A new method for the synthesis of the marine alkaloid fascaplysin

A new method for the synthesis of the marine alkaloid fascaplysin has been developed via a simple and practical approach to pyrido[1,2-a:3,4-b′]diindole ring system formation. Conversion of the marine alkaloid homofascaplysin C into fascaplysin is also described.     

Variation in the regioselectivity of levulinic acid bromination in ionic liquids

The reaction of levulinic acid and its esters with bromine in ionic liquids results in the formation of 3-bromo derivatives as the major products and not the 5-bromo substituted isomers, which are typically formed in organic solvents. The bromination of levulinic acid in ionic liquids in the presence of urea leads to the formation of 5-bromolevulinic acid.     

Tautomeric and conformational properties of malonamide, NH2C(O)-CH2-C(O)NH2: electron diffraction and quantum chemical study

The geometric structure of malonamide, NH2C(O)-CH2-C(O)NH2, has been investigated by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximations with 6-311++G(3df,pd) basis sets). Both GED and quantum chemistry result in the existence of a single diketo conformer in the gas phase. According to GED refinement this conformer possesses (sc,ac) conformation with one C=O bond in synclinal orientation (dihedral angle tau(O=C-C-C)=49.0(3.0) degrees) and the other C=O bond in anticlinal orientation (dihedral angle tau(O=C-C-C)=139.5(3.3) degrees). The experimental geometric parameters are reproduced very closely by the B3LYP method.     

Poly(vinyl alcohol)/heteropolyacid nanocomposites as new materials for radiochromic dosimetry in radiation processing

Radiochromic films composed of polymer matrices and organic dyes are widely used for routine dosimetry purposes in operation of various radiation facilities—gamma and X-ray-irradiation, electron accelerators, and so on. However, the sensitivity of these films rapidly decreases at doses exceeding 30–50 kGy due to a saturation of their optical response, making them unsuitable for accurate dosimetry in radiation processing of polymers and composites where doses up to 200 kGy are typically employed. To overcome this limitation, the use of inorganic substances as the coloring agents of polymer-based radiochromic films was proposed in this paper, specifically, heteropolyacidacid H₃PW₁₂O₄₀ (tungstophosphoric acid) in the matrix of poly(vinyl alcohol) (PVA). Nanocomposite PVA/H₃PW₁₂O₄₀ films were prepared by solution casting and their optical responses toward ⁶⁰Co gamma radiation and beams of 6 MeV electrons for a dose range of 10–200 kGy were investigated. It was established that upon exposure to gamma rays and electron beams, the films turn blue and a broad absorption band at 750 nm appears in their spectra. Importantly, the radiation-induced optical absorption increases in a linear fashion up to the dose of 150 kGy and only slightly deviates from linearity at 200 kGy. Moreover, it was found that the PVA/H₃PW₁₂O₄₀ films have a long shelf life, are dose-rate independent within a wide range, and color-stable after irradiation. All these features make the nanocomposite PVA/H₃PW₁₂O₄₀ films promising for use as routine dosimeters and dose labels in a much wider range of high doses as compared to radiochromic films based on organic dyes.     

Poly[μ2‐chloro‐μ2‐1,4‐oxathiane‐κ2S:S‐copper(I)]

The title complex, [CuCl(C₄H₈OS)]_n, contains infinite spiral (CuS)_n chains linked by bridging Cl atoms into layers. The Cl atoms do not form polymeric fragments with Cu^I, but combine into isolated centrosymmetric Cu₂Cl₂ units. The compound is non‐isomorphous with the Br‐containing analogue, which contains Cu₈S₈ rings linked by Br atoms into chains. The O atom of the 1,4‐oxathiane mol­ecule does not realize its coordination abilities in the known copper(I)–halide complexes, while in copper(II)–halide complexes, oxathiane is coordinated via the S and O atoms. This falls into a pattern of the preferred inter­actions, viz. weak acid (Cu^I atom) with weak base (S atom) and harder acid (Cu^II atom) with harder base (O atom).     

Oxidation of bridging groups by carboxylate coordinated ligands in palladium clusters

Thermolysis of tetranuclear palladium clusters Pd₄(-Q)₄ Pd₄(-Q)₄(-O₂CR)₄ (Q=CPh₂ or CO;R=Me, CMe₃, Ph, CH₂Cl or CF₃) has been found to involve innersphere oxidation of carbene or carbonyl ligands during which an oxygen atom transfer occurs from the carboxylate group to the carbene or carbonyl ligand. The thermolysis of the carbonyl clusters gives rise to the products of CO₂ insertion into the C–H bond of benzene or toluene used as solvents forming benzoic acid from benzene and a mixture of phenylacetic and toluic acids from toluene. The reaction of [Pd(OAc)₂(PPh₃)]₂ with HCO₂H includes the transfer of an O atom from formate ligand to the P atom and cleavage of the P-Ph bond accompanied by transfer of the Ph group from PPh₃ ligand to the palladium atom. The structure of the complex formed, [Pd(-O₂PPh₂)(C₆H₅)(PPh₃)]₂, has been resolved by X-ray analysis.     

Evidence for an Ordering Transition near 120 K in an Intrinsically Disordered Protein,Casein

Intrinsically disordered proteins (IDPs) are proteins that possess large unstructured regions. Their importance is increasingly recognized in biology but their characterization remains a challenging task. We employed field swept Electron Spin Echoes in pulsed EPR to investigate low-temperature stochastic molecular librations in a spin-labeled IDP, casein (the main protein of milk). For comparison, a spin-labeled globular protein, hen egg white lysozyme, is also investigated. For casein these motions were found to start at 100 K while for lysozyme only above 130 K, which was ascribed to a denser and more ordered molecular packing in lysozyme. However, above 120 K, the motions in casein were found to depend on temperature much slower than those in lysozyme. This abrupt change in casein was assigned to an ordering transition in which peptide residues rearrange making the molecular packing more rigid and/or more cohesive. The found features of molecular motions in these two proteins turned out to be very similar to those known for gel-phase lipid bilayers composed of conformationally ordered and conformationally disordered lipids. This analogy with a simpler molecular system may appear helpful for elucidation properties of molecular packing in IDPs.     

Polyoxotungstate Archetype {P4W27} and its 3d Derivatives

The propensity of the new, phenylphosphonate-stabilized polyoxotungstate [(C₆H₅P^VO)₂P₄W₂₄O₉₂]¹⁶⁻ to act as a precursor for new 3d metal-functionalized polyanions has been investigated. Reactions with Mn^II and Cu^II induce the formation of the previously unknown polyoxotungstate archetype {P₄W₂₇}, isolated as salts of the polyanions [Na⊂{Mn^II(H₂O)}{WO(H₂O)}P₄W₂₆O₉₈]¹³⁻ ( 1 ) and [K⊂{Cu^II(H₂O)}{W(OH)(H₂O)}P₄W₂₇O₉₉]¹⁴⁻ ( 2 ), which were characterized in the solid state (single-crystal X-ray diffraction, elemental and TG analyses, IR spectroscopy, SQUID magnetometry) and in aqueous solution (UV/Vis spectroscopy, cyclic voltammetry).     

Conformational polymorphs of 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole

The dipharmacophore compound 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole, C₁₂H₁₁N₅O, was studied on the assumption of its potential biological activity. Two polymorphic forms differ in both their molecular and crystal structures. The monoclinic polymorphic form was crystallized from more volatile solvents and contains a conformer with a higher relative energy. The basic molecule forms an abundance of interactions with relatively close energies. The orthorhombic polymorph was crystallized very slowly from isoamyl alcohol and contains a conformer with a much lower energy. The basic molecule forms two strong interactions and a large number of weak interactions. Stacking interactions of the `head‐to‐head' type in the monoclinic structure and of the `head‐to‐tail' type in the orthorhombic structure proved to be the strongest and form stacked columns in the two polymorphs. The main structural motif of the monoclinic structure is a double column where two stacked columns interact through weak C—H…N hydrogen bonds and dispersive interactions. In the orthorhombic structure, a single stacked column is the main structural motif. Periodic calculations confirmed that the orthorhombic structure obtained by slow evaporation has a lower lattice energy (0.97 kcal mol^?1) compared to the monoclinic structure.