South African Journal of Chemistry

Trace nickel analysis in water samples via paper-based devices coupled with co-precipitation

2023-06-06T08:25:19+00:00

A simple, fast, low-cost and sensitive microfluidic paper-based analytical device (μ-PADs) integrated with the co-precipitation enrichment procedure was developed to analyse Ni(II) in tap and mineral water samples. The impacting factors, including pH, centrifugation (5 min at 4000 rpm), and amounts of reagents were optimized. The limit of detection of 0.009 mg L⁻¹ and linear range of 0.03–2.00 mg L⁻¹ were achieved with good intra- and inter-day precision (4.7 and 5.6% RSD, respectively). The recovery tests were conducted by spiking tap and mineral water samples and analyzed using the μ-PADs after co-precipitation enrichment. The results obtained by the proposed method were validated by inductively coupled plasma-optical emission spectrometry (ICP-OES). The recoveries of the present method and ICP-OES were ranged from 92.4–106.8% and 92.9–97.2%, respectively. The two sets of (μ-PADs and ICP-OES) results were in good agreement, as a paired t-test indicated no significant differences. The proposed method could be utilized for analyzing trace levels of Ni(II) in water samples in developing countries where the availability of conventional analytical instruments are significant problems.

Quinoline-benzofuran and quinoline-benzothiophene derivatives as antiplasmodium agents

2023-06-06T08:29:18+00:00

Two series of coupled heterocyclic systems have been synthesised and found to be efficacious against the NF54 chloroquine sensitive strain of P. falciparum in an in vitro assay. Quinolines were coupled with benzofurans in the first series and benzothiophenes in the second series. Compounds with an amide linkage are more efficacious by one order of magnitude than the ester equivalent. No other clear pattern was discernible. Compounds were also tested for toxicity using an MTT assay. All compounds tested showed selectivity towards P. falciparum. Barring one, all compounds tested showed greater efficacy than chloroquine against β-hematin inhibition. But no correlation was observed between β-hematin inhibition and efficacy against P. falciparum.

A simple method for colourimetric determination of silver using a home-made double beam photometer

2023-06-06T08:32:22+00:00

The present study proposes a simple and inexpensive photometric method for the selective determination of Ag(I). This method employed a home-made double beam photometer for the determination of silver ions based on an optode sensor prepared by immobilization of 5-(P-Dimethylaminobenzylidene)-rhodanine (PDR) on triacetyl cellulose (TAC) membrane. Two green LEDs as sources of light and light-dependent resistors (LDRs) as detectors were used in the proposed device. The LEDs are turned on by a programmable microcontroller that receives signals from light passed through the sensor, and the absorbance is calculated and displayed on a Liquid-crystal display (LCD) screen. With the optimum conditions, the calibration plot was linear in the concentration range of 0.5–6 μg mL⁻¹. For five replicate determinations of 2 μg mL⁻¹ Ag(I) and the related detection limits, the relative standard deviations were 2.29% and 0.25 μg mL⁻¹, respectively. The method was applied successfully for determining silver in a silver sulphadiazine cream, a radiology effluent, and radiology film samples and the results obtained were in good agreement with those of the standard flame atomic absorption spectroscopy (FAAS) method.

Re-screening and preliminary in vitro evaluation of resorcinol based Hsp90 inhibitors for potential protocidal activity

2023-06-06T08:38:25+00:00

This study explored a series of resorcinol derivatives originally identified as heat shock protein 90 inhibitors for activity against protozoan parasites. The repurposing of this series revealed that some of these compounds are active against chloroquine-sensitive Plasmodium falciparum (3D7) and Trypanosoma brucei brucei strains with IC₅₀ values below 10 μM without obvious cytotoxic effects against human cervix adenocarcinoma (HeLa) cells at 25 μM.

Effects of calcination temperature of eggshell-derived CaO as a catalyst for biodiesel production from waste cooking oil

2023-06-06T08:41:17+00:00

Biodiesel is considered to be more friendly to the environment than petroleum-based fuels, cheaper and capable for producing greener energy which contributed positively in boosting bio-economy. In this work, waste cooking oil (WCO) is converted into biodiesel utilizing a waste eggshell (CaO) nano-catalyst in an effort to discover environmentally beneficial and economically viable processes for social and economic development. The eggshell-based CaO catalyst developed for the production of ecologically friendly biodiesel at a reduced price is calcined at temperatures between 600 and 1100 °C. The synthesized catalysts were assessed in terms of their physical and chemical qualities via BET, TGA and XRD analysis. This revealed that, besides displaying exceptional transesterification activity, the catalyst synthesised at 950 °C also offered the greatest biodiesel yield. Transesterification, used in biodiesel generation, was used to evaluate the catalytic performance of manufactured catalysts under several reaction circumstances. Under prime reaction conditions i.e., a reaction time of 3 hours, an ethanoloil molar ratio of 9:1, and a catalyst amount of 4 wt.%, it was ascertained that a catalyst which had calcined at 950 °C demonstrated excellent transesterification activity and delivered a ceiling yield of 88% fatty acid ethyl esters. The production of FAME was confirmed by using gas chromatography-mass spectroscopy (GC–MS). Fuel properties of fatty acid ethyl ester complied with ASTM D 6751 which indicated that it would be an appropriate alternative form of fuel.

The coordination behaviour of 2-((E)-(tert-butylimino)methyl) phenol towards lanthanide nitrate and chloride salts

2023-06-06T08:47:51+00:00

Five novel complexes were prepared by reacting 2-((E)-(tert-butylimino)methyl)phenol (HL2) with Ln(NO3)3∙xH2O (Ln = Gd and Dy ; x = 6 and 5, respectively) and LnCl₃∙6H₂O (Ln = Nd, Gd and Dy). The crystal structures of the former two Ln(III) nitrate complexes are isostructural and the coordination sphere is composed of three monodentate HL₂ ligands bonded to the metal centre through the phenolic oxygen atom and three nitrate ions coordinated in a bidentate fashion. Both complexes are nine-coordinate and SHAPE analysis reveals that they adopted a muffin polyhedra geometric type. The average Ln-O_nitrate and Ln-O_phenolate bond lengths are 2.5059 and 2.2816 Å, respectively. The complexes derived from the chloride salts exhibited an octahedral geometry with four monodentate Schiff base ligands [Ln-O_phenolate distances range from 2.229(4) to 2.2797(18) Å] coordinating in the equatorial positions and two chloride ions [average Ln-Cl bond length is 2.6530 Å, and average Cl-Ln-Cl angles is 180°] in axial positions. The ligand coordinated through the phenolate oxygen with the phenolic proton migrating to the imino nitrogen to give a zwitterionic form of the ligand. There are weak C-H∙∙∙Cl interactions present and O-H∙∙∙N hydrogen bonds are also observed in the crystal packing.