Khalid S. Khairou

Pectate polyelectrolyte ionotropic gels: 1. Kinetics and mechanisms of formation of manganate (VI)–pectate intermediate complex during the oxidation of pectate polysaccharide by alkaline permanganate

Abstract The kinetics of formation of the [Pect MnVIO2−4] intermediate complex formed during the oxidation of pectate polysaccharide by permanganate ions in alkaline solutions at pH⩾12 have been measured by a conventional spectrophotometric technique. The reaction showed a first-order dependence on permanganate concentration and a fractional order with respect to the pectate concentration for the complex formation. Kinetic and spectrophotometric evidence revealed the formation of manganate (VI) transient species. The results obtained indicated that the rate of formation is base catalyzed. Thermodynamic parameters were evaluated and a suitable mechanism consistent with the kinetic results was suggested.

Fabrication and characterization of bimetallic Pt-Au nanowires supported on FSM-16 and their catalytic activities toward water-gas shift reaction.

A facile, previously unexplored, method to synthesize bimetallic Pt-Au nanowires (20nm diameter×120-170nm long) on mesoporous FSM-16 (2.7nm) was fabricated by co-impregnation of H(2)PtCl(6) with HAuCl(4) followed by evacuation at 300K and finally exposure to the CO/H(2)O gas mixture (60:5Torr) at 323K for 1.0h. On the other hand, spherical monometallic nanoparticles of pure Pt (7.0nm diameter) and Au (7-26nm diameter) were synthesized as well, by impregnation, at the same reaction conditions. The catalysts were characterized by in situ FTIR spectroscopy, UV-vis absorption spectroscopy, TEM, TPR and TPCOR. The catalytic activities toward the water-gas shift reaction (WGSR) were also examined under atmospheric pressure and at the margin of 323-373K. The optical absorption spectra showed a remarkable shift and broadening of Pt-Au surface Plasmon resonance band at 515nm apart from those of individual analogue emphasizing bimetallic formation. Results from in situ FTIR spectroscopy indicated that incorporation of Au assisted and stabilized the formation of carbonyl clusters of Pt-Au-CO (2084cm(-1)) and Pt-CO (1888cm(-1)) inside the host FSM-16. The Pt-Au carbonyl clusters built up at the moment of vanishing the linear carbonyl band of the charged Au (Au(+)-CO, 2186cm(-1)) along with a concomitant increase in the reduced gold (Au(0)-CO, 2124cm(-1)) species. TPR profiles showed that the H(2) consumed was higher for Pt/FSM-16 than for Pt-Au/FSM-16 verifying the facile reduction of Pt moieties after addition of Au. The CO adsorption peak maximum, in TPCOR, for Pt/FSM-16 occurred at higher temperature than that of Pt-Au/FSM-16, which exhibited higher amounts of CO(2) produced. The relative decrease in CO bindings on bimetallic surface was responsible for increasing the CO oxidation activity mainly through an association mechanism. Accordingly, the activity of Pt-Au/FSM-16 towards WGS showed a marked increase (8-23 times) compared with those of monometallics emphasizing the dependence of this reaction on the electronic defects of the nanowires. A straightforward reduction mechanism was deduced for Pt-Au alloy formation in view of the results obtained.

Theoretical investigations of the stability of degradation products of polystyrene and poly(4-vinylpyridine)

Abstract The products of thermal degradation of polystyrene and poly(4-vinylpyridine) have been rationalized using ASED-MO theory. The calculations explain the formation of styrene dimer and the absence of 4-vinylpyridine dimer during the thermal degradation, which may be due to the high reactivity of 4-vinylpyridine dimer. According to frontier molecular orbital (FMO) treatment, the reactivity of the molecule is controlled by the energy separation between HOMO and LUMO. It was found that 4-vinylpyridine dimer is more reactive than styrene dimer due to its smaller energy separation.

Thermal stability of poly(4-vinyl pyridine) and polymer complexes of 4-vinyl pyridine with some transition metal chlorides

Abstract Poly(4-vinyl pyridine) homopolymer and polymer complexes of 4-vinyl pyridine with CuCl 2 , CoCl 2 and NiCl 2 have been prepared and characterized by elemental analyses, electronic and vibration spectroscopic studies and magnetic moments. The thermal stabilities of the homopolymer and the polymer complexes were studied by means of thermogravimetric analysis. The activation energies of the degradation of the homopolymer and the polymer complexes were calculated.

Physicochemical Studies on some Cross-linked Trivalent Metal-alginate Complexes especially the Electrical Conductivity and Chemical Equilibrium related to the Coordination Geometry

The electrical conductivity of cross-linked lanthanum(III)- and cerium(III)-alginate complexes in the form of circular discs has been studied as a function of temperature. The Arrhenius plots of log σ versus 1/ T showed a sharp increase in the electrical conductivity values at elevated temperatures, whereas no changes in σ values were observed at lower temperatures (< 450 K). This behavior was explained by the degradation of the complexes at higher temperatures to give rise to metal oxide products at the final stages. The heterogeneous chemical equilibrium for exchange of La 3+ and Ce3+ metal ions by H+ ions has been investigated complexometrically and titrimetrically. The X-ray diffraction pattern indicated that these complexes are amorphous in nature. Infrared absorption spectra indicated the presence of chelated La3+ and Ce3+ metal ions with alginate macromolecular chains. A geometrical structure for chelation of lanthanum(III) and cerium(III) to the carboxylate and hydroxyl functional groups of the alginate macromolecule is suggested and discussed in terms of complex stability.

Efficient synthesis and antimicrobial evaluation of some Mannich bases from 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones

AbstractBackgroundThiazolidinone, has been employed in the preparation of different important drugs required for treatment of inflammations, bacterial infections, and hypertension. Mannich bases have been shown to exhibit diverse biological activities, such as antibacterial, and antifungal activities. Spiroheterocycles including thiazolidine moiety have antimicrobial activity.ResultsIn this study, a novel, rapid, and efficient protocol is developed for the synthesis of various 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones using sodium dodecylbenzene sulfonate (DBSNa) as an inexpensive and readily available reagent in acetic acid at room temperature. High yields, easy work-up, and short reaction times are advantages of this procedure. The synthesized arylidines were undergone Mannich reaction with formaldehyde and secondary amines in absolute ethanol at room temperature to afford the corresponding N-Mannich bases. All prepared Mannich bases were evaluated for their antimicrobial activity.ConclusionsGood activity was noted for Mannich bases from 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones, with some members recorded higher antimicrobial activity. Graphical abstractSynthesis of Mannich bases of 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones.

Sonochemistry: Synthesis of Bioactive Heterocycles

Abstract In recent years, green chemistry using environmentally benign reagents and conditions has become one of the most fascinating developments in the synthesis of widely used organic compounds. This review describes the theory and importance of ultrasound as an efficient tool in the synthesis of heterocyclic compounds. GRAPHICAL ABSTRACT

QSPR for HLB of Nonionic Surfactants Based on Polyoxyethylene Group

Relation between the molecular structure and the hydrophile lipophile balance (HLB) of nonionic surfactants were investigated using qualitative structure-properties relationship (QSPR) technique. Several descriptors having physical significances on the behaviour of surfactants in portioning between oil and water were selected. Particularly, number of oxygen per a nonionic surfactant molecular weight (χ); octanol/water partition coefficient (log P), maximum surface area (Γ), molar volume (VM), dipole moment (μ), energy of hydration (EH) and molecular polarizability (α), parachor (ξ), and others Wiener index (W), Randics molecular connectivity index (R), Kier and Hall valence connectivity index (K & H), average information content (AIC). Principal component analysis (PCA) and multiple linear regression(MLR) technique were performed to examine the relationship between the selected descriptors and the HLB values of nonionic surfactants. The results of PCA explain the inter-relationships between HLB and different variables. The linear relationship between the selected descriptors and HLB was modelled according to the better statistical results. The best model has coefficient of determination (R2 = 0.9825), statistical significance (F = 1301), and standard errors (s2 = 1.0521). The obtained a QSPR model allows estimating of HLB for nonionic surfactants using theoretical-calculated descriptors.

Competent, selective and high yield of 7-hydroxy-4-methyl coumarin over sulfonated mesoporous silica as solid acid catalysts

Highly ordered mesoporous MCM-41 and SBA-15 have been synthesized and functionalized with different amounts of propyl sulfonic acid groups using 3-mercaptopropyltrimethoxysilane as sulfur source. The synthesized catalysts have been well-characterized by different techniques such as XRD, FTIR and BET surface area and pore size distribution by BJH method. FTIR spectra of chemisorbed pyridine and temperature programmed desorption of NH3 techniques have been successfully used to characterize the acidic sites. The results showed that, both surface area, mean pore diameter and pore volume decrease as the extent of sulfonation increase. XRD results and TEM images confirm the stability of mesoporous long range order even after sulfonation process done. In addition, the study also showed that, sulfonation enhances the surface acidity and new moderate and strong acid sites were created. All the sulfonated catalysts under investigations have been found to be highly active and selective for the Pechmann condensation reaction of resorcinol with ethyl acetoacetate. More than 98% yield of 7-hydroxy-4-methyl coumarin was obtained with 100% selectivity. Presence of high number of moderate and strong Brönsted acid sites in sulfonated catalysts help in achieving high yields. Furthermore, the MCM-41 sulfonated catalysts showed higher catalytic performance due to their higher surface acidities.

Design of Thermochromic Polynorbornene Bearing Spiropyran Chromophore Moieties: Synthesis, Thermal Behavior and Dielectric Barrier Discharge Plasma Treatment

A new class of thermochromic polynorbornene with pendent spiropyran moieties has been synthesized. Functionalization of norbornene monomers with spirobenzopyran moieties has been achieved using Steglich esterification. These new monomeric materials were polymerized via Ring Opening Metathesis Polymerization (ROMP). In spite of their poor solubility, polynorbornenes with spirobenzopyran exhibited thermochromic behavior due to the conversion of their closed spiropyran moieties to the open merocyanine form. Moreover, these polymers displayed bathochromic shifts in their optical response, which was attributed to the J-aggregation of the attached merocyanine moieties that were associated with their high concentration in the polymeric chain. The surface of the obtained polymers was exposed to atmospheric pressure air Dielectric Barrier Discharge (DBD) plasma system, which resulted in the reduction of the surface porosity and converted some surface area into completely non-porous regions. Moreover, the plasma system created some areas with highly ordered J-aggregates of the merocyanine form in thread-like structures. This modification of the polymers’ morphology may alter their applications and allow for these materials to be potential candidates for new applications, such as non-porous membranes for reverse osmosis, nanofiltration, or molecular separation in the gas phase.