Excess volumes (V
E), viscosity deviation (Δη), excess refraction (ΔR), and surface excess (σE) of water +
ethylene glycol have been determined over the entire composition range at a number of temperatures.
The results are fitted to a Redlich−Kister equation, and the corresponding parameters are derived. All
the properties have negative values and exhibit a minimum at the same water-rich region of the solution.
The results are discussed in terms of molecular interactions.
Electrospray ionization of uranyl nitrate dissolved in water generates gaseous species containing either hydroxo-uranyl [UO(2)(OH)](+) or nitrato-uranyl [UO(2)(NO(3))](+) contact ion pairs solvated by up to four water molecules. Furthermore, uranyl clusters of the general type [U(m)O(2m)(X,Y)(2m-1)(H(2)O)(n)](+) (X,Y = OH, NO(3)) with m = 1-5 and n = 2-4 are formed. Collision-induced dissociation experiments are used to probe the structures and the stoichiometries of the uranyl ions generated. A detailed investigation of the concentration-dependent behavior of the formed gaseous uranyl complexes reveals a preference for nitrate- over hydroxide-containing species with increasing concentration of the sprayed solution. This behavior reflects changes in the pH value of the bulk solutions that can be attributed to solvolysis of UO(2)(2+) in water. Further, the tendency for generation of polynuclear cluster ions is amplified with increasing concentration and can be explained by a mechanism which involves the association of cations present in solution with neutral species such as UO(2)(OH)(2), UO(2)(OH)(NO(3)), and UO(2)(NO(3))(2). The observed dependences of the cluster-ion intensities in the mass spectra from the concentration of the solutions fed to the electrospray source are used to suggest a scheme for a quantitative correlation between the gas-phase and solution-phase data. The results inter alia indicate that the effective concentrations of the spraying solution can be several orders of magnitude larger than those of the feed solutions entering the electrospray ionization source.
Electrospray ionization-mass spectrometry (ESI-MS) is used to investigate the complexation of nickel(II) by N, N-dimethylformamide (DMF) in different water/DMF mixtures. The types of solvated cations observed are independent of the solvent composition and are part of the series [Ni(DMF) n ] 2+ with n ) 2-6 and [Ni-(DMF) n X] + with n ) 1-4 (where X ) Cl, Br, NO 3 ). The number of ligands, n, and thus the extent of solvation depends on the cone voltage (U C ) of the ESI source. At low U C multiply ligated ions prevail, whereas ligation drops with rising U C and further increase of U C causes dissociation of the solvent molecules as well as reduction of Ni(II) to Ni(I). The collision-induced dissociation (CID) spectra of the multiply ligated ions [Ni(DMF) n ] 2+ with n g 3 and [Ni(DMF) n X] + with n g 2 show only losses of neutral DMF ligands. Quite different is the behavior of the bisligated ions [Ni(DMF) 2 ] 2+ and [Ni(DMF)X] + . In the CID spectrum of [Ni(DMF) 2 ] 2+ , electron transfer from DMF to the metal leads to the reduced complex [Ni(DMF)] + concomitant with ionized DMF + . Charge-stripping spectra of mass-selected monocations [Ni(DMF) n ] + (n ) 1, 2) confirm that the dication [Ni(DMF) 2 ] 2+ is stable, whereas monoligated [Ni(DMF)] 2+ appears to be intrinsically unstable toward Coulomb explosion. In the CID spectra of [Ni(DMF)Cl] + and [Ni(DMF)Br] + , bond activation of the solvent takes place, and in the case of [Ni(DMF)NO 3 ] + the formation of a cationic species is observed which formally corresponds to the solvated metal-oxide cation [(DMF)NiO] + .
IntroductionElectrospray ionization (ESI) is a soft ionization technique, developed by Fenn and co-workers, 1 which allows the transfer of solvated ions from solution to the gas phase. Quite often, ESI leads to multiply charged ions, thereby reducing the massto-charge ratio of the analyte. Therefore, the ESI-mass spectrometry (MS) is particularly useful for the study of large and/or labile molecules such as proteins, enzymes, and polymers.  In addition, ESI-MS has widely been used for the detection and analysis of doubly and triply charged transitionmetal complexes and it can provide information concerning the structure, stoichiometry, and the metal's oxidation state for the multiply charged ions which are difficult to probe by other techniques.In the initial stage of the ESI process, large charged droplets are formed at atmospheric pressure by nebulization. Evaporation of the solvent leads to shrinkage of the droplets, thereby increasing the charge density until solvated ions are formed by charge separation ("Coulomb explosion"). The solvated ions move across an electric field and pass to the mass spectrometer through a skimmer forming a molecular beam which contains various ions in aggregation with solvent molecules. Solvent evaporation can be further aided by an additional "drying" gas (usually nitrogen) in the interface region of the instrument. It is known that the product ions observed in the gas phase are related to the che...
Complexes of Mn(II) with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bipy) are investigated by means of electrospray ionization (ESI) mass spectrometry. Under the conditions used, [MnL(n)]2+ with n = 2 and 3, [MnL(n)Cl]+ with n = 0-2, and [Mn2L(n)Cl3]+ with n = 2 and 3 are produced (where L = phen or bipy). The collision-induced dissociation (CID) spectra of the mass-selected ions show various dissociation pathways, most notable among them is the reduction of the ligated Mn(II) to Mn(I) by intracomplex electron transfer. CID experiments of mixed-ligand complexes formed upon ESI from solutions which contain both phen and bipy exhibit preferential eliminations of bipy, indicating that bipy is a significantly weaker ligand for Mn(II) than phen. This effect is mainly attributed to the flexibility of the bipy ligand concomitant with thermodynamic control in ion dissociation. To support this hypothesis, mixed complexes with some methylated derivatives as well as those containing 4,5-diazafluorene (daf) are examined also. Interestingly, the differences between the ligands diminish in charge-separation reactions of dicationic Mn(II) complexes, due to the joined operation of thermodynamic as well as kinetic effects. In addition, the complexes [Mn(bipy)]+, [Mn(phen)]+, [Mn(bipy)]2+, [Mn(phen)]2+, and [Mn(bipy)(phen)]2+ are computed using the mPW1PW91 hybrid density functional along with the Stuttgart-Cologne-type pseudopotential and basis-set suite, and relative energies for charge-separation reactions and losses of neutral ligands are evaluated.
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