Crystallizing the switch to hydrogen

Compressing hydrogen gas or liquefying it at -250 °C are two ways to increase its energy content by volume. However, chemists are developing a more attractive strategy using specially designed compounds, called metal hydride clusters, to produce high hydrogen-storage densities without extreme temperatures or pressures. The metal atoms within these molecules bind to large numbers of hydrogen atoms, producing a solid that can reversibly add or remove hydrogen using mild heating or cooling.

Now, Zhaomin Hou from the RIKEN Advanced Science Institute in Wako and an international team of colleagues have isolated a new class of ‘heterometallic’ hydride clusters (Fig. 1) that may spur development of lighter and longer-lived fuel cell devices. By incorporating multinuclear rare-earth metals into their compounds, the team has produced the first high-density storage molecules that have hydrogen addition properties that can be monitored directly using x-ray diffraction—a technique that provides clear insights into cluster structure and functionality.

Rare combinations

For the past 25 years, chemists have paired so-called ‘d-block transition metals’, such as tungsten (W) and molybdenum (Mo), with lightweight rare-earth metals, such as yttrium (Y), to increase the storage capacity of hydride clusters. Because the nuclei of rare earths are shielded by many electrons, these metals can pack high numbers of hydrogen atoms into small crystal volumes without suffering electronic repulsions. Unfortunately, once hydrogen gas binds to a rare-earth metal, it tends to stay there. Mixing in d-block metals alters the rare-earth reactivity so that on-demand hydrogen storage and release can occur.

Until now, most of these combined metal hydrides were constructed using mononuclear rare-earth building blocks, such as YH, with a mononuclear d-block metal. Using a different strategy, Hou and his colleagues recently devised innovative protocols to isolate polynuclear rare-earth hydrides using large molecular ligands to trap these typically unstable compounds in place. Polynuclear hydrides feature dense, interconnected networks of ‘bridging’ hydrogen atoms connected to two or more metals—characteristics that led the researchers to explore their potential for hydrogen storage applications. 

Enlarge

Figure 2: Monitoring the reversible addition and release of a hydrogen gas molecule to a molybdenum-yttrium cluster in real time with x-ray crystallography has revealed the first atom-resolved insights into hydrogen storage by organometallic crystals. Credit: 2011 Zhaomin Hou

“It is not difficult to imagine that hydrogen atoms could bond to multiple metal atoms in a polynuclear polyhydride complex, and the [mode of] bonding could be different with different metal combinations,” says Hou. “However, it is not easy to prepare quality polyhydride samples for high-precision structure determinations. Hydride complexes containing both rare-earth and d-block transition metals are even more difficult to prepare because of their air- and moisture-sensitivity.”

A five-way first

Performing their experiments inside nitrogen-filled and humidity-free enclosures, the team mixed one of their carefully prepared polynuclear complexes—four yttrium metals and eight hydrogen atoms held together by bulky organic ligands—with either a Mo or W pentahydride. After precipitating crystals out of the reaction, they used x-ray and neutron diffraction experiments to view their product’s atomic structure. These measurements showed that the two metallic components fused together, yielding a Y4MH11 (M = Mo, W) hydride with double-, triple-, and quadruple-bridged hydrogen atoms.

Zapping the penta-metallic polyhydride with ultraviolet light enabled the team to remove a protective phosphorus ligand and increase the hydrogen bridging density within the cluster. This produced the first hydride cluster where hydrogen is bonded to five metals in a distinctive symmetry known as trigonal bipyramidal. “The confirmation of a penta-coordinated hydrogen atom in this geometry is unprecedented,” says Hou.

Step-by-step scrutiny

Hou and colleagues’ experiments then demonstrated that their heterometallic clusters possessed critical hydrogen storage and release capabilities. Heating H2 and Y4WH11 to 80 °C caused an oxidative addition of the gas molecule to the cluster, which they could reverse through ultraviolet-light treatment. Despite the Y4MoH11 molecule not responding to the same chemical tricks, the researchers discovered that applying a vacuum could suck H2 from the cluster, giving a new Y4MoH9 complex. Exposing this compound to hydrogen gas at room temperature spontaneously regenerated the original molecule (Fig. 2).

According to Hou, the most striking aspect of this chemistry is that the hydrogen addition to the Y4MoH9 cluster can be followed from single crystal to single crystal—meaning that the starting material, the reaction intermediates, and the product all retain the same rigid morphology. “No metal hydrides have previously shown such excellent crystallinity,” he notes.

After gingerly sealing a Y4MoH9 crystal into a thin, hydrogen-filled capillary tube, the researchers monitored the spontaneous addition reaction over 60 hours. As the cluster gradually took in hydrogen and changed color from black to red, they watched—at precision greater than one-millionth of a meter—yttrium and molybdenum atoms separate and shift within the crystal unit cell. By providing the first-ever atom-resolved views of active sites and bonding modes for hydrogen addition to an organometallic crystal, these findings should aid design of more sophisticated alloys in the future.

Theoretical calculations performed by the researchers indicated that combining two metals with starkly different electronic properties played a big role in giving the clusters their unique reactivity. With wide swaths of the periodic table available for exploring using this technique, breakthroughs in heterometallic hydride materials may have only just begun.

More information: Shima, T., et al. Molecular heterometallic hydride clusters composed of rare-earth and d-transition metals. Nature Chemistry 3, 814–820 (2011). doi:10.1038/nchem.1147 
Nishiura, M. & Hou, Z. Novel polymerization catalysts and hydride clusters from rare-earth metal dialkyls. Nature Chemistry 2, 257–268 (2010). doi:10.1038/nchem.595

Provided by RIKEN (news : web)

Imaging instruction: Researchers produce 'primer' to guide the use of STORM

To correct the situation, Zhuang, working with postdoctoral associate Joshua Vaughan and graduate students Graham Dempsey, Kok Hao Chen, and Mark Bates, has developed a “primer” that identifies the best photo-switchable dyes or fluorescent proteins — called “probes” — to use in STORM imaging.

Described recently in a paper published on Nature Methods’ website, the work also identified the key characteristics that are useful for STORM imaging, giving researchers a framework for evaluating other probes, or even designing custom-made molecules to use in imaging.

“This paper is service to the community,” Zhuang said. “We are trying to educate people about two things — what properties a probe needs to have to produce high-quality STORM images and [a] list [of] the probes that we have found to have superior qualities for this purpose.

“Though our imaging method is relatively easy to use, it is still capable of producing low-quality images if the wrong probes or imaging conditions are used. That’s why we felt it was particularly important that we tell people that there are some criteria to keep in mind when selecting a probe,” Zhuang added.

Their research, Zhuang said, identified two properties that are critical to producing a quality image — the amount of light given off by a specific probe, and its “duty-cycle” — the fraction of time that the probe spends in a bright state. Other important properties identified in the paper include the number of times each probe can be switched on and off, and how each reacts to “activation light.”

In addition to helping researchers identify which probes will produce the best results, Zhuang said the research, because it defines the probe properties that are important for STORM imaging, provides researchers with a roadmap for the development of even more efficient probes.

To illustrate the importance of a probe’s brightness and duty-cycle, Dempsey asked a recent visitor to the lab to imagine a circle.

“If you want to image that, you need to identify enough spots, and they need to outline the shape of that circle,” he said. “If the brightness is too low, when you try to localize the molecules, the precision will be relatively low and the resulting image will end up blurry. If the duty-cycle is too high, you will end up with too few spots to outline the circle, regardless of how precise each spot is positioned.”

As part of the paper, Chen, Dempsey, and Vaughan meticulously studied the characteristics of more than two dozen probes, eventually identifying several that produce the highest-quality images. By using the best probes in four separate spectral ranges, the team was able to produce high-quality multicolor images with low crosstalk between channels, a highly nontrivial task for super-resolution imaging.

“There was a lot of trial and error, and a lot of labor involved in getting this much data together,” said Vaughan of the research. “But this is the type of thing where, if you don’t take the time to do systematically, there is no way to take a step back and rely on anything other than anecdotal experience. A researcher who is new to STORM would have to repeat the same trial-and-error process to get these results. This way, we have already done all that work.”
This story is published courtesy of the Harvard Gazette, Harvard University’s official newspaper. For additional university news, visit Harvard.edu.

Provided by Harvard University (news : web)

Scientists propose new names for elements 114 and 116

 The International Union of Pure and Applied Chemistry (IUPAC) have recommended new proposed names for elements 114 and 116, the latest heavy elements to be added to the periodic table.

Scientists of the Lawrence Livermore National Laboratory (LLNL)-Dubna collaboration proposed the names as Flerovium for element 114 and Livermorium for element 116.

In June 2011, the IUPAC officially accepted elements 114 and 116 as the heaviest elements, more than 10 years after scientists from the Joint Institute for Nuclear Research in Dubna and Lawrence Livermore chemists discovered them.

Flerovium (atomic symbol Fl) was chosen to honor Flerov Laboratory of Nuclear Reactions, where superheavy elements, including element 114, were synthesized. Georgiy N. Flerov (1913-1990) was a renowned physicist who discovered the spontaneous fission of uranium and was a pioneer in heavy-ion physics. He is the founder of the Joint Institute for Nuclear Research. In 1991, the laboratory was named after Flerov -- Flerov Laboratory of Nuclear Reactions (FLNR).

Livermorium (atomic symbol Lv) was chosen to honor Lawrence Livermore National Laboratory (LLNL) and the city of Livermore, Calif. A group of researchers from the Laboratory, along with scientists at the Flerov Laboratory of Nuclear Reactions, participated in the work carried out in Dubna on the synthesis of superheavy elements, including element 116. (Lawrencium -- Element 103 -- was already named for LLNL's founder E.O. Lawrence.)

In 1989, Flerov and Ken Hulet (1926-2010) of LLNL established collaboration between scientists at LLNL and scientists at FLNR; one of the results of this long-standing collaboration was the synthesis of elements 114 and 116.

"Proposing these names for the elements honors not only the individual contributions of scientists from these laboratories to the fields of nuclear science, heavy element research, and superheavy element research, but also the phenomenal cooperation and collaboration that has occurred between scientists at these two locations," said Bill Goldstein, associate director of LLNL's Physical and Life Sciences Directorate.

LLNL scientists Ken Moody, Dawn Shaughnessy, Jackie Kenneally and Mark Stoyer were critical members of the team along with a team of retired LLNL scientists including John Wild, Ron Lougheed and Jerry Landrum. Former LLNL scientists Nancy Stoyer, Carola Gregorich, Jerry Landrum, Joshua Patin and Philip Wilk also were on the team. The research was supported by LLNL Laboratory Research and Development funds (LDRD).

Scientists at LLNL have been involved in heavy element research since the Laboratory's inception in 1952 and have been collaborators in the discovery of six elements -- 113,114,115,116,117 and 118.

Livermore also has been at the forefront of investigations into other areas related to nuclear science such as cross-section measurements, nuclear theory, radiochemical diagnostics of laser-induced reactions, separations chemistry including rapid automated aqueous separations, actinide chemistry, heavy-element target fabrication, and nuclear forensics.

The creation of elements 116 and 114 involved smashing calcium ions (with 20 protons each) into a curium target (96 protons) to create element 116. Element 116 decayed almost immediately into element 114. The scientists also created element 114 separately by replacing curium with a plutonium target (94 protons).

The creation of elements 114 and 116 generate hope that the team is on its way to the "island of stability," an area of the periodic table in which new heavy elements would be stable or last long enough for applications to be found.

The new names were submitted to the IUPAC in late October and now remain in the public domain. The new names will not be official until about five months from now when the public comment period is over.

Story Source:

The above story is reprinted from materials provided by DOE/Lawrence Livermore National Laboratory.

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

New coatings process lowers fuel consumption

The coatings have textures that could reduce the carbon footprint of the transport industry by lowering the drag of moving through air or water. In turn, vessels will consume less energy in propulsion.

The team of physicists at the University of Surrey is now collaborating with six companies through funding from an EPSRC Knowledge Transfer Account (KTA). The project is developing ways for industrial manufacturers to use the process to create novel coatings to decorate household goods.

Using their simple, low-cost process, it is possible to create plastic coatings with small bumps and ridges in sizes ranging from less than a millimetre to a couple of centimetres. With the right design, this texture will reduce the drag forces when large vessels pass through air or water.

Professor Joseph Keddie, of the Department of Physics, who led the research, said: “It’s an exciting prospect to have an impact on the energy consumed by planes and ships through a straightforward, inexpensive technology. Our process can create coatings with nearly any desired texture to meet the particular requirements of an application.

“This new technology has grown out of several years of polymer and colloids research within the Soft Matter Physics Group in collaboration with industrial partners. Our KTA project will help to transfer our research ideas into industrial manufacturing.”

There are also other numerous high-tech applications where the University of Surrey’s work can be used, such as to create tiny lenses to focus light. Applications of these “micro lenses” are in digital cameras, photocopiers, and solar cells.

The researchers call their process “infrared radiation-assisted evaporative lithography.” They use beams of infrared light to heat certain spots on wet coatings made of tiny plastic particles in water. The hotter spots evaporate more quickly, and the plastic particles are then guided there as the evaporating water is replaced. The process is simple to use and does not require expensive equipment. The textured coatings can be used to cover nearly any surface.

The research has recently been published, with co-authors at AkzoNobel and at the University of Cambridge, as a cover article in the prestigious Royal Society of Chemistry journal, Soft Matter. The scientists have also filed an international patent application on their process and are looking for partners to apply the new technology in applications.

The coatings can also have an attractive visual appearance and interesting textures, making them exciting for new designs on domestic products.

“Our novel process uses fundamental concepts of science to create objects with tremendous aesthetic appeal. The coatings are beautiful to see,” said Dr Argyrios Georgiadis, whose experimental work paved the way for the technology.

More information: Bespoke periodic topography in hard polymer films by infrared radiation-assisted evaporative lithography, Soft Matter, 2011, 7, 11098-11102. DOI: 10.1039/C1SM06527K

Abstract
Polymer coatings with periodic topographic patterns, repeating over millimetre length scales, are created from lateral flows in an aqueous dispersion of colloidal particles. The flow is driven by differences in evaporation rate across the wet film surface created by IR radiative heating through a shadow mask. This new process, which we call IR radiation-assisted evaporative lithography (IRAEL), combines IR particle sintering with the concept of evaporative lithography. We show that the height of the surface features increases with an increase in several key parameters: the initial thickness of the film, the volume fraction of particles, and the pitch of the pattern. The results are interpreted by using models of geometry and particle transport. The patterned coatings can function as “paintable” microlens arrays, applicable to nearly any surface. Compared with existing methods for creating textured coatings, IRAEL is simpler, inexpensive, able to create a wide variety of bespoke surfaces, and applicable to nearly any substrate without prior preparation.

Provided by University of Surrey

Chemistry professor links feces and caffeine

The researchers took water samples from streams, brooks and storm sewer outfall pipes that collect storm waters across the Island of Montreal, and analyzed them for caffeine, fecal coliforms, and a third suspected indicator, carbamazepine. Shockingly, all the samples contained various concentrations of these contaminants, which would suggest that contamination is widespread in urban environments. Carbamazepine is an anti-seizure drug which is also increasingly used for various psychiatric treatments, and the researchers thought it might be a useful indicator because it degrades very slowly. However, unlike with caffeine, no correlation was found.

Caffeine degrades within a few weeks to 2-3 months in the environment and is very widely consumed. The presence of caffeine is also a sure indicator of human sewage contamination, as agriculture and industry do not tend to release caffeine into the environment. The team also noted that the data suggest that Montreal's storm water collection system is widely contaminated by domestic sewers. On the other hand, the researchers observed high levels of fecal coliforms but little or no caffeine in some of the samples, which they attribute to urban wildlife. "This data reveals that any water sample containing more than the equivalent of ten cups of coffee diluted in an Olympic-size swimming pool is definitely contaminated with fecal coliforms," Sauvé said. "A caffeine sampling program would be relatively easy to implement and might provide a useful tool to identify sanitary contamination sources and help reduce surface water contamination within an urban watershed."

More information: "Fecal coliforms, caffeine and carbamazepine in stormwater collection systems in a large urban area" was published online in Chemosphere on November 8, 2011.

Provided by University of Montreal (news : web)