Polyfunctional imidazoles: II. Synthesis and reactions with nucleophilic reagents of 1-substituted 2,4-dichloro-1<Emphasis Type="Italic">H</Emphasis>-imidazole-5-carbaldehydes

1-Alkyl(aryl)imidazolidine-2,4-diones reacted with Vilsmeier-Haack reagent affording 1-alkyl(aryl)-2,4-dichloro-1H-imidazole-5-carbaldehydes whose reactions with sodium azide, sodium alkoholates, with phenols, thiols, and secondary cycloalkylamines led to the substitution of chlorine in the position 2 of the imidazole ring. The reaction with primary amines resulted in the condensation products at the aldehyde group.     

Calculated and experimental geometries and infrared spectra of metal tris-acetylacetonates: vibrational spectroscopy as a probe of molecular structure for ionic complexes. Part II

Following on from our previous work on Sc, Fe, Cr, and Al (Part I; see J. Phys. Chem. A, 105 (2001) 238), the geometries and infrared spectra of the trivalent metal tris-acetylacetonate complexes (M[O2C5H7]3; M = Ti, V, Mn, Co) have been studied both experimentally and theoretically using nonlocal hybrid density functional theory with a split-valence plus polarization basis for the ligand and valence triple-zeta for the metal. Unlike the D3 complexes studied in Part I, those of Ti, V and Mn are candidates for Jahn-Teller distortion due to fractional d-shell occupancy. Using scale factors transferred from Part I, our calculated frequencies are in very good agreement with experimentally observed fundamentals. Our investigation shows that the V and Mn complexes distort to C2 ground states, but D3 Ti tris-acetylacetonate is stable. Further investigation of the weak band observed around 800 cm(-1) in the Fe complex (and present in almost all studied first-row transition metal tris-acetylacetonates), which we were unable to assign theoretically in Part I, supports the argument that this band is not a fundamental but is due to Fermi resonance.     

The Reactivity of Associates of Aminomethylated Calix [4] Resorcinolarenes towards P-Nitrophenyl Esters of Phosphorus Acids

Abstract

The kinetics of reactions of aminoinethylated calixarenes (AMC) of different structure (substituents at nitrogen atom as well as on the “lower” rim of cavity are varied) with esters of phosphorus acids has been studied under pseudofirst order conditions in water-DMF and water-alcohol (i-PrOH) solutions by spectrophotometry. The dependences of the observed rate constants of the reactions on the concentrations of AMC reach a plateaus at the investigated values of pH 8 - 1 1. This indicates binding of the substrates by the aggregates of AMC and allows to calculate the parameters of the reactions: CCA, k_a, K_b. It was shown by NMR ³¹P method, that AMC are the catalysts of hydrolysis of esters of phosphorus acids in water-DMF solutions. The higher reactivity of AMC as compared with the one of calix[4]resorcinolarenes and o-aminomethylphenols was found. It was revealed AMC preceeds in both media, however the reactivity of the aggregates is considerably less in the water - alcohol solutions than those in the water - DMF solutions.     

Functional analogues of the dioxygen reduction site in cytochrome oxidase: mechanistic aspects and possible effects of Cu(B)

Catalytic reduction of O(2) and H(2)O(2) by new synthetic analogues of the heme/Cu site in cytochrome c and ubiquinol oxidases has been studied in aqueous buffers. Among the synthetic porphyrins yet reported, those employed in this study most faithfully mimic the immediate coordination environment of the Fe/Cu core. Under physiologically relevant conditions, these biomimetic catalysts reproduce key aspects of the O(2) and H(2)O(2) chemistry of the enzyme. When deposited on an electrode surface, they catalyze the selective reduction of O(2) to H(2)O at potentials comparable to the midpoint potential of cytochrome c. The pH dependence of the half-wave potentials and other data are consistent with O-O bond activation at these centers proceeding via a slow generation of a formally ferric-hydroperoxo intermediate, followed by its rapid reduction to the level of water. This kinetics is analogous to that proposed for the O-O reduction step at the heme/Cu site. It minimizes the steady-state concentration of the catalytic intermediate whose decomposition would release free H(2)O(2). The maximum catalytic rate constants of O(2) reduction by the ferrous catalyst and of H(2)O(2) reduction by both ferric and ferrous catalysts are comparable to those reported for cytochrome oxidase. The oxidized catalyst also displays catalase activity. Comparison of the catalytic properties of the biomimetic complexes in the FeCu and Cu-free forms indicates that, in the regime of rapid electron flux, Cu does not significantly affect the turnover frequency or the stability of the catalysts, but it suppresses superoxide-releasing autoxidation of an O(2)-catalyst adduct. The distal Cu also accelerates O(2) binding and minimizes O-O bond homolysis in the reduction of H(2)O(2).     

On the Effects of UV Radiation on the Release Ability of Glucose Embedded in Hydroxypropyl Cellulose Films

New drug delivery systems based on hydroxypropyl cellulose (HPC) and different percents of glucose were prepared and characterized to check their suitability as UV resistant patches. The spectral absorption properties of the HPC and HPC-glucose blends before and after UV irradiation were analyzed. The surface polarity and hydrophilicity were correlated with the morphology of the films and analyzed with respect to the UV exposure time and the embedded amount of glucose. The effects of UV radiation on in vitro evaluation of glucose release from the HPC films are reported. The mechanism involved in the drug release process, evaluated using the Korsmeyer-Peppas equation, was dependent on the introduced amount of glucose and less on the UV exposure time. A more polar, smoother, and less dense surface releases the glucose over larger periods of time, making the system with lower percents of glucose more adequate for the pursued purpose.     

Influence of pH of solution on phase composition of samarium-strontium cobaltite powders synthesized by wet chemical technique

Powders of Sm_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.

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Ionic liquid matrices for MALDI mass spectrometry of lignin

Analytical and Bioanalytical Chemistry - The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the study of lignin is still extremely limited due to its low...     

Room temperature MgI2-catalyzed Friedel–Crafts reaction between electron-rich (het)arenes and ethyl glyoxylate

Magnesium iodide-catalyzed addition of electron-rich (het)arenes to ethyl glyoxylate proceeds at room temperature with high chemoselectivity to afford ethyl 2-(het)aryl- 2-hydroxyacetates in yields up to 95%.