Biomedical subjects
Publications and source records attributed to I M Kolthoff.
A brief review is given on the use of crown ethers in solubilizing salts of alkali and alkaline earth ions in organic polar or apolar solvents. Use of crown ethers can also be made in testing e.g. lithium salts for potassium by extraction as LKpicrate, L being 18-crown-6.
Stability constants, K(f)LM(n+) (in which L = ligand and M(n+) = metal ion), of complexes of sodium, potassium, silver, thallium(I), and barium with dibenzocryptand 2.2.2 were determined at 25 degrees C in water and methanol. Also determined were transfer activity coefficients between methanol and water of two ligands, dibenzocryptand 2.2.2 and 18-crown-6. From these data, transfer activity coefficients of complexes of these two ligands with the above cations have been calculated. For univalent ion complexes of these ligands and, in addition, for such complexes of dibenzo-18-crown-6 and cryptand 2.2.2, the logarithms of the transfer activity coefficients are of the order of 2.5 units more positive than those of the ligands. Even though methanol is a good hydrogen bond donor, as is water, it is concluded that in methanol only the first solvation layer is built around an ether oxygen of the uncomplexed ligand as compared with several hydration layers in water. Hydrogen bonding to these ether oxygens when these ligands are complexed is greatly decreased as a result of ionic M(n+)-O bonding. Transfer activity coefficients of the barium complexes are found to be the same as those of the ligands. This is attributed to extensive solvation of LBa(2+).
Between dipolar aprotic solvents S(1) and S(2), the transfer activity coefficients, (S(1) )gamma(S(2) ), of complexed sodium, potassium, thallium(I), and silver ions with cryptand 2.2.2 have been found to be equal to that of the cryptand. With reference to methanol (S(1)), this equality does not hold, the cryptates being more or less solvated by hydrogen bonding in this solvent. In water as a solvent, the cryptates are on a considerably higher level of free energy than in the organic solvents. This is attributed to hydrophobic hydration of the cryptates.
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In ammonia buffers of varying composition and pH, native bovine serum albumin and completely reduced bovine serum albumin, denoted by p(SH)35, yield quite different Brdicka current-voltage (i-E) curves, but they are identical in the presence of 5 mM calcium chloride. This means that in the presence of calcium, bovine serum albumin becomes completely reduced to p(SH)35. In 8 M urea and ammonia buffers the Brdicka i-E patterns of serum albumin and p(SH)35 are identical even in the absence of calcium, the effect of calcium on the first wave being negligible while calcium slightly increases the second wave. The maximum polarographic effect is attained at urea concentrations of about 5-6 M. Quite generally, the appearance of a second Brdicka wave is attributed to complexation of Co(II) with S- and a group of ligands that is different on the second than on the first wave. The effect of calcium on Brdicka currents of bovine serum albumin in the absence of urea is attributed to an orientation of the protein on the surface of the electrode such that all disulfide groups are reduced and with other ligands can complex with Co(ii). Denaturation of bovine serum albumin in buffers with a pH less than 10.5, and which are 8 M in area, is (polarographically) completely reversible if dilution is made within 15 minutes after preparation. Changes in Brdlcka I-E patterns upon longer aging at varying pH are attributed-in part at least-to dimerization of the denatured protein by interaction of pS- in one molecule with -S-S-in another.
Tetraethyl-, tetrapropyl-, and tetrabutylammonium ions are capillary-active on the interface water-mercury. In the adsorbed state they increase Brdicka and presodium currents. These currents drop sharply at potentials where tetrabutylammonium ions are desorbed, these potentials being -1.60, -1.66, -1.72, and -1.79 V versus the saturated calomel electrode (SCE) at tetrabutyla-mmonium concentrations of 0.1, 0.25, 1, and 5 mM, respectively. Indications are that tetraethylammonium ions at a concentration of 50 mM are desorbed at a potential of the order of -1.9 V (versus SCE). The increase of Brdicka currents is attributed--at least in part--to a decrease in the rate of electroreduction of cobalt(II). In the desorbed state the effect--if any--of tetrabutylammonium ions on Brdicka and presodium currents is very small. Tetrabutylammonium ions also greatly increase Brdicka currents observed with cysteine, the effect disappearing after these ions attain their desorption potential. The effect of tetraphenylarsonium on Brdicka currents is very similar to that of tetrabutylammonium, while that of diphenylguanidine is similar to that of tetraethylammonium ions.
Brdicka currents observed with bovineserum albumin in ammoniacal buffers with Co(III) and Co(II) as catalysts are identical only when the concentrations of ammonia and ammonium chloride are at least 0.5 M and 0.05 M, respectively. When these conditions are not fulfilled, and in all Tris and borate buffers, the pattern of Brdicka currents with Co(III) are quite different from those with Co(II). In such buffers the Co(II) is rapidly reduced at potentials slightly more negative than that at which the Brdicka current attains a peak value. In several such buffers the Brdicka current may then reduced to zero. In buffers of low ionic strength (about 0.02) and with Co(III), small concentrations of alkali salts greatly increase Brdicka currents. When the ionic strength of the buffer is 0.05 M or greater, the effect of alkali salts (up to 0.2 M) is small, but even traces of calcium have a large effect in all buffers with Co(III) as catalyst. Evidence is presented that in the presence of calcium all 17 disulfide groups in bovine-serum albumin are reduced at the dropping mercury electrode. Traces of tetraalkyl salts greatly increase Brdicka currents, but the effects is quite different from that of calcium.
Conditions are described under which the catalytic Brdicka currents observed in ammoniacal buffer solutions containing cobalt(III) hexammine chloride or cobalt(II) and very little bovine-serum albumin (0.1-0.2 muM) are purely kinetically controlled. Under these conditions the kinetic current at pH 9.3-10.3 exhibits a sharp maximum followed by a decrease of the current to a well-defined minimum. The maximum and minimum are eliminated in the presence of 5 mM or more concentrated calcium chloride when a short plateau occurs at the potential of the maximum followed by a well-defined second wave. Both currents are kinetically controlled. When the albumin concentration is 2 muM or greater, the kinetic currents approach diffusion control, the rate of diffusion of cobalt(III) or (II) being close to rate determining. Under these conditions the currents become proportional to the cobalt(III) or (II) concentration in the concentration range between 25 and 200 muM.
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