Danger? Nanotube-Infested Waters Created in the Lab

 

Carbon nanomaterials can mix in water despite being hydrophobic, raising the possibility of a spreading spill in the future.

Carbon nanotubes--and their spherical cousins known as buckyballs--are proving to have myriad uses, finding employ in improved solar cells, electronics and medical probes. But the production volume of the tricky nanomaterials remains nanoscale when compared with the production volume of other industrial components. Nevertheless, environmental engineers have begun investigating how such materials might interact with natural environments if accidentally released and have discovered that at least some of the hydrophobic (water fearing) materials persist quite readily in natural waters.
Jae-Hong Kim of the Georgia Institute of Technology and his colleagues investigated how so-called multiwalled carbon nanotubes--layered, straws-within-straws of carbon atoms--interacted with natural water, in this case samples taken from the nearby Suwannee River. To their surprise, the carbon nanomaterial did not clump together as it tried to avoid water molecules, rather it interacted with the negatively charged natural organic matter in the river water. This organic matter seemed to shield the nanotubes and allow them to disperse throughout the water after an hour of mixing, instead of clumping and settling. "At the beginning, the solution is very black and, over time, it becomes grayish," Kim says. "What is interesting is that it is still grayish after a month." In other words, the nanotubes do not settle even after this time period.
This monthlong suspension means that Suwannee River water was actually better at promoting the dispersal of carbon nanotubes than chemical surfactants, which can maintain nanotubes in solution for roughly four days, according to the paper presenting the finding published online in Environmental Science and Technology. Similar studies with buckyballs--stable balls of 60 carbon atoms, also known as C₆₀--had required copious organic solvents in order to maintain suspensions.

Because of the presence of such solvents, toxicity tests on C₆₀ have been open to question as to whether the buckyballs or the solvents caused the damaging effects. Environmental engineers Volodymyr Tarabara and Syed Hashsham of Michigan State University and their colleagues tested the toxic effects of such buckyballs in water--without solvents--on lymphocytes, human immune cells. The researchers created solutions of C₆₀ and water using ethanol at levels previously proven to have no toxic impact and using weeks worth of magnetically powered stirring.
At concentrations as low as 2.2 micrograms per liter, the clumps of C₆₀ damaged the DNA of the immune cells, according to microscopic analysis presented in the December 1 issue of Environmental Science and Technology. The exact mechanism by which C₆₀causes the DNA damage remains unclear, particularly because imaging could not detect the smallest of the buckyball clumps, but its DNA damaging effect was dose dependent. "We are not sure if very very small particles exist, one or two nanometers big," Tarabara says. "They may be very important as far as cellular damage."
Regardless, such nanopollution is unlikely to occur anytime soon: "The fact of the matter is that it takes weeks of mixing to generate appreciable concentrations in the size range where the particles are small enough not to settle," Tarabara notes. "It's not something that we can expect to be out there loose." But the environmental engineers argue that such research should be carried out before any widespread adoption of the new carbon nanomaterials takes place, especially because they seem to have a few surprises in store. "One thing is definite," Kim says, "these materials were not traditionally considered an aqueous-based contaminant." He adds: "I am saying, 'Well, it seems possible.'" --David Biello

[source: www.sciam.com]

No Sex For 40 Million Years? No Problem

Science Daily — A group of organisms that has never had sex in over 40 million years of existence has nevertheless managed to evolve into distinct species, says new research published today. The study challenges the assumption that sex is necessary for organisms to diversify and provides scientists with new insight into why species evolve in the first place.

Scanning electron micrographs showing morphological variation of bdelloid rotifers and their jaws. Have these asexual animals really diversified into evolutionary species? (Credit: Diego Fontaneto / Courtesy of PLoS Biology)

The research, published in PLoS Biology, focuses on the study of bdelloid rotifers, microscopic aquatic animals that live in watery or occasionally wet habitats including ponds, rivers, soils, and on mosses and lichens. These tiny asexual creatures multiply by producing eggs that are genetic clones of the mother -- there are no males. Fossil records and molecular data show that bdelloid rotifers have been around for over 40 million years without sexually reproducing, and yet this new study has shown that they have evolved into distinct species.

Using a combination of DNA sequencing and jaw measurements taken using a scanning electron microscope, the research team examined bdelloid rotifers living in different aquatic environments across the UK, Italy and other parts of the world. They found genetic and jaw-shape evidence that the rotifers had evolved into distinct species by adapting to differences in their environment.

Dr Tim Barraclough from Imperial College London's Division of Biology explained: "We found evidence that different populations of these creatures have diverged into distinct species, not just because they become isolated in different places, but because of the differing selection pressures in different environments.

"One remarkable example is of two species living in close proximity on the body of another animal, a water louse. One lives around its legs, the other on its chest, yet they have diverged in body size and jaw shape to occupy these distinct ecological niches. Our results show that, over millions of years, natural selection has caused divergence into distinct entities equivalent to the species found in sexual organisms."

Previously, many scientists had thought that sexual reproduction was necessary for speciation because of the importance of interbreeding in explaining speciation in sexual organisms. Asexual creatures like the bdelloid rotifers were known not to be all identical, but it had been argued that the differences might arise solely through the chance build-up of random mutations that occur in the 'cloning' process when a new rotifer is born. The new study proves that these differences are not random and are the result of so-called 'divergent selection', a process well known to cause the origin of species in sexual organisms.

Dr Barraclough adds: "These really are amazing creatures, whose very existence calls into question scientific understanding, because it is generally thought that asexual creatures die out quickly, but these have been around for millions of years.

"Our proof that natural selection has driven their divergence into distinct species is another example of these miniscule creatures surprising scientists -- and their ability to survive and adapt to change certainly raises interesting questions about our understanding of evolutionary processes."

Note: This story has been adapted from a news release issued by Imperial College London.

(c) www.sciencedaily.com

Uni.Science Tags: Sex, Time, DNA, Biology

Searching for Signs of Life on Mars

by Guy Webster, Dwayne Brown

 

Urey Instrument. Credit: NASA/JPL

NASA-funded researchers are refining a tool that could not only check for the faintest traces of life's molecular building blocks on Mars, but could also determine whether they have been produced by anything alive.

The instrument, called Urey: Mars Organic and Oxidant Detector, has already shown its capabilities in one of the most barren climes on Earth, the Atacama Desert in Chile. The European Space Agency has chosen this tool from the United States as part of the science payload for the ExoMars rover planned for launch in 2013. Last month, NASA selected Urey for an instrument-development investment of $750,000.

Artist's concept of ExoMars. Credit: European Space Agency

The European Space Agency plans for the ExoMars rover to grind samples of Martian soil to fine powder and deliver them to a suite of analytical instruments, including Urey, that will search for signs of life. Each sample will be a spoonful of material dug from underground by a robotic drill.
"Urey will be able to detect key molecules associated with life at a sensitivity roughly a million times greater than previous instrumentation," said Dr. Jeffrey Bada of Scripps Institution of Oceanography at the University of California, San Diego. Bada is the principal investigator for an international team of scientists and engineers working on various components of the device.
To aid in interpreting that information, part of the tool would assess how rapidly the environmental conditions on Mars erase those molecular clues.
Dr. Pascale Ehrenfreund of the University of Leiden in the Netherlands, said, "The main objective of ExoMars is to search for life. Urey will be a key instrument for that because it is the one with the highest sensitivity for organic chemicals." Ehrenfreund, one of two deputy principal investigators for Urey, coordinates efforts of team members from five other European countries.
Urey can detect several types of organic molecules, such as amino acids, at concentrations as low as a few parts per trillion.
All life on Earth assembles chains of amino acids to make proteins. However, amino acids can be made either by a living organism or by non-biological means. This means it is possible that Mars has amino acids and other chemical precursors of life but has never had life. To distinguish between that situation and evidence for past or present life on Mars, the Urey instrument team will make use of the knowledge that most types of amino acids can exist in two different forms. One form is referred to as "left-handed" and the other as "right-handed." Just as the right hand on a human mirrors the left, these two forms of an amino acid mirror each other.
Amino acids from a non-biological source come in a roughly 50-50 mix of right-handed and left-handed forms. Life on Earth, from the simplest microbes to the largest plants and animals, makes and uses only left-handed amino acids, with rare exceptions. Comparable uniformity -- either all left or all right -- is expected in any extraterrestrial life using building blocks that have mirror-image versions because a mixture would complicate biochemistry.
"The Urey instrument will be able to distinguish between left-handed amino acids and right-handed ones," said Allen Farrington, Urey project manager at NASA's Jet Propulsion Laboratory, which will build the instrument to be sent to Mars.
If Urey were to find an even mix of the mirror-image molecules on Mars, that would suggest life as we know it never began there. All-left or all-right would be strong evidence that life now exists on Mars, with all-right dramatically implying an origin separate from Earth life. Something between 50-50 and uniformity could result if Martian life once existed, because amino acids created biologically gradually change toward an even mixture in the absence of life.
The 1976 NASA Viking mission discovered that strongly oxidizing conditions at the Martian surface complicate experiments to search for life. The Urey instrument has a component, called the Mars oxidant instrument, for examining those conditions.
The oxidant instrument has microsensors coated with various chemical films. "By measuring the reaction of the sensor films with chemicals present in the Martian soil and atmosphere, we can establish if organisms could survive and if evidence of past life would be preserved," said Dr. Richard Quinn, a co-investigator on Urey from the SETI Institute, Mountain View, Calif., who also works at NASA Ames Research Center, Moffett Field, Calif.

"In order to improve our chances of finding chemical evidence of life on Mars, and designing human habitats and other equipment that will function well on Mars' surface, we need to improve our understanding of oxidants in the planet's surface environment," said Dr. Aaron Zent, a Urey co-investigator at NASA Ames.
A Urey component called the sub-critical water extractor handles the task of getting any organic compounds out of each powdered sample the ExoMars rover delivers to the instrument. "It's like an espresso maker," explained JPL's Dr. Frank Grunthaner, a deputy principal investigator for Urey. "We bring the water with us. It is added to the sample, and different types of organic compounds dissolve into the liquid as the temperature increases. We keep it under pressure the whole time."
The dissolved compounds are highly concentrated by stripping away water in a tiny oven. Then a detector checks for fluorescent glowing, which would indicate the presence of amino acids, some components of DNA and RNA, or other organic compounds that bind to a fluorescing chemical added by the instrument.
A Urey component called the micro-capillary electrophoresis unit has the critical job of separating different types of organic compounds from one another for identification, including separation of mirror-image amino acids from each other. "We have essentially put a laboratory onto a single wafer," said Dr. Richard Mathies of the University of California, Berkeley, a Urey co-investigator. The device for sending to Mars will be a small version incorporating this detection technology, which is already in use for biomedical procedures such as law-enforcement DNA tests and checking for hazardous microbes.
Switzerland will provide electronics design and packaging expertise for Urey. Micro-Cameras and Space Exploration S.A., Neuchatel, will collaborate with JPL and the European Space Agency to accomplish this significant contribution to the heart of the instrument. Dr. Jean-Luc Josset, Urey co-investigator at the University of Neuchatel will coordinate this effort and help provide detector selection and support.

(c) www.physorg.com

Scientists discover new class of polymers

Since the late 1990s, Lauterbach and Snively have been developing a method to make extremely thin polymer layers on surfaces. The film covering the surface of these metal samples is at least 1,000 times thinner than a human hair. Photo by Kathy F. Atkinson

For years, polymer chemistry textbooks have stated that a whole class of little molecules called 1,2-disubstituted ethylenes could not be transformed into polymers--the stuff of which plastics and other materials are made.

This photo shows an ultra-thin polymer film of fumaronitrile, which formerly was believed to be 'unpolymerizable,' on a tantalum foil. The film is circular due to the shape of the window where ultraviolet light is emitted into the vacuum chamber during the film deposition process. Photo courtesy of Lauterbach Laboratory, University of Delaware

However, the UD scientists were determined to prove the textbooks wrong. As a result of their persistence, the researchers have discovered a new class of ultra-thin polymer films with potential applications ranging from coating tiny microelectronic devices to plastic solar cells.
The discovery was reported as a "communication to the editor" in the Nov. 28 edition of Macromolecules, a scientific journal published by the American Chemical Society.
The research, which also involved doctoral student Seth Washburn, focused on formerly nonpolymerizable ethylenes. Among them are several compounds that are derived from natural sources, such as cinnamon, and and are FDA-approved for use in fragrances and foods. One of the compounds is found in milkshakes, according to the scientists.
"There's been a rule that these molecules wouldn't polymerize," Snively, who is a research associate in Lauterbach's laboratory group, noted. "When I first saw that in a textbook when I was in graduate school, I said to myself, 'Don't tell me I can't do this.'"
And thus, the quest to disprove a widely accepted scientific rule of thumb began.
Polymerization is a chemical reaction in which monomers, which are small molecules with repeating structural units, join together to form a long chain-like molecule--a polymer. Each polymer typically consists of 1,000 or more of these monomer "building blocks."
There are lots of natural polymers in the world, ranging from the DNA in our bodies to chewing gum. Plastics, of course, are one of the most common groups of manmade polymers. These synthetic materials first came on the scene in the mid-1800s and are found today in a wide range of applications, including foam drinking cups, carpet fibers, epoxy and PVC pipes.
Since the late 1990s, Lauterbach and Snively have been developing a method to make extremely thin polymer layers on surfaces. These nanofilms--at least 1,000 times thinner than a human hair--are becoming increasingly important as coatings for optics, solar cells, electrical insulators, advanced sensors and numerous other applications.
Formerly, to make a pound of polymer, scientists would take a monomer and a solvent and subject them to heat or light. Recently, Lauterbach and Snively developed a new polymer-making technique that eliminates the need for a solvent.
Their deposition-polymerization (DP) process takes place in a vacuum chamber, where the air is pumped out and the pressure is similar to outer space. The material to be coated, such as a piece of metal, is placed in the chamber, and the metal is cooled below the monomer's freezing point, which causes the monomer vapor to condense on the metal. Then the resulting film is exposed to ultraviolet light to initiate polymerization. The two-step process allows for the formation of uniform, defect-free films with thicknesses that can be controlled to within billionths of a meter.
The process is fairly "green," in that not only are no solvents used, but there also is very low energy consumption using this method, according to Lauterbach.
"You also can do photolithography with it," he said, meaning that the polymer will appear only where the light hits the monomer film.
While their polymerization technique was reported a few years ago, the class of materials the UD scientists have applied it to lately is new and unique.
"We can make nanometer-thick films, but we can't make a gram of the material yet," Snively noted. "We're working on ways to scale up the process."
The scientists also want to find out if the materials may be stronger, tougher or possess unique properties compared to other polymers.
"It's exciting because you don't really know what all their properties are yet," Snively said.
As for all the potential applications, Lauterbach said, "we're kind of in the discovery phase, looking to see where all these materials could be used."
The scientists say their collaboration has been so productive not just because their personalities mesh but because knowledge in each of their respective disciplines is essential to solving the scientific questions they seek to answer.
"We get more done together than either of us could alone," Lauterbach says.
Lauterbach has a doctorate in physical chemistry from the Free University of Berlin and the Fritz-Haber Institute of the Max Planck Society, and a bachelor's degree in physics from the University of Bayreuth, Germany.
Snively, a research assistant professor in the materials science and engineering department, has a doctorate in macromolecular science from Case Western Reserve University.
The two scientists came to UD in 2002 from Purdue University, where Lauterbach won the National Science Foundation's prestigious Faculty Early Career Development Award, as well as Union Carbide's Innovation Recognition Award.
Soon, the UD researchers may be applying the new class of polymers they've discovered to plastic solar cells through collaborative research in UD's new Sustainable Energy from Solar Hydrogen program.
This effort, which focuses on transforming UD graduate students into "energy experts" through interdisciplinary,
problem-based research, is supported by a five-year, $3.1 million grant from the National Science Foundation's Integrative Graduate Education and Research Training (IGERT) program.
UD's program, which began this fall, includes students and faculty from electrical and computer engineering, mechanical engineering, chemical engineering, materials science, chemistry, physics, economics and policy.
"We're looking forward to participating with our students in that program," Lauterbach said.
And until the current polymer textbooks are revised, Lauterbach and Snively also will take great relish when they ask their students to make note of a change in the margins.
"Right now, the excitement for us is that we've proven textbooks wrong," Lauterbach said.

(c) www.physorg.com

Secret Worlds: The Universe Within

  

View the Milky Way at 10 million light years from the Earth. Then move through space towards the Earth in successive orders of magnitude until you reach a tall oak tree just outside the buildings of the National High Magnetic Field Laboratory in Tallahassee, Florida. After that, begin to move from the actual size of a leaf into a microscopic world that reveals leaf cell walls, the cell nucleus, chromatin, DNA and finally, into the subatomic universe of electrons and protons.

Notice how each picture is actually an image of something that is 10 times bigger or smaller than the one preceding or following it. The number that appears on the lower right just below each image is the size of the object in the picture. On the lower left is the same number written in powers of ten, or exponential notation. Exponential notation is a convenient way for scientists to write very large or very small numbers. For example, compare the size of the Earth to the size of a plant cell, which is a trillion times smaller:

Earth = 12.76 x 10⁺⁶ = 12,760,000 meters wide
(12.76 million meters) Plant Cell = 12.76 x 10^-6 = 0.00001276 meters wide
(12.76 millionths of a meter)  

Scientists examine things in particular ways using a combination of very sophisticated equipment, everyday instruments, and many unlikely tools. Some phenomena that scientists want to observe are so tiny that they need a magnifying glass, or even a microscope. Other things are so far away that a powerful telescope must be used in order to see them. It is important to understand and be able to compare the size of things we are studying. To learn more about the relative sizes of things, visit our Perspectives: Powers of 10 activity site.

(C) www.micro.magnet.fsu.edu