Mechanism of the formation of microphase separated water clusters in a water-mediated physical network of perfluoropolyether tetraol.

Perfluoropolyether tetraol (PFPE tetraol) possesses a hydrophobic perfluoropolyether chain in the backbone and two hydroxyl groups at each chain terminal, which facilitates the formation of hydrogen bonds with water molecules resulting in the formation an extended physical network. About 3 wt% water was required for the formation of the microphase separated physical network of PFPE tetraol. The mechanism responsible for the microphase separation of water clusters in the physical network was studied using a combination of techniques such as NMR spectroscopy, molecular dynamics (MD) simulations and DSC. MD simulation studies provided evidence for the formation of clusters in the PFPE tetraol physical network and the size of these clusters increased gradually with an increase in the extent of hydration. Both MD simulations and NMR spectroscopy studies revealed that these clusters position themselves away from the hydrophobic backbone or vice versa. The presence of intra- and inter-chain aggregation possibility among hydrophilic groups was evident. DSC results demonstrated the presence of tightly and loosely bound water molecules to the terminal hydroxyl groups of PFPE tetraol through hydrogen bonding. The data from all the three techniques established the formation of a physical network driven by hydrogen bonding between the hydrophilic end groups of PFPE tetraol and water molecules. The flexible nature of the PFPE tetraol backbone and its low solubility parameter favour clustering of water molecules at the terminal groups and result in the formation of a gel.

Static vs dynamic DFT prediction of IR spectra of flexible molecules in the condensed phase: The (ClCF2CF(CF3)OCF2CH3) liquid as a test case.

First-principles molecular dynamics (FPMD) simulations in the framework of Density Functional Theory (DFT) are carried out for the prediction of the infrared spectrum of the fluorinated molecule ClCF2CF(CF3)OCF2CH3 in liquid and gas phase. This molecule is characterized by a flexible structure, allowing the co-existence of several stable conformers, that differ by values of the torsional angles. FPMD computed spectra are compared to the experimental ones, and to Boltzmann weighted IR spectra based on gas phase calculations.

FT-IR spectroscopy and DFT calculations on fluorinated macromer diols: IR intensity and association properties.

Fluorinated macromeric diols have been investigated by means of Fourier transform infrared (FT-IR) spectroscopy; the absolute intensities of characteristic bands of OH stretching have been determined and related to aggregation phenomena. Main results show that the ratio between "free" and "hydrogen-bonded" OH groups strictly depends on the polarity of chemical environment (macromeric-polymeric matrix). The intepretation of the experimental data has been supported by density functional theory (DFT) calculations on suitable molecular models, validating the results obtained both qualitatively and quantitatively.

The poor outcome of ischemic stroke in very old people: a cohort study of its determinants.

OBJECTIVES: To assess how much of the excess risk of poor outcome from stroke in people aged 80 and older aging per se explains, independent of other prognostic determinants. DESIGN: Cohort, observational. SETTING: University hospital. PARTICIPANTS: One thousand five hundred fifty-five patients with first-ever ischemic stroke consecutively referred to an in-hospital Clinical Pathway program were studied. MEASUREMENTS: The relationship between age and 1-month outcome (death, disability (modified Rankin Scale 3-5), and poor outcome (modified Rankin Scale 3-6)) was assessed, with adjustment for several prognostic factors. RESULTS: Six hundred twelve patients aged 80 and older showed worse outcome after 1 month than those who were younger, in terms of mortality (19% vs 5%, hazard ratio (HR)=3.85, 95% confidence interval (CI)=2.8-5.4) and disability (51% vs 33%, odds ratio (OR)=3.16, 95% CI=2.5-4.0), although in multivariate models, the adjusted HR for mortality decreased to 1.47 (95% CI=1.0-2.16) and the ORs for disability and poor outcome decreased to 1.76 (95% CI=1.32-2.3.) and 1.83 (95% CI=137-2.43), respectively. Stroke severity, the occurrence of at least one medical complication, and premorbid disability explained most of the risk excess in the oldest-old. CONCLUSION: Stroke outcome is definitely worse in very old people, and most of the excess risk of death and disability is attributable to the higher occurrences of the most-severe clinical stroke syndromes and of medical complications in the acute phase. These represent potential targets for preventive and therapeutical strategies specifically for elderly people.