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1. Experimental and computational studies of the effects of free DHA on a model phosphatidylcholine membrane

Author

Marcela A. Morini, Viviana Isabel Pedroni, María Belén Sierra, L. M. Alarcón, Gustavo A. Appignanesi, and A.R. Verde

Subjects
0301 basic medicine, MEMBRANE STRUCTURE, 1,2-Dipalmitoylphosphatidylcholine, Docosahexaenoic Acids, Membrane Fluidity, MOLECULAR DYNAMICS SIMULATIONS, Lipid Bilayers, Molecular Dynamics Simulation, Biochemistry, 03 medical and health sciences, chemistry.chemical_compound, Phosphatidylcholine, Química Coloidal, Membrane fluidity, Transition Temperature, DPPC LIPOSOME, Lipid bilayer, Molecular Biology, FLUIDITY, Liposome, 030102 biochemistry & molecular biology, Organic Chemistry, Ciencias Químicas, Membrane structure, Water, Cell Biology, DHA, 030104 developmental biology, Membrane, chemistry, Docosahexaenoic acid, Dipalmitoylphosphatidylcholine, Liposomes, Biophysics, lipids (amino acids, peptides, and proteins), ZETA POTENTIAL, CIENCIAS NATURALES Y EXACTAS
Abstract

Docosahexaenoic acid (DHA, 22:6) is a natural active compound that has raised considerable interest due to its several biological effects. In this work, effects of free DHA on the physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) liposomes are investigated in terms of lipid membrane structure, by means of temperature-dependent zeta potential measurements, density studies and molecular dynamics simulations. Experimental results predict, in good agreement with simulations that DHA readily incorporates into DPPC liposomes, localizing at the lipid headgroup region. These data show that DHA induces changes in the lipid bilayer structure as well as in membrane fluidity. Fil: Verde, Alejandro Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Sierra, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Pedroni, Viviana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Morini, Marcela Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2018
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2. Comparing the performance of two structural indicators for different water models while seeking for connections between structure and dynamics in the glassy regime

Author

Sebastián R. Accordino, Gustavo A. Appignanesi, Joan Manuel Montes de Oca, L. M. Alarcón, and A.R. Verde

Subjects
Work (thermodynamics), STRUCTURE, Físico-Química, Ciencia de los Polímeros, Electroquímica, Shell (structure), General Physics and Astronomy, 010402 general chemistry, 01 natural sciences, Measure (mathematics), purl.org/becyt/ford/1 [https], 0103 physical sciences, Water model, purl.org/becyt/ford/1.4 [https], WATER, Statistical physics, Physical and Theoretical Chemistry, Preference (economics), Mathematics, 010304 chemical physics, Ciencias Químicas, Contrast (statistics), 0104 chemical sciences, Constraint (information theory), Orders of magnitude (time), CIENCIAS NATURALES Y EXACTAS, DYAMICS, SUPERCOOLED
Abstract

In this work, we compare the performance of two structural indicators based on the degree of translational order up to the second coordination shell in three water models: SPC/E, TIP4P/2005, and TIP5P. Beyond directly contrasting their distributions for different temperatures to evidence their usefulness in estimating the fraction of structured and unstructured molecules and, when possible, their classification capability, we also correlate them with an indirect measure of structural constraint: the dynamic propensity. Furthermore, this procedure enables us to show the existence of evident correlations between structural and dynamical information. More specifically, we find that locally structured molecules display a preference for low dynamic propensity values and, more conspicuously, that locally unstructured molecules are extremely subject to high dynamic propensity. This result is particularly relevant for the supercooled regime where the establishment of firm links between the structure and dynamics has remained rather elusive since the occurrence of dynamics that vary in orders of magnitude upon supercooling usually contrast with barely noticeable overall structural changes. Fil: Verde, Alejandro Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Montes de Oca, Joan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Accordino, Sebastián R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcón, Laureano M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2019

3. Structural features of high-local-density water molecules: Insights from structure indicators based on the translational order between the first two molecular shells

Author

Joan Manuel Montes de Oca, Gustavo A. Appignanesi, A.R. Verde, Sebastián R. Accordino, and L. M. Alarcón

Subjects
Physics, Work (thermodynamics), STRUCTURE, Basis (linear algebra), Point particle, Físico-Química, Ciencia de los Polímeros, Electroquímica, Structure (category theory), Shell (structure), Ciencias Químicas, 01 natural sciences, 010305 fluids & plasmas, purl.org/becyt/ford/1 [https], Molecular dynamics, Order (biology), DENSITY, 0103 physical sciences, HYDROGEN BONDS, Water model, purl.org/becyt/ford/1.4 [https], WATER, Statistical physics, 010306 general physics, CIENCIAS NATURALES Y EXACTAS
Abstract

The two-liquids scenario for liquid water assumes the existence of two competing preferential local molecular structural states characterized by either low or high local density. While the former is expected to present good local order thus involving privileged structures, the latter is usually regarded as conforming a high-entropy unstructured state. A main difference in the local arrangement of such "classes" of water molecules can be inferred from the degree of translational order between the first and second molecular shells. This is so, since the low-local-density molecules present a clear gap between the first two shells while in the case of the high-local-density ones, one or more molecules from the second shell have collapsed toward the first one, thus populating the intershell region. Some structural indicators, like the widely employed local structure index and the recently introduced ζ index, have been devised precisely on the basis of this observation, being successful in detecting well-structured low-local-density molecules. However, the nature of the high-local-density state has been mainly disregarded over the years. In this work we employ molecular dynamics simulations for two water models (the extended simple point charge model and the five-site model) at the liquid and supercooled regimes combined with the inherent dynamics approach (energy minimizations of the instantaneous configurations) in order to both rationalize the detailed structural and topological information that these indicators provide and to advance in our understanding of the high-density state. Fil: Montes de Oca, Joan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Accordino, Sebastián R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Verde, Alejandro Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcón, Laureano M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2019

4. Effect of Xanthone and 1-Hydroxy Xanthone on the Dipole Potential of Lipid Membranes

Author

Hugo Alejandro Pérez, C. Menéndez, Jimena del Pilar Cejas, L. M. Alarcón, María de los Ángeles Frías, Antonio Sebastian Rosa, Gustavo A. Appignanesi, and Anibal Disalvo

Subjects
1-OH XANTHONE, Population, Ether, 010402 general chemistry, 01 natural sciences, chemistry.chemical_compound, Molecular dynamics, Colloid and Surface Chemistry, Xanthone, Materials Chemistry, Molecule, Physical and Theoretical Chemistry, education, education.field_of_study, XANTHONES, 010405 organic chemistry, Otras Ciencias Químicas, HYDRATION, technology, industry, and agriculture, Ciencias Químicas, CARBONYL GROUPS, DIPOLE POTENTIAL, 0104 chemical sciences, Surfaces, Coatings and Films, Crystallography, Dipole, Membrane, LIPID MONOLAYERS, chemistry, lipids (amino acids, peptides, and proteins), Laurdan, CIENCIAS NATURALES Y EXACTAS, Biotechnology
Abstract

Xanthone (Xa) and 1-OH Xanthone (1-OHXa) in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membranes increase the dipole potential. Results with 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (Ether PC), lacking carbonyl groups, indicate that the CO dipole of Xa molecule does not contribute to the increase of dipole potential. Molecular Dynamics calculations confirm that CO group of Xa locates parallel to the membrane interphase. Xa decreases the area per lipid in DPPC monolayers and the membrane polarity as measured by GP of Laurdan explaining the dipole potential increase. This rearrangement of water in the CO region is consistent with Fourier Transform Infrared Spectroscopy results indicating that CO of Xa are buried in the membrane phase. In contrast, CO groups of DPPC show an additional population of bound COs that seems to be more exposed to water, which contributes to the increase in dipole potential. These results are also corroborated by MD simulations. Fil: Cejas, Jimena del Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina Fil: Rosa, Antonio Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina Fil: Pérez, Hugo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Menéndez, Cintia Anabella. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Disalvo, Edgardo Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina Fil: Frías, María de los Ángeles. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina

Published
2018

5. Influence of temperature, anions and size distribution on the zeta potential of DMPC, DPPC and DMPE lipid vesicles

Author

María Belén Sierra, Viviana Isabel Pedroni, Gustavo A. Appignanesi, Edgardo Anibal Disalvo, Marcela A. Morini, and L. M. Alarcón

Subjects
Anions, Models, Molecular, 1,2-Dipalmitoylphosphatidylcholine, Físico-Química, Ciencia de los Polímeros, Electroquímica, Lipid Bilayers, Static Electricity, Molecular Conformation, Multilamellar vesicles, SURFACE CHARGE-ANIONS-WATER, VESICLES, Colloid and Surface Chemistry, Zeta potential, Particle Size, Physical and Theoretical Chemistry, Unilamellar Liposomes, Chromatography, Chemistry, Phosphatidylethanolamines, Vesicle, Ciencias Químicas, Electric Conductivity, Temperature, MULTILAMELAR, Surfaces and Interfaces, General Medicine, UNILAMELLAR VESICLES, PHOSPHOLIPIDS, Crystallography, Models, Chemical, Lipid vesicle, Dimyristoylphosphatidylcholine, ZETA POTENTIAL, CIENCIAS NATURALES Y EXACTAS, Biotechnology
Abstract

The purpose of the work is to compare the influence of the multilamellarity, phase state, lipid head groups and ionic media on the origin of the surface potential of lipid membranes. With this aim, we present a new analysis of the zeta potential of multilamellar and unilamellar vesicles composed by phosphatidylcholines (PC) and phosphatidylethanolamines (PE) dispersed in water and ionic solutions of polarizable anions, at temperatures below and above the phase transition. In general, the adsorption of anions seems to explain the origin of the zeta potential in vesicles only above the transition temperature (Tc). In this case, the sign of the surface potential is ascribed to a partial orientation of head group moiety towards the aqueous phase. This is noticeable in PC head groups but not in PEs, due to the strong lateral interaction between PO and NH group in PE. Fil: Morini, Marcela Ana. Universidad Nacional del Sur. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina Fil: Sierra, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Pedroni, Viviana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Alarcon, Laureano Martin. Universidad Nacional del Sur. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Universidad Nacional del Sur. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina Fil: Disalvo, Edgardo Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero; Argentina

Published
2015
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6. Effects of hydroxy-xanthones on dipalmitoylphosphatidylcholine lipid bilayers: A theoretical and experimental study

Author

Marcela A. Morini, Flavia Edith Buffo, L. M. Alarcón, Viviana Isabel Pedroni, María Belén Sierra, and D. Gerbino

Subjects
Dppc liposomes, 1,2-Dipalmitoylphosphatidylcholine, Chemical Phenomena, Xanthones, MOLECULAR DYNAMICS SIMULATIONS, Lipid Bilayers, Molecular Dynamics Simulation, 01 natural sciences, Biochemistry, chemistry.chemical_compound, Molecular dynamics, Computational chemistry, 0103 physical sciences, Xanthone, Zeta potential, Organic chemistry, DPPC LIPOSOME, Lipid bilayer, Molecular Biology, FLUIDITY, Liposome, 010304 chemical physics, XANTHONES, 010405 organic chemistry, Bilayer, Otras Ciencias Químicas, Organic Chemistry, Ciencias Químicas, Temperature, Cell Biology, 0104 chemical sciences, chemistry, Dipalmitoylphosphatidylcholine, lipids (amino acids, peptides, and proteins), ZETA POTENTIAL, CIENCIAS NATURALES Y EXACTAS
Abstract

Xanthones and derivatives are natural active compounds whose interest has been increased due to its several pharmacological effects. In this work, effects of hydroxy-xanthones on the physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) liposomes have been investigated in terms of lipid bilayer fluidity, by means of molecular dynamics simulations and temperature dependence of zeta potential studies. Experimental results predict, in good agreement with simulations, that xanthones are able to be incorporated into DPPC liposomes with certain localization, fluidizing the bilayer. Both effects, localization and fluidity were found to be dependent of the number of hydroxilic substituents of the xanthone and the lipid phase state. Fil: Sierra, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Gerbino, Darío César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Pedroni, Viviana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Buffo, Flavia Edith. Universidad Nacional del Sur. Departamento de Matemática; Argentina Fil: Morini, Marcela Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2016

7. Water populations in restricted environments of lipid membrane interphases

Author

Gustavo A. Appignanesi, L. M. Alarcón, M. de los Angeles Frías, M. Belén Sierra, E. Anibal Disalvo, and Marcela A. Morini

Subjects
1,2-Dipalmitoylphosphatidylcholine, Lipid Bilayers, Population, Biophysics, 02 engineering and technology, Carbon nanotube, Molecular Dynamics Simulation, 010402 general chemistry, 01 natural sciences, law.invention, Nanoclusters, chemistry.chemical_compound, Molecular dynamics, law, Molecule, General Materials Science, Lipid bilayer, education, education.field_of_study, Nanotubes, Carbon, Chemistry, Otras Ciencias Químicas, Ciencias Químicas, Water, LIQUIDS AND COMPLEX FLUIDS [FLOWING MATTER], Surfaces and Interfaces, General Chemistry, 021001 nanoscience & nanotechnology, 0104 chemical sciences, Solvation shell, Chemical physics, Dipalmitoylphosphatidylcholine, 0210 nano-technology, CIENCIAS NATURALES Y EXACTAS, Biotechnology
Abstract

We employ molecular dynamics simulations to study the hydration properties of Dipalmitoylphosphatidylcholine (DPPC) bilayers, both in the gel and the liquid crystalline states. We show that while the tight hydration centers (PO and CO moieties) are significantly hydrated in both phases, the gel-fluid transition involves significant changes at the second hydration shell, particularly at the buried region between the hydrocarbon tails. Thus, while almost no buried water population exists in the gel state below the carbonyls, this hydrophobic region becomes partially water accesible in the liquid crystalline state. We shall also show that such water molecules present a lower H-bond coordination as compared to the molecules at the primary hydration shell. This means that, while the latter are arranged in relatively compact nanoclusters (as already proposed), the buried water molecules tend to organize themselves in less compact structures, typically strings or branched strings, with a scarce population of isolated molecules. This behavior is similar to that observed in other hydration contexts, like water penetrating carbon nanotubes or model hydrophobic channels or pores, and reflects the reluctance of water to sacrifice HB coordination. Graphical abstract: [Figure not available: see fulltext.] Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Frías, María de los Ángeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; Argentina Fil: Morini, Marcela Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Sierra, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Disalvo, Edgardo Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; Argentina

Published
2016
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8. Structure and orientation of water molecules at model hydrophobic surfaces with curvature: From graphene sheets to carbon nanotubes and fullerenes

Author

Gustavo A. Appignanesi, Erica Patricia Schulz, David C. Malaspina, Marisa Alejandra Frechero, and L. M. Alarcón

Subjects
GRAPHENE, Surface (mathematics), HYDROPHOBIC HYDRATION, FULLERENES, Fullerene, Graphene, Chemistry, Físico-Química, Ciencia de los Polímeros, Electroquímica, Ciencias Químicas, General Physics and Astronomy, Ice Ih, Nanotechnology, Carbon nanotube, Curvature, CARBON NANOTUBES, law.invention, Molecular dynamics, Chemical physics, law, WATER, Physical and Theoretical Chemistry, Surface water, CIENCIAS NATURALES Y EXACTAS, Physics::Atmospheric and Oceanic Physics
Abstract

We study the structure and orientation of water molecules at model hydrophobic surfaces by means of molecular dynamics. We focus here on the role of geometry in water hydration by comparing the situation for a planar graphene sheet with convex surfaces with different curvature: the exterior surfaces of carbon nanotubes and fullerenes of different radii. In all cases, we find the first water hydration layer to be more structured than the bulk. Additionally, the first water layers are found to be well oriented with respect to the surface normal in a way consistent with a local Ice Ih-like structuring, but differently form the water-air interface (along the opposite direction with respect to ice Ih basal plane). We also show that as the curvature of the surface gets more pronounced, the water molecules get less structured and oriented. This monotonic loss of local structure for proximal water represents a smooth tendency whenever we deal with an extended surface. However, when the surface becomes partially or completely non-extended (within the sub-nanometric regime), the surface water layer becomes to quickly lose structuring and orientation. Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Malaspina, David Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Schulz, Erica Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Frechero, Marisa Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2011
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9. Particle mobility and metabasin exploration in model glass-formers

Author

L. M. Alarcón, Gustavo A. Appignanesi, and Marisa Alejandra Frechero

Subjects
Statistics and Probability, Physics, Work (thermodynamics), Range (particle radiation), business.industry, SUPERCOOLED LIQUIDS, Otras Ciencias Químicas, Ciencias Químicas, Condensed Matter Physics, String (physics), GLASS TRANSITION, Molecular dynamics, Optics, Particle, Local environment, MOLECULAR DYNAMICS, Statistical physics, business, CIENCIAS NATURALES Y EXACTAS
Abstract

In this work, we assess the relevance of different range particle displacements and string motions to the metabasin (MB) dynamics of a simple glass former. We find that MB transitions are triggered by the occurrence of massive rearrangements termed as "democratic clusters" or d-clusters which last on average less than 1% of the α-relaxation time. Thus, at variance from previous investigations that focused on large displacements and strings, our work points to the essential role of medium-range particle displacements: we find that d-clusters are compact objects since the local neighborhoods of the most mobile particles exhibit significant rearrangements with a clear prevalence of medium-range displacements (of around 20% of the interparticle distance). This is in contrast to the string-like movements for which we demonstrate that many of them fully develop in isolation (their local environment being mostly insensitive to them) and at times different from that of MB transitions, being thus irrelevant to the α-relaxation. Additionally, from the analysis of the MB dynamics, preliminary support to the dynamics facilitation scenario is provided. Fil: Appignanesi, Gustavo Adrian. Universidad Nacional del Sur. Departamento de Química. Laboratorio de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina Fil: Frechero, Marisa Alejandra. Universidad Nacional del Sur. Departamento de Química. Laboratorio de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcon, Laureano Martin. Universidad Nacional del Sur. Departamento de Química. Laboratorio de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2007
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10. Activated dynamics and timescale separation within the landscape paradigm: signature of complexity, diversity and glassiness

Author

L. M. Alarcón, Gustavo A. Appignanesi, R.A. Montani, J. A. Rodriguez Fris, and Marisa Alejandra Frechero

Subjects
Time Factors, Chemical Phenomena, Relation (database), Físico-Química, Ciencia de los Polímeros, Electroquímica, Biophysics, Complex system, RELAXATION, Context (language use), Nanotechnology, Biology, Biochemistry, ULTRAMETRIC SPACES, GLASSY SYSTEMS, Variational principle, Statistical physics, COMPLEX SYSTEMS, Chemistry, Physical, Organic Chemistry, Temperature, Ciencias Químicas, Signature (logic), Variety (cybernetics), HIERARCHICAL SYSTEMS, Dynamics (music), ACTIVATED DYNAMICS, MOLECULAR DYNAMICS, Glass, Relaxation (approximation), BIOPOLYMER FOLDING, CIENCIAS NATURALES Y EXACTAS
Abstract

The landscape paradigm has become a widespread picture within the realm of complex systems. Complex systems include a great variety of systems, ranging from glasses to biopolymers, which display a common dynamical behavior. Within this framework, the dynamics of a such a system can be envisioned as the search it performs on its (potential energy) landscape. This approach rests on the belief that the relaxation behavior depends only on generic features, irrespective of specific details and lies on the validity of a timescale separation scenario computationally corroborated but not properly validated yet form first principles. In this work we shall show that the prevalence of activated dynamics over other kinds of mechanisms determines the emergence of complex dynamical behavior. Thus, complexity and diversity are not intrinsic properties of a system but depend on the kind of exploration of the landscape. We shall focus mainly on an ample generic context (complex hierarchical systems which have been used as models of glasses, spin glasses and biopolymers) and a specific one (model glass formers). For the last case we shall be able to reveal (in mechanistic terms) the microscopic rationale for the occurrence of timescale separation. Furthermore, we shall explore the connections between these two up to now mostly unrelated contexts and the relation to a variational principle, and we shall reveal the conditions for the applicability of the landscape approach. Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Rodriguez Fris, Jorge Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Frechero, Marisa Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Montani, Rosana A.. Universidad Nacional del Sur. Departamento de Química; Argentina

Published
2005
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11. Hydrophobicity and geometry: Water at curved graphitic-likesurfaces and within model pores in self-assembled monolayers

Author

J. A. Rodriguez Fris, Sebastián R. Accordino, L. M. Alarcón, Gustavo A. Appignanesi, and J. M. Montes de Oca

Subjects
Pore size, HYDROPHOBICITY, GRAPHENE, Work (thermodynamics), Chemistry, Graphene, Físico-Química, Ciencia de los Polímeros, Electroquímica, General Chemical Engineering, SAMS, Ciencias Químicas, General Physics and Astronomy, Geometry, Self-assembled monolayer, Carbon nanotube, Curvature, CARBON NANOTUBES, law.invention, purl.org/becyt/ford/1 [https], Molecular dynamics, law, Monolayer, purl.org/becyt/ford/1.4 [https], WATER, Physical and Theoretical Chemistry, CIENCIAS NATURALES Y EXACTAS
Abstract

In this work we perform molecular dynamics simulations of water in contact with simple modelhydrophobic surfaces and pores in order to test the role of local geometry on hydrophobicity. Specif-ically, we study different quantities like orientational ordering, density fluctuations and water residencetimes (autocorrelation functions) around graphene sheets, at the exterior of single-walled carbon nano-tubes, at alkane-like self-assembled monolayers (SAMs) and at pores of different sizes carved in suchSAMs. We show that in the case of the convex graphitic-like surfaces, the cuvature does not affect thelocal hydrophobicity. However, significant curvature dependence will be made evident for the concavesurfaces of the pores carved in the SAMs. The geometrically induced dehydration that occurs as the poresize reaches the subnanometric regime might be operative in realistic settings like protein binding siteswhich require water remotion upon ligand binding. Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Montes de Oca Avalos, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Accordino, Sebastian Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Rodriguez Fris, Jorge Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina

Published
2014

12. Determining the heterogeneity in time of the dynamics within a slowly relaxing region of a supercooled liquid: Role of sharp relaxation events

Author

Gustavo A. Appignanesi, Marisa Alejandra Frechero, L. M. Alarcón, and R.A. Montani

Subjects
Physics, SUPERCOOLED LIQUIDS, Otras Ciencias Químicas, Dynamics (mechanics), DYNAMICAL HETEROGENEITIES, Ciencias Químicas, Small systems, RELAXATION, purl.org/becyt/ford/1 [https], Nuclear magnetic resonance, Orders of magnitude (time), Homogeneous, Chemical physics, purl.org/becyt/ford/1.4 [https], Relaxation (physics), GLASSY LIQUID, Supercooling, CIENCIAS NATURALES Y EXACTAS
Abstract

Supercooled liquids have been shown to be dynamically heterogeneous with different regions of the system presenting dynamics that vary from each other even by orders of magnitude. Computer simulations have confirmed such a picture by detecting that the mobile particles in model glass formers are not homogeneously distributed within the system but arranged in clusters. More recently, the dynamics of small systems has been characterized by demonstrating that their structural relaxation is not homogeneous in time, in the sense that it does not evolve gradually but it is signed by rapid bursts of mobility characterized by relative compact clusters of mobile particles. These events (which have been named d clusters) are fast and sparse and trigger the transitions the system experiences between metabasins (MB) of its potential-energy surface. The MB residence times are much larger than the time scales of occurrence of the d clusters, and it has been suggested that the events that occur within them scarcely contribute to the structural relaxation of the system. Thus, the picture of glassy relaxation that emerges would indicate that at any time a supercooled liquid may present different spatial regions, each one characterized by different structural relaxation times. In turn, each of such regions would not relax smoothly or gradually but by means of sporadic sharp relaxation events. Here, we assess for a model glass former the relative relevance of the MB exploration events and of the d clusters both in small systems and within regions of large systems, to show that the structural relaxation at the region level is indeed extremely heterogeneous in time and utterly governed by the latter. © 2009 The American Physical Society. Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur. Departamento de Química; Argentina Fil: Frechero, Marisa Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur. Departamento de Química; Argentina Fil: Montani, Ruben Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur. Departamento de Química; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur. Departamento de Química; Argentina

Published
2009
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13. Time evolution of dynamic propensity in a model glass former. The interplay between structure and dynamics

Author

Gustavo A. Appignanesi, L. M. Alarcón, and J. A. Rodriguez Fris

Subjects
Glass structure, DYNAMICS, STRUCTURE, Chemistry, Otras Ciencias Químicas, Dynamics (mechanics), Time evolution, Structure (category theory), Ciencias Químicas, General Physics and Astronomy, GLASS, purl.org/becyt/ford/1 [https], Crystallography, Potential energy surface, purl.org/becyt/ford/1.4 [https], Relaxation (physics), Statistical physics, DYNAMICAL PROPENSITY, Physical and Theoretical Chemistry, CIENCIAS NATURALES Y EXACTAS
Abstract

By means of the isoconfigurational method we calculate the change in the propensity for motion that the structure of a glass-forming system experiences during its relaxation dynamics. The relaxation of such a system has been demonstrated to evolve by means of rapid crossings between metabasins of its potential energy surface (a metabasin being a group of mutually similar, closely related structures which differ markedly from other metabasins), as collectively relaxing units (d-clusters) take place. We now show that the spatial distribution of propensity in the system does not change significantly until one of these d-clusters takes place. However, the occurrence of a d-cluster clearly de-correlates the propensity of the particles, thus ending up with the dynamical influence of the structural features proper of the local metabasin. We also show an important match between particles that participate in d-clusters and that which show high changes in their propensity. Fil: Rodriguez Fris, Jorge Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Alarcon, Laureano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Published
2009
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