Search results for "405"
showing 10 items of 3208 documents
Host–Guest Chemistry: Oxoanion Recognition Based on Combined Charge‐Assisted C−H or Halogen‐Bonding Interactions and Anion⋅⋅⋅Anion Interactions Media…
2016
Several bis-triazolium-based receptors have been synthesized and their anion-recognition capabilities have been studied. The central chiral 1,1'-bi-2-naphthol (BINOL) core features either two aryl or ferrocenyl end-capped side arms with central halogen- or hydrogen-bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge-assisted aliphatic and heteroaromatic C-H noncovalent interactions and combinations of C-H hydrogen and halogen bonding. The receptors are able to selectively interact with HP2 O7 (3-) , H2 PO4 (-) , and SO4 (2-) anions, and the value of the association constant follows the sequence: HP2 O7 (3-) >SO4 (2-) >H2 PO4 (-) . The …
Iodine Clathrated: A Solid‐State Analogue of the Iodine–Starch Complex
2019
Co-crystallizing iodine with a simple dicationic salt (1,8-diammoniumoctane chloride) results in the clathration of the iodine (I2 ) molecules inside trigonal and hexagonal helical channels of the crystal lattice with 72 wt % overall I2 loading. The I2 inside the bigger trigonal channel forms a I-I⋅⋅⋅I-I⋅⋅⋅I-I halogen-bonded infinite helical chain, while the I2 in the smaller hexagonal channel is disordered. In both channels the I2 interaction with the channel wall happens through I-I⋅⋅⋅Cl- halogen bonds. The helical channels in the crystal lattice are constructed via the strong charge-assisted H2 N+ H⋅⋅⋅Cl- hydrogen bonds between the dications and the chloride anions. The structure shows a…
Counterion influence on the N–I–N halogen bond
2015
A detailed investigation of the influence of counterions on the [N–I–N]+ halogen bond in solution, in the solid state and in silico is presented. Translational diffusion coefficients indicate close attachment of counterions to the cationic, three-center halogen bond in dichloromethane solution. Isotopic perturbation of equilibrium NMR studies performed on isotopologue mixtures of regioselectively deuterated and nondeuterated analogues of the model system showed that the counterion is incapable of altering the symmetry of the [N–I–N]+ halogen bond. This symmetry remains even in the presence of an unfavorable geometric restraint. A high preference for the symmetric geometry was found also in …
N-Alkyl Ammonium Resorcinarene Salts: A Versatile Family of Calixarene-Related Host Molecules
2016
This chapter presents a review of the recent advances in the chemistry of N-alkylammonium resorcinarenes salt receptors. The Mannich condensation between amines (primary and secondary) and resorcinarenes result in resorcinarene tetrabenzoxazines and tetra-azoxazines. Only 2 isomers out of 16 potential isomers are formed. The resorcinarene tetrabenzoxazines possess deeper cavities than the parent resorcinarenes which are suitable for binding neutral and cationic guests. In the presence of mineral acids, the six-membered oxazine ring in the resorcinarene tetrabenzoxazines is opened, resulting in N-alkylammonium resorcinarene salts (NARSs). The NARSs possess four spatially-fixed anions within …
Hierarchy of Asymmetry at Work: Chain-Dependent Helix-to-Helix Interactions in Supramolecular Polymers.
2018
A detailed investigation of the hierarchy of asymmetry operating in the self-assembly of achiral (1) and chiral ((S)-2 and (R)-3) 1,3,5-triphenylbenzenetricarboxamides (TPBAs) is reported. The aggregation of these TPBAs is conditioned by the point chirality at the peripheral side chains for (S)-2 and (R)-3. An efficient helix-to-helix interaction that goes further in the organization of fibrillar bundles is experimentally detected and theoretically supported only for the achiral TPBA 1. The effective interdigitation of the achiral aliphatic side chains produces a social self-sorting to form preferentially heterochiral macromolecular aggregates.
Tailor‐Made Amino Acids and Fluorinated Motifs as Prominent Traits in Modern Pharmaceuticals
2020
Structural analysis of modern pharmaceutical practices allows for the identification of two rapidly growing trends: the introduction of tailor-made amino acids and the exploitation of fluorinated motifs. Curiously, the former represents one of the most ubiquitous classes of naturally occurring compounds, whereas the latter is the most xenobiotic and comprised virtually entirely of man-made derivatives. Herein, 39 selected compounds, featuring both of these traits in the same molecule, are profiled. The total synthesis, source of the corresponding amino acids and fluorinated residues, and medicinal chemistry aspects and biological properties of the molecules are discussed.
Bridgehead isomer effects in bis(phosphido)-bridged diiron hexacarbonyl proton reduction electrocatalysts
2017
The influence of the substitution, orientation and structure of the phosphido bridges in [Fe2(CO)6(μ-PR2)2] electrocatalysts of proton reduction has been studied. The isomers e,a-[Fe2(CO)6{μ-P(Ar)H}2] (1a(Ar): Ar = Ph, 2′-methoxy-1,1′-binaphthyl (bn′)), e,e-[Fe2(CO)6{μ-P(Ar)H}2] (1b(Ar): Ar = Ph, bn′) were isolated from reactions of iron pentacarbonyl and the corresponding primary phosphine, syntheses that also afforded the phosphinidene-capped tri-iron clusters, [Fe3(CO)9(μ-CO)(μ3-Pbn′)] (2) and [Fe3(CO)9(μ3-PAr)2] (3(Ar), Ar = Ph, bn′). A ferrocenyl (Fc)-substituted dimer [Fe2(CO)6{μ:μ′-1,2-(P(CH2Fc)CH2)2C6H4}] (4), in which the two phosphido bridges are linked by an o-xylyl group, was al…
Conformational stability of oligoferrocene oligoamide foldamers
2016
Abstract Organometallic oligoamides built from three to four ferrocene amino acid units ( H-Fca-OH , 1-amino-1′-ferrocene carboxylic acid) fold into hydrogen bonded secondary structures featuring eight-membered rings by cooperative hydrogen bonds. NMR studies and DFT calculations (CAM-B3LYP, LANL2DZ, IEFPCM (THF)) reveal that the organometallic zigzag foldamer structures are highly resistant toward denaturation by hydrogen bond acceptors such as dimethyl sulfoxide and 2,4-lutidine. Replacing one ferrocene amino acid unit by the organic α -amino acid glycine at the C -terminal end (Fca → Gly) significantly destabilizes the secondary zigzag structure facilitating denaturation by DMSO. Highly …
A general concept for the introduction of hydroxamic acids into polymers.
2019
Polyethers (PEG) with hydroxamic acid groups enable chelation of a variety of metal ions, coating of metal oxide surfaces and stabilization of nanoparticles. In contrast to catechol, hydroxamic acids are oxidation stable and biocompatible.
Divalent metal phosphonates – new aspects for syntheses, in situ characterization and structure solution
2016
Abstract Divalent metal phosphonates are promising hybrid materials with a broad field of application. The rich coordination chemistry of the phosphonate linkers enables the formation of structures with different dimensionalities ranging from isolated complexes and layered structures to porous frameworks incorporating various functionalities through the choice of the building blocks. In brief, metal phosphonates offer an interesting opportunity for the design of multifunctional materials. Here, we provide a short review on the class of divalent metal phosphonates discussing their syntheses, structures, and applications. We present the advantages of the recently introduced mechanochemical pa…