Lignin Biodegradation by a Cytochrome P450 Enzyme: A Computational Study into Syringol Activation by GcoA

A recently characterized cytochrome P450 isozyme GcoA activates lignin components through a selective O-demethylation or alternatively an acetal formation reaction. These are important reactions in biotechnology and, because lignin is readily available; it being the main component in plant cell walls. In this work we present a density functional theory study on a large active site model of GcoA to investigate syringol activation by an iron(IV)-oxo heme cation radical oxidant (Compound I) leading to hemiacetal and acetal products. Several substrate-binding positions were tested and full energy landscapes calculated. The study shows that substrate positioning determines the product distributions. Thus, with the phenol group pointing away from the heme, an O-demethylation is predicted, whereas an initial hydrogen-atom abstraction of the weak phenolic O-H group would trigger a pathway leading to ring-closure to form acetal products. Predictions on how to engineer P450 GcoA to get more selective product distributions are given.     

First report of isolation of maleamic acid from natural source Polygonatum cirrhifolium—A potential chemical marker for identification

Polygonatum cirrhifolium (Meda) plant is being used in number of rejuvenating Ayurvedic formulations. Ever rising demands, lack of natural sources, and insufficient quantity, to meet the requirements of market, the raw material has led toward the use of official substitutes recommended by the Department of AYUSH that has further encouraged manufacturers for adulteration of formulations by other substandard/spurious raw drugs. Literature reveals that more than 60% Ayurvedic parameters as well as pharmacological actions of Ashtawarga plants do not match with their substitutes leading to reduced efficacy of the drugs along with loss of faith for use of herbal drugs. Consumers are forced to pay for the material which has never been used for high-cost claimed formulation. The situation is being exploited by manufacturers because regulatory authorities lack the tools (marker compound) needed for identification of authentic plant. Methanolic extract of rhizomes of plant was subjected to column chromatography. Isolated compound has been characterized as (Z)-4-amino-4-oxobut-2-enoic acid (maleamic acid/maleamate/maleic monoamide/maleic acid monoamide) by chemical test, melting point, IR/NMR/mass/UV spectral analysis. It is the first report in Polygonatum genus and can be used as a marker for identification of the plant in market formulations.     

Mechanism of Fenpropathrin Resistance in Red Spider Mite, <Emphasis Type="Italic">Oligonychus coffeae</Emphasis> (Acarina: Tetranychidae), Infesting Tea [<Emphasis Type="Italic">Camellia sinensis</Emphasis> L. (O. Kuntze)]

Red spider mite (RSM), Oligonychus coffeae (Nietner) (Acarina: Tetranychidae), has gained special attention in view of their widespread occurrence as a pest on tea [Camellia sinensis L. (O. Kuntze)]. The development of acaricide (fenpropathrin) resistance has been screened in field populations (FPs) of RSMs from different tea-growing regions of south India and compared with a laboratory-susceptible population (SP) based on toxicity bioassay, detoxifying enzyme activities, analysis of acetylcholine esterase gene (AChE, 2064 bp), and their expression pattern using semiquantitative RT-PCR. The increased resistance ratio (RR, 1.39 to 2.13) in LC₅₀ of fenpropathrin observed in field populations of RSM provides a baseline for screening the development of resistance to fenpropathrin. This resistance developed due to hyperexpression of detoxifying enzymes, i.e., esterase (RR of 1.43 to 2.53) and glutathione S-transferase (RR of 1.11 to 1.86), and overexpression of AChE gene at 1.4 to 2.7-fold. These results necessitate molecular studies and warrant the continuous monitoring of acaricide susceptibility and resistance pattern in order to analyze the usefulness of AChE gene as target for developing alternate pest control strategies and management of pesticide resistance in tea ecosystem.     

18O(p,p′γ)18O nuclear reaction in the determination of oxygen by proton induced γ-ray emission

Journal of Radioanalytical and Nuclear Chemistry - Particle induced gamma-ray emission method was used to quantify total fluorine (F) concentrations in soil and food samples obtained from fluoride...     

High electrical conductivity for the partially oxidised d8 Ru–Ru bonded chain [Ru(bpy)(CO)2]n (bpy = 2,2′-bipyridine) and its wide range redox control

High, electrochemically controlled electrical conductivity (0.2–0.3 S cm^?1) was measured for the first time for the metal–metal bonded polymeric compound [Ru(bpy)(CO)₂]_n (bpy = 2,2′-bipyridine). The conductivity depended on the degree of partial oxidation of the initially zero-valent Ru to Ru^I in the chains and was found to increase by four orders of magnitude after 5% oxidative doping. Linear conductance vs. doping level dependence was found for low levels and the conductivity of films could repeatedly be switched on and off. The conduction process is ascribed to charge delocalisation on the Ru chains in analogy to that of other similar chains formed by stacking of planar transition metal d⁸ complexes.     

How Does the Axial Ligand of Cytochrome P450 Biomimetics Influence the Regioselectivity of Aliphatic versus Aromatic Hydroxylation?

How deep is your orbital? Density functional theory studies on the axial ligand effect of aliphatic versus aromatic hydroxylation of ethylbenzene by iron–oxo complexes with a variable axial ligand show that strong (anionic) ligands pull the metal inside the plane of the haeme and destabilise cationic intermediates through orbital interactions (see picture).

     

Origin of the Correlation of the Rate Constant of Substrate Hydroxylation by Nonheme Iron(IV)–oxo Complexes with the Bond‐Dissociation Energy of the C?H Bond of the Substrate

A series of hydrogen‐abstraction barriers of a nonheme iron(IV)–oxo oxidant mimicking the active species of taurine/α‐ketoglutarate dioxygenase (TauD) are rationalized by using a valence‐bond curve‐crossing diagram (see figure). It is shown that the barriers correlate with the strength of the C? H bond. Furthermore, electronic differences explain the differences between nonheme and heme iron(IV)–oxo hydrogen‐abstraction barriers.

     

Determination of senkirkine and senecionine in Tussilago farfara using microwave-assisted extraction and pressurized hot water extraction with liquid chromatography tandem mass spectrometry

Tussilago farfara (Kuan Donghua) is an important Chinese herbal medicine which has been shown to contain many bioactive compounds and widely used to relieve cough and resolve phlegm. However, besides therapeutic bioactive compounds, this herb has been found to contain toxic pyrrolizidine alkaloids (PAs), mainly senkirkine and traces of senecionine. In this report, conditions for microwave-assisted extraction (MAE) and pressurized hot water extraction (PHWE) were optimized for the extraction of the PAs. The results were compared against heating under reflux. It was found that the binary mixture of MeOH:H₂O (1:1) acidified using HCl to pH 2-3 was the optimal solvent for the extraction of the PAs in the plant materials. Liquid chromatography (LC) with ultra-violet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) in the positive mode was used for the determination and quantitation of senkirkine and senecionine in the botanical extract. The proposed extraction methods with LC/MS allow for the rapid detection of the major and the minor alkaloids in T. farfara in the presence of co-eluting peaks. With LC/MS, the quantitative analysis of PAs in the extract was done using internal standard calibration and the precision was found to vary from 0.6% to 5.4% on different days. The limits of detection (LODs) and limits of quantitation (LOQs) for MAE and PHWE were found to vary from 0.26 μg/g to 1.04 μg/g and 1.32 μg/g to 5.29 μg/g, respectively. The method precision of MAE and PHWE were found to vary from 3.7% to 10.4% on different days. The results showed that major and minor alkaloids extracted using MAE and PHWE were comparable to that by heating under reflux. Our data also showed that significant ion suppression was not observed in the analysis of senkirkine and senecionine in the botanical extracts with co-eluting peaks.     

Nanocomposite of CeVO4/BiVO4 Loaded on Reduced Graphene Oxide for the Photocatalytic Degradation of Methyl Orange

A facile procedure, involving one-pot synthesis of CeVO₄/BiVO₄ and in-situ reduction of graphene oxide (GO), has been used to prepare CeVO₄/BiVO₄/rGO nanocomposites. Different ratios of the CeVO₄–BiVO₄ were prepared to afford composites represented as CBVG3, CBVG5, and CBVG7. The ternary nanocomposite materials were characterized by using powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), photoluminescence and UV–vis spectroscopic techniques. Photocatalytic efficiency of the as-prepared ternary nanocomposites was investigated through the photo degradation of methyl orange under a visible light irradiation at 470 nm. The photocatalytic performance was enhanced by loading the CeVO₄/BiVO₄ nanoparticles on reduced graphene oxide (rGO), given MO degradation rate of 57, 65, 80, and 90% for BVG, CBVG3, CBVG5, and CBVG7, respectively after exposure to visible light for 120 min. Effects of experimental process parameters including initial dye concentration, catalysts loading and effect of different modification regimes were studied using CBVG7, which exhibited the highest efficiency. The improvement in the photocatalytic efficiency may be attributed to increased surface area of the nanocomposites, enhanced light absorption capacity and improved charge separation. The study showed a one-pot synthesis route to prepare promising CeVO₄/BiVO₄/GO nanocomposites for the photo-enhanced degradation of dye contaminants.

     

Aryne-Enabled C−N Arylation of Anilines

Anilines are potentially high-value arylating agents, but are limited by the low reactivity of the strong C−N bond. We show that the reactive intermediate benzyne can be used to both activate anilines, and set-up an aryl transfer reaction in a single step. The reaction does not require any transition metal catalysts or stoichiometric organometallics, and establishes a metal-free route to valuable biaryl products by functionalizing the aniline C−N bond.