Rapid, easy-to-use, and portable devices that can provide a read-out without the need for expensive equipment represent the future of sensing technology, with applications in areas like environmental, food, chemical, and biological safety. Enzymes immobilized on a surface function as micropumps in the presence of species (e.g., substrate, cofactor, or biomarker) that trigger the enzymatic reaction. The flow speed in these devices increases with increasing reaction rate. This allows the detection of substances that inhibit the enzymatic reaction. Using this principle, sensors for toxic substances, like mercury, cadmium, cyanide, and azide, were designed using urease and catalase-powered pumps, respectively, with limits of detection well below the concentrations permitted by the Environmental Protection Agency. The study was also extended to other inhibitors for these enzymes. The sensing range of fluid flow-based inhibitor assays depends on the type of inhibition, the enzyme concentration on the sensing platform, and, for competitive inhibition, the concentration of substrate used.

While momentum transfer from active particles to their immediate surroundings has been studied for both synthetic and biological micron-scale systems, a similar phenomenon was presumed unlikely to exist at smaller length scales due to the dominance of viscosity in the ultralow Reynolds number regime. Using diffusion NMR spectroscopy, we studied the motion of two passive tracers—tetramethylsilane and benzene—dissolved in an organic solution of active Grubbs catalyst. Significant enhancements in diffusion were observed for both the tracers and the catalyst as a function of reaction rate. A similar behavior was also observed for the enzyme urease in aqueous solution. Surprisingly, momentum transfer at the molecular scale closely resembles that reported for microscale systems and appears to be independent of swimming mechanism. Our work provides new insight into the role of active particles on advection and mixing at the Ångström scale.

While momentum transfer from active particles to their immediate surroundings has been studied for both synthetic and biological micron-scale systems, a similar phenomenon was presumed unlikely to exist at smaller length scales due to the dominance of viscosity in the ultralow Reynolds number regime. Using diffusion NMR spectroscopy, we studied the motion of two passive tracers—tetramethylsilane and benzene—dissolved in an organic solution of active Grubbs catalyst. Significant enhancements in diffusion were observed for both the tracers and the catalyst as a function of reaction rate. A similar behavior was also observed for the enzyme urease in aqueous solution. Surprisingly, momentum transfer at the molecular scale closely resembles that reported for microscale systems and appears to be independent of swimming mechanism. Our work provides new insight into the role of active particles on advection and mixing at the Ångström scale.

Nanoroboter, die scheinbar wundersame Aufgaben ausführen, kennen wir aus dem Reich der Science-Fiction.1 Obwohl natürlich Vieles davon immer Fiktion bleiben wird, haben Wissenschaftler einige der physikalischen Herausforderungen, die mit dem Betrieb von Funktionseinheiten auf kleinster Skala einhergehen, überwunden und die erste Generation von autonomen energieautarken Nanomotoren und Nanopumpen entwickelt. Diese Motoren können durch chemische und Lichtgradienten gelenkt werden, Fracht aufnehmen und transportieren und kollektives Verhalten zeigen.

Carbohydrates, such as fructose, can be fully dehydroxylated to 2,5-dimethyltetrahydrofuran (DMTHF), a valuable chemical and potential gasoline substitute, by the use of a dual catalytic system consisting of HI and RhX₃ (X=Cl, I). A mechanistic study has been carried out to understand the roles that both acid and metal play in the reaction. HI serves a two-fold purpose: HI acts as a dehydration agent (loss of 3 H₂O) in the initial step of the reaction, and as a reducing agent for the conjugated carbinol group in a subsequent step. I₂ is formed in the reduction step and metal-catalyzed hydrogenation reforms HI. The rhodium catalyst, in addition to catalyzing the reaction of iodine with hydrogen, functions as a hydrogenation catalyst for CO and CC bonds. A general mechanistic scheme for the overall reaction is proposed based on identification of intermediates, independent reactions of the intermediates, and deuterium labeling studies.

The use of swarms of nanobots to perform seemingly miraculous tasks is a common trope in the annals of science fiction.1 Although several of these remarkable feats are still very much in the realm of fiction, scientists have recently overcome many of the physical challenges associated with operating on the small scale and have generated the first generation of autonomous self-powered nanomotors and pumps. The motors can be directed by chemical and light gradients, pick up and deliver cargo, and exhibit collective behavior.

Titanium dioxide (TiO₂) possesses high photocatalytic activity, which can be utilized to power the autonomous motion of microscale objects. This paper presents the first examples of TiO₂ micromotors and micropumps. UV-induced TiO₂ reversible microfireworks phenomenon was observed and diffusiophoresis has been proposed as a possible mechanism.

Existing technologies to produce liquid fuels from biomass are typically energy-intensive, multistep processes. Many of these processes use edible biomass as starting material. Carbohydrates, such as mono- and polysaccharides and cellulose, typically constitute 50–80 % of plant biomass. Herein, we report that hexose from a wide range of biomass-derived carbohydrates, cellulose, and even raw lignocellulose (e.g., corn stover) can be converted into 2,5-dimethyltetrahydrofuran (DMTHF) in one step, in good yields and under mild conditions in water. Under the same conditions, 2-methyltetrahydrofuran is formed from pentose. The reaction employs a soluble rhodium catalyst, dihydrogen, and HI/HCl+NaI. The catalytic system is robust and can be recycled repeatedly without loss of activity. DMTHF is superior to ethanol and has many of the desirable properties currently found in typical petroleum-derived transportation fuels.

The first copolymerization of acrylate and methacrylate with nonpolar 1-alkenes in the presence of Brønsted acids as complexation agents has been reported. The addition of both homogeneous and heterogeneous Brønsted acids resulted in increased monomer conversion and 1-alkene incorporation. Further, the heterogeneous Brønsted acids can be recycled without loss of activity. A direct correlation exists between the ability of the Lewis or Brønsted acid to bind to the ester group of the acrylate/methacrylate monomer and its ability to promote the copolymerization reaction. For Lewis acids, there is also a direct correlation between the charge/size ratio at the metal center and their ability to promote copolymerizations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5499–5505, 2008