Synthesis of 2,2'-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) in aqueous medium at room temperature

The reaction of dimedone with various aromatic aldehydes produces 2,2'-arylmethylene bis (3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) in excellent yields. The reactions occur in water as solvent at room temperature and avoiding the addition of any catalyst. The workup procedure is very simple and the products do not required further purification.     

One-pot synthesis of highly functionalized stable ketenimines of 2,2,2-trifluoro-N-aryl-acetamides

Three-component reaction of alkyl isocyanides and dialkyl acetylenedicarboxylates in the presence of 2,2,2-trifluoro-N-aryl-acetamides in dichloromethane at ambient temperature afforded dialkyl 2-(N-(aryl)-2,2,2-trifluoroacetamido)-3-(alkylimino) methylene-succinate derivatives in excellent yields.     

Development and validation of a HPLC method for the determination of buprenorphine hydrochloride, naloxone hydrochloride and noroxymorphone in a tablet formulation

A simple isocratic reversed-phase high-performance liquid chromatographic method (RP-HPLC) was developed for the simultaneous determination of buprenorphine hydrochloride, naloxone hydrochloride dihydrate and its major impurity, noroxymorphone, in pharmaceutical tablets. The chromatographic separation was achieved with 10 mmol L⁻¹ potassium phosphate buffer adjusted to pH 6.0 with orthophosphoric acid and acetonitrile (17:83, v/v) as mobile phase, a C-18 column, Perfectsil Target ODS3 (150 mm × 4.6 mm i.d., 5 μm) kept at 35 °C and UV detection at 210 nm. The compounds were eluted isocratically at a flow rate of 1.0 mL min⁻¹. The average retention times for naloxone, noroxymorphone and buprenorphine were 2.4, 3.8 and 8.1 min, respectively. The method was validated according to the ICH guidelines. The validation characteristics included accuracy, precision, linearity, range, specificity, limit of quantitation and robustness. The calibration curves were linear (r > 0.996) over the concentration range 0.22-220 μg mL⁻¹ for buprenorphine hydrochloride and 0.1-100 μg mL⁻¹ for naloxone hydrochloride dihydrate and noroxymorphone. The recoveries for all three compounds were above 96%. No spectral or chromatographic interferences from the tablet excipients were found. This method is rapid and simple, does not require any sample preparation and is suitable for routine quality control analyses.     

Modification of Lipid Bilayer Structure by Diacylglycerol: A Comparative Study of Diacylglycerol and Cholesterol

Diacylglycerols (DAGs) are important second messengers in biomembranes, and they can activate protein kinase C and many other enzymes and receptors. However, their interactions with cholesterol and other lipids have not been previously studied using molecular dynamics (MD) simulation. In this study, nine independent atomistic MD simulations were performed to specifically investigate the interactions between di16:0DAG, 16:0,18:1-phosphatidylcholine (POPC), and cholesterol. Despite of their substantial differences in chemical structure, DAG and cholesterol produce some very similar effects in POPC bilayers: increasing acyl chain order and bilayer thickness, reducing volume-per-lipid, and decreasing lateral diffusion of molecules. More significantly, DAG also produces a strong "condensing effect" in PC bilayers. In comparison, cholesterol is more effective than DAG in producing the above effects. The driving force for the condensing effect is their molecular shape: DAG and cholesterol both have small polar headgroups and large hydrophobic bodies. In a lipid bilayer, in order to avoid the unfavorable exposure of their hydrophobic parts to water, neighboring phospholipid headgroups move toward cholesterol or DAG to provide cover. Thus, seemingly complex interactions between DAG, cholesterol and phospholipid can be clearly explained using the Umbrella Model. Our simulations confirmed the hypothesis that DAG increases the spacing between phospholipid headgroups, which is important for activating protein kinase C and other enzymes. Interestingly, our simulations also show that the conventional wisdom that the spacing created by a DAG is directly above the DAG molecule is incorrect; instead, the largest spacing usually occurs between the first and the second nearest-neighbor PC headgroups from a DAG, due to the umbrella effect.     

Conductometric study of complex formation between benzylbisthiosemicarbazone and metal cations in acetonitrile,dimethylformamide, and their binary mixtures

We report on conductometric study of complexation between benzylbisthiosemicarbazone [(2E,2′E)-2,2′-(1,2-diphenylethane-1,2-diylidene)bis(hydrazine-1-carbothioamide)] with Zn²⁺, Cr³⁺, Co²⁺, and Ni²⁺ cations at different temperatures in acetonitrile-dimethylformamide binary solvents of varied composition. The equilibrium constant and standard thermodynamic parameters (Δ_c H ⁰ and Δ_c S ⁰) of the complexes formation have been determined and found to be dependent on the binary solvent composition, the metal ion nature, and temperature.     

Solvent-controlled dehydration and diastereoselective formation of indenone-fused thiazolo[3,2-a]pyridines via a one-pot four-component reaction

A solvent-controlled four-component reaction has been described for the preparation of either hydroxy-tetrahydro-thiaza-cyclopenta[c]fluoren-6-one or dihydro-thiaza-cyclopenta[c]fluoren-6-one from nitroketene dithioacetals, cysteamine hydrochloride, 1,3-indandione and aromatic aldehydes starting materials by changing solvent systems. These reactions proceed under catalyst-free conditions affording a range of two types of skeletally distinct thiazolo[3,2-a]pyridines-based heterocycles. Hydroxy-tetrahydro-thiaza-cyclopenta[c]fluoren-6-one was obtained in H₂O/EtOH (3:1, v/v) in high yield and diastereoselectivity but in contrast dihydro-thiaza-cyclopenta[c]fluoren-6-one was synthesised in EtOH in moderate to good yields and in the longer reaction time. The structural diversities have been confirmed spectroscopically, by IR ¹H and ¹³C NMR, and EI-MS spectra, which agree with the proposed structures.     

H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>-catalyzed one-pot synthesis of <Emphasis Type="Italic">bis</Emphasis>(indole) derivatives under silent and ultrasonic irradiation conditions in aqueous media

A convenient and direct approach has been developed for the preparation of bis(indole) derivatives by one-pot four-component condensing of indole, aldehydes and active methylene compounds in the presence of 12-tungstophosphoric acid in aqueous media under silent and ultrasound methods. The remarkable advantages are the simplicity of the experimental procedures, short reaction times and high yields with the green aspects by avoiding toxic catalysts and solvents.     

Numerical analysis of the internal flow and the mixing chamber length effects on the liquid film thickness exiting from the effervescent atomizer

Journal of Thermal Analysis and Calorimetry - Two-phase flow was simulated within the effervescent atomizer by the volume of fluid interface tracing model. Different gas-to-liquid mass ratios...     

Determination of trace amounts of aromatic amines after magnetic solid‐phase extraction using silver‐modified Fe3O4/graphene nanocomposite

In this work, a fast and simple magnetic dispersive solid phase extraction methodology was developed utilizing Ag@magnetite nanoparticles@graphene nanocomposite as an efficient magnetic nanosorbent for preconcentration and determine of five aromatic amines in water samples. The sorbent was characterized by diverse characterization techniques. After the extraction, high‐performance liquid chromatography with UV detection was utilized to analysis the aromatic amines. The effects of different factors on the extraction process were studied thoroughly via design of experiment and desirability function. Detection limits and linear dynamic ranges were obtained in the range of 0.10–0.20 and 0.3–300 μg/L, respectively. The relative standard deviations (n = 5) were in the range of 4.3–6.5%. Eventually, the method was employed for determination of target aromatic amines in various water samples.