Stabilizing entangled spaghetti-like materials: Controling forces between oppositely charged polymers opens new route for gene therapy vectors

Gene therapy can only be effective if delivered by a stable complex molecule. Now, scientists have determined the conditions that would stabilise complex molecular structures that are subject to inherent attractions and repulsions triggered by electric charges at the surfaces of the molecules, in a study about to be published in the European Physical Journal E, by Valentina Mengarelli and her colleagues from the Solid State Physics Laboratory at the Paris-Sud University in Orsay, France, in collaboration with Paris 7 and Évry Universities scientists.

The authors studied soluble complexes made of negatively charged DNA or another negatively charged polymer -- polystyrene-sulfonate (PSSNa) -- and a so-called condensation agent, which is a negatively charged polymer, known as linear polyethyleneimine (PEI). PEI participates in the condensation process by tying onto a molecule such as DNA, like tangled hair, to form an overall positively charged DNA/polymer complex structure. Previous research focused mainly on non-soluble complexes, while the few attempts at focusing on soluble complexes dealt either with smaller polymers or those with a weaker electric charge, which may therefore be easier to stabilise.

The French team thus confirmed experimentally that the complexation process does not depend on the rigidity of the original molecule, be it DNA or PSSNa, but on the positive/negative electric charge ratio and on the polymer concentrations. It is the interactions between electrically charged parts within the complex that govern its properties. When the condensation agent is in excess, the positively charged complex is then attracted to negatively charged biological cell membranes. This could be used to deliver the DNA into a targeted cell nucleus as part of gene therapy treatment.Future work will focus on using long DNA molecules and novel polymers to form complexes of controlled size and electric charge for gene therapy.

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The above story is reprinted from materials provided by Springer.

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Journal Reference:

Mengarelli V, Auvray L, Pastré D, and Zeghal M,. Charge inversion, condensation and decondensation of DNA and Polystyrene sulfonate by polyethylenimine. European Physical Journal E (EPJE), 2011; 34, 127 DOI: 10.1140/epje/i2011/11127-3

Award funds research on the mysteries of charged droplets

A UC Davis chemical engineer has won a five-year, $420,000 early career development award from the National Science Foundation to support research on electrical charges of fluid droplets.

William Ristenpart, an assistant professor who has appointments in both the UC Davis Department of Food Science and Technology and the Department of Chemical Engineering and Materials Science, uses high-speed video and a high-resolution electrochemical measuring technique known as “chronocoulometry” to answer fundamental questions about how droplets of various liquids acquire an electrical charge.

Findings from these studies are expected to have applications in a number of fields including petroleum and food-oil processing, and manufacture of microchips that are capable of performing multiple laboratory functions.

“The amount of charge obtained by metal spheres has been known since the time of Maxwell in the 1860s, but 150 years later, we still don’t understand charge transfer into liquid drops,” Ristenpart said. “I’m excited that this research will shed light on a fundamental problem with applications ranging from food science to atmospheric science.”

Ristenpart’s research team investigates the physical, chemical and biological phenomena of fluids, including fluid motion caused by electrical fields, how different food metabolites affect red blood cells, and the behavior of fluids at the microminiaturized scale.

Provided by UC Davis (news : web)

Neutral atoms made to act like electrically charged particles

Completing the story they started by creating synthetic magnetic fields, scientists from the Joint Quantum Institute (JQI), a collaboration of the National Institute of Standards and Technology (NIST) and the University of Maryland, have now made atoms act as if they were charged particles accelerated by electric fields.

Reported in the journal Nature Physics, these synthetic electric fields make each atom in a gas act, individually, as if it were a charged particle, but collectively they remain neutral, uncharged particles. This dual personality will help researchers simulate and study fundamental electrical phenomena and may lead to a deeper understanding of exotic phenomena involving charged particles such as superconductivity, the flow of electricity without resistance, or the quantum Hall effect, used by NIST to create a standard of electrical resistance.

Some aspects of electricity are difficult to study because, although oppositely charged particles are attracted to one another, similarly charged particles are repelled by one another. To get around this, NIST physicist Ian Spielman and his colleagues realized that they could make atoms, which are typically electrically neutral, act as if they are charged particles in an electric field -- extending their earlier method for making neutral atoms act like charged particles in a magnetic field.

The researchers create their synthetic electric field in an ultracold gas of several hundred thousand rubidium atoms. Using lasers, the team alters the atoms' energy-momentum relationship. This had the effect of transferring a bit of the lasers' momentum to the atoms, causing them to move. The force on each atom is physically identical -- and mathematically equivalent -- to what a charged particle would feel in an electric field.

So while the neutral atoms each experience the force of this synthetic electric field individually, they do not repel each other as would true charged particles in an ordinary electric field. This is analogous to an experienced group of dancers all following the moves of their instructor without getting in each other's way.

According to Spielman, this work may enable scientists to study the Hall effect, a phenomenon where an electromagnetic field can cause charged particles traveling through a conductor to experience a sideways force, which has of yet been unobserved in cold-atom systems. The work may also facilitate measurements of the atomic equivalents of electrical quantities such as resistance and inductance. For neutral atoms in synthetic electric fields, inductance is a measure of the energy that is stored as a result of the atoms' motion, and resistance is a measure of the dissipation, or energy loss, in the system. Measuring these quantities could provide insights into the properties of charged particles in analogous systems, including superconductors.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Y-J. Lin, R. L. Compton, K. Jiménez-García, W. D. Phillips, J. V. Porto, I. B. Spielman. A synthetic electric force acting on neutral atoms. Nature Physics, 2011; DOI: 10.1038/nphys1954