Is human hair a proper 210Po and 210Pb monitor of their increased activity in the human body?

Journal of Radioanalytical and Nuclear Chemistry - The study focused on 210Po and 210Pb activity concentrations determination in human hair as well as investigation its utility as an easy and safe...     

A Multicoincidence Study of Fragmentation Dynamics in Collision of γ‐Aminobutyric Acid with Low‐Energy Ions

Fragmentation of the γ‐aminobutyric acid molecule (GABA, NH₂(CH₂)₃COOH) following collisions with slow O⁶⁺ ions (v≈0.3 a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH₂CH₂⁺, HCNH⁺, CH₂CH₂⁺, and COOH⁺ fragments. State‐of‐the‐art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential‐energy surface. For example, the weak contribution at [M?18]⁺, where M is the mass of the parent ion, can be interpreted as resulting from H₂O loss that follows molecular folding of the long carbon chain of the amino acid.     

Designs for life: protocell models in the laboratory

Compartmentalization of primitive biochemical reactions within membrane-bound water micro-droplets is considered an essential step in the origin of life. In the absence of complex biochemical machinery, the hypothetical precursors to the first biological cells (protocells) would be dependent on the self-organization of their components and physicochemical conditions of the environment to attain a basic level of autonomy and evolutionary viability. Many researchers consider the self-organization of lipid and fatty acid molecules into bilayer vesicles as a simple form of membrane-based compartmentalization that can be developed for the experimental design and construction of plausible protocell models. In this tutorial review, we highlight some of the recent advances and issues concerning the construction of simple cell-like systems in the laboratory. Overcoming many of the current scientific challenges should lead to new types of chemical bio-reactors and artificial cell-like entities, and bring new insights concerning the possible pathways responsible for the origin of life.     

Axial Ligand and Spin‐State Influence on the Formation and Reactivity of Hydroperoxo–Iron(III) Porphyrin Complexes

The present study focuses on the formation and reactivity of hydroperoxo–iron(III) porphyrin complexes formed in the [Fe^III(tpfpp)X]/H₂O₂/HOO^? system (TPFPP=5,10,15,20‐tetrakis(pentafluorophenyl)‐21H,23H‐porphyrin; X=Cl^? or CF₃SO₃^?) in acetonitrile under basic conditions at ?15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high‐spin [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] could be observed with the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O? O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo‐ to heterolytic O? O bond cleavage is observed for high‐ [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron‐rich porphyrin ligands, electron‐deficient [Fe^III(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe^III(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)–oxo porphyrin π‐cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Tilted algebras and short chains of modules

We provide an affirmative answer for the question raised almost 20 years ago in Reiten et al. (Proc. Am. Math. Soc. 117:343–354, 1993) concerning the characterization of tilted artin algebras by the existence of a sincere finitely generated module which is not the middle of a short chain.     

Reorthogonalized block classical Gram–Schmidt

A reorthogonalized block classical Gram–Schmidt algorithm is proposed that factors a full column rank matrix $A$ into $A=QR$ where $Q$ is left orthogonal (has orthonormal columns) and $R$ is upper triangular and nonsingular. This block Gram–Schmidt algorithm can be implemented using matrix–matrix operations making it more efficient on modern architectures than orthogonal factorization algorithms based upon matrix-vector operations and purely vector operations. Gram–Schmidt orthogonal factorizations are important in the stable implementation of Krylov space methods such as GMRES and in approaches to modifying orthogonal factorizations when columns and rows are added or deleted from a matrix. With appropriate assumptions about the diagonal blocks of $R$ , the algorithm, when implemented in floating point arithmetic with machine unit $\varepsilon _M$ , produces $Q$ and $R$ such that $\Vert I- Q ^T\!~ Q \Vert =O(\varepsilon _M)$ and $\Vert A-QR \Vert =O(\varepsilon _M\Vert A \Vert )$ . The first of these bounds has not been shown for a block Gram–Schmidt procedure before. As consequence of these results, we provide a different analysis, with a slightly different assumption, that re-establishes a bound of Giraud et al. (Num Math, 101(1):87–100, 2005) for the CGS2 algorithm.     

A multicoincidence study of fragmentation dynamics in collision of γ-aminobutyric acid with low-energy ions

Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3?a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH(2)CH(2)(+), HCNH(+), CH(2)CH(2)(+), and COOH(+) fragments. State-of-the-art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential-energy surface. For example, the weak contribution at [M-18](+), where M is the mass of the parent ion, can be interpreted as resulting from H(2)O loss that follows molecular folding of the long carbon chain of the amino acid.     

New alkyl-phosphate bonded stationary phases for liquid chromatographic separation of biologically active compounds

A new type of bonded stationary phase for liquid chromatography, with the properties of immobilized artificial membranes, has been synthesized. Alkyl-phosphate adsorbents were obtained by modification of aminopropyl silica gel. The structures of the synthesized materials were confirmed by use of instrumental techniques--elemental analysis, infrared spectroscopy (FTIR), and (13)C and (29)Si CP/MAS NMR. Analysis revealed that the adsorbents mimic the phospholipids present in natural cell membranes. The new synthesized alkyl-phosphate stationary phases may be used for liquid chromatographic separation of biologically active compounds of different polarity.