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SYNTHESES, ELECTROCHEMISTRY AND SPECTROSCOPIC STUDIES OF METALLOCENE-CONTAINING PORPHYRIN COMPLEXES WITH BIOMEDICAL APPLICATIONSShago, Rebotsamang Florence 24 May 2013 (has links)
In this study, a series of carboxylic acid functionalised pyrrole derivatives and ferrocene- and
ruthenocene-containing dipyrromethanes were synthesised. Porphyrin complexes bearing a
mono-carboxylic acid functional group in the β-position as well as ferrocene or ruthenocene in
the -5-, or -5,10-, or -5,15- meso positions have been prepared from these pyrrole derivatives.
A series of metal-free tetraphenylporphyrins containing nitro, amino or carboxylic acid
functional groups on the para position of one of the phenyl rings were synthesised from pyrrole
and a substituted benzaldehyde. In addition, a series of metal-free porphyrins containing an
electron-withdrawing CF3 group in the ortho, meta or para positions of a phenyl group in one or
two of the four meso porphyrin position as well as three or two electron-donating ferrocenyl or
ruthenocenyl group in the other meso porphyrin positions were synthesised though a modified
statistical condensation procedure of a substituted dipyrromethane and an appropriately
functionalised benzaldehyde. Copper and nickel were also inserted into the cavities of these
porphyrins. Techniques to synthesise water-soluble polymers bearing a porphyrin side chain
were also developed. All complexes were fully characterised inter alia with 1H NMR, IR and
UV/vis spectroscopic methods and by electrochemical studies.
The new porphyrins described in this study may enhance cancer therapy by synergistic effects
between the chemotherapeutically active metallocene groups and the photodynamically active
porphyrin macrocycle. The availability of water-soluble porphyrins via the water-soluble ADF quantum chemical computations were performed on peripherally and non-peripherally
substituted phthalocyanines to optimise gas phase structures and to generate theoretically
predicted UV/vis spectra. The result indicated that DFT calculations could be utilised to design a
phthalocyanine that possesses Q-band λmax values in its electronic spectra that is red-shifted
enough to render the phthalocyanine appropriate for application in photodynamic therapy of
cancer.
polymeric drug delivery systems synthesised in this study may enhance clinical administration of
these new antineoplastic drugs to patients.
Electrochemical studies revealed that all ferrocene-containing porphyrins exhibited chemically
and electrochemically reversible one-electron transfer steps for the Fc/Fc+ couple. Because of the
use of [NBu4][B(C6F5)4] as supporting electrolyte, an electrochemical reversible Rc/Rc+ couple
could be identified, rather than the usual irreversible Cp2RuII/Cp2RuIV couple. The metallocenefree
porphyrins exhibited two one-electron oxidation waves as well as two one-electron
reduction waves. The metallocene-containing porphyrins exhibited only one one-electron
oxidation wave; the second went-off scale in the potential window that CH2Cl2 as solvent allows.
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A SOLID STATE NMR AND MS CHARACTERISATION OF THE CHEMICAL COMPOSITION OF MIMOSA BARK EXTRACTSenekal, Nadine D 27 May 2013 (has links)
Mimosa (Acacia mearnsii) also known as black wattle, and quebracho (Schinopsis balansae,
Schinopsis lorentzii) are the major commercial sources of natural condensed tannins
(proanthocyanidin oligomers) used today. Mimosa bark is harvested from commercial
plantations in South Africa which, according to a survey done by the Department of Water
Affairs and Forestry for 2001, cover an area of about 107 000 hectares in South Africa.
Quebracho is extracted from the wood of natural forests in Brazil and Argentina. Mimosa
bark is extracted with water (about 50% by weight). Tara (Cæsalpinia spinosa) and Italian
chestnut (Castanea sativa) are the major commercial sources of hydrolysable tannins.
The ability of water soluble hydrolysable and condensed tannins (polyphenols) to react with
proteins, presumably via hydrogen bonds, lies at the heart of their ability to transform raw
hide into leather and their commercial application as tannin agents. It explains their
existence in nature as anti-feeding agents as it renders plants indigestible to insects and
herbivores. It also explains the use of milk in tea where the complexation of milk proteins
with tea tannins reduces astringency. The chemistry of this process however remains
uncertain. The polyphenolic nature also renders tannin extracts very susceptible to oxidation
and further polymerisation and rearrangements that render the extracts even more complex.
This is evident in the transformation of green tea (high flavan-3-ol content and low
condensed tannin content) into Indian or black tea (low flavan-3-ol content and high
condensed tannin content). The quality of red wine is to a large extent determined by the
amount and composition (which changes during ageing in a poorly understood way) of its
condensed tannin. The tannins react with protein receptors on the tongue to impart âmouth
feelâ characteristics. Wood-aged wine not only contains condensed tannins from grape skin,
but also hydrolysable tannins from the wooden barrels it is aged in.
The polyphenolic nature of the aromatic rings allows reaction with electrophiles. This forms
the basis of adhesive manufacturing, where formaldehyde is used to polymerise tannin
extracts to form adhesives. Other commercial applications of tannin extracts include the use as anti-foaming agents in oil drilling and the manufacturing of amine containing resins (via
the Mannich reaction) for water purification applications (removal of heavy metals).
The production of mimosa condensed tannin is a sustainable process as trees are harvested
every eight years. Tannins will become a more important source of feedstock nutrients, as
crude oil, which is currently used, becomes depleted. It also creates employment in rural
areas.
Higher oligomers of condensed tannins are built up by successive addition of flavan-3-ol
monomer extension units via C-4 to C-8 or C-4 to C-6 interflavanyl bonds. Higher oligomers
are impossible to purify by chromatography and other methods of analysis are required.
Acid catalysed fission of the interflavanyl bonds and trapping of the monomer intermediates
with toluene-α-thiol or floroglucinol followed by analysis of the trapped products with HPLC
is normally used to analyse condensed tannin composition. The analysis of mimosa and
quebracho tannins is however compounded by the resorcinol type A-ring in these
compounds. The absence of a 5-OH group imparts stability to the interflavanyl bond against
acid hydrolysis. The high temperatures thus required to hydrolyse the interflavanyl bond in
mimosa and quebracho tannins leads to decomposition. Mass spectrometry and 13C NMR
(nuclear magnetic resonance) spectrometry in solution have also been used with varying
degrees of success.
The analysis of hydrolysable tannins is even more complex than that of condensed tannins.
As a result, the composition of condensed and hydrolysable tannin extracts remains
uncertain, after more than 50 years of research. Of particular interest are the average chain
length of tannin extracts from different sources and the composition of the constituent
monomers.
In this thesis the potential of solid state NMR and electrospray mass spectroscopy to solve
vexing problems in tannin chemistry was investigated. Solid state NMR is particularly useful
to investigate insoluble samples, overcoming problems associated with selective extraction,
chemical modifications during extraction and sample preparation and uncertainty regarding compounds that are not extracted. Electrospray mass spectrometry complements MALDITOF
mass spectrometry in that molecules with masses below 500 Dalton are detected.
We were able to assign all the resonances in solid state NMR of hydrolysable and condensed
tannins by comparing liquid and solid state spectra of pure flavonoids and tannin extract.
This allowed us to distinguish unequivocally between condensed tannins and hydrolysable
tannins with a simple routine experiment, avoiding laborious chemical tests. A method was
developed to identify and distinguish with confidence between quebracho and mimosa
condensed tannins. This method is the only available method to identify quebracho, which is
of interest to oenology (quebracho tannins are added to wine) and could hitherto only be
identified chemically because it tests negatively for all the available tests for tannins.
We established that no insoluble higher oligomeric condensed tannins or tannins covalently
bonded to other insoluble bark components remain in spent mimosa bark (after extraction of
tannins). It promises an easy way for the wattle industry to investigate lower extraction
temperatures and extraction time and the associated energy savings. A fingerprinting method
for mimosa was developed and is already used by the industry (Annex A).
As the gum resonances do not overlap with the tannin resonances, the bark can be analysed
directly without the requirement of manufacturing an extract. The only sample preparation
required is to grind the bark (about 100mg) finely and pack the solid state NMR rotor. As
carbon is magnetised via hydrogen, less than 30 minutes NMR time is required per sample.
This provides an easy way to identify the bark of quebracho, mimosa and hydrolysable
tannins. A solid state NMR spectrum of the spent bark not only indicated that no condensed
tannins remain, but also supports the conclusion that spent bark consists of water insoluble
gums (polymers of glucose and other sugars). We believe that this method will find
application in identifying novel sources of tannins from indigenous plants.
We expanded our investigation into tanned leather and developed an easy method to
determine whether leather was tanned with mimosa, quebracho, Italian chestnut, tara, synthetic tanning material, chromium or aluminium. We believe this method can be used by
the leather industry to determine tannin loading of tanned leathers.
By combining our electrospray mass spectrometry data with published MALDI-TOF mass
spectrometry data we could calculate the relative composition of monomers, dimers, trimers,
tetramers etc. in condensed tannin sample. These calculations were used by the mimosa and
quebracho tannin industry to comply with new European Union (EU) REACH (Registration,
Evaluation, Authorisation and Restriction of Chemical substances) legislation. Without
compliance mimosa extract cannot be exported to the EU.
Sulfitation (treating mimosa and particularly quebracho extract with bisulfite) is routinely
used in industry to enhance the extractâs properties (e.g. increase water solubility) and
products with different levels of sulfitation are commercially available. The chemical
changes associated with sulfitation remain speculation. The solid state NMR indicated that
the C-ring is opened during the process. The electrospray MS conclusively demonstrated the
existence of condensed tannin-sulfonate molecules for the first time. The m/e values
correspond with ring opening and introduction of a sulfonate group on the C-2 position.
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INVESTIGATION OF PHASE CHANGE CONDUCTING MATERIALS PREPARED FROM POLYETHYLENES, PARAFFIN WAXES AND COPPERMolefi, Jonathan Andrew 19 June 2013 (has links)
Phase change materials based on polyethylene (LDPE, LLDPE and HDPE) and copper (micro
and nano) blended with soft paraffin wax were studied in this work. The purpose of this study
was to form composites that can store energy as well as conduct heat. The influence of wax
content, as well as copper content and copper particle size, on the morphology and thermal,
mechanical and conductivity properties was investigated. The scanning electron microscopy
results show that both the Cu micro-and nano-particles were well dispersed in the matrix. The
nano-particles, did, however, also form agglomerates. The results also show that the Cu
micro-particles have a greater affinity for the wax than for the polyethylenes, giving rise to
preferable crystallization of the wax around the Cu particles. The differential scanning
calorimetry results show that the Cu micro- and nano-particles influence the crystallization
behaviour of the polyethylenes in different ways. The extent to which the copper particles
influence the crystallization behaviour of the polyethylenes also depends on the respective
morphologies of the different polyethylenes. All the polyethylene/wax blends are immiscible
or only partially miscible at wax contents of 30, 40 and 50%. The presence of wax in the
polyethylene/wax blends reduces the melting temperatures of all three polyethylenes,
indicating the plasticizing effect of the molten wax in the polyethylene matrix. The
thermogravimetric analysis results show observable influence of both the presence of copper
and the sizes of the copper particles, as well as the presence and amount of wax, on the
thermal stabilities of the blends and composites. The thermal conductivities of the composites
show a non-linear increase with an increase in Cu particle content. The presence of wax
slightly decreases these values, confirming the preferable crystallization of wax around the Cu
particles. The thermal conductivities of the Cu nano-particle containing composites, at the
same copper contents, are almost the same as those of the micro-particle containing
composites. Youngâs moduli increased with an increase in copper content in both the
polyethylene composites and the polyethylene/wax blend composites, except in the case of
HDPE where a decrease was observed. The dynamic mechanical analysis storage moduli
determined through dynamic mechanical analysis show the same trends as the Youngâs
moduli. The tensile strengths show variable behaviour, but mostly these values decrease with
increasing Cu and wax contents. The energy storage results show that the heat transport is
faster in the case of the blend composites compared to the polyethylene/wax blends, and the
heat transport in the polyethylene/wax blends is also faster than in the neat polyethylene
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PARAMETERS INFLUENCING REGIOSELECTIVITY IN THE PALLADIUM CATALYSED CARBONYLATION OF STILBENES AND RELATED ALKENESSerdyn, Maretha 16 July 2013 (has links)
Flavonoids are polyphenolic naturally occurring compounds with a wide variety of biological and
physiological activities, like anti-platelet, anti-inflammatory, antioxidant, antiviral, antiallergenic, and
antitumor properties. The potential therapeutic value of these compounds gave impetus to the development
of numerous synthetic routes to not only get access to more material than possible through the isolation
thereof from natural sources, but also to have access to flavonoids with substitution patterns different to
those of naturally occurring analogues. Existing synthetic methodologies, however, involve tedious
multistep processes, stoichiometric amounts of sometimes toxic reagents that produce large amounts of
waste, harsh reaction conditions and are not always high yielding.
With this in mind, it was envisaged that isoflavonoids might be accessible via a catalytic process entailing
hydroesterification of 2-hydroxystilbenes. If the desired regio-isomer could be obtained during this
reaction, cyclization between the 2-hydroxy group and the introduced ester moiety would give rise to the
heterocyclic C-ring of the corresponding isoflavonoid. Although it is known that steric factors play a
prominent role in regioselective control during hydroesterification processes, little is known about the role
of the electronic environment around the double bond during these reactions. To address this issue and
determine the feasibility of hydroesterification methodology for the synthesis of isoflavonoids, various
stilbenes with electron-withdrawing and electron-donating groups, respectively on the two aromatic rings
were envisaged as substrates to be subjected to palladium catalysed hydroesterification reactions.
Since the Wittig reaction is well-known for the formation of alkenes such as the envisaged stilbenes, this
approach was followed in order to prepare the required starting materials. Although the phosphonium salts,
benzyltriphenylphosphonium bromide and p-methoxybenzyltriphenylphosphonium chloride, required as
reactant in the Wittig reaction, could easily be prepared from the benzyl halide and triphenylphosphine
(PPh3) in good yields (98 % and 76 %, respectively), preparation of the p-methoxybenzyl bromide/chloride
were more challenging and led to an overall yield for the phosphonium salt of only 45 %. Other
methodologies towards the synthesis of substituted phosphonium salts, i.e. treatment of p-methoxybenzyl
alcohol with PPh3 in trifluoroacetic acid and cleavage of the benzyl methyl ether, p-methoxybenzyl methyl
ether, with PPh3
.HBr, were therefore investigated but yields of only 10 and 38 %, respectively, were
obtained.
With the best methodology for the synthesis of phosphonium salts determined, attention was subsequently
turned towards the final step in the preparation of the envisaged starting materials, i.e. synthesis of the
oxygenated stilbenes. Methoxystilbene was therefore prepared according to the traditional Wittig reaction
between benzyltriphenylphosphonium bromide and p-anisaldehyde, with BuLi as base and the product
obtained in only 33 %. In an effort to improve on the yield, the same Wittig reaction was performed
utilizing an organic/aqueous (aldehyde and aq. NaOH) biphasic solvent system with NaOH as base, which led to an increase in yield (54 %). Application of the same methodology to the synthesis of 2-
methoxystilbene and 4-ethoxymethoxystilbene resulted in the formation of the desired products in 53 and
55 % yields, respectively. The latter compound, 4-ethoxymethoxystilbene, was subsequently subjected to
acid catalysed deprotection (quantitative yield) followed by reaction with trifluoromethanesulfonyl chloride
and triethylamine to obtain a stilbene, 4-trifluorosulfonyloxystilbene, protected with an electronwithdrawing
substituent in 54 % yield. In an effort to improve the yields obtained for the stilbene
preparation process to beyond ca. 50 %, a microwave assisted Perkin-type reaction between phydroxybenzaldehyde
and phenylacetic acid with a piperidine-imidazole catalyst system and PEG-400 as
solvent, was embarked upon and hydroxystilbene obtained in 42 % yield. Although the yield was almost the
same as what was found with the Wittig method, this reaction did not require protection of the free phenolic
hydroxy group or the time consuming preparation of starting materials and needed reaction times of only 10
minutes, as well as the added advantage of it being an environmentally more favourable procedure
compared to the Wittig reaction.
Since Pd(OAc)2 together with PPh3 and the Lewis acid activator/co-catalyst Al(OTf)3 have been reported as
one of the best catalyst systems for the methoxycarbonylation of many different aliphatic alkenes, this
catalyst system was utilized in the methoxycarbonylation (35 bar CO pressure, 95 °C) of model substrates
like hex-1-ene, styrene and allylbenzene and obtained conversions to the corresponding methyl ester
products of 70, 99 and 57 %, respectively. When trans-stilbene was, however subjected to the same
reaction conditions and catalyst system, virtually no product was formed, so it was decided to use the model
substrate, trans-β-methylstyrene, for determining the best catalyst system and reaction conditions for the
methoxycarbonylation of substrates that has the double bond in conjugation with an aromatic ring. While it
was found during this investigation that the reaction conditions of 35 bar and 95 °C was indeed the
optimum for trans-β-methylstyrene, PdCl2 proved to be more reactive than Pd(OAc)2 when applied to the
methoxycarbonylation of substrates with conjugated double bonds, with a 90 % conversion to the products,
methyl 4-phenylbutanoate, methyl 2-methyl-3-phenylpropanoate and methyl 2-phenylbutanoate, in a 6:2:1
ratio. Due to the insolubility of trans-stilbene in pure methanol, a solvent study was embarked upon and
MeOH:THF (1:1) was found to be the best alternative to pure methanol (conversion of 61 vs. 90 % in pure
MeOH).
With the optimum reaction conditions determined, the influence of a higher degree of substitution around
the double bond as well as position of substituents attached to the double bond were investigated, it was
also decided to evaluate the effect of the electron-donating and electron-withdrawing substituents attached
to the aromatic ring, on the outcome of the reaction. Subjecting α-methylstyrene and 2-methyl-1-
phenylprop-1-ene to the reaction conditions, led to the conversion (38 and 22 %, respectively) and isolation
of the expected products, methyl 3-phenylbutanoate and methyl 3-methyl-4-phenylbutanoate, indicating
that the steric environment around the double bond indeed has a significant influence on the reaction. The
electronic effects were studied through the methoxycarbonylation of trans-anethole (the p-methoxy
equivalent of trans-β-methylstyrene) and 1-(4'-trifluoromethanesulfonyloxyphenyl)prop-1-ene and, while the three expected products were obtained, it was found that an aromatic methoxy substitutent has an
inhibiting effect on the reaction (21 % vs. 90 % conversion of trans-β-methylstyrene), while the substrate
with the deactivating group showed a much improved conversion (31 %) compared to the p-methoxy
analogue. Performing the methoxycarbonylation of trans-β-methylstyrene (in MeOH) in the presence of
anisole (1:1) proved that aromatic methyl ethers indeed have a detrimental effect on the reaction, since only
trace amounts of the products could be detected in this instance.
Since chiral induction during the enantioselective synthesis of isoflavonoids has been achieved through
utilization of amide chiral auxiliaries, like 2-imidazolidinones, it was decided to investigate the possibility
of transforming an alkene into an amide in a one-step reaction and therefore circumvent the need for a
second reaction to obtain the desired amide. Trans-β-methylstyrene was therefore subjected to the
methoxycarbonylation conditions developed before [PdCl2/Al(OTf)3/PPh3, 35 bar CO, 95 °C], but in an
inert solvent (THF) containing aniline as nucleophile and 53 % conversion to N,2-diphenylbutanamide and
2-methyl-N,3-diphenylpropanamide in a 6:1 ratio was obtained. Encouraged by the success of the first ever
palladium catalysed aminocarbonylation reaction, the scope of the reaction was extended to include
substrates like benzamide, n-butylamine and piperidine, but these nucleophiles were found to be unreactive,
so more work is clearly needed to determine the conditions necessary for the successful utilization of these
compounds in aminocarbonylation reactions.
Finally, attention was turned to the methoxycarbonylation of the stilbenes, therefore trans- and cis-stilbene
as well as trans-2-methoxystilbene were subjected to the palladium catalysed reaction, but only very low
conversions (trace amounts up to 4 %) were found. Since everything pointed towards the electronic effect
of conjugation, which deactivates the double bond to such an extent that the reaction with the palladium
catalyst is supressed, being the cause of the failure of stilbenes to undergo methoxycarbonylation, 1,3-
diphenylprop-1-ene, a substrate with the double bond not in conjugation with the two aromatic rings, were
therefore subjected to the reaction and a conversion of 27 % to the product, methyl 2,4-diphenylbutanoate,
was obtained. This result clearly demonstrates that the failure of stilbenes to undergo hydroesterification
reactions originates in the fact that the double bond is in conjugation with two aromatic rings.
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COMPUTATIONAL, STRUCTURAL AND ELECTROCHEMICAL PROPERTIES OF METAL(III) TRIS-BETADIKETONATO COMPLEXESFreitag, Roxanne 16 July 2013 (has links)
A series of MnIII(β-diketonato)3 complexes (β-diketonato = acac, ba, dbm, tfaa, tfth, tffu, tfba
and hfac) were synthesized and characterized with the aid of mass spectroscopy, elemental
analysis, X-ray diffraction (crystallography) and melting point measurements. The
electrochemical study (cyclic voltammetry) showed that for MnIII(β-diketonato)3 complexes with
more electron withdrawing R and R' groups on the β-diketonato ligands (RCOCHCOR')-, the
redox potential of the [MnIII(β-diketonato)3] + e- [MnII(β-diketonato)3] redox reaction was
found to shift to more positive potentials. The reduction potential of the the MnIII/MnII couple
was correlated to electronic parameters (acid dissociation constant (pKa) of the uncoordinated b-
diketones (RCOCH2COR'), the total group electronegativities [Σ(cR + cR')] and total Hammett
sigma meta constant [Σ(ÏR + ÏR')] of the R and R' side groups of the b-diketonato ligands
(RCOCHCOR') and the calculated electron affinity of Mn(β-diketonato)3 complexes. DFT
computational studies were done on the Mn(acac)3 and Mn(dbm)3 complexeto understand the
Jahn-Teller distortion that that MnIII(β-diketonato)3 complexes undergo.
Electrochemical (cyclic voltammetry) studies were done on M(acac)3 complexes where M = V,
Cr, Mn, Fe and Co. The reduction potential of the MIII/MII couple was correlated to electronic
parameters such as the metal electronegativity (cPauling and cMulliken), calculated electron affinity
and LUMO energy. DFT computational studies were done on the symmetry of V(acac)3 to
investigate the Jahn-Teller distortion of the V(acac)3 complex. A DFT computational study was
used to illustrate the d-orbital occupations of the M(acac)3 complexes ( M = V, Cr, Mn, Fe and
Co).
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CRYSTALLOGRAPHIC, COMPUTATIONAL AND MECHANISTIC STUDY OF RHODIUM ENAMINOKETONATO COMPLEXESVenter, Gertruida Jacoba Susanna 18 July 2013 (has links)
This study includes the investigation of enaminoketones as ligand systems in rhodium complexes
with possible future application in catalysis. In order to evaluate the influence of substituents on
the phenyl ring on activity of the complex, a range of 4-(phenylamino)pent-3-en-2-onate
(PhonyH) derivatives with chloride substituents on different positions on the phenyl ring were
synthesized and characterized through X-ray crystallography as well as infrared and NMR
spectroscopy. The compounds crystallize in a range of space groups and varying crystal systems,
are stable in air over a period of several years and soluble in most solvents. The optimized
structures of these compounds were calculated using DFT methods. The relative energies of the
optimized structures adopt a cumulative nature â the relative energy of 2,4-Cl2-PhonyH with
regard to unsubstituted PhonyH is roughly equal to the sum of the relative energies of 2-Cl-
PhonyH and 4-Cl-PhonyH, while the relative energy of 2,6-Cl2-PhonyH is twice the relative
energy of 2-Cl-PhonyH. The distortion of the phenyl ring from the ideal planar position
presented in the calculated structures corresponds to the distortion observed in the solid state.
The synthesis of the uncoordinated compounds was followed by the synthesis and
characterization of a range of substituted dicarbonyl-[4-(phenylamino)pent-3-en-2-onato]-
rhodium(I) complexes. The complexes crystallized in varying crystal systems and space groups.
The trans influence of nitrogen was confirmed through the difference in the Rh-CO bonds: the
Rh-C bond trans to the nitrogen atom is longer than the Rh-C bond trans to oxygen. The impact
of the chloride substituents was observed from differences in geometrical parameters and is
supported by information from the calculated structures and literature. The optimized structures
of these complexes were calculated using DFT methods, and their optimized energies follow the
same cumulative trend as observed in the uncoordinated compounds.
A range of carbonyl-[4-(phenylamino)pent-3-en-2-onato]-triphenylphosphine-rhodium(I)
{[Rh(N,O-Bid)(CO)(PPh3)]} complexes were synthesized and characterized, containing both
electron-withdrawing chloride atoms and electron-donating methyl groups. These complexes
displayed poor solubility, but once dissolved, were stable over a period of several months. Isomorphism was observed between [Rh(2,6-Cl2-Phony)(CO)(PPh3)] and [Rh(2,6-Me2-
Phony)(CO)(PPh3)].
[Rh(2,6-Cl2-Phony)(CO)(PPh3)] and [Rh(2,6-Me2-Phony)(CO)(PPh3)] were chosen to investigate
the exchange of triphenylphosphine coordinated in [Rh(N,O-Bid)(CO)(PPh3)] complexes with
the uncoordinated phosphine, allowing for the comparison of the electronic effect of the
substituents on the phenyl rings. The method chosen for the investigation was magnetization
spin transfer, an NMR technique which utilizes the magnetic properties of nuclei and determines
the kinetic properties of the exchange reaction by following the rate at which magnetic
equilibrium is restored.
The rate of the phosphine exchange reaction in [Rh(2,6-Cl2-Phony)(CO)(PPh3)] was determined
as approximately three times faster than the rate of reaction for phosphine exchange in [Rh(2,6-
Me2-Phony)(CO)(PPh3)]. The decreased electron density surrounding the rhodium atom in
[Rh(2,6-Cl2-Phony)(CO)(PPh3)] allows for the reversal of the reaction as indicated by the k-1
values of approximately 11 s-1 calculated from the [Rh(2,6-Cl2-Phony)(CO)(PPh3)] exchange
reaction. This value is absent in the reaction of the [Rh(2,6-Me2-Phony)(CO)(PPh3)] complex.
The activation parameters of the exchange reaction in [Rh(2,6-Cl2-Phony)(CO)(PPh3)] (ÎHâ¡ =
25(3) kJ.mol-1 and ÎSâ¡ = -117(9) J.K-1.mol-1) correlate well with the parameters of the exchange
reaction in [Rh(2,6-Me2-Phony)(CO)(PPh3)] (ÎHâ¡ = 24(4) kJ.mol-1 and ÎSâ¡ = -124(12) J.K-1.mol-
1). In both cases the value for entropy, ÎSâ¡, is negative, indicating an associative mechanism.
The relative contribution of TÎSâ¡ to ÎGâ¡ is approximately 60% for both complexes, whereas the
enthalpy (ÎHâ¡) terms are correspondingly small. This indicates that the activation process is
primarily controlled by entropy and involves the formation of a stable, well-ordered transition
state while bond weakening is less important. The relatively constant values for ÎGâ¡ imply that
the exchange reaction is not very sensitive to changes in temperature.
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POLYHEDRAL OLIGOMERIC SILSESQUIOXANES (POSS) BASED POLYMER NANOCOMPOSITESHato, Mpitloane Joseph 23 July 2013 (has links)
This work reports on the preparation and characterization of polyhedral oligomeric
silsesquioxanes (POSS)-containing polymer nanocomposites. The nanocomposites
investigated in this study consist of two different types of POSS particles [octamethyl-T8-
POSS and poly((propylmethacryl-heptaisobutyl-POSS)-co-(methyl-methacrylate))] dispersed
in two different polymer matrices such as linear low-density polyethylene (LLDPE) and
poly(methyl methacrylate) (PMMA). The melt-blending technique was used for the
preparation of various nanocomposites. The morphology and structure of various
nanocomposites were characterized by using x-ray diffraction (XRD), small angle x-ray
scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and polarized
optical microscopy (POM). The influence of different loadings of POSS particles on the
thermal, thermomechanical, tensile, impact, and melt-state viscoelastic properties of
nanocomposites was investigated.
The morphology of the freeze-fractured surfaces of the LLDPE/POSS nanocomposites
investigated by means of FE-SEM, revealed a homogeneous dispersion of the octamethyl-T8-
POSS particles into the LLDPE matrix at a low filler content. The thermal properties of pure
LLDPE and various nanocomposites showed double melting behaviour of the neat LLDPE
matrix and the nanocomposite samples. The thermomechanical properties were investigated
by stress-strain controlled rheometry using a solid-state rectangular fixture. The results
showed a moderate improvement in both the storage and loss moduli of the neat LLDPE upon
the incorporation of the POSS particles. The thermal stability of pure LLDPE and its
nanocomposites was investigated in both air and nitrogen atmospheres. Two degradation steps
were observed for all studied samples under nitrogen atmosphere. An improvement in the
thermal stability of the samples studied in air in the high-temperature region was observed.
The melt-state rheological properties measurements showed that the POSS particles were
highly immiscible with the LLDPE matrix. POSS-containing LLDPE composites did not
show any improvement in tensile properties. A decrease in impact properties of the LLDPE at
higher POSS loadings was observed. The heat distortion temperature of the LLDPE samples
increased with increasing the POSS loading in the polymer matrix. In the case of PMMA/POSS nanocomposites, the FE-SEM results did not give any
information about the dispersion of the POSS particles in the PMMA matrix. However, the
XRD studies indicated that the POSS particles were dispersed throughout the PMMA matrix.
Both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA)
showed a single glass transition for all the investigated samples. A decrease in the glass
transition temperature was observed with increasing POSS loading in the polymer matrix. The
rheological studies showed a gel-like character for all the investigated samples. An increase in
the storage modulus for the 5 wt % POSS-containing sample was observed when compared
with pure PMMA.
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PHASE CHANGE MATERIALS BASED ON POLYETHYLENE, PARAFFIN WAX AND WOOD FLOURMngomezulu, Mfiso Emmanuel 23 July 2013 (has links)
Phase change material (PCM) composites based on high-density polyethylene (HDPE) with
soft (M3) and hard (H1) Fischer-Tropsch paraffin waxes and alkali-treated wood flour (WF)
were investigated in this study. Both the blends and composites were prepared using a meltmixing
method with a Brabender-Plastograph. SEM, DSC, TGA, DMA, tensile testing and
water absorption were used to characterize the structure and properties of the blends and
composites. The HDPE as the supporting matrix kept the molten waxes in compact shape
during its phase transition from solid to liquid. Immiscibility of the PCMs (waxes) and the
supporting matrix (HDPE) is a necessary property for effective energy storage. M3 wax
blends were immiscible, whereas H1 wax blends seemed to be partially miscible and cocrystallized
with the polymer matrix. In the presence of WF, the wax seems to crystallize
around and in the pores of the WF particles, thus reducing co-crystallization with the HDPE
and improving the energy storage capacity. TGA results showed a reduction in the thermal
stabilities of the blends and composites in the presence of both WF and waxes. The storage
modulus was reduced in the presence of wax, but improved when both WF and wax are
present, although the improvement was less significant in the case of the M3 wax. Depending
on the type of wax, the γ- and α-transitions were influenced differently, and there was an
emergence of a β-relaxation in the case of the M3 wax blends. Both waxes had different
influences on the tensile modulus and strength of the blends, with H1 increasing and M3
decreasing these properties. The PCM composites, on the other hand, had high moduli. High
content of WF in the composites showed high water absorption. However, in the wax
containing composites, there was a general decrease in water uptake.
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DEVELOPMENT OF NEW âGREENâ METHODOLOGY FOR THE SYNTHESIS OF SUBSTITUTED PHENYLACETIC ACID DERIVATIVES AS PRECURSORS TO ISOFLAVONOIDS AND RELATED COMPOUNDSPieterse, Tanya 23 July 2013 (has links)
Flavonoids and isoflavonoids are known to exhibit many important physiological properties
and are especially promising candidates for cancer chemoprevention. Similar to most natural
products, studies directed at the synthesis of flavonoids have, therefore, emerged from the
search for new compounds with beneficial biological properties. Metabolic studies related to
flavonoids are, however, frequently hampered by the inaccessibility of a variety of optically
active compounds. While a single method for the synthesis of enantiomerically enriched
isoflavonoids has been published, this process utilizes phenylacetic acid derivatives which are
not always readily available in all naturally occurring substitution patterns. Even though the
synthesis of phenylacetic acids are possible via a number of routes, these are based on ancient
low yielding chemical processes utilizing harsh reaction conditions, stoichiometric quantities
of reagents and in many cases, poisonous heavy metals like lead and thallium.
In order to address the availability of phenylacetic acid derivatives of variable substitution
patterns, the current study was aimed at the development of methodology for the synthesis of
phenylacetic acid derivatives that would be high yielding, environmentally benign, have a
limited number of process steps, and are applicable to all naturally occurring flavonoid
substitution patterns. In this regard it was envisaged that ozonolysis of substituted
allylbenzenes would comply with all of the stated criteria and was therefore investigated as
methodology for the synthesis of phenylacetic acid derivatives that could serve as building
blocks during isoflavonoid preparations.
Since substituted allylbenzenes of all oxygenation patterns are not available commercially,
the allylic moiety was introduced into the required phenols by means of a allyl phenyl ether
intermediate, through utilization of Williamson ether synthesis (allyl bromide; K2CO3,
refluxing CH3CN) followed by Claisen rearrangement of the neat allyl phenyl ethers, allyl 3-
methoxyphenyl ether and allyl 3,5-dimethoxyphenyl ether, under microwave irradiation (at
200 ºC in 15 min. intervals and 0ô¯200 W variable power) to obtain the desired allylphenols,
1-allyl-2-hydroxy-4-methoxybenzene and 1-allyl-2-hydroxy-4,6-dimethoxy-benzene, in 44
and 88 % yield, respectively. Apart from the desired allylphenol, Claisen rearrangement of
allyl 3-methoxyphenyl ether, however, also led to the formation of 1-allyl-2-hydroxy-6-
methoxybenzene in 45% yield, indicating a lack of selectivity towards the formation of the
sterically less hindered product under the prevailing reaction conditions. Since free phenolic
substituents on the aromatic rings of the envisaged substrates might have a negative effect during ozonolysis reactions, the commercially available allylphenols as well as the two
substrates prepared by allylation and Claisen rearrangement (vide supra) were subjected to
methylation (MeI; K2CO3; refluxing acetone or acetonitrile) and the respective fully
methylated analogues, 1-allyl-3,4-dimethoxybenzene, 1-allyl-2,4-dimethoxybenzene, 1-allyl-
2,4,6-trimethoxy-benzene, and 1-allyl-3,4,5-trimethoxybenzene, obtained in 79, 96, 80, and
77% yield, respectively.
Ozonolysis [O3 (6ô¯8 min.), DCM, 0 °C] with reductive work-up [N-methylmorpholine-Noxide
(NMMO)] of 1-allyl-2-methoxybenzene, 1-allyl-4-methoxybenzene, and 1-allyl-3,4-
dimethoxybenzene afforded the corresponding phenylacetaldehydes in 58, 88 and 15% yield,
respectively. Ozonolysis of the highly oxygenated substrates, 1-allyl-2-hydroxy-4-
methoxybenzene, 1-allyl-2,4,6-trimethoxybenzene, and 1-allyl-3,4,5-trimethoxybenzene,
however, only led to cleavage of the aromatic ring and formation of unidentifiable product
mixtures. Cleavage of the aromatic rings of these substrates was confirmed by 1H NMR
analysis of the reaction mixture [O3 (6ô¯8 min.), CDCl3, -78 °C] where the formation of the
1,2,4-trioxolane intermediate could be detected for the substrates that gave the desired
phenylacetaldehydes but not for the highly oxygenated analogues.
In order to reduce electron density on the aromatic ring of the highly oxygenated substrates
and prevent ring ozonolysis in this way, the free hydroxy function on each substrate was
changed into a trifluoromethanesulfonyl ester and the subtrates, 1-allyl-2-
trifluoromethanesulfonyloxy-4-methoxybenzene, 1-allyl-4-trifluoromethanesulfonyloxy-3-
methoxybenzene, 1-allyl-4-trifluoromethanesulfonyloxy-3,5-dimethoxybenzene, and 1-allyl-
2-trifluoromethanesulfonyloxy-4,6-dimethoxybenzene submitted to ozonation with NMMO
work-up again. While the phloroglucinol based sulfonyl ester gave the desired
phenylacetaldehyde in 71% yield, the other three substrates furnished NMMO induced
double bond migration with the subsequent formation of the benzaldehyde equivalent
products. When the ozonation reaction was repeated on the resorcinol, catechol and
pyrogallol trifluoromethanesulphonyl esters, with replacement of the NMMO with dimethyl
sulphide (DMS) as reductant, the desired phenylacetaldehydes or trioxolanes were, however,
obtained in 63, 32 and 31% yield, respectively.
Ozonolysis with oxidative work-up [(i) O3/MeOH; (ii) Ac2O-Et3N] applied to the
monomethoxy substrates, 1-allyl-2-methoxybenzene and 1-allyl-4-methoxybenzene, afforded
the desired methyl phenylacetates in 91 and 32% yield, respectively. Similar to what was found for the reductive work-up procedure, the higher oxygenated substrates had to be
converted to their respective triflates before ozonolysis of the allylic double bond could be
effected successfully and the phenylacetic acid esters, methyl 4-trifluoromethanesulfonyloxy-
3-methoxyphenyl acetate, methyl 4-trifluoromethanesulfonyloxy-3,5-
dimethoxyphenyl acetate, and methyl 2-trifluoromethanesulfonyloxy-4,6-dimethoxyphenyl
acetate obtained in 9, 17 and 65% yield, respectively.
Since the published process for the stereoselective synthesis of isoflavonoids would require
the phenyl acetates prepared through ozonolysis to be transformed into the corresponding
amides, the possibility of direct formation of the nitrogen derivatives, like anilides, during the
ozonolysis reaction was subsequently investigated. While first attempts at having the aniline
present during the ozonolysis reaction only led to nitrogen oxidation, the process was
amended to addition of the nitrogen nucleophile after formation of the 1,2,4-trioxolane,
which resulted in the desired 2-methoxyphenylacetanilide being formed in 37% yield. The
scope of this novel reaction was subsequently extended to the reaction of 1-allyl-4-
methoxybenzene with acetamide leading to the product being obtained in 39% yield. While
this reaction gave indications that deactivated nitrogen nucleophiles could also be used in this
process, the reaction with 2-imidazolidinone, a secondary amide, did not succeed indicating
that the new reaction still needs to be optimized to be useful in the enantioselective synthesis
of isoflavonoids.
Finally, it was shown during the current study that the phenylacetic acid derivatives prepared
via ozonolysis could be transformed into deoxybenzoins, another isoflavonoid precursor,
through formation of the acid chloride followed by reaction with a phenyl Grignard reagent.
Thus phenylacetyl chloride could be reacted successfully with phenylmagnesiumbromide at -
78 oC in diethyl ether to give the deoxybenzoin in almost 60% yield.
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THE ANALYSIS OF NATURAL AND SULFITED COMMERCIAL QUEBRACHO (SCHINOPSIS LORENTZII) AND ACACIA (ACACIA MEARNSII) PROATHOCYANIDIN EXTRACTS WITH ELECTROSPRAY IONISATION MASS SPECTROMETRYJordaan, Maryam Amra 23 July 2013 (has links)
Quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood and black wattle
(Acacia mearnsii) bark extracts are important renewable industrial sources of
proanthocyanidins (PACs). These extracts are used industrially in leather tanning and
adhesive manufacturing. These applications are derived from their chemical properties. The
poly hydroxy groups of PACs complex with proteins via hydrogen bonds and thus transforms
raw skin into leather. The phloroglucinol or resorcinol type A-rings are nucleophilic and
polymerise with aldehydes to form natural adhesives. The ortho hydroxy group on the B-ring
form insoluble complexes with heavy metals and can be used in water purification
applications. The extracts are often treated with sodium hydrogen sulphate (sulfitation) to
enhance their industrial usefulness. From a literature search and discussions with role players
in the black wattle and quebracho PAC extract manufacturing industry, it became evident that
knowledge on the composition of commercial PACs extracts and chemical changes that takes
place during sulfitation is unsatisfactory.
These PAC extracts are complex due to variable hydroxylation patterns of the constituent
flavan-3-ol aromatic rings, different configurations of the C-2, C-3 and C-4 stereogenic
centres, different degrees of polymerisation, and the existence of angular oligomers. Gel or
paper chromatography fractionations of the complex extracts are hampered by poor
resolution due to their hydrophilic polyphenolic nature and efforts to isolate pure compounds
have been restricted to the isolation of mainly monomers and a few dimers and trimers.
PACs of the commercially important quebracho (Schinopsis lorentzii and Schinopsis
balansae) and black wattle (Acacia mearnsii) extracts have a strong and stable interflavanyl
bond. This stability is important from an industrial point of view as it leads to durable leather
and adhesive products. It is attributed to the absence of 5-OH groups in the aromatic moieties
of the extender fisetinidol and robinetinidol flavan-3-ols units. However, from an analytical
point of view it is not advantageous. The high temperatures thus required to hydrolyse the
interflavanyl bonds with weak acids; leads to decomposition of the intermediate monomers
that renders conventional thiolysis and phloroglucinolysis based analytical methods
unreliable. In this thesis we used electrospray mass spectrometry (ESI-MS) to investigate the
composition of PACs in black wattle extract and the changes that takes place in the chemical
composition of quebracho PACs during sulfitation. We furthermore use all the information
available from literature on the phytochemistry of flavan-3-ols and PACs and the syntheses
of flavan-3-ol oligomers to guide us in our ESI-MS interpretations.
Previous research in our group established that quebracho PACs always consist of a catechin
starter unit to which one, two or more fisetinidol extender units are attached. The first and
second extender units are always attached to the relatively reactive phloroglucinol A-ring of
the catechin starter unit to form predominantly dimers and angular trimers. Further extender
units are attached to the relatively less reactive resorcinol A-rings of already incorporated
fisetinidol extender units. This explains the relatively short degree of polymerisation of
quebracho PAC extracts and their popularity as a tanning agent. Large PACs will not
penetrate the spaces between skin proteins and cannot act as a tanning agent.
In this thesis we established that black wattle PACs have, in addition to catechin starter units,
also gallocatechin starter units and, in addition to fisetinidol extender units, also robinetinidol
extender units. Acacia PACs are thus more complex combinations of catechin, gallocatechin,
fisetinidol and robinetinidol monomers. This contrasts with quebracho PACs that only
contain catechin and fisetinidol monomers. The higher degree of hydroxylation of
gallocatechin and robinetinidol explains the higher water solubility of black wattle PACs and
the less frequent need for sulfitation.
We also established that during sulfitation of quebracho PACs, a sulfonic acid moiety is
introduced in both the C-2 and C-4 position of the pyran heterocyclic C-ring. In the case of
C-2 sulfitation, the heterocyclic ring is opened. This enhances the reactivity of the A-ring
towards the reaction with formaldehyde (adhesive formation) and increases water solubility
due to removal of rigidity and introduction of a polar sulfonic acid group. In the case of C-4
sulfitation, the interflavanyl bond is broken. Polarity and water solubility is thus not only increased via an additional sulfonic acid moiety, but due to the presence of shorter oligomers
and a smaller average chain length. We also developed a chromatographic method to estimate
the degree of sulfitation of quebracho PAC extract.
We believe that we have made a valuable contribution towards a better understanding of the
composition of black wattle and sulfited quebracho PAC extracts and have identified a
number of misconceptions.
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