PRESS-NEWS.org - Press Release Distribution
PRESS RELEASES DISTRIBUTION

Molecules pass through nanotubes at size-dependent speeds

2013-09-12
(Press-News.org) CAMBRIDGE, MA -- Like a pea going through a straw, tiny molecules can pass through microscopic cylinders known as nanotubes. This could potentially be used to select molecules according to size — for example, to purify water by allowing water molecules to pass through while blocking salt or other substances.

Now, researchers at MIT, Seoul University in Korea and Ursinus College in Pennsylvania have found that such tubes are more selective than had been thought: Molecules of a precise size can zip through five times faster than those that are a bit smaller or larger. The new findings are published in the journal Nature Communications by MIT professor Michael Strano, graduate students Wonjoon Choi and Zachary Ulissi, and three others.

This size-dependence in nanotube transport was completely unexpected, says Strano, a professor of chemical engineering at MIT. "This work illustrates how transport in pores of this type remains exotic and relatively unexplored," he says.

The team "looked at ion transport through the smallest single nanopores that have been studied," Strano says. The carbon nanotubes they studied had widths ranging from 0.9 to 2 nanometers — about the diameter of a DNA helix — and were about 1 millimeter long.

"What we found was not predicted by theory," he says: Up to a certain diameter, the flow of ions through a nanotube increased steadily — but then beyond that diameter, the flow decreased. "The dependence is a volcano-shaped plot," Strano says.

The peak flow, at the center of that plot, allows transport that is five times greater than transport at smaller or larger diameters. "The experimental results are counterintuitive," Strano says, "that there appears to be an optimal diameter."

This size-dependence of transport could turn out to be useful in a variety of technologies, he suggests, including proton-exchange membrane (PEM) fuel cells, where molecules of oxygen or hydrogen must pass through tiny pores in a membrane to produce electricity. Another potential application is in DNA-sequencing devices, where DNA segments typically hurtle through pores much too quickly to be analyzed. The new understanding may provide a method for "tuning" the transit speed to slow the DNA sequences enough for analysis.

The unexpected size-dependence results from two phenomena, Strano suggests. According to a theory developed by the team, there is first an attractive force, in which ions' electrical charge causes them to be pulled by an electric field through the pore. Since the ions and the tubes are all submerged in water, some water gets pulled along as well.

Up to a certain diameter, those water molecules form a layer, or a few layers, around the ion and are pulled along with it, the team theorizes. But as the opening gets bigger, the water behaves as a bulk material, slowing the ions' passage. "This explanation is consistent with our experimental observations and molecular simulations of water inside of nanotubes of this type," Strano says — though he stresses that while the data on the ion flow is clear-cut, additional theoretical work is needed to fully understand this process.

The finding may help in designing better membranes for desalination of water. The biggest problem with today's membranes is the tradeoff between selectivity versus flow rates: Bigger pores let the water flow through faster, but are less selective. Nanotubes' nonlinear response may provide a way around that.

"The results suggest that by using nanopores of a specific diameter, it may be possible to achieve maximum selectivity with maximum throughput" by optimizing the pore size, Strano says.

The work could also lead to new sensors capable of detecting specific contaminants in water, the team says. For example, arsenic contamination of groundwater is a serious health concern in some regions, but there is no reliable way of testing arsenic concentrations in water. The selectivity of nanotubes might make it possible to design a simple detector that could measure such contamination, Strano says.

INFORMATION:

In addition to Choi and Ulissi, the work was carried out by MIT graduate students Steven Shimizu and Darin Bellisario, as well as Mark Ellison of Ursinus.

The work was supported by the U.S. Department of Energy and Department of Defense.

Written by David Chandler, MIT News Office

END



ELSE PRESS RELEASES FROM THIS DATE:

A century of human impact on Arctic climate indicated by new models, historic aerosol data

2013-09-12
(RENO): The Arctic is the most rapidly warming region of the globe, but warming has not been uniform and the drivers behind this warming not fully understood even during the 20th century. A new study authored by Canadian and American investigators and published in Scientific Reports, a primary research publication from the publishers of Nature, suggests that both anthropogenic and natural factors – specifically sulphate aerosols from industrial activity and volcanic emissions, in addition to greenhouse gas releases from fossil fuel burning – account for Arctic surface ...

Acetylcholine secretion by motor neuron-like cells from UC-MSC

2013-09-12
Basic fibroblast growth factor exhibits a high affinity for heparin. Heparin combined with basic fibroblast growth factor significantly contributes to the differentiation of umbilical cord mesenchymal stem cells into motor neurons. Xueyuan Liu and colleagues from Liaoning Medical University found that the third passage of umbilical cord mesenchymal stem cells induced with heparin and basic fibroblast growth factor exhibited neuronal morphology, and Hb9 expression and acetylcholine levels increased following induction with heparin combined with basic fibroblast growth factor. ...

Does longer sevoflurane preconditioning contribute to better neuroprotective effects?

2013-09-12
Sevoflurane belongs to volatile anesthetics, and preconditioning with sevoflurane has been shown to exert protective effects against ischemic injury in the brain. But the mechanism is unclear. Although studies have shown the neuroprotective effects of sevoflurane preconditioning in the transient cerebral ischemia model, its effect in the permanent focal cerebral ischemia model remains unclear. Dr. Qiu and colleagues from Sichuan University found that 60-minute sevoflurane preconditioning significantly reduced the infarct volume and the number of apoptotic cells in the ischemic ...

Inner ear hair cell regeneration: A look from the past to the future

2013-09-12
Since Moffat and Ramsden for the first time discovered the possibility of the auditory system in humans in 1977, over the last two decades, great progress has been made in physiopathological research on neurosensory hearing loss. Jørgensen and Mathiesen were the first authors to note the capacity for regeneration of the normal vestibular epithelium in adult Australian parrots. Later, Roberson et al studied the normal vestibular epithelium of 12-day-old white Leghorn chicks using tritiated thymidine and bromodeoxyuridine. Francisco Santaolalla and colleagues from Basurto ...

Researchers hit virtual heads to make safer games

2013-09-12
PULLMAN, Wash. – Two nearly identical softballs, both approved for league play, can have dramatically different effects when smacked into a player's head. Those are the findings from a study conducted by Professor Lloyd Smith in the School of Mechanical and Materials Engineering and project engineer Derek Nevins that they will present at the Asia Pacific Congress on Sports Technology later this month in Hong Kong. Their work was published in the journal, Procedia Engineering. Smith's group developed a unique model of a softball that they electronically throw at a virtual ...

The efficient choice among combustion engines

2013-09-12
Researchers at ETH Zurich have developed an internal combustion engine that emits less than half the CO2 compared to a regular engine without compromising performance. This corresponds to fuel consumption of less than 2.4l per 100km. This natural gas-diesel hybrid engine is based on a system of sophisticated control engineering. The global energy markets are changing. New extraction methods are tapping into oilfields and natural gas deposits that have been inaccessible until now. The US, for example, is able to cover up to 83% of its total energy needs today; the government ...

Delaying climate policy would triple short-term mitigation costs

2013-09-12
Higher costs would in turn increase the threshold for decision-makers to start the transition to a low-carbon economy. Thus, to keep climate targets within reach it seems to be most relevant to not further postpone mitigation, the researchers conclude. "The transitional economic repercussions that would result if the switch towards a climate-friendly economy is delayed, are comparable to the costs of the financial crisis the world just experienced," lead-author Gunnar Luderer says. The later climate policy implementation starts, the faster – hence the more expensive – ...

Pulsating dust cloud dynamics modeled

2013-09-12
The birth of stars is an event that eludes intuitive understanding. It is the collapse of dense molecular clouds under their own weight that offers the best sites of star formation. Now, Pralay Kumar Karmakar from the Department of Physics at Tezpur University, Assam province, India, and his colleague have proposed a new model for investigating molecular cloud fluctuations at sites of star formation and thus are able to study their pulsational dynamics, in a paper published in EPJ D. Dust molecular clouds are a type of astrophysical plasmas, which are composed of a primordial ...

More than just type 1 or type 2: DiMelli study points to different forms of diabetes

2013-09-12
The DiMelli (Diabetes Mellitus Incidence Cohort Registry) study examines the frequency and characteristics of diabetes phenotypes in children and young adults below the age of 20. The study was commissioned to investigate the increasing incidence of diabetes mellitus, particularly in childhood and early adulthood. The project is funded by the German Center for Diabetes Research (DZD). Bioprobe measurements were performed centrally by the Central Medical Laboratory (LMZ) at the Helmholtz Zentrum München (HMGU) so as to guarantee the high quality and comparability of laboratory ...

Codeine could increase users' sensitivity to pain

2013-09-12
Using large and frequent doses of the pain-killer codeine may actually produce heightened sensitivity to pain, without the same level of relief offered by morphine, according to new research from the University of Adelaide. Researchers in the Discipline of Pharmacology have conducted what is believed to be the world's first experimental study comparing the pain relieving and pain worsening effects of both codeine and morphine. The University's Professor Paul Rolan, who is also a headache specialist at the Royal Adelaide Hospital, says codeine has been widely used as ...

LAST 30 PRESS RELEASES:

Reality check: making indoor smartphone-based augmented reality work

Overthinking what you said? It’s your ‘lizard brain’ talking to newer, advanced parts of your brain

Black men — including transit workers — are targets for aggression on public transportation, study shows

Troubling spike in severe pregnancy-related complications for all ages in Illinois

Alcohol use identified by UTHealth Houston researchers as most common predictor of escalated cannabis vaping among youths in Texas

Need a landing pad for helicopter parenting? Frame tasks as learning

New MUSC Hollings Cancer Center research shows how Golgi stress affects T-cells' tumor-fighting ability

#16to365: New resources for year-round activism to end gender-based violence and strengthen bodily autonomy for all

Earliest fish-trapping facility in Central America discovered in Maya lowlands

São Paulo to host School on Disordered Systems

New insights into sleep uncover key mechanisms related to cognitive function

USC announces strategic collaboration with Autobahn Labs to accelerate drug discovery

Detroit health professionals urge the community to act and address the dangers of antimicrobial resistance

3D-printing advance mitigates three defects simultaneously for failure-free metal parts 

Ancient hot water on Mars points to habitable past: Curtin study

In Patagonia, more snow could protect glaciers from melt — but only if we curb greenhouse gas emissions soon

Simplicity is key to understanding and achieving goals

Caste differentiation in ants

Nutrition that aligns with guidelines during pregnancy may be associated with better infant growth outcomes, NIH study finds

New technology points to unexpected uses for snoRNA

Racial and ethnic variation in survival in early-onset colorectal cancer

Disparities by race and urbanicity in online health care facility reviews

Exploring factors affecting workers' acquisition of exercise habits using machine learning approaches

Nano-patterned copper oxide sensor for ultra-low hydrogen detection

Maintaining bridge safer; Digital sensing-based monitoring system

A novel approach for the composition design of high-entropy fluorite oxides with low thermal conductivity

A groundbreaking new approach to treating chronic abdominal pain

ECOG-ACRIN appoints seven researchers to scientific committee leadership positions

New model of neuronal circuit provides insight on eye movement

Cooking up a breakthrough: Penn engineers refine lipid nanoparticles for better mRNA therapies

[Press-News.org] Molecules pass through nanotubes at size-dependent speeds