Two (Z)-dehydrobutyrine-containing microcystins from a hepatotoxic bloom of Oscillatoria agardhii from Soulseat Loch, Scotland

Two (Z)-dehydrobutyrine(Dhb)-containing microcystins, [d-Asp3, (Z)-Dhb7]microcystin-HtyR (1) and [d-Asp3, (Z)-Dhb7]microcystin-LR (2), were isolated from a hepatotoxic bloom of the cyanobacterium Oscillatoria agardhii from a freshwater lake in Scotland. The geometrical structure of the Dhb units in the microcystins was determined as Z on the basis of NOE and ROESY experiments.     

Continuum theory of micromorphic electromagnetic thermoelastic solids

A continuum theory is introduced for micromorphic thermoelastic solids subject to electromagnetic interactions. Frame-independent, linear constitutive equations, satisfying thermodynamic restrictions are constructed. Constitutive equations display several new phenomena arising from microstructural interactions. Field equations are given. The theory presented here is important to studying high frequency, short wave-length modes of microstructural solids.     

Effects of Er,Cr:YSGG laser parameters on dentin bond strength and interface morphology

Previous studies have shown the effects of Er,Cr:YSGG laser irradiation on the dentin bond strength; but there are few reports that show the significance of the irradiation with different laser parameters on dentin bond strength and interface morphology. This in‐vitro study attempted to evaluate the microtensile bond strength (μTBS) and interface morphology of resin‐dentin interfaces, either followed by treatment with Er,Cr:YSGG laser irradiation with different parameters or not. The flattened dentin samples of 35 bovine teeth were embedded into acrylic blocks and randomly divided into seven groups according to surface treatments using Er,Cr:YSGG lasers with different parameters: 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz, 1.5 W/20 Hz, 1.5 W/35 Hz, 1.5 W/50 Hz, or no laser treatment (n = 5). Composite buildups were done over bonded surfaces and stored in water (24 hours at 37°C). Specimens were sectioned into sticks that were subjected to μTBS testing and observed under FE‐SEM. Control groups (27.70 ± 7.0) showed statistically higher values than laser‐irradiated groups. There were no significant differences among laser groups. Despite that, increasing the pulse frequency yielded slightly higher bond strength. Depending on laser settings, Er,Cr:YSGG laser irradiation caused interfacial gaps and resin tags with wings morphology. With the parameters used in this study, Er,Cr:YSGG laser irradiation promoted morphological changes within resin‐dentin interfaces and negatively influenced the bond strength of adhesive systems. Microsc. Res. Tech. 78:1104–1111, 2015. © 2015 Wiley Periodicals, Inc.     

Measurements of Microhardness and Thermal and Electrical Properties of the Binary Zn-0.7wt.%Cu Hypoperitectic Alloy

Zn-0.7wt.%Cu hypoperitectic alloys were directionally solidified upwards with different temperature gradients (3.85 K/mm to 9.95 K/mm) at a constant growth rate (0.042 mm/s), and with different growth rates (0.0083 mm/s to 0.436 mm/s) at a constant temperature gradient (3.85 K/mm), using a Bridgman-type growth apparatus. Measurements of microhardness of the directionally solidified samples were carried out. The dependence of micro- hardness (HV) on growth rate (V) and temperature gradient (G) was analyzed. According to these results, it has been found that, for increasing values of G and V, the value of HV increases. Variations of electrical resistivity (ρ) and electrical conductivity (σ) for cast samples with temperature from 300 K to 670 K were also measured by using a standard direct-current (DC) four-point probe technique. The variation of the Lorenz coefficient with temperature for the Zn-0.7wt.%Cu hypoperitectic alloy was determined using the measured values of electrical conductivity and thermal conductivity. The enthalpy of fusion for the same alloy was determined by means of differential scanning calorimetry (DSC) from the heating trace during the transformation from liquid to solid.     

Synthesis and characterization of graft copolymers of melamine: Thermal stability, electrical conductivity, and optical properties

In this study, novel three Schiff bases of melamine were synthesized via condensation reaction of melamine with salicylaldehyde, 3-hydroxybenzaldehyde, and 4-hydroxybenzaldehyde namely N,N′,N′′,-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (2-HPMTT), N,N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (3-HPMTT), N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (4-HPMTT), respectively. Then, oligo/polyphenol derivatives of these Schiff bases were obtained by grafting melamine onto oligosalicylaldehyde (OSA), oligo-3-hydroxybenzaldehyde, and oligo-4-hydroxybenzaldehyde that have generate names of poly-N,N′,N′′-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-2-HPMTT), poly-N, N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-3-HPMTT), and oligo-N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (O-4-HPMTT), respectively. The structures of the synthesized compounds were confirmed by FT-IR, UV–vis, ¹H NMR, and ¹³C NMR techniques. The characterization was made by TG-DTA, DSC, size exclusion chromatography (SEC), and solubility tests. Electrical conductivities of the synthesized materials were measured by four-point probe technique using a Keithley 2400 electrometer showing that the synthesized oligo/polyphenols have higher electrical conductivities than the monomeric Schiff bases. Also considerable increases in the conductivities were observed when they were doped with iodine as a doping agent. The order of increase rates of the conductivities were found as follows: 2-HPMTT > P-2-HPMTT > P-3-HPMTT > 3-HPMTT > 4-HPMTT > P-4-HPMTT. Additionally, the optical band gaps (E_g) were calculated by using the absorption spectra and found to be 2.78, 2.17, 3.58, 3.30, 4.03, and 2.82 eV for 2-HPMTT, P-2-HPMTT, 3-HPMTT, P-3-HPMTT, 4-HPMTT, and O-4-HPMTT, respectively.     

Evaluation of sorption properties of Turkish tarhana powder

Moisture adsorption isotherms of commercial tarhana powder, a popular Turkish food used in soup making, were determined at 10 °C, 20 °C and 30 °C. Gravimetric static method was applied at 0.08–0.92 water activity range. The data was fitted to Guggenheim-Anderson-deBoer(GAB), Oswin, Hendersonand Brunauer-Emmett-Teller(BET)equations. Mean relative deviation (%E) was used to compare the goodness of fit. The BET was found the best equation for the range of water activity 0.08–0.58. The GAB equation was found adequate and gave similar result with the Oswinequation at 10 °C and 20 °C, while the Oswinequation was better for characterizing the adsorption behavior of tarhana sample for the whole range of temperature and water activity studied.     

Development of New Collagen/Clay Composite Biomaterials

The fabrication of collagen-based biomaterials for skin regeneration offers various challenges for tissue engineers. The purpose of this study was to obtain a novel series of composite biomaterials based on collagen and several types of clays. In order to investigate the influence of clay type on drug release behavior, the obtained collagen-based composite materials were further loaded with gentamicin. Physiochemical and biological analyses were performed to analyze the obtained nanocomposite materials after nanoclay embedding. Infrared spectra confirmed the inclusion of clay in the collagen polymeric matrix without any denaturation of triple helical conformation. All the composite samples revealed a slight change in the 2-theta values pointing toward a homogenous distribution of clay layers inside the collagen matrix with the obtaining of mainly intercalated collagen-clay structures, according X-ray diffraction analyses. The porosity of collagen/clay composite biomaterials varied depending on clay nanoparticles sort. Thermo-mechanical analyses indicated enhanced thermal and mechanical features for collagen composites as compared with neat type II collagen matrix. Biodegradation findings were supported by swelling studies, which indicated a more crosslinked structure due additional H bonding brought on by nanoclays. The biology tests demonstrated the influence of clay type on cellular viability but also on the antimicrobial behavior of composite scaffolds. All nanocomposite samples presented a delayed gentamicin release when compared with the collagen-gentamicin sample. The obtained results highlighted the importance of clay type selection as this affects the performances of the collagen-based composites as promising biomaterials for future applications in the biomedical field.     

The polymerization of acrylamide initiated with CE(IV) and KMNO4 redox systems in the presence of glycine

Glycine-Ce(IV) salts and −KMnO₄ initiator systems were used for the polymerization of acrylamide, resulting in water-soluble polyacrylamide, which contains amino acid end groups. The dependence of polymerization yields and molecular weights of polymers on the mole ratio of acrylamide monomer to glycine, the polymerization time, the temperature, and the concentration of sulfuric acid were investigated. The decrease in the mole ratio of acrylamide to glycine resulted in a decrese in the molecular weight, and an increase in the yield of acrylamide polymer, which contains a glycine end group. With increasing acid concentration of the polymeric solution, the polymerization yield and the molecular weight of polymer decrease. Ce(IV) and Mn(IV) reduced to Ce(III) and Mn(II) in the polymerization reaction. The amounts of Ce(III) and Mn(II) bound to polymer were determined. The composition of the polymerization product was investigated and a bimodal character of the molecular weight distribution was observed. The mechanism of this phenomena is discussed. © 1996 John Wiley & Sons, Inc.     

In situ fluorescence experiments for real-time monitoring of annealed high-T latex film dissolution

A new technique, based on steady-state fluorescence measurements, is introduced for studying dissolution of polymer films. These films are formed from naphthalene and pyrene labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene. Diffusion of solvent (chloroform) into the annealed latex film was followed by desorption of polymer chains. Annealing was performed above T_g at various temperatures for 30-min time intervals. Desorption of pyrene labeled PMMA chains was monitored in real time by the pyrene fluorescence intensity change. Desorption coefficients were found to be between 1 and 4 × 10⁻¹⁰ cm²/s and two different dissolution mechanisms were detected. © 1996 John Wiley & Sons, Inc.