Solvation dynamics of electron produced by two-photon ionization of liquid polyols. III. Glycerol

The solvation dynamics of excess electrons in glycerol have been measured by the pump-probe femtosecond laser technique at 333 K. The electrons are produced by two-photon absorption at 263 nm. The change in the induced absorbance is followed up to 450 ps in the spectral range from 440 to 720 nm. The transient signals of electron solvation have been analyzed by two kinetic models: a stepwise mechanism and a continuous relaxation model, using a Bayesian data analysis method. The results are compared with those previously published for ethylene glycol (J. Phys. Chem. A 2006, 110, 175) and for propanediols (J. Phys. Chem. A 2007, 111, 4902). From the comparison, it is pointed out that solvation dynamics in glycerol is very fast despite its high viscosity. This is interpreted as the existence of efficient traps for the electrons in glycerol with low potential energy. The small shift of the absorption band of the excess electron indicates that the potential of these traps is very close to that corresponding to the fully solvated electron.

Solvation dynamics of the electron produced by two-photon ionization of liquid polyols. 1. Ethylene glycol

Solvated electrons have been produced in ethylene glycol by two-photon ionization of the solvent with 263 nm femtosecond laser pulses. The two-photon absorption coefficient of ethylene glycol at 263 nm is determined to be beta = (2.1 +/- 0.2) x 10(-11) m W(-1). The dynamics of electron solvation in ethylene glycol has been studied by pump-probe transient absorption spectroscopy. So, time-resolved absorption spectra ranging from 430 to 710 nm have been measured. A blue shift of the spectra is observed for the first tens of picoseconds. Using the Bayesian data analysis method, the observed solvation dynamics are reconstructed with different models: stepwise mechanisms, continuous relaxation models, or combinations of stepwise and continuous relaxation. Comparison between models is in favor of continuous relaxation, which is mainly governed by solvent molecular motions.

Solvation dynamics of electron produced by two-photon ionization of liquid polyols. II. Propanediols

Temporal evolution of transient absorption spectra of electrons produced by two-photon ionization of two isomers, propane-1,2-diol (12PD) and propane-1,3-diol (13PD), with 263 nm femtosecond laser pulses has been studied on picosecond time scale. The two-photon absorption coefficients of 12PD and 13PD at 263 nm were determined to be beta = (2.0 +/- 0.3) x 10(-11) and (2.4 +/- 0.3) x 10(-11) m W(-1), respectively. Time-resolved absorption spectra ranging from 440 to 720 nm have been measured, showing a blue shift for the first tens of picoseconds for both solvents. However, the observed solvation dynamics of electron appears faster in 13PD than in 12PD. The transient signals of electron solvation have then been reconstructed with different models (stepwise mechanism or continuous relaxation model) using a Bayesian data analysis method. Results are discussed, compared with those previously obtained in ethylene glycol (J. Phys. Chem. A 2006, 110, 1705) and corroborate the interpretation, according to which the solvation of electrons is mainly governed by continuous solvent molecular motions.

Fournier's gangrene: an unusual presentation for rectal carcinoma

We report a case of a large perforated adenocarcinoma of the rectum manifesting as an ischiorectal abscess progressing to Fournier's gangrene in an insulin-dependent diabetic man. Recognition and management of this rare syndrome in the setting of a common disease is discussed.

Production of soluble virulence factor by Escherichia coli

Experimental evidence suggests that adherence is a prerequisite for bacterial infection. We demonstrated that transitional cells at the surface of the bladder are coated with glycosaminoglycans (proteoglycans and mucus) whose presence efficiently decreases bacterial adherence to the mucosa. Exposure of mucus to protamine sulfate, a quaternary amine (known to form salts with glycosaminoglycans and inactivate them) significantly increases the bacterial adherence to the bladder. Investigators have primarily focused on bacterial surface factors (that is pili or fimbriae, glycocalix) in relation to the ability to adhere. We explored the hypothesis that Escherichia coli produces a soluble virulence factor that increases the infection rate in rabbits by promoting bacterial adherence to the bladder mucosa. In addition, it was proposed that this factor is a quaternary amine similar to protamine. For these studies an in vivo bacterial infection assay (which we described previously in rabbits) was used to examine E. coli metabolic products (soluble virulence factor) that could promote bacterial persistence in the bladder by perturbing mucus (glycosaminoglycans), and promote bacterial adherence and virulence. E. coli was grown in human urine and a bacterial-free supernatant was collected. Rabbit bladders were then exposed to either this supernatant or to the same human urine that was not infected with E. coli. Results show a significantly higher bacterial persistence (bacterial count) in bladders pretreated with urine containing the E. coli supernatants compared to controls pretreated with uninfected urine (p = 0.03). The molecular weight of the putative soluble virulence factor is less than 3.5 kD. (p = 0.056) based on dialysis studies and binds to heparin agarose affinity chromatography matrix, suggesting that it is cationic and capable of adhering to the highly anionic bladder mucus (glycosaminoglycans).