Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “TITRATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed1978

Redox titrations of cytochrome c oxidase. An analysis of a multi-electron system.

Equilibrium redox titrations of cytochrome c oxidase available in the literature are discussed in terms of models with interactions both with respect to oxidation-reduction potentials and the particular property studied. 2. The interaction is restricted to be pairwise. For the present data more complicated forms of interaction are not required. In addition, with this limitation a simple matrix formulation can be used. 3. The EPR titrations require potential interaction involving the hemes and the undetectable Cu. In this way the low intensity of the g6 signal can be accounted for. However, it is shown that there is no unique solution to the problem. 4. The optical titrations at 605 nm can be fitted reasonalby well with the potentials from the EPR data with no spectral interaction. 5. Simulated titrations of magnetic susceptibility show a sensitivity to the model chosen indicating the usefulness of future experiments in this area.

Copper↗
PubMed1979

Redox titration of electron acceptor Q and the plastoquinone pool in photosystem II.

The primary photochemical quencher Q and the secondary electron acceptor pool in Photosystem II have been titrated. We used particles of Scenedesmus mutant No. 8 that lack System I and allowed the system to equilibrate with external redox mediators in darkness prior to measurement of the fluorescence rise curve. The titration of Q, as indicated by the dark level of Fi, occurs in two discrete steps. The high-potential component (Qh) has a midpoint potential of +68 mV (pH 7.2) and accounts for approximately 67% of Q. The pH sensitivity of the midpoint potential is -60 mV, indicating the involvement of 1 H+/e. The low-potential component (Q1) accounts for the remaining 33% of Q and shows a midpoint potential near--300 mV (pH 7.2). The plastoquinone pool, assayed as the half-time of the fluorescence rise curve, titrates as a single component with a midpoint potential 30--40 mV more oxidizing than that of Qh, i.e., at 106 mV (pH 7.2). The Em shows a pH sensitivity of -60 mV/pH unit, indicating the involvement of 1 H+/e. The observation that all 12--14 electron equivalents in the pool titrate as a single component indicates that the heterogeneity otherwise observed in the secondary acceptor system is a kinetic rather than a thermodynamic property. Illumination causes peculiar, and as yet unclarified, changes of both Q and the secondary pool under anaerobic conditions that are reversed by oxygen.

Chlorophyta↗
PubMed1985

Complexity in the redox titration of the dihaem cytochrome c4.

Redox titration of the dihaem, two domain cytochromes c4 from Pseudomonas aeruginosa, Pseudomonas stutzeri and Azotobacter vinelandii showed complex behaviour indicative of the presence of two redox components. In the case of the P. stutzeri cytochrome c4, two spectroscopically distinct components were present during the redox titration. In contrast, cytochrome c-554(548) from a halophilic Paracoccus species is a stable dimer of a monohaem cytochrome which shows close homology to cytochrome c4, but does not show complexity in its redox titration. The presence of chemically distinct haem environments or anti-cooperative interactions between identical haem groups are two possible explanations for the redox complexity of cytochrome c4. The simple redox titration of cytochrome c-554(548) shows that haems situated relatively close together need not interact, but direct cleavage, separation and study of the domains will be necessary to decide whether they do or do not interact in the case of cytochrome c4.

Animals↗
PubMed1986

A theoretical study of double-inhibitor-titration curves in free-energy-transducing networks.

The general relationship between the double-inhibitor-titration curves and the kinetic properties of pumps in a delocalized chemiosmotic free-energy-transducing network is studied. The kinetic conditions for a delocalized system to generate the observed double-inhibitor-titration results are derived and the effectiveness of double-inhibitor experiments in discriminating between the localized and the delocalized proton-coupling mechanisms is assessed. It is found that, using simple enzymatic cycles for the kinetics of the pumps in a delocalized network, one can reproduce the experimentally measured double-inhibitor-titration curves that were widely used to argue against the delocalized mechanism. This implies that double-inhibitor-titration curves alone are not sufficient to discriminate between localized and delocalized coupling systems. Additional information concerning the kinetic responses of isolated pumps on the proton gradient across the membrane and inhibitor concentrations are required.

Adenosine Diphosphate↗
PubMed1988

Analysis of mechanisms of free-energy coupling and uncoupling by inhibitor titrations: theory, computer modeling and experiments.

The rates of ATP synthesis and of ATP-driven NAD reduction have been measured in bovine heart submitochondrial particles as a function of the fraction of inhibited redox pumps (in titrations with either antimycin or rotenone) and of the fraction of inhibited ATPases (in titrations with DCCD). The flux control coefficients of the redox and ATPase proton pumps on the rates of ATP synthesis and of ATP-driven NAD reduction have been derived and found to be equal to 1 for both pumps; i.e., both pumps appear to be 'completely rate limiting'. A theoretical analysis of the inhibitor titration approach based on kinetic models of chemiosmotic coupling and on the theory of metabolic control is presented. This analysis (i) shows that the results of the single inhibitor titrations are incompatible with a delocalized chemiosmotic mechanism of energy coupling if the proton conductance of the membrane is sufficiently low with respect to the conductances of the pumps; and (ii) suggests an experimental approach based on the determination of the P/O and the respiratory control ratios at different degrees of inhibition of the proton pumps to establish the origin of the 'loose coupling' of submitochondrial particle preparations. Three independent types of observation show that the 'loose coupling' of the particle preparation is not mainly due to an increased membrane proton conductance. The same and other independent observations are consistent with the view that the loose coupling of submitochondrial particle preparation is due mainly to inhomogeneity, i.e. to the presence of a subpopulation of highly leaky non-phosphorylating vesicles respiring at maximal rate. The results as a whole together with the simulations and analysis presented lead to the conclusion that the mechanism of free-energy coupling in submitochondrial particles is not completely delocalized.

Adenosine Triphosphatases↗
PubMed1990

The effect of pH on redox titrations of haem a in cyanide-liganded cytochrome-c oxidase: experimental and modelling studies.

Isolated cytochrome-c oxidase ligated with cyanide was titrated by Flash-Induced chemical photoREduction (FIRE) (Moody, A.J. and Rich, P.R. (1988) EBEC Short Rep. 5, 69) using cytochrome c as a redox indicator. Haem a is found to titrate in a complex manner consistent with its interacting anticooperatively with at least two other components. We assign CuB as the major interactant at neutral pH, and CuA as the minor interactant. In the pH range 7.0-8.1 the strength of the interaction with CuB is found to decrease with increasing pH, while the interaction with CuA remains essentially constant. The decrease in the interaction with CuB appears to continue above pH 8.1 such that at pH 9.2 the titration curve for haem a is only slightly distorted from an 'n = 1' shape, although it is not possible from the titration data to assess the relative contributions of CuB and CuA to the total interaction observed at pH values greater than 8.1. Haem a and CuB show similar pH-dependence and, to account for this, we present a model in which the oxidoreductions of both haem a and CuB are linked to the (de)protonation of a common acid/base group. The model predicts a pH-dependent indirect cooperative interaction between haem a and CuB in addition to the direct anticooperative interaction, thereby explaining the observed pH-dependence of the redox interaction between haem a and CuB.

Animals↗
PubMed1978

Spectrophotometric titration of phenolic groups of pepsin.

The ionization of tyrosine residues in diazotized pepsin under various solvent conditions was studied. All tyrosyl residues of the protein titrated normally with a pK of 10.02 in 6 M guanidine hydrochloride solution. On the other hand, two stages in the phenolic group titration curve were observed for the inactivated protein in the absence of guanidine hydrochloride; only about 10 tyrosine residues ionized reversibly up to pH 11, above which titration was irreversible. The irreversible titration zone corresponds to the pH range 11--13 in which unfolding, leading to the random coil state, was shown to occur by circular dichroism and viscosity measurements. The number of tyrosine residues exposed in the native and alkali-denatured (pH 7.5) states of diazotized protein were also studied by solvent perturbation techniques; 10 and 12 groups are exposed in the native and denatured states, respectively.

Animals↗
PubMed1980

Meperidine's effect under shock titration and shock discrimination procedures.

Meperidine's effects were examined under a schedule of shock titration and under a shock intensity discrimination in which squirrel monkeys discriminated between the presence and absence of a low intensity shock. Meperidine did not increase the intensity at which monkeys maintained the shock in the shock titration procedure, nor did meperidine alter the percentage of correct responses under the shock intensity discrimination although meperidine did increase the time to respond in the presence and absence of shock. When meperidine was combined with a dose of SKF-525A, which did not alter responding when given alone, the intensity at which monkeys maintained the shock under the shock titration procedure was increased. Moreover, the percentage of correct responses in the presence of shock under the shock titration procedure was decreased by the combination of meperidine and SKF-525A.

Animals↗
PubMed1992

Titrating matching-to-sample performance: effects of drugs of abuse and intertrial interval.

Previous reports have shown that increasing the length of the intertrial interval (ITI) in a matching-to-sample schedule of reinforcement results in increased matching accuracy. This has traditionally been interpreted in the context of proactive inhibition, the disruption of memory for a stimulus as a consequence of events that occurred prior to the presentation of the stimulus. In an effort to more fully characterize a titrating matching-to-sample baseline, the effect of ITI ranging from 0-30 s was determined in pigeons trained to respond under the titrating matching-to-sample procedure. In addition, the effect of ITI length on the dose-response curve for pentobarbital, phencyclidine, D-amphetamine, and cocaine were determined. Surprisingly, performance under the titrating matching-to-sample was not altered as a function of ITI length, nor did the effects of the four drugs of abuse change as a function of ITI length. These results suggest that performance under the titrating matching-to-sample is under a different control than matching-to-sample using fixed delays.

Amphetamine↗
PubMed1985

An automated differential thermal and potentiometric titration apparatus for binding studies.

A differential pH-thermal titration apparatus is described which can detect pH differences with a sensitivity of +/- 0.0001 pH units and a thermal sensitivity of +/- 0.00002 degree C at a time constant of 0.1 s. With a reaction which yields 1 kcal mol-1, the current system can detect concentrations as low as 4 X 10(-6) M or, in a 2 ml volume, a total amount of 40 nmol. With a time constant of 0.1 s, the sensitivity is 20 +/- 4 micro degrees C. The experimental protocol is specified by a microprocessor and three modes of operation are possible: titration at constant rate of reagent addition, titration at variable rates of addition so that the contents of both cells are at either constant pH or at a constant temperature and variable rate when a rate of change is specified. Experimental data are collected in files, corrected for heat loss, initial baseline drift, and changes in volume. The final corrected data from the standardized run of 0.01338 M HCl in 0.2 M KCl at 25 degrees C calibrate the pH scale and yield the calorimetric conversion constants and pKw which are calculated and stored for subsequent corrections for the titration of an unknown acid or the measurement of binding constants and heats.

Calorimetry↗
PubMed1986

Titration of poliovaccines: improvement of end-point microassays by means of dose-response curves.

The W.H.O.'s titration method for attenuated poliovaccines, using two-fold dilution steps, was assayed concurrently with an alternative method, using four-fold dilution steps. For the two-fold dilution method, the dispersion of the observed proportions of response was very wide, inducing biased estimations for titers and their standard-error by means of simple usual calculation procedures. On the other hand, the use of the four-fold dilution method constantly provides more accurate estimates for the titers and their confidence limits and thus increases the reliability of the titration results. In addition, replicate poliovirus titrations were performed in three cell lines (HEp-2, LLC-MK2 and Vero), applying a restricted experimental design, in order to characterize statistically their sensitivity for poliovaccine titrations, and their consistency for infectivity titers. Means of improving the reliability of live poliovaccine potency estimates are suggested.

Analysis of Variance↗
PubMed1990

Method for improving accuracy of virus titration: standardization of plaque assay for Junin virus.

Titrating infective virus is one of the most important and common techniques in virology. However, after many years of widespread use, the parameters governing the accuracy of titration values are still not well understood. It was found that under conditions currently used for virus titration, only a small percentage of virus in the inoculum is adsorbed onto the cells and thereby detected in the titration assay. The objective of our work was to establish the conditions for a plaque assay which could estimate more accurately the titer of Junin virus. Two different stain methods were compared and several parameters governing plaque formation were studied. The volume of the inoculum appeared as the most important factor affecting observed titer. A linear relationship between the volume of inoculum and the reciprocal apparent titer allowed us to estimate an absolute titer by extrapolation. The approach described here is likely to be applicable to the more accurate estimation of the titer of a wide range of virus.

Adsorption↗
PubMed1994

Quantitation of human cytomegalovirus DNA in leukocytes by end-point titration and duplex polymerase chain reaction.

The presence of human cytomegalovirus (CMV) DNA and cellular DNA in leukocytes was detected by duplex polymerase chain reaction (PCR) and quantitated by end-point titration. Two different duplex PCR methods were used to co-amplify CMV DNA and a 536 bp fragment of globin DNA. MIE-globin PCR amplified a 435 bp fragment of the major immediate early (MIE) gene of CMV DNA whereas the LA-globin PCR amplified a 200 bp fragment of the late antigen (LA) gene of CMV DNA. PCR products were separated by electrophoresis in 3% agarose gels and detected by ethidium bromide staining. Amplification of globin DNA was included in the PCR as a positive control to monitor the accuracy and reproducibility of the PCR assay and to provide a reference point for CMV DNA levels. End-point titration PCR using known amounts of recombinant CMV DNA and human placental DNA showed that the end-point titres of the amplified CMV DNA correlated directly with the amount of CMV DNA in the sample. The limit of detection of MIE-globin and LA-globin PCR was 1 ng for placental DNA, and 10 fg (1000 copies) for CMV-MIE DNA and 1 fg (100 copies) for CMV-LA DNA, respectively. The amount of CMV DNA was quantitated in leukocytic lysates of 16 immunocompromised patients, who were tested for the presence of CMV in blood by cell culture, and of four normal controls. The blood concentration of CMV DNA, calculated as the number of copies of CMV DNA per microgram of leukocyte DNA, varied between 10(4) and 10(7) in the seven bloods that were CMV-cell-culture-positive, and between 10(2) and 10(4) in the blood of five patients that were CMV-cell-culture-negative. CMV DNA was undetected by PCR in the blood of another eight CMV-negative cases. This study shows that end-point titration and duplex PCR can be used as a simple and rapid method to quantitate CMV DNA in blood of patients that are either CMV-positive or CMV-negative by cell culture. Quantitation of CMV DNA in blood by end-point titration PCR has potential to differentiate between asymptomatic CMV infection and symptomatic CMV disease, and to monitor viral load during viral therapy.

AIDS-Related Opportunistic Infections↗
PubMed1991

Development of an equation for potentiometric titration of polyelectrolytes using a periodic lattice model. A numerical analysis of interactions among ionizable groups.

A numerical method is presented for analysing the potentiometric titration behavior of linear polyelectrolytes. A polyelectrolyte molecule is treated as a one-dimensional lattice containing a large number of lattice points, each of which has an identical ionizable group. In this method, the polyelectrolyte model lattice is divided into identical repeating unit cell systems with a finite number of ionizable groups to calculate the thermodynamic partition function of the system of polyelectrolyte solution. The electrostatic interaction between ionized groups adopted in the present study is given by the Debye-Hückel type screened Coulombic potential. The titration behavior as well as several thermodynamic quantities is derived by making a canonical ensemble summation of all states in a unit cell system under an appropriate periodic boundary condition. This method serves as a model of the two-step ionization often appearing in polyions with strong neighboring interactions such as homo- and copolymers of maleic acid. Several characteristics of the titration behavior of these polyelectrolytes are well reproduced by using a lattice model with pairwise intervals, including the effects of hydrogen bond formation and change in dielectric constant of the medium around an ionizable group. In addition, this method is valid for a more detailed analysis of the titration behavior of polyelectrolytes with various kinds of arrangements of charged groups.

Journal Article↗
PubMed2005

Multithermal titration calorimetry: a rapid method to determine binding heat capacities.

Herein a new method that allows binding DeltaCp to be determined with a single experiment is presented. Multithermal titration calorimetry (MTC) is a simple extension of isothermal titration calorimetry (ITC) that explicitly takes into account the thermal dependences of DeltaH and the binding constant. Experimentally, this is accomplished by performing a single stepwise titration with ITC equipment, allowing temperature re-adjustments of the system at intermediate states of the titration process. Thus, from the resulting multitherm, DeltaCp can also be determined. The experimental feasibility of MTC was tested by using the well-characterized lysozyme-chitotriose complex as a model system.

Algorithms↗
PubMed2006

Solubility measurement of polymorphic compounds via the pH-metric titration technique.

In drug development, the thermodynamically most stable form of a compound is preferred because metastable forms are prone to transform to the stable form during processing, formulation, or storage [Guillory, J.K., 1999. Generation of polymorphs, hydrates, solvates, and amorphous solids. In: Brittain, H.G. (Ed.), Polymorphism in Pharmaceutical Solids. Marcel Dekker, New York, pp. 183-226]. It is therefore important to discover and characterize the stable form as early as possible. One of the most important properties to determine is thermodynamic solubility. However, due to compound and time constraints this solubility value is usually not determined until late in discovery. This report explores the ability of the pH-metric titration method to measure intrinsic solubility of the stable form of compounds that exist in one or more polymorphic forms. One metastable form and the stable form of eight compounds were examined. Intrinsic solubility was measured via pH-metric titration. The technique was performed on a larger scale in order to monitor polymorphic form changes by powder X-ray diffraction. Shake-flask solubility and corresponding X-ray diffraction data of each form was also determined. The results of this study indicate that, in general, when starting with a metastable polymorph, the pH-metric titration method is able to achieve the solubility of the stable form by the third titration, while the traditional shake-flask solubility method is unable to consistently determine the stable form solubility.

Acetaminophen↗
PubMed2004

Surface characterization of plasma sprayed oxide materials: estimation of surface acidity using mass titration.

The aim of this study was to characterize the influence of plasma spraying on the point of zero charge (PZC) of Al2O3-, Cr2O3- and TiO2-based materials. PZC is one of the most important parameter, which describes the acidity of oxide material in aqueous environments. PZC values of several plasma sprayed oxides were determined using mass titration method. Studies were performed for initial spray powders and plasma sprayed coating materials. In addition, mass titration experiments were performed for water-washed and nonwashed samples. It was found that mass titration is a suitable method to estimate the surface acidity of relatively coarse sample powders. It was found for most of the studied materials that the limiting pH values (assumed to be close PZC) were close to those reported in literature for the PZC values of traditionally manufactured oxide materials. On the other hand, mass titration curves of some oxide samples showed unexpected deviation in curve shapes and limiting pH. These deviations were probably due to selective dissolution of sample contaminations or sample material.

Journal Article↗
PubMed2005

Sensitivity of the acid-base properties of clays to the methods of preparation and measurement. 2. Evidence from continuous potentiometric titrations.

The effects of experimental procedures on the acid-base consumption titration curves of montmorillonite suspension were studied using continuous potentiometric titration. For that purpose, the hysteresis amplitudes between the acid and base branches were found to be useful to systematically evaluate the impacts of storage conditions (wet or dried), the atmosphere in titration reactor, the solid-liquid ratio, the time interval between successive increments, and the ionic strength. In the case of storage conditions, the increase of the hysteresis was significantly higher for longer storage of clay in suspension and drying procedures compared to "fresh" clay suspension. The titration carried out under air demonstrated carbonate contamination that could only be cancelled by performing experiments under inert gas. Interestingly, the increase of the time intervals between successive increments of titrant strongly emphasized the amplitude of hysteresis, which could be correlated with the slow kinetic process specifically observed for acid addition in acid media. Thus, such kinetic behavior is probably associated with dissolution processes of clay particles. However, the resulting curves recorded at different ionic strengths under optimized conditions did not show the common intersection point required to define point of zero charge. Nevertheless, the ionic strength dependence of the point of zero net proton charge suggested that the point of zero charge of sodic montmorillonite could be estimated as lower than 5.

Journal Article↗