Photophysical and Photochemical Properties of 3‐methylpterin as a New and More Stable Pterin‐type Photosensitizer

Abstract

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 ( O ) 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.

Unveiling Photodegradation and Photosensitization Mechanisms of Unconjugated Pterins

“…The results presented herein are consistent with the experimental observations of formation of long-lived triplet states. First, the calculated vertical T 1 !S 0 emission (2.48 eV, 500 nm) coincides with the experimental phosphorescence wavelengths (480 nm for PT, [9] 505 nm for 3-methylpterin [35] ). Also, intersystem crossing to S 0 would be energetically prevented since the 3 ππ*/S 0 crossing points coincide with the C2P and C4CO funnels, which lie up to 2 eV higher in energy relative to the T 1 minimum.…”

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

“…Recently, A.H. Thomas with co-authors have measured the phosphorescence of a non-trivial pterin derivative 3-methyl-pterin, which has only a lactim form. Its phosphorescence lifetime was lower than of pterin: 0.86 s and 1.1 s, respectively [ 193 ].…”

Indocyanine green assembled free oxygen-nanobubbles towards enhanced near-infrared induced photodynamic therapy

“…Particularly, photodynamic therapy (PDT) has shown capable potential with high specificity and low side effects towards clinical applications [6][7][8][9][10][11]. In principle, PDT provides potential for killing tumor cells with reactive oxygen species (ROS) or singlet oxygen ( 1 O 2 ), which are generated by the combination of three factors such as appropriate optical irradiation, photosensitizer molecules, and environmental oxygen [12][13][14][15][16][17][18]. To achieve efficient PDT, considerable attention has been paid to design and synthesize new photosensitizers [19][20][21][22] with efficient ROS or 1 O 2 efficiency.…”