Increase In Ionic Radius Research Articles

Interaction of lanthanide cations and uranyl ion with the calcium/proton antiport system in Mycobacterium phlei

Uranyl ions (UO 2 2+) and lanthanide cations (La 3+, Nd 3+, Sm 3+, Eu 3+, Tb 3+ and Dy 3+) at 100–200 μM concentration inhibited active transport of Ca 2+, mediated by respiratory linked substrates as well as by ATP hydrolysis, without affecting respiration and membrane-bound ATPase activity, in inside-out membrane vesicles of Mycobacterium phlei. The extent of inhibition in the uptake of Ca 2+, mediated by ATP hydrolysis, increased with increase in ionic radii of these cations. Lanthanide cations did not dissipate the formation of a proton gradient, as measured by determining the effect either on the uptake of [ 14C]methylamine or energy-linked quenching of the fluorescence of 9-aminoacridine. However, uranyl ion (UO 2 2+) caused reversal of the energy-linked quenching of 9-aminoacridine. UO 2 2+ concentration yielding 50% of V max ( S 0.5 ) was approx. 15 μM. Kinetic studies revealed that inhibition in the uptake of Ca 2+ was competitive with UO 2 2+ while non-competitive with rare-earth metals. It is proposed that inhibition in the uptake of Ca 2+ by uranyl ion occurs as a result of UO 2 2+ transport into the interior of vesicles in exchange for protons, while lanthanide cations are not being transported but affect the binding of Ca 2+ to the membrane, presumably to the Ca 2+/H + antiporter.

Reverse osmosis separation of alkaline metal ions through hydrophobic membranes

AbstractA very thin hydrophobic membrane separated alkaline metal ions under a pressure gradient. The membrane was prepared by coating polystyrene or other polymers on a Teflon membrane filter. The permeabilities of alkaline metal ions under a pressure gradient decreased with increasing ion radius, while the diffusion fluxes in a dialysis experiment increased with increasing ion radius. The selectivity was enlarged in the mixed salts solution of a low concentration at a high pressure.

A multinuclear nuclear magnetic resonance study of the monovalent-divalent cation sites of pyruvate kinase.

The effectiveness of measuring distances between monovalent and divalent cation sites on enzymes has been examined by 6Li, 7Li, I4N, 15N, 23Na, 39K, 85Rb, 87Rb, and 133Cs nuclear magnetic resonance (NMR). Measurements were made of the paramagnetic effect of enzyme-bound Mn2+ on the longitudinal spin-lattice relaxation rate ( l/Tl) of the monovalent cations by using MnZ+ at the divalent cation site of pyruvate kinase. Distances from MnZ+ to the monovalent cations in the enzyme-Mn2+-M+ complex are as follows: 6Li+, 8.5 A; 7Li+, 8.4 A; 15NH5+, 7.0 A; 133Cs+, 7.7 A. The mea- sured distances in the enzyme-Mn2+-M+-phosphoenol- pyruvate (PEP) complex are as follows: 6Li+, 5.7 A; 7Li+, 5.7 A; I4NH4+, 4.4 A; 15NH4+, 4.4 A; 133Cs+, 6.0 A. In the complex with PEP, a lower limit distance could be placed on MnZ+ to 23Na+ (24.5 A), 39K+ (23.7 A), and 87Rb+ (24.1 A). These results show a 2-3-A reduction in the distance between MnZ+ and the monovalent cation upon addition of PEP to the enzyme. Additionally, the MnZ+ to monovalent cation dis- A large number of enzymes display an absolute requirement for the addition of a monovalent cation for maximal activity (Suelter, 1970). The most studied enzyme of this group is pyruvate kinase which shows a wide range of maximal ac- tivities depending on the monovalent cation used to activate the enzyme (Kayne, 1973). For example, lithium activates only 2% as well as does potassium. The other monovalent cations are of intermediate activity (Kayne, 1973). It has been observed that the degree of activation of pyruvate kinase by the various monovalent cations appears to correlate with the crystalline ionic radius of these cations. The amount of ac- tivation is found to decrease as the ionic radius increases or decreases relative to that for K+ (Kachmar & Boyer, 1953). However, the precise function of these monovalent cations in catalysis is not known. In an attempt to determine the exact location of the mo- novalent cation site relative to the sites for the other ligands of pyruvate kinase, a number of laboratories have undertaken measurements of the distance from enzyme-bound Mn2+ to the monovalent cation site by using nuclear magnetic resonance (NMR).' Reuben & Kayne (1971) have reported distances of 4.9 and 8.2 A between 205Tl+ and Mn2+ in the enzyme- Mn2+-T1+-phosphoenolpyruvate (PEP) complex and the en- zyme-Mn2+-T1+ complex, respectively. In a 7Li NMR study, Hutton et al. (1977) reported distances of 5.8 and 11 .O A for these enzyme-Mn2+ complexes with 7Li+. Since Li+ activates

Permeability of ionic salts through poly(γ-methyl L-glutamate) membrane

Abstract The permeability of various ionic salts through poly(γ-methyl L-glutamate) (PMLG) membrane, which consists of noncharged α-helical molecules, was studied. Based on the results, the mechanism of ion transport and the degree of hydration of ions in the membrane and their relation to salt rejection is discussed. The permeability coefficient of salt, PS, is almost independent of salt concentration over a wide range of concentration in aqueous solution, which contrasts with the case of charged membranes. The activation energy for PS is about 15 kcal/mole, which is almost half of that for cellulose acetate membranes. The ionic diffusion coefficient Di. decreases with increase of ionic radius, but it does not obey Stokes' law. The behavior is analyzed by the free volume theory, and it is found that the degree of ion hydration in PMLG membranes is depressed especially in the case of strongly hydrated ions in aqueous solution. This fact also explains the good permeability of salt through the rather hydrop...

Infrared spectra of anhydrous alkali metal sulphates

The i.r. spectra of the three main crystalline phases of sodium sulphate stable between ambient temperature and 300°C (Phases V, III and I) and of the ambient temperature phases of potassium, caesium and lithium sulphates have been characterized over the region 4000-200 cm −1. Each spectrum is discussed in relation to the site group approximation. The frequency of the symmetric stretching mode (ν 1) of the sulphate group decreases linearly from 1011 cm −1 to 967 cm −1 with increase in ionic radius through the alkali cation series from Li to Cs.

Ionic Diffusion in Quartz

MORTLEY1 has suggested that diffusion through quartz is limited to small univalent ions and occurs through lattice channels in the 〈 0001 〉 direction, and also that these channels (of radius 1 A) act as an ionic sieve, allowing only the smaller ions to pass. Diffusion is certainly limited to the univalent ions, but it is not restricted to those ions with an ionic radius of 1 A or less. Verhoogen2 has reported the diffusion of potassium (ionic radius 1.33 A), and I have diffused rubidium (ionic radius 1.49 A) and caesium (ionic radius 1.65 A), using an experimental procedure similar to that previously described3. An increase in the size of the ion decreases the conductivity, and it was found that the value for lithium diffusion at 500° C (2 × 10−6 Ω−1 cm−1) is two hundred times that for caesium. The activation energies increase, and the values obtained for alkali diffusion through basal sections of quartz were (kcalories): lithium, 18; sodium, 21; potassium, 28; rubidium, 30; and caesium, 33; each result being the average of many determinations. These values show a linear increase with an increase in ionic radius, and therefore the channels resist the movement of larger ions, but they do not prevent ionic motion.

The Synergistic Effect in Solvent Extraction—The Correlation of the Ionic Radius of Rare Earth Elements with the Stability Constants of Rare Earth Benzoyltrifluoroacetonate Adducts with n-Hexyl Alcohol, TBP and TOPO

Abstract The synergistic effects of n-hexyl alcohol, TBP and TOPO on the extraction of rare earth ions with benzoyltrifluoroacetone in benzene have been studied. The stability constants of the adducts were determined by means of the curve-fitting method. The equation based on the shift of pH1⁄2 (−ΔpH1⁄2) was also employed to analyse the data. The results were discussed in relation to the ionic radius of rare earth elements and summarized as follows: (1) The stability of rare earth benzoyltrifluoroacetonate decreases but that of the adducts increases, as the ionic radius increases. (2) The maximum number of base molecules bonding to one molecule of the metal chelate is 2, except that in the case of lutetium adduct with TOPO, where the formation of secondary adducts is not observed. (3) Although the overall stability constant of the adduct increases in the following order; lutetium < terbium < europium < lanthanum, as mentioned above, the first stability constant does not show such a distinct sequence. Therefore the contribution of the second stability constant seems to be an important factor. (4) Organic bases studied form stable adducts with rare earth benzoyltrifluoroacetonates in the following order; n-hexyl alcohol<TBP<TOPO. This order corresponds to the donating power of lone pair electrons of the oxygen atoms in these compounds.