Ester Guaus | Universitat Politecnica de Catalunya (original) (raw)

Papers by Ester Guaus

Journal of Colloid and Interface Science, 2019

Contact lenses (CL) provide visual correction but their use may also induce several adverse effec... more Contact lenses (CL) provide visual correction but their use may also induce several adverse effects causative of discomfort and conditions that lead to stop or discontinue their use. Discomfort is mainly caused by insufficient wetting, impairment of the antioxidant defence system and eye infections. The current work reports on a single step sonochemical coating of CL with ZnO nanoparticles (NPs), chitosan (CS) and gallic acid (GA). GA and CS are expected to improve the comfort of CL by imparting respectively antioxidant properties and enhanced wettability, while their combination with ZnO NPs provides the CL with antimicrobial properties. The ternary composite coating presents high antibacterial efficiency (> 4.5 logs reduction) against S. aureus causative of CL-related conditions, and maintains good biocompatibility (> 72 %) with human cell lines. The obtained multi-functionality on the CL did not affect their geometry and refractive properties.

The European Physical Journal E, 2016

The relevance of biomimetic membranes using galactolipids has not been expressed in an extensive ... more The relevance of biomimetic membranes using galactolipids has not been expressed in an extensive experimental study of these lipids. On the one hand, we present an intensive literature work about the presence and role of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) in thylakoid membranes, their physical states and their applications. On the other hand, we use the Langmuir and Langmuir-Blodgett (LB) techniques to prepare biomimetic monolayers of saturated galactolipids MGDG, DGDG and MGDG:DGDG 2:1 mixture (MD)-biological ratio-. These monolayers are studied using surface pressurearea isotherms and their data are processed to light their physical states and mixing behaviour. These monolayers, once transferred to a solid substrate at several surface pressures are topographically studied on mica using atomic force microscopy (AFM) and using cyclic voltammetry for studying the electrochemical behaviour of the monolayers once transferred to indium-tin oxide (ITO), which has good optical and electrical properties. Moreover, MD present other differences in comparison with its pure components that are 2 explained by the presence of different kind of galactosyl headgroups that restrict the optimal orientation of the MGDG headgroups.

Procedia - Social and Behavioral Sciences, 2012

The European Physical Journal E, 2017

Artificial lipid bilayers have been extensively studied as models that mimic natural membranes (b... more Artificial lipid bilayers have been extensively studied as models that mimic natural membranes (biomimetic membranes). Several attempts of biomimetic membranes inserting ubiquinone (UQ) have been performed to enlighten which the position of UQ in the lipid layer is, although obtaining contradictory results. In this work, pure components (DPPC and UQ) and DPPC:UQ mixtures have been studied using surface pressure-area isotherms and Langmuir-Blodgett (LB) films of the same compounds have been transferred onto solid substrates being topographically characterized on mica using atomic force microscopy and electrochemically on indium tin oxide slides. DPPC:UQ mixtures present less solid-like physical state than pure DPPC indicating a higher order degree for the later. UQ influences considerably DPPC during the fluid state, but it is mainly expelled after the phase transition at ≈ 26 mN•m-1 for the 5:1 ratio and at ≈ 21 mN•m-1 for lower UQ content. The thermodynamic studies confirm the stability of the DPPC:UQ mixtures before that event, although presenting a non-ideal behaviour. The results indicate that UQ position can be tuned by means of the surface pressure applied to obtain LB films and the UQ initial content. The UQ positions in the biomimetic membrane are distinguished by their formal potential: UQ located in "diving" position with the UQ placed in the DPPC matrix in direct contact with the electrode surface (-0.04 ± 0.02 V), inserted between lipid chains without contact to the substrate (0.00 ± 0.01 V) and parallel above the lipid chains (0.09 ± 0.02 V).

Bioelectrochemistry, 2016

In this work biomimetic monolayers of a MGDG, monogalactosyldiacylglycerol, and DGDG, digalactosy... more In this work biomimetic monolayers of a MGDG, monogalactosyldiacylglycerol, and DGDG, digalactosyldiacylglycerol mixture (MD), in a ratio close to that of the thylakoid membranes of oxygenic photosynthetic organisms, have been prepared. The lipid mixture incorporates plastoquinone-9 (PQ), that is the electron and proton shuttle of the photosynthetic reaction centres. The MD:PQ mixtures have been firstly studied using surface pressure-area isotherms. Langmuir-Blodgett (LB) films of those mixtures have been transferred onto a substrate forming a monolayer that mimics one of the bilayer side of the thylakoid membranes. These monolayers have been characterized topographically and electrochemically. The results show the influence of PQ in the MD matrix and its partial expulsion when increasing the surface pressure, obtaining two main PQ positions in the MD matrix. The calculated apparent electron transfer rate constants indicate a different kinetic control for the reduction and the oxidation of the PQ/PQH2 couple, being kRapp(I)= 0.7•10-6 s-1 , kRapp(II)= 2.2•10-9 s-1 , kOapp(I)= 7.4•10-4 s-1 and kOapp(II)= 5.2•10-5 s-1 , respectively. The comparison of the different galactolipid:PQ systems that our group have studied is also presented, concluding that the PQ position in the galactolipid matrix can be tuned according to several controlled variables.

The study of biomimetic membranes and natural processes occurring in them are on the top science ... more The study of biomimetic membranes and natural processes occurring in them are on the top science targets. Some quinone compounds such as ubiquinone (UQ) and plastoquinone (PQ) are involved in redox processes in the respiratory and photosynthetic pathways [1]. Liposome formation and extension as supported planar bilayers (SPB) and the Langmuir-Blodgett (LB) film formation [2] on solid electrodes can be used in these studies. In the present work the insertion of UQ or PQ in dipalmitoylphosphatidylcholine (DPPC) liposomes and LB films is performed and the SPB and LB films are characterized by Atomic Force Microscopy, Force Spectroscopy, Surface Potential Force Microscopy and Cyclic Voltammetry. Indium tin oxide (ITO) has been selected as electrode material. Several DPPC:Quinone compositions have been tested. Results show that quinone molecules incorporate in the DPPC liposomes and LB films, and that they behave as confined species in the phospholipid film.

The Langmuir technique has been applied to the study of natural tears and the results obtained fr... more The Langmuir technique has been applied to the study of natural tears and the results obtained from surface pressure-area isotherms have been correlated with those of clinical tests (the Schirmer and the TFBUT tests). The population studied only included people aged over 45. Natural tears were collected from Schirmer strips, which were placed in contact with the water subphase of a Langmuir trough for recording the surface pressure-area isotherms. These isotherms have been classified as good or weak according to the characteristics obtained. From the isotherms, characteristic values such as π limit , C S -1 max and π max were also obtained. The analysis from the Chi-squared test indicates dependence between the Schirmer test and the type of isotherms (P 0.05 indicates that the independence cannot be discarded with the significance criteria imposed. Working with the same criteria of significance, we obtain moderate or good Pearson correlation coefficients with statistical significanc...

Trends in Nanotechnology, 2007

Optica Applicata

The use of terahertz-based techniques has grown very fast since they are capable of performing ev... more The use of terahertz-based techniques has grown very fast since they are capable of performing evaluations at molecular level, being very suitable for the analysis of biological samples and biomaterials such those for contact lenses. These biomaterials are continuously evolving to enhance the lens wearer's comfort by improving their hydration state and surface wettability. Therefore, this study examines a novel terahertz system for the assessment of the temporary in-vitro dehydration of hydrogel contact lenses, which provides a new index to assess their state of hydration. Several conventional and silicone hydrogel contact lenses and lens care solutions were analysed. Traditional methods such as the gravimetric determination of water content and the measurement of the static contact angle were also carried out for the validation of the developed system. The dehydration rate measurements of contact lenses obtained with the proposed system correlated with the values provided by traditional methods. As a whole, conventional hydrogel contact lenses exhibited the lowest values for dehydration rate. The tests conducted on various solutions showed a correlation between the wetting action of the solution and the dehydration rate of the contact lens material.

Thin Solid Films, 2014

In this work we report the fabrication of Langmuir and Langmuir-Blodgett (LB) films of a substitu... more In this work we report the fabrication of Langmuir and Langmuir-Blodgett (LB) films of a substituted ZnPc (octakis(oxyoctyl)phthalocyanine of zinc), and their characterization by means of several techniques. These characterization techniques include surface pressure (π-A) and surface potential (∆V-A) isotherms as well as UV-Vis Reflection spectroscopy and Brewster Angle Microscopy (BAM) for the films at the air-water interface together with UV-Vis absorption and IR spectroscopies and Atomic Force Microscopy (AFM) for the LB films. The π-A and ∆V-A isotherms and BAM images indicate a phase transition at a surface pressure of ca. 9 mN/m and a multilayer formation at surface pressures around 19-20 mN/m; at a surface pressure around 27 mN/m a disordered collapse of the film occurs. In addition, AFM images of LB films at π=10 mN/m and π =20 mN/m show a monomolecular and a multilayered film, respectively. The comparison of the UV-Vis spectrum of ZnPc in solution, the reflection spectra of the Langmuir films and UV-Vis spectra of LB films reveals a significant reduction in the Q band intensity for the films, indicative of an organization of ZnPc in the Langmuir and LB films versus the random distribution in solution. The UV-Vis reflection spectra are also consistent with multilayer formation at surface pressures around 19-20 mN/m. The relative intensities of the IR spectrum bands change from the KBr pellet to the LB film which is also attributable to orientation effects in the film. Cyclic voltammetic experiments of LB films incorporating the ZnPc derivative show peaks that can be correlated with redox processes occurring in the phthalocyanine ring. A small but significant influence of the surface pressure and the number of deposited layers in the electrochemical behaviour is observed. The electrochemical response of cast films exhibits some differences with respect to that of LB films which have been attributed to their different molecular organization.

Se ha diseñado un itinerario de aprendizaje en el que se han incorporado nuevas metodologías doce... more Se ha diseñado un itinerario de aprendizaje en el que se han incorporado nuevas metodologías docentes (aprendizaje cooperativo y aprendizaje basado en problemas) y que podría responder a las exigencias establecidas por el MEC respecto al diseño establecido en la nueva estructuración de los estudios universitarios, para el primer año común, en la asignatura de Química. Este itinerario se ha elaborado teniendo en cuenta los siguientes parámetros: 1. Entrevistas a profesores de Química de Bachillerato . 2. Reuniones de los profesores de Química implicados en el proyecto . 3. Análisis de los exámenes finales de química de primer año/cuatrimestre de la titulación. 4. Análisis de las pruebas de selectividad desde el 2002 hasta el 2005. 5. Entrevistas a responsables de la elaboración de las pruebas de química a nivel español. 6. Diseño establecido en la web de autoaprendizaje “avalquim on line!”. Algunas de las conclusiones de los profesores UPC son: 1. Dificultad de coordinar objetivos de...

Portugaliae Electrochimica Acta, 2003

The zinc electrochemical behaviour from sulphate and sulphate-gluconate baths was studied both on... more The zinc electrochemical behaviour from sulphate and sulphate-gluconate baths was studied both on a vitreous carbon and a copper electrode. The voltammetric response depends on the complexing agent concentration, the electrode material, the pH and the cathodic potential limit. The reduction of zinc ions proceeds with hydrogen evolution, and at less negative potentials on the copper electrode than on the vitreous carbon electrode, specially in absence of gluconate. Gluconate decreases the efficiency of the process. On the other hand, gluconate favours zinc electrodeposition on vitreous carbon but retards it on copper.

Portugaliae Electrochimica Acta, 2007

A Langmuir-Schaefer (LS) film of a thiomacrocyclic (ThM) compound was deposited on the surface of... more A Langmuir-Schaefer (LS) film of a thiomacrocyclic (ThM) compound was deposited on the surface of a glassy carbon electrode (GCE) rod, from a subphase containing Cu(II) ions. The voltammetric response of this modified GCE when the ThM was bonded to Cu 2+ , showed that the LS film moved the oxidation peaks of copper to more positive values. On the other hand, a LS film of the ThM compound was deposited on the surface of a GCE rod from a subphase of pure water. When the voltammetric response of the GCE-ThM electrode was studied in a Cu 2+ -SO 4 2solution, it was found that the modified electrode increases its sensitivity respect to Cu 2+ at low bulk Cu 2+ concentrations in solution, and a surface-complexation reaction is proposed to explain the effect of the LS film on the GCE surface.

Biochimica et biophysica acta, Jan 11, 2015

The photosynthesis is the process used by plants and bacteria cells to convert inorganic matter i... more The photosynthesis is the process used by plants and bacteria cells to convert inorganic matter in organic thanks to the light energy. This process consist on several steps, being one of them the electronic transport from the photosystem II to the cytochrome thanks to plastoquinone-9 (PQ). Here we prepare membranes that mimic the characteristics and composition of natural photosynthetic cell membranes and we characterize them in order to obtain the PQ molecules position in the membrane and their electrochemical behaviour. The selected galactolipid is digalactosyldiacylglycerol (DGDG) that represents the 30% of the thylakoid membrane lipid content. The results obtained are worthful for several science fields due to the relevance of galactolipids as anti-algal, anti-viral, anti-tumor and anti-inflammatory agents and the antioxidant and free radical scavenger properties of prenylquinones. Both pure components (DGDG and PQ) and the DGDG:PQ mixtures have been studied using surface pressu...

Bioelectrochemistry, 2015

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Portugaliae Electrochimica Acta, 2005

The electrodeposition of tin in presence of tartrate ions has been analysed by electrochemical te... more The electrodeposition of tin in presence of tartrate ions has been analysed by electrochemical techniques, mainly chronoamperometry, and by scanning electron microscopy (SEM). The obtained values of nucleus density with both techniques have been compared and discussed. The electrodeposition process follows an instantaneous nucleation with 3D growth under diffusion control at the initial times of the process, but a second nucleation process occurs at higher times. The influence of tartrate and of agitation conditions is also inferred from the crystal morphology.

Portugaliae Electrochimica Acta, 2001

... References [ I) KN Strafford, A. Reed, Coatings and Surface Treatment for Corrosion and Wear ... more ... References [ I) KN Strafford, A. Reed, Coatings and Surface Treatment for Corrosion and Wear Resistance, (1984)74 [2] R Sabitha, Malathy Pushpavanam, M Mahesh Sujatha, T. Vasudevan, Trans. ... 261 - [13; V S. Vasantha, Malathy Pushpavanam and VS Muralidharan, Met. ...