Kinetics and mechanism of benzoin oxidation using iron(III) in the presence of ferrozine or 2,2'‐bipyridine in acidic medium

Kinetics and mechanism of oxidation of benzoin (H₂B) by ferrozine (Fz) or 2,2'‐bipyridine (bipy) have been carried out in aqueous HNO₃ medium. The rate shows first‐order dependence on [H₂B] and [Fe³⁺] and inverse second‐order dependence on [H⁺]. The rate of reaction increased with increase in the ligand concentration. The increase in dielectric constant will increase the rate, while increase in [HNO₃] decreased it. Substituent and temperature effects on the rates have been investigated. The rate laws derived are in excellent agreement with the experimental results. Plausible mechanisms are suggested. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 444–449, 2005     

Self-similar Solutions of Nonlinear Elasticity and Poroelasticity Equations

Recent advances in nonlinear wave propagation in elastic and porous elastic (poro-elastic) material have presented new nonlinear evolutionary equations. The derivation of these equations in three-dimensional space is based on the semilinear Biot theory. The nonlinear elastodynamic equations are derived form the more general model of poro-elastodynamic using consistency arguments. For simplicity, we discuss and carry out the analysis for the nonlinear elastic model. It is found in this article that the methods of symmetry groups and self-similar solutions can furnish solutions to the nonlinear elastodynamic wave equation. It is also found that these models lead to shock wave development in finite time. Necessary conditions for the existence of the solution are given and well-posedness of the Cauchy problem is discussed.     

Prednisone/Cyclodextrin Inclusion Complexation: Phase Solubility,Thermodynamic, Physicochemical and Computational Analysis

Guest–host interaction of prednisone (PN) with cyclodextrins (CDs) have been investigated using phase solubility diagrams (PSD), differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), scanning electron microscopy (SEM) and molecular mechanical modeling (MM). Estimates of the complex formation constant (K ₁₁) show that the tendency of PN to complex with CDs follows the order: β-CD>γ-CD>HP-β-CD>α-CD. At the same pH of 7.0, β-CD forms soluble 1:1 and insoluble 1:2 PN/CD complexes (B_S-type PSDs). The thermodynamic functions for 1:1 PN/β-CD estimated at pH = 7.0 (ΔG ₁₁^o=−20.8 kJ⋅mol⁻¹) show that complexation is driven by enthalpy (−30.7 kJ⋅mol⁻¹) but retarded by entropy (ΔS ₁₁^o=−33.1 J⋅mol⁻¹⋅K⁻¹) changes. The MM modeling study indicates the formation of different isomeric 1:1 complexes with CDs. PSD, DSC, XRPD, SEM and MM studies established the formation of inclusion complexes in solution and the solid state.     

Experimental and Molecular Mechanical Studies of Complexation of Some 2H- and 3H- Indole Derivatives with Aqueous β-Cyclodextrin

Phase solubility diagrams (PSDs) at 25 ^∘C and molecular mechanical (MM) modeling were used to study the aqueous complexation of some 2H- and 3H-indole derivatives with β-cyclodextrin (β-CD). Among the 3H-indole derivatives investigated in this work, indole-3H-butyric acid forms the most stable 1:1 complex of the B _s -type PSD, whereas shorter chain derivatives form soluble 1:1 complexes (A _L -type PSDs) with their stability increasing as the chain length increases. Indole-2 carboxylic acid forms highly stable 1:1 and 1:2 complexes, with the lower-order complex reaching saturation first (B _s -type PSD). MM modeling indicates that the stability of the complex is highly correlated with the flexibility of the 3H-indole hydrocarbon chain, which yields a better geometrical fit within the β-CD cavity resulting from different hydrophilic interactions. These interactions are represented in the H-bonding of the carboxyl group with the primary hydroxyl group network that is situated at the narrow rim of the cavity, and also by a favorable interaction of the aromatic ring with the hydroxyl group network at the other rim.     

Molecular Mechanics Study of the Inclusion Complexes of Some 1,2,4-Oxadiazole Derivatives of 3,3′-Bis (1,2,4-Oxadiazol-5(4H)-one) with β-Cyclodextrin

Molecular mechanics calculations were employed to study the inclusion of some 1,2,4-oxadiazol derivatives in β-cyclodextrin in vacuum and in the presence of water as a solvent using MM + force field. The driving forces for complexation in both environments are dominated by nonbonded van der Waals host–guest interactions with little electrostatic contribution. Among 1,2,4-oxadiazole derivatives investigated in this work, 3,3′-bis(1,2,4-oxadiazol-5(4H)-one) (H₂OD) forms the least stable 1:1 complex and the stability increases as the chain length increases.     

Crystal structure of cis-[Rh(biq)2Cl2]Cl·3H2O: Solid-state characterization and crystal packing analysis

The title compound, cis-[Rh(biq)₂Cl₂]Cl·3H₂O (biq = 2,2′-biquinoline) crystallized in the monoclinic space group P2 ₁ /n with a = 11.231(2) Å, b = 20.895(4) Å, c = 14.081(3) Å, β = 94.76(3)°, V = 3293.0(11) ų, D _c = 1.565 g cm⁻³, μ = 0.806 mm⁻¹, F(000) = 1576 and Z = 4. It contains a monomeric [Rh(biq)₂Cl₂]⁺ cation, a chloride ion and three molecules of H₂O. The rhodium(III) ion is hexa coordinated forming a distorted octahedral arrangement. The mean Rh(III)–N distance for the four Rh(III)–N bonds is 2.0625 Å. The two chloride atoms are bonded in a cis configuration [Rh(III)–Cl bond distances are 2.329(3) and 2.341(4) Å]. The structure shows a curling stacks of cationic complexes interacting via offset-face-to-face (OFF) π–π aryl interaction motif. Water molecules and chloride ions are hydrogen bonded (H₂O···H–OH and Cl···H–OH) and links the curling stacks by hydrogen bonding via Rh–Cl···H–OH interactions.     

Surface plasmons reveal spin crossover in nanometric layers

Nano-objects and thin films displaying molecular spin-crossover phenomena have recently attracted much attention. However, the investigation of spin crossover at reduced sizes is still a big challenge. Here we demonstrate that surface plasmon polariton waves propagating along the interface between a metal and a dielectric layer can be used to detect the spin-state changes in the latter with high sensitivity, even at the nanometer scale.     

Optical scattering noise in high Q fiber ring resonators and its effect on optoelectronic oscillator phase noise

Nonlinear phenomena occurring in an optical fiber ring resonator featuring ultrahigh Q factor are experimentally studied. The laser is locked onto the resonator, and the optical power induced in the resonator is controlled. The onset of the first stimulated Brillouin scattering wave occurs at an optical input power as low as -9 dBm in these resonators. When the resonator is used as the frequency reference device in an optoelectronic oscillator (OEO), it has been found that these parasitic signals mix with the OEO signal and degrade its phase noise. More than 20 dB improvement of the OEO phase noise has been demonstrated by limiting these nonlinear optical effects.     

Investigation of the Interactions in Complexes of Low Molecular Weight Chitosan with Ibuprofen

Complexation between ibuprofen and low molecular weight chitosan (LMWC) was studied. LMWC was prepared from high molecular weight chitosan using the acid hydrolysis method. The complexes were investigated by using DSC, FT-IR and liquid-state ¹H-NMR. Molecular mechanics (MM) calculations were used to give insight into the stoichiometry of the interaction of chitosan with ibuprofen. The results showed that complexation of ibuprofen with LMWC involves ionic interaction between the ammonium group of LMWC and the carboxylate anion of ibuprofen. It was also shown that it is more efficient to prepare the complexes using lower concentration solutions of the polymer. These results were supported by molecular mechanics calculations. The experimental results may explain the discrepancies in the literature where, in many studies, the concentration of chitosan and its low average molecular weight were not considered to be important factors in the complexation process.     

Intermolecular interactions involved in the crystal structure of 2-amino-5-methylpyridinium hexabromostannate (IV), (C<Subscript>6</Subscript>H<Subscript>9</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>[SnBr<Subscript>6</Subscript>]

The salt bis(2-amino-5-methylpyridinium) hexabromostannate(IV) (C₆H₉N₂)₂[SnBr₆] is monoclinic, P2 ₁ /c, with the following cell parameters: a=9.1636(18) ?, b=28.767(7) ?, c=16.956(17) ?, β=101.008(5)°, V=4387.5(17) ?³, Z=8, formula units. X-ray crystallography revealed that the structure can be regarded as a semi-regular three-dimensional array of anions, with pairs of cations forming layers perpendicular to b axis in the cavities between the anions. The cohesion forces that connects molecules in the organic layers are hydrophilic N⋯HCH₂ and HN⋯HN hydrogen bonding as well as hydrophobic π-π stacking and CH₃⋯π interactions. Cations and anions are connected via strong Br⋯H hydrogen bonding. Supplementary material CCDC 276493 contains the supplementary crystallographic data. These data can be obtained free of charge via www.ccdc. cam.ac.uk/data_request/cif, by e-mailing data_ request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033.