Investigation of phenolic acids in yacon (Smallanthus sonchifolius) leaves and tubers

Thin-layer chromatographic (TLC) screening of crude extracts of dried leaves and tubers of yacon (Smallanthus sonchifolius, Asteraceae) and products of acid hydrolysis of tubers on the silica gel HPTLC plates using the developing solvents ethyl acetate-formic acid-water (85:10:15, v/v/v) and n-hexane-ethyl acetate-formic acid (20:19:1, v/v/v) proved the presence of chlorogenic, caffeic and ferulic acid. These phenolic acids were isolated from the crude extract of yacon leaves by preparative TLC, and identified after elution by HPLC/MS, as well as by direct injection of the crude extract into the HPLC/MS system. Acid hydrolysis of tubers released the increased amount of phenolic acids (e.g. caffeic acid and ferulic acid), flavonoid quercetin and an unidentified flavonoid, which was detected by TLC analysis. Ferulic acid, isomers of dicaffeoylquinic acid and still an unidentified derivative of chlorogenic acid (Mr = 562) as constituents of yacon leaves and ferulic acid as constituent of yacon tubers are reported here for the first time. These acids gave significant contribution to the radical scavenging activity detected directly on the TLC plate sprayed with 1,1-diphenyl-2-picrylhydrazyl (DPPH).     

Thermodynamics of saturated and unsaturated ketones C<Subscript>13</Subscript> and C<Subscript>18</Subscript> and the energy of specific intermolecular interactions

P-T dependences of the saturated vapor of pseudoionone, hexahydropseudoionone, and saturated and unsaturated ketones C₁₈ were studied using the statistical approach, and the enthalpies and entropies of its vaporization were calculated. The presence of monomer forms of the molecules of these compounds was established by studying the unsaturated vapor pressure. It was demonstrated that the role of isostructural methyl group in ketones is not related to the all-explaining steric effect concealing the real nature of the specific interaction. The energies of specific intermolecular interactions were determined in liquid symmetrical and unsymmetrical ketones.     

Synthesis of sodium tungstate from the system Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaNO<Subscript>3</Subscript>-WO<Subscript>3</Subscript>

The physicochemical basis of the heterogeneous reaction between the components of the system (sodium oxalate)-(sodium nitrate)-(tungsten(VI) oxide) has been studied. The reaction of WO₃ with sodium oxalate-nitrate mixtures occurs at a lower temperature and at a higher rate than the reaction with pure sodium carbonate. A high-yield process for the synthesis of high-purity sodium tungstate has been developed on the basis of this study.     

Features of the oxidation of C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerites as studied by IR spectroscopy

Features of the oxidation of C₆₀ and C₇₀ fullerites were studied by infrared spectroscopy. It was shown that for C₆₀ fullerite, the presence of toluene residue reduces the temperature at which oxidation starts. The form of the toluene (solvate or nonsolvate) is not important. A low-frequency shift in the valence C-O-C vibrations of C₇₀ fullerene due to local steric strains was discovered.     

The enthalpy of formation of fullerene fluoride C<Subscript>60</Subscript>F<Subscript>18</Subscript> and the C-F bond energy

The enthalpy of combustion of crystalline fullerene fluoride C₆₀F₁₈ was determined in an isoperibolic calorimeter with a rotating platinized bomb, and the enthalpy of formation of the compound was calculated. The enthalpy of sublimation of C₆₀F₁₈ measured earlier was used to calculate the enthalpy of formation of fullerene fluoride in the gas phase and the mean enthalpy of dissociation of C-F bonds in this compound.     

Structure of heteroassociates formed in the HF-(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>O liquid system

The aim of this work was to determine the structure of stable heteroassociates (HAs) with the stoichiometric ratios 1:2, 2:1, and 4:1 of molecules formed in the HF-(C₂H₅)₂O binary liquid system. The stretching frequencies of HF molecules found for each HA using a special procedure for processing IR spectra were compared with the calculated frequencies V HF of the stable molecular complexes (HF)_m ((C₂H₅)₂O)_n (m = 1, 2, 4, 8; n = 1, 2) with different topologies by the density functional method (B3LYP/6-31++G(d,p)). As a result, it was shown that the most stable (among H-bonded complexes with the same stoichiometric ratio of molecules) HAs HF((C₂H₅)₂O)₂, (HF)₄ ((C₂H₅)₂O)₂, and (HF)₈-((C₂H₅)₂O)₂ formed in HF solutions in diethyl ether. All of them had a cyclic structure and a common peculiarity of structure: only one lone electron pair of the oxygen atom of the (C₂H₅)₂O molecules is involved in hydrogen bonding.     

Interconversion of stannylium ions in the C<Subscript>4</Subscript>H<Subscript>11</Subscript>Sn<Superscript>+</Superscript> system

B3LYP method with the LANL2DZ basis for tin and aug-cc-pVDZ basis for carbon and hydrogen were used to obtain the equilibrium geometry of the main (with a positive charge on the tin) isomers in the C₄H₁₁Sn⁺ system and the transition states at their interconversion. As in the case of silicon and germanium, the cations of lighter elements of the 14th group, the most stable isomer is shown to be the tertiary ion, however, the energy of its complexes with ethane and propane is higher only by several kJ mol⁻¹. Nevertheless, the formation of these complexes from the tertiary ion requires overcoming a rather high barrier (293 and 272 kJ mol⁻¹, respectively). The barrier for isomerization of the secondary ion in the ethane complex is somewhat lower (222 kJ mol⁻¹), but still is significantly greater than the energy gained at the appearance of the nucleogenic ion. The most probable transformation pathways of the nucleogenic stannylium ions are the formation of complexes with ethylene, which requires overcoming barriers of 130 and 117 kJ mol⁻¹ for the tertiary and secondary ions, respectively.     

Kinetics of the oxidation of diethyl sulfide in the B(OH)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O system

Data obtained for the kinetics of oxidation of diethyl sulfide (Et₂S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O₂H)(OH) ₃ ⁻ and diperoxoborates B(O₂H)₂(OH) ₂ ⁻ are the active species. The rates of the reactions of Et₂S with B(O₂H)(OH) ₃ ⁻ and B(O₂H)₂(OH) ₂ ⁻ are 2.5 and 100 times greater than with H₂O₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 38–42, January–February, 2007.     

Mechanism of the initiation of combustion in CH<Subscript>4</Subscript>(C<Subscript>2</Subscript>H<Subscript>2</Subscript>)/Air/O<Subscript>3</Subscript> mixtures by laser excitation of the O<Subscript>3</Subscript> molecules

The possibility of enhancing the ignition and combustion of the CH₄/air/O₃ and C₂H₂/air/O₃ mixtures by exciting the asymmetric vibrations of the O₃ molecule with CO₂ laser radiation is considered. Even the admixture of small amounts of O₃ (2.5–5.0 vol %) into the hydrocarbon/air mixtures intensifies ignition and shortens the induction period. The excitation of the O₃ molecules with 9.7-μm radiation speeds up the chain process and further reduces the induction period and the ignition temperature. The induction period can be shortened by a factor of 10–100 even at low radiation energies absorbed by the gas (E _S = 10^?3-10^?2 J/cm³).     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Molecular structure of NiO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> from gas-phase electron diffraction and quantum chemical data

Gas-phase electron diffractometry was used to study the molecular structure of N,N′-ethylenebis(salicylaldiminato)nickel(II), NiO₂N₂C₁₆H₁₄, [hereinafter Ni(salen)] at 583(5) K. The molecule has C ₂ symmetry with a practically planar structure of the NiN₂O₂ coordination unit and with internuclear distances r _α (Ni-O) = 1.882(21) Å and r _α (Ni-N) = 1.889(22) Å. The results of B3LYP/CEP-31G molecular structure calculations are in good agreement with experimental data, whereas the RHF/CEP-31G method significantly overestimates the Ni-N internuclear distance and gives worse results for other structural parameters. According to 3LYP/CEP-31G calculations, the ¹ A low-spin state is 28 kJ/mole lower in energy than the ³ B high-spin state.     

Generation of fullerenyl radicals and chemiluminescence in the (C<Subscript>60</Subscript>—R<Subscript>3</Subscript>Al)—O<Subscript>2</Subscript> system

Fullerenyl radicals (FR) RC₆₀ ^· and chemiluminescence (CL) are generated in the presence of O₂ in C₆₀—R₃Al (R = Et, Buⁱ) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R^· radical, which is an intermediate of R₃Al autooxidation, to C₆₀. Mass spectroscopy and HPLC were used to identify Et_nC₆₀H_m (n, m = 1–6), Et_pC₆₀ (p = 2–6), and dimer EtC₆₀C₆₀Et as stable products of FR transformations. As found by ESR, the EtC₆₀ ^· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C₆₀— R₃Al)—O₂ system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O₂, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C₆₀—R₃Al)—O₂ system is much brighter (I _max = 1.86·10⁸ photon s⁻¹ mL⁻¹) than the known background CL (I _max = 6.0·10⁶ photon s⁻¹ mL⁻¹) for the autooxidation of R₃Al and is localized in a longer-wavelength spectral region (λ_max = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter ³CH₃CHO* to the products of FR transformation: R_nC₆₀H_m, R_pC₆₀, and EtC₆₀C₆₀Et. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007.     

Direct Mass Spectrometric Study of the Ionic Species Content of a C<Subscript>2</Subscript>HCl<Subscript>3</Subscript>/He/O<Subscript>2</Subscript> Microwave Discharge Plasma

Direct on-line studies of a C₂HCl₃/He/O₂ microwave discharge plasma made possible the evolution and detection of many unfamiliar ionic species. Numerous ionic chlorocarbons, chlorohydrocarbons, oxygenated chlorohydrocarbons, oxygenated hydrocarbon radicals, and simple hydrocarbon species were identified mass spectrometrically as by-products: C _m Cl _n (m = 1–4, 6, 8; n = 1–8), C _m H _n Cl _x (m = 1–4, 6, 7, 10; n, x = 1–6), C _m H _n Cl _x O _y (m = 1–5, 12; n = 1–7; x = 1, 2, 4, 6; y = 1–3), C _n H_2n−1O (n = 2, 3), C _m H _n (m = 2, 4, 6, 8; n = 2, 4), and so on. The studies clearly showed the presence of various unfamiliar positive ionic O-containing species such as C₂ClO₂, CCl₃CO, C₂H₂Cl₄O₂, and C₄H₂Cl₆O₃. It is apparent that positive-ion reactions play a significant role in producing many ionic species in the chemistry of C₂HCl₃ plasmas.     

Liquid chromatography/tandem mass spectrometry studies of the phenolic compounds in honey

An improved and simplified analytical method which offers rapid, accurate determination and identification of phenolic compounds in honey samples is reported. The honey samples were diluted by acidified water (pH 2), and analyzed by HPLC–ESI-MS/MS. Simultaneously determination of phenolic acids and flavonoids was carried out by a liquid chromatography–mass spectrometry. Comparison between atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) was performed by analysis of standards. Fragmentation of analytes for subsequent selective Multiple Reaction Monitoring (MRM) analysis was investigated in negative mode. Sample preparation without separation of sugars and clean-up procedure, followed by fast chromatographic separation using a narrow-bore column C18 (50 mm × 2.1 mm, 3 μm) allowed the analysis to be completed in a short run time. LODs were ranged between 1 and 15 ng L⁻¹ for p-coumaric acid and naringenin, respectively. The method was applied for determination of phenolic acids and flavonoids in honey samples from different botanical origin.     

Synthesis of nanocrystalline ZnO by the thermal decomposition of [Zn(H<Subscript>2</Subscript>O)(O<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>7</Subscript>)<Subscript>2</Subscript>] in isoamyl alcohol

It was studied how the conditions of heat treatment of a [Zn(H₂O)(O₂C₅H₇)₂] solution in isoamyl alcohol at 120–140°C for 2–60 min affect the precursor decomposition mechanism and the characteristics of the obtained nanocrystalline zinc oxide. In all the cases, the product was a crystalline substance with the wurtzite structure and a size of crystallites of 14–18 nm, which was independent of the synthesis conditions. The thermal behavior and microstructure of the separated and dried nanostructured ZnO powder were investigated. It was determined how the duration and temperature of the heat treatment of the precursor solution affects the microstructure of ZnO coatings dip-coated onto glass substrates using dispersions produced at 120 and 140°C. The nanosized ZnO application procedure was shown to be promising for creating a gas-sensing layer of chemical gas sensors for detecting 1% H₂ (\(R_0 /R_{H_2 } \) was 58 ± 2 at an operating temperature of 300°C) and 4 ppm NO₂ (\(R_{NO_2 } /R_0\) were 15 ± 1 and 1.9 ± 0.1 at operating temperatures of 200 and 300°C, respectively).     

<Superscript>27</Superscript>Al NMR Study of the Metal Cluster Compound Al<Subscript>50</Subscript>C<Subscript>120</Subscript>H<Subscript>180</Subscript>

We present an ²⁷Al NMR study of the metal cluster compound Al₅₀Cp*₁₂ which is composed of (identical) Al₅₀ clusters, each surrounded by a Cp* ligand shell, and arranged in a crystalline 3D array (here Cp* = pentamethylcyclopentadienyl = C₅(CH₃)₅). The compound is found to be non-conducting, the nuclear spin-lattice relaxation in the temperature range 100–300 K being predominantly due to reorientational motions of the Cp* rings. These lead to a pronounced maximum in the relaxation rate at T ∼ 170 K, corresponding to an activation energy of about 850 K. Data for the related compound Al₄Cp*₄, containing very much smaller Al₄ clusters are also presented. A comparison is drawn with the quadrupolar relaxation recently observed for the non-conducting fraction of Ga₈₄ molecules in the metal cluster compound Ga₈₄[N(SiMe₃)₂]₂₀-Li₆Br₂(thf)₂₀·2toluene. It is our pleasure to dedicate this paper to our colleague professor Günter Schmid at the occasion of his 70th birthday.     

Alkyl (C<Subscript>10</Subscript>, C<Subscript>12</Subscript>, C<Subscript>14</Subscript> and C<Subscript>16</Subscript>) triphenyl phosphonium bromide influenced cloud points of nonionic surfactants (Triton X 100, Brij 56 and Brij 97) and the polymer (Polyvinyl methyl ether)

The clouding points (CP) of the nonionic surfactants p-tert-octyl phenyl polyoxyethylene ether (Triton X 100), Brij-56 and Brij-97, and the water soluble polymer polyvinylmethylether (PVME) have been measured in the presence of the ionic surfactants alkyl (C₁₀, C₁₂, C₁₄ and C₁₆) triphenyl phosphonium bromides (ATPBs). The threshold additive concentrations required for efficient CP enhancement of the systems that were studied have been determined. Considering CP as the threshold state of phase separation, the energetics of the process at different additive concentrations has been evaluated. The spontaneity of free energy of the clouding process (G _c ⁰ ) at the transition concentrations followed the order PVME > TX 100  Bj 56 > Bj 97. The clouding process has been found to be energetically endothermic with fairly large enthalpy and entropy changes that nicely compensate each other. The compensation temperature has been evaluated and compared with different types of the clouding agents.This revised version was published online in January 2005 with corrections to the names of the authors.     

Distribution coefficients in the water-dodecane system and the heats of adsorption of C<Subscript>1</Subscript>-C<Subscript>8</Subscript> alcohols on silica

Distribution coefficients in the water-dodecane system and the heats of adsorption of C₁-C₈ alcohols on silica (Silochrom S-80) were determined by gas chromatography. At low temperatures, C₁-C₄ alcohols were largely distributed in the aqueous phase, and C₆-C₉ alcohols were predominantly dissolved in the organic phase; C₅ alcohols had intermediate properties. Permittivity was found to correlate with log K _d, which allowed us to predict the character of the distribution of alcohols in the water-oil system. The heats and isotherms of adsorption were determined for the alcohols studied. The heats of adsorption of alcohols on silica monotonically increased in the series under consideration. For C₅-C₈ alcohols, they exceeded the heat of adsorption of water. The isotherms of adsorption were described by the Freundlich equation.     

Giant correlation effects in the photoelectron spectrum of Ni(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>: clues from accurate calculation of ionization cross-sections

Several general issues relating to the strong correlation effects present in the ionic states and the interpretation of molecular photoelectron spectra are discussed in the context of the Ni(C₃H₅)₂ molecule, and the problematic assignment of its spectrum is considered. Accurate calculations of photoionization cross-sections relative to all the valence ionizations are computed and compared with the available experimental evidence. It is shown that most ambiguities are resolved by a careful analysis of cross-section profiles and branching ratios, which reveal a wealth of details on the complex electronic structure of this molecule.