Self-assembled peptide tubelets with 7 A pores

Here we report the preparation and structural characteristics of self-assembling peptide tubelets composed of 32-membered rings formed of alternating alpha-amino acids and cis-3-aminocyclohexanecarboxylic acids. The tubelets possess a partial hydrophobic core environment, provided by the projection of the cyclohexane C2 methylene moiety into the lumen, and a Van der Waals pore diameter of about 7 A.     

Ambiphilic boryl groups in a neutral Ni(ii) complex: a new activation mode of H2

The concept of metal–ligand cooperation opens new avenues for the design of catalytic systems that may offer alternative reactivity patterns to the existing ones. Investigations of this concept with ligands bearing a boron center in their skeleton established mechanistic pathways for the activation of small molecules in which the boron atom usually performs as an electrophile. Here, we show how this electrophilic behavior can be modified by the ligand trans to the boron center, evincing its ambiphilic nature. Treatment of diphosphinoboryl (PBP) nickel–methyl complex 1 with bis(catecholato)diboron (B₂Cat₂) allows for the synthesis of nickel(ii) bis-boryl complex 3 that promotes the clean and reversible heterolytic cleavage of dihydrogen leading to the formation of dihydroborate nickel complex 4. Density functional theory analysis of this reaction revealed that the heterolytic activation of H₂ is facilitated by the cooperation of both boryl moieties and the metal atom in a concerted mechanism that involves a Ni(ii)/Ni(0)/Ni(ii) process. Contrary to 1, the boron atom from the PBP ligand in 3 behaves as a nucleophile, accepting a formally protic hydrogen, whereas the catecholboryl moiety acts as an electrophile, receiving the attack from the hydride-like fragment. This manifests the dramatic change in the electronic properties of a ligand by tuning the substituent trans to it and constitutes an unprecedented cooperative mechanism that involves two boryl ligands in the same molecule operating differently, one as a Lewis acid and the other one as a Lewis base, in cooperation with the metal. In addition, reactivity towards different nucleophiles such as amines or ammonia confirmed the electrophilic nature of the Bcat moiety, allowing the formation of aminoboranes.

A bis(boryl)nickel complex promotes the facile and reversible activation of H₂ through a cooperative mechanism that involves the metal and both boryl moieties in a concerted five-center process.     

Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.     

KMo5O13 and KNb1.76Sb3.24O13

The title compounds, potassium pentamolybdenum oxide, KMo₅O₁₃, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb_1.76Sb_3.24O₁₃, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO₆ octahedra sharing edges to form Mo₂O₆ pairs and Mo₃O₉ triplets, which, in turn, form layers by sharing corners. These layers are linked together in the [100] direction, yielding a three‐dimensional network similar to that of KSb₅O₁₃. This framework delimits interconnected tunnels, running approximately along the [110] and [10] directions, in which K⁺ ions are located. In the isomorphous KNb_1.76Sb_3.24O₁₃ structure, one of the Mo sites in KMo₅O₁₃ is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb.     

Influence of the halogen ligand on the near-UV-visible spectrum of [Ru(X)(Me)(CO)2(alpha-diimine)] (X = Cl, I; alpha-diimine = Me-DAB, iPr-DAB; DAB = 1,4-diaza-1,3-butadiene): an ab initio and TD-DFT analysis

The near-UV-vis electronic spectroscopy of [Ru(X)(Me)(CO)(2)(iPr-DAB)] (X = Cl or I; iPr-DAB = N,N'-di-isopropyl-1,4-diaza-1,3-butadiene) is investigated through CASSCF/CASPT2 and TD-DFT calculations on the model complexes [Ru(X)(Me)(CO)(2)(Me-DAB)] (X = Cl or I). Convergence of the calculated transition energies for the low-lying metal-to-ligand charge-transfer (MLCT), X-to-ligand charge-transfer (XLCT, X halide ligand), or sigma-bond-to-ligand charge-transfer (SBLCT) to experimental values is analyzed for both methods. On the basis of these accurate calculations, it is shown that whereas the lowest singlet state can be assigned to a nearly pure XLCT state in [Ru(I)(Me)(CO)(2)(Me-DAB)], its character is mainly MLCT in [Ru(Cl)(Me)(CO)(2)(Me-DAB)]. These results are in agreement with time-resolved emission/IR and resonance Raman experimental data. The experimental UV-vis bands are well reproduced by the CASSCF/CASPT2 calculations. The TD-DFT transition energies to the long-range charge transfer states are dramatically affected by the nature of the functional, with lowering leading to meaningless values in the case of nonhybrid functionals. Both methods reproduce well the red shift of the absorption bands on going from the chloride to the iodide complex as well as the shift of the strongly absorbing higher MLCT transition from the visible to the UV domain of energy.     

Synthetic Strategies To Obtain V-P-O Open Frameworks Containing Organic Species as Structural Directing Agents. Crystal Structure of the V(IV)-Fe(III) Bimetallic Phosphate [H(3)N(CH(2))(2)NH(3)](2)[H(3)N(CH(2))(2)NH(2)][Fe(III)(H(2)O)(2)(V(IV)O)(8)(OH)(4)(HPO(4))(4)(PO(4))(4)].4H(2)O

A general synthetic approach to rationalize the solution preparative chemistry of oxovanadium phosphates containing organic species as structural directing agents is presented. Careful attention is payed to the hydrolysis and condensation processes involving the ionic species in solution, and a simple restatement of the partial charge model (PCM) has been used in order to organize the experimental results. The structure of a new V(IV)-Fe(III) bimetallic oxovanadium phosphate, [H(3)N(CH(2))(2)NH(3)](2)[H(3)N(CH(2))(2)NH(2)] [Fe(III)(H(2)O)(2)(V(IV)O)(8)(OH)(4)(HPO(4))(4)(PO(4))(4)].4H(2)O, has been determined by X-ray single crystal diffraction methods. This compound crystallizes in the monoclinic system, space group P2(1)/n and the cell dimensions are as follows: a = 14.383(3) ?, b = 10.150(2) ?, c = 18.355(4) ?, and beta = 90.39(3) degrees (Z = 2). The existence of a complex intercrossing channel system, including a very large channel of 18.4 ? of diameter (in which both water molecules and ethylenediamine species are located), is the more interesting feature of this structure. Thermal decomposition, including the dehydration/rehydration process, has been studied by thermal analysis and variable temperature X-ray powder diffraction techniques. A complementary SEM study of the different intermediate decomposition products is presented.     

Crystal Structure of a New Ammonium Potassium Selenomolybdate Compound K3.31(NH4)0.69[Se2Mo5O21]·2H2O

An inorganic compound formulated as K_3.31(NH₄)_0.69[Se₂Mo₅O₂₁]·2H₂O has been synthesized by conventional solution method and characterized by scanning electron microscopy, IR, UV-Vis spectroscopies behaviors. The structure of the title compound has been determined from a single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2₁/n, with a?=?9.9371(2) ?, b?=?23.3545(2) ?, c?=?10.5179(2) ?, β?=?114.12(3)°, V?=?2227.7(5) ?³ and Z?=?4. It was revealed that the Strandberg-type polyoxoselenomolybdate cluster can be considered as a ring formed by five distorted edge- and corner-sharing MoO₆ octahedra, capped on both poles by a selenate pyramids sharing three vertices with the ring molybdenum centers. The Strandberg clusters are connected with ammonium ions and water molecules through hydrogen-bonding interactions which ensure the cohesion of the structure into a three-dimensional network.     

A new distance measure including the weak preference relation: Application to the multiple criteria aggregation procedure for mixed evaluations

We introduce a new distance measure between two preorders that captures indifference, strict preference, weak preference and incomparability relations. This measure is the first to capture weak preference relations. We illustrate how this distance measure affords decision makers greater modeling power to capture their preferences, or uncertainty and ambiguity around them, by using our proposed distance measure in a multiple criteria aggregation procedure for mixed evaluations.     

Double Orthogonal Click Reactions for the Development of Antimicrobial Peptide Nanotubes

A new class of amphipathic cyclic peptides, which assemble in bacteria membranes to form polymeric supramolecular nanotubes giving them antimicrobial properties, is described. The method is based on the use of two orthogonal clickable transformations to incorporate different hydrophobic or hydrophilic moieties in a simple, regioselective, and divergent manner. The resulting cationic amphipathic cyclic peptides described in this article exhibit strong antimicrobial properties with a broad therapeutic window. Our studies suggest that the active form is the nanotube resulted from the parallel stacking of the cyclic peptide precursors. Several techniques, CD, FTIR, fluorescence, and STEM, among others, confirm the nanotube formation.