Structure and properties of a new double-stranded tetranuclear [Cu(II)2]2 helicate

A novel double-stranded tetranuclear helicate composed of a pair of [Cu(II)(2)] dimers has been prepared and characterized by exploiting the flexibility, chelating ability and bridging potential of a hexadentate bis-oximate ligand.     

Unique asymmetric (CuII4) double-stranded helicate from a hexadentate piperazine-based ligand: ligand conformation isomerism upon coordination

In methanol, the reaction of Cu(ClO(4))(2).6H(2)O and a sterically constrained piperazine imine phenol ligand (H(2)L), in the presence of NEt(3), affords a novel tetranuclear copper(II) complex of formula [Cu(II)(4)(mu(3)-L)(2)(mu-OH)(2)(H(2)O)(2)](ClO(4))(2).H(2)O (1). The X-ray structure of this complex shows an elongated Cu(4) quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-mu(3)-piperazine bridging ligands. Variable-temperature magnetic studies show an S(t) = 0 spin ground state resulting from antiferromagnetic interactions between Cu(II) ions within the complex.     

The role of the ring nitrogen and the amino group in the solvent dependence of the excited-state dynamics of 3-aminoquinoline

The nonradiative rate in 3-aminoquinoline is found to exhibit anomalous solvent dependence, being rather fast in nonpolar solvents and remarkably slower in more polar and especially, more protic ones. The cause of such behavior is investigated by studying the dependence of fluorescence spectral and temporal parameters on the solvent properties such as polarity and hydrogen bonding ability. Complementary quantum mechanical calculations have been performed and the picture that emerges from these studies is that of an excited state with a short radiative lifetime due to the flipping of the amino group. This state is selectively populated in nonpolar, nonhydrogen bonding solvents, but is destabilized with respect to the more polar intramolecular charge transfer (ICT) state in polar solvents and even more so in protic solvents and dimethylsulfoxide. The slower nonradiative rates in the ICT state is attributed to the more restricted motion of the amino group in this state. The role of hydrogen bonding of the amino group and the ring nitrogen in stabilization/destabilization of the ICT state and therefore on the nonradiative rate is also explored.     

p-adic string theories provide lattice Discretization to the ordinary string worldsheet

A class of models called p-adic strings is useful in understanding the tachyonic instability of string theory. These are found to be empirically related to the ordinary strings in the p-->1 limit. We propose that these models provide discretization for the string worldsheet and argue that the limit is naturally thought of as a continuum limit in the sense of the renormalization group.     

Pressure generation at the junction of two microchannels with different depths

In this study, we report the design of a microchip‐based hydraulic pump that comprises three glass conduits arranged in a T‐geometry, one of which has a 2 mm long segment shallower (0.5–3 μm in depth) than the remaining 15 μm deep microfluidic network. Upon application of an electric field across this microchannel junction, a mismatch in EOF rate is introduced due to a differential in the fluid conductivity across the deep and shallow segments. Using the reported micropump, pressure‐driven velocities up to 3.2 mm/s have been generated in a 15 μm deep separation channel for an applied voltage of 1.75 kV allowing us to operate under separation conditions that yield the minimum plate height. Moreover, we have shown that this flow velocity can be maximized by optimizing the depth in the shallow region of the T‐geometry. Interestingly however, a simple theory accounting for fluid conductivity differences across microchannels of different depths significantly underestimates the pressure‐driven velocities observed in our experiments. The Taylor dispersion coefficient in our system on the other hand compares well with the theoretical predictions reported in the literature. Finally, the functionality of our device has been demonstrated by implementing a reverse‐phase chromatographic separation that was driven by the pressure‐driven flow generated on‐chip.     

Preferential solvation in three component systems: Evaluation of Kirkwood-Buff parameters

The extent of local excess or deficiency of a component solvent near the solute in a mixed binary solvent has been calculated using the Hall formalism for the Kirkwood-Buff equation. The possibility of calculation of the two solute-solvent Kirkwood-Buff parameters using the values is discussed. A model calculation using literature data for preferential solvation in mixed binary solvents is presented. The solute-solvent and solvent-solvent interactions and the relative size of the solvents are also shown to be relevant factors in determining the values.     

BiCl3‐catalyzed carbon‒carbon cross‐coupling of organoboronic acids with aryl iodides

A procedure for BiCl₃‐catalyzed carbon‐carbon cross‐coupling reaction of organoboronic acids with aryl iodides is described. This protocol has a wide substrate scope and uses an inexpensive and non‐toxic catalyst. Copyright © 2013 John Wiley & Sons, Ltd.     

Mohr's salt catalyzed oxidation of aldehydes with t‐BuOOH

Various aromatic, aliphatic and conjugated aldehydes were transformed to the corresponding carboxylic acids with 70% t‐BuOOH solution (water) in the presence of catalytic amounts (10 mol%) of Mohr's salt. This method possesses functional group compatibility, does not involve cumbersome work‐up, exhibits chemoselectivity since other functional groups remain intact and proceeds under mild conditions. The resulting products are obtained in good yields within reasonable times. Copyright © 2011 John Wiley & Sons, Ltd.