Limited contribution of permafrost carbon to methane release from thawing peatlands

Models predict that thaw of permafrost soils at northern high-latitudes will release tens of billions of tonnes of carbon (C) to the atmosphere by 21001-3. The effect on the Earth's climate depends strongly on the proportion of this C which is released as the more powerful greenhouse gas methane (CH4), rather than carbon dioxide (CO2)1,4; even if CH4 emissions represent just 2% of the C release, they would contribute approximately one quarter of the climate forcing5. In northern peatlands, thaw of ice-rich permafrost causes surface subsidence (thermokarst) and water-logging6, exposing substantial stores (10s of kg C m-2, ref. 7) of previously-frozen organic matter to anaerobic conditions, and generating ideal conditions for permafrost-derived CH4 release. Here we show that, contrary to expectations, although substantial CH4 fluxes (>20 g CH4 m 2 yr-1) were recorded from thawing peatlands in northern Canada, only a small amount was derived from previously-frozen C (<2 g CH4 m-2 yr-1). Instead, fluxes were driven by anaerobic decomposition of recent C inputs. We conclude that thaw-induced changes in surface wetness and wetland area, rather than the anaerobic decomposition of previously-frozen C, may determine the effect of permafrost thaw on CH4 emissions from northern peatlands

Targeting the hypoxic fraction of tumours using hypoxia activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high priority target and one therapeutic strategies designed to eradicate hypoxic cells in tumours are a group of compounds known collectively as hypoxia activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (i) the ability of oxygen to either reverse or inhibit the activation process and (ii) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples

Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells

This work was supported by the Engineering and Physical Sciences Research Council (grant number EP/I013288/1) and from the European Union Seventh Framework Programme under grant agreement 321305.The morphology of bulk heterojunction organic photovoltaic cells defines many of the device performance characteristics. Measuring the morphology is challenging due to the small length scales and low contrast between organic materials. Here we have utilised nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high performance blend. We show that optimised blends consist of elongated fullerene-rich and polymer-rich fibre-like domains which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion which helps extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene spheres show a much lower efficiency of charge extraction of ~45% which is attributed to poor electron and hole transport. Our results show that formation of narrow and elongated domains are desirable in bulk heterojunction solar cells.Publisher PDFPeer reviewe