Month: June 2001

from the Molectronics dept.
Researchers led by Paul S. Weiss at Penn State and and James M. Tour at Rice University, report in the 22 June 2001 issue of Science have demonstrated single molecules that switch between "on" and "off" states, and then hold in a state for hours at a time. The function of their molecular switches is based in part on conformational changes — which happen when molecules alter their arrangement by rotation of their atoms around a single bond, effectively changing shape by moving or turning — determine how and when that conductance switching occurs in those molecules. Additional coverage can be found in this article ("Single-molecule computer switches advance", by K. Hearn, 21 June 2001) from United Press International.

As described in their report, they tracked over time the conductance switching of single and bundled phenylene ethynylene oligomers isolated in matrices of alkanethiolate monolayers. The persistence times for isolated and bundled molecules in either the ON or OFF switch state ranged from seconds to tens of hours. When the surrounding matrix is well ordered, the rate at which the inserted molecules switch is low. When the surrounding matrix is poorly ordered, the inserted molecules switch more often. As a result, the team concluded that the switching is a result of conformational changes in the molecules or bundles, rather than electrostatic effects of charge transfer.
Funding for the research was provided by the Army Research Office, the Defense Advanced Research Projects Agency, the National Science Foundation, the Office of Naval Research, and Zyvex LLC

Although the Science paper is not freely available on the web, supplemental data and images that show the single and bundled molecules switching on and off within the matrices, are available on the Weiss group website.

from the RNA-World dept.
Researchers at the Whitehead Institute for Biomedical Research have created a custom-designed RNA catalyst, or a ribozyme. The ribozyme can use information from a template RNA to make a third, new RNA. It functions with more than 95 percent accuracy, and most importantly, its ability is not restricted by the length or the exact sequence of letters in the original template. The ribozyme can extend an RNA strand, adding up to 14 nucleotides, or letters, to make up more than a complete turn of an RNA helix. The study also provides some insights into the possibility that RNA catalysts were important in the early evolution of living systems. The results are described in the 18 May 2001 issue of Science.

from the just-a-moment dept.
Researchers have devised a method to determine the alignment of a molecule's axis, the "poles" that govern how a molecule will interact with others. The advancement will help scientists and engineers predict the ways that atoms and molecules exchange energy, possibly enhancing solar energy devices or helping biochemists better understand proteins. The research, appearing in the 4 June 2001 issue of Physical Review Letters, shows how a tightly-focused laser employing a new kind of polarization can produce valuable images of individual molecules in three dimensions.
The new method takes a snapshot of a phenomenon called the "molecular dipole moment." This "moment" is an axis that runs through the molecule like a north and south pole, along which energy is emitted and absorbed. If two molecules are positioned so that their respective poles align, they are more likely to exchange energy. If they are completely misaligned, then an interaction is more difficult. The researchers hope the work may lead to control of the alignment to direct chemical reactions at the atomic level.

from the in-a-spin dept.
A research team at the University of California at Berkeley has built a scanning tunneling microscope that can measure for the first time the quantum spin of an electronic state of a single atom, in this case an impurity atom embedded in the material. Previously, scientists have had to trap isolated atoms and zap them with a laser to measure their spin state. While the technique already has improved understanding of high temperature superconductors, it also can help probe the spin states of atoms in metals and semiconductors, as well as new materials such as carbon nanotubes or strontium ruthenate superconductors. The researchers also believe their work has potential application in quantum computers. It is thought that quantum computers could take advantage of two-level quantum states such as this to perform calculations far faster than conventional transistor-based computers, and in the process shrink the size of computers immensely. "One of the holy grails of solid state physics is to write and store information in just one atom," said J. C. Seamus Davis, the head of the Berkeley team.

More information is available on the research teamís website.