Friday, January 8, 2010

SUPERATOMS MIMIC ELEMENTS: RESEARCH GIVES NEW PERSPECTIVE ON PERIODIC TABLE

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Transforming lead into gold is an impossible feat, but a similar type of "alchemy" is not only possible, but cost-effective too. Three Penn State researchers have shown that certain combinations of elemental atoms have electronic signatures that mimic the electronic signatures of other elements.

According to the team's leader A. Welford Castleman Jr., Eberly Distinguished Chair in Science and Evan Pugh Professor in the Departments of Chemistry and Physics, "the findings could lead to much cheaper materials for widespread applications such as new sources of energy, methods of pollution abatement, and catalysts on which industrial nations depend heavily for chemical processing."

The researchers also showed that the atoms that have been identified so far in these mimicry events can be predicted simply by looking at the periodic table. The team used advanced experimentation and theory to quantify these new and unexpected findings. "We're getting a whole new perspective of the periodic table," said Castleman. The team's findings were published in the 28 December 2009 early on-line issue of the journal Proceedings of the National Academy of Sciences, and at a later date in the print edition of the journal.

Castleman and his team -- which includes Samuel Peppernick, a former Penn State graduate student who now is a postdoctoral researcher at the Pacific Northwest National Laboratory, and Dasitha Gunaratne, a Penn State graduate student -- used a technique, called photoelectron imaging spectroscopy, to examine similarities between titanium monoxide and nickel, zirconium monoxide and palladium, and tungsten carbide and platinum. "Photoelectron spectroscopy measures the energy it takes to remove electrons from various electronic states of atoms or molecules, while simultaneously capturing snapshots of these electron-detachment events with a digital camera," said Castleman. "The method allows us to determine the binding energies of the electrons and also to observe directly the nature of the orbitals in which the electrons resided before they were detached. We found that the amount of energy required to remove electrons from a titanium-monoxide molecule is the same as the amount of energy required to remove electrons from a nickel atom. The same is true for the systems zirconium monoxide and palladium and tungsten carbide and platinum. The key is that all of the pairs are composed of isoelectronic species, which are atoms with the same electron configuration." Castleman noted that, in this case, the term isoelectronic refers to the number of electrons present in the outer shell of an atom or molecule.

The team looked at images of the photoelectron spectroscopy data. Bright spots in the images, which correspond to the energy of the electrons emitted during their removal from the atoms' outer shells, appeared to be similar between the pairs of species in the three systems studied. Likewise, graphical displays of energy peaks were similar between the pairs, and theoretical calculations also resulted in the pairs having matching energy levels.

Castleman explained that the molecules titanium monoxide, zirconium monoxide, and tungsten carbide are superatoms of nickel, palladium, and platinum, respectively. Superatoms are clusters of atoms that exhibit some property of elemental atoms. Former work in Castleman's lab has involved investigating the notion of superatoms. One of his previous experiments showed that a cluster of 13 aluminum atoms behaves like a single iodine atom. Adding a single electron to this aluminum-atom system results in the cluster behaving like a rare-gas atom. Further, he showed that a cluster of 14 aluminum atoms has a reactivity similar to an alkaline earth atom.

Now, Castleman's new research takes the superatom idea to a new level and provides a sound quantitative foundation for the concept of superatoms. "It looks like we can predict which combinations of elemental atoms mimic other elemental atoms," he said. "For example, by looking at the periodic table, you can predict that titanium monoxide will be a superatom of nickel. Simply start at titanium, which has four outer-shell electrons, and move six elements to the right, because atomic oxygen possesses six outer-shell electrons. The element you end up on is nickel, whose 10 outer-shell electrons make it isoelectronic with the 10 outer-shell electron molecule resulting from the combination of titanium and oxygen. We thought this finding must be a curious coincidence, so we tried it with other atoms and we found that a pattern emerged."

Castleman said that he doesn't know if the pattern will occur across the entire periodic table or if it will be confined to only a part of it. Right now, he and his team are working through the transition-metal atoms. In the future, they plan to take the research a step further to investigate whether or not the superatoms are chemically similar to their respective single atoms. "Platinum is used in nearly all catalytic converters in automobiles, but it is very expensive," said Castleman. "In contrast, tungsten carbide, which mimics platinum, is cheap. A significant amount of money can be saved if catalytic-converter manufacturers are able to use tungsten carbide instead of platinum. Likewise, palladium is used in certain combustion processes, yet it is mimicked by zirconium monoxide, which is less expensive by a factor of 500. Our new findings are exciting from both a scientific as well as a practical point of view."

(Photo: Castleman lab, Penn State)

The Pennsylvania State University

EXPOSURE TO TOBACCO SMOKE IN CHILDHOOD HOME ASSOCIATED WITH EARLY EMPHYSEMA IN ADULTHOOD

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Children regularly exposed to tobacco smoke at home were more likely to develop early emphysema in adulthood. This finding by researchers at Columbia University's Mailman School of Public Health suggests that the lungs may not recover completely from the effects of early-life exposures to tobacco smoke (ETS). The study was published in the December 2009 American Journal of Epidemiology.

This population-based research is the first to examine the association of childhood ETS with early emphysema by CT scan in nonsmokers. Approximately half of the participants in this large multiethnic cohort had at least one regular cigarette smoker in their childhood home. Participants with more childhood ETS exposure had more emphysema-like lung pixels; an average of 20% of scan pixels were emphysema-like for those who lived with two or more smokers as a child, compared with 18% for those who lived with one regular smoker, or 17% for those who said that they did not live with a regular inside smoker as a child.

The researchers studied CT scans of 1,781 non-smokers without clinical cardiovascular disease recruited from six communities in the United States, including northern Manhattan and the Bronx, New York. Those reporting childhood ETS exposure were somewhat younger, with an average age of 61; were more likely to be non- Hispanic white; and less likely to have been born outside the United States. These differences were statistically controlled in the analyses.

"We were able to detect a difference on CT scans between the lungs of participants who lived with a smoker as a child and those who did not," observed Gina Lovasi, PhD, MPH, assistant professor of epidemiology at Columbia's Mailman School of Public Health. "Some known harmful effects of tobacco smoke are short term, and this new research suggests that effects of tobacco smoke on the lungs may also persist for decades."

Previous studies have found evidence that childhood ETS exposure affects perinatal and childhood health outcomes, and that adult exposure may affect adult respiratory health outcomes, including lung function and respiratory symptoms.

Although childhood ETS was not associated with adult lung function in this healthy population, this does not contradict the results for early emphysema, since airflow obstruction and anatomic damage are theoretically and clinically distinguishable. "However, emphysema may be a more sensitive measure of damage compared with lung function in this relatively healthy cohort,"

Dr. Lovasi notes. Combined emphysema and chronic obstructive pulmonary disease are projected to become the third leading cause of death worldwide by 2020.

The exposure information in this study does not provide information on the timing of ETS exposure during childhood, making it difficult to distinguish as exposure in utero. "The association between childhood ETS and early emphysema among participants whose mothers did not smoke, suggests that the effect we are detecting is for smoke exposure in the home during childhood rather than in utero exposure alone," observed Dr. Lovasi.

Columbia University

NEUROSCIENTISTS AT CASE WESTERN RESERVE UNIVERSITY STORE INFORMATION IN ISOLATED BRAIN TISSUE

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Ben W. Strowbridge, PhD, associate professor of neuroscience and physiology/biophysics, and Phillip Larimer, PhD, a MD/PhD student in the neurosciences graduate program at Case Western Reserve University School of Medicine, are the first to create stimulus-specific sustained activity patterns in brain circuits maintained in vitro.

Their study, entitled, "Representing information in cell assemblies: Persistent activity mediated by semilunar granule cells" will be published in the February 2010 issue of Nature Neuroscience and is currently available online.

Neuroscientists often classify human memory into three types: declarative memory, such as storing facts or remembering specific events; procedural memory, such as learning how to play the piano or shoot basketballs; and working memory, a type of short-term storage like remembering a phone number. With this particular study, Strowbridge and Larimer, were interested in identifying the specific circuits that could be responsible for working memory.

Using isolated pieces of rodent brain tissue, Larimer discovered a way to recreate a type of working memory in vitro. He was studying a particular type of brain neuron, called mossy cells, which are often damaged in people with epilepsy and are part of the hippocampus.

"Seeing the memory deficits that so many people with epilepsy suffer from led me to wonder if there might be a fundamental connection between hippocampal mossy cells and memory circuits", said Larimer.

Mossy cells are unusual because they maintain much of their normal activity even when kept alive in thin brain slices. The spontaneous electrical activity Larimer and Strowbridge found in mossy cells was critical to their discovery of memory traces in this brain region.

When stimulating electrodes were inserted in the hippocampal brain slice the spontaneous activity in the mossy cells remembered which electrode had been activated. The memory in vitro lasted about 10 seconds, about as long as many types of working memories studied in people.

"This is the first time anyone has stored information in spontaneously active pieces of mammalian brain tissue. It is probably not a coincidence that we were able to show this memory effect in the hippocampus, the brain region most associated with human memory," said Strowbridge.

The scientists measured the frequency of synaptic inputs onto the mossy cells to determine whether or not the hippocampus had retained memory.

"Memory was not evident in one cell but it was evident in a population of cells," said Strowbridge.

Larimer, who had just published another paper with Strowbridge on experiments recording electrical signals simultaneously inside four brain cells (Journal of Neuroscience, November 2008, "Nonrandom local circuits in the dentate gyrus"), was already familiar with recording from multiple cells/neurons.

"Like our own memories, the memories we created in isolated brain slices were stored in many different neurons or cells, that's why we had to watch several different cells to see the stored information," said Strowbridge.

Larimer and Strowbridge also found the brain circuit that enabled the hippocampus to remember which input pathway had been activated. The memory effect occurred because of a rare type of brain cell called semilunar granule cells, described in 1893 by the father of neuroscience, Ramón y Cajal. The semilunar granule cells have an unusual form of persistent activity, allowing them to maintain memory and connect to the mossy cells. That was the foundation for this paper. The semilunar granule cells remained an obscurity for more than a century until Strowbridge's group rediscovered them in a paper they published in 2007.

Semilunar granule cells are the third type of brain cell that Strowbridge's group has uncovered. In 2006, Strowbridge's group published a report in the journal Neuron about Blanes cells, which Cajal named for one of his medical students that are involved in the sense of smell. That study opened a new approach to understanding the memory impairment in Alzheimer's disease, a disease that often involves changes in the perception of smells.

Strowbridge's group is now looking into how much information they can store in the hippocampus.

"It took us four years to be able to reproducibly store two bits of information for 10 seconds" says Larimer. "Our findings should progress faster now that we know what to look for and have found the brain circuit that actually holds the memory."

Case Western Reserve University

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