Showing papers on "Titration published in 1976"

On the Interaction of Melanoidin with Metallic Ions

Abstract: Melanoidin, which is obtained from the browning solution prepared from glycine-D-glucose system by acid precipitation, displays a noticeable character attributable to an amphoteric polyvalent electrolyte with the isoelectric point at pH 2.5. The number of proton released during titration from the isoelectric point to pH 11.0 is ca. 500 per one molecule of melanoidin. Thus, melanoidin shows a remarkable coagulation in the presence of various metallic ions though affected by metal concentration, pH and the presence of other chelating agent such as EDTA. The behavior of melanoidin towards metallic ions is in common with anionic hydrophillic colloids. The metal binding ability of melanoidin was confirmed on the basis of difference spectra, titration curves and dialysis equilibria. The stability constants and the number of binding sites were approximately calculated from the results of dialysis equilibria in respect to Fe3+ and Cu2+. Melanoidin was evaluated as a powerful metal scavenger in an attempt to eluci...

Yeast Hexokinase: Substrate‐Induced Association‐ Dissociation Reactions in the Binding of Glucose to Hexokinase P‐II

Abstract: A method is described for the purification of native hexokinases P-I and P-II from yeast using preparative isoelectric focussing to separate the isozymes. The binding of glucose to hexokinase P-II, and the effect of this on the monomer-dimer association-dissociation reaction have been investigated quantitatively by a combination of titrations of intrinsic protein fluorescence and equilibrium ultracentrifugation. Association constants for the monomer-dimer reaction decreased with increasing pH, ionic strength and concentration of glucose. Saturating concentrations of glucose did not bring about complete dissociation of the enzyme showing that both sites were occupied in the dimer. At pH 8.0 and high ionic strength, where the enzyme existed as monomer, the dissociation constant of the enzyme glucose complex was 3 × 10−4 mol1 −2 and was independent of the concentration of enzyme. Binding to the dimeric form at low pH and ionic strength (I = 0.02 mol1−1, pH < 7.5) was also independent of enzyme concentration (in the range 10–1000.μg ml−1) but was much weaker. The process could be described by a single dissociation constant, showing that the two available sites on the dimer were equivalent and non-cooperative; values of the intrinsic dissociation constant varied from 2.5 × 10−3 mol 1−1 at pH 7.0 to 6 × 10−3 at pH 6.5. Under intermediate conditions (pH 7.0, ionic strength = 0.15 mol l−1), where monomer and dimer coexisted, the binding of glucose showed weak positive cooperativity (Hill coefficient 1.2); in addition, the binding was dependent upon the concentration of enzyme in the direction of stronger binding at lower concentrations. The results show that the phenomenon of half-sites reactivity observed in the binding of glucose to crystalline hexokinase P-II does not occur in solution; the simplest explanation of our finding the two sites to be equivalent is that the dimer results from the homologous association of two identical subunits.

Removal of copper and iron prior to water hardness titration

Abstract: Silica gel was reacted with 3-aminopropyltriethoxysilane or with the N-methyl derivative of the same reagent to produce a material with an amino silyl functional group. If a water sample in the pH range of 5.0 to 7.5 is passed through a short column of this material, iron(II) and copper(II) are completely retained, while calcium(II) and magnesium(II) pass through. This permits an accurate water hardness titration withoug adding any cyanide. (auth)

Automatic process titration system

Abstract: An automatic titration system and method in which the titrant is generated electrolytically and a two-position slider type ceramic sample valve, reliably, accurately and repetitively obtains a volumetric sample from a process loop and introduces it to a titration cell containing a generator or working compartment and an auxiliary compartment separated by a porous frit. The system also includes a two-position slider type ceramic reagent valve for introducing reagent into the titration cell. Titrant created at a generator electrode surface is dispersed into the bulk of the solution by a magnetically coupled impeller in the working compartment which mixes and also pumps the contents of the cell through the reagent and sample valves in a closed loop. Generator and auxiliary electrodes are connected to a current source which provides the electrolysis current. The progress of the titration is monitored by indicating and reference electrodes in the titration cell connected to an appropriate endpoint indicator, output of which is compared to a known setpoint corresponding to the titration endpoint. The total charge delivered to the generator and auxiliary electrodes during titration is measured by a timer or integrator and read out as a trend output signal. The automatic titration system and method of this invention advantageously lends itself to microprocessor control over the titration reaction and titrator sequencing.

Nuclear magnetic resonance studies of the acid–base chemistry of amino acids and peptides. III. Determination of the microscopic and macroscopic acid dissociation constants of α,ω-diaminocarboxylic acids

Abstract: The acid–base chemistry of 2,3-diaminopropionic acid (dap), 2,4-diaminobutyric acid (dab), ornithine (orn), and lysine (lys) has been studied by 13C and proton nmr spectroscopy. Macroscopic acid dissociation constants for titration of the two ammonium groups of each molecule have been calculated from the 13C chemical shift titration curves for the alkyl carbon atoms by nonlinear least squares curve fitting methods. Microscopic acid dissociation constants for the simultaneous titration of the two ammonium groups of protonated orn and lys have been obtained from their proton chemical shift titration curves and from the 13C titration curves for orn and dap. The results indicate that the α-ammonium group of each of these α,ω-diaminocarboxylic acids is more acidic than its ω-ammonium group, but that the difference decreases as the number of carbons separating the ammonium groups decreases so that the acidities of the two ammonium groups of dap are almost identical. Results of pmr studies of the acid–base chemi...

Chemiluminescent titration of F(g) with Cl2(g) and microwave production of atomic fluorine

Abstract: Chemiluminescent titration of atomic fluorine with Cl2 in a low pressure (133 Pa) flow apparatus has been investigated to establish the accuracy of this titration method and the efficiency of F atom production in a microwave discharge. Up to 90 % dissociation of F2(0.5–10 % in Ar) is achieved by a 100 W Evenson-type cavity 2450 MHz discharge when the microwave power exceeds 2500 kJ mol–1 F and discharge residence time exceeds 0.7 ms. Heterogeneous F atom loss on the fluorine-passivated Al2O3 discharge tube walls occurs with a recombination probability, γF≈ 2 × 10–4.Heterogeneous Cl atom recombination does not interfere with the chemiluminescent F/Cl2 titration in glass apparatus since, in the presence of fluorine, γCl(pyrex) < 8 × 10–5. However, homogeneous three-body recombination to form ClF and/or Cl2 produces errors in the titration endpoint which exceed 10 % if the product of F atom partial pressure, total pressure and the mean residence time between titrant addition and chemiluminescent intensity measurement exceeds 160 Pa2 s at 300 K.

Hydrogen adsorption and hydrogen-oxygen titration on ruthenium powder

Abstract: Hydrogen adsorption at 77–753 K, oxygen adsorption at 293 K and hydrogenoxygen titration at 293–673 K were investigated on Ru powder of known surface area. The kinds of hydrogen adsorbed, stoichiometry of oxygen chemisorption and the relevance of the data in determining metal dispersion are discussed.

Hydrogen ion titration of horse heart ferricytochrome c.

Abstract: Continuous hydrogen ion titration curves of deionized solutions of horse heart ferricytochrome c have been obtained at 25 degrees C. at a constant ionic strength of 0.10 from pH 3.0 to 11.0. Titration of the oxidized protein in KCl required 28.4 equiv over that pH range, and a small hysteresis between the forward and reverse limbs was displayed. The Linderstrom-Lang approximation, which takes into account electrostatic interactions between charged groups on the protein surface, was used in a computer simulation program to analyze the forward and reverse limbs of the titration curve separately. The results indicated 1 alpha-, 12 beta- and gamma-, and 1 heme propionic carboxylic, 1 imidazole, 1 phenolic, and 18 epsilon-amino residues appear to titrate normally. Variations in the electrostatic interaction factor omega suggest conformational changes in the protein at the extremes of pH, although the relationship of the variations in omega to the magnitude of the conformational changes does not appear to be strictly quantitative for cytochrome c. These results show the acid-base behavior of cytochrome c to be complex in nature, and suggest that the Lindenstrom-Lang model may not be adequate for cytochrome c.

Proton Equilibria in the Binding of Zn2+ and of Methylmercuric Iodide to Papain

Abstract: The proton liberation on the binding of zinc chloride and methylmercuric iodide to the (essential) thiol group of papain has been examined as a function of pH. This was carried out by (a) direct titration of the protons on the addition of the metal compound to active papain and (b) measurement of the extent of inhibition of enzyme activity by the metal compound as a function of pH. It was found that in the neutral pH range the thiol group or the neighbouring imidazole group in the free enzyme carries one proton, at low pH both groups do so, whereas at high pH neither group carries a proton. The pK values of the free enzyme that govern the proton release, 4.2 and 8.5, correspond to those that govern overall activity. Both from the experiments with methylmercuric iodide and from fluorescence measurements of methylmercuric papain, it was established that the imidazole group in the latter compound exhibits a pK of 5.4. Taking recent data into account, it was considered that the ion pair of thiolate anion and imidazolium cation, proposed by Polgar, is the best approximation to describe the charge distribution in the active centre and to explain the reaction mechanism.

Redox titration of fluorescence yield of photosystem II

Abstract: The variable fluorescence yield of photosystem II is dependent on the redox state of the fluorescence quencher molecule or the primary electron acceptor of the system. We have carried out redox titrations of fluorescence yield of a photochemically active photosystem-II reaction-center particle and have measured the redox potential of the photosystem-II primary acceptor.During reductive titrations using dithionite as the reductant, only a single quenching transition was observed. For instance, at pH 7.0, the midpoint potential of the fluorescence transition is -325 mV, and those at a pH between 6.0 and 7.5 are consistent with a pH dependence of about 60 mV/pH unit. At a given pH, the midpoint potential of the transition closely corresponds to that of the most negative transition previously measured in unfractionated chloroplasts (both by chemical reductive titration). Oxidative titrations using ferricyanide as the oxidant yielded hysteresis in the titration curves.Similar changes in fluorescence yield were observed in redox titrations by electrochemical reduction or oxidation. Electrochemical reductive and oxidative titrations yielded reversible transitions, contrary to the hysteresis observed during chemical oxidative titration. From coulometric-titration data, we have estimated that most likely one electron is involved in the redox transition of the fluorescence-quencher or primary-electron-acceptor molecule of photosystem II. These findings are consistent with the current proposal that a membrane-bound plastoquinone functions as the primary acceptor of photosystem II.

Titration of Anionic Surfactants in a Mixture, Using a Surfactant Exthactive Electrode

Abstract: Mixtures of sodium octylsulfate with sodium dodecyl-benzenesulfonate or sodium di-2-ethylhexglsulfosuccinate (Aerosol OT) were determined potentiometrically. The titration curve permits the simultaneous determination of both components with en accuracy of 1.0%.