154 research outputs found
Water Oxidation Catalysis by Molecular Metal-Oxides
Abstract Water oxidation catalysis is recognized as the bottleneck for the development of efficient devices based on artificial photosynthesis, that is the light driven water splitting into hydrogen and oxygen. A recent breakthrough in this field, is the development of a molecular, fast and robust water oxidation catalyst namely a fully inorganic tetranuclear ruthenium complex with polyoxometalate ligands. The crystal structure of [Ru4(μ-O)4(μ-OH)2(H2O)4(SiW10O36)2]10-, 1, evidences the entrapment of an adamantane like, tetranuclear ruthenium(IV)-oxo core, by two decatungtosilicate units. Several spectroscopic techniques confirm the maintenance of the structure in aqueous solution. In the presence of Ce(IV) as sacrificial electron acceptor, 1 catalyzes water oxidation to oxygen, showing up to 500 turnovers and a turnover frequency of 0.125 s-1. The synergistic effect of the four ruthenium centres has a fundamental effect on such astounding performance, as confirmed by spectroscopic and computational characterization of five competent intermediates involved in the catalytic cycle, in strict analogy with the natural paradigm of the oxygen evolving centre in Photosystem II. Interestingly, 1 efficiently catalyzes water oxidation in the presence of photogenerated oxidants, as well; this fundamental feature is probably related to very fast hole scavenging of anionic 1 from cationic photogenerated oxidants, such as Ru(bpy)33+. Thus, 1 is an ideal candidate for the assembly of high efficient oxygenevolving anodes into nanostructured devices for artificial photosynthesis
Efficacy of a new technique - INtubate-RECruit-SURfactant-Extubate - "IN-REC-SUR-E" - in preterm neonates with respiratory distress syndrome: Study protocol for a randomized controlled trial
Background: Although beneficial in clinical practice, the INtubate-SURfactant-Extubate (IN-SUR-E) method is not successful in all preterm neonates with respiratory distress syndrome, with a reported failure rate ranging from 19 to 69 %. One of the possible mechanisms responsible for the unsuccessful IN-SUR-E method, requiring subsequent re-intubation and mechanical ventilation, is the inability of the preterm lung to achieve and maintain an "optimal" functional residual capacity. The importance of lung recruitment before surfactant administration has been demonstrated in animal studies showing that recruitment leads to a more homogeneous surfactant distribution within the lungs. Therefore, the aim of this study is to compare the application of a recruitment maneuver using the high-frequency oscillatory ventilation (HFOV) modality just before the surfactant administration followed by rapid extubation (INtubate-RECruit-SURfactant-Extubate: IN-REC-SUR-E) with IN-SUR-E alone in spontaneously breathing preterm infants requiring nasal continuous positive airway pressure (nCPAP) as initial respiratory support and reaching pre-defined CPAP failure criteria. Methods/design: In this study, 206 spontaneously breathing infants born at 24+0-27+6 weeks' gestation and failing nCPAP during the first 24 h of life, will be randomized to receive an HFOV recruitment maneuver (IN-REC-SUR-E) or no recruitment maneuver (IN-SUR-E) just prior to surfactant administration followed by prompt extubation. The primary outcome is the need for mechanical ventilation within the first 3 days of life. Infants in both groups will be considered to have reached the primary outcome when they are not extubated within 30 min after surfactant administration or when they meet the nCPAP failure criteria after extubation. Discussion: From all available data no definitive evidence exists about a positive effect of recruitment before surfactant instillation, but a rationale exists for testing the following hypothesis: a lung recruitment maneuver performed with a step-by-step Continuous Distending Pressure increase during High-Frequency Oscillatory Ventilation (and not with a sustained inflation) could have a positive effects in terms of improved surfactant distribution and consequent its major efficacy in preterm newborns with respiratory distress syndrome. This represents our challenge. Trial registration: ClinicalTrials.gov identifier: NCT02482766. Registered on 1 June 2015
LEVELLING OF SUBSTITUENT EFFECTS ON ACIDITIES IN THE GAS PHASE COMPARED WITH THOSE IN SOLUTION
Substituent effects on a series of ionization reactions of neutral and positively charged acids have been studied in different media (gas phase, water and dimethyl sulphoxide) through linear plots of relative free energies (deltaDeltaG) using the ionization of benzoic acids in the same medium as a reference. While the absolute magnitudes of deltaDeltaAG values in solution are lower than in the gas phase (this effect being well known as 'solvent attenuation'), we show that rho values in the gas phase are levelled to values close to unity for all reactions considered, while in solution they are spread over a range of values. Therefore, if substituent effects in a given system are calculated by making reference to an equilibrium in the same system, structural effects on reactivities are actually better differentiated in solution than in the gas phase
Acid-Base Properties of Organic Solvents
The protonation equilibria of organic compounds commonly employed as dipolar nonhydroxylic solvents (including amides, nitriles, sulfones, and nitro compounds) have been measured at 25 C in aqueous sulfuric acid with an NMR technique. The definition of the protonation parameters pKBH+ and m* allows comparison of the relative basicities in water and in concentrated acids. An inversion of relative basicities is observed between dimethylformamide and hexamethylphosphoric triamide on going from dilute to concentrated solutions. The relative basicity scale for dipolar nonhydroxylic solvents in aqueous sulfuric acid is amides > dimethyl sulfoxide > acetone >> acetonitrile > sulfones > nitromethane. The last three functional groups are only 20-50% protonated in 100% sulfuric acid. Hexamethylphosphoric triamide is oxygen-protonated in aqueous acids, and in oleum mixtures it is largely diprotonated; diprotonation also occurs (to a lesser extent) for tetramethylurea
Site of ionization of polyfunctional bases and acids .1. Ab initio proton affinities
The acid-base equilibria of a series of monofunctional and polyfunctional bases and acids have been investigated with ab initio theoretical methods; the structures and energies of the neutral form and of the forms ionized at all ionization sites have been determined. Predictions concerning the preferred site of ionization are made on the basis of the energetics. a) For bases of the type NHm-XHn (X = O,S) the preferred protonation site (by 20-30 kcal/mol) is the nitrogen, but the preference is less marked (deltaE = 7 kcal/mol) for X=P. (b) Amides deriving from weak acids (carboxylic, thiocarboxylic, cyanic, nitrous, sulfinic, etc.) protonate preferentially at the acid residue rather than at the nitrogen, with deltaE\u2019s between 10 and 30 kcal/mol. (c) Amides deriving from strong acids (nitric, sulfonic) do not show a marked preference, deltaE forthe two tautomeric protonated forms being ca.2-3 kcal/mol. (d) Carboxylic acids and esters are protonated at the carbonyl oxygen, O-alkyl protonation being less favored by20 kcal/mol. (e) Dimethylsulfoxide is O-protonated. N-protonation of some non-carboxylic amides and O-alkyl protonation of carboxylic acids and esters leads to a substantial lengthening of the bond between N or O and the acid residue and to overall structural changes indicating dissociation. The gas-phase energetics are used for the estimation of relative solution basicities by means of the energies of solvation of simple models
Stability and solvation of carbenium ions deriving from protonation-dehydration of arylcarbinols
The protonation-dehydration equilibria of several diaryl, triaryl, and diarylalkylcarbinols leading to carbenium ions have been investigated by the excess acidity method. The results are firstly employed for an assessment of the acidity functions (H-R and H-R) determined from those data. It is shown that both acidity functions are faulty in several respects, e.g. because they were determined from indicators for which parallelism of plots was hardly attained. In contrast, the excess acidity method is shown to yield protonation parameters (m* and pK(R+)) which can be interpreted in terms of structural and solvation effects on the stability of carbenium ions. The relationship of these parameters with enthalpies of reaction with FSO3H is also discussed
Selectivity in proton transfer, hydrogen bonding, and solvation
The site of protonation (or deprotonation) of polyfunctional bases and acids can be determined through the comparison of experimental NMR properties (chemical shift and relaxation rates) with the corresponding data calculated by quantum chemical methods. The results can be interpreted in terms of the competition between intrinsic base strengths and solvation. Qualitatively similar criteria are found to hold for hydrogen bonding. The selective enrichment in a cosolvent in the solvation shell of a solute dissolved in a solvent mixture (preferential solvation) can be determined through the analysis of intermolecular cross-peak intensities in NOESY spectra
Site of ionization of polyfunctional bases and acids .2. Ab initio electric field gradients at nitrogen, oxygen, phosphorus, and sulfur in neutral and ionized forms
The electric field gradients (efg) at nitrogen, oxygen, phosphorus, and sulfur have been investigated with ab initio theoretical methods for a series of monofunctional and polyfunctional bases and acids and their ionized forms. Absolute efg values of neutral species are compared with theoretical results from the literature and used to give estimates of NMR linewidths insolution. Efg changes occurring upon the acid-base process, expressed as effective nuclear quadrupolar coupling constants, are used to predict changes in the NMR relaxation
rates of the pertinent quadrupolar nuclei (14N, 17O, 33S) upon ionization. This information, joined to relative proton affinities, allows one to predict the preferred ionization site in solution of a given polyfunctional acid or base and to establish criteria whereby such equilibria can be investigated by heteronuclear NMR
Ion chemistry of chloroethanes in air at atmospheric pressure
Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500-1500 ppm) at atmospheric pressure were investigated at 30 °C and at 300 °C. Spectral changes due to collisional activation of the ions achieved by increasing δV, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+•, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M - H]+ and [M - HCl]+• species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing δV, the [M - HCl]+• ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl- and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X-) (M)n where X- is a background ion of the APCI plasma, namely O2 -,O3 - and, in some cases, (NO)2 -. Peculiar to 1,1,1-trichloroethane are species attributed to Cl- complexes with phosgene, (Cl-)(Cl2C=O)n(n = 1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl-)(Cl2C=O)n and (Cl-)(M)n happen to be isobaric
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