Chemistry
Permanent URI for this collection
Browse
Browsing Chemistry by Author "Kolawole, G.A."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- ItemCobalt(III) complexes of a-w- diaminocarboxylic acids and chloroquine(2001) Govender, kuvasani; Kolawole, G.A.; O'Brien, P.a-w-Diaminocarboxylic acids, such as lysine and 2,3-diaminopropionic acid (2,3-DAPH), are trifunctional, and thus, when only two sites are available for coordination, an interesting question is posed as to which functional groups are utilised in chelation. A series of cobalt(III) complexes of the formulation [Co(en)2AA]2+, where en is ethylenediamine and AA represents lysine and DL-2,3-DAP, were prepared. In addition, complexes of the type [Co(AA)(AAH)Cl2] and [Co(AA)2]+, where AA is DL-2,3-DAP, have been synthesised. The compounds were characterised using elemental analysis, NMR, IR and electronic spectroscopy and mass spectrometry. The reaction of czs-[Co(en)2Cl2]Cl with lysine yielded two products notably, [Co(en)2(lys)]2+, within which lysine coordinates via the a-nitrogen and oxygen donor atoms, and [Co(en)3]3+. The reaction of c/s-[Co(en)2Cl2]Cl with DL-2,3-DAPH, however, yielded three products, viz. [Co(en)2(2,3-DAP)]2+, in which the glycinate portion of 2,3-DAP is involved in chelation, [Co(2,3-DAP)2]+ where 2,3-DAP acted as a tridentate ligand, and [Co(en)3]3+. In [Co(2,3-DAP)(2,3-DAPH)Cl2], one of the 2,3-DAP ligands coordinated via the two amino groups leaving the carboxylic acid group free whilst the second ligand coordinated via the glycinate portion leaving the terminal amino group free.
- ItemMetal(ii) schiff base complexes and the insulin-mimetic Studies on the oxovanadium(iv) complexes(2009) Nejo, Adeola Ayodeji; Kolawole, G.A.; Opoku, A.R.Sixteen symmetrical and four unsymmetrical tetradentate Schiff bases with the N2O2 chromophore were isolated in pure form and fully characterized by elemental analyses, melting point, IR and 1H NMR. The appearance of two different peaks for each of the azomethine protons and phenolic protons confirm the asymmetry nature of the unsymmetrical Schiff bases. All the Schiff bases were successfully coordinated to oxovanadium (IV) ion to form the corresponding complexes. The unsymmetrical Schiff bases were also successfully coordinated to cobalt(II), nickel(II) and copper(II) ions to form their corresponding complexes. In all thirty-two metal(II) Schiff bases complexes were isolated. These complexes were characterized by elemental analyses, melting point, IR, EPR, cyclic voltammetry, magnetic susceptibility measurements, differential scanning calorimetry and electronic spectra. The isolation of the unsymmetrical tetradentate Schiff bases and their complexes as well as some of the symmetrical tetradentate Schiff bases and their complexes are considered to be novel. The purity and composition of both the Schiff bases and the metal (II) complexes were established by elemental analyses. The comparison of the IR spectra of the Schiff-bases and their metal complexes indicated that the Schiff bases acted as tetradentate ligands. The observed shifts in the stretching frequencies of (C=N) and (C¯O) are indicative of the formation of these complexes. Further conclusive evidence of the coordination of these Schiff-bases with the metal ions was shown by the appearance of new bands due to (M¯N) and (M¯O) in the metal complexes. Most of the oxovanadium (IV) complexes exhibit a strong band in the range 959−989 cm−1, which have been assigned to (V=O) in a monomeric square pyramidal coordination environme oxovanadium (IV) complexes with trimethylene bridge, in which their (V=O) appeared at 848−860 cm.1, have been assigned polymeric structure with [V=O∙∙∙•V=O] interactions, which afforded distorted octahedral coordination geometry. The electronic spectral and magnetic susceptibility measurements were used for assigning the stereochemistry of each metal complex. Electronic spectra indicate a square-planar geometry for all the cobalt(II), nickel(II) and copper(II) complexes. This was also corroborated by the effective magnetic moment of the complexes. The electronic spectra of the oxovanadium ( IV) complexes suggest a diversity of geometries. The electronic spectra indicate a square-pyramidal geometry for the fivecoordinate species and distorted octahedral geometry for the six-coordinate species. The room temperature magnetic moments of 1.6.1.8 BM are normal for V(IV) d1 configuration. The solution EPR spectra of the oxovanadium ( IV) are consistent with square pyramidal geometry. The cyclic voltammetry of the oxovanadium ( IV) complexes revealed only one quasi-reversible wave for each complex and they all showed redox couples with peak- to peak separation values ( Ep) ranging from 74 to 83 mV, indicating a single step one electron transfer process. In vitro glucose uptake was carried out on all the oxovanadium (IV) complexes using C2C12 cell line. All the complexes tested increased glucose utilization in C2C12 cells over basal values except two of the complexes whose percentage glucose uptake was lower than the basal glucose uptake (DMSO). Eighteen of the complexes significantly increased glucose uptake when compared to the basal glucose uptake of the solvent vehicle (DMSO). Cytotoxic test carried out on all the complexes using M at both low and high concentrations. Two of the complexes showed activities comparable or greater than that of insulin. Four unsymmetrical and five symmetrical Schiff base complexes of oxovanadium(IV) have been tested in vivo for their insulin mimetic activities. An acute oral administration of the four unsymmetrical Schiff base complexes of oxovanadium (IV) elicited a progressive reduction in plasma glucose over 6 h in STZ rats. Two of the unsymmetrical Schiff base complexes of oxovanadium( IV) induced a significant reduction in plasma glucose over a 6 h period. Oral administration of the five symmetrical complexes also elicited a progressive reduction in plasma glucose over 6hrs. Two of these complexes induced a significant reduction in plasma glucose during the 6 hour period.TT assay showed that the complexes were not toxic to the cells.
- ItemPhotochemical synthesis and characterization of mono- and bi-nuclear tungsen tetracarbonyl complexes of 2,2'-biquinoline and 2,3-bis(2- pyridyl) pyrazine(2002) Musetha, Phumudzo Luvhengo; Kolawole, G.A.The mononuclear and binuclear complexes of the type [W(CO)4JL] and [{W(CO)4}2]L, where L= 2,3-bis(2-pyridyl)pyrazine(BPPX 2,2' -biquinoline^QN), 2,2,-bipyrimidine(BPY]Vf)J and 2,2'-bipyidine(BPY), have been synthesized by direct photolysis of the metal hexacarbonyl and indirect route via THF substitution. In the second method, tungsten hexacarbonyl was first irradiated in THF to yield [W(CO)sTHF| and the THF was then replaced by the desired ligand. All complexes were characterised by a combination of infrared, UV-visible, *H NMR, mass spectroscopy and elemental analysis. Infrared spectra indicate that the complexes have approximately Cz* local symmetry. The absorption spectra of the complexes show intraligand band in the UV region and a broad metal-to-ligand charge-transfer (MLCT). The latter bands are red-shifted in the binuclear complexes. For comparison purposes, the properties of free ligands have also been studied. The complexes have electronic spectra dominated by intense MLCT transition in the visible region of the spectrum.
- ItemStudies on semiconductor nanoparticles and polymer nanocomposites(2002) Nair, P. Sreekumari; Revaprasadu, N; Kolawole, G.A.Synthesis of nanometer-sized semiconductor materials using various synthetic methods has been an area of intense activity over the past decade. The emphasis has been mainly on the synthesis of semiconductor particles belonging to II-VI and III-V groups. These particles exhibit an increase in their electronic band gap with decreasing particle size, a property which is attributed to a strong quantum confinement effect. The ability to tune the physical properties of nanocrystallites makes them an important category of materials with potential use in a wide range of technological applications. This project deals with the synthesis, characterisation and investigation of the properties of semiconductor nanoparticles and semiconductor-polymer nanocomposites. The strategy for the synthesis of nanoparticles involves the use of various single-source precursors, which are thermolysed in a coordinating solvent, tri-w-octylphosphine oxide (TOPO). In the present study the focus has been mainly to prepare CdS nanoparticles using various single source precursors. Attempts have been made to correlate the precursor characteristics and the size, size distribution and morphology of the nanoparticles synthesised using these precursors. The other nanocrystallites studied in the present project include ZnS, Mn doped ZnS and Mn doped CdS. The single-source precursors used for the synthesis of CdS nanoparticles are cadmium(II) complexes of: Ethylxanthicacid; N,N' bis(thiocarbamoyl)hydrazine; N,N' -dioctyl thiourea; N,N'-diisopropyl thioureap; Thiocarbohydrazide; N,N' -dicyclohexyldithiooxamide; Thiosemicarbazide; 1 -(1 -carboxypropionyl)thiosemicarbazide; Glyoxalbis(thiosemicarbazone); 2,6-Diacetylpyridine bis(thiosemicarbazone); Zinc(H) complexes of: Ethylxanthicacid; N,N' -dioctyl thiourea; N.N; -bis(thiocarbamoyl)hydrazine The second part of the project involves the synthesis, characterisation and investigation of the properties of CdS, HgS and PbS nanoparticles in polymer matrices. Various synthetic methods have been used for the preparation of the polymer nanocomposites. The polymeric media that have been used include polyacrylamide, polystyrene and polyaniline. The structural characterisation of the composite materials confirm their nanosized nature. The thermal decomposition pattern of all precursors were studied by TGA. The optical properties of the nanoparticles and nanocomposites were investigated by UV-vis and photoluminescence (PL) spectroscopy. The structural properties were investigated by X-ray diffraction (XRD), energy dispersion analytical X-ray (EDAX), selected area electron diffraction (SAED), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR).
- ItemSynthesis and characterisation of ligand-bridged tungsten and chromium penta- and tetra-carbonyl complexes(2002) Sinuka, Ludwe; Kolawole, G.A.Ligand bridged metal carbonyl complexes of the form [5(CO)MLM(CO)5], [4(CO)MLM(CO)4] and [4(CO)ML], where M is either tungsten or chromium and L is either trans-l,2-(bis-4-pyridyl)ethylene(TBE) or 3,6-di-2-pyridyl-l,2,4,5-tetrazine (DPT) have been synthesised. They were characterised using IR, UV-Vis and NMR, MS, TLC and microanalysis. Electronic spectral studies showed that both the dinuclear, [4(CO)CrDPTCr(CO)4] and mononuclear, [4(CO)CrDPT] complexes have MLCT transitions at 900.88 nm and 652.52 nm respectively. The dinuclear MLCT is more intense and broad and is deemed to have overlapped with the d-d transitions observed in the mononuclear complex at 909.45 nm. However, intra-ligand transitions were observed at 279.97 nm, 303.53 nm and 382.75 nm for both mononuclear and dinuclear complexes. Photoluminescence spectra showed two emissions for [TBE{W(CO)5}2]; with the emission at 530 nm originating from an MLCT transition, and the one at 353 nm originating from an intra-ligand transition. For [4(CO)CrDPTCr(CO)4] and [4(CO)CrDPT], a single broad emission was observed at 523 nm and 460 nm respectively. A small peak at 400 nm in the dinuclear complex is observed and is tentatively attributed to an intra-ligand transition. A structure of distorted octahedron is proposed for pentacarbonyl/ro^-l^-(bis-4-pyridyl) emyIenetungsten.
- ItemSynthesis and characterization of N-alkylthiourea and N, N -dialkylthiourea complexes of Cu, Cd and Pb, and their use as single source precursors for the synthesis of metal sulfide nanoparticles(University of Zululand, 2005) Moloto, Makwena Justice; Revaprasadu, N.; Kolawole, G.A.A number of complexes of various thiourea derivatives with different metals have been synthesized and characterized by a combination of spectroscopic studies, elemental analysis, melting points and X-ray crystallography. Infrared and NMR spectroscopy studies reveal the interaction between a metal and the ligands, thioureas, is mainly through bonding to sulfur. A series of cadmium(II) complexes with N-alkyl/aryl and N, N'-dialkyl/aryl thioureas (RNHCSNHR'; where R = R* = CH3, CH2CH3, CeHs and /or R' = H) have been synthesized and characterized. The structures of [CdCl3(CS(NH2)(NHCH3)3]n (I) and CdCl2(CS(NH2)NHCH2CH3)2 (II), CdCl2(CS(NH2)-NHCeHs^ (III) and CdCI2(CS(NH-CH3)2)2 (IV) were determined by single crystal X-ray methods. Complex I have a six coordinate polymeric chain with a CdCl3S3 core, which together with complex III (a monomer) gave a distorted octahedral geometry. Complexes II and IV are monomers with a distorted tetrahedral geometry around the cadmium(II) ion. The lH (nuclear magnetic resonance) NMR spectra in deuterated dimethyl sulfoxide (CD3SOCD3) at room temperature reveal the broadened NH peaks in the lower field region (6.0 - 10.0 ppm) and the presence of both syn and aw/z'-isomers for the N-alkylthioureas. All the spectral data obtained is consistent with the coordination of ligands by sulphur atom to the metal ion. Lead complexes were prepared in aqueous media to give white powder in a four coordinate form. Unlike cadmium and lead, copper gave multinuclear complexes resulting from the reduction of copper (II) to copper (I) by the thiourea ligands to form specifically tetranuclear copper complexes with thiourea behaving as the bridging ligands. Thermal behavior of these complexes both in air and under inert atmosphere gave residues after decomposition, which was predominantly metal sulfides, with little impurities. The presence of the metal sulfide was established by the XRD analysis of the residue from the thermo gravimetric analysis. These alkyl substituted thiourea complexes of Cd, Pb and Cu were easy to prepare, stable in air, inexpensive, obtained in good yields and decompose at temperatures about 200 -220 °C, which is convenient to thermal decomposition of precursors in the high boiling solvents or the suitable capping agents to prepare surface capped metal sulfide nanoparticles. Some of the complexes have been used as single-source molecular precursors in the preparation of copper sulfide, cadmium sulfide and lead sulfide nanoparticles by a process driven by thermal decomposition. Good crystalline particles were obtained from thermolysis of the precursors in tri-n-octylphosphine oxide (TOPO) as a solvent and capping agent, at different temperatures. All nanoparticles, CdS, PbS and CuxSy, were prepared from alkylthiourea complexes, cleanly decomposing to give average size ranges 4 - 26 nm at reasonably lower temperatures. The small size of these particles is a consistent property with the observed blue shift in the band edge of their optical spectra. Photoluminescence spectra of most samples were broadened with a red shift in relation to the band edge indicating the broad size distribution. Some relative quantity of bulk particles of copper sulfide and lead sulfide were obtained from the large yield of the products as insoluble particles in hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO). X-ray powder diffraction (powder XRD) patterns are consistent with predominantly hexagonal phase although copper sulfide showed evidence of various stoichiometric ratios. These phases were also confirmed by the images from the transmission electron microscope (TEM), although the CdS nanoparticles showed instability due to quick agglomeration in TOPO. Their patterns were confirmed by the XRD to be predominantly hexagonal. The morphology for most of the particles were close to those of thin needle-like plates, although the collapse is more of spheres which is a preferred mode of arrangement of the CdS particles when they settle on the carbon coated copper grids. High resolution transmission electron microscope (HRTEM) revealed the lattice fringes of all different types of nanoparticles including CdS, which tend to give agglomerates, hence it was difficult to determine particle sizes from the TEM images. All solution studies viz. ultraviolet-visible spectroscopy, photoluminescence and copper-coated grid-TEM were all consistent with particles in the nano-size regime. The copper and lead complexes of these thiourea derivatives have been used to prepare PbS and CuxSy, and gave crystalline, cubic or rod-shaped nanoparticles. CdS, PbS and CuxSy nanoparticles showed quantum confinement effects with a blue shift in their absorption spectra. The materials were further characterized by HRTEM images, XRD and selected area electron diffraction (SAED) patterns.
- ItemThe use of metal complexes to deposit metal chalcogenide thin films and nanoparticles(2006) Musetha, Phumudzo Luvhengo; Revaprasadu, N.; Kolawole, G.A.This thesis consists of four chapters. The first chapter describes the properties, methods of deposition and applications of semiconductors. The second chapter focuses on the deposition of metal chalcogenides thin films from single molecular precursors of the type [M {N(EPR2)2}2], were M = Pt, Pd, Ni; E = S or Se and R = fPr or Ph. Ligands of the type R2P(E)NP(E)R2, where R = *Pr or Ph were prepared to synthesize these precursors. Single X-ray structures of fP^NfP^PSe^h] and [Pd{N(SPh2)2}2] are reported and discussed. The X-ray structure of the platinum complex shows a square-planar conformation whereas the six membered PtSe2P2N ring adopts a distorted "boat" conformation. The third chapter describes the deposition of metal sulphide thin films from [M(S2COR)2], were M = Pt, Pd, Ni, Cd, Co, Cu and R = Et or dPr. Single X-ray structures of [M(S2COR)2j M = Pt, Pd, and Ni, R = Et are reported and discussed. The NiS thin films are polycrystalline and their 0 values are in good agreement with the literature values. The phases do not seem to be affected by temperature whereas the morphology of the films changes with temperature. The morphology of the films has been found to be greatly influenced by varying the temperature. All the ligands and precursors were characterised by elemental analysis and by using spectroscopic techniques such as infrared (IR), mass spectrometry (MS), proton and carbon nuclear magnetic resonance (*H and !3C NMR). Thin films of PtSea, Pt, PdSe2, PaUSe, Pdi7Sei5, PdS, and PdS2 were deposited by aerosol assisted chemical vapour deposition (AACVD) and low pressure metal-organic vapour deposition (LP-MOCVD) using metal complexes of irninobis(dialkylphosphinato)dichalcogenide ligands. Thin films of NiS, CdS, Pt, PdS, Pdi6S7, and CogSg were deposited by AACVD using the respective metal xanthate complexes. The films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The fourth chapter focuses on the preparation of nanoparticles and nanorods from cadmium complexes. The synthesis of CdS nanoparticles and nanorods are described in detail. The synthetic route used for the synthesis of the CdS nanoparticles is the thermolysis of metal complexes, [Cd(S2CNMe2)2] and [Cd{-SC(=S)OCH(CH3)2}4], in tri-octylphosphine oxide (TOPO) and hexadecylamine (HDA). The optical properties of the nanoparticles were studied by using ultraviolet (UV)-visible and photoluminescence (PL) spectroscopy. There were blue shifts in the band gaps for all CdS samples; however, photoluminescence was very poor. The hexagonal phase of CdS was observed for all CdS samples using XRD measurements. The transmission electron microscopy (TEM) images show that the TOPO capped CdS nanoparticles have a spherical shape whereas the HDA capped particles are rod shaped. Nanoparticles of CdS were characterised by UV-vis, PL, XRD and TEM.