6,6′-Dimethyl-1,1′,5,5′-tetraaza-6,6′-bi(bicyclo[3.1.0]hexane): synthesis and investigation of molecular structure by quantum-chemical calculations,NMR spectroscopy and X-ray diffraction analysis

Structural Chemistry - A new diaziridine derivative with two bicyclic diaziridine-containing moieties in one molecule,...     

Synthesis,Antitumor and Antibacterial Studies of New Shortened Analogues of (KLAKLAK)2-NH2 and Their Conjugates Containing Unnatural Amino Acids

(1) Background: (KLAKLAK)₂ is a representative of the antimicrobial peptide group which also shows good anticancer properties. (2) Methods: Herein, we report synthesis using SPPS and characterization by HPLC/MS of a series of shortened analogues of (KLAKLAK)₂. They contain single sequence KLAKLAK as C-terminal amides. In addition, substitution of some natural amino acids with unnatural β-Ala and nor-Leu is realized. In addition, these structures are conjugated with second pharmacophore with well proven anticancer properties 1,8-naphthalimide or caffeic acid. Cytotoxicity, antiproliferative effect and antimicrobial activity of newly synthesized structures were studied. (3) Results: The obtained experimental results reveal significant selective index for substances with common chemical structure KLβAKLβAK-NH₂. The antibacterial properties of newly synthesized analogues at two different concentrations 10 μM and 20 μM, were tested against Gram-negative microorganisms Escherichia coli K12 407. Only two of the studied compounds KLAKLAK-NH₂ and the one conjugated with second pharmacophore 1,8-naphthalimide and unnatural amino acid nor-Leu showed moderate activity against tested strains at concentration of 20 μM. (4) Conclusions: The obtained results reveal that the introducing of 1,8-naphthalimideGly- and Caf- increase the cytotoxicity and antiproliferative activity of the peptides but not their selectivity. Only two compounds KLAKLAK-NH₂ and 1,8-naphthalimideGKnLAKnLAK-NH₂ show moderate activity against Escherichia coli K12 at low concentration of 20 μM.     

Computed Regioselectivity and Conjectured Biological Activity of Ene Reactions of Singlet Oxygen with the Natural Product Hyperforin

Hyperforin is a constituent of St. John's wort and coexists with the singlet oxygen sensitizer hypericin. Density functional theory, molecular mechanics and Connolly surface calculations show that accessibility in the singlet oxygen “ene” reaction favors the hyperforin “southwest” and “southeast” prenyl (2‐methyl‐2‐butenyl) groups over the northern prenyl groups. While the southern part of hyperforin is initially more susceptible to oxidation, up to 4 “ene” reactions of singlet oxygen can take place. Computational results assist in predicting the fate of adjacent hydroperoxides in hyperforin, where the loss of hydrogen atoms may lead to the formation of a hydrotrioxide and a carbonyl instead of a Russell reaction.     

Reactive Compatibilization of Polyethylene/Ground Tire Rubber Inhomogeneous Blends via Interactions of Pre-Functionalized Polymers in Interface

Summary: Reactive compatibilization of recycled low- or high-density polyethylenes (LDPE and HDPE, respectively) and ground tire rubber (GTR) via chemical interactions of pre-functionalized components in their blend interface has been carried out. Polyethylene component was functionalized with maleic anhydride (MAH) as well as the rubber component was modified via functionalization with MAH or acrylamide (AAm) using chemically or irradiation (γ-rays) induced grafting techniques. The grafting degree and molecular mass distribution of the functionalized polymers have been measured via FTIR and Size Exclusion Chromatography (SEC) analyses, respectively. Thermoplastic elastomer (TPE) materials based on synthesized reactive polyethylenes and GTR as well as ethylene-propylene-diene rubber, EPDM were prepared by dynamic vulcanization of the rubber phase inside thermoplastic (polyethylene) matrix and their phase structure, and main properties have been studied using DSC and mechanical testing. As a final result, the high performance TPE with improved mechanical properties have been developed.     

On conditions of existence of permanent rotations of connected rigid bodies system about vertical vector

In contrast to the classical problem of motion of a heavy rigid body about a fixed point where the permanent rotations are well known and completely investigated [7, 3] as the most simple and good visually demonstrated type of motions, in multibody mechanics under an increasing of quantity of the system bodies, mechanical parameters and the order of differential motion equations the study of such motions is more complicated problem. The problem on permanent rotations of two connected rigid bodies under influence of gravity force was investigated in [2, 4]. In this paper a system consisting of arbitrary constant quantity, n, of heavy rigid bodies which are sequentially jointed in a chain is considered. The conditions of existence of motions when each body permanently rotates about the vertical vector are determined. These conditions are analyzed in a general case when the bodies angular velocities are different.     

Intracellular concentration map of magnesium in whole cells by combined use of X-ray fluorescence microscopy and atomic force microscopy

We report a novel experimental approach to derive quantitative concentration map of light elements in whole cells by combining two complementary nano-probe methods: X-ray fluorescence microscopy (XRFM) and atomic force microscopy (AFM). The concentration is derived by normalizing point-by-point the elemental (here Mg) spatial distribution obtained by XRFM, by the thickness measured using AFM. The considerable difference between the elemental distribution and the concentration maps indicates that this procedure is essential to obtain reliable information on the role and function of elements in whole cells.     

Thermodynamics of protonation of amines in aqueous solutions at elevated temperatures

The dissociation constants, pK_a, of monoethanolamine (MEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), 2(2-aminoethyl)etanolamine (AEEA), and piperazine (Pz) were measured by potentiometric titration over the temperature range (298.15 to 363.15) K. Enthalpies of protonation, ΔH_p, were measured calorimetrically at temperatures from (298.15 to 393.15) K for MEA, MDEA, and AMP, and from (298.15 to 353.15) K for AEEA and Pz. In addition, the effect of the ionic strength of the solutions on the protonation of MDEA was studied using NaCl as background salt {(0 to 5.5) mol/kg-H₂O)}. Correlations for the reaction equilibrium constants for proton dissociation are proposed for the studied amines based on the experimental data from literature and from this work. Both experimental enthalpy data and dissociation constants were used for fitting. The results from this work may be used for thermodynamic modeling of CO₂ capture processes using amines.     

Copper (II)-catalyzed regio- and stereoselective addition of H/P(O)R2 to alkynes

Cu(acac)₂ is the new universal catalyst for β-E regio- and stereoselective syn-addition of the H–P(O)-bond of diphenylphosphine oxide, H-phosphinates, dialkylphosphites to various alkynes in the synthesis of P(O)-containing alkenes. Without additives and ligands Cu(II)-compounds showed better results than CuI or Ni(acac)₂. The catalytic system developed is tolerant to typical organic functional groups present in the alkynes and to the nature of different substituents in the H–P(O)-compounds.     

Decarboxylation and ring fragmentation reactions of sydnone N-oxides

4-Carboxylated sydnone N-oxides are readily decarboxylated by benzylation to give 2,4-dibenzylsydnone-N-oxides. Ring cleaveage results from their oxidation with bromine which leads to a nitrile N-oxide which is isolated as its furazan dimer.