Electroanalysis may be used in the Vanillin Biotechnological Production

This study shows that electroanalysis may be used in vanillin biotechnological production. As a matter of fact, vanillin and some molecules implicated in the process like eugenol, ferulic acid, and vanillic acid may be oxidized on electrodes made of different materials (gold, platinum, glassy carbon). By a judicious choice of the electrochemical method and the experimental conditions the current intensity is directly proportional to the molecule concentrations in a range suitable for the biotechnological process. So, it is possible to imagine some analytical strategies to control some steps in the vanillin biotechnological production: by sampling in the batch reactor during the process, it is possible to determine out of line the concentration of vanillin, eugenol, ferulic acid, and vanillic acid with a gold rotating disk electrode, and low concentration of vanillin with addition of hydrazine at an amalgamated electrode. Two other possibilities consist in the introduction of electrodes directly in the batch during the process; the first one with a gold rotating disk electrode using linear sweep voltammetry and the second one requires three gold rotating disk electrodes held at different potentials for chronoamperometry. The last proposal is the use of ultramicroelectrodes in the case when stirring is not possible

Thermo-physical and structural studies of sodium zinc borovanadate glasses in the region of high concentration of modifier oxides

This paper reports investigation of Na2O and ZnO modified borovanadate glasses in the highly modified regime of compositions. These glasses have been prepared by microwave route. Ultraviolet (UV) and visible, infrared (IR), Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies have been used to characterize the speciation in the glasses. Together with the variation of properties such as molar volume and glass transition temperatures, spectroscopic data indicate that at high levels of modification, ZnO tends to behave like network former. It is proposed that the observed variation of all the properties can be reasonably well understood with a structural model. The model considers that the modification and speciation in glasses are strongly determined by the hierarchy of group electronegativities. Further, it is proposed that the width of the transitions of glasses obtained under same condition reflects the fragility of the glasses. An empirical expression has been suggested to quantify fragility on the basis of width of the transition regions. (C) 2012 Elsevier Ltd. All rights reserved

Ion transport studies in lithium phospho-molybdate glasses containing Cl- ion

Ion conducting glasses in xLiCl-20Li(2)O-(80-x) 0.80P(2)O(5)-0.20MoO(3)] glass system have been prepared over a wide range of composition (X = 5, 10, 15, 20 and 25 mol%). The electrical conductivity and dielectric relaxation of these glasses were analyzed using impedance spectroscopy in the frequency range of 10 Hz-10 MHz and in the temperature range of 313-353 K. D.c. activation energies extracted from Arrhenius plots using regression analysis, decreases with increasing LiCl mol%. A.c. conductivity data has been fitted to both single and double power law equation with both fixed and variable parameters. The increased conductivity in the present glass system has been correlated with the volume increasing effect and the coordination changes that occur due to structural modification resulting in the creation of non-bridging oxygens (NBO's) of the type O-Mo-O- bonds in the glass network. Dielectric relaxation mechanism in these glasses is analyzed using Kohlrausch-Williams-Watts (KWW) stretched exponential function and stretched exponent (beta) is found to be insensitive to temperature

Impedance spectroscopic studies on microwave synthesized NaPO3-V2O5 glasses containing SO42- ions

Impedance spectroscopic studies on modified phospho-vanadate glasses containing SO42- ions have been carried out over wide range of frequency. Modulated DSC studies suggest that the addition of alkali salt makes the glass less rigid and more fragile. The frequency dependent impedance data has been used to calculate d.c conductivity and activation energies. These values are comparable with the other ionic liquids. The conductivity and relaxation phenomenon was rationalized using universal a.c conductivity power law and modulus formalism. The activation energies for relaxation mechanism was also determined using imaginary parts of electrical modulus peaks which were close to those of the d.c conductivity implying the involvement of similar energy barriers in both the processes. Kohlrausch-William-Watts (KWW) stretched exponent beta, is temperature insensitive and power law (s) exponent is temperature dependent. The enhanced conductivity in these glasses is attributed to the depolymerised structure in which migration of Na+ ions proceeds in an expanded network comprising SO42- ions in the interstitials. The effect of structure on activation energy is well supported by abinitio DFT computations. (C) 2015 Elsevier B.V. All rights reserved

Nanocrystalline TiO(2) preparation by microwave route and nature of anatase-rutile phase transition in nano TiO(2)

Nanopowders of TiO(2) has been prepared using a microwave irradiation-assisted route, starting from a metalorganic precursor, bis(ethyl-3-oxo-butanoato)oxotitanium (IV), [TiO(etob)(2)](2). Polyvinylpyrrolidone (PVP) was used as a capping agent. The as-prepared amorphous powders crystallize into anatase phase, when calcined. At higher calcination temperature, the rutile phase is observed to form in increasing quantities as the calcination temperature is raised. The structural and physicochemical properties were measured using XRD, FT-IR, SEM, TEM and thermal analyses. The mechanisms of formation of nano-TiO(2) from the metal-organic precursor and the irreversible phase transformation of nano TiO(2) from anatase to rutile structure at higher temperatures have been discussed. It is suggested that a unique step of initiation of transformation takes place in Ti(1/2)O layers in anatase which propagates. This mechanism rationalizes several key observations associated with the anatase rutile transformation

Fragility correlates thermodynamic and kinetic properties of glass forming liquids

In our earlier communication we proposed a simple fragility determining function, (NBO]/(VmTg)-T-3), which we have now used to analyze several glass systems using available thermal data. A comparison with similar fragility determining function, Delta C-p/C-p(1), introduced by Chryssikos et al. in their investigation of lithium borate glasses has also been performed and found to be more convenient quantity for discussing fragilities. We now propose a new function which uses both Delta C-p and Delta T and which gives a numerical fragility parameter, F whose value lies between 0 and 1 for glass forming liquids. F can be calculated through the use of measured thermal parameters Delta C-p, C-p(1), T-g and T-m. Use of the new fragility values in reduced viscosity equation reproduces the whole range of viscosity curves of the Angell plot. The reduced viscosity equation can be directly compared with the Adam-Gibbs viscosity equation and a heat capacity function can be formulated which reproduces satisfactorily the Delta C-p versus In(T-r) curves and hence the configurational entropy. (C) 2014 Elsevier Ltd. All rights reserved

Electrical conductivity and dielectric relaxation studies on microwave synthesized Na2SO4 center dot NaPO3 center dot MoO3 glasses

Electrical conductivity and dielectric relaxation studies on SO4 (2-) doped modified molybdo-phosphate glasses have been carried out over a wide range of composition, temperature and frequency. The d.c. conductivities which have been measured by both digital electrometer (four-probe method) and impedance analyser are comparable. The relaxation phenomenon has been rationalized using electrical modulus formalism. The use of modulus representation in dielectric relaxation studies has inherent advantages viz., experimental errors arising from the contributions of electrode-electrolyte interface capacitances are minimized. The relaxation observed in the present study is non-Debye type. The activation energies for relaxation were determined using imaginary parts of electrical modulus peaks which were close to those of the d.c. conductivity implying the involvement of similar energy barriers in both the processes. The enhanced conductivity in these glasses can be attributed to the migration of Na+, in expanded structures due to the introduction of SO4 (2-) ions

Correlations between EPR and optical properties: Diborovanadate glasses in a highly modified regime

Glasses with composition x V2O5 - 10PbO- (90- x) NaBO2 with 10 <= x <= 30 were prepared by a novel, energy-efficient and economical microwave method. The Electron Paramagnetic Resonance (EPR) spectra of all the glasses investigated exhibited a well-defined hyperfine structure, from which the spin Hamiltonian parameters of the VO2+ ion, dipolar hyperfine coupling parameters, and the fermi-contact interaction term (K) have been calculated. The values of g-tensor reveal the existence of the VO2+ ion in octahedral coordination with a tetragonally compressed site. The variations seen in P, K, P beta K-2 and PK/gamma with V2O5 content indicate the s character of the magnetic spin of vanadium which arises due to the partial unpairing of s-electrons. Also, a decrease in K with V2O5 mol% suggests a strong V=O interaction, makes the bond length (V-O) in the vanadyl group shorter and distorts the vanadyl group from O-h to C-4v. The EPR and UV-Vis parameters are analyzed on the basis of structural motifs formed due to the network modification. The molecular orbital coefficients a2 and gamma(2) have been calculated. The ratio, (1-gamma(2)/1-alpha(2)) increases with increasing V2O5 mol%, suggesting that the a-bonding between the V atom and the equatorial ligand is weakening. IR studies reveal the presence of BO3/2](0), BO4/2](-) and B2V2O9](2-) structural groups in the glass matrix

Voltametrické stanovení sumy ethylvanilinu a methylvanilinu ve vybraných vzorcích potravin pomocí uhlíkové pastové elektrody modifikované dodecylsíranem sodným

A new voltammetric method without using high cost and health risk nanomaterials has been developed for quantitative determination of ethylvanillin and methylvanillin sum, compounds that are used as food additives. The method is based on direct electrochemical oxidation of these biologically active compounds using square wave voltammetry at carbon paste electrode with surface modified by sodium dodecyl sulfate (SDS/CPE) performed in 0.1 M phosphate pH 6.0 buffer. Working conditions such as pH value of supporting electrolyte, type of surfactant, accumulation time of surfactant, and parameters of square wave voltammetry were optimized. In comparison with bare carbon paste electrode, excellent reproducibility characterized by a relative standard deviation of approximately 0.3% was obtained at the SDS/CPE. Linear range from 1.0 x 10(-6) to 2.0 x 10(-5) M, limits of quantification 9.8 x 10(-8) M and detection 2.9 x 10(-8) M were found at pulse amplitude 70 mV and frequency 50 Hz selected as optimum for ethylvanillin quantification. For methylvanillin, a linear range from 7.0 x 10(-8) to 2.0 x 10(-5) M and limits of quantification 7.0 x 10(-8) M and detection 2.0 x 10(-8) M were also determined. The procedure was validated using standard high-performance liquid chromatography method in the analysis of selected complex foodstuffs such as commercial baking sugar, biscuits, and an alcoholic drink. The results showed that a direct voltammetric approach is economically advantageous and reliable for the determination of ethyl- and methylvanillin, which is fully comparable to the reverse phase HPLC used as the ISO standard.Byla vyvinuta nová voltametrická metoda pro kvantitativní stanovení celkové sumy potravinářských aditiv ethylvanilinu a methylvanilinu bez použití vysokonákladových nanomateriálů vykazujících zdravotní rizika. Tato metoda je založena na přímé elektrochemické oxidaci těchto biologicky aktivních sloučenin s použitím square wave voltametrie na uhlíkové pastovité elektrodě povrchově modifikované dodecylsulfátem sodným (SDS/CPE) v prostředí 0,1 M fosfátového pufru o pH 6,0. Byly optimalizovány pracovní podmínky, jako je hodnota pH použítého elektrolytu, typ povrchově aktivníholátky, doba akumulace a parametry použité voltametrické techniky. Ve srovnání s nemodifikovanou elektrodou byla u SDS/CPE dosažena vynikající reprodukovatelnost charakterizovaná relativní směrodatnou odchylkou přibližně 0,3%. Lineární rozsah kalibrace od 1,0 x 10 (-6) do 2,0 x 10 (-5) M byl zjištěn limit kvantifikace 9,8 x 10 (-8) M a detekce 2,9 x 10 (-8) M při amplitudě 70 mV a frekvenci 50 Hz, které byly vybrány jako optimální pro kvantifikaci ethylvanilinu. Pro methylvanilin byl také stanoven lineární rozsah od 7,0 x 10 (-8) do 2,0 x 10 (-5) M a limit kvantifikace 7,0 x 10 (-8) M a detekce 2,0 x 10 (-8) M. Metoda byla dále validována pomocí standardní metody vysokoúčinné kapalinové chromatografie při analýze vybraných potravin, jako byl komerční pekárenský cukr, sušenky a alkoholický nápoj. Výsledky ukázaly, že přímý voltametrický přístup je ekonomicky výhodný a spolehlivý pro stanovení ethyl- a methylvanilinu, který je plně srovnatelný s HPLC na reverzní fázi používané jako ISO norma