Performing chemical reactions in virtual capillary of surface tension-confined microfluidic devices

In this paper we report a new method of fabrication of surface tensionconfined microfluidic devices on glass. We have also successfully carried out some well-known chemical reactions in these fluidic channels to demonstrate the usefulness of these wall-less microchannels. The confined flow path of liquid was achieved on the basis of extreme differences in hydrophobic and hydrophilic characters of the surface. The flow paths were fabricated by making parallel lines using permanent marker pen ink or other polymer on glass surfaces. Two mirror image patterned glass plates were then sandwiched one on top of the other, separated by a thin gap-created using a spacer. The aqueous liquid moves between the surfaces by capillary forces, confined to the hydrophilic areas without wetting the hydrophobic lines, achieving liquid confinement without physical side-walls. We have shown that the microfluidic devices designed in such a way can be very useful due to their simplicity and low fabrication cost. More importantly, we have also demonstrated that the minimum requirement of such a working device is a hydrophilic line surrounded by hydrophobic environment, two walls of which are constituted of air and the rest is made of a hydrophobic surface.     

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

To probe the intrinsic stress distribution in terms of spatial Raman shift (ω) and change in the phonon linewidth (Γ), here we analyze self‐assembled graphene oxide fibers (GOF) ‘Latin letters’ by confocal Raman spectroscopy. The self‐assembly of GOF ‘Latin letters’ has been explained through surface tension, π–π stacking, van der Waals interaction at the air–water interface and by systematic time‐dependent investigation using field emission scanning electron microscopy analysis. Intrinsic residual stress due to structural joints and bending is playing a distinct role affecting the E_2g mode (G band) at and away from the physical interface of GOF segments with broadening of phonon linewidth, indicating prominent phonon softening. Linescan across an interface of the GOF ‘letters’ reveals Raman shift to lower wavenumber in all cases but more so in ‘Z’ fiber exhibiting a broader region. Furthermore, intrinsic stress homogeneity is observed for ‘G’ fiber distributed throughout its curvature with negligible shift corresponding to E_2g mode vibration. This article demonstrates the significance of morphology in stress distribution across the self‐assembled and ‘smart‐integrable’ GOF ‘Latin letters’. Copyright © 2016 John Wiley & Sons, Ltd.     

Applicability and effectiveness of classifications models for achieving the twin objectives of growth and outreach of microfinance institutions

Measuring performance of microfinance institutions (MFIs) is challenging as MFIs must achieve the twin objectives of outreach and sustainability. We propose a new measure to capture the performance of MFIs by placing their twin achievements in a 2 × 2 grid of a classification matrix. To make a dichotomous classification, MFIs that meet both their twin objectives are classified as ‘1’ and MFIs who could not meet their dual objectives simultaneously are designated as ‘0’. Six classifiers are applied to analyze the operating and financial characteristics of MFIs that can offer a predictive modeling solution in achieving their objectives and the results of the classifiers are comprehended using technique for order preference by similarity to ideal solution to identify an appropriate classifier based on ranking of measures of performance. Out of six classifiers applied in the study, kernel lab-support vector machines achieved highest accuracy and lowest classification error rate that discriminates the best achievement of the MFIs’ twin objective. MFIs can use both these steps to identify whether they are on the right path to attaining their multiple objectives from their operating characteristics.     

Control of molecular architecture by steric factors: mononuclear vs polynuclear manganese(III) compounds with tetradentate N2O2 donor Schiff bases

Three manganese(III) compounds, [Mn(III)(vanoph)(DMF)(H(2)O)]ClO(4) (1), [Mn(III)(vanoph)(N(3))(H(2)O)]·2H(2)O (2) and [Mn(III)(saloph)(μ(1,3)-N(3))](n) (3), where H(2)vanoph = N,N'-(1,2-phenylene)-bis(3-methoxysalicylideneimine), H(2)saloph = N,N'-(1,2-phenylene)-bis(salicylideneamine) are tetradentate N(2)O(2) ligands and DMF = N,N-dimethylformamide, have been prepared and characterised by elemental analysis, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction studies. Compounds 1 and 2 are monomeric but compound 3 consists of a chain system with the repeating unit [Mn(III)(saloph)(N(3))] bridged by μ-1,3 azide. Compound 1 crystallises in monoclinic space group P2(1)/n with cell dimensions of a = 11.1430(2), b = 16.3594(3), c = 15.4001(3) ?, β = 108.417(1), Z = 4 whereas compounds 2 and 3 crystallise in orthorhombic space groups Pbca and Pna2(1), respectively, with cell dimensions of a = 16.069(3), b = 15.616(3), c = 18.099(4) ?, Z = 8 (for 2) and a = 18.760(9), b = 13.356(5), c = 6.616(3) ?, Z = 4 (for 3). In all the compounds, Mn(III) has a six-coordinated pseudo-octahedral geometry in which O(2), O(3), N(1) and N(2) atoms of the deprotonated di-Schiff base constitute the equatorial plane. In both compounds 1 and 2, water molecules are present in the fifth coordination sites in the apical positions. The sixth coordination sites are occupied by one O atom of a solvent DMF in compound 1 and an N atom of azide in compound 2. The coordinated water initiates hydrogen-bonded networks in both compounds 1 and 2 to form well-isolated supramolecular dimers. At room temperature the χ(M)T values for the compounds 1 and 2 remain almost constant until 30 K. Below this temperature, the χ(M)T values drastically drop to 0.72 cm(3) mol(-1) K for 1 and 0.52 cm(3) mol(-1) K for 2. The best fits were obtained with J = -0.92 cm(-1), |D| = 2.05 cm(-1), g = 2.0 and R = 8.1 × 10(-4) for 1 and J = -1.16 cm(-1), |D| = 2.05 cm(-1), g = 2.0 and R = 1.2 × 10(-3) for 2. However, in compound 3, two axial positions are occupied by the azide ions. The Mn···Mn repeating distance is 6.616 ? along the chain. Magnetic characterisation shows that the μ(1,3)-bridging azide ion mainly transmits an antiferromagnetic interaction (J = -6.36 cm(-1)) between Mn(III) ions. The presence of two methoxy groups increases the steric crowding in the H(2)vanoph moiety and thereby inhibits the formation of a polynuclear compound with this ligand.     

Enantiodivergent synthetic entry to the quinolizidine alkaloid lasubine II

Intramolecular cycloaddition of the syn- and the anti-nitrone 9 and 13 leads stereoselectively to the azabicyclic compounds 10 and 14 which may provide access to both enantiomers of the quinolizidine alkaloid lasubine II.     

Geometric and electronic structures of peroxomanganese(III) complexes supported by pentadentate amino-pyridine and -imidazole ligands

Three peroxomanganese(III) complexes [Mn(III)(O(2))(mL(5)(2))](+), [Mn(III)(O(2))(imL(5)(2))](+), and [Mn(III)(O(2))(N4py)](+) supported by pentadentate ligands (mL(5)(2) = N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine, imL(5)(2) = N-methyl-N,N',N'-tris((1-methyl-4-imidazolyl)methyl)ethane-1,2-diamine, and N4py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) were generated by treating Mn(II) precursors with H(2)O(2) or KO(2). Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD data demonstrate that these complexes have very similar electronic transition energies and ground-state zero-field splitting parameters, indicative of nearly identical coordination geometries. Because of uncertainty in peroxo (side-on η(2) versus end-on η(1)) and ligand (pentadentate versus tetradentate) binding modes, density functional theory (DFT) computations were used to distinguish between three possible structures: pentadentate ligand binding with (i) a side-on peroxo and (ii) an end-on peroxo, and (iii) tetradentate ligand binding with a side-on peroxo. Regardless of the supporting ligand, isomers with a side-on peroxo and the supporting ligand bound in a tetradentate fashion were identified as most stable by >20 kcal/mol. Spectroscopic parameters computed by time-dependent (TD) DFT and multireference SORCI methods provided validation of these isomers on the basis of experimental data. Hexacoordination is thus strongly preferred for peroxomanganese(III) adducts, and dissociation of a pyridine (mL(5)(2) and N4py) or imidazole (imL(5)(2)) arm is thermodynamically favored. In contrast, DFT computations for models of [Fe(III)(O(2))(mL(5)(2))](+) demonstrate that pyridine dissociation is not favorable; instead a seven-coordinate ferric center is preferred. These different results are attributed to the electronic configurations of the metal centers (high spin d(5) and d(4) for Fe(III) and Mn(III), respectively), which results in population of a metal-peroxo σ-antibonding molecular orbital and, consequently, longer M-O(peroxo) bonds for peroxoiron(III) species.     

Photophysical and theoretical insights on non-covalently linked fullerene-zinc phthalocyanine complexes

The photo-physical aspects of non-covalently linked assemblies of a series of fullerenes, namely, C60, C70, tert-butyl-(1,2-methanofullerene)-61-carboxylate (1) and [6,6]-phenyl C70 butyric acid methyl ester (2) with a designed zinc phthalocyanine (ZnPc), viz., zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (3) in toluene medium are studied employing absorption spectrophotometric, steady state and time resolved fluorescence spectroscopic measurements. Of central interest in these investigations is the preferential binding of various fullerenes with ZnPc in toluene. The ground state interaction between fullerenes and 3 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 3 in presence of both underivatized and derivatized fullerenes. K values for the complexes of C60, C70, 1 and 2 with 3 are determined to be 6500, 22,230, 47,800 and 54,770 dm3 mol(-1), respectively. The magnitude of K suggests that 3 preferentially binds C70 and derivatized C70 in comparison to C60 and 1. Time resolved emission measurements establish that C(70)-3 and 2-3 complexes are stabilized much more in comparison to C(60)-3 and 1-3 systems in terms of charge separation process. Semi empirical calculations employing third parametric method substantiate the strong binding of C70 and its derivative with 3 in terms of heat of formation values of the respective complexes, and at the same time, determine the orientation of bound guest (here fullerenes) with the molecular plane of 3.     

Surface Coating Rescues Proteins from Magnetite Nanoparticle Induced Damage

The presence of magnetic nanoparticles (NPs) in physiological systems induces toxicity through its effects on mitochondrial function and reactive oxygen species (ROS) imbalance. Magnetic NP induced cytotoxicity has been elaborately evaluated for impending threats, however, a detailed investigation is lacking. It is shown that the interaction of Fe₃O₄ NPs with cytochrome c can lead to different events based on the NPs to protein ratio, the solution conditions, and the type of surface protection. At low NPs concentration, rapid binding and subsequent electron transfer are the preferred events while at higher concentration slow oxidative modification of the protein is initiated. The slow event of protein modification yields conformational disorientation, loss of stability, and formation of amyloid‐like structures with cytochrome c. The possibility that the NP induced oxidative stress and age can work in concert to compromise different aspects of cellular quality control processes is discussed. Suitable surface modifications of the NPs inhibit their direct binding to the protein molecules and minimize NP induced toxicity.