Friday, April 8, 2011

New device promises safer way to deliver powerful drugs

A new drug delivery device designed and constructed by Jie Chen, Thomas Cesario and Peter Rentzepis promises to unlock the potential of photosensitive chemicals to kill drug-resistant infections and perhaps cancer tumors as well.

Photosensitive chemicals are molecules that release single oxygen atoms and chemical radicals when illuminated. These radicals are very active chemically, and can rip apart and destroy bacteria, said Peter Rentzepis, a professor of chemistry at University of California, Irvine.

Yet photosensitive chemicals are not approved for use in the United States, and used relatively rarely in Europe. This is because they are highly toxic and difficult to activate beneath the skin, since light only penetrates a few millimeters into the body.

Photosensitive chemicals also cause severe reactions, including headaches, nausea, and light sensitivity for 30 days. They kill healthy cells as well as bacteria. Although several have therapeutic potential, they are too toxic for human use by injection.

The researchers solved this problem with an optical fiber-based device that can deliver very small amounts of photosensitive chemicals to internal organs with pinpoint accuracy.

The device consists of three components. The first is an imaging component similar to the charge coupled devices (CCDs) in digital cameras. It enables a physician to guide the device to the infection.

A 1-millimeter-diameter flexible optical fiber attached micro sized high-power LED or laser diode provides the light for the CCD. Once the physician positions the device, the same light source shines with greater intensity to activate the medicine.

The third component is a hollow tube connected to a syringe of medicine to deliver the medicine to the infection. Rentzepis adds glycol, a thickening agent used in surgical soaps, to keep the medicine from spreading to healthy cells.

Pulling the syringe backwards creates a vacuum that sucks up any remaining chemical after the procedure.

"We can insert the instrument through the nose, bowels, mouth, or almost any opening and direct it where we want," Rentzepis said. "It lets us deliver very small amounts of these chemicals right to an infection or tumor, then remove them before they damage healthy cells."

The researchers plan to test the device on animals with infections and cancer.

Story Source:

The above story is reprinted  from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

‘Nanocrystal doping’ results in semiconductor nanocrystals with enhanced electrical function

Researchers at the Hebrew University of Jerusalem have achieved a breakthrough in the field of nanoscience by successfully altering nanocrystal properties with impurity atoms -- a process called doping -- thereby opening the way for the manufacture of improved semiconductor nanocrystals.

Semiconductor nanocrystals consist of tens to thousands of atoms and are 10,000 times smaller than the width of a human hair. These tiny particles have uses in a host of fields, such as solid-state lighting, solar cells and bio-imaging. One of the main potential applications of these remarkable materials is in the semiconductor industry, where intensive miniaturization has been taking place for the last 50 years and is now in the nanometer range.

However, these semiconductors are poor electrical conductors, and in order to use them in electronic circuits, their conductivity must be tuned by the addition of impurities. In this process, foreign atoms, called impurities, are introduced into the semiconductor, causing an improvement in its electrical conductivity.

Today, the semiconductor industry annually spends billions of dollars in efforts to intentionally add impurities into semiconductor products, which is a major step in the manufacturing of numerous electronic products, including computer chips, light emitting diodes and solar cells.

Due to the importance of doping to the semiconductor industry, researchers worldwide have made continuing attempts at doping nanocrystals in order to achieve ever greater miniaturization and to improve production methods for electronic devices. Unfortunately, these tiny crystals are resistant to doping, as their small size causes the impurities to be expelled. An additional problem is the lack of analytical techniques available to study small amounts of dopants in nanocrystals. Due to this limitation, most of the research in this area has focused on introducing magnetic impurities, which can be analyzed more easily. However, the magnetic impurities don't really improve the conductivity of the nanocrystal.

Prof. Uri Banin and his graduate student, David Mocatta, of the Hebrew University Center for Nanoscience and Nanotechnology, have achieved a breakthrough in their development of a straightforward, room- temperature chemical reaction to introduce impurity atoms of metals into the semiconductor nanocrystals. They saw new effects not previously reported. However, when the researchers tried to explain the results, they found that the physics of doped nanocrystals was not very well understood.

Bit by bit, in collaboration with Prof. Oded Millo of the Hebrew University and with Guy Cohen and Prof. Eran Rabani of Tel Aviv University, they built up a comprehensive picture of how the impurities affect the properties of nanocrystals. The initial difficulty in explaining this process proved to be a great opportunity, as they discovered that the impurity affects the nanocrystal in unexpected ways, resulting in new and intriguing physics.

"We had to use a combination of many techniques that when taken together make it obvious that we managed to dope the nanocrystals. It took five years but we got there in the end," said Mocatta.

This breakthrough was reported recently in the journal Science. It sets the stage for the development of many potential applications with nanocrystals, ranging from electronics to optics, from sensing to alternative energy solutions. Doped nanocrystals can be used to make new types of nanolasers, solar cells, sensors and transistors, meeting the exacting demands of the semiconductor industry.

Story Source:

The above story is reprinted from materials provided by The Hebrew University of Jerusalem, via EurekAlert!, a service of AAAS.

Journal Reference:

D. Mocatta, G. Cohen, J. Schattner, O. Millo, E. Rabani, U. Banin. Heavily Doped Semiconductor Nanocrystal Quantum Dots. Science, 2011; 332 (6025): 77 DOI: 10.1126/science.1196321

The 'molecular octopus': A little brother of 'Schroedinger’s cat'

For the first time, the quantum behaviour of molecules consisting of more than 400 atoms was demonstrated by quantum physicists based at the University of Vienna in collaboration with chemists from Basel and Delaware. The international and interdisciplinary team of scientists has set a new record in the verification of the quantum properties of nanoparticles.

In addition, an important aspect of the famous thought experiment known as 'Schroedinger's cat' is probed. However, due to the particular shape of the chosen molecules the reported experiment could be more fittingly called 'molecular octopus'.

The researchers report their findings in Nature Communications.

'Schroedinger's cat': simultaneously dead and alive?

Since the beginning of the 20th century, quantum mechanics has been a pillar of modern physics. Still, some of its predictions seem to disagree with our common sense and the observations in our everyday life. This contradiction was brought to the fore 80 years ago by the Austrian physicist Erwin Schroedinger; he wondered whether it was possible to realize states of extreme superposition such as, for example, that of a cat which is simultaneously dead and alive. This experiment has not been realized with actual cats for good reasons. Nevertheless, the successful experiments by Gerlich et al. show that it is possible to reproduce important aspects of this thought experiment with large organic molecules.

'Superposition' demonstrated for larger and larger molecules

In quantum physics, the propagation of massive particles is described by means of matter waves. In a certain sense, this means that the particles loose their classical property of a well-defined position and their quantum wave function can extend simultaneously over a large area. Formally, this state resembles that of a cat that is at the same time dead and alive. In quantum physics this is called a 'superposition'. Markus Arndt and his team at the University of Vienna tackle the question, up to which degree of complexity the amazing laws of quantum physics still apply. To this end, they investigate the quantum behaviour of molecules of increasing size, in particular their superposition at various positions in an interferometer. The high instability of most organic complexes, however, poses a major challenge in the process.

Tailor-made molecules solve the problem of instability

Many molecules break apart during the preparation of the thermal particle beam. Therefore, a close collaboration with chemists from Switzerland and the United States was crucial for the success of the recent experiments. The team of Marcel Mayor at the University of Basel and Paul J. Fagan from Central Research and Development of DuPont in Wilmington, DE, accomplished the synthesis of massive molecule complexes, which can survive the critical evaporation process.

A new record

The use of specifically synthesized organic molecules consisting of complexes of up to 430 atoms enabled the researchers to demonstrate the quantum wave nature in mass and size regimes that hitherto had been experimentally inaccessible. These particles are comparable in size, mass and complexity to Insulin molecules and exhibit many features of classical objects. Nevertheless, in the current experiment the tailor-made molecules can exist in a superposition of clearly distinguishable positions and therefore -- similar to 'Schroedinger's cat' -- in a state that is excluded in classical physics.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Vienna.

Journal Reference:

Stefan Gerlich, Sandra Eibenberger, Mathias Tomandl, Stefan Nimmrichter, Klaus Hornberger, Paul J. Fagan, Jens Tüxen, Marcel Mayor, Markus Arndt. Quantum interference of large organic molecules. Nature Communications, 2011; 2: 263 DOI: 10.1038/ncomms1263

Element germanium under pressure matches predictions of modern condensed matter theory

Although its name may make many people think of flowers, the element germanium is part of a frequently studied group of elements, called IVa, which could have applications for next-generation computer architecture as well as implications for fundamental condensed matter physics.

New research conducted by Xiao-Jia Chen, Viktor Struzhkin, and Ho-Kwang (Dave) Mao from Geophysical Laboratory at Carnegie Institution for Science, along with collaborators from China, reveals details of the element's transitions under pressure. Their results show extraordinary agreement with the predictions of modern condensed matter theory.

Germanium (atomic number 32) is used in fiber-optic systems, specialized camera and microscope lenses, circuitry, and solar cells. Under ambient conditions it is brittle and semiconducting. But under pressure, the element should exhibit superconductivity, meaning that there is no resistance to the flow of an electric current.

The team's research, published in Physical Review Letters, discovered that under pressure of 66 GPa (about 650,000 atmospheres), germanium undergoes a structural change from one type of solid material to another that is metallic -- meaning it conducts electricity. It then undergoes another structural change under pressure of 90 GPa (about 890,000 atmospheres). These findings matched theoretical predictions about the element's behavior under extreme pressure.

"A series of phase transitions was observed on compression of germanium that creates structures with increased density," Chen said. "We found extraordinary agreement between theory and experiment for the structures, energies, and compressional behavior. Though some of this behavior had been noted earlier, the agreement between the new highly accurate experimental results and theory really was quite remarkable."

The team's results show that superconductivity in this simple element is caused by phonons, or collective vibrations in the crystal structures that germanium assumes under pressure.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Carnegie Institution.

Journal Reference:

Xiao-Jia Chen, Chao Zhang, Yue Meng, Rui-Qin Zhang, Hai-Qing Lin, Viktor Struzhkin, Ho-kwang Mao. ß-tin›Imma›sh Phase Transitions of Germanium. Physical Review Letters, 2011; 106 (13) DOI: 10.1103/PhysRevLett.106.135502

Exploring the possibilities for zeolites: Team creates database of 2.6 million varieties of molecular sieves

 Some people collect stamps and coins, but when it comes to sheer utility, few collections rival the usefulness of Rice University researcher Michael Deem's collection of 2.6 million zeolite structures.

Zeolites are materials -- including some natural minerals -- that act as molecular sieves, thanks to a Swiss-cheese-like arrangement of pores that can sort, filter, trap and chemically process everything from drugs and petroleum to nuclear waste. Zeolites are particularly useful as catalysts -- materials that spur chemical reactions. There are about 50 naturally occurring zeolites and almost three times as many human-made varieties.

Deem's database, which is described in a new paper that will be featured on the cover of an upcoming issue of the Royal Society of Chemistry's journal Physical Chemistry Chemical Physics, hints at the untapped possibilities for making even more synthetic zeolites.

"For many catalytic applications only a single material has been found," said Deem, the John W. Cox Professor in Biochemical and Genetic Engineering and professor of physics and astronomy. "Expanding the diversity of the zeolite structures would be helpful to improve performance in existing applications, to explore novel functions and to answer basic scientific questions."

Zeolites are useful because of the particular way atoms are mixed and arranged in their porous interiors. Based on these arrangements, zeolites can cause chemicals to react in particular ways, and even subtle changes in the arrangements can alter the reactions that are spurred. Deem's database was created to explore the many zeolite structures that are physically possible, and he said several researchers are already using the information to identify zeolites that could be used for carbon sequestration and other applications.

"Computational methods can play a stimulatory role in the synthesis of new zeolite materials," Deem said. "That is the motivation; that is the challenge that brings us back to zeolites time and again."

In 2007, Deem and his students used both supercomputers and unused computing cycles from more than 4,300 idling desktop PCs to painstakingly calculate every conceivable atomic formulation for zeolites. They created a database of more than 3.4 million atomic formulations of the porous silicate minerals.

In the current study, Deem, Rice graduate student Ramdas Pophale and Purdue University computational analyst Phillip Cheeseman designed tools to examine and compare the physical properties of each entry. Using these tools, they pared down the larger set by removing potential redundancies as well as "low-energy" structures that would either be unstable or impossible to synthesize.

For each of the 2.6 million remaining structures in the database, the team carried out calculations to find specific physical and chemical properties -- including X-ray diffraction patterns, ring-size distributions and dielectric constants -- that could help guide researchers interested in synthesizing them or in finding a new type of zeolite for a specific application.

Deem said the new database has been deposited in the publicly available Predicted Crystallography Open Database.

The research was funded by the National Science Foundation.

Story Source:

The above story is reprinted from materials provided by Rice University.

Journal Reference:

Ramdas Pophale, Phillip A. Cheeseman, Michael W. Deem. A database of new zeolite-like materials. Physical Chemistry Chemical Physics, 2011; DOI: 10.1039/C0CP02255A

First polymer solar-thermal device heats home, saves money

A new polymer-based solar-thermal device is the first to generate power from both heat and visible sunlight -- an advance that could shave the cost of heating a home by as much as 40 percent.

Geothermal add-ons for heat pumps on the market today collect heat from the air or the ground. This new device uses a fluid that flows through a roof-mounted module to collect heat from the sun while an integrated solar cell generates electricity from the sun's visible light.

"It's a systems approach to making your home ultra-efficient because the device collects both solar energy and heat," said David Carroll, Ph.D., director of the Center for Nanotechnology and Molecular Materials at Wake Forest University. "Our solar-thermal device takes better advantage of the broad range of power delivered from the sun each day."

Research showing the effectiveness of the device appears in the March issue of the peer-reviewed journal Solar Energy Materials and Solar Cells.

A standard, rooftop solar cell will miss about 75 percent of the energy provided by the sun at any given time because it can't collect the longest wavelengths of light -- infrared heat. Such cells miss an even greater amount of the available daily solar power because they collect sunlight most efficiently between 10 a.m. and 2 p.m.

"On a rooftop, you have a lot of visible sunlight and heat from the infrared radiation," Carroll said. "The solar-cell industry has for the most part ignored the heat."

The design of the new solar-thermal device takes advantage of this heat through an integrated array of clear tubes, five millimeters in diameter. They lie flat, and an oil blended with a proprietary dye flows through them. The visible sunlight shines into the clear tube and the oil inside, and is converted to electricity by a spray-on polymer photovoltaic on the back of the tubes. This process superheats the oil, which would then flow into the heat pump, for example, to transfer the heat inside a home.

Unlike the flat solar cells used today, the curve of the tubes inside the new device allows for the collection of both visible light and infrared heat from nearly sunrise to sunset. This means it provides power for a much greater part of the day than does a normal solar cell.

Because of the general structure and the ability to capture light at oblique angles, this is also the first solar-thermal device that can be truly building-integrated -- it can be made to look nearly identical to roofing tiles used today.

Tests of the solar-thermal device have shown 30 percent efficiency in converting solar energy to power. By comparison, a standard solar cell with a polymer absorber has shown no greater than 8 percent conversion efficiency.

The research team will build the first square-meter-size solar-thermal cell this summer, a key step in getting the technology ready for market.

Story Source:

The above story is reprinted from materials provided by Wake Forest University, via EurekAlert!, a service of AAAS.

Chemists produce first high-resolution RNA 'nano square'

Chemists at UC San Diego have produced the first high resolution structure of a nano-scale square made from ribonucleic acid, or RNA.

The structure was published in a paper in this week's early online edition of the Proceedings of the National Academy of Sciences by a team of chemists headed by Thomas Hermann, an assistant professor of chemistry and biochemistry at UCSD.

The scientists said the ability to carry structural information encoded in the sequence of the constituent building blocks is a characteristic trait of RNA, a key component of the genetic code. The nano square self-assembles from four corner units directed by the sequence that was programmed into the RNA used for preparing the corners.

Hermann said the RNA square has potential applications as a self-assembling nano platform for the programmed combination of molecular entities that are linked to the corner units.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - San Diego. The original article was written by Kim McDonald.

Journal Reference:

Sergey M. Dibrov, Jaime Mclean, Jerod Parsons, Thomas Hermann. Self-assembling RNA square. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1017999108