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PubMed1998

Monte Carlo studies on potentiometric titration of poly(glutamic acid).

The potentiometric titration of poly(glutamic acid) with special attention to its helix-coil transition is investigated in terms of the previously developed Monte Carlo method. The simulations of the potentiometric titration are carried out for helical and coiled form of the peptide, separately. A cylindrical rod with spherical ionizable groups is adopted as each conformational model of poly(glutamic acid) molecule. A spherical charge with a hard core potential is assumed as a mobile hydrated ion. The helix-coil transition curves are analyzed by the Zimm-Bragg theory. A satisfactory agreement is achieved for the titration curves with the experimental data in most cases. The significance and the limitations of the simulation method are discussed.

Journal Article↗
PubMed1998

Amine-based aqueous polymers for the simultaneous titration and extraction of lactic acid in aqueous two-phase systems.

The partitioning of 10% (w/w) lactic acid in ethylene oxide propylene oxide (EOPO) random copolymers and dextran T500 aqueous two-phase systems was studied. An analysis of variance design was applied to investigate the effect of pH, polymer concentration, and addition of polyethyleneimine to the aqueous two-phase systems. The lowest lactate partition coefficient of 0.09 was obtained at pH 6 in the systems containing 7.2% (w/w) polyethyleneimine. The use of polyethyleneimine as titrating base during the fermentative production of lactic acid was evaluated in batch fermentations with 100 g/l glucose. Yield and productivity of polyethyleneimine titrated fermentations compared with those obtained in fermentations titrated with NaOH and KOH.

Chemistry Techniques, Analytical↗
PubMed1996

The interference of penicilloic acids with Karl Fischer titration of penicillins.

Phenoxymethylpenicilloic acid monohydrate was titrated with 12 different brands of Karl Fischer reagent. It was shown that only the four pyridine-containing reagents gave correct results for water content, providing that the sample solution was cooled in an ice bath or that the delay time of the amperometric end-point determination was 10 s instead of 30 s, as prescribed by the European Pharmacopoeia. The other reagents always gave results, which were too high. When these reagents were used to titrate the water in sodium amoxicillin, sodium carbenicillin or sodium ticarcillin the same conclusions could be drawn with regard to the accuracy of the results, the usefulness of the reagents and the reaction conditions. These penicillins may contain up to 9% penicilloic acids. The maximum relative error obtained with pyridine-free reagents was about 50% for ticarcillin. It has been confirmed that penicilloic acids interfere with Karl Fischer titration of water and that this interference is greatly dependent on the brand of reagent and on the reaction conditions.

Indicators and Reagents↗
PubMed1997

Effect of water content in perchloric acid on the non-aqueous potentiometric titration of nitrogen-containing compounds.

In the United States Pharmacopeia (USP), 0.1 N perchloric acid in acetic acid volumetric solution (hereafter HClO4 VS) used for non-aqueous titration has specified a water content between 0.02 and 0.05%. Preparing this titrant with such a narrow range of water content is very time consuming, precludes the use of commercially available titrants, and, consequently, prompted an investigation to try and expand the range up to 0.5%. In this study, the titrimetric results obtained using HClO4 VS containing more water were very close to those obtained using the USP specified titrants. A maximum assay difference of 0.7% in the titrations of three selected nitrogen-containing compounds, clonidine hydrochloride, dipyridamole, and adenosine were observed. The titrimetric results obtained using these titrants were also precise with RSDs of not more than 0.4%. Therefore, a wider range of water content in HClO4 VS between 0.02 and 0.5% is suggested for the USP potentiometric titration of nitrogen-containing compounds.

Indicators and Reagents↗
PubMed2002

Dose conversion and titration with a novel, once-daily, OROS osmotic technology, extended-release hydromorphone formulation in the treatment of chronic malignant or nonmalignant pain.

The objective of this open-label, repeated-dose, single-treatment, multicenter study was to evaluate the outcomes associated with a standardized conversion from prior opioid therapy to a novel, once-daily, OROS osmotic technology, extended-release (ER) hydromorphone formulation in an outpatient population with chronic malignant or nonmalignant pain. The study period was divided into 3 phases: the prior opioid stabilization phase (> or =3 days), the conversion and titration phase (3-21 days), and the maintenance phase (14 days). Patients were evaluated at 5 visits during the study period. Analgesic efficacy was measured using the Brief Pain Inventory (BPI). At baseline, patients were required to have daily oral morphine equivalent requirements of > or =45 mg. Prior oral or transdermal opioid therapy was converted to single daily doses of ER hydromorphone (8, 16, 32, and 64 mg tablets) at a 5:1 (morphine equivalent to hydromorphone) ratio. Immediate-release (IR) hydromorphone was given as rescue medication for breakthrough pain. Among the 445 patients who enrolled, 404 received the study medication. Of these, 73 (18.1%) had chronic malignant pain and 331 (81.9%) had chronic nonmalignant pain. Dose stabilization (defined as a 3-day period during which the total daily dose of ER hydromorphone remained unchanged and < or =3 doses of IR hydromorphone per day were required) was attained by 73.8% of patients (298/404), of whom 70.1% (209/298) were stabilized with < or =2 titration steps. The mean +/- standard deviation (SD) time to dose stabilization was 12.1 +/- 5.7 days (range of 3 to 33 days). The mean +/- SD final daily dose of ER hydromorphone was 63.4 +/- 129.2 mg. The mean +/- SD final daily dose of IR hydromorphone was 11.5 +/- 36.4 mg, and the mean +/- SD final number of daily doses of IR hydromorphone was 1.7 +/- 1.3. Intent-to-treat and completer analysis demonstrated significant improvements in BPI ratings from prior opioid therapy to the end of ER hydromorphone therapy (P < 0.01 for all pairwise comparisons). Adverse events were consistent with those expected of an opioid agonist in such a patient group, affecting primarily the gastrointestinal and central nervous systems. This uncontrolled study delineates a regimen by which patients with chronic malignant or nonmalignant pain can be readily converted from prior opioid therapy and titrated to an appropriate maintenance dose of ER hydromorphone. Controlled longitudinal studies are required to further evaluate the use of ER hydromorphone in patients with discrete chronic malignant or nonmalignant pain conditions.

Adult↗
PubMed2003

Intravenous fentanyl for cancer pain: a "fast titration" protocol for the emergency room.

Patients with cancer sometimes are admitted to the emergency room due to severe pain. Despite the fact that morphine's hydrophilicity can delay its peak effects after intravenous administration up to 30 minutes, it is still the most commonly used opioid during cancer pain emergencies. Fentanyl is a synthetic, lipophilic opioid, more potent than morphine, and achieves peak effects after intravenous administration in 5 minutes. According to our observations, intravenous fentanyl could be safely used in the emergency room to treat patients who need fast titration of an opioid to control their pain. In our study, fentanyl was employed in a four-step protocol to treat patients admitted to our palliative care emergency room due to severe pain, regardless of the previous use of morphine at home. Titration with intravenous fentanyl was successfully employed in 18/18 (100%) of patients, with an average time for pain control at about 11 minutes, and without relevant adverse effects. We conclude that intravenous fentanyl could be safely used for severe cancer pain when rapid titration is being considered.

Adult↗
PubMed2001

pH-metric solubility. 3. Dissolution titration template method for solubility determination.

The main objective of this study was to develop an effective potentiometric saturation titration protocol for determining the aqueous intrinsic solubility and the solubility-pH profile of ionizable molecules, with the specific aim of overcoming incomplete dissolution conditions, while attempting to shorten the data collection time. A modern theory of dissolution kinetics (an extension of the Noyes-Whitney approach) was applied to acid-base titration experiments. A thermodynamic method was developed, based on a three-component model, to calculate interfacial, diffusion-layer, and bulk-water reactant concentrations in saturated solutions of ionizable compounds perturbed by additions of acid/base titrant, leading to partial dissolution of the solid material. Ten commercial drugs (cimetidine, diltiazem hydrochloride, enalapril maleate, metoprolol tartrate, nadolol, propoxyphene hydrochloride, quinine hydrochloride, terfenadine, trovafloxacin mesylate, and benzoic acid) were chosen to illustrate the new titration methodology. It was shown that the new method is about 10 times faster in determining equilibrium solubility constants, compared to the traditional saturation shake-flask methods.

Acids↗
PubMed1989

Titration of Coxiella burnetii in Buffalo green monkey (BGM) cell cultures.

Titration of Coxiella burnetii, strain Nine Mile, phase I, and strain Frankfurt, phase II, in Buffalo green monkey (BGM) cover slip cell cultures yielded reproducible infectivity titers after centrifugation of infected cell cultures (3000 g, 30 min, 37 degrees C) and a subsequent 4-day incubation at 37 degrees C in Minimal Essential Medium (MEM). Compared to other titration procedures (plaque assays, titration in embryonated chicken eggs), this technique proved to be fast, less laborious and economical.

Animals↗
PubMed2006

Pilot study of labor induction with titrated oral misoprostol.

OBJECTIVE: To evaluate the safety and efficacy of titrated oral misoprostol for labor induction at term. MATERIALS AND METHODS: Seventy-seven pregnant women (37 nullipara and 40 multipara), with medical or obstetric indications for labor induction after 37 weeks of gestation and unfavorable cervices (Bishop's score < 7), were induced according to the principles of titrated oral doses of misoprostol against uterine response. Our primary outcome measurements were the percentage of patients who had a vaginal delivery within 24 hours of induction and the interval from induction to vaginal delivery. Secondary measurements included oxytocin requirement, total misoprostol dosage, number of cesarean deliveries, induction failure, uterine hyperstimulation rates and neonatal outcomes. RESULTS: Seventy-five women (97.4%) experienced active labor within 24 hours, with 72 (93.5%) completing vaginal delivery within 24 hours. The mean interval from induction to vaginal delivery for all the women was 9.7 hours, with a 2.3-hour active phase. The mean misoprostol dosage was 206 microg, with eight women (10.4%) requiring oxytocin augmentation. There was no uterine hyperstimulation or induction failure, except for seven cases of uterine tachysystole (9.1%). CONCLUSION: Titrated oral misoprostol is a safe and effective method of labor induction because the dosage can be adjusted according to individual response.

Adolescent↗
PubMed2003

Sweat conductivity and chloride titration for cystic fibrosis diagnosis in 3834 subjects.

Sweat test is the standard for cystic fibrosis (CF) diagnosis. Conductivity is an alternative method not yet approved, in spite of its good correlation with chloride concentration. The aim was to assess the capacity of sweat conductivity to discriminate between CF and non-CF subjects. Automated measurements of conductivity and chloride concentration were carried out on the same sweat samples from subjects with clinical suspicion of CF. Sweat samples from 3,834 subjects, median age 1.8 years (range 1 month-54 years) were analysed, and those with chloride titration >60 mmol/l were considered as CF patients (n=294). Conductivity median values in CF and non-CF subjects were 111 mmol/l (82-148) and 36 mmol/l (12-89), respectively. The Spearman correlation between chloride titration and conductivity was r=0.60 (P<0.001). The receiver operating characteristics (ROC) curve showed very high agreement between two methods. The best conductivity cut-off value to diagnose CF was > or =90 mmol/l (sensitivity 99.7%, specificity 100%, positive and negative predictive values of 100% and 99.97%, respectively, and kappa=0.998). Likewise, the best conductivity cut-off value to exclude CF was <75 mmol/l. The sweat conductivity method showed good correlation with chloride titration, and accurately discriminated between subjects with and without CF. In accordance with this, CF diagnosis might be confirmed for conductivity values > or =90 mmol/l and excluded for <75 mmol/l. Values between 75 and 89 mmol/l should correspond to an equivocal range. However, more studies are needed to confirm the role of conductivity in definitive CF diagnosis.

Adolescent↗
PubMed1997

Differential titration of plasmin and plasminogen in milk using sandwich ELISA with monoclonal antibodies.

Two sandwich enzyme-linked immunosorbent assays (ELISA) have been developed for quantitation of bovine milk plasminogen and plasmin. The assays used two monoclonal antibodies, one specific for plasminogen and the other specific for plasminogen plus plasmin. Plasmin concentration was obtained by subtracting the first concentration from the second. The assays were sensitive (linear range, 5-75 ng/ml), repeatable (CV, 8 and 5% for plasmin and plasminogen titration respectively), specific (no cross reactivity with the major milk proteins) and directly applicable to skimmed milk with no particular pretreatment of the sample. However, ELISA did not permit complete titration of milk plasminogen and plasmin (only 60-90% could be quantified). This lack of accuracy was due to casein interfering with the plasmin-plasminogen titration by ELISA. Results obtained with ELISA or an enzymic technique on 20 milk samples collected from individual cows milked throughout pregnancy showed that the ELISA was particularly suitable for analysis of late lactation or mastitic milk where proteinase inhibitors interfered with enzymic quantitation.

Animals↗
PubMed2001

Improved detection limits and sensitivities of potentiometric titrations.

Zero-current ion fluxes through polymer membranes of ion-selective electrodes (ISEs) may lead to biased endpoints of potentiometric titrations. The bias is eliminated, and the sensitivity of the end-point detection is improved through reducing transmembrane ion fluxes by an appropriate choice of the inner solution. Surprisingly, ISE membranes that have a significant primary ion flux toward the inner solution show much larger sensitivities than expected by titration theory; however, depending on the experimental conditions, their application may bias the endpoint. With the optimal systems, endpoint detection is now possible with total sample concentrations below 10(-6) M, as demonstrated by the titration of EDTA with a Pb2+ solution.

Edetic Acid↗
PubMed2006

Titration force microscopy on supported lipid bilayers.

The use of chemically modified atomic force microscopy (AFM) probes allows us to measure the surface charges of supported planar lipid bilayers with high sensitivity through the force spectroscopy operation mode. By controlling the chemistry of the tip, we can perform a classical analytical chemistry titration where the titration agent is a weak acid (attached to the AFM tip) with the particularity of being performed in surface rather than in solution and, especially, at the nanometric scale. Thus, the AFM tip acts as a real "nanosensor". The approaching curves of the force plots reveal that electrostatic interactions between the tip and the supported membrane play a key role. Besides, the plot of the adhesion force (measured from the retracting curve of the force plots) versus pH displays a nonsigmoidal shape with a peak in the adhesion force attributed to high-energy hydrogen bonds. One of these peaks corresponds to the pKa of the surface under study and the other to the pKa of the titrating probe attached to the tip.

Dimyristoylphosphatidylcholine↗
PubMedDate not supplied

Characterization of antibody-chelator conjugates: determination of chelator content by terbium fluorescence titration.

Fluorescence titrations were performed by adding varying mole ratios of terbium(III) to antibody conjugates formed by benzyl isothiocyanate derivatives of three different polyaminopolycarboxylate chelators (NTA, EDTA, and DTPA) and the results compared to values for average chelator content obtained by cobalt-57 binding assays. For two different murine monoclonal antibodies, the average chelator content obtained by terbium fluorescence titration correlated closely with that measured by the cobalt-57 binding assay. It is concluded that lanthanide fluorescence titrations provide a useful alternative to radiometal binding assays for the determination of chelator content in protein-chelator conjugates.

Antibodies, Monoclonal↗
PubMed1995

Localization of tolbutamide binding sites on human serum albumin using titration calorimetry and heteronuclear 2-D NMR.

The sulfonylureas are a class of oral hypoglycemic agents used to treat type II diabetes mellitus, and tolbutamide is a "first generation" member of this family. It is a nonpolar, weakly acidic drug that binds to serum albumin in the circulation. In the present study, we have examined the interactions of tolbutamide with human serum albumin by isothermal titration calorimetry and heteronuclear multiple-quantum coherence NMR spectroscopy. Calorimetric titrations revealed that tolbutamide binds to albumin at three independent sites with the same or comparable affinity. This result was independently confirmed by NMR experiments which resolved three resonances at 1H chemical shifts of 2.07, 2.11 and 2.14 ppm, corresponding to [methyl-13C]tolbutamide bound to three discrete binding sites. The binding affinity quantitated by calorimetry (Kd = 21 +/- 9 microM at pH 7.4, 37 degrees C) was approximately 5 times lower than the most frequently reported value. Tolbutamide titrations of albumin complexed with three other drugs whose binding sites have been localized by X-ray crystallography (salicylate, clofibric acid, and triiodobenzoic acid) demonstrated direct competition for common binding sites. NMR experiments with samples containing [methyl-13C]tolbutamide and these competing drugs permitted assignment of the resonances at 2.07 and 2.14 ppm to tolbutamide bound to the aspirin sites in albumin subdomains IIIA and IIA, respectively. These findings permit the first assignment of tolbutamide binding sites to specific locations on the albumin molecule within the context of the recently published crystal structure of human serum albumin. In addition, this information provides a molecular basis for predicting unfavorable drug interactions involving tolbutamide in patients with type II diabetes.

Binding Sites↗
PubMed1992

Thermodynamics of ion binding to phosphatidic acid bilayers. Titration calorimetry of the heat of dissociation of DMPA.

The heat of dissociation of the second proton of 1,2-dimyristoylphosphatidic acid (DMPA) was studied as a function of temperature using titration calorimetry. The dissociation of the second proton of DMPA was induced by addition of NaOH. From the calorimetric titration experiment, the intrinsic pK0 for the dissociation reaction could be determined by applying the Gouy-Chapman theory. pK0 decreases with temperature from ca. 6.2 at 11 degrees C to 5.4 at 54 degrees C. From the total heat of reaction, the dissociation enthalpy, delta Hdiss, was determined by subtracting the heat of neutralization of water and the heat of dilution of NaOH. In the temperature range between 2 and 23 degrees C, delta Hdiss is endothermic with an average value of ca. 2.5 kcal.mol-1 and shows no clear-cut temperature dependence. In the temperature range between 23 and 52 degrees C, delta Hdiss calculated after subtraction of the heat of neutralization and dilution is not the true dissociation enthalpy but includes contributions from the phase transition enthalpy, delta Htrans, as the pH jump induces a transition from the gel to the liquid-crystalline phase. The delta Cp for the reaction enthalpy observed in this temperature range is positive. Above 53 degrees C, the pH jump induces again only the dissociation of the second proton, and the bilayers stay in the liquid-crystalline phase. In this temperature range, delta Hdiss seems to decrease with temperature. The thermodynamic data from titration calorimetry and differential scanning calorimetry as a function of pH can be combined to construct a complete enthalpy-temperature diagram of DMPA in its two ionization states.

Calorimetry, Differential Scanning↗
PubMed1994

Quantitative determination of helical propensities from trifluoroethanol titration curves.

The formation of local secondary structure is an essential step in the folding of a polypeptide from a random coil to a well-defined native conformation. Detection of hidden structural propensities in amino acid sequences may provide important insight into how this is accomplished. 2,2,2-Trifluoroethanol (TFE) has been shown to induce helical structure in polypeptides, and TFE titration has been used as a qualitative probe for helical tendency. We have investigated the propensity of five synthetic peptides to adopt helical structure in TFE. The free energy of helix formation exhibits linear dependence on the mole ratio of TFE to water, and the constant of proportionality (m-value) can be perturbed systematically by altering the peptide length and unsystematically by altering the temperature. Three peptides with closely related sequences but different N-cap residues show different titration behavior from 5 to 75 degrees C, suggesting that TFE acts only within the context of a preexisting helix-coil equilibrium. These observations can be reconciled with a model for TFE/H2O exchange at peptide binding sites. Our results support the viability of TFE titration as a tool for extrapolation of quantitative helix-coil equilibrium constants for peptides with little or no apparent helical content in aqueous solution.

Amino Acid Sequence↗
PubMed2001

Thermodynamics of ion-induced RNA folding in the hammerhead ribozyme: an isothermal titration calorimetric study.

The hammerhead ribozyme undergoes a well-defined two-stage conformational folding process, induced by the binding of magnesium ions. In this study, we have used isothermal titration calorimetry to analyze the thermodynamics of magnesium binding and magnesium ion-induced folding of the ribozyme. Binding to the natural sequence ribozyme is strongly exothermic and can be analyzed in terms of sequential interaction at two sites with association constants K(A) = 480 and 2840 M(-1). Sequence variants of the hammerhead RNA give very different isothermal titration curves. An A14G variant that cannot undergo ion-induced folding exhibits endothermic binding. By contrast, a deoxyribose G5 variant that can undergo only the first of the two folding transitions gives a complex titration curve. However, despite these differences the ITC data for all three species can be analyzed in terms of the sequential binding of magnesium ions at two sites. While the binding affinities are all in the region of 10(3) M(-1), corresponding to free energies of Delta G degrees = -3.5 to -4 kcal mol(-1), the enthalpic and entropic contributions show much greater variation. The ITC experiments are in good agreement with earlier conformational studies of the folding of the ion-induced folding of the hammerhead ribozyme.

Adenine↗