Infrared dynamics study of thermally treated perfluoroimide acid proton exchange membranes.

The temperature induced dehydration process of the 3M Brand perfluoroimide acid (PFIA), an advanced proton exchange membrane for fuel cells, was studied by in situ infrared spectroscopy to understand proton transport processes under conditions of low hydration levels. A comprehensive assignment of the vibrational bands of PFIA in the mid infrared region is provided. Investigation of the kinetics in conjunction with 2D correlation spectroscopy methods revealed the sequential process of the hydration and dehydration in a conclusive model. The results indicate that at a lower water content the sulfonate group of the PFIA side chain is preferentially ionised and involved in a hydrogen bonding structure with the sulfonyl imide acid group, until a sufficient amount of water is present to ionise the second ionic site. Comparison to the well-understood NAFION™ membrane revealed that under low humidity conditions a higher amount of water is retained in PFIA in a state most similar to liquid water. The results contribute to a better understanding of water retention capability and thus proton conductivity under high-temperature and low-humidity conditions.

Self-association of organic solutes in solution: a NEXAFS study of aqueous imidazole.

N K-edge near-edge X-ray absorption fine-structure (NEXAFS) spectra of imidazole in concentrated aqueous solutions have been acquired. The NEXAFS spectra of the solution species differ significantly from those of imidazole monomers in the gas phase and in the solid state of imidazole, demonstrating the strong sensitivity of NEXAFS to the local chemical and structural environment. In a concentration range from 0.5 to 8.2 mol L(-1) the NEXAFS spectrum of aqueous imidazole does not change strongly, confirming previous suggestions that imidazole self-associates are already present at concentrations more dilute than the range investigated here. We show that various types of electronic structure calculations (Gaussian, StoBe, CASTEP) provide a consistent and complete interpretation of all features in the gas phase and solid state spectra based on ground state electronic structure. This suggests that such computational modelling of experimental NEXAFS will permit an incisive analysis of the molecular interactions of organic solutes in solutions. It is confirmed that microhydrated clusters with a single imidazole molecule are poor models of imidazole in aqueous solution. Our analysis indicates that models including both a hydrogen-bonded network of hydrate molecules, and imidazole-imidazole interactions, are necessary to explain the electronic structure evident in the NEXAFS spectra.

The electronic structure of perfluorodecalin studied by soft X-ray spectroscopy and electronic structure calculations.

Fluorine and carbon K absorption and emission spectra of liquid perfluorodecalin are presented and analyzed in terms of density functional calculations-configuration interaction. A comprehensive view of the electronic structure is given, and site-specific intramolecular interactions are investigated in detail. It is found that, while the outer fluorine atoms have excess charge in the ground state, the lowest excitations must be associated with charge transfer towards the inner carbon atoms.

The association of the Friesinger score and estimated glomerular filtration rate in an urban South Asian patient population.

AIM: The correlation between kidney function and coronary artery disease (CAD) severity as assessed by an angiographic score has not yet been studied in the South Asian population. We sought to estimate the association by performing a single-center, cross-sectional study. PATIENTS AND METHODS: The estimated glomerular filtration rate (eGFR) calculated by the CKD-EPI equation and the Friesinger score to quantify the severity of CAD were the primary endpoints in patients undergoing coronary angiograms. RESULTS: The mean eGFR was significantly lower in participants with a Friesinger score of > 5 compared to participants with a score of < 5 (73 vs. 86 ml/min/1.73 m(2) by MDRD). In univariate analysis, an eGFR of < 55 ml/min/1.73 m(2) was associated with a 9.5-fold increased odds of a higher Friesinger score compared to an eGFR >= 55 ml/min/1.73 m2 (p = 0.043), which was unchanged in multivariate analysis. In multivariate analysis, a 10 ml/min/1.73 m(2) decrease in eGFR was associated with a 1.63-fold increased odds of a higher score (95% CI 1·10 - 2.37, p = 0.042). Traditional risk factors such as a history of previous CAD, hypertension, and dyslipidemia remained predictors of a higher Friesinger score. CONCLUSION: Our study demonstrates that kidney function as assessed by eGFR is a significant independent predictor of severity of CAD as determined by the Friesinger score.

Femtosecond modification of electron localization and transfer of angular momentum in nickel.

The rapidly increasing information density required of modern magnetic data storage devices raises the question of the fundamental limits in bit size and writing speed. At present, the magnetization reversal of a bit can occur as quickly as 200 ps (ref. 1). A fundamental limit has been explored by using intense magnetic-field pulses of 2 ps duration leading to a non-deterministic magnetization reversal. For this process, dissipation of spin angular momentum to other degrees of freedom on an ultrafast timescale is crucial. An even faster regime down to 100 fs or below might be reached by non-thermal control of magnetization with femtosecond laser radiation. Here, we show that an efficient novel channel for angular momentum dissipation to the lattice can be opened by femtosecond laser excitation of a ferromagnet. For the first time, the quenching of spin angular momentum and its transfer to the lattice with a time constant of 120+/-70 fs is determined unambiguously with X-ray magnetic circular dichroism. We report the first femtosecond time-resolved X-ray absorption spectroscopy data over an entire absorption edge, which are consistent with an unexpected increase in valence-electron localization during the first 120+/-50 fs, possibly providing the driving force behind femtosecond spin-lattice relaxation.