875 resultados para Symmetries groups
Resumo:
A convenient methodology has been developed for the selective removal of the anomeric acyl group of carbohydrate derivatives using HCI04-Si02 under acidic reaction conditions. Anomeric benzoyl groups can also be removed selectively following similar reaction conditions. The yields were excellent in all cases.
Resumo:
The past decade has witnessed a period of intense economic globalisation. The growing significance of international trade, investment, production and financial flows appears to be curtailing the autonomy of individual nation states. In particular, globalisation appears to be encouraging, if not demanding, a decline in social spending and standards. However, many authors believe that this thesis ignores the continued impact of national political and ideological pressures and lobby groups on policy outcomes. In particular, it has been argued that national welfare consumer and provider groups remain influential defenders of the welfare state. For example, US aged care groups are considered to be particularly effective defenders of social security pensions. According to this argument, governments engaged in welfare retrenchment may experience considerable electoral backlash (Pierson 1996; Mishra 1999). Yet, it is also noted that governments can take action to reduce the impact of such groups by reducing their funding, and their access to policy-making and consultation processes. These actions are then justified on the basis of removing potential obstacles to economic competitiveness (Pierson 1994; Melville 1999).
Resumo:
The synthesis is reported of a new series of oligo(aryleneethynylene) (OAE) derivatives of up to ca. 6 nm in molecular length (OAE9) using iterative Pd-mediated Sonogashira cross-coupling methodology. The oligo-p-phenyleneethynylene cores of the molecular wires are functionalized at both termini with pyridyl units for attachment to gold leads. The molecular structures determined by single-crystal X-ray analysis are reported for OAE4, OAE5, OAE7, and OAE8a. The charge transport characteristics of derivatives OAE3–OAE9 in single-molecular junctions have been studied using the mechanically controlled break junction technique. The data demonstrate that the junction conductance decreases with increasing molecular length. A transition from coherent transport via tunneling to a hopping mechanism is found for OAE wires longer than ca. 3 nm.