2017 Impact factor 2.240

EPJE Colloquium – Theories that help us understand self-assembling soft matter with strong interacting groups

Amphiphilic molecules contain both hydrophilic and lipophilic moieties. When in solution they produce structures coming from cooperative interactions of many functional units acting in synergy. Most self-assembling soft matter systems involve strong specific interactions of functional units leading to qualitatively new structures of highly soluble micellar or fibrillar aggregates. In this EPJ E Colloquium, Nyrkova and Semenov focus on the systems with the incorporated into unimer molecules and discuss the effects of packing frustrations and unimer chirality as well as the origins of spontaneous morphological chirality in the case of achiral unimers. They describe several theoretical approaches (overcoming the limitations of weak interaction models) including the concepts of super-strong segregation, geometrical mismatch and orientational frustration. They also review some recently developed phenomenological theories of surfactant membranes and multiscale hierarchical approaches based on all-atomic modeling of packing structures of amphiphilic molecules with strongly interacting groups.

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EPJ E Review - Making sense of particles at fluid interfaces

The relative position of a particle in relation to the interfacial plane

In this EPJ E Topical Review, Armando Maestro and colleagues unravel the physico-chemical bases underlying the attachment of particles to fluid interfaces. Their focus is on the relaxation mechanisms involved in the equilibration of particle-laden interfaces.

Particle-laden interfaces play a key role in many systems that are used in industrial and technological applications, such as the stabilization of foams, emulsions, or thin films, flotation processes, encapsulation, pharmaceutical formulations, food technology and catalysis.

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EPJ E Colloquium - Laboratory models to understand and control the drying of colloidal systems

Nano-container based anti-corrosion coating

The drying of complex solutions, such as colloidal dispersions, is a phenomenon of great interest, both scientific and technical, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art. This EPJ E Colloquium discusses a wide variety of problems related to the drying of colloidal systems, from the stabilization of dairy products to cracking phenomena that occur at the surface of planets or on an oil painting. The diversity of these processes lies in the great variability in size and/or time scales and makes it very hard to understand and analyse the mechanisms at play. The results presented in this review attest to the reliability of experimental modelling in the laboratory, a clever way to use the drying of complex fluids to reproduce and study original mechanisms.

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EPJ E Highlight - Switching DNA and RNA on and off

Caption: Electric field (E) dependence of polarisation (P) for a cytosine nucleobase

Natural switching of DNA and RNA polarisation opens possibilities to develop novel biosensors and high-capacity data storage

DNA and RNA are naturally polarised molecules containing electric dipole moments due to the presence of a significant number of charged atoms at neutral pH. Scientists believe that these molecules have an in-built polarity that can be reoriented or reversed fully or in part under an electric field—a property referred to as bioferroelectricity. However, the mechanism of these properties remains unclear. In a new study published in EPJ E, See-Chuan Yam from the University of Malaya, Kuala Lumpur, Malaysia, and colleagues show that all the DNA and RNA building blocks, or nucleobases, exhibit a non-zero polarisation in the presence of polar atoms or molecules such as amidogen and carbonyl. They have two stable states, indicating that DNA and RNA basically have memory properties, just like a ferroelectric or ferromagnetic material. This is relevant for finding better ways of storing data in DNA and RNA because they have a high capacity for storage and offer a stable storage medium. Such physical properties may play an important role in biological processes and functions. Specifically, these properties could also be extremely useful for possible applications as a biosensor to detect DNA damage and mutation.

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EPJ E Highlight - Electrical disorder acts like a traffic light for a biological gate

Synthetic polyelectrolytes and a protein at the entrance of a pore.

New study of how positive and negative electrical charge disorder at the ends of polymers acts like a green or red light for proteins to pass through biological membranes

Nature’s way of allowing proteins across its gates, through porous biological membranes, depends, among others, on their electrical charge. For a protein to cross this type of membrane, it needs to be stimulated by an electrical field. A new study focuses on a particular kind of proteins that have multiple functions - dubbed Intrinsically Disordered Proteins - because the electric charge disorder on their surface makes it possible for them to take multiple shapes. In the work, recently published in EPJ E, Albert Johner from the Charles Sadron Institute (part of the CNRS) in Strasbourg, France and Jean-Francois Joanny from Paris reveal how the mixed electrical charge at the ends of the proteins influences biological membrane crossing. This has potential implications for our understanding of how proteins travel across the body, and of disease mechanisms.

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EPJ E Colloquium - How to simulate patchy particles

Patchy particles is the name given to a large class of systems of mesoscopic particles characterized by a repulsive core and a discrete number of short-range and highly directional interaction sites. Numerical simulations have contributed significantly to our understanding of the behaviour of patchy particles, but, although simple in principle, advanced simulation techniques are often required to sample the low temperatures and long time-scales associated with their self-assembly behaviour.

In this EPJ E colloquium paper, Rovigatti et al. review the most popular simulation techniques that have been used to study patchy particles, with a special focus on Monte Carlo methods.

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EPJ E Highlight - Physical properties of solids elucidated by zooming in and out of high resolution

Setup of an adaptative resolution simulation for solids.

A new study shows how to couple highly accurate and simplified models of the same system to extract thermodynamics information using simulations

Computer simulations are used to understand the properties of soft matter - such as liquids, polymers and biomolecules like DNA - which are too complicated to be described by equations. They are often too expensive to simulate in full, given the intensive computational power required. Instead, a helpful strategy is to couple an accurate model - applied in the areas of the system that require greater attention - with a simpler, idealised model. In a recent paper published in EPJ E, Maziar Heidari, from the Max Planck Institute for Polymer Research, Mainz, Germany and colleagues make the accurate model in high-resolution coincide seamlessly with an exactly solvable representation at lower resolution.

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EPJ E Highlight - Remote control of transport through nanopores

Dynamics of dextran sulfate transport through aerolysin nanopore.

New study outlines key factors affecting the transfer of molecules through biological channels

In our bodies, the transfer of genetic information, viral infections and protein trafficking, as well as the synthesis and the degradation of biomolecules, are all phenomena that require the transport of molecules through channels. Improving our control of these channels and the capacity of molecules to get across could have many potential applications in the fields of energy, biotechnology and medicine. These include ultra-fast DNA sequencing, detection of biological markers used in disease diagnostics, protein folding, high-resolution determination of the size of biological molecules or even the control of ion or biomolecule transport through the protein sensor. In a new study published in EPJ E, Manuela Pastoriza-Gallego from the University Paris-Seine, France, and colleagues have shown how to alter external factors, such as external voltage, to control the transport of a dextran sulfate molecule - a polyelectrolyte - through the nanopores of the aerolysin protein channel.

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EPJE Highlight - Tumorcode, a software to simulate vascularized tumors

Rendering of a bulk tissue tumor simulation.

An open source software that is able to construct synthetic blood vessel networks in 3D, matching the properties observed in real tumor samples.

The tumor vasculature is a major target of anticancer therapies. Rieger, Fredrich and Welter at Saarland University, Germany have been pursuing a quantitative analysis of the physical determinants of vascularized tumors for several years [1]. With the help of computer simulations they have been able to recapitulate the knowledge accrued from in vitro research of tumor spheroids, animal models and clinical studies and have re-created a vascularized tumor system in silico.

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EPJ E Highlight - Simulations document self-assembly of proteins and DNA

Representation of a charged patchy particle with two different patches.

Colloidal model featuring rigid bodies with two interaction sites explains how biological entities such as protein/DNA combinations can self-assemble

What makes particles self-assemble into complex biological structures? Often, this phenomenon is due to the competition between forces of attraction and repulsion, produced by electric charges in various sections of the particles. In nature, these phenomena often occur in particles that are suspended in a medium - referred to as colloidal particles - such as proteins, DNA and RNA. To facilitate self-assembly, it is possible to "decorate" various sites on the surface of such particles with different charges, called patches. In a new study published in EPJ E, physicists have developed an algorithm to simulate the molecular dynamics of these patchy particles. The findings published by Silvano Ferrari and colleagues from the TU Vienna and the Centre for Computational Materials Science (CMS), Austria, will improve our understanding of what makes self-assembly in biological systems possible.

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Editor-in-Chief
Paolo Biscari
On behalf of the authors, I gratefully acknowledge the Editors and the Editorial and Production Office for their attention in the revision and editing of the manuscript.

Davide Rotta, Università di Milano Bicocca, Italy

ISSN: 2190-5444 (Electronic Edition)

© Società Italiana di Fisica and
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