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PubMed1977

Interference by acetylated aminoacetic acid in nonaqueous titration of nicotinic acid.

A nonaqueous titration procedure is described for determining aminoacetic acid and nicotinic acid in mixtures and elixirs. The effect of acetylated aminoacetic acid on the potentiometric titration of nicotinic acid is discussed. Above a 2:1 ration of aminoacetic acid to nicotinic acid, the former interferes with titration. The titration curve of nicotinic acid becomes progressively flatter with increasing amounts of the acetylated compound. Above this ratio, nicotinic acid had to be separated from the mixture by dissolving in ethanol for a successful titration.

Drug Combinations↗
PubMed2004

Titration of poly(dA-dT) . poly(dA-dT) in solution at variable NaCl concentration.

CD and uv absorption data showed that high molecular weight poly(dA-dT) . poly(dA-dT), at 298 K, undergoes an acid-induced transition from B-double helix to random coil in NaCl solutions of different concentrations, ranging from 0.005 to 0.600M. Similarly, titration of the polynucleotide with a strong base causes duplex-to-single strands transition. The base- and acid-induced transitions were both reversible by back-titration (with an acid or, respectively, with a base): the apparent pKa were the same in both directions. However, the number of protons per titratable site (adenine N1) required to reach half-denaturation was in great excess over the stoichiometric value; to a much larger extent, the same effect was observed also for the deprotonation of the N3H sites of thymine. Moreover, in the basic denaturation experiments, at low salt concentrations ([NaCl]< or =0.300M) less acid than calculated was needed to back-titrate the base excess to half-denaturation. Both effects could be qualitatively justified on the basis of the counterion condensation theory of polyelectrolytes and considering the energy barrier created by the negatively charged phosphodiester groups to the penetration of the OH- ions inside the double helix and the screening effect of the Na+ ions on such charges, in the deprotonation experiments.

Chemistry Techniques, Analytical↗
PubMed2006

Stability constants: comparative study of fitting methods. Determination of second-order complexation constants by (23)Na and (7)Li NMR chemical shift titration.

NMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal-ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second-order association constants for the LiClO(4):12-crown-4 system in acetonitrile and the NaClO(4):12-crown-4 system in methanol are reported. Formation of both 1:1 and 1:2 metal-ligand complexes are considered. The LiClO(4):12-crown-4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants.

Journal Article↗
PubMed1996

Fluorometric titration of the mitochondrial ADP/ATP carrier protein in muscle homogenate with atractyloside derivatives.

We describe here the chemical synthesis of the novel methylanthraniloyl (Mant-) derivative of atractyloside (ATR), which is a specific inhibitor of the mitochondrial ADP/ATP carrier. The spectral properties of Mant-ATR and naphthoyl-ATR (N-ATR) are analyzed. Both derivatives bind to the membrane-bound ADP/ATP carrier at the same sites as ATR and carboxyatractyloside (CATR). When Mant-ATR and N-ATR are displaced by CATR, their fluorescence emissions are decreased and increased, respectively. These fluorescence changes allow the titration of the CATR binding sites and therefore the quantitation of the amount of ADP/ATP carrier protein in a biological preparation. The validity of the fluorometric titration was tested with beef heart mitochondria and confirmed by binding assays using radioactive ATR. The fluorometric method was applied to rabbit skeletal muscle homogenate and the results of titration were confirmed by binding assays of radioactive ATR. The reliability of the fluorometric method was assessed by comparing the amounts of CATR binding sites and the content of heme aa3 in muscle homogenates and in isolated mitochondria from the same homogenates. Because of its high sensitivity, the fluorometric titration of the ADP/ATP carrier requires small amounts of tissue. Mant-ATR and N-ATR can therefore be considered as convenient, reliable, and sensitive probes to quantify the amount of ADP/ATP carrier and detect a putative carrier protein deficiency in biopsy samples from human patients suffering from myopathies with no clear identified etiology.

Animals↗
PubMed1998

Determination of binding constants by equilibrium titration with circulating sample in a surface plasmon resonance biosensor.

A commercial surface plasmon resonance biosensor, BIACORE X, is employed as a detector in a closed loop of a small sample volume. The sample is continuously circulated by an external syringe pump over two sensor spots, one functionalized with immobilized binding sites to a soluble binding partner in the mobile phase and one serving as a reference surface. A binding isotherm for the interacting macromolecules can be obtained by a stepwise titration of the soluble reactant into the circulating loop, each step followed by observation of the signal increase until equilibrium is attained. Binding constants can be measured under conditions free of mass transport artifacts and without the requirement for regeneration of the immobilized binding sites. This procedure is similar to the stepwise titration procedure described for the cuvette-based sensor design (D. R. Hall and D. J. Winzor, 1997, Anal. Biochem. 244, 152-160). In the presented configuration, the high baseline stability of the instrument combined with the availability of a reference surface for the detection of nonspecific binding permits refractive index changes upon addition of the aliquots to be measured, as well as accounting for temperature or instrumental drifts, and allows for a very long experimental time. This feature extends the applicability of equilibrium titration to systems with higher affinity or slower dissociation rate constants. Furthermore a solution competition titration is described that avoids artifacts from the immobilization procedure to provide a method for measurement of binding constants in solution. Kinetic information on the complex dissociation can also be obtained by combination of sample delivery via the external pump with the injection of competitor via the microfluidics of the biosensor. The rapid injection of high concentrations of competitor allows the observation of fast dissociation processes under conditions minimizing rebinding.

Animals↗
PubMed2001

An isothermal titration calorimetric method to determine the kinetic parameters of enzyme catalytic reaction by employing the product inhibition as probe.

An isothermal titration calorimetric (ITC) method was developed to measure the kinetic parameters of ribonuclease A catalytic hydrolysis of cytidine 2',3'-cyclic monophosphate. Employing the inhibition of product as a probe, the K(m), K(i), k(c), and DeltaH(m) can be determined by two simple calorimetric measurements. First, the substrate was titrated into the cell containing high concentration of enzyme. The molar reaction heat was calculated from the titration peak area divided by substrate moles per titration, and the initial catalytic reaction rate in the presence of various concentrations of product can be calculated from the peak height and the molar reaction heat. From Michaelis-Menten function in the presence of inhibitors, the relationship between K(m) and K(i) can be obtained. Then, the dissociation constant, which is equal to K(i), was measured by a regular ITC experiment. Thus, K(m) and k(c) can be calculated. The method developed here can be applied in other enzyme catalytic systems with inhibitive products.

Binding Sites↗
PubMed2001

Surface Chemistry of Activated Carbons: Combining the Results of Temperature-Programmed Desorption, Boehm, and Potentiometric Titrations.

Three samples of activated carbon were used for this study: two of wood and one of coal origin. The samples were further oxidized to study the effect of oxidation on the surface chemistry. The surface chemistry was characterized by using Boehm and potentiometric titrations, temperature-programmed desorption (TPD), and DRFTS. The results showed that oxidation introduces a variety of functional groups to the surface, making it more heterogeneous. Titration methods provide comparable results, whereas TPD detects more oxygen-containing groups. Discrepancies in the obtained results are due to limitations of the titration methods where only acidic and basic sites of certain strength can be detected. On the other hand, TPD can assess all functional groups but with less quantitative information. Moreover, comparison of TPD and titration methods leads to the detection of functional groups containing atoms other than oxygen and carbon as, for instance nitro groups, introduced to the carbon matrix via the nitration mechanism during oxidation with HNO(3). Copyright 2001 Academic Press.

Journal Article↗
PubMed1980

Titration of human brain monoamine oxidase -A and -B by clorgyline and L-deprenil.

The interaction of clorgyline and L-deprenil with the -A and -B forms of human brain monoamine oxidase (MAO) has been studied. Both compounds inhibit cerebrocortical MAO in a manner consistent with a 'suicide' inactivation of the enzyme. The interaction of clorgyline with the -A form of the enzyme appears to take place almost entirely at specific binding sites, and the conditions required for this inhibitor to 'titrate' the concentrations of MAO-A have been elucidated. L-Deprenil has also been used to titrate the concentration of the -B form of MAO in cerebrocortical homogenates, but there is a considerable degree of non-specific binding of this compound. The two inhibitors have been used to titrate the concentrations of the two enzyme forms in frontal cortex homogenates from different age groups. There was a significantly higher MAO-B activity for the age range 73--95 years than for the age range 2--63 years. No significant differences between the two age groups were found for MAO-A. The activity of MAO-A in the samples correlated very well with the concentration of this enzyme form. Titration of the B-form of the enzyme with L-deprenil indicated an increased enzyme concentration with age, although other factors, such as the non-specific binding of this compound, could contribute to this effect.

Adult↗
PubMed1985

The efficacy of quantitative and qualitative chloride titrators in the estimation of human salt intake.

We evaluated the utility of chloride titrator sticks for facilitating the assessment of dietary salt intake, in a systematic series of clinical trials. These inexpensive devices were applied daily to 24-h or nocturnal urine specimens, thereby avoiding the inter- and intra-subject variability in salt excretion which confounds the use of occasional 24-h urine collections. Chloride and sodium concentrations in urine were highly correlated (r greater than 0.92) in either nocturnal, diurnal, or 24-h collections. The quantitative chloride titrator estimates and measured chloride concentrations were highly correlated as well (r greater than 0.99). The qualitative chloride titrator was graded on a simple scale, and was successfully employed by outpatients attempting to limit their salt intake. Commonly used antihypertensive medications did not interfere with the determinations. Additional chloride intake, such as supplemental potassium chloride, interfered with estimates of salt ingestion, but if the daily amount of potassium chloride supplement was constant, adjustments in interpretation could be made. Renal insufficiency introduced a systematic over-estimation of salt intake by the qualitative chloride tirator, but only at high salt intakes. Relative estimates of salt intake in subjects with renal failure were still possible. We conclude that chloride titrators can facilitate the management of patients who require a prescribed salt intake.

Adult↗
PubMed2000

Peroperative titration of morphine improves immediate postoperative analgesia after total hip arthroplasty.

PURPOSE: To determine the Influence of peroperative titrated morphine on postoperative pain control. METHODS: Forty patients received general anesthesia for total hip arthroplasty (THA) and were divided into two groups of 20. In the Peroperative group (Perop group;) morphine was titrated at the end of surgery (3 mg i.v. every 5 or 10 min) in spontaneously breathing intubated patients, until the respiratory rate (RR) decreased. No morphine was administered to Postop group. In the Post Anesthesia Care Unit (PACU) patients in Perop and Postop groups received morphine until adequate pain relief VAS < or = 30 mm. Patients used patient-controlled analgesia (PCA) for the next 24 hr. In the PACU, the delay for analgesia, doses of morphine used and incidence of side effects were recorded. RESULTS: In the Perop group, patients received 10.3 +/- 1.3 mg (2-20 mg) as peroperative titration and had achieved adequate analgesia more rapidly than in the Postop group (42 +/- 7 min vs 76 +/- 7 min); P = 0.0026). Analgesia in the PACU in the Postop group required larger doses of morphine (15.4 +/- 1.5 mg;) than in the Perop group (7.3 +/- 1.3 mg; P = 0.0004). The respiratory rate decrease during peroperative morphine titration was correlated to the morphine dose needed in the PACU (P = 0.035). Respiratory depression in the PACU was more common in the Postop group than in the Perop group (five patients vs no patient P = 0.017). CONCLUSION: This study demonstrated that the peroperative administration of morphine can facilitate immediate postoperative pain management.

Adult↗
PubMed1999

FTIR-monitored thermal titration reveals different mechanisms for the alkaline isomerization of tuna compared to horse and bovine cytochromes c.

Fourier transform infrared (FTIR) spectroscopy is used to compare the thermally induced conformational changes in horse, bovine and tuna ferricytochromes c in 50 mM phosphate/0.2 M KCl. Thermal titration in D2O at pD 7.0 of the amide II intensity of the buried peptide NH protons reveals tertiary structural transitions at 54 degrees C in horse and at 57 degrees C in bovine c. These transitions, which occur well before loss of secondary structure, are associated with the alkaline isomerization involving Met80 heme-ligand exchange. In tuna c, the amide-II-monitored alkaline isomerization occurs at 35 degrees C, followed by a second amide II transition at 50 degrees C revealing a hitherto unreported conformational change in this cytochrome. Amide II transitions at 50 degrees C (tuna) and 54 degrees C (horse) are also observed during the thermal titration of the CN(-)-ligated cytochromes (where CN- displaces the Met80 ligand), but a well-defined 35 degrees C amide II transition is absent from the titration curve of the CN- adduct of tuna c. The different mechanisms suggested by the FTIR data for the alkaline isomerization of tuna and the mammalian cytochromes c are discussed. After the alkaline isomerization, loss of secondary structure and protein aggregation occur within a 5 degrees C range with Tm values at 74 degrees C (bovine c), 70 degrees C (horse c) and 65 degrees C (tuna c), as monitored by changes in the amide I' bands. The FTIR spectra were also used to compare the secondary structures of the ferricytochromes c at 25 degrees C. Curve fitting of the amide I (H2O) and amide I' (D2O) bands reveals essentially identical secondary structure in horse and bovine c, whereas splitting of the alpha-helical absorption of tuna c indicates the presence of less-stable helical structures. CN- adduct formation results in no FTIR-detectable changes in the secondary structures of either tuna or horse c, indicating that Met80 ligation does not influence the secondary structural elements in these cytochromes. The data provided here demonstrate for the first time that the selective thermal titration of the amide II intensity of buried peptide NH protons in D2O is a powerful tool in protein conformational analysis.

Alkalies↗
PubMed1996

A simple method for the titration of multicomponent acid-base mixtures.

A titration method has been developed to analyze acid mixtures, in which the pK values differed by 0.5 to 1 pH units. Instead of the use of equivalence points a buffer capacity curve is numerically derived from the titration curve resulting in a presentation similar to chromatograms and spectra. The consumption of the NaOH titrant is determined within pH intervals of 0.2-0.6 units around the pK values of the components. The buffer capacity measured is expressed as the consumption of NaOH over the pH interval. The amounts of compounds are found from these results using simple models of chemometrics. The method has been applied to a mixture of formic and acetic acids with concentrations of 0-3 mmol/20 ml with an error of 0-0.05 mmol. Furthermore a curve-fitting method based on a theoretical equation of buffer capacity can be applied with an error slightly larger than with the previous method. In this case, the pK values were also computed. For titrations beyond the pH range 4-10, the buffer capacity of water has to be subtracted from the titration results. The whole procedure requires including the computations about 3-6 min.

Journal Article↗
PubMed1996

Simulation of titration curves indicated with two indicator electrodes (biamperometry).

A rigorous method to simulate titration curves with indication using two indicator electrodes (biamperometry) is presented. Computer simulations can be carried out for reversible as well as for irreversible systems. The different parameters like the area of the individual electrodes, applied potential difference, heterogeneous rate constant, and the kinetic parameter alpha were varied and investigated as to their influence upon the shape of the titration curves. The theoretically derived effects match with the effects obtained by experiment. Considering the effects described here, it is possible to tailor the shape of the titration curve by the experimental conditions for specific applications in order to get an optimum shape at the end point of the titration.

Journal Article↗
PubMed2005

Impact of a standardized titration protocol with carvedilol in heart failure: safety, tolerability, and efficacy-a report from the GESICA registry.

Grupo de Estudio de la Sobrevida en la Insuficiencia Cardiaca en Argentina (GESICA) studied whether a standardized protocol for the initiation and titration of the beta-blocker carvedilol in a multicenter, open-label program would optimize beta-blocker use in heart failure (HF) patients. The program included: (1) the carvedilol initiation and titration period, and (2) long-term follow-up at 6 and 12 months. Of 1299 patients in the registry, 504 were excluded due to current therapy; of the remaining 795 eligible patients, 293 were excluded due to contraindications. Of the included patients with follow-up data (n = 316), 93.3% tolerated carvedilol initiation and 47.7% of the patients reached the target dose of 50 mg/day for a mean dose of 39 mg/day. Rates were comparable in the elderly (n = 83), of which 53% achieved a target dose for a mean dose of 43.08 mg/day. This protocol improved therapy rates and achieved target doses quickly (average of 4 visits). Concomitant medications did not have to be adjusted and there were low withdrawal rates (10%) and hospital admissions (7.2%) for HF. Patients were able to maintain carvedilol therapy at 6 and 12 months. These results indicate that a standardized titration protocol, as used in GESICA, for the initiation and titration of beta-blockers is well tolerated and may improve beta-blocker use in carefully selected heart failure patients.

Adrenergic beta-Antagonists↗
PubMed2004

CPAP compliance in sleep apnea patients with and without laboratory CPAP titration.

Advances in auto-adjusting positive airway pressure technology for obstructive sleep apnea now permit this treatment to be initiated outside of the sleep laboratory environment, bypassing the need for laboratory-based titration studies. Thus far, little research has addressed how such developments may affect compliance to continuous positive airway pressure (CPAP). We tested the effect of laboratory CPAP exposure and technologist support in a retrospective chart review of 98 veterans with obstructive sleep apnea to determine whether patients who received standard laboratory CPAP titration complied better with CPAP than did patients who received no laboratory CPAP titration. Fifty patients underwent standard technician-attended polysomnography (PSG) with CPAP titration, and 48 patients underwent unattended PSG with no laboratory trial of CPAP (first CPAP exposure was at home). Objective CPAP compliance measures were obtained from CPAP units at follow-up visits. Attended-PSG patients wore CPAP significantly longer per night on average (5.0 hours vs 3.9 hours) and tended to wear CPAP on more nights (76.5% vs 64.2%) compared with unattended-PSG patients. These findings suggest that patients' sleep laboratory experience with CPAP and the support and education provided by sleep technologists are important factors in facilitating CPAP compliance.

Continuous Positive Airway Pressure↗
PubMed1989

A spectroelectrochemical cell designed for low temperature electron paramagnetic resonance titration of oxygen-sensitive proteins.

In this paper we describe an anaerobic titrator made virtually from glass with a small amount of high vacuum epoxy mounted directly to a quartz EPR tube. A complete titration may be carried out with as little as 600 microliters of sample. This cell features the anaerobic manipulation of an electrochemically poised solution from an electrochemical pouch to an EPR tube. The cell uses a gold foil working electrode and Ag/AgCl reference and counter electrodes. The reference and counter electrodes are isolated from the sample by leached Vycor glass. In the work reported here, we used this cell to determine the equilibrium redox potential of methyl viologen in an EPR titration. With methyl viologen as an indicator we found that the cell has a residual oxygen level of 1.5 microM with a leak rate of 0.005 nmol/min. After moving the solution into the EPR tube, freezing, performing EPR, and thawing, the potential of the methyl viologen solution drifted only 2 mV. During the titration, the poised potentials were stable, drifting only 1 mV/min. Formal potentials as low as -630 mV in a vitamin B12-type protein have been determined with this cell (S. R. Harder, W.-P. Lu, B. A. Feinberg, and S. W. Ragsdale (1989) Biochemistry, in press).

Anaerobiosis↗
PubMed1992

A novel spectroscopic titration method for determining the dissociation constant and stoichiometry of protein-ligand complex.

We offer a new titration protocol for determining the dissociation constant and binding stoichiometry of protein-ligand complex, detectable by spectroscopic methods. This approach neither is limited to the range of protein or ligand concentrations employed during titration experiment nor relies on precise determinations of the titration "endpoint," i.e., the maximal signal changes upon saturation of protein by ligand (or vice versa). In this procedure, a fixed concentration of protein (or ligand) is titrated by increasing volumes of a stock ligand (or protein) solution, and the changes in the spectroscopic signal are recorded after each addition of the titrant. The signal for interaction between protein and ligand first increases, reaches a maximum value, and then starts decreasing due to dilution effect. The volume of the titrant required to achieve the maximum signal changes is utilized to calculate the dissociation constant and the binding stoichiometry of the protein-ligand complex according to the theoretical relationships developed herein. This procedure has been tested for the interaction of avidin with a chromophoric biotin analogue, 2-(4'-hydroxyazobenzene)benzoic acid by following the absorption signal of their interaction at 500 nm. The widespread applicability of this procedure to protein-ligand complexes detected by other spectroscopic techniques and its advantages over conventional methods are discussed.

Avidin↗
PubMed1992

Multicenter trial of automated nitroprusside infusion for postoperative hypertension. Titrator Multicenter Study Group.

Hypertension is common after a cardiac operation and may result in postoperative hemorrhagic and other complications. Most often this problem has been treated using manually controlled doses of intravenous sodium nitroprusside. To evaluate the clinical impact of an automated closed-loop administration system on patients after cardiotomy, a prospective trial was conducted at nine clinical centers. Patients with hypertension were managed by either manual nitroprusside titration (n = 532) or a closed-loop automated titration system (n = 557). Patient groups were not significantly different in age, weight, or height. Moreover, the types of surgical procedures were comparable: primary coronary artery bypass grafting, 59.2% and 58.9%, manual group versus automated group; repeat coronary artery bypass grafting, 10.5% and 8.6%, respectively; valve procedures, 11.3% and 15.1%, respectively; and other cardiac procedures, 19.0% and 17.4%, respectively (all p = not significant). The automated group showed a significant reduction in the number of hypertensive episodes per patient (1.8 +/- 0.2 versus 0.6 +/- 0.07; p = 0.0001. At the same time, the number of hypotensive episodes per patient was reduced with automated closed-loop titration (0.40 +/- 0.05 versus 0.30 +/- 0.03; p = 0.02). Chest tube drainage (866 +/- 37 mL versus 693 +/- 23 mL [mean +/- standard error of the mean]; p = 0.0001), percentage of patients receiving transfusion (40.0% versus 33.0%; p = 0.02), and total amount transfused (2.4 +/- 0.12 units versus 2.0 +/- 0.10 units; p = 0.0003) were all reduced significantly by the use of an automated titration system.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Transfusion↗