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The authors have created a complex system designed to hold DNA fragments in solution between the hydrophilic layers of a matrix of fatty substances (also known as lipids) combined with a surfactant (used to soften the layers' rigidity). One possible application that has yet to be tested is gene therapy.

Although gene therapy was initially delivered using viral vectors, recent attempts at devising alternative vectors have exploited positively charged lipids to form complex structures holding DNA fragments with electrostatic forces. However the positively charged ions (cations) used in this type of vector have proven toxic for human cells.

Until now, only positively charged fatty substance were thought capable of holding DNA in a complex vector. The authors of this study have proved otherwise by creating an electrically neutral matrix, structured like a multi-layered cake, which holds the DNA fragments at a high concentration in solution between the layers.

It appears that DNA fragments within the complex self-organise over time. These fragments spontaneously align parallel to one another and form rectangular and hexagonal structures across the layers. This ordering in a special matrix holds the key to creating non-toxic gene therapy delivery vectors. The change of atomic-level interactions within the layers and the appearance of interactions at the interface between the layers and the DNA molecules may explain the emergence of ordered structures at high DNA concentrations.

The next step of this research involves elucidating the precise physical forces that hold the complex together. Applications of such technology go beyond gene therapy vector design, as the same principle can be applied for the delivery of other particles such as chemical drugs.

What is the the condition for model cavity and tunnel structures resembling the binding sites of proteins to stay dry without losing their ability to react, a prerequisite for proteins to establish stable interactions with other proteins in water? To answer this, models of nanometric-scale hydrophobic cavities and tunnels are used to understand the influence of geometry on the ability of those structures to stay dry in solution. The authors study the filling tendency of cavities and tunnels carved in a system referred to as an alkane-like monolayer, chosen for its hydrophobic properties, to ensure that no factors other than geometrical constraints determine their ability to stay dry.

They show that the minimum size of hydrophobic cavities and tunnels that can be filled with water is in the nanometer range. Below that, the structure stays dry because it provides a geometric shield; if a water molecule was to penetrate the cavity it would pay an excessive energy cost to release its hydrogen bonds. By comparison, water fills carbon nanotubes that are twice smaller (but slightly less hydrophobic) than the alkane monolayer, making them less prone to stay dry.

It is also shown that the filling of nanometric cavities and tunnels with water is a dynamic process that goes from dry to wet over time. Water molecules inside the cavities or tunnels may arrange in a network of strong cooperative hydrogen bonds. Their disruption through thermal fluctuations induces the temporary drying of the holes until new bonds are re-established. Among many potential applications, one in biophysics would be to study water-exclusion sites of proteins, and understand the physical phenomenon linked to the geometry of those sites, underpinning the widespread biological process of protein-protein associations.

One important message emerging from developments of effective field theories and effective Hamiltonians for nuclear physics is that many-body forces are inevitable whenever degrees of freedom are eliminated. At the same time, first-principles calculations have shown that two-body forces alone are not able to give an accurate account of the energies of light nuclei and the saturation of nuclear matter. Three- (possibly more-) body forces are thus essential in low-energy nuclear physics. The construction of effective interactions through elimination of degrees of freedom can be done either by imposing a cut-off on the Hilbert space or by applying a transformation putting the Hamiltonian into a simpler form, such as a diagonal matrix.

The Similarity Renormalization Group follows the latter route by means of a continuous set of transformations. It has proved to be a powerful tool in low-energy nuclear physics, when applied mainly in the context of expansions using harmonic-oscillator basis states. The present paper provides the first application of this method to three-body interactions in a momentum-space basis. Although the models studied are simple ones (bosons in 1D), the structure of the evolution equations has the full complexity of any set of three-body equations. The results show the expected decoupling of high- from low-momentum states for both two- and three-body interactions, which means that only low-momentum matrix elements of the evolved potentials are needed to describe low-energy states. This work paves the way for applications to few-nucleon scattering processes and nuclear matter, starting from realistic nuclear forces in three dimensions.