Gold-catalysed synthesis of amino acid-derived 2,5-disubstituted oxazoles

Amino acid-derived propargylic amides are cyclised in a one-pot, Au(III)-catalysed operation to yield 5-bromomethyl oxazoles. These compounds are further elaborated to bis-heterocycles, dipeptide mimics and more.     

Effect of surface modes on the six-dimensional molecule-surface scattering dynamics of H2-Cu(100) and D2-Cu(111) systems

We include the phonon modes originating from the three layers of Cu(100)/Cu(111) surface atoms on the dynamics of molecular [H(2)(v,j)/D(2)(v,j)] degrees of freedom (DOFs) through a mean field approach, where the surface temperature is incorporated into the effective Hamiltonian (potential) either by considering Boltzmann probability (BP) or by including the Bose-Einstein probability (BEP) factor for the initial state distribution of the surface modes. The formulation of effective potential has been carried out by invoking the expression of transition probabilities for phonon modes known from the "stochastic" treatment of linearly forced harmonic oscillator (LFHO). We perform four-dimensional (4D?2D) as well as six-dimensional (6D) quantum dynamics on a parametrically time and temperature-dependent effective Hamiltonian to calculate elastic/inelastic scattering cross-section of the scattered molecule for the H(2)(v,j)-Cu(100) system, and dissociative chemisorption-physisorption for both H(2)(v,j)-Cu(100) and D(2)(v,j)-Cu(111) systems. Calculated sticking probabilities by either 4D?2D or 6D quantum dynamics on an effective potential constructed by using BP factor for the initial state distribution of the phonon modes could not show any surface temperature dependence. In the BEP case, (a) both 4D?2D and 6D quantum dynamics demonstrate that the phonon modes of the Cu(100) surface affect the state-to-state transition probabilities of the scattered H(2) molecule substantially, and (b) the sticking probabilities due to the collision of H(2) on Cu(100) and D(2) on Cu(111) surfaces show noticeable and substantial change, respectively, as function of surface temperature only when the quantum dynamics of all six molecular DOFs are treated in a fully correlated manner (6D).     

Redox-rich spin-spin-coupled semiquinoneruthenium dimers with intense near-IR absorption

Using the [RuCl(μ-tppz)ClRu](2+) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] platform for bridging two o-quinone/catecholate two-step redox systems (unsubstituted, Q(n), or 3,5- di-tert-butyl-substituted, DTBQ(n)), we have obtained the stable complexes [(Q(?-))Ru(II)Cl(μ-tppz)ClRu(II)(Q(?-))] (1) and the structurally characterized [(DTBQ(?-))Ru(II)Cl(μ-tppz)ClRu(II)(DTBQ(?-))] (2). The compounds exhibit mostly quinone-ligand-based redox activity within a narrow potential range, high-intensity near-IR absorptions (λ(max) ≈ 920 nm; ε > 50,000 M(-1) cm(-1)), and variable intra- and intermolecular spin-spin interactions. Density functional theory calculations, electron paramagnetic resonance (EPR), and spectroelectrochemical results (UV-vis-near-IR region) for three one-electron-reduction and two one-electron-oxidation processes were used to probe the electronic structures of the systems in the various accessible valence states. EPR spectroscopy of the singly charged doublet species showed semiquinone-type response for 1(+), 2(+), and 2(-), while 1 exhibits more metal based spin, a consequence of the easier reduction of Q as compared to DTBQ. Comparison with the analogous redox series involving a more basic N-phenyliminoquinone ligand reveals significant differences related to the shifted redox potentials, different space requirements, and different interactions between the metals and the quinone-type ligands. As a result, the tppz bridge is reduced here only after full reduction of the terminal quinone ligands to their catecholate states.     

Immobilization of bio-macromolecules on self-assembled monolayers: methods and sensor applications

Attachment of biomolecules on gold, silicon or glass surfaces has direct implications for the development of novel biosensors in the context of nanoscale detection of pathogens and other metabolites related to issues of human health. In this critical review, we have highlighted the current developments in various techniques of immobilization of biomolecules, specifically biological macromolecules on surfaces through the modification of a functional self-assembled monolayer. The utility of such immobilized biomolecules in the area of biosensing in nanoscale has been surveyed. Merits and demerits of some of the methods with reference to sensitivity of detection and practical use have been discussed (221 references).     

Thermally controlled cyclic insertion/ejection of dopant ions and reversible zinc blende/wurtzite phase changes in ZnS nanostructures

We report a reversible phase transformation of platelet-shaped ZnS nanostructures between wurtzite (WZ) and zinc blende (ZB) phases by reversible insertion/ejection of dopant Mn(II) ions induced by a thermocyclic process. In a reaction flask loaded with WZ ZnS platelets and Mn molecular precursors, during heating Mn ions are incorporated and change the phase of the host nanostructures to ZB; during cooling Mn ions are spontaneously ejected, returning the host nanoplatelets to the original WZ phase. These reversible changes are monitored for several cycles with PL, EPR, XRD, and HRTEM. Interestingly, the (0001) WZ platelets transform to (110) ZB following a nucleation and growth process triggered by a local increase/depletion of the Mn(2+) concentration in the nanocrystals.     

Particle deposition onto Janus and patchy spherical collectors

An Eulerian model (convection-diffusion-migration equation) is presented to study colloid deposition behavior on Janus and patchy spherical collectors using Happel cell geometry. The model aims to capture the effect of the collector surface charge heterogeneity on the particle deposition rate. Two separate cases of surface charge distribution are presented. In the first case, the surface heterogeneity is modeled as half the collector favoring deposition and the other half hindering it (Janus collectors). For the second case, the surface heterogeneity is modeled as alternate stripes of attractive and repulsive regions on the collector (patchy collectors). The model also considers fluid flow approaching the collector at different angles in addition to the standard gravity assisted and gravity hindered flow conditions to analyze the effect of the collector orientation on the deposition. It was observed that particles tend to deposit at the edges of the favorable stripes and the extent of this preferential accumulation varies along the tangential position of the collector due to the nonuniform nature of the collector. The predicted deposition behavior is compared to the patchwise heterogeneity model. The study brings to fore how recent developments in synthesis of chemically heterogeneous particles and beads can be used for improved particle capture in porous media and for designing filter beds with enhanced life.     

Study of the vibrational spectra of SO2, H2O and D2O using the U(4) algebraic model

Using the U(4) algebraic model, in this work we report a study of the vibrational spectra of SO₂, H₂0¹⁸ and D₂O¹⁶. The inclusion of intermode couplings in algebraic models has been stated to give a deep insight into detailed spectroscopy for these bent XY₂ molecules. Improved set of algebraic parameters has been reported to provide improved RMS deviations for these molecules.     

Flux decline during cross flow membrane filtration of electrolytic solution in presence of charged nano-colloids: a simple electrokinetic model

An electrokinetic transport based approach for quantification of reversible flux decline due to the concentration polarization of an electrolyte solution in presence of charged colloids is presented. The model envisions the electrolyte transport across a charged cake or gel layer as transport of ions through charged cylindrical capillaries. This model is coupled with the standard theory of concentration polarization during cross flow membrane filtration. The analysis is carried out entirely in terms of generalized, non-dimensional variables. A dimensionless group termed as the scaled gel layer resistance evolves from the analysis, which accounts for the electrical properties of the charged nano-colloids and the electrolyte solution. A parametric study is performed to elucidate the coupled influence of mass transfer, membrane resistance, gel resistance, and electrical properties of the gel-electrolyte polarized layer. The effects of these parameters are examined on the filtration performance through the model equations.