Composition, stability, and lability of copper(II) dipeptide complexes

Complex formation of copper(II) with glycylglycine (HL) has been studied spectrophotometrically over a wide range of ligand concentration (0.005-1.0 mol dm-3) and pH (0.5-13) in aqueous potassium nitrate (1.0 mol dm-3 KNO3). The complexes [CuL]+, [Cu(HL)]2+, [Cu(LH-1)], [Cu(LH-1)(OH)]-, [Cu(LH-1)L]-, [Cu(LH-1)2]2-, and [Cu2(LH-1)2(OH)]- were found and their formation constants determined. The ligand in [Cu(HL)]2+ is co-ordinated through the carboxylate group, and the terminal amino group remains protonated. Such a co-ordination mode is more favourable for depeptides as compared to amino acids. Both of the ligands in [Cu(LH-1)2]2- are bound to the metal ion in a bidentate mode through the terminal amino nitrogen and the deprotonated peptide nitrogen. The species [Cu2(LH-1)2(OH·)]- has an intense absorption band in the near-u.v. region which indicates that the OH- group is bridging. The lability of complexes [Cu(LH-1)L]- with five aliphatic dipeptides has been investigated by n.m.r. relaxation of water protons. The ligand-exchange rates (Rex) in solutions of these complexes follow the kinetic equation Rex = (k1 + k2[L-])[Cu(LH-1)L-]. Increasing the size of the side chain of the dipeptides leads to a lower Rex, and a good correlation between log k2 and the steric constants Es0 of the side-chain substituents is observed. The high values for k1 obtained indicate a considerable trans effect of the deprotonated peptide group

Determination of ionol by voltammetry and coulometric titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10 -4 to 1.0 × 10-2 M (RSD = 9%) and from 3.0 × 10-5 to 4.0 × 10-3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10-4 and 1.0 × 10-5 M, respectively. The detection limit in coulometric titration was 20 μg/mL

The effect of the core morphology of Eu(III)-doped nanoparticles on the ion exchange versus energy transfer between Eu(III) in the core and Cu(II) ions at the interface

The report represents the comparative analysis of luminescent properties of Eu(III) complex in colloids of silica-coated and layer-by-layer-fabricated nanoparticles. The diverse morphologies of these nanoparticles greatly affect their photophysical properties. The interfacial binding with d-ions exemplified by Cu(II) and the contributions of the ion exchange and energy transfer processes between Eu(III) ions confined within polymeric coating and Cu(II) ions at the interface of nanoparticles also depend on their morphology. The silica coating of Eu(III) complex does not prevent it from the efficient ion displacement by the interfacial Cu(II) ions, which results in the irreversible quenching of Eu(III)-centered luminescence. The lack of the ion exchange and the predominant energy transfer between Eu(III) ions in the core and interfacial Cu(II) ions are revealed in the colloids of Eu(III) complex reprecipitated from organic to aqueous solution and coated by the layer-by-layer-fabricated polyelectrolyte multilayer. The obtained results represent the synthetic route of the insertion of Cu(II) ions into the polyelectrolyte multilayer fabricated onto Eu(III) complex. © 2012 Springer Science+Business Media B.V

Composition, stability, and lability of copper(II) dipeptide complexes

Complex formation of copper(II) with glycylglycine (HL) has been studied spectrophotometrically over a wide range of ligand concentration (0.005-1.0 mol dm-3) and pH (0.5-13) in aqueous potassium nitrate (1.0 mol dm-3 KNO3). The complexes [CuL]+, [Cu(HL)]2+, [Cu(LH-1)], [Cu(LH-1)(OH)]-, [Cu(LH-1)L]-, [Cu(LH-1)2]2-, and [Cu2(LH-1)2(OH)]- were found and their formation constants determined. The ligand in [Cu(HL)]2+ is co-ordinated through the carboxylate group, and the terminal amino group remains protonated. Such a co-ordination mode is more favourable for depeptides as compared to amino acids. Both of the ligands in [Cu(LH-1)2]2- are bound to the metal ion in a bidentate mode through the terminal amino nitrogen and the deprotonated peptide nitrogen. The species [Cu2(LH-1)2(OH·)]- has an intense absorption band in the near-u.v. region which indicates that the OH- group is bridging. The lability of complexes [Cu(LH-1)L]- with five aliphatic dipeptides has been investigated by n.m.r. relaxation of water protons. The ligand-exchange rates (Rex) in solutions of these complexes follow the kinetic equation Rex = (k1 + k2[L-])[Cu(LH-1)L-]. Increasing the size of the side chain of the dipeptides leads to a lower Rex, and a good correlation between log k2 and the steric constants Es0 of the side-chain substituents is observed. The high values for k1 obtained indicate a considerable trans effect of the deprotonated peptide group

Composition, stability, and lability of copper(II) dipeptide complexes

Complex formation of copper(II) with glycylglycine (HL) has been studied spectrophotometrically over a wide range of ligand concentration (0.005-1.0 mol dm-3) and pH (0.5-13) in aqueous potassium nitrate (1.0 mol dm-3 KNO3). The complexes [CuL]+, [Cu(HL)]2+, [Cu(LH-1)], [Cu(LH-1)(OH)]-, [Cu(LH-1)L]-, [Cu(LH-1)2]2-, and [Cu2(LH-1)2(OH)]- were found and their formation constants determined. The ligand in [Cu(HL)]2+ is co-ordinated through the carboxylate group, and the terminal amino group remains protonated. Such a co-ordination mode is more favourable for depeptides as compared to amino acids. Both of the ligands in [Cu(LH-1)2]2- are bound to the metal ion in a bidentate mode through the terminal amino nitrogen and the deprotonated peptide nitrogen. The species [Cu2(LH-1)2(OH·)]- has an intense absorption band in the near-u.v. region which indicates that the OH- group is bridging. The lability of complexes [Cu(LH-1)L]- with five aliphatic dipeptides has been investigated by n.m.r. relaxation of water protons. The ligand-exchange rates (Rex) in solutions of these complexes follow the kinetic equation Rex = (k1 + k2[L-])[Cu(LH-1)L-]. Increasing the size of the side chain of the dipeptides leads to a lower Rex, and a good correlation between log k2 and the steric constants Es0 of the side-chain substituents is observed. The high values for k1 obtained indicate a considerable trans effect of the deprotonated peptide group

Composition, stability, and lability of copper(II) dipeptide complexes

Complex formation of copper(II) with glycylglycine (HL) has been studied spectrophotometrically over a wide range of ligand concentration (0.005-1.0 mol dm-3) and pH (0.5-13) in aqueous potassium nitrate (1.0 mol dm-3 KNO3). The complexes [CuL]+, [Cu(HL)]2+, [Cu(LH-1)], [Cu(LH-1)(OH)]-, [Cu(LH-1)L]-, [Cu(LH-1)2]2-, and [Cu2(LH-1)2(OH)]- were found and their formation constants determined. The ligand in [Cu(HL)]2+ is co-ordinated through the carboxylate group, and the terminal amino group remains protonated. Such a co-ordination mode is more favourable for depeptides as compared to amino acids. Both of the ligands in [Cu(LH-1)2]2- are bound to the metal ion in a bidentate mode through the terminal amino nitrogen and the deprotonated peptide nitrogen. The species [Cu2(LH-1)2(OH·)]- has an intense absorption band in the near-u.v. region which indicates that the OH- group is bridging. The lability of complexes [Cu(LH-1)L]- with five aliphatic dipeptides has been investigated by n.m.r. relaxation of water protons. The ligand-exchange rates (Rex) in solutions of these complexes follow the kinetic equation Rex = (k1 + k2[L-])[Cu(LH-1)L-]. Increasing the size of the side chain of the dipeptides leads to a lower Rex, and a good correlation between log k2 and the steric constants Es0 of the side-chain substituents is observed. The high values for k1 obtained indicate a considerable trans effect of the deprotonated peptide group

Determination of ionol by voltammetry and coulometric titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10 -4 to 1.0 × 10-2 M (RSD = 9%) and from 3.0 × 10-5 to 4.0 × 10-3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10-4 and 1.0 × 10-5 M, respectively. The detection limit in coulometric titration was 20 μg/mL

THE PREVALENCE AND CLINICAL SIGNIFICANCE OF CARDIAC ARRHYTHMIAS

Arrhythmias are one of the most complex, insufficiently studied, and therefore one of the most urgent problems of modern cardiology. A wide spectrum of clinical manifestations of cardiac rhythm disorders (CRDs), their detection both in various diseases and in healthy people, necessitate the study of their prevalence in populations. In the majority of conducted epidemiological studies a single recording of electrocardiogram (ECG) was used. This is the most usable method for examination of large populations but a little informative for detecting arrhythmias. The small frequency of CRDs detected during ECG recording is due to the short duration of its registration. An increase in the duration of ECG recording (ECG recording for 2 minutes, continuous recording of 100 cardiocycles) leads to an increase in arrhythmias frequency. With a wide introduction in the practice of ECG monitoring by Holter as well as the use of individual recorders of electrocardiogram ("handheld ECG recording") data appeared indicating a much higher frequency of CRDs. Data obtained in numerous studies on the prevalence of arrhythmias are very contradictory and depend both on the characteristics of populations and on methodological approaches, which requires further epidemiological studies. At the same time, the main initiating point of such researches is the clinical significance of certain CRDs. However, if the clinical significance of ventricular tachyarrhythmias and atrial fibrillation does not currently cause any doubt, the clinical significance of extrasystoles is highly controversial, despite the high their prevalence, including this in prognostically unfavorable groups of patients. In recent years, the results of a number of studies have been published that allow to think about the adverse effects of both supraventricular and ventricular extrasystoles of the course of certain cardiovascular diseases. Very heterogeneous results of the performed studies, as well as data about the high clinical significance of individual CRDs, make further epidemiological studies in this field extremely urgent

Determination of ionol by voltammetry and coulometric titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10 -4 to 1.0 × 10-2 M (RSD = 9%) and from 3.0 × 10-5 to 4.0 × 10-3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10-4 and 1.0 × 10-5 M, respectively. The detection limit in coulometric titration was 20 μg/mL

Determination of ionol by voltammetry and coulometric titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10 -4 to 1.0 × 10-2 M (RSD = 9%) and from 3.0 × 10-5 to 4.0 × 10-3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10-4 and 1.0 × 10-5 M, respectively. The detection limit in coulometric titration was 20 μg/mL