Synthesis,vibrational, and conformational properties of novel polyazadioxime chain molecules

Novel large polyazadioxime molecules 4,5,8,9-tetraaza-3,6,7,10-tetramethyl -3,5,7,9-dodecatetraene-2, 11-dione-2, 11-dioxime (H₂doxN₄) and 4,5,8,9,12, 13-hexaaza-3,6,7,10,11,14-hexamethyl-3, 5,7,9,11,13-hexadecahexane-2,15-dione-2, 15-dioxime (H₂doxN₆) were synthesized. The molecular geometries of these molecules as well as smaller dioxime molecules, H₂dox and H₂doxN₂ were optimized by using modified intermediate neglect of differential overlap (MNDO) calculations. The optimized conformations for all the molecules under study are close to the all-E, all-s trans conformation of C_2h symmetry group. However, the energy barriers of internal rotation around the N-N single bonds were found to be low. Therefore some distortions of the polyazabackbone through internal rotation the N-N bonds have been evidenced. By infrared and Raman spectroscopies in the solid state as well as in solution. From the MNDO calculations and vibrational spectroscopy, the polyaza chain molecules under study appear as a poorly conjugated system and can be represented as a sequence of single and double bond alternation.     

Kinetics of free radical polymerization—XXXI. Solvent effect on the polymerization rate of ethyl acrylate

The free radical polymerization of ethyl acrylate was investigated in benzene and dimethyl formamide solutions at 50°. The effects of initiator and monomer concentration were studied over a wide range. The overall rate of polymerization was proportional to (initiator concentration)^{$\text{1}\text{2}$} but not to the concentration of the monomer. We attempted to interpret this solvent effect on the basis of (i) the diffusion theory, (ii) the theory of charge transfer complexes and (iii) the theory of hot radicals. Our experimental results could only be explained quantitatively in terms of hot radicals.     

Fused heterocycles,VI: Reactions of 3-arylidenechromanones and -1-thiochromanones with thiourea

Summary Reactions of 3-arylidenechromanones (1 – 4) and -1-thiochromanones (5 – 8) with thiourea gave thiazines (9 – 16) under acidic and pyrimidine derivatives (17 – 21) under alkaline reaction conditions

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Kondensierte Heterocyclen, VI: Umsetzungen von 3-Arylidenchromanonen und-1-thiochromanonen mit Thioharnstoff

Zusammenfassung Die Umsetzung von 3-Arylidenchromanonen1 – 4 und -1-thiochromanonen5 – 8 mit Thioharnstoff liefert unter sauren Bedingungen die Thiazine9 – 16 und in basischem Milieu die Pyrimidine17 – 21.

     

Assessing the biocompatibility of NiTi shape memory alloys used for medical applications

The present paper reviews aspects related to the biocompatibility of NiTi shape memory alloys used for medical applications. These smart metallic materials, which are characterised by outstanding mechanical properties, have been gaining increasing importance over the last two decades in many minimal invasive surgery and diagnostic applications, as well as for other uses, such as in orthodontic appliances. Due to the presence of high amounts of Ni, the cytotoxicity of such alloys is under scrutiny. In this review paper we analyse work published on the biocompatibility of NiTi alloys, considering aspects related to: (1) corrosion properties and the different methods used to test them, as well as specimen surface states; (2) biocompatibility tests in vitro and in vivo; (3) the release of Ni ions. It is shown that NiTi shape memory alloys are generally characterised by good corrosion properties, in most cases superior to those of conventional stainless steel or Co–Cr–Mo-based biomedical materials. The majority of biocompatibility studies suggest that these alloys have low cytotoxicity (both in vitro and in vivo) as well as low genotoxicity. The release of Ni ions depends on the surface state and the surface chemistry. Smooth surfaces with well-controlled structures and chemistries of the outermost protective TiO₂ layer lead to negligible release of Ni ions, with concentrations below the normal human daily intake.     

Comparison of the Temperature Effect on the π∗←n and π∗←π Electronic Transition Bands of NO<Subscript>3</Subscript><Superscript>−</Superscript>(aq)

The effect of temperature on the π∗←π transition band in the UV absorption spectrum of NO₃⁻(aq) centered at ≈200 nm was studied in the temperature range 10–70 ^∘C. The observed temperature independence of this band was in contrast to the significant influence of temperature on the nitrate π∗←n transition reported recently by us. However, taking into account the electronic states involved in both the transitions, it was concluded that this finding was in accordance with our previous assumption that interconversion between spectrally distinct (with respect to π∗←n band) nitrate species included the rupture/formation of hydrogen bond(s) in the hydration shell of the nitrate ion.     

Monodisperse chloromethyl-functionalized macroporous polymer particles by seeded polymerization in aqueous media

This study presents a method to produce monodisperse chloromethyl-functionalized macroporous poly(styrene-co-divinylbenzene) polymer particles by seeded polymerization in aqueous media. We observed that the molecular structure of polystyrene seed particles, the composition of the secondary monomer mixtures, and the type of solvents were very important factors that determine the morphology and porosity of the final particles. This study proposes that the molecular chemistry of polystyrene seed polymers, increasing molecular weight or crosslinking, is another factor that can control the porosity of the final particles. Also, the selection of a poor solvent was effective in forming the larger surface area. In this study, it was confirmed that the chloromethyl groups introduced on the surface of porous particles were quantified chemically and their effective incorporation had a close relationship with the surface area.     

Mössbauer study of LaNiSn and NdNiSn compounds and their deuterides

Summary LaNiSn and NdNiSn compounds and their deuterides have been studied by variable temperature ¹¹⁹Sn M?ssbauer spectroscopy. The hyperfine parameters obtained experimentally are in good agreement with those derived from first principle calculations. The enlargement of quadrupole splitting observed for LaNiSn after deuteration confirms the lower symmetry of electron density around tin atoms indicated by the calculation of partial Sn-p density of states (DOS). Magnetic ordering is observed at low temperature in deuterided NdNiSn.     

Structural Changes of Cellulose Crystallites Induced by Mercerisation in Different Solvent Systems; Determined by Powder X-ray Diffraction Method

The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure, treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process. On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on cellulose alkalisation while over-pressure prevented crystal changes.     

Facile generation of platinum(IV) compounds with mixed labile moieties. Hydrogen peroxide oxidation of platinum(II) to platinum(IV) compounds

Hydrogen peroxide oxidation of platinum(II) compounds containing labile groups such as Cl, OH, and alkene moieties has been carried out and the products characterized. The reactions of [Pt^II (X)₂ (N–N)] (X = Cl, OH, X₂ = isopropylidenemalorate (ipm); N–N 2,2-dimethyl-1,3-propanediamine [(dmpda), N-isopropyl-1,3-propanediamine (ippda)] with hydrogen peroxide in an appropriate solvent at room temperature affords [Pt^IV (OH)(Y)(X)₂(N–N)] (Y = OH, OCH₃). The crystal structures of [Pt^IV(OH)(OCH₃)(Cl)₂(dmpda)]·2H₂O (P-1 bar, a = 6.339(2) Å , b = 9.861(1) Å, c = 11.561(1) Å, a = 92.078(9)°, β = 104.78(1)°, γ=100.54(1)°, V = 684.3(2) ų, Z = 2R = 0.0503) and [Pt^IV(OH)₂(ipm)(ippda)]·3H₂O (C 2/c, a = 27.275(6) Å, b=6.954(2) Å, c = 22.331(4) Å, β = 118.30(2)°, V = 3729(2) ų, Z = 8, R = 0.0345) have been solved and refined. The local geometry around the platinum(IV) atom approximates to a typical octahedral arrangement with two added groups (OH and OCH₃; OH and OH) in a transposition. The platinum(IV) compounds with potential labile moieties may be important intermediate species for further reactions.     

A new thermostable peroxidase from garlic Allium sativum

Analysis of peroxidase activity by native polyacrylamide gel electrophoresis (PAGE) from a garlic bulb (Allium sativum L) extract showed two major activities (designated POX1 and POX2). The POX2 isoenzyme was purified to homogeneity by ammonium sulfate precipitation, gel filtration, and cation-exchange chromatography. The purified enzyme was found to be monomeric with a molecular mass of 36.5 kDa, as determined by sodium dodecyl sulfate-PAGE. The optimum temperature ranged from 25 to 40 degrees C and optimum pH was about 5.0. The apparent Km values for guaiacol and H2O2 were 9.5 and 2 mM, respectively. POX2 appeared highly stable since 50% of its activity was conserved at 50 degrees C for 5 h. Moreover POX2 was stable over a pH range of 3.5-11.0. Immobilization of POX2 was achieved by covalent binding of the enzyme to an epoxy-Sepharose matrix. The immobilized enzyme showed great stability toward heat and storage when compared with soluble enzyme. These properties permit the use of this enzyme as a biosensor to detect H2O2 in some food components such as milk or its derivatives.