Barium azacryptand sodide,the first alkalide with an alkaline Earth cation,also contains a novel dimer, (Na(2))(2-)

The first barium sodide, with stoichiometry Ba(2+)(H(5)Azacryptand[2.2.2](-))Na(-).2MeNH(2), was synthesized by the reaction of Ba, Na, and H(6)Azacryptand[2.2.2] in NH(3)-MeNH(2) solution. It was characterized by X-ray crystallography, (23)Na MAS NMR, hydrogen evolution, DSC, optical spectroscopy, and magnetic susceptibility. This is the first sodide in which the sodium anions form (Na(2))(2)(-) dimers. Previous theoretical predictions were verified by a calculation of the potential energy curve for the dimer in the field of the surrounding charges, whose positions were determined from the crystal structure.     

Inverse sodium hydride: density functional theory study of the large nonlinear optical properties

"Inverse sodium hydride" (AdzH(+)Na-) is an alkalide compound synthesized in recent experiments containing the unusual charge distribution H+ and Na- (inverse charge state). The new class of compounds interests scientists to investigate their especial structures and properties. In this paper, the structures of three alkalides compounds, (Me)3NH(+)Na-, AdzH(+)Na-, and AdzLi(+)Na-, have been obtained in theory. Especially, the structure of AdzLi(+)Na- is still researched by experimental scientists. We investigated the NLO properties of the alkalides complexes for the first time and found that inverse sodium hydride AdzH(+)Na- has a considerably large NLO response beta0 = 5.7675 x 10(4) au by density functional theory (DFT). To understand the essential features of the large NLO properties, four related systems have been also calculated. Their first hyperpolarizabilities are beta0 = 7.357 x 10(3) au for (Me)3NH(+)Na-, beta0 = 3.9 au for (Me)3NH+, beta0 = 1.10 x 10(2) au for (Me)3NH(+)Cl-, and beta0 = 6.20681 x 10(5) au for AdzLi(+)Na-, respectively. By comparing, we found that, first, the Na- anion plays a crucial role in the considerably large first hyperpolarizability of inverse sodium hydride and, second, the first hyperpolarizability of inverse sodium hydride increases with the charge value of the sodium anion. The above results are useful for designing potential NLO materials.     

Novel acetate polyoxomolybdate "host" accommodating a zigzag-chainlike "guest" of five edge-shared sodium cations: Na(21)[[Na(5)(H(2)O)(14)]within[Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]].CH(3)COONa. approximately equal to 95H(2)O

A novel ESR-silent polyoxomolybdate Na(21)([Na(5)(H(2)O)(14)][Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]).CH(3)COONa.approximately equal to 90H(2)O (3) was simply synthesized in high yield by reducing an acidified aqueous solution of Na(2)MoO(4).2H(2)O and CH(3)COONa.3H(2)O. The structure of 3 is constructed by a 46-member crown-shaped anion, [Na(5)(H(2)O)(14)]within[Mo(V)(20)Mo(VI)(26)O(134)(OH)(10)(mu-CH(3)COO)(4)](21-), 3a, which is built up by three different but related building blocks in a new mode and further connected into layers via Na(+) and hydrogen bonds. Crystal data of compound 3: triclinic space group P(-1); a = 16.4065(3), b = 17.4236(2), c = 20.8247(3) A; alpha= 87.57, beta= 67.9810(10), gamma= 80.6970(10)o; V = 5445.08(14) A(3); Z = 1; D(calcd) = 2.902. Structure solution and refinement are based on 19014 reflections, R = 0.0750.     

The competitive adsorption of counter-ions at the surface of anionic surfactants solution

We have determined the surface excess of surface active anion and counter-ions in a non-aqueous polar solution of anionic surfactants blends, as well as their distributions near the solution surface. The blends of two anionic surfactants, sodium dodecyl sulfate (SDS) and cesium dodecyl sulfate (CDS), with different contents were used as solutes to prepare the solutions. According to the isotherms that are separately fitted to the pure SDS and the pure CDS solutions (C. Wang and H. Morgner, Langmuir, 2010, 26, 3121), CDS has a slightly but significantly higher surface excess than SDS (CDS is 14.8% higher) at the concentration of 0.04 molal kg(-1) solvent. Therefore, in this work we chose 0.04 molal kg(-1) solvent as total anion concentration and varied the contents of surfactants. From present experimental results, we found that the surface excess of anion increases slightly with the CDS in the bulk content. Importantly, the fractions of Cs(+) in cationic surface excess are higher than its contents in the bulk for all three solutions. This demonstrates that Cs(+) is more competitive than Na(+) in the adsorption. The surface structure of the solutions have been characterized by concentration-depth profiles, of Cs(+), Na(+) and of sulfur which is used to identify dodecyl sulfate. Those profiles evidence that Cs ions penetrate deeper than sodium ions into the layer formed by the heads of the anions, reducing the electrical potential of the surface more efficiently. This can be used to explain the adsorption competition between those two counter-ions. The cause that makes Cs(+) more competitive than Na(+) in the adsorption can be attributed to its less tightly bound solvation shell, and thus, to its effectively smaller ion size.     

Monovalent ion adsorption at the muscovite (001)-solution interface: relationships among ion coverage and speciation, interfacial water structure, and substrate relaxation

The interfacial structure between the muscovite (001) surface and aqueous solutions containing monovalent cations (3 × 10(-3) m Li(+), Na(+), H(3)O(+), K(+), Rb(+), or Cs(+), or 3 × 10(-2) m Li(+) or Na(+)) was measured using in situ specular X-ray reflectivity. The element-specific distribution of Rb(+) was also obtained with resonant anomalous X-ray reflectivity. The results demonstrate complex interdependencies among adsorbed cation coverage and speciation, interfacial hydration structure, and muscovite surface relaxation. Electron-density profiles of the solution near the surface varied systematically and distinctly with each adsorbed cation. Observations include a broad profile for H(3)O(+), a more structured profile for Li(+) and Na(+), and increasing electron density near the surface because of the inner-sphere adsorption of K(+), Rb(+), and Cs(+) at 1.91 ± 0.12, 1.97 ± 0.01, and 2.26 ± 0.01 ?, respectively. Estimated inner-sphere coverages increased from ~0.6 to 0.78 ± 0.01 to ~0.9 per unit cell area with decreasing cation hydration strength for K(+), Rb(+), and Cs(+), respectively. Between 7 and 12% of the Rb(+) coverage occurred as an outer-sphere species. Systematic trends in the vertical displacement of the muscovite lattice were observed within ~40 ? of the surface. These include a <0.1 ? shift of the interlayer K(+) toward the interface that decays into the crystal and an expansion of the tetrahedral-octahedral-tetrahedral layers except for the top layer in contact with solution. The distortion of the top tetrahedral sheet depends on the adsorbed cation, ranging from an expansion (by ~0.05 ? vertically) in 3 × 10(-3)m H(3)O(+) to a contraction (by ~0.1 ?) in 3 × 10(-3) m Cs(+). The tetrahedral tilting angle in the top sheet increases by 1 to 4° in 3 × 10(-3) m Li(+) or Na(+), which is similar to that in deionized water where the adsorbed cation coverages are insufficient for full charge compensation.     

Surfactant behavior of "ellipsoidal" dicarbollide anions: a molecular dynamics study

We report a molecular dynamics study of cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)X(3))(2)Co](-) (XCD(-)) commonly used in liquid-liquid extraction (X = H, Me, Cl, or Br), showing that these anions, although lacking the amphiphilic topology, behave as anionic surfactants. In pure water, they display "hydrophobic attractions", leading to the formation of aggregates of different sizes and shapes depending on the counterions. When simulated at a water/"oil" interface, the different anions (HCD(-), MeCD(-), CCD(-), and BrCD(-)) are found to be surface active. As a result, the simulated M(n+) counterions (M(n+) = Na(+), K(+), Cs(+), H(3)O(+), UO(2)(2+), Eu(3+)) concentrate on the aqueous side of the interface, forming a "double layer" whose characteristics are modulated by the hydrophobic character of the anion and by M(n+). The highly hydrophilic Eu(3+) or UO(2)(2+) cations that are generally "repelled" by aqueous interfaces are attracted by dicarbollides near the interface, which is crucial as far as the mechanism of assisted cation extraction to the oil phase is concerned. These cations interact with interfacial XCD(-) in their fully hydrated Eu(H(2)O)(9)(3+) and UO(2)(H(2)O)(5)(2+) forms, whereas the less hydrophilic monocharged cations display intimate contacts via their X substituents. The results obtained with the TIP3P and OPLS models for the solvents are confirmed with other water models (TIP5P or a polarizable 4P-Pol water) and with more polar "oil" models. The importance of interfacial phenomena is further demonstrated by simulations with a high oil-water ratio, leading to the formation of a micelle covered with CCD's. We suggest that the interfacial activity of dicarbollides and related hydrophobic anions is an important feature of synergism in liquid-liquid extraction of hard cations (e.g., for nuclear waste partitioning).     

Influence of the Li+ on the structure of the [Cu3phis3]3+ cation

When [Cu(3)(phis)(3)](ClO(4))(3), obtained from Cu(ClO(4))(2).6H(2)O with the Na(+) or K(+) salt of the phis anion (Hphis = N-(2-pyridylmethyl)-l-histidine), is reacted with LiClO(4), the tricopper cationic structure rearranged to accommodate a Li(+) ion to form [(ClO(4))Li[Cu(3)(phis)(3)]](ClO(4))(3) which can also be prepared directly by reacting Cu(ClO(4))(2).6H(2)O with the Li(+) salt of the phis anion.     

The proton complex of a diaza-macropentacycle: structure, slow formation, and chirality induction by ion pairing with the optically active 1,1'-binaphthyl-2,2'-diyl phosphate anion

The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 x H](+)) and doubly (o(+)o(+) [1 x 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 x H](+) being the thermodynamic product. i(+)o [1 x H](+) is C3 helically chiral in the solid state and in solution. The barrier to racemization (DeltaG(double dagger)) of the [1 x H](+) propeller is >71 kJ mol(-1). The ammonium proton is encapsulated in the tetrahedral coordination sphere provided by the endo (i) nitrogen bridgehead atom and the three proximal thioether sulfurs, which makes [1 x H](+) a proton complex. Use of the optically active acid (R)-(-)- or (S)-(+)-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNPH) in chloroform allowed us to induce a significant diastereomeric excess (24% de), which produced a detectable ICD. The de was decreased in acetone-d6 (10%), suggesting that the sense of chirality of [1 x H](+) is controlled by ion-pair interactions. Detailed NMR studies allowed us to locate the chiral anion on the endo side of [1 x H](+), in the cavity lined by endo t-Bu groups, and to establish that the rate of anion exchange in [1 x H][(S,R)-(+/-)-BNP] was higher than the rate of propeller inversion of [1 x H](+).     

Uptake of cesium, strontium and europium by a poly(sodium acrylate-acrylic acid) hydrogel

The uptake of cesium, strontium and europium from dilute nitric acid solutions by a poly(sodium acrylate-acrylic acid) PAA hydrogel has been investigated. pH variations are consistent with cation exchange processes: COO(-), Na (+)H (+), COO(-), Na (+)M (m+) ( M (m+) = Cs (+)and Sr (2+)) and COOH Eu (3+). Saturation of the gel is achieved for metal/carboxylate ratios R = 0.5. The swelling ratios of gels loaded with metal cations are those of uncharged, shrunk gels (Sr, Eu) or of charged, swollen gels (Cs) in agreement with the formation of uncharged (COO)(2)Sr, (COO)(2)EuX (X = NO(3) or OH) type complexes and (COO(-), Cs(+)) ion pairs. The metal cations are extracted in the gels following the order of their affinities with carboxylic groups Eu(3+) > Sr(2+) > Cs(+). An increase of the ionic strength of the metal aqueous solution up to 0.5M NaNO(3) leads to slightly decrease the europium uptake by the PAA hydrogel, but 0.1M NaNO(3) is sufficient to prevent the Sr and Cs extractions.     

Group 1 coordination chains and hexagonal networks of host cyclotriveratrylene with halogenated monocarbaborane anions

Halogenated carbaborane ions [CB(11)H(6)X(6)](-) in which X=Cl or Br have been combined with the host molecule cyclotriveratrylene (CTV) and Group 1 metal cations to give crystalline materials. The complexes [Na(ctv)(H(2)O)(CB(11)H(6)X(6))](CF(3)CH(2)OH) feature chiral Na-CTV coordination chains with complexation of the [CB(11)H(6)X(6)](-) ion by the Na(+) ion, together with the CTV molecular cavity. The coordination chains are hydrogen bonded together to give a puckered two-dimensional hexagonal grid structure. [K(ctv)(CB(11)H(6)Cl(6))(CF(3)CH(2)OH)(0.5)] is essentially isostructural. Complexes [Rb(ctv)(CB(11)H(6)Br(6))(H(2)O)] and [Cs(ctv)(CB(11)H(6)X(6))(CH(3)CN)] are coordination polymers with related distorted hexagonal grid structures. Use of N,N'-dimethylformamide (DMF) as a solvent results in an entirely different type of assembly, with [Na(2)(dmf)(4)(H(2)O)(2)(ctv)][(dmf)(0.5)(ctv)][CB(11)H(6)Br(6)](2) showing unusual [Na-mu-(dmf)-Na] bridges, and once again forming a distorted hexagonal coordination polymer.     

New extended magnetic systems based on oxalate and iron(III) ions

A series of oxalate-bridged iron(III) complexes have been synthesized by the reaction of FeCl 3 with oxalic acid (H 2ox) and XCl, where X is a substituted univalent ammonium or an alkaline cation. We have obtained basically two different types of compounds by varying the nature and the shape of the counterion, with the dimensionality of the resulting product being strongly influenced by the counterion. Three-dimensional (3D) networks of oxo- and oxalato-bridged iron(III) ions of the general formula {X 2[Fe 2O(ox) 2Cl 2]. pH 2O} n have been obtained for X = Li (+) ( 1), Na (+) ( 2), and K (+) ( 3) with p = 4 and X = MeNH 3 (+) ( 4), Me 2NH 2 (+) ( 5), and EtNH 3 (+) ( 6) with p = 2. Similar 3D hydroxo- and oxalato-bridged iron(III) networks of the formula {X[Fe 2(OH)(ox) 2Cl 2].2H 2O} n resulted for X = EtNH 3 (+) ( 7a) and PrNH 3 (+) ( 8). Compound 7a undergoes a solid-to-solid transformation, leading to a new species of the formula {(H 3O)(EtNH 3)[Fe 2O(ox) 2Cl 2].H 2O} n ( 7b). Chainlike compounds of the formula {X 2[Fe 2(ox) 2Cl 4]. pH 2O} n [X = Me 2NH 2 (+)( 9, p = 1), Me 3NH (+) ( 10, p = 2), and Me 4N (+) ( 11, p = 0)] have been obtained for the bulkier alkylammonium cations. Magnetic susceptibility measurements in the temperature range 1.9-295 K show the occurrence of weak ferromagnetic ordering due to spin canting in the 3D networks 1- 8, with the value of the critical temperature ( T c) varying with the cation in the range 26 K ( 2) to 70 K ( 8) without significant structural modifications. The last three one-dimensional compounds exhibit the typical behavior of antiferromagnetically coupled chains of interacting spin sextets [ J = -8.3 ( 9), -6.9 ( 10), and -8.4 ( 11) cm (-1) with H = - J summation operator i S i S i+1 ].     

Hydration energies in the gas phase of select (MX)mM+ ions, where M+ = Na+, K+, Rb+, Cs+, NH4+ and X- = F-, Cl-, Br-, I-, NO2-, NO3-. Observed magic numbers of (MX)mM+ ions and their possible significance

The sequential hydration energies and entropies with up to four water molecules were obtained for MXM(+) = NaFNa(+), NaClNa(+), NaBrNa(+), NaINa(+), NaNO(2)Na(+), NaNO(3)Na(+), KFK(+), KBrK(+), KIK(+), RbIRb(+), CsICs(+), NH(4)BrNH(4)(+), and NH(4)INH(4)(+) from the hydration equilibria in the gas phase with a reaction chamber attached to a mass spectrometer. The MXM(+) ions as well as (MX)(m)M(+) and higher charged ions such as (MX)(m)M(2)(2+) were obtained with electrospray. The observed trends of the hydration energies of MXM(+) with changing positive ion M(+) or the negative ion X(-) could be rationalized on the basis of simple electrostatics. The most important contribution to the (MXM-OH(2))(+) bond is the interaction of the permanent and induced dipole of water with the positive charge of the nearest-neighbor M(+) ion. The repulsion due to the water dipole and the more distant X(-) has a much smaller effect. Therefore, the bonding in (MXM-OH(2))(+) for constant M and different X ions changes very little. Similarly, for constant X and different M, the bonding follows the hydration energy trends observed for the naked M(+) ions. The sequential hydration bond energies for MXM(H(2)O)(n)(+) decrease with n in pairs, where for n = 1 and n = 2 the values are almost equal, followed by a drop in the values for n = 3 and n = 4, that again are almost equal. The hydration energies of (MX)(m)M(+) decrease with m. The mass spectra with NaCl, obtained with electrospray and observed in the absence of water vapor, show peaks of unusually high intensities (magic numbers) at m = 4, 13, and 22. Experiments with variable electrical potentials in the mass spectrometer interface showed that some but not all of the ion intensity differentiation leading to magic numbers is due to collision-induced decomposition of higher mass M(MX)(m)(+) and M(2)(MX)(m)(2+) ions in the interface. However, considerable magic character is retained in the absence of excitation. This result indicates that the magic ions are present also in the saturated solution of the droplets produced by electrospray and are thus representative of particularly stable nanocrystals in the saturated solution. Hydration equilibrium determinations in the gas phase demonstrated weaker hydration of the magic ion (NaCl)(4)Na(+).     

Inverse sodium hydride: a theoretical study

A recent experimental investigation in which a salt containing the unusual charge distribution H(+) and Na(-) was synthesized and characterized prompted us to undertake an ab initio theoretical investigation. In the salt synthesized, the H(+) is bound to the nitrogen center of an amine and the Na(-) alkalide is "blocked" from approaching the protonated amine site by steric constraints of a cage structure. Although one expects that the Na(-) would deprotonate an unprotected R(3)N-H(+) cation, we decided to further explore this issue. Using extended atomic orbital basis sets and M?ller-Plesset and coupled-cluster treatments of electron correlation, we examined the relative stabilities of the prototype (Me)(3)N + NaH, (Me)(3)N + Na(+) + H(-), (Me)(3)N-H(+) + Na(-), and (Me)(3)N-Na(+) + H(-) as well as the ion pair complexes (Me)(3)N-H(+).Na(-) and (Me)(3)N-Na(+).H(-). The primary focus of this effort was to determine whether the high-energy (Me)(3)N-H(+).Na(-) ion pair, which is the analogue of what the earlier workers termed "inverse sodium hydride", might be stable with respect to proton abstraction under any reasonable solvation conditions (which we treated within the polarized continuum model). Indeed, we find that such ion pairs are metastable (i.e., locally geometrically stable with a barrier to dissociation) for solvents having dielectric constants below approximately 2 but spontaneously decompose into their constituent ions for solvents with higher dielectric constants. We suggest that amines with large proton affinities and/or metals with weaker MH bond strengths should be explored experimentally.     

Cation-specific interactions with carboxylate in amino acid and acetate aqueous solutions: X-ray absorption and ab initio calculations

Relative interaction strengths between cations (X = Li (+), Na (+), K (+), NH 4 (+)) and anionic carboxylate groups of acetate and glycine in aqueous solution are determined. These model systems mimic ion pairing of biologically relevant cations with negatively charged groups at protein surfaces. With oxygen 1s X-ray absorption spectroscopy, we can distinguish between spectral contributions from H 2O and carboxylate, which allows us to probe the electronic structure changes of the atomic site of the carboxylate group being closest to the countercation. From the intensity variations of the COO (-) aq O 1s X-ray absorption peak, which quantitatively correlate with the change in the local partial density of states from the carboxylic site, interactions are found to decrease in the sequence Na (+) > Li (+) > K (+) > NH 4 (+). This ordering, as well as the observed bidental nature of the -COO (-) aq and X (+) aq interaction, is supported by combined ab initio and molecular dynamics calculations.     

Design and synthesis of luminescence chemosensors based on alkynyl phosphine gold(I)-copper(I) aggregates

Receptor-containing polynuclear mixed-metal complexes of gold(I)-copper(I) 1-3 based on a [{Au(3)Cu(2)(C≡CPh)(6)}Au(3){PPh(2)-C(6)H(4)-PPh(2)}(3)](2+) (Au(6)Cu(2)) core with benzo-15-crown-5, oligoether and urea binding sites were designed and synthesized, respectively. These complexes exhibited remarkably strong red emission at ca. 619-630 nm in dichloromethane solution at room temperature upon photoexcitation at λ > 400 nm, with the emission quantum yield in the range 0.59-0.85. The cation-binding properties of 1 and 2 and the anion-binding properties of 3 were studied using UV-vis, emission and (1)H NMR techniques. Complex 1, with six benzo-15-crown-5 pendants, was found to show a higher binding preference for K(+), with a selectivity trend of K(+)? Cs(+) > Na(+) > Li(+). The addition of metal ions (Li(+), Na(+), K(+) and Cs(+)) to complex 1 led to a modest emission enhancement with a concomitant slight blue shift in energy and well-defined isoemissive points, which is attributed to the rigidity of the structure and the inhibited PET (photo-induced electron transfer) process from the oxygen to the aggregate as a result of the binding of the metal ion. The six urea receptor groups on complex 3 were found to form multiple hydrogen bonding interactions with anions, with the positive charge providing additional electrostatic interaction for anion-binding. The anion selectivity of 3 follows the trend F(-) > Cl(-)≈ H(2)PO(4)(-) > Br(-) and the highest affinity towards F(-) is attributed to the stronger basicity of F(-), as well as its good size match with the cavity of the urea pocket.     

Combination effects of cation and anion of ionic liquids on the cadmium metal-organic frameworks in ionothermal systems

The effects of cation and/or anion of two groups of ionic liquids ([EMI]X and [PMI]X, where EMI = 1-ethyl-3-methylimidazolium; PMI = 1-propyl-3-methylimidazolium; X = Cl, Br, and I) on the ionothermal reactions between Cd(NO 3) 2.4H 2O and 1,3,5-benzenetricarboxylic acid (H 3BTC) were studied. Three different Cd-BTC metal-organic frameworks, [EMI][Cd2(BTC)Cl2](1), [EMI][Cd(BTC)](2), and [PMI][Cd(BTC)](3), were formed into crystalline phases. 1 was obtained from reactions in [EMI]Cl, while the same reactions with Cl replaced by Br or I produced a known compound 2. The replacement of EMI(+) by PMI(+) produced 3, irrespective of the nature of X.     

Mechanisms of acid decomposition of dithiocarbamates. 5. Piperidyl dithiocarbamate and analogues

In this work, the acid cleavage at 25 degrees C in 20% v/v aqueous ethanol of a series of analogues of piperidine dithiocarbamate X(C2H4)2NCS2(-) (X = CH2, CHCH3, NH, NCH3, S, O) was studied. The pH-rate profiles were obtained in the range of H(o)-5 and pH 5. They all presented a dumbell shaped curve with a plateau from which the pH-independent first-order rate constant k(o) (or the specific acid catalysis k(H)) was calculated, in addition to the acid dissociation constant of the free (pKa) and conjugate acid (pK(+)) species of the DTC. LFERs of the kinetically determined pKa and pK(+) versus pKN (pKa of parent amine) were used to characterize the reactive species and the structure of the transition state of the rate-determining step. For X = CH2, CH3CH the values of k(H) agree with those of alkDTCs in the strong base region of the Br?nsted plot of log k(H) versus pKN where the transition state is close to a zwitterion formed by intramolecular water-catalyzed S-to-N proton transfer of the dithiocarbamic acid. However, when X = NH, CH 3N, O, S, the reactive species is the DTC anion, which is as reactive as an arylDTC, and similarly, the pK(+) values correspond to a parent amine that is about 3-4 pK units more basic. The solvent isotope effect indicated that the acid decomposition of these dithiocarbamate anions is specifically catalyzed by a Hydron anchimerically assisted by the heteroatom through a boat conformation.     

Relative hydrophobicity and hydrophilicity of some "ionic liquid" anions determined by the 1-propanol probing methodology: a differential thermodynamic approach

The excess partial molar enthalpy of 1-propanol (1P), H(E) (1P), was experimentally measured in ternary 1P-[NaPF(6), NaCF(3)SO(3) (OTF) or NaN(SO(2)CF(3))(2) (TFSI)]-H(2)O system. From the H(E) (1P), the enthalpic 1P-1P interaction function, H(E) (1P-1P), which is the compositional derivative of H(E) (1P), was evaluated graphically. On addition of the Na salt, the x(1P)-dependence pattern of H(E) (1P-1P) showed a characteristic change. This induced change is used as a probe to elucidate the effect of the sample Na-salt on H(2)O. Because we know the effect of Na(+) from our previous work, we show that each anion works as an amphiphile with hydrophobic and hydrophilic effects. Furthermore, the present method can quantify its relative hydrophobicity and hydrophilicity separately. The results indicate that the relative hydrophobicity ranking was in the order of TFSI(-) > PF(6-) approximately OTF(-), and the hydrophilicity TFSI(-) > PF6(- )> OTF-. Namely, TFSI- is the strongest amphiphile with the strongest hydrophobicity and the strongest hydrophilicity among the ionic liquid (IL) anions studied here. Using our earlier similar studies for normal ions, we map their relative hydrophobicity/hydrophilicity scales on a two-dimensional map together with those of the IL ions. The resulting map shows that the typical constituent ions for "ionic liquids" are strong amphiphiles; with more strongly hydrophobic and more strongly hydrophilic propensities than normal ions. Although the number of data points is limited, the melting points of ionic liquids consisting of TFSI(-) with the strongest hydrophobicity and the strongest hydrophilicity within the anions studied here are the lowest.     

Fullerenols revisited as stable radical anions

The first exhaustive purification and characterization of the much-studied "fullerenols", prepared by reaction of C(60) in toluene with an oxygenated, aqueous NaOH solution using tetrabutylammonium hydroxide as a phase transfer catalyst, has been performed. The resulting fullerenol is not simply polyhydroxylated C(60) but rather is a structurally and electronically complex C(60) radical anion with a molecular formula of Na(+)(n)[C(60)O(x)(OH)(y)](n)(-) (where n = 2-3, x = 7-9, and y = 12-15) for three different, but identical, preparations. Surprisingly, Na(+)-fullerenol is paramagnetic, exhibiting mu(B) values in aqueous solution of 1.9-2.1 B.M. at 0.5 T and 300 K and R(1) proton relaxivities of 0.55-0.77 mM(-1)s(-1) at 20 MHz and 40 degrees C, values both slightly higher than those expected for a pure S = 1/2 spin system. ESR studies (ESE-FS and 2D nutation) of frozen aqueous solutions at 1.5 and 5.0 K establish that Na(+)-fullerenol is mainly S = 1/2 with a minor, but significant, component of S = 1. Thus, this is the first report to characterize these widely studied, water-soluble fullerenols as stable radical anions. The stability of the S = 1/2 Na(+)-fullerenol radical is likely due to a highly derivatized C(60) surface that protects a cyclopentadienyl radical center on the fullerene.     

Influence of "alternative" C-terminal amino acids on the formation of [b3 + 17 + Cat]+ products from metal cationized synthetic tetrapeptides

The aim of this study was to investigate the dissociation patterns, and in particular the relative abundance of [b(3) + 17 + Cat](+), for peptides with C-termini designed to allow transfer of the -OH required to generate the product ion, but not necessarily as the most favored pathway. Working with the hypothesis that formation of a five-membered ring intermediate, including intramolecular nucleophilic attack by a carbonyl oxygen atom, is an important mechanistic step, several model peptides with general sequence AcFGGX were synthesized, metal cationized by electrospray ionization and subjected to collision-induced dissociation (CID). The amino acid at position X was one that either required a larger ring intermediate (beta-alanine, gamma-aminobutyric acid and epsilon-amino-n-caproic acid to generate six-, seven- or nine- membered rings, respectively) to transfer -OH, lacked a structural element required for nucleophilic attack (aminoethanol) or prohibited cyclization because of the inclusion of a rigid ring (p- and m-aminobenzoic acid). For Ag(+), Li(+) and Na(+) cationized peptides, our results show that amino acids requiring the adoption of larger ring intermediates suppressed the formation of [b(3) + 17 + Cat](+), while amino acids that prohibit cyclization eliminated the reaction pathway completely. Formation of [b(3) - 1 + Cat](+) from the alkali metal cationized versions was not a favorable process upon suppression or elimination of the [b(3) + 17 + Cat](+) pathway: the loss of H(2)O to form [M - H(2)O + Cat](+) was instead the dominant dissociation reaction observed. Multiple-stage dissociation experiments suggest that [M - H(2)O + Cat](+) is not [b(4) - 1 + Cat](+) arising from the loss of H(2)O from the C-terminus, but may instead be a species that forms via a mechanism involving the elimination of an oxygen atom from an amide group.