Effects of Electrolytes on the Configuration Change of Cobalt(II)-Halide Complexes in Chloroform/Water Reverse Micelle Systems

Abstract

As nanometer-size water droplets or "water pools," relatively large amounts of water can be stabilized in nonpolar organic solvents by a variety of surfactants; this kind of micelle system is called a reversed or reverse micelle. 1 The size of the "water pool" may vary from ~1 nm to ~10 nm, as a linear function of the W value, where W = [H2O]/[surfactant]. 1,2 The "water pools" provide very specific reaction fields; many studies have demonstrated that the water in "water pool" in reverse micelles considerably differs from that of normal water. 1,3 The extraction of proteins using reverse micelles has received great attention in the field of bioseparation. 4 At W > 12, the character of the water in the "water pool" remains that of normal water. However, at W < 6, almost all water molecules may lose their character as bulk water; 3b such water has been regarded as bound water.Recently, Shervani and Ikushima 5 demonstrated that the ET(30) value in the core region of water/AOT/SC ethane micelles at W = 1.0 corresponds to that in pure ethanol (ET(30) = 51.9, cf. 63.1 for bulk water), 6 where AOT represents the sodium salt of bis(2-ethylhexyl)-2-sulfosuccinate and SC ethane means supercritical ethane.Shirota and Horie 7 have investigated the solvation dynamics of nonaqueous (methanol and acetonitrile instead of H2O) reverse micelles. The solvation dynamics of methanol in reverse micelles depended strongly on the ratio of w; however, the solvation dynamics of acetonitrile in reverse micelles was independent of w, where w = [polar solvent]/[AOT]. They concluded that the different features of the solvation dynamics would be attributed to the role of the hydrogen bonds in methanol and its absence in acetonitrile. The neutron scattering data for the (water + NaCl)/AOT/heptane system have appeared to show that the droplet size is increased by the presence of an electrolyte. 8 We have proposed a model for water containing highly concentrated salts. 9 In a highly concentrated salt solution (≥ 5 mol dm -3 ), too many ions are present to be fully solvated by H2O molecules. Under such extreme conditions, the network by hydrogen bonding of the solvent may almost be destroyed. Isolated molecules of H2O are very different from bulk water (H-O-H); they could behave just as an "alcohol" ([R](H)-O-H), or even as "dihydrogen ether" ([R](H)-O-(H)[R]).10 Our model for water containing highly concentrated salts has been supported by the Raman spectra of D2O containing concentrated Et4NBr. With this model, concentrated salt effects on the solvolysis rates of aliphatic halides and related compounds (RX) in organic solvent-water mixed media, such as methanol-H2O, 9 acetone-H2O, 11 1,4-dioxane-H2O, 10 and acetonitrile-H2O, 12 have been successfully elucidated. In addition, an expansion of the use of the Hammett equation for salt effects has been proposed. 10On the other hand, we have conclusively

Evaluation of Colloids and Activation Agents for Determination of Melamine Using UV-SERS

“…This observed Raman signal increase upon addition of a salt might be due to solvation or changes in the pH value. Similar observations have been reported by Nagayama et al, who observed intensity changes within the Raman spectrum of D 2 O upon addition of LiBr.…”

“…This observed Raman signal increase upon addition of a salt might be due to solvation or changes in the pH value. Similar observations have been reported by Nagayama et al, 42 who observed intensity changes within the Raman spectrum of D 2 O upon addition of LiBr. Figure 4B−E summarizes the results of the influence of an activation salt in combination with a metal colloid on the observed melamine Raman peak area at 685 cm −1 .…”

Great Enhancement in the Oxidation Ability of Dilute Nitric Acid in Nanoscale Water-Droplets of Reverse Micelle Systems

“…8 we observed that a rather strong yellow-color developed only when (dilute) nitric acid was present in Br À ion rich conditions; the possibility of formation of yellow-colored cobalt(II) and cobalt(III) complexes was denied by our careful examination of many cobalt complexes. Kimura et al 20,21 have reported the reactions of nitrous and phosphinic acids with the iodide ion in the presence of molecular oxygen in acidic solutions.…”

“…The amounts of acidic impurities (e.g., R 3 NH þ ) in CTAB and CTAC were evaluated to be %0:03 and %0:05 mol %, respectively. 8 Chloroform was obtained from Wako and Aldrich as GR grade and ACS reagent grade, containing 0.3-1.0% ethanol and amylenes as the stabilizer, respectively. The chloroform containing ethanol as the stabilizer was used in the experiments, unless otherwise stated.…”

“…7 We have been studying the structure of water in nanoscale water-droplets of reverse micelles, stabilized by surfactants in organic solvents. 8 The size of the ''water-pool'' or ''water-droplet'' may vary from 1 to %100 8 It is well known that the properties of water localized in the interior of reverse micelles differ from those of bulk water, and the difference becomes progressively smaller as the amount of water in the micelle system increases.10 …”