The study of the mechanical impedance of foods and biomaterials to characterize their linear viscoelastic behavior at high frequencies

A new instrumental setup, which is based on the oscillatory squeezing flow model, was developed to characterize the viscoelastic properties of foods and biopolymers. Analysis of the data was performed by two different approaches. The first approach employed principles of vibration to determine viscous damping and elasticity of the sample harmonically compressed between two plates. The second approach involved the use of additional calculations based on the squeezing flow model which were linked to concepts of vibration analysis, such as mechanical impedance, to determine fundamental rheological parameters like complex viscosity and related (elastic and viscous) moduli. The experimental setup for the method is simple to use and could be attached to existing commercial instruments such as texture analyzers and universal testing machines. The use of the proposed method with this type of instruments would provide them with the additional capability of performing dynamic rheological testing. The dynamic mass of the instrument was significantly low when compared to that of other instruments that use similar principles. This low dynamic mass enabled the use of relatively higher frequencies for the testing of the samples. Comparison of the viscous and elastic moduli obtained with the proposed method and from conventional rheometers for a variety of foods and biopolymers showed good agreements.     

N,N,N′,N′‐Tetra­methyl­ethyl­enedi­ammonium dichloride

The structure of the title compound, C₆H₁₈N₂²⁺.2Cl^?, has been determined and has a centre of symmetry. The mol­ecule has strong intermolecular hydrogen bonding between each Cl^? and an N—H bond [Cl?N = 3.012 (3) Å].     

Polyurethane Films for Wound Dressing Applications

Polyurethane films based on renewable sources were prepared as an alternative to petroleum-based polyurethane. The effects of the structure and ratio of diisocyanate components on polymer properties were investigated. Hexamethylene diisocyanate (HMDI) and diphenylmethylene diisocyanate (MDI) were chosen as the diisocyanate components in polymer synthesis. Membranes were prepared by casting-evaporation technique and characterized for their gas permeability, film and mechanical properties. The oil-based membranes were found to be suitable for wound dressing applications.     

Dipolar cycloadditions of imidazoline 3-oxides with N-arylmaleimides. Synthesis and diethylamine induced ring-opening of exo and endo hexahydro-7-oxa-2,5,6a-triaza-cyclopenta[a]pentalene-1,3-diones

1,4-Diarylimidazoline 3-oxides react with N-arylmaleimides in benzene to give predominantly the corresponding endo adducts. Chiral imidazoline 3-oxides react diastereospecifically (cis configuration of the tetrahydroimidazo ring) and diastereoselectively to give cis-endo adducts. The effects of substituents on the aromatic ring of the maleimide was investigated. The presence of electron-withdrawing or releasing groups have minor effect on the total yields but more pronounced is the effect on the ratio of exo and endo diastereomers. The adducts undergo an interesting and unprecedented ring-opening in the presence of secondary amines to give deoxygenated 3-imidazoline 3-oxides instead of the expected double cis elimination products. Tertiary amines did not induce any reaction.     

Thiophenol derivatives as a reducing agent for in situ generation of Cu(I) species via electron transfer reaction in copper‐catalyzed living/controlled radical polymerization of styrene

The copper‐catalyzed living radical polymerization (LRP) of styrene (St) was carried out in the presence of thiophenol derivative such as sodium thiophenolate (PhSNa) or p‐methoxythiophenol as a reducing agent for Cu(II) by using either 1‐chloro‐1‐phenyl ethane or ethyl‐2‐bromoisobutyrate as an initiator and N,N,N′,N″,N″‐pentamethyldiethylenetriamine as ligand at 110 °C. Kinetic experiments were carried out to reveal the effect of PhSNa concentration on copper‐catalyzed LRP of St. This technique was successfully applied for the preparation of both chain‐extended polymer and block copolymer polystyrene‐b‐poly(methyl methacrylate). The obtained polymers were characterized using GPC, ¹H‐NMR, and MALDI‐TOF measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5923–5932, 2006     

Some new oscillation results for a nonlinear dynamic system on time scales

We study the oscillation of a system of two first order nonlinear equations on time scales. This form includes the classical Emden-Fowler differential equation and many of its extensions. We generalize some well-known results of Atkinson, Bohner, Erbe, Peterson and others. We illustrate the results by several examples, including a superlinear Emden-Fowler dynamic system.     

Halogen-Bonded BODIPY Frameworks with Tunable Optical Features**

The ability to tune the optical features of BODIPY materials in the solid state is essential for their photorelated application and requires efficient control of the crystal packing. In this study, such control of BODIPY supramolecular assemblies was achieved by deliberate design and synthesis of a BODIPY containing a strong halogen-bond (XB) acceptor (−NO₂) and donor (I, Br) to mediate XB interactions. The di-halogenated structures formed isostructural mono-coordinate motif B3 , B4 (1D tubular structure) and symmetric bifurcated motif B4-II (1D zigzag chains structure) through N−O⋅⋅⋅I, Br XB interactions. These XB interactions promote singlet-to-triplet intersystem crossing and triplet-to-singlet reverse intersystem crossing due to partial delocalization of oxygen electrons onto Br and I, which leads to unexpected fluorescence enhancement of B4-II . Finally, the indirect optical band gaps of B3 , B4 and B4-II were amenable to tuning in the range of 1.85–2.50 eV by XB-driven crystal packings.     

A Novel and Selective Methylene Blue Imprinted Polymer Modified Carbon Paste Electrode

In this study, methylene blue (MB) imprinted microbeads were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).Differential pulse voltammetric responses of carbon paste electrodes modified with MB imprinted polymer were used to evaluate the adsorption and selectivity features of the polymer. For selectivity studies two basic dyestuffs (thionine blue and toluidine blue) which have similar structure to MB were chosen. Comparison of the voltammetric responses obtained with pure carbon paste and carbon paste modified with either imprinted or nonimprinted polymer electrodes revealed that MB imprinted polymer presented a higher selectivity to the template molecule MB in contrast to structurally similar molecules, thionine blue and toluidine blue.     

Determination of Cu(II), Fe(III), Mn(II) and Zn(II) in various samples after preconcentration with Rhizopus oryzae loaded natural cellulose (almond bark)

A procedure for the pre-concentration of Cu(II), Fe(III), Mn(II) and Zn(II) is described utilising a minicolumn of natural cellulose (almond bark) modified with fungus (Rhizopus oryzae) prior to their determination by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). The optimum pre-concentration conditions such as pH and flow rate for the analytes have been investigated. The analytes were quantitatively retained on the column between pH 6 and 8. Elution was made with 10 mL 1 M HCl solution. Under the optimum conditions, recoveries were found as 97 ± 3%, 96 ± 3%, 98 ± 3% and 94 ± 2% for Cu(II), Fe(III), Mn(II) and Zn(II), respectively, at 95% confidence level. The detection limits obtained from preconcentration of 50 mL of blank solutions (n = 11) were 1.6, 1.8, 2.8 and 1.2 µg L^?1 for Cu(II), Fe(III), Mn(II) and Zn(II), respectively. Relative standard deviations (RSD) of the recoveries for five replicate analyses were lower than 3%. The proposed method was validated by analysing certified reference materials (Peach Leaves SRM 1547 and Fish Tissue IAEA-407). Determination of the Cu(II), Fe(III), Mn(II) and Zn(II) in K?z?l?rmak River water, green beans, beans leave and tomato leaves and fish (Tinca tinca) tissue samples was performed by the proposed method.