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Chemical Function (chemical + function)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Tribochemistry of tetrahedral hydrogen-free amorphous carbon coatings in the presence of OH-containing lubricants

LUBRICATION SCIENCE, Issue 2 2008
C. Matta
Abstract Diamond-like carbon (DLC) films are gaining attention for its use in a wide range of tribological applications because of their low friction coefficient and high wear resistance. Recently, ultra-low friction or superlubricity as low as 0.006 has been observed between hydrogen-free DLC films lubricated with oil containing a glycerol mono-oleate (GMO) additive. Consequently, there are many efforts to understand their detailed tribological behaviour. In this study, first, a characterisation of a pristine hydrogen-free tetrahedral amorphous DLC coating (denoted as ta-C) is presented. The technique used for ta-C characterisation is the energy-filtered transmission electron microscopy studied on a focus ion beam cross section of the coating. Then, to simulate the action of GMO, which is used as an additive in engine oils, and to understand its mechanism of action in boundary lubrication conditions, simple and shorter molecules such as pure glycerol and hydrogen peroxide are used in friction tests. These two molecules and GMO have the same alcohol chemical function. Friction tests in the presence of pure glycerol and hydrogen peroxide are presented. Moreover, to understand the properties of these two molecules, the overtone of GMO and their reaction mechanism in boundary lubrication, liquid phase lubrication was simulated by gas phase lubrication. Results show that very low friction coefficients are obtained with no apparent wear. Finally, the mechanisms of ultra-low friction are investigated by the wetting method and the X-ray photoelectron spectroscopy (XPS) technique. These two techniques are used to identify the physical (wetting method) and chemical (XPS) changes occurring at the ta-C surface after friction. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Finding evolutionary relations beyond superfamilies: Fold-based superfamilies

PROTEIN SCIENCE, Issue 10 2003
Keiko Matsuda
Abstract Superfamily classifications are based variably on similarity of sequences, global folds, local structures, or functions. We have examined the possibility of defining superfamilies purely from the viewpoint of the global fold/function relationship. For this purpose, we first classified protein domains according to the ,-sheet topology. We then introduced the concept of kinship relations among the classified ,-sheet topology by assuming that the major elementary event leading to creation of a new ,-sheet topology is either an addition or deletion of one ,-strand at the edge of an existing ,-sheet during the molecular evolution. Based on this kinship relation, a network of protein domains was constructed so that the distance between a pair of domains represents the number of evolutionary events that lead one from the other domain. We then mapped on it all known domains with a specific core chemical function (here taken, as an example, that involving ATP or its analogs). Careful analyses revealed that the domains are found distributed on the network as >20 mutually disjointed clusters. The proteins in each cluster are defined to form a fold-based superfamily. The results indicate that >20 ATP-binding protein superfamilies have been invented independently in the process of molecular evolution, and the conservative evolutionary diffusion of global folds and functions is the origin of the relationship between them. [source]

Engineered Polymer Brushes by Carbon Templating

ADVANCED MATERIALS, Issue 28 2009
Marin Steenackers
A general method for the fabrication of stable polymer brushes of programmable three-dimensional shapes and different chemical functions is presented. The carbon templating method allows the functionalization of a broad variety of substrates without the need of a specific surface chemistry. As an example, the AFM scan of complex polymer brush structures on a bare GaAs substrate is shown. [source]

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008
Michiya Fujiki
Abstract Strong chemical forces such as covalent and ionic bonds are responsible for building discrete molecules, nature dwells on noncovalent forces weaker by three orders in magnitude, like the hydrophobic effect, hydrogen bonding, and van der Waals forces. Despite being weak, they possess the potential to drive spontaneous folding or unfolding of proteins and nucleic acids and the recognition between complimentary molecular surfaces. The power of these forces lies in the cooperativity with which they act, thereby generating a cumulative effect of many bonding interactions occurring together. Many ongoing research aims to translate the potential of these forces to the synthetic world to create desired structures with specific chemical functions. Achieving this offers unlimited opportunities for designing and synthesizing the most complex structures with specific applications. This highlight aims to reflect the critical role these noncovalent forces play in controlling macromolecular structures, which hold immense untapped potential for applications defying conventions, and briefly touches on the concept of homochirality in nature based on chiral and weak noncovalent interactions in synthetic nonpolar Si-catenated polymers. It sheds some light on the discovery and characterization of Si/F-C interactions in fluoroalkylated polysilanes in chemosensing of fluoride ions and nitroaromatics with a great sensitivity and selectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4637,4650, 2008 [source]