Marijana Jukić

Rapid Determination of Oxalate by an Amperometric Oxalate Oxidase‐Based Electrode

An enzymatic biosensor for determination of oxalate in different real food samples (spinach, sesame seed, tea leaves, and strawberries) as well as in human urine is described and evaluated. Amperometric oxalate biosensor is made from graphite (spetroscpic purity) electrode modified with chromium (III) heksacyanoferrate (II) film (CrHCF). Oxalate oxidase was immobilized using bovine serum albumin and glutaraldehyde cross-linking procedure. This enzyme biocatalyses the oxidation of oxalate to hydrogen peroxide and carbon dioxide. CrHCF film enables one to measure a current resulting in the reduction in the reduction of hydrogen peroxide at low potential (0 V vs. Hg/Hg_2Cl_2/3M KCl electrode), proportional to oxalate concentration. The electrocatalytic properties of CrHCF electrode were well pronounced in 0.05 M succinic buffer, pH 3.8, containing 0.1 M KCl and 5.4 mM EDTA. For determination of oxalate in some food matrices (tea leaves and strawberries) dialysis membrane as an outer coat was necessary to prevent electrochemical interferents. The sensitivity of biosensor was 31microA/(mM cm^2) in synthetic oxalic acid solutions. The biosensor has shown good linearity (R^2=0.9984) in the oxalate concentration range between 2.5 and 400 microM and its half-lifetime was longer than one month. The performance of the metod was compared with the reference enzymatic spectrophotometric method and a very good correlation was obtained between these results.

Ferrocene compounds. XXV.* Synthesis and characterization of ferrocene-containing oligoamides, their precursors, and analogues

A general method for preparation of ferrocene-containing monoamines (5–7) and diamines (10, 11) starting from the corresponding quaternary ammonium iodide 3 and ferrocene mono- (4) and dithiaaliphatic acids (8, 9) was developed. Amines obtained have been characterized as acet- and benzamides (12–15). The oligoamide precursors (16, 17, 22, 23) were synthesized by reactions of succinic or glutaric anhydride with amines (6, 7, 10, 11). Their conversion into oligoamide analogs (20, 21, 25) failed. The desired diamides (20, 21) were prepared by condensation of amines (6, 7) with alkanedioyl chlorides, (CH2)n(COCl)2 (n = 0, 1, 2, 3). Reactions of diamine 10 with succinic or glutaric anhydride gave amino acids 28—formal monomers for the planned oligomerization. Oligomers 29 were synthesized by condensation of equimolar amounts of diamines 10 and the above mentioned alkanedioyl chlorides in dichloromethane at 0°C. The structure of oligomers 29 was indicated from their IR and 1H-NMR spectra in comparison with the model substances 12–28. The degree of polymerization of compounds 29 was determined by 1H-NMR end-group analysis (DPn = 4–6).

A One-Pot Synthesis and Structure Determination of 3-(1-Phenyl-5-p-tolylpyrazol-3-yl)-2-p-tolylindole Ethanol Solvate

The Fischer indolization afforded the title compound C31H25N3·C2H5OH as the major product in the reaction of 1,5-di(p-tolyl)pentane-1,3,5-trione with phenylhydrazine hydrochloride in ethanol. The structure assignment of this novel pyrazolylindole derivative is based on the data of elemental analysis, IR, 1H NMR, and 13C NMR spectroscopy. The structure is also confirmed by means of X-ray crystallography. The molecule crystallizes in the orthorhombic space group P 212121, with a = 10.298(2), b = 14.984(5), c = 18.133(3) A, Z = 8, V = 2798.0(12) A3. The absolute structure has been determined. The ethanol molecule forms intermolecular hydrogen bonds with the pyrazole and indole nitrogen atoms.

Utjecaj ekstrakcije potpomognute mikrovalovima na udjel fenolnih spojeva i antioksidacijski kapacitet cvijetova trnine

This research was undertaken to investigate the influence of extraction parameters during microwave-assisted extraction on total phenolic content, total flavonoids, total hydroxycinnamic acids and total flavonols of blackthorn flowers as well as to evaluate the antioxidant capacity by two different methods (2,2-diphenyl-1-picrylhydrazyl free radical scavenging capacity and ferric reducing antioxidant power assays). The investigated extraction parameters were: solvent type and volume fraction of alcohol in solvent (50 and 70% aqueous solutions of ethanol and methanol), extraction time (5, 15 and 25 min) and extraction temperature (40, 50 and 60 °C) controlled by microwave power of 100, 200 and 300 W. Multivariate analysis of variance (MANOVA) was used to evaluate the differences at a 95% confidence level (p≤0.05). The obtained results show that aqueous solution of ethanol was more appropriate solvent for extraction of phenolic compounds (total flavonoids, total hydroxycinnamic acids and total flavonols) than aqueous solution of methanol. The amount of phenolic compounds was higher in 70% aqueous solution of ethanol or methanol, while higher antioxidant capacity was observed in 50% aqueous solution of methanol. Higher temperature of extraction improved the amount of phenolic compounds and also antioxidant capacity determined by 2,2-diphenyl-1-picrylhydrazyl free radical scavenging capacity assay. Extensive duration of extraction (15- to 25-minute interval) has a significant effect only on the increase of total phenolic content, while specific phenolic compound content and antioxidant capacity were the highest when microwave extraction time of 5 min was applied.

Ferrocene compounds. XXXVIII. Dimethyl ferrocene-1,1'-dicarboxylate.

In the title compound, [Fe(C(7)H(7)O(2))(2)], the cyclopentadienyl rings and the two attached methoxycarbonyl groups, in an anti arrangement, form an extended pi-conjugated system. The Fe-C distances range from 2.035 (3) to 2.061 (3) A and the average value of the C-C bond lengths in the two cyclopentadienyl rings is 1.419 (5) A. The rings are almost parallel to one another [1.0 (2) degrees ] and are mutually twisted from an eclipsed conformation by only 1.8 (3) degrees (average value). The methoxycarbonyl groups are twisted out of the plane of the cyclopentadienyl rings by 6.5 (4) and 15.7 (4) degrees, respectively. The molecules are joined into dimers by intermolecular C-H.O hydrogen bonds that form ten-membered rings. The same types of hydrogen bonds form eight-membered rings and infinite chains along the b axis.

An Efficient Synthesis of Pyridoxal Oxime Derivatives under Microwave Irradiation

Quaternary salts of pyridoxal oxime have been synthesized by the quaternization of pyridoxal oxime with substituted phenacyl bromides using microwave heating. Microwave-assisted rapid synthesis was done both in solvent (acetone) and under solvent-free conditions. Good to excellent yields (58%–94%) were obtained in acetone in very short reaction times (3–5 min) as well as in the solvent-free procedure (42%–78%) in very short reaction times (7–10 min) too. Effective metodologies for the preparation of pyridoxal oxime quaternary salts, having the advantagies of being eco-friendly, easy to handle, and performed in shorter reactions time are presented. The structure of compound 7, in which a 4-fluorophenacyl moiety is bonded to the pyridinium ring nitrogen atom, was unequivocally confirmed by the single-crystal X-ray diffraction method.

Ferrocene Compounds. XXXI. Structure of 3-Ferrocenylpropanoic Acid

AbstractThe title compound was prepared by modified procedure and characterized by means of IR, [1H] and [13C] NMR spectroscopy. The structure was also determined by a single-crystal X-ray diffraction (XRD). 3-Ferrocenylpropanoic acid crystallizes as orange prisms in the triclinic space group P

The effect of microwave assisted extraction on the isolation of anthocyanins and phenolic acids from sour cherry Marasca (Prunus cerasus var. Marasca)

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