Philosophiae Doctor - PhD / Energy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading-edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT). / 2023-12-01

Petroleum powered vehicles emit volatile organic compounds (VOCs) through combustion that contributes to the pollution of the environment. A technique in the 1970s was developed to decrease these emissions, especially for nitrogen oxides (NOx) and sulphuric oxides (SOx) which is called exhaust gas recirculation (EGR). The technique works by recirculating a portion of the combusted gas back into the engine, this limits the NOx and SOx emissions because of lower temperatures and less available oxygen. The problems that follow these effects is the formation and condensation of acids that corrode the material of the EGR system, which are created by many different reactions. It is of importance to understand how the compounds in the EGR system behaves through analysis of authentic and simulated condensates, which is why a quantitative method for these compounds are of interest. The aim of the project was to develop a simple quantitative analysis method for formic acid, acetic acid, and lactic acid in aqueous solution, which was done at Gränges Sweden AB. The technique used for detection and quantification was gas chromatography (GC) coupled to a flame ionization detector (FID) and a water compatible polyethylene glycol (PEG) column. Fractional factorial design (FFD) was used for determination of adequate operating parameters of the GC method and the sample preparation. Sample preparation only required filtration and pH adjustment prior to direct aqueous injection (DAI) to the chromatographic instrument. Detection of the analytes was very difficult because of non-compatibility with the FID, and quantification of asymmetric peak shapes made this problem worse, omitting lactic acid from further analysis. Limit of detection (LOD) and limit of quantification (LOQ) was 490 and 1640 ppm for formic acid and 120 and 400 ppm for acetic acid, with an injection volume of 0.3 μL and split ratio 10:1. Limits were too high for every EGR sample leaving no peaks detected for the sample preparation used. Further development should be done with complementary techniques and sample reprocessing in order to quantify the compounds.

Cancer is responsible for upward of 13% of human deaths. Contemporary chemotherapy of disseminated cancer is often thwarted by dose limiting systemic toxicity and by multi-drug resistance (MDR). Riminophenazines are a novel class of potential anticancer agents that possess a potent multi-mechanistic antineoplastic action. Apart from their broad action against intrinsic, non-classical resistance, Riminophenazines inhibit the action of Pgp and hypothetically all ABC transporters demonstrating their great utility against classical MDR. Considering that combination chemotherapy is the norm, the vision directing R&D efforts was that Riminophenazines could be used with benefit within many standard chemotherapeutic regimes. The strategic intent of this project was to attain improved therapeutic benefit for patients through gains in both pharmaco dynamic and pharmacokinetic specificity for cancer cells over what is currently available. Tactically, this was driven through the use of synergistic Fixed-Ratio Drug Combinations (FRDC) encapsulated within tumour-targeting Nanoparticulate Drug Delivery Systems (NDDS). Long-term aims of this R&D project were to: 1) Screen FRDC of clofazimine (B663) and the lead derivative (B4125) with etoposide, paclitaxel and vinblastine for synergistic drug interactions in vitro. 2) Design, assemble and characterize a novel nanoparticulate, synergistic, anticancer co-formulation. 3) Evaluate the in vivo safety and efficacy of the developed product/s in accordance with international regulatory guidelines. Using the median effect and combination index equations, impressive in vitro synergistic drug interactions (CI<1) were shown for various FRDC of the three standard chemotherapeutics tested (etoposide, paclitaxel and vinblastine) in combination with either B663 or B4125 against MDR neoplastic cell cultures. Considering in vitro results and with the view to advance quickly to clinical studies, the already approved clofazimine (B663) was elected as the combination partner for paclitaxel (PTX). Considering the potency and wide action of PTX, a novel coformulation (designed to circumvent drug resistance) has the potential to greatly impact upon virtually all cancer types, particularly if selectively delivered through innovative delivery systems and loco-regional administration. A passively tumour targeting, micellular NDDS system called Riminocelles™ that encapsulates a synergistic FRDC of B663 and PTX has been designed, assembled using thin film hydration methods and characterized in terms of drug loading, particle size, zeta potential, CMC and drug retention under sink conditions. An acute toxicity and a GLP repeat dose toxicity study confirmed Riminocelles to be well tolerated and safe at clinically relevant dosages whilst Taxol® (QDx7) produced statistically significant (P<0.05) weight loss within 14 days. The same study demonstrated statistically significant (P<0.05) tumour growth delays superior to that of Taxol at an equivalent PTX dosage of 10 mg/kg. Importantly, all components (amphiphiles and drugs) used in assembly of Riminocelles are already individually approved for medicinal use - this promotes accelerated development towards advanced clinical trials and successful registration. Although these results are very promising (outperforming Taxol), this system was however found in a pharmacokinetic study to suffer from in vivo thermodynamic instability due to the high concentration (abundance) of albumin present in plasma. For this reason, in vivo longevity within circulation, permitting passive tumour accumulation was not fully realized. A second NDDS called the RiminoPLUS™ imaging system was additionally developed. This lipopolymeric nanoemulsion system has successfully entrapped Lipiodol® Ultra fluid (an oil based contrast agent) within the hydrophobic core of a monodisperse particle population with a size of roughly 100 nm and a stability of one week. This formulation is therefore thought capable of CT imaging of tumour tissue and drug targeting after either intravenous or loco-regional injection. In vivo proof of the imaging concept is warranted. The results of this study serve to highlight the great potential of in vitro optimized synergistic FRDC against drug resistant cancers. Lipopolymeric micelles are an effective way to formulate multiple hydrophobic drugs for intravenous administration and present a means by which cancer can be readily targeted; provided that the delivery system possess the prerequisite in vivo stability and surface attributes. Further experiments exploring synergistic drug and biological combinations as well as “intelligent” NDDS actively guided through specific molecular recognition are called for. / Thesis (PhD)--University of Pretoria, 2012. / Pharmacology / unrestricted

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / The present study includes the use of a green synthetic method to prepare copper and silver nanoparticles using chitosan, aqueous extracts of Camellia sinensis, Combretum molle and Melia azedarach linn leaves. This study aims to investigate the influence of capping and precursor concentration on the properties of silver nanoparticles with emphasis on the medicinal plants chosen. The effect of capping agent on the properties of copper nanoparticles is also investigated. The phytochemical properties of plant extracts and the antimicrobial activity of the synthesized particles were also studied; this was achieved by using microdilution bioassay. Decoction method was used to extract secondary metabolites from plant leaves. Preliminary phytochemical screening carried out on the aqueous extracts of the plant leaves showed the presence of tannins, proteins, flavonoids, phenols, and carbohydrates. The total phenolic and flavonoids content of the aqueous extract was determined using spectroscopic methods. The highest phenolic content was found in the aqueous extract of Combretum molle (135 mg/g), and the highest flavonoid content was found in the aqueous extract of Camellia sinensis (0.4 mg/g). Characterization was done by a combination of spectroscopic, microscopy and XRD techniques. Both the size and shape of the synthesized silver nanoparticles were dependent on the identity of the capping molecule, precursor and capping agent concentration as depicted from their TEM and XRD results. Silver nanoparticles were found to be predominantly spherical. The capping agent concentration was also found to influence the degree of agglomeration, with an increase in capping agent concentration giving lesser agglomeration. FTIR spectral analysis showed that silver nanoparticles interact with bioactive compounds found in the plants through the hydroxyl functional group. Other shapes including diamond were observed for the effect of precursor concentration. The XRD micrographs revealed a face-centered cubic geometry and the phase remained the same with an increase in precursor concentration. The synthesized silver nanoparticles were all blue shifted compared to the bulk material. The TEM results revealed that copper nanoparticles with different sizes and shapes were successfully synthesized. All the prepared copper and silver nanoparticles showed satisfactory antifungal and antibacterial activity against Candida albicans, Cryptococcus neoformans, Staphylococcus aureus, Enterococcus faecalis, Klebsiella pneumonia and Pseudomonas aeruginosa. The capping molecules used in this study also showed some antibacterial and antifungal activity against the selected strains. However nanoparticles performed better than these capping molecules. Both silver and copper nanoparticles were found to be more active against gram-negative bacteria compared to gram-positive bacteria. Amongst all the prepared silver nanoparticles Combretum molle capped nanoparticles were found to be the most active nanoparticles. Also with copper nanoparticles, it was found that Combretum molle capped nanoparticles were the most active nanoparticles. Between the two metal nanoparticles, silver nanoparticles showed high antibacterial and antifungal activity compared to copper nanoparticles. The antioxidant activity of silver nanoparticles was assessed using 2.2-diphenyl-1-picrylhydrazyl. Silver nanoparticles were found to have some antioxidant activity. However, the capping molecules were found to be more active than the synthesized nanoparticles. This observation is attributed to the presence of some bioactive compounds in the plant extracts.

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (−)-trans-dihydroxygirinimbine and the assignment of its absolute configuration. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Mixed association of calix[4]resorcinarene with ethyl sulfonate groups on the lower rim and dimethylaminomethyl groups on the upper rim (CR) and cationic surfactant 4-aza-1-hexadecyl-azoniabicyclo[2.2.2]octane bromide (DABCO-16) is studied by methods of tensiometry, conductometry, potentiometry and NMR spectroscopy at fixed CR concentration and varied surfactant concentration. Beyond ca. 0.4 mM of DABCO-16, mixed aggregates enriched by CR are proved to be formed due to electrostatic forces, while beyond ca. 5 mM, aggregates enriched by surfactant occur due to the hydrophobic effect. Spectrophotometry monitoring of the solubilization of a hydrophobic dye, Orange OT, demonstrated that only the second type of mixed aggregate enriched by DABCO-16 is capable of binding the organic probe, while the mixed system where the surfactant is a minor component shows no binding capacity towards Orange OT. This finding can be used for the design of nanocontainers with controllable binding/release properties. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Diese Arbeit widmet sich der Untersuchung der dynamischen und strukturellen Eigenschaften sowie des Phasenverhaltens konzentrierter flüssiger Elektrolyte und ihrer Anwendung in Energiespeichern mittels Methoden der statistischen Mechanik und mithilfe atomistischer Molekulardynamik (MD) Simulationen. Zuerst untersuchen wir die Struktur-Eigenschafts-Beziehungen in konzentrierten Elektrolytlösungen wie sie in Lithium-Schwefel (Li/S), durch wir ein MD Simulationsmodell repräsentativer state-of-the-art Elektrolyt-Systeme für Li/S-Batterien bestehend aus Polysulfiden, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) und LiNO 3 Elektrolyten mit jeweils unterschiedlichen Kettenlängen gemischt in organischen Lösungsmitteln aus 1,2-dimethoxyethane and 1,3-dioxolane erstellen. Als Zweites befassen wir uns mit der Phasenseparation, die auftritt, wenn sich die physikalisch-chemischen Eigenschaften flüssiger Gemische voneinander unterscheiden. Diese Systeme bestehen üblicherweise aus einem konzentrierten anorganischen Salz und einer ionischen Flüssigkeit. In dieser Arbeit untersuchen wir eine Vielfalt von hochkonzentrierten wässrigen Elektrolytlösungen, die aus unterschiedlichen Zusammensetzungen von LiCl und LiTFSI bestehen. Daraufhin beantworten wir die Frage, wie unterschiedlich die Komponenten in der wässrigen Lösung gemischt sein sollten, damit eine solche flüssig-flüssig-Phasentrennung stattfinden kann. Als letztes untersuchen wir die Ladungsabschirmung, die ein grundlegendes Phänomen ist, das die Struktur von Elektrolyten im Bulk und an Grenzflächen bestimmt. Wir haben in dieser Arbeit die Abschirmlängen für verschiedene Elektrolyte von niedrigen bis zu hohen Konzentrationen untersucht. / Electrolytes can be found in numerous applications in daily life as well as in scientific research. The increases in demand for energy-storage systems, such as fuel cells, supercapacitors and batteries in which liquid electrolyte properties are critical for optimal function, draw critical attention to the physical and chemical properties of electrolytes. Those energy-storage devices contain intermediate or highly concentrated electrolytes where established theories, like the Debye-Hückel (DH) theory, are not applicable. Despite the efforts to describe the physical properties of intermediate or highly concentrated electrolytes, theoretical atomistic-level studies are still lacking. This thesis is devoted to critically investigate the transport/structural properties and a phase behavior of concentrated liquid electrolytes and their application in energy-storage devices, using statistical mechanics and atomistic molecular dynamics (MD) simulations. Firstly, we investigate the structure-property relationship in concentrated electrolyte solutions in next-generation lithium-sulfur (Li/S) batteries. Secondly, phase separation may exist if the physio-chemical properties of liquid mixtures are very different. Recently, the coexistence phase of two aqueous solutions of different salts at high concentrations was found, called aqueous biphasic systems. We explore a wide range of compositions at room temperature for highly concentrated aqueous electrolytes solutions that consist of LiCl and LiTFSI. Lastly, charge screening is a fundamental phenomenon that governs the structure of liquid electrolytes in the bulk and at interfaces. From the DH theory, the screening length is expected to be extremely small in highly concentrated electrolytes. Yet, recent experiments show unexpectedly high screening lengths in those. This intriguing phenomenon has prompted a new set of theoretical works. We investigate the screening lengths for various electrolytes from low to high concentrations.

Mit der Entwicklung der Weltwirtschaft steigt der Energieverbrauch weiterhin stark an. Darüber hinaus reduzieren sich die nicht erneuerbaren Energiequellen, wie Öl, Erdgas und Kohle und die Umweltverschmutzung wird größer. Daher soll die Energienutzung in eine neue, erneuerbare und umweltfreundliche Richtung gehen. Die Arbeit hat zum Ziel innovative, wässrige Akkumulatoren zu entwickeln. Im Allgemeinen können wässrige Akkumulatoren gemäß der Elektrolyte in drei verschiedenen Kategorien eingeteilt werden. Es gibt feste, organische und wässrige Elektrolyte einschließlich saurer, alkalischer und neutraler. In Bezug auf metallbasierte negative Elektroden können sie auch als Lithiumbatterie, Natriumbatterie sowie Magnesiumbatterie etc. bezeichnet werden. Daher werden im ersten Kapitel einige typische Akkumulatoren, wie die Lithiumionenbatterien, Daniell-Element, Weston-Zelle, Nickel-Cadmium-Batterie und Bleibatterie vorgestellt. Im Vergleich zu organischen Elektrolyten wurden wässrige Akkumulatoren aufgrund ihrer billigen, leichten und sicheren Bauweise in den letzten Jahren umfassend untersucht. Zusätzlich dazu ist die ionische Leitfähigkeit von wässrigen Elektrolyten um zwei Größenordnungen höher als die von organischen Elektrolyten. Dies garantiert eine hohe Entladungsrate für wässrige wiederaufladbare Batterien. Somit bieten wiederaufladbare Batterien potentielle Anwendungen in der Energiespeicherung und -umwandlung. Allerdings verursachen starke Säuren oder Basen, die als Elektrolyte für sekundäre Batterien eingesetzt werden, eine starke Korrosion. Somit wären neutrale wässrige Elektrolyten (oder Elektrolytlösungen) mit einem pH-Wert in der Nähe von sieben, wie zum Beispiel schwach basisch oder sauer, die beste Wahl für wässrige Akkumulatoren. Aktive Elektrodenmaterialien der Batterien, die hochgiftige Schwermetalle wie Blei, Quecksilber und Cadmium enthalten, belasten die Umwelt. Um die Menge an Schwermetallen und Säure (oder Basen) zu verringern, sowie die spezifische Kapazität von Batterien zu erhöhen, untersucht diese Dissertation vor allem die elektrochemische Leistung der PbSO4/0,5M Li2SO4/LiMn2O4-Zelle, der Cd/0,5M Li2SO4+10mM Cd(Ac)2/LiCoO2-Zelle und von C/Cu/CNT-Gemischen als negative Materialien in 0,5 M K2CO3–Elektrolyt-Halbzellen. Die zugehörigen experimentellen Ergebnisse werden wie folgt zusammengefaßt: Im Kapitel 3 wurde eine säurefreie Bleibatterie auf Basis des LiMn2O4-Spinells als positive Elektrode, PbSO4 als negativer Elektrode und der wässrigen Lösung von 0,5 M Li2SO4 als Elektrolyt zusammengesetzt. Die spezifische Kapazität auf Basis von LiMn2O4 beträgt 128 mA•h•g-1 und die durchschnittliche Entladungsspannung beträgt 1,3 V. Die berechnete Energiedichte ist 68 W•h•kg-1, bezogen auf die praktischen Kapazitäten der beiden Elektroden. Diese Ergebnisse zeigen, dass die positive Elektrode der Bleibatterie (PbO2) vollständig durch umweltfreundliches und billiges LiMn2O4 ersetzt werden kann, wodurch 50 % des Bleis eingespart werden können. Außerdem wird Schwefelsäure nicht benötigt. Kapitel 4 zeigt eine wässrige wiederaufladbare Lithiumionenbatterie, die metallisches Cadmium als negative Elektrode, LiCoO2-Nanopartikel als positive Elektrode und eine wässrige, neutrale Lösung von 0,5 M Li2SO4 und 10 mM Cd(Ac)2 als Elektrolyt enthält. Die durchschnittliche Entladungsspannung beträgt 1,2 V und die spezifische Entladungskapazität beträgt 107 mA•h•g-1 auf Basis von LiCoO2. Die berechnete Energiedichte beträgt 72 W•h•kg-1, bezogen auf die praktischen Kapazitäten der beiden Elektroden. Wie bereits oben beschrieben demonstrieren die Ergebnisse, dass 100 % von Quecksilber und der alkalischen Elektrolyt im Vergleich zur Weston-Zelle bzw. der Ni-Cd-Batterie, eingespart werden können. Kapitel 5 zeigt einen Verbundwerkstoff von Kupfer, das auf der Oberfläche von CNTs durch eine Redoxreaktion zwischen Kupferacetat und Ethylenglykol, zur Verwendung als negative Elektrode bei hohen Strömen in der Energiespeicherung, hergestellt wurde. Der so hergestellte C/Cu/CNT-Verbundwerkstoff zeigt ein besseres Geschwindigkeitsverhalten und eine höhere Kapazität ebenso wie eine exzellente Zyklusstabilität in wässrigen 0,5 M K2CO3-Lösungen im Vergleich zu einfachem Kupfer. Die Kohlenstoffbeschichtung kann die Auflösung von Kupfercarbonatkomplexen verhindern, die Elektrodenleitfähigkeit erhöhen und die Oberflächenchemie des aktiven Materials verbessern. / With the economic development of the world, energy consumption continues to rise sharply. Moreover, non-renewable energy sources including fossil oil, natural gas and coal are declining gradually and environmental pollution is becoming more severe. Hence, energy usage should go into a new direction of development that is renewable and environmental-friendly. This thesis aims to explore innovative aqueous rechargeable batteries. Generally, rechargeable batteries could be classified into three categories according to the different electrolytes. There are solid electrolytes, organic electrolytes and aqueous electrolytes including acidic, alkaline and neutral. In terms of metal-based negative electrodes, they also could be named lithium battery, sodium battery as well as magnesium battery etc. Therefore, some typical rechargeable batteries are introduced in Chapter 1, such as lithium ion batteries, Daniell-type cell, Weston cell, Ni-Cd battery and lead-acid battery. Compared to organic electrolytes, aqueous rechargeable batteries have been investigated broadly in recent years because they are inexpensive, easy to construct and safe. Additionally, the ionic conductivity of aqueous electrolytes is higher than that of organic electrolytes by about two orders of magnitude. Furthermore, it ensures high rate capability for aqueous rechargeable battery. Consequently, aqueous rechargeable batteries present potential applications in energy storage and conversion. However, strong acid or alkaline, which is used as the electrolyte for secondary batteries, will cause serious corrosion. Thus, neutral aqueous electrolyte (or pH value of electrolyte solution close to 7 such as weak alkaline and acid) would be the best choice for aqueous rechargeable battery. In addition, the electrode active materials of batteries containing highly toxic heavy metals such as Pb, Hg and Cd, pollute the environment. As a result, in order to reduce the amount of heavy metals and acid (or alkaline) as well as increase the specific capacity of batteries, this dissertation mainly studies the electrochemical performance of PbSO4/0.5M Li2SO4/LiMn2O4 full battery, Cd/0.5M Li2SO4+10 mM Cd(Ac)2/LiCoO2 full battery and C/Cu/CNT composites as negative material in 0.5 M K2CO3 electrolyte as half cell. The related experimental results are as follows: In Chapter 3, an acid-free lead battery was assembled based on spinel LiMn2O4 as the positive electrode, PbSO4 as the negative electrode, and 0.5 M Li2SO4 aqueous solution as the electrolyte. Its specific capacity based on the LiMn2O4 is 128 mA•h•g-1 and the average discharge voltage is 1.3 V. The calculated energy density is 68 W•h•kg-1 based on the practical capacities of the two electrodes. These results show that the positive electrode of the lead acid battery (PbO2) can be totally replaced by the environmentally friendly and cheap LiMn2O4, which implies that 50 % of Pb can be saved. In addition, H2SO4 is not needed. Chapter 4 shows an aqueous rechargeable lithium ion battery using metallic Cd as the negative electrode, LiCoO2 nanoparticles as the positive electrode, and an aqueous neutral solution of 0.5 M Li2SO4 and 10 mM Cd(Ac)2 as the electrolyte. Its average discharge voltage is 1.2 V and the specific discharge capacity is 107 mA•h•g-1 based on the LiCoO2 . In addition, the calculated energy density based on the capacities of the electrodes is 72 W•h•kg-1. As described above, the results demonstrate that 100 % of Hg and alkaline electrolyte can be saved compared with the Weston cell and the Ni-Cd battery, respectively. The work reported in Chapter 5 deals with a composite of copper grown on the surface of CNTs as prepared by a redox reaction between copper acetate and ethylene glycol for use as negative electrode at high currents in energy storage. The as-prepared C/Cu/CNTs composite exhibits better rate behavior and higher capacity as well as excellent cycling stability in aqueous 0.5 M K2CO3 solution compared to the unsupported copper. The carbon coating can effectively prevent the dissolution of copper carbonate complexes, increase the electrode conductivity, improve the surface chemistry of the active material and protect the electrode from direct contact with electrolyte solution.

The performance and lifetime of lithium-ion batteries are strongly influenced by their composition. One category of critical components are electrolyte additives, which are included primarily to stabilize electrode/electrolyte interfaces in the battery cells by forming passivation layers. The presented study aimed to identify and study such an additive that could form a hydrogen-evolution-suppressing solid electrolyte interphase (SEI) in lithium-ion batteries based on aqueous electrolytes. A promising molecular additive, ethyl 2,2-difluoroacetate (EDFA), was found to hold the qualities required for an SEI former and was herein further analyzed electrochemically. Analysis of the battery cells were performed with linear sweep voltammetry and cyclic voltammetry with varying scan rate and EDFA concentrations. Results show that both 1 and 10 w-% EDFA in the electrolyte produced hydrogen-evolution-suppressing SEI:s, although the higher concentration provided no apparent benefit. Lithium-ion full-cells based on LiMn2O4 vs. Li4Ti5O12 active materials displayed poor, though partly reversible, dis-/charge cycling despite the operation of the electrode far outside the electrochemical stability window of the electrolyte. Inclusion of reference electrodes in the lithium-ion cells proved to be immensely challenging with unpredictable drifts in their electrode potentials during operation. To summarize, HER-suppressing electrolyte additives are demonstrated to be a promising approach to stabilize high-voltage operation of aqueous lithium-ion cells although further studies are necessary before any practical application thereof can be realized. Electrochemical evaluation of the reaction mechanism and efficiency of the electrolyte additives relies however heavily on the use of reference electrodes and further development thereof is necessary.

Doctor Pharmaceuticae - DPharm / An aqueous extract prepared from the leaves and smaller stems of Leonotis leonurus was used to investigate the potential effects on certain cardiovascular parameters, such as left ventricular systolic pressure, end-diastolic pressure, developed pressure, heart rate, cardiac work and coronary perfusion pressure in isolated rat hearts. Hearts were perfused at constant flow for 3min using the modified Langendorf! perfused model of the heart. Effects of adrenaline and digoxin solutions on the isolated heart were compared to that of the plant extract. Adrenaline produced both positive inotropic and chronotropic effects. Adrenaline increased (p<O.Ol) the left ventricular systolic pressure and hence the left ventricular developed pressure by 40.6% and 43.9% at peak, and 24.3% and 31.9%, after 3min, respectively. Simultaneously, the heart rate and the cardiac work were increased (p<0.01) by 22.5% and 89.4% at peak, and 24.6% and 63%, after 3rnin, respectively. There were no significant effects on the left ventricular diastolic pressure and the coronary perfusion pressure. Digoxin solution (2.5ng/ml) significantly (p<O.Ol) increased the left ventricular systolic pressure by 5.1% after 3min and the left ventricular diastolic pressure by 9.7% at peak and 5.3% after 3min. The heart rate was significantly (p<O.OI) decreased by 3.7% at peak. The cardiac work was increased by 4.5% after 3rnin. Digoxin did not significantly affect the left end diastolic pressure and the coronary perfusion pressure. The extract of Leonons leonurus at O.lmg/ml increased (p<O.OI) the left ventricular systolic pressure and hence the left ventricular diastolic pressure by 9.7% and 10.7% at peak, and 5.4% and 5.5% after 3rnin, respectively. The cardiac work was increased (p<O.Ol) by 10.1% at peak. Leonotis leonurus (0.1mg/ml) did not significantly affect the left ventricular end diastolic pressure, the heart rate and the coronary perfusion pressure. At 0.5mg/ml, the left ventricular systolic pressure and hence the left ventricular diastolic pressure were increased (p<0.01) by 14.8% and 15.4% at peak and 7.4% and 7.8% after 3rnin, respectively with a corresponding decrease (p<O.OI) in the coronary perfusion pressure of 8.5% at peak and 4.4% after 3rnin. The cardiac work was increased (p<O.OI) by 13.6% at peak and 5.2% after 3rnin. The extract at 1.0mg/ml increased (p<O.Ol) the left ventricular systolic pressure and hence the left ventricular diastolic pressure by 25.4% and 29.4% at Peak, and 23.1% and 26.3% after 3rnin, respectively. The heart rate was reduced (p<O.OI) by 34.7% at peak and 28.3% after 3min. The cardiac work and the coronary perfusion pressure were decreased (p<O.OI) by 15.9% and 12.1% at Peak and 3.3% and 11.4% after 3rnin. However, at 2.0mg/ml, the left ventricular systolic pressure and the left ventricular diastolic pressure were increased (p<O.OI) by 14.9% at peak. The left ventricular diastolic pressure was decreased (p<O.OI)by 9.8% over the 3rnin. The heart rate was drastically decreased (p<O.OI) by 42.7% after 3rnin. The cardiac work was reduced (p<O.Ol) by 48.8% over the 3min period. Also, the coronary perfusion pressure was decreased (p<0.01) by 16.9% at peak. Thus, Leonatis leonurus produced both positive inotropic and negative chronotropic effects after 3min perfusion, accompanied by a decreased coronary perfusion pressure. Thus, it appears that the extract seemed to contain certain constituents associated with positive inotropic and negative chronotropic agents as wel! as constituents associated with coronary vasodilation. However, at the higher concentration, it seemed to contain some constituents associated with toxic effects on the isolated heart. Therefore, further studies are needed to isolate the various constituents and examine their possible pharmacological effects on the heart individually before it could be considered safe to recommend this plant for its use in the treatment of cardiovascular disease.