The present PhD thesis describes the synthesis and characterisation of Co(2+/3+) complexes with triarylamine-substituted polypyridyl-based ligands. A light- or temperature-induced intramolecular electron transfer between the Co and the triarylamine moieties was found in the tri-cationic complexes, which was examined with electrochemical measurements, DFT calculations, optical and dynamic 1H NMR spectroscopy. This process is coupled to a high-spin <--> low-spin transition on the metal. The emphasis of this PhD thesis was the adjustment of a redox equilibrium between the paramagnetic ([Co2+(L+)(L)]3+) and diamagnetic ([Co3+(L)2]3+) formulation (L = triarylaminedecorated ligands) via the electron transfer. The position of this equilibrium is influenced by the complexes' structure and environment. Constitutional changes in the ligand topology were performed to modify the electronic properties of the triarylamine substituents and to vary the distance between the redox centres, namely the Co ion and the triarylamine nitrogen atom. If they are located within their van-der-Waals radii, photochemical excitation of the diamagnetic ground state leads to the paramagnetic excited state. A temperature-dependent redox equilibrium was found with an increased distance between the redox centres (d = 8 Å), due to the different entropies of the redox isomers.

Ce mémoire vise à montrer l’intérêt de nanoparticules (NPs) de TiO2 comme plateforme pour immobiliser dans un environnement proche des complexes de coordination pouvant interagir par transfert d’électron photoinduit. Nous nous sommes intéressés à l’étude de nanomatériaux hybrides associant le complexe [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) comme photosensibilisateur aux complexes [Cr(ttpy)2]3+ ou [Mn(ttpy)(CO)3Br] (ttpy = 4'-(p-tolyl)-2,2':6',2''-terpyridine) comme accepteurs d'électrons. Pour immobiliser les différents complexes à la surface du TiO2, une fonction acide phosphonique a été introduite sur une des bipyridines du centre [Ru(bpy)3]2+ et sur la terpyridine des complexes [Cr(ttpy)2]3+. L’étude des processus de transferts de charges photo-induits sous irradiation en lumière visible sur le colloïde TiO2/RuII montre que l'état à charges séparées (e-)TiO2/ RuIII possède une longue durée de vie, ce qui rend possible l'utilisation des charges dans des réactions successives d’oxydation ou de réduction. Notamment l’irradiation du colloïde TiO2/RuII en présence de [Cr(ttpy)2]3+ et de triéthanolamine (TEOA) comme donneur d'électron sacrificiel permet la réduction à deux électrons du [Cr(ttpy)2]3+. Par la suite, le complexe [Cr(ttpy)2]3+ est immobilisé sur les NPs de TiO2/RuII pour former un assemblage RuII/TiO2/CrIII au sein duquel les processus de transfert d'électrons photo-induits sont étudiés. De manière à proposer un système pour la réduction photocatalytique du CO2, le complexe [Mn(ttpy)(CO)3Br] a été co-immobilisé avec le [Ru(bpy)3]2+ suivant une approche de chimie sur surface pour former le colloïde RuII/TiO2/MnI. Ce système présente une excellente sélectivité vis-à-vis du HCOOH comme seul produit de la photoréduction du CO2 en présence de 1-benzyl-1,4-dihydronicotinamide (BNAH) comme donneur d'électron sacrificiel. Un système hybride associant le [Ru(bpy)3]2+ portant des fonctions pyrroles et immobilisé sur TiO2 a également été synthétisé et étudié. Sous irradiation lumineuse, le transfert de charges (e-)TiO2/[Ru-pyr]3+ permet d’induire la polymérisation du pyrrole. Le nanocomposite TiO2/poly(Ru-pyr) obtenu et déposé sur une électrode génère, en présence de TEOA, un photocourant anodique stable de plus de 10 μA.cm-2. L’ensemble des résultats montre que les NPs de TiO2 peuvent être un moyen d’assembler des complexes dans un environnement proche en limitant les interactions à l’état fondamental, mais permettant des transferts d’électrons photoinduits entre eux. Suivant les potentiels redox des différents composants, les transferts d’électron ont lieu soit via la nanoparticule soit en surface de celle-ci. / This thesis aims to investigate the possibility of using TiO2 nanoparticles (NPs) as a platform to immobilize proximal coordination complexes that can interact with each other by photoinduced electron transfer. We have studied hybrid nanomaterials combining [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a photosensitizer and [Cr(ttpy)2]3+ or [Mn(ttpy)(CO)3Br (ttpy = 4'-(p-tolyl)-2,2':6',2''-terpyridine) as electron acceptors. To immobilize the various complexes on the surface of TiO2, a phosphonic acid functional group was introduced on one of the bipyridines of the [Ru(bpy)3]2+ center and on the terpyridines of the [Cr(ttpy)2]3+ complex. Under visible light, the TiO2/RuII colloid undergoes a photo-induced charge transfer process leading to a long-lived charge separation state (e )TiO2/RuIII, which makes it possible to be engaged in successive oxidation or reduction reactions. In particular, the visible irradiation of the TiO2/RuII colloid in the presence of [Cr(ttpy)2]3+ and triethanolamine (TEOA) as a sacrificial electron donor allows the two-electron reduction of [Cr(ttpy)2]3+. Subsequently, the [Cr(ttpy)2]3+ complex has been immobilized on the TiO2/RuII NPs to form a RuII/TiO2/CrIII assembly in which the photoinduced electron transfer processes were investigated. In order to propose a system for the photocatalytic reduction of CO2, the [Mn(ttpy)(CO)3Br] and [Ru(bpy)3]2+ complexes were co-immobilized on TiO2 NPs following a chemistry on surface approach to form a RuII/TiO2/MnI triad. Under irradiation at 470 nm, this system exhibits excellent selectivity towards HCOOH as the only product of CO2 photoreduction in DMF/TEOA solvent mixture, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial electron donor. Another hybrid system linking a [Ru(bpy)3]2+ unit to two pyrrole functions and being immobilized on TiO2 has also been synthesized and studied. Under visible light, the transient (e-)TiO2/[Ru-pyr]3+ species induce the polymerization of pyrrole to form a TiO2/poly(Ru-pyr) nanocomposite. The nanocomposite deposited on an electrode generates, in the presence of TEOA, a stable anodic photocurrent of more than 10 μA.cm-2. All the results show that TiO2 NPs can be used to associate different complexes in a close environment by limiting the interactions in the ground state but allow photoinduced electron transfer processes between them. Depending on the redox potentials of the different components, the electron transfer takes place either through the semiconducting NPs or on the surface.

The consecutive synthesis of 1,3,5-triferrocenyl-2,4,6-tris(ethynylferrocenyl)benzene (6c) is described using 1,3,5-Cl3-2,4,6-I3-C6 (2) as starting compound. Subsequent Sonogashira C,C cross-coupling of 2 with FcC[triple bond, length as m-dash]CH (3) in the molar ratio of 1 : 4 afforded solely 1,3,5-Cl3-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (4c) (Fc = Fe(η5-C5H4)(η5-C5H5)). However, when 2 is reacted with 3 in a 1 : 3 ratio a mixture of 1,3,5-Cl3-2-(FcC[triple bond, length as m-dash]C)-4,6-I2-C6 (4a) and 1,3,5-Cl3-2,4-(FcC[triple bond, length as m-dash]C)2-6-I-C6 (4b) is obtained. Negishi C,C cross-coupling of 4c with FcZnCl (5) in the presence of catalytic amounts of [Pd(CH2C(CH3)2P(tC4H9)2)(μ-Cl)]2 gave 1,3-Cl2-5-Fc-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6a), 1-Cl-3,5-Fc2-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6b) and 1,3,5-Fc3-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6c) of which 6b is the main product. Column chromatography allowed the separation of these organometallic species. The structures of 4a,b and 6a in the solid state were determined by single crystal X-ray diffractometry showing a π–π interacting dimer (4b) and a complex π–π pattern for 6a. The electrochemical properties of 4a–c and 6a–c were studied by cyclic voltammetry (=CV) and square wave voltammetry (=SWV). It was found that the FcC[triple bond, length as m-dash]C-substituted benzenes 4a–c show only one reversible redox event, indicating a simultaneous oxidation of all ferrocenyl units, whereby 4c is most difficult to oxidise (4a, E°′1 = 190, ΔEp = 71; 4b, E°′1 = 195, ΔEp = 59; 4c, E°′1 = 390, ΔEp = 59 mV). In case of 4c, the oxidation states 4cn+ (n = 2, 3) are destabilised by the partial negative charge of the electronegative chlorine atoms, which compensates the repulsive electrostatic Fc+–Fc+ interactions with attractive electrostatic Fc+–Clδ− interactions. When ferrocenyl units are directly attached to the benzene C6 core, organometallic 6a shows three, 6b five and 6c six separated reversible waves highlighting that the Fc units can separately be oxidised. UV-Vis/NIR spectroscopy allowed to determine IVCT absorptions (=Inter Valence Charge Transfer) for 6cn+ (n = 1, 2) (n = 1: νmax = 7860 cm−1, εmax = 405 L mol−1 cm−1, Δν1/2 = 7070 cm−1; n = 2: νmax = 9070 cm−1, εmax = 620 L mol−1 cm−1, Δν1/2 = 8010 cm−1) classifying these mixed-valent species as weakly coupled class II systems according to Robin and Day, while for 6a,b only LMCT transitions (=ligand to metal charge transfer) could be detected. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Electrochemical methods have been used to study electron transfer reactions at the interface between an aqueous phase of less than 1 femto liters in volume and a bulk organic phase. The small aqueous phase is formed at the end of a slightly recessed platinum electrode. When a negative potential is applied between the Pt electrode and the aqueous phase, Ru(NH3)63+ in the aqueous phase could be reduced to Ru(NH3)62+. Because the volume of the aqueous phase is very small, the electrochemically formed Ru(NH3)62+ could instantly reach the interface between the aqueous phase and the organic phase which contains 7,7,8,8-Teteracyanoquinodimethane (TCNQ), and be oxidized to form Ru(NH3)63+ by giving electrons to TCNQ at the interface. Our results showed a positive shift in the E1/2 comparing the reaction undertaken in the recessed cavity and the bulk solution.

Rare earth and actinide metals, critical to security, medicine, and the economy, have been processed through methods such as solvent extraction and electrorefining. To minimize radiological waste and improve yield, a 'chloride volatility' process--also known as the chlorination and volatilization process (CVP)--has been proposed and demonstrated for processing rare earths. The process takes advantage of the low vapor pressure of rare earth chlorides (<700 >°C), CaCl2 was added to LaCl3 to lower the melting temperature. LaCl3 electrochemical behavior has not previously been studied in CaCl2. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were applied to LaCl3 salts in CaCl2-LiCl and CaCl2 to study the metal ion behavior. Various electrode materials were compared at low CV scan rates (s-1) to determine compatibility with chlorine gas evolution. Experiments of eutectic LaCl3-CaCl2 were performed and analyzed to determine the efficacy of chlorine gas generation via electrolysis for the CVP. Through galvanostatic electrolysis, oxidation of chloride ions and subsequent chlorination of rare earth was demonstrated, with cerium chosen as the representative rare earth metal. Through a quadrupole mass spectrometer plumbed in line with the electrolytic cell, the quality of the generated gas was analyzed.

Mit der Entdeckung von Graphen begann ein neuer Zeitabschnitt für die Entwicklung von Elektronik und Sensoren aufgrund der einzigartigen elektronischen Struktur Graphens. Graphen ist breit vertreten, beispielsweise in Anwendungsbereichen von Sensorik, Energiespeicherung und Katalyse. Elektronentransferprozesse sind fundamentale Prozesse für eben solche Anwendungen. Die Eigenschaften des heterogenen Elektronentransfers von Graphen sind sehr umstritten und es gibt immer noch kein einheitliches Bild, um eben jenen zu verstehen, da oft voneinander abweichende Eigenschaften in der Literatur dargestellt werden. Diese Arbeit präsentiert systematische Untersuchungen der Elektronentransfereigenschaften von einlagigen Graphenelektroden. Als weiterer Teil dieser Arbeit werden die Elektronentransfereigenschaften durch den Entwurf einer neuen Graphen-Hybridelektrode gezielt verändert. Der erste Teil ist auf die Verbesserung der Herstellungsschritte und der anschließenden Untersuchung des Einflusses von Kupferrückständen auf die Kinetik des Elektronentransfers von einlagigen Graphenelektroden fokussiert. Die Kupferrückstände kommen von der Herstellung und dem Transfer von Graphen. Die Elektronentransferkinetik von klassischen Redoxmediatoren mit inner-sphere Elektronentransfermechanismus nimmt nach erfolgreichen Entfernen von Kupferrückständen ab. Im Gegensatz dazu bleibt die Kinetik von outer-sphere Redoxmediatoren unberührt. Hier wird gezeigt, dass die Elektronentransferkinetik von solchen Redoxmediatoren vom pH-Wert der Lösung abhängig ist, obwohl bei dem Elektronentransfer Protonen nicht involviert sind. Weiterhin wird hier festgestellt, dass der Elektronentransfer von Kationen an Graphen am schnellsten in neutralem pH stattfindet, während der Elektronentransfer von Anionen am schnellsten in saurem Millieu abläuft. Diese pH-Abhängigkeit wird den elektrostatischen Wechselwirkungen zwischen den dissoziierten Redoxmediatoren und der Ladung der Graphen-Flüssigkeit-Grenzschicht zugeschrieben. Dieses Verhalten wird auch für Graphenelektroden auf anderen isolierenden Substraten und sogar mit einer unter dem Graphen liegenden Schicht von hexagonalem Bornitrid (hBN) gefunden. Basierend darauf ist die Schlussfolgerung, dass diese pH-Abhängigkeit für den Elektronentransfer von geladenen Redoxmediatoren an Graphenelektroden intrinsisch und spezifisch für Graphen ist. Mit Metallsubstraten unter dem Graphen kann dieser pH-Effekt unterdrückt werden, was für einen verstärkten elektrokatalytischen Effekt vom darunterliegenden Metall spricht, welcher dem vorher diskutierten elektrostatischen Effekt, vermutlich durch die Zunahme der gesamten Elektronendichte, überwiegt. Basierend darauf wurde eine neue Art von Graphenelektrode entwickelt: die Graphen-Sandwichelektrode. Diese Elektrode besteht aus zwei aufeinanderliegenden Graphenschichten mit dazwischenliegenden Metallpartikeln. Diese Sandwichelektrode nutzt die elektrochemischen Eigenschaften der in der Mitte liegenden Metallpartikeln aus, obwohl das Metall durch eine Graphenschicht bedeckt ist und nicht in Kontakt mit der Lösung kommt. Bei der Verwendung von Platinpartikeln wird die obere Graphenschicht mit elektrokatalytischen Eigenschaften versehen. Als Ergebnis wird die Bildung von Wasserstoff (HER) und die Reduktion von Sauerstoff (ORR) an dieser Elektrode katalysiert. Des Weiteren wird dieser Effekt hier dafür genutzt um Wasserstoffperoxid zu messen, auch wenn eine solche Reaktion an einer „normalen“ Graphenelektrode nicht beobachtet werden kann. Hierdurch wird eine neue Klasse von optimierten Elektroden mit maßgeschneiderten elektrokatalytischen Eigenschaften realisiert. Diese Ergebnisse heben den Einfluss eines unter Graphen liegenden Metalls auf die Elektrochemie von Graphen hervor. Der zweite Teil dieser Arbeit konzentriert sich auf die Untersuchungen von Ladungen an der Graphen-Flüssigkeit-Grenzschicht auf einem lokalen und räumlich aufgelösten Niveau mit Hilfe von Rasterionenleitfähigkeitsmikroskopie (Scanning Ion Conductance Microscope - SICM). Dafür sind weiche Trägerflächen benötigt, die die Spitzen von Glaskapillaren nicht beschädigen. Diesbezüglich werden drei Protokolle für den Transfer von Graphen auf ein weiches Polymersubstrat, dem Polydimetyhlsiloxan (PDMS), entwickelt. Die dadurch erhaltenen Graphenproben werden mit Hilfe von optischer und Rasterkraftmikroskopie charakterisiert. Anhand von Annäherungskurven aus der SICM kann die Oberflächenladung qualitativ charakterisiert werden. Die Oberflächenladung einer Graphenoberfläche kann als negativ geladen in einem pH-Wert von 7 entschlüsselt werden. Zusätzlich werden Herausforderungen und Hindernisse beim Arbeiten mit SICM zu Grenzflächenuntersuchungen von einlagigem Graphen diskutiert. Diese Ausarbeitung zeigt die Bedeutung von Grenzflächenladungen und den Einfluss von unter dem Graphen liegenden Metall auf Graphen und graphenverwandte Elektroden auf. Dieses Wissen kann genutzt werden, um neue graphenbasierte Sensoren und auch hybride Elektroden für Elektrokatalyse zu entwickeln. / The discovery of graphene initiated a new era of electronic and sensor development due to graphene's unique electronic structure. Graphene covers a wide range of applications including sensing, energy storage and catalysis. The heterogeneous electron transfer (ET) is the most fundamental and most important process happening at devices in such applications. However, the ET properties of graphene are highly debated and still no coherent picture can be drawn to understand them since differing ET rates are presented in literature. This work presents systematic investigations of the ET characteristics of graphene monolayer electrodes. Furthermore, the ET properties are engineered by the fabrication of a novel graphene-based hybrid electrode. The first part focusses on the improvement of the fabrication steps and subsequent investigation of the influence of Cu trace residues on the ET kinetics of graphene monolayer electrodes. The residual Cu traces come from the fabrication process of graphene as well as from the transfer process of graphene monolayer electrodes. The ET kinetics of a classical inner-sphere redox probe decreases after a successful removal of Cu particles. In contrast to this, the ET kinetics for outer-sphere redox probes stay unaffected. Most importantly, the ET kinetics of both kinds of redox probes are found to be dependent on the solution pH, although these reactions are proton independent. ET at graphene with cations is found to be fastest in neutral pH, while the ET kinetics of anions are fastest in acidic media. This pH dependency is attributed to electrostatic interactions between the dissociated redox probes and the interfacial charge at the graphene-liquid interface (GLI). This behavior is further observed for graphene monolayer electrodes on other insulating substrates. Even with an underlying hexagonal boron nitride (hBN) layer that shields the graphene monolayer from the substrate, the same pH effect can be observed. Based on this, it can be concluded that the pH dependency of ET at graphene for charged redox species is intrinsic to graphene. By using a subsurface metal substrate, the pH effect is suppressed, indicating an enhanced electrocatalytic effect from the metal underneath that dominates the afore discovered electrostatic effect, most likely due to an increase of the overall electron density. By exploiting this effect, a new kind of graphene electrode is designed: the graphene sandwich electrode. This electrode consists of two graphene monolayers, with electrodeposited metal particles between both layers. This sandwich electrode exploits electrochemical properties of the metal in between, even though the metal is covered by a graphene monolayer and hence not exposed to the liquid. By using Pt particles, the upper graphene layer gets rendered with electrocatalytic properties. As a result, the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) are found to be clearly catalyzed at this electrode. Furthermore, this effect is exploited for hydrogen peroxide sensing, while this reaction is not observable on pristine graphene. Thus, a new kind of engineered electrode with rendered novel electrocatalytic properties was designed. These findings highlight the influence of a subsurface metal on to the electrochemistry of graphene. The second part of this work focusses on using scanning ion conductance microscopy (SICM) to investigate interfacial charges at the GLI at a local and spatially resolved level. First, for investigations using an SICM, soft samples are needed for avoiding damage of SICM tips. For this, three different protocols are developed and discussed for transferring a graphene monolayer on a soft poly(dimethylsiloxane) (PDMS) substrate. The obtained graphene samples are characterized using optical and atomic force microscopy. By utilizing approach curves in SICM, the surface charge can be characterized qualitatively. At a graphene surface in pH 7, an overall negative surface charge can be deciphered. In addition, challenges and obstacles are discussed when using SICM for interfacial investigations of graphene monolayers. Taken together, this work presents systematic investigations of the ET of graphene monolayer and graphene sandwich electrodes. These findings improve the understanding of graphene electrochemistry and highlights the importance of interfacial charge and the influence of a subsurface metal on graphene and graphene-related electrodes. This knowledge can be used to design new graphene-based sensors and hybrid electrodes for electrocatalysis.

Qu’il s’agisse de s’éclairer, de se chauffer, de s’alimenter sainement, de se soigner, de se véhiculer, de s’informer ou encore de se distraire, l’énergie a toujours été au centre des préoccupations et sa conversion en électricité est désormais omniprésente. Le lourd constat environnemental à la suite de l’exploitation intensive de sources fossiles a mené à une indispensable transition vers les énergies renouvelables. Souvent intermittentes, il est nécessaire de les stocker, généralement grâce à des batteries. Parmi les différentes technologies, cette thèse traite des batteries lithium-ion pour le stockage de l’énergie solaire. En effet, cette thèse a pour but l’étude d’un dispositif « tout-en-un » capable de convertir l’énergie solaire et de la stocker. Pour se faire, un semi-conducteur organique photoactif de la famille des pérylènes diimides (PDI) a été emprunté au domaine des cellules solaires organiques et couplé à un matériau phare et durable des batteries lithium-ion : le LiFePO4 (LFP). Cette thèse se décompose en trois parties selon une méthodologie qui vise à la compréhension fondamentale de transferts électroniques photoinduits, en amont du développement d’un dispositif. Pour aboutir à une preuve de concept, une étude de l’extinction de fluorescence du PDI en présence de LFP a d’abord été menée, afin de vérifier l’injection d’électrons en provenance du matériau de batterie dans le semi-conducteur excité. Ce travail a été fait en solution puis à l’état solide, pour la mise au point d’une photoélectrode. Ces deux études ont permis de comprendre les pré-requis du matériau d’électrode positive de batterie pour qu’il soit photoxydé, puis des résultats de spectroscopie Raman ont démontré l’importance des interfaces dans la mise en contact du PDI et du LFP. Finalement, forts d’une première preuve expérimentale de photocharge au sein d’un dispositif « photobatterie », le PDI a été polymérisé et son implémentation dans une photoélectrode de batterie lithium-ion a pu être optimisée. Ses rôles multiples (photoactif, photooxydant, conducteur électronique et liant) ont permis de générer un photocourant sans que cela ne soit au détriment du fonctionnement de la batterie. / Converting energy to electricity is ubiquitous because it plays a vital role in daily life whether for lighting, heating, health, transport, information or entertainment. Societal energy demands are often met with fuel fossils that have had deleterious environmental effects. Transitioning to renewables can mitigate these adverse outcomes. Renewable energy is often intermittent, requiring it to be stored for use during periods when the energy is unavailable. Batteries have become viable means to this end. Among the different technologies, this manuscript examines lithium-ion batteries for solar energy storage. Indeed, this work puts forward an all-in-one device: a device capable of converting and storing solar energy. To this end, a well-known photoactive organic semi-conductor in solar cells (perylene diimide; PDI) was coupled to a conventional and durable electrode material (LiFePO4; LFP) for lithium-ion batteries. This manuscript is divided into three discrete parts following the methodology to demonstrate the fundamental underlying processes of the future all-in-one device before its development: light harvesting and electron transfer. Towards a proof of concept, the thesis systematically studied the light mediated processes in solution, in the solid state, and in an operating device. Initial studies examined the fluorescence quenching of PDI with LFP. This was to validate the injection of electrons from the battery material to the photoexcited semi-conductor indeed occurred. The same emission studies were applied in the solid state for developing a photoelectrode. The two studies generated knowledge about the compositional and architectural requirements of the positive electrode material for it be photoxidized by PDI. Raman spectroscopy further demonstrated the importance of interfaces between the battery material and the organic semiconductor. These enabled a photocharge when the photobattery was illuminated. The PDI was next polymerized and enabled a photocurrent in the battery, courtesy of its collective properties (light harvester, photo-oxidant, electronic conductor, and binder).

No description available.

Based on the success of diacyl-tert-butylhydrazines RH-5849 and RH-1266 in controlling agricultural crop pests, we endeavored to synthesize our own diacylbenzyl- and arylhydrazine derivatives for use against the malaria vector Anopheles gambiae. In the process of producing a library of compounds for assay against An. gambiae, it became clear that employing regioselective acylation techniques (in molecules that feature two nucleophilic, acyclic nitrogen atoms α to one another) would be imperative. Synthesis of the library derivatives proceeded rapidly and after topical assay, we found three compounds that were more toxic than the RH-series leads. One of the three displayed an LD50 value of half that of RH-1266, though patch clamp assay concluded that toxicity was not necessarily linked to inhibition of mosquito K+ channel Kv2.1. The acylation of monoarylhydrazines appears simple, but its regioselectivity is poorly understood when assumed as a function of basicity correlating to nucleophilic strength. We determined the ratio of the rate constants for distal to proximal N-acylation using 19F NMR spectroscopic analysis of reactions of 4-fluorophenylhydrazine with limiting (0.2 equiv) acylating agent in the presence of various bases. Acid anhydrides gave consistent preference for distal acylation. The selectivity of acylation by acyl chlorides when using pyridine gives strong distal preference, whereas use of triethylamine or aqueous base in conjunction with aroyl chlorides showed a moderate preference for proximal acylation. This observation yielded a convenient one-step method to synthesize proximal aroylarylhydrazines in yields comparable or superior to that provided by the standard three-step literature approach. Combined with NMR evidence of the distal nitrogen as the unambigiously stronger base of the two nitrogens, we propose a single electron transfer mechanism that predicts the regiochemistry of arylhydrazines toward acylating agents better than the nucleophilicity model based on pKa values. While synthesizing the acylhydrazine library for assay against An. gambiae, NMR spectroscopy revealed rotational isomerisms of two types: chiral helicity (M)/(P) and acyl (E)/(Z)-isomerism due to hindered rotation. Variable temperature NMR allowed the measurement of N-N bond rotational barriers, as well as estimate the barrier of (E)/(Z) interconversion. We obtained the X-ray crystal structures of four diacylhydrazines to test this hypothesis and revealed both the twist conformation around the N-N bond axis and (E)/(Z)-isomerism around the proximal acyl group. Computation (which agreed with the crystal structures) allowed us to estimate which (E)/(Z)-isomers were most likely being observed in solution at room temperature by NMR spectroscopy. In addition, we were able to calculate transition structures corresponding to N-N bond rotational barriers of (E,Z)- and (Z,Z)-isomers of model molecules and rationalize the difference in coalescence temperatures between (E,Z)- and (Z,Z)-isomers. / Ph. D.

No description available.