A series of water-soluble platinum(II) terpyridine complexes with functionalized alkynyl ligands and a boronic acid-containing polymer, PAAPBA, have been synthesized and characterized. The photophysical and electrochemical properties of all the platinum(II) complexes have been studied. Some of the complexes have been demonstrated to show ground-state aggregation in organic solvents and aqueous solutions at high concentrations, leading to Pt…Pt and/or π–π interactions and hence the emergence of metal-metal-to-ligand charge transfer (MMLCT) transitions in both the UV−visible and emission spectra. The induced self-assembly of [Pt(tpy)(C≡CC6H4−CH2NMe3-4)](OTf)2 by PAAPBA has been explored for the development of glucose sensing protocols and α-glucosidase assay by monitoring the triplet metal-metal-to-ligand charge transfer (3MMLCT) emission in the near-infrared (NIR) region. [Pt(tpy){C≡CC6H4− {NHC(=NH2+)(NH2)}-4}](OTf)2 has been observed to undergo induced aggregation in the presence of citrate, with good selectivity over other mono- and dicarboxylates in the tricarboxylic acid (TCA) cycle. Enzymatic activity of citrate lyase has also been probed by the emission spectral changes of the complex in the NIR region. A series of water-soluble alkynylplatinum(II) terpyridine complexes and water-soluble conjugated polyelectrolytes (CPEs) have been synthesized and characterized. The UV–vis absorption and emission properties of the platinum(II) complexes and CPEs have been investigated in organic solvents and/or aqueous buffer solutions. The electrochemical properties and ground-state aggregation at high concentrations of the platinum(II) complexes have also been examined. Two-component ensembles containing selected platinum(II) complexes and PPE-SO3− have been studied, and Förster resonance energy transfer (FRET) has been demonstrated from the PPE-SO3− donor to the aggregated complexes as acceptors. The ensemble containing PPE-SO3− and [Pt(tpy)(C≡CC6H4CH2NMe3-4)](OTf)2 has been employed for a “proof-of-principle” label-free detection of human serum albumin (HSA) in pH 3 buffer solutions with high selectivity and sensitivity, while another ensemble containing PPE-SO3− and [Pt{tpy(C6H4CH2NMe3-4)-4’}(C≡CC6H5)](OTf)2 has been utilized for selective label-free detection of G-quadruplex structure of the human telomeric DNA in physiological buffer solutions. A series of water-soluble platinum(II) terpyridine complexes with stimuli-responsive alkynyl ligands and a series of water-soluble platinum(II) metallosupramolecular triblock copolymers have been synthesized and characterized. The photophysical and electrochemical properties as well as the ground-state aggregation of the complexes have been investigated. Some of them have been found to show different electronic absorption and emission properties in aqueous solution at different pHs due to aggregation/deaggregation of the complexes. One of the complexes has been employed for live-cell imaging experiments to locate acidic organelles, such as lysosomes, in MDCK cells. The water-soluble platinum(II) metallosupramolecular triblock copolymers have been found to show an increase in 3MMLCT emission intensity in the red-NIR region with temperature, which has been attributed to the formation of spherical polymeric micelles. The platinum(II) triblock copolymer with pH-responsive –CH2NMe2 moieties has been demonstrated as a NIR-emitting dual sensor for pH and temperature through the changes in hydrophilicity and hence the emission properties with pH and temperature simultaneously. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

A number of cationic water-soluble alkynylplatinum(II) terpyridine complexes, [Pt(tpy){C≡CCH2OC6H3-(CH2OH)2-3,5}]OTf, [Pt(tBu3tpy){C≡CCH2OC6H3- (CH2OH)2-3,5}]Cl, [Pt(tpy){C≡CCH2OC6H4-(CH2OH)-4}]OTf, [Pt(tpy){C≡CC6H3- (CH2OH)2-3,5}]OTf, [Pt(tpy){C≡CC6H4-(CH2OH)-4}]OTf, [Pt(tpy)(C≡C－C≡CH)]OTf and [Pt(tpy){C≡CC6H4(CH2NMe3)-4}](OTf)2, have been synthesized. Phosphate anion derivatives of polyanionic nature, e.g. adenosine triphosphate and tyrosine-containing phosphopeptide, were employed to investigate the induced supramolecular helical assembly behaviors of several of the water-soluble platinum(II) complexes through the study of their UV-vis absorption, emission and circular dichroism (CD) spectroscopies. The extent of such induced self-aggregation properties has been shown to be dependent on the concentration of substrates and capable of screening their respective structurally similar analogues. Two of the complexes were further explored for their use as label-free detection probes for real-time monitoring of the conversion of these phosphate anion derivatives to their metabolic products catalyzed by several biologically important enzymes. Michaelis-Menten analyses have been performed to determine the kinetic parameters. Supramolecular self-assembly and disassembly behaviors of water-soluble platinum(II) complexes have also been explored for their sensing applications for biomacromolecules with quantitative analyses based on UV-vis, emission and CD spectral titration studies. Making use of the selective binding affinity of aptamers towards their target substrates, the extent of self-assembly of the platinum(II) complexes in the presence of lysozyme and thrombin, which arose from their electrostatic interactions with the negatively charged aptamers, could be modulated for the quantification of these substrates. The potential applicability of this probing strategy in real biological environment has been assessed. Other than that, CD spectroscopic studies revealed the formation of supramolecular helical assembly of the platinum(II) complexes upon electrostatic interaction with heparin. Such helical conformation of the heparin–complex mixture together with the distribution of the negatively charged functionalities on the heparin have endowed the complex with high differentiating power for screening possible interfering analogues. Insulin has also been employed as a template for inducing the self-assembly of the platinum(II) complex. Changes in negative surface charge distribution on insulin, brought about by its conformational changes upon conversion to insulin amyloid under destabilizing conditions, have resulted in different extent of induced self-assembly of the metal complex. Spectral changes of the platinum(II) complex has provided a convenient monitoring of insulin amyloid formation, with kinetic parameters determined. A number of platinum(II) complexes with nucleobase-functionalized alkynyl ligands, [Pt(tpy)(C≡CCH2-T-1)]OTf, [Pt(tBu3tpy)(C≡CCH2T-1)]OTf, [Pt(tpy)(C≡C– CH2-A-9)]OTf, [Pt(tpy)(C≡CCH2-C-1)]OTf and [Pt(tpy)(C≡CCH2-G-9)]OTf (T = thymine; A = adenine; C = cytosine; and G = guanine), and amide-functionalized terpyridine ligands, [Pt{tpy–(CONHPh)2}(C≡CPh)]PF6 and [Pt{tpy–(CONHC6H13)2} (C≡CPh)]PF6, have been synthesized. Cation-binding properties of [Pt(tpy)(C≡CCH2-T-1)]OTf have been examined using UV-vis and emission spectroscopies, and ESI-MS. Pronounced selectivity towards Hg2+ ions was obtained due to the formation of thymine–Hg2+–thymine base pair, through which the Pt… Pt interactions were turned on. Such binding mechanism has been confirmed with the use of a control complex [Pt(tBu3tpy)(C≡CCH2T-1)]OTf and resonance light-scattering experiments. Anion-binding properties of the complexes with amide-functionalized terpyridine moieties towards spherical and non-spherical anions have been examined with UV-vis and emission spectral titration studies. Drastic color changes were observed for [Pt{tpy–(CONHC6H13)2} (C≡CPh)]PF6 in acetone upon F– ion addition, which was attributed to the F– ion-induced deprotonation of the amide functionalities. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Two new potentially biodegradable aminopolycarboxylic acid ligands, iminodiglutaric acid tetra sodium salt (IDG-4Na) and iminoglutaricsuccinic acid tetra sodium salt (IGS- 4Na), were synthesized in reasonably good yield and purity. The commercially unavailable precursor for the two ligands, ethyl p-aminoglutarate, was synthesised in high yield and purity, and together with the two ligands were fully characterized by means of melting point measurements and various spectrometric techniques CH-NMR, 13C-NMR, MS and IR). For the first time, an electrochemical study has been conducted on the complexes of these ligands with selected transition metal ions (Zn2+, Cu2+ and Cd2+). An electrochemical technique, cyclic voltammetry (CV), was utilized on the study of the complexing ability of the ligands to the selected metal ions. An electrochemical cell comprising three electrodes was employed: thin film mercury coated carbon microelectrode was used as the working electrode, a Platinum wire as the auxiliary electrode, and a Ag/AgCI as the reference electrode. CV has been used and proven to offer a convenient route towards the determination of metal-ligand complex stability constants in aqueous media". The values of the logarithms of the metal-ligand formation constants obtained by this technique, when compared with other widely used aminopolycarboxylic acids (APCAs), show better complexing ability of the ligands with the transition metal ions. When the two ligands are compared, IGS showed greater affinity towards the selected transition metal ions. This is due to the fact that, in aqueous media, as the side chain ligators decrease, the stabilization energy of the complex increases. The formation stability constants were determined by plotting the change in the reduction potential (ΔE) against solution pH. A process making use of a modification of lingane equation was used. / AFRIKAANSE OPSOMMING: Twee nuwe potensieel bio-afbreekbare amienpolikarboksielsuurligande, iminobiglutaarsuur -tetranatriumsout (IBG-4Na) en iminoglutaarsuksiensuurtetranatriumsout (IGS-4Na), was vervaardig met redelike goeie opbrengs en suiwerheid. Die kommersïeel onverkrygbare voorloper van die twee ligande, etiel-B-aminoglutaraat, was berei met hoë obrengs en suiwerheid, en was saam met die twee ligande ten volle geïdentifiseer deur middel van smeltpunt bepalings en verskeie spektrometriese tegnieke CH-KMR, 13C-KMR, MS en IR.). Vir die eerste keer is 'n elektrochemiese studie uitgevoer op die komplekse van hierdie ligande met selektiewe oorgangsmetaalione (Zn2+, Cu2+, en Cd2+). 'n Elektrochemiese tegniek, sikliese voltametrie (SV), is gebruik om die komplekseringsvermoë van die ligande ten opsigte van die geselekteeerdr metaalione te bestudeer. 'n Elektrochemiese sel wat bestaan uit drie elektrodes is gebruik: 'n Dunlaag kwikelektrode bedek met koolstof is gebruik as die werkselektrode, 'n platinumdraad as die bykomende elektrode en 'n Ag/AgCI elektrode as die verwysingselektrode. SV is voorheen gebruik en bewys as 'n gerieflike metode vir die bepaling van metaalligandkompleksstabiliteitskonstantes in waterige media'. Die waardes van die logaritmes van die metaalligandvormingskonstantes wat verkry word deur hierdie tegniek, soos vergelyk met ander algemeen gebruikte amienpolikarboksielsure (APKSe), vertoon beter komplekseringsvermoë met die ligande deur middel van die oorgangsmetaalione. Wanneer die twee ligande met mekaar vergelyk word, het IGS-4Na groter affiniteit gehad vir die oorgangsmetaalione. Dit is as gevolg van die feit dat die stabiliteitsenergie van die kompleks in waterige media verminder word soos wat die sykettings van die ligande toeneem. Die vormingstabilitietskonstantes was bepaal deur 'n varandering in reduksie potensiaal (ΔE) teenoor die pH van die oplossings te plot. Die grafieke is verkry deur 'n aanpassing van die Lingnane-vergelyking te gebruik.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

Ph.D. / Chapter 1 presents a brief overview on the development of platinum, ruthenium and gold anti-cancer complexes. The clinical success of cisplatin has been a tremendous impetus for the design of metal-based antitumor drugs. Its mechanism of action is therefore briefly discussed, as well as the toxic side effects of its clinical use and the cellular resistance to the drug. It is its side effects and drug resistance that have stimulated the development of cisplatin analogues and other metal based anti-cancer agents. Compounds showing most promise are ruthenium complexes which are structurally different but have the same stability and show similar modes of binding to DNA. The last part of the introduction deals with the development of gold(I) and gold(III) complexes, the main topics of the research described in this thesis. Chapter 2 reports on the attempted preparation of dppf and dippf gold(III) complexes. However, the reaction of these diphosphines with H[AuCl4] and Na[AuCl4] all led to isolation of gold(I) complexes (dppf)Au2X2 (X = Cl (1), Br (3)) and (dippf)Au2X2 (X = Cl (2), Br (4)). In an attempt to oxidize the gold(I) complexes, (dppf)Au2Br2 (3) and (dippf)Au2Br2 (4) were reacted with excess bromine yielding two new complexes (C5H4Br3)(PR2)AuBr (R = Ph, 5; R = i-Pr, 6). This bromination reaction could be extended to the ligands and bromination of the free diphosphinoferrocene ligands produced the expected brominated cyclopentenes (C5H4Br3)(PR2) (R = Ph, 7; R = i-Pr, 8) in good yields. However, these could not be complexed to gold due to reduced basicity of 7 and 8. When the bromination was performed under wet aerobic conditions the oxidized pseudo-centrosymmetric product, [doppf][FeBr4] (9) {doppf = 1,1’-bis(oxodiphenylphosphino)ferrocene, was obtained as the major product. Solid-state structures of 1, 2, 4, 6, and 9 were established by means of single-crystal X-ray crystallography. Chapter 3 reports on the use of chiral Josiphos and Walphos diphosphine ligands to form palladium, platinum and gold complexes. The platinum complexes were prepared by reacting the ligands with [PtCl2(cod)] while the palladium complexes were prepared from [PdCl2(NCMe)2]. The complexes obtained had the general formula [MCl2(P-P)], where M = Pd, Pt, and P-P = Josiphos or Walphos ligand, and were obtained in good yields. The X-ray structures of a palladium(II) and a platinum(II) complex of the same Josiphos ligand were determined. The Josiphos complexes 12 and 14 show good solubility in common solvents. Furthermore, the complexes remained soluble and stable in a 40:60 water:DMSO mixture. The Walphos complexes 13 and 15 rapidly precipitated under the same conditions. In line with this limited solubility 13 and 15 showed minimal cytotoxic effects when compared to their Josiphos counterparts 12 and 14 whose cytotoxic effects (in terms of IC50 values ) were six to seven times less than cisplatin. Reaction of the Walphos ligand and H[AuCl4] in a 1:1 ratio gave a dinuclear gold(I) complex 18 while the same reaction with Josiphos gave a mixture of intractable materials. However a 1:1 reaction of the Josiphos with AuCl(tht) gave a mononuclear three-coordinate gold(I) complex 16. A P^N chiral ligand comprising of a diphenylphosphine and a pyrazole moiety was also prepared and was complexed with AuCl(tht) to give a phosphine bound gold(I) complex 19. The structure of this complex was determined by X-ray studies. From the studies it became evident that apart from increasing the basicity of compound the pyrazolyl moiety remains dangling and the complex shows bond parameters similar to those observed with monophosphine ferrocenyl complexes. Chapter 4 reports on the bidentate and monodentate gold(III) complexes based on the (pyrazolylmethyl)pyridine ligands together with their platinum(II) complexes. The denticity of the complexes depended on the position of the pyrazolyl moiety relative to the pyridine nitrogen. When ortho-substituted ligands were reacted in a 1:1 ratio with H[AuCl4] in a mixture of water and ethanol at room temperature, bidentate cationic complexes of the general formula [AuCl2(PyCH2R2pz)][X], where R = Me (20), X = AuCl4-; R = Ph (21), X = Cl-; t-Bu (22), X= Cl- and p-tol (23), X = AuCl4-, were obtained. When para-substituted ligands were used under same reaction conditions, neutral monodentate complexes [AuCl3(PyCH2R2pz)], where R = Me (24) and R = Ph (25), were obtained. Platinum(II) complexes were obtained using K2[PtCl4] in a mixture of water and ethanol under reflux, and affords neutral complexes of the type [PtCl2(PyCH2R2pz)], where R = Me (27), Ph (28), t-Bu (29) and p-tol (30). When acetone was used instead of ethanol monoacetonylplatinum(II) complex (29a) was formed and on prolonged heating formation of the diacetonyl complex (28b) was observed. Both the platinum and the gold complexes were evaluated for their anti-cancer potency. The gold(III) complexes were devoid of any activity while the platinum complex 30 showed activity 8 times lower than cisplatin. The structures of 23, 25, 28, 29 and 29a were determined from single-crystal X-ray diffraction studies. In Chapter 5, tridentate complexes based on bis(pyrazolylethyl)amine are reported. These were prepared with the aim of improving water-solubility and cytotoxicity of the resulting complexes. New synthetic methods for preparation of the ligands NH(CH2CH2pz)2 (R = Me (L7), H (L8), t-Bu (L9)) under mild reaction conditions were developed albeit the yields obtained were generally low. The reaction of these ligands with H[AuCl4] gave corresponding tridentate dicationic gold(III) complexes [NH(CH2CH2pz)2][X]2 (R = Me (31), H (32), X = AuCl4 , and R = t-Bu (33), X = Cl-). Despite the ligands stabilizing the gold(III) ion, they showed no solubility in water. In an attempt to make the ligand system water soluble, a thiocarbamate analogue with pyrazolyl groups replaced by hydroxyl groups was prepared. However the resulting gold(III) complex [Au{CS2N(CH2CH2OH)2}2][AuCl2] (34) was found to be only soluble in DMSO.

Abstract not available

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Ruthenium carbene complexes, with the general structure, [LL’Ru=CHR], are commonly known as Grubbs type catalysts, named after the discoverer of these metathesis catalysts. The discovery was quite revolutionary, since the catalysts proved to be easy to handle, tolerant towards various functional groups and more stable with regard to air and water than previous transition metal catalysts. Another important advantage was that all types of olefin metathesis reactions could be initiated without the help of co-catalysts or promoters. Today Grubbs type catalysts find wide application in especially organic and synthetic chemistry. A well-known example is the SHOP-process which produces long chain -olefins, while other important applications include the synthesis of macro-cyclic and cyclic olefins. The current study involved experimental and theoretical work to investigate various aspects comprising synthetic procedures, reactivity, kinetics, geometry and electronic properties of the complexes. Results are discussed briefly in the following paragraphs. The first aim of the project was to synthesise a Grubbs type catalyst. Initial efforts were focused on the preparation of a first generation catalyst through various methods. This included modifying the reported method for the synthesis of [(PPh3)2Cl2Ru=CH-CH=CMe2] to yield [(PPh2Cy)2Cl2Ru=CHCH= CMe2] instead; a phosphine exchange reaction with the complex [(PPh3)2Cl2Ru=CH-CH=CMe2] and free phosphine PPh2Cy; and utilising the analogue arsine ligand, AsPh3, to synthesise [(AsPh3)2Cl2Ru=CHCH=CMe2]; but unfortunately no success was achieved. However, it was possible to synthesise a novel second generation Grubbs type catalyst, [(IMesH2)(PPh2Cy)Cl2Ru=CHPh], through the phosphine exchange reaction of [(IMesH2)(NC5H5)2Cl2Ru=CHPh] and PPh2Cy. The new complex was tested in kinetic reaction studies and phosphine exchange reactions. Results showed that [(IMesH2)(PPh2Cy)Cl2Ru=CHPh] was catalytically active for the ring closing metathesis of commercial diethyl diallylmalonate. The reaction was first order with regard to the olefin, contrary to the second order kinetic results reported for similar reactions catalysed by first generation Grubbs catalysts. The phosphine exchange reactions were very successful and a rate constant could be determined. The rate constant was independent of the free phosphine concentration and activation parameters had relatively large, positive values; results indicative of a dissociative mechanism. These findings are in correlation with literature reports. A kinetic investigation was done on the catalyst-olefin coordination involving the functionalized olefins vinyl acetate, allyl acetate and allyl cyanide; and the first generation Grubbs catalyst, [(PCy3)2Cl2Ru=CHPh]. A two-step rate law, similar to an interchange mechanism, was determined. Phobcat, [(PhobCy)2Cl2Ru=CHPh], is modified first generation Grubbs type catalyst with rigid bicyclic phosphine rings which was recently developed by the Sasol Homogeneous Metathesis Group. In the current study Phobcat was compared to Grubbs1-PCy3 in the cross metathesis reaction of 1-octene. Results showed that Phobcat was up to 60% more active and had a 5 hour longer lifetime than Grubbs 1-PCy3. Theoretical studies were done on the three functionalized olefins of the earlier experimental study to gain fundamental understanding of steric and electronic influences on these catalyst-olefin systems. Without exception, coordination via the heteroatom of the olefin was significantly more favourable than coordination via the double bond functionality. This result indicates that metathesis of these olefins is highly unlikely, since the stable heteroatom coordination will suppress the parallel Ru=C/C=C interaction which is compulsory for the metathesis reaction. Orbital studies highlighted the difference between coordination of acetate and cyanide, but no trend of an electronic nature could be recognised. / Prof. A. Roodt

The aim of this investigation was to study model complexes containing strong p- ligands as potential nitrogen, oxygen and ligand transfer catalysts. Nitrido containing cyano complexes of group 6 to 8 metals were selected as potential nitrogen transfer catalysts. Solid state and solution studies, investigating different aspects of these systems, were performed. Finally, the knowledge on mechanistic studies were applied to selected examples of 1st generation Grubbs catalyst [Ru(=CR)(PX3)2Cl2] (=CR = carbene) to investigate olefin coordination and oxygen decomposition reactions (both involving strong p-interactions at the metal center thereof). / Prof. A. Roodt