Search results for " bonding"
showing 10 items of 934 documents
Self-Assembly of Zr(C2O4)44– Metallotectons and Bisimidazolium Cations: Influence of the Dication on H-Bonded Framework Dimensionality and Material P…
2011
Assemblies involving [Zr(C2O4)4]4– metallotectons (C2O42– = oxalate) and linear, flexible, or V-shaped organic cations (H2-Lx)2+ derived from the 1,4-bisimidazol-1-ylbenzene molecule have been envisioned to elaborate porous frameworks based on ionic H-bonds. Five architectures of formula [{(H2-L1)2Zr(C2O4)4}·2H2O] (1), [{(H2-L2)2Zr(C2O4)4}·6H2O] (2), [{(H2-L3)2Zr(C2O4)4}·6H2O] (3), [{(H2-L4)2Zr(C2O4)4}·H2O] (4), and [{(H2-L5)2Zr(C2O4)4}·6H2O] (5) (with L1 = p-bis(imidazol-1-yl)benzene, L2 = p-bis(2-methylimidazol-1-yl)benzene, L3 = p-bis(imidazol-1-yl)-2,5-dimethylbenzene, L4 = p-bis(imidazol-1-ylmethyl)benzene, L5 = m-bis(imidazol-1-yl)benzene) have been obtained; 1–3, and 5 show an open-f…
Coordination properties of imino(2-pyridyl)methylpalladium(II) compounds. Reactions with the chloride-bridged allyl dimers [MCl(η3-2-MeC3H4)]2 (MPd,…
1990
Abstract The imino(2-pyridyl)methylpalladium(II) compounds py-2-CR 1 NR [R 1 = trans -PdCl(PPh 3 ) 2 , R = C 6 H 4 OMe- p ( Ia ), Me ( Ib ), CMe 3 ( Ic ); R 1 = Pd(dmtc)(PPh 3 ), R = C 6 H 4 OMe- p ( Id )] react with [MCl(η 3 - 2-MeC 3 H 4 )] 2 (M = Pd, Pt) in a molar ratio 1/0.5 and in the presence of NaClO 4 to yield the binuclear cationic complexes II , [M(η 3 -2-MeC 3 H 4 )(py-2-CR 1 NR)]ClO 4 , where the α-diimino group acts as σ,σ N , N ′ chelating ligand. In the absence of NaClO 4 and with a molar ratio 1/1, the reaction leads initially to formation of a ionic intermediate A , [M(η 3 - 2-MeC 3 H 4 )(py-2-CR 1 NR)] [MCl 2 (η 3 -2-MeC 3 H 4 )], which subsequently undergoes exchange …
New complex polycyclic compounds: Synthesis, antiproliferative activity and mechanism of action
2020
Abstract Polycyclic or O-glycoconiugate polycyclic compounds 1a-g were previously tested for their in vitro antiproliferative activity. In this series of compounds, activity increases as log P decreases. Specifically, compounds 1d and 1g showed lower log P values together with the best antiproliferative profiles. With the aim of extending our understanding of the structure–activity relationship (SAR) of this class of compounds, we prepared new polycyclic derivatives 2a-c, which bear on each of the two phenyl rings hydrophilic substituents (OH, SO2NH2 or NHCOCH3). These substituents are able to form hydrogen bonds and to decrease the partition coefficient value as compared with compound 1d. …
Structural and magnetic characterization of the tridimensional network [Fe(HCO2)3]n·nHCO2H
2013
In this work we report the structural and magnetic characterization of a new three-dimensional porous metal–organic framework (MOF) based on iron(III) and the formate anion, [Fe(HCO2)3]n·nHCO2H (1), which was obtained by solvothermal synthesis. The tridimensional structure crystallizes in the trigonal space group Rc and is formed by highly regular octahedral Fe(OHCO)6 units. These units contain six equal Fe–O distances, with angles slightly different from 90° or 180°. The packing of 1 corresponds to a 3D covalent network defined by face sharing between the parallelepipeds, which are formed by the interactions of Fe(OHCO)6 units through formate ligands, thus generating a 41263 topology. This…
Straightforward Synthesis of Donor‐Stabilised Phosphenium Adducts from Imidazolium‐2‐carboxylate and Their Electronic Properties (Eur. J. Inorg. Chem…
2007
The cover picture shows one of donor-stabilized phosphenium compounds which have been obtained by direct addition of chlorophosphanes to the 1,3-dimethylimidazolium-2-carboxylate without any further purification step. Their stronger κ-acceptor character similar to phosphites and their ionic nature render these ligands very promising in the development of new continuous-flow catalytic processes. Details of phosphorylation mechanisms of imidazolium-2-carboxylate as well as the electronic and steric properties of these adducts are discussed in the article by J. Andrieu et al. on p. 4877 ff.
Diffusion of ionic and non-ionic contrast agents in articular cartilage with increased cross-linking--contribution of steric and electrostatic effect…
2013
Abstract Objective To investigate the effect of threose-induced collagen cross-linking on diffusion of ionic and non-ionic contrast agents in articular cartilage. Design Osteochondral plugs (O=6mm) were prepared from bovine patellae and divided into two groups according to the contrast agent to be used in contrast enhanced computed tomography (CECT) imaging: (I) anionic ioxaglate and (II) non-ionic iodixanol. The groups I and II contained 7 and 6 sample pairs, respectively. One of the paired samples served as a reference while the other was treated with threose to induce collagen cross-linking. The equilibrium partitioning of the contrast agents was imaged after 24h of immersion. Fixed char…
Unveiling the Ionic Diels-Alder Reactions within the Molecular Electron Density Theory
2021
The ionic Diels–Alder (I-DA) reactions of a series of six iminium cations with cyclopentadiene have been studied within the Molecular Electron Density Theory (MEDT). The superelectrophilic character of iminium cations, ω >
Compensation of steric demand by cation–π interactions, cobaltocenium cations as guests in tetraurea calix[4]arene dimers
2003
The affinities of ferrocene (2) and the cobaltocenium cation (3+), which have roughly the same size and differ in their charge, towards the inner cavity of the dimeric capsule formed by tetraurea calix[4]arene (1) were studied in C2D4Cl2 solutions. While 3+, which occupies more than 75% of the internal volume of the dimer, is readily encapsulated this is not the case for 2. This is probably due to cation-pi interactions, which operate only between 3+ and the aromatic rings of the calix[4]arene dimer. We found that the affinity of the cobaltocenium cation is higher than that of the tropylium cation (4+) and is only 2-3 times less than that of the tetraethylammoniun cation (5+). From the vari…
Two dimensional self-assembly of bis-acylureas having various functional end groups.
2011
We present the synthesis and morphology study of thirteen bis-acylurea molecules with various functional end groups. The bis-acylureas have two acylurea groups, -NH-CO-NH-CO-, divided by a pentamethylene spacer, -(CH(2))(5)-, and two symmetric functional end groups, such as, aliphatic, benzyl, mono- and bi-thiophenyl, sulfur-containing, and propargyl (HC[triple bond]CCH(2)-) moieties. The bis-acylureas were synthesized by the coupling reactions of ureas with pimeloyl chloride or pimelic acid. Upon cooling from hot isotropic solutions, the bis-acylureas spontaneously form supermolecules. In the cases of aliphatic, benzyl, mono- and bi-thiophenyl functional groups, two dimensional supramolecu…
Energy interactions in amyloid-like fibrils from NNQQNY.
2014
We use large-scale MP2 calculations to analyze the interactions appearing in amyloid fibers, which are difficult to determine experimentally. To this end, dimers and trimers of the hexapeptide NNQQNY from the yeast prion-like protein Sup35 were considered as model systems. We studied the energy interactions present in the three levels of organization in which the formation of amyloid fibrils is structured. The structural changes in the hydrogen bonds were studied too. It was found that the most energetic process is the formation of the β-sheet, which is equally due to both hydrogen bonds and van der Waals interactions. The aromatic rings help stabilize these aggregates through stacking of t…