Selective microdetermination of phosphate based on Volhard's titration

A selective method for the microdetermination of phosphate has been developed. The phosphate is precipitated from homogeneous solutions as silver phosphate, which after being filtered and washed is dissolved in dilute nitric acid, and the silver ions set free are determined by Volhard's titration. Whereas the halide ions interfere if the conventional precipitation is adopted, they do not interfere if precipitation is conducted from homogeneous solutions. The method is simple and accurate to a maximum error of ±1%.     

Crystal structure and magnetic interactions in nickel(II) dibridged complexes formed by two azide groups or by both phenolate oxygen-azide, -thiocyanate, -carboxylate, or -cyanate groups

Tridentate/tetradentate Schiff base ligands L(1) and L(2), derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L(1))(micro(1,1)-N(3))Ni(L(1))(N(3))(OH(2))].H(2)O (1), [[Ni(L(1))(micro(1,1)-NCS)Ni(L(1))(NCS)(OH(2))][Ni(L(1))(micro-CH(3)COO)Ni(L(1))( NCS) (OH(2))]] (2) [[2A][2B]], [Ni(L(1))(micro(1,1)-NCO)Ni(L(1))(NCO)(OH(2))].H(2)O (3), and [Ni(L(2)-OMe)(micro(1,1)-N(3))(N(3))](2) (4), where L(1) = Me(2)N(CH(2))(2)NCHC(6)H(3)(O(-))(OCH(3)) and L(2) = Me(2)N(CH(2))(2)NCHC(6)H(3)N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a micro(1,1) mode and micro(2)-phenolate oxygen ion for 1-3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic susceptibility (chi(M)) versus temperature measurements. The chi(M) nus T plot reveals that compounds 1 and 4 are strongly ferromagnetically coupled, 3 shows a weak ferromagnetic behavior, and 2 is very weakly antiferromagnetically coupled.     

Unprecedented Blue Intrinsic Photoluminescence from Hyperbranched and Linear Polyethylenimines: Polymer Architectures and pH‐Effects

The intrinsic photoluminescence properties of hyperbranched polyethylenimines (PEIs) and their linear counterpart (LPEIs) have been studied in absence of any classical fluorescent probes. The comparison of the inherent fluorescence emission between hyperbranched polyethylenimines and their linear analogues demonstrates that linear polyamines are capable of producing strong intrinsic photoluminescence species having long excited lifetimes without need of having a tridimensional‐branched structure. The creation of inherently fluorescent polymeric centers from hyperbranched and linear polyethyleimines can be modulated by specific chemical modification and oxidation of amine groups as well as by adjusting the acidity of the polymer.

     

Set point identification of a tribocharging process for mixed granular solids

Identification of the optimal operating conditions is a critical issue for the industrial application of tribocharging techniques. The aim of this paper is to formulate a set of recommendations regarding the choice of tray length, vibration amplitude and material feed-rate values for a vibratory-type tribocharger. The study was carried out on a laboratory vibratory feeder with granular plastics originating from waste electrical and electronic equipment. Several one-factor-at-a-time experiments followed by a composite factorial experiment were performed based on a two-step strategy: 1) identifying the domain of variation of the controlled variables; 2) finding the best choice of the set point.     

Algèbres de Lie quasi-réductives

We study the class of algebraic Lie algebras for which the generic stabilizer of the coadjoint action is reductive modulo the center.     

A reusable polymer‐supported copper(I) catalyst for triazole click reaction on water: An experimental and computational study

In the search for establishing a clickable copper‐catalysed (3 + 2) Huisgen azide–alkyne cycloaddition (CuAAC) reaction under strict conditions, in particular in terms of preventing the presence of copper particles/traces in reaction products and using an environmentally benign medium such as water, we describe here the synthesis of an aminomethyl polystyrene‐supported copper(I) catalyst (Cu(I)‐AMPS) and its characterization by means of Fourier transform infrared and energy‐dispersive X‐ray spectroscopies and scanning electron microscopy. Cu(I)‐AMPS was found to be highly active in the CuAAC reaction of various organic azides with alkynes affording the corresponding 1,4‐disubstituted 1,2,3‐triazoles in a regioselective manner in air at room temperature and using water as solvent. The insolubility and/or partial solubility of the organic azide and alkyne precursors as well as the heterogeneous Cu(I)‐AMPS catalytic system points to the occurrence of the cycloaddition at the organic–water interface ‘on water’ affording quantitative yields of water‐insoluble 1,2,3‐triazoles. A mechanistic study was performed using density functional theory aiming at explaining the observed reactivity and selectivity of the Cu (I)‐AMPS catalyst in CuAAC reactions.     

Existence of positive solutions of (p(x),q(x))-Laplacian parabolic systems with right hand side defined as a multiplication of two separate functions

The paper deals with the study of the existence of weak positive solutions for a new class of the system of parabolic differential equations with respect to the symmetry conditions by using sub-super solutions method. Our results are natural extensions from our previous ones in (Bol. Soc. Mat. Mex. 2019; 25:145-162) and (Appl. Math E-Notes. 2018; 18:209-218), where we have already studied the existence of positive solutions for some classes of Laplacian elliptic problems by using one classical method.     

Ternary Inclusion System of Chair Conformation of 4,6,10,12,16,18,22,24-Octahydroxy-2,8,14,20-tetraphenyl-resorcin[4]arene: Selective Green Synthesis,Supramolecular Behavior,and Biological Activity

Calix[4]resorcinarenes form different types of structural conformations. When their methylene carbons are substituted by four phenyl groups, the molecule can adopt both chair and cone conformations depending on the reaction temperature. The solvent-free synthesis of 4,6,10,12,16,18,22,24-octahydroxy-2,8,14,20-tetraphenyl-resorcin[4]arene led to the formation of chair conformer (C_2h) rather than the cone conformer forming a ternary inclusion complex upon crystallization from wet DMSO. The solid state structure of the ternary inclusion system was determined by single-crystal X-ray diffraction and proved that the host has adopted the chair conformation. The supramolecular interactions in the crystal structure of the solvated compound were carefully investigated. Studies on antimicrobial activities showed that the compound inhibited the growth of Gram-positive bacteria.