Search results for "supramolekulaarinen kemia"
showing 10 items of 82 documents
An aryl-fused redox-active tetrathiafulvalene with enhanced mixed-valence and radical-cation dimer stabilities.
2018
Molecular recognition of stable organic radicals is a relatively novel, but important structural binding motif in supramolecular chemistry. Here, we report on a redox-switchable veratrole-fused tetrathiafulvalene derivative VTTF which is ideally suited for this purpose and for the incorporation into stimuli-responsive systems. As revealed by electrochemistry, UV/Vis measurements, X-ray analysis, and electrocrystallisation, VTTF can be reversibly oxidised to the corresponding radical-cation or dication which shows optoelectronic and structural propterties similar to tetrathiafulvalene and tetrakis(methylthio)tetrathiafulvalene. However, theoretical calculations, variable temperature EPR, and…
Protonation of a Spherical Macrotricyclic Tetramine: Water Inclusion, Allosteric Effect, and Cooperativity
2017
The spherical macrotricyclic cryptand tetramine "C24" (1) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which pKa values of 11.17±0.05, 10.28±0.04, 6.00±0.06 and 3.08±0.08 have been determined at 298 K. The unusually close values for the first two protonations provide evidence for the encapsulation of a water molecule serving as effector for the second protonation, which is consistent with earlier observations that the exchange of protons bound in the diprotonated species with solvent protons is unusually slow and that 17 O NMR spectra show the presence of an oxygen centre in the same species quite distinct from that of solvent water. Encap…
Enantiomeric Resolution of Asymmetric-Carbon-Free Binuclear Double-Stranded Cobalt(III) Helicates and Their Application as Catalysts in Asymmetric Re…
2018
A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.
Short X···N Halogen Bonds With Hexamethylenetetraamine as the Acceptor
2021
Hexamethylenetetramine (HMTA) and N-haloimides form two types of short (imide)X···N and X–X···N (X = Br, I) halogen bonds. Nucleophilic substitution or ligand-exchange reaction on the peripheral X of X–X···N with the chloride of N-chlorosuccinimide lead to Cl–X···N halogen-bonded complexes. The 1:1 complexation of HMTA and ICl manifests the shortest I···N halogen bond [2.272(5) Å] yet reported for an HMTA acceptor. Two halogen-bonded organic frameworks are prepared using 1:4 molar ratio of HMTA and N-bromosuccinimide, each with a distinct channel shape, one possessing oval and the other square grid. The variations in channel shapes are due to tridentate and tetradentate (imide)Br···N coordi…
Water Structure Recovery in Chaotropic Anion Recognition: High-Affinity Binding of Dodecaborate Clusters to γ-Cyclodextrin
2015
Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25 kcal mol(-1)) and entropies (TΔS up to -18.4 kcal mol(-1), both for B12I12(2-)), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous …
Experimental investigation of anion-π interactions : Applications and biochemical relevance
2015
Chemical communications 52(9), 1778 - 1795(2016). doi:10.1039/C5CC09072E
Modulating the reaction pathway of phenyl diazonium ions using host–guest complexation with cucurbit[7]uril
2022
Aryl diazonium ions are known to be an important intermediate in the divergent synthesis of azo compounds and substituted aromatics. The presence of more than one electrophilic center in a diazonium ion could lead to undesirable side reactions during a synthesis. Herein, we report that the electrophilic α-carbon on a phenyl diazonium [PhN2]+ ion can be selectively deactivated upon host–guest complexation with cucurbit[7]uril (CB7) in aqueous media, achieving a ∼60-fold increase in the half-life of [PhN2]+. Notably, however, the electrophilic nitrogen of the encapsulated diazonium ion remains active towards diazo coupling with strong nucleophiles, allowing the formation of azo compounds usin…
Damming an electronic energy reservoir: ion-regulated electronic energy shuttling in a [2]rotaxane
2021
We demonstrate the first example of bidirectional reversible electronic energy transfer (REET) between the mechanically bonded components of a rotaxane. Our prototypical system was designed such that photoexcitation of a chromophore in the axle results in temporary storage of electronic energy in a quasi-isoenergetic “reservoir” chromophore in the macrocycle. Over time, the emissive state of the axle is repopulated from this reservoir, resulting in long-lived, delayed luminescence. Importantly, we show that cation binding in the cavity formed by the mechanical bond perturbs the axle chromophore energy levels, modulating the REET process, and ultimately providing a luminescence read-out of c…
Cation binding resorcinarene bis-crowns: the effect of lower rim alkyl chain length on crystal packing and solid lipid nanoparticles
2012
A group of seven resorcinarene bis-crown ethers (CNBC5) with two polyether bridges at the upper rim and either propyl, butyl, pentyl, heptyl, nonyl, decyl or undecyl groups at the lower rim were synthesized and their binding properties with Cs+ were investigated by NMR titration. The bis-crowns form 1:2 complexes with Cs+ with binding constants of logK 4–5. Crystal structures of bis-crowns and their Cs+ and K+ complexes were studied and different packing motifs were found depending on the alkyl chain length. Short ethyl, propyl and butyl alkyl chains gave a layer or pillar packing where the polar and non-polar regions cannot be distinguished, whereas longer pentyl and decyl chains formed bi…
Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers
2019
Pyridine[4]arenes have previously been considered as anion binding hosts due to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected and studied by multiple gas-phase techniques, ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, as well as DFT calculations. The comparison of classical resorcinarenes with pyridinearenes by MS and NMR experiments reveals clear differences in their host–guest chemistry and implies that cation encapsulation in pyridine[4]arene…