South African Journal of Chemistry - latest Issue

The use of RNA macromolecules as therapeutic agents for HIV and other infectious diseases is promising but limited by suboptimal delivery to the target site. With HIV infection, this is particularly challenging since lymphocytes are particularly difficult to transfect. This paper describes an innovative strategy for the intracellular delivery of a novel single-stranded RNA (oligoribonucleotide) with putative anti-HIV activity. This strategy is based on a PEGylated gold nanoparticle scaffold covalently linked to the thiol-modified oligoribonucleotide via a cleavable N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) linker molecule. The nanoparticle was then coated with a cationic polymer (polyethyleneimine) to facilitate cell entry and endosomal escape. A synthetic anti-CD4 cyclic targeting peptide was attached to the polyethyleneimine-coated nanoparticle via an SPDP linker molecule, in an attempt to enhance uptake and selectivity. Synthesis, characterization, SPDP and RNA loading, cytotoxicity and antiviral activity of the nanoparticle are described. Approximately 45 000 strands of RNA were taken up per lymphocyte. Uptake was limited by relatively inefficient loading ofRNAonto the gold nanoparticle surface (1 strand per 4.8 nm2 of nanoparticle surface area) and significant aggregation of the nanoparticle in physiological solutions. No antiviral activity was demonstrated, possibly due to insufficient intracytoplasmic delivery of the RNA.

A low-cost adsorbent produced from Mn²⁺-modified bentonite clay was evaluated for groundwater defluoridation. Batch experiments were used to evaluate the effect of contact time at various adsorbent dosages, adsorption isotherms and the effect of pH on fluoride removal. The results showed that the optimum F^– uptake occurred within the first 30 min contact time and the percentage removal increased with increasing adsorbent dosage. The data fitted better to pseudo-second-order reaction indicating that F^– adsorption occurred via chemisorption. The Weber-Morris model of intra-particle diffusion revealed that both surface and intra-particle diffusion processes were involved during the F^– adsorption process. Furthermore, the batch results showed that pH of the solution governed the percentage of fluoride removal with the optimum of 75.2 % fluoride removal achieved at pH 4. The adsorbent chemical stability assessment showed that chemical species were leached at trace concentrations which are within the South African National Standards (SANS) limits. Electrostatic attraction and ion-exchange were established as the major mechanisms responsible for fluoride adsorption at acidic pH and at moderate to alkaline pH levels, respectively. The study demonstrated that Mn²⁺ intercalated bentonite clay has potential for application in defluoridation of groundwater.

A LC-HRMS (liquid chromatography coupled with high resolution mass spectrometry) method for the detection and quantitation of several synthetic cannabinoids (JWH-018, JWH-019, JWH-073, JWH-081, JWH-122 JWH-200, JWH-250, AM-2201, (±)-CP 47,497, (C8)-CP 47,497, HU-211) and selected metabolites (JWH-018 N-(4-hydroxypentyl) and JWH-073 N-(3-hydroxybutyl)) in whole blood and urine was developed and validated. These methods were applied to postmortem cases from the Johannesburg Forensic Pathology Services Medicolegal Laboratory (FPS-MLL) to assess the prevalence of these synthetic cannabinoids amongst the local postmortem population. Urine samples were extracted utilizing a solid phase extraction (SPE) method, while blood samples were extracted utilizing liquid-liquid extraction (LLE) method. The accuracy of the analytes ranged from 88–107 % in whole blood (relative standard deviation (RSD) = 7.5–15.0 %), and from 95–109 % in urine (RSD = 4.9–11.9 %). The limits of detection (LOD) and the limits of quantitation (LOQ) for the analytes ranged between 0.675 ng mL^–1 and 3.375 ng mL^–1 in whole blood, and between 0.225 ng mL^–1 to 3.375 ng mL^–1 in urine. None of the postmortem cases tested positive for any of the targeted analytes. The sample population could be extended to living subjects such as those in drug rehabilitation centres or in hospitals to obtain a more accurate representation of the overall usage in South Africa.

The aluminium corrosion inhibition behaviour in the presence of Areca palm leaves (AL) extract in hydrochloric acid (0.5 M) medium was examined by chemical (mass loss), AC impedance spectroscopy, potentiodynamic polarization and surface (scanning electron microscopy) methods. Aluminium protection rates increased with an increase in the amount of AL extract to the 0.5 M HCl system and decreased with increasing in the contact time of aluminium metal and temperature of 0.5 M HCl solution. Arrhenius equation was applied in the determination of activation energy values. The other activation parameters such as activation entropy and enthalpy values were obtained from the transition state plot. The adsorption of AL extract species on the Al surface in 0.5 M HCl solution follows the Langmuir adsorption mechanism. Tafel curves reflect the mixed (both anodic and cathodic) inhibition behaviour of green inhibitor (AL extract species) on electrode surface (Al) in 0.5 M system. Impedance method indicates that the Al dissolution in hydrochloric acid environment was fully hindered by charge transfer process. The Al surface morphology was examined by applying scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques.

A fast and sensitive method was developed for determination of glyphosate, using flow injection analysis. The analyte was converted to a photoactive product that shows maximum absorbance at 405 nm. Beer’s law was obeyed over a range of 0.7–20 μg mL^–1. The limit of detection and quantification were found to be 0.20±0.01 and 0.70±0.02 μg mL^–1 with a high sample throughput of 60 samples h^–1. The investigation of interference effect shows that among the compounds studied, only aminomethyl phosphonic acid exhibits a signal enhancing effect when present in higher concentration ratio with the analyte and this can be assumed to be a limitation of the present method. The percentage recoveries and residue of glyphosate in wheat grains samples, were found in the range of 90.0 ± 0.6 % to 93.0 ± 0.6 % and 1.13 ± 0.009 μg g^–1, respectively.

This paper gives an overview of the application of hydrazide derivatives in acid media as corrosion inhibitors of mild steel. In chemical and petrochemical industries, mild steel is the major constructional material widely used. Acid solutions have been commonly used in these industries as pickling agents to remove rust or any scale from the mild steel surface. The excessive dissolution of mild steel in such aggressive medium can be best controlled by addition of suitable organic inhibitors. Hydrazide derivatives are widely used in such applications as mild steel corrosion inhibitors. The various factors which influence the corrosion inhibition efficiency of different hydrazide derivatives have been discussed. The information provided is useful for various industries where corrosion inhibitors are needed to protect mild steel structures which are being exposed to hydrochloric or sulphuric acid solutions.

Response surface methodology was applied to predict the optimum control of mild steel corrosion in acid medium with bitter kola leaf extract as inhibitor. The experiment was carried out to investigate the mutual interactions between the considered independent variables and the expected responses. Thermometric, gravimetric, potentiodynamics polarization and electrochemical impedance spectroscopy were used in the corrosion inhibition study. As a supplementary technique, infrared spectroscopy was used to analyze the pure extract and corrosion products and it was observed that some peaks shifted while some disappeared. Inhibition efficiencies of 88.24 %, 86.81 %, 90 %, 89.5 % and 85.3 % were obtained from optimization, thermometric, gravimetric, potentiodynamics polarization and electrochemical impedance spectroscopic techniques, respectively. The bitter kola leaf extract behaved as a mixed-mode inhibitor. Application of response surface methodology in this study was found to be good in predicting the optimum range for controlling of metal corrosion thereby reducing the number of experimental runs.

A highly efficient and simple reaction under exceptionally mild conditions is shown for the synthesis of biologically and pharmaceutically active molecules of homopropargyl alcohol using HZSM-5 as the catalyst. Products analyzed by IR, 1H NMR, 13CNMR and GC-MS showed consistent yields of 98 % of the alcohol, even with respective recycles of the regenerated catalyst. The reaction was also carried out with selected mineral acids, acidic oxides and other acidic catalysts to compare reactivity and the influence of the type of acidity involved in the reaction. The results indicate that the presence of both Brønsted and Lewis acidity is beneficial for inducing a high rate of reaction when compared to systems having either predominantly Brønsted or Lewis acidity.

Samples of hematite (α-Fe2O3) nanoparticles have been synthesized through the co-precipitation route in cetyltrimethyl-ammonium bromide (Hem_PR), via a citric acid sol-gel method (Hem_SG) and a modified sol-gel method in Tween 20 (Hem_TW), and each were annealed at three different temperatures (400, 500 and 600 °C). The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission and high-resolution electron microscopy (TEM and HRTEM), Mössbauer spectroscopy and by means of a vibrating sample magnetometer (VSM). In addition, the photocatalytic behaviour of each sample was tested on the degradation of rhodamine B (RhB) in solution. All the characterization techniques showed the formation of phases of pure hematite nanoparticles with improved crystallinity after higher temperature annealing. However, the nanoparticles synthesized in Tween 20 showed the smallest particle size and highest BET surface area, saturation magnetization and photocatalytic activity. Of particular note was the ability of Tween 20 to control the growth of the particles so that grain sizes well below 10 nm were obtained. Thus, Tween 20, when used as a surfactant in the sol-gel route, can serve to improve the physical properties of synthesized hematite nanoparticles.

An HPLC method using an UV detector was developed for the simultaneous determination of nitrites, nitrates and phosphates in environmental samples. Chromatographic separation was achieved isocratically on a Phenomenex Synergi Polar-RP LC column using acetonitrile and acidified water (pH 2.7) at 60:40 v/v as mobile phase. Baseline resolution of all the three analytes was achieved within 3 min. The developed method was applied to water samples obtained from the wastewater treatment plant in Gaborone, Botswana. The use of HPLC technique in this study demonstrated its ability to carry out a simultaneous determination of NO₂ ^–, NO₃ ^– and PO₄ ^3– in water samples. The treatment plant was found to be functioning within expectations, removing 97.6% NO₂ ^–, 88.0% NO₃ ^– and 90.9% PO₄ ^3– from the received wastewater. Results of the developed method were comparable with those of the traditional ion chromatography method, showing accuracy values between 95.22% and 98.04 %. The precision of the method for the determination of all analytes was determined by RSD values, all of which were lower than 5%. The method is of low cost, fast, has an easy procedure and avoids the use of many reagents – some of which may be hazardous.

In this study, the levels and status of dichlorodiphenyltrichloroethane (DDT) residues in fish samples collected from Eastern Lake Tanganyika were investigated. The analytes were determined using gas chromatography equipped with an electron capture detector (GC–ECD) and by gas chromatography-mass spectrometry (GC-MS). The compounds p,p’-DDE (4,4’-DDE), p,p’-DDD (4,4’-DDD), o,p’-DDT (2,4’-DDT) and p,p’-DDT (4,4’-DDT) were detected in all the samples, with total DDT concentrations ranging from 23 ± 8.3 to 339 ± 27 μg kg^–1 fresh weight and 1736 ± 1388 μg kg^–1 to 25 552 ± 4241 μg kg^–1 lipid weight. The highest concentrations of total DDT were detected in Lates stappersii species. The ratios of the metabolites (DDD + DDE) to the parent compound (p,p’-DDT) were low (< 1) in all the fish samples, indicating exposure to fresh DDT. The concentrations of the DDT residues exceeded the extraneous maximum residue limit of 1.0 μg kg^–1, indicating risks and concerns for public health and the environment because of the indication of fresh application of banned pesticides and bioaccumulation. There is need for continued monitoring of the residues in Lake Tanganyika environs and controlling the pesticides used in the area.