Researchers discover new shapes of microcompartments

In nature and engineering, microcompartments — molecular shells made of proteins that can encapsulate cellular components — provide a tiny home for important reactions. In bacterial organelles, for example, microcompartments known as carboxysomes trap carbon dioxide and convert it into sugar as an energy source.

These shells naturally buckle into a specialized 20-sided shape called an icosahedron. But now researchers at Northwestern University's McCormick School of Engineering and Applied Science have discovered and explored new shapes of microcompartment shells. Understanding just how these shells form could lead to designed microreactors that mimic the functions of these cell containers or deliver therapeutic materials to cells at specific targeted locations.

The research, led by Monica Olvera de la Cruz, professor of materials science and chemical and biological engineering and chemistry, with Graziano Vernizzi, research assistant professor, and research associate Rastko Sknepnek, was recently published in the Proceedings of the National Academy of Sciences.

Olvera de la Cruz and her group knew how shells made up of just one structural unit worked — their elasticity and rigidity cause them to naturally buckle into icosahedra. But they began considering how to create heterogenous shells by using more than one component. Using physical concepts, mathematical analysis, and running simulations, they formulated a new model for the spontaneous faceting of shells.

"The question was: if a shell is made up of components that have different rigidities or different mechanical properties, what would be the shape it takes?" Olvera de la Cruz said.

The only faceted shape previously known for molecular closed shells, such as viruses and fullerenes, was the icosahedron. But Olvera de la Cruz and her colleagues discovered that when a shell is made up of two components with different elasticities, they buckle into many different shapes, including dodecahedra (12 sides) and octahedra (8 sides) and irregular polyhedra, which surfaces are "decorated" by the natural segregation of components to yield the lowest energy conformation.

Some of these shapes had been seen in nature before — sometimes in the bacterial organelles' carboxysomes — but they were just called "quasi-icosahedra" because nobody knew how to characterize them and how they worked. Armed with their model, however, engineers could now potentially design shells to perform specific tasks.

"If you just want to pack something into a shell, you use a sphere," she said. "But if you want to create a shell that has intelligence and can fit somewhere perfectly because it is decorated with the right proteins, then you can use different shapes."

These designed shells could act as containers or microreactors within the body. "It's a very efficient way to deliver something," she said.

Next the group hopes to determine how general their model is and continue researching how different shapes are made.

"I think it can open a new field of research," Olvera de la Cruz said.

Does fluoride really fight cavities by 'the skin of the teeth'?

In a study that the authors describe as lending credence to the idiom, "by the skin of your teeth," scientists are reporting that the protective shield fluoride forms on teeth is up to 100 times thinner than previously believed. It raises questions about how this renowned cavity-fighter really works and could lead to better ways of protecting teeth from decay, the scientists suggest. Their study appears in ACS's journal Langmuir.

Frank Müller and colleagues point out that tooth decay is a major public health problem worldwide. In the United States alone, consumers spend more than $50 billion each year on the treatment of cavities. The fluoride in some toothpaste, mouthwash and municipal drinking water is one of the most effective ways to prevent decay. Scientists long have known that fluoride makes enamel — the hard white substance covering the surface of teeth — more resistant to decay. Some thought that fluoride simply changed the main mineral in enamel, hydroxyapatite, into a more-decay resistant material called fluorapatite.

The new research found that the fluorapatite layer formed in this way is only 6 nanometers thick. It would take almost 10,000 such layers to span the width of a human hair. That's at least 10 times thinner than previous studies indicated. The scientists question whether a layer so thin, which is quickly worn away by ordinary chewing, really can shield teeth from decay, or whether fluoride has some other unrecognized effect on tooth enamel. They are launching a new study in search of an answer.

More information: "Elemental Depth Profiling of Fluoridated Hydroxyapatite: Saving Your Dentition by the Skin of Your Teeth?" Langmuir.

Provided by American Chemical Society (news : web)

Atom-thick sheets unlock future technologies

A new way of splitting layered materials, similar to graphite, into sheets of material just one atom thick could lead to revolutionary new electronic and energy storage technologies.

An international team, led by Oxford University and Trinity College Dublin scientists, has invented a versatile method for creating these one-atom thick 'nanosheets' from a range of materials using mild ultrasonic pulses, like those generated by jewellery cleaning devices, and common solvents. The new method is simple, fast, and inexpensive, and could be scaled up to work on an industrial scale.

The team publish a report of the research in this week's Science.

Each one-millimetre-thick layer of graphite is made up of around three million layers of graphene -- a flat sheet of carbon one atom thick -- stacked one on top of the other.

'Because of its extraordinary electronic properties graphene has been getting all the attention, including a recent Nobel Prize, as physicists hope that it might, one day, compete with silicon in electronics,' said Dr Valeria Nicolosi of Oxford University's Department of Materials, who led the research with Professor Jonathan Coleman of Trinity College Dublin. 'But in fact there are hundreds of other layered materials that could enable us to create powerful new technologies.'

Professor Coleman, of Trinity College Dublin, said: 'These novel materials have chemical and electronic properties which are well suited for applications in new electronic devices, super-strong composite materials and energy generation and storage. In particular, this research represents a major breakthrough towards the development of efficient thermoelectric materials.'

There are over 150 of these exotic layered materials -- such as Boron Nitride, Molybdenum disulfide, and Tungsten disulfide -- that have the potential to be metallic, semi-metallic or semiconducting depending on their chemical composition and how their atoms are arranged.

For decades researchers have tried to create nanosheets of these kind of materials as arranging them in atom-thick layers would enable us to unlock their unusual electronic and thermoelectric properties. However, all previous methods were extremely time consuming and laborious and the resulting materials were fragile and unsuited to most applications.

'Our new method offers low-costs, a very high yield and a very large throughput: within a couple of hours, and with just 1 mg of material, billions and billions of one-atom-thick graphene-like nanosheets can be made at the same time from a wide variety of exotic layered materials,' said Dr Nicolosi.

Nanosheets created using this method can be sprayed onto the surface of other materials, such as silicon, to produce 'hybrid films' which, potentially, enable their exotic abilities to be integrated with conventional technologies. Such films could be used to construct, among other things, new designs of computing devices, sensors or batteries.

The work was conducted by a team including scientists from Oxford University, Trinity College Dublin, Imperial College London, Korea University, and Texas A&M University (USA).

Story Source:

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

Journal Reference:

J. N. Coleman, M. Lotya, A. O'Neill, S. D. Bergin, P. J. King, U. Khan, K. Young, A. Gaucher, S. De, R. J. Smith, I. V. Shvets, S. K. Arora, G. Stanton, H.-Y. Kim, K. Lee, G. T. Kim, G. S. Duesberg, T. Hallam, J. J. Boland, J. J. Wang, J. F. Donegan, J. C. Grunlan, G. Moriarty, A. Shmeliov, R. J. Nicholls, J. M. Perkins, E. M. Grieveson, K. Theuwissen, D. W. McComb, P. D. Nellist, V. Nicolosi. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science, 2011; 331 (6017): 568 DOI: 10.1126/science.1194975

Chemist focuses on education for real-world sustainability challenges

 Introductory college science classes need to improve their coverage of issues related to sustainability, a noted chemistry educator told the American Association for the Advancement of Science.

"Across the nation, we have a problem," said Catherine Middlecamp, a distinguished faculty associate in chemistry at the University of Wisconsin-Madison. "We are using a 20th-century curriculum, and this is the 21st century."

Students, Middlecamp says, want a curriculum that will prepare them for upcoming challenges related to climate change, pollution and environmental health.

"You can see, from the questions they ask, the volunteer projects they undertake and the papers they write, that they are intensely concerned about the fate of the planet and the living realm. And because many of our students will not be taking another science course, it's vital that our introductory courses prepare them for their future," she says.

Middlecamp discounts the idea that a focus on sustainability will make courses less rigorous. "The chemical equation I balanced in 1968 is still balanced the same way today, but when I teach about energy, air quality or climate change, the data and the interpretations are changing all the time. They are a moving target," she says.

Rather than being watered down, "teaching in context, teaching that is connected to the real world is actually tougher," Middlecamp says, "because the curriculum that some consider rigorous actually has most of the answers in the back of the book, whereas we are dealing with issues where we don't know the exact nature of the question, much less what the best answers will be."

Middlecamp supervised the new edition of "Chemistry in Context," a textbook published by the American Chemical Society, and wrote its new chapter on sustainability. She has taught introductory chemistry at UW-Madison for 30 years.

In her courses, Middlecamp must teach the basics about chemical reactions and bonding, but to that she adds key concepts for environmental sustainability, such as the carbon cycle and the nitrogen cycle.

"Here's a key concept: Everything comes from somewhere and goes somewhere," she says.

Elise Niedermeier, who took Middlecamp's introductory chemistry class in 2007 and is now in graduate school at the University of Minnesota, says, "I was struck by the way [Middlecamp] connected her lessons to everyday life. Her enthusiasm and expert teaching made the material she presented on sustainability compelling and easy to link to everyday life."

Middlecamp notes that sustainability allows her to approach standard chemistry topics from new directions. "A class can start by discussing pollution from diesel engines, and still cover bonding and how to balance chemical reactions. At the same time, it satisfies a desire to learn about energy and air quality," she says.

The real world -- and its future -- are always on Middlecamp's mind as she teaches. "A chemistry course ought to be the start of a conversation, not the end of one," she says. "Often, the response I get is, 'Thank you for teaching a course that connects with my life today and the kind of things I will be doing, and for caring about for the rest of my life.'"

Change in the curriculum could be coming faster, Middlecamp says. "It takes time to change a course, especially one that is taught at a large university to thousands of students each semester, but colleagues are definitely thinking about this," she says. "These topics are exciting, timely and urgent, and these changes would benefit not only the discipline, but also our students and the university. It's not a choice between teaching content or teaching in context. We can do both, and we must do both.

"Students are looking to make the world a better place, and we need to do what we can to help."

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Wisconsin-Madison, via EurekAlert!, a service of AAAS.

‘Cornell dots’ that light up cancer cells go into clinical trials

 "Cornell Dots" -- brightly glowing nanoparticles -- may soon be used to light up cancer cells to aid in diagnosing and treating cancer. The U.S. Food and Drug Administration (FDA) has approved the first clinical trial in humans of the new technology. It is the first time the FDA has approved using an inorganic material in the same fashion as a drug in humans.

"The FDA approval finally puts a federal approval stamp on all the assumptions we have been working under for years. This is really, really nice," said Ulrich Wiesner, the Spencer T. Olin Professor of Materials Science and Engineering, who has devoted eight years of research to developing the nanoparticles. "Cancer is a terrible disease, and my family has a long history of it. I, thus, have a particular personal motivation to work in this area."

The trial with five melanoma patients at Memorial Sloan-Kettering Cancer Center (MSKCC) in New York City will seek to verify that the dots, also known as C dots, are safe and effective in humans, and to provide data to guide future applications. "This is the first product of its kind. We want to make sure it does what we expect it to do," said Michelle Bradbury, M.D., radiologist at MSKCC and assistant professor of radiology at Weill Cornell Medical College.

C dots are silica spheres less than 8 nanometers in diameter that enclose several dye molecules. (A nanometer is one-billionth of a meter, about the length of three atoms in a row.) The silica shell, essentially glass, is chemically inert and small enough to pass through the body and out in the urine. For clinical applications, the dots are coated with polyethylene glycol so the body will not recognize them as foreign substances.

To make the dots stick to tumor cells, organic molecules that bind to tumor surfaces or even specific locations within tumors can be attached to the shell. When exposed to near-infrared light, the dots fluoresce much brighter than unencapsulated dye to serve as a beacon to identify the target cells. The technology, the researchers say, can show the extent of a tumor's blood vessels, cell death, treatment response and invasive or metastatic spread to lymph nodes and distant organs. The safety and ability to be cleared from the body by the kidneys has been confirmed by studies in mice at MSKCC, reported in the January 2009 issue of the journal Nano Letters (Vol. 9 No. 1).

For the human trials, the dots will be labeled with radioactive iodine, which makes them visible in PET scans to show how many dots are taken up by tumors and where else in the body they go and for how long.

"We do expect it to go to other organs," Bradbury said. "We get numbers, and from that curve derive how much dose each organ gets. And we need to find out how fast it passes through. Are they cleared from the kidney at the same rate as in mice?"

One of many advantages of C dots, Bradbury noted, is that they remain in the body long enough for surgery to be completed. "Surgeons love optical," she said. "They don't need the radioactivity, but [our study] confirms what the optical signal is. As you learn that, eventually you no longer need the radioactivity."

On the other hand, she added, the dots also may serve as a carrier to deliver radioactivity or drugs to tumors. "This is step one to jump-start a process we think will do multiple things with one platform," she said.

First-generation Cornell dots were developed in 2005 by Hooisweng Ow, then a graduate student working with Wiesner. Wiesner, Ow and Kenneth Wang '77 have co-founded the company Hybrid Silica Technologies to commercialize the invention. The dots, Wiesner said, also have possible applications in displays, optical computing, sensors and such microarrays as DNA chips.

Wiesner's original research was funded by the National Science Foundation, New York state and Phillip Morris USA.

Story Source:

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