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M.Tech (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Dithiocarbamate ligands and their complexes has been a subject of interest in various fields but they found much interest in medical applications as potential anti-microbial agents. The dithiocarbamate ligands were used to prepare complexes of copper and zinc. All the prepared ligands and complexes were characterized using techniques such as IR and 13CNMR spectroscopy and thermogravimetric analysis (complexes). The data obtained from the spectroscopies was consistent with the coordination of the ligand to the metal ion through the sulfur atoms of the dithiocarbamate or thioureide moiety. The thermal analysis of the prepared complexes gave a final residue of metal sulfide, thus indicating the potential of the prepared complexes as single molecular precursor for the synthesis of metal sulfide nanoparticles. The prepared complexes were then used to synthesize metal sulfide nanoparticles. The nanoparticles were successfully prepared by thermal decomposition of a single-source precursor (dithiocarbamate complexes) in a solution of hexadecylamine (HDA) or tri-n-octylphosphine oxide (TOPO). The investigated parameters were the capping molecule (HDA and TOPO), and capping molecule concentration (3 g and 6 g) to see their effect on the shape and size of the synthesized nanomaterials. The synthesized metal sulfide nanoparticles were characterized using techniques such as UV-vis spectroscopy, photoluminescence spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The absorption study showed some interesting features in the prepared nanomaterials. The first was the red-shifted spectra of the ZnS nanoparticles which was attributed to the impurities and that assumption was further confirmed by the XRD analysis that showed a sulfur impurity and other amorphous peaks. The second was the localized surface plasmon resonances on the copper sulfide nanoparticles that suggested the formation of electron deficient copper sulfide stoichiometry that was further confirmed by XRD analysis that gave hexagonal phase copper sulfide covellite. The TEM images of the prepared nanoparticles showed that the concentration and the capping molecule has an effect on the size and shape of the synthesized nanoparticles. The increase in capping concentration gave a decrease in particle size in most of the prepared nanoparticles, while they were few exceptions. The capping molecule effect showed that most of the nanoparticles prepared from TOPO were spherical in shape and were well dispersed compared to the mixed morphological nanoparticles prepared from HDA. There were also exceptions of the well dispersed HDA-capped nanoparticles.

I introduce the concept of modular materials and give a brief overview of their history and widespread occurrence in many areas of chemistry. I then discuss some of the many applications in which modular materials may find a use and link them to the following chapters. Chapter 1 describes the layered superatomic material Re₆Se₈Cl₂ and the induction of superconducting behavior in its single crystals through a current annealing technique. We suggest that this superconductivity arises through electron doping, as a result of dissociation of the apical Cl atoms from the clusters. Chapters 2-4 explore other types of superatomic materials and their properties, centered on the well-studied Co₆X₈ unit, where X is a chalcogen. Chapter 2 describes a Co₆Te₈-C₇₀ co-crystal that exhibits multiple phase changes with temperature, each giving rise to unique electronic, thermal, and structural properties. Chapter 3 describes a series of “solid solutions” of Co₆Se₈ and Cr₆Te₈ units. By varying the ratios of the component superatoms, transport properties of the crystals can be tuned, and unexpected behavior arises as a result of structural heterogeneity. Chapter 4 presents another study of Co₆Se₈ co-crystallized with rod-shaped C₁₄₀ fullerenes. The packing and electronic properties are found to be greatly affected by the degree of solvent inclusion. Chapters 5-6 examine another class of cluster-based materials: atomically precise gold nanoparticles. In Chapter 5 the cluster Au₂₁ is shown to self-assemble depending on the surface “hook” ligands, with corresponding differences in electronic transport. Chapter 6 discusses an interesting phase transition and thermally-induced hysteresis observed in crystals of the Au₁₀₃ cluster, also related to the surface ligand configuration. Chapters 7-8 take a different approach to modular materials, in the form of organic polymers. Using the robust, electroactive pigment molecule PDI as a common building block, we synthesize extended networks that are found to be exceptional pseudocapacitive energy storage materials. Chapter 7 introduces the honeycomb-shaped PDI-triptycene polymer, establishes its pseudocapacitive nature, and explores the role of cyclization in tuning its behavior. Chapter 8 expands upon the concept by combining PDI with hexaazatrinaphthalene to create a “contorted” network with best-in-class energy storage performance. In addition to in-depth kinetic analyses to elucidate the mechanism of storage, we fabricate two-electrode cells to demonstrate the material’s potential in real-world devices.

Catalytic enantioselective desymmetrization of meso-epoxides is widely used in many areas of chemistry. Such process is usually catalyzed by a transition metal complex with a chiral ligand. Recently, a synthesis of an analogue of Bolm's 2,2'-bipyridine ligand was developed and its combination with metal salts were tested in various reactions. In this master's thesis, a catalytic system composed of Sc(OTf)3/Bolm's ligand analogue was studied in alcoholysis and aminolysis of the meso- epoxides. The reaction has been extended to a broad range of alcohols providing 1,2-diol monoethers in excellent enantioselectivity up to 99% ee. The aminolysis of meso-epoxides has been optimized, as well. The catalyst loading could be lowered to 1 mol% with only marginal effects on the enantioselectivity. Key words: epoxides, enantioselective catalysis, chiral ligands.

Um das Verhalten von Actiniden im Menschen (Stoffwechsel), in geologischen und in biologischen Systemen vorherzusagen, ist es erforderlich deren Speziation genau zu kennen. Zur Bestimmung dieser wird das chemische Verhalten des Urans hinsichtlich Komplexbildungsreaktionen und Redoxreaktionen in Modellsystemen untersucht. Anhand der gewonnenen thermodynamischen Konstanten und dem Redoxverhalten können Risikoabschätzungen für das jeweilige untersuchte System getroffen werden. Das umweltrelevante Uran(IV)-Uran(VI)-Redoxsystem besitzt mit der metastabilen fünfwertigen Oxidationsstufe einen zumeist kurzlebigen Zwischenzustand. Innerhalb dieser Arbeit gelang es erstmalig die Uran(V)-Fluoreszenz mittels laserspektroskopischer Methoden nach zu weisen. Beispielsweise konnte das Bandenmaximum von aquatischem Uranyl(V) im perchlorhaltigem Medium (λex = 255 nm) mit 440 nm, bei einer Fluoreszenzlebensdauer von 1,10 ± 0,02 μs bestimmt werden. Die fluoreszenzspektroskopische Untersuchung eines aquatischen [U(V)O2(CO3)3]5--Komplexes (λex= 255 nm und 408 nm) zeigte bei Raumtemperatur keine Fluoreszenz. Durch Anwendung der Tieftemperaturtechnik wurden bekannte Quencheffekte des Carbonats unterdrückt, so dass bei beiden Anregungswellenlängen ein für Uran(V) typisches Fluoreszenzspektrum im Bereich von 375 nm bis 450 nm, mit Bandenmaxima bei 401,5 nm (λex = 255 nm) und 413,0 nm (λex = 408 nm) detektiert werden konnte. Darüber hinaus konnte bei 153 K (λex = 255 nm) eine Fluoreszenzlebensdauer von 120 ± 0,1 μs bestimmt werden. Untersetzt wurden diese fluoreszenzspektroskopischen Nachweise durch mikroskopische Studien verschiedener Uran(IV)-Festphasen (Uraninit…UO2, Uran(IV)-Tetrachlorid…UCl4) und einer sulfathaltigen Uran(IV)-Lösung (UIVSO4). Diese wurden durch kontinuierliche Sauerstoffzufuhr zu Uran(VI) oxidiert. Die ablaufende Oxidation wurde mit dem konfokalen Laser Scanning Mikroskop (CLSM) verfolgt, wobei die Proben mit einer Wellenlänge von 408 nm zur Fluoreszenz angeregt wurden. Die auftretenden Bandenmaxima bei 445,5 nm (UO2), bei 445,5 nm (UCl4) und bei 440,0 nm (UIVSO4) konnten eindeutig der Uran(V)-Fluoreszenz zugeordnet werden. Zur Bestimmung thermodynamischer Konstanten mit Hilfe der Tieftemperaturfluoreszenz wurde zunächst der Einfluss der Temperatur auf das Fluoreszenzverhalten des freien Uranyl(VI)-Ions näher betrachtet. Es zeigte sich, dass mit Erwärmung der Probe (T>298 K) die Fluoreszenzlebensdauer von 1,88 μs (298 K) deutlich absinkt. Die Fluoreszenzintensität verringerte sich dabei um 2,3 % pro 1 K zwischen 273 K und 313 K. Im Gegensatz dazu, steigt die Fluoreszenzlebensdauer um das 150-fache auf 257,9 μs bei einer Verminderung der Temperatur (T <298 K) auf 153 K. Das weitere Absenken der Temperatur (T <153 K) zeigte keinen Einfluss auf die Fluoreszenzlebensdauer. Die Lage der Hauptemissionsbanden des freien Uranyl(VI)-Ions (488,0 nm, 509,4 nm, 532,4 nm, 558,0 nm, 586,0 nm) zeigte bei diesen Untersuchungen keine temperaturabhängige Verschiebung. Die Validierung der Tieftemperaturtechnik zur Bestimmung thermodynamischer Konstanten mittels zeitaufgelöster laserinduzierten Fluoreszenzspektroskopie erfolgte anhand des Uran(VI)-Citrat-Systems. Im Gegensatz zu bisherigen fluoreszenzspektroskopischen Betrachtungen bei Raumtemperatur wurde das Fluoreszenzsignal bei tiefen Temperaturen mit einsetzender Komplexierung nicht gequencht, woraus die Ausprägung einer gut interpretierbaren Fluoreszenz resultierte. Die Analyse der spektralen Daten mit SPECFIT ergaben mit log β 101 = 7,24 ± 0,16 für den [UO2(Cit)]--Komplex und log β 202 = 18,90 ± 0,26 für den [(UO2)2(Cit)2]2--Komplex exakt die in der Literatur angegebenen Stabilitätskonstanten. Zudem konnten Einzelkomponentenspektren mit Bandenmaxima bei 475,3 nm, 591,8 nm, 513,5 nm, 537,0 nm und 561,9 nm für den 1:0:1-Komplex und 483,6 nm, 502,7 nm, 524,5 nm, 548,1 nm und 574,0 nm für den 2:0:2-Komplex und Fluoreszenzlebensdauern von 79 ± 15 μs (1:0:1) und 10 ± 3 μs (2:0:2) bestimmt werden. Zur Modellkomplexierung des Uran-Citrat-Systems wurde in dieser Arbeit auch das Komplexbildungsverhalten von U(IV) in Gegenwart von Citronensäure untersucht. Hierbei wurden über den gesamten pH-Wertbereich gelöste Uran-Citrat-Spezies spektroskopisch nachgewiesen und die Stabilitätskonstanten sowie die Einzelkomponentenspektren für die neu gebildeten Uran(IV) und (VI)-Spezies bestimmt. Für die neu gebildeten Citrat-Komplexe des sechswertigen Urans wurden Komplexbildungskonstanten von log β 203 = 22,67 ± 0,34 ([(UO2)2(Cit)3]5-) und log β 103 = 12,35 ± 0,22 ([UO2(Cit)3]7-) und für die Komplexe des vierwertigen Urans von log β 1-21 = -9,74 ± 0,23 ([U(OH)2Cit]-) und log β 1-31 = -20,36 ± 0,22 ([U(OH)3Cit]2-) bestimmt. Untersuchungen zum Redoxverhalten von Uran in Gegenwart von Citronensäure zeigten unter aeroben und anaeroben Versuchsbedingungen eine photochemische Reduktion vom U(VI) zu U(IV), welche spektroskopisch nachgewiesen werden konnte. Dabei zeigt speziell die Reaktion unter oxidierenden Bedingungen, welchen großen Einfluss vor allem organischen Liganden auf das chemische Verhalten des Urans haben können. Sowohl die Reduktion unter O2- als auch die unter N2-Atmosphäre, weisen ein Maximum bei einem pH-Wert von 3,5 bis 4 auf. Unter anaeroben Bedingungen reduziert die Citronensäure mit ca. 66 %, 14 % mehr Uran(VI) zu Uran(IV) als unter anaeroben Bedingungen mit ca. 52 %. Ab einem pH-Wert von 7 konnte eine Reduktion nur unter sauerstofffreien Bedingungen festgestellt werden. Die Wechselwirkung von U(VI) in Gegenwart von Glucose wurde hinsichtlich Reduktion und Komplexierung des Uran(VI) betrachtet. Mit Hilfe der zeitaufgelösten laserinduzierten Fluoreszenzspektroskopie bei tiefen Temperaturen wurde dabei ein Uranyl(VI)-Glucose-Komplex nachgewiesen. Die Komplexierung wurde lediglich bei pH 5 beobachtet und weist eine Komplexbildungskonstante von log β I=0,1 M = 15,25 ± 0,96 für den [UO2(C6H12O6)]2+-Komplex auf. Mit einer Fluoreszenzlebensdauer von 20,9 ± 2,9 μs und den Hauptemissionsbanden bei 499,0nm, 512,1 nm, 525,2 nm, 541,7 nm und 559,3 nm konnte der Uranyl(VI)-Glucose-Komplex fluoreszenzspektroskopisch charakterisiert werden. Unter reduzierenden Bedingungen wurde, ab pH-Wert 4 eine auftretende Umwandlung vom sechswertigen zum vierwertigen Uran durch Glucose in Gegenwart von Licht beobachtet. Der Anteil an gebildetem Uran(IV) steigt asymptotischen bis zu einem pH-Wert von 9, wo das Maximum mit 16 % bestimmt wurde. Als Reaktionsprodukt der Redoxreaktion wurde eine Uran(VI)-Uran(IV)-Mischphase mit der Summenformel [UIV(UVIO2)5(OH)2]12+ identifiziert. Mit Hilfe der cryo-TRLFS wurde, durch Verminderung von Quencheffekten die Uranspeziation in natürlichen Medien (Urin, Mineralwasser) direkt bestimmt. Proben mit Uran-Konzentrationen von < 0,1 μg/L konnten dadurch analysiert werden. In handelsüblichen Mineralwässern wurde die zu erwartende Komplexierung durch Carbonat nachgewiesen. Im Urin zeigte sich in Abhängigkeit vom pH-Wert eine unterschiedliche Uranspeziation. Die fluoreszenzspektroskopische Untersuchung wies bei niedrigerem pH-Wert (pH<6) eine Mischung aus Citrat- und Phosphat-Komplexierung des U(VI) und bei höheren pH-Wert (pH>6) eine deutliche Beteilung von Carbonat an der Komplexierung auf. Diese Ergebnisse stehen in sehr guter Übereinstimmung mit theoretischen Modellrechnungen zur Uranspeziation im Urin. Die in dieser Arbeit gewonnenen Ergebnisse zeigen, dass für eine zuverlässigere Prognose des Urantransportes in Geo- und Biosphäre in Zukunft nicht nur Betrachtungen zur Komplexchemie, sondern auch zum Redoxverhalten des Urans nötig sind, um die Mobilität in der Natur richtig abschätzen zu können.

The cellular degradation of the low density lipoprotein (LDL) receptor, and its ligand, LDL, were investigated in order to clarify certain mechanistic aspects of these important processes. Long-term lymphoblastoid cell lines and cultured human skin fibroblasts were used to examine the fate of ¹²⁵I-LDL subsequent to its uptake via receptor-mediated endocytosis. In both cases, binding activity was saturable, depended on the presence of calcium ions in the medium, and was calculated to have an equilibrium dissociation constant at 4ᵒC of 2 μg ¹²⁵I-LDL/ml. No high-affinity binding was detected when the ligand was modified by acetylation. After incubating the monolayers at 37°C LDL/LDL receptor complexes were internalized, and the receptors were recycled back to the surface within about 10 minutes. Apolipo-protein B in the LDL particles was largely degraded to the amino acid level: chloroquine, a lysosomotropic agent, inhibited the formation of the ¹²⁵I-LDL degradation products. Cells obtained from a number of heterozygous and homozygous familial hypercholesterolemic patients, as expected, bound markedly reduced amounts of ligand. The half-life of ¹²⁵I-LDL was measured after it had been introduced into cultured fibroblasts by one of the following processes: (i) uptake via receptor-mediated endocytosis in human skin fibroblasts with normal LDL receptors, or (ii) incorporation via scrape-loading into fibroblasts defective in LDL receptor content. The half-lives obtained were about 1 hour and 50 hours, respectively, indicating that efficient degradation of LDL occurred only when it was deIivered to lysosomes via receptor-mediated endocytosis.

Combinatorial libraries are used in the search for ligands that bind to target proteins. Fmoc solid-phase peptide synthesis is routinely used to generate such libraries. Microwave-assisted peptide synthesis was employed here to decrease reaction times by 80-90%. Two One-Bead-One-Compound combinatorial libraries were synthesized on 130μm beads (one containing 750 members and the other 16, 807). The use of smaller solid supports would have many important practical advantages including; increased library diversity per unit mass, smaller quantities of library needed to generate hits, and screening could be conducted by using a standard flow cytometer. To this end, a miniaturized peptide library was synthesized on 20 μm beads to demonstrate proof of principle. A small sample from the 16,807-member library was screened against transferrin-AlexaFluro 647, a protein responsible for iron transport in vivo. A number of hits were identified and sequenced using techniques coupling nanomanipulation with nanoelectrospray mass spectrometry.

The tetraphosphine DPPEPM reacts with [PtMe2(cod)] to produce [PtMe2(DPPEPM-PP)] (1) in near quantitative yield. On standing in solution, the free P atoms become oxidized to give [PtMe2(DPPEPM(O) 2-PP)] (1a), which has been characterized by X-ray crystallography. In contrast, reactions of DPPEPM with [MCl2(cod)] (M = Pd, Pt) yield ionic products of the form [M(DPPEPM-PP)2]MCl4 (3, 4). When a solution of the platinum complex was allowed to stand, crystals of [Pt(μ-Cl)(μ-DPPEPM)2]Cl3 (5) were obtained. In a third set of reactions, treatment of [PtClR(cod)] (R = Me, Ph) or [PdClMe(cod)] with DPPEPM gives species of the type [MR(DPPEPM-PPP)]Cl (6-8), in which one of the internal P atoms is uncoordinated. Reactions of [PtR2(DPPEPM-PP)] with [PtR2′(cod)] or [MCl2(cod)] (M = Pd, Pt), or of [PtR(DPPEPM-PPP)]Cl with [MCl2(cod)], lead to unsymmetrical bimetallic complexes. [PtMe2(μ-DPPEPM)PdCl2] (11) and [PtClPh(μ-DPPEPM)PdCl2] (14) have been characterized crystallographically. Trimetallic complexes of the form [{PtR 2(μ-DPPEPM)}2M][MCl4] (M = Pd, Pt, 15-17) are produced by reaction of [PtR2(DPPEPM-PP)] with [MCl 2(cod)].

Purpose: In vivo screening of phage-displayed random peptide libraries (RPLs) has been used to identify peptide ligands to targets found on endothelial cells of blood vessels supplying specific tissues such as brain, kidney, and tumor tissue. Peptides that bind specifically to blood vessels supplying tumor tissue have been conjugated to cytotoxic agents and used to successfully eradicate tumors in a mouse model. With the ultimate goal of developing similar methods for treating human cancer, we describe an in vivo RPL screening process that, unlike previous in vivo experiments, does not harm the animal being screened. Methods: RPLs were administered to FVB, BalbC, and tumor-bearing MRL/MpJ-fasLPR mice in a variety of dosing formats. Tumor nodules were excised 10 min following infusion and phage were amplified from the specimens. Phage were reinjected into the same animal within 48 h. This process was repeated twice for a total of three in vivo screens of mouse tumor tissue within the same animal. Mice were observed for systemic side effects, histopathologic damage, and presence of phage in organs. Peptide sequences were determined from several third-pan phage clones. Results: Overall there was minimal toxicity from administration of single or repeat doses of RPLs. Amino acid consensus sequences were identified and some of the sequences were similar to those of peptide ligands that bind matrix metalloproteinases. Conclusions: Serial administration of an RPL is well tolerated and serial panning in individual mice leading to consensus sequence motifs is possible. Based on these preclinical data the Food and Drug Administration has approved the implementation of human clinical trials with this technique.

Since Swiatoslaw Trofimenko first reported their synthesis in 1966, poly(pyrazolyl)borate ligands, [R”ₓB(pz，ᴿ⋅ᴿ’)₄₋ₓ], have found widespread utility in modern coordination chemistry, undoubtedly as a consequence of the numerous facets of the ligand scaffold that can be readily altered. Relative to the extensive efforts directed towards the incorporation of pyrazolyl moieties with different substituents and towards the installation of groups other than hydrogen on the bridgehead boron, comparatively few attempts have been dedicated to elucidating synthetic approaches to altering the identity of the bridgehead atom itself. Such manipulations have the potential to generate new compounds that exhibit both structural and electronic properties previously unobserved or inaccessible for the parent boron compound, and the research summarized herein is motivated both by the paucity of these derivatives and by this potential. Chapter 1 explores the use of aluminum and gallium as linker atoms to afford heavier congeners of traditional poly(azolyl)borates. This study has utilized LiEH₄ (E = Al, Ga) in place of LiBH₄, and significantly has afforded the first structurally characterized examples of tris(pyrazolyl)hydrogallates and of tris(pyrazolyl)methylgallates featuring substituted pyrazolyl groups. Moreover, the structures of {[R”ETpᴿ⋅ᴿ’]Li}₂ (E = Al, Ga) have been found to vary as a consequence of the identity of both the pyrazolyl substituents (R, R’) and the substituent on the linker atom (R”), and in some instances differ significantly from the structures of the corresponding boron derivatives. Additionally, the reactions of LiEH4 with tert-butylmercaptoimidazole, HmimBut, have afforded the first examples of tris(mercaptoimidazolyl) ligands to feature aluminum and gallium bridgeheads. The molecular structures of these derivatives similarly display interesting coordination modes which, in some cases, contrast greatly to those of the parent boron ligands. In Chapter 2, synthetic approaches for the preparation of novel dianionic tris(pyrazolyl) ligands, obtained via the use of magnesium and zinc as linker atoms, are summarized. Interestingly, the otherwise neutral {[MeMTpᴹᵉ²][Li₂]} fragment is found to associate with an additional Lipzᴹᵉ² molecule, thereby affording a series of [MeMTpᴹᵉ²][Li3(pzᴹᵉ²)Ln] compounds in which each lithium is coordinated to two pyrazolyl nitrogen atoms. Both chloride and iodide anions can also serve as capping ligands for the {[MeMTpᴹᵉ²][Li₃]}+ moieties, suggesting that the trilithio scaffold can be viewed as a trifold receptor for anions. Additionally, the tetrakis(pyrazolyl) derivatives, [(THF)2Li{μ-[M(pzᴹᵉ²)₄]}Li(THF)₂], have also been prepared and structurally characterized. Chapter 3 details the preparation, characterization, and reactivity of symmetric homodinuclear magnesium and zinc complexes, [MeM(pzᴹᵉ²)₃MMe]–, in which the two metal centers are bridged by three exo-bidentate pyrazolyl ligands. The bridging of two identical metal centers by more than two pyrazolyl groups is a rare structural motif, and so [MeM(pzᴹᵉ²)₃MMe]– represent important contributions to not only the chemistry of magnesium and zinc, but also to that of the pyrazolyl ligand. The reactivity of [MeZn(pzᴹᵉ²2)₃ZnMe]– towards protic reagents and trimethyltin halides has been investigated, and has most notably afforded a rare example of an anionic terminal zinc fluoride complex, [FZn(pzᴹᵉ²)₃ZnF]–. Additionally, the homodinuclear zinc hydride complex, [HZn(pzᴹᵉ²)₃ZnH]–, has been obtained and structurally characterized, and represents the first example of an anionic terminal zinc hydride compound. The spectroscopic characterization of both [HZn(pzMe2)₃ZnH]– and its isotopologue, [DZn(pzᴹᵉ²)₃ZnD]–, are summarized, as are the results of preliminary reactivity studies with CO2 and CS2, which suggest that insertion of these heterocumulenes into the Zn–H bonds is facile and affords, inter alia, zinc formate and zinc dithioformate species, respectively. Chapter 4 summarizes the exocyclic N-methylation of Nitron(S), a 1,2,4-triazole thione derived from Nitron. The molecular structures of both Nitron(S) and of the methylated derivative, Nitron(S)Me, are reported, and a comparison of metrical data indicates that (i) the structures of these thiones differ significantly from the dominant tautomer of Nitron and (ii) the structures of these thiones compare favorably with the NHC tautomer of Nitron. Analyses of these compounds using natural bond orbital (NBO) and natural resonance theory (NRT) methods are in accord with the experimental structures.