Rapid test methods for minor components analysis of hydraulic cement. Spectrophotometric determination of manganese oxide content of Portland cement and cement raw meal

A rapid, sensitive and highly selective spectrophotometric method for the determination of manganese oxide content of Portland cement and cement raw meal is developed. The method is based on the reaction of manganese(II) with 1,2,4 trihydroxyanthraquinone (purpurin, PURP) in 50% v/v ethanol-water solution at pH 8.5. The solution equilibria of manganese chelates are demonstrated and characterized for delineating optimal conditions of the complexation reaction and analytical aspect of the Mn-PURP system. The analysis of cement materials of variable manganese content is feasible over the concentration range 1.67-8.13 microg ml(-1) Mn, the limit of detection (at the 95% confidence level) of the method is 68 ng ml(-1) for manganese. Under optimum conditions, the use of first derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometric method and allows the determination of 0.5 microg ml(-1) of manganese.     

Cathodic stripping voltammetric determination of 2-mercaptobenzothiazole using the catalytic cobalt peak

Previously, thiols have been determined indirectly by cathodic stripping voltammetry (CSV) after accumulation as their mercury and copper(I) salts. Following a previous report of the first use of the catalytic nickel peak (for the determination of cysteine), this paper reports the first use of the catalytic cobalt peak in CSV (for the determination of 2-mercaptobenzothiazole (MBT)): only a very ill-defined catalytic cobalt peak had been observed previously with cysteine, and was unreported. MBT is accumulated at pH 4 (Britton-Robinson buffer) as its cobalt(II) complex at -0.1 V, and is then determined indirectly by observing the reduction of the cobalt(II) in the complex at -0.95 V, i.e., with a much lowered overpotential: hydrated cobalt(II) is reduced at -1.2 V. The peak is catalytic because the thiol released on reduction of the complex complexes further cobalt ions and causes their reduction. The detection limit for the determination of MBT was calculated to be 2.5 x 10(-9) M (3sigma) using an accumulation time of 1 min. The sensitivity is about three times that obtained with the corresponding catalytic nickel peak.     

A new kinetic approach to the evaluation of rate constants for the spin trapping of superoxide/hydroperoxyl radical by nitrones in aqueous media

A new kinetic approach to the evaluation of rate constants for the spin trapping of superoxide/hydroperoxyl radical by nitrones in buffered media is described. This method is based on a competition between the superoxide trapping by the nitrone and the spontaneous dismutation of this radical in aqueous media. EPR spectra are recorded as a function of time at various nitrone concentrations, and kinetic curves are obtained after treatment of these spectra using both singular value decomposition and pseudo-inverse deconvolution methods. Modelling these curves permits the determination of the rate constants k(T) and k(D) for the superoxide trapping and the adduct decay reactions, respectively. Kinetics parameters thus obtained with six nitrones, namely the 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (EMPO), the 5-diethoxyphosphoryl-5-methyl-3,4-dihydro-5H-pyrrole N-oxide (DEPMPO), the 5,5-dimethyl-3,4-dihydro-5H-pyrrole N-oxide (DMPO), the 1,3,5-tri[(N-(1-diethylphosphono)-1-methylethyl)-N-oxy-aldimine]benzene (TN), the N-benzylidene-1-ethoxycarbonyl-1-methylethylamine N-oxide (EPPN), and the N-[(1-oxidopyridin-1-ium-4-yl)methylidene]-1-ethoxycarbonyl-1-methylethylamine N-oxide (EPPyON), indicate that cyclic nitrones trapped superoxide faster than the linear ones. However, the low k(T) values obtained for compounds show that there is still a need for new molecules with better spin trapping capacities.     

Backward errors for eigenvalues and eigenvectors of Hermitian,skew-Hermitian,H-even and H-odd matrix polynomials

We discuss the perturbation analysis for eigenvalues and eigenvectors of structured homogeneous matrix polynomials with Hermitian, skew-Hermitian, H-even and H-odd structure. We construct minimal structured perturbations (structured backward errors) such that an approximate eigenvalue and eigenvector pair (finite or infinite eigenvalues) is an exact eigenvalue eigenvector pair of an appropriately perturbed structured matrix polynomial. We present various comparisons with unstructured backward errors and previous backward errors constructed for the non-homogeneous case and show that our results generalize previous results.     

Efficient photodegradation of resorcinol with Ag2O/ZnO nanorods heterostructure under a compact fluorescent lamp irradiation

Ag₂O/ZnO heterostructure has been recently synthesized using a facile chemical-precipitation method. X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy results confirmed the Ag₂O nanoparticles loading on ZnO nanorods. The Ag₂O addition increased the visible light absorption ability and a red shift for Ag₂O/ZnO heterostructure appeared when compared to pure ZnO. Photoluminescence spectra showed lower emission yield on the Ag₂O/ZnO heterostructure than on pure ZnO. Such a decrease in the emission yield represents the fraction of the excited state Ag₂O sensitizer involved in the charge injection process. Under compact fluorescent lamp irradiation, the Ag₂O/ZnO heterostructure demonstrated higher photocatalytic activity than pure ZnO in the degradation of resorcinol, which can be attributed to the high separation efficiency of the photogenerated electron-hole pairs based on the cooperative roles of Ag₂O loading on ZnO nanarods. All these characteristics represent a significant contribution of the Ag₂O/ZnO heterostructure to the practical applications in indoor environmental remediation.     

Synthesis,XRD, spectral (IR,UV–Vis,NMR) characterization and quantum chemical exploration of benzoimidazole‐based hydrazones: A synergistic experimental‐computational analysis

Present study advocates the joint experimental and computational studies of two potent benzoimidazole‐based hydrazones with chemical formula C₂₃H₁₈F₂N₄O ( 5a ) and C₂₅H₂₂FN₅O₃ ( 5b ). Both 5a and 5b were synthesized and resolved into their crystal structures using SC‐XRD for the assessment of bond lengths, bond angles, unit cells and space groups. The structures of 5a and 5b were chemically characterized using infrared (FT‐IR), UV–Visible, nuclear magnetic resonance (¹H‐NMR and ¹³C‐NMR), EIMS and elemental analysis. DFT at M06‐2X/6‐31G(d,p) level of theory was performed to get optimized structures and countercheck the experimental findings. Overall, DFT findings show excellent concurrence with the experimental data which confirms the purity of both compounds. FMO, NBO analysis, MEP surfaces and nonlinear optical (NLO) properties were explored at same level of theory. UV–Vis analysis at TDDFT/M06‐2X/6‐31G(d,p) level of theory showed that 5b is red shifted with λ_max 331.69 nm as compared to 5a with λ_max 240.25 nm. Global reactivity parameters were estimated using energy of FMOs indicated the greater harness value than the softness values of 5a and 5b . NBO analysis confirmed that the presence of non‐covalent interactions, hydrogen bonding and hyper conjugative interactions are pivotal cause for the existence of 5a and 5b in the solid‐state. NLO results of 5a and 5b were observed better than standard molecule recommended the NLO activity of said molecules for optoelectronic applications.     

Full control of polymer properties during the two‐stage on‐demand free‐radical photopolymerization of fiber‐reinforced polymers

The effect of a two‐step free‐radical photopolymerization of an acrylate resin on the polymer properties in the presence of glass fibers is studied. It is found that a first irradiation leading to a partial conversion is effective for the fabrication of a preimpregnated glass‐fiber composite, which can be further processed and fully polymerized through a second irradiation. DMA analysis evidences the formation of a first relatively soft polymer embedding unreacted double bonds during the preirradiation. Further process allows the completion of the photopolymerization together with a reinforcement of the polymer network. This obviously affects the final mechanical properties of the photocomposite. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1440–1447