DSpace Angular :: Browsing by Author "Revaprasadu, N."

Browsing by Author "Revaprasadu, N."

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Analysis of the effects of Gold nanoparticles on the functional integrity of select serum proteins and heat shock proteins of mammalian origin
(2012) Luthuli, Duncan Sifiso; Shonhai, A.; Revaprasadu, N.
Gold nanoparticles (AuNPs) are a natural starting point for understanding nanoparticle-protein interaction due to their possible applications in biomedical functions, such as disease diagnosis and drug delivery. This has driven interest to understand the effects of AuNPs on the functional and structural integrity of heat shock proteins (Hsp) and serum proteins. When AuNPs are used for medical purposes through the intravenous route, they may be modified by serum proteins and these modifications may give rise to pathologies, or alter the intended purpose of the nanoparticle. Furthermore, Hsp are ubiquitous proteins that occur in cells and are upregulated under stress. It is envisaged that Hsp may also interact with AuNPs delivered to cells and/or the blood circulatory system. In this study, I sought to analyse the interaction between AuNPs and bovine serum albumin (BSA), citrate synthase (CS), malate dehydrogenase (MDH) as well as human heat shock protein 70 (Hhsp70). AuNPs were synthesised by a citrate reduction method in the presence of cysteine as the capping agent, and analysed using UV/visible spectroscopy and transmission electron microscopy (TEM). The effects of AuNPs on the stability of BSA, MDH, Hhsp70 and CS to heat stress were assessed spectroscopically, both in the presence and absence of AuNPs. I further investigated the effects of AuNPs on the function of Hhsp70 in suppressing the aggregation of MDH. Data observed in this study suggested that, the interaction between AuNPs and proteins (BSA and Hhsp70) may be facilitated by sulfhydryl (SH) groups present in them. It was also observed that AuNPs have capabilities of suppressing heat induced aggregation of MDH and CS. Thus AuNPs have chaperone activity as they are capable of maintaining proteins in their soluble, functional forms during heat stress.
Cadmium and lead thiosemicarbazide complexes : precursors for the synthesis of CdS nanorods and PbS nanoparticles
(2005) Mlondo, Sibusiso Nkosikhona; Revaprasadu, N.
This work reports the shape controlled synthesis of metal sulfide nanomaterials with varying morphologies using single source precursors based on the thiosemicarbazide ligand. The single crystal X-ray structures of [Cd(NH2CSNHNH2)CI2]n, [Cd(NH2CSNHNH2)2Cl2]n and [Pb(NH2CSNHNH2 )(N03)2] precursor complexes are reported and discussed. The non crystalline analogue of the cadmium complexes, [Cd(NH2CSNHNH2)2Cl2] was also synthesized and principally used to determine the effect of the precursor concentration and the growth temperature on the growth and final morphology of the CdS nanoparticles. The precursors were thermolysed in a hot co-ordinating solvent such as hexadecylamine (HDA) for CdS and tri-w-octylphosphine (TOPO) for PbS, using the "one-pot" single-molecule precursor route. The shape was found to move from short rods and dots to long rods at higher temperatures, where the growth is not easy to control. By contrast, at moderate temperatures the shape evolution was the opposite with the precursor concentration being the variation, as we moved from higher to lower concentrations. On the temperature variable's front, higher temperatures were found to favour the formation of shorter rods and dots whereas lower temperatures favour longer rods. By varying the important parameters such as precursor concentration and reaction temperature, various nanomaterials with a range of morphologies and sizes could be prepared. The effect of the nature of the precursor was also varied by synthesising nanoparticles from different crystalline complexes of the same metal (cadmium) and ligand (thiosemicarbazide) as precursors, which were found to give the nanoparticles of different crystallinity and aspect ratios. [Pb(NH2CSNHNH2 )(N03)2] was also used to synthesize PbS nanoparticles, in which determination shape control could not in be achieved. UV/Vis and photoluminescence spectra were used to study the materials optical properties of the material. The structural properties of the materials were studied by X-ray diffraction and TEM instruments.
Deposition of CoxSy, NixSy MnS and CdS thin films from their alkylthiourea precursors using the Aerosol Assisted Chemical Vapour Desposition (AACVD) technique
(2008) Mgabi, Londiwe Patience; Revaprasadu, N.; Moloto, J.
Various complexes of Co (II), Ni (II), Mn (II) and Cd (II) thiourea and alkylthiourea have been successfully synthesized, using the 1:2 mole ratio metal salts of (NiCl^ C0CI2, MnCfe and CdCh) with their respective ligands. These complexes were characterized using melting points and elemental analysis to distinguish their monomelic character and confirm the purity of the complexes. Single X-ray crystal structures of [NiCl2(SC (NHC6Hn)2]2 and [MnCl2(CS(NH2)2)4] were obtained. Thermogravimetric studies on each complex were conducted to elucidate their volatility, for the deposition of thin films. Their decomposition patterns were found to yield predominantly a 2-stage TGA profiles with the resultant leading to the formation of the respective metal sulfide. Thin films were successfully deposited via the single source precursor method on glass and GaAs substrates by the Aerosol Assisted Chemical Vapour Deposition (AACVD) technique. Their lower volatility nature yielded less uniform deposition of thin films such that the substrate was changed as well the suspension of the substrate on the stubs with improved uniformity of the thin film. The respective metal chalcogenide thin films deposited were characterized by X-ray Diffraction (XRD) for their crystallinity, Scanning Electron Microscopy (SEM) for their morphological properties, Ultraviolet (UV) - Visible (Vis) spectra for their optical properties and Energy Dispersive X-ray (EDAX) for the composition of the films. Thin film measurement was performed using the Interferometer method. The X-ray diffraction pattern revealed different phases for the metal chalcogenide film, stoichiometric cobalt sulfide exhibited a mixture of cubic linnaeite C03S4 and cattierite C0S2, stoichiometric NiS, NiS2 (pyrite), |3- NiS (millerite), Ni3.xS2 and NiSi.97, Manganese sulfide revealed the presence of the a - alabandite phase and CdS showed the mixture of hexagonal and orthorhombic (300-350 C) and cubic phase at (400-450 C) respectively. Their morphological properties demonstrated the presence of mostly granulated spheres for the stoichiometric CoS, star-fish like rods for stoichiometric NiS, polycrystalline growth for the MnS films and mostly cubic and spore-like rods for CdS. Their absorption spectra revealed blue-shifted spectra with a mostly a higher optical band gap energy relative to that of bulk for all the metal chalcogenides. Thickness measurements showed that most thin films were deposited uniformly with minor contours and showed optimum adherence to the substrates.
Developing a low-cost ceramic micro-porous water filter for removal of microorganisms that cause common diseases
(University of Zululand, 2012) Simonis, Jean Jacques; Kelbe, B.E.; Revaprasadu, N.; Basson, A.K.
Africa is one of the most water-scarce continents on earth and the lack of potable water is responsible for the death of approximately 4 900 children every day. Water can be effectively decontaminated by using a household ceramic water filter. The local production of low-cost water filters suitable for the removal of suspended material and pathogenic bacteria from water sources, especially in rural areas, provides a promising solution to the problem and is therefore important to pursue. The traditional slip casting process was used develop a micro-porous ceramic water filter. The method was found to be more suitable than either extrusion or die casting for manufacturing a locally suitable, low cost ceramic water filter. Slip casting, requiring limited expensive equipment, usage of locally available raw materials, labour and expertise makes this the only promising method for manufacturing ceramic filters in a rural, non-technical setting. Using milled lithium alumino-silicate had the main advantages of thermal shock resistance and dimensional stability because of the material’s zero thermal expansion at firing temperatures. Milling tests based on the Andreasen packing model were used for obtaining the best particle packing for the raw material recipe. The material also provides dilatant rheology matching the rheology of the organic carbon poreformer. The candle- type filter required less raw material compared to the other low cost filter such as the pot- type filter from (PfP). The particle size of the pore-former provided us with small pores around 3 microns after firing for the elimination of bacteria from drinking water. These pores were much smaller and more effective when compared with Potters for Peace (PfP’s) pore size of 16-25 micron. The zero thermal expansion (adopted ZTE product name) helped to prevent damage (cracking) to the product during heating and gave accurate control of the ultimate filter size after sintering. The large apparent porosity results of between 67-73 per cent for the finished product provide a specific surface area of 7 m2 g-1 and a high flow rate which explains the filtration efficiency of the filter. The 32 minute retention time of water further helps with the filtration effectiveness. Bacteriological testing exceeded all expectations. The product was tested using water contaminated with high concentrations of selected bacterial cultures as well as with water from local polluted streams. -i v - The product complies with the WHO (2011) recommendation requirement for household water treatment (HWT) technologies of a LRV ≥ 4 (log reduction value). With correct cleaning and basic maintenance, this filter can effectively provide clean drinking water for rural families affected by polluted surface water sources. This product can immediately be useful to families placed in situations where polluted drinking water causes distress. The filter could provide a low-cost solution for the millions of people without access to potable water in Africa. Furthermore, such a project provides opportunities for local financing and innovation. The method of slip casting for the manufacture of porous ceramic used in this study has been showed to work very successfully. The filter requires fewer raw materials, energy for the shaping- and firing- process, finishing, storage space, it is small, compact, and more effective against bacterial load and has a flow rate 3-4 times faster than any other low cost manufactured filter. The low unit manufacturing cost, places Outbac in a strong position, to also compete on a price-only-basis with other low cost, ceramic filter producers in the world.
Evaluation of the effects of gold nanoparticles (AuNPs) on protein folding in Escherichia coli
(University of Zululand, 2014) Makumire, Stanley; Shonhai, A.; Revaprasadu, N.
Gold nanoparticles have shown promising applications, more especially in the biomedical industry. This has seen major improvements in disease diagnostics, therapeutics, imaging and treatment. All this is owed to the unique physicochemical properties possessed by the AuNPs. More studies continue to be carried out on AuNPs as the uses of these nanometer-sized particles are limitless. Water soluble citrate capped gold nanoparticles were synthesized through a slightly modified citrate method. In order to determine size, shape, dispersion and the crystalline nature of the AuNPs, characterization was done using Transmission electron microscopy (TEM) and High resolution transmission electron microscopy (HRTEM). The AuNPs were used to ascertain bacterial-nanoparticle interactions, their effect on E.coli growth as well as the effect on the solubility of E.coli proteins. The in vitro effects on DNA and protein integrity was also determined. The bacteria work was done by exposing E.coli to AuNPs. Imaging was done through TEM and bacterial growth monitored by measuring optical density at hourly intervals. AuNPs were assimilated by the bacterial cells with minimal effects on cellular integrity in DnaK- cells. DnaK + cells exhibited containment of AuNPs in the cytosol. AuNPs also inhibited E.coli growth marginally and had no observable effect on the solubility of E.coli proteins at the concentrations tested (25-75 μg/mL) in DnaK+ cells. MDH and MDH in the presence of PfHsp70 were exposed to AuNPs. The AuNPs effect was ascertained by SDS-PAGE. Citrate AuNPs managed to suppress MDH aggregation at low concentrations (2.5-25 μg/mL). At all the concentrations used, the citrate AuNPs complemented the ability of PfHsp70 in suppressing MDH aggregation. The stability of DNA exposed to AuNPs was confirmed by agarose gel electrophoresis and transformations into E.coli XL1 blue cells. DNA damage was observed at concentrations (25-100 μg/mL) after exposure for forty-eight (48) hours and for damaged DNA preparations no or fewer colony forming units were observed on agar plates. These findings show that citrate AuNPs are less cytotoxic and iii can maintain proteins in soluble form. Although their effect on protein solubility is valuable, citrate AuNPs impact on protein function and are damaging to DNA. Further studies need to be carried out in order to fine tune the physicochemical properties of these particles as a way of improving the biosafety of the AuNPs.
Extraction of cellulose from SCB and its applications in CNC/metal nanocomposites
(University of Zululand, 2018) Mzimela, Zimele N.T.; Revaprasadu, N.; Motaung, T.E.
The past few years have seen an increased interest in enforcing the principles of green chemistry in the scientific community. The aim of these principles is to reduce chemical related impacts on human health and virtually eliminate contamination of the environment through dedicated and sustainable prevention programs. In the present study, of the many (12) green chemistry principles, we have put into implementation waste prevention, the use of safer solvents and/ or auxiliaries in syntheses, and the use of less hazardous chemicals in syntheses by undertaking a project that makes use of sugarcane bagasse, which is an agricultural waste material obtained when sugarcane is crushed to extract its juices during the production of sugar. From bagasse, cellulose was extracted through five different methods. Through acid hydrolysis, cellulose nanocrystals were synthesised from the extracted cellulose and in turn used as a template, reducing- and stabilizing agent in the synthesis of cellulose nanocrystal/metal (silver and gold) nanocomposites. The fifth cellulose-extraction method yielded the most thermally stable and pure cellulose. This was shown by TGA and XRD analyses. As a result, the cellulose extracted through the fifth method was used to synthesize cellulose nanocrystals, which were then successfully used as a stabilizing and reducing agent in the formation of CNC/metal nanocomposites, as evident from FTIR, TGA, XRD, UV and TEM analyses.
A facile hybrid method to synthesize metal and metal chalcogenide nanoparticles using various capping groups
(2014) Mntungwa, Nhlakanipho; Revaprasadu, N.; Pullabhotla, V.S.R. Rajasekhar
The synthesis of bismuth (Bi), antimony (Sb) and tin (Sn) metal and metal chalcogenide nanoparticles is presented using a novel hybrid solution based high temperature method. Furthermore is the synthesis of zinc telluride (ZnTe) and cadmium telluride (CdTe) nanostructured materials also described. The nanomaterials are predominantly capped by organic ligands. The use of water soluble ligands such as triethanolamine (TEA) and cysteine is also reported. The synthetic method involves the reduction of a metal salt followed by the introduction of the chalcogenide source in the case of metal chalcogenide nanoparticle synthesis. The metal or metal chalcogenide prepared is thermolysed into a high boiling point ligand at high temperature. For the water soluble nanoparticles after reduction there is a simultaneous addition of a chalcogenide source and a ligand at room temperature. The Bi and Sb nanoparticles showed similar spherical morphology when capped with tri-noctylphosphine oxide (TOPO). Bismuth particles in the form of dots, branched nanorods and self assembled cubes were obtained at different reaction conditions. The cubed shaped Bi and Sb nanoparticles which appear to self-assemble were obtained when using oleylamine (OA) as a capping group. The Bi2S3, Bi2Se3 and Bi2Te3 nanoparticles were elongated when capped using alkylamines such as hexadecylamine (HDA) and OA, however at low temperature of 90oC they appeared to be close to spherical. The antimony chalcogenides, Sb2S3, Sb2Se3 and Sb2Te3 gave a similar rod shape morphology. The Sn nanoparticles appeared aggregated to some extent. A triangular shaped morphology is observed for the OA capped SnS nanoparticles. HDA capped ZnTe nanoparticles were synthesized using NaHTe and ZnCl2 as the tellurium and zinc sources respectively. The particles synthesized at reaction temperatures of 230 oC and 270 oC were spherical in shape. The blue shift in the absorption spectra confirms that the particles undergo quantum confinement. The photoluminescence studies show that the particles emit at a wavelengths close to their band edge. The water soluble cysteine and TEA capped ZnTe particles appear as nanorods which are aggregated. Finally water soluble CdTe nanoparticles were synthesized using TEA and cysteine as capping groups. The results showed that both cysteine and TEA are effective capping groups for water soluble CdTe nanoparticles. The optical properties of the particles synthesized in both capping groups revealed absorption features due to the Cd-ligand complex. The photoluminescence spectra showed reasonably narrow emission peaks. The cadmium salt was varied to study its effect on the morphology of the CdTe nanoparticles. The nitrate source gave well defined, crystalline, close to spherical nanoparticles. The FT-IR measurements confirmed the presence of the capping ligand on the surface of CdTe nanoparticles.
An in vitro assessment of the potential toxicity of Cadmium Selenide nanoparticles
(2012) Dunpall, Rekha; Shonhai, A.; Opoku, A.R.; Revaprasadu, N.
Nanotechnology is steadily finding its application in all aspects of the consumer industry, science and engineering. At a relative pace Cadmium Selenide (CdSe) nanoparticles are gaining increased attention for their potential use in biomedical applications such as bioimaging of tissues, disease diagnosis and biological labelling due to its unique optical and electronic properties. Exposure of these particles to humans and other biological systems raise huge concerns with regards to their safety. In this study, water soluble cysteine capped CdSe nanocrystals, were prepared through a one pot green route method. The prepared CdSe nanocrystals were characterized using Transmission electron microscopy (TEM), High resolution transmission electron microscopy (HRTEM), Ultra violet spectroscopy (UV) and Photoluminescence (PL) analysis to establish the size, shape, dispersion, aggregation state, crystalline nature and optical properties of CdSe nanoparticles. The in vitro effects of CdSe nanoparticles on DNA stability, red blood cells (RBC’s) and blood platelets were evaluated. DNA was exposed to CdSe nanoparticles and its assessment on DNA stability was confirmed by agarose gel electrophoresis and spectrophotometry. Damage to DNA structure was observed at 200 μg/ml of CdSe. In vitro assays carried out on RBC damage included reducing power and chelating activity of iron. The results showed that the CdSe nanocrystals exhibited high reducing power and sufficient chelating activity, which would be able to impair the function of haemoglobin. CdSe nanoparticles promoted platelet aggregation in a dose dependent manner. Based on the findings of this study the biosafety of CdSe nanoparticles is not guaranteed and further studies need to be conducted to ascertain the safety of CdSe nanoparticles for possible use in biological systems.
N,N'-diisopropylthiourea and N,N'-dicyclohexylthiourea zinc(II) complexes as precursors for the synthesis of ZnS nanoparticles
(Academy of Science of South Africa, 2009) Moloto, N.; Revaprasadu, N.; Moloto, M.J.; O'Brien, P.
The single X-ray crystal structures of zinc (II) complexes of N,N'-diisopropylthiourea and N,N'-dicyclohexylthiourea were determined. These complexes, similar to other alkylthioureas, were found to be effective as precursors for the preparation of hexadecylamine-capped ZnS nanoparticles. The complexes are air-stable, easy to prepare and inexpensive. They pyrolyse cleanly to give high-quality ZnS nanoparticles, which show quantum confinement effects in their absorption spectra and close to band-edge emission. Their broad diffraction patterns are typical of nanosized particles while their transmission electron microscopy images showed agglomerates of needle-like platelet nanoparticles.
A new approach to the synthesis of selenium based nanoparticles
(2008) Oluwafemi, Samuel Oluwatobi; Revaprasadu, N.
We report the synthesis of high quality aqueous and organically soluble selenide nanoparticles by a novel greener, quick, facile, environmentally-benign and effective non-organometallic solution-based method. Briefly, the method involves the reduction of selenium powder to produce selenide ions which act as the selenide source, followed by the addition of MCI2 (M = Cd or Zn) or Zn(CH3COO)2. The nanoparticles were passivated with organic surfactants such as hexadecylamine (HDA) and tri-octylphosphine oxide (TOPO), for their solubility and stability in organic solvents, while passivation with biomolecules such as L-cysteine ethyl ester hydrochloride, methionine, ascorbic acid, starch, polyvinyl alcohol (PVA) and poly (vinylpyrroiidone) (PVP), rendered them water-soluble and aJso acted as an agent of stabilisation and facilitate conjugation with biomolecules. CdSe/ZnSe nano-composite and core-shell nanoparticles were also synthesised, using this new synthetic approach. The high quality of the as-synthesised nanoparticles was confirmed using absorption and photoluminescence spectroscopy (PL), Fourier transform infrared spectroscopy (FT-ER), powder x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area dififractometry (SAD) and energy dispersive spectroscopy (EDS). All measurements were performed without any post-preparative size separation of the nanoparticles. The thesis is divided into six chapters. Chapter one deals with the introduction and comprehensive review on previous works done on the synthesis of nanoparticies, VIII highlighting their advantages and disadvantages. The aim and objective of the study is also stated in this chapter. In chapter two, the systematic study of the effects of the capping group, growth time, temperature, reduction time and monomer concentration on the size, optical properties and morphology of the as-synthesized TOPO and HDA-capped CdSe nanoparticles was investigated. All the as-synthesised particles are blue-shifted in relation to the bulk band-gap of CdSe. The absorption and emission maxima are shifted to higher band-gap (lower wavelengths) as the reduction time increases from 2 to 6 hrs, indicating a decrease in particle size for the HDA-capped CdSe. The particle size ranges between, 2.3-3.2 (5-30 mins) 2.4-3.0 nm (5 -30 mins) and 2.5- 2.7 nm (15-30 mins) for the reduction time of 2,4 and 6 hrs respectively. At higher temperature (200 °C), particles with different shapes, i.e dot, rod and multi armed rods are produced. The presence of the elongated particles was attributed to the phenomenon of oriented attachment (self-assembly), due to dipole-dipole interactions between the highly charged surfaces of II-VI semiconductor nanocrystals. The synthesis of TOPO and HDA-capped ZnSe nanoparticles were investigated in chapter three. Increasing the monomer concentration and temperature, led to a faster growth rate, increase in particle sizes and narrowing of the size distribution. XRD analysis show phase transitions from sphalerite cubic to wurtzite hexagonal phase, on increasing the monomer concentration. The mean average particle diameters are, 3.71 ± 0.40 run 3.26 ± 0.37 nm and 2.95 ± 0.32 nm for the reduction time of 2. 4 and 6 hrs respectively. Chapter four describes the synthesis of water-soluble CdSe and ZnSe nanoparticles. The synthesis was carried-out at elevated and room temperatures, using biomolecules and polymers as passivating agents. A systematic study of the effects of parameters such as pH, reaction time, concentration, refluxing time, reactant ratio, passivating ligand and temperature on dispersibility, size, optical properties and morphology of the nanoparticles, was also investigated. At elevated temperature, the particle size decreases while the luminescence properties improve with increasing pH. Increasing the cadmium to cysteine ratio systematically from 1:10 to 1:60 at different pH, did not have any significant effect on the luminescence intensity of the nanoparticles. In contrast to the synthesis at higher temperature, particles with very sharp excitonic shoulders, absorption edges and high luminescence with narrower size distributions, are produced at room temperature. Particles with the first absorption peak at a wavelength as low as 415 nm, with a clearly resolved higher energy electronic transition, high luminescence without trap emission and particles size as small as 1.68 nm are obtained at pH 11. The synthesis and characterisation of highly monodispersed HDA-capped CdSe-ZnSe nanocomposites and CdSe/ZnSe core/shell nanoparticles were reported in chapter five. The study of the core/shell growth at different reaction times and the effect of temperature on the optical and structural properties, was also investigated. The absorption and emission maxima of the CdSe/ZnSe core/shell nanoparticles are red-shifted in relation to the core CdSe, with a visible second absorption band at higher temperature (250 °C). The emission spectra confirmed that separate ZnSe nanoparticles are not formed in the solution. XRD analysis indicates that the diffraction is predominantly due to the CdSe core. The average particle diameter of the CdSe/ZnSe are 3.99 ± 0.16 nm (230 °C) and 4.51 ± 0.27 run at 30 mins reaction time. The absorption and emission maxima of the CdSe-ZnSe nanocomposite are blue-shifted in relation to pure CdSe, with a small particle size (2.91 ± 0.20 nm) as compared to the core CdSe (3.00 ± 0.24 nm). The XRD analysis shows a phase transition from the hexagonal phase of the pure CdSe to the cubic phase. Chapter six gives a short description of the experimental details. Without any further post preparation, the qualities of the particles formed by this new method, are comparable to that of the best CdSe and ZnSe nanocrystals reported in literature, synthesised by the high temperature conventional organometallic methods. This new synthetic route is safe, inexpensive, involve the use of non-toxic chemicals, reproducible and can be readily used for large scale synthesis. We believe the knowledge gained from this work, will enable the direct green synthesis of functionalised organic and water-soluble selenide nanoparticles for large-scale production and commercial purposes, due to the economical and environmentally-benign nature of the synthetic method.
Synthesis and catalytic evaluation of chiral ferrocenyl p^p and p^n palladium(II) complexes
(University of Zululand, 2013) Masikane, Siphamandla Cecil; Segapelo, T.V.; Revaprasadu, N.
Chapter 2 outlines initial attempts made to synthesize analogues of the P,N-type chiral ligands (η5-C5H5)Fe(η5-C5H3-PPh2)C*H(OH)(3,5-R2pz) R = H SPNa and R = Me SPNb first prepared by Togni, and the P,P-type chiral ligands (η5-C5H5)Fe(η5-C5H3-PR2)C*H(OH)(PPh2) R = Ph SPPa, R = i-Pr SPPb of the Josiphos family. In these ligands, the methyl group on the stereogenic carbon is replaced with a hydroxyl group. The preparation of SPNa and SPNb included the use of the scaffolds (η5-C5H5)Fe(η5-C5H4)(CO)(3,5-R2pz) R = H 3a and R = Me 3b which were prepared from the reaction of ferrocenoyl chloride with appropriate pyrazolyl moieties. It was unfortunately discovered that neither 3a nor 3b could be reduced to the corresponding alcohol derivatives (η5-C5H5)Fe(η5-C5H4C*H(OH)(3,5-R2pz) R = H 3-OHa and R = Me 3-OHb which were the required intermediates towards the preparation of SPNa and SPNb. The preparation of SPPa and SPPb used the scaffold (η5-C5H5)Fe(η5-C5H4)(CO)(PPh2) 4 which was prepared similarly to ligands 3a and 3b using lithium diphenylphosphine. Disappointingly, scaffold 4 was obtained in yields less than 10%. Furthermore, it could also not be reduced to the required intermediate (η5-C5H5)Fe(η5-C5H4)C*H(OH)(PPh2) 4-OH as it was the case for 3a and 3b. The alternative scaffolds (η5-C5H5)Fe(η5-C5H4-COMe) 5 and (η5-C5H5)Fe(η5-C5H4-PPh2) 7 were then synthesized. Compound 5 could be reduced to (η5-C5H5)Fe(η5-C5H4) C*H(OH)(Me) 5-OH which was subsequently used to prepare the ligand intermediates (η5-C5H5)Fe(η5-C5H4)C*H(3,5-R2pz)(Me) where R = H 6a and R = Me 6b by a substitution reaction with appropriate pyrazolyl moieties. The lithiatiation of 6b followed by the reaction with chlorodiphenylphosphine yielded the chiral ligand (η5-C5H5)Fe(η5-C5H3-PPh2)C*H(3,5-Me2pz)(Me) LPNb. Friedel-Crafts acetylation of 7 with acetyl chloride afforded a heteroannular intermediate (η5-C5H4-PPh2)Fe(η5-C5H4-COMe) 8 instead of the desired homoannular intermediate. This intermediate could be reduced to (η5-C5H4-PPh2)Fe(η5-C5H4)C*H(OH)(Me) 8-OH which was then used as a starting material in the attempts to synthesize heteroannulated analogues of the alternative P,N and P,P-type ligands proposed previously. Decomposed products were obtained when substitutions with pyrazolyl and diphenylphosphino moieties were attempted. Palladium(II) complexes of the ligands 6a, 6b and LPNb were then prepared using PdCl2(NCMe)2 as the metal precursor, while the one for 7 was prepared using PdCl2 as the metal precursor. In Chapter 3, the prepared complexes [PdCl2{(η5-C5H5)Fe(η5-C5H4)C*H(3,5-R2pz)(Me)}2] R = H CNa and R = Me CNb, [PdCl2(η5-C5H5)Fe(η5-C5H3- PPh2)C*H(3,5-Me2pz)(Me)] CPNb and [PdCl2{(η5-C5H5)Fe(η5-C5H4-PPh2)}2] CP1 were catalytically evaluated in a Suzuki-Miyaura coupling reaction of phenylboronic acid with iodobenzene to obtain biphenyl as the product. Interestingly, CNb could catalyse this reaction to give yields of at least 50% at 30 °C. However, the best yields were obtained when the temperature is doubled, using 2 M sodium hydroxide as the base in tetrahydrofuran. From the tested complexes, CNa and CP1 gave maximum conversions of over 90%, although the former achieved these conversions in half the time.
Synthesis and characterization of cadmium selenide and zinc selenide nanoparticles
(University of Zululand, 2012) Dlamini, Nkosinathi Norman; Revaprasadu, N.
An environmentally friendly synthetic route has been used to synthesize cadmium selenide and zinc selenide nanoparticles. Both aqueous and organically soluble selenide based nanoparticles have been synthesized via mild conditions. The synthesis involved the reduction of selenium powder to produce selenium ions. The complete reduction of selenium is followed by the addition of a metal source MX (M = Cd or Zn and X = Cl or CO). Biocompatible passivating agents such as cysteine or triethanolamine (TEA) induced the solubility of the nanoparticles in water, while the solubility of the nanoparticles in the organic solvents was facilitated by hexadecylamine (HDA). The evidence for the formation of the nanoparticles with a desired quality was confirmed by using different techniques such as UV-Vis absorption spectroscopy, photoluminescence spectroscopy (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (FT-IR).
The synthesis and characterization of gold nanoparticles in water-soluble polymers A
(2010) Chili, Muntuwenkosi M.; Revaprasadu, N.
Nanomaterials with critical dimensions at the nanoscale currently attract considerable attention as they show distinct chemical and physical properties that are dependent on their size and shape. A number of techniques have been used to synthesize metal nanoparticles. This thesis presents modified methods for the synthesis of gold nanoparticles, CdSe and Au-CdSe hybrid nanoparticles, capped with water soluble polymers. Chapter one reviews some basic concepts of nanostructured materials. The electronic structure and properties of gold nanoparticles are discussed. The general synthetic routes of gold nanoparticles are also reviewed with special emphasis on their preparation in water soluble polymers. A few applications of nano-gold including electronics, catalysis and biomedical applications are presented. Finally the characterization techniques used in this study are discussed. Chapter two describes the synthesis of gold nanoparticles from various chemical reduction techniques. These techniques have yielded a combination of both spherical and anisotropic shaped nanoparticles. Different reducing agents, such as sodium borohydride, presence of sodium hydroxide, ascorbic acid, sodium citrate, tri-sodium citrate and hydrogen peroxide have been used in the reduction of Au3+ ions to Au0. Water soluble polymers such as poly vinylpyrrolidone (PVP), poly vinyl alcohol (PVA) and organic ligands tri-n-octylphosphine oxide (TOPO) and octadecylamine (ODA) were used as capping agents for the gold nanoparticles. Seed-mediated and two-phase techniques were also employed to yield anisotropic nanorods of gold. Different structure-directing agents and phase-transfer agents were used in the formation of anisotropic nanoparticles. The optical properties of the gold nanoparticles were studied by UV/Vis spectroscopy. The structure and morphology of the as prepared particles was determined using powder X-ray diffraction (XRD) and electron microscopy, respectively. In Chapter three the anisotropic gold nanoparticles synthesized by a UV-irradiation technique through the interaction of HAuCl4 and a stabilizing agent, poly (vinyl pyrrolidone) (PVP) are presented. The effect of irradiation time on the size and shape of gold nanoparticles was investigated by UV-Visible spectroscopy and Transmission Electron Microscopy (TEM). The other effects that were varied include; capping agent, polymer concentration, precursor concentration, lamp wavelength, solvent, and lastly the presence of citric acid in other reactions. The absorption spectra of all samples show a broad band with the characteristic surface plasmon resonance (SPR) peak visible at around 530 nm. The presence of an additional low intensity absorption peak at a longer wavelength suggests the presence of non-spherical nanoparticles. The TEM measurements show evidence of particle shapes such as spheres, hexagons, decahedrons and truncated triangles as the reaction time was varied. Chapter four describes the synthesis of CdSe semiconductor nanoparticles at room temperature in the presence of PVP as the capping agent. Different cadmium sources were used and the mole ratios of the starting materials were varied in order to obtain monodispersed CdSe nanoparticles. L-cysteine and PVP-capped Au-CdSe hybrid nanostructures were synthesized at room temperature. The UV-Vis of these hybrid materials showed gold absorption features for the PVP-capped Au-CdSe while for cysteine capped hybrid particles very little features were observed on the spectrum. The denser spherical gold particles are distinctly visible in the TEM images. The high resolution TEM clearly showed the lattice fringes that confirm the crystallinity of the PVP capped Au-CdSe hybrid nanoparticles.
Synthesis and characterization of ruthenium and rhodium sulfide thin films and nanoparticles
(2004) Sosibo, Ndabenhle Mercury; Revaprasadu, N.; Compton, D.
The reaction of the metal salt (MClynH20) with the solution mixture of carbon disulfide (CS2), dialkylamine (R2NH) and sodium hydroxide (NaOH) yields a dithiocarbamate complex of formulation [M(S2CNR2)n], (M = Ru and Rh; R = alkyl group; n = 2 or 3). In this work, these complexes were synthesized and characterized, using such techniques as thermogravimetric analysis (TGA), infrared (IR), nuclear magnetic resonance (NMR), mass spectroscopy (MS) and elemental analysis. The complexes were then used as single-source molecular precursors for the synthesis of metal chalcogenide thin films and nanoparticles. The deposition of RI12S3 and RuS2 thin films was achieved by the decomposition of [Rh(S2CNEt2)2] and [Ru(S2CNEt2)3] dissolved in toluene using aerosol assisted chemical vapour deposition (AACVD) technique. The precursors gave good yields of high quality materials and pyrolyze cleanly to give the required films at reasonably high growth rates. Shiny, adherent thin films were deposited on glass substrates at 350-450 °C. The thin films were characterized using X-ray diffraction (XRD), UV-Vis absorption, ellipsometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Metal chalcogenide nanoparticles were also synthesized using complexes [Ru(S2CNEt2)3] and [Rh(S2CNEt2}2] as single source molecular precursors. Both TOPO and HDA were used as capping agents for the nanoparticles. Materials of sizes up to 20 run were synthesized from the precursors. Characterization of the nanoparticles was done using UV-Vis absorption spectroscopy, TEM and photoluminescence (PL).
Synthesis and Cytotoxicity Studies of Gold Nanoparticle Systems
(2010) Sosibo, Ndabenhle Mercury Sosibo; Revaprasadu, N.; Tshikhudo, T.
In this work, the immobilisation of different biomolecules on thioalkylated polyethelene glycol (PEG)-capped gold monolayer protected clusters (MPCs) has been successfully conducted. This followed a series of aqueous and nonaqueous synthetic protocols carried out to synthesize gold nanoparticles and MPCs of sizes ranging between 4 – 200 nm. Hetero-bifunctional PEG ligands possessing functionalities such as carboxyl, hydroxyl, biotin and nitrilotriacetic acid (NTA) were introduced resulting in stable, biocompatible gold MPCs, templates for biomolecular functionalisation reactions. Biomolecular functionalisation strategies such as carbodiimide coupling, biotin-avidin interaction and Ni-NTA-histidine interactions following the introduction of the bivalent hexadentate Ni(II) onto the NTA matrix of the MPCs, were conducted to formulate the biomolecular hybrid systems. A range of biomolecules including the cell-penetrating TAT peptide (YGRKKRRQRRR), mitogen-activated protein kinase (MAP kinase), streptavidin and fluorescent-labelled FAM-TAT peptide were successfully immobilised on the gold MPCs. The simplicity of the synthetic approaches and the stability of the resultant biomolecular systems strengthened their potential applications in targeted drug delivery, molecular recognition tools for diagnostics and in the purification, quantification and beneficiation of tagged fusion biomolecules. The colloidal gold nanoparticles, MPCs and bioconjugates were further investigated for inherent biologic effects through a series of end-point based in vitro assays. The cytotoxicity, namely the causation of necrotic cell death was studied using the neutral red assay on CHO22 cell line. All three system types showed benign cytotoxicity properties; demonstrating minor dose-dependence decline in cell viability through necrotic cell death. Additionally, dose-dependent patterns were also observed in the apoptosis-induction effects of these gold systems on CHO22 and CD4 expressing Jurkat cell lines. Overall, this work demonstrated facile protocols of synthesis for colloidal gold nanoparticles, MPCs and bioconjugates, and subsequently through in vitro cellular interaction assays, demonstrated these systems as useful tools for application in life sciences and related fields.
Synthesis and growth dynamics study of silver nanoparticles
(2009) Mdluli, Phumlane Selby; Revaprasadu, N.
The concept of shape-controlled synthesis of metal nanoparticles is investigated by considering the growth mechanism of metal nanoparticles. This thesis is divided into four chapters, chapter one presents a general introduction about various physiochemical aspects of nanornaterials. The different characteristic properties of nanomaterials, their chemically synthesized protocols, characterization techniques, and their applications are discussed in brief. Based on these reviews, the context scope and objective of the present work are outlined. Chapter two deals with the theory of kinetically growth of nanoparticles. The basic optical properties of metal nanoparticles as well as the structural evolution of nanoparticles are also mentioned in this chapter In Chapter three the synthesis of silver nanoparticles with varying morphologies using different synthetic routes are described in detail. Silver nanowires were synthesized by an aqueous route using dimethyl formamide (DMF) as the reducing agent in the presence of poly (iV-vinylpyrrolidone) (PVP) without the addition of seeds. The products were characterized by UV-visible spectroscopy and transmission electron microscopy (TEM). This work was followed by a profound dig-out, to try and comprehend the mechanism for reduction and the kinetics of the reduction of silver nitrate to silver nanoparticles. It was established that in the alkaline medium the reduction of AgNC>3 is enhanced, which resulted to the formation of rod-like silver nanoparticles which were confirmed by TEM and UV-visible spectroscopy. Silver nanodendrites, with an elongated central backbone and distinguished branches were synthesized by die reduction of silver nitrate with formamide using polyvinyl pyrrolidone (PVP) as the surfactant. The drastic evolution of the dendritic nanostructures was due to the variation of the concentration of the reactants. At low PVP concentration isotropic silver nanoparticles are visible in the transmission electron microscopy (TEM) images. The morphological evolution is confirmed by the optical measurements. The growth mechanism for the nanodendrites is discussed in some detail. The use of single molecular precursors is a common route to synthesize nanostructured materials. There have been relatively few reports for the use of sophisticated precursors to synthesize metal nanoparticles at high temperatures. The N-(Diisoproppylthiophosphoryl) thiourea complexes of silver were synthesised using a previously reported literature method. The complexes were then used as single molecule precursors for the synthesis of hexadecylamine (HDA) and tri-octylphosphine oxide (TOPO) capped silver nanoparticles. The absorption spectra of the HDA and TOPO-capped silver nanoparticles exhibit surface plasmon resonance (SPR) absorption in 400-420 nm regions. In chapter four, the morphological evolution of silver nanoparticles prompted the development of a Density Function Theory (DFT) model to understand the adsorption of Pyrrolidinone on the surface of silver and gold nanoparticles. The interaction between PVP and the metal atoms on the surface of silver and gold nanoparticles, was studied using Surface Enhanced Raman Spectroscopy (SERS) and modeled using Density Function Theory (DFT). The SERS analysis was carried out on pyrrolidinone and N-methyl pyrrolidinone in silver and gold colloids, whereas the assignments of bands in the pyrrolidinone molecules were performed by density function theory (DFT) quantum chemical calculations.
Synthesis and shape control of functionalized cadmium telluride nanoparticles
(2010) Mntungwa, Nhlakanipho; Revaprasadu, N.
The synthesis of organically and water soluble cadmium telluride nanoparticles by a facile hybrid solution high temperature method is presented. This method involves the reaction by the addition of an aqueous suspension or solution of a cadmium salt (chloride, acetate, nitrate or carbonate) to a freshly prepared NaHTe solution. The nanoparticles were prepared by passivating with organic surfactants such as hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO) for their solubility and stability in organic solvents. To stabilize and make the nanoparticles water soluble, L-cysteine ethyl ester hydrochloride and triethanolamine were used as capping agents. The absorption and photoluminescence spectroscopy, fourier transform infrared spectroscopy, powder X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy techniques were used to confirm the quality of the as-synthesized nanoparticles. All measurements were performed without any post preparative size separation of the nanoparticles. The dissertation comprises of four chapters. The first chapter is a brief description of the properties of nanomaterials and a literature review on some of the principal routes to synthesize nanomaterials. The mechanisms of particle growth and shape control are also discussed. Finally some key applications of CdTe are described. The second chapter deals with the synthesis of HDA and TOPO-capped CdTe nanoparticles. The reaction parameters such as reaction time, reduction time of tellurium, Cd:Te ratio, reaction temperature and cadmium source were varied to investigate their influence on the optical properties and morphology of the particles. Details of the absorption features such as excitonic peaks and band edges are presented. The emission properties are also discussed. The morphology of the particles was investigated by electron microscopy and powder X-ray diffraction techniques. It was found that the cadmium source (chloride, carbonate, acetate and nitrate) had a profound effect on the final morphology of the particles. A detailed mechanism for the particle growth is presented. The synthesis of cysteine and TEA-capped CdTe nanoparticles are described in Chapter three. A systematic study of the effects of the capping group, pH, reaction time and cadmium source was carried out for the water soluble CdTe nanoparticles. The absorption and emission data for the particles are discussed in detail. The electron microscopy images confirm the nanosize and crystalline nature of the particles. In addition fourier transform infrared spectroscopy was used to confirm the capping of the particles by cysteine and TEA. All the cadmium sources were found to be successful in producing high quality water soluble CdTe particles. The final chapter four is a summary of general conclusions of the study.
Synthesis of Cadmium, Lead and Iron Sulfide Thin Films and Nanoparticles
(University of Zululand, 2016) Mlowe, Sixberth; Revaprasadu, N.
The usefulness and application of semiconductor nanomaterials continue to expand the frontier of research in bringing their benefits via technological applications. Several synthetic methods for the preparation of semiconductor nanoparticles have been established. The design and development of a simple technique that is able to fabricate very pure, high quality and tunable morphology thin films and nanoparticles is therefore important and pressing. In this research project, Cadmium Sulfide, Lead Sulfide and Iron Sulfide nanoparticles and thin films were selected and synthesized because of their unique properties and applications. The use of single source precursors for the fabrication of these nanomaterials has been used by several routes such as hot injection, chemical vapour deposition and pyrolysis methods. Therefore, in this study, the synthesis of nine (9) heterocyclic dithiocarbamate metal complexes namely; bis(piperidinedithiocarbamato)cadmium(II) (1), bis(tetrahydroquinolinedithiocarbamato)cadmium(II) (2) and the pyridine adduct of bis(piperidinedithiocarbamato)cadmium(II) (3), bis-(piperidinedithiocarbamato)lead(II) (4) and bis-(tetrahydroquinolinedithiocarbamato)lead(II) (5), tris-(piperidinedithiocarbamato)iron(III) (6) and tris-(tetrahydroquinolinedithiocarbamato)iron(III) (7), bis-(piperidinedithiocarbamato)iron(II) (8) and bis-(tetrahydroquinolinedithiocarbamato)iron(II) (9) are presented. Single crystal structures of four single source precursors (1), (3), (6) and (7) have been elucidated in this study. These complexes have been used as single-source precursors (SSPs) for the fabrication of cadmium sulfide (CdS), lead sulfide (PbS) and iron sulfide (FeS) thin films by aerosol-assisted chemical vapour deposition (AACVD) and spin coating methods for PbS. Also, nanoparticles of similar metal sulfide were made by the hot injection and pyrolysis routes. Various parameters such as temperature, solvent and time were used to ascertain their properties. The morphological, structural, optical properties and composition of the as-synthesized materials were found to depend on the reaction conditions used during the synthesis. The synthesized CdS thin films and nanoparticles were found to exhibit blue shifted optical properties, which were size and morphological dependent. Their morphologies and structural properties were investigated using different electron microscopy and diffraction techniques. Similarly, PbS thin films deposited were studied and their optical and structural properties show formation of high quality nanomaterials which are also temperature dependent. Optical properties of the deposited PbS thin films show blue shift compared to the bulk PbS. Best morphologies of PbS films deposited by spin coating method highlighted the usefulness of this route. Iron sulfide thin films deposited by AACVD method show that variation of parameters could result in the formation of high quality nanostructures. Furthermore, optically active greigite and pyrrhotite-iron sulfide nanoparticles were prepared by simply varying the temperature of the hot solvent. Pyrrhotite-Fe1-XS sensor device showed interesting performance when tested for humidity and different nitrogenous gases such NO2 and NH3. The gas sensors further revealed that stoichiometric structure of iron sulfide nanostructures have significant effect on the end-user device performance.
Synthesis of organically capped and water soluble metal sulfide semiconductor nanoparticles
(University of Zululand, 2013) Nejo, Ayorinde Olufunke; Revaprasadu, N.
Well-defined faceted shaped organically and water soluble metal sulfide nanoparticles have been successfully synthesized using a hybrid solution based high temperature colloidal route in the presence of organic surfactants as both stabilizers and crystal growth modifiers. The structure and morphology of the as-prepared metal sulfide nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV-Vis and photoluminescence spectrophotometry. By varying important parameters such as the metal precursors, reaction temperature, reaction time and organic surfactants, various nanomaterials with a range of morphologies and sizes were obtained. The morphologies of the organically soluble PbS nanoparticles was influenced by the variation in lead sources and organic surfactant. By varying the lead source HDA capped particles with morphologies ranging from close to spheres, elongated particles and perfect cubes were formed. When the capping group was changed to TOPO, predominantly rod shaped particles were obtained. The growth mechanism for the anisotropic HDA capped PbS is mostly likely due an oriented attachment mechanism. The formation of the rod shaped TOPO capped PbS is due to the impurities in TOPO. The X-ray diffraction and high resolution electron microscopy studies show that the particles are crystalline.
The synthesis, characterisation and bioapplications of Novel Gold-Zinc Telluride Core-shell Nanoparticles
(University of Zululand, 2016) Dunpall, Rekha; Revaprasadu, N.; Opoku, A.R.
There is a growing demand for the development of innovative nano-drug delivery systems that can both target and improve cancer therapies more effectively than conventional chemotherapy. Novel Au-ZnTe nanoparticles was designed to support biocompatibility features that can be utilised for drug delivery and bio-imaging applications. Au, ZnTe and Au-ZnTe nanoparticles were synthesized and analysed for optical, morphological, crystalline and surface chemistry characterisation. Subsequent to materials characterisation, Au-ZnTe nanoparticles was evaluated for its potential toxicity using in vitro and in vivo systems. The nanoparticle was surface modified through conjugation with 5-FU and human epidermal growth factor antibody to facilitate targeted anti-cancer drug delivery, followed by the in vitro drug efficacy application. The Au-ZnTe nanoparticles displayed core-shell morphology with an average particle size of 7 ± 3.74 nm. The absorption wavelength of Au-ZnTe nanoparticles was dominated by the optical properties of gold and photoluminescence analysis showed that ZnTe dominated the emission properties of Au-ZnTe nanoparticles. Crystalline analysis displayed peaks attributed to both parental materials. The biosafety and cytotoxicity of these nanoparticles was established using normal human colon, mammary epithelial and cancer cells of breast, prostate and colon origin. Moreover, under certain conditions the particles expressed cytokines in low concentrations and induced an insignificant (20%) cytotoxic response when exposed to human peripheral blood mononuclear cells. Additionally systemic circulation of Au-ZnTe particles displayed no adverse effects in the blood, liver and kidney functions of female Sprague Dawley rats. TEM, FTIR, Zeta potential and optical measurements were performed to confirm the surface conjugation and interaction of 5-FU and EGF to Au-ZnTe nanoparticles. The in vitro anti-cancer therapeutic efficacy study was performed using the MTT cytotoxicity assay on breast cancer cells. The cytotoxicity studies have shown that all components in the 5-FU-EGF-Au-ZnTe nanoparticle formulation work synergistically to attack MCF7 cancer cells displaying 24.74 % increased efficacy than 5-FU at equivalent concentrations. Furthermore receptorligand mediated uptake of nano-drug formulations was demonstrated using 5-FU-Au-ZnTe. Several attempts were made to induce and develop a tumour model using Sprague Dawley rats and BALB/c mice. The presence of an external tumour mass was unsuccessful and therefore limited the ability to demonstrate the in vivo therapeutic efficacy of 5-FU-EGf-Au-ZnTe nanoparticles. These findings however lay a foundation for future work involving the synthesis and application of biocompatible nanoparticles that can support and improve current medical technologies. This study has generated valuable new knowledge that will help scientists within the field of biotechnology, nanomedicine, biochemistry and materials chemistry, to develop and optimize strategies for more efficient therapeutic application of nanomaterials.

Browsing by Author "Revaprasadu, N."

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