Benzimidazole condensed ring systems. 1. Syntheses and biological investigations of some substituted pyrido[1,2-a]benzimidazoles

The synthesis of some substituted 3-hydroxy-1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbonitriles and 4-ethyl carboxylates 3 and their 0- and N-dialkyl derivatives 5,6 is described. 3-Ethoxy-5-ethyl-2-phenyl-1H,5H-pyrido[1,2-a]benzimidazol-1-one 7 was obtained during the course of ethylating the parent ester 3t with triethyl phosphate. Chlorination of 3 with phosphorus oxychloride afforded the corresponding 1,3-dichloropyrido[1,2-a]benzimidazoles 8 which were converted to a variety of azido, amino, morpholino and methoxy derivatives of the system. The synthesis of the indolopyridobenzimidazole 15 is also described. Two compounds exhibited in vitro antibacterial activity. Many compounds were screened for antileukemic, antimicrobial, herbicidal and plant antifungal potencies but were inactive.     

Adsorption and controlled release of Chlortetracycline HCl by using multifunctional polymeric hydrogels

Adsorption and controlled release of Chlortetracycline HCl to and from multifunctional polymeric materials (HEMA/MAA) hydrogels were investigated. P(HEMA/MAA) hydrogels were synthesized by gamma radiation-induced copolymerization of 2-hydroxyethylmethacrylate (HEMA) and methacrylic acid (MAA) in aqueous solution. The influence of copolymer composition and pH value of the surrounding medium on the type of water diffusion into the glassy polymer were discussed. Drug, Chlortetracycline HCl containing hydrogels, with different drug concentration to polymer ratios, was loaded by direct adsorption method. The influence of MAA content in the gel on the adsorption capacities of hydrogel was studied. Chlortetracycline HCl adsorption capacity of hydrogels was found to increase from 8 to 138 mg Chlortetracycline HCl per gram dry gel with increasing amount of MAA in the gel system and drug concentration. The effect of pH on the releasing behavior of Chlortetracycline HCl from gel matrix was investigated. In vitro drug release studies in different buffer solutions show that the basic parameters affecting the drug release behavior of hydrogel are the pH of the solution and MAA content of hydrogel.     

Benzimidazole condensed ring systems. 2. New synthesis of substituted 1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbonitriles and related derivatives

The synthesis of some 3-substituted and 2,3-disubstituted-1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbo-nitriles 5,6 by fusing 1H-benzimidazole-2-acetonitrile 1 with some β-keto esters 2,4 in the presence of ammonium acetate or with ethyl β-aminocrotonate 3 is described. The tricyclic compounds were converted to their N-5 methyl of N-5 ethyl derivatives 8,9. Vilsmeir-Haack formylation of 3-methyl-1-oxo-1H,5H-pyrido[1,2-a]-benzimidazole-4-carbonitrile 5a afforded its 2-formyl derivative 10. Chlorination of 5 and 6 with phosphorus oxychloride yielded the respective 1-chloropyrido[1,2-a]benzimidazole-4-carbonitriles 11,12 which were utilized to prepare the 1-azido, 1-amino, 1-piperidino and 1-methoxy derivatives of the ring system. Compound 11a exhibited strong in vitro activity against S. aureus. Four compounds were screened against P-388 lymphocytic leukemia in mice but were inactive.     

The optically detected coherent lattice oscillations in silver and gold monolayer periodic nanoprism arrays: the effect of interparticle coupling

Using femtosecond transient spectroscopy, we studied the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography. In this method, the same size of polystyrene sphere and the same vacuum conditions are used. Under these circumstances, the gold nanoprisms formed are found to have sharper tips than the corresponding silver nanoprisms. For both gold and silver nanoparticles, the surface plasmon absorption maximum is found to depend linearly on size. The coherent lattice oscillation periods are also found to depend linearly on size. However, although the observed dependence for the silver nanoparticle is found to follow the calculated dependence of a single particle on size (based on a one-dimensional standing wave model), the gold nanoparticle deviates from this model, and the deviation is found to increase with the size of the nanoparticles. This deviation can be explained by considering interparticle coupling. A simple interparticle lattice oscillating dipolar coupling model of the dimer is found to qualitatively account for both the sign and the size dependence of the deviation. The absence of this deviation in the silver nanoparticle arrays is blamed on the weak interparticle coupling due to their rounded tips and the possibility of oxidation of their surfaces.     

On the mechanism of photoinduced nucleation in a diffusion cloud chamber

Photoinduced nucleation of NO₂ in supersaturated nonane has been studied in a diffusion cloud chamber. The photonucleation spectrum is found to correlate with the yield spectrum for the production of reactive radical species (O + NO) and not with the absorption spectrum of the nucleation inducing agent. A mechanism is proposed in which hydrogen abstraction by O from the nonane produces radicals which then react with each other or with NO₂ to produce species of low volatility that lead to nucleation. Studies of photoinduced nucleation by several alkyl iodides (known to produce radicals upon UV absorption) further support the proposed radical mechanism for photoinduced nucleation.     

Adsorption of valeric acid from aqueous solution onto activated carbons: role of surface basic sites

Adsorption of valeric acid was studied on two activated carbons of different origins, wood and bituminous coal. The effect of oxidation on the adsorption uptake was investigated. Both initial samples were oxidized with nitric acid, which caused the introduction of a significant number of oxygen-containing groups onto the carbon surface. Boehm titration, potentiometric titration, thermal analysis, and sorption of nitrogen were used for detailed surface characterization. Valeric acid adsorption from aqueous solution was measured at 333 K. The calculated isotherms showed a good fitting to the Freundlich equation. The capacity coefficients revealed a direct correlation with the number of basic groups present on the surface. The amount of valeric acid adsorbed at its low concentration is dependent on the number of basic groups, whereas at high concentration the amount adsorbed depends on the volume of micropores smaller than 10 A, where the adsorption potential is the strongest.     

Synthesis of acetylenic β-diketones and their conversion into 4H-pyran-4-ones,pyrazoles, and 1-hydroxy-4-pyridones

A simple method for the synthesis of acetylenic β-diketones is described. They can be cyclized to the corresponding 4H-pyran-4-ones with acids. Their reaction with hydrazine hydrate gave pyrazole derivatives isomeric with those obtained from 4H-pyran-4-ones. With hydroxyl-amine hydrochloride in ethanol, 1-hydroxy-4-pyridones are formed.     

Study of some reactions of ethyl 4-phenyl-3-benzoyl-2-pyrazoline-5-carboxylate

Several reactions of the pyrazoline 1a were investigated. With bromine water, potassium permanganate, hydrogen peroxide, or potassium hydroxide, different pyrazole derivatives were formed. While the reaction with hydroxylamine or some hydrazines gave the corresponding pyrazoline Schiff bases, with aroylhydrazines, pyrazole Schiff bases were formed.     

Thermodynamics of uranium extraction from nitric acid solution by TBP loaded on inert supporting material

Thermodynamic investigation of the extraction of both uranium(VI) and uranium(IV) from nitric acid solutions using tri-n-butyl phosphate (TBP) loaded on polyacrylic acid polymer (SM-7) as an inert supporting material has been done using batch technique. The effect of temperature on the equilibrium extraction values has been utilized to evaluate the change in standard thermodynamic quantities (viz. DH, DS, and DG). The Freundlich isotherm was successfully applied to the extraction data of both metal ions. The Dubinin-Radushkevich (D-R) isotherm was found to be valid only in case of U(IV) extraction. Based on the D-R expression, the maximum extraction capacity of loaded TBP and the mean free energy of U(IV) extraction have been determined.     

The low energy two-photon spectrum of pyrazine using the phosphorescence photoexcitation method

The two-photon phosphorescence excitation spectrum of neat pyrazine crystal at 1.6 K has been examined in the region 6800-4250 A. A discussion of two-photon allowed and vibronically induced transitions is given. The theoretical discussion shows that, due to the added possibility of vibronic mixing in the intermediate state, in general more non-totally symmetric vibrations are expected to show intensity in a symmetry forbidden two-photon spectrum than in a forbidden one-photon spectrum. An estimate of the relative intensities of allowed and vibronically induced (n, π*) two photon transitions in pyrazine have been carried out using the Cl energies and MO transition moments obtained by Wadt and Goddard. Comparison of these results with the normalized spectrum obtained with polarized light indicates the absorptions observed in the region 30 000–35 000 cm⁻¹ are analyzable in terms of a single electronic transition with a forbidden origin which coincides with the ¹B_3u ← ¹A_g one-photon transition origin. Several of the prominent false origins appearing in this region have been tentatively assigned and indicate that, unlike symmetric modes, frequencies of asymmetric vibrations are significantly altered in the excited state. A lower limit of 0.8 eV is set for the ¹B_3u-¹B_2g splitting which results from the interactions of the two pyrazine lone pair orbitals.