研究目的
To analyze how the nature of the lateral substituent affects the photoreactions between oxidized pterins and molecular oxygen, including energy and electron transfer processes, using quantum chemical calculations.
研究成果
Oxidized pterins participate in photoreactions with molecular oxygen, generating singlet oxygen and potentially superoxide-anion radicals indirectly. Compounds with electronegative substituents (formyl, carboxyl) have higher ionization potentials. Neutral forms do not directly transfer electrons to oxygen, while anionic forms do. The difference in singlet oxygen quantum yield between forms is attributed to variations in triplet state formation quantum yields, influenced by internal conversion rates and aggregation processes. Pterins are recommended as potential agents for photodynamic therapy due to their inability to directly generate superoxide-anion radicals.
研究不足
The study is theoretical and relies on computational methods, which may have inherent approximations (e.g., DFT limitations, basis set choices). Experimental validation is not performed in this paper. The COSMO model simplifies solvation effects. Only specific pterin compounds and forms are considered, potentially limiting generalizability. Assumptions about reaction mechanisms (e.g., autoionization) are based on energy criteria and may not fully capture kinetic or dynamic aspects.
1：Experimental Design and Method Selection:
The study employed density functional theory (DFT) and time-dependent DFT (TD-DFT) with the B3LYP functional and various basis sets (e.g., 6-31G+(d,p), 6-311G++(2d,2p)) for geometry optimization, excitation energy calculations, and property estimation. The COSMO model was used to account for aqueous solvation effects.
2：Sample Selection and Data Sources:
Six pterin compounds with different substituents at the C6 position (e.g., pterin, biopterin, hydroxymethylpterin, formylpterin, carboxypterin, dimethylpterin) in both acid and base forms were selected based on their relevance to biological systems and previous experimental studies.
3：List of Experimental Equipment and Materials:
Computational software including Orca v. 3, ChemCraft v.
4：6, and Spartan v. 14 were used for quantum chemical calculations, visualization, and conformational analysis. No physical equipment was mentioned. Experimental Procedures and Operational Workflow:
Conformational analysis was performed using molecular mechanics (MMFF force field) in Spartan to identify low-energy conformers. Geometry optimization was done with B3LYP/6-31G+(d,p). TD-DFT calculations for excitation energies, ionization potentials, and electron affinities were conducted using B3LYP/6-311G++(2d,2p). The COSMO model with parameters for water (ε=80, n=
5：33) was applied. Data analysis involved comparing calculated values with experimental data from literature. Data Analysis Methods:
Statistical comparison of calculated and experimental excitation energies, correlation analysis (e.g., between ionization potential and singlet oxygen quenching rate constants), and energy-based estimation of reaction feasibilities (e.g., using IPT1 and E(O2?-) values).
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