| 1. |
- Agmo Hernández, Víctor, et al.
(author)
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Electrochemistry of Adhesion and Spreading of Lipid Vesicles on Electrodes
- 2013
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In: Applications of Electrochemistry in Medicine. - Boston, MA : Springer US. - 9781461461487 ; , s. 189-247
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Book chapter (other academic/artistic)abstract
- Biological membranes have developed to separate different compartments of organisms and cells. There is a large number of rather different functions which membranes have to fulfil: (1) they control the material and energy fluxes of metabolic processes, (2) they provide a wrapping protecting the compartments from chemical and physical attacks of the environment, (3) they provide interfaces at which specific biochemical machineries can operate (e.g., membrane bound enzymes), (4) they are equipped for signal transduction, (5) they possess the necessary stability and flexibility to allow cell division, and endo- and exocytosis as well as migration, (6) they present anchoring structures that enable cell-to-cell and cell-to-matrix physical interactions and intercellular communication. These are certainly not all functions of membranes as new functionalities are continuously reported. Since the biological membranes separate essentially aqueous solutions, such separating borders—if they should possess a reasonable stability and also flexibility combined with selective permeability—have to be built up of hydrophobic molecules exposing to both sides a similar interface. It was one of the most crucial and most lucky circumstances for the development and existence of life that certain amphiphilic molecules are able to assemble in bilayer structures (membranes), which—on one side—possess a rather high physical and chemical stability, and—on the other side—are able to incorporate foreign molecules for modifying both the physical properties as well as the permeability of the membranes for defined chemical species. The importance of the chemical function of membranes and all its constituents, e.g., ion channels, pore peptides, transport peptides, etc., is generally accepted. The fluid-mosaic model proposed by Singer and Nicolson [1] is still the basis to understand the biological, chemical, and physical properties of biological membranes. The importance of the purely mechanical properties of membranes came much later into the focus of research. The reasons are probably the dominance of biochemical thinking and biochemical models among biologists and medical researchers, as well as a certain lack of appropriate methods to probe mechanical properties of membranes. The last decades have changed that situation due to the development of techniques like the Atomic Force Microscopy, Fluorescence Microscopy, Micropipette Aspiration, Raman Microspectroscopy, advanced Calorimetry, etc. This chapter is aimed at elucidating how the properties of membranes can be investigated by studying the interaction of vesicles with a very hydrophobic surface, i.e., with the surface of a mercury electrode. This interaction is unique as it results in a complete disintegration of the bilayer membrane of the vesicles and the formation of an island of adsorbed lipid molecules, i.e., a monolayer island. This process can be followed by current-time measurements (chronoamperometry), which allow studying the complete disintegration process in all its details: the different steps of that disintegration can be resolved on the time scale and the activation parameters can be determined. Most interestingly, the kinetics of vesicle disintegration on mercury share important features with the process of vesicle fusion and, thus, sheds light also on mechanisms of endocytosis and exocytosis. Most importantly, not only artificial vesicles (liposomes) can be studied with this approach, but also reconstituted plasma membrane vesicles and even intact mitochondria. Hence, one can expect that the method may provide in future studies also information on the membrane properties of various other vesicles, including exosomes, and may allow investigating various aspects of drug action in relation to membrane properties (transmembrane transport, tissue targeting, bioavailability, etc.), and also the impact of pathophysiological conditions (e.g., oxidative modification) on membrane properties, on a hitherto not or only hardly accessible level.
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| 2. |
- Agmo Hernandez, Victor, et al.
(author)
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Study of the temporal distribution of the adhesion-spreading events of liposomes on a mercury electrode
- 2009
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In: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 13:7, s. 1111-1114
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Journal article (peer-reviewed)abstract
- The formal analysis of the mechanism of adhesion spreading of liposomes at mercury electrodes shares several characteristics with the mechanism of metal nucleation at electrodes. It is shown that the description of the temporal distribution of the adhesion-spreading events is similar to that of the temporal distribution of metal clusters. Both processes are stochastic in nature and can be described by the Poisson distribution. Using this approach, a previously proposed model for the overall adhesion-spreading mechanism, considering the formation of active sites on the liposome and the actual attachment of the liposomes to the mercury surface, is validated.
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| 3. |
- Agmo Hernández, Víctor, 1980-, et al.
(author)
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The electrochemistry of liposomes
- 2008
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In: Israel Journal of Chemistry. - 0021-2148. ; 48, s. 169-184
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Review (peer-reviewed)
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| 4. |
- Agmo Hernández, Víctor, et al.
(author)
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The lipid composition determines the kinetics of adhesion and spreading of liposomes on mercury electrodes
- 2008
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In: Bioelectrochemistry. - : Elsevier BV. - 1567-5394 .- 1878-562X. ; 74:1, s. 149-156
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Journal article (peer-reviewed)abstract
- The dependence of membrane properties on their composition was studied by following the adhesion and spreading of unilamellar and multilamellar liposomes on static mercury electrodes with the help of chronoamperometry. The analysis of the peak-shaped signals allows determining the kinetic parameters of the three-step adhesion-spreading process. The presence of cholesterol in the membrane stabilizes the bilayer in the liquid-crystal line phase, and destabilizes the gel phase. The kinetic parameters also show the effect of superlattice formation in the DMPC-cholesterol system. The detergent triton X-100 is only incorporated in the liquid-crystalline DMPC membranes, and it is expelled to the solution when the membrane is transformed to the gel phase. In the liquid-crystalline membrane, it enhances the adhesion-spreading of liposomes on mercury. The lyric peptides mastoparan X and melittin affect the adhesion-spreading in a similar manner. For the rupture-spreading step, their effect is explained by pore formation. The results obtained with lecithins of different length suggest that the bilayer opening process has much in common with flip-flop translocations. For this process the activation energies were found to be independent of the chain length of the lecithin molecules, while the preexponential factor in the Arthenius equation decreases drastically for longer chains.
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| 5. |
- Agmo Hernandez, Victor, et al.
(author)
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The overall adhesion-spreading process of liposomes on a mercury electrode is controlled by a mixed diffusion and reaction kinetics mechanism
- 2009
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In: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 13:4, s. 639-649
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Journal article (peer-reviewed)abstract
- Using high-resolution chronoamperometric measurements, with sampling each 1.333 micro s, the initial step of the adhesion-spreading of liposomes on a mercury electrode was studied. These measurements allow getting a deeper insight into the first interaction of the liposomes with the mercury electrode, and they show that the overall adhesion-spreading process at different potentials is partially controlled by a fast but weak interaction equilibrium resulting in a mixed diffusion- and reaction-kinetics-controlled mechanism of the overall reaction.
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| 6. |
- Hellberg, D, et al.
(author)
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Kinetics of liposome adhesion on a mercury electrode
- 2005
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109, s. 14715-14726
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Journal article (peer-reviewed)abstract
- The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islands of lecithin monolayers. Integration of the current-time transients gives charge-time transients that can be fitted by the empirical equation Q(t) = Q(0) + Q(1)(1 - exp(-t/tau(1))) + Q(2)(1 - exp(-t/tau(2))), where the first term on the right side is caused by the docking of the liposome on the mercury surface, the second term is caused by the opening of the liposome, and the third term is caused by the spreading of the lecithin island on the mercury surface. The temperature dependence of the two time constants tau(1) and tau(2) and the temperature dependence of the overall adhesion rate allow determination of the activation energies of the opening, the spreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determining process. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria of the intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reaction scheme supports the empirical equation used for fitting the charge-time transients. The developed kinetic model of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusion of liposomes. The new approach can be used to probe the stability of liposome membranes.
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| 7. |
- Hernandez, Victor Agmo, et al.
(author)
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Kinetics of the adhesion of DMPC liposomes on a mercury electrode. Effect of lamellarity, phase composition, size and curvature of liposomes, and presence of the pore forming peptide Mastoparan X
- 2006
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22, s. 10723-10731
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Journal article (peer-reviewed)abstract
- Liposomes suspended in aqueous electrolyte solutions can adhere at mercury electrodes. The adhesion is a complex process that starts with the docking and opening and leads to a spreading, finally resulting in the formation of islands of adsorbed lecithin molecules. The adhesion process can be followed by chronoamperometry, and a detailed analysis of the macroscopic and microscopic kinetics can be performed yielding rate constants and activation parameters. By using giant unilamellar liposomes and multilamellar liposomes, the effect of lamellarity and liposome size could be elucidated for liposomes in the liquid crystalline, gel, and superlattice phase states. Below the phase transition temperature, the time constant of opening of the liposomes (i.e., the irreversible binding of the lecithin molecules on the preliminary contact interface liposome vertical bar mercury and the therewith associated disintegration of the liposome membrane on that spot) is shown to be strongly size dependent. The activation energy, however, of that process is size independent with the exception of very small liposomes. That size dependence of time constants is a result of the size dependence of the initial contact area. The time constant and the activation energies of the spreading step exhibit a strong size dependence, which could be shown to be due to the size dependence of rate and activation energy of pore formation. Pore formation is necessary to release the solution included in the liposomes. This understanding was corroborated by addition of the pore inducing peptide Mastoparan X to the liposome suspension. The obtained results show that electrochemical studies of liposome adhesion on mercury electrodes can be used as a biomimetic tool to understand the effect of membrane properties on vesicle fusion.
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| 8. |
- Hernandez, Victor Agmo, et al.
(author)
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One redox probe (dmfc) can drive the transfer of anions and cations across the aqueous electrolyte ionic liquid interface
- 2006
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In: Electrochemistry communications. - : Elsevier BV. - 1388-2481 .- 1873-1902. ; 8, s. 967-972
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Journal article (peer-reviewed)abstract
- Three-phase electrodes consisting of droplets of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate containing decamethylferrocenium (dmfc(+)) cations, immobilized on the surface of graphite electrodes and immersed in aqueous electrolyte solutions have been employed to study the redox driven transfer of anions and cations. Very surprisingly, it has been observed that anions as well as cations can be transferred with one redox probe (dmfc/dmfc(+)) because the Gibbs energies of ion transfer of the different ions are rather similar. (C) 2006 Elsevier B.V. All rights reserved.
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| 9. |
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| 10. |
- Hernandez, Victor Agmo, et al.
(author)
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The adhesion and spreading of thrombocyte vesicles on electrode surfaces
- 2008
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In: Bioelectrochemistry. - : Elsevier BV. - 1567-5394 .- 1878-562X. ; 74, s. 210-216
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Journal article (peer-reviewed)abstract
- The interaction of thrombocyte vesicles with the surface of metal electrodes, i.e., mercury, gold and gold electrodes modified with self assembled monolayers (SAM), was studied with the help of chronoamperometry, atomic force microscopy, and quartz crystal microbalance measurements. The experimental results show that the interaction of the thrombocyte vesicles with the surface of the electrodes depends on the hydrophobicity of the latter: whereas on very hydrophobic surfaces (mercury and gold functionalized with SAM) the thrombocyte vesicles disintegrate and form a monolayer of lipids. on the less hydrophobic gold surface a bilayer is formed. The chronoamperometric measurements indicate the possibility of future applications to probe membrane properties of thrombocytes. (C) 2008 Elsevier B.V. All rights reserved.
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