Plane J.M.C.,University of Leeds
Chemical Society Reviews | Year: 2012
This review discusses the magnitude of the cosmic dust input into the earth's atmosphere, and the resulting impacts from around 100 km to the earth's surface. Zodiacal cloud observations and measurements made with a spaceborne dust detector indicate a daily mass input of interplanetary dust particles ranging from 100 to 300 tonnes, which is in agreement with the accumulation rates of cosmic-enriched elements (Ir, Pt, Os and super-paramagnetic Fe) in polar ice cores and deep-sea sediments. In contrast, measurements in the middle atmosphere - by radar, lidar, high-flying aircraft and satellite remote sensing - indicate that the input is between 5 and 50 tonnes per day. There are two reasons why this huge discrepancy matters. First, if the upper range of estimates is correct, then vertical transport in the middle atmosphere must be considerably faster than generally believed; whereas if the lower range is correct, then our understanding of dust evolution in the solar system, and transport from the middle atmosphere to the surface, will need substantial revision. Second, cosmic dust particles enter the atmosphere at high speeds and undergo significant ablation. The resulting metals injected into the atmosphere are involved in a diverse range of phenomena, including: the formation of layers of metal atoms and ions; the nucleation of noctilucent clouds, which are a sensitive marker of climate change; impacts on stratospheric aerosols and O 3 chemistry, which need to be considered against the background of a cooling stratosphere and geo-engineering plans to increase sulphate aerosol; and fertilization of the ocean with bio-available Fe, which has potential climate feedbacks. © The Royal Society of Chemistry 2012. Source
Halcrow M.A.,University of Leeds
Chemical Society Reviews | Year: 2011
Spin-crossover compounds are becoming increasingly popular for device and sensor applications, and in soft materials, that make use of their switchable colour, paramagnetism and conductivity. The de novo design of new solid spin-crossover compounds with pre-defined switching properties is desirable for application purposes. This challenging problem of crystal engineering requires an understanding of how the temperature and cooperativity of a spin-transition are influenced by the structure of the bulk material. Towards that end, this critical review presents a survey of molecular spin-crossover compounds with good availability of crystallographic data. A picture is emerging that changes in molecular shape between the high- and low-spin states, and the ability of a lattice to accommodate such changes, can play an important role in determining the existence and the cooperativity of a thermal spin-transition in the solid state (198 references). © 2011 The Royal Society of Chemistry. Source
Halcrow M.A.,University of Leeds
Chemical Society Reviews | Year: 2013
This tutorial review discusses the structural and electronic consequences of the Jahn-Teller effect in transition metal complexes, focussing on copper(ii) compounds which tend to be the most studied. The nature of a Jahn-Teller distortion in molecular complexes and extended lattices can be manipulated by application of pressure or temperature, by doping a molecule into a host lattice, or simply by molecular design. Many of these results have been achieved using compounds with a trans-[CuX4Y2] coordination sphere, which seems to afford copper centres that are particularly sensitive to their environment. Jahn-Teller distortions lead to some unusual phenomena in molecular magnetism, and are important to the functionality of important classes of conducting and superconducting ceramics. © 2013 The Royal Society of Chemistry. Source
University of Leeds | Date: 2014-03-21
There are provided collagen based polymeric materials comprising collagen molecules and/or collagen derived molecules which have been functionalised by the addition of one or more ethylenically unsaturated moieties and which have been cross-linked via said moieties. Also provided are collagen based compositions and methods of producing collagen based polymeric materials.
University of Leeds | Date: 2015-10-20
There is described a material comprising tapes, ribbons, fibrils or fibres characterized in that each of the ribbons, fibrils or fibres have an antiparallel arrangement of peptides in a -sheet tape-like substructure.