Palladium-mediated dealkylation of N-propargyl-floxuridine as a bioorthogonal oxygen-independent prodrug strategy

Herein we report the development and biological screening of a bioorthogonal palladium-labile prodrug of the nucleoside analogue floxuridine, a potent antineoplastic drug used in the clinic to treat advanced cancers. N-propargylation of the N3 position of its uracil ring resulted in a vast reduction of its biological activity (~6,250-fold). Cytotoxic properties were bioorthogonally rescued in cancer cell culture by heterogeneous palladium chemistry both in normoxia and hypoxia. Within the same environment, the reported chemo-reversible prodrug exhibited up to 1,450-fold difference of cytotoxicity whether it was in the absence or presence of the extracellular palladium source, underlining the precise modulation of bioactivity enabled by this bioorthogonally-activated prodrug strategy

Opto-Chemical Micro-Capillary Clocks

Opto-chemical capillary clocks are presented that are based on the measurement of a colored segment in a microchannel (a capillary). Color is created by a chromogenic chemistry involving the oxidation of a (virtually colorless) leuco-dye. Poly(ethylene glycol) (PEG) is used as a solvent, and indigo and thioindigo (in their reduced leuco forms) act as oxygen-sensitive dyes. The clock is started by removing one seal at the end of the capillary. A visible color change occurs as air diffuses into the microchannel due to an irreversible color reaction. The length of the colored segment is proportional to the time elapsed. PEGs of different average molar mass affect the diffusion rate of oxygen in the microchannel and thereby affect the rate of the migration of the color front. Both temperature and relative humidity exert a strong effect. Six types of such clocks are described that enable times to be determined in the range from 1 day to 6 months, possibly of even decades

Merging of metal nanoparticles driven by selective wettability of silver nanostructures

The welding and sintering of nanomaterials is relevant, for example, to form electrical contacts between metallic particles in printed electronic devices. Usually the welding of nanoparticles is achieved at high temperatures. Here we find that merging of two different metals, silver and gold nanoparticles, occurs on contact at room temperature. The merging process was investigated by experimental and molecular dynamics simulations. We discovered that the merging of these particles is driven by selective wettability of silver nanoparticles, independent of their size and shape (spheres or rods); silver behaves as a soft matter, whereas gold as a hard surface being wetted and retaining its original morphology. During that process, the silver atoms move towards the surface of the Au nanoparticles and wrap the Au nanoparticles in a pulling up-like process, leading to the wetting of Au nanoparticles. © 2014 Macmillan Publishers Limited

Active Control of Droplet Formation Process in Microfluidics

Controlling the size and the monodispersity of droplets is an important task in droplet-based microfluidics. A closed-loop control mechanism with actuation and sensing of droplet size is ideal for systems that require a high degree of monodispersity. Most droplet-based microfluidic systems control the size of droplets using the flow rates, applied pressures, and flow rate ratios. These concepts are based on the hydrodynamic interactions during the formation process of droplets and requires a relatively long time to stabilize. Changing flow rates and pressures requires the control of external components such as pumps and pressure controllers. This chapter discusses in situ active control of the formation process. The advantage of this approach is that the control signal in the form of a voltage or a current can be induced into the system allowing immediate response. The control schemes are categorized and discussed according to their actuation concepts: thermal and magnetic actuation.No Full Tex