Entity

Time filter

Source Type


Corral A.,Campus Universitari | Osso A.,Autonomous University of Barcelona | Llebot J.E.,Autonomous University of Barcelona
Nature Physics | Year: 2010

The influence of climate variability and global warming on the occurrence of tropical cyclones is a controversial issue 1-10. Existing historical databases on the subject are not fully reliable 9,11-13, but a more fundamental hindrance is the lack of basic understanding regarding the intrinsic nature of tropicalcyclone genesis and evolution 14. It is known that tropical cyclones involve more than a passive response to changing external forcing 15, but it is not clear which dynamic behaviour best describes them. Herewe present an approach based on the application of the power dissipation index, which constitutes an estimation of released energy 3, to individual tropical cyclones. A robust law emerges for the statistics of power dissipation index, valid in four different ocean basins and over long time periods. In addition to suggesting a description of the physics of tropical cyclones in terms of critical phenomena 16,17, the scaling law enables us to quantify their response to changing climatic conditions, with an increase in the largest power dissipation index values with sea surface temperature or the presence of El Niño phenomena, depending on the basin under consideration. In this way, we demonstrate that the recent upswing in North Atlantic hurricane activity does not involve tropical cyclones that are quantitatively different from those in other sustained high-activity periods before 1970. © 2010 Macmillan Publishers Limited. All rights reserved. Source


Haq S.,University of Liverpool | Hanke F.,University of Liverpool | Sharp J.,University of Liverpool | Persson M.,University of Liverpool | And 3 more authors.
ACS Nano | Year: 2014

The heterocoupling of organic building blocks to give complex multicomponent macromolecules directly at a surface holds the key to creating advanced molecular devices. While "on-surface" synthesis with prefunctionalized molecules has recently led to specific one-and two-component products, a central challenge is to discover universal connection strategies that are applicable to a wide range of molecules. Here, we show that direct activation of C-H bonds intrinsic to π-functional molecules is a highly generic route for connecting different building blocks on a copper surface. Scanning tunneling microscopy (STM) reveals that covalent π functional macromolecular heterostructures, displaying diverse compositions, structures and topologies, are created with ease from seven distinct building blocks (including porphyrins, pentacene and perylene). By exploiting differences in C-H bond reactivity in the deposition and heating protocols we also demonstrate controlled synthesis of specific products, such as block copolymers. Further, the symmetry and geometry of the molecules and the surface also play a critical role in determining the outcome of the covalent bond forming reactions. Our "pick-mix-and-link" strategy opens up the capability to generate libraries of multivariate macromolecules directly at a surface, which in conjunction with nanoscale probing techniques could accelerate the discovery of functional interfaces. © 2014 American Chemical Society. Source


Rodrigues M.,University of Barcelona | Calpena A.C.,University of Barcelona | Amabilino D.B.,Campus Universitari | Garduno-Ramirez M.L.,Autonomous University of the State of Morelos | Perez-Garcia L.,University of Barcelona
Journal of Materials Chemistry B | Year: 2014

A novel physical gel was obtained using a gemini imidazolium-based amphiphilic molecule dissolved in ethanol-water mixtures. The structure of the gel is comprised of intertwining nanofibres with widths of approximately 80 nm. The ethanol/water ratio has an important influence on the gelation process: the gelator is sparingly soluble in water and soluble in ethanol. The gelator is capable of incorporating anionic drugs in its fibrillar network easily; sodium ibuprofenate, indomethacin and the sodium salt of methotrexate were used as model drugs that were incorporated into the quickly forming gels. The characterization of these composite xerogels was made by different microscopy techniques as well as X-ray powder diffraction. The ability of the amphiphile to form a gel is largely maintained in the presence of the different model drugs and the overall morphology of the gels (that present a fibre like structure in all cases with intertwined ribbons) is very similar. Furthermore the in vitro release of the drugs from the gel and the in vivo anti-inflammatory efficacy was studied. The overall results show better release profiles and anti-inflammatory efficacy for indomethacin, and prove the promise of this molecular gel in controlled drug release, in the present case dermatological application. © 2014 the Partner Organisations. Source


Haq S.,University of Liverpool | Hanke F.,University of Liverpool | Dyer M.S.,University of Liverpool | Persson M.,University of Liverpool | And 4 more authors.
Journal of the American Chemical Society | Year: 2011

The direct coupling of complex, functional organic molecules at a surface is one of the outstanding challenges in the road map to future molecular devices. Equally demanding is to meet this challenge without recourse to additional functionalization of the molecular building blocks and via clean surface reactions that leave no surface contamination. Here, we demonstrate the directional coupling of unfunctionalized porphyrin molecules- large aromatic multifunctional building blocks- on a single crystal copper surface, which generates highly oriented one-dimensional organometallic macromolecular nanostructures (wires) in a reaction which generates gaseous hydrogen as the only byproduct. In situ scanning tunneling microscopy and temperature programmed desorption, supported by theoretical modeling, reveal that the process is driven by C-H bond scission and the incorporation of copper atoms in between the organic components to form a very stable organocopper oligomer comprising organometallic edge-to-edge porphyrin-Cu-porphyrin connections on the surface that are unprecedented in solution chemistry. The hydrogen generated during the reaction leaves the surface and, therefore, produces no surface contamination. A remarkable feature of the wires is their stability at high temperatures (up to 670 K) and their preference for 1D growth along a prescribed crystallographic direction of the surface. The on-surface formation of directional organometallic wires that link highly functional porphyrin cores via direct C-Cu-C bonds in a single-step synthesis is a new development in surface-based molecular systems and provides a versatile approach to create functional organic nanostructures at surfaces. © 2011 American Chemical Society. Source


Riobe F.,Campus Universitari | Schenning A.P.H.J.,TU Eindhoven | Amabilino D.B.,Campus Universitari
Organic and Biomolecular Chemistry | Year: 2012

Induction of chirality in achiral aggregates of an oligo(p- phenylenevinylene) has been used to detect the enantiomeric excess in acids used in the resolution of chiral compounds. The chiral acids which induce helicity in the aggregates are present at only 10% of the concentration of the chromophore, whose chiroptical activity can be detected using circular dichroism spectroscopy. An ee of 10% in mixtures of (+) and (-) acids has been clearly evidenced in a series of samples using only 1.5 μg and concentration of approximately 10 μM of the chiral compound. The composition of both carboxylic and phosphoric acid derivatives can be detected, thanks to their binding to the dimerised core ureidotriazine unit attached at one end of the oligo(p-phenylenevinylene) which induces a preferred twist in the aggregated aromatic rod. This chiral arrangement is reflected in the Cotton effects that the assemblies show. The sign of the induced dichroic signal can be affected by the substituents around a stereogenic centre of otherwise identical configuration, and can lead to ambidextrous assemblies as seen in Cotton effects at different positions for different acids. While this technique can be used to detect enantiomeric excess, screening of the pure enantiomers is wise prior to the use of the method to detect scalemic mixtures. This supramolecular approach to evaluation of chiral content in samples could also be applied to other types of aggregates based on achiral molecules which show sensitivity to molecular chiral inducers. © 2012 The Royal Society of Chemistry. Source

Discover hidden collaborations