Chemists figure out a way to force apart click chemistry bonds

 Normally when chemists think of methods to urge chemical reactions, brute force is not really very high on the list; while such techniques might be useful for breaking apart materials, i.e. bashing cement to get smaller pieces of cement; it’s generally not been a useful way to tear apart the molecules that actually comprise the compound itself. At least till now. Christopher Bielawski and colleagues at the University of Texas, as described in their paper in Science, have figured out a way to unbind triazole to get back its original components azide and alkyne, using nothing but force.

Triazole is a ring shaped chemical compound that is formed during the reaction that occurs between azide and alkyne when mixed with copper. Its formation is considered to be a type of “click” or snap-together chemistry reaction due to the fact that the components click together in a very tight formation; sort of like wooden floor panels that click together to keep from sliding apart under constant abuse from foot traffic. Such bonds once formed have traditionally been very difficult to force apart, even under intense heat. Now however, Bielawski and his team have figured out a way to do it using brute force.

To pull the components of triazole apart, the team attached polymer chains to either side of the individual molecules, then immersed them in a solution and applied ultrasound. Doing so caused tiny bubbles to form of a certain size that soon collapsed, leaving a vacuum behind. The vacuum force then pulled the components of the molecule apart by yanking on the polymer chains. The end result is azide and alkyne, the original components in their original forms.

The experiment is the first of its kind, showing that such compounds can be torn apart by force, opening the door to all kinds of other possibilities where researchers wish to be able to take compounds apart piece by piece without impacting anything else in the surrounding environment.

In their paper the team points out that such types of forced reactions might already be taking place in nature leading to failures of materials in previously unexplainable ways; or worse in pharmaceuticals that break down in the body leading to perhaps dangerous consequences.

Looking towards the future, this new method of tearing apart chemical bonds might lead to new types of sensors that can detect stress or be used as a type of “bodyguard” for other compounds that can be taken apart and removed when its usefulness has run its course.

More information: Unclicking the Click: Mechanically Facilitated 1,3-Dipolar Cycloreversions, Science 16 September 2011: Vol. 333 no. 6049 pp. 1606-1609. DOI: 10.1126/science.1207934

ABSTRACT
The specific targeting of covalent bonds in a local, anisotropic fashion using mechanical methods offers useful opportunities to direct chemical reactivity down otherwise prohibitive pathways. Here, we report that embedding the highly inert 1,2,3-triazole moiety (which is often prepared using the canonical “click” coupling of azides and alkynes) within a poly(methyl acrylate) chain renders it susceptible to ultrasound-induced cycloreversion, as confirmed by comprehensive spectroscopic and chemical analyses. Such reactivity offers the opportunity to develop triazoles as mechanically labile protecting groups or for use in readily accessible materials that respond to mechanical force.

 

Building better memories with supramolecular structures that act as tiny magnets

In a step towards realizing ultrahigh-density storage devices based on individual molecules behaving as magnets, researchers in Japan have developed a candidate building block -- a supramolecular ferromagnet, which is a caged molecule with magnetic properties. The Japanese research team was led by Takuzo Aida at the RIKEN Advanced Science Institute, Wako, and Kentaro Tashiro at the National Institute for Materials Science, Tsukuba.

The researchers’ supramolecular magnet is based on a metallofullerene dubbed La@C82 -- a lanthanum ion trapped within an 82-carbon spherical cage. La@C82 has well-known paramagnetic properties: it becomes magnetized in the presence of an external magnetic field. However, like all paramagnets, La@C82 loses its magnetization once the external field is removed, rendering it useless for data storage.

Endeavoring to overcome this loss of magnetization, Aida and his colleagues designed a molecular component that combines with La@C82 to form the supramolecular ferromagnet. They built a copper-containing structure, itself paramagnetic, to house La@C82 within an internal cavity. When mixed together, the two components self-assembled into a host–guest complex. To lock the La@C82 in place, the researchers clipped together extra arms on the host structure, converting it into a cage.

Assessing the magnetic properties of the locked and unlocked complexes, however, revealed a surprise, says Aida. Thanks to the interaction of the paramagnetic character of the two components, the unlocked caged complex did behave as a ferromagnet. However, when the researchers locked the supramolecular cage, that ferromagnetism was lost. 

“It is difficult to predict the magnetic behavior of host–guest complexes,” says Aida. “We envisaged that the caged structure would give rise to a ferromagnetic property, but this was not the case.”

According to calculations run by the team, the switch in ferromagnetic behavior is all down to geometry. The La@C82 guest is a tight fit within the cavity of its host, and the unlocked cage forms an asymmetric, twisted structure. When the arms of the cage are closed, the structure is forced into a symmetrical shape for which the ferromagnetic state is no longer energetically favorable (Fig. 1).

The researchers are continuing to work with the unlocked supramolecular ferromagnet, building up arrays of the structure on a solid support—an essential step towards developing a practical memory device, says Aida. The most important point is that the cage must be properly oriented such that the resultant material retains its ferromagnetism, he says.

More information: Hajjaj, F., et al. Ferromagnetic spin coupling between endohedral metallofullerene La@C82 and a cyclodimeric copper porphyrin upon inclusion. Journal of the American Chemical Society 133, 9290–9292 (2011). 

 

Small molecule receptor detects lipid's telltale sign of cell death

Researchers from Boston College have developed a new class of small molecule receptors capable of detecting a lipid molecule that reveals the telltale signs of cellular death, particularly cancer cells targeted by anti-cancer drugs, the team reports in the current electronic edition of the Journal of the American Chemical Society.

Researchers led by Assistant Professor of Chemistry Jianmin Gao successfully grafted the key residues of the milk protein lactadherin onto the molecular scaffolding of a short but sturdy circular chain of amino acids to create cyclic lactadherin (cLac) mimics capable of binding to apoptotic, or dying, cells.

Gao said his team spent a year and a half focused on a finding a new method of measuring cell death. The team wanted to create an alternative to traditional tests that measure whether or not a tumor has shrunk in size after several weeks of treatment. The team's focus was on finding a way to measure the presence of dead cells, not the absence of tumor cells.

"We started by looking for a method to detect dying cells," said Gao. "The sensitivity of scientific and medical imaging is better if you look for the appearance of something, rather than the disappearance. What we wanted to look for is that in the initial stages of treatment the therapy's molecules are beginning to trigger the death of cancer cells. That can give you an idea a drug is working much sooner than the current methods of evaluation."

The newly engineered cLac molecules could prove useful as a prognostic tool which could enable oncologists to determine the effectiveness of anti-cancer drugs in a matter of days rather than several weeks, said Gao, who added that further research and testing will need to be conducted.

"Given the small size and ease of synthesis and labeling, cLacs hold great promise for noninvasive imaging of cell death in living animals and, ultimately, in human patients," Gao said.

The cLac molecule is relatively small, built upon on a cyclic peptide scaffold of approximately a dozen amino acids, yet Gao's laboratory tests show it is capable of capturing the lipid molecule phosphatidylserine (PS) – a function nature accomplishes by using proteins of several hundred amino acids, Gao said. In apoptotic cells PS flows to the surface where cLac is able to latch onto the dying cells while bypassing living cells. In the current report, researchers colored cLac with a fluorescent dye in order to highlight apoptotic cells for fluorescence microscopy. By using appropriate tracing agents, cLac should be detectable through commonly used imaging technology, including MRI and PET.

The cLac molecule could offer a cost-effective, more stable and cleaner alternative to natural PS-binding proteins used for similar purposes, Gao said. Those proteins are bulky and relatively unstable, contain metal cofactors that make results difficult to interpret and show poor ability to penetrate tissue because of their size.

Gao said cLac could also serve as a useful tool for researchers who use protein as a cell death indicator to screen for millions of compounds. The use of the small, peptide-binding molecule could substantially reduce costs for researchers, Gao said.

Provided by Boston College (news : web)

Biochemical cell signals quantified for first time

Just as cell phones and computers transmit data through electronic networks, the cells of your body send and receive chemical messages through molecular pathways. The term "cell signaling" was coined more than 30 years ago to describe this process.

Now, for the first time, scientists have quantified the data capacity of a biochemical signaling pathway and found a surprise – it's way lower than even an old-fashioned, dial-up modem.

"This key biochemical pathway is involved in complex functions but can transmit less than one bit – the smallest unit of information in computing," says Ilya Nemenman, an associate professor of physics and biology at Emory University. "It's a simple result, but it changes our view of how cells access chemical data."

The journal Science is publishing the discovery by Nemenman and colleagues from Johns Hopkins University, including Andre Levchenko, Raymond Cheong, Alex Rhee and Chiaochun Joanne Wang.

During the 1980s, cell biologists began identifying key signaling pathways such as nuclear factor kappa B (NF-kB), known to control the expression of genes in response to everything from invading pathogens to cancer. But the amount of information carried by chemical messengers along these pathways has remained a mystery.

"Without quantifying the signal, using math and computer analysis to attach a number to how much information is getting transmitted, you have a drastically incomplete picture of what's going on," says Nemenman, a theoretical biophysicist.

He and Levchenko, a biomedical engineer, began discussing the problem back in 2007 after they met at a conference.

Levchenko developed microfluidic and measurement techniques to conduct experiments on bio-chemical signaling of the NF-kB pathway, and measure the transmissions occurring on the pathway in many thousands of cells at one time. Nemenman formulated the theoretical framework to analyze and quantify the results of the experiments.

"It was a shock to learn that the amount of information getting sent through this pathway is less than one bit, or binary digit," Nemenman says. "That's only enough information to make one binary decision, a simple yes or no."

And yet NF-kB is regulating all kinds of complex decisions made by cells, in response to stimuli ranging from stress, free radicals, bacterial and viral pathogens and more. "Our result showed that it would be impossible for cells to make these decisions based just on that pathway because they are not getting enough information," Nemenman says. "It would be like trying to send a movie that requires one megabit per second through an old-style modem that only transmits 28 kilobits per second."

They analyzed the signals of several other biochemical pathways besides NF-kB and got a similar result, suggesting that a data capacity of less than one bit could be common. So if cells are not getting all the information through signaling pathways, where is it coming from?

"We're proposing that cells somehow talk with each other outside of these known pathways," Nemenman says. "A single cell doesn't have enough information to consider all the variables and decide whether to repair some tissue. But when groups of cells talk to each other, and each one adds just a bit of knowledge, they can make a collective decision about what actions to take."

He compares it to a bunch of people at a cocktail party, with cell phones that have weak signals pressed to their ears. Each person is receiving simple messages via their phones that provide a tiny piece to a puzzle that needs to be solved. When the people chatter together and share their individual messages, they are able to collectively arrive at a reliable solution to the puzzle.

A similar phenomenon, called population coding, had been identified for the electrical activity of neural networks, but Nemenman and his colleagues are now applying the idea to bio-chemical pathways.

They hope to build on this research by zeroing in on the role of cell signaling in specific diseases.

In particular, Nemenman wants to analyze and compare the signaling capacities of a cancerous cell versus a normal cell.

"Cancerous cells divide when they shouldn't, which means they are making bad decisions," he says. "I would like to quantify that decision-making process and determine if cancer cells have reduced information transduction capacities, or if they have the same capacities as healthy cells and are simply making wrong decisions."

Nemenman uses a malfunctioning computer as an example. "If you push the 'a' key on your computer and a 'd' always shows up, that means the computer is misprogrammed but the information from your keystroke gets through just fine," he says. "But if you keep pressing the letter 'a' and different, random letters show up, that indicates a problem with the way the information is being transmitted."

Provided by Emory University (news : web)

Researchers identify potential molecular target to prevent growth of cancer cells

Researchers have shown for the first time that the protein fortilin promotes growth of cancer cells by binding to and rendering inert protein p53, a known tumor suppressor. This finding by researchers at the University of Texas Medical Branch may lead to treatments for a range of cancers and atherosclerosis, which p53 also helps prevent, and appears in the current print issue of the Journal of Biological Chemistry.

"The p53 protein is a critical defense against cancer because it activates genes that induce apoptosis, or the death of cells. However, p53 can be made powerless by mutations and inhibitors like fortilin," said Dr. Ken Fujise, lead author of the study and director, Division of Cardiology at UTMB.

Fortilin, an amino acid polypeptide protein, works in direct opposition to p53, protecting cells from apoptosis. Fujise discovered fortilin in 2000 and the protein has become a central focus of his research. This study marks the first time that scientists have been able to show the exact mechanism whereby fortilin exerts its anti-apoptotic activity.

Fujise and his team used cell cultures and animal models to show that fortilin binds to and inhibits p53, preventing it from activating genes, such as BAX and Noxa, that facilitate cell death. Thus, cells that would be killed are allowed to proliferate.

"When normal cells become cancer cells, our bodies' natural biological response is to activate p53, which eliminates the hopelessly damaged cells," said Fujise. "This process explains why the majority of people are able to stay cancer-free for most of their lives. Conversely, mutated p53 genes are seen in more than half of all human cancers, making them the most frequently observed genetic abnormality in cancer."

According to Fujise, upon further research and validation of the biological mechanism described in this study, scientists can begin exploring compounds that could modulate fortilin's activity on p53.

Such a compound would be a powerful chemotherapy agent and, because p53 inhibition has also been associated with atherosclerosis, could also protect against coronary disease and its many complications, including heart attack and stroke.

"Though we are in the early stages of this research, once screening for compounds is initiated, we could have a potential new drug to investigate in a very short period of time," said Fujise. With the support of National Institutes of Health high-throughput screening programs, which make it possible to screen very large numbers of compounds against a drug target, the process of identifying a new drug could potentially be shortened to months rather than years, he added.

Other authors include scientists at UTMB and other institutions: Yanjie Chen, Takayuki Fujita, Di Zhang, Hung Doan, Decha Pinkaew, Zhihe Liu, Jiaxin Wu, Yuichi Koide, Andrew Chiu, Curtis Chen Jun Lin, Jui-Yoa Chang; and Ke-He Ruan.

The study was supported in part by the National Institutes of Health, the American Heart Association, and MacDonald General Research Fund.

Provided by University of Texas Medical Branch at Galveston (news : web)