pH-metric Study Research Articles

Gastroesophageal reflux and bronchial asthma: prevalence and effect of cisapride therapy.

We evaluated the prevalence of gastroesophageal reflux in 36 children, 22 (61.2%) male and 14 (38.8%) female (median age, 75.5 months; range, 18-178), with noncontrolled asthma by means of prolonged (22-24 h) esophageal pH monitoring. None of the children had gastrointestinal symptoms suggesting gastroesophageal reflux. Atopy was seen in 21 of 36 (58.3%) patients. Pathological gastroesophageal reflux was present in 27 (75%) children. All patients were given cisapride (0.2 mg/kg q.i.d.) for 3 months. A clinical and pharmacological score was determined, and a second pH-metric study was made at the end of the follow-up period. The following pH-metric parameters were evaluated: the total percentage of time pH was < 4, the number of reflux episodes, the number of reflux episodes lasting > 5 min, the length of the longest single reflux episode, and the percentage of time the esophageal pH was < 4 during sleep. The study was completed in 11 of 27 children. The percentage of time that esophageal pH was < 4 improved in nine of 11 (81.8%) patients (p = 0.013). The percentage of time that esophageal pH was < 4 during sleep showed the most significant decrease (p = 0.002) after treatment. Improvement in both clinical and pharmacological scores was highly significant (p < 0.0001) in 19 of 27 patients, eight of whom did not want to repeat the pH study. We conclude therefore that gastroesophageal reflux is frequently associated with noncontrolled asthma and that medical therapy for reflux may improve the further course of respiratory disease.

Ternary copper(II) complexes with 2,2′-bipyridine and N-tosyl-substituted amino acids. Part 1. Polarographic and pH-metric study

The solution behaviour of ternary complexes of Cu2+ with 2,2′-bipyridine (bipy) and N-tosyl (toluene-4-sulphonyl) derivatives of asparagine and glutamine was investigated by pH-metric and polarographic tools, and compared with the corresponding binary Cu2+–N-tosylamino acidate systems. The experimental techniques agree about the type and stability of the complex species, in which the amino acidic ligands co-ordinate through the carboxylate group (HL–) or act as bidentate ligands through the carboxylic oxygen and the deprotonated sulphonamide nitrogen (L2–)[HL– and L2–=N-tosyl-DL-asparaginate (or -L-glutaminate) monoanion and dianion respectively]. The following prevailing species were detected: [Cu(bipy)(HL)2], [Cu(bipy)L], and [Cu(bipy)L2]2–. Evidence has also been obtained for the presence of the species [Cu(bipy)(HL)]+ and [Cu2(bipy)2L2(OH)]–. The copper(II)-promoted sulphonamide deprotonation of the amino acidic ligands in the ternary systems is observed at lower pH values than that in the corresponding binary systems (pH ≈ 5 vs. pH ≈ 7); this effect was not observed for the peptide-nitrogen deprotonation of the ternary copper(II) complexes of peptides with 2,2′-bipyridine.

Tyrosinate and lysinate as bridging residues in copper(II) dipeptide complexes

A pH-metric study, together with some supporting spectroscopy (u.v.–visible, c.d., and e.s.r.), was made on copper(II) complexes of L-phenylalanyl-L-tyrosine, L-tyrosyl-L-phenylalanine, L-lysyl-L-tyrosine, and L-tyrosyl-L-lysine at 25 °C and l= 0.2 mol dm–3(KCl). It was established that in dilute aqueous solutions, besides metal–ligand co-ordination characteristic of simple dipeptides, there are interactions between copper(II) and the side-chain phenolate group of the tyrosine residue and/or the Iµ-amino group of the lysine residue. In these dimeric species, both the lysine and the tyrosine moieties can behave as bridges between monomeric complexes.

Spectroscopic and potentiometric study of protonation and copper(II) complex formation of 3-amino-L-tyrosine

A pH-metric and spectroscopic (u.v.–visible and e.s.r.) study has been made of the proton and copper(II) complexes of 3-amino-L-tyrosine at 25 °C and I= 0.2 mol dm–3(KCl). The acid–base chemistry of the ligand has been characterised at both macroscopic and molecular levels by determining the microscopic constants of the overlapping protonation processes. It has been established that the ligand displays a marked ambidentate character in the copper(II) complexes. Accordingly, various monomeric complexes involving aminocarboxylate- and aminophenolate-type co-ordination, and dimeric complexes involving simultaneous metal-ion co-ordination at both binding sites, are formed.

PH-metric study of the complexation equilibria of alkaline-earth cations with [1]- and [2]- cryptands in methanol

The stability constants of the complexes of the alkaline-earth cations Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ with the monocyclic cryptands 11, 21 and 22 and the bicyclic cryptands 211, 221 and 222 were determined by pH-metry at 25 °C. The results confirm, within experimental uncertainties, most of those which were previously established by a competitive potentiometric method using Ag + . or estimated. Selectivity, size charge and solvent effects, as well as the magnitude and thermodynamic origin of the macrobicyclic effect, are discussed.

Metal Chelates of Some N-Acyl Hydroxamic Acids Containing Sulphonimido Group. Part I : pH-Metric Study of the Complex Formation of Cu(II) with N(N-Benzene Sulphonyl Glycyl) N-Phenyl Hydroxyl Amine

Metal Chelates of Some N-Acyl Hydroxamic Acids Containing Sulphonimido Group. Part I : pH-Metric Study of the Complex Formation of Cu(II) with N(N-Benzene Sulphonyl Glycyl) N-Phenyl Hydroxyl Amine

Complexes of 3,4-dihydroxyphenyl derivatives. II. Complex formation processes in the nickel(II)-L-DOPA and zinc(II)-L-DOPA systems

A pH-metric study (at 25 °C and 0.2 M ionic strength) of the nickel(II)-L-3,4-dihydroxyphenylalanine (L-DOPA) and zinc(II)-L-DOPA systems was used to determine the stoichiometric compositions and stability constants of the species formed. From the results obtained for the nickel(II) and zinc(II)- alaninate-pyrocatecholate systems, and UV and visible spectral studies of the corresponding DOPA complexes, conclusions were drawn on the mode of bonding of the complexes formed. It was found that complexes containing aminoacid-like and pyrocatechol-like bonds are formed in both systems: the latter are favoured in the case of zinc(II), and the former in the case of nickel(II). This is so marked that in the nickel(II)-DOPA system the 1:2 complex containing only (O,O) bonds is not formed at all. In both systems mixed complexes containing both (N, O) and (O,O) bonds occur to appreciable extents. It was established for some species that not only a given arrangement of donor atoms belongs to a given stoichiometric composition, but complexes with different structures are in equilibrium with one another.