Mathew Mupa

Evaluation of norbornene- β-cyclodextrin-based monomers and oligomers as chiral selectors by means of nonaqueous capillary electrophoresis

Norbornen‐5‐yl carboxylic acid and norbornen‐5‐ylmethylsilyl ether‐based β‐cyclodextrins (β‐CDs) containing up to three norbornene ester and up to five norbornene silyl ether units have been prepared from β‐CD and norbornen‐5‐carboxylic chloride and norbornen‐5‐ylmethyldichlorosilane, respectively. Oligomers (n = 2—4) were prepared therefrom using ring‐opening metathesis polymerization (ROMP). Monomeric and oligomeric substituted β‐CDs were evaluated as chiral selectors in nonaqueous capillary zone electrophoresis using 35 mM sodium bicarbonate in N‐methylformamide (NMF) as background electrolyte. Both monomeric and oligomeric norbornene ester‐ and norbornene silyl ether‐type selectors showed good enantioresolution for dansylated (DNS‐) amino acids using concentrations of the chiral selector of up to 4% w/v. A significant improvement in resolution was observed upon the introduction of up to five norbornene silyl ether units into a β‐CD molecule, whereas higher degrees of substitution with norbornen‐5‐yl‐carboxyl groups lead to a reduction in enantioresolution of DNS‐amino acids. Thus, pentakis(norbornen‐5‐ylmethylhydroxysiloxyl)‐β‐CD turned out to be superior to mono(norbornen‐5‐ylmethylhydroxysiloxyl)‐β‐CD in terms of enantioresolution. Moreover, norbornene silyl ether‐type selectors were found to be more efficient than norbornene ester‐type selectors. Finally, oligomeric selectors were found to possess superior or at least comparable enantioselectivity in the separation of DNS‐amino acids compared to the parent monomers. A maximum in enantioresolution was obtained with oligo(pentakis(norbornen‐5‐ylmethylhydroxysiloxyl)β‐CD).

Tailor-made polymer supports via metathesis polymerization : Concepts and applications

Ring opening metathesis polymerization (ROMP) and alkyne polymerization have been applied to the preparation of surface-functionalized inorganic and organic supports using various coating, grafting, precipitation and bulk-polymerization techniques. Well-defined carrier materials in terms of particle diameter, specific surface, pore volume and functionalization have been prepared. The resulting materials have been used for applications in heterogeneous catalysis (e. g. Heck couplings) as well as in bioanalytical (e. g. protein) separations.

Preparation of rice hull activated carbon for the removal of selected pharmaceutical waste compounds in hospital effluent

The adsorbent (activated carbon) was prepared from rice hull obtained from communal farmers in Mutoko North (Zimbabwe) by chemical activation using phosphoric acid and was used in the adsorption of aspirin, paracetamol and ibuprofen from hospital effluent. Characterization of the rice hull activated carbon was carried out using the following methods: SEM, XRD, FT- IR. Physical properties such as iodine number, porosity, ash content, moisture content and volatile matter content were also determined. Iodine number was found to be 815.0 ± 2.52 mg/g. FT-IR analysis showed the presence of various functional groups such as C=O, C=C, –OH, and C-H on the surface of the adsorbent whereas SEM micrograph showed that the external surface of the rice hull activated carbon is full of regular cavities. XRD pattern showed broad peaks indicating that rice hull activated carbon produced has amorphous structure. The effect of adsorbent dose, contact time, initial concentration and pH was studied. Adsorption of aspirin fits the Freundlich isotherm, whereas ibuprofen and paracetamol fit the Langmuir isotherm. Kinetic studies showed that adsorption of ibuprofen, aspirin and paracetamol obey pseudo-second order kinetics. Aspirin, paracetamol and ibuprofen were detected in two hospital wastewaters at the concentrations of 0.117 ± 0.0058 mg/L, 0.100 mg/L and 0.010 ± 0.0006 mg/L respectively. The studies showed that pharmaceutical compounds studied can be removed from wastewater using rice hull derived activated carbon.

Lead Content of Lichens in Metropolitan Harare, Zimbabwe. Air Quality and Health Risk Implications

Many studies have shown that inhaled lead is one of the major contributors of lead poisoning. Lead poisoning affects all systems within the body. Lead amount in metropolitan Harare atmosphere was estimated by measuring the amount of lead in lichens found in the area. Lead pollution of the atmosphere is of major concern because continuous exposure of low levels of lead may cause serious effects. Furthermore there are no agreed safety limits for children. The concentration of Pb in different species was determined by atomic absorption spectrometry. Lead concentration varied from not detectable quantities to 3.31 ± 0.04 ppm. Harare central hospital recorded the highest lead content 3.31 ± 0.04 ppm in Parmelia species while the lowest was observed at centers far from the CBD, Botanic gardens, Christonbank and Mwenje dam. Generally the relationship between distance, lead content and species diversity was significant for most lichens except that for Lecanora caesiopallens (r = 0.72) and Lecanora atraaeformis (r = 0.71) student t-test p > 0,05 showing presence of increased pollution in the CBD . It is suggested that all possible sources of lead poisoning and their contributions to atmospheric lead content should be ascertained to determine the actual daily exposure rate. Such data would help in formulating policies to reduce lead poisoning in the general public.

Selective Acetylation of 2-Naphthol to 2-Naphthyl Acetate with Ni Homogeneous Catalysts: An Environmentally Friendly Protocol

An efficient, selective and simple route for the synthesis of 2-Naphthyl acetate has been developed. In reflux conditions the acetylation of 2-naphthol acetylation with a catalytic amount of Nickel nitrate catalysts afforded 2-Naphthyl acetate in moderate to excellent yields. Nickel nitrate showed the best catalytic performance compared to other Nickel salts. Different weights of nickel salts have been evaluated for the title reaction with 30mg NiNO3 afforded the Best conversions. Different acylating reagents were evaluated acetic acid, acetyl chloride and acetic anhydride, and it was observed that acetic acid was the best acetylating reagent. The protocol has advantages including short reaction times, high chemoselectivity towards acylated product simple work-up. Additionally, nickel nitrate, other additives are not required to enhance the reactions.

Green Synthesis of Silver Nanoparticles Using Euphorbia Confinalis Stem Extract, Characterization and Evaluation of Antimicrobial Activity

Green Synthesis of Silver Nanoparticles Using Euphorbia Confinalis Stem Extract, Characterization and Evaluation of Antimicrobial Activity Silver nanoparticles were synthesized using Euphorbia Confinalis stem extract which is an eco-friendly and cost effective method compared to other synthesis protocols like chemical and physical methods. Euphorbia Confinalis which is used traditionally for therapeutic uses was responsible for capping and reducing silver ions to silver nanoparticles. Silver was of a particular interest for this process due to its evocative physical and chemical properties. The silver nanoparticles synthesized were quantified and characterized using visual examination of the color changes, UV-Visible spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, Dynamic Light Scattering and Fourier Transform Infrared spectroscopy. The antimicrobial activity of the synthesized nanoparticles was done by agar disc diffusion method tested against Escherichia coli (Gram-Negative) and Staphylococcus aureus (Gram-Positive). The synthesis of silver nanoparticles was confirmed by color change of AgNO3 to reddish brown upon addition of the Euphorbia Confinalis stem extract. The UV-Vis spectrum showed broad absorption band at 433nm corresponding to that of Surface Plasmon Resonance of silver nanoparticles. The FTIR analysis showed the presence of aromatic, aliphatic and amines and these observations suggested the presence and binding of organic compounds with silver nanoparticles.