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 | Angewandte Chemie
Biology in a twist -- deciphering the origins of cell behavior
31.03.2015 | National University of Singapore
Speech dynamics are coded in the left motor cortex
31.03.2015 | Universitätsmedizin Göttingen - Georg-August-Universität
In an experiment at the Department of Energy's SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as...
The IPH presents a solution at HANNOVER MESSE 2015 to make ship traffic more reliable while decreasing the maintenance costs at the same time. In cooperation with project partners, the research institute from Hannover, Germany, has developed a sensor system which continuously monitors the condition of the marine gearbox, thus preventing breakdowns. Special feature: the monitoring system works wirelessly and energy-autonomously. The required electrical power is generated where it is needed – directly at the sensor.
As well as cars need to be certified regularly (in Germany by the TÜV – Technical Inspection Association), ships need to be inspected – if the powertrain stops...
When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure--and lives--can be saved.
The Atlantic overturning is one of Earth’s most important heat transport systems, pumping warm water northwards and cold water southwards. Also known as the Gulf Stream system, it is responsible for the mild climate in northwestern Europe.
Scientists now found evidence for a slowdown of the overturning – multiple lines of observation suggest that in recent decades, the current system has been...
Because they are regularly subjected to heavy vehicle traffic, emissions, moisture and salt, above- and underground parking garages, as well as bridges, frequently experience large areas of corrosion. Most inspection systems to date have only been capable of inspecting smaller surface areas.
From April 13 to April 17 at the Hannover Messe (hall 2, exhibit booth C16), engineers from the Fraunhofer Institute for Nondestructive Testing IZFP will be...
25.03.2015 | Event News
19.03.2015 | Event News
17.03.2015 | Event News
31.03.2015 | Life Sciences
31.03.2015 | Materials Sciences
31.03.2015 | Earth Sciences