The evolution of electronic structures, properties and stabilities of neutral and cationic molybdenum encapsulated germanium clusters (Mo@Gen, n = 1 to 20) has been investigated.

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A simple, sensitive and specific LC-MS/MS method for the determination of lipoic acid was developed and validated over the linearity range 5-1000 ng/mL (r2 > 0.99) with 200 microL rat plasma using rosigliatzone as an internal standard (IS). The assay procedure involved a simple one-step liquid-liquid extraction of lipoic acid and IS from plasma into ethyl acetate. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Hichrom RPB column (4.6 x 250 mm, 5 microm). Separation of lipoic acid and IS was achieved with a mobile phase consisting of 0.05 M formic acid:acetonitrile (40:60, v/v) at a flow rate of 1.0 mL/min. The API-3000 LC-MS/MS was operated under the multiple reaction monitoring mode (MRM) using the electrospray ionization technique. Positive and negative ion acquisition within the same chromatographic run was used in the present method. For lipoic acid a pseudo-molecular ion transition pair was acquired in negative polarity, whereas for IS the transition pair was acquired in positive polarity. Quantitation was determined for both analyte and IS in MRM scan mode. Absolute recovery of lipoic acid and IS was >70 and 97%, respectively. The lower limit of quantification (LLOQ) of lipoic acid was 5.0 ng/mL. The inter- and intra-day precision in the measurement of quality control (QC) samples 5, 15, 400 and 800 ng/mL were in the range 2.18-5.99% relative standard deviation (RSD) and 0.93-13.77% RSD, respectively. Accuracy in the measurement of QC samples was in the range 87.40-114.40% of the nominal values. Analyte and IS were stable in the battery of stability studies, viz. bench-top, auto-sampler and freeze-thaw cycles. Stability of lipoic acid was established for 1 month at -80 degrees C. The application of the assay to a pharmacokinetic study in rats confirmed the utility of the assay.

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The present study reports the geometry, electronic structure, growth behavior and stability of neutral and ionized nickel encapsulated germanium clusters containing 1-20 germanium atoms within the framework of a linear combination of atomic orbital density functional theory (DFT) under a spin polarized generalized gradient approximation. In the growth pattern, Ni-capped Gen and Ni-encapsulated Gen clusters appear mostly as theoretical ground state at a particular size. To explain the relative stability of the ground state clusters, variation of different parameters, such as average binding energy per atom (BE), embedding energy (EE) and fragmentation energy (FE) of the clusters, were studied together with the size of the cluster. To explain the chemical stability of the clusters, different parameters, e.g., energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap), ionization energy (IP), electron affinity (EA), chemical potential (μ), chemical hardness (η), and polarizability etc. were calculated and are discussed. Finally, natural bond orbital (NBO) analysis was applied to understand the electron counting rule applied in the most stable Ge10Ni cluster. The importance of the calculated results in the design of Ge-based superatoms is discussed.