10-09 :: September 2010

nanotimes News in Brief

then re-divided this sub-library into smaller units. These libraries then competed again in the same test reaction. This process was continued until the best individual catalysts were identified. Using this method, it was possible to identify excellent cata- lysts from a library of 120 by means of 17 individual experiments for each different class of substrate. This approach is clearly superior to the classic pro- cedure in which all 120 catalysts must be tested in parallel (therefore entailing 120 experiments) and a corresponding number of reaction analyses perfor- med. The approach is universally applicable and should be transferable to many problems associated with chemical and biochemical catalysis.

Joerg Wieland & Bernhard Breit: A combinatorial ap- proach to the identification of self-assembled ligands for rhodium-catalysed asymmetric hydrogenation, In: Nature Chemistry, Vol. 2(2010), October 2010, No 10, Pages 832-837, DOI:10.1038/nchem.800: http://dx.doi.org/10.1038/nchem.800

Researcher at Eindhoven University of Technolo- gy, The Netherlands, and European Synchrotron Radiation Facility (ESRF), France, disclose a stra- tegy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing out attractive noncovalent forces within the hydrophobic core of the polymerizing building blocks with electrostatic repulsive interactions on the hydrophilic rim we managed to switch from elongated, rod-like assemblies to small and discrete objects. Intriguingly this rod-to-sphere transition is expressed in a loss of cooperativity in the tempe- rature-dependent self-assembly mechanism. The

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aggregates were characterized using circular dichro- ism, UV and 1H-NMR spectroscopy, small angle X- ray scattering, and cryotransmission electron micro- scopy. In analogy to many systems found in biology, mechanistic details of the self-assembly pathways emphasize the importance of cooperativity as a key feature that dictates the physical properties of the produced supramolecular polymers.

Pol Beseniusa, Giuseppe Portaleb, Paul H. H. Bomansc, Henk M. Janssend, Anja R. A. Palmansa, and E. W. Meijer: Controlling the growth and shape of chiral supramolecu- lar polymers in water, In: PNAS Early Edition, October 4, 2010, DOI:10.1073/pnas.1009592107: http://dx.doi.org/10.1073/pnas.1009592107

The study of researchers from the Freiburg Insti- tute for Advanced Studies (FRIAS), University of Freiburg, Germany, Laboratoire de Chimie Bio- physique/ISIS, Universit de Strasbourg, France, and Physikalisch-Chemisches Institut, University Zurich, Switzerland provides both a structural and quantitative characterization of kinetically homogeneous substates present in bulk water. They find that the conformation-space network is highly modular, and that structural properties of water molecules are spatially correlated over at least two solvation shells. From a kinetic point of view, the free energy surface is characterized by multiple heterogeneous metastable regions with different populations and marginal barriers separating them. The typical time scale of hopping between them is 200−400 fs. A scanning in temperature reveals that those substates can be stabilized either entropical- ly or enthalpically. The latter resembles an icelike