The stabilization of managese(III) by azide ions in aqueous solution.

The evidences of spontaneous oxidation of Mn(II) by the dissolved oxygen in azide buffer medium, which is dependent on the N (-)(3)HN (3) concentration, suggested a formation of stable Mn(III) complexes due to marked colour changes. Spectrophotometric studies combined with coulometric generation of Mn(III), in presence of large excess of Mn(II), showed a maximum absorbance peak at 432 nm. The molar absorptivity increases with azide concentration (0.44-3.9 mol 1(-1)) from 3100 to 6300 mol(-1) 1 cm(-1), showing a stepwise complex formation. Potential measurements of the Mn(III) Mn(II) system in several azide aqueous buffers solutions: 1.0 x 10(-2) mol 1(-1) HN(3), (0.50-2.0 mol 1(-1)) N(-)(3) and 5.0 x 10(-2) mol 1(-1) Mn(II) and constant ionic strength 2.0 mol 1(-1), kept with sodium perchlorate, leads to the conditional potential, E(0')x, in several azide concentrations at 25.0 +/- 0.1 degrees C. Considering the overall formation constants of Mn(II) N (-)(3), from former studies, and the potential, E(0')s = 1.063 V versus SCE, for Mn(III) Mn(II) system in non-complexing media, it was possible to calculate the Fronaeus function, F(0)(L), and the following overall formation constants: beta(1) = 1.2 x 10(5) M(-1), beta(2) = 6.0 x 10(8) M(-2), beta(3) = (2.4 +/- 0.7) x 10(11) M(-3), beta(4) = (1.5 +/- 0.5) x 10(11) M(-4) and beta(5) = (9.6 +/- 0.8) x 10(11) M(-5) for the Mn(III) N (-)(3) complexes. These data give important support to understand the importance of Mn(II) and Mn(III) synergistic effect on the analytical method of S(IV) determination based on the Co(II) autoxidation.

[Single x double phototherapy for the treatment of hyperbilirubinemia in high risk newborn infants]. / Fototerapia simples x dupla no tratamento da hiperbilirrubinemia em recém-nascidos de risco.

This is a randomized, prospective, controlled study to compare the efficacy of single versus double halogen phototherapy in high risk patients admitted to a newborn intensive care unit. Eighty patients were allocated to receive single (N=43) or double (N=37) phototherapy. The groups were similar in clinical and laboratory characteristics. Total serum bilirubin (SB), hematocrit and total serum protein were assessed by microanalysis prior to the beginning of the study and at 6, 12, 18 and 24 hours of treatment. The percent decline of SB was significantly higher in the double phototherapy group. This difference is first noted at 12h of treatment (10% vs 1.8%, p< 0.01) and is acentuated at the end of the study (19.4% vs 1.6%, p< 0.0001). Weight loss, variations in the hematocrit and total serum protein were similar in both groups. Cutaneous rash and temperature instability were not noted among the patients studied.Our results demonstrate that double phototherapy is more efficient than single phototherapy in treating hyperbilirubinemia in high risk newborn infants.

Study of complex formation in the manganese(II)/azide system.

The complex formation between Mn(II) cations and N(3)(-) anions was studied in aqueous medium at 25 degrees C and ionic strength 2.0 M (NaClO(4)). Data of average ligand number, n (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N(3)(-)/HN(3) system followed by integration to obtain Leden's function, F(0)(L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: beta(1)=4.15+/-0.02 M(-1), beta(2)=6.61+/-0.04 M(-2), beta(3)=3.33+/-0.02 M(-3), beta(4)=0.63+/-0.01 M(-4). A linear plot of log K(n) vs. (n-1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N(3)(-) concentration is greater than 1.0 M.

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion.

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95-99% as Y(4-) anion) precipitates with Ag(+) cations to form the Ag(4)Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y(4-) to form a complex, AgY(3-). Equilibrium studies at 25 degrees C and ionic strength 0.50 M (NaNO(3)) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) beta(1) = (1.93 +/- 0.07) x 10(5) M(-1) and the solubility products are K(S0) = [Ag +](4)[Y(4-)] = (9.0 +/- 0.4) x 10(-18) M(5) and K(S1) = [Ag +](3)[AgY(3-)] = (1.74 +/- 0.08) x 10(-12)M(4). The presence of Na(+), rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: beta(1) = (1.19 +/- 0.03) x 10(6) M(-1), K(S0) = (1.6 +/- 0.4) x 10(-19) M(5) and K(S1) = (1.9 +/- 0.5) x 10(-13) M(4); at ionic strength tending to zero; beta(1) = (1.82 +/- 0.05) x 10(7) M(-1), K(S0) = (2.6 +/- 0.8) x 10(-22) M(5) and K(S1) = (5 +/- 1) x 10(-15) M(4). The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO(3). Well-defined potentiometric titration curves can be taken in the range 1-2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142 degrees C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135-157 degrees C), tending to pure silver at 600 degrees C, consistent with the original Ag(4)Y salt.

Solvent extraction of Fe(III) by dehydrated castor oil fatty acids.

The effect of temperature on the extraction of FE(III) by dehydrated castor oil fatty acids (DCOFA) has been studied in the temperature range 283-313 K at 1.0M constant ionic strength (NaClO(4)). The temperature dependence of the conditional constant of extraction is given in the form: ln K(ext)=31.95 - 12800(1/T). Also, it was found that the average thermodynamic parameters, DeltaH degrees (ext), DeltaG degrees (ext), and DeltaS degrees (ext) are 106.5 kJ/mole, 27.3 kJ/mole, and 0.3 kJ. mole(-1).K(-1), respectively. The extracted species in toluene solution were identified as FeR(3).HR and Fe(OH)R(2), where HR represents the fatty acid used.

Analytical data: Potentiometric study of the association constant of isothiocyanic acid.

The association constant of isothiocyanic acid, HNCS, has been determined potentiometrically and found to be 0.135 +/- 0.007 and 0.168 +/- 0.007 at ionic strengths (NaClO(4)) of 2.0 and 4.0M respectively. The indicator electrode was Hg(SCN)(2-)(4)/Hg. For accuracy and precision the metal phase was used in the form of a dropping electrode. Because the association constant is so low, liquid-junction potentials would cause significant errors, since a strong acid was added to the working solutions in the procedure, and an estimate of this effect was taken into account.

Spectrophotometric study of the equilibria in aqueous copper(II) azide solutions.

The reaction between copper (II) and azide has been studied spectrophotometrically at four wavelengths, at 25 degrees , and ionic strength 4.00M (sodium perchlorate). The formation constants beta(2) and beta(3) found are 2.90 +/- 0.08 x 10(4) and 3.02 +/- 0.07 x 10(6) respectively. The results obtained from potentiometric measurements with a solid-state electrode disagree with those calculated from the spectrophotometric data. Causes of the discrepancy are discussed.

Spectrophotometric determination of the pseudohalide 1,2,3,4-thiatriazol-5-thiolate ion, CS(2)N(-)(3).

A critical study of the analytical methods available for the CS(2)N(-)(3) ion is reported. A modification of the argentimetric method is proposed. An oxidative study gave evidence of various steps corresponding to incompletely oxidized intermediates. The absorption maximum of the 1,2,3,4-thiatriazol-5-thiolate ion at 313 nm, with molar absorptivity of 7.4 x 10(-3)1.mole(-1).cm(-1) is utilized to develop a new analytical method. The spectrophotometric procedure is rapid and free from interference by many ions. A value of 1.51 +/- 0.02 was found for pK of HCS(2)N(3) at an ionic strength of 1.00M and at 25 degrees . The spectrum of CS(2)N(-)(3) is changed by increasing acidity of the medium, due to the formation of HCS(2)N(3); an isosbestic point is observed at 251 nm.