Jun Nishimoto

Ion-Pair Extraction of Metalloporphyrins into Acetonitrile for Determination of Copper(II)

Equilibrium study of ion-pair extraction of a cationic water-soluble porphyrin [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H(2)tmpyp(4+)] and its metalloporphyrins (MP) into the acetonitrile layer, separated by addition of sodium chloride (4.00 mol dm(-)(3)) to a 1:1 (v/v) acetonitrile-water mixed solvent, was carried out to develop a new and useful method for the determination of a subnanogram amount of copper(II). M denotes Zn(2+), Cu(2+), Co(3+), Fe(3+), and Mn(3+), and P(2)(-) is porphyrinate ion. The extraction and dissociation constants of the ion-pair complexes, defined by K(ex) = [MP(ClO(4))(4)](org)[MP(4+)](aq)(-)(1)[ClO(4)(-)](aq)(-)(4), K(dis,1) = [MP(ClO(4))(3)(+)](org)[ClO(4)(-)](org)[MP(ClO(4))(4)](org)(-)(1), and K(dis,2) = [MP(ClO(4))(2)(2+)](org)[ClO(4)(-)](org)[MP(ClO(4))(3)(+)](org)(-)(1), were determined by taking into account the partition constant of sodium perchlorate (K(D) = 1.82 ± 0.01). The equilibrium constants were found to be K(ex)K(dis,1) = (7.2 ± 1.3) × 10(4), (6.4 ± 0.9) × 10(4), (1.35 ± 0.13) × 10(5), (4.8 ± 0.6) × 10(3), (1.23 ± 0.05) × 10(4), and (1.42 ± 0.07) × 10(3) at 25 °C for the free base porphyrin (H(2)tmpyp(4+)) and the metalloporphyrins of zinc(II), copper(II), cobalt(III), iron(III), and manganese(III), respectively. The K(dis,2) values were (2.9 ± 1.4) × 10(-)(2), (3.1 ± 1.1) × 10(-)(2), (8.0 ± 4.9) × 10(-)(3), and (5.1 ± 2.2) × 10(-)(2) for the free base porphyrins and the metalloporphyrins of zinc(II), copper(II), and cobalt(III), respectively. The results were developed for determination of a trace amount of copper(II) (3 × 10(-)(8)-4 × 10(-)(6) mol dm(-)(3)) in natural water samples using H(2)tmpyp(4+) with a molar absorptivity of 3.1 × 10(5) mol(-)(1) dm(3) cm(-)(1) at a precision of 1.3% (RSD). The determination of copper(II) was not interfered by the presence of 10(-)(4) mol dm(-)(3) of Mn(2+), Co(2+), Ni(2+), Hg(2+), Cd(2+), Ag(+), Cr(3+), V(5+), Al(3+), Mg(2+), Ca(2+), Br(-), I(-), SCN(-), and S(2)O(3)(2)(-) and 10(-)(5) mol dm(-)(3) of Fe(3+), Zn(2+), and Pd(2+).

Strongly polarized water at the interfacial region in reversed micelles containing 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) as a probe

The change in the polarization of water in sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) reversed micelles has been investigated spectrophotometrically using 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) cation, [Ni(tmc)]2+, as a probe of electron-pair acceptance. Although above a water-to-AOT molar ratio (R) of 10 the spectrum of [Ni(tmc)]2+ is very similar to that in bulk water, below R= 10 the peaks of the five-coordinated complex shift to longer wavelengths and at R≈ 1 the spectrum is very similar to that of the hydroxide ion-coordinated complex. This shows that a decrease in the R value obviously leads to a gradual increase in the polarization of water coordinated to [Ni(tmc)]2+ owing to the cooperative influence of the sulfo ion of AOT and [Ni(tmc)]2+ through hydrogen bonding at the water/surfactant interface.

Increased basicity and hydrogen-bonding donor ability of water by hydrogen bonding to dimethyl sulphoxide and its coordination to 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) in nitrobenzene

The axial coordination of the four-coordinated 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) cation ([Ni(tmc)]2+) by water which is hydrogen-bonded to dimethyl sulphoxide (DMSO) has been investigated spectrophotometrically in nitrobenzene (NB) containing < 0.05 mole fraction DMSO at 25 °C. Although water in NB is only weakly coordinated to the cation, water which is hydrogen-bonded to DMSO in NB can be easily coordinated to form the five-coordinated [Ni(tmc)(WS)]2+ cation with a coordination constant of 24.0 dm3 mol–1, where W is water, S is DMSO, and WS is the 1:1 water–DMSO species H—text-decoration:underlineO—H⋯S. (—text-decoration:underlineO— is the coordinating oxygen atom and the formation constant for WS was determined by using NMR methods.) The residual hydrogen atom of the coordinated water in WS can be hydrogen-bonded to further species, including additional DMSO and either WS or NB-solvated water, to form two additional kinds of five-coordinated complexes: [Ni(tmc)(WS–S)]2+ and either [Ni(tmc)(WS—WS)]2+ or [Ni(tmc)(WS—W)]2+, where WS–S is S⋯H—text-decoration:underlineO—H⋯S, WS—WS is S⋯H—text-decoration:underlineO—H⋯OH—H⋯S, and WS—W is S⋯H—text-decoration:underlineO—H⋯OH—H. The corresponding equilibrium constants for the hydrogen bonding of water were 1.5 dm3 mol–1 for WS, 12.3 for [Ni(tmc)(WS–S)]2+, 8.6 for [Ni(tmc)(WS—WS)]2+ and 1.3 for [Ni(tmc)(WS—W)]2+. The increased hydrogen-bonding donor ability and basicity are discussed in terms of polarization of the O—H bond through hydrogen bonding and coordination.

Cooperative interactions between ions and water in the chloride ion and water coordination to a square-planar nickel complex ion in concentrated aqueous solutions

In concentrated aqueous solutions (1–6 mol dm–3) of various kinds of salts such as sodium chloride, calcium chloride, tetramethylammonium chloride and sodium perchlorate, salt effects on coordination of the chloride ion and water to [Ni(tmc)]2+(tmc: 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) have been investigated spectrophotometrically. In water at 25 °C 63% of the nickel complex is coordinated by water as a five-coordinate species. Addition of perchlorates to the complex solution decreases the fraction of the five-coordinate complex without shifting the absorption peaks and 6.5 mol dm–3 perchlorate gives 100% of the four-coordinate species. With sodium chloride, the fraction of the four-coordinate species is increased with concomitant red shifts in wavelength and decreases in absorbance at the absorption peaks for the five-coordinate species. On the other hand, tetramethylammonium chloride decreases the fraction of the four-coordinate species with similar red shifts of the five-coordinate peaks. The red shift is attributed to coordination of the chloride ion. The different effect caused by sodium chloride compared with tetramethylammonium chloride is discussed in terms of the difference in cooperative interactions between the chloride ion and the counter-cations through hydrated water molecules.

Equilibrium studies on lithium(I) transfer into ionic liquid with a water-soluble octabromoporphyrin (H2(OBTMPyP)4+) from aqueous phase

A water-soluble octabromoporphyrin 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (H2(OBTMPyP)4+), H2P4+) and its lithium complex, Li(OBTMPyP)3+, (LiP3+), transferred quantitatively to an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+PF6-) with no addition of other counter ions. The acid-dissociation constants of H2(OBTMPyP)4+ between aqueous and BMIM+PF6- phases were determined spectrophotometrically and found to be 10-7.67 and 10-11.33 at I = 0.1 for Ka1,IL = [H+]aq[HP3+]IL/[H2P4+]IL and Ka2,IL = [H+]aq[P2+]IL/[HP3+]IL, respectively. Since the acid-dissociation constants involve the partition of H2(OBTMPyP)4+ between aqueous and IL phases, the determined values are ten times as low as those observed in aqueous solution. The transfer equilibrium constants of LiP3+ and NaP3+ to IL defined by KMP,IL = [MP3+]IL/[M+]aq[P2+]IL (M = Li+ or Na+) were found to be 104.83 and 101.31 for KLiP,IL and KNaP,IL, respectively. LiP3+ transferred selectively in the presence of Na+ (KLiP,IL/KNaP,IL = 103.52) to IL phase through an ion-exchange mechanism between BMIM+PF6- and Li(OBTMPyP)3+.