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Sulfates in extreme places, DNA tied in knots and magnetic cooling at crystallography meeting

WASHINGTON, May 23, 2011The Annual Meeting of the American Crystallographic Association (ACA) will be held May 28 June 2, 2011, in New Orleans, Louisiana. Crystallography is the science devoted to exploring the arrangement of atoms in regular crystalline solids and in complicated molecules. The study of biomolecules, such as proteins and DNA, and the structure of important materials are often calculated by crystallographers using beams of X-rays sent into laboratory samples.

The ACA is the largest professional society for crystallography in the United States, and this is its main meeting. All scientific sessions, workshops, poster sessions, and events will be held at the Sheraton New Orleans Hotel located in the heart of downtown New Orleans.

The meeting summary and program can be accessed here:
Main meeting website:
Exhibit show:


The conference features a comprehensive technical program with talks covering the wide span of crystallography research. Here is information about three notable talks:


Information coding for making proteins and sustaining life is not the only interesting thing about DNA molecules. Another virtue of DNA is its ability to undergo geometric folding. Nadrian C. Seeman, a chemistry professor at NYU, can produce objectstwo-and three-dimensional crystalsand nanomechanical devices using segments of DNA as building blocks. (See images at

The DNA elements are typically double stranded molecules and connected by cohesive "sticky ends" that are single stranded. The object shapes include cubes and truncated octahedrons. The resultant structures are imaged using X-ray crystallography. An important goal of this work is to make DNA-based nano-sized robots and DNA-based computers. Paper SP.05, a plenary talk.


The magnetocaloric effect is a change in the temperature of a magnetic material because of the change in the surrounding magnetic field. Thus turning on or off a nearby magnet can result in refrigeration. Of all magnetic materials, ferromagnets show the largest and potentially the most practical magnetocaloric effects at temperatures near their ordering (Curie) temperatures. The Curie temperature (named after Pierre Curie) is the temperature at which a material undergoes marked changes in its magnetic properties. Yurij Mozharivskyj, a chemist at McMaster University, is at the ACA meeting to receive the ACA's Etter Award for his research in these materials. He will report on efforts to improve the process.

The magnetocaloric effect can be significantly enhanced when a ferromagnetic ordering is combined with a structural transition. Such effect is known as a giant magnetocaloric effect and was first discovered in Gd5Si2Ge2 and related compounds. Modification of the electron concentration is a powerful tool to tune the structure and magnetism of the compounds.

While currently there are no commercial magnetic refrigerators, there are a few laboratory prototypes, with a rotary magnetic refrigerator developed by the Astronautics Corporation of America in 2001 being the most promising. This rotary magnetic refrigeration, operating on the Gd and Gd-Er materials, can achieve the temperature span of 24oC. Unfortunately, the temperature span decreases with an increase in the heat load. It is predicted that once technology development is complete, the magnetic refrigerator will be 20-30 percent more efficient than the current vapor compression based systems.

Mozharivskyj's research looks at the factors that control the structure and magnetic properties of Gd5Si2Ge2 and related phases. He has shown that tuning both the structural and magnetic behavior of these materials can be achieved. He can't yet prepare a material whose properties exceed those of Gd5Si2Ge2; he has, however, developed an effective chemical toolbox for optimizing magnetocaloric properties. Paper SP.01. Lab website at:


Ronald Peterson of Queen's University in Kingston, Ontario, will report the discovery of a new mineral, meridianiite (MgSO4-11H2O). Sulfate minerals occur in a wide variety of natural environments where they often precipitate from aqueous solution. Sulfate minerals also occur in mine waste through the interaction of water, oxygen, and sulphide minerals, such as the pyrite in the fine-grained waste rock discarded to the surface environment. These sulfate minerals are able to form in a wide range of temperature, relative humidity, and pH and often their crystal structures control the means by which metals and semi-metals are sequestered and then released from mine waste over time. Once crystallized, these minerals often continue to react in nature as environmental conditions change. These materials can react very quickly when removed from the conditions under which they are stable. The samples must be stabilized for transport or studied in place in the field.

The TERRA portable X-ray diffractometer allows the identification of these reactive materials as they are sampled. The new mineral meridianiite was found in sub-zero temperature fieldwork. The TERRA instrument is a commercial version of the X-ray diffractometer that will be aboard the NASA Mars Science Laboratory scheduled for launch in the fall of 2011.

Fieldwork was conducted with the Canadian Space Agency on Axel Heiberg Island, Canada.

Another special challenge is that many sulfate minerals have very similar appearance and physical properties and therefore to make effective use of field time in remote areas it is necessary to have a portable diffractometer system available to allow the researcher to adjust sampling strategies and priorities as the locality demands. The discovery of another new mineral, (cranswickite MgSO4-4H2O), at a remote deposit in northwest Argentina was made possible through the use of a portable powder diffractometer. The mineral is named after Lachlan Cranswick, whose work is commemorated by a special session at the 2011 ACA annual meeting.


Contact: Phillip Schewe
American Institute of Physics

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