Angewandte Chemie

Power from the sea?

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Triboelectric nanogenerator extracts energy from ocean waves.

As sources of renewable energy, sun and wind have one major disadvantage: it isn’t always sunny or windy. Waves in the ocean, on the other hand, are never still. American researchers are now aiming to use waves to produce energy by making use of contact electrification between a patterned plastic nanoarray and water. In the journal Angewandte Chemie, they have introduced an inexpensive and simple prototype of a triboelectric nanogenerator that could be used to produce energy and as a chemical or temperature sensor.

Power from the sea? Triboelectric nanogenerator extracts energy from ocean waves

The triboelectric effect is the build up of an electric charge between two materials through contact and separation – it is commonly experienced when removal of a shirt, especially in dry air, results in crackling. Zhong Lin Wang and a team at the Georgia Institute of Technology in Atlanta have previously developed a triboelectric generator based on two solids that produces enough power to charge a mobile telephone battery. However, high humidity interferes with its operation. How could this technology work with waves in water? The triboelectric effect is not limited to solids; it can also occur with liquids. The only requirement is that specific electronic levels of two substances are close enough together. Water just needs the right partner – maybe a suitable plastic.

As a prototype, the researchers made an insulated plastic tank, whose lid and bottom contain copper foil electrodes. Their system is successful because the inside of the lid is coated with a layer of polydimethylsiloxane (PDMS) patterned with tiny nanoscale pyramids. The tank is filled with deionized water. When the lid is lowered so that the PDMS nanopyramids come into contact with the water, groups of atoms in the PDMS become ionized and negatively charged. A corresponding positively charged layer forms on the surface of the water. The electric charges are maintained when the PDMS layer is lifted out of the water. This produces a potential difference between the PDMS and the water. Hydrophobic PDMS was chosen in order to minimize the amount of water clinging to the surface; the pyramid shapes allow the water to drop off readily. Periodic raising and lowering of the lid while the electrodes are connected to a rectifier and capacitor produces a direct current that can be used to light an array of 60 LEDs. In tests with salt water, the generator produced a lower output, but it could in principle operate with seawater.

The current produced decreases significantly as temperature increases, which could allow this device to be used as a . It also decreases when ethanol is added to the , which suggests potential use of the system as a chemical sensor. By attaching probe molecules with specific binding partners, it may be possible to design sensors for biomolecules.

Scripps Research Institute Scientists Invent a Better Way to Make Antibody-Guided Therapies

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Chemists at The Scripps Research Institute (TSRI) have devised a new technique for connecting drug molecules to antibodies to make advanced therapies.

Antibody-drug conjugates, as they’re called, are the basis of new therapies on the market that use the target-recognizing ability of antibodies to deliver drug payloads to specific cell types—for example, to deliver toxic chemotherapy drugs to cancer cells while sparing most healthy cells. The new technique allows drug developers to forge more stable conjugates than are possible with current methods.

“A more stable linkage between the drug molecule and the antibody means a better therapy—the toxic drug is less likely to fall off the antibody before it’s delivered to the target,” said Carlos F. Barbas III, the Janet and Keith Kellogg II Chair at TSRI.

Barbas and two members of his laboratory, Research Associates Narihiro Toda and Shigehiro Asano, report the finding in the chemistry journal Angewandte Chemie, where their paper was published recently online ahead of print and selected as a “hot” contribution.

A Popular Approach with Limitations

The new method for making more stable antibody-drug conjugates comes as the first generation of these powerful therapies are entering the market. Two such conjugates are now in clinical use. Brentuximab vedotin (Adcetris®), approved by the FDA in 2011, has shown powerful effects in clinical trials against otherwise treatment-resistant lymphomas. It uses an antibody to deliver the cell-killing compound monomethyl auristatin E to cells that bear the CD30 receptor, a major marker of lymphoma. The other conjugate, ado-trastuzumab emtansine (Kadcyla®), approved just this year for metastatic breast cancer, delivers the toxic compound mertansine to breast cancer cells that express the receptor HER2.

The success of these antibody-drug conjugates and the broad potential of the technology have made them popular with drug companies, particularly those trying to develop new anticancer medicines. “The current development pipeline is full of antibody-drug conjugates,” says Barbas.

Yet the chemical method that has been used to make these conjugates has significant limitations. The method involves the use of compounds derived from maleimide, which can be easily added to small drug molecules. The maleimide molecule acts as a linker or bridge, making strong bonds with cysteine amino acids that can be engineered into an antibody protein. In this way, a single antibody protein can be tagged with one or more maleimide-containing drug molecules. The main problem is that these maleimide-to-cysteine linkages are susceptible to several forms of degradation in the bloodstream. When such a cut occurs, the disconnected “payload” drug-molecule—typically a highly toxic compound—is liable to cause unwanted collateral damage to the body, like a “smart bomb” gone astray. This instability of current maleimide-based conjugates probably accounts for at least some of their considerable toxicity.

A more stable linkage would mean less toxicity and higher efficacy for antibody-drug conjugates, and for the past several years research chemistry laboratories around the world have been looking for a way to achieve this.

Improved Linkages

Now Barbas and his colleagues appear to have found one in the form of a novel Thiol-Click reaction. In their new paper, they have described a way to make improved linkages using compounds based on methylsulfonyl-substituted heterocycles instead of maleimides. “This method turns out to enable more stable linkages to an antibody protein, as well as more specific linkages, so the drug attaches to the right place on the right protein,” said Barbas.

Coincident with the report of the new linking compounds in Angewandte Chemie, the chemical supplier Sigma-Aldrich Corporation will begin selling the compounds, so that pharmaceutical companies can start working with them to make more stable antibody-drug conjugates. Under a recent agreement (see http://www.scripps.edu/news/press/2013/20130718sigma.html), Sigma-Aldrich markets new chemical reagents from Barbas’s and several other TSRI laboratories as soon as the papers describing them are released.

“Improved antibody–drug conjugate technologies are a top-priority research area in the pharmaceutical industry and exactly the type of fundamental research issue that our partnership with Scripps will continue to address,” said Amanda Halford, vice president of academic research at Sigma-Aldrich.

Although linking drug molecules to target-homing antibodies is the best-known therapeutic application of the new method, Barbas emphasized its broad relevance. “It should be useful for many types of protein conjugation,” he said. These include the conjugation of proteins to fluorescent beacon molecules for laboratory experiments, as well as the linkage of drug compounds to polyethylene glycol molecules—“pegylation”—to slow their clearance from the body and thus keep them working longer.

Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time.

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By creating a small electrical field that removes salts from seawater, chemists at The University of Texas at Austin and the University of Marburg in Germany have introduced a new method for the desalination of seawater that consumes less energy and is dramatically simpler than conventional techniques. The new method requires so little energy that it can run on a store-bought battery.

 

The process evades the problems confronting current desalination methods by eliminating the need for a membrane and by separating salt from water at a microscale.

The technique, called electrochemically mediated seawater desalination, was described last week in the journal Angewandte Chemie. The research team was led by Richard Crooks of The University of Texas at Austin andUlrich Tallarek of the University of Marburg. It’s patent-pending and is in commercial development by startup company Okeanos Technologies.

“The availability of water for drinking and crop irrigation is one of the most basic requirements for maintaining and improving human health,” said Crooks, the Robert A. Welch Chair in Chemistry in the College of Natural Sciences. “Seawater desalination is one way to address this need, but most current methods for desalinating water rely on expensive and easily contaminated membranes. The membrane-free method we’ve developed still needs to be refined and scaled up, but if we can succeed at that, then one day it might be possible to provide fresh water on a massive scale using a simple, even portable, system.”

This new method holds particular promise for the water-stressed areas in which about a third of the planet’s inhabitants live. Many of these regions have access to abundant seawater but not to the energy infrastructure or money necessary to desalt water using conventional technology. As a result, millions of deaths per year in these regions are attributed to water-related causes.

“People are dying because of a lack of freshwater,” said Tony Frudakis, founder and CEO of Okeanos Technologies. “And they’ll continue to do so until there is some kind of breakthrough, and that is what we are hoping our technology will represent.”

To achieve desalination, the researchers apply a small voltage (3.0 volts) to a plastic chip filled with seawater. The chip contains a microchannel with two branches. At the junction of the channel an embedded electrode neutralizes some of the chloride ions in seawater to create an “ion depletion zone” that increases the local electric field compared with the rest of the channel. This change in the electric field is sufficient to redirect salts into one branch, allowing desalinated water to pass through the other branch.

“The neutralization reaction occurring at the electrode is key to removing the salts in seawater,” said Kyle Knust, a graduate student in Crooks’ lab and first author on the paper.

Like a troll at the foot of the bridge, the ion depletion zone prevents salt from passing through, resulting in the production of freshwater.

Thus far Crooks and his colleagues have achieved 25 percent desalination. Although drinking water requires 99 percent desalination, they are confident that goal can be achieved.

“This was a proof of principle,” said Knust. “We’ve made comparable performance improvements while developing other applications based on the formation of an ion depletion zone. That suggests that 99 percent desalination is not beyond our reach.”

The other major challenge is to scale up the process. Right now the microchannels, about the size of a human hair, produce about 40 nanoliters of desalted water per minute. To make this technique practical for individual or communal use, a device would have to produce liters of water per day. The authors are confident that this can be achieved as well.

If these engineering challenges are surmounted, they foresee a future in which the technology is deployed at different scales to meet different needs.

“You could build a disaster relief array or a municipal-scale unit,” said Frudakis. “Okeanos has even contemplated building a small system that would look like a Coke machine and would operate in a standalone fashion to produce enough water for a small village.”

Source: http://www.utexas.edu