Micellar effect upon the rate of alkaline hydrolysis of carboxylic and carbonate esters

AbstractThe alkaline hydrolysis of carboxylate (1-naphthylbutyrate) and carbonate esters (2-(methylsulfonyl)-ethyl-4-nitrophenylcarbonate) in the presence of different surfactants has been studied. The rate of hydrolysis of these esters was determined under pseudo first order condition in which the concentration of NaOH was kept in large excess over the [ester]. The cationic micelles of cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium sulfate ((CTA)2SO4) enhanced the rate of hydrolysis of esters to a maximum value and thereafter, the increasing concentration of surfactant decreased the reaction rate. The anionic micelles of sodium dodecyl sulfate (SDS) inhibited the rate of the hydrolysis. The reaction proceeds through the attack of OH− ions on the carbonyl carbon forming tetrahedral intermediate. The tetrahedral intermediate is unstable and collapses immediately to yield respective acid and alcohol. The micelles influence the stability of tetrahedral intermediate, in turn, altering the rate of hydrolysis. The variation in the rate of hydrolysis by micelles was treated by considering the pseudophase ion-exchange model and Menger–Portnoy model. The added salts viz. NaBr, NaCl, and LiCl inhibited the rate of the reaction in the presence of cationic and anionic micelles. The kinetic parameters i.e. km and Ks were determined from the rate–[surfactant] profile

The use of nanohybrid curcumin to inhibit some types of local yeasts Isolate

The objective of this study was to use nanohybrid Curcumin Cur-ZnO and Cur-MgO as well as free curcumin to detect, isolate, characterize, and inhibit the development of certain yeasts locally isolated from some spoilage foods. Yeasts responsible for spoiling were recovered in 21 different colonies from cheese, cooked cheese, pickles, fig jam, apple jam, dates, rice, canned chickpeas, and dried figs. Nine yeast isolates were chosen for further morphological and biochemical investigation using VITK 2. Six different genera and species of yeast were found, with three of them, all members of the genus Candida (Candida inconspicua/lambica, Candida krusei, and Candida famata), being the most common. It was determined that between one and two isolations belonged to the genus Zygosccharomyces SPP, and that one isolation belonged to each of the races Trichosporon asahii, Malassezia furfur, Kloekera SPP, and Rhodotorula, with probabilities ranging from.87 – 96%. The results showed that the concentration-dependent inhibition was greatest for the Cur-ZnO nanohybrid, next for the Cur-MgO nanohybrid, and finally for the free curcumin

Experimental study on high velocity impact behaviors of Kevlar/epoxy polymer composites

In this study, Kevlar/epoxy composite materials with 6.5 mm thickness were subjected to high velocity impact tests which are conducted from 456 m/s to 801 m/s using single-stage gas gun system experimentally, because the resistance of composite materials to high-velocity impacts depends on the thickness and type of fibers used in many applications such as defensive and aerospace structures in the aerospace sector. The case of military applications, shocks such as shells and missiles have a high-velocity impact. Composite materials were manufactured by vacuum assisted resin infusion moulding (VARIM) method. Waterjet cutting machine was used to prepare the samples with 100 mm x 100 mm. The result shows that, residual velocity increases by increasing impact velocity. However, percent reduction in velocity decreases by increasing impact velocity</p

A comparative study on ballistic impact behaviors of glass/epoxy composites

This paper presents an experimental and numerical study to evaluate the ballistic performance of E-glass/epoxy and S2-glass/epoxy composites. Composite materials were produced by vacuum assisted resin infusion molding method. All the specimens were then subjected to ballistic impact tests by gas-gun system. Residual velocities were measured by high-speed camera for different velocities. Ballistic limits of all composites were obtained by curve fitting residual velocity-impact velocity data. It was found that S2-glass/epoxy composite has a higher ballistic limit than E-glass/epoxy. S2-glass/epoxy has also more specific absorbed energy and absorbed energy density than E-glass/epoxy. Numerical results were in good agreement with experimental results

Baseline distribution of petroleum hydrocarbon contamination in the marine environment around the coastline of Qatar

Levels of organic contaminants (TPHs, PAHs) were simultaneously determined in both abiotic (sediments, seawater) and biotic (Pinctada radiata oysters) samples at four sites along the coastline of Qatar (Arabian Gulf) in 2017-2018. TPHs and PAHs were more frequently detected in oyster tissues than sediment and seawater samples collected from the same areas. While levels of TPHs and PAHs in seawater and sediments were lower than previous local studies and worldwide studies, PAHs levels observed in pearl oyster tissue (25.9- 2240 μg/kg) were relatively higher than in previous studies in Qatar. In general, eight PAHs compounds were detected in oyster tissue, with benzo(a)pyrene displaying the highest concentration. The coast of Qatar could be affected by seasonal patterns of pollutants, where TPHs and PAHs levels increased in winter compared to summer. These results provide key information on the use of the pearl oyster as a bioindicator species and Qatar’s marine environment

Micromorphological and Anatomical Characteristics of the Genus Chrysophthalmum Schultz Bip. (Asteraceae) Growing in Turkey

The genus Chrysophthalmum (Asteraceae) is represented by five species in the world. Three species of this genus are naturally grown in Turkey. The species growing in Turkey are C. montanum (DC.) Boiss., C. dichotomum Boiss. and Heldr. and C. gueneri Aytac and Anderb. Except C. montanum; the other species are endemic for Turkey. In the present study, micromorphological and anatomical characteristics of these species by using light microscopy (LM) and scanning electronmicroscopy (SEM) have been comparatively presented for the first time. Themicromorphological studies are related to trichomes and cypsela. In anatomical studies, crosssections of the stem, and leaf have been examined. In addition, to show stomatal distribution and anatomy on adaxial and abaxial leaves, surface sections of the leaves have been taken and stomatal index calculated. The features of stems, leaves, trichomes and cypsela have been found to be significant to distinguish the species. Mesophyll structure, number of vascular bundles in midrib, presence or absence of sclerenchymatous fibers in leaf, trichome types, presence or absence of pappus in cypsela, presence or absence of hair on cypsela surface are important diagnostic characters. A diagnostic key based on combined leaf, trichome and cypsela characteristics of the Chrysophthalmum species has been given