Design of experiments in 241Am alpha source preparation by electrodeposition: an approach to process optimization

This work describes a procedure to improve the quality of an ²⁴¹Am alpha source obtained by means of electrodeposition. The technique of design of experiments (DoE) was applied in order to perform a multivariate analysis of the experimental variable effects taking into consideration the following: i—amperage, d—cathode–anode distance, t—time and PP—polishing process. A 3⁴⁻² fractional design was employed using four experimental factors, three levels per factor, and three response variables were studied: H_area = electrodeposited active area, %R = activity recovery percentage, and Δ_1/2 = width at half-height. Thanks to this simple design, 9 experiments were enough, done in triplicate, to discern how Δ_1/2 and %R are modified when experimental factors change. Additionally, this work provides tools to perform effect statistical analysis of experimental factors, and to pose linear models applying significant terms. The models obtained were validated by analysis of variance and they were of help to verify the choice of significant factors by means of DoE and to approximate to the optimization of the preparation method of a ²⁴¹Am alpha source by means of contour plots of Δ_1/2 and %R.

     

Type-I intermittency with discontinuous reinjection probability density in a truncation model of the derivative nonlinear Schrödinger equation

In previous papers, the type-I intermittent phenomenon with continuous reinjection probability density (RPD) has been extensively studied. However, in this paper type-I intermittency considering discontinuous RPD function in one-dimensional maps is analyzed. To carry out the present study the analytic approximation presented by del Río and Elaskar (Int. J. Bifurc. Chaos 20:1185–1191, 2010) and Elaskar et al. (Physica A. 390:2759–2768, 2011) is extended to consider discontinuous RPD functions. The results of this analysis show that the characteristic relation only depends on the position of the lower bound of reinjection (LBR), therefore for the LBR below the tangent point the relation \(\left\langle l \right\rangle \propto \varepsilon ^{-1/2}\) , where \(\varepsilon \) is the control parameter, remains robust regardless the form of the RPD, although the average of the laminar phases \(\left\langle l \right\rangle \) can change. Finally, the study of discontinuous RPD for type-I intermittency which occurs in a three-wave truncation model for the derivative nonlinear Schrodinger equation is presented. In all tests the theoretical results properly verify the numerical data.     

Shape memory epoxies based on networks with chemical and physical crosslinks

Epoxies are an important family of shape memory polymers (SMP) due to their excellent stability and thermo-mechanical endurance and the high values of shape fixity and shape recovery. Actuators based on these materials can be designed for large tensile elongations (e.g., 75% or higher) or large recovered stresses (e.g., 3 MPa or higher). However, meeting these requirements simultaneously is a difficult task because changes in the crosslink density affect both variables in opposite ways. We show that an SMP based on an epoxy network with both chemical and physical crosslinks could be strained up to 75% in four repeated shape memory cycles with tensile stresses close to 3 MPa. Shape fixity and shape recovery values were close to 98% and 96%, respectively, for everyone of the cycles, without any significant change between the first and subsequent cycles.     

On the mechanism of Re(I)-carboxylate bond cleavage by perchloric acid: a kinetic and spectroscopic study

We have studied the reaction between pz-CO(2)-Re(CO)(3)(bpy) and perchloric acid in acetonitrile by following the UV-vis and IR spectral changes in the reaction mixture. A fast equilibrium was found to be established between solvated protons, pz-CO(2)-Re(CO)(3)(bpy), and the protonated intermediate [pz-C(OH)O-Re(CO)(3)(bpy)](+) which finally yields pz-COOH and Re(CO)(3)(bpy)(CH(3)CN)(+) as reaction products. This intermediate has been characterized by UV-vis and IR spectroscopies and by DFT calculations. The fully optimized DFT/CPCM structures for pz-CO(2)-Re(CO)(3)(bpy) and [pz-C(OH)O-Re(CO)(3)(bpy)](+) were compared with the X-ray structure of pz-CO(2)-Re(CO)(3)(bpy). The structural parameters associated with the carboxyl group in the protonated intermediate are between those of pz-CO(2)-Re(CO)(3)(bpy) and pz-COOH. Multivariate curve resolution methods were employed to obtain the spectrum of the protonated intermediate and the concentration profiles from the full matrix of time-resolved UV-vis spectra. The proposed mechanism was numerically simulated by using Runge-Kutta methods. Model parameters were estimated by nonlinear regression fitting of the concentration profiles, yielding values of log(K) = 4.9 ± 0.3 and k = 0.16 ± 0.03 min(-1) for the formation equilibrium constant and the decay rate constant of the protonated intermediate, respectively.     

Graphene oxide as an electrophile for carbon nucleophiles

The covalent, surface functionalization of graphene oxide with the malononitrile anion has been demonstrated. Once installed, these surface-bound "molecular lynchpins" can be chemically modified to increase the solubility of the graphene derivative in either organic or aqueous environments.     

Synthesis,structure and cytotoxicity studies on diorganotin (R = Me,Et) complexes of N-methylpyridoxine (MePN,PN = Vitamin B6) containing different anions

The interaction of dimethyl- and diethyltin(IV) cations with methylpyridoxine iodide ([MePN]I; PN = pyridoxine) was studied in ethanol/water (80:20(v/v) containing Cl^?, NO₃^? or I^? ions in different molar ratios. Several compounds containing the deprotonated (MePN-H) or neutral (MePN) ligand were isolated and characterized by elemental analysis, IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy and FAB mass spectrometry. The compounds [SnMe₂(MePN-H)](I₃), [SnEt₂(MePN-H)](I₃), [SnMe₂(MePN-H)(NO₃)], [SnEt₂(MePN-H)(NO₃)] and [SnMe₂(MePN)₂]I₂ were studied by X-ray diffractometry. The compounds in which the MePN-H ligand is present can be described as containing dinuclear [SnR₂(MePN-H)]₂²⁺ (R = Me, Et) units, in which two bridging chelating methylpyridoxinato ligands link two metal atoms. Interactions also exist between the metal and the I₃^? or NO₃^? anions and these interactions differ in degree and type. On the other hand, in the only example of a complex containing the MePN ligand, the mononuclear [SnMe₂(MePN)₂]²⁺ unit is present. The in vitro antitumor activity of these complexes against the HeLa, A2780 and A2780cis cell lines was determined and compared with that of the equivalent PN derivatives.     

Linking origin of the electric field-assisted β-PbF2 crystallization in lead oxyfluoroborate glasses below T g to simultaneous cathode/anode-compensated electrochemical reactions

Full validation of the electrochemical mechanisms so far postulated as driving force of electric field-assisted non-spontaneous crystallization development in given glasses has suffered experimental restrictions. In this work, we looked into origin of this phenomenon in lead oxyfluoroborate glasses, resulting in β-PbF₂ growth even below the corresponding glass transition temperatures, through achieving a systematic study of not only Pt,Ag/Glass/Ag,Pt- but also Pt,Ag/Glass/YSZ:PbF₂/Ag,Pt-type cells, where YSZ:PbF₂ represents a two-phase system (formed by Y₂O₃-doped ZrO₂ and PbF₂). It is demonstrated that crystallization induction in these glasses involves Pb²⁺ ions reduction at the cathode, the phenomenon being, however, confirmed only when the F⁻ ions were simultaneously also able to reach the anode for oxidation, after assuring either a direct glass–anode contact or percolation pathways for free fluoride migration across the YSZ:PbF₂ mixtures. A further support of this account is that the electrochemically induced β-PbF₂ phase crystallizes showing ramified-like microstructure morphology that arises, accordingly, from development of electroconvective diffusion processes under electric field action.     

Synthesis of 3-methoxy-9-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H-benzo[7]annulen-4-ol,a potent antineoplastic benzosuberene derivative for anti-cancer chemotherapy

Benzosuberene 8 is a tubulin polymerization inhibitor that possesses remarkable potency against a variety of cancer cell lines. Herein, an efficient synthetic route for 8 is described featuring a Claisen rearrangement/RCM sequence and a late stage Suzuki coupling as the key steps. By adopting this strategy 8 was synthesized in eight steps in 18% overall yield starting from known compound 18.     

Influence of plant densities and fertilization on maize grains by near-infrared spectroscopy

Near-infrared spectroscopy is a rapid process analytical technology for measuring a wide range of constituents of biological materials. The objective of the current study was to investigate maize grains grown under different levels of fertilization and plant densities using near-infrared spectroscopy. Maize grains from the same plant density had their protein content increased with doses of nitrogen. In addition, it was observed the decrease in protein content with the increase in plant densities. Except for ash content, models for the assessed parameters indicated that near-infrared spectra has the potential for fast assessment of maize grains.