Photoelectron spectroscopy of [Mo6X14]2- dianions (X = Cl-I).

Photoelectron spectroscopy and theoretical investigations have been performed to systematically probe the intrinsic electronic properties of [Mo6X14]2- (X = halogen). All three PE spectra of gaseous [Mo6X14]2- (X = Cl, Br, I) dianions, which were generated by electrospray ionization, exhibit multiple resolved peaks in the recorded binding energy range. Theoretical investigations on the orbital structure and charge distribution were performed to support interpretation of the observed spectra and were further extended onto [Mo6F14]2-, a dianion that was not available for the experimental study. The measured adiabatic (ADE) and vertical detachment energies (VDE) for X = Cl-I were well reproduced by density functional theory calculations (accuracy ∼0.1 eV). Corresponding ADE/VDE values for the dianions were found to be 1.48/2.13 (calc.) and 2.30/2.65, 2.30/2.62, and 2.20/2.42 eV (all expt.) for X = F, Cl, Br, and I, respectively, showing an interesting buckled trend of electron binding energy (EBE) along the halogen series, i.e., EBE (F) ≪ EBE (Cl) ∼ EBE (Br) > EBE (I). Molecular orbital analyses indicate different mixing of metal and halogen atomic orbitals, which is strongly dependent on the nature of X, and suggest that the most loosely bound electrons are detached mainly from the metal core for X = F and Cl, but from halide ligands for X = Br and I. The repulsive Coulomb barrier (RCB), estimated from the photon energy dependent spectra, decreases with increasing halogen size, from 1.8 eV for X = Cl to 1.6 eV for X = I. Electrostatic potential modeling confirms the experimental RCB values and predicts that the most favorable electron detaching pathway should lie via the face-bridging halide ligands.

Photoelectron spectroscopy of solvated dicarboxylate and alkali metal ion clusters, M+[O2C(CH2)2CO2]2- [H2O]n (M = Na, K; n = 1-6).

We present results of combined experimental photoelectron spectroscopy and theoretical modeling studies of solvated dicarboxylate species (-O2C(CH2)2CO2-) in complex with Na+ and K+ metal cations. These ternary clusters serve as simple models for the investigation of aqueous ion/solute specific effects that play an important role in biological systems. The experimental characterization of these systems was performed in the presence of up to six solvating waters. In both Na+ and K+ cases, we observe the presence of one major broad band that gradually shifts to higher electron binding energy (EBE) with an increasing number of waters. In the Na+ case further detailed analysis of experimental spectra was performed using ab initio calculations. In particular, we have identified the structures of the lowest energy clusters whose EBE values match well the major band in the experimental spectra. Our results show that evolution of an aqueous solvation shell emphasizes the coordination of the negatively charged carboxylate groups accompanied by simultaneous interaction with metal cations. Calculations also indicate that in the solvation range investigated experimentally (up to 6 waters), Na+ retains direct contact with the dicarboxylate species, i.e. a contact ion-pair (CIP) complex. Preliminary modeling studies show evidence of an alternative solvent separated ion-pair complex once the solvation range approaches 8 waters, however its energy still remains above that of (∼7-8 kcal/ mol-1) the CIP complex. At a higher number of waters (n = 3 for Na+ and n = 5 for K+), the experimental spectra also show the development of a weak low energy band. Its origin cannot be precisely identified. Our calculations in the Na+ case point out the existence of a quaternary complex consisting of Na+, H2O, OH- and a singly protonated dicarboxylate anion (HO2C(CH)2CO2-). Such a complex appears to be stabilized in the solvation range corresponding to the appearance of the low EBE band and does match its peak, even though the energy of such a complex is fairly high compared to the ternary structure.

Initial hydration behavior of sodium iodide dimer: photoelectron spectroscopy and ab initio calculations.

We investigated (NaI)2(-)(H2O)n (n = 0-6) clusters to examine the initial solvation process of (NaI)2 in water, using negative ion photoelectron spectroscopy and theoretical calculations. The structures of these clusters and their neutrals were determined by comparing ab initio calculations with experimental results. It is found that bare (NaI)2(-) is a L-shaped structure and the corresponding neutral is a rhombus. In (NaI)2(-)(H2O), the water molecule prefers to interact with the middle Na atom of the L-shaped (NaI)2(-). For (NaI)2(-)(H2O)n clusters with n = 2-3, two types of structures are nearly degenerate in energy: one is L-shaped and the other is pyramid-shaped. As for (NaI)2(-)(H2O)n with n = 4-6, the dominant structures are pyramid-shaped. For the anionic clusters, one of the Na-I distances increases abruptly when n = 2; for the neutral clusters, rapid lengthening of the Na-I distances occurs when n = 4. Additionally, analyses of the reduced density gradient were carried out, and the results reveal that Na(+)-water interactions dominate in (NaI)2(-)(H2O)n for n≤ 4, whereas I(-)-water and water-water interactions are significantly enhanced when n increases to 5.

Hydration of potassium iodide dimer studied by photoelectron spectroscopy and ab initio calculations.

We measured the photoelectron spectra of (KI)2-(H2O)n (n = 0-3) and conducted ab initio calculations on (KI)2-(H2O)n anions and their corresponding neutrals up to n = 6. Two types of spectral features are observed in the experimental spectra of (KI)2-(H2O) and (KI)2-(H2O)2, indicating that two types of isomers coexist, in which the high EBE feature corresponds to the hydrated chain-like (KI)2- while the low EBE feature corresponds to the hydrated pyramidal (KI)2-. In (KI)2-(H2O)3, the (KI)2- unit prefers a pyramidal configuration, and one of the K-I distances is elongated significantly, thus a K atom is firstly separated out from the (KI)2- unit. As for the neutrals, the bare (KI)2 has a rhombus structure, and the structures of (KI)2(H2O)n are evolved from the rhombus (KI)2 unit by the addition of H2O. When the number of water molecules reaches 4, the K-I distances have significant increment and one of the I atoms prefers to leave the (KI)2 unit. The comparison of (KI)2(H2O)n and (NaI)2(H2O)n indicates that it is slightly more difficult to pry apart (KI)2 than (NaI)2 via hydration, which is in agreement with the lower solubility of KI compared to that of NaI.

Microsolvation of LiI and CsI in water: anion photoelectron spectroscopy and ab initio calculations.

In order to understand the microsolvation of LiI and CsI in water and provide information about the dependence of solvation processes on different ions, we investigated the LiI(H2O)n(-) and CsI(H2O)n(-) (n = 0-6) clusters using photoelectron spectroscopy. The structures of these clusters and their corresponding neutrals were investigated with ab initio calculations and confirmed by comparing with the photoelectron spectroscopy experiments. Our studies show that the structural evolutions of LiI(H2O)n and CsI(H2O)n clusters are very different. The Li-I distance in LiI(H2O)n(-) increases abruptly at n = 3, whereas the abrupt elongation of the Li-I distance in neutral LiI(H2O)n occurs at n = 5. In contrast to the LiI(H2O)n(-) clusters, the Cs-I distance in CsI(H2O)n(-) increases significantly at n = 3, reaches a maximum at n = 4, and decreases again as n increases further. There is no abrupt change of the Cs-I distance in neutral CsI(H2O)n as n increases from 0 to 6. Water molecules interact strongly with the Li ion; consequently, water molecule(s) can insert within the Li(+)-I(-) ion pair. In contrast, five or six water molecules are not enough to induce obvious separation of the Cs(+)-I(-) ion pair since the Cs-water interaction is relatively weak compared to the Li-water interaction. Our work has shown that the structural variation and microsolvation in MI(H2O)n clusters are determined by the delicate balance between ion-ion, ion-water, and water-water interactions, which may have significant implications for the general understanding of salt effects in water solution.

Interaction of TiO2(-) with water: photoelectron spectroscopy and density functional calculations.

The interactions of titania with water molecules were studied via photoelectron spectroscopy and density functional calculations of TiO(OH)2(-) and Ti(OH)4(H2O)n(-) (n = 0-5) clusters which are corresponding to the TiO2(H2O)(-) and TiO2(H2O)n+2(-) (n = 0-5) systems, respectively. Experimental observation and theoretical calculations confirmed that TiO(OH)2(-) was produced when TiO2(-) interacts with one water molecule, and Ti(OH)4(H2O)n(-) (n = 0-5) were produced successively when TiO2(-) interacts with two or more water molecules. The structures of Ti(OH)4(H2O)n(-) with n = 4, 5 are slightly different from those of n = 1-3. The structures of Ti(OH)4(H2O)1-3(-) can be viewed as the water molecules interacting with the Ti(OH)4(-) core through hydrogen bonds; however, in Ti(OH)4(H2O)4,5(-), one of the water molecules interacts directly with the Ti atom via its oxygen atom instead of a hydrogen bond and distorted the Ti(OH)4(-) core.

Interaction of glycine with Li+ in the (H2O)n (n = 0-8) clusters.

CONTEXT: We investigated the interaction between glycine and Li+ in water environment based on the Gly·Li+(H2O)n (n = 0-8) cluster. Our study shows that for Gly·Li+, Li+ binds to both carbonyl oxygen and amino nitrogen to form a bidentate structure, and the first three water molecules preferentially interact with Li+. For n = 0-5, the complexes of Gly·Li+(H2O)n exist in neutral form, and when the water number reached 6, the complex can coexist in neutral and zwitterionic form, then zwitterionic structures are dominant for n = 7, 8. The analyses by RDG, AIM, and ESP in conjunction with the calculated interaction energies show that the interaction between Li+ and Gly decreases gradually with the water molecules involved successively from n = 1 to 6 and then increases for n = 7-8. Additionally, the infrared spectra of Gly·Li+(H2O)n (n = 0-8) are also calculated. METHODS: The initial structures were optimized using Gaussian 09 program package in B3LYP-D3 (BJ)/6-311G(d, p) method, and the frequency was calculated with 6-311 + G(2d, p) basis set. GaussView5.0.9 was used to view simulation infrared spectra. The noncovalent interaction method (NCl), energy decomposition (EDA), atoms in molecules (AIM) analysis, and electrostatic potential (ESP) analyses were conducted using Multiwfn software to gain a deeper understanding of the interaction properties of Gly, Li+, and water.

Hydrogen bonds in the nucleobase-gold complexes: photoelectron spectroscopy and density functional calculations.

The nucleobase-gold complexes were studied with anion photoelectron spectroscopy and density functional calculations. The vertical detachment energies of uracil-Au(-), thymine-Au(-), cytosine-Au(-), adenine-Au(-), and guanine-Au(-) were estimated to be 3.37 ± 0.08 eV, 3.40 ± 0.08 eV, 3.23 ± 0.08 eV, 3.28 ± 0.08 eV, and 3.43 ± 0.08 eV, respectively, based on their photoelectron spectra. The combination of photoelectron spectroscopy experiments and density functional calculations reveals the presence of two or more isomers for these nucleobase-gold complexes. The major isomers detected in the experiments probably are formed by Au anion with the canonical tautomers of the nucleobases. The gold anion essentially interacts with the nucleobases through N-H···Au hydrogen bonds.

[The study on Delphi filtering the indicators of evaluation on the diagnosis, treatment and management of MDR-TB].

OBJECTIVE: To filter the indicators of evaluation on the diagnosis, treatment and management of MDR-TB through Delphi. METHODS: Three rounds Delphi was implemented by asking for the 30 experts'score and suggestion of 60 evaluation indicators. The experts were selected from experienced MDR-TB workers. Then the concentration degree (with each indicator's score average and full mark rate to reflect) and coordination degree (with coordination coefficient w to reflect) were analyzed, and the coefficient of variation of each indicator, enthusiasm and authority coefficient Cr etc were calculated. After that, new indicators system was constructed and the experts' were asked for suggestion again. The enthusiasm and coordinate coefficient were used to measure the effect of Delphi. RESULTS: All of the enthusiasm coefficients of experts in three rounds were 100% (30/30), and 40% (12/30), 53% (16/30) and 10% (3/30) of the experts gave suggestions. The degrees of experts' authority in the first 2 rounds were high and the averages were 0.82 and 0.86, respectively. A total of 34 indicators were left after 6 indicators modified and 26 indicators deleted. The 10 indicators were the core indicators, and the average scores of 34 indicators were all higher than 4.7 and the coefficients of variation were less than 0.1, respectively. The coordination coefficients of specialists' opinion were 0.36, 0.25 and 0.68, respectively. CONCLUSION: The final evaluation indicator system include 34 indicators, and the result of the filtering indicators on the diagnosis, treatment and management of MDR-TB through Delphi is good.

Interaction of Cysteine with Li+ and LiF in the Presence of (H2O) n (n = 0-6) Clusters.

The interaction between cysteine with Li+ and LiF in the microcosmic water environment was investigated to elucidate how ions interact with amino acids and the cation-anion correlation effect involved. The structures of Cys·Li+(H2O) n and Cys·LiF(H2O) n (n = 0-6) were characterized using ab initio calculations. Our studies show that the water preferentially interacts with Li+/LiF. In Cys·Li+(H2O)0-6, Li+ interacts with amino nitrogen, carbonyl oxygen, and hydrophobic sulfur of Cys to form a tridentate mode, whereas in Cys·LiF(H2O) n , Li+ and F- work in cooperation and interact with carbonyl oxygen and hydroxyl hydrogen of Cys to form a bidentate type. The neutral and zwitterionic forms are essentially isoenergetic when the water number reaches three in the presence of Li+, whereas this occurs at four water molecules in the presence of LiF. Further research revealed that the interaction between Li+/LiF and Cys was mainly electrostatic, followed by dispersion, and the weakest interaction occurs at the transition from the neutral form to zwitterionic form. Natural population analysis charge analyses show that for Cys·Li+(H2O) n , the positive charge is mostly concentrated on Li+ except for the system containing three water molecules. For Cys·LiF(H2O) n , the positive charge is centered on the LiF unit in the range n = 0-6, and at n = 5, electron transfer from Cys to water occurs. Our study shows that the contribution of anions in zwitterionic state stabilization should be addressed more generally along with cations.