[6-C]-(2S,4S)-5-Chloroleucine: synthesis and incubation studies with cultures of the cyanobacterium, Lyngbya majuscula

[6-¹³C]-(2S,4S)-5-Chloroleucine 12 was prepared in six steps and 26% overall yield from protected l-glutamic acid using ¹³CH₃I as the source of isotopic label. On feeding 12 to cultures of L. majuscula no incorporation of isotopic label into the trichlorinated marine natural product barbamide was detected. The synthesis of a novel dichloroleucine derivative 16 is also described.     

Magnetic movement of biological fluid droplets

Magnetic fields can be used to control the movement of aqueous drops on non-patterned, silicon nanowire superhydrophobic surfaces. Drops of aqueous and biological fluids are controlled by introducing magnetizable carbonyl iron microparticles into the liquid. Key elements of operations such as movement, coalescence, and splitting of water and biological fluid drops, as well as electrochemical measurement of an analyte are demonstrated. Superhydrophobic surfaces were prepared using vapor–liquid–solid (VLS) growth systems followed by coating with a perfluorinated hydrocarbon molecule. Drops were made from aqueous and biological fluid suspensions with magnetizable microparticle concentrations ranging from 0.1 to 10 wt%.     

A remarkably simple chemicoenzymatic approach to structurally complex bicyclo[3.1.0]hexane carbocyclic nucleosides

[reaction: see text] Intramolecular cyclopropanation of a carbene engendered from the corresponding diazo beta-ketoester produced the desired bicyclo[3.1. 0]hexane pseudosugar. Purine nucleosides obtained via Mitsunobu coupling were resolved with adenosine deaminase. The requisite beta-ketoester was assembled in one step from ethyl acetoacetate and acrolein.     

Conformationally constrained analogues of diacylglycerol. 24. Asymmetric synthesis of a chiral (R)-DAG-lactone template as a versatile precursor for highly functionalized DAG-lactones

[structure: see text] Commercially available 2-methylenepropane-1,3-diol was converted to chiral epoxide (R)-2 via Sharpless asymmetric epoxidation in >96% ee. Regiospecific epoxide ring opening and reduction of the intermediate alkyne set the stage for a one-pot lactonization to give (R)-6, a convenient precursor for all functionalized chiral DAG-lactones used as potent PK-C ligands. The synthesis of the most potent DAG-lactones known to date, (Z)-10 and (E)-10, served to confirm PK-C's exclusive preference for the (R)-stereochemistry in this class of compounds.     

Synthesis of transition metal complexes containing a Schiff base ligand derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-aminobenzenethiol

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-aminobenzenethiol subunits is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-aminobenzenethiol leads to the isolation of 2,9-bis(2-benzothiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with cobalt, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptophenyl)-2-azaethene]-1,10-phenanthroline (L). The [Cu(L)ClO₄][ClO₄] and [M(L)X₂] complexes (where M = Co(II), Ni(II) and Zn(II) and X = Br) were characterized by physical and spectroscopic measurements which indicated that the ligand is acting probably as a tetradentate N₄ chelating agent.     

Nucleation rate measurement of colloidal crystallization using microfluidic emulsion droplets

An emulsion crystallization method has been demonstrated to measure the nucleation rate of a thermoresponsive colloidal poly-N-isopropylacrylamide (PNIPAM) system. The colloidal PNIPAM suspension was injected into a microfluidic flow-focusing device to generate monodispersed droplets in oil. The temperature was controlled to fine tune the volume fraction of the PNIPAM particles, and the microfluidic flow rate was varied to change the droplet sizes, thus altering the nucleation volume. Using independent droplets, we can isolate the nucleation events to eliminate the interactions among crystallites that existed in bulk or large droplet systems. Therefore, we were able to carry out accurate nucleation rate measurements of colloidal crystals. This emulsion crystallization method is promising for bridging the gap among theories, simulations, and experiments for nucleation kinetics studies.     

Temperature-responsive semipermeable capsules composed of colloidal microgel spheres

We present semipermeable, hollow capsules (colloidosomes) that expand and contract upon heating and cooling. The capsules are composed of micrometer-sized poly(N-isopropylacrylamide)-co-acrylic acid microgel particles, which exhibit a reversible size transition near 34 degrees C. The microgel particles assemble on the surfaces of water droplets in oil. Addition of the diblock copolymer poly(butadiene-b-N-methyl 4-vinyl pyridinium iodide) to the oil results in soft, elastic membranes of microgel particles that remain intact after the droplet interfaces are dissolved. Under heating, the capsules contract reversibly by 13% or irreversibly by 40% in radius. These stimulus-responsive colloidosomes might be useful for controlled release or as microscopic actuators.