Layer-by-layer grown scalable redox-active ruthenium-based molecular multilayer thin films for electrochemical applications and beyond

Here we report the first study on the electrochemical energy storage application of a surface-immobilized ruthenium complex multilayer thin film with anion storage capability. We employed a novel dinuclear ruthenium complex with tetrapodal anchoring groups to build well-ordered redox-active multilayer coatings on an indium tin oxide (ITO) surface using a layer-by-layer self-assembly process. Cyclic voltammetry (CV), UV-Visible (UV-Vis) and Raman spectroscopy showed a linear increase of peak current, absorbance and Raman intensities, respectively with the number of layers. These results indicate the formation of well-ordered multilayers of the ruthenium complex on ITO, which is further supported by the X-ray photoelectron spectroscopy analysis. The thickness of the layers can be controlled with nanometer precision. In particular, the thickest layer studied (65 molecular layers and approx. 120 nm thick) demonstrated fast electrochemical oxidation/reduction, indicating a very low attenuation of the charge transfer within the multilayer. In situ-UV-Vis and resonance Raman spectroscopy results demonstrated the reversible electrochromic/redox behavior of the ruthenium complex multilayered films on ITO with respect to the electrode potential, which is an ideal prerequisite for e.g. smart electrochemical energy storage applications. Galvanostatic charge–discharge experiments demonstrated a pseudocapacitor behavior of the multilayer film with a good specific capacitance of 92.2 F g−1 at a current density of 10 μA cm−2 and an excellent cycling stability. As demonstrated in our prototypical experiments, the fine control of physicochemical properties at nanometer scale, relatively good stability of layers under ambient conditions makes the multilayer coatings of this type an excellent material for e.g. electrochemical energy storage, as interlayers in inverted bulk heterojunction solar cell applications and as functional components in molecular electronics applications.

Study of Basic Wood Decay Mechanisms and Their Biotechnological Applications

The overall objective of this thesis was to gain further understanding of the non-enzymatic mechanisms involved in brown-rot wood decay, especially the role of pH, oxalic acid, and low molecular catecholate compounds on the dissolution and reduction of iron, and the formation of reactive oxygen species. Another focus of this study will be the potential application of a biomimetic free radical generating system inspired from fungi wood decay process, especially the non-enzymatic mechanism. The possible pathways of iron uptake and iron redox cycling in non-enzymatic brown-rot decay were investigated in this study. UV-Vis spectroscopy and HPLC were employed to study the kinetics and pathways of the interaction between iron and model catecholate compounds under different pH and chelator/iron molar ratio conditions. Iron chelation and reduction during early non-enzymatic wood decay processes have been studied in this thesis. The results indicate that the effects of the chelator/iron ratio, the pH, and other reaction parameters on the hydroxyl radical generation in a Fenton type system can be determined using ESR spin-trapping techniques. Data also support the hypothesis that superoxide radicals are involved in chelator-mediated Fenton processes. The mechanisms involved in free radical activation of Thermal Mechanical Pulp fibers were investigated. The activation of TMP fibers was evaluated by ESR measurement of free phenoxy radical generation on solid fibers. The results indicate that low molecular weight chelators can improve Fenton reactions, thus in turn stimulating the free radical activation of TMP fibers. A mediated Fenton system was evaluated for decolorization of several types of dyes. The result shows that the Fenton system mediated by a catecholate-type chelator effectively reduced the color of a diluted solution of synthetic dyes after 90 minutes of treatment at room temperature. The results show that compared to a neat Fenton process, the mediated Fenton decolorization process increased the production, and therefore the effective longevity, of hydroxyl radical species to increase the decolorization efficiency.

Water chemistry, and pigments and geochemistry of sediments from northern Victoria Land lakes

Total concentrations of algal pigments, organic C, C, N, P and S were determined in surface sediments from the littoral zone of 21 lakes in ice-free areas of northern Victoria Land (Antarctica) with different climatic and environmental conditions. Concentrations of major ions and nutrients were also determined in water samples from the same lakes. The latter samples had extremely variable chemical compositions; however, all the lakes resulted oligotrophic. Pigment concentrations in surface sediments were comparable to those reported for other Antarctic lakes and lower than those in oligotrophic lakes at lower latitudes. Cyanophyta, Chlorophyta and Bacillariophyta were the main taxa identified. These taxa correspond to those reported in previous microscopy-based studies on Antarctic phytoplankton and phytobenthos. Discriminant Function Analysis and Canonical Correspondence Analysis of data indicate that the distribution of pigments in these Victoria Land lakes depends mainly on their geographical location (particularly the distance from the sea) and nutrient status.

New Intermediate band sulphide nanoparticles acting in the full visible light range spectra as an active photocatalyst

Nowadays one of the challenges of materials science is to find new technologies that will be able to make the most of renewable energies. An example of new proposals in this field are the intermediate-band (IB) materials, which promise higher efficiencies in photovoltaic applications (through the intermediate band solar cells), or in heterogeneous photocatalysis (using nanoparticles of them, for the light-induced degradation of pollutants or for the efficient photoevolution of hydrogen from water). An IB material consists in a semiconductor in which gap a new level is introduced [1], the intermediate band (IB), which should be partially filled by electrons and completely separated of the valence band (VB) and of the conduction band (CB). This scheme (figure 1) allows an electron from the VB to be promoted to the IB, and from the latter to the CB, upon absorption of photons with energy below the band gap Eg, so that energy can be absorbed in a wider range of the solar spectrum and a higher current can be obtained without sacrificing the photovoltage (or the chemical driving force) corresponding to the full bandgap Eg, thus increasing the overall efficiency. This concept, applied to photocatalysis, would allow using photons of a wider visible range while keeping the same redox capacity. It is important to note that this concept differs from the classic photocatalyst doping principle, which essentially tries just to decrease the bandgap. This new type of materials would keep the full bandgap potential but would use also lower energy photons. In our group several IB materials have been proposed, mainly for the photovoltaic application, based on extensively doping known semiconductors with transition metals [2], examining with DFT calculations their electronic structures. Here we refer to In2S3 and SnS2, which contain octahedral cations; when doped with Ti or V an IB is formed according to quantum calculations (see e.g. figure 2). We have used a solvotermal synthesis method to prepare in nanocrystalline form the In2S3 thiospinel and the layered compound SnS2 (which when undoped have bandgaps of 2.0 and 2.2 eV respectively) where the cation is substituted by vanadium at a ?10% level. This substitution has been studied, characterizing the materials by different physical and chemical techniques (TXRF, XRD, HR-TEM/EDS) (see e.g. figure 3) and verifying with UV spectrometry that this substitution introduces in the spectrum the sub-bandgap features predicted by the calculations (figure 4). For both sulphide type nanoparticles (doped and undoped) the photocatalytic activity was studied by following at room temperature the oxidation of formic acid in aqueous suspension, a simple reaction which is easily monitored by UV-Vis spectroscopy. The spectral response of the process is measured using a collection of band pass filters that allow only some wavelengths into the reaction system. Thanks to this method the spectral range in which the materials are active in the photodecomposition (which coincides with the band gap for the undoped samples) can be checked, proving that for the vanadium substituted samples this range is increased, making possible to cover all the visible light range. Furthermore it is checked that these new materials are more photocorrosion resistant than the toxic CdS witch is a well know compound frequently used in tests of visible light photocatalysis. These materials are thus promising not only for degradation of pollutants (or for photovoltaic cells) but also for efficient photoevolution of hydrogen from water; work in this direction is now being pursued.

Fotodiodos basados en (Zn,Mg)O para la detección de luz ultravioleta

La presente tesis fue ideada con el objetivo principal de fabricar y caracterizar fotodiodos Schottky en capas de ZnMgO y en estructuras de pozo cuántico ZnMgO/ZnO para la detección de luz UV. La elección de este material semiconductor vino motivada por la posibilidad que ofrece de detectar y procesar señales simultáneamente, en un amplio margen de longitudes de onda, al igual que su más directo competidor el GaN. En esta memoria se da en primer lugar una visión general de las propiedades estructurales y ópticas del ZnO, prestando especial atención a su ternario ZnMgO y a las estructuras de pozo cuántico ZnMgO/ZnO. Además, se han desarrollado los conocimientos teóricos necesarios para una mejor compresión y discusión de los resultados alcanzados. En lo que respecta a los resultados de esta memoria, en esencia, estos se dividen en dos bloques. Fotodiodos desarrollados sobre capas delgadas de ZnMgO no-polar, y sobre estructuras de pozo cuántico de ZnMgO/ZnO no-polares y semipolares Fotodiodos de capas delgadas de ZnMgO. Es bien conocido que la adición de Mg a la estructura cristalina del ZnO desplaza el borde de absorción hacia energías mayores en el UV. Se ha aprovechado esto para fabricar fotodiodos Schottky sobre capas de ZnMgO crecidas por MOCVD y MBE, los cuales detecten en un ventana de energías comprendida entre 3.3 a 4.6 eV. Sobre las capas de ZnMgO, con diferentes contenidos de Mg(5.6-18.0 %), crecidas por MOCVD se han fabricado fotodiodos Schottky. Se han estudiado en detalle las curvas corrientevoltaje (I-V). Seguidamente, se ha realizado un análisis de la respuesta espectral bajo polarización inversa. Tanto los valores de responsividad obtenidos como el contraste UV/VIS están claramente aumentados por la presencia de ganancia. Paralelamente, se han realizado medidas de espectroscopia de niveles profundos (DLOS), identificándose la presencia de dos niveles profundos de carácter aceptor. El papel desempeñado por estos en la ganancia ha sido analizado meticulosamente. Se ha demostrado que cuando estos son fotoionizados son responsables directos del gran aumento de la corriente túnel que se produce a través de la barrera Schottky, dando lugar a la presencia de la ganancia observada, que además resulta ser función del flujo de fotones incidente. Para extender el rango detección hasta 4.6 eV se fabricaron fotodiodos sobre capas de ZnMgO de altísima calidad cristalina crecidas por MBE. Sobre estos se ha realizado un riguroso análisis de las curvas I-V y de las curvas capacidad-voltaje (CV), para posteriormente identificar los niveles profundos presentes en el material, mediante la técnica de DLOS. Así mismo se ha medido la respuesta espectral de los fotodetectores, la cual muestra un corte abrupto y un altísimo contraste UV/VIS. Además, se ha demostrado como estos son perfectos candidatos para la detección de luz en la región ciega al Sol. Por otra parte, se han fabricado fotodiodos MSM sobre estas mismas capas. Se han estudiado las principales figuras de mérito de estos, observándose unas corrientes bajas de oscuridad, un contraste UV/VIS de 103, y la presencia de fotocorriente persistente. Fotodiodos Schottky de pozos cuánticos de ZnO/ZnMgO. En el segundo bloque de esta memoria, con el objeto final de clarificar el impacto que tiene el tratamiento del H2O2 sobre las características optoelectrónicas de los dispositivos, se ha realizado un estudio detallado, en el que se han analizado por separado fotodiodos tratados y no tratados con H2O2, fabricados sobre pozos cuánticos de ZnMgO/ZnO. Se ha estudiado la respuesta espectral en ambos casos, observándose la presencia de ganancia en los dos. A través de un análisis meticuloso de las características electrónicas y optoeletrónicas de los fotodiodos, se han identificado dos mecanismos de ganancia internos diferentes en función de que la muestra sea tratada o no-tratada. Se han estudiado fotodetectores sensibles a la polarización de la luz (PSPDs) usando estructuras de pozo cuántico no-polares y semipolares sobre sustratos de zafiro y sustratos de ZnO. En lo que respecta a los PSPDs sobre zafiro, en los cuales el pozo presenta una tensión acumulada en el plano, se ha visto que el borde de absorción se desplaza _E _21 meV con respecto a luz linealmente polarizada perpendicular y paralela al eje-c, midiéndose un contraste (RE || c /RE c)max _ 6. Con respecto a los PSPDs crecidos sobre ZnO, los cuales tienen el pozo relajado, se ha obtenido un 4E _30-40, y 21 meV para las heteroestructuras no-polar y semipolar, respectivamente. Además el máximo contraste de responsividad fue de (RE || c /RE c)max _ 6 . Esta sensibilidad a la polarización de la luz ha sido explicada en términos de las transiciones excitónicas entre la banda de conducción y las tres bandas de valencia. ABSTRACT The main goal of the present thesis is the fabrication and characterization of Schottky photodiodes based on ZnMgO layers and ZnMgO / ZnO quantum wells (QWs) for the UV detection. The decision of choosing this semiconductor was mainly motivated by the possibility it offers of detecting and processing signals simultaneously in a wide range of wavelengths like its main competitor GaN. A general overview about the structural and optical properties of ZnO, ZnMgO layers and ZnMgO/ZnO QWs is given in the first part of this thesis. Besides, it is shown the necessary theoretical knowledge for a better understanding of the discussion presented here. The results of this thesis may be divided in two parts. On the one hand, the first part is based on studying non-polar ZnMgO photodiodes. On the other hand, the second part is focused on the characterization of non-polar and semipolar ZnMgO / ZnO QWs Schottky photodiodes. ZnMgO photodiodes. It is well known that the addition of Mg in the crystal structure of ZnO results in a strong blue-shift of the ZnO band-gap. Taking into account this fact Schottky photodiodes were fabricated on ZnMgO layers grown by MOCVD and MBE. Concerning ZnMgO layers grown by MOCVD, a series of Schottky photodiodes were fabricated, by varying the Mg content from 5.6% to 18 %. Firstly, it has been studied in detail the current-voltage curves. Subsequently, spectral response was analyzed at reverse bias voltage. Both the rejection ratio and the responsivity are shown to be largely enhanced by the presence of an internal gain mechanism. Simultaneously, measurements of deep level optical spectroscopy were carried out, identifying the presence of two acceptor-like deep levels. The role played for these in the gain observed was studied in detail. It has been demonstrated that when these are photoionized cause a large increase in the tunnel current through the Schottky barrier, yielding internal gains that are a function of the incident photon flux. In order to extend the detection range up to 4.6 eV, photodiodes ZnMgO grown by MBE were fabricated. An exhaustive analysis of the both I-V and CV characteristics was performed. Once again, deep levels were identified by using the technique DLOS. Furthermore, the spectral response was measured, observing sharp absorption edges and high UV/VIS rejections ratio. The results obtained have confirmed these photodiodes are excellent candidates for the light detection in the solar-blind region. In addition, MSM photodiodes have also been fabricated on the same layers. The main figures of merit have been studied, showing low dark currents, a large UV/VIS rejection ratio and persistent photocurrent. ZnMgO/ZnO QWs photodiodes. The second part was focused on ZnMgO/ ZnO QWs. In order to clarify the impact of the H2O2 treatment on the performance of the Schottky diodes, a comparative study using treated and untreated ZnMgO/ZnO photodiodes has been carried out. The spectral response in both cases has shown the presence of gain, under reverse bias. Finally, by means of the analysis of electronic and optoelectronic characteristics, two different internal gain mechanisms have been indentified in treated and non-treated material. Light polarization-sensitive UV photodetectors (PSPDs) using non-polar and semipolar ZnMgO/ZnO multiple quantum wells grown both on sapphire and ZnO substrates have been demonstrated. For the PSPDs grown on sapphire with anisotropic biaxial in-plain strain, the responsivity absorption edge shifts by _E _21 meV between light polarized perpendicular and parallel to the c-axis, and the maximum responsivity contrast is (RE || c /RE c)max _ 6 . For the PSPDs grown on ZnO, with strain-free quantum wells, 4E _30-40, and 21 meV for non-polar and semipolar heterostructures, and maximum (R /R||)max _10. for non-polar heterostructure was achieved. These light polarization sensitivities have been explained in terms of the excitonic transitions between the conduction and the three valence bands.

Designing conditions for in vitro formation of amyloid protofilaments and fibrils

We have been able to convert a small α/β protein, acylphosphatase, from its soluble and native form into insoluble amyloid fibrils of the type observed in a range of pathological conditions. This was achieved by allowing slow growth in a solution containing moderate concentrations of trifluoroethanol. When analyzed with electron microscopy, the protein aggregate present in the sample after long incubation times consisted of extended, unbranched filaments of 30–50 Å in width that assemble subsequently into higher order structures. This fibrillar material possesses extensive β-sheet structure as revealed by far-UV CD and IR spectroscopy. Furthermore, the fibrils exhibit Congo red birefringence, increased fluorescence with thioflavine T and cause a red-shift of the Congo red absorption spectrum. All of these characteristics are typical of amyloid fibrils. The results indicate that formation of amyloid occurs when the native fold of a protein is destabilized under conditions in which noncovalent interactions, and in particular hydrogen bonding, within the polypeptide chain remain favorable. We suggest that amyloid formation is not restricted to a small number of protein sequences but is a property common to many, if not all, natural polypeptide chains under appropriate conditions.

Lifetimes of intermediates in the β-sheet to α-helix transition of β-lactoglobulin by using a diffusional IR mixer

The extremely slow α-helix/β-sheet transition of proteins is a crucial step in amylogenic diseases and represents an internal rearrangement of local contacts in an already folded protein. These internal structural rearrangements within an already folded protein are a critical aspect of biological action and are a product of conformational flow along unknown metastable local minima of the energy landscape of the compact protein. We use a diffusional IR mixer with time-resolved Fourier transform IR spectroscopy capable of 400-μs time resolution to show that the trifluoroethanol driven β-sheet to α-helix transition of β-lactoglobulin proceeds via a compact β-sheet intermediate with a lifetime of 7 ms, small compared with the overall folding time of β-lactoglobulin.

Molecular approaches to smart materials via interface recognition and conformationally switchable cavitands

In this thesis the molecular level design of functional materials and systems is reported. In the first part, tetraphosphonate cavitand (Tiiii) recognition properties towards amino acids are studied both in the solid state, through single crystal X-ray diffraction, and in solution, via NMR and ITC experiments. The complexation ability of these supramolecular receptors is then applied to the detection of biologically remarkable N-methylated amino acids and peptides using complex dynamic emulsions-based sensing platforms. In the second part, a general supramolecular approach for surface decoration with single-molecule magnets (SMMs) is presented. The self-assembly of SMMs is achieved through the formation of a multiple hydrogen bonds architecture (UPy-NaPy complexation). Finally we explore the possibility to impart auxetic behavior to polymeric material through the introduction of conformationally switchable monomers, namely tetraquinoxaline cavitands (QxCav). Their interconversion from a closed vase conformation to an extended kite form is studied first in solution, then in polymeric matrixes via pH and tensile stimuli by UV-Vis spectroscopy.

Preparação e caracterização de nanopartículas de prata para aplicação no desenvolvimento de imunoensaio para imunoglobulina G humana

Neste trabalho, anticorpos anti-IgGh foram conjugados às nanopartículas de prata (NPAg) para detectar imunoglobulina G humana (IgGh). Um imunoensaio colorimétrico baseado na diminuição da agregação devido ao aumento da repulsão eletrostática após a interação ligante-alvo. A agregação é induzida pela variação da força iônica e uma mudança da coloração da suspensão coloidal de amarelo para vermelho pode ser observada. Na presença de IgGh, a agregação é inibida e a coloração da suspensão coloidal não se altera. As nanopartículas foram obtidas por meio de cinco procedimentos diferentes e caracterizadas por espectroscopia UV-Vis, espalhamento dinâmico de luz, difração de raios-X e microscopia eletrônica. Glicose e borohidreto de sódio foram utilizados como agentes redutores, enquanto CTAB e β-ciclodextrina foram utilizados como estabilizantes. Citrato de sódio foi utilizado como agente redutor e/ou estabilizante. Nanoesferas de carbono foram obtidas por tratamento hidrotérmico de uma solução aquosa de glicose e também foram utilizadas no preparo das nanopartículas. As nanopartículas foram funcionalizadas com ácido mercaptossuccínico e a conjugação ocorreu devido à interação entre grupos aminas e grupos carboxílicos ionizados, presentes no anticorpo e agente de acoplamento, respectivamente. A estabilidade dos conjugados e o efeito da adição de IgGh foram avaliados para todos os sistemas preparados. As nanopartículas de prata preparadas com borohidreto de sódio e citrato de sódio foram selecionadas para serem aplicadas no desenvolvimento do imunoensaio e as condições experimentais foram avaliadas. Em condições ótimas, observou-se uma correlação linear entre a diminuição da agregação do sistema (NPAg-anti-IgGh) e a concentração de IgGh (0 a 200 ng mL-1). O limite de detecção foi estimado em 25 ng mL-1. O método colorimétrico apresentou boa seletividade para a detecção de IgGh. Além disso, foi obtido um resultado satisfatório ao aplicar o método para determinação do fator IX de coagulação. Foi desenvolvido também um método para determinação de ATP baseado na agregação de nanopartículas de ouro. Aptâmeros foram utilizados como elemento de reconhecimento. Em princípio, o método pode ser aplicável à determinação de outros analitos, por meio da substituição do aptâmero utilizado neste trabalho pelo oligonucleotídeo específico para o alvo de interesse.

Estudo comparativo de técnicas numéricas de inversão para obtenção de distribuição de tamanho de gotas em emulsões.

O desenvolvimento de algoritmos computacionais para a obtenção de distribuições de tamanho de partícula em dispersões e que utilizam dados espectroscópicos em tempo real e in-line a partir de sensores permitirá uma variedade de aplicações, como o monitoramento de propriedades em fluidos de corte industriais, acompanhamento de processos de polimerização, tratamento de efluentes e sensoriamento atmosférico. O presente estudo tem como objetivo a implementação e comparação de técnicas para resolução de problemas de inversão, desenvolvendo algoritmos que forneçam distribuição de tamanho de partículas em dispersões a partir de dados de espectroscopia UV-Vis-Nir (Ultravioleta, Visível e Infravermelho próximo). Foram implementadas quatro técnicas, sendo uma delas um método alternativo sem a presença de etapas de inversão. Os métodos que utilizaram alguma técnica de inversão evidenciaram a dificuldade em se obter distribuições de tamanho de gotas (DTG) de boa qualidade, enquanto o método alternativo foi aquele que se mostrou mais eficiente e confiável. Este estudo é parte de um programa cooperativo entre a Universidade de São Paulo e a Universidade de Bremen chamado programa BRAGECRIM (Brazilian German Cooperative Research Initiative in Manufacturing) e é financiado pela FAPESP, CAPES, FINEP e CNPq (Brasil) e DFG (Alemanha).

Electroquímica de sustancias de interés en los sistemas agroalimentario y de sanidad animal. Desarrollo de biosensores electroquímicos. Aplicaciones analíticas.

Se estudiarán los mecanismos de reacción electroquímica de las micotoxinas (metabolitos tóxicos generados por hongos) citrinina (CIT), patulina (PAT) y moniliformina (MON), de los antioxidantes naturales alfa, beta, gama y delta tocoferoles, de los flavonoides fisetina (FIS), morina (MOR), luteolina (LUT), rutina (RUT), buteina (BUT), naringenina (NAR) y miricetina (MIR) y de las hormonas esteroides estradiol (EDIOL), estrona (EONA) y estriol (ETRIOL). Por otra parte, se implementarán técnicas electroanalíticas para la detección y cuantificación de estos sustratos en muestras de matrices naturales que los contengan. Se realizará el diseño y caracterización de biosensores enzimáticos a partir de peroxidasas y/o fosfatasa alcalina para la determinación de la micotoxina CIT y de los flavonoides y, por otro, de inmunosensores para las micotoxinas ocratoxina A (OTA) y PAT y hormonas. Para el anclaje de enzimas y/o anticuerpos, se estudiarán las propiedades de electrodos modificados por monocapas autoensambladas, nanotubos de carbono y partículas magnéticas. Se usarán las técnicas de voltamperometría cíclica, de onda cuadrada y de redisolución con acumulación adsortiva, espectroscopías de impedancia electroquímica, electrólisis a potencial controlado, uv-vis e IR, microbalanza de cristal de cuarzo y microscopías de alta resolución (SEM, TEM, AFM). La importancia de este proyecto apunta a la obtención de nuevos datos electroquímicos de los sustratos indicados y conocimientos relacionados con la aplicación de electrodos modificados en la preparación de biosensores y en el desarrollo de técnicas alternativas para la determinación de los analitos mencionados precedentemente.

Synthesis and characterization of cobalt(III) complexes with sinambic amplector ligands

The synthesis of the hexadentate ligand 5,6-dimethyl-2,2,9,9-tetra(methyleneamine)-4,7-dithiadecane (1,2-Me(2)EtN(4)S(2)amp) is reported. The diastereiosomers were separated as cobalt(III) complexes using cation exchange chromatography. The rac and mesa isomers were characterized by NMR (C-13, H-1, Co-59), ESI-MS, UV-Vis spectroscopy and cyclic voltammetry. Single crystals of [Co(rac-1,2-Me(2)EtN(4)S(2)amp)] Cl-2(ClO4) (.) 2H(2)O were characterized by X-ray diffraction. The low-temperature (11 K) absorption spectra of the complexes have been measured in Nafion films and from the observed positions of both spin-allowed (1)A(1g) --> T-1(1g) and (1)A(1g) --> T-1(2g) and spin forbidden (1)A(1g) --> T-3(2g) bands, octahedral ligand-field parameters (10Dq, B and C) were determined. These results, in conjunction with the Co-59 NMR data, are used to further explore the relationship between the Co-59 magnetogyric ratio (gamma(Co)) and the product of the nephelauxetic ratio and the wavelength of the (1)A(1g) --> T-1(1g) transition (beta(DeltaE)(-1)) for complexes of mixed donor nitrogen-thioether ligands. (C) 2004 Elsevier Ltd. All rights reserved.

Gold nanoparticles decorated with oligo(ethylene glycol) thiols:kinetics of colloid aggregation driven by depletion forces

We have studied the kinetics of the phase-separation process of mixtures of colloid and protein in solutions by real-time UV-vis spectroscopy. Complementary small-angle X-ray scattering (SAXS) was employed to determine the structures involved. The colloids used are gold nanoparticles functionalized with protein resistant oligo(ethylene glycol) (OEG) thiol, HS(CH(2))(11)(OCH(2)CH(2))(6)OMe (EG6OMe). After mixing with protein solution above a critical concentration, c*, SAXS measurements show that a scattering maximum appears after a short induction time at q = 0.0322 angstrom(-1) stop, which increases its intensity with time but the peak position does not change with time, protein concentration and salt addition. The peak corresponds to the distance of the nearest neighbor in the aggregates. The upturn of scattering intensities in the low q-range developed with time indicating the formation of aggregates. No Bragg peaks corresponding to the formation of colloidal crystallites could be observed before the clusters dropped out from the solution. The growth kinetics of aggregates is followed in detail by real-time UV-vis spectroscopy, using the flocculation parameter defined as the integral of the absorption in the range of 600-800 nm wavelengths. At low salt addition (<0.5 M), a kinetic crossover from reaction-limited cluster aggregation (RLCA) to diffusion-limited cluster aggregation (DLCA) growth model is observed, and interpreted as being due to the effective repulsive interaction barrier between colloids within the depletion potential. Above 0.5 M NaCl, the surface charge of proteins is screened significantly, and the repulsive potential barrier disappeared, thus the growth kinetics can be described by a DLCA model only.

Synthetic, crystallographic, and computational study of copper(II) complexes of ethylenediaminetetracarboxylate ligands

Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands Heda3p and Heddadp (Heda3p = ethylenediamine-N-acetic-N,N',N'-tri-3-propionic acid; H eddadp = ethylenediamine-N,N'-diacetic-N,N'-di-3- propionic acid) have been prepared. An octahedral trans(O) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8HO compound, while Ba[Cu(eddadp)]·8HO is proposed to adopt a trans(O ) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV-vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O-Cu-N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial ß-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

Gold nanoparticles decorated with oligo(ethylene glycol) thiols:protein resistance and colloidal stability

The interactions between proteins and gold colloids functionalized with protein-resistant oligo(ethylene glycol) (OEG) thiol, HS(CH(2))(11) (OCH(2)CH(2))(6)OMe (EG(6)OMe), in aqueous solution have been studied by small-angle X-ray scattering (SAXS) and UV-vis spectroscopy. The mean size, 2R, and the size distribution of the decorated gold colloids have been characterized by SAXS. The monolayer-protected gold colloids have no correlations due to the low volume fraction in solution and are stable in a wide range of temperatures (5-70 degrees C, pH (1.3-12.4), and ionic strength (0-1.0 M). In contrast, protein (bovine serum albumin) solutions with concentrations in the range of 60-200 mg/mL (4.6-14.5 vol show a pronounced correlation peak in SAXS, which results from the repulsive electrostatic interaction between charged proteins. These protein interactions show significant dependence on ionic strength, as would be expected for an electrostatic interaction (Zhang et al. J. Phys. Chem. B 2007, 111, 251). For a mixture of proteins and gold colloids, the protein-protein interaction changes little upon mixing with OEG-decorated gold colloids. In contrast, the colloid-colloid interaction is found to be strongly dependent on the protein concentration and the size of the colloid itself. Adding protein to a colloidal solution results in an attractive depletion interaction between functionalized gold colloids, and above a critical protein concentration, c*, the colloids form aggregates and flocculate. Adding salt to such mixtures enhances the depletion effect and decreases the critical protein concentration. The aggregation is a reversible process (i.e., diluting the solution leads to dissolution of aggregates). The results also indicate that the charge of the OEG self-assembled monolayer at a curved interface has a rather limited effect on the colloidal stabilization and the repulsive interaction with proteins.