Search results for "supramolecular chemistry"
showing 10 items of 721 documents
From Bowls to Capsules: Assembly of Hexanuclear Ni II Rings Tailored by Alkali Cations
2020
An anionic hexanuclear NiII metallamacrocycle with endo and exo linking sites has been employed as a building block to generate a series of capsules and bowls of nanometric size. The supramolecular arrangement of the {Ni6 } rings was tailored by the size of the alkali cations, showing the transition from {Ni6 -M2 -Ni6 } capsules (M=LiI and NaI ) to {Ni6 -M} bowls (M=KI and CsI ). The alkyl co-cations are determinant to stabilize the assemblies by means of CH⋅⋅⋅π interactions on the exo side of the metallamacrocycles. The effect on the topology of the supramolecular assemblies of the cation size, cation charge, Et3 NH+ or Me4 N+ counter cations has been analyzed. Magnetic measurements reveal…
Synthesis of all-syn Functionalized Triphenylene Ketals
2011
The stereoselective synthesis of triphenylene ketals offers access to unique scaffolds. For a good performance in supramolecular applications an all-syn orientation of the functional groups is essential. The oxidative trimerization of catechol ketals by molybdenum pentachloride or mixtures with titanium tetrachloride leads to a template-directed formation. Several heterocyclic moieties are suitable for this transformation. A template-directed isomerization of anti,anti,syn isomers to the desired C 3 -symmetric derivative was demonstrated in two cases.
Synthesis and Characterization of theO-Alkylation Products of Resorcinarene
2013
O-Substitution reactions of tetramethoxyresorcinarene with alkyl halides produced a variety of partially O-alkylated resorcinarene derivatives with terminal alkyne functionality. The degree of alkylation was affected by the reactivity of the alkylating halide used. NMR spectroscopy proved to be an ideal tool for analyzing the complex reaction mixtures and the isolated products based on the symmetry and degree of alkylation of the resorcinarene derivatives. Single-crystal X-ray diffraction studies furthermore showed diversity in the self-assembly of the various O-alkylation products that was greatly affected by the degree of alkylation, as well as the nature of the alkyne moiety.
Synthesis and characterisation of tetrazole compounds: 3 series of new ligands representing versatile building blocks for iron(II) spin-crossover com…
2005
Abstract New tetrazole compounds were synthesized and characterised by NMR and FTIR spectroscopy as well as by single crystal X-ray diffraction. We present in this paper mono- and ditetrazoles, which represent a versatile class of building blocks for the formation of mononuclear iron(II) complexes with monotetrazoles as terminal ligands as well as iron(II) coordination polymers with ditetrazoles as bridging ligands. Especially, the series of α,ω-bis[tetrazol-1-yl]-alkanes open the field of fascinating supramolecular structures with spin transition properties.
Halogen bonding enhances nonlinear optical response in poled supramolecular polymers
2015
We demonstrate that halogen bonding strongly enhances the nonlinear optical response of poled supramolecular polymer systems. We compare three nonlinear optical chromophores with similar electronic structures but different bond-donating units, and show that both the type and the strength of the noncovalent interaction between the chromophores and the polymer matrix play their own distinctive roles in the optical nonlinearity of the systems. acceptedVersion Peer reviewed
Pollutant Adsorbtion and Detection: Methyl-Substituted α-Cyclodextrin as Affinity Material for Storage, Separation, and Detection of Trichlorofluorom…
2018
The cover image depicts the hazard caused by chlorofluorocarbons such as CFC‐11, which are used, for example, as blowing agents for polyurethane foams, and the protective effect of the oligosaccharide, hexakis‐(2,3,6‐tri‐O‐methyl)‐α‐cyclodextrin, which is capable of binding CFC‐11 by supramolecular complexation and thus protecting the stratospheric ozone layer from the harmful trichlorofluoromethane. Further details can be found in article number 1800057 by Ralf Hellmann, Siegfried R. Waldvogel, and co‐workers.
1991
Thermoanalytical studies on an order-disorder transition resulting from supramolecular organization of hydrogen bond motifs in an unpolar (polymer-) matrix are reported. Functional groups having two potential sites for hydrogen bonding (4-carboxyphenylarazole) are located statistically along the polybutadiene backbone. Multistep hydrogen bond formation leads to the formation of association chains whose lengths can be controlled by addition of monofunctional groups (phenylurazole) like in conventional stepgrowth polymers. The association chain length is estimated from the variation of transition enthalpy and «melting» temperature
Supramolecular Thermotropic Liquid Crystalline Materials with Nematic Mesophase Based on Methylated Hyperbranched Polyethylenimine and Mesogenic Carb…
2006
Supramolecular interaction of fully methylated hyperbranched polyethylenimines (PEI) with a mesogen-based carboxylic acid, 5-(p-cyanobiphenoxy)pentanoic acid, results in the formation of supramolecular complexes exhibiting thermotropic liquid crystalline (LC) mesophases. In contrast to the common smectic mesophases of most dendritic LC polymers, nematic LC phase were observed. The complexation of PEI and the mesogen units is due to electrostatic interaction between the carboxylate groups and the ammonium end groups of PEI. LC properties were investigated by a combination of differential scanning calorimetry, polarizing light optical microscopy, and X-ray diffractometry.
Switchable Supramolecular Crosslinking of Cyclodextrin-Modified Hyperbranched Polyethylenimine via Anthraquinone Dyes
2011
Two anthraquinone dyes, 5,8-di-N-adamantylamino-1,4-dihydroxyanthraquinone (AQ-OH) and 1,4-di-N-adamantylaminoanthraquinone (AQ-H), are synthesized. The combination of AQ-OH and AQ-H with hyperbranched polyethylenimine (PEI) bearing covalently attached β-cyclodextrin spontaneously formed host–guest complexes with hydrodynamic diameters of about 260 nm. Even enlarged structures of the trifunctional AQ-H were observed via DLS. Repeated measurements show that their assembly and disassembly is reversible with a critical point at 26 °C and therefore switchable via temperature. Also superstructures up to 100 μm were detected via TEM, cryo-TEM-, and SEM. Hence, a smart colored network of switchabl…
Supramolecular Nanocycles Comprisingβ-Cyclodextrin-click-Ferrocene Units: Rings of Rings of Rings
2010
We applied 1,3-dipolar cycloaddition to bind ethynylferrocene onto 6I-azido-6I-deoxycyclomaltoheptaose under microwave assisted conditions. The process was investigated by (1) H NMR, FT-IR spectroscopy, and MALDI-TOF mass spectrometry. The ability of the synthesized compound to self-organize to cyclic supramolecular structures was investigated by dynamic light scattering measurements and cryo-transmission electron microscopy.