Effect of precipitation medium and thermal treatment on structure and textural properties of chromium orthophosphates

The effect of the precipitation agent on the structure and textural properties of CrPO₄ (Cr/P=1) catalysts has been studied. Catalysts obtained in propylene oxide-aqueous ammonia exhibited higher thermal stability and, hence, greater surface areas and pore volumes than catalysts obtained in propylene oxide or aqueous ammonia exclusively. The former also showed a small surface area decrease on increasing calcination temperature up to 1073 K. Nevertheless, calcination at 1273 K develops in all cases crystalline CrPO₄, showing the -structure. Moreover, CrPO₄ catalysts thermally treated below 1273 K only exhibited hydrogen bonded hydroxy groups .     

Synthesis of tris- and tetrakis(pyrazol-1-yl)borate gold(III) complexes. Crystal structures of [Au[kappa(2)-N,N'-BH(Pz)(3)]Cl(2)] (pz = pyrazol-1-yl) and [Au[kappa(2)-N,N'-B(Pz)(4)](kappa(2)-C,N-C(6)H(4)CH(2)NMe(2)-2)]ClO(4).CHCl(3)

Na[BH(pz)(3)] and Na[AuCl(4)].2H(2)O react in water (1:1) to give [Au[kappa(2)-N,N'-BH(pz)(3)]Cl(2)] (1) or, in the presence of NaClO(4) (2:1:1), the cationic complex [Au[kappa(2)-N,N'-BH(pz)(3)](2)]ClO(4) (2). The reactions of Na[B(pz)(4)] with the cyclometalated gold complexes [AuRCl(2)] and NaClO(4) (1:1:1) produce [Au[kappa(2)-N,N'-B(pz)(4)](R)]ClO(4) [R = kappa(2)-C,N-C(6)H(4)CH(2)NMe(2)-2 (3)] or [Au[kappa(2)-N,N'-B(pz)(4)](R)Cl] [R = C(6)H(3)(N=NC(6)H(4)Me-4')-2-Me-5 (4)], respectively, although 4 is better obtained in the absence of NaClO(4). The crystal structures of 1 and 3.CHCl(3) are reported. Both complexes display the gold center in square planar environments, two coordination sites being occupied by the chelating poly(pyrazolyl)borate ligands.     

Analytical possibilities of pyridine-2-acetaldehyde benzoylhydrazone as a chromogenic reagent

With a view to the use of pyridine-2-acetaldehyde benzoylhydrazone is an analytical reagent, a study of the physical properties and fundamental solution chemistry of the complexes formed by PABH with Fe(II), Fe(III), Ni(II), Pd(II), V(V), Ti(IV), Hg(II), Mn(II), Zn(II), Bi(III), Co(II), Cu(II), Pb(II), and Ga(III) metal ions has been carried out. A critical comparison of pyridine-2-carbaldehyde and pyridine-2-acetaldehyde salicyloylhydrazones and pyridine-2-acetaldehyde benzoylhydrazone as analytical reagents is given.     

Mononuclear (Pd, Pt), heterodinuclear (PdAg, PtAg), and tetranuclear (Pd2Ag2, Pt2Ag2) 1,1-ethylenedithiolato complexes

lp;&-5q;1 The reactions of [Tl2[S2C=C[C(O)Me]2]]n with [MCl2L2] (1:1) or with [MCl2(NCPh)2] and PPh3 (1:1:2) give complexes [M[eta2-S2C=C[C(O)Me]2]L2] [M = Pt, L2 = 1,5-cyclooctadiene (cod) (1); L2 = bpy, M = Pd (2a), Pt (2b), L = PPh3, M = Pd (3a), Pt (3b)] whereas with MCl2 and QCl (2:1:2) anionic derivatives Q2[M[eta2-S2C=C[C(O)Me]2]2] [M = Pd, Q = NMe4 (4a), Ph3P=N=PPh3 (PPN) (4a'), M = Pt, Q = NMe4 (4b)] are produced. Complexes 1 and 3 react with AgClO4 (1:1) to give tetranuclear complexes [[ML2]2Ag2[mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2]](ClO4)2 [L = PPh3, M = Pd (5a), Pt (5b), L2 = cod, M = Pt (5b')], while the reactions of 3 with AgClO4 and PPh3 (1:1:2) give dinuclear [[M(PPh3)2][Ag(PPh3)2][mu2,eta2-(S,S')-S2C=C[C(O)Me]2]]]ClO4 [M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 3b, 4a, and two crystal forms of 5b have been determined. The two crystal forms of 5b display two [Pt(PPh3)2][mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2] moieties bridging two Ag(I) centers.     

Harmonic force field for glycine oligopeptides

The need for much more useful molecular dynamics simulations of nanosized system requires precise and unambiguous methods to determine force field parameters avoiding fitting procedures in favor of first principles ones. We use a procedure FUERZA to calculate force constant parameters for glycine oligopeptides using as an input the Hessian tensor from an ab initio calculation. For a molecular system having n atoms, The FUERZA procedure reduces the 3n × 3n problem to 3n 3 × 3 matrices representing atom‐atom interactions. The procedure reproduces quite well most of the frequencies and as expected, it overestimates somehow stretching frequencies of bonds with terminal atoms such as hydrogens but it yields precise results for all other frequencies. A harmonic force field is reported for glycine oligopeptides. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Enantioselective Formation of 2‐Azetidinones by Ring‐Assisted Cyclization of Interlocked N‐(α‐Methyl)benzyl Fumaramides

The synthesis of optically active interlocked and non‐interlocked 2‐azetidinones by intramolecular cyclization of N‐(α‐methyl)benzyl fumaramide [2]rotaxanes is described. Two different strategies of asymmetric induction were tested in which the chiral group was located either proximal or distal to the reacting center of the thread. During these experiments, an interesting equilibration process inside the macrocyclic void occurred, thus leading to the cyclization through the (α‐methyl)benzyl carbon atom and giving rise to β‐lactams, with a quaternary carbon atom, in an enantio‐ and diastereocontrolled manner. This cyclization also proceeds in kinetically stable chiral pseudo[2]rotaxanes, thus allowing further dethreading to provide enantioenriched 3,4‐disubstituted trans‐2‐azetidinones. The stereochemical outcomes of the cyclizations inside and outside the macrocycle demonstrated noticeable differences.     

Tandem on-line continuous separations for atomic spectroscopic indirect analysis: Iodide determination by ICP-AES

A sensitive and selective indirect determination of iodide by inductively coupled plasma emission spectrometry (ICP-AES) based on the principle of tandem on-line continuous separations as an alternative means of introducing samples into plasmas is proposed. Iodide is continuously extracted as an ion-pair into xylene by mixing the sample with Hg(II) and dipyridil solutions. The organic phase (containing the analyte in [Hg(Dipy)₂]I₂ form) is on-line continuously mixed with NaBH₄ (in DMF) and acetic acid solutions. Mercury vapour continuously generated from this organic phase is separated in a classical U-type gas-liquid separation device. The system has been optimized for the continuous extraction of KI, for the direct generation of cold mercury vapour from xylene and for the final ICP-AES determination of mercury. The optimised method has been applied to the determination of iodide (detection limit 20 ng/ml of iodide) in table salt and in synthetic samples. Very good agreement between found and certified results was observed. The usefulness and convenience of such alternative sample chemical pretreatment/presentation to the ICP is thus demonstrated for indirect determinations to be carried out by atomic spectroscopy methods.     

Rheology of wormlike micelles from non-equilibrium molecular dynamics

In this work, the rheology of complex fluids, i.e., surfactants of varying concentration in a Lennard–Jones fluid, is analyzed with non-equilibrium molecular dynamics simulations. The molecular model considers that the surfactant molecule is composed of a hydrophilic head, affine to solvent, and a hydrophobic tail made of four monomers. The solvent is modeled by a Lennard–Jones fluid, which shows mostly a Newtonian behavior, but at relatively high shear rates, a slight shear-thinning followed by a slight shear thickening are exhibited. The intermolecular potential produces an equilibrium configuration, in which the surfactant molecules self-assemble in a wormlike micelle. With the aim to analyze the system behavior with various stress fields, two flows are simulated under non-equilibrium conditions: (1) simple shear and (2) Poiseuille's flow. In simple shear, by keeping the velocity of the upper plate of the flow cell constant, a monotonic flow curve is predicted within a range of shear rates. At low shear rates, a concentration-dependent Newtonian region of viscosity η₀ corresponds to an isotropic condition in which the wormlike micelle preserves its equilibrium conformation. At intermediate shear rates, the solution exhibits a slight shear thinning, generating bands placed normal to the gradient direction (gradient banding). At high shear rates the solution exhibits shear-thickening, with bands now generated normal to the vorticity direction. These predictions by molecular models explain, to our knowledge for the first time, experiments in shear-thickening wormlike micellar solutions, where shear-thickening appears simultaneously with bands generated perpendicular to the vorticity axis. In Poiseuille's flow, we also find agreement between predictions of the model with theoretical developments and experiments performed by other authors.     

Synthesis,characterization and properties of N‐maleimide side‐chain liquid crystalline copolymers

A homologous series of side‐chain liquid crystalline (SCLC) poly{[N‐[10‐((4‐(((4′‐n‐hexyloxy)benzoyl)oxy)phenoxy)carbonyl)‐n‐decyl]maleimide]‐co‐[N‐(n‐octadecyl)maleimide]} [(ME6)‐co‐(MI‐18)] random copolymers with various MI‐18 contents have been synthesized and their properties studied. The high content in threo‐disyndiotactic sequences of the maleimide main chain seems responsible for the stability of the highly ordered smectic mesophase. The relationship between structure and composition on thermotropic mesophase was investigated by polarizing optical microscopy, differential scanning calorimetry, and X‐ray diffraction. For copolymers with mesogenic unit contents less than ～0.655 molar fraction the transition from (S_A) texture to isotropic (I) is maintained, as shown by the T_Cl, ΔH_Cl and ΔS_Cl amounts and intermolecular spacing 4.42–4.53 Å and intralayer correlation lengths of 44.2–45.2 Å. The layer thickness does not appreciably depend on copolymer composition. However, copolymers with non‐mesogenic comonomer MI‐18 molar contents larger than >0.655 molar fraction X(M), are no longer liquid crystalline materials, despite its packing is preserved without any detectable appearance of birefringence. Thermodynamic boundaries of the liquid crystalline state have been established through a phase diagram. The properties of this n‐hexyloxy pendant group‐based series are compared to those of the analogous materials containing methoxy pendant groups (ME1), and differences are accounted for in terms of the local side‐chain packing within the mesophase. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011