Amine-Linked Single Molecule Circuits: Systematic Trends Across Molecular Families

A comprehensive review is presented of single molecule junction conductance measurements across families of molecules measured while breaking a gold point contact in a solution of molecules with amine end groups. A theoretical framework unifies the picture for the amine-gold link bonding and the tunnel coupling through the junction using Density Functional Theory based calculations. The reproducible electrical characteristics and utility for many molecules is shown to result from the selective binding between the gold electrodes and amine link groups through a donor-acceptor bond to undercoordinated gold atoms. While the bond energy is modest, the maximum force sustained by the junction is comparable to, but less than, that required to break gold point contacts. The calculated tunnel coupling provides conductance trends for all 41 molecule measurements presented here, as well as insight into the variability of conductance due to the conformational changes within molecules with torsional degrees of freedom. The calculated trends agree to within a factor of two of the measured values for conductance ranging from 10-7 G0 to 10-2 G0, where G0 is the quantum of conductance (2e2/h).Comment: Invited paper for forthcoming special issue of Journal of Physics: Condensed Matte

Oil. Geopolitics Reborn: Oil, Natural Gas, and Other Vital Resources

Competition over vital resources is a potent source of international friction among nations and within states. The result is the increasing interplay of international and internal struggles and the growing militarization of the global energy resource quest

From Scarcity to Abundance: The Changing Dynamics of Energy Conflict

Energy security and geopolitics have played a pivotal role in international affairs for a very long time, ever since the development of oil-powered vehicles and weapons of war. Until recently, the geopolitics of energy have largely been governed by perceptions of scarcity—the assumption that oil and other energy reserves were relatively limited, and that competition over their exploitation would lead to recurring crisis and conflict. However, the recent utilization of advanced extractive technologies—including deep-sea drilling and hydraulic fracturing—have resulted in unexpected production gains and fostered a sense that abundance, rather than scarcity, will govern the future energy picture. This perception, in turn, has led to expectations that conflict over energy will diminish. But the deployment of the new technologies has engendered new conflicts of its own, as in the disputes over offshore oil and natural gas deposits in the Arctic Ocean and the East and South China Seas. Also, many nations view energy as a critical source of wealth and power, and so they continue to spar over the ownership and exploitation of valuable reserves. Accordingly, the prospects for relative abundance are not likely to eliminate the risk of conflict over critical energy supplies

The New Geography of Conflict

During the Cold War, strategic planning focused on diverging ideological views between the United States and the Soviet blocs located in central and southeastern Europe and Northeast Asia. In the last decade these regions lost much strategic significance for the U.S. whereas other regions (e.g., Caspian Sea basin, the Gulf states, South China Sea) are receiving increased attention from Washington and other industrialized countries. A renewed concern of global resources, especially oil and natural gas, has created a new international, national and local geography of conflict. China and Russia have made their presence felt in key energy producing areas through foreign policy emphasis while Japan has demonstrated its concern by strengthening its fleet of warships and aircraft. Also industrializing nations of the developing world (e.g., Brazil, Malaysia, Turkey) have similar energy concerns. On a local scale conflicts have occurred over control of valuable timber, diamond fields and other export commodities. The mapping and spatial analysis of natural resources reveals that many critical sources of vital materials are located in contested or chronically unstable areas. Resource shortages and conflicts extend into other problems such as environmental degradation, transnational crime and ethnic conflicts. An analysis of global resource trends and their associated geopolitical phenomena provide policymakers with a basic tool towards resolving or reducing the risk of violent conflicts

The crystal structure of the C-terminal domain of the salmonella enterica pduo protein: An old fold with a new heme-binding mode

The two-domain protein PduO, involved in 1,2-propanediol utilization in the pathogenic Gram-negative bacterium Salmonella enterica is an ATP:Cob(I)alamin adenosyltransferase, but this is a function of the N-terminal domain alone. The role of its C-terminal domain (PduOC) is, however, unknown. In this study, comparative growth assays with a set of Salmonella mutant strains showed that this domain is necessary for effective in vivo catabolism of 1,2-propanediol. It was also shown that isolated, recombinantly-expressed PduOC binds heme in vivo. The structure of PduOC co-crystallized with heme was solved (1.9 \uc5 resolution) showing an octameric assembly with four heme moieities. The four heme groups are highly solvent-exposed and the heme iron is hexa-coordinated with bis-His ligation by histidines from different monomers. Static light scattering confirmed the octameric assembly in solution, but a mutation of the heme-coordinating histidine caused dissociation into dimers. Isothermal titration calorimetry using the PduOC apoprotein showed strong heme binding (Kd = 1.6 7 10 127 M). Biochemical experiments showed that the absence of the C-terminal domain in PduO did not affect adenosyltransferase activity in vitro. The evidence suggests that PduOC:heme plays an important role in the set of cobalamin transformations required for effective catabolism of 1,2-propanediol. Salmonella PduO is one of the rare proteins which binds the redox-active metabolites heme and cobalamin, and the heme-binding mode of the C-terminal domain differs from that in other members of this protein family

Light Weapons and Civil Violence: Policy Options for the International Community

Looks at the correlation between conflict and poverty in relation to inter-communal conflict within states and calls for policy initiatives to reduce the global diffusion of small arms and light weapons