Department of Chemistry

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Cashew nut shell: a potential bio-resource for the production of bio-sourced chemicals
(Green Chemistry, 2019) Mgaya, James; Shombe, Ginena B; Masikane, Siphamandla C; Mlowe, Sixberth; Mubofu, Egid B; Revaprasadu, Neerish
Exploitation of agricultural waste as green starting materials to produce various valuable products is attracting the attention of academic, industrial and other practitioners. Cashew nut shell (CNS) and its liquid extract (CNSL) in particular have been identified as agro-wastes rich in valuable and functional renewable products. The unique structural features of the CNSL constituents offer the possibility for different modifications to suit various applications. This review article provides recent developments in CNS and CNSL as green sources for use in the production of biorenewable chemicals, materials and energy. Extraction methods and applications of CNS, CNSL and isolates are discussed. Furthermore, a literature survey of the current status and efforts made on the utilization of these agricultural and food wastes for different applications is well outlined.
Castor Oil Production and Applications
(Nova Science Publishers, 2018) Mlowe, Sixberth; Masikane, Siphamandla C; Kyobe, Joseph W; Mubofu, Egid B; Revaprasadu, Neerish
Castor oil extracted from the castor oil seeds of Ricinus communis is an important naturally occurring oil identified as a useful raw material for diverse industrial applications. Historically, the oil has been used in medicinal fields (as a laxative agent) as well as in cosmetics. The main attractive attributes of this oil include biodegradability and non-volatility. Thus, this has recently enabled derivatization to afford value-added chemicals through alternative green synthetic protocols. The oil contains a large percentage of an unusual fatty acid, 12-hydroxy-9-cisoctadecenoic acid, commonly known as ricinoleic acid. Ricinoleic acid can be easily extracted through chemical processes and subsequently exploited as a biosource for the production of high-grade lubricants, transparent typewriter and printing inks, textile dyes, leather preservation agents and polyamide nylon-type fibres. The most recent advances identify castor oil and its major isolate (ricinoleic acid) as potential green solvents and/or capping agents in the synthesis of high quality nanomaterials and nanocomposites.
CdS thin films deposition by AACVD: effect of precursor type, decomposition temperature and solvent.
(Journal of Materials Science: Materials in Electronics, 2018-09) Ketchemen, Kevin IY; Mlowe, Sixberth; Nyamen, Linda D; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, Neerish
ABSTRACT Hexagonal cadmium sulfide (CdS) thin films were deposited on glass substrates by Aerosol Assisted Chemical Vapour Deposition (AACVD) using cadmium(II) dithiocarbamate and xanthate complexes in tetrahydrofuran (THF) and mixed solvents (THF+ chloroform) at 400 and 450 oC. The surface morphology and size of the CdS films determined using scanning electron microscopy (SEM), showed the formation of films of various morphologies depending on the precursor, the deposition temperature and solvent used. An increase in temperature resulted in an increase in particle size and a change in morphology with the formation of CdS films with distorted structures. The CdS films showed an overall blue shift in their absorption band edge (2.35 – 2.49 eV) compared to the bulk CdS. In dithiocarbamates, a slight blue shift was observed with a shift to high wavelengths with the reduction of the carbon chain of the dithiocarbamate and an increase in temperature; while in xanthate, a strong blue shift was observed at both deposition temperatures. The use of mixed THF + chloroform solvent at 450 oC showed the formation of films with irregular structures compared to those deposited using THF solvent alone, indicating the role of the solvent in the shape direction of the films formation. The elemental composition determined by energy dispersive X-ray spectroscopy (EDX) measurements revealed the 1:1 (Cd:S) ratio in all the samples confirming the stoichiometry of the CdS films.
A common molecular signature of patients with sickle cell disease revealed by microarray meta-analysis and a genome-wide association study
(PLoS ONE, 2018) Hamda, Cherif B; Sangeda, Raphael; Mwita, Liberata; Meintjes, Ayton; Nkya, Siana; Panji, Sumir; Mulder, Nicola; Guizani-Tabbane, Lamia; Benkahla, Alia; Makani, Julie; Ghedira, Kais
A chronic inflammatory state to a large extent explains sickle cell disease (SCD) pathophysiology. Nonetheless, the principal dysregulated factors affecting this major pathway and their mechanisms of action still have to be fully identified and elucidated. Integrating gene expression and genome-wide association study (GWAS) data analysis represents a novel approach to refining the identification of key mediators and functions in complex diseases. Here, we performed gene expression meta-analysis of five independent publicly available microarray datasets related to homozygous SS patients with SCD to identify a consensus SCD transcriptomic profile. The meta-analysis conducted using the MetaDE R package based on combining p values (maxP approach) identified 335 differentially expressed genes (DEGs; 224 upregulated and 111 downregulated). Functional gene set enrichment revealed the importance of several metabolic pathways, of innate immune responses, erythrocyte development, and hemostasis pathways. Advanced analyses of GWAS data generated within the framework of this study by means of the atSNP R package and SIFT tool identified 60 regulatory single-nucleotide polymorphisms (rSNPs) occurring in the promoter of 20 DEGs and a deleterious SNP, affecting CAMKK2 protein function. This novel database of candidate genes, transcription factors, and rSNPs associated with SCD provides new markers that may help to identify new therapeutic targets.
Deposition of Bi2S3 thin films from heterocyclic bismuth (III) dithiocarbamato complexes.
(Polyhedron, 2018) Kun, Walter N; Mlowe, Sixberth; Nyamen, Linda D; Akerman, Matthew P; O'Brien, Paul; Ndifon, Peter T; Revaprasadu, Neerish
Two heterocyclic dithiocarbamate complexes, tris- (piperidinedithiocarbamato)bismuth(III) (1) and tris-(tetrahydroquinolinedithiocarbamato) bismuth(III) (2) were synthesized and characterized by elemental analysis and thermogravimetric analysis. The structure of complex (1) was confirmed by single-crystal X-ray analysis. Both complexes were used as single source precursors for the deposition of bismuth sulfide thin films by aerosol assisted chemical vapour deposition (AACVD) at 350, 400, 450 °C and spin coating followed by thermal treatment at 350 °C, 400 °C and 450 °C. Both deposition methods, gave sulfur deficient polycrystalline films of bismuthinite. Scanning electron microscopy (SEM) images of the films showed morphology was dependent on the solvent mixture, temperature, precursor type and method of deposition. AACVD gave films with hexagonal nanoplatelets, leaf-like platelet, ribbon-like fibre, needle-like fibre morphologies. Films in the form of rods and interwoven nanowires were obtained from spin coating.
Fetal Hemoglobin is Associatedwith Peripheral Oxygen Saturation in Sickle Cell Disease in Tanzania
(EBioMedicine, 2017) Nkya, Siana; Mgaya, Josephine; Urio, Florence; Makubi, Abel; Thein, Swee L; Menzel, Stephan; Cox, Sharon E.; Newton, Charles R; Kirkham, Fenella J; Mmbando, Bruno P; Makani, Julie
Fetal hemoglobin (HbF) and peripheral hemoglobin oxygen saturation (SpO2) both predict clinical severity in sickle cell disease (SCD), while reticulocytosis is associated with vasculopathy, but there are few data on mechanisms. HbF, SpO2 and routine clinical and laboratorymeasureswere available in a Tanzanian cohort of 1175 SCD individuals aged ≥ 5 years and the associationwith SpO2 (as response variable transformed to a Poisson distribution) was assessed by negative binomial model with age and sex as covariates. Increase in HbF was associated with increased SpO2 (rate ratio, RR = 1.19; 95% confidence intervals [CI] 1.04, 1.37 per natural log unit of HbF; p = 0.0004). In univariable analysis, SpO2 was inversely associated with age, reticulocyte count, and log (total bilirubin) and directly with pulse, SBP, hemoglobin, and log(HbF). In multivariable regression log(HbF) (RR 1.191; 95%CI 1.04, 1.37; p = 0.013), pulse (RR 1.01; 95%CI 1.00, 1.01; p = 0.026), SBP (RR 1.008; 95%CI 1.00, 1.02; p=0.014), and hemoglobin (1.120; 95%CI 1.05, 1.19; p=0.001) were positively and independently associated with SpO2 while reticulocyte count (RR 0.985; 95%CI 0.97, 0.99; p =0.019) was independently inversely associated with SpO2. In SCD, improving SpO2, in part through cardiovascular compensation and associated with reduced reticulocytosis, may be a mechanism by which HbF reduces disease severity.
g(HbF): a genetic model of fetal hemoglobin in sickle cell disease.
(Blood advances., 2018) Gardner, Kate; Fulford, Tony; Silver, Nicholas; Rooks, Helen; Angelis, Nikolaos; Allman, Marlene; Nkya, Siana; Makani, Julie; Howard, Jo; Kesse-Adu, Rachel; Rees, David C; Stuart-Smith, Sara; Yeghen, Tullie; Awogbade, Moji; Sangeda, Raphael; Mgaya, Josephine; Patel, Hamel; Newhouse, Stephen; Menzel, Stephan; Thein, Swee L
Fetal hemoglobin (HbF) is a strong modifier of sickle cell disease (SCD) severity and isassociated with 3 common genetic loci. Quantifying the genetic effects of the 3 loci wouldspecifically address the benefits of HbF increases in patients. Here, we have applied statisticalmethods using the most representative variants:rs1427407andrs6545816inBCL11A,rs66650371(3-bp deletion) andrs9376090inHMIP-2A,rs9494142andrs9494145inHMIP-2B,andrs7482144(Xmn1-HBG2in theb-globin locus) to createg(HbF), a genetic quantitativevariable for HbF in SCD. Only patients aged$5 years with complete genotype and HbFdata were studied. Five hundred eighty-one patients with hemoglobin SS (HbSS) or HbSb0thalassemia formed the“discovery”cohort. Multiple linear regression modeling rational-ized the 7 variants down to 4 markers (rs6545816,rs1427407,rs66650371, andrs7482144)eachindependentlycontributing HbF-boosting alleles, together accounting for 21.8% of HbFvariability (r2) in the HbSS or HbSb0patients. The model was replicated with consistentr2in 2 different cohorts: 27.5% in HbSC patients (N5186) and 23% in 994 Tanzanian HbSSpatients.g(HbF), our 4-variant model, provides a robust approach to account for the geneticcomponent of HbF in SCD and is of potential utility in sickle genetic and clinical studies
Heterocyclic lead(II) thioureato complexes as single-source precursors for the aerosol assisted chemical vapour deposition of PbS thin films
(Inorganica Chimica Acta, 2018) Ketchemen, Kevin IY; Mlowe, Sixberth; Nyamen, Linda D; Aboud, Ahmed A; Akerman, Matthew P; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, Neerish
The lead N’-benzoylthioureato complexes of N-morpholine (1) and N-pyrrolidine (2) were synthesized and characterized by elemental analysis, Fourier Transform Infra-Red (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H nmr) and thermogravimetric analyses (TGA). The X-ray single crystal structure of complex (1) was determined. The compounds were both used as single source precursors to deposit PbS films on glass substrates at 350, 400 and 450 °C using aerosol assisted chemical vapour deposition (AACVD) The surface morphology of PbS films were determined by scanning electron microscopy (SEM), the crystalline phases established by powder X-ray diffraction (p-XRD) analyses and composition by energy dispersive X-ray spectroscopy (EDX). The particle sizes were found to range between 82 and 85 nm from complex (1) and 70–105 nm for (2) The PbS films were studied by Near Infra-red (NIR) UV–Vis spectroscopy, band gap ranging from 1.46 to 1.55 eV were observed.
Lead(II) halide cinnamaldehyde thiosemicarbazone complexes as single source precursors for oleylamine-capped lead sulfide nanoparticles
(Journal of Materials Science: Materials in Electronics, 2018) Masikane, Siphamandla C; Mlowe, Sixberth; Gervas, Charles; Revaprasadu, Neerish; Pawar, Amol S; Garje, Shivram S
Different PbX2 (X = AcO, Cl, Br, I) metal salts were complexed to cinnamaldehyde thiosemicarbazone ligand. The resulting complexes were characterised using Fourier Transform Infrared spectroscopy, 1H and 13C {1H} Nuclear Magnetic Resonance spectroscopy, elemental analysis and thermogravimetric analysis techniques. They were then used as single source precursors for the preparation of lead sulfide (PbS) nanoparticles using the colloidal thermolysis route where oleylamine is used as the passivating agent. Each SSP is thermolysed at reaction temperatures of 190, 230 and 270 °C. Predominantly cubic-shaped PbS nanoparticles were obtained, with an exception of the truncated nanocubes obtained from thermolysis of the SSP prepared from lead bromide. Varying particle sizes are obtained when the halogen is varied, ranging from ca. 50 to 400 nm. The optical absorbance of the PbS nanoparticles in the UV-Vis- NIR range was found to be blue-shifted when compared to bulk PbS.
Phase pure Ni3S2 and NiS from bis(N′-ethyl-N-piperazinylcarbodithioato-S,S′)–nickel(II) via solvent thermolysis and aerosol assisted chemical vapour deposition.
(New Journal of Chemistry, 2018) Gervas, Charles; Mlowe, Sixberth; Akerman, Matthew P; Revaprasadu, Neerish
A bis(N′-ethyl-N-piperazinylcarbodithioato-S,S′)–nickel(II) complex was prepared and characterized using infrared spectroscopy, thermogravimetric and elemental analyses. The crystal X-ray structure for bis(N′-ethyl-N-piperazinylcarbodithioato-S,S′)–nickel(II) was determined. The complex was subsequently used as a single source precursor (SSP) for the synthesis of phase pure Ni3S2 and NiS nanoparticles and thin films via hot injection thermolysis and aerosol assisted chemical vapour deposition (AACVD) routes, respectively. For the hot injection thermolysis route, hexadecylamine (HDA) and oleylamine (OLA) were used as capping groups at varying temperatures. Chloroform was used as the solvent in the AACVD experiments. Powder X-ray revealed that the capping group does not change the phase of nanoparticles formed whereas the AACVD technique produced different phases. Variation of temperature did not affect the phase purity of the nanomaterials formed. The morphology of the thin films obtained via AACVD depended largely on the deposition temperature, whereas for the nanoparticles, temperature and the capping group had a significant impact.
Preparation of Iron Sulfide Nanomaterials from Iron (II) Thiosemicarbazone Complexes and Their Application in Photodegradation of Methylene Blue
(Journal of Inorganic and Organometallic Polymers and Materials, 2018-05) Suroshe, Jagruti S; Mlowe, Sixberth; Garje, Shivram S; Revaprasadu, Neerish
Iron sulfide nanomaterials were prepared by the solvothermal decomposition of two single source precursors i.e. [FeCl2(cinnamtscz)2] (1) (cinnamtscz = cinnamaldehyde thiosemicarbazone) and [FeCl2(benztscz)2] (2) (benztscz = benzaldehyde thiosemicarbazone) at different temperatures of 230 and 300 °C in the presence of oleylamine. Powder X-ray diffractometry shows the formation of the pyrrhotite phase at both reaction temperatures. The solvothermal decomposition of [FeCl2(cinnamtscz)2] and [FeCl2(benztscz)2] at 230 °C produced iron sulfide nanoparticles in the form of spheres. When the temperature was increased to 300 °C, particles in the form of hexagons and nanorods were obtained. Furthermore, the photocatalytic activities of all the four iron sulfide nanomaterials were tested for the degradation of methylene blue under visible light irradiation. Amongst all the materials, nanospheres of iron sulfide obtained by the solvothermal decomposition of [FeCl2(benztscz)2] at 230 °C showed the highest photocatalytic efficiency (88.40%).
Progress in Green Solvents for the Stabilisation of Nanomaterials: Imidazolium Based Ionic Liquids
(IntechOpen., 2018) Tshemese, Zikhona; Masikane, Siphamandla C; Mlowe, Sixberth; Revaprasadu, Neerish
For over a decade, ionic liquids (ILs) have attracted enormous attention from scientists across the globe. The history of these compounds traces back to 1914 where the inception of the first IL with a melting point of 12°C was made. Years later, a progression of the remarkable related compounds have been discovered. Out of many analogous compounds realized from time to time, the imidazolium class of ionic liquid is the most studied because of their air and moisture stability. The physicochemical properties of ILs differ significantly depending on the anionic/cationic species and alkyl chain length. ILs have found application in many scientific fields the most recent being good solvents and stabilizing agents in the nanomaterial synthesis. Studies have showed that ILs not only stabilize as synthesized nanomaterials but also provide environmentally green routes towards nanomaterials engineering.
Synthesis and characterization of PbS nanoparticles in an ionic liquid using single and dual source precursors
(Materials Science and Engineering: B, 2018) Tshemese, Zikhona; Khan, Malik D; Mlowe, Sixberth; Revaprasadu, Neerish
We report a green route for the synthesis of PbS nanoparticles in an imidazolium based ionic liquid (IL) (1-ethyl-3-methylimidazolium methanesulfonate) using single source and dual source precursor methods. Lead ethyl xanthogenate complex was used as single source molecular precursor for the synthesis of PbS nanoparticles, whereas in dual source approach organic sulfur (1-dodecanethiol) and inorganic sulfur (sodium sulfide) sources were used to observe the suitability of different sulfur sources on formation of PbS nanoparticles. The results showed that the temperature has an effect on the as prepared nanoparticles for both routes. X-ray diffraction (XRD) studies confirmed formation of cubic phase of PbS from both routes. Electron microscopy techniques showed that the nanoparticle morphologies differed significantly depending on the synthetic factors such as temperature, nature of precursors and ranged from spherical to cubic shapes.
Tailoring Shape and Crystallographic Phase of Copper Sulfide Nanostructures Using Novel Thiourea Complexes as Single Source Precursors
(Journal of Inorganic and Organometallic Polymers and Materials, 2019-05) Ketchemen, Kevin IY; Khan, Malik D; Mlowe, Sixberth; Nyamen, Linda D; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, Neerish
Copper sulfide thin films and nanoparticles have been prepared via aerosol assisted chemical vapour deposition and solvothermal hot injection routes, respectively. Both routes employed heterocyclic amine based benzoylthioureato-copper(II) complexes as single source precursors. Copper sulfide thin films of diverse morphologies ranging from cubic to snowy or irregular crystallites depending on the deposition temperature were observed. Powder X-ray diffraction studies of the as deposited thin films have indicated the formation of hexagonal and cubic phases of copper sulfide. In the case of the nanoparticles, Roxbyite (Cu1.75S) phase was obtained in dodecanethiol at temperatures of 150, 190 and 230 °C. However, a preferred growth of nanoparticles was observed in the presence of oleylamine whereas the roxbyite phase was obtained at temperatures of 150, 200 and 250 °C. Also transmission electron microscopy showed the formation of close to spherical, hexagonal nano-disk and rod shaped nanoparticles.
A ten year review of the sickle cell program in Muhimbili National Hospital, Tanzania
(BMC Hematology, 2018) Makani, Julie; Tluway, Furahini; Makubi, Abel; Soka, Deogratius; Nkya, Siana; Sangeda, Raphael; Mgaya, Josephine; Rwezaula, Stella; Kirkham, Fenella J; Kindole, Christina; Osati, Elisha; Meda, Elineema; Snow, Robert W; Newton, Charles R; Roberts, David; Aboud, Muhsin; Thein, Swee L; Cox, Sharon E.; Luzzatto, Lucio; Mmbando, Bruno P
Background:Africa has the highest burden of Sickle cell disease (SCD) but there are few large, systematic studiesproviding reliable descriptions of the disease spectrum. Tanzania, with 11,000 SCD births annually, established theMuhimbili Sickle Cell program aiming to improve understanding of SCD in Africa. We report the profile of SCD seenin the first 10 years at Muhimbili National Hospital (MNH).Methods:Individuals seen at MNH known or suspected to have SCD were enrolled at clinic and laboratory testingfor SCD, haematological and biochemical analyses done. Ethnicity was self-reported. Clinical and laboratory featuresof SCD were documented. Comparison was made with non-SCD population as well as within 3 different agegroups (< 5, 5–17 and≥18 years) within the SCD population.Results:From 2004 to 2013, 6397 individuals, 3751 (58.6%) SCD patients, were enrolled, the majority (47.4%) in agegroup 5–17 years. There was variation in the geographical distribution of SCD. Individuals with SCD compared tonon-SCD, had significantly lower blood pressure and peripheral oxygen saturation (SpO2). SCD patients had higherprevalence of severe anemia, jaundice and desaturation (SpO2< 95%) as well as higher levels of reticulocytes, whiteblood cells, platelets and fetal hemoglobin. The main causes of hospitalization for SCD within a 12-month periodpreceding enrolment were pain (adults), and fever and severe anemia (children). When clinical and laboratoryfeatures were compared in SCD within 3 age groups, there was a progressive decrease in the prevalence of splenicenlargement and an increase in prevalence of jaundice. Furthermore, there were significant differences withmonotonic trends across age groups in SpO2, hematological and biochemical parameters.Conclusion:This report confirms that the wide spectrum of clinical expression of SCD observed elsewhere is alsopresent in Tanzania, with non-uniform geographical distribution across the country. Age-specific analysis is consistentwith different disease-patterns across the lifespan.
Thermolytic synthesis of cobalt and cobalt sulfide nanoparticles using Cobalt(II) NO Schiff base complexes as single molecular precursors
(Turkish Journal of Chemistry, 2018) Khoza, Sandile H; Masikane, Siphamandla C; Mlowe, Sixberth; Ezekiel, Itegbeyogene P; Moyo, Thomas; Revaprasadu, Neerish
Two novel N^O-type Schiff base ligands and the corresponding Co(II) complexes are reported. Thermo-gravimetric analysis indicated that the complexes are potential molecular precursors for the fabrication of cobalt andcobalt-containing nanomaterials. The significant difference in the thermal decomposition profiles is recognized as aninfluence of structural differences on the complexes. Thus, the complexes were thermally decomposed using the melt andhot injection methods to examine the properties of the obtained cobalt and cobalt sulfide nanoparticles, respectively.The reaction parameters employed during the fabrication processes, in addition to structural differences, influencedthe morphological and crystallographic phases and magnetic properties of the synthesized nanoparticles. We have in-vestigated the morphological properties and the crystallographic phase compositions of the nanoparticles by variouselectron microscopy and diffraction techniques, as well as energy-dispersive X-ray spectroscopy. The melt reactionsproduced phase-pure cobalt nanoparticles, which exhibit ferromagnetic behavior. The hot injection method utilized 1-dodecanethiol (DDT) as both sulfur source and capping agent. We indexed the DDT-capped cobalt sulfide nanoparticlesto cubic Co9S8and Co3S4phases using powder X-ray diffraction, high-resolution transmission electron microscopyimaging, and selected area electron diffraction. The crystallite sizes for Co9S8and Co3S4nanoparticles, based on theScherrer equation, were 12.4 nm and 14.1 nm, respectively. We find significant differences in the magnetic properties,attributed to nonmagnetic inclusions and vacancies due to the presence of S atoms.

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