Juan Torrent-Burgués

Tin–zinc electrodeposition from sulphate–gluconate baths

Abstract The electrodeposition of tin–zinc alloys with 20–30% Zn by weight from sulphate–gluconate baths at pH 4 and different [Sn(II)], [Zn(II)] and [gluconate]/([Sn(II)]+[Zn(II)]) ratios was studied. The anodic stripping analysis of the deposits was correlated with their morphology, composition and phase structure. When [Zn(II)] is equal to or not much greater than [Sn(II)], a eutectic type Sn–Zn alloy is obtained, with a Zn content of around 20% by weight, which is greater than that of a thermal eutectic alloy. The morphology of the electrodeposited eutectic Sn–Zn alloy tends to disappear at high deposition charges and a second crystalline coating, richer in Sn, is obtained.

Initial stages of tin electrodeposition from sulfate baths in the presence of gluconate

Tin electrodeposition in its initial stages in acid sulfate/gluconate baths was studied with varying tin and gluconate concentrations using potential-controlled electrochemical techniques. The deposit morphology was observed by scanning electron microscopy (SEM). A comparison with tin electrodeposition from acid sulfate baths in the absence of gluconate was also carried out. Use of a highly acidic bath leads to nonuniform deposits, even in the presence of gluconate; at pH 4 deposits are uniform, brilliant and suitable for finishing applications. Tin crystallites have a well defined morphology which depends on bath agitation conditions. In the absence of agitation, the crystallites have the same tetragonal shape as in a sulfate bath without gluconate.

Biomimetic monolayer films of monogalactosyldiacylglycerol incorporating ubiquinone.

Ubiquinone and plastoquinone are two of the main electron and proton shuttle molecules in biological systems, and monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the thylakoid membrane of chloroplasts. Saturated MGDG, ubiquinone-10 (UQ) and MGDG:UQ mixed monolayers at the air/water interface have been studied using surface pressure-area isotherms and Brewster Angle Microscopy. Moreover, the transferred Langmuir-Blodgett films have been observed by Atomic Force Microscopy. The results show that MGDG:UQ mixtures present more fluid phase than pure MGDG, indicating a higher order degree for the later. It is also observed an important influence of UQ on the MGDG matrix before UQ collapse pressure and a low influence after this event, due to UQ expulsion from the MGDG matrix. This expulsion leads to a similar remaining UQ content for all the tested mixtures, indicating a limiting content of this molecule in the MGDG matrix at high surface pressures. The thermodynamic studies confirm the stability of the MGDG:UQ mixtures at low surface pressures, although presenting a non-ideal behaviour. Results point to consider UQ as a good candidate for studies of artificial photosynthesis.

Incorporation of ubiquinone in supported lipid bilayers on ITO.

Ubiquinone (UQ) is one of the main electron and proton shuttle molecules in biological systems, and dipalmitoylphosphatidylcholine (DPPC) is one of the most used model lipids. Supported planar bilayers (SPBs) are extensively accepted as biological model membranes. In this study, SPBs have been deposited on ITO, which is a semiconductor with good electrical and optical features. Specifically, topographic atomic force microscopy (AFM) images and force curves have been performed on SPBs with several DPPC:UQ ratios to study the location and the interaction of UQ in the SPB. Additionally, cyclic voltammetry has been used to understand the electrochemical behavior of DPPC:UQ SPBs. Obtained results show that, in our case, UQ is placed in two main different positions in SPBs. First, between the DPPC hydrophobic chains, fact that originates a decrease in the breakthrough force of the bilayer, and the second between the two leaflets that form the SPBs. This second position occurs when increasing the UQ content, fact that eventually forms UQ aggregates at high concentrations. The formation of aggregates produces an expansion of the SPB average height and a bimodal distribution of the breakthrough force. The voltammetric response of UQ depends on its position on the bilayer.

Improved conformational stability of the visual G protein-coupled receptor rhodopsin by specific interaction with docosahexaenoic acid phospholipid.

Rhodopsin is the photoreceptor located in the rod cells of the retina. It has seven transmembrane helices and is a prototypic member of the G protein‐coupled receptor superfamily. The structures and functions of these receptors are clearly affected by the lipid composition of the cell membrane, and their study in a purified recombinant form is usually performed in detergent solution. There is a need to study these receptors in a physiologically relevant environment because the lipid environment is known to have an important effect on their function. In this work, rhodopsin reconstituted in docosahexaenoic acid (DHA) liposomes is shown to have more thermal stability than when it is solubilised with the neutral detergent dodecyl maltoside. Moreover, the specific interaction between rhodopsin and DHA was followed by means of Langmuir experiments with insertion of rhodopsin into lipid monolayers; this showed high affinity for the lipid–receptor interaction. Furthermore, fluorescence spectroscopy measurements indicate that the conformation of opsin obtained after photobleaching is preserved in DHA‐containing liposomes, thereby allowing retinal to re‐enter the binding pocket even long after bleaching. Overall, our results demonstrate that liposomes of this specific lipid provide a more stable environment for ground‐state inactive rhodopsin in the dark, than dodecyl maltoside detergent, and that this lipid can also preserve the native correctly folded ligand‐free opsin conformation obtained after illumination. This strategy will be used in further studies on mutations of rhodopsin associated with congenital retinopathies.

Escherichia coli and Pseudomonas aeruginosa eradication by nano-penicillin G

The transformation of penicillin G into nano/micro-sized spheres (nanopenicillin) using sonochemical technology was explored as a novel tool for the eradication of Gram-negative bacteria and their biofilms. Known by its effectiveness only against Gram-positive microorganisms, the penicillin G spherization boosted the inhibition of the Gram-negative Pseudomonas aeruginosa 10-fold (from 0.3 to 3.0 log-reduction) and additionally induced 1.2 log-reduction of Escherichia coli growth. The efficient penetration of the spheres within a Langmuir monolayer sustained the theory that nanopenicillin is able to cross the membrane and reach the periplasmic space in Gram-negative bacteria where they inhibit the β-lactam targets: the transferases that build the bacteria cell wall. Moreover, it considerably suppressed the growth of both bacterial biofilms on a medically relevant polystyrene surface, leaving majority of the adhered cells dead compared to the treatment with the non-processed penicillin G. Importantly, nanopenicillin was found innocuous towards human fibroblasts at the antibacterial-effective concentrations.

Monogalactosyldiacylglycerol and digalactosyldiacylglycerol role, physical states, applications and biomimetic monolayer films

Abstract.The relevance of biomimetic membranes using galactolipids has not been expressed in any extensive experimental study of these lipids. Thus, on the one hand, we present an in-depth article 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 pressure-area isotherms and their data are processed to enlighten 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 presents other differences in comparison with its pure components that are explained by the presence of different kinds of galactosyl headgroups that restrict the optimal orientation of the MGDG headgroups.Graphical abstract

AFM in peak force mode applied to worn siloxane-hydrogel contact lenses

The objective of this work is to apply Atomic Force Microscopy in Peak Force mode to obtain topographic characteristics (mean roughness, root-mean-square roughness, skewness and kurtosis) and mechanical characteristics (adhesion, elastic modulus) of Siloxane-Hydrogel Soft Contact Lenses (CLs) of two different materials, Lotrafilcon B of Air Optix (AO) and Asmofilcon A of PremiO (P), after use (worn CLs). Thus, the results obtained with both materials will be compared, as well as the changes produced by the wear at a nanoscopic level. The results show significant changes in the topographic and mechanical characteristics of the CLs, at a nanoscopic level, due to wear. The AO CL show values of the topographic parameters lower than those of the P CL after wear, which correlates with a better comfort qualification given to the former by the wearers. A significant correlation has also been obtained between the adhesion values found after the use of the CLs with tear quality tests, both break-up-time and Schirmer.

Electrochemistry of LB films of mixed MGDG:UQ on ITO.

The electrochemical behaviour of biomimetic monolayers of monogalactosyldiacylglycerol (MGDG) incorporating ubiquinone-10 (UQ) has been investigated. MGDG is the principal component in the thylakoid membrane and UQ seems a good substitute for plastoquinone-9, involved in photosynthesis chain. The monolayers have been performed using the Langmuir and Langmuir-Blodgett (LB) techniques and the redox behaviour of the LB films, transferred at several surface pressures on a glass covered with indium-tin oxide (ITO), has been characterized by cyclic voltammetry. The cyclic voltammograms show that UQ molecules present two redox processes (I and II) at high UQ content and high surface pressures, and only one redox process (I) at low UQ content and low surface pressures. The apparent rate constants calculated for processes I and II indicate a different kinetic control for the reduction and the oxidation of UQ/UQH2 redox couple, being k(Rapp)(I) = 2.2 · 10(-5) s(-1), k(Rapp)(II) = 5.1 · 10(-14) k(Oapp)(I) = 3.3 · 10(-3) s(-1) and k(Oapp)(II) = 6.1 · 10(-6) s(-1), respectively. The correlation of the redox response with the physical states of the LB films allows determining the positions of the UQ molecules in the biomimetic monolayer, which change with the surface pressure and the UQ content. These positions are known as diving and swimming.

Biomimetic monolayer films of digalactosyldiacylglycerol incorporating plastoquinone.

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 pressure-area isotherms. These isotherms give information about the film stability and indicate the thermodynamic behaviour of the mixture and their physical state. The Langmuir-Blodgett (LB) film has been transferred forming a monolayer that mimics the bottom layer of the biological membranes. This monolayer on mica has been topographically characterized using AFM and both the height and the physical state that they present have been obtained. Moreover, these monolayers have been transferred onto ITO that is a hydrophilic substrate with good optical and electrical features, so that, it is suitable for studying the electrochemical behaviour of these systems and it is a good candidate for energy producing devices.