Dipole moments of derivatives of glucose,galactose and lactose part I

Summary The dipole moments of the- and-isomers of 2, 3, 4, 6 tetraacetyl aoetyl D-glucose and 2, 3, 4, 6 tetraacetyl methyl D-glucose have been determined in solutions of benzene, by the application of the method of Halverstadt and Kumler. This is expected to remove from the older data the uncertainties introduced by the extrapolation methods.The moments of the penta-methyl derivatives of D-glucose, of the penta-acetyl derivative of-D-galactose and of the octaacetate of-lactose are also recorded.The effect of temperature on the dipole moments has not been found to be pronounced, in the range 30–40°C.

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Zusammenfassung Dipolmomente einiger Derivate von Glukose, Galaktose und Laktose wurden teilweise erstmals aus benzolischer Lösung ermittelt: Extrapolationsmethode auf unendliche Verdünnung nach Halverstadt und Kumler. Beseitigung einiger Unsicherheiten in früheren Bestimmungen. Es wurde kein wesentlicher Temperatureinfluß im Bereich von 30–40°C gefunden.

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The author wishes to express his gratitude to Dr. S. K. K. Jatkar, and to Dr. B. Sanjiva Rao for his unstinting and valuable help. He is thankful to Dr. R. J. W. Le Fèvre for his kind interest in the work. His thanks are also to the Indian Institute of Science for providing facilities for investigations.     

A new derivative for improved GLC separation of mannose,galactose and glucose

Summary The procedure involving oxime formation followed by silylation for the analysis of standard hexoses by GC resulted in unseparated peaks for D-glucose, D-mannose and D-galactose. This procedure was therefore modified to obtain clear separation of hexoses. STOX (hydroxylamine containing phenyl--D-glucopyranoside as the internal standard) was mixed with trimethylsilylimidazol or hexamethyldisilazane, and then added to a standard sugar mixture containing D-glucose, D-galactose and D-mannose. The mixture was analyzed by gas chromatography with OV-17/OV-22 as the stationary phase, resulting in three distinct peaks.     

Gas-liquid chromatography of isopropylidene-glucose and glucose as their trimethylsilyl derivatives

Summary This paper describes the gas chromatographic separation of the mixture of di- and mono-O-isopropylidene-D-glucose and D-glucose as their trimethylsilyl derivatives. The use of OV-101 as liquid phase provides a complete separation for the all components in the mixture. Quantative analysis was performed using xylitol as the internal standard for di- and mono-O-isopropylidene-D-glucose, and sorbitol as the internal standard for -and -glucose.     

Preparation and properties of insoluble films of cyclodextrin condensation polymers

The preparation and properties of smooth and stable films of cyclodextrin polymers are described. The commercially available water soluble prepolymers of-, -, and-cyclodextrin of low molecular masses were crosslinked with glutaric dialdehyde. Side-chain unreacted aldehyde groups were reduced with sodium borohydride. For the-cyclodextrin polymer, optimum film performance was found for a 1:10 mass ratio of glutaric dialdehyde to prepolymer, which corresponds to a molar ratio of glutaric dialdehyde to cyclodextrin units of about 1.75: 1. Such films, of thickness 2.4 µm, were prepared on metallic or glassy-carbon substrates for characterization by scanning-electron microscopy, and for studies with the electrochemical quartz-crystal microbalance.     

Effect of Plasticizer on the Performance of the Surfactant-Selective Electrode Based on a Poly(Vinyl Chloride) Membrane with no Added Ion-Exchanger

The effect of different plasticizers in the sensing membrane on the performance of a surfactant ISE based on a PVC membrane with no added ion-exchanger was investigated. o-nitrophenyl octyl ether (NPOE), o-nitrophenyl decyl ether (NPDE), o-nitrophenyl dodecyl ether (NPDOE) and o-nitrophenyl tetradecyl ether (NPTE) were used as plasticizers. Electrodes based on NPDE, NPDOE and NPTE produced better results than NPOE-plasticized PVC membrane electrodes in terms of low detection limits. Electrodes based on NPDE, NPDOE and NPTE displayed a Nernstian slope in the concentration range of 10^–6 to 10^–2M. NPOE-plasticized PVC membrane electrodes displayed a Nernstian slope in the concentration range of 10^–5 to 10^–2M. The three electrodes other than the NPOE-plasticized PVC membrane electrode showed a similar performance to that of the NPOE-plasticized PVC membrane electrode concerning low detection limits and slope sensitivity. The four electrodes examined in this study are excellently selective for the dodecyltrimethylammonium ion over inorganic anions, but interference from other cationic surfactants such as tetradecyltrimethylammonium ions is significant. With respect to slope sensitivity, selectivity, response time and pH effect, the four electrodes showed a similar performance.     

Structure of Narcissus tazetta Glucomannan

Naturally acetylated glucomannan with MW 31,000 and []_D ²⁰ -29.1° was isolated from bulbs of Narcissus tazetta L. Chemical methods and IR and ¹³C NMR spectroscopies were used to show that the polysaccharide contains 12.9% O-Ac groups and consists of D-mannose and D-glucose in a 1:5.6 ratio that form a linear polymer through -1,4-glycoside bonds.     

Noteworthy electroanalytical features of the stage 4 to stage 3 phase transition in lithiated graphite

A careful study of electrochemical lithiation of a composite graphite electrode at elevated temperatures was performed using a potentiostatic intermittent titration technique. Special emphasis was placed on the stage 4 to stage 3 phase transition, occurring in the range of x (in Li_xC₆) between 0.12 and 0.22 (this corresponds to the partial dimensionless intercalation level ranging from 0 to 1). An abrupt increase in the Li chemical diffusion coefficient, D_chem, when approaching the relative coverage level =1/3, and a specific non-Arrhenius shape of the plot of D_chem vs. the inverse of the absolute temperature were observed. These two features of the phase transition seem to be in agreement with a recent thermodynamic model for adatoms diffusing on a surface with two considerably different barrier energy sites.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic     

Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

Amperometric Detection of Dopamine in the Presence of Ascorbic Acid Using a Nafion Coated Glassy Carbon Electrode Modified with Catechin Hydrate as a Natural Antioxidant

Catechin hydrate (trans-3,3,4,5,7-penta-hydroxyflavone) is a derivative of catechol, and it is one of the natural antioxidant and anticarcinogenic compounds found in many fruits and agricultural foods. A new electrode was prepared by electrodeposition of a catechin-hydrate film on the surface of an activated glassy carbon electrode, followed by coating with nafion layer. Cyclic voltammetry was used for the deposition process, and the resulting modified electrode was found to retain the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The cyclic voltammograms of the modified electrode indicated that the surface-confined catechin-hydrate was strongly dependent on the solution pH. The electrochemical behaviour and stability of the modified electrode were studied by cyclic voltammetry. The apparent charge transfer rate constant (k _s ) and electron transfer coefficient () between the electrode surface and adsorbed catechin hydrate were calculated as 0.41 and 0.31s^z–1 0.31, respectively. The modified electrode exhibits an electrocatalytic effect on dopamine oxidation in the pH range of 2 to 7. The modified electrode was used for the electrocatalytic oxidation of dopamine in the presence of ascorbic acid and the elimination of the interference by ascorbic acid (AA) when present in a 200-fold concentration excess. A very large decrease (400mV) in the overpotential for the oxidation of dopamine and current increase were observed on the surface of the modified electrode. Dopamine was determined amperometrically at the modified electrode in the concentration range of 100nM to 0.1mM. The detection limit (signal to noise is 3) and sensitivity are 11nM and 16nA/µM, respectively. The modified electrode was employed to determine DA in biological mediums.     

Electrocatalysis of Tryptophan at Multi-Walled Carbon Nanotube Modified Electrode

Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5×10^–7 to 1.0×10^–4molL^–1, and the detection limit is 2.7×10^–8molL^–1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity.     

Stripping voltammetric determination of trace amounts of mercury using a carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone

A carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone was used for the voltammetric determination of mercury(II). Mercury was preconcentrated onto the surface of the modified electrode only by the complexing effect of the modifier without application of potential (i.e. in open-circuit conditions). After exchange of the medium, the accumulated amount of mercury(II) was determined by differential pulse anodic stripping voltammetry. The response depended on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 0.1 g 1^–1 Hg(II) for a preconcentration time of 15 min. Preconcentration for suitable times yielded a linear calibration graph from 0.5 to 6000 g 1^–1 Hg(II). For multiple determinations (5 runs), the relative standard deviation was 5% for a concentration of 100 g 1^–1 Hg(II). The proposed procedure was used to determine trace mercury in plant and sewage sludge samples with good results.On leave from Hainan University, Hainan Peoples Republic of China     

Potentiodynamic and cyclic voltammetric behaviour of a lead electrode in NaOH solution

Summary The electrochemical behaviour of lead in NaOH solution was studied by potentiodynamic and cyclic voltammetric techniques in combination with X-ray diffraction analysis. The active dissolution of lead involves a small shoulderA1 followed by a peakA1 prior to a passive region. The shoulderA1 is assigned to the electroformation of a Pb(OH)₂ film, whereas peakA1 is due to the formation of PbO. Beyond the passive region, the current density increases again, forming a small shoulderA2 and a peakA2 prior to the oxygen evolution potential. The shoulderA2 and the peakA2 are correlated to the electrooxidation of PbO to Pb₃O₄ and PbO₂, respectively. The intensity of the anodic peaks increases with increasing alkali concentration, temperature and scan rate. In cyclic voltammetry, the reverse scan shows two cathodic peaksC1 andC2 which are correlated to the electroreduction of PbO and PbO₂ respectively, to Pb.

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Potentiodynamisches und cyclovoltammetrisches Verhalten einer Bleielektrode in NaOH-Lösung

Zusammenfassung Das elektrochemische Verhalten von Blei in NaOH wurde mittels potentiodynamischer und cyclovoltammetrischer Techniken unter Zuhilfenahme der Röntgenbeugungsanalyse untersucht. Die aktive Auflösung von Blei verläuft über eine SchulterA1, die von einem einer passiven Region vorgelagerten PeakA1 gefolgt wird. Die SchulterA1 wird der elektrochemischen Bildung eines Pb(OH)₂-Films, der PeakA1 der Bildung von PbO zugeschrieben. Jenseits der passiven Region steigt die Stromdichte wieder an, und vor Erreichen des Sauerstoffpotentials treten eine kleine SchulterA2 und ein PeakA2 auf, die mit der Elektrooxidation von PbO zu Pb₃O₄ und PbO₂ korrelieren. Analog dazu beobachtet man in der cyclischen Voltammetrie zwei kathodische PeaksC1 undC2, die der Elektroreduktion von PbO und PbO₂ zu Pb entsprechen. Die Intensität der anodischen Peaks steigt mit steigender Alkalikonzentration, Temperatur und Scangeschwindigkeit.

     

A new steroid glycoside,taccaoside, fromTacca cheancer

A new steroid glycoside of the spirostan series — taccaoside (I) — has been isolated from an ethanolic extract of the roots ofTacca cheancer (familyTaccaceae). An acid hydrolysate was found to contain the aglycone diosgenin (II) and the sugars D-glucose and L-rhamnose in a ratio of 1:2. By methylation and hydrolysis of the permethylate (IV) it has been established that the two terminal L-rhamnose residues are attached at C-2 and C-3 of the D-glucose molecule which, in its turn, substitutes the hydroxy group at C-3 of diosgenin. Glycoside (I) has the structure of (25R)-spirost-5-en-3-ol 3-0-{[0--L-rhamnopyranosyl-(12)][0--L-rhamnopyranosyl-(13)]--D-glucopyranoside}.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Institute of Chemistry of the Scientific-Research Center, Socialist Republic of Vietnam. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 352–354, May–June, 1980.     

Nickel Ion-Selective PVC Membrane Electrode Based on a New t-Octyl-Calix[6]arene Derivative

This study presents a PVC membrane based on 5,11,17,23,29,35-Hexakis-t-octyl-37,38,39,40,41,42-hexakis(N-phenylthiocarbamoylmethoxy)calix[6]arene which is used as an electroactive substance. The electrode reveals a Nernstian response for Ni²⁺ over a wide pH range with a slope of linear portion (5×10^–6–1×10^–2M, R=0.988) of 29.75±0.2mV·decade^–1 at 25°C. The electrodes sensitivity is enhanced upon the introduction of sodium tetraphenylborate into the membrane as a negatively charged lipophilic additive. The selectivity coefficients of various interfering ions were determined using the fixed interference method (FIM). The membrane reveals good selectivity for nickel ions over the other metal ions investigated. The lifetime of this electrode is about one month. This electrode has been applied to the determination of nickel ions in wastewater from the electroplating industry.     

Horseradish peroxidase-based organic-phase enzyme electrode

An organic-phase enzyme electrode (OPEE) based on horseradish peroxidase (HRP) immobilized within Nafion on spectroscopic graphite was investigated in acetonitrile. The amperometric electrode response to hydrogen peroxide and cumene hydroperoxide present was found to be the result of the reduction of oxygen, produced upon enzymatic decomposition of both hydroperoxides (i.e., by the catalase-like activity of HRP). The electrode response was found to depend linearly on the hydroperoxide concentration up to 700 M within the range of potentials from –200 to –400 mV (versus Ag|AgCl). Detection limits of approximately 45 M for H₂O₂ and 100 M for cumene hydroperoxide were determined under the selected experimental conditions. Nernstian dependence (the open circuit voltage of HRP-based electrode versus logarithm of H₂O₂ concentration) was obtained between 0.2 and 2.0 mM, with a slope of approximately 23 mV per logarithmic unit, suggesting a catalase-like, two-electron disproportionation of the substrate in acetonitrile.     

Potentiometric Investigation of Fluoride Complexes of Zirconium(IV) and Hafnium(IV) in 1 <Emphasis Type="Italic">M</Emphasis> (H,Na)ClO<Subscript>4</Subscript> Medium Using a Fluoride Ion Selective Electrode

The stability constants of zirconium(IV) and hafnium(IV) fluoride complexes in 1 M (H,Na)ClO₄ medium were measured potentiometrically at 293 K for the first time using a fluoride ion selective electrode (F-ISE). This technique has been recommended by IUPAC as the best tool for studying fluoride complexes. A number of precautions were taken to ensure the stabilization of zirconium or hafnium in 1 M (H,Na)ClO₄ medium and to prevent the formation of polynuclear hydroxo complexes. The formation of only mononuclear complexes was indicated. The average log values of the overall stability constants of zirconium(IV)-fluoride complexes, ₁, ₂, ₃ and ₄ were computed by varying the concentration of metal ion and were found to be 8.49 ± 0.11, 15.76 ± 0.15, 21.57 ± 0.10, and 26.68 ± 0.16, respectively, whereas the corresponding values for hafnium(IV)-fluoride complexes were 8.22 ± 0.06, 15.48 ± 0.15, 21.76 ± 0.14, and 27.42 ± 0.15, respectively. The thermodynamic stability constant, ₁, calculated for these complexes follows the same trend as expected from the linear correlation based on the Brown Sylva Ellies (BSE) model for metal-fluoride complexes provided the effective charge on Zr is taken as +4.1 instead of the formal charge of +4. Without considering this adjustment of formal charge, an attempt has also been made to explain the trend in ₁ values of group(IV) metal-fluoride complexes based on electronegativity values. A good linear correlation was obtained that could explain the ability of these group(IV) ions to form different fluoride complexes with varying number of fluoride ions.     

pHh-dependent permselectivity of the fibrinogen-modified carbon paste electrode

The modification of carbon paste matrices with fibrinogen is reported. The effect of the pH of the solution on the CV peak currents of positively or negatively charged redox analytes was examined at the fibrinogen-modified carbon paste electrode. In the presence of the coating, pH-dependent selectivity in electrochemical detection of charged species was demonstrated depending on the sign of the supported charge. Above the isoelectric pH attributed to the immobilized protein (5.5), the current response of anionic redox probes [Fe(CN)/Fe(CN)] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH₃)/Ru(NH₃) cationic redox analytes.     

Study on the electroreduction of In(III) ions at gold from acidic bromide solutions by the rotating ring-disc electrode technique

The mechanism of the indium electrodeposition on gold from acidic KBr solutions has been investigated by means of the rotating ring-disc electrode technique. The measurements showed that the overall electrode reaction In(III) + 3 e In consists of two successive charge transfer steps, i.e. In(III) + 2 e In(I) and In(I) + e In, with soluble monovalent indium as an intermediate. The current efficiency for In(I) generation under steady-state conditions is 100% in the case of low disc current densities. The disproportionation of In(I) in the bulk of solution occurs in slightly acidified solutions,pH=2, in addition to the In(I) electrochemical reduction. Based on the ring current transients, it was established that the two-electron transfer step is preceded by the formation of a thin passive film of indium metal.

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Untersuchung der elektrochemischen Reduktion von In(III)-Ionen an Gold in sauren Bromidlösungen mit der rotierenden Ring-Scheiben-Elektrode

Zusammenfassung Mit Hilfe der rotierenden Ring-Scheiben-Elektrode wurde der Mechanismus der kathodischen Abscheidung von Indium auf Gold in sauren KBr-Lösungen untersucht. Aus den Messungen folgt, daß die Bruttoreaktion In(III) + 3e In über zwei aufeinanderfolgende Durchtrittsreaktionen, In(III) + 2 e In(I) und In(I) + e In, mit löslichem einwertigem Indium als Zwischenprodukt abläuft. Bei kleinen Stromdichten werden die In(I)-Ionen mit 100%iger Stromausbeute erzeugt. In schwächer sauren Lösungen (pH=2) konnte außer der elektrochemischen Reduktion von In(I) zusätzlich dessen Disproportionierung innerhalb der Lösung ermittelt werden. Auf Grund der Ringstrom-Zeit-Kurven wurde auch festgestellt, daß die Bildung von einer dünnen In-Metallschicht, die ein passives Verhalten aufweist, dem Zweielektronenübergang vorangegangen ist.

     

Alkali metal ion-selective electrodes based on relevant alkali metal ion doped manganese oxides

Potentiometric properties of manganese oxides doped with alkali metal ions (Na⁺, K⁺, Rb⁺ and Cs⁺), which were prepared by heating mixed solutions (starting solution) of each alkali metal and Mn²⁺ ions, were examined. Electrodes based on mixed phases of Nao₄₄MnO₂/Mn₂O₃ and hollandite KMn₈O₁₆/M₂O₃ found by X-ray powder diffraction (XRD) exhibited Na⁺- and K⁺-selective responses with a near-Nernstian slope, respectively, when the molar ratio of alkali metal ion to Mn²⁺ ion in the starting solution was 0.1. When no alkali metal ions were added in the manganese oxide films, no significant potentiometric response was observed to any alkali metal ions. The selectivity coefficients of these electrodes were = 6.7 × 10^–2, = 7.1 × 10^–3, < 9 × 10^–4 and < 9x 10^–4 for the Na_0.44MnO₂/Mn₂O₃, and <4 × 10^–4 <4x 10^–4, =60 × 10^–2 ×10^–4, < 4 × 10^–4, for the KMn₈O₁₆/Mn₂O₃, respectively. Electrodes based on manganese oxides made from mixed solutions of Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ also responded to the respective primary ions, that is, Rb⁺ and Cs⁺ ions, although XRD patterns for the manganese oxides thus made did not show any peaks except for Mn₂O₃ (bixbyite); it was concluded in these cases that some amorphous type manganese oxides were formed in the Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ systems and they responded to the respective ions. Conditioning of these electrodes in an aerated indifferent electrolyte solution, 0.1M tetramethylammonium nitrate (TMA-NO₃), for relatively long time, typically more than 2 hours, was found to be a prerequisite for near-Nernstian response to the respective alkali metal ions. During this electrode conditioning, vacant sites (template) suitable in size for selective uptake of primary ions seemed to be formed by releasing the doped alkali metal ions from the solid phase into the adjacent electrolyte solution accompanying oxidation of the manganese oxide film.