q&more
My watch list
my.chemie.de  
Login  

News

How to separate nanoparticles by “shape”

New strategy to separate molecules

Pexels, pixabay.com, CC0

Symbolic image

13-Jun-2019: In our daily lives, the purpose and function of an item is defined by either its material, e.g. a rain jacket is fabricated of water-proof material, or its shape, e.g. a wheel is round to enable a rolling motion. What is the impact of the two factors on the nanoscale?  The impact of material, i.e. the chemistry of the building block, has been excessively varied and the impact on polymer properties investigated leading to new functional materials, as for example slush powders. On the contrary, the impact of ’shape’ has not been elucidated yet, since we are lacking reliable shape-sensitive separation techniques. Scientists of the University of Vienna and the International School of Advanced Studies in Triest, have overcome this hurdle.

The researchers developed a strategy how to separate knotted ring polymers from unknotted ones. Polymers are long molecules, consisting of  the periodic repetition of a building block called a monomer. Lisa Weiß and Christos Likos of the University of Vienna together with Cristian Micheletti and Mattia Marenda of the International School of Advanced Studies (SISSA) investigated the influence of topology, which is the mathematical precise expression for ‘shape’, on polymers and how to separate them. Distinct topologies in polymer science are the unknot, which can be imagined as a closed pearl necklace, each pearl representing a monomer, or various knotted structures captured on a ring polymer, corresponding to knotting a necklace and permanently closing it afterwards.

The key idea is to use  modulated nanochannels; i. e., channels of a small radius, which is increasing and decreasing periodically along the channel axis. On such length and time scales thermal motion, known as well as Brownian motion, is an important player, determining the magnitude of diffusion, a term describing the random displacement of polymers.

Without flow, the channel modulation inverts the ranking of diffusivities compared to an unconfined system, such that the fastest diffusing species in bulk is the slowest in a modulated channel.  Unfortunately, due to the random nature of diffusion, it cannot be employed for separation. Therefore, the researchers applied weak flows, using special simulation techniques, which correctly take into account the solvent mediated momentum transfer. For sufficiently small flow strengths they can indeed separate distinctly knotted molecules.

This mechansim is based on the fact that the average transport velocity due to flow is smaller compared to the random displacement per typical polymer time scale, and polymers have enough time to diffusively explore the channel cross-section before being transported to the next chamber. As long as this condition is met,  unknotted polymers can be transported up to ten times as fast as their knotted counterparts, leading to a reliable separation. Interestingly, the size of the constriction is not of crucial importance. Nevertheless, the ratio of  constriction size to the average size of a knot can be used to control whether the knot is leading or trailing behind the rest of the polymer, establishing thereby preference for different translocation modes.

The collaboration took place in the framework of the Marie-Curie research network Nanotrans, allowing to combine the Viennese knowledge on hydrodynamics with the knot expertise based in Trieste.

Original publication:
Lisa B. Weiss, Mattia Marenda, Cristian Micheletti, and Christos N. Likos; "Hydrodynamics and Filtering of Knotted Ring Polymers in Nanochannels"; Marcomolecules; 2019

Facts, background information, dossiers

More about Universität Wien

  • News

    Atomic images reveal unusually many neighbors for some oxygen atoms

    The identification of new chemical bonds is crucial for the design of new material structures. A team led by Jani Kotakoski at the University of Vienna and Jannik Meyer at the University of Tübingen has found unexpected new configurations of oxygen and nitrogen in graphene. Direct images of ... more

    The fast dance of electron spins

    Metal complexes show a fascinating behavior in their interactions with light, which for example is utilized in organic light emitting diodes, solar cells, quantum computers, or even in cancer therapy. In many of these applications, the electron spin, a kind of inherent rotation of the elect ... more

    When changing one atom makes molecules better

    The development and improvement of pharmaceuticals plays the central role in the ongoing battle against human disease. Organic synthesis is the field that enables these developments as it offers the toolbox to diversify chemical structures. The group of Nuno Maulide, recently named the Scie ... more

  • q&more articles

    An all-round superfood?

    Whether the web community wants to lose weight or eat healthily, chia is their constant companion and seen by some as an all-round “superfood”. The relevant internet forums are busy swapping a whole host of recipes for chia pudding and chia fresca, followed by ideas for muffins and even mar ... more

  • Authors

    Prof. Dr. Susanne Till

    Susanne Till holds a doctorate in biology (main subject botany) and has worked as a lecturer in the Dept. of Nutritional Sciences at the University of Vienna for over 30 years. In her teaching work, Dr Till focuses on botany and biology, spices and native wild plants in human nutrition, as ... more

More about SISSA

  • News

    The superionic form of water

    An original state, both solid and liquid at the same time: this is the latest news on a substance -water- so familiar to everyone but which appears to hold always fresh surprises for scientists. Its name is "superionic water"; it doesn't exist on Earth but it could be abundant inside certai ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by:

 

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE