Antioxidant and photoprotective properties of two natural acridone derivatives namely Paratrimerin C (1) and Citrusinine-I (2) have been studied by DFT and TD-DFT at the M05-2X/6-311++G(3df, 3p)//M05-2X/6-31+G(d) level of theory. Three common mechanisms characterized for the antioxidant properties including H-atom transfer (HAT) and proton transfer (PT) towards HOO • /HO • radicals and single electron transfer (SET) were investigated in the gas phase, water and pentyle thanoate. The DFT results revealed that both compounds can efficiently scavenge HOO • and HO • radicals via HAT mechanism in all media. Particularly, the HAT reactions of 2 with HO • radical in water are the most favored reaction (∆H -37.7 kcal/mol). In addition, the efficient UV-absorption ability of the studied compound was elucidated by TD-DFT. All compounds can absorb UV radiations in the range of 200-335 nm, for which the easiest excitations are at 334-332 nm and the strongest absorptions were found at 234-227 nm, for 1 and 2, respectively. The HOMO to LUMO and HOMO-3 to LUMO (π-π*) transitions are assigned for the corresponding UV-absorption.
Surface‐enhanced Raman spectroscopy (SERS), a surface‐sensitive technique, allows the practicability of detecting chemical compounds in ultra‐low concentration. In this work, a chemical enhancement mechanism of SER process of Thiram pesticide adsorbed on copper nanomaterial surface was proposed based on density functional theory (DFT) approaches. Structural and electronic properties of Thiram and Thiram‐Cu20 complexes were optimized using PBE method with LanL2DZ basis set for copper atoms and cc‐pVDZ basis set for the non‐metal atoms. In the most stable adsorption configuration, Thiram interacted with Cu20 cluster via two S(sp2) atoms. The main peaks on normal Raman spectrum of Thiram were characterized at 371, 576, 1414 and 1456 cm‐1 responsible for the stretching vibrations of C–S, C=S, S–C–S and C–N groups, respectively. Otherwise, the main peaks of Thiram‐Cu20 SERS spectrum were found at 534, 874, 982, 1398 and 1526 cm‐1 corresponding to the stretching vibrations of S–S, C‐S, S–C–S, C–N and CH3–N bonds, respectively. The SERS chemical enhancement of Thiram by Cu20 cluster was about 2 and 6 times stronger than those obtained from Ag20 and Au20 cluster, respectively. The chemical enhancement mechanism was also explained by analyzing HOMO and LUMO energies gap and density of states.
Antioxidant potential of five compounds include ochraceopone F (1), aspertetranone D (2), cycloechinulin (3), wasabidienone E (4) and mactanamide (5) in the extracts from marine fungus Aspergillus flocculosus in Nha Trang was investigated by computational chemistry methods. All calculations were performed at the theoretical level M05-2X/6-311++G(d, p)//M05-2X/6-31+G(d) in the gas phase. The physicochemical properties such as bond dissociation energies (BDE), ionization energies (IE), electron affinity (EA) characterizing HAT (Hydrogen atom transfer) and SET (Single electronic transfer) antioxidant mechanisms were calculated.As a result, the H-atom donating ability of the studies compounds increases in the descending order of BDE value (1) > (2) > (3) > (4) » (5). Wherein the compounds (4) and (5) represent as the most potential antioxidant with the lowest BDE in the gas phase being 74.9 and 75.1 kcal/ mol. Moreover, the electronic donating ability of the compounds increases as function of the descending order of IE value (2) > (1) > (5) > (3) > (4). And the electron accepting abitlity decreases in decreasing EA value (4) > (3) > (2) > (5) > (1). Compound (4) (wasabidienone E) has the smallest IE value of 6.56 eV and has the largest EA value of 2.33 eV.
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