Concurrent quantification of oleanolic acid, β-sitosterol and lupeol by a validated high-performance thin-layer chromatography method in Urginea indica Kunth bulb

A validated high-performance thin-layer chromatography (HPTLC) method was developed for the simultaneous quantification of oleanolic acid, β-sitosterol and lupeol in the bulb of Urginea indica Kunth. Separation of metabolites was done in mobile phase using toluene‒ethyl acetate‒methanol‒acetone (7:2:0.2:0.2, V/V) and quantification was done after derivatization by dipping in aninsaldehyde‒sulphuric acid; densitometric scan was performed at 530 nm. The proposed method for quantification was linearly calibrated in the range of 200‒1000 ng/spot for oleanolic acid and β-sitosterol; 100‒500 ng/spot for lupeol, and it was found specific and repeatable. The R_F values were found at 0.44 ± 0.03, 0.55 ± 0.05 and 0.68 ± 0.08, limit of detection and limit of quantification were 1.045, 0.524, 0.525 µg/spot and 3.167, 1.588, 1.592 µg/spot for oleanolic acid, β-sitosterol and lupeol, respectively. Precision and recovery study for sample and standards were within the limit of the International Council for Harmonization guidelines. Oleanolic acid, β-sitosterol and lupeol were found to be 0.113%, 0.105% and 0.036%, respectively, in methanolic extract of plant on dry weight basis. This study will help in checking routine quality control of herbal drugs as well as herbal formulations containing U. indica.

     

Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine

Benzene imine (1) ⇌ 1H-azepine (2) isomerization occurs through sequential valence and endo–exo isomerism. Quantum chemical and quasiclassical trajectory (QCT) simulations reveal the coupled reaction pathway – ring-expansion followed by N-inversion to the most stable isomer, exo-1H-azepine (Exo-2). Direct-dynamics produce a mixture of endo- and exo-1H-azepine stereoisomers and govern the endo-1H-azepine (Endo-2) ⇌ exo-1H-azepine (Exo-2) ratio. Exo-2 is computationally identified as the most stable product while Endo-2 is fleetingly stable with a survival time (S_T) ∼50 fs. N-Methyl substitution exclusively results in an exo-1-methyl-1H-azepine isomer. F-substitution at the N-site increases the barrier for N-inversion and alters the preference by stabilizing Endo-2. Interestingly, the exo-1-fluoro-1H-azepine (minor product) is formed through bifurcation via non-statistical dynamics. A highly concaved Arrhenius plot for 1a → 2a highlights the influence of heavy-atom tunneling on valence isomerism, particularly at low temperatures. Heavy-atom tunneling also results in a normal N–H(D) secondary KIE above 100 K even though the increase in hybridization from sp² to sp³ at nitrogen should cause an inverse KIE classically.

Non-classical processes such as heavy-atom tunneling and post transition-state dynamics govern stereoselectivity for benzene imine ⇌ 1H-azepine.     

Synthesis of novel fluorescent benzo[a]pyrano[2,3-c]phenazine and benzo[a]chromeno[2,3-c]phenazine derivatives via facile four-component domino protocol

An efficient and practical route to novel fluorescent benzo[a]pyrano[2,3-c]phenazine framework has been developed by one-pot, four-component reaction of 2-hydroxynaphthalene-1,4-dione, 1,2-phenylenediamines, aromatic aldehydes, and Meldrum’s acid in glacial acetic acid at 70 °C. Photophysical studies of these compounds have been reported. Reactions involving cyclohexane-1,3-dione/5-methylcyclohexane-1,3-dione/dimedone in the place of Meldrum’s acid yielded corresponding benzo[a]chromeno[2,3-c]phenazine derivatives. Crystal structure of 3k established the regioisomer formed. Mild reaction conditions, good yields, short reaction time, and easy separation are some of the salient features of the present protocol.     

Multicomponent reactions and supramolecular catalyst: A perfect synergy for eco-compatible synthesis of pyrido[2,3-d]pyrimidines in water

In this article, we have developed a straightforward, easy and exceedingly competent approach for the synthesis of 5-phenyl-5,6-dihydropyrido[2,3-d]pyrimidine-2,4,7(1H,3H,8H)-triones obtain in superior yields in a sole reaction pace with an air and humidity steady catalyst in water as a green solvent at 100^°C. The present procedure paves the approach for the synthesis of biologically fascinating molecular frameworks and has reward in conditions of little catalyst loading with palpable ambiguous and straightforward-to-do reaction circumstances with easy purification process. The used β-cyclodextrin catalyst was recuperated and repeated several times devoid of noteworthy loss of catalytic activity, which is a crucial parameter of green synthesis.     

Determination of biogenic amines in lake water by micellar electrokinetic chromatography with fluorescence detection after derivatization with fluorescamine

A simple and rapid method has been developed for the determination of biogenic amines in lake water using micellar electrokinetic chromatography with fluorescence detection. Separation of fluorescamine derivatized biogenic amines was accomplished by using borate buffer of pH 9.5 containing 40 mM of sodium dodecyl sulphate. The method has been optimized with respect to fluorescamine concentration, reaction pH, reaction time, separation voltage and injection time. Detection was performed by using UG-11 excitation filter and 495 nm emission filter. The proposed method for histamine, tyramine and dopamine allowed their separation within 2 min with detection limits in nM range. The interday and intraday reproducibility of peak areas were less than 6.5%. Recovery of spiked samples was 95.76–116.31%.     

Separation of uranium from different uranium oxide matrices employing supercritical carbon dioxide extraction

Uranium from different uranium oxide matrices was extracted with tri-n-butyl phosphate–nitric acid (TBP–HNO₃) adduct using supercritical carbon dioxide (SC CO₂). While 30 min dissolution time at 323 K was sufficient for U₃O₈ and UO₂ powder, UO₂ granule (at 333 K) and crushed green pellet (at 353 K) required 40 min. Crushed sintered pellet required 60 min at 353 K for complete dissolution. Influence of various experimental parameters such as temperature, pressure, volume of TBP–HNO₃ adduct, acidity of nitric acid used for preparing TBP–HNO₃ adduct and extraction time on uranium extraction efficiency was also investigated. For UO₂ powder, temperature of 323 K, pressure of 15.2 MPa, 1 mL TBP–HNO₃ adduct, 10 M nitric acid and 30 min extraction time was found to be optimum. ~70% uranium extraction efficiency was obtained on extraction with SC CO₂ alone which increased to 90% with the addition of 2.5% TBP in SC CO₂ stream. Extraction efficiency was found to vary linearly with TBP percentage and nearly complete uranium extraction (~99%) was observed with 20% TBP. Nearly complete extraction was also achieved with addition of 2.5% thenoyltrifluoroacetylacetone (TTA) in methanol. The optimized procedure was extended to remove uranium from simulated tissue paper waste matrix smeared with uranium oxide solids.     

N-Heterocyclic Olefins on a Silicon Surface

The adsorption of N-heterocyclic olefins (NHOs) on silicon is investigated in a combined scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory study. We find that both of the studied NHOs bind covalently, with ylidic character, to the silicon adatoms of the substrate and exhibit good thermal stability. The adsorption geometry strongly depends on the N-substituents: for large N-substituents, an upright adsorption geometry is favored, while a flat-lying geometry is found for the NHO with smaller wingtips. These different geometries strongly influence the quality and properties of the obtained monolayers. The upright geometry leads to the formation of ordered monolayers, whereas the flat-lying NHOs yield a mostly disordered, but denser, monolayer. The obtained monolayers both show large work function reductions, as the higher density of the flat-lying monolayer is found to compensate for the smaller vertical dipole moments. Our findings offer new prospects in the design of tailor-made ligand structures in organic electronics and optoelectronics, catalysis, and material science.     

Thermal decomposition kinetics,flammability, and mechanical property study of wood polymer nanocomposite

Melamine formaldehyde-furfuryl alcohol copolymer was impregnated into softwood in combination with 1,3-dimethylol-4,5-dihydroxy ethyleneurea, a crosslinking agent, nanoclay, and a renewable polymer, collected as gum from a local plant (Moringa oleifera) under vacuum condition and polymerized by catalyst heat treatment. Fourier-transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the nanocomposites. Transmission electron microscopy showed uniform distribution of nanoclay in the composites. The mechanical properties were improved after the addition of plant polymer. The plant polymer had a marked influence on the flammability and thermal stability of the prepared composites. The apparent activation energy was determined by Ozawa-Flynn-Wall’s and Vyazovkin methods. The activation energy of the composites decreased up to a certain decomposed fraction thereafter it remained constant. Higher the plant polymer content higher was the activation energy of the prepared composites which indicated a better interfacial adhesion and thermal stability.     

Exploring beta amyloid cleavage enzyme-1 inhibition and neuroprotective role of benzimidazole analogues as anti-alzheimer agents

Beta amyloid cleavage enzyme-1 (BACE1) is the key enzyme involved in Aβ peptide formation in Alzheimer's disease pathogenesis. We intend to target this enzyme by exploring benzimidazole analogues against BACE1 as potential anti-Alzheimer agents. Docking studies were performed to determine the hydrogen bond interactions between the designed molecules and the target protein's active site. Research indicates the relationship between oxidative stress and Aβ effect in precipitating neurodegeneration; hence, the series was also studied in vitro to ascertain its neuroprotective role by performing the lipid peroxidation assay. In silico absorption, distribution, metabolism, and excretion studies were undertaken to assess the drug-like suitability of the analogues. To judge the effect of the synthesized analogues on central nervous system (CNS), toxicity and memory model studies were conducted on mice. Thus, overall results showcase analogues 11 and 14 as the most promising ones with the dual role of BACE1 inhibition and neuroprotection, along with memory retention.     

Surface Functionalization of Green-synthesized Reduced Graphene Oxide with PPIX Enhances Photosensitization of Cancer Cells

Photosensitizer-functionalized reduced graphene oxide (rGO) nanoparticles are promising materials for photodynamic therapy in cancer management. In this study, rGO is synthesized by a green route employing glucose as the reducing agent and functionalized with photosensitizer, protoporphyrin IX (PPIX) in a convenient, single-step procedure. PPIX-functionalized rGO exhibits photodynamic effect against cancer cells (HeLa) at 0.001 mg mL⁻¹ under visible light illumination (635 nm). A 50% elimination of HeLa cells after 5 min irradiation is observed while very low phototoxicity (80% cell viability) is noted against normal dermal fibroblast cells. A positive correlation with ROS accumulation and increased expression of caspase-3 in PPIX-functionalized rGO-treated cancer cells is also established. The results evidence a simple and cost-effective route for developing photosensitizer-functionalized rGO for effective and selective killing of cancer cells.