Club Chemistry

25 February, 2011

Stretched Polymer Snaps Back Smaller Than It Started

Crazy bands are cool because no matter how long they've been stretched around a kid's wrist, they always return to their original shape, be it a lion or a kangaroo.

A ring-like polymer molecule called gDFC was stretched by an ultrasonic process and then sprung back somewhat smaller than before (right). (Credit: Image courtesy of Duke University)

Now a Duke and Stanford chemistry team has found a polymer molecule that's so springy it snaps back from stretching much smaller than it was before.
Duke graduate student Jeremy Lenhardt and associate professor Stephen Craig have been systematically hunting through a library of polymers in search of a molecule that might be useful for "self-healing" materials. They hope to find a polymer that can trigger a chemical reaction when it is stretched and enable a material to build its own repairs.
Imagine a sheet of Saran Wrap that could fix a microscopic puncture before the hole ever got big enough to see. This would require that the polymer molecules immediately around the tear could somehow jump into action and perform new chemistry to build bridges across the hole.
To stretch polymers and see what happens to them, Lenhardt uses an apparatus that pumps up and down on a solution filled with polymers, pressurizing it and depressurizing it 20,000 times a second which causes tiny bubbles to form fleetingly. The void created by the bubbles exerts a tug on the ends of some of the polymers in the solution and stretches them, if only for a billionth of a second.
"Think of two rafts going down a river with a rope between them," Craig explained. "As the first raft enters a rapids and accelerates forward, that rope -- the polymer -- gets pulled taught and stretches."
Over and over Lenhardt ran the experiment, characterizing different polymer species that became more reactive when stretched, potentially able to do "stress-induced chemistry."
Then, while looking at polymers that contained tiny ring-shaped molecules called gem-difluorocyclopropanes (gDFC), he was surprised to find that some of these molecules emerged from the stretching noticeably shorter than when they went in.
"I ran up to his office," Lenhardt said. " 'Steve, something funny is going on here. Look at this!' " A technique called nuclear magnetic resonance had revealed the shapes of the rings after pulling and shown that they were, in fact, shorter.
But not only were the gDFCs snapping back smaller than they started, it also appeared that before snapping back they were actually trapped in an unusual stretched state far longer than normal, a reactive state called a 1,3-diradical.
Normally, as a molecule goes through a reaction, it passes through a special point known as a transition state, and stays there for only ten to a hundred femtoseconds, "a tenth of a millionth of a millionth of a second," Craig said. This makes it extraordinary hard to actually watch chemistry happen, so chemists usually can only infer what happens at the transition state by what they've seen before and after.
Work by their Stanford collaborators showed that the trapped 1,3-diradicals are in fact one type of these usually fast-moving transition states, but in Lenhardt's experiments they were essentially stopped in their tracks and trapped for nanoseconds, tens of thousands of times longer than usual.
This might be a window for watching transition states in action, Craig said. "We can trap these things long enough to probe new facets of their reactivity."
Lenhardt has begun doing just that, stretching the polymers to learn more about these transition states and seeing if he can watch other molecules by using this technique as a sort of stop-action camera.
"Every chemical reaction has a high energy state that you have to guess at," Lenhardt said. "But maybe, in some cases, you don't have to guess anymore."
The team's findings appear Aug. 27 in Science.
Other team members include Duke undergraduate Robert Choe and at Stanford, graduate student Mitchell Ong, postdoc Christian Evenhuis and professor Todd Martinez.
The research was funded by the U.S. Army Research Laboratory and the Army Research Office.

Chào tất cả các bạn. Hhorg ra đời dựa trên nền tảng "Kiến thức - Kinh nghiệm - Kĩ năng - Phương pháp - Tài nguyên". Nhằm đáp ứng nhu cầu học tập của các bạn sinh viên sư phạm và giảng dạy của giáo viên Hóa học. Tiêu chí của chúng tôi là "Thế giới Hóa học của chúng ta". Rất mong nhận được sự đóng góp ý kiến, bài viết để cùng học tập và giảng dạy tốt và cũng rất mong được làm quen với tất cả các bạn trên toàn quốc và trên thế giới.

Thank u for visting my website! Thông tin tác giả Ngô Xuân Quỳnh:
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Birthday: 17/08/198x
Location: Hai Duong
Phone: 0979817885
Job: Chemist !!!

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Nanobiotechnology Advances Point to Medical Applications

Two new groundbreaking scientific papers by researchers at UC Santa Barbara demonstrate the synthesis of nanosize biological particles with the potential to fight cancer and other illnesses. The studies introduce new approaches that are considered "green" nanobiotechnology because they use no artificial compounds.

Top row, three different RNA objects rendered from molecular computer models: from left, RNA antiprism composed of eight RNAs, a six-stranded RNA cube, and a 10-stranded RNA cube. Bottom row, the corresponding three-dimensional reconstructions of the objects obtained from cryo-electron microscopy. (Credit: Cody Geary and Kirill A. Afonin)

Luc Jaeger, associate professor of chemistry and biochemistry at UCSB, explained that there is nothing short of a revolution going on in his field -- one that permeates all areas of biochemistry, especially his area of nanobiotechnology. The revolution involves understanding the role of RNA in cells.
"Considering the fact that up to 90 percent of the human genome is transcribed into RNA, it becomes clear that RNA is one of the most important biopolymers on which life is based," said Jaeger. "We are still far from understanding all the tremendous implications of RNA in living cells."
Jaeger's team is putting together complex three-dimensional RNA molecules -- nanosize polyhedrons that could be used to fight disease. The molecules self assemble into the new shapes. The work is funded by the National Institutes of Health (NIH), and there is a patent pending jointly between NIH and UCSB on the new designs.
"We are interested in using RNA assemblies to deliver silencing RNAs and therapeutic RNA aptamers to target cancer and other diseases," said Jaeger. "It is clear that RNA is involved in a huge number of key processes that are related to health issues."
Jaeger believes the RNA-based approaches to delivering new therapies in the body will be safer than those using artificial compounds that might have undesirable side effects down the line.
"By using RNA molecules as our primary medium, we are practicing 'green' nanobiotechnology," explained Jaeger. "The research program developed in my lab at UCSB aims at contributing in a positive way to medicine and synthetic biology. We try to avoid any approaches that raise controversial bioethical issues in the public square. It's not an easy task, but I am convinced that it will pay off in the long run."
The more recent of the two scientific papers describing the new work -- "In vitro assembly of cubic RNA-based scaffolds designed in silicon" -- published online August 30 by Nature Nanotechnology. The earlier paper -- "A polyhedron made of tRNAs" by Severcan and colleagues -- was published online on July 18 by Nature Chemistry. The print edition of this article will be published in Nature Chemistry's September issue.
The second author on the Nature Chemistry paper is Cody Geary, a postdoctoral fellow in Jaeger's lab. Kirill A. Afonin, also a postdoctoral fellow in Jaeger's lab, is the first author on the Nature Nanotechnnology article.
Bruce Shapiro, a senior author on the Nature Nanotechnology article, is based at the National Cancer Institute in Frederick, Md. and is also funded by NIH. Jaeger and his team worked with Shapiro to develop a computerized approach for facilitating the design of self-assembling RNA strands. Further assistance came from the National Resource for Automated Molecular Microscopy located at Scripps Institute in La Jolla, Calif.

Chào tất cả các bạn. Hhorg ra đời dựa trên nền tảng "Kiến thức - Kinh nghiệm - Kĩ năng - Phương pháp - Tài nguyên". Nhằm đáp ứng nhu cầu học tập của các bạn sinh viên sư phạm và giảng dạy của giáo viên Hóa học. Tiêu chí của chúng tôi là "Thế giới Hóa học của chúng ta". Rất mong nhận được sự đóng góp ý kiến, bài viết để cùng học tập và giảng dạy tốt và cũng rất mong được làm quen với tất cả các bạn trên toàn quốc và trên thế giới.

Thank u for visting my website! Thông tin tác giả Ngô Xuân Quỳnh:
Full Name: Ngo Xuan Quynh
Birthday: 17/08/198x
Location: Hai Duong
Phone: 0979817885
Job: Chemist !!!

Trang web: http://hoahoc.org
Yahoo: netthubuon

Alzheimer's Disease: New Study Shows How Amyloid Beta Disrupts One of the Brain's Anti-Oxidant Proteins, Points Way to Protect It

Researchers suspect that a protein superstructure called amyloid beta is responsible for much of the neural damage of Alzheimer's disease.

Clear strands of toxic aggregated amyloid beta peptides, a hallmark of Alzheimer's disease, interact with proteins such as the anti-oxidant enzyme catalase, shown in red. The interaction disables catalase, resulting in oxidative damage to neural cells in culture. Protein-resistant coating (blue) on the aggregated amyloids inhibit these harmful interactions and protect of cells from amyloid beta-induced oxidative stress and toxicity. (Credit: Christopher Burke for UC San Diego)

A new study at the University of California, San Diego, shows that amyloid beta disrupts one of the brain's anti-oxidant proteins and demonstrates a way to protect that protein, and perhaps others, from amyloid's harmful effects.
"Amyloid seems to cause damage to cells," said chemistry professor Jerry Yang. "We have reported in a very detailed way one potential interaction of how amyloid can cause disease, and we found a way to stop it." His group's report of their results will appear in the Journal of Biological Chemistry in December.
Their study focused on catalase, an enzyme that mops up excess oxidants, because catalase normally helps to prevent the kind of damage seen in the brains of patients with Alzheimer's disease and previous work had found catalase proteins deposited within amyloid plaques.
Lila Habib, a bioengineering graduate student and the first author of the report, added amyloid to cultured neural cells and looked at its effects.
"We were able to determine that amyloid beta and this anti-oxidant enzyme, catalase, interact, and that this interaction harmed catalase so it wasn't able to perform its physiological function: to degrade hydrogen peroxide into oxygen and water," she said.
When Habib coated the amyloid with a small molecule designed to prevent its interaction with other proteins, she was able to restore the activity of catalase and return hydrogen peroxide to normal levels within the cells.
The coating Habib used to probe the interaction between amyloid and catalase is a candidate drug -- one of a class of molecules that Yang's lab has developed.
"Not only are we learning more about the disease, but we are also developing a potential strategy for treatment," said Yang, who is currently testing the new approach in a mouse model of the disease.
Michelle Lee, an undergraduate chemistry student, synthesized the amyloid-coating molecule and is a co-author of the article.

Chào tất cả các bạn. Hhorg ra đời dựa trên nền tảng "Kiến thức - Kinh nghiệm - Kĩ năng - Phương pháp - Tài nguyên". Nhằm đáp ứng nhu cầu học tập của các bạn sinh viên sư phạm và giảng dạy của giáo viên Hóa học. Tiêu chí của chúng tôi là "Thế giới Hóa học của chúng ta". Rất mong nhận được sự đóng góp ý kiến, bài viết để cùng học tập và giảng dạy tốt và cũng rất mong được làm quen với tất cả các bạn trên toàn quốc và trên thế giới.

Thank u for visting my website! Thông tin tác giả Ngô Xuân Quỳnh:
Full Name: Ngo Xuan Quynh
Birthday: 17/08/198x
Location: Hai Duong
Phone: 0979817885
Job: Chemist !!!

Trang web: http://hoahoc.org
Yahoo: netthubuon

2010 Nobel Prize in Chemistry: Creating Complex Carbon-Based Molecules Using Palladium

The Royal Swedish Academy of Sciences has awarded the Nobel Prize in Chemistry for 2010 to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for developing new ways of linking carbon atoms together that has allowed scientists to make medicines and better electronics.

New ways of linking carbon atoms together has allowed scientists to make medicines and better electronics. (Credit: iStockphoto/Liang Zhang)

American citizen Richard F. Heck, 79, of the University of Delaware in Newark, Delaware, Japanese citizens Akira Suzuki, 80, of Hokkaido University in Sapporo, Japan, and Ei-Ichi Negishi, 75, of Purdue University in West Lafayette, Indiana, will share the 10 million Swedish crowns ($1.5 million) award for their development of "palladium-catalyzed cross couplings in organic systems."
Carbon, the atom that is the backbone of molecules in living organisms, is usually very stable and it can be difficult in the laboratory chemically to synthesize large molecules containing carbon. In the Heck reaction, Negishi reaction and Suzuki reaction, carbon atoms meet on a palladium atom, which acts as a catalyst. The carbon atoms attach to the palladium atom and are thus positioned close enough to each other for chemical reactions to start. This allows chemists to synthesize large, complex carbon-containing molecules.
The Academy said it's a "precise and efficient" tool that is used by researchers worldwide, "as well as in the commercial production of for example pharmaceuticals and molecules used in the electronics industry."
Great art in a test tube
Organic chemistry has developed into an art form where scientists produce marvelous chemical creations in their test tubes. Humankind benefits from this in the form of medicines, ever-more precise electronics and advanced technological materials. The Nobel Prize in Chemistry 2010 awards one of the most sophisticated tools available to chemists today.
This year's Nobel Prize in Chemistry is awarded to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for the development of palladium-catalyzed cross coupling. This chemical tool has vastly improved the possibilities for chemists to create sophisticated chemicals -- for example, carbon-based molecules as complex as those created by nature itself.
Carbon-based (organic) chemistry is the basis of life and is responsible for numerous fascinating natural phenomena: colour in flowers, snake poison and bacteria killing substances such as penicillin. Organic chemistry has allowed man to build on nature's chemistry; making use of carbon's ability to provide a stable skeleton for functional molecules. This has yielded new medicines and revolutionary materials such as plastics.
In order to create these complex chemicals, chemists need to be able to join carbon atoms together. However, carbon is stable and carbon atoms do not easily react with one another. The first methods used by chemists to bind carbon atoms together were therefore based upon various techniques for rendering carbon more reactive. Such methods worked when creating simple molecules, but when synthesizing more complex molecules chemists ended up with too many unwanted by-products in their test tubes.
Palladium-catalyzed cross coupling solved that problem and provided chemists with a more precise and efficient tool to work with. In the Heck reaction, Negishi reaction and Suzuki reaction, carbon atoms meet on a palladium atom, whereupon their proximity to one another kick-starts the chemical reaction.
Palladium-catalyzed cross coupling is used in research worldwide, as well as in the commercial production of for example pharmaceuticals and molecules used in the electronics industry.