N-Amination of pyrrole and indole heterocycles with monochloramine (NH2Cl)

A survey of several electrophilic ammonia reagents for the N-amination of indole- and pyrrole-containing heterocycles revealed that monochloramine (NH(2)Cl) is an excellent reagent for this transformation. Pyrroles and indoles containing a variety of substitution were aminated on nitrogen with isolated yields ranging from 45% to 97%.     

A comparison of the solid-state structures of a series of phenylseleno-halogen and pseudohalogen compounds,PhSeX (X = Cl,CN, SCN)

Structural and spectroscopic data on the series of compounds “PhSeX”, where X = Cl, CN or SCN, are reported and compared with previously reported data on “PhSeX” systems (X = Br and I). The chloro-compound displays a “square” motif, Ph₄Se₄Cl₄, in the solid state, linked by long Se–Se bonds [2.993(3)–3.035(3) Å], and forms a loosely held network of Se₄ and Cl₄ squares in its extended structure. In contrast, the pseudohalogen derivatives, PhSeCN and PhSeSCN, consist of essentially monomeric units, which form chains held together by weak Se?N interactions in the solid state. These Se?N interactions are much shorter in PhSeCN, 3.023(3)–3.065(4) Å, than in PhSeSCN, 3.348(4) Å. Weaker Se?N contacts are also present between the chains. The structure of PhSeSCN described here is the first reported crystallographic study of a selenium thiocyanate compound. Spectroscopic studies suggest that all three compounds exist as monomers in solution. The results reported herein illustrate the subtle differences in the solid-state structures of PhSeX compounds.     

Tunable band structure effects on ballistic transport in graphene nanoribbons

Graphene nanoribbons (GNR) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of the applied fields on its own preserves the even symmetry Ek=E−k of the subband dispersion. When applied together, they reverse the dispersion parity to be odd and gives Ee,k=−Eh,−k and mix the electron and hole subbands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range.     

Growth and dc conductivity studies of tripotassium sodium dichromate single crystal

DC electrical conductivity studies were carried out along the three crystallographic axes for tripotassium sodium dichromate (K₃Na(CrO₄)₂ or KNCr). Earlier studies of phase transition in this crystal show successive phase transitions at 239 K and 853 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303–430 K along the crystallographic axes. An anomaly in conductivity was obtained around 326 K along both the axes. This may be attributed as due to a newly observed phase transition in the crystal. DSC taken for the sample also shows exothermic peak supporting the occurrence of newly observed phase transition.     

Microfluidic cell arrays for metabolic monitoring of stimulated cardiomyocytes

An array of PDMS microchambers was aligned to an array of sensor electrodes and stimulating microelectrodes, which was used for the electrochemical monitoring of the metabolic activity of single isolated adult ventricular myocytes inside the chamber array, stimulated within a transient electric field. The effect of the accumulation of metabolic byproducts in the limited extracellular volume of the picolitre chambers was demonstrated by measuring single muscle cell contraction optically, while concomitant changes in intracellular calcium transients and pH were recorded independently using fluorescent indicator dyes. Both the amplitude of the cell shortening and the magnitude of the intracellular calcium transients decreased over time and both nearly ceased after 20 min of continuous stimulation in the limited extracellullar volume. The intracellular pH decreased gradually during 20 min of continuous stimulation after which a dramatic pH drop was observed, indicating the breakdown of the intracellular buffering capacity. After continuous stimulation, intracellular lactate was released into the microchamber through cell electroporation and was detected electrochemically at a lactate microbiosensor, within the chamber. A mitochondrial uncoupler was used to mimic ischaemia and thus to enhance the cellular content of lactate. Under these circumstances, intracellular lactate concentrations were found to have risen to ～15 mM. This array system has the potential of simultaneous electrochemical and optical monitoring of extracellular and intracellular metabolites from single beating heart cells at a controlled metabolic state.