μ-Nitrido-bridged diiron porphyrins and phthalocyanines are known to be efficient oxidants that are able to oxidize some of the strongest C−H bonds in nature, such as the one in methane. The origin of their catalytic efficiency is poorly understood, and in order to gain insight into the structural and electronic features of this chemical system, we performed a detailed and systematic study into their chemical properties and reactivities using density functional theory. Our work shows that μ-nitrido-bridged diiron porphyrins and phthalocyanines are highly active catalytic oxidants, which react with methane with very low reaction barriers and a rate-determining hydrogen-atom-abstraction step. Furthermore, the μ-nitridobridged diiron porphyrin and phthalocyanine complexes react with a free energy of activation that is more than 10 kcal mol −1 lower in energy than that found for cytochrome P450 Compound I, which is known to be one of the most efficient C−H hydroxylating agents in Nature. We have analyzed the electronic configuration of reactants and transition states in detail and have identified the key properties of the oxidants that lead to this rate enhancement. In particular, the potency of the oxidant is related to the orbital mixing patterns along the Fe−O axis, whereby the axial iron(IV)-nitrido group donates sufficient electron density to affect the pK a of the oxo group as well as the strength of the O−H bond formed in the iron(IV)-hydroxo complex. The studies confirm that μ-nitrido diiron-oxo complexes should react via oxygen atom transfer readily even with strong C−H bonds as in methane. The results are analyzed with orbital diagrams, valence bond, and thermochemical cycles and explain the intricate details of the mechanism and the properties of the oxidant.

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A time-correlated mass spectrometry (MS)-based metabolic profiling was performed for rice koji made using the substrates with varying degrees of milling (DOM). Overall, 67 primary and secondary metabolites were observed as significantly discriminant among different samples. Notably, a higher abundance of carbohydrate (sugars, sugar alcohols, organic acids, and phenolic acids) and lipid (fatty acids and lysophospholipids) derived metabolites with enhanced hydrolytic enzyme activities were observed for koji made with DOM of 5-7 substrates at 36 h. The antioxidant secondary metabolites (flavonoids and phenolic acid) were relatively higher in koji with DOM of 0 substrates, followed by DOM of 5 > DOM of 7 > DOM of 9 and 11 at 96 h. Hence, we conjecture that the rice substrate preprocessing between DOM of 5 and 7 was potentially optimal toward koji fermentation, with the end product being rich in distinctive organoleptic, nutritional, and functional metabolites. The study rationalizes the substrate preprocessing steps vital for commercial koji making.

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Background: Plants have been used as an important source of indispensable bioactive compounds in various cosmetics, foods, and medicines. However, the subsequent functional annotation of these compounds seems arduous because of the largely uncharacterized, vast metabolic repertoire of plant species with known biological phenotypes. Hence, a rapid multi-parallel screening and characterization approach is needed for plant functional metabolites. Results: Fifty-one species representing three plant families, namely Asteraceae, Fabaceae, and Rosaceae, were subjected to metabolite profiling using gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) and ultrahigh-performance liquid chromatography quadrupole orbitrap ion trap tandem mass spectrometry (UHPLC-Qorbitrap-MS/MS) as well as multivariate analyses. Partial least squares discriminant analysis (PLS-DA) of the metabolite profiling datasets indicated a distinct clustered pattern for 51 species depending on plant parts (leaves and stems) and relative phylogeny. Examination of their relative metabolite contents showed that the extracts from Fabaceae plants were abundant in amino acids, fatty acids, and genistein compounds. However, the extracts from Rosaceae had higher levels of catechin and ellagic acid derivatives, whereas those from Asteraceae were higher in kaempferol derivatives and organic acids. Regardless of the different families, aromatic amino acids, branch chain amino acids, chlorogenic acid, flavonoids, and phenylpropanoids related to the shikimate pathway were abundant in leaves. Alternatively, certain amino acids (proline, lysine, and arginine) as well as fatty acids levels were higher in stem extracts. Further, we investigated the associated phenotypes, i.e., antioxidant activities, affected by the observed spatial (leaves and stem) and intra-family metabolomic disparity in the plant extracts. Pearson's correlation analysis indicated that ellagic acid, mannitol, catechin, epicatechin, and quercetin derivatives were positively correlated with antioxidant phenotypes, whereas eriodictyol was positively correlated with tyrosinase inhibition activity. Conclusions: This work suggests that metabolite profiling, including multi-parallel approaches and integrated bioassays, may help the expeditious characterization of plant-derived metabolites while simultaneously unraveling their chemodiversity.