La integración local: reactivar una solución olvidada

La posibilidad de integrar localmente a los refugiados se ha visto reforzada gracias a determinados acontecimientos históricos simultáneos, un cambio en las políticas gubernamentales y la reanudación de las actividades de ACNUR

Ligand and counterion control of Ag(I) architectures: Assembly of a {Ag-8} ring cluster mediated by hydrophobic and Ag center dot center dot center dot Ag interactions

A strategy combining ligand design and counterion variation has been used to investigate the assembly of silver(I) complexes. As a result, dinuclear, octanuclear, and polymeric silver(I) species have been synthesized by complexation of the rigid aliphatic amino ligands cis-3,5-diamino-trans-hydroxycyclohexane (DAHC), cis-3,5-diamino- transmethoxycyclohexane (DAMC), and cis-3,5-diamino-trans-tert-butyidimethylsilylanyloxycyclohexane (DATC) with silver(I) triflate, nitrate, and perchlorate. The compositions of these aggregates, established by X-ray crystallography and elemental analysis, are [fAg(DAHC)}(2)](CF3SO3)(2) (1), [{Ag(DAMC)}(2)](CF3SO3)(2) (2), [{Ag(DAMC)}(2)](NO3)(2) (3), [{Ag-(DATC)}(6){Ag(DAHC)}(2)](NO3)(8) (4), and [{Ag(DATC}(n)](NO3)(n) (5), where the DAHC present in 4 is formed by in situ hydrolysis of the acid labile silyl ether group. The type of aggregate formed depends both upon the noncoordinating O-substituent of the ligand and the (also noncoordinating) counterion, with the normal preference of the ligand topology for forming Ag2L2 structures being broken by introduction of the bulky, lipophilic O-tert-butyidimethylsilyl (TBDMS) group. Of particular note is the octanuclear silver ring structure 4, which is isolated only when both the O-TBDMS group and the nitrate counteranion are present and is formed from four Ag2L2 dimers; connected by Ag center dot center dot center dot Ag and hydrogen-bonding interactions. Diffusion rate measurement of this {Ag-8} complex by H-1 NMR (DOSY) indicates dissociation in CD3OD and CD3CN, showing that this supramolecular ring structure is formed upon crystallization, and establishing a qualitative limit to the strength of Ag center dot center dot center dot Ag interactions in solution. When solutions of the {Ag-8} cluster in methanol are kept for several days though, a new UV-vis absorption is observed at around 430 nm, consistent with the formation of silver nanoparticles.</p

Optimal design and operation for a droplet-based PCR chip

A two-temperature continuous-flow PCR polymer chip has been constructed that takes advantage of droplet technology to avoid sample contamination and adsorption at the surface. Samples contained in aqueous droplets are continuously moved by an oil carrier-fluid through various temperature zones, introducing the possibility of real-time quantitative PCR. The use of droplet technology also makes it possible to perform high throughput analyses of single cells allowing the study of populations of cells and facilitating a more comprehensive understanding of biological variance with relation to disease. In the present device, the thermal cycling time is significantly reduced and the PCR samples are exposed to more uniform temperatures. This paper investigates many of the factors affecting droplet-based PCR chip design, including specific heat capacity, density, flow rate, and thermal resistance. The study focuses particularly on the fluid and substrate temperature distribution within the PCR chip and the droplet residence times in critical temperature zones. The results show that, in general, the carrier-fluid should have a low thermal mass to ensure minimal heating and cooling times. It was found that the predicted temperature distribution in the chip arises from a subtle thermal interaction between the substrate and the carrier-fluid. The simulations demonstrate that the flow rate strongly affects the carrier-fluid's temperature field. Above a critical flow rate, the carrier-fluid fails to achieve the temperatures required for DNA amplification. Moreover, the thermal resistance of the different layers is shown to have a major impact on the temperature profile in the channel

Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 μg L−1 and 0.6 μg L−1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals. Graphical abstract