5-year survival was 59.5% (I, 90.9%; II, 57.5%; III, 42.7% and IV, 13.3%). Elevated creatinine, anemia, tumor size, parametrial involvement and hydronephrosis were factors that affected survival. No significant relation was found between histological type and survival. The presence of anemia (adjusted hazard ratio [aHR]: 2.5; 95% confidence interval [CI 95%]: 1.6-4.0) and hydronephrosis (aHR: 1.6; CI 95%: 1.0-4.0) were independently associated with survival; likewise, the parametrial commitment with (aHR: 3.3; CI 95%: 1.5-7.2) or without (aRH: 2.6; CI 95%: 1.3-5.3) extension to the pelvic bone. Conclusions Cervical cancer in young Peruvians is diagnosed in advanced stages. Overall survival in each stage is similar to the reported in older patients. The importance of conventional prognosis- related factors was confirmed. Anemia was an important independent prognostic factor requiring further investigations.

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UV-A radiation (320-400nm), 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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Biopterin (Bip) and its photoproducts 6-formylpterin (Fop) and 6-carboxypterin (Cap) accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. These compounds absorb in the UV-A inducing a potential photosensitizing action that can cause damage to DNA and other biomolecules. In this work, we have investigated the capability of these pterin derivatives (Pt) to act as photosensitizers under UV-A irradiation for the degradation of 2'-deoxyadenosine 5'-monophosphate (5'-dAMP) in aqueous solutions, as model DNA target. Steady-state and time-resolved experiments were performed and the effect of pH was evaluated. The results showed that photosensitized degradation of 5'-dAMP was only observed under acidic conditions, and a mechanistic analysis revealed the participation of the triplet excited state of the pterin derivatives ((3)Pt*) by electron transfer yielding the corresponding pair of radical ions (Pt(•-) and 5'-dAMP(•+)), with successive photosensitizer recovery by electron transfer from Pt(•-) to O2. Finally, 5'-dAMP(•+) participates in subsequent reactions to yield degradation products.

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Pterins are normal components of cells and they have been previously identified as good photosensitizers under UV-A irradiation, inducing DNA damage and oxidation of nucleotides. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the oxidation of another class of biomolecules, amino acids, using tryptophan (Trp) as a model compound. Irradiation of Ptr in the UV-A spectral range (350 nm) in aerated aqueous solutions containing Trp led to the consumption of the latter, whereas the Ptr concentration remained unchanged. Concomitantly, hydrogen peroxide (H2O2) was produced. Although Ptr is a singlet oxygen ((1)O2) sensitizer, the degradation of Trp was inhibited in O2-saturated solutions, indicating that a (1)O2-mediated process (type II oxidation) was not an important pathway leading to Trp oxidation. By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism, initiated by an electron transfer from the Trp molecule to the Ptr triplet excited state, yielding the corresponding radical ions (Trp(·+)/Trp(-H)· and Ptr(·-)). The Trp reaction products that could be identified by UPLC-mass spectrometry are in agreement with this conclusion.

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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 (1)O(2) 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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Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O(2) and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Φ(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Φ(F), lifetimes (τ(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Φ(F) and τ(F) values obtained lie in the ranges 3-9 × 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.

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7,8-Dihydroneopterin (H(2) Nep) is secreted during the oxidative burst of stimulated macrophages. The photochemistry of H(2) Nep was investigated in neutral aqueous solutions exposed to UV-A radiation (320-400nm) at room temperature. The kinetics were followed by UV/Vis spectrophotometry and HPLC, whereas the photoproducts were analyzed by electrospray ionization mass spectrometry. Excitation of H(2) Nep leads to the formation of isomeric dimers with molecular masses equal to exactly twice the molecular mass of the reactant. The corresponding quantum yield of H(2) Nep consumption (Φ(-R) =(3.8±0.5)×10(-2)) was independent of O(2) and reactant concentrations. Mechanistic implications are discussed.

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