Active and driven hydrodynamic crystals

Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structures of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single-particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals.     

Hamiltonian traffic dynamics in microfluidic-loop networks

Recent microfluidic experiments revealed that large particles advected in a fluidic loop display long-range hydrodynamic interactions. However, the consequences of such couplings on the traffic dynamics in more complex networks remain poorly understood. In this Letter, we focus on the transport of a finite number of particles in one-dimensional loop networks. By combining numerical, theoretical, and experimental efforts, we evidence that this collective process offers a unique example of Hamiltonian dynamics for hydrodynamically interacting particles. In addition, we show that the asymptotic trajectories are necessarily reciprocal despite the microscopic traffic rules explicitly break the time-reversal symmetry. We exploit these two remarkable properties to account for the salient features of the effective three-particle interaction induced by the exploration of fluidic loops.     

Synthesis of 4H-3,1-benzoxazines, quinazolin-2-ones, and quinoline-4-ones by palladium-catalyzed oxidative carbonylation of 2-ethynylaniline derivatives

An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 degrees C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu(4)NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.     

Intestinal absorption of tellurium studied with stable tracers

An investigation on tellurium metabolism by administration of stable tellurium isotopes¹²⁴Te and¹²⁶Te has been performed. Fractional intestinal absorption was determined in rabbits by the double tracer technique. The investigated subjects were given an enriched solution of one tellurium isotope orally and a few minutes later an enriched solution of the other isotope intravenously. The¹²⁴Te and¹²⁶Te contents in plasma samples were determined by proton nuclear activation. The methodology described offers a means to study tellurium metabolism in humans without radiation risk.     

Stable and radioactive tracers in Ru biokinetic studies

The feasibility of ruthenium metabolism studies by stable tracer administration, with a methodology based on proton nuclear activation, is presented. In order to test that the amount of stable tracer administered does not perturb significantly the mechanism investigated, a series of comparative experiments with administration of both radioactive and stable tracers has been performed on animals. As the most critical pathway seems to be the intravenous injection, four male rabbits were given an intravenous injection of radioactive¹⁰⁶Ru. Successively, the rabbits were given either a further injection of radioactive¹⁰⁶Ru or injection of different quantities of natural Ru. The activity of¹⁰⁶Ru and the concentration of natural Ru were measured in plasma samples withdrawn at different time intervals from the injections and the results were compared. Some biokinetic parameters and tissue distribution of Ru in rabbits were determined.Died on February 21, 1993.     

A palladium iodide-catalyzed carbonylative approach to functionalized pyrrole derivatives

A novel and convenient approach to functionalized pyrroles is presented, based on Pd-catalyzed oxidative heterocyclization-alkoxycarbonylation of readily available N-Boc-1-amino-3-yn-2-ols. Reactions were carried out in alcoholic solvents at 80-100 °C and under 20 atm (at 25 °C) of a 4:1 mixture of CO-air, in the presence of the PdI(2)-KI catalytic system (2-5 mol % of PdI(2), KI/PdI(2) molar ratio = 10). In the case of N-Boc-1-amino-3-yn-2-ols 3, bearing alkyl or aryl substituents, the carbonylation reaction led to a mixture of Boc-protected and N-unsubstituted pyrrole-3-carboxylic esters 4 and 5, respectively. This mixture could be conveniently and quantitatively converted into deprotected pyrrole-3-carboxylic esters 5 by a simple basic treatment. In the case of diastereomeric (3RS,4RS)- and (3RS,4SR)-N-Boc-3-amino-2-methyldec-5-yn-4-ol (syn-3f and anti-3f, respectively, whose relative configuration was determined by X-ray crystallographic analysis), no particular difference was observed in the reactivity of the two diastereomers between them and with respect to the diastereomeric mixture (3S,4S) + (3S,4R). Interestingly, N-Boc-2-alkynyl-1-amino-3-yn-2-ols 6, bearing an additional alkynyl substituent α to the hydroxyl group, spontaneously underwent N-deprotection under the reaction conditions and regioselective water addition to the alkynyl group at C-3 of the corresponding pyrrole-3-carboxylic ester derivative, thus directly affording highly functionalized pyrrole derivatives 7 in one step. In a similar manner, a novel functionalized dihydropyrrolizine derivative 9 was directly synthesized starting from (S)-7-(pyrrolidin-2-yl)trideca-5,8-diyn-7-ol 8.     

A Palladium‐Catalyzed Carbonylation Approach to Eight‐Membered Lactam Derivatives with Antitumor Activity

The reactivity of 2‐(2‐alkynylphenoxy)anilines under PdI₂/KI‐catalyzed oxidative carbonylation conditions has been studied. Although a different reaction pathway could have been operating, N‐palladation followed by CO insertion was the favored pathway with all substrates tested, including those containing an internal or terminal triple bond. This led to the formation of a carbamoylpalladium species, the fate of which, as predicted by theoretical calculations, strongly depended on the nature of the substituent on the triple bond. In particular, 8‐endo‐dig cyclization preferentially occurred when the triple bond was terminal, leading to the formation of carbonylated ζ‐lactam derivatives, the structures of which have been confirmed by XRD analysis. These novel medium‐sized heterocyclic compounds showed antitumor activity against both estrogen receptor‐positive (MCF‐7) and triple negative (MDA‐MB‐231) breast cancer cell lines. In particular, ζ‐lactam 3 j′ may represent a novel and promising antitumor agent because biological tests clearly demonstrate that this compound significantly reduces cell viability and motility in both MCF‐7 and MDA‐MB‐231 breast cancer cell lines, without affecting normal breast epithelial cell viability.