Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Levitating Crystals

10.09.2013
Magnetic levitation separates crystal polymorphs by their density

The effectiveness of crystalline pharmaceuticals is not only influenced by molecular composition; the structure of the crystals is also important because it determines both the solubility and the rate of dissolution, which in turn affect the bioavailability.

Researchers from Cambridge, Massachusetts (USA) have recently developed a method by which different crystals can be separated by their density in a magnetic field. In the journal Angewandte Chemie, they have now demonstrated the extraordinary efficiency of separation through “magnetic levitation”.

Many organic substances crystallize in multiple crystal structures known as polymorphs. Drugs are not the only class of products for which this can lead to problems. Different crystal structures can lead to color variation in pigments and dyes; in explosives it can lead to changes in sensitivity.

It is not always possible to control the crystallization process to obtain only the desired polymorph. Clean separation is often difficult, and occurs either by chance or through long and complex procedures. A team led by Allan S. Myerson at the Massachusetts Institute of Technology and George M. Whitesides at Harvard University has recently developed a simple method that makes it possible to separate polymorphs conveniently and reliably within minutes through magnetic levitation. The technique is based on the fact that different crystal modifications almost always have different densities.

Their clever method works like this: Two magnets are placed one over the other at 4.5 cm apart with like poles facing. This produces a magnetic field with a linear gradient and a minimum in the middle, between the two magnets. The crystals to be separated are suspended in a solution of paramagnetic ions and placed in a tube within the magnetic field. The gravitational force causes the crystals to sink down to the bottom of the tube.

By doing so, a crystal “displaces” its own volume of the paramagnetic fluid “upwards”. Yet, this is unfavorable, because the paramagnetic fluid is attracted by the magnet — the attraction gets stronger closer to the face of the magnet. The crystal sinks as long as it reaches a distance above the magnet where the gravitational force and the magnetic attraction on the equivalent volume of the paramagnetic fluid are balanced. At this point, the crystal will “float” in the fluid. As the strength of the gravitational force depends on the density of the crystal, the “floating point” is different for different crystal modification. The solution is then removed from the tube with a cannula and divided into multiple fractions.

Through separation of different polymorphs of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophencarbonitrile, sulfathiazole, carbamazepine, and trans-cinnamic acid, the scientists have presented impressive evidence of the efficiency of their new technique, which allows for the separation of crystal forms with a difference in density as low as 0.001 g/cm3.

About the Author
George M. Whitesides is the Woodford L. and Ann A. Flowers University Professor at Harvard University, with a background in chemistry, biochemistry, and materials science. He and his students study subjects ranging from “diagnostics for the developing world” to “the origin of life”, and magnetic levitation and the measurement of density is one part of a program designed to develop new tools for medicinal chemistry, and for molecular and cellular biology.
Author: George M. Whitesides, Harvard University, Cambridge (USA), http://gmwgroup.harvard.edu/content.php?page=contact
Title: Using Magnetic Levitation to Separate Mixtures of Crystal Polymorphs
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201305549

George M. Whitesides | Angewandte Chemie
Further information:
http://pressroom.angewandte.org

More articles from Life Sciences:

nachricht Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>