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At least 19 recordsLinked to original sources
PubMed1977

Albumin/calcium association at different pH, as determined by potentiometry.

Calcium binding by albumin was determined potentiometrically at physiological ionic strength and temperature as a function of pH. The binding data indicate at least 30 different binding sites with different association constants and different H+ interaction. One site appears to be responsible for the major binding at physiological pH and substance concentration of free calcium, together with three other sites that bind with less affinity.

Calcium↗
PubMed1979

X-ray fluorescence and potentiometry compared for determining iodine content of thyroid glands.

We compare results for iodine quantitation by x-ray fluorescence of excised thyroid glands with results of the quantitation by means of an original, newly developed chemical method, a Schöniger combustion technique, in which iodie is quantitated potentiometrically. Subsequently, we establish the accuracy and clinical suitability of the former technique in quantifying the intrathyroidal iodine.

Humans↗
PubMed1979

Potentiometric determination of iodine in pharmaceutical preparations.

Methods for the determination of organically bound iodine were compared. A preliminary destruction of the sample was preferable. The sample was mineralized using the Schöniger combustion. Since direct potentiometry of the iodide ion was used, further reduction of the sample was necessary. Several reductors were compared, and the best results were obtained with Devarda alloy. The proposed method was amployed for the determination of iodine in X-ray contrast products. Pure compounds and pharmaceutical preparations were investigated. The coefficient of variation of the method was 0.9%.

Iodine↗
PubMed1976

EPR and optical spectroscopic properties of the electron carrier intermediate between the reaction center bacteriochlorophylls and the primary acceptor in Chromatium vinosum.

1. A reaction center-cytochrome c complex has been isolated from Chromatium vinosum which is capable of normal photochemistry and light-activated rapid cytochrome c553 and c555 oxidation, but which has no antenna bacteriochlorophyll. As is found in whole cells, ferrocytochrome c553 is oxidized irreversibly in milliseconds by light at 7 K. 2. Room temperature redox potentiometry in combination with EPR analysis at 7 K, of cytochrome c553 and the reaction center bacteriochlorophyll dimer (BChl)2 absorbing at 883 nm yields identical results to those previously reported using optical analytical techniques at 77 K. It shows directly that two cytochrome c553 hemes are equivalent with respect to the light induced (BChl)2+. At 7 K, only one heme can be rapidly oxidized in the light, commensurate with the electron capacity of the primary acceptor (quinone-iron) being unity. 3. Prior chemical reduction of the quinone-iron followed by illumination at 200K, however, leads to the slow (t1/2 approximately equal to 30 s) oxidation of one cytochrome c553 heme, with what appears to be concommitant reduction of one of the two bacteriophytins (BPh) of the reaction center as shown by bleaching of the 760 nm band, a broad absorbance increase at approx. 650 nm and a bleaching at 543 nm. The 800 nm absorbing bacteriochlorophyll is also involved since there is also bleaching at 595 and 800 nm; at the latter wave-length the remaining unbleached band appears to shift significantly to the blue. No redox changes in the 883 absorbing bacteriochlorophyll dimer are seen during or after illumination under these conditions. The reduced part of the state represents what is considered to be the reduced form of the electron carrier (I) which acts as an intermediate between the bacteriochlorophyll dimer and quinone-iron. The state (oxidized c553/reduced I) relaxes in the dark at 200K in t1/2 approx. 20 min but below 77 K it is trapped on a days time scale. 4. EPR analysis of the state trapped as described above reveals that one heme equivalent of cytochrome becomes oxidized for the generation of the state, a result in agreement with the optical data. Two prominent signals are associated with the trapped state in the g = 2 region, which can be easily resolved with temperature and microwave power saturation: one has a line width of 15 g and is centered at g = 2.003; the other, which is the major signal, is also a radical centered at g = 2.003 but is split by 60 G and behaves as though it were an organic free-radical spin-coupled with another paramagnetic center absorbing at higher magnetic field values; this high field partner could be the iron-quinone of the primary acceptor. The identity of two signals associated with I-. is consistent with the idea that the reduced intermediary carrier is not simply BPh-. but also involves a second radical, perhaps the 800 nm bacteriochlorophylls in the reduced state...

Bacterial Chromatophores↗
PubMedDate not supplied

PVC membrane electrode without inner reference solution for the direct determination of ephedrine in pharmaceutical preparations.

A PVC membrane electrode, without inner reference solution, based on an ion association extraction system responding to ephedrine is described. It incorporates an ephedrine-tetrakis (4-chlorophenyl)borate ion-pair complex in 2-nitrophenyloctyl ether. The prepared electrode exhibits a near Nernstian response (57.5 mV per decade) over the concentration range of 2 x 10(-5)-10(-1) M ephedrine in solutions of pH 2.5-9. The reproducibility of the electrode potentials were +/- 1 mV by day during at least 6 months. Response time was about 6 s for ephedrine concentrations between 10(-5) and 10(-1) M. Determinations of ephedrine in pharmaceutical preparations (tablets, nasal drops and syrups) by direct potentiometry gave an average recovery of 99.1% (w/w) and a mean standard deviation of 1.9% (w/w).

Chemistry, Pharmaceutical↗
PubMed1978

EPR determination of the oxidation-reduction potentials of the hemes in cytochrome c3 from Desulfovibrio vulgaris.

EPR spectroscopy in conjunction with oxidation-reduction potentiometry has been used to determine the half-reduction potentials of the four hemes of cytochrome c3. As predicted, the four hemes of cytochrome c3 have different mid-point potentials. The Em values are: Heme I,--284 mV; Heme II,--310 mV; Heme III,--324 mV and Heme IV,--319 mV. The n-values in each case was near one.

Cytochrome c Group↗
PubMed1979

Electron-paramagnetic-resonance measurements of the electron-transfer components of the reaction centre of Rhodopseudomonas viridis. Oxidation--reduction potentials and interactions of the electron acceptors.

Oxidation-reduction potentiometry was carried out on Rhodopseudomonas viridis chromatophores. Measurements of e.p.r. signals of the semiquinone-iron type at g=1.82 have revealed a more complex situation than previously reported. The presence of three different components is indicated. The midpoint potential (E(m)) of the primary acceptor quinone/semiquinone couple was found to be approx. -165mV at pH10, with a pK being reached at around pH7.5. The primary acceptor also accepts a second electron with an E(m) of -525mV, but this redox transition exhibits a hysteresis effect. Interaction effects indicate the presence of another component with E(m) values at pH10 of approx. -165mV (pK reached at around pH7.5) for single reduction and -350mV (pK at pH10 or greater) for double reduction. It is suggested that this component is the secondary acceptor. Another semiquinone-iron-type component which gives a g=1.82 signal is also present. This component is distinguishable from the primary acceptor by its e.p.r. spectrum, which shows a double peak at g=1.82 and a g(x) line at g=1.76. This component has E(m) values at pH10 for single and double reduction of -15mV and approx. -150mV respectively. Both of these E(m) values are pH-dependent. The presence of an interaction between this component and the photoreduced primary acceptor indicates the close proximity of these components. However, the midpoint potential of this component indicates a function as a secondary electron-transport component rather than an electron acceptor in the reaction centre. The dependence of the bacteriopheophytin intermediate (I) doublet e.p.r. signal on the presence of the semiquinone-iron form of the primary acceptor is demonstrated. The midpoint potential of the I/I(-) couple is estimated to be lower than -600mV.

Bacterial Chromatophores↗
PubMed1978

The redox potential of dithionite and SO-2 from equilibrium reactions with flavodoxins, methyl viologen and hydrogen plus hydrogenase.

1. It has been shown that redox equilibria can be formed between dithionite ion (plus SO-2) and (bi)sulphite, and the low-potential electron carriers flavodoxin and methyl viologen. The equilibria were established either by treating the oxidized electron carriers with dithionite, or by treating flavodoxin hydroquinone or methyl viologen semiquinone with (bi)sulphite. Similar redox equilibria were established between dithionite/(bi)sulphite and hydrogen using catalytic amounts of hydrogenase in the presence of a low-potential electron carrier. The effects of pH and temperature on the equilibria were determined. 2. The equilibria were analyzed to determine the redox potential of the dithionite/(bi)sulphite system. In accordance with the results of earlier kinetic studies, it was assumed that the reductant in dithionite solutions is the dissociation product SO-2. The calculated midpoint redox potential E' for the couple SO-2/HSO-3 at pH 7 and 25 degrees C was -0.66 V. The reductant is present largely as the dimer at concentrations of dithionite above about 10nM. Consequently, the midpoint potential, Em, of dithionite solutions becomes less negative as the concentration of dithionite is increased (deltaEm/deltalog S2O2-4 = 29 mV). The theoretical potential of a solution of 1 M S2O2-4 and 2 M (bi)sulphite at pH 7 was calculated to be -0.386V. This value is 59 mV more negative than that determined in 1911 by potentiometry, but considerably more positive than other values in the literature. The effects of pH on the equilibria showed that E' is controlled by the pK of (bi)sulphite at 6.9; the slope deltaE'/deltapH was -59 mV below the pK and -118 mV above the pK. The effects of temperature on the equilibria suggested that Em for dithionite changed by -1.6 mV/degrees C for a rise in temperature between 2 degrees C and 40 degrees C. If sodium dithionite is contaminated with small amounts of (bi)sulphite, its addition in large excess to a low potential electron carrier can cause oxidation of the carrier.

Anaerobiosis↗
PubMed1979

The calcium selective electrode--a possible tool in dental research.

Ion selective potentiometry is widely used for analytical purposes in biologic research. The Ca selective electrode offers an inexpensive and easily handled means for studying ionized calcium. It does not affect the process studied, and may, for example, combined with an automatic recorder, give running information on dynamic systems. The calcium electrode responds in accordance with the Nernst equation and has a theoretical range of 1--10(-6) M Ca2+. The electrode is influenced by changes in temperature, in pH and also in concentration of buffer solution. The Ca sensitive membrane is adversely affected by acetic acid but tolerates lactate/lactic acid buffers. Best linearity in calibration curves for Ca2+ in lactate buffers is found in concentrations from 10(-4) M to 10(-2) M Ca. In a 5% Na lactate/lactic acid buffer, pH 5, with 0.5 M KNO3 as an ionic strength adjuster, a straight calibration curve, Nernstian slope factor 27 mV/decade, is found from 10(-4) to 1 M Ca.

Buffers↗
PubMed1979

Potentiometric analysis of Escherichia coli cytochromes in the optical absorbance range of 500 nm to 700 nm.

The oxidation-reduction potentials of Escherichia coli cytochromes have been studied by a recently described technique for automated electrodic potentiometry (Hendler, R.W., Songco, D., and Clem, T.R. (1977) Anal. Chem. 49, 1908-1913; Hendler, R.W. (1977) Anal. Chem. 49, 1914-1918), where entire spectra are recorded at a series of solution potentials. New techniques for resolution of the spectra versus voltage data have been applied. The results indicate that a 1-electron transport chain conducts electrons from substrate to cytochrome d, which is the cytochrome oxidase. Cytochrome d contains several components which appear to increase electron transfer first to a 2-electron stage and then to a 4-electron stage for the final reduction of a molecule of oxygen to 2 molecules of water.

Cell Membrane↗
PubMed1977

Physicochemical properties of beta-lactam antibiotics: oil-water distribution.

Apparent partition coefficients Papp, of beta-lactam antibiotics were determined in octanol-water and 2-methylpropanol-water systems at various pH values. The pKa values also were determined by potentiometry under the conditions of partition experiments. The intrinsic partition coefficients for the unionized form, Pu, and the ionized form, Pi, of beta-lactam antibiotics were calculated from the equation Papp = Pu[aH+/(Ka + aH+)] + Pi[Ka/(Ka + aH+)]. The correlation between Pu and Pi values and lipophilic parameters of penicillins measured in other systems was examined.

Octanols↗