Sesquiterpene lactones from Centaurea rhizantha C.A. Meyer

Two new sesquiterpene lactones, rhizantholide A (1) and rhizantholide B (2), together with five known compounds (3-7) have been isolated from the aerial parts of Centaurea rhizantha (Asteraceae). Sesquiterpene lactones belong to guaianolide class, and rhizantholide B is a rare guaianolide characterized by a free primary alcoholic function at C-10 along with a 3β,10β-epoxy function. Their structures have been established on the basis of 1D and 2D NMR experiments, as well as HR-ESIMS. The antimicrobial activity of compounds 1-7 has been evaluated against Gram-positive and Gram-negative strains. Only deacylcynaropicrin 8-O-[3′-hydroxy-2′-methylpropionate] (5) showed moderate antibacterial activity against Staphylococcus aureus with a MIC/MBC value of 500 μg/mL. All isolated compounds have been also evaluated for their cytotoxic activities against cancer cells. Among them, compound 5 showed the highest cytotoxic activity with IC₅₀ values in the range 5.02–16.76 μg/mL.     

State‐of‐the‐Art and Trends in Synthesis,Properties, and Application of Quantum Dots‐Based Nanomaterials

Quantum dots (QDs) with a nanoscale size range have attracted significant attention in various areas of nanotechnology due to their unique properties. Different strategies for the synthesis of QD nanoparticles are reported in which various factors, such as size, impurities, shape, and crystallinity, affect the QDs fundamental properties. Consequently, to obtain QDs with appropriate physical properties, it is required to select a synthesis method which allows enough control over the surface chemistry of QDs through fine‐tuning of the synthesis parameters. Moreover, QDs nanocrystals are recently used in multidisciplinary research integrated with biological interfaces. The state‐of‐the‐art methods for synthesizing QDs and bioconjugation strategies to provide insight into various applications of these nanomaterials are discussed herein.     

The synthesis of R-3-alkoxy-1-(1′-hydroxyethyl)-4-methoxy-2-(1″-propenyl)benzenes utilizing Corey-Bakshi-Shibata asymmetric reductions

Pyrolysis of the 3-O-allyl derivative 7 of isovanillin followed by alkylation of the derived allylphenol 8 afforded a series of benzaldehyde derivatives 9-11 each of which was transformed by initial treatment with methylmagnesium bromide followed by oxidation of the corresponding alcohols with activated manganese dioxide into a series of ketones 15-17. Palladium(0) catalysed isomerization of the double bond in the prop-2′-enyl side-chain afforded ketones 36-38 which were subjected to the Corey-Bakshi-Shibata asymmetric reduction protocol to afford the R-3-alkoxy-1-(1′-hydroxyethyl)-4-methoxy-2-(1″-propenyl) benzenes 42-44 in yields of approximately 60% and with ee's of 75%.     

Chemometric study of the aggregation of alcohol dehydrogenase and its suppression by beta-caseins: a mechanistic perspective

Molecular chaperones interact preferentially with certain aggregation-prone intermediates of target protein molecules. An estimation of the chaperone activity based on suppression of aggregation is required to be mechanistically understood. In this study, the multivariate curve resolution chemometric technique was applied on horse alcohol dehydrogenase (ADH) UV-spectra under thermal stress, to obtain the required information about the number and change in concentrations of the species involved. Chemometric analysis of UV-absorption spectra of horse ADH under thermal stress, led to the existence of three different molecular species including native (N), aggregation-prone intermediate (I) and final aggregate (A) species. Appearance and buildup of two molecular species I and A were connected to the disappearance of N-species. In the presence of β-caseins (BCN), however, a new complex between I and BCN (I-BCN) was formed. Meanwhile, by accretion of concentration of I-BCN complex, the light scattering intensity diminished. The data presented in this study clearly demonstrate that the interaction of BCN as a chaperone molecule with I-species takes place in a temperature-dependent manner and leads to a reversible I-BCN complex. In the absence of chaperones, I-state is subsequently converted to the final aggregate species. In the presence of BCN, this molecular species could be converted to the final aggregate state and/or form the I-BCN complex.     

A bucky gel consisting of Fe3O4 nanoparticles,graphene oxide and ionic liquid as an efficient sorbent for extraction of heavy metal ions from water prior to their determination by ICP-OES

Microchimica Acta - Bucky gels are gelatinous composite materials consisting of carbon nanotubes and ionic liquids. The authors describe the synthesis of a bucky gel containing Fe3O4 nanoparticles...     

Ultrasound-assisted emulsification microextraction method based on applying low density organic solvents followed by gas chromatography analysis for the determination of polycyclic aromatic hydrocarbons in water samples

In this study, a fast, simple and efficient ultrasound-assisted emulsification microextraction (USAEME) method was successfully developed based on applying low density organic solvents. Fourteen microliters of toluene was injected slowly into a 12 mL home-designed centrifuge glass vial containing an aqueous sample that was located inside the ultrasonic water bath. The formed emulsion was centrifuged and 2 μL of separated toluene (about 4 μL) was injected into a gas chromatographic system equipped with a flame ionization detector (GC-FID) for analysis. Some polycyclic aromatic hydrocarbons (PAHs) were selected as model compounds for developing the method and evaluating its performance and to compare the efficiency of the proposed method with previously reported techniques. Several factors influencing the emulsification, extraction and collection efficiency such as the nature and volume of organic solvent, emulsification–extraction temperature, ionic strength and equilibrium and centrifugation times were investigated and optimized. Under the optimum conditions, preconcentration factors (PFs) in a range of 1776–2714 were obtained. The performance of the proposed method was studied in terms of linear dynamic range (LDRs from 0.05 to 100 μg L⁻¹), linearity (R² ≥ 0.994), precision (repeatability: RSD% ≤ 7.9, reproducibility: RSD% ≤ 14.6) and extraction percents (59.2–90.5%). Limits of detection (LODs) in the range of 0.02–0.05 μg L⁻¹ were obtained for different PAHs. The applicability of the proposed method was evaluated by the extraction and determination of PAHs from several natural water samples.     

Simultaneous voltammetric determination of ascorbic acid and dopamine at the surface of electrodes modified with self-assembled gold nanoparticle films

Gold nanoparticles (GNs) could be efficiently immobilized on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol and 1-octanethiol (nano-Au/SAMs gold electrode). This GN chemically modified electrode was used for electrochemical determination of ascorbic acid (AA) and dopamine (DA) in aqueous media. The result showed that the GN-modified electrode could clearly resolve the oxidation peaks of AA and DA, with a peak-to-peak separation (∆E _p) of 110 mV enabling determination of AA and DA in the presence of each other. The linear analytical curves were obtained in the ranges of 0.3–1.4 mM for AA and 0.2–1.2 mM for DA concentrations using differential pulse voltammetry. The detection limits (3σ) were 9.0 × 10⁻⁵ M for AA and 9.0 × 10⁻⁵ M for DA.