DFT Study of the Reaction Mechanisms of Carbon Dioxide and its Isoelectronic Molecules CS2 and OCS Dissolved in Pyrrolidinium and Imidazolium Acetate Ionic Liquids.

The reaction mechanisms of CO2 and its isoelectronic molecules OCS and CS2 dissolved in N-butyl-N-methylpyrrolidinium acetate and in 1-butyl-3-methylimidazolium acetate were investigated by DFT calculations in "gas phase". The analysis of predicted multistep pathways allowed calculating energies of reaction and energy barriers of the processes. The major role played by the acetate anion in the degradation of the solutes CS2 and OCS as well as in the capture of OCS and CO2 by the imidazolium ring is highlighted. In both ionic liquids, this anion governs the conversion of CS2 into OCS and of OCS into CO2 through interatomic S-O exchanges between the anion and the solutes with formation of thioacetate anions. In imidazolium acetate, the selective capture of CS2 and OCS by the imidazolium ring competes with the S-O exchanges. From the calculated values of the energy barriers a basicity scale of the anions is proposed. The (13)C NMR chemical shifts of the predicted adducts were calculated and agree well with the experimental observations. It is argued that the scenario issued from the calculated pathways is shown qualitatively to be independent from the functionals and basis set used, constitute a valuable tool in the understanding of chemical reactions taking place in liquid phase.

[Very preterm births in French Polynesia: update and proposal for follow-up]. / La grande prématurité en Polynésie française : évaluation et perspectives de prise en charge.

INTRODUCTION: The care of premature infants in French Polynesia is complicated by this country's geographic isolation. We undertook an evaluation of the medical care of very premature infants (VPIs) to find local solutions to this problem. OBJECTIVES: The objectives were to determine the incidence, mortality, and the short- and long-term outcome of very preterm infants in French Polynesia. METHODS: We retrospectively reviewed the medical charts of all infants born alive at<32 gestational age (GA) and>24 GA from January 2007 to December 2011. Perinatal characteristics and outcomes were examined by univariate and multivariate analysis. RESULTS: In total, 204 VPIs were born during the 5-year study period, comprising 0.9% of all births. Infants less than 28 GA comprised 0.1% of all births. Sixty-two percent of mothers were of extreme age including 43% less than 25 years old. Prematurity was attributed to spontaneous preterm labor in 63% of cases and preeclampsia in 29%. Spontaneous multiple pregnancies comprised 15% of the cases. Alcohol and tobacco consumption were frequently noted (>8% and 26% mothers, respectively). Seventy-eight percent of VPIs had received prenatal steroids. Intrauterine growth was normal in 89%. Mortality occurred in 9.3% (19 patients). Mortality was higher with lower gestational age (P<0.05) and absence of prenatal steroids (P<0.05) in univariate and multivariate analysis. The primary cause of death was sepsis. Hyaline membrane disease occurred in 44% of patients, 80% of whom received surfactant therapy. In total, 16.2% newborns developed bronchodysplasia, 3.4% necrotizing enterocolitis, 3% cerebral hemorrhage, and 1.5% leukomalacia. Long-term outcome was marked by 52% of the patients lost to follow-up by 2 years of age, mostly because of geographic isolation. For the 72 patients followed-up, four developed asthma and three cerebral palsy; 70% were attending school by 3 years of age. CONCLUSIONS: The incidence, mortality, and morbidity of very preterm birth in French Polynesia are comparable to reports from metropolitan centers in France. Conversely, nearly one-half of the patients were lost to follow-up, precluding meaningful information on intellectual development and other outcomes. We recommend organizing a long-term follow-up network to detect cognitive sequelae and adapting such a system to the geographical residence of French Polynesian families.

Assessing the non-ideality of the CO2-CS2 system at molecular level: a Raman scattering study.

The dense phase of CO2-CS2 mixtures has been analysed by Raman spectroscopy as a function of the CO2 concentration (0.02-0.95 mole fractions) by varying the pressure (0.5 MPa up to 7.7 MPa) at constant temperature (313 K). The polarised and depolarised spectra of the induced (ν2, ν3) modes of CS2 and of the ν1-2ν2 Fermi resonance dyad of both CO2 and CS2 have been measured. Upon dilution with CO2, the evolution of the spectroscopic observables of all these modes displays a "plateau-like" region in the CO2 mole fraction 0.3-0.7 never previously observed in CO2-organic liquids mixtures. The bandshape and intensity of the induced modes of CS2 are similar to those of pure CS2 up to equimolar concentration, after which variations occur. The preservation of the local ordering from pure CS2 to equimolar concentration together with the non-linear evolution of the spectroscopic observables allows inferring that two solvation regimes exist with a transition occurring in the plateau domain. In the first regime, corresponding to CS2 concentrated mixtures, the liquid phase is segregated with dominant CS2 clusters, whereas, in the second one, CO2 monomers and dimers and CO2-CS2 hetero-dimers coexist dynamically on a picosecond time-scale. It is demonstrated that the subtle interplay between attractive and repulsive interactions which provides a molecular interpretation of the non-ideality of the CO2-CS2 mixture allows rationalizing the volume expansion and the existence of the plateau-like region observed in the pressure-composition diagram previously ascribed to the proximity of an upper critical solution temperature at lower temperatures.

Carbon dioxide in 1-butyl-3-methylimidazolium acetate. I. Unusual solubility investigated by Raman spectroscopy and DFT calculations.

The unusual solubility of carbon dioxide in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been studied by Raman spectroscopy and DFT calculations. It is shown that the solubility results from the existence of two distinct solvation regimes. In the first one (CO(2) mole fraction ≤ 0.35), the usual Fermi dyad is not observed, a fact never reported before for binary mixtures with organic liquids or ionic liquids (IL). Strong experimental evidence complemented by effective DFT modeling shows that this regime is dominated by a chemical reaction leading to the carboxylation of the imidazolium ring accompanied by acetic acid formation. The reactive scheme proposed involves two concerted mechanisms, which are a proton exchange process between the imidazolium cation and the acetate anion and the carboxylation process itself initiated from the formation of "transient" CO(2)-1-butyl-3-methylimidazole 2-ylidene carbene species. In that sense, CO(2) triggers the carboxylation reaction. Moreover, this dynamic picture circumvents consideration of a long-lived carbene formation in dense phase. The second regime is characterized by the detection of the CO(2) Fermi dyad showing that the carboxylation reaction has been strongly moderated. This finding has been interpreted as due to the interaction of the acetic acid molecules with the COO group of acetate anions involved in monodentate forms with the cation. The observation of the Fermi doublet allows us to infer that CO(2) essentially preserves its linear geometry and that the nature and strength of the interactions with its environment should be comparable to those existing in organic liquids and other IL as well. These results have been supported by DFT calculations showing that the CO(2) molecule interacts with energetically equivalent coexisting structures and that its geometry departs only slightly from the linearity. Finally, we find that the CO(2) solvation in Bmim Ac and 1-butyl-3-methylimidazolium trifluoroacetate (Bmim TFA) cannot be straightforwardly compared neither in the first regime due to the existence of a chemical reaction nor in the second regime because CO(2) interacts with a variety of environments not only consisting of ions pairs like in Bmim TFA but also with carboxylate and acetic acid molecule.

Solubility of CO2 in 1-butyl-3-methyl-imidazolium-trifluoro acetate ionic liquid studied by Raman spectroscopy and DFT investigations.

The polarized and depolarized Raman spectra of 1-butyl-3-methyl-imidazolium-trifluoro acetate (Bmim TFA) ionic liquid and of the dense phase obtained after introduction of supercritical carbon dioxide (313K) under pressure (from 0.1 MPa up to 9 MPa) in the ionic liquid have been recorded. The spectrum of the pure ionic liquid has been assigned by comparison with the spectra of ionic liquids sharing the same cation and using literature data concerning the vibrational modes of the TFA anion. It was found that the spectra of the ionic liquid is almost unaffected by the CO(2) dilution. The only noticeable perturbation concerns a weak enhancement of the mode assigned here to the symmetric stretch vibration of the COO group of the TFA anion. The band shape analysis of the ν(CC) band in pure Bmim TFA shows that the carboxylate groups probe a variety of environments which are almost not affected by the dilution in carbon dioxide. The analysis of the Fermi dyad of carbon dioxide shows that this molecule is perturbed upon dilution in the ionic liquid. The spectra suggest the presence of carbon dioxide in two different environments. In the first one, carbon dioxide molecules interact with themselves, whereas in the second environment, this molecule interacts with the COO group of the TFA anion. This is supported by B3LYP-DFT calculations aimed at assessing the interaction between an ion pair dimer and a carbon dioxide molecule. It is shown that dissolved CO(2) molecules preferentially interact with the TFA anion through a weak charge transfer interaction taking place between the carbon atom of CO(2) (acting as a Lewis acid) and a oxygen atom of the COO group of TFA (as a Lewis base). The results show that Bmim TFA is able to accommodate a large amount of carbon dioxide without having its short-range local structure significantly perturbed. Most CO(2) is hosted in the voids existing among the ion pairs, while some also weakly interact with the anion. It is finally argued that the evolution of the local organization of the IL upon carbon dioxide dilution presents similarities with the microsegregation phenomena reported for IL upon increasing the alkyl chains lengths.

[Capsule endoscopy in children: which are the best indications?]. / Quelles indications pour l'endoscopie du grêle par vidéocapsule en pédiatrie?

BACKGROUND AND STUDY AIMS: Capsule endoscopy (CE) is a novel and noninvasive means of investigating the small bowel. In children, the best CE indications have not yet been fully appraised. The aim of this study was to evaluate the diagnostic yield of CE in different pediatric pathologies. PATIENTS AND METHODS: We retrospectively reviewed every CE performed in children in two French pediatric hospitals between March 2002 and June 2009. Seventy-nine CEs were performed on 70 children (mean age, 10.6 years; range, 2.2-18.0); 52 boys and 18 girls. The indications were iron deficiency anemia (24%), obscure gastrointestinal bleeding (14%), polyposis syndromes (16%), suspected Crohn disease (15%), unresponsive Crohn disease (10%), graft-versus-host disease (10%), and other (10%). RESULTS: Of the 79 CEs, 69 reached the cecum (87%). Only one occlusion occurred in a case of stenosing Crohn disease, requiring surgical removal. In addition, technical difficulties led to an incomplete small bowel study in 12 cases (16%). The CE showed small bowel lesions in 42 cases (53%). The diagnostic yield was 27% in obscure gastrointestinal bleeding, 37% in iron-deficiency anemia, 42% in suspected Crohn disease, 88% in unresponsive Crohn disease, 62% in polyposis syndromes, and 88% in graft-versus-host disease. CONCLUSION: In children, CE is well tolerated and can be performed in children as young as 2.2 years of age. Its diagnostic yield is highest in polyposis syndromes, unresponsive Crohn disease, and graft-versus-host disease.

Interaction of water highly diluted in 1-alkyl-3-methyl imidazolium ionic liquids with the PF6(-) and BF4(-) anions.

We have investigated water highly diluted in 1-alkyl-3-methyl imidazolium ionic liquids (ILs) with hexafluorophosphate {PF(6)(-)} and tetrafluoroborate {BF(4)(-)} anions using vibrational spectroscopic measurements in the nu(OH) spectral domain of water (3600-3800 cm(-1)) and DFT calculations. The measured profiles exhibit two well-defined bands at coinciding vibrational transitions assigned with the nu(1) symmetric and nu(3) antisymmetric OH stretching modes of monodispersed water. The local organization and the vibrational spectra of water diluted in ILs have been assessed by DFT calculations (using the B3LYP functional and 6-31+G** basis set). We show that the predicted structures of water interacting (minimally) with two anions in nearly "symmetric" structures of type (A...H-O-H...A) lead to spectral features consistent with the previous spectroscopic observations as well as with those reported here. We emphasize the role of the non additive interaction forces (especially the 3-bodies electrostatic interactions) in the structural organization taking place between the cation-anion couples and for determining preferentially (A...H-O-H...A) associations of water with the anions as well as their consequences on the vibrational spectra of water. We show that the doubly hydrogen-bonded character of water in such associations leads to well-defined spectral features, which are the shifts of the nu(1) and nu(3) stretching modes of water, the separation Delta nu(13) between them (about 80 cm(-1)), and the intensity ratio estimates R = I nu(3)/I nu(1) (IR absorption and Raman). Finally, we evoke the fact that the H-bond interactions of water diluted in these ILs involve a more noticeable electrostatic character than for H-bond interactions of water in usual molecular solvents. In this context, we emphasize that the appearance of the Raman band of the nu(3) mode of water originates from a significant polarization of water due to the local electrostatic fields induced by surrounding ions.

Transient complex formation in CO2-hexafluorobenzene mixtures: a combined raman and ab initio investigation.

The polarized and depolarized Raman spectra of CO2 in binary mixtures with hexafluorobenzene have been measured in the dense phase along the isotherm 313 K as a function of concentration (0.03-0.7 molar fraction in CO2) by varying the pressure (0.5-6.2 MPa). Experimental observations in the nu2 bending region, in the nu1-2nu2 Fermi resonance dyad, and in the spectral domain between the Fermi dyad peaks on CO2 are reported. These results are discussed in comparison with those obtained in previous studies on CO2-C6H6 and CO2-acetone mixtures. We conclude in agreement with previous investigations that CO2 molecules can probe two environments. In one of them carbon dioxide interacts "specifically" with hexafluorobenzene molecules to form a transient heterodimer, whereas in the other environment CO2 interacts "nonspecifically" with its neighbors. New ab initio calculations reported here allow rationalizing most of the experimental results. However, the observation of weak spectral features (bending mode and Fermi dyad regions) shows that a slight departure from the predicted structure (C6v symmetry) should exist in the dense phase. Finally, the greater solubility of CO2 in perfluorinated benzene versus perhydrogenated benzene has been discussed on the basis of this study in connection with thermodynamic measurements interpreted in the scaled particle theory framework.