Polyoxomolybdodiphosphonates: examples incorporating ethylidenepyridines

We have synthesized and structurally characterized three pyridylethylidene-functionalized diphosphonate-containing polyoxomolybdates, [{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](6-) (1), [{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](8-) (2), and [{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)](12-) (3). Polyanions 1-3 were prepared in a one-pot reaction of the dinuclear, dicationic {Mo(V)(2)O(4)(H(2)O)(6)}(2+) with 1-hydroxo-2-(3-pyridyl)ethylidenediphosphonate (Risedronic acid) in aqueous solution. Polyanions 1 and 2 are mixed-valent Mo(VI/V) species with open tetranuclear and hexanuclear structures, respectively, containing two diphosphonate groups. Polyanion 3 is a cyclic octanuclear structure based on four {Mo(V)(2)O(4)(H(2)O)} units and four diphosphonates. Polyanions 1 and 2 crystallized as guanidinium salts [C(NH(2))(3)](5)H[{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·13H(2)O (1a) and [C(NH(2))(3)](6)H(2)[{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·10H(2)O (2a), whereas polyanion 3 crystallized as a mixed sodium-guanidinium salt, Na(8)[C(NH(2))(3)](4)[{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)]·8H(2)O (3a). The compounds were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analyses. The formation of polyanions 1 and 3 is very sensitive to the pH value of the reaction solution, with exclusive formation of 1 above pH 7.4 and 3 below pH 6.6. Detailed solution studies by multinuclear NMR spectrometry were performed to study the equilibrium between these two compounds. Polyanion 2 was insoluble in all common solvents. Detailed computational studies on the solution phases of 1 and 3 indicated the stability of these polyanions in solution, in complete agreement with the experimental findings.     

Bohr radius for subordinating families of analytic functions and bounded harmonic mappings

The class consisting of analytic functions f   in the unit disk satisfying f+αzf^′+γz²f^″$f+\alpha z{f}^{\prime }+\gamma z^2{f}^{″}$ subordinated to some function h is considered. The Bohr radius for this class is obtained when h is respectively convex or starlike. The Bohr radius for analytic functions mapping the unit disk into a concave-wedge domain as well as for bounded harmonic mappings are also established.     

Effect of solvent and structure on the kinetics and mechanism of the aquation of bromopentaamine cobalt(III) complex in binary aqueous mixtures

The kinetics of aquation of bromopentaamine cobalt(III) complex have been investigated spectrophotometrically in aqueous‐organic solvent media using acetonitrile, urea, and dimethyl sulfoxide as co‐solvents at 45 ≤ T (°C) ≤ 65. The logarithms of rate constant of the aquation reaction vary nonlinearly with the reciprocal of the dielectric constant for all cosolvent mixtures, indicating a specific solute–solvent interaction. Also, the rate constants are correlated with the total number of moles of water and the organic solvents. However, the solvent effects on the solvation components of the enthalpy of activation, ΔH^?, and the entropy of activation, ΔS^?, have been studied. Analysis of the solvent effect confirmed a common I_d mechanism for the aquation of the cobalt(III) complex. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:494–499, 2004     

Approximate Homomorphisms

which ``almost everywhere' looks like an ultrafilter has to be close to some fixed ultrafilter. Received: August 20, 1997     

Acetylation and stepwise solvent-exchange to modify hydrophilic cellulose whiskers to polychloroprene-compatible nanofiller

The acetylation of cellulose nanofiber (CNF) introduced hydrophobicity to the surface making it compatible with non-polar matrix, and also making it an effective nanofiller for polychloroprene (PCR) composite. The CNF was extracted from oil palm empty fruit bunches. Previously, CNF was dispersed in water, and this water was subsequently substituted with N,N-dimethylacetamide, in which CNF was acetylated by acetic anhydride with a pyridine catalyst. IR spectroscopy revealed that the acetylation extent was controllable by the reaction time. After the reaction, the DMAc was replaced by dichloromethane, and finally mixed with PCR. The CNF–PCR mixture was cast and composite film was formed at room temperature. Structural analysis and mechanical tests indicated that acetylation treatment made CNF compatible with PCR, and that nano-dispersed CNF raised the mechanical strength of the PCR–CNF nanocomposite.     

Synthesis and characterization of original calix-salen type ligands

Polycondensation reactions between various modified disalicylaldehyde derivatives and two chiral diamines afforded in each case macrocyclic structures, named calix-salen. Mixtures of oligomers (dimers to pentamers) were qualitatively analyzed by Maldi-Tof and ¹H NMR DOSY experiments allowed their easy quantitative investigation. Tuning the reaction conditions and namely the concentration of both monomeric partners led interestingly to the selective preparation of the dimer or the tetramer as main products, in diluted or concentrated media, respectively.     

A single point mutation converts a proton-pumping rhodopsin into a red-shifted,turn-on fluorescent sensor for chloride

The visualization of chloride in living cells with fluorescent sensors is linked to our ability to design hosts that can overcome the energetic penalty of desolvation to bind chloride in water. Fluorescent proteins can be used as biological supramolecular hosts to address this fundamental challenge. Here, we showcase the power of protein engineering to convert the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride in detergent micelles and in live Escherichia coli. This non-natural function was unlocked by mutating D121, which serves as the counterion to the protonated retinylidene Schiff base chromophore. Substitution from aspartate to valine at this position (D121V) creates a binding site for chloride. The binding of chloride tunes the pK_a of the chromophore towards the protonated, fluorescent state to generate a pH-dependent response. Moreover, ion pumping assays combined with bulk fluorescence and single-cell fluorescence microscopy experiments with E. coli, expressing a GR1 fusion with a cyan fluorescent protein, show that GR1 does not pump ions nor sense membrane potential but instead provides a reversible, ratiometric readout of changes in extracellular chloride at the membrane. This discovery sets the stage to use natural and laboratory-guided evolution to build a family of rhodopsin-based fluorescent chloride sensors with improved properties for cellular applications and learn how proteins can evolve and adapt to bind anions in water.

By utilizing laboratory-guided evolution, we have converted the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride.     

Synthesis and surface characterization of alkylthioacetyl-capped self-assembled monolayers on gold surface

A novel alkylthioacetyl-capped hydroxyethyl methacrylate monomer and its corresponding homopolymer have been synthesized and characterized. Direct chemisorption of these moieties have been carried out on gold-coated substrate and found to form a strong surface bonding. The surface coverage and the properties of the resultant self-assembled layers have been investigated by multiple surface characterization techniques (i.e. ellipsometry, GA-FTIR, XPS, AFM, and contact angle measurements). These analyses have all confirmed the occurrence of complete chemisorption reactions with typical n-alkanethiol self-assembled characteristics.     

Network flow-based approaches for integrated aircraft fleeting and routing

Given a schedule of flights to be flown, the aircraft fleeting and routing problem (AFRP) consists of determining a minimum-cost route assignment for each aircraft so as to cover each flight by exactly one aircraft while satisfying maintenance requirements and other activity constraints. We investigate network flow-based heuristic approaches for this problem. Computational experiments conducted on real-data given by TunisAir show that the proposed heuristic consistently yields very near-optimal solutions while requiring modest CPU effort.