Concentrated LiCl Research Articles

Radiolysis of concentrated solutions. 2. Pulse and .gamma.-radiolysis studies of direct and indirect effects in lithium iodide solutions

In the preceding study of the radiolysis of concentrated aqueous LiCl solutions, one of the hypotheses used to explain the apparent inefficacy of Cl/sub 2//sup -/ formation by the direct effect was that molecular chlorine, not detectable by spectrophotometry, could be formed during the early stages of water radiolysis. Such an hypothesis is confirmed here for pulse and ..gamma..-radiolysis of concentrated aqueous neutral LiI solutions. Indeed, it is shown that, 10 ns after the pulse, molecular iodine, detected as I/sub 3//sup -/, is formed with a yield that increases with the LiI concentration. The experimental results yields values of 4.8 and 7.3 respectively for the indirect and direct effects of total oxidation G/sub I/sub 2//sup -// + 2G/sub I/sub 3//sup -//. This last high value is discussed.

Photoelectron emission from metal into concentrated electrolytes: Part II. Thermalization path-length of low-energy electrons and eaq− bulk reactions

Laser-induced photoelectron emission from metal into electrolyte solutions has been used for determining thermalization path-lengths ( l) of low-energy (0.5 eV⩽ E⩽2.7 eV) electrons, as well as absolute rate constants of reactions e aq −+N 2O and e aq −+ e aq − ( K a and K c, respectively) in aqueous solutions with varying concentration of KCl (0.25 M-4.15 M), CsCl (0.5 M-6.8 M), and LiCl (0.5 M-14 M). Two regions of l ( E) dependences have been observed in all solutions: l remains approximately constant at E≲2.2 eV and does not depend on composition of solution. viz. l=2.7±0.6 nm. Increase of l takes place in the range 2.2–2.7 eV, diminishing with electrolyte concentration. The observed l ( E) dependence is attributed to different mechanisms of energy losses. At E≲2 eV the resonance electron scattering from water molecules provides the main mechanism of thermalization. The dipol e mechanism of slowing down is preferred at E>2.2 eV. The decrease of l, observed in this energy range at higher electrolyte concentration, can be connected with electron scattering from ions. K a and K c are shown to be inversely proportional to viscosity (η) of solution, expect for concentrated LiCl solutions for which K aη increases with c at c>10 M, whilst K cη decreases at c≳5 M. The results obtained lead to the conclusion that the reaction ( e aq −+N 2O) is a diffusion-controlled one, the reaction diameter being independent of the properties of solution. Changes in K aη take place only when all water molecules are included in hydration shells of ions. The decrease in K c with rise in c is attributed to transition from the diffusion region into the kinetic one at c≳5 M, at which association of ions leads to changes in e aq − cluster structure.

Microwave dielectric relaxation of water in hydrated melts: system Ca(NO3)2.4H2O

The microwave complex permittivities of hydrated melts of composition Ca(NO3)2 3.9 H2O, in the frequency range 8.2–79 GHz, and temperature range 40–55°C, are reported. The real and imaginarry coefficients of the complex permittivity show a dielectric relaxation process, which can be described in most of the frequency range by a Debye function for a single relaxation. Some deviation becomes apparent, however, at the upper end of the frequency range investigated. Eyring plots of the inverse of the relaxation time vs the inverse of temperature give the activation parameters for the process. The latter is interpreted as due to the rotation of water in the melts, all the water being probably coordinated with the cations. Compared to the activation parameters in pure water one notices an increase in both the enthalpy and entropy of activation. An increase in the activation energy in concentrated aqueous LiCl has been already reported in the literature.

Oxygen Isotope Fractionation and the Structure of Aqueous Alkali Halide Solutions

Abstract The oxygen isotope effects between H2O and D2O solutions of various alkali-halides and the respective pure solvents have been measured by means of the CO2 equilibration technique. In general, the effects for H2O are smaller than those for D2O. With "hydration numbers" estimated from the angular distributions of the water dipoles around the ions obtained from MD-simulations and with the plausible assumption that in highly concentrated LiCl solutions the effect is purely cationic, the measured effects are separated into effects between the hydration shells of the individual ionic species (Li, Na, K, Cs, CI, Br, I) and bulk water. The cationic effects thus obtained are compared with the corresponding effects between free water-cation-pairs and bulk water calculated on the basis of the energy surfaces published by Kistenmacher et al. It is found that, in general, the trends coincide but the former effects are smaller than the latter ones.

Conformation and reactivity of DNA: VI. Circular dichroism studies of salt-induced conformational changes of DNAs of different base composition

The CD of various DNAs over a wide range of base composition has been measured in different alkali salt solutions. The salt-induced changes of the CD spectra depend on base composition and on the nature of the cation and anion of the supporting salt in the solution. Very different CD spectra, typical for d(G · C)-rich and d(A · T)-rich DNA, are obtained in concentrated LiCl solution, but the nature of CD changes (depression of the positive CD band with almost no change to the negative band) are similar. In the presence of the salts investigated, LiCl, NaCl, CsCl and NaClO 4, the CD amplitudes are lowered monotonically with increasing salt molarities. In the presence of high concentrations of NaClO 4 and trifluoroacetate relatively high CD amplitudes appear, particularly for d(G · C)-rich DNA compared to the very weak CD maxima under the action of chloride or acetate. The variation of the CD amplitude at 267 and 283 nm as a function of decreasing water activity coefficients indicates that very d(A · T)-rich DNA is relatively less changed in comparison to DNA of high and medium G+C content. In the presence of NaClO 4, however, changes of d(G · C)-rich DNA are also weak in contrast to NaCl at the same water activity. The base-composition dependent conformational changes found at reduced water activity are explained by the different abilities of d(A · T)-rich and d(G · C)-rich regions to undergo the B- to C-like transition, which in turn may be interpreted by different abilities to increase the helix winding angle. Thus certain d(A · T)-rich regions seem to be restricted to an increased helix winding. Comparison with poly(dA) · poly(dT) and poly(dA-dT) · poly(dA-dT) shows that long homooligonucleotide sequences are probably responsible for this restriction while alternating structures tend to increase the helix winding. The differential effects of anions on CD spectra show a close correlation to their effectiveness in decreasing the activity coefficients of the bases as reported by Robinson, D.R. and Grant, M.E. (1966) J. Biol. Chem. 241, 4030–4042. Different melting temperature changes produced by those salts agree with their results. Thus the perchlorate-induced conformational variations are interpreted in terms of unwinding of the double-helical structure by an influence of the polar anions with the primary (phosphate sites) and secondary (bases) hydration sites.

Chemiluminescence analysis for trace pollutants.

Abstract The sensitivity of luminol chemiluminescence to small catalyst concentrations can be exploited for environmental analysis in several ways. Selective methods for Cr(III) and Fe(II) in complex solutions have been applied to natural samples. The detection limits are 0.03 mcg/l and 0.005 mcg/l, respectively. Species that do not catalyze luminol chemiluminescence can be determined by titration with reagents that catalyze the reaction. For example, arsenic and aqueous sulfur dioxide can be titrated with iodine, an efficient catalyst. MnO4-, OCl-, V(II), and Cr(II) are other catalysts that can be used as titrants. Preliminary ion exchange separation in concentrated LiCl solutions extends chemiluminescence to other catalysts of the luminol reaction: Ni(II), Co(II), Mn(II), Cu(II), and V(IV).

Light Scattering in Aqueous LiCl Solutions; Evidence for a Low Temperature Immiscibility

Rayleigh and Brillouin light scattering spectra have been obtained in a number of concentrated aqueous LiCl solutions. The scattering from density fluctuations shows the dispersion effects typical of viscoelastic relaxation as the temperature is decreased. In the same temperature region the Rayleigh scattering associated with fluctuations in concentration becomes quite intense. This is interpreted as portending the presence of a miscibility gap in the LiCl–H2O system. The upper consolute temperature associated with this immiscibility is quite near the glass transition region so that no large-scale phase separation can be seen. In addition it appears there is yet another mechanism producing Rayleigh scattering in the solutions. We have tentatively identified this as arising from fluctuations in the order parameter(s) describing the progress of ionic hydration reaction(s).

Comparison of Shear and Conductivity Relaxation Times for Concentrated Lithium Chloride Solutions

Shear viscosity measurements over the temperature interval 23 –− 124 °C (5×10−2– 108 P) and shear impedance measurements at 88 MHz over the interval −75–−130°C have been performed for concentrated aqueous lithium chloride solutions in the concentration range R=4.49 – 5.77 where R is the mole ratio of water to salt. Average shear relaxation times, 〈 τs 〉, have been calculated from these results and compared with average conductivity relaxation times, 〈 τσ 〉, reported previously by Moynihan, Bressel, and Angell. 〈 τs 〉 and 〈 τσ 〉 are within 30% of one another at the low viscosity end ( ∼104 P) of the range of comparison, but at higher viscosities the 〈τs 〉/〈τσ 〉 ratio becomes significantly larger than unity (2–3 at the highest viscosities for which data are available). Estimated 〈τs 〉/〈τσ 〉 ratios for other ionic liquids suggest that the occurrence of 〈τs 〉/〈τσ 〉 ratios greater than unity at high visosities may be a common phenomenon. Description of the shear relaxation process for concentrated LiCl—H2O solutions is found to require a fairly broad, asymmetric (Cole—Davidson) distribution of relaxation times.

Biosynthesis of 50 s ribosomal subunit in Escherichia coli

Two intermediate particles of 50 s ribosome formation, i.e. [30 s]- and 40 s nascent or precursor particles, were isolated from exponentially growing Escherichia coli cells. Particles indistinguishable from these nascent ribosomal particles were found in the extracts of the cells treated with a low concentration of chloramphenicol. The [30 s]-particles contain undermethylated 23 s rRNA and three main protein components. The 40 s particles also possess undermethylated 23 s rRNA and, in addition to the three protein components found in the [30 s]-particles, 9 other components out of 19 components detectable in the 50 s ribosomal subunit. Both particles include little 5 s RNA. Based on the above findings, a scheme for the biosynthesis of 50 s ribosomal subunits is presented. The protein compositions and 5 s RNA contents of the nascent ribosomal particles are compared with those of protein-deficient particles obtained by exposing 50 s ribosomal subunits to a concentrated LiCl solution. The molecular compositions of these two kinds of particles are found to be similar, but not exactly the same.

Release of ribosomal proteins from Escherichia coli ribosomes with high concentrations of lithium chloride.

Abstract The sequential release of ribosomal proteins from Escherichia coli ribosomes under the influence of concentrated LiCl solutions was studied. Treatment of 50 s or 30 s ribosomal subunits with various concentrations of LiCl containing 2.5 × 10 −2 m -Tris buffer (pH 7.8) and 10 −1 m -magnesium acetate or 5 × 10 −3 m -EDTA produced a series of protein-deficient particles having sedimentation coefficients of 40, 36, 28 and 25 s (from a 50 s subunit), and of 25, 23, 21, 19 and 16 s (from a 30 s subunit). The protein components of these particles have been analysed by carboxymethyl-cellulose column chromatography. It was shown that release of protein from ribosomes does not occur in a random fashion but follows a certain definite order. Furthermore, this release proceeds in more or less discrete steps as already pointed out by Lerman, Spirin, Gavrilova & Golov (1966). Ribonucleoprotein particles having a single (or two) protein component are obtained by exposing the 30 or 50 s ribosome subunits to 3.5 m -LiCl in the absence of magnesium ions for 82 hours.

Alpha radiation effects on concentrated LiCl solutions containing HCl, and the use of methanol as an inhibitor of acid radiolysis

The principal effect of alpha radiation on 1 10 M LiCl-0·02 M HCl solution is the loss of approximately 0·1 mole of HCl per day for each litre of solution exposed to 10 W of radioactivity. Methanol completely inhibited the loss of acid due to radiolysis and nearly stopped the production of radiolytic gases.

THE ACIDITY FUNCTION, H0, IN AQUEOUS CONCENTRATED ACID AND SALT SOLUTIONS

Some H0 measurements in concentrated LiCl solutions are reported. It is shown that the H0 values in 1–9 M LiCl, 1–9 M HClO4, and 1–11 M HCl solutions can be calculated using the equation[Formula: see text]where aw is the activity of water, C is either the molar or molal concentration, and n and B are least-squares constants. Values of n = 2 (molar equation) and n = 1 (molal equation) fit the experimental data better than does n = 4. With the molar equation a non-integral value of n for HClO4 is required to give reasonable H0 values. The adequacy and significance of integral and non-integral values of n are considered. The nature of the constant B is also discussed. A more general equation is developed which under certain conditions reduces to the simpler equation. The more general equation is based upon a model which assumes the existence of more than one hydrated form of the indicator base, its conjugate acid, and H3O+. Some of the implications of this more general equation are considered

Structure in Ionic Solutions. II

The diffraction patterns of concentrated KOH and LiCl solutions have been analyzed. The results indicate that the hydration number for the OH— ion is 6. Previous work on less concentrated KOH solutions had indicated a hydration number of 4 for the K+ ion and a substitutional entry of the cation into the water lattice. The present work agrees with these findings. The dissolution process in LiCl appears to be of a different nature, in that there is a breakdown of the water structure, probably caused by the Li+ ion. The water molecules and the hydrated Li+ ions then pack around the large Cl— ion to give an apparent hydration member for Cl— of 8–9.