Solvation structures of iodide on and below a surface of aqueous solution studied by photodetachment spectroscopy

We investigated solvation structures of I(-) on and below a surface of an aqueous solution by photodetachment spectroscopy. An aqueous solution of an alkali halide was introduced to the vacuum as a continuous liquid flow (liquid beam), and the liquid beam was irradiated with a UV laser pulse. The intensity of electrons emitted from the surface by the laser excitation was measured as a function of wavelength (photodetachment spectroscopy), and we obtained absorption spectrum of I(-) on and below the solution surface. From the absorption spectrum, we found that I(-) starts to appear on the solution surface as the bulk NaI concentration increases. Similar concentration dependence was observed for the KI solution. We also found that I(-) located inside the solution is pushed to the surface, when NaCl is added to the solution. These changes are explained in terms of the difference in the polarizability of halide ions.     

Electrochemical nanostructuring of fullerene films--spectroscopic evidence for C60 polymer formation and hydrogenation

Electrochemical reduction of ordered C60 fullerene films in aqueous solution was studied by AFM, FTIR and Raman spectroscopy, mass spectrometry and elastic recoil detection analysis. During the irreversible reduction process the film morphology changed from a heteroepitaxial (111) surface to a nanostructured array with clusters of 20 to 50 nm lateral size on average. On the molecular level the initial C60 underwent electrochemical reactions to form C60 polymers and hydrogenated C60. Chemical follow-up reactions of electrochemically formed C60- with water are responsible for the different reduction behaviour of C60 films in aqueous solution compared to C60 reduction in organic solvents and to C60 doping with alkali metals. Based on the spectroscopic analysis a reaction scheme accounting for the chemical processes at the C60 / aqueous electrolyte interface is presented.     

Electrospray mass spectrometric detection of products and short-lived intermediates in aqueous aerosol microdroplets exposed to a reactive gas

The intermediates ISO3- (m/z=207) and IS2O3- (m/z=239) generated in aqueous (NaI/Na2S2O3) microdroplets traversing dilute O3 gas plumes are detected via online electrospray mass spectrometry within approximately 1 ms, and their stabilities gauged by collisionally induced dissociation. The simultaneous detection of anionic reactants and the S2O62-, HSO4-, IO3-, and I3- products as a function of experimental conditions provides evidence of genuinely interfacial reaction kinetics. Although O3(aq) reacts about 3 times faster with I- than with S2O32- in bulk solution, only S2O32- is significantly depleted in the interfacial layers of [I-]/[S2O32-]=10 microdroplets below [O3(g)] approximately 50 ppm.     

High-sensitivity negative-ion laser spray for liquid chromatography/mass spectrometry.

A negative-ion mode laser spray interface for use in liquid chromatography/mass spectrometry (LC/MS) has been developed and investigated. The laser spray gave sensitivities that were orders of magnitude better than the negative-ion electrospray for all samples investigated with the exception of sugars. Fragment ions, HSO(-4)and SO(-3), were formed from the laser-sprayed aqueous solution of cholesterol 3-sulfate sodium salt. This suggests that structural information may be obtained directly from the laser-spray mass spectra for thermally labile compounds.     

Computational studies of nonstoichiometric sodium auride clusters

The molecular structures of low-lying isomers of anionic and neutral sodium auride clusters have been studied computationally at the second-order M?ller-Plesset perturbation theory level using quadruple-ζ basis sets augmented with a double set of polarization functions. The first vertical detachment energies were calculated at the M?ller-Plesset level as the energy difference between the cluster anion and the corresponding neutral cluster. The photodetachment energies of higher-lying ionization channels were calculated by adding electronic excitation energies of the neutral clusters to the first vertical detachment energy. The excitation energies were calculated at the linear response approximate coupled-cluster singles and doubles level using the anionic cluster structures. The obtained ionization energies for NaAu(-), NaAu(2)(-), NaAu(3)(-), NaAu(4)(-), Na(2)Au(2)(-), Na(2)Au(3)(-), Na(3)Au(3)(-), and Na(2)Au(4)(-) were compared to values deduced from experimental photoelectron spectra. Comparison of the calculated photoelectron spectra for a few energetically low-lying isomers shows that the energetically lowest cluster structures obtained in the calculations do not always correspond to the clusters produced experimentally. Spin-component-scaled second-order M?ller-Plesset perturbation theory calculations shift the order of the isomers such that the observed clusters more often correspond to the energetically lowest structure, whereas the spin-component-scaled approach does not improve the photodetachment energies of the sodium aurides. The potential energy surface of the sodium aurides is very soft, with several low-lying isomers requiring an accurate electron correlation treatment. The calculations show that merely the energetic criterion is not a reliable means to identify the structures of the observed sodium auride clusters; other experimental information is needed to ensure a correct assignment of the cluster structures. The cluster structures of nonstoichiometric anionic sodium aurides have been determined by comparing calculated ionization energies for low-lying structures of the anionic clusters with experimental data.     

Imaging of uranium on rat brain sections using laser ablation inductively coupled plasma mass spectrometry: a new tool for the study of critical substructures affined to heavy metals in tissues

The specific toxicity of trace metals and compounds largely depends on their bioavailability in different organs or compartments of the organism considered. Imaging mass spectrometry (IMS) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with a spatial resolution in the 100 microm range was developed and employed to study heavy metal distribution in brain tissues for toxicological screening. Rat brain post-mortem tissues were stained in an aqueous solution of either uranium or neodymium (metal concentration 100 microg g(-1)) for 3 h. The incubation of heavy metal in thin slices of brain tissue is followed by an imaging mass spectrometric LA-ICP-MS technique. Stained rat brain tissue (thickness 30 microm) were scanned with a focused laser beam (wavelength 266 nm, diameter of laser crater 100 microm and laser power density 3 x 10(9) W cm(-2)). The ion intensities of (235)U(+), (238)U(+), (145)Nd(+) and (146)Nd(+) were measured by LA-ICP-MS within the ablated area. For quantification purposes, matrix-matched laboratory standards were prepared by dosing each analyte to the pieces of homogenized brain tissue. Imaging LA-ICP-MS allows structures of interest to be identified and the relevant dose range to be estimated. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Interaction of NaI with solid water and methanol

The interaction of NaI with amorphous solid water (ASW) and methanol (MeOH) has been investigated with metastable impact electron spectroscopy (MIES), UPS(HeI), and temperature programmed desorption (TPD). We have studied the electron emission from the ionization of the highest-lying states of H(2)O, CH(3)OH, and of 5pI. We have prepared NaI layers on ASW (MeOH) films at about 105 K and annealed them up to about 200 K. Surface segregation of iodide is observed in ASW, as predicted for NaI aqueous solutions. On the other hand, surface segregation is not observed in MeOH, again as predicted for the interaction of NaI with liquid methanol. Electronic properties (ionization potentials, optical band gaps) and water binding energies are reported and are analyzed on the basis of available DFT results for hydrated NaI clusters.     

Monitoring the degradation of tetracycline by ozone in aqueous medium via atmospheric pressure ionization mass spectrometry

The degradation of tetracycline (1) by ozone in aqueous solution was investigated. High performance liquid chromatography (HPLC), UV-visible spectroscopy (UV-Vis), and total organic carbon (TOC) analyses revealed that although tetracycline was quickly consumed under this oxidative condition, it did not mineralize at all. Continuous monitoring by electrospray ionization mass spectrometry in the positive ion mode, ESI(+)-MS, revealed that tetracycline (1), detected in its protonated form ([1 + H]+) of m/z 445, reacted to yield almost exclusively two unprecedented oxidation products (2 and 3) via a net insertion of one and two oxygen atoms, respectively. Compound 2, suggested to be formed via an initial 1,3-dipolar cycloaddition of ozone at the C11a-C12 double-bond of 1, and Compound 3, proposed to be produced via a subsequent ozone attack at the C2-C3 double-bond of 2, were detected in their protonated forms in the ESI(+)-MS, i.e., [2 + H]+ of m/z 461 and [3 + H]+ of m/z 477, and were further characterized by ESI(+)-MS(n). LC-APCI(+)-MS (liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry in the positive ion mode) experiments corroborated the results.     

Time-resolved photoelectron spectroscopy of solvated electrons in aqueous NaI solution

Time-resolved photoelectron spectroscopy was used to study the energetics and dynamics of solvated electrons in aqueous solution. Solvated electrons are generated by ultrafast photodetachment in a 100 mM aqueous NaI solution. Initially, an ensemble of strongly bound ("cold") solvated electrons and an ensemble of weakly bound ("hot") electrons in an unequilibrated solvent environment are observed. We report an ultrafast recombination channel for the "hot" electrons with a rate of (800 fs)(-1) which is in competition with thermalization occurring with a rate of (1.1 ps)(-1). The thermalized electrons recombine with the iodide radical with a rate of (22 ps)(-1). About 35% of the thermalized electrons escape geminate recombination and form free, solvated electrons. The vertical detachment energy for the solvated electron is determined to be 3.40 eV. No indication for a surface-bound electron at lower binding energies was observed.     

On the dissolution processes of Na2I+ and Na3I2+ with the association of water molecules: mechanistic and energetic details

The sequential association energies for one through six water molecules clustering to Na(2)I(+), as well as one and two water molecules clustering to Na(3)I(2)(+), are measured. The association energies show a pairwise behavior, indicating a symmetric association of water molecules to the linear Na(2)I(+) and Na(3)I(2)(+) ions. This pairwise behavior is well reproduced by Density Functional Theory (DFT) calculations. DFT calculations also suggest that a significant separation of charge for the Na-I ion pair occurs when four or more water molecules cluster to a single sodium center. Two different solvent-separated ion pairs have been identified with the DFT calculations. Experiments also show that the dissolution processes, loss of a neutral NaI unit, occurs when six or more water molecules have been added to Na(2)I(+) cluster. However, one or two water molecules are able to detach an NaI unit from the Na(3)I(2)(+) cluster. The difference in solubility of the Na(2)I(+) and Na(3)I(2)(+) ions is due to the difference in the energies required to lose an NaI unit from these two species. The experiment also confirms that the loss of a neutral NaI unit, instead of an Na(+) ion, occurs during the dissolution processes of Na(3)I(2)(+). The microsolvation schemes proposed to explain our experimental observations are supported by DFT and phase space theory (PST) calculations.     

Field desorption mass spectrometry of oligosaccharides in the presence of metallic salts

In the field desorption mass spectrometry of oligosaccharides, traces of contaminating salts in polar solvents decrease the detection sensitivity, and in some cases no ion could be detected in the molecular range. The present work shows that the addition of alkaline salts (NaI or KI) greatly increases the sensitivity, and cationized molecular ions are obtained. The influence of the molar ratio sugar/salt on the nature and relative intensity of the desorbed species has been studied on mixtures of α-D -trehalose and NaI. At the low salt ratio (100:1), high molecular weight clusters [X M + Na]⁺ are preferentially formed. At the high salt ratio (1:10), mixed clusters [M + NaI + Na]⁺, doubly charged ions [M + 2Na]²⁺ and monomeric cationized ions [M + Na]⁺ are observed along with salt clusters [NaI + Na]⁺ and [2NaI + Na]⁺. In the range of molar ratios sugar/salt of 10:1 to 1:1, the field desorption mass spectra exhibit a cationized ion [M + Na]⁺, which contributes more than 80% of Σ₁₀₀. This cationization technique has been applied to the field desorption mass spectrometry of several oligosaccharides. In all cases, the salt effect causes the replacement of the [M + H]⁺ ion by a [M + C]⁺ ion. (Note: the term [M + C]⁺ and similar ones mean an association between the whole molecule studied (M) and an alkaline cation [C]⁺ ([K)]⁺, [Na]⁺, [Li]⁺).) Thus, di, tri- and tetrasaccharides exhibit intense [M + Na]⁺ ions in the presence of NaI and only a few fragment peaks are observed in their field desorption mass spectra. This technique has been applied successfully to the detection of the hexasaccharide ajugose in a natural sample of pentasaccharide, and has also allowed the unambiguous determination of the composition of a mixture of partially methylated trehaloses. The salt effects are dicussed in terms of selective adsorption on the emitter, pre-existing soluble complexes sugar-salt, interactions between these species in the electric field and dissociative desorption of ionic complexes.     

Time-resolved self-assembly of a fullerene-topology core-shell cluster containing 68 uranyl polyhedra

A complex core-shell cluster consisting of 68 uranyl peroxo polyhedra, 16 nitrate groups, and ~44 K(+) and Na(+) cations was obtained by self-assembly in alkaline aqueous solution under ambient conditions. Crystals formed after a month and were characterized. The cluster, designated as {U(1)?U(28)?U(40R)}, contains a fullerene-topology cage built from 28 uranyl polyhedra. A ring consisting of 40 uranyl polyhedra linked into five-membered rings and 16 nitrate groups surrounds this cage cluster. Topological pentagons in the cage and ring are aligned, and their corresponding rings of uranyl bipyramids are linked through K(+) cations located between the two shells. A partially occupied U site is located at the center of the cluster. Time-resolved small-angle X-ray scattering and electrospray ionization mass spectrometry demonstrated that the U(28) cage cluster formed in solution within an hour, whereas the U(40R) shell formed around the cage cluster after more than several days.     

六氢吡啶团簇的研究

The 6H-pyridine clusters have been studied by the TOF mass spectrometry, the VUV from synchrotron radiation and the molecular beam technique. Three-type clusters are observed in the VUV photoionization mass spectroscopy: Pn+(n=2-5,P stands for 6H-pyridine molecule), PnH+ (n=2-4) and Pn (H2O)m+(n=4,5, m=1;n=6, m=1,2). The PnH+ clusters may have the chain structures, the Pn+ and Pn(H2O)m+ clusters may have the cyclic structures, all of these are formed by the hydrogen-bond.     

Electrospray ionization tandem mass spectrometric study of salt cluster ions. Part 1--investigations of alkali metal chloride and sodium salt cluster ions

Salt cluster ions of alkali metal chlorides ACl (A = Li(+), Na(+), K(+), Rb(+) and Cs(+)) and sodium salts NaB (B = I(-), HCOO(-), CH(3)COO(-), NO(2)(-), and NO(3)(-)), formed by electrospray ionization, were studied systematically by mass spectrometry. The influences on the total positive ion and negative ion currents of variation of solvent, solution concentration, desolvation temperature, solution flow-rate, capillary voltage and cone voltage were investigated. Only cone voltage was found to influence dramatically the distribution of salt cluster ions in the mass spectra observed. Under conditions of normal cone voltage of approximately 70 V, cluster ions having magic numbers of molecules are detected with high relative signal intensity. Under conditions of low cone voltage of approximately 10 V, the distribution of cluster ions detected is characterized by a relatively low average mass/charge ratio due to the presence of multiply charged cluster ions; in addition, there is a marked reduction in cluster ions having a magic number of molecules. Product ion mass spectra obtained by tandem mass spectrometry of cluster ions are characterized by a base peak having a magic number of molecules that is less than and closest to the number of molecules in the precursor ion. Structures have been proposed for some dications and some quadruply charged ions. At pH 3 and 11, the mass spectra of NaCl clusters show the presence of mixed clusters of NaCl with HCl and NaOH, respectively. The effects of ionic radius on 20 distributions of cluster ions for 10 salts were investigated; however, the fine structure of these effects is not readily discerned.     

Translational and rotational energy content of benzene molecules IR-desorbed from an in vacuo liquid surface

Benzene molecules were desorbed from an in vacuo aqueous liquid beam by direct irradiation of the beam with an IR laser tuned to the 2.85 μm absorption band of water. Spectroscopic interrogation of the desorbed benzene molecules was performed via 1 + 1 Resonance-Enhanced Multi-photon Ionisation (REMPI). Rotational contour analyses of the 6 vibronic transition of benzene were performed to determine the rotational temperature of those molecules ejected during the desorption event. At the peak of the desorption plume density, the rotational temperatures were found to be up to ～100 K lower than that recorded for molecules spontaneously evaporating from the liquid surface. At longer IR-UV laser delay times the benzene rotational temperatures are found to return to those observed following spontaneous evaporation. No evidence of IR desorbed neutral or cationic benzene-containing clusters was observed. However, ionic clusters were observed to be formed after REMPI of the benzene monomer. Analysis of the benzene intensity and that of post-REMPI formed clusters as a function of IR-UV delay shows that number density and local translational temperature vary along the desorption plume.     

Analysis of polypropyleneglycols using electrospray ionization mass spectrometry. Effects of cationizing agents on the mass spectra

In electrospray ionization mass spectrometry (ESI-MS) of polypropyleneglycol (PPG), effects of cationizing agents were examined. When NaI was used as a cationizing agent, the distribution of multiply-charged ions in the spectra was greatly affected by the ratio of cationizing agent and PPG. However, the distribution was not affected by the use of CH(3)COONH(4). With an increase of cone voltage, fragmentation occurred by in-source collision-induced dissociation (CID) when CH(3)COONH(4) was used. On the contrary, no decomposition of the PPG backbone was observed with NaI. Instead, the intensity of the lower-charged ions, whose mass-to-charge (m/z) ratios are larger, increased because of the elimination of Na(+) with increase of cone voltage. Under optimum conditions for ESI-MS analysis, PPGs that have different molecular weights, different initiators or end groups were easily and accurately characterized. A tandem mass spectrometry (MS/MS) study of NH(4)(+) adduct ions of PPG indicated that a vinyl-terminated linear structure is formed at the end group during the fragmentation.     

Photodissociation of yttrium and lanthanum oxide cluster cations

Transition metal oxide cations of the form M n O m (+) (M = Y, La) are produced by laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. Cluster oxides for each value of n form only a limited number of stoichiometries; MO(M2O3)x(+) species are particularly intense. Cluster cations are mass selected and photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Multiphoton excitation is required to dissociate these clusters because of their strong bonding. Yttrium and lanthanum oxides exhibit different dissociation channels, but some common trends can be identified. Larger clusters for both metals undergo fission to make certain stable cation clusters, especially MO(M2O3) x (+) species. Specific cations are identified to be especially stable because of their repeated production in the decomposition of larger clusters. These include M3O4(+), M5O7(+), M7O10(+), and M9O13(+), along with Y6O8(+). Density functional theory calculations were performed to investigate the relative stabilities and structures of these systems.     

Organic-soluble fluorescent Au8 clusters generated from heterophase ligand-exchange induced etching of gold nanoparticles and their electrochemiluminescence

A unique heterophase ligand exchange induced etching process was used to transform gold nanoparticles into organic-soluble fluorescent gold clusters which were assigned to Au(8) by optical spectroscopy and MALDI-TOF mass spectrometry. Both the annihilation electrochemiluminescence of fluorescent Au(8) clusters in organic solution and the coreactant electrochemiluminescence of Au(8) cluster film in aqueous solution were studied.