Electron Transfer Mediated by Iron Carbonyl Clusters Enhance Light-Driven Hydrogen Evolution in Water by Quantum Dots.

Photocatalytic water splitting has become a promising strategy for converting solar energy into clean and carbon-neutral solar fuels in a low-cost and environmentally benign way. Hydrogen gas is such a potential solar fuel/energy carrier. In a classical artificial photosynthetic system, a photosensitizer is generally associated with a co-catalyst to convert photogenerated charge into (a) chemical bond(s). In the present study, assemblies consisting of CdSe quantum dots that are coupled with one of two molecular complexes/catalysts, that is, [Fe2 S2 (CO)6 ] or [Fe3 Te2 (CO)9 ], using an interface-directed approach, have been tested as catalytic systems for hydrogen production in aqueous solution/organic solution. In the presence of ascorbic acid as a sacrificial electron donor and proton source, these assemblies exhibit enhanced activities for the rate of hydrogen production under visible light irradiation for 8 h in aqueous solution at pH 4.0 with up to 110 µmol of H2 per mg of assembly, almost 8.5 times that of pure CdSe quantum dots under the same conditions. Transient absorption and time-resolved photoluminescence spectroscopies have been used to investigate the charge carrier transfer dynamics in the quantum dot/iron carbonyl cluster assemblies. The spectroscopic results indicate that effective electron transfer from the molecular iron complex to the valence band of the excited CdSe quantum dots significantly inhibits the recombination of photogenerated charge carriers, boosting the photocatalytic activity for hydrogen generation; that is, the iron clusters function as effective intermediaries for electron transfer from the sacrificial electron donor to the valence band of the quantum dots.

Quantitative ultrasonography and magnetic resonance imaging of the parotid gland: can they replace the histopathologic studies in patients with Sjogren's syndrome?

OBJECTIVE: To assess the diagnostic value of parotid gland quantitative assessment using ultrasound (US) as well as magnetic resonance imaging (MRI) in patients with Sjogren's syndrome (SS) and to evaluate the possibility of using such modalities as a predictor of the histopathologic score of salivary gland biopsy in this group of patients. METHODS: Sonographic and MRI studies were performed on the parotid glands of 47 patients diagnosed to have primary SS, 20 healthy control subjects of matched sex and age, and 20 subjects with sicca symptoms but without any evidence of SS. The patients and the control subjects were scored according to the structural changes seen in both radiologic modalities. In addition, sialography and labial gland biopsy were done for all patients as well as the control subjects and scored according to the degree of affection. RESULTS: Parenchymal inhomogenity (PIH) was seen in 93.6% of the patients studied by US, while nodular pattern was seen in 97.8% in the MRI study. The US and MRI results correlated significantly with the histopathologic score of the minor salivary glands (r = 0.82, 0.84, respectively) as well as sialography score (r = 0.69, 0.60, respectively). There was good agreement between US and MRI findings (r = 0.87) in both SS cases and control subjects. CONCLUSION: US and MRI are equally sensitive tools for the diagnosis of salivary involvement in patients with SS. Quantitative assessment of US and MRI images seem to represent an advance in the diagnosis of SS as they offer a good prediction of the pathology score of the salivary gland. MRI seems unnecessary as a routine diagnostic tool and should be considered as the second option in case of normal US.