Photophysical and Electrochemical Investigations on Photoconducting Poly(6-tert-butyl-3,4-dihydro-2H- 1,3-benzoxazine)

Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine) was synthesized by thermally activated cationic ring opening polymerization. The structure of the polymer was confirmed by spectral and thermal studies. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated using cyclic voltammetry and optical absorption. Modulated photocurrent measurement technique was employed to study the spectral and field dependence of photocurrent. Photocurrent of the order of 1.5 micro A/m2 was obtained for polymer at a biasing electric field of 40 V/mico m.

Electrochemical investigations on the capacity of flavonoids to protect DNA against damage caused by textile disperse dyes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Vibrational spectroscopic and electrochemical investigations of multi-centered heme proteins in biomimetic membrane architectures

Membrane proteins play a major role in every living cell. They are the key factors in the cell’s metabolism and in other functions, for example in cell-cell interaction, signal transduction, and transport of ions and nutrients. Cytochrome c oxidase (CcO), as one of the membrane proteins of the respiratory chain, plays a significant role in the energy transformation of higher organisms. CcO is a multi centered heme protein, utilizing redox energy to actively transport protons across the mitochondrial membrane. One aim of this dissertation is to investigate single steps in the mechanism of the ion transfer process coupled to electron transfer, which are not fully understood. The protein-tethered bilayer lipid membrane is a general approach to immobilize membrane proteins in an oriented fashion on a planar electrode embedded in a biomimetic membrane. This system enables the combination of electrochemical techniques with surface enhanced resonance Raman (SERRS), surface enhanced reflection absorption infrared (SEIRAS), and surface plasmon spectroscopy to study protein mediated electron and ion transport processes. The orientation of the enzymes within the surface confined architecture can be controlled by specific site-mutations, i.e. the insertion of a poly-histidine tag to different subunits of the enzyme. CcO can, thus, be oriented uniformly with its natural electron pathway entry pointing either towards or away from the electrode surface. The first orientation allows an ultra-fast direct electron transfer(ET) into the protein, not provided by conventional systems, which can be leveraged to study intrinsic charge transfer processes. The second orientation permits to study the interaction with its natural electron donor cytochrome c. Electrochemical and SERR measurements show conclusively that the redox site structure and the activity of the surface confined enzyme are preserved. Therefore, this biomimetic system offers a unique platform to study the kinetics of the ET processes in order to clarify mechanistic properties of the enzyme. Highly sensitive and ultra fast electrochemical techniques allow the separation of ET steps between all four redox centres including the determination of ET rates. Furthermore, proton transfer coupled to ET could be directly measured and discriminated from other ion transfer processes, revealing novel mechanistic information of the proton transfer mechanism of cytochrome c oxidase. In order to study the kinetics of the ET inside the protein, including the catalytic center, time resolved SEIRAS and SERRS measurements were performed to gain more insight into the structural and coordination changes of the heme environment. The electrical behaviour of tethered membrane systems and membrane intrinsic proteins as well as related charge transfer processes were simulated by solving the respective sets of differential equations, utilizing a software package called SPICE. This helps to understand charge transfer processes across membranes and to develop models that can help to elucidate mechanisms of complex enzymatic processes.

Electrochemical Investigations into Blended Electrolytes Containing Ionic Liquids and a Glyme Solvent for Li-O­2 batteries

The Li-O2 battery may theoretically possess practical gravimetric energy densities several times greater than the current state-of-the-art Li-ion batteries.1 This magnitude of development is a requisite for true realization of electric vehicles capable of competing with the traditional combustion engine. However, significant challenges must be addressed before practical application may be considered. These include low efficiencies, low rate capabilities and the parasitic decomposition reactions of electrolyte/electrode materials resulting in very poor rechargeability.2-4 Ionic liquids, ILs, typically display several properties, extremely low vapor pressure and high electrochemical and thermal stability, which make them particularly interesting for Li-O2 battery electrolytes. However, the typically sluggish transport properties generally inhibit rate performance and cells suffer similar inefficiencies during cycling.5,6

In addition to the design of new ILs with tailored properties, formulating blended electrolytes using molecular solvents with ILs has been considered to improve their performance.7,8 In this work, we will discuss the physical properties vs. the electrochemical performance of a range of formulated electrolytes based on tetraglyme, a benchmark Li-O2 battery electrolyte solvent, and several ILs. The selected ILs are based on the bis{(trifluoromethyl)sulfonyl}imide anion and alkyl/ether functionalized cyclic alkylammonium cations, which exhibit very good stability and moderate viscosity.9 O2 electrochemistry will be investigated in these media using macro and microdisk voltammetry and O2 solubility/diffusivity is quantified as a function of the electrolyte formulation. Furthermore, galvanostatic cycling of selected electrolytes in Li-O2 cells will be discussed to probe their practical electrochemical performance. Finally, the physical characterization of the blended electrolytes will be reported in parallel to further determine structure (or formulation) vs. property relationships and to, therefore, assess the importance of certain electrolyte properties (viscosity, O2supply capability, donor number) on their performance.

This work was funded by the EPSRC (EP/L505262/1) and Innovate UK for the Practical Lithium-Air Batteries project (project number: 101577).

1. P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nat. Mater., 11, 19 (2012).

2. S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Barde and P. G. Bruce, Angew. Chem., Int. Ed., 50, 8609 (2011).

3. B. D. McCloskey, A. Speidel, R. Scheffler, D. C. Miller, V. Viswanathan, J. S. Hummelshøj, J. K. Nørskov and A. C. Luntz, J. Phys. Chem. Lett., 3, 997 (2012).

4. D. G. Kwabi, T. P. Batcho, C. V. Amanchukwu, N. Ortiz-Vitoriano, P. Hammond, C. V. Thompson and Y. Shao-Horn, J. Phys. Chem. Lett., 5, 2850 (2014).

5. Z. H. Cui, W. G. Fan and X. X. Guo, J. Power Sources, 235, 251 (2013).

6. F. Soavi, S. Monaco and M. Mastragostino, J. Power Sources, 224, 115 (2013).

7. L. Cecchetto, M. Salomon, B. Scrosati and F. Croce, J. Power Sources, 213, 233 (2012).

8. A. Khan and C. Zhao, Electrochem. Commun., 49, 1 (2014).

9. Z. J. Chen, T. Xue and J.-M. Lee, RSC Adv., 2, 10564 (2012).

DNA cleavage and antitumour activity of platinum(II) and copper(II) compounds derived from 4-methyl-2-N-(2-pyridylmethyl)aminophenol: spectroscopic, electrochemical and biological investigation

The reaction of the redox-active ligand, Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol) with K2PtCl4 yields monofunctional square-planar [Pt(pyrimol)Cl], PtL-Cl, which was structurally characterised by single-crystal X-ray diffraction and NMR spectroscopy. This compound unexpectedly cleaves supercoiled double-stranded DNA stoichiometrically and oxidatively, in a non-specific manner without any external reductant added, under physiological conditions. Spectro-electrochemical investigations of PtL-Cl were carried out in comparison with the analogue CuL-Cl as a reference compound. The results support a phenolate oxidation, generating a phenoxyl radical responsible for the ligand-based DNA cleavage property of the title compounds. Time-dependent in vitro cytotoxicity assays were performed with both PtL-Cl and CuL-Cl in various cancer cell lines. The compound CuL-Cl overcomes cisplatin-resistance in ovarian carcinoma and mouse leukaemia cell lines, with additional activity in some other cells. The platinum analogue, PtL-Cl also inhibits cell-proliferation selectively. Additionally, cellular-uptake studies performed for both compounds in ovarian carcinoma cell lines showed that significant amounts of Pt and Cu were accumulated in the A2780 and A2780R cancer cells. The conformational and structural changes induced by PtL-Cl and CuL-Cl on calf thymus DNA and phi X174 supercoiled phage DNA at ambient conditions were followed by electrophoretic mobility assay and circular dichroism spectroscopy. The compounds induce extensive DNA degradation and unwinding, along with formation of a monoadduct at the DNA minor groove. Thus, hybrid effects of metal-centre variation, multiple DNA-binding modes and ligand-based redox activity towards cancer cell-growth inhibition have been demonstrated. Finally, reactions of PtL-Cl with DNA model bases (9-Ethylguanine and 5'-GMP) followed by NMR and MS showed slow binding at Guanine-N7 and for the double stranded self complimentary oligonucleotide d(GTCGAC)(2) in the minor groove.

Investigation of the corrosion behaviour of AA 2024-T3 in low concentrated chloride media

Aluminium alloy (AA) 2024-T3 is an important engineering material due to its widespread use in the aerospace industry. However, it is very prone to localized corrosion attack in chloride containing media, which has been mainly associated to the presence of coarse intermetallics (IMs) in its microstructure. In this work the corrosion behaviour of AA 2024-T3 in low concentrated chloride media was investigated using microscopy and electrochemical methods. TEM/EDS observations on non-corroded samples evidenced the heterogeneous composition within the IMs. In addition, SEM observations showed that intermetallics with the same nominal composition present different reactivity, and that both types of coarse IMs normally found in the alloy microstructure are prone to corrosion. Moreover, EDS analyses showed important compositional changes in corroded IMs, evidencing a selective dissolution of their more active constituents, and the onset of an intense oxygen peak, irrespective to the IM nature, indicating the formation of corrosion products. On the other hand, the results of the electrochemical investigations, in accordance with the SEM/EDS observations, evidenced that IMs corrosion dominates the electrochemical response of the alloy during the first hours of immersion in the test electrolyte. (c) 2008 Elsevier Ltd. All rights reserved.

Study of copper electrodeposition mechanism from a strike alkaline bath prepared with 1-hydroxyethane-1,1-diphosphonic acid through cyclic voltammetry technique

Copper strike baths are extensively used in metal plating industry as they present the ability to plate adherent copper layers on less-noble metal substrates such as steel and zinc die castings. However, in the last few years, due to environmental controls and safety policies for operators, the plating industry has been interested in replacing the toxic cyanide copper strike baths with environmentally friendly baths. A broad bibliographic review showed that the published papers, referring to the new nontoxic copper strike baths, are patents, having little or no emphasis focused on electrodeposition mechanisms. Therefore, it was decided to study the copper electrodeposition mechanism from a strike alkaline bath prepared with one of the most nontoxic chelating agents cited in many patents which is the 1-hydroxyethane-1,1-diphosphonic acid, known as HEDP. This acid forms very stable water soluble complexes with Cu(2+) ions, thus cupric sulfate was used for preparing the plating bath. The results obtained through a cyclic voltammetry technique showed that Cu(2+) ion reduction to Cu from an HEDP electrodeposition bath occurs via a direct reduction reaction without a formation of Cu(+) intermediates. (C) 2010 Elsevier Ltd. All rights reserved.

Effect of W on PtSn/C catalysts for ethanol electrooxidation

Binary and ternary Pt-based catalysts were prepared by the Pechini-Adams modified method on carbon Vulcan XC-72, and different nominal compositions were characterized by TEM and XRD. XRD showed that the electrocatalysts consisted of the Pt displaced phase, suggesting the formation of a solid solution between the metals Pt/W and Pt/Sn. Electrochemical investigations on these different electrode materials were carried out as a function of the electrocatalyst composition, in acid medium (0.5 mol dm(-3) H2SO4) and in the presence of ethanol. The results obtained at room temperature showed that the PtSnW/C catalyst display better catalytic activity for ethanol oxidation compared to PtW/C catalyst. The reaction products (acetaldehyde, acetic acid and carbon dioxide) were analyzed by HPLC and identified by in situ infrared reflectance spectroscopy. The latter technique also allowed identification of the intermediate and adsorbed species. The presence of linearly adsorbed CO and CO2 indicated that the cleavage of the C-C bond in the ethanol substrate occurred during the oxidation process. At 90 degrees C, the Pt85Sn8W7/C catalyst gave higher current and power performances as anode material in a direct ethanol fuel cell (DEFC).

Synthese und Charakterisierung neuer symmetrischer und unsymmetrischer Spiro-p-oligophenyle

In der vorliegenden Arbeit wurden neue symmetrische Spiro-p-oligophenyle der allgemeinen Form Spiro-o-Φ[n,n] mit der Gesamtkettenlänge o=2n+2 Phenylringen (o > 10) und der Zahl n der Phenylringe in den p-Oligophenylsubstituenten am Spirobifluorenkern, dargestellt. Neben den symmetrischen Verbindungen wurden erstmals auch unsymmetrische Spiro-p-oligophenyle der allgemeinen Form Spiro-o-Φ[n,m] mit o=n+m+2 (o = 3-7) und n ≠ m synthetisiert. Aufgrund der sehr geringen Löslichkeit der größeren Verbindungen wurden löslichkeitssteigernde Substituenten an den endständigen Phenylringen angebracht. Bei den Verbindungen, die mit Trimethylsilyl-Gruppen (TMS-) in den endständigen meta-Positionen „3“ und „5“ substituiert wurden, konnte die Löslichkeit um mehrere Größenordnungen gesteigert werden, sodass die Darstellung der symmetrischen Verbindungen bis zu einer Kettenlänge von 16 Phenylringen möglich wurde. Nach erfolgreicher Synthese und Aufreinigung wurden die TMS-Gruppen wieder entfernt und die erhaltenen, unsubstituierten Verbindungen charakterisiert. Zusätzlich wurden auch die TMS-Derivate untersucht. Zur Charakterisierung zählten neben der Reinheits- und Strukturanalytik unter anderem auch spektroskopische (UV/Vis-Absorption, Fluoreszenz, Fluoreszenzquantenausbeute), elektrochemische (Cyclovoltammetrie) und thermische (Thermogravimetrie, Dynamische Differenzkalorimetrie) Untersuchungen. Hier wurde unter anderem der Einfluss der Kettenlänge und der Position der Spiroverknüpfung auf isomere Verbindungen gleicher Kettenlänge untersucht. Bei den spektroskopischen Messungen konnte eine Konvergenz der längstwelligen Absorptionsbanden, bzw. kürzestwelligen Fluoreszenzbanden mit zunehmender Kettenlänge beobachtet werden. Die effektive Konjugationslänge konnte so aus experimentellen Daten bestimmt werden zu 12 Phenylringen in der Absorption und 14 Phenylringen in der Fluoreszenz. Bei den Isomeren gleicher Kettenlänge zeigte sich in der Absorption eine hypsochrome Verschiebung der Absorptionsmaxima mit zunehmender Verschiebung der Spiroverknüpfung zum Kettenende hin, während die Position der Spiroverknüpfung keinen messbaren Einfluss auf die Verschiebung der Fluoreszenzbanden hatte. Die Substitution mit TMS in den meta-Positionen zeigte keinen messbaren Einfluss auf die Absorptions- bzw. Fluoreszenzbanden. Die elektrochemischen Untersuchungen zeigten mit zunehmender Kettenlänge eine erleichterte Oxidation und Reduktion, während bei Isomeren gleicher Kettenlänge die Oxidation mit Verschiebung der Spiroverknüpfung zum Kettenende hin erschwert und die Reduktion erleichtert war. Die thermogravimetrischen Analysen (TGA) zeigten eine außerordentlich hohe thermische Stabilität (5% Massenabnahme unter Schutzgas) der Spiro-p-oligophenyle von Td,5% = 474°C bei Spiro-5Φ[1,2] bis 570°C bei Spiro 8Φ[3,3]. Ebenso blieben hohe Rückstandsmassen unter Schutzgas bei 850°C zurück, wie das Beispiel Spiro 8Φ[3,3] mit 68% zeigt. Die Verbindungen zeigten hohe Schmelzpunkte (max. 496°C bei Spiro-6Φ[0,4]) und Glasübergangstemperaturen (max. 434°C bei p-TMS-Spiro-8Φ[3,3]). Viele der Verbindungen, besonders die in den meta-Positionen TMS-substituierten Verbindungen, bildeten stabile amorphe Gläser.

Ferrocene-Based Pyridylphosphine Ligands – Coordination Chemistry of Group 10, 11 and 12 Metals

English: The present thesis describes the synthesis of 1,1’-ferrocendiyl-based pyridylphosphine ligands, the exploration of their fundamental coordination chemistry and preliminary experiments with selected complexes aimed at potential applications. One main aspect is the synthesis of the bidentate ferrocene-based pyridylphosphine ligands 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene, 1-(Pyrid-3-yl)-1’-diphenylphosphinoferrocene and 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene. A specific feature of these ligands is the ball-bearing like flexibility of the ferrocenebased backbone. An additional flexibility element is the rotation around the C–C single bonds. Consequently, the donor atoms can realise a wide range of positions with respect to each other and are therefore able to adapt to the coordination requirements of different metal centres. The flexibility of the ligand also plays a role in another key aspect of this work, which concerns the coordination mode, i. e. bridging vs. chelating. In addition to the flexibility, also the position of the donor atoms to each other is important. This is largely affected by the position of the pyridyl nitrogen (pyrid-2-yl vs. pyrid-3-yl) and the methylen group in 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene. Another interesting point is the combination of a soft phosphorus donor atom with a harder nitrogen donor atom, according to the HSAB principle. This combination generates a unique binding profile, since the pi-acceptor character of the P site is able to stabilise a metal centre in a low oxidation state, while the nitrogen sigma-donor ability can make the metal more susceptible to oxidative addition reactions. A P,N-donor combination can afford hemilabile binding profiles, which would be ideal for catalysis. Beyond 1,2-substituted ferrocene derivatives, which are quite successful in catalytic applications, 1,1’-derivatives are rather underrepresented. While a low-yield synthetic pathway to 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene was already described in the literature [I. R. Butler, Organometallics 1992, 11, 74.], it was possible to find a new, improved and simplified synthetic pathway. Both other ligands were unknown prior to this work. Satisfactory results in the synthesis of 1-(Pyrid-3-yl)-1’-diphenylphosphinoferrocene could be achieved by working in analogy to the new synthetic procedure for 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene. The synthesis of 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene has been handled by the group of Prof. Petr Stepnicka from Charles University, Prague, Czech Republic. The synthesis of tridentate ligands with an analogous heterodentate arrangement, was investigated briefly as a sideline of this study. The major part of this thesis deals with the fundamental coordination chemistry towards transition metals of the groups 10, 11 and 12. Due to the well-established catalytic properties of analogous palladium complexes, the coordination chemistry towards palladium (group 10) is of particular interest. The metals zinc and cadmium (group 12) are also of substantial importance because they are redox-inert in their divalent state. This is relevant in view of electrochemical investigations concerning the utilisation of the ligands as molecular redox sensors. Also mercury and the monovalent metals silver and gold (group 11) are included because of their rich coordination chemistry. It is essential to answer questions concerning aspects of the ligands’ coordination mode bearing in mind the HSAB principle.

Bis(calix[4]diquinone) receptors: cesium- and rubidium-selective redox-active ionophores

A new class of redox-active ionophore comprised of two calix[4]diquinone moieties connected through either alkylene or pyridylene linkages has been developed. Spectroscopic and electrochemical investigations, X-ray crystal structure analyses, and molecular modeling studies show butylene- and propylene-linked members of this family of redox-active receptors exhibit remarkable selectivity preferences and substantial electrochemical recognition effects toward cesium and rubidium cations.

Transition metal-directed self-assembly of calix[4]arene based dithiocarbamate ligands

The transition metal-directed self-assembly of dithiocarbamate ligand functionalised upper and lower rim calix[4]arenes affords novel dimeric bimetallic bis(calix[4]arene) species as determined by a combination of analytical methods including X-ray crystallography. An exception is a zinc(II) dithiocarbamate upper rim calix[4]arene assembly which is monomeric in nature. Electrochemical investigations reveal the bimetallic copper(II) bis(calix[4]arene) systems can electrochemically sense dihydrogen phosphate and carboxylate anions via significant cathodic perturbations of the respective copper(II)/(III) dithiocarbamate oxidation wave.

Investigation of the corrosion behaviour of AA 2024-T3 in low concentrated chloride media

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The role of coarse intermetallics in the localized corrosion behaviour of AA 2024-T3 in low concentrated chloride media

Aluminium alloy (AA) 2024-T3 is an important engineering material due to its widespread use in the aerospace industry. However, it is very prone to localized corrosion attack in chloride containing media, which has been mainly associated to the presence of coarse intermetallics (IMs). In this work the corrosion behaviour of aluminium alloy 2024-T3 in low concentrated chloride media was investigated using microscopy and electrochemical methods. SEM observations have shown that intermetallics with the same nominal composition present heterogeneous reaction rates, and that both types of coarse IMs normally found in the AA 2024-T3 microstructure corrode. Moreover, EDS analyses have shown important compositional changes in the corroded IMs, evidencing the selective corrosion of their more active constituents and the onset of an intense oxygen peak, irrespective to the IM nature. TEM/EDS observations on non-corroded samples have evidenced the heterogeneous composition within the IMs. On the other hand, the results of the electrochemical investigations, in accordance with the SEM/EDS observations, have evidenced that IMs corrosion dominates the electrochemical response of the alloy during the first hours of immersion in the test electrolyte. © 2009 by NACE International.