Not only jewelry-loving ladies but also scientists and technologists are fascinated by gold–particularly in the form of the smallest clumps imaginable. Gold nanoparticles stand out through their unique optical, electronic, and catalytic properties and are the ideal "building blocks" for nanostructures. Composite materials with a one or two-dimensional arrangement of the gold nanoparticles are especially interesting for the construction of components on the nanoscale. Japanese scientists have now shown that crystals of organic compounds are the ideal partner for such gold composite materials. Gold nanoparticles do not colonize all the surfaces of the organic crystal evenly, they are choosy, and occupy only certain faces. The researchers working with Seiji Shinkai and Kazuki Sada employ millimeter-sized single crystals of the amino acid L-cystine. A single crystal is composed of a single, uniform crystal lattice. Cystine crystallizes in the form of hexagonal prisms. Such a crystal has two parallel hexagonal surfaces the edges of which are linked together by six rectangular faces. If the transparent crystal is immersed for two hours in a solution of gold nanoparticles it becomes purple. Under the microscope it can be seen that only the two hexagonal faces are purple. The sides, that is, the rectangular faces remain colorless. The purple coloration arises from deposited gold nanoparticles. Clearly the tiny gold particles are choosy and populate exclusively the hexagonal faces of the prism.
Why? The cystine molecules are arranged in layers in the crystal, these layers are parallel to the hexagonal faces. The layers are held together by a two-dimensional network of hydrogen bonds that run between the amino and the acid groups of the amino acid. These polar groups lie on the surface of the two hexagonal faces and attract the gold particles by electrostatic interactions. The rectangular faces, however, are made up of alternating layers of polar and nonpolar groups. The density of attractive polar groups here is too low to draw the gold particles onto these faces.
The face-selective coverage also works with microscale crystals. The gold coating could be used, for example, to selectively bind other materials. Through the attractive and repulsive forces between coated and uncoated faces of the crystals it should be possible to make the crystals stack in a direction-dependent manner and so form defined aggregate structures in a targeted fashion.
Author: Kazuki Sada, Kyushu University, Fukuoka (Japan), http://www.cstm.kyushu-u.ac.jp/shinkai/101/sada_H.htm
Title: Anisotropic Decoration of Gold Nanoparticles onto Specific Crystal Faces of Organic Single Crystals
Angewandte Chemie International Edition 2006, 45, No. 29, 4764–4767, doi: 10.1002/anie.200601470
Kazuki Sada | Angewandte Chemie
Novel mechanisms of action discovered for the skin cancer medication Imiquimod
21.10.2016 | Technische Universität München
Second research flight into zero gravity
21.10.2016 | Universität Zürich
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences