Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Molecular Chains Line Up to Form Protopolymer

08.12.2004


First observation of extended chains of molecules that exhibit a strong interaction without forming chemical bonds


Protopolyphenylene is composed of molecules lined up for reaction and held in place by the copper substrate surface and intermolecular interactions. The image of a 270-angstrom (27-nanometer) square area of the surface was recorded with a scanning tunneling microscope at 77 K in ultrahigh vacuum. The ridged ring structure is the protopolymer; the angled lines are one-atom-high steps of the copper substrate.



A new chemical state, designated a "protopolymer," has been observed by Penn State researchers in chains of phenylene molecules on a crystalline copper surface at low temperature. Protopolymers form when monomers, small molecules that link together chemically to form long chains, align and interact without forming chemical bonds. The novel structures were discovered by Paul S. Weiss, professor of chemistry and physics at Penn State and Gregory S. McCarty, a graduate student at time of discovery and now a research assistant professor of engineering science and mechanics. While surface-mediated pairing and other interactions have previously been seen on metal surfaces, this is the first observation of extended chains of molecules that exhibit a strong interaction without forming chemical bonds. This type of alignment could be used to control growth and assembly of molecules and for manipulation of nanostructured materials, which are assembled on an atomic or molecular scale. Nanostructured materials often exhibit very different properties from those made by conventional techniques. A paper describing the research results, titled "Formation and Manipulation of Protopolymer Chains," will be published in the Journal of the American Chemical Society on 15 December 2004.

Weiss points out that in substrate-mediated interactions, those in which the surface participates in the electronic interactions between molecules, the surface itself acts as a catalyst, holding molecules in place and enabling them to align for reaction. "If we use substrate-mediated interactions to direct the arrangement of monomers prior to chemical bonding, we may be able to build atomically precise structures," says Weiss. "The key is to understand how the electronic functions of the molecule-surface interaction drive reactions and how they can be used to enhance chemical selectivity."


The researchers carried out the experiments in a low temperature scanning tunneling microscope (STM) under ultrahigh vacuum by exposing a close-packed copper surface to p-diiodobenzene molecules. On the surface, the molecules dissociate into phenylene (cyclic C6H4) reaction intermediates and two iodine atoms. The positions of these phenylene molecules are observed by STM. Extended structures self-assembled as long chains on the surface. While individual phenylene molecules remain mobile, molecules in the chains did not move under the imaging conditions. They were able to extract molecules from the chains, however, by applying voltage pulses to the STM tip. This suggests that the chains are not covalently bound together, but instead are held by electronic reactions between molecules that are mediated by the surface. These chains extended across atomic steps on the copper surface where the level of the surface drops by one atom, resembling a stair step. This is a region in which electronic perturbations would be expected to disrupt the continuity. "It amazed us that these extended structures could cross step boundaries," Weiss says. "These monomers have not yet formed covalent chemical bonds, which would link them together as a large molecule, but they are aligned and their interaction is much stronger than any previously observed."

Weiss and McCarty were surprised to find that although the protopolymer is ’ready’ to form a molecule, individual units can still be manipulated and even pulled out of the chain. The protopolymer chains were stationary on the copper surface, but short chains on a phenylene-coated copper surface could be moved with the STM tip. The existence of this bonding state could potentially have significant implications for supramolecular design. These intermolecular interactions could be used to place compounds together like a jigsaw puzzle into complex structures based on the choice of assembly units and substrate surfaces--one more step toward the molecular design and engineering of new nanostructured materials.

This research was funded, in part, by the National Science Foundation, the Defense Advanced Research Projects Agency (DARPA), and the Office of Naval Research.

Barbara K. Kennedy | EurekAlert!
Further information:
http://www.psu.edu

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Mice provide insight into genetics of autism spectrum disorders

28.06.2017 | Health and Medicine

New photoacoustic technique detects gases at parts-per-quadrillion level

28.06.2017 | Physics and Astronomy

Funding of Collaborative Research Center developing nanomaterials for cancer immunotherapy extended

28.06.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>