Sonia Menéndez

Elemental and molecular mass spectrometry for integrated selenosugar speciation in liver and kidney tissues of maternal feeding and supplemented rats

The development of methods assessing the nutritional value and metabolism of selenium are of growing interest. In this work, the integrated used of a methodology based on HPLC-isotope pattern deconvolution (IPD)-ICP-MS and a molecular tandem mass spectrometric technique, such as HPLC-APCI-MS/MS, in the selected reaction monitoring (SRM) mode, was applied to quantify and identify the selenosugar SeGalNAc in liver and kidney tissues of lactating rats fed with formula milk supplemented with 77selenite. The SeGalNAc levels found in liver and kidney of maternal feeding rats (kidney 23 ± 3 ng g−1; liver 26 ± 3 ng g−1) were much higher than those found in supplemented (kidney 9.9 ± 0.3 ng ng−1; liver 10 ± 4 ng g−1) and non-supplemented rats (kidney 3.4 ± 0.5 ng g−1; liver 4 ± 1 ng g−1). The percentage of exogenous SeGalNAc for the supplemented group in kidney and liver reached 32 ± 1% and 30 ± 10%, respectively. Conversely, the percentage of exogenous selenium in high molecular weight selenospecies reached values higher than 58%. Thereby, most exogenous selenium seems to be incorporated into the synthesis of selenoproteins, indicating that the turnover rates are different for the different species and their synthesis might occur in different tissue compartments. Finally, the identification of SeGalNAc was confirmed in liver and, for the first time to our knowledge, in the kidney cytosol of maternal feeding and supplemented rats. Overall, we expect that the judicious use of elemental and molecular mass spectrometry tools to obtain integrated quantitative Se speciation information might help to expand our knowledge of selenium metabolism.

Synthesis and DFT Study of a Diphenylsilanone-Bridged Dimolybdenum Complex

Reaction of the 30-electron benzylidyne complex [Mo2 Cp2 (μ-CPh)(μ-PCy2 )(μ-CO)] with excess Ph2 SiH2 under visible-UV irradiation yields the silylene-bridged complex [Mo2 Cp2 (μ-CPh)(μ-PCy2 )(μ-SiPh2 )]. This compound undergoes selective oxidation with O2 to give the unsaturated complex [Mo2 Cp2 (μ-CPh)(μ-PCy2 )(μ-κ(1) :κ(1) -OSiPh2 )], which contains an unprecedented bridging diphenylsilanone ligand, as confirmed by X-ray diffraction analysis and DFT calculations. The bonding within the central Mo2 SiO ring of this complex approaches the extreme description of a dimetallacyclosiloxane according to the relevant solid-state bond lengths and theoretical calculations.