Gold-copolymer nanoparticles: Poly(ε-caprolactone)/poly(N-vinyl-2-pyrrolydone) Biodegradable triblock copolymer as stabilizer and reductant

Block copolymers have been extensively used in the synthesis of many types of nanoparticles, where generally are considered as stabilizer and protective agent. In this work a double function of the biodegradable triblock copolymer poly(N-vinyl-2-pyrrolidone)-b-poly(ε-caprolactone)-b-poly(N-vinyl-2-pyrrolidone), (PVP-PCL-PVP) in the gold nanoparticle-copolymer synthesis is reported.Gold-copolymer composed nanoparticles were synthesized using the triblock copolymer (PVP-PCL-PVP) and potassium tetrachloro aurate (III), both in aqueous solution. The copolymer work as both, reductant and stabilizer agent. The obtained nanoparticles were characterized by FT-IR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The shape and the size of the obtained nanoparticles are dependent on the copolymer/salt of gold concentration ratio used in the synthesis.To complement the experimental results about the copolymer role in the nanoparticles synthesis, computational tools were used to characterize the reactivity of the reactant species.     

Synthesis of telehelic oligodimethylsiloxanes with 4-carboxypyrrolidone fragments: rheological and thermal properties

Telehelic oligodimethylsiloxanes containing 4-carboxypyrrolidone fragments were synthesized by the reactions of oligodimethylsiloxanes bearing terminal 3-aminopropyl groups with itaconic acid. The thermal and rheological properties of the obtained polymers were studied. The activation energies of viscous flow of the oligomers obtained and the previously synthesized oligodimethylsiloxanes containing terminal fragments of undecenoic or benzoic acid are compared.

     

Effect of fluorinated tetrahydrocarbazole derivatives on the enzymes of oxidative deamination of biogenic amines and on the process of lipid peroxidation

The effect of two fluorinated derivatives of tetrahydrocarbazoles on mitochondrial en-zymes catalyzing the oxidative deamination of biogenic amines such as monoamine oxidase A and B (MAO-A and MAO-B) has been investigated. A dose-dependent effect of the studied compounds on the enzymatic activity MAO-A was shown. It was revealed that both com-pounds are MAO-B inhibitors. Inhibition mechanisms were established and MAO-B inhibi-tion constants were calculated. The above derivatives exhibit strong antioxidant and antirad-ical activity.     

Sur la répartition des valeurs de la fonction d'Euler

Let (x) denote the number of those integers n with (n) x, where denotes the Euler function. Improving on a well-known estimate of Bateman (1972), we show that (x)-Ax R(x), where A=(2)(3)/(6) and R(x) is essentially of the size of the best available estimate for the remainder term in the prime number theorem.     

Colorimetric determination of iron in infant fortified formulas by sequential injection analysis

 A procedure is described for the colorimetric determination of iron in infant fortified formulas based on sequential injection analysis (SIA). Iron(III) complexation with thiocyanate is used as colour developing reaction. The system enables the determination of iron in the samples (after digestion by dry ashing and treatment with 0.2 mol/L nitric acid in the range of 0.50–20.0 mg/L, consuming 140 μL of the sample and 8 mg thiocyanate per determination. The reactor geometry and the adjustment of the ionic content of the calibration solutions is important for the accuracy of the results. A regression line according to the equation [Fe(III) (mg/L)]_SIA=−0.3(±0.4)+1.03(±0.04) [Fe(III) (mg/L)]_FAAS was obtained after comparative analysis of a set of 12 samples. The measurement rate was 34 s, thus allowing to analyze 100 samples per hour with a relative standard deviation lower than 2%. Received: 30 July 1996/Revised: 1 October 1996/Accepted: 4 October 1996     

Poly(itaconates) monolayers behavior at the air/water interface. Study at different surface concentration

Polymer monolayers spread at the air/water interface were obtained for: poly(monooctyl itaconate) (PMOI), poly(monodecyl itaconate) (PMDI), poly(monododecyl itaconate) (PMDoI), poly(monobenzyl itaconate) (PMBzI), poly(methyldodecyl itaconate) (PMeDoI) and the alternating copolymer (monooctyl itaconate-alt-maleic anhydride) (MOI-alt-MA). By monolayer compression at constant temperature, the respective Langmuir isotherms for these polymers were obtained. For all polymers the zero-pressure limiting area per repeating unit (ru) Ao, and the collapse pressure π_c were determined. At low surface polymer concentrations, the monolayers characterization was carried out according to the surface pressure expressed as a function of the surface concentration. The behavior observed was described by the virial expansion development. At the semidilute region, the surface pressure variation was expressed in terms of the scaling laws as a power function of the surface concentration.     

Electron diffraction study on the molecular structure of methane sulphonyl fluoride

The molecular structure of methane sulphonyl fluoride in the vapour state was studied by electron diffraction. Assuming a value of 2.480A?for the distance between the oxygen atoms from a microwave determination, the following geometrical parameters (r_a structure) have been obtained: r(C-H) = 1.093±0.010Å, r(S-O) = 1.410±0.003Å, r(S-F) = 1.561 ±0.004Å, r(S-C) = 1.759±0.006Å, ∠F-S-C = 98.2±1.5°, ∠-S-F = 106.2±0.4°, ∠-O-S-O = 123.1 ±1.5° and ∠H-C-H = 112.9±1.9°. All the observed variations in the molecular geometries of (CH₃)₂SO₂, CH₃SO₂Cl, CH₃SO₂F and SO₂F₂ may be accounted for by the valence shell electron pair repulsion theory. It is particularly advantageous to combine electron diffraction and microwave data in studying sulphone molecular geometries.     

The Distribution of the Sojourn Time for the Brownian Excursion

The solutions of various problems in the theories of queuing processes, branching processes, random graphs and others require the determination of the distribution of the sojourn time (occupation time) for the Brownian excursion. However, no standard method is available to solve this problem. In this paper we approximate the Brownian excursion by a suitably chosen random walk process and determine the moments of the sojourn time explicitly. By using a limiting approach, we obtain the corresponding moments for the Brownian excursion. The moments uniquely determine the distribution, enabling us to derive an explicit formula.     

Dynamic mechanical and dielectric relaxations of poly(difluorobenzyl methacrylates)

This work reports the mechanical and dielectric relaxation spectra of three difluorinated phenyl isomers of poly(benzyl methacrylate), specifically, poly(2,4‐difluorobenzyl methacrylate), poly(2,5‐difluorobenzyl methacrylate) and poly(2,6‐difluorobenzyl methacrylate). The strength of the dielectric glass–rubber relaxation of the 2,6 difluorinated phenyl isomer is, respectively, nearly three and two times larger than the strengths of the 2,5 and 2,4 isomers. The 2,4 isomer presents a mechanical α peak the intensity of which is nearly two times that of the other two isomers. Both the mechanical and dielectric relaxation spectra display a subglass process, called γ relaxation, centered in the vicinity of −50 °C at 1 Hz and, in some cases, a subglass β absorption is detected at higher temperature partially masked by the glass–rubber relaxation. The mean‐square dipole moments per repeating unit, 〈μ2〉/x, measured at 25 °C in benzene solutions, are 2.5 D², 1.9 D², and 5.0 D² for poly(2,4‐difluorobenzyl methacrylate), poly(2,5‐difluorobenzyl methacrylate) and poly(2,6‐difluorobenzyl methacrylate), respectively. These results, in conjunction with Onsager type equations, permit to conclude that auto and cross‐correlation contributions to the dipolar correlation coefficient may have the same time‐dependence. On the other hand, dipole intermolecular interactions, rather than differences in the flexibility of the chains, seem to be responsible for the relatively high calorimetric glass‐transition temperature of the 2,6 diphenyl isomer, which is, respectively, nearly 36 °C and 32 °C above the T_g's of the 2,4 and 2,5 isomers. Molecular Mechanics calculations give a good account of the differences observed in the polarity of the polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2179–2188, 2000