Here, ten guidelines are presented for a standardized definition of type I and II photosensitized oxidation reactions. Because of varied notions of reactions mediated by photosensitizers, a checklist of recommendations is provided for their definitions. Type I and type II photoreactions are oxygen-dependent and involve unstable species such as the initial formation of radical cation or neutral radicals from the substrates and/or singlet oxygen (1O2 1Δg) by energy transfer to molecular oxygen. In addition, superoxide anion radical (O2•−) can be generated by a charge transfer reaction involving O2 or more likely indirectly as the result of O2-mediated oxidation of the radical anion of type I photosensitizers. In subsequent reactions, O2•− may add and/or reduce a few highly oxidizing radicals that arise from the deprotonation of the radical cations of key biological targets. O2•− can also undergo dismutation into H2O2, the precursor of the highly reactive hydroxyl radical (•OH) that may induce delayed oxidation reactions in cells. In the second part several examples of type I and type II photosensitized oxidation reactions are provided to illustrate the complexity and the diversity of the degradation pathways of mostly relevant biomolecules upon one-electron oxidation and singlet oxygen reactions.

A new series of decyl chain [-(CH)CH] pterin conjugates have been investigated by photochemical and photophysical methods, and with theoretical solubility calculations. To synthesize the pterins, a nucleophilic substitution (S2) reaction was used for the regioselective coupling of the alkyl chain to the O site over the N site. However, the O-alkylated pterin converts to N-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 (Φ) and increased singlet oxygen quantum yields (Φ). It is shown that the DMF-condensed pterins were more photostable compared to the N- and O-alkylated pterins bearing a free amine group. The alkyl chain pterins efficiently intercalate in large unilamellar vesicles, which is a good indicator of their potential use as photosensitizers in biomembranes. Our study serves as a starting point where the synthesis can be expanded to produce a wider series of lipophilic, photooxidatively active pterins.

LL37-capped silver nanoparticles have antibacterial properties including inhibition of Pseudomonas aeruginosa biofilm formation, but do not affect human skin fibroblast proliferation.

It has been well documented that β-carboline alkaloids, particularly the 9-methyl derivatives, are efficient photosensitizers. However, structure-activity relationships are missing and the photochemical mechanisms involved in the DNA photodamage still remain unknown. In the present work, we examined the capability of three 9-methyl-β-carbolines (9-methyl-norharmane, 9-methyl-harmane and 9-methyl-harmine) to induce DNA damage upon UVA excitation at physiological pH. The type and extent of the damage was analyzed together with the photophysical and binding properties of the β-carboline derivatives investigated. The results indicate that even at neutral pH most of the DNA damage is generated from the protonated form of the excited β-carbolines in a type-I reaction. Oxidized purine residues are produced in high excess over oxidized pyrimidines, single-strand breaks and sites of base loss. In addition, the excited neutral form of the β-carbolines is responsible for significant generation of cyclobutane pyrimidine dimers (CPDs) by triplet-triplet-energy transfer. In the case of 9-methyl-norharmane, the yield of CPDs is increased in D2O, probably due to less rapid protonation in the deuterated solvent.

β-Carbolines (βCs) are a group of alkaloids present in many plants and animals. It has been suggested that these alkaloids participate in a variety of significant photosensitized processes. Despite their well-established natural occurrence, the main biological role of these alkaloids and the mechanisms involved are, to date, poorly understood. In the present work, we examined the capability of three important βCs (norharmane, harmane and harmine) and two of its derivatives (N-methyl-norharmane and N-methyl-harmane) to induce DNA damage upon UV-A excitation, correlating the type and extent of the damage with the photophysical characteristics and DNA binding properties of the compounds. The results indicate that DNA damage is mostly mediated by a direct type-I photoreaction of the protonated βCs after non-intercalative electrostatic binding. Reactive oxygen species such as singlet oxygen and superoxide are not involved to a major extent, as indicated by the only small influence of D(2)O and of superoxide dismutase on damage generation. An analysis with repair enzymes revealed that oxidative purine modifications such as 8-oxo-7,8-dihydroguanine, sites of base loss and single-strand breaks (SSB) are generated by all βCs, while only photoexcited harmine gives rise to the formation of cyclobutane pyrimidine dimers as well.

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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 electrontransfer 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 nature 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 production of ROS by pterin derivatives and their reactivity with these species are discussed.

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.