Fingerprinting uranium: X-rays identify mobile, stationary forms of atomic pollutant

"This is the first time that anyone has formalized this approach and showed how broadly useful it is," said Dr. Eugene Ilton, a PNNL geochemist.

Uranium poses risks around the world. At one U.S. site, 200,000 kg or about 220 tons of uranium entered the environment. Whether the radionuclide travels to nearby water sources depends on its oxidation state, the number of electrons around the atom. Ilton and Bagus' method accurately pinpoints uranium's oxidation state. Using this method allows scientists to more accurately predict the atomic pollutant's behavior.

This technique begins with XPS, which is used commercially and scientifically to determine the chemical state, elemental composition, and other details about materials. The instrument directs a beam of X-rays at the sample, which is placed under ultra high vacuum. The beam excites electrons within the sample, forcing the electrons to leap off. Sensors within the instrument measure the number of electrons that escape at a particular kinetic energy.

The data is plotted as the number of electrons versus kinetic energy, or binding energy, forming peaks that are characteristic of an element in the material. The kinetic energy and binding energy are related by a simple formula discovered by Albert Einstein. Scientists can interpret the size, shape, and energy of the peaks to characterize the samples. The peaks fall roughly into two categories: primary and secondary. The primary peaks are usually larger than the secondary peaks, which are called satellites.

Ilton and Bagus analyzed samples containing very dilute amounts of uranium using the XPS in EMSL and also did a broad literature search on previous XPS work on uranium compounds. They focused on the satellite structures and showed that the energy separation between the satellite and primary peaks was diagnostic of uranium oxidation states over a broad range of  compounds with very different compositions.

This led to the development of a methodical process for taking XPS data and determining the oxidation state of uranium. While the team was not the first to use uranium satellite structures in this way, they showed that the method is broadly applicable to a wide range of uranium-bearing materials.

"Using XPS can provide a definitive fingerprint of the oxidation state of uranium," said Ilton.

Ilton and Bagus are working on theoretical approaches to pull more information from the XPS spectra. The data they provide can be used in other studies examining the oxidation state of uranium and other metal compounds.

More information: ES Ilton and PS Bagus. 2011. "XPS Determination of Uranium Oxidation States." Surface and Interface Analysis 143(13):1549-1560. DOI: 10.1002/sia.3836

Provided by Pacific Northwest National Laboratory (news : web)

Novel polymers release their drug cargo in response to body temperature

Yiyan Yang and Jeremy Tan from the A*STAR Institute of Bioengineering and Nanotechnology, working in collaboration with researchers from the IBM Almaden Research Center and Stanford University in the USA, have reported the preparation of biodegradable, water-soluble polymers that can be loaded with the cancer drug Paclitaxel and injected directly into tumor tissues. Warming to body temperature causes the release of the therapeutic cargo with the system showing improvement in killing cancer cells over treatment with the drug alone.

Rather than being made from repeating units of a single monomer, the polymers described are a type of block copolymer—a polymer with one block that contains hydrophilic and hydrophobic groups and another block that contains hydrophobic groups. It is through the careful balance between these groups that the temperature-responsive property of the polymer is achieved.

To make the copolymers, Yang and co-workers used the process of living polymerization, which allows the polymer chains to keep growing until the supply of monomer is exhausted. When more monomers are added, polymerization will restart. The approach allows polymers with different sized blocks of hydrophilic and hydrophobic groups to be built easily to optimize the properties. It also results in polymers with a narrow distribution of molecular weights—an important factor in producing polymers with consistent properties throughout a sample.

Thermoresponsive polymers have been studied before, with one of the most intensively investigated being poly(N-isopropylacrylamide) (PNIPAAm), which was first synthesized in the 1950s. The critical difference in the new polymers described by Yang and co-workers is that they are both non-toxic and biodegradable. “After these polymers performed their task of delivering their important cargos, they should break down and be excreted without significant additional side effects,” says Yang. “We are now planning to further work with the IBM Almaden Research Center and other industrial partners to evaluate the in vivo toxicity and efficacy of this system for the delivery of therapeutics.”

More information: Research article in Biomaterials

Provided by Agency for Science, Technology and Research (A*STAR)

Researchers figure out how to outperform nature's photosynthesis

Says io9: “They frankensteined together proteins from Synechococcus sp. with those from Clostridium acetobutylicum using molecular wire to create a 'hybrid biological/organic nanoconstruct' that was more efficient than either on their own.”

These researchers have created a tiny solar-powered device that works twice as fast as nature to produce hydrogen biofuel. In describing their research they say that although solar biohydrogen systems using photosystem I (PSI) have been developed, few attain the electron transfer throughput of oxygenic photosynthesis.

They say they optimized a nanoconstruct that tethers FB, the terminal [4Fe-4S] cluster of PSI from Synechococcus sp. PCC 7002, to the distal [4Fe-4S] cluster of the [FeFe]-hydrogenase (H2ase) from Clostridium acetobutylicum.

“On illumination, the PSI-[FeFe]-H2ase nanoconstruct evolves H2 at a rate of 2,200 ± 460 µmol mg chlorophyll-1 h-1, which is equivalent to 105 ± 22 e-PSI-1 s-1. Cyanobacteria evolve O2 at a rate of approximately 400 µmol mg chlorophyll-1 h-1, which is equivalent to 47 e-PSI-1 s-1, given a PSI to photosystem II ratio of 1.8.

“The greater than twofold electron throughput by this hybrid biological/organic nanoconstruct over in vivo oxygenic photosynthesis validates the concept of tethering proteins through their redox cofactors to overcome diffusion-based rate limitations on electron transfer.”

The researchers are among scientists in general who are looking at photosynthesis to invent materials and design new processes that can help save our planet. Associate Professor John Stride, of the University of New South Wales, commented to the ABC that “nature has had millennia to solve problems, and photosynthesis is very efficient.”

In turning to biomimicry, scientists are designing devices based on photosynthesis. As for the study authors, in making their biofuel device they replaced the FNR enzyme with hydrogenase.

One of the co-authors, Penn State Professor Donald Bryant, said there are good prospects for using some of these biological photosynthesis systems to produce biofuels for the future.

More information: Solar hydrogen-producing bionanodevice outperforms natural photosynthesis, PNAS, Published online before print December 12, 2011, doi: 10.1073/pnas.1114660108

Abstract
Although a number of solar biohydrogen systems employing photosystem I (PSI) have been developed, few attain the electron transfer throughput of oxygenic photosynthesis. We have optimized a biological/organic nanoconstruct that directly tethers FB, the terminal [4Fe-4S] cluster of PSI from Synechococcus sp. PCC 7002, to the distal [4Fe-4S] cluster of the [FeFe]-hydrogenase (H2ase) from Clostridium acetobutylicum. On illumination, the PSI–[FeFe]-H2ase nanoconstruct evolves H2 at a rate of 2,200 ± 460 µmol mg chlorophyll-1 h-1, which is equivalent to 105 ± 22 e-PSI-1 s-1. Cyanobacteria evolve O2 at a rate of approximately 400 µmol mg chlorophyll-1 h-1, which is equivalent to 47 e-PSI-1 s-1, given a PSI to photosystem II ratio of 1.8. The greater than twofold electron throughput by this hybrid biological/organic nanoconstruct over in vivo oxygenic photosynthesis validates the concept of tethering proteins through their redox cofactors to overcome diffusion-based rate limitations on electron transfer.

? 2011 PhysOrg.com

New evidence that bacteria in large intestine have a role in obesity

Sandrine P. Claus, Jeremy K. Nicholson and colleagues explain that trillions of bacteria live in the large intestine of healthy people, where they help digest food and make certain vitamins. In recent years, however, scientists have realized that these bacteria do more — they interact with the rest of the body in ways that affect the use of energy and its storage as fat and finely tune the immune system. Claus and Nicholson decided to see how intestinal bacteria might affect the activity of brown fat. The "good" fat that burns calories quickly before they can be stored as fat, brown fat exists in small deposits in the neck area and elsewhere — not like "white fat" in flab around the waist and buttocks. No one had checked to see if those bacteria could have an effect on brown fat, the researchers noted.

In experiments that compared "germ-free" (GF) mice, which don't have large-intestine bacteria, and regular mice, the scientists uncovered evidence suggesting that the bacteria do influence the activity of brown fat. Brown fat in the GF mice seemed to be more active, burning calories faster than in regular mice. Large-intestine bacteria also seemed to be linked with gender differences in weight. Normal male mice were heavier and fattier than females, but those differences vanished in the GF mice. The research also uncovered major differences in the interactions between males and females and their intestinal bacteria that might help explain why the obesity epidemic is more serious and rapidly developing in women. Those and other findings may point the way toward approaches that kick-up the activity of brown fat in humans to prevent or treat obesity.

More information: Gut Microbiota Modulate the Metabolism of Brown Adipose Tissue in Mice, J. Proteome Res., Article ASAP. DOI: 10.1021/pr200938v

Abstract
A two by two experimental study has been designed to determine the effect of gut microbiota on energy metabolism in mouse models. The metabolic phenotype of germ-free (GF, n = 20) and conventional (n = 20) mice was characterized using a NMR spectroscopy-based metabolic profiling approach, with a focus on sexual dimorphism (20 males, 20 females) and energy metabolism in urine, plasma, liver, and brown adipose tissue (BAT). Physiological data of age-matched GF and conventional mice showed that male animals had a higher weight than females in both groups. In addition, conventional males had a significantly higher total body fat content (TBFC) compared to conventional females, whereas this sexual dimorphism disappeared in GF animals (i.e., male GF mice had a TBFC similar to those of conventional and GF females). Profiling of BAT hydrophilic extracts revealed that sexual dimorphism in normal mice was absent in GF animals, which also displayed lower BAT lactate levels and higher levels of (D)-3-hydroxybutyrate in liver, plasma, and BAT, together with lower circulating levels of VLDL. These data indicate that the gut microbiota modulate the lipid metabolism in BAT, as the absence of gut microbiota stimulated both hepatic and BAT lipolysis while inhibiting lipogenesis. We also demonstrated that 1H NMR metabolic profiles of BAT were excellent predictors of BW and TBFC, indicating the potential of BAT to fight against obesity.

Provided by American Chemical Society (news : web)