Radical-scavenging activity of the reaction products of isoeugenol with thiol, thiophenol, mercaptothiazoline or mercaptomethylimidazole using the induction period method

The reaction products in the presence of Lewis acid of isoeugenol (1) with ethanethiol, thiophenol, 2-mercaptothiazoline or 2-mercapto-1-methylimidazole (ISO-S1-ISO-S-4) were obtained. The radical-scavenging activity of these compounds was investigated using the induction period method for polymerization of methyl methacrylate (MMA) initiated by thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO) and monitored by differential scanning calorimetry (DSC). For BPO, the stoichiometric factor (number of free radicals trapped by one mole of antioxidant moiety, n) declined in the order isoeugenol (1.8) > ISO-S-1 (1.6) > ISO-S-2 (1.2) > ISOS- 3 (0.9) > ISO-S-4 (0.3), whereas for AIBN, their n values were about 1, except for ISOS- 3 (0.6). The ratio of the rate constant of inhibition to that of propagation (k(inh)/k(p)) for BPO declined in the order ISO-S-4 (56) > ISO-S-3 (15) > ISO-S-2 (11) >ISO-S-1 (9) > isoeugenol (8). Similarly, for AIBN the k(inh)/k(p) of the reaction products (33-57) was greater than that of isoeugenol (31). The reaction products of isoeugenol with a SH group showed greater inhibition rate constants (kinh) than the parent compound isoeugenol.     

Radical-scavenging activity of natural methoxyphenols vs. synthetic ones using the induction period method

The radical-scavenging activities of the synthetic antioxidants 2-allyl-4-X-phenol (X = NO2, Cl, Br, OCH3, COCH3, CH3, t-(CH3)3, C6H5) and 2,4-dimethoxyphenol, and the natural antioxidants eugenol and isoeugenol, were investigated using differential scanning calorimetry (DSC) by measuring their anti-1,1-diphenyl-2-picrylhydrazyl (DPPH) radical activity and the induction period for polymerization of methyl methacrylate (MMA) initiated by thermal decomposition of 2,2'-azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO). 2-Allyl-4-methoxyphenol and 2,4-dimethoxy-phenol scavenged not only oxygen-centered radicals (PhCOO*) derived from BPO, but also carbon-centered radicals (R*) derived from the AIBN and DPPH radical much more efficiently, in comparison with eugenol and isoeugenol. 2-Allyl-4-methoxyphenol may be useful for its lower prooxidative activity.     

Radical-scavenging activity of dietary phytophenols in combination with co-antioxidants using the induction period method

The radical-scavenging activity of dietary phytophenols has been investigated by many researches due to their antioxidant, anti-inflammatory and anticancer property but the radical-scavenging effect of 2-phytophenol and the phytophenol:co-antioxidants, vitamin C and thiol combination under nearly anaerobic conditions still remains unknown. The radical-scavenging activity for seventeen phytophenols and for six synthetic phenols (positive controls) was investigated using the induction period method in the polymerization of methyl methacrylates (MMA) initiated by thermal decomposition of benzoyl peroxide (BPO) by monitoring differential scanning calorimetery (DSC). The k(inh) for the phytophenols was likely with the range 0.5 × 103 M?1s?1-2.2 × 103 M?1s?1, whereas that for synthetic phenols, hydroquinone and galvinoxyl, was with the range 7 × 103 M?1s?1-8 × 103 M?1s?1. Also, the additive scavenging effect of the (-)-epigallocatechin (EGC):(-)-epicatechin (EC) and the (+)-catechin:epicatechin (EC) combination was observed at 1:1 molar ratio, whereas that of the EC:quercetin combination showed the cancel (prooxidative) effect. Furthermore, the EGC:ASDB (L-ascorbyl 2,6-dibutylate) or 2-ME (2-mercaptoethanol) combination showed the prooxidative effect. Such enhancement of prooxidation in the combination may increase their toxic effects due to their cooxidation. Also, the synergic, additive or cancel effects of the flavonoid:vitamins E combination on the induction period in the BPO (a PhCOO* radical) and 2,2'-azobisisobutyronitrile (AIBN, an R* radical) systems are discussed.     

2- and 3-furancarboxylic acids: a comparative study using calorimetry, IR spectroscopy and X-ray crystallography

A thermophysical study by DSC for the 2- and 3-isomers of furancarboxylic acid, in the temperature intervals between T=268 K and their respective melting temperatures has been carried out, and an enhancement in the heat capacity curve of the 3-isomer was observed. The IR spectroscopy did not show significant changes either in the frequency band or in the relative band intensity in the temperature range where the small heat absorption occurs. The X-ray analysis reveals that the main differences in their supramolecular structure consist of the assembly of the carboxylic dimers into sheets.     

A comparative ab initio study of the geometry and force field of thionformic acid with formic and thiolformic acids

The energy and force field for the planar cis and trans conformers of thionformic acid have been calculated using the 4–31 G basis set, augmented by a complete set of d-functions on the sulfur atom, with full geometry optimization. Extensive comparisons are made between the changes in geometry and selected force constants in going from cis- (chain) to the trans- (ring) structures of thionformic, thiolformic and formic acid. These changes are discussed in terms of a hydrogen bonding type of interaction in the O---HS, S---HO and O---HO structural units respectively. Of the thioacid conformers, the trans-thiol is found to be the most stable; the trans-thion and cis-thiol both about 10 kJ mol⁻¹ less stable; and the cis-thion the least stable by about 38 kJ mol⁻¹.     

A safe and selective method for reduction of 2-nitrophenylacetic acid systems to N-aryl hydroxamic acids using continuous flow hydrogenation

The cyclic hydroxamic acid functional group is critical to the biological activity of numerous natural products and drug candidates. Efficient, reliable, and green synthetic methods to produce cyclic hydroxamic acids are needed. Herein, flow hydrogenation has been explored as a novel approach toward achieving the selective partial reduction of 2-nitrophenylacetic acid to 1-hydroxyindolin-2-one. The bidentate ligand, 1,10-phenanthroline, has been identified as a unique inhibitor for modulating product selectivity in this Pt/C-catalyzed process. Under the newly optimized reaction conditions, the targeted hydroxamic acid is produced with high selectivity (49:1) over the lactam by-product. The scope of the reaction is demonstrated for a variety of 2-nitrophenylacetic acid derivatives.     

A comparative MP2 study between water- and acid-assisted proton transfer: allophanic acid as a case of study

Electronic structures of allophanic acid were studied using MP2/6-311++G(d,p) level of theory. Five most stable tautomers were selected and stability of them was studied in detail. Obtained data showed that tautomer 1 having hydrogen atom in the central nitrogen N3 and also in a trans conformation of carbonyl and amino functional groups becomes the most stable one. Then, interconversion of these tautomers to each other was investigated step by step through internal rotation and proton transfer routes. Results indicated that movement of protons determines rate-determining step of all paths A–E. Effects of different solvents were carefully surveyed for each tautomer, and among investigated solvents, water made slight stabilization. Activation barrier for proton exchange assisted by one water molecule and one formic acid molecule was also studied, separately. Both molecules had a great influence on lowering barrier especially for proton transfer routes. Comparative MP2 study showed that the barrier will be lowered much more when acid-assisted proton exchange takes place.     

One-step fabrication and high photocatalytic activity of porous TiO2 hollow aggregates by using a low-temperature hydrothermal method without templates

Porous TiO2 hollow aggregates have been synthesized on a large scale by means of a simple hydrothermal method without using any templates. The as-prepared products were characterized by means of field emission scanning electron microscopy, XRD, TEM, nitrogen adsorption, UV/Vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The photocatalytic activity of the aggregates was demonstrated through the photocatalytic degradation of Rhodamine B. Structural characterization indicates that the porous TiO2 aggregates are 500-800 nm in diameter and display mesoporous structure. The average pore sizes and BET surface areas of the aggregates are 12 nm and 168 m2 g-1, respectively. Optical adsorption investigations show that the aggregates possess an optical band-gap energy of 3.36 eV. The as-prepared products were substantially more effective photocatalysts than the commercially available photocatalyst P25. The dye degradation rate of the porous TiO2 hollow aggregates is more than twice that of P25. The high photoactivities of the aggregates can be attributed to the combined effects of several factors, namely, large surface areas, the existence of mesopores, and the high band-gap energy. In addition, the as-prepared products can be easily recycled.     

A study of the antioxidative behavior of phenolic acids, in aqueous herb extracts, using a dsDNA biosensor

Electrochemical DNA biosensors are promising tools for the fast, inexpensive and simple in vitro analysis for the determination of free radicals and antioxidants. High concentrations of antioxidants in such compounds as phenolic acids and plant extracts, act as free radical terminators which reduce the effect of the oxidative dam-age on DNA. The electrochemical behavior of three representative phenolic acids, caffeic acid, gallic acid and trolox were studied by cyclic voltammetry. Moreover, the determination of the above antioxidants under the optimized conditions (scan rate, deposition potential and time) using differential pulse voltammetry was also investigated. In vitro studies focused on their antioxidative effect were performed by adsorptive transfer stripping voltammetry and dsDNA biosensor. Using Fenton’s system, with FeSO₄ and H₂O₂ was chosen as a strong oxidative system. This biosensor was applied as a screening antioxidant test in order to estimate the antioxidant capacity of aqueous herb extracts.      

A novel method for the preparation of alpha,alpha'-difluoroesters and acids using BrF3

Alkyl-, haloalkyl-, and ketoalkyl-2-ethoxycarbonyl-1,3-dithianes were easily made from the appropriate primary or secondary alkyl bromides, 1,3-dithiane, and ethyl chloroformate. They were reacted with BrF(3) to form the corresponding alpha,alpha-difluoro esters in 65-75% yield. Reaction conditions are very mild (1-2 min, 0 degrees C). The two sulfur atoms of the dithiane are essential for the reaction.     

A method for the measurement of catechol-O-methyltransferase activity using norepinephrine, an endogenous substrate

We propose a highly sensitive method for the measurement of catechol-O-methyltransferase (COMT) activity with norepinephrine (NE), an endogenous native substrate. The product, normetanephrine, was determined by high-performance liquid chromatography (HPLC)-peroxyoxalate chemiluminescence reaction detection or, if required, less sensitive fluorescence detection. For the measurement of membrane-bound (MB)-COMT activity in the rat erythrocyte, the HPLC-peroxyoxalate chemiluminescence reaction detection was employed. Soluble (S)- and MB-COMT activities in the rat erythrocyte were 22.9 +/- 2.5 and 4.62 +/- 1.23 pmol min-1 (mg protein)-1, respectively (n = 5). The Km values obtained for S- and MB-COMT were 366 +/- 31 mumol l-1 and 12.0 +/- 1.1 mumol l-1, respectively (n = 5), suggesting that the use of NE as a substrate would give more precise information on the role of both isoenzymes. However, with dihydroxybenzoic acid as an artificial substrate, the Km values for S- and MB-COMT were similar, with values of 69.2 +/- 11.4 mumol l-1 and 72.2 +/- 9.2 mumol l-1, respectively. The proposed method is thought to be useful for the measurement of both S-COMT and MB-COMT activities, and would give us critical information on the role of metabolism of catecholamines in rat tissues.     

A theoretical study on the pyrolysis of perfluorobutanoic acid as a model compound for perfluoroalkyl acids

The potential energy surface is mapped out for all plausible reactions in the self-decomposition of perfluorobutanoic acid (CF₃CF₂CF₂COOH) as a model compound for the notoriously toxic and bio-accumulative perfluoroalkyl acids. Initial decomposition of perfluorobutanoic acid is found to be controlled by HF elimination and the formation of an α-lactone intermediate. The fate of this intermediate is predicted to be dominated by two competing channels, namely formation of pentafluoropropanoyl fluoride (CF₃CF₂COF) and the closed-shell singlet CF₃CF₂CF:. Direct elimination of CO₂ through decarboxylation is found to be retarded by strong hyperconjugation effects induced by fluorine atoms on the carbon chain. The results presented herein provide insightful information towards a comprehensive understanding of the decomposition of perfluoroalkyl acids in thermal systems.     

A comparative study of rotational temperatures using diatomic OH,O2 and N2+ molecular spectra emitted from atmospheric plasmas

From the application point of view, gas temperature is one of the most important parameters for atmospheric plasmas. Based on the fact that the gas temperature is closely related with the rotational temperature of an atmospheric plasma, a spectroscopic method of measuring the rotational temperature is described in this work by analyzing OH, O₂ and N₂⁺ molecular spectra emitted from the atmospheric plasma in ambient air. The OH and N₂⁺ molecular spectra are emitted because of the oxygen, hydrogen and nitrogen atoms existing in the ambient air. The O₂ diatomic molecular spectrum is emitted from the oxygen plasma that is frequently produced for atmospheric plasma applications. In order to utilize a spectrometer with modest spectral resolution, a synthetic diatomic molecular spectrum was compared with the experimentally obtained spectrum. The rotational temperatures determined by the above three different molecular spectra are in good agreement within 2.4% error. In the case of a plasma with low gas temperature, the temperature measured by a thermocouple was compared to verify the accuracy of the spectroscopic method, and the results show excellent agreement. From the study, it was found that an appropriate diatomic molecular species can be chosen to be used as a thermometer depending on experimental circumstances.     

Determination of the antibiotic fludalanine in plasma and urine by high-performance liquid chromatography using a packed-bed, post-column reactor with o-phthalaldehyde and 2-mercaptoethanol

Fludalanine is a novel anti-bacterial agent active against gram-negative and gram-positive bacteria. A high-performance liquid chromatographic assay has been developed using ion-pair chromatography to resolve fludalanine and the internal standard 3,3-difluoro-D-alanine from plasma and urine background. The mobile phase contains sodium dodecyl sulfonate and methanol in a phosphate buffer. Fludalanine is derivatized post-column with o-phthalaldehyde via a packed-bed chemical reactor. The adduct is detected fluorometrically. The plasma and urine assays are sensitive to 0.25 and 0.5 micrograms/ml, respectively.     

A rapid HPLC method for the determination of carboxylic acids in human urine using a monolithic column

A rapid HPLC method for the determination of carboxylic acids in urine samples using a Chromolith Performance RP/18e 100/4.6 with Chromolith Guard Cartridge RP/18e 10/4.6 (Merck KgaA, Darmstadt, Germany) was developed. The method facilitates the simultaneous determination of aromatic hydrocarbon metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene and ethylbenzene, hippuric acid (HA) from toluene and 2-, 3-, 4-methylhippuric acids (MHA) from xylene. 3-Hydroxybenzoic acid (3-HBA) was used as internal standard. A chromatographic run is completed within less than 5 min for styrene, ethylbenzene and toluene metabolites, and within 10 min for xylene metabolites. The detection limits are 9 mg L^–1 urine for MA, 1.25 mg L^–1 urine for PGA, 4.9 mg L^–1 urine for HA, 22 mg L^–1 urine for 2-MHA, and 18.5 mg L^–1 urine for 3-MHA.No significant differences of the MA, PGA and HA concentrations in human urine samples obtained by HPLC chromatography on LiChrosorb RP 18 and on Chromolith RP/18e columns were found. The results were evaluated by using ANOVA.Abbreviations MA mandelic acid - PGA phenylglyoxylic acid - HA hippuric acid - MHA methylhippuric acid - 3-HBA 3-hydroxybenzoic acid - ANOVA analyses of variance - GC gas chromatography - HPLC high-performance liquid chromatography     

A study of the mechanism of the reaction of 1,3-dioxanes with derivatives of acyclic boronic acids using the AM1 method

Estimation of the energy of intermediate compounds in the reaction of 1,3-dioxanes with acyclic derivatives of boric acids by the AM1 method showed that the reactivity of the initial heterocycles which were converted into 1,3,2-dioxaborinanes was determined by the relative stability of the bipolar structure in the stage preceding, the formation of the endocyclic B−O bond. A. V. Bogatskii Physical Chemical Institute, National Academy of Sciences of Ukraine, 86 Lyustdorfskaya Doroga, Odessa 65080, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 218–221, July–August, 2000.