Inhibition efficiency and adsorption mechanism of 4-aminobenzoic acid for copper corrosion in nitric acid medium: a combined experimental and theoretical investigation

Structural Chemistry - A combined experimental and theoretical study is presented to predict and analyze the inhibition efficiency and adsorption mechanism of 4-aminobenzoic acid molecule for...     

Studies with enaminones: The reaction of enaminones with aminoheterocycles. A route to azolopyrimidines,azolopyridines and quinolines

The enaminones 1b,d,f react with 4‐phenyl‐3‐methyl‐5‐pyrazoleamine 3a to yield the pyrazole derivatives 4a‐c that cyclised readily on reflux in pyridine solution in presence of hydrochloric acid to yield the pyrazolo[1,5‐a]pyrimidines 5a‐c. Similarly 3(5)‐amino‐1H‐triazole (3b) reacted with 1b,d,f to yield the triazolo[1,5‐a]pyrimidines 5d‐f. In contrast attempted condensation of the 5‐tetrazoloamine (3c) with 1a,d,e resulted in its trimerisation and only triaroylbenzene 8a,d,e was isolated. The reaction of 1a,b,d with anthranilonitrile 9a and the reaction of 1a‐c with the 2‐aminocyclohexene thiophene‐3‐nitrile 10a afforded the cis enaminones 11a‐c and 12a‐c. Similarly, reaction of 1a‐c with the methylanthranilate 9b and reaction of 1b,e with ethyl 2‐aminocyclohexene thiophene‐3‐carboxylate 10b afforded the cis enaminones 11d‐f and 12d,e respectively. Attempted cyclization of 11a‐c into quinoline failed. Successful cyclization of 11d into the quinolinone 13 could be affected, on heating for five minutes in a domestic microwave oven at full power. The reaction of 1a‐c,f with piperidine afforded the trans enaminones 14a‐d. Similarly, trans 14e was formed from the reaction of 1b with morpholine. The coupling reaction of 1b with excess of benzene diazonium chloride afforded the formazane 16. The enaminone 2 reacted with heterocyclic amines to yield the pyridones 17,18.     

Synthesis of New Pyrazolo[1.5.4-de]quinoxalines

New pyrazolo[1.5.4-de]quinoxaline derivatives were prepared by the action of 7-aminoindazole 1 on diethyl and dimethyl acetylene dicarboxylates. The structures of the obtained compounds and the direction of cyclization were investigated through a crystallographic study of compound 2. Further alkylation, hydrogenation, and bromination were also explored. The action of potassium thiocyanate on the obtained halo product led to a tetracyclic compound of 1.3-thiazolo[3.4-a]pyrazolo[1.5.4-de]quinoxaline series.     

Synthesis, microwave spectrum, and dipole moment of allenylisocyanide (H2C═C═CHNC), a compound of potential astrochemical interest

An improved synthesis of a compound of potential astrochemical interest, allenylisocyanide (H(2)C═C═CHNC), is reported together with its microwave spectrum, which has been investigated in the 8-120 GHz spectral range to facilitate a potential identification in interstellar space. The spectra of the ground vibrational state and of five vibrationally excited states belonging to three different vibrational modes have been assigned for the parent species. A total of 658 transitions with a maximum value of J = 71 were assigned for the ground state and accurate values obtained for the rotational and quartic centrifugal distortion constants. The spectra of five heavy-atom ((13)C and (15)N) isotopologues were also assigned. The dipole moment was determined to be μ(a) = 11.93(16) × 10(-30) C m, μ(b) = 4.393(44) × 10(-30) C m, and μ(tot) = 12.71(16) × 10(-30) C m. The spectroscopic work has been augmented by theoretical calculations at the CCSD/cc-pVTZ and B3LYP/cc-pVTZ levels of theory. The theoretical calculations are generally in good agreement with the experimental results.     

Synthesis and characterization of active ester-functionalized polypyrrole-silica nanoparticles: application to the covalent attachment of proteins

Novel ester-functionalized polypyrrole-silica nanocomposite particles were prepared by oxidative copolymerization of pyrrole and N-succinimidyl ester pyrrole (50/50% initial concentrations), using FeCl3 in the presence of ultrafine silica nanoparticles (20 nm diameter). The N-succinimidyl ester pyrrole monomer was prepared in aqueous solution using 1-(2-carboxyethylpyrrole) and N-hydroxysuccinimide in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. The resulting nanocomposites (N-succinimidyl ester polypyrrole-silica) are raspberry-shaped agglomerates of silica sol particles "glued" together by the insoluble poly(pyrrole-co-N-succinimidyl pyrrole). The N-succinimidyl ester polypyrrole-silica particles were characterized in terms of their size, density, copolymer content, and polydispersity. Scanning electron microscopy and disk centrifuge sedimentometry confirmed that the nanocomposite particles had narrow size distributions. X-ray photoelectron spectroscopy analysis indicated a silica-rich surface and a high surface concentration of N-succinimidyl ester groups. These nanoparticles exhibited good long-term dispersion stability. The chemical stability of the ester functions in aqueous media after several weeks of storage was monitored by FTIR spectroscopy. The functionalized nanocomposites were tested as bioadsorbents of human serum albumin (HSA). The very high amount of immobilized HSA determined by UV-visible spectroscopy is believed to be due to covalent binding. Incubation of the HSA-grafted nanocomposite with anti-HSA resulted in immediate flocculation, an indication that they are alternative candidates for visual diagnostic assays.     

Structural and magnetic properties of iron(II) complexes with 1,4,5,8,9,12-hexaazatriphenylene (HAT)

Reactions of Fe(II) salts with the ligand 1,4,5,8,9,12-hexaazatriphenylene (HAT) led to the isolation and characterization of four new compounds: [Fe3(HAT)(H2O)12](SO4)3.3.3H2O (1), [Fe2(HAT)(SO4)(H2O)5](SO4).2H2O.CH3OH (2), [Fe2(HAT)(SO4)(H2O)5](SO4).3H2O (3), and [Fe3Cl5(HAT)(CH3OH)4(H2O)]Cl (4). Compound 1 crystallizes as a trinuclear cluster in which HAT acts as a tris-chelating ligand. Compounds 2 and 3 are two polymorphs of an infinite one-dimensional structure in which the Fe atoms are coordinated to HAT and then connected into the chain through bridging sulfate anions. Compound 4 exhibits a similar chain structure, but with bridging chloride ligands. The magnetic behavior of the new compounds is indicative of weak antiferromagnetic coupling between the Fe(II) centers through the HAT ligand.     

The Hydraulic Exchanges between the Main Water Reservoirs of the Moroccan Middle Atlas Region Measured by Solid State Nuclear Track Detectors

Uranium and thorium contents were evaluated in water samples collected from different sources of the piedmont of the Middle Atlas mountains by using two types of solid state nuclear track detectors (SSNTD). In addition, the radon (²²²Rn) and thoron (²²⁰Rn) -activities per unit volume of the water samples were also determined. The influence of the water flow rate and altitude on the radon concentration of the water samples belonging to the piedmont of the Middle Atlas mountains was investigated. The hydraulic exchanges between the Middle Atlas water reservoirs and the Turonian aquifer of the neighbouring Tadla plain have been quantified. The results were compared with data given in literature.     

Aryl to aryl palladium migration in the Heck and Suzuki coupling of o-halobiaryls

A novel 1,4-palladium migration between the o- and o'-positions of biaryls has been observed in organopalladium intermediates derived from o-halobiaryls. The organopalladium intermediates generated by this migration have been trapped either by a Heck reaction employing ethyl acrylate or by Suzuki cross-coupling using arylboronic acids. This palladium migration can be activated or deactivated by choosing the appropriate reaction conditions. Chemical and computational evidence supports the presence of an equilibrium that correlates with the C-H acidity of the available arene positions.     

Spectroscopic characterization and theoretical simulation of 1,4-diallylquinoxaline-2,3-dione self dimer

Room temperature UV-vis absorption and emission spectra of the 1,4-diallylquinoxaline-2,3-dione (DAQX) are measured in solution at different concentrations. Even at very low concentration (approximately 10(-7)M), DAQX is shown to form ground state van der Waals dimers and excited dimers. These later species do not seem to rearrange into an excimer geometry. The theoretical simulation of the dimer, performed using the analytical atom-atom pair potential described below, predicts a non sandwich face-to-reverse slipped structure with head-to-tail orientation. The allowed absorption transitions, calculated using ZINDO/S package, reproduce satisfactory the experimental spectrum for both the monomer and the simulated dimer.     

Preparation of Arabinoxylan and its Sorption on Bacterial Cellulose During Cultivation

The sorption of arabinoxylan (AX) on bacterial cellulose was investigated by adding AX to the culture medium of Gluconacetobacter xylinus. The starting AX material was produced by alkaline extraction of oat spelts. To investigate the impact of varying AX quality, the residual lignin was reduced by ClO₂ bleaching. Furthermore, bleached and unbleached xylans were subjected to xylanase hydrolysis in order to produce fractions of varying molar mass. Of all samples only the water soluble fractions were used for sorption experiments. A reduced molar mass resulted in a lower sorption of AX to the cellulose, while the lignin content increased the sorption of AX on bacterial cellulose. The sorption of AX resulted in a reduction of bacterial cellulose crystallinity and cellulose Iα content. In combined treatments of AX with xyloglucan and β-glucan no synergistic effect of those polysaccharides on the AX sorption was found.