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This study provides the evidence for hydrophobic hydration of CH[sub 3]COOD as its aqueous solution was compressed by high pressure. On going from neat CH[sub 3]COOD to diluted CH[sub 3]COOD/D[sub 2]O mixtures, the C-H vibration absorption bands do not reveal the solvent shift in frequency upon dilution, while the C-H absorption bands are altered into one prominent band at ∼2955 cm[sup -1] as the pressure was applied above 0.3 GPa. The possible explanation is the enhancement of C-H-O interactions between C-H and D[sub 2]O under the condition of high pressure. Ab initio calculations predict that the CH[sub 3] stretching frequencies and intensities of acetic acid are hardly affected by the presence of water, if the methyl group does not participate in the complex formation. Nevertheless, the strongest absorption peak at ∼2928 cm[sup -1] is predicted in several low-energy (acetic acid)-(water)[sub χ]complexes with the participation of C-H-O hydrogen bond. The reorganization of hydrogen-bond network or geometry is suggested to be responsible for the formation of C-H-O hydrogen bond. [ABSTRACT FROM AUTHOR]

C-H—O interactions of a self-assembled triple helix based on the 1-acetamido-3(2-pyrazinyl)-imidazolium cation has been probed by high pressure. The infrared spectroscopic profiles and ab initio calculations allow us to make a vibrational assignment of this compound. The C-H bonds forming C-H—O interactions shorten as the pressure was elevated, while free C-H vibration modes show low sensitivity to high pressure. The pressure-dependent results can be attributed to the strengthening of C-H—O electrostatic-dispersion interactions upon increasing pressure. The appearance of the free-NH infrared absorption indicates that the conventional NH—O hydrogen bond does not dominate the inter-strand packing in the compound. It is proposed that the charge-enhanced C-H—O interactions, forming a helical hydrogen-bonding network, disturb the formation of inter-strand N-H—O hydrogen-bonding in order to form a maximum number of hydrogen bonds. Applying high-pressure seems not to change the C=O bond length in contrast to the trend of blue-shift in frequency of C-H vibrations. London dispersion energy is suggested to be required for understanding the pressure-dependent results, although more additional terms, such as the effect in the presence of charge, are needed for the correct explanation. This work demonstrates that high-pressure studies may have the potential to provide insight into the C-H—O structural properties of biological related systems. [ABSTRACT FROM AUTHOR]

The infrared spectroscopic profiles of HCOOD/D[sub 2]O mixtures were measured as a function of pressure and concentration. The C–H bond of HCOOD shortens as the pressure is elevated, while the increase in C–H bond length upon diluting HCOOD with D[sub 2]O was observed. Based on the experimental results, the shift in frequency of C–H stretching band is concluded to relate to the mechanism of the hydration of the C–H group and the water structure in the vicinity of the C–H group. The pressure-dependent results can be attributed to the strengthening of C–H---O electrostatic/dispersion interaction upon increasing pressure. The observations are in accord with ab initio calculation forecasting a blueshift of the C–H stretching mode via C–H---O interaction in HCOOD-water/(HCOOD)[sub 2]-(D[sub 2]O) complexes relative to the noninteracting monomer/dimer. Hydrogen-bonding nonadditivity and the size of water clusters are suggested to be responsible to cause the redshift in C–H stretching mode upon dilution HCOOD with D[sub 2]O. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Objective: To investigate the related factors and pathogens of ventilator-associated pneumonia (VAP) after heart surgery., Methods: VAP was diagnosed in 105 patients out of 1688 cases (6.2%) who underwent heart surgery in our department between January 2004 and January 2011. Clinical data, pathogens and treatments were analyzed., Results: Incidence of VAP was 6.2% (105/1688), and 53.0% (105/198) in patients who required more than 48 hours of mechanical ventilation. One hundred and ninety-eight pathogen strains were isolated by bacterial culture, in which Gram negative bacteria accounted for 69.2% (137/198), Gram positive bacteria 27.8% (55/198), and fungi for 3.0% (6/198). Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, Escherichia coli, and Staphylococcus aureus were the main pathogens of VAP. The independent risk factors for VAP were: age > 70 years, emergent surgery, perioperative transfusions, reintubation and days of mechanical ventilation (all P < 0.01). Median length of stay in the ICU for patients who developed VAP or not was (24.7 ± 4.5) days versus (3.2 ± 1.5) days, respectively (P < 0.05) and in-hospital mortality was 25.7% (27/105) versus 2.9% (46/1583) respectively (P < 0.05)., Conclusions: Patients undergoing heart surgery have a high frequency of developing VAP, especially in patients that require more than 48 hours of mechanical ventilation. VAP is associated with high in-hospital mortality. Age > 70 years, emergent surgery, perioperative transfusions, reintubation and prolonged mechanical ventilation use are independent risk factors for VAP in patients following cardiac surgery. Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, Escherichia coli, and Staphylococcus aureus are the main pathogens of VAP.