STUDY ON THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY POLYPROPYLENE-BASED VANADYL POLYIMIDODIACETATE——THIOUREA REDOX SYSTEM

The present paper deals with the kinetics of polymerization of acrylonitrile (AN) initialed by the redox system of polypropylene-based vanadyi polyimidodiacetate (PV)-thiourea (TU)in aqueous sulfuric acid in the temperature range from 25 to 40℃. The polymerization rate was measured by varying the concentrations of monomer, vanadyl polyimidodiacetate, thiourea and sulfuric acid. The overall rate of polymerization was summarized asRp=2.2×10~5e~(-6.560/RT) [AN]~(1.0)[PV]~(0.50)[TU]~(1.5)[H_2SO_4]~(2.0)The molecular weight of polyacrylonitrile based on the experimental data was:(?)=k 1/T [pv]~(0.50)[TU]~(1.5)[H_2SO_4]~(2.0)These results indicated that the chain radicals are terminated by combination and/or disproportionation rather than chain transfer. The cooperation effect of carboxylic groups and the macromolecular field effect of polymer supporter are the characters of vanadyl polyimidodiacetate such as the case reported in early paper.     

Thermal behavior of vanadyl complexes with Schiff bases derived from trans-N,N′-bis(salicylidene)-1,2-cyclohexadiamine (t-Salcn)

Several Schiff bases coordinated to vanadyl, VO(Schiff base), were synthesized, characterized and studied by thermogravimetry in order to evaluate their thermal stability and thermal decomposition pathways. The number of steps and, in particular, the starting temperature of decomposition of these complexes depend on the equatorial ligand. The intermediates of the thermal decomposition processes were characterized by their IR spectra.     

Monosaccharides and the VO(IV) metal ion: Equilibrium,thermal studies and hypoglycemic effect

Protonation and complexation equilibriums of monosaccharides and the VO(IV) metal ion in aqueous solution were studied as well as their effect on the hyperglycemia of diabetic rats. The complexes formed were characterized by potentiometric titrations, paramagnetic resonance spectroscopy (EPR) and thermogravimetric–differential scanning calorimetry (TGA–DSC). The system involving d-gluconic acid (HGlu) and oxovanadium(IV) (VO²⁺) was chosen to study the serum glucose levels in alloxan-induced diabetic rats. A binuclear species was detected in small quantities, which was formed by coordination of two HGlu molecules and two VO²⁺ ions through a hydroxide bridge. The mononuclear species formed by HGlu and VO²⁺ were confirmed by EPR. The anisotropic spectra obtained from aqueous frozen solutions (77 K) are characteristic of mononuclear VO-hexoses. The cyclic sugars d-ribone-1,4-lactone (Riblac), d-galactone-1,4-lactone (Galac) and 2-deoxy-d-glucopyranose (dGlu) showed weak interactions with the metal ion and they are not able to hold the metal in solution above pH 4.6 resulting in hydrolysis of the metal ion. Also, the acute treatment with sugar complexes of HGlu–VO led to a significant hypoglycemic effect (23% and 18% by intraperitoneal or oral gavage treatment, respectively) in diabetic rats. These results show the potential effectiveness of VO–HGlu complexes as anti-hyperglycemic agents through intraperitoneal injection in alloxan-induced diabetic rats.     

Catalytic carbon-sulfur bond formation by amphoteric vanadyl triflate: exploring with thia-Michael addition, thioacetalization, and transthioacetalization reactions

A series of thiols have been examined as protic nucleophiles for Michael-type additions to α,β-unsaturated carbonyls as well as double nucleophilic condensations with aldehydes, ketones, and acetals catalyzed by amphoteric, water-tolerant vanadyl triflate under mild and neutral conditions. The newly developed C-S bond formation protocols were carried out smoothly in good to high yields in a highly chemoselective manner.     

Ferromagnetic oxovanadium(IV) complexes chelated with tetrahalosalen ligands

Five oxovanadium(IV) complexes [VO(X₄salen)] have been prepared and characterized, where each benzene ring was substituted with two halogen atoms in salen (H₂salen = N,N′-disalicylideneethylenediamine). The X-ray diffraction study on 3,3′,5,5′-tetrachloro-, 3,3′,5,5′-tetrabromo-, and 4,4′,6,6′-tetrachlorosalen derivatives clarified their polymeric structure with the (-VO-)_n repeating unit. The interatomic V···V distances are 3.710(3), 3.695(3), and 3.749(3) Å, respectively, being shorter than that of known [VO(salpn)] (3.83 Å; H₂salpn = N,N′-disalicylidenepropylenediamine). The exchange coupling parameters (J) were determined by fitting the magnetic susceptibility data to the one-dimensional ferromagnetic model, giving 2J/k_B = 8.2-16 K, which are the largest in the [VO(salen)] and [VO(salpn)] family.