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 New Model of T Cell Activation
27.05.2016 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht Fungi – a promising source of chemical diversity
27.05.2016 | Leibniz-Institut für Naturstoff-Forschung und Infektionsbiologie - Hans-Knöll-Institut (HKI)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Worldwide Success of Tyrolean Wastewater Treatment Technology

A biological and energy-efficient process, developed and patented by the University of Innsbruck, converts nitrogen compounds in wastewater treatment facilities into harmless atmospheric nitrogen gas. This innovative technology is now being refined and marketed jointly with the United States’ DC Water and Sewer Authority (DC Water). The largest DEMON®-system in a wastewater treatment plant is currently being built in Washington, DC.

The DEMON®-system was developed and patented by the University of Innsbruck 11 years ago. Today this successful technology has been implemented in about 70...

Im Focus: Computational high-throughput screening finds hard magnets containing less rare earth elements

Permanent magnets are very important for technologies of the future like electromobility and renewable energy, and rare earth elements (REE) are necessary for their manufacture. The Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany, has now succeeded in identifying promising approaches and materials for new permanent magnets through use of an in-house simulation process based on high-throughput screening (HTS). The team was able to improve magnetic properties this way and at the same time replaced REE with elements that are less expensive and readily available. The results were published in the online technical journal “Scientific Reports”.

The starting point for IWM researchers Wolfgang Körner, Georg Krugel, and Christian Elsässer was a neodymium-iron-nitrogen compound based on a type of...

Im Focus: Atomic precision: technologies for the next-but-one generation of microchips

In the Beyond EUV project, the Fraunhofer Institutes for Laser Technology ILT in Aachen and for Applied Optics and Precision Engineering IOF in Jena are developing key technologies for the manufacture of a new generation of microchips using EUV radiation at a wavelength of 6.7 nm. The resulting structures are barely thicker than single atoms, and they make it possible to produce extremely integrated circuits for such items as wearables or mind-controlled prosthetic limbs.

In 1965 Gordon Moore formulated the law that came to be named after him, which states that the complexity of integrated circuits doubles every one to two...

Im Focus: Researchers demonstrate size quantization of Dirac fermions in graphene

Characterization of high-quality material reveals important details relevant to next generation nanoelectronic devices

Quantum mechanics is the field of physics governing the behavior of things on atomic scales, where things work very differently from our everyday world.

Im Focus: Graphene: A quantum of current

When current comes in discrete packages: Viennese scientists unravel the quantum properties of the carbon material graphene

In 2010 the Nobel Prize in physics was awarded for the discovery of the exceptional material graphene, which consists of a single layer of carbon atoms...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking 4.0: International Laser Technology Congress AKL’16 Shows New Ways of Cooperations

24.05.2016 | Event News

Challenges of rural labor markets

20.05.2016 | Event News

International expert meeting “Health Business Connect” in France

19.05.2016 | Event News

 
Latest News

3-D model reveals how invisible waves move materials within aquatic ecosystems

30.05.2016 | Materials Sciences

Spin glass physics with trapped ions

30.05.2016 | Materials Sciences

Optatec 2016: Robust glass optical elements for LED lighting

30.05.2016 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>