Concentration Of Adsorption Sites Research Articles

Development of carriers with controlled concentration of charged surface groups in aqueous solutions: II. Modification of γ-Al 2O 3 with various amounts of lithium and fluoride ions

Two series of carriers were prepared by doping γ-Al 2O 3 with various amounts of Li + and F − ions and the point of zero charge (ZPC), the surface acidity constants as well as the concentration of the charged surface groups, AlOH 2 + and AlO − were determined potentiometrically over a wide pH range. It was found that 0.621 mmol Li + per g of γ-Al 2O 3 were sufficient to cause a shift of the ZPC from 5.30 to 9.80. Accordingly, the concentration of adsorption sites for negative species ( AlOH 2 + ) was increased, while the surface acidity constants decreased and the formation of AlO − sites was inhibited. Further increase in the lithium content causes a marked increase in the concentration of the AlOH + 2 groups at pH lower than 8.0. Comparison of the effects caused due to the lithium doping with those observed after sodium modification studied previously, showed that lithium can be used instead of sodium in the cases where the latter causes catalytic deactivation. However, larger amounts of lithium, as compared with that of sodium, are necessary in order for the same increase in the concentration of the AlOH 2 + groups at a given pH to be achieved. A mechanism similar to that adopted for the sodium-doped alumina has been used to explain the Li + effects observed in the present study. Concerning the doping by F − ions it was observed that modification of γ-Al 2O 3 with 0.125 mmol F − per g of γ-Al 2O 3 decreases the ZPC from 5.30 to 3.40. F − doping thus can be used to extend the pH range, where positive species could be deposited on γ-Al 2O 3 by adsorption, at lower pH values. Moreover, this modification brings about an increase in the concentration of the adsorption sites for positive species, AlO − , as well as in the values of the surface acidity constants. Additional increase in the concentration of the F − ions provokes a considerable increase in the concentration of the AlO − groups at pH higher than 3.40 though it does not further affect the values of ZPC and surface acidity constants.

Characterization of oxide-supported ligand-protected osmium cluster catalysts

Os 6(CO) 18 has been impregnated on to silica and on to alumina from non-aqueous solution; the freshly impregnated materials acquire catalytic activity after thermal activation. Ultraviolet/visible diffuse reflectance spectroscopy and extended X-ray absorption fine-structure spectroscopy (EXAFS) have confirmed the presence of metal clusters in both the freshly impregnated materials and in the thermally activated materials. Confirmation has been obtained by examination of infrared absorption spectra in the carbonyl stretching region. The number and nature of the protecting ligands and the concentration of adsorption sites possessed by the catalytically active clusters have been evaluated by (i) the analysis of gases evolved during thermal activation and (ii) conventional adsorption measurements. Structures for the catalytically active clusters await further interpretation of the EXAFS spectra; this work is in progress.

A quantitative study of the biospecific desorption of rat liver (M4) lactate dehydrogenase from 10-carboxydecylamino-Sepharose. Determination of the number of ligand-binding sites blocked on adsorption

1. The theory of Nichol, Ogston, Winzor & Sawyer [(1974) Biochem. J. 143, 435-443] for quantitative affinity chromatography, when adapted for use with a non-specific column from which a multi-site protein can be specifically desorbed by its free ligand, permits determination of the concentration of adsorption sites on the column, their adsorptive affinity (as an association constant) and either the intrinsic (site) constant for ligand-binding to the protein or an 'occlusion coefficient' (defined as the number of ligand-binding sites blocked on adsorption), one of which must be known. 2. The theory has been applied to the NADH-specific desorption of rat liver M4 lactate dehydrogenase from 10-carboxydecylamino-Sepharose. It suggests that most of the enzyme molecules are adsorbed with at least two NADH-binding sites blocked, indicating an extensive adsorption interface in relation to the protein surface. Other chromatographic parameters were also determined for the system. 3. Among topics discussed are (a) factors affecting the experimentally determined value for the number of blocked sites, (b) the nature of the adsorption sites on the column and (c) the similarity of the analysis to that for determining Hill coefficients, and other possible applications.

Adsorption of Phosphate on Synthetic Silica–Alumina Possessing Lewis-acid Sites

Abstract It was confirmed from measurements of the adsorption isotherms of phosphates in aqueous solutions that there were adsorption sites with very high reactivity on the surface of silica–alumina. The concentration of adsorption sites which is estimated from the adsorption amount extrapolated to zero equilibrium concentration is nearly twice the concentration of Lewis-acid sites for silica–alumina of higher alumina content. Furthermore, the concentration of phosphate adsorbed on the surface of various silica–alumina is relatively well correlated with the concentration of Lewis-acid sites.

Superficial migration of tritium physisorbed on monocrystalline nickel (111)

Abstract The aim of this study is the measurement of superficial migration coefficient of tritium physisorbed on monocrystalline nickel without chemisorbed sublayer. The chosen crystalline orientation was (111) because it offers the greatest concentration of adsorption sites per square centimeter. A clean surface sample is obtained by mechanical polishing, chemical etching and finally ionic bombardment by high purity argon gas. The pressure in the experimental vessel is maintained below 10 −9 torr, by liquid helium cryopumping after zeolite sorption pumping. A little spot of adsorbed tritium is produced by introduction of a finite amount of tritium gas on the clean surface of the nickel sample through a stainless steel tube. Temperatures of nickel and of the gas introduction tube are respectively regulated at 5 K and 35 K. Tritium is used as a radioactive marker and its 10 keV β-radiation is measured by a channeltron type detector which permits the localization of the deposit without acting on the surface. We observed that tritium sorbed at 5 K is quite immobile (at the time scale of our experiment). After heating up to a fixed temperature T chosen between 10 K and 20 K, the deposite profile variation in function of time is observed to determine the superficial diffusion coefficient D . For the values of T from 13 K to 20 K, D varies from 10×10 −6 to 150×10 −6 cm 2 sec −1 . A diffusion activation energy of 200 cal mole −1 is deduced from the exponential increase of the curve. A vibrational frequency can be evaluated to 3×10 12 sec −1 . The rate of desorption permits the evaluation of sorption energy at about 1800 cal mole −1 in good agreement with usual results concerning physorption of H 2 on metals.

Studies on Ion Distribution in Living Cells: II. Cooperative Interaction between Intracellular Potassium and Sodium Ions

New steady levels of K(+) and Na(+) ion in frog sartorius muscle were reached in 72 hr at 25 degrees C in environments containing 100-mM Na(+)-ion and K(+)-ion concentrations varying from near zero to 10 mM. These steady levels follow a pattern predicted by a cooperative adsorption isotherm presented in 1964. From a total of 13 sets of experiments carried out over a five year period, the average concentration of adsorption sites is 109 mumoles/g of fresh cells. The average intrinsic equilibrium constant for the Na --> K exchange is 135, and the average free energy of nearest neighbor interaction is 0.54 kcal/mole. These values are in good agreement with those obtained by Jones and Karreman from studies on canine carotid arteries.

Studies on ion accumulation in muscle cells.

A comparison is made between the quantitative predictions of equilibrium ionic distribution in living cells according to the membrane theory (Donnan equilibrium) and according to the association-induction hypothesis. This comparison shows that both theories predict competitive effects of one permeant ion on the equilibrium concentration of another permeant ion; but within the limit of experimental accuracy only the association-induction model predicts quantitatively significant specific competition of one specified ion with the accumulation of another specified ion. The equilibrium distributions of K(+), Rb(+), and Cs(+) ions in frog sartorius muscle were studied and quantitatively significant specific competition was demonstrated; these results favor the association-induction hypothesis (adsorption on cell proteins and protein complexes and partial exclusion from cell water). Based on this model we estimated that at 257deg;C, the apparent association constants for K(+), Rb(+), and Cs(+) ion are 665, 756, and 488 (mole/liter)(-1). We found that the total concentration of adsorption sites (no less than 240 mmole/kg of fresh cells) agrees with the analytically determined concentrations of beta- and gamma-carboxyl groups of muscle cell proteins (260 to 288 mmole/kg).