Thursday, December 15, 2011

Copper-carbene catalysts to help turn waste carbon dioxide into chemical feedstocks

Organic boron compounds are attractive substrates because they readily participate in carbon–carbon bond-forming reactions. Recently, chemists have used transition metal catalysts to activate hydrocarbons bonded to oxygenated boron esters; addition of then splits off the activated group and generates a carboxylic acid derivative. However, attempts to reproduce this chemistry with alkylboranes—a widespread class of important synthetic reagents—have had limited success because the so-called ‘catalytic transition metal alkyl’ intermediates are usually unstable and decompose before reacting with CO2.

Hou and colleagues turned to an innovative chemical system to resolve this instability. By combining electron-donating, bulky molecules called N-heterocyclic carbenes (NHCs) with copper atoms, they made metal alkyl complexes that can promote carbon–carbon bond formation with CO2 under mild conditions and at lower cost than most precious metal catalysts—ideal characteristics for sustainably recycling CO2 emissions.

First, the researchers produced an easily activated alkylborane by connecting borabicyclononane (BBN)—a highly strained set of boron–hydrocarbon rings—to the terminal atom of a carbon–carbon double bond. In this approach, the target hydrocarbon for CO2 addition is physically and electronically quite different from the two carbon–boron bonds of the BBN rings.

Hou and colleagues then mixed the alkylborane with the copper–NHC catalyst, a base, and CO2 in a pressurized chamber. After one day at 70 °C, they found that the target had transformed into a new carboxylic acid with near-quantitative yields. Diverse molecules bearing aromatic, halogenated, and bulky functional groups could all act as CO2 fixation substrates using this technique.

The copper–NHC catalyst offered another advantage to the team: a unique chemical environment that enabled isolation of several catalytic intermediates as solid crystals. X-ray measurements of these structures provided the first hard evidence that bonding interactions between alkoxide base molecules, copper atoms, and alkylboranes are critical to enabling CO2 addition (Fig. 1). “Fine-tuning the combination of central metals, bases, and supporting ligands will eventually lead to more efficient and selective catalysts,” notes Hou.

More information: Ohishi, T., Zhang, L., Nishiura, M. & Hou, Z. Carboxylation of alkylboranes by N-heterocyclic carbene copper catalysts: Synthesis of carboxylic acids from terminal alkenes and carbon dioxide. Angewandte Chemie International Edition 50, 8114–8117 (2011). http://onlinelibra … 769/abstract

Provided by RIKEN (news : web)

Cancer drug cisplatin found to bind like glue in cellular RNA

Medical researchers have long known that , a platinum compound used to fight tumors in nearly 70 percent of all human cancers, attaches to DNA. Its attachment to RNA had been assumed to be a fleeting thing, says UO chemist Victoria J. DeRose, who decided to take a closer look due to recent discoveries of critical RNA-based .

"We're looking at RNA as a new ," she said. "We think this is an important discovery because we know that RNA is very different in tumors than it is in regular healthy cells. We thought that the platinum would bind to RNA, but that the RNA would just degrade and the platinum would be shunted out of the cell. In fact, we found that the platinum was retained on the RNA and also bound quickly, being found on the RNA as fast as one hour after treatment."

The National Institutes of Health-supported research is detailed in a paper placed online ahead of regular publication in ACS , a . Co-authors with DeRose, a member of the UO chemistry department and Institute of Molecular Biology, were UO doctoral students Alethia A. Hostetter and Maire F. Osborn.

The researchers applied cisplatin to rapidly dividing and RNA-rich (Saccharomyces cerevisiae, a much-used eukaryotic in biology). They then extracted the DNA and RNA from the treated cells and studied the density of platinum per nucleotide with mass spectrometry. Specific locations of the were further hunted down with detailed sequencing methods. They found that the platinum was two to three times denser on DNA but that there was a much higher whole-cell concentration on RNA. Moreover, the drug bound like glue to specific sections of RNA.

DeRose is now pursuing the ramifications of the findings. "Can this drug be made to be more or less reactive to specific RNAs?" she said. "Might we be able to go after these new targets and thereby reduce the drug's toxicity?"

While cisplatin is effective in reducing tumor size, its use often is halted because of toxicity issues, including renal insufficiency, tinnitus, anemia, gastrointestinal problems and nerve damage.

The extensive roles of RNA have come under intense scrutiny since completion of the human genome opened new windows on DNA, life's building blocks. It had been assumed that RNA was simply a messenger that coded for protein activity. New technologies, DeRose said, have shown that a vast amount of RNA performs an amazing level of different functions in gene expression, controlling it in specific ways during development or disease, particularly in cancer cells.

In this project, DeRose's team only explored cisplatin's binding on two forms of RNA: ribosomes, where the highest concentration of the drug was found; and messenger RNA. There are more areas to be looked at, said DeRose, whose group initially developed experience using and mapping platinum's activity as a mimic for other metals in her research on RNA enzymes.

DeRose is now planning work with UO colleague Hui Zong, a biologist studying how cancer emerges, to extend the research into mouse cells to see if the findings in yeast RNA hold up. An additional collaboration with UO chemist Michael Haley involves the creation of new platinum-based drugs with "reaction handles" that will allow researchers to easily pull the experimental drugs out of cells, while still attached to their biological targets. New developments in 'deep' RNA sequencing, available through the UO's Genomic Core Facilities, could then provide a much broader view of platinum's preferred resting sites in the cell.

Provided by University of Oregon (news : web)

The interplay of dancing electrons

 Negative ions play an important role in everything from how our bodies function to the structure of the universe. Scientists from the University of Gothenburg, Sweden, have now developed a new method that makes it possible to study how the electrons in negative ions interact in, which is important in, for example, superconductors and in radiocarbon dating.

"By studying atoms with a negative charge, 'negative ions', we can learn how electrons coordinate their motion in what can be compared to a tightly choreographed dance. Such knowledge is important in understanding phenomena in which the interaction between electrons is important, such as in superconductors," says Anton Lindahl of the Department of Physics at the University of Gothenburg.

A negative ion is an atom that has captured an extra electron, giving it a negative charge. Negative ions are formed, for example, when salt dissolves in water. We have many different types of negative ion in our bodies of which the most common is chloride ions. These are important in the fluid balance of the cells and the function of nervous system, among other processes.

Increased knowledge about negative ions may lead to a better understanding of our origin. This is because negative ions play an important role in the chemical reactions that take place in space, being highly significant in such processes as the formation of molecules from free atoms. These molecules may have been important building blocks in the origin of life.

"I have worked with ions in a vacuum, not in water as in the body. In order to be able to study the properties of individual ions, we isolate them in a vacuum chamber at extremely low pressure. This pressure is even lower than the pressure outside of the International Space Station, ISS."

Anton Lindahl's doctoral thesis describes studies in which he used laser spectroscopy to study how the electrons in negative ions interact.

"In order to be able to carry out these studies, I have had to develop measurement methods and build experimental equipment. The measurements that the new equipment makes possible will increase our understanding of the dance-like interplay."

The new measurement methods that Anton has developed are important in a number of applications. One example is the measurement of trace substances in a technique known as 'accelerator mass spectrometry' or AMS. The technology and knowledge from Gothenburg are being used in a collaborative project between scientists in Gothenburg, Vienna (Austria) and Oak Ridge (USA) to increase the sensitivity of AMS measurements. One application of AMS is radiocarbon dating, which determines the age of organic matter. Another application is measurements on ice cores drilled from polar ice, which can be used to investigate the climate hundreds of thousands of years into the past.

Story Source:

The above story is reprinted from materials provided by University of Gothenburg.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

C. Diehl, K. Wendt, A. O. Lindahl, P. Andersson, D. Hanstorp. Ion optical design of a collinear laser-negative ion beam apparatus. Review of Scientific Instruments, 2011; 82 (5): 053302 DOI: 10.1063/1.3587617

Controlled disorder -- scientists find way to form random molecular patterns

The researchers have been studying molecules which resemble tiny rhombus/diamond shaped tiles, with a side length of around 2 nanometres — 2 billionths of a metre.

The fundamental research, published in the prestigious journal Nature Chemistry, has shown that they can prompt the 'tiles' to form a range of random patterns by adjusting the conditions in which the experiment is conducted.

Lead author Dr Andrew Stannard, in the University's School of Physics and Astronomy said: "To construct some sort of nanoscale device comprised of molecules, one needs to understand how those molecules will interact with one another.

"Typically, a useful device would be one in which the molecules arrange themselves in some perfectly ordered, regular manner. What we have studied here is almost the complete opposite — we have purposely tried to make the assemblies of as random as possible.

"However, if we can gain a complete understanding of how randomness and disorder arises in these types of molecular structures, we can better understand how to eradicate that disorder when we want to create something functional."

Tilings of various geometrical shapes have interested scientists, mathematicians, and artists for centuries, and a wide range of tilings can be seen adorning many medieval architectural structures, as well as for practical purposes in our more modern kitchens and bathrooms.

But tile effects occur naturally within nature and science too and tilings of rhombuses are of particular interest to physicists, mathematicians and computer scientists because of their ability to form both periodic (regular, repeating patterns) and nonperiodic (random) patterns.

The Nottingham scientists have demonstrated for the first time that the generation of molecular rhombus tilings with varying degrees of orderliness — some very random, some very ordered — can be achieved by varying the conditions of the experiment in which they are created.

The achievement is all the more remarkable considering the range of experimental conditions in which this can be achieved is extremely narrow, requiring the scientists to achieve a delicate balance between energy and entropy — the subjects of the first and second laws of thermodynamics, some of the fundamental laws of physics and, in the case of entropy, are linked to order and disorder within a thermodynamic system.

Provided by University of Nottingham (news : web)

First molybdenite microchip

 Molybdenite, a new and very promising material, can surpass the physical limits of silicon. EPFL scientists have proven this by making the first molybdenite microchip, with smaller and more energy efficient transistors.

After having revealed the electronic advantages of molybdenite, EPFL researchers have now taken the next definitive step. The Laboratory of Nanoscale Electronics and Structures (LANES) has made a chip, or integrated circuit, confirming that molybdenite can surpass the physical limits of silicon in terms of miniaturization, electricity consumption, and mechanical flexibility.

"We have built an initial prototype, putting from two to six serial transistors in place, and shown that basic binary logic operations were possible, which proves that we can make a larger chip," explains LANES director Andras Kis, who recently published two articles on the subject in the scientific journal ACS Nano.

In early 2011, the lab unveiled the potential of molybdenum disulfide (MoS2), a relatively abundant, naturally occurring mineral. Its structure and semi-conducting properties make it an ideal material for use in transistors. It can thus compete directly with silicon, the most highly used component in electronics, and on several points it also rivals graphene.

Three atoms thick

"The main advantage of MoS2 is that it allows us to reduce the size of transistors, and thus to further miniaturize them," explains Kis. It has not been possible up to this point to make layers of silicon less than two nanometers thick, because of the risk of initiating a chemical reaction that would oxidize the surface and compromise its electronic properties. Molybdenite, on the other hand, can be worked in layers only three atoms thick, making it possible to build chips that are at least three times smaller. At this scale, the material is still very stable and conduction is easy to control.

Not as greedy

MoS2 transistors are also more efficient. "They can be turned on and off much more quickly, and can be put into a more complete standby mode," Kis explains. Molybdenite is on a par with silicon in terms of its ability to amplify electronic signals, with an output signal that is four times stronger than the incoming signal. This proves that there is "considerable potential for creating more complex chips," Kis says. "With graphene, for example, this amplitude is about 1. Below this threshold, the output voltage would not be sufficient to feed a second, similar chip."

Built in flexibility

Molybdenite also has mechanical properties that make it interesting as a possible material for use in flexible electronics, such as eventually in the design of flexible sheets of chips. These could, for example, be used to manufacture computers that could be rolled up or devices that could be affixed to the skin.

Story Source:

The above story is reprinted from materials provided by Ecole Polytechnique Fédérale de Lausanne. The original article was written by Sarah Perrin.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal References:

Branimir Radisavljevic, Michael Brian Whitwick, Andras Kis. Integrated Circuits and Logic Operations Based on Single-Layer MoS2. ACS Nano, 2011; 111110093932007 DOI: 10.1021/nn203715cSimone Bertolazzi, Jacopo Brivio, Andras Kis. Stretching and Breaking of Ultrathin MoS2. ACS Nano, 2011; 111116094409009 DOI: 10.1021/nn203879f