Assessment of chemical core potentials for the computation on enthalpies of formation of transition-metal complexes

Proportional coexistence of okanin chalcone glycoside and okanin flavanone glycoside in Bidens pilosa leaves and theoretical investigation on the antioxidant properties of their aglycones

Bidens pilosa plant has been shown to produce okanin flavanone glycoside and its chalcone derivative. In most other plants, due to chalcone isomerase enzyme, the flavanone tends to exist in higher proportions than their chalcone precursors. Herein we have utilized liquid chromatography-mass spectrometry approach and shown that within the leaves of Bidens pilosa plant the two okanin glycosides exist in unusual equal proportional distribution, which indicates that Bidens pilosa plant is an alternative rich source of these highly sought-after antioxidant molecules. The aglycone okanin chalcone (ONC) and okanin flavanone (ONF) have experimentally been shown to exhibit antioxidant activity. However, experimental findings have not conclusively determined which of the two compounds is a more potent antiradical than the other. Herein, the density functional theory (DFT) method is utilized to establish, from structural and thermodynamic energetic considerations, the preferred antioxidant molecule between the two aglycone okanins. A theoretical study on the antioxidant properties of ONC and ONF has been performed by considering their radical scavenging and metal cation (Mⁿ⁺, where M = Cu(II) or Fe (III)) chelation ability. The study has been performed using B3LYP/6-31 + G(d,p) method. In the case of the metal chelation mechanism, the LANL2DZ pseudo-potential was selected to describe the selected Mⁿ⁺ cations. The results of the study suggest that ONC is a better radical scavenger than ONF because of the extended electron delocalization on its neutral radical, which is due to the presence of conjugation within the ONC neutral radical after hydrogen atom abstraction. In the metal chelation mechanism, it is noted that the binding energies depend on the media, the nature of the ligand and the cation and the cation coordination site on the ligand. The charge and the spin density on Mⁿ⁺ decrease on coordination to the ligand. The ability of the ligands to reduce Mⁿ⁺ cations, coupled with the strong Mⁿ⁺ binding properties, has significant implication on the antioxidant ability of both okanins. However, since ONC⋅⋅⋅M⁺ⁿ interaction results in higher binding energy than ONF⋅⋅⋅M⁺ⁿ interaction, the implication is that ONC is a preferred free metal ion chelator than ONF.

Synthesis, X-ray structure, photophysical properties, and theoretical studies of six-membered cyclometalated iridium(iii) complexes: revisiting Ir(pnbi)2(acac)

We have determined the X-ray structure of Ir(pnbi)2(acac) (pnbi = 2-phenanthren-9-yl-1-phenyl-1H-benzimidazole; acac = acetylacetonate), which exhibits a six-membered metallocycle around the Ir center. This result stands in sharp contrast to previously postulated structures of Ir(pnbi)2(acac), which assumed a five-membered metallocycle. In this paper, we focus on the relative stability of five- and six-membered Ir(C^N) ring structures. DFT calculations of the total energies of Ir-(C^N) complexes indicated that six-membered structures are more stable when bulky substituents are present in the benzimidazole unit. When the phenanthrene group of pnbi was replaced with a naphthalene moiety, DFT calculations predicted that five-membered cycles are more stable than six-membered rings, which was confirmed experimentally by a single-crystal X-ray diffraction analysis. The steric bulk of the phenanthrene-containing polyaromatic ring ligand thus induces greater interligand repulsion between the two ligands, which plays an important role in determining the cyclometalation route. The Ir complexes examined in this study exhibit red emission (λem ≈ 660 nm) with relatively low quantum yields.

A theoretical study on the antioxidant properties of methoxy-substituted chalcone derivatives: A case study of kanakugiol and pedicellin through their Fe (II and III) coordination ability

A theoretical study on the antioxidant properties of two chalcone derivatives, kanakugiol and pedicellin, is performed by considering their Fe[Formula: see text] and Fe[Formula: see text] coordination ability. The objective of the study is to elucidate the factors influencing the stability of the isolated conformers, the nature of the complexes, metal[Formula: see text]ligand stability, metal ion affinities (MIA) and electronic properties of the cations before and after coordination to the ligand. The study is performed using the B3LYP/6–311[Formula: see text]G(2d,p)//B3LYP/6–31[Formula: see text]G(d,p) method. The LANL2DZ pseudopotential is selected to describe the Fe[Formula: see text] ions. Time-dependent density functional theory (TDDFT) method is used to assess the electronic UV–Vis spectra of the isolated chalcones and their complexes with Fe[Formula: see text] ions. The results suggest that the preferred complexes are those in which the Fe ion is coordinated at the hydroxyl-methoxy and hydroxyl-keto sites for kanakugiol and methoxy-keto site for pedicellin. Both kanakugiol and pedicellin have potential to chelate iron ions as demonstrated by their high MIA values in vacuo and in water solution. However, the ability of pedicellin to chelate iron is slightly lower than that of kanakugiol, indicating that the presence of the hydroxyl group has an effect of enhancing the metal binding abilities of the chalcone derivatives. In all the complexes obtained in vacuo, kanakugiol and pedicellin exhibit the ability to reduce the Fe[Formula: see text] ion. In water solution (which mimics the environment in biological systems or studies performed in vivo), Fe[Formula: see text] is reduced to Fe[Formula: see text] upon coordination to the ligand while the oxidation number of Fe[Formula: see text] upon coordination to the ligand remains virtually unchanged.