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Dicopper and dirhodium phosphorusbipyridyl ligand-bridged complexes : electrocatalysts for carbon dioxide reduction.Sookraj, Sadesh Harichand. January 1994 (has links)
Abstract available in pdf file.
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Chiral aldehydes in the synthesis of tetrahydrofurans.Njamela, Owen Lungile. January 1994 (has links)
Abstract available in pdf file.
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Ruthenium and silver complexes of potentially binucleating phosphoruspyridyl and phosphorusbipyridyl ligands.Parry, Campbell John. January 1994 (has links)
Abstract available in pdf file.
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Isolation and identification of novel compounds from indigenous plants.Sehlapelo, Bethuel (Tiny) Matshene. January 1993 (has links)
Abstract available in pdf file.
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Stereoselective studies in the Baylis-Hillman reaction.Manickum, Thavrin. January 1992 (has links)
Abstract available in pdf file.
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Chemical constituents of plants native to Venda.Mashimbye, Mahlori Jeffrey. January 1993 (has links)
Abstract available in pdf file.
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Heterometallic ruthenium (II)-platinum (II) complexes : a new paradigm : a kinetic, mechanistic and computational investigation into substitution behaviour.Shaira, Aishath. 17 October 2014 (has links)
Thermodynamic and kinetic analysis of the ligand substitution reactions of different
heterometallic Ru(II)-Pt(II) complexes with a series of bio-relevant thiourea nucleophiles
of different steric demands and ionic nucleophiles have been investigated as a function of
concentration and temperature using UV/visible and stopped-flow spectrophotometric
techniques. To achieve this, five different sets of complexes involving mono di and
multinuclear homo and heterometallic complexes with tridentate N-donor ligands of
different linker ligands were synthesized and characterized by various spectroscopic
methods. The substitution reactions of the chloride complexes were studied in methanol
in the presence of 0.02 M LiCf3SO3 adjusted with LiCl to prevent possible solvolysis. The
aqua complexes were studied in acidic aqueous medium at pH 2.0. All reactions were
investigated under pseudo first-order conditions. Density functional theory (DFT)
calculations were used to aid further interpretations and understandings of the
experimental results.
Substitution reactivity of heterometallic Ru(II)-Pt(II) and Co(II)-Pt(II) complexes bridged
by tetra-2-pyridyl-1,4-pyrazine (tppz) ligand was investigated for the first time. The
reactions proceeded via two steps. The pseudo first-order rate constants, kobs(1st and 2nd)
for
the substitution of the chloride ligand(s) from the Pt(II) complexes and subsequent
displacement of the linker. The dechelation step was confirmed by 1H NMR and
195Pt NMR studies. Incorporation of Ru(tppz) moiety increases the substitution reactivity
and is ascribed to the increased π-back donation from the tppz ligand which increases
the electrophilicity of the metal centre, overall charge and the global electrophilicity index
of the complex. However, when changed the second metal centre from a Ru(II) to a
Co(II), the rate of substitution decreased by a factor of four due to the weaker π-
backbonding from Co(II).
The substitution reactivity of another set of heterometallic Ru(II)-Pt(II) complexes with
a semi-rigid linker, 4’-pyridyl-2,2’:6’,2”-terpyridine (qpy) showed that replacing the cis
pyridyl group by a (tpy)Ru(qpy) moiety lowers the energy of anti-bonding LUMO (π*)
orbitals and increases the metal-metal interactions and electronic transition within the
complex whereby enhancing the reactivity of Pt(II) centre. However, when two Pt(II)
moieties are linked to a (qpy)Ru(qpy), the orthogonal geometry at the Ru(II) metal
centre prevents the extended π-electron density to flow through the three metal centres.
The kinetic results obtained were supported by pKa and 195Pt NMR studies.
Substitution reactions of the mononuclear Pt(II) complexes revealed that the
polyethylene glycoxy pendent units act as a σ-donors including the lone pair electrons on
the first oxygen atom thereby decreasing the reactivity of the parent Pt(II) terpyridine
complex. However, this σ-donation towards the terpyridine moiety was found to be
effective only up to one unit of the ethylene glycoxy pendant, beyond which the
reactivity was sterically controlled. The dinuclear Pt(II) complexes bridged by
polyehtyleneglycol ether units show that the reactivity of the complexes depend on the
Pt···Pt distance and the steric hindrance at the Pt(II) centre. The substitution reactivity
of heterometallic Ru(II)-Pt(II) complexes bridged by the same polyehtyleneglycol ether
units indicate that the presence of Ru(tpy)2 moiety influences the structural geometry of
the complex system which in turn controls the reactivity of the Pt(II) centre. This is
further driven by the entrapment effect of the nucleophile due to the V-shape geometry
adopted by the heterometallic complexes. In all cases the reactivity was also controlled by
steric and electronic effects. However, when two metal centres are bridged by a flexible
non-aromatic linker, the electronic transitions and the metal-metal interactions were
found to be minor, especially for the longer linkers.
The 1H and 195Pt NMR spectroscopic techniques were used to further understand the
observed substitution kinetics and to confirm the degradation of the bridging ligand
from the metal centre(s). In all cases, the negative activation entropies obtained support
the associative mode of substitution This investigation reveals that the length and the
nature of the bridging linker plays an important role in controlling the reactivity of the
heterometallic complexes. It is envisaged that the findings of this project would offer a
significant contribution to the pharmacological design of effective anticancer drugs. / Ph.D. University of KwaZulu-Natal, Pietermaritzburg 2013.
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Structural, physical and biological studies of gold (lll) bis(pyrrolide-imine) Schiff base macrocyclic and pseudomacrocyclic complexes : targeted chemotherapeutic agents.Akerman, Kate J. 26 June 2014 (has links)
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Competitive transport, extraction and coordination chemistry of a number of ligands with selected transition and post-transition metal ionsSheng, Xia 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The competitive transport, extraction, and coordination chemistry for a series of N-
(thio)phosphorylated (thio)amide and N-(thio)phosphorylated (thio)urea ligands were
investigated with the seven transition and post-transition metal ions Co(II), Ni(II),
Cu(II), Zn(II), Ag(I), Cd(II) and Pb(II). Three N-benzylated derivatives of 1,4,7,10-
tetraazacyclododecane (cyclen) were synthesized and a similar study carried out with
the same metal ions and the deprotonated precursors. The ligands were all potential
specific carriers (ionophores) in the organic phase. The seven metal ions had equal
concentrations in the source phase.
The experimental arrangement for the transport studies employed a set-up involving
three phases: a source phase and a receiving phase (both aqueous), separated by a
chloroform membrane (organic phase). Competitive metal ion solvent extraction
involved two phases: an aqueous phase and an organic phase. Similar conditions
were used in transport and extraction studies. The metal ion concentrations in the
aqueous phases were analyzed by atomic absorption spectroscopy (AAS).
The transport results of deprotonated N-(thio)phosphorylated (thio)amides and N-
(thio)phosphoryated (thio)ureas showed that PhC(S)NPO(OPri)2 (L1),
BrPhC(S)NPO-(OPri)2 (L11) and PriNHC(S)NPO(OPri)2 (L16) transported Ag(I) into
the receiving phase. Under these experimental conditions, L1 had the highest Ag(I)
transport efficiency, at 36.3%, while L11 only transported one metal ion, viz. Ag(I).
With NH2C(S)NP(S)(OPri)2 (L4), 94.6% of Ag(I) remained in the membrane phase.
Thus L4 appeared to have the highest formation constant with Ag(I). A small amount
of Cu(II) was also transported by L1, NH2C(S)NP(O)(OPri)2 (L9), L16 and
ButNHC(S)-NPO(OPri)2 (L20). L20 had the highest selectivity for Cu(II).
Results of competitive metal ion extraction studies revealed that most ligands
extracted up to 100% Ag(I), except L1 and morpholine substituted ligands (L7, L17) .
The formation constant of L1 effects a subtle balance between metal uptake and
metal loss into and out of the respective membrane phase. HL7 and HL17 had low
solubility in chloroform. L4 extracted the highest percentage of Cu(II) (49%).
Two neutral ligands, PhCONHPO(OPri)2 (1) and BrPhCONHPO(OPri)2 (2) were
isolated and their molecular structure determined. They had monoclinic unit cells in the space groups C2/c and P21/n, respectively. An unprecedented octanuclear
[Ag(I)(L4-S,N)]8 (3) complex was also crystallized. The extended structure showed
three different cavities alternating with two unique 16-membered rings, creating a
novel AgS2N2 cage. Two polynuclear Cu(I) chelates with deprotonated L4 and L6
(tBuNHC(S)NP(S)(OPri)2) were isolated by the same crystallization method. The
complex [Cu(I)(L4–S,S)]9 (4) consisted of a hexagonal-prismatic hexamer, which
exhibited an unusual and unprecedented supramolecular “honeycomb” packing. The
trinuclear [Cu(I)(L6–S,S)]3 (5) consisted of a 6-membered Cu3S3 ring attached to a
hydroxy tetrahydrofuran molecule.
Di-, tri- and tetra-benzyl-1,4,7,10-tetraazacyclododecane (cyclen) was synthesized,
and characterized. None of these compounds was effective in metal transport under
these experimental conditions. Nevertheless, Tetra-benzyl cyclen showed the
highest extraction efficiency for Ag(I), at 100%, and the highest selectivity for Ag(I)
extraction, compared to Cu(II).
An intermediate of dibenzyl cyclen compound dibenzylated dioxocyclen (6) was
crystallized and found a host THF molecule in the lattice. The crystal and molecular
structure confirmed the cis-configuration. The X-ray structure of the Cu(II) complex
with dibenzylated cyclen (7) was determined for the first time. It was found to have
an ideal square pyramidal coordination geometry around the central metal ion.
A serendipitous organic compound of isopropylammonium(isopropylamino)-
oxoacetate mono-hydrate (8) was crystallized. The crystal was held together by
inter-molecular hydrogen bonds, which lead to two-dimensional layers with
hydrophobic interactions.
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Material study and properties of polymers used in composite high voltage insulatorsElbuzedi, Mohamed 12 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Silicone rubber, particularly poly(dimethylsiloxane) (PDMS), has been increasingly used
in the manufacture of outdoor high voltage insulators in the recent years. PDMS offers
several advantages that make it suitable for outdoor use, such as low weight, a
hydrophobic surface, stability, and excellent performance in heavily polluted
environments. PDMS surfaces can, however, become progressively hydrophilic due to
surface oxidation caused by corona discharge, UV radiation and acid rain.
In this study, PDMS samples of controlled formulations as well as six commercial
insulator materials four PDMS based and two ethylene propylene diene monomer
(EPDM) based were exposed to various accelerated weathering conditions for various
periods of time in order to track changes in the material over time. The ageing regimes
developed and used to simulate the potential surface degradation that may occur during
in-service usage included needle corona and French corona ageing, thermal ageing, UV-B
irradiation (up to 8000 hours) and acid rain (up to 200 days).
Both the chemical and physical changes in the materials were monitored using a wide
range of analytical techniques, including: static contact angle measurements (SCA),
optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive
spectroscopy (EDS), gas chromatography (GC), gas chromatography/mass spectroscopy
(GC/MS), size-exclusion chromatography (SEC), Fourier-transform infrared photoacoustic
spectroscopy (FTIR-PAS) and slow positron beam techniques (PAS).
A low molecular weight (LMW) uncrosslinked PDMS model compound was used to
further study the chemical effects of corona exposure on PDMS materials.
PDMS showed far better performance than EPDM, in terms of resistance to the various
ageing regimes and “hydrophobicity recovery”. / AFRIKAANSE OPSOMMING: Silikoonrubber, spesifiek polidimetielsiloksaan (PDMS), is gedurende die afgelope paar
jaar toenemend gebruik in die vervaardiging van buitelughoogspanningisolators. PDMS
het baie voordele vir gebruik in elektriese isolators soos ‘n laer massa, ʼn hidrofobiese
oppervlak, stabiliteit en uitstekende werking in hoogsbesoedelde omgewings. Die
hidrofobiese oppervlakte kan egter gelydelik hidrofilies word weens oppervlakoksidasie
as gevolg van korona-ontlading, UV-bestraling en suurreën.
In hierdie studie is PDMS monsters van verskillende samestellings sowel as ses
kommersiële isolators (vier PDMS en twee etileenpropileenrubber (EPDM)) blootgestel
aan verskillende versnelde weersomstandighede vir verskillende periodes om die
veranderinge in die materiale te monitor. Die verskillende materiale is gerangskik
volgens hulle werking oor ‘n periode van tyd. Dit het ook ‘n geleentheid gebied om die
eienskappe van die verskillende samestellings te bestudeer. Die tegnieke wat ontwikkel is
om die moontlike oppervlakdegradasie te simuleer, het naald-korona, “French” korona,
UVB-bestraling (tot 8000 uur) en suurreën (tot 200 dae) ingesluit.
Beide die chemiese en die fisiese veranderinge in die materiale is gemonitor met behulp
van verskeie tegnieke soos statiese kontakhoekbepaling, optiese mikroskopie,
skandeerelektronmikroskopie, energieverspreidingsspektroskopie, gaschromatografie,
grootte-uitsluitingschromatografie, foto-akoestiese Fouriertransforminfrarooi (PASFTIR)
en stadige-positronspektroskopie (PAS). ʼn Lae molekulêre massa PDMS
modelverbinding is gebruik om die chemiese effek van korona te bestudeer.
Die PDMS materiale het baie beter vertoon teenoor die EPDM materiale in terme van
hulle herstel van hidrofobisiteit.
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