Association of model peptides and dehydropeptides: N-acetyl-l-alanine- and dehydroalanine N′,N′-dimethylamides

The comparative studies on the association of Ac-ΔAla-NMe₂ and Ac-l-Ala-NMe₂ in carbon tetrachloride were performed by the analysis of their average molecular weight, dipole moments and FTIR spectra. To aid spectroscopic interpretation and gain some deeper insight into the nature of associates, the geometries of the minimum energy of the dimers of Ac-ΔAla-NMe₂ and Ac-l-Ala-NMe₂ were calculated by the B3LYP/6-31+G** method. The average molecular weight in the studied concentration range, for the ΔAla and l-Ala peptide, as determined by the osmometric method, did not exceed 1.5 and 1.2 of the monomeric mass, respectively. Accordingly, the percentage of the monomeric form (α) decreased as concentration was increased more significantly for the ΔAla analogue than for its saturated counterpart. In the studied concentrations, the dipole moment of the unsaturated compound decreases and that of its counterpart is almost constant. We identified a wider range of dimeric forms of Ac-ΔAla-NMe₂ than those of Ac-l-Ala-NMe₂. While Ac-ΔAla-NMe₂ mainly forms cyclic dimers, built of open conformers H/F, specific for α,β-dehydroamino acids, Ac-l-Ala-NMe₂ forms cyclic and linear dimers, characteristic for the usual amino acids. Ac-ΔAla-NMe₂ has a greater tendency to associate than its saturated variant, which is the result of stronger hydrogen bonds.     

Preparation and characterization of electrodeposited Ni-Ru alloys: morphological and catalytic study

Nickel-ruthenium alloys with various compositions have been deposited by electrodeposition for the first time. Cyclic voltammetry and linear stripping voltammetry measurements show that codeposition of nickel with ruthenium is possible below the potential value of nickel reduction. High-quality alloys containing nickel and ruthenium can be plated at cathodic potentials ranging from − 0.5 to − 1.0 V vs SCE. Deposited coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The diffractograms obtained show that an increase of nickel concentration in alloy will lead to a change in the phase composition and formation of NiRu (100) and (101) phases which is observed to be 78 mas.% Ni. SEM studies confirm the surface homogeneity and presence of small, regular grains. AFM observation allows the estimation of the real surface area of obtained alloys which increase with more negative electrodeposition potentials. Ni-Ru alloys were found to be highly electroactive in the water splitting process, which can be connected with the presence of the NiRu phase and a well-developed electroactive area.

Electrochemical deposition of Ni-Ru alloys with various composition and their catalytic activity in water splitting process

     

Structure and properties of the dinuclear complex [Co2(μ-OAc)2(OAc)2(μ-H2O)(phen)2]

The dinuclear complex [Co₂(μ-OAc)₂(OAc)₂(μ-H₂O)(phen)₂] has been prepared and its structure was determined. The compound crystallizes in the monoclinic space group P2(1)/c. The Co–Co distance is 3.574 Å and is similar to the Fe–Fe distance in the reduced methane monooxygenase hydroxylase. The electronic and IR spectra of the complex confirm octahedral coordination of the cobalt atoms and formation of strong O–HO hydrogen bonds in the solid state. The dependence of the magnetic susceptibility of the complex on temperature indicates an antiferromagnetic interaction, the value of the isotropic exchange parameter J was estimated to be −2.1 cm⁻¹. The ¹H NMR spectra show that in organic solvents the structure of compound is the same as in the solid state, however, in water solution the complex dissociates giving compounds with different Co:phen ratios.     

Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory

Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is significantly lower for the E isomer (Boc-Gly-(E)-ΔPhe-NHMe), both in gas phase and in chloroform solution.

     

Highly selective synthesis of novel (E)-styrylsilatranes via ruthenium-catalyzed trans-silylation

Protocols for the synthesis of cage-substituted 1-vinylsilatranes have been developed and updated. The 1-vinylsilatranes with organic substituents attached to silatrane cage were functionalized in ruthenium-catalyzed trans-silylation with olefins, leading to novel styrylsilatranes in high yields.     

Formation of DNA‐Copolymer Fibrils Through an Amyloid‐Like Nucleation Polymerization Mechanism

Conjugation of a hydrophobic poly(2‐oxazoline) bearing tertiary amide groups along its backbone with a short single stranded nucleotide sequence results in an amphiphilic comb/graft copolymer, which organizes in fibrils upon direct dissolution in water. Supported by circular dichroism, atomic force microscopy, transmission electron microscopy, and scattering data, fibrils are formed through inter‐ and intramolecular hydrogen bonding between hydrogen accepting amide groups along the polymer backbone and hydrogen donating nucleic acid grafts leading to the formation of hollow tubes.

     

Composition of oxygen precipitates in Czochralski silicon wafers investigated by STEM with EDX/EELS and FTIR spectroscopy

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO₂. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO₂ was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm^–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO₂. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Octacyanidorhenate(V) Ion as an Efficient Linker for Hysteretic Two-Step Iron(II) Spin Crossover Switchable by Temperature,Light, and Pressure

A two-step hysteretic Fe^II spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy)₂][Re(CN)₈]}⋅H₂O ( 1 ) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged Fe^II-Re^V square grid sheets bonded by Cs⁺ ions. The presence of two non-equivalent Fe^II sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs⁺, [Re^V(CN)₈]³⁻ ions, and 3-CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin-transition phenomenon could be tuned by an external pressure giving the room-temperature range of SCO, as well as by visible-light irradiation, inducing an efficient recovery of the high-spin Fe^II state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe^II SCO effect.     

Dialkenylgermanes as Precursors of Silsesquioxane‐based Macromolecular Structures

Herein we report a study of highly efficient platinum‐catalyzed hydrosilylation of dialkenylgermanes with silsesquioxanes and spherosilicates. The use of divinyl‐ and diallylgermanes allowed the synthesis of new classes of compounds, i. e., dumbbell‐type systems, silsesquioxanes with alkenyl pendant group, and oligomeric derivatives. The results are supported by detailed data from in situ FT‐IR and NMR measurements, enabling precise monitoring of the reaction progress and determination of regioselectivity of the formed products.     

Bases,solvates and salts: new benzimidazole‐ and pyridine‐scaffolded ligands

The intermolecular interactions in the structures of a series of Schiff base ligands have been thoroughly studied. These ligands can be obtained in different forms, namely, as the free base 2‐[(2E)‐2‐(1H‐imidazol‐4‐ylmethylidene)‐1‐methylhydrazinyl]pyridine, C₁₀H₁₁N₅, 1 , the hydrates 2‐[(2E)‐2‐(1H‐imidazol‐2‐ylmethylidene)‐1‐methylhydrazinyl]‐1H‐benzimidazole monohydrate, C₁₂H₁₂N₆·H₂O, 2 , and 2‐{(2E)‐1‐methyl‐2‐[(1‐methyl‐1H‐imidazol‐2‐yl)methylidene]hydrazinyl}‐1H‐benzimidazole 1.25‐hydrate, C₁₃H₁₄N₆·1.25H₂O, 3 , the monocationic hydrate 5‐{(1E)‐[2‐(1H‐1,3‐benzodiazol‐2‐yl)‐2‐methylhydrazinylidene]methyl}‐1H‐imidazol‐3‐ium trifluoromethanesulfonate monohydrate, C₁₂H₁₃N₆⁺·CF₃O₃S^?·H₂O, 5 , and the dicationic 2‐{(2E)‐1‐methyl‐2‐[(1H‐imidazol‐3‐ium‐2‐yl)methylidene]hydrazinyl}pyridinium bis(trifluoromethanesulfonate), C₁₀H₁₃N₅²⁺·2CF₃O₃S^?, 6 . The connection between the forms and the preferred intermolecular interactions is described and further studied by means of the calculation of the interaction energies between the neutral and charged components of the crystal structures. These studies show that, in general, the most important contribution to the stabilization energy of the crystal is provided by π–π interactions, especially between charged ligands, while the details of the crystal architecture are influenced by directional interactions, especially relatively strong hydrogen bonds. In one of the structures, a very interesting example of the nontypical F…O interaction was found and its length, 2.859 (2) Å, is one of the shortest ever reported.