Coulomb blockade and the Kondo effect in single-atom transistors

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.     

Angiotensin-converting enzyme 2 is an essential regulator of heart function

Cardiovascular diseases are predicted to be the most common cause of death worldwide by 2020. Here we show that angiotensin-converting enzyme 2 (ace2) maps to a defined quantitative trait locus (QTL) on the X chromosome in three different rat models of hypertension. In all hypertensive rat strains, ACE2 messenger RNA and protein expression were markedly reduced, suggesting that ace2 is a candidate gene for this QTL. Targeted disruption of ACE2 in mice results in a severe cardiac contractility defect, increased angiotensin II levels, and upregulation of hypoxia-induced genes in the heart. Genetic ablation of ACE on an ACE2 mutant background completely rescues the cardiac phenotype. But disruption of ACER, a Drosophila ACE2 homologue, results in a severe defect of heart morphogenesis. These genetic data for ACE2 show that it is an essential regulator of heart function in vivo.     

Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors

One of the central aims of ecology is to identify mechanisms that maintain biodiversity. Numerous theoretical models have shown that competing species can coexist if ecological processes such as dispersal, movement, and interaction occur over small spatial scales. In particular, this may be the case for non-transitive communities, that is, those without strict competitive hierarchies. The classic non-transitive system involves a community of three competing species satisfying a relationship similar to the children's game rock-paper-scissors, where rock crushes scissors, scissors cuts paper, and paper covers rock. Such relationships have been demonstrated in several natural systems. Some models predict that local interaction and dispersal are sufficient to ensure coexistence of all three species in such a community, whereas diversity is lost when ecological processes occur over larger scales. Here, we test these predictions empirically using a non-transitive model community containing three populations of Escherichia coli. We find that diversity is rapidly lost in our experimental community when dispersal and interaction occur over relatively large spatial scales, whereas all populations coexist when ecological processes are localized.     

Rutile U-Pb age for the ultrahigh pressure eclogite from the Dabie Mountains,central China: Evidence for rapid cooling

The U-Pb isotope compositions of rutile, omphacite and garnet in the eclogite from the Jinheqiao area in the Southern Dabie ultrahigh-pressure metamorphic zone were analyzed. The consistent high precision U-Pb age (218 ± 1.2) Ma of rutile in eclogite from the Dabie Mountains was obtained by two ways of isochron and common Pb correction based on the composition of omphacite. This proves that the omphacite in eclogite has a U/Pb ratio (m = 2.8) low enough to be used for common Pb correction in the analyses of rutile. Under the rapid cooling condition (40℃/Ma) the closure temperature for U-Pb diffusion in rutile is about 470℃. Thus, this U-Pb age of rutile proves that 218 Ma should be the cooling age of eclogite at 470℃ instead of the peak metamorphic age.     

Differential multiplicity of MDR alcohol dehydrogenases: enzyme genes in the human genome versus those in organisms initially studied

Screens were made for alcohol dehydrogenase (ADH) of the classical type (the MDR superfamily) in translations of human and other relevant genomes, corresponding to the organism types from which the enzyme was initially purified. Considerable multiplicities were detected in the dimeric enzymes from higher eukaryotes: seven forms in the human (plus three pseudogenes), all genes on chromosome 4, in the order class IV --> class Igamma --> class Ibeta --> class Ialpha --> class V --> class II --> class III, and eight forms in Arabidopsis thaliana (plus one pseudogene). These multiplicity patterns, and the species variability in the animal (human/mouse) and plant (Arabidopsis/pea) lines, suggest parallel but separate duplicatory events, giving rise to three families of dimeric MDR-ADH: class III, the animal non-class III, and the plant non-class III enzymes, with functions in formaldehyde elimination, in alcohol/aldehyde detoxication and in special pathways in higher eukaryotes. Multiplicity, although to a lesser extent, was also noted in tetrameric MDR-ADH, suggesting functional divergence between the dimeric and tetrameric enzymes. Combining these observations, at least five levels of divergence are reflected in the present ADH forms, corresponding to nodes at the SDR/MDR, the dimer/tetramer, the class III/non-class III, the class I/P, and the more recent class splits, each branch associated with separate functional patterns.