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Jordi Marti's Homepage

Contact Details

Name Dr. Jordi Martí i Rabassa hawaii.jpg
Address

Department of Physics,

Technical University of Catalonia-Barcelona Tech,

B5-209, Northern Campus,

Jordi Girona 1-3, 08034 Barcelona

Catalonia (Spain)

Telephone

FAX
+34 934017184

+34 934017100
e-Mail jordi.martiarroba.jpgupc.edu

 

Research Interests

My main interest concerns the study of Condensed Matter Physics and Statistical Mechanics, focussing my work on the liquid phase. I spend most of my research activity working in theory and applications to the structure and dynamics of simple and complex liquids, with special attention paid to water, alcohols and aqueous electrolyte solutions. I have performed computer simulations with several methods: Molecular Dynamics, Monte Carlo, Empirical Valence Bond, Transition Path Sampling. In recent years, I have participated in studies of rare events and its applications to biological systems, in the modeling and simulation of cell membranes and in the study of liquid, supercritical water and ionic solutions under confinement in hydrophobic surfaces, considering mainly organic containers, in particular several forms of carbon, such as single-walled carbon nanotubes and graphene. I'm also working on proton transfer in aqueous environments and under restricted geometries.

 

Selected Topics

A. Liquid water and aqueous solutions

Liquid and supercritical water

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A tetrahedral network of water molecules is the main structural trend, due to the existence of four hydrogen-bonds per molecule (on average). The lifetime of such hydrogen-bonds is around 1 ps. Hydrogen-bonding is the main responsible of the amazing properties of liquid water. Water beyond its critical point (T > 647.13 K, d > 0.322 g/cm³, P > 220.55 bar) shows surprising new properties, like the capacity of mixing with oil. In supercritical water there is no longer distinction between the liquid and vapor phase. We have observed the breakdown of the tetrahedral structure and its substitution by cavities and water clusters. The lifetime of hydrogen-bonds is now about 0.3-0.5 ps. This part of my research has been carried out in collaboration with Prof. Elvira Guàrdia (UPC) and with Prof. Carmen Gordillo (University Pablo de Olavide, Seville).

Aqueous ionic solutions at finite concentration


The effect of ion concentration is relevant to the local organization of water around ionic species and it has strong influence on dielectric properties and on dynamics, such as conductivity and diffusion coefficients or on hydrogen-bond structure and lifetimes. Our main contribution in this field has been the use and development of polarizable models for water and ions, which have greatly improved the quality of simulation results at interfaces. This work has been done in collaboration with Elvira Guàrdia (UPC) and PhD Jonas Sala (UPC).



B. Rare events in chemical physics and biophysics

Lipid chain performing a flip-flop transition in a biological membrane
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The study of rare events is a computational challenge due to the tiny amount of trajectories in phase space which lead to such phenomena, compared with the total amount of trajectories described by a microscopical system. A new technique named transition path sampling, which is able to analyze reactive trajectories in configurational space without preconceived information about potential energy surfaces or transition states of the system, was developed by the research group of Prof. David Chandler in the University of California at Berkeley. We have employed that technique to study the transition state structure of NaCl dissociation in water and, more recently, flip-flop transitions of lipids in biomembranes. That reserach was done in collaboration with David Chandler (University of California, Berkeley) concerning NaCl dissociation and also Félix S. Csajka (PhD from U.C.Berkeley) about NaCl dissociation and lipid transitions.

 

C. Liquid and supercritical water under confinement

Liquid water at 298 K adsorbed in a carbon nanotube of radius 40 nm
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When liquids are constrained inside solid devices, its behavior can suffer dramatic changes. In the case of water, confinement produces marked loss of structural order and modifications in its microscopic dynamics. We have simulated several liquid and supercritical water samples when constrained by rigid and soft carbon nanotube walls. One of the most relevant cases is that of quasi-one dimensional liquid water, when liquid water is simply composed by linear chains constrained inside a nanotube with a radius of approximately 26 nm! The influence of the tubes is especially relevant concerning hydrogen stretching vibrations and diffussive behavior. This research work was produced in collaboration with M.C.Gordillo (Pablo de Olavide University at Seville), Dr. Carles Calero and Elvira Guàrdia (UPC).

 

The water-solid interface

As another example of confinement, we have simulated liquid water imbedded in between two flat graphite layers. This is a "classical" system in simulation studies which we will use to learn further about modifications in the structure and dynamics of water under extreme confinement. In the limit, we are able to speak about 2D water.The influence of the tubes is especially relevant concerning hydrogen stretching vibrations and diffussive behavior. This research work was produced in collaboration with M.C.Gordillo (Pablo de Olavide University at Seville), Prof. Gabor Nagy (Atomic Energy Research Institute of the Hungarian Academy of Sciences) and Carles Calero and Elvira Guàrdia (UPC).

The most recent studies in this field are those concerning the behaviour of liquid water near a single flat graphene sheet and adsorbed at boron-nitride single sheets.

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D. Proton transfer in aqueous environments

 

Bulk supercritical water at 673 K.

A study of structure and dynamics of water plus an excess proton at the supercritical isotherm of 673 K was reported in 2004 and revealed new features. For instance, the diffusion behaviour of the lone charge does not follow the Grotthus mechanism, differently of what happens for water at ambient conditions. In supercritical water, the spectral features of the excess proton reveal a tendency to form  Eigen-like complexes, instead of the typical behaviour of Zundel pairs at 298 K. This part of my research was carried out in collaboration with Elvira Guàrdia (UPC) and with Prof. Daniel Laria, from the National Comission of Atomic Energy in Buenos Aires (Argentina) .

 

Excess protons in reverse micelles.

More recently, the analysis of the characteristics of  the excess proton in a water droplet located inside a reverse non-ionic micelle Diethylene Glycol Monodecyl Ether has been performed.  Is such system, we observe a quick diffusion of proton to the external surface of the micelle, in a similar fashion as it happens when  larger ionic  charges are dilutes near solid or gas-like interfaces. In this particular problem, we observed how the most common configuration is that of the excess proton forming Eigen-like complexes, which have long lifetimes of the order of nanoseconds, prior to tits eventual transfer to other water molecules. This part of my research was carried out in collaboration with Elvira Guàrdia (UPC) and with Daniel Laria and Dr. Javier Rodriguez, from the National Comission of Atomic Energy in Buenos Aires (Argentina).

Proton transfer in 2D-confined water.

Very recently, a study about the physical and chemical properties of the excess proton in constrained geometries around 2D surfaces has been performed, together with PhD Amani Tahat (UPC). The study have analyzed structure and dynamics of water plus an excess proton when constrained near hydrophobic and hydrophilic surfaces. We found new features in the transfer mechanism and indentified vibrational modes related to proton transfer, in agreement with recent works which indicate that the type and topology of the confining device will likely alter the diffusion and hydrogen-bond structure of the bulk liquid.


E. Modeling and simulation of cell membranes


Recently (2011), I started a new research line based on the modeling and simulation of cell membranes, made of bilayer lipid surfactants inside an aqueous environment. We simulate the cell membrane at atomic level, including all sites and interactions. It means, for instance, to move 128 lipid sites of DMPC lipid molecules inside a sea of 3654 water molecules. This work is a collaboration with PhD Jing Yang, with Dr. Carles Calero (University of Barcelona) and with PhD student Huixia Lu (who received a Chinese Scholarship Council' s grant in 2016). Our main aim is to significantly improve the realism of the membrane, including ionic species, cholesterol and selected proteins and, especially, to enlight the interactions of small proteins and drugs within the membrane. The most recent developments involve the simulation of tryptophan in a DPPC membrane in aqueous solution.

Publication list

Books

"A course in quantum field theory", J.Martí and J.Fernández. Publicacions Promocions Universitàries. Barcelona, 1993.

Articles

Liquid water and aqueous solutions (bulk and at interfaces)

Proton transfer in aqueous systems

Interdisciplinary topics

Rare events in biochemical systems. Cell membranes

 

Scientific parameters (Google Scholar, may 2017)

Index h: 29

Index i10: 52

Citations: 2700

 

PhD students and topics

Actually I'm the thesis advisor of one PhD student, Huixia Lu (Chinese Scholarship Council research fellow at the Technical University of Catalonia), working on "Molecular modeling and simulation of neurotransmitters inside biomembranes composed by phospholipids and cholesterol in ionic aqueous solution".


Teaching activities

  1. Advanced Methods in Simulation, electible topic for students of the interuniversitary Master of Science on Atomistic and Multiscale Computational Modelling in Physics, Chemistry and Biochemistry (UB-UPC
  2. Physics for computer science students, Faculty of Computer Science, UPC, Barcelona.

  3. Computer Simulation in Condensed Matter, electible topic at the degree of Physics Engineering at UPC, Barcelona
  4. Physics of Memory Devices, electible topic at the degree of Computer Science at the Faculty of Computer Science, UPC, Barcelona.