Saturday, September 3, 2011

Scientists develop new approaches to predict the environmental safety of chemicals

 Baylor University environmental researchers have proposed in a new study a different approach to predict the environmental safety of chemicals by using data from other similar chemicals.

For many chemicals in use every day, scientists do not have enough information to understand all of the effects on the environment and human health. In response to this, the European Union enacted the REACH regulation, which places greater responsibility on industry to manage the risks from chemicals and to provide safety information on the substances. The Registration, Evaluation, Authorisation and Restriction of Chemical Substances (REACH) regulation was enacted in 2006 and requires manufacturers and importers to gather information on the properties of their chemical substances and to register the information in a central database. Regulators say the goal of REACH is to improve the protection of human health and the environment through better and earlier identification of the harmful properties of chemical substances.

In the Baylor study, researchers suggest using data from other chemicals, such as what concentrations can cause toxicity in aquatic organisms to predict the toxicity of another chemical that scientists expect causes toxicity in the same way.

"This study proposes one approach to advance the three R's of sustainability -- reduce, replace, refine -- for studying biological impacts of chemicals in the environment," said study co-author Dr. Bryan Brooks, associate professor of environmental science and biomedical studies and director of environmental health science at Baylor. "Identifying, testing and implementing new approaches to leverage available information to support better environmental decision-making remains a critical need around the world."

Baylor researchers used statistical and mathematical techniques called chemical toxicity distributions to understand the relative potency of two groups of chemicals. They then used these findings to develop environmental safety values, which they hope will help determine the environmental impacts of chemical substances without unnecessary testing on animals.

"The biggest hurdle we face when protecting public health and the environment is the general lack of information," said study co-author Dr. Spencer Williams, a research scientist at Baylor. "The approach we propose should help prioritize the selection of chemicals and organisms for additional safety assessments. Instead of having to test similar chemicals on many organisms over and over again, scientists could estimate safety levels using fewer tests, which could be more efficient without compromising environmental safety."

The study appears online in the journal Environmental Toxicology and Chemistry.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Baylor University.

Journal Reference:

E. Spencer Williams, Jason P. Berninger, Bryan W. Brooks. Application of chemical toxicity distributions to ecotoxicology data requirements under REACH. Environmental Toxicology and Chemistry, 2011; 30 (8): 1943 DOI: 10.1002/etc.583

Molecular scientists develop color-changing stress sensor

 It is helpful -- even life-saving -- to have a warning sign before a structural system fails, but, when the system is only a few nanometers in size, having a sign that's easy to read is a challenge. Now, thanks to a clever bit of molecular design by University of Pennsylvania and Duke University bioengineers and chemists, such warning can come in the form of a simple color change.

The study was conducted by professor Daniel Hammer and graduate students Neha Kamat and Laurel Moses of the Department of Bioengineering in Penn's School of Engineering and Applied Science. They collaborated with associate professor Ivan Dmochowski and graduate student Zhengzheng Liao of the Department of Chemistry in Penn's School of Arts and Sciences, as well as professor Michael Therien and graduate student Jeff Rawson of Duke.

Their work was published in the Proceedings of the National Academy of Sciences.

The researchers' work involves two molecules: porphyrins, a class of naturally occurring pigments, and polymersomes, artificially engineered capsules that can carry a molecular payload in their hollow interiors. In this case, Kamat and Liao hypothesized that polymersomes could be used as stress sensors if their membranes were embedded with a certain type of light-emitting porphyrins.

The Penn researchers collaborated with the Therien lab, where the porphyrins were originally developed, to design polymersomes that were studded with the light-emitting molecules. When light is shined on these labeled polymersomes, the porphyrins absorb the light and then release it at a specific wavelength, or color. The Therien lab's porphyrins play a critical role in using the polymersomes as stress sensors, because their configuration and concentration controls the release of light.

"When you package these porphyrins in a confined environment, such as a polymersome membrane, you can modulate the light emission from the molecules," Hammer said. "If you put a stress on the confined environment, you change the porphyrin's configuration, and, because their optical release is tied to their configuration, you can use the optical release as a direct measure of the stress in the environment."

For example, the labeled polymersomes could be injected into the blood stream and serve as a proxy for neighboring red blood cells. As both the cells and polymersomes travel through an arterial blockage, for example, scientists would be able to better understand what happens to the blood cell membranes by making inferences from the stress label measurements.

The researchers calibrated the polymersomes by subjecting them to several kinds of controlled stresses -- tension and heat, among others -- and measuring their color changes. The changes are gradations of the near infrared spectrum, so measurements must be made by computers, rather than the naked eye. Rapidly advancing body-scanning technology, which uses light rather than magnetism or radiation, is well suited to this approach.

Other advances in medicine could benefit, as well. As cutting-edge pharmaceutical approaches already use similar molecular technology, the researchers' porphyrin labeling system could be integrated into medicine-carrying polymersomes.

"These kinds of tools could be used to monitor drug delivery, for example," Kamat said. "If we have a way to see how stressed the container is over time, we know how much of the drug has come out."

And, though the researchers chose the engineered polymersomes due to the wide range of stress they can endure, the same stress-labeling technique could soon be applied directly to naturally occurring tissues.

"One future application for this is to use dyes like these porphyrins but include them directly in a cellular membranes," Kamat said. "No one has taken a look at the intrinsic stress inside a membrane so these molecules would be perfect for the job."

The work was supported by the National Institutes of Health, the National Science Foundation and its Materials Research Science and Engineering Center program and the National Center for Research Resources.

Kamat is an NSF Graduate Fellow.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Pennsylvania.

Journal Reference:

N. P. Kamat, Z. Liao, L. E. Moses, J. Rawson, M. J. Therien, I. J. Dmochowski, D. A. Hammer. Sensing membrane stress with near IR-emissive porphyrins. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1102125108

Engineers discover nanoscale balancing act that mirrors forces at work in living systems

 A delicate balance of atomic forces can be exploited to make nanoparticle superclusters that are uniform in size -- an attribute that's important for many nanotech applications but hard to accomplish, University of Michigan researchers say.

The same type of forces are at work bringing the building blocks of viruses together, and the inorganic supercluster structures in this research are in many ways similar to viruses.

U-M chemical engineering professors Nicholas Kotov and Sharon Glotzer led the research. The findings are newly published online in Nature Nanotechnology.

In another instance of forces behaving in unexpected ways at the nanoscale, they discovered that if you start with small nanoscale building blocks that are varied enough in size, the electrostatic repulsion force and van der Waals attraction force will balance each other and limit the growth of the clusters. This equilibrium enables the formation of clusters that are uniform in size.

"The breakthrough here is that we've discovered a generic mechanism that causes these nanoparticles to assemble into near perfect structures," Glotzer said. "The physics that we see is not special to this system, and could be exploited with other materials. Now that we know how it works, we can design new building blocks that will assemble the same way."

The inorganic superclusters -- technically called "supraparticles" -- that the researchers created out of red, powdery cadmium selenide are not artificial viruses. But they do share many attributes with the simplest forms of life, including size, shape, core-shell structure and the abilities to both assemble and dissemble, Kotov said.

"Having these functionalities in totally inorganic system is quite remarkable," Kotov said. "There is the potential to combine them with the beneficial properties of inorganic materials such as environmental resilience, light adsorption and electrical conductivity."

Zhiyong Tang, a collaborating professor at the National Center of Nanoscience and Technology in China, said, "It is also very impressive that such supraparticles can be further used as the building blocks to fabricate three-dimensional ordered assemblies. This secondary self-assembly behavior provides a feasible way to obtain large-scale nanostructures that are important for practical application."

Kotov is currently working on "breeding" these supraparticles to produce synthetic fuels from carbon dioxide. The work also has applications in drug delivery and solar cell research and it could dramatically reduce the cost of manufacturing large quantities of supraparticles.

"By replicating the self-assembly processes that allow living organisms to grow and heal, we can simplify the production of many useful nanostructured systems from semiconductors and metals so much so that they can be made in any high school laboratory," Kotov said.

This research is funded by the Department of Defense, the National Science Foundation and the U.S. Army Research Office.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Michigan.

Journal Reference:

Yunsheng Xia, Trung Dac Nguyen, Ming Yang, Byeongdu Lee, Aaron Santos, Paul Podsiadlo, Zhiyong Tang, Sharon C. Glotzer, Nicholas A. Kotov. Self-assembly of self-limiting monodisperse supraparticles from polydisperse nanoparticles. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.121

How nitrous oxide is decomposed: Researchers identify structure of enzyme that breaks down potent greenhouse gas

Nitrous oxide (N2O) is a harmful climate gas. Its effect as a greenhouse gas is 300 times stronger than that of carbon dioxide. Nitrous oxide destroys the ozone layer. In industrial agriculture, it is generated on excessively fertilized fields when microorganisms decompose nitrate fertilizers. Decomposition of nitrous oxide frequently is incomplete and strongly depends on environmental conditions. Researchers from Freiburg, Constance, and KIT have now identified the structure of the enzyme that decomposes nitrous oxide and the decomposition mechanism.

Their results are published in the journal Nature.

The study demonstrated that the N2O-reductase enzyme possesses active centers made up of four copper atoms and two sulfur atoms. "Surprisingly, we found that microbiologists all over the world have assumed an incorrect structure so far," explains Professor Oliver Einsle, group leader at the Institute of Organic Chemistry and Biochemistry of the University of Freiburg. Scientists have assumed a single sulfur atom only and have not been able to completely identify the nitrous oxide decomposition mechanism. Based on the new data, the reaction sequence of the enzyme can be modeled much better. Future investigations are to provide further details and help understand which influence environmental conditions have on the process.

"It was of decisive importance that all steps of our investigation were executed in the absence of air oxygen," emphasizes Walter G. Zumft, retired professor of Karlsruher Institute of Technology. In contact with oxygen, parts of the enzyme react and the enzyme changes its structure. Together with Dr. Anja Pomowski from the University of Freiburg, the bacteria were cultivated under an oxygen-free atmosphere, the enzymes were isolated on a large scale, crystallized, and the structure was analyzed using X-rays. The team of four authors was completed by Professor Peter Kroneck from the University of Constance.

"The current study provides interesting and complementary insight into the nitrogen cycle," says Dr. Ralf Kiese from the KIT Institute of Meteorology and Climate Research. Nitrous oxide and nitrogen production on fields, pastures, and in forests depends on a multitude of often opposing effects. Last year, a KIT study demonstrated that animal husbandry may lead to less nitrous oxide unter certain conditions (doi:10.1038/nature08931). Detailed knowledge of microbial processes and their dependence on environmental conditions might help to better model the nitrous oxide contribution to the climate. In the long term, it might even be feasible to use the knowledge in order to prevent nitrous oxide from being released into the atmosphere, for example, by additives in fertilizers that preserve the functioning of N2O-reductase or by optimized processes in sewage treatment plants.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Karlsruhe Institute of Technology.

Journal References:

Anja Pomowski, Walter G. Zumft, Peter M. H. Kroneck, Oliver Einsle. N2O binding at a [4Cu:2S] copper–sulphur cluster in nitrous oxide reductase. Nature, 2011; DOI: 10.1038/nature10332Benjamin Wolf, Xunhua Zheng, Nicolas Br├╝ggemann, Weiwei Chen, Michael Dannenmann, Xingguo Han, Mark A. Sutton, Honghui Wu, Zhisheng Yao, Klaus Butterbach-Bahl. Grazing-induced reduction of natural nitrous oxide release from continental steppe. Nature, 2010; 464 (7290): 881 DOI: 10.1038/nature08931