Spectral and electrochemical investigation of p-sulfonatocalix[4]arene-stabilized vitamin E aggregation

The host–guest interaction of α-tocopherol (vitamin E) with p-sulfonatocalix[4]arene (p-SC4) in solution state is studied using emission and cyclic voltammetric techniques. The lipid soluble α-tocopherol (α-T) forms a solid complex with p-SC4. FTIR and NMR spectral analysis of the solid complex reveals the tight packing of α-T inside the cavity of p-SC4. The structural deformation is confirmed by XRD analysis. SEM images differentiate the highly porous gel like structure of vitamin E aggregate and the solid structure of the host–guest complex prepared. NOESY spectra confirm the tight penetration of α-T within the hydrophobic cavity of p-SC4.     

Supramolecular control over LCST behavior of hybrid macrocyclic system based on pillar[5]arene and crown ether

A hybrid system containing a pillar[5]arene unit and ten crown ether moieties was developed. The LCST behavior and thermo-responsiveness were successfully introduced into this pillar[5]arene-crown ether system. Both host-guest interactions and salting-out effect displayed great effects in realizing the supramolecular control over LCST properties and thermo-responsiveness. Compared with the individual macrocycles, this hybrid macrocycle system dramatically amplified the supramolecular control effect over LCST behavior.     

Cobalt(III) Supramolecuar Complex: Synthesis,Crystal Structure and Anions Recognition Properties of 6,7-Dinitroquinoxaline-2,3-dione

A 3D supramolecular complex [Co(III)(Phen)₂Cl₂][DNQ]Cl·H₂O (DNQ = 6,7-dinitroquinoxaline-2,3-dione) has been synthesized and determined by single-crystal X-ray analysis. Anion binding studies carried out using ¹H NMR and UV-visible revealed that a genuine hydrogen bond interaction between anion receptor 2 and Cl^?  can be detected, but fluoride is deprotonating the anion receptor 2. X-ray analysis results show that it is not possible for the two amide nitrogen atoms of anion receptor to form hydrogen bonds to a chloride ion in the presence of small aliquots of water.     

Supramolecular Self-organization of Potential Hydrogelators on Attracting Surfaces

This article highlights the aggregation behaviour of potential low molecular weight hydrogelators on attracting surfaces. Our goal was the development of a method, which enables the finding of new hydrogelators that are not easily recognizable as such because they only form instable or no hydrogels in aqueous solution. To this end, a series of negatively charges azo-dyes was synthesized and positive charged glass slides were immersed into their aqueous solutions. All dyes showed supramolecular organization and significant concentration on the attracting glass surface. Microscopic investigations mostly revealed the formation of crystals. However, one compound, (1-(2-n-octylphenylazo)-2-hydroxy-6-naphthalenesulphonate, selectively formed a hydrogel on the surface whereas it does not gel in aqueous solution. This reveals the hydrogel as the stable form of this compound under equilibrium conditions. This method of surface-induced hydrogelation might facilitate the identification of new hydrogelators. Further more, it might also allow the mimicking of surface gelation as a process of biological relevance.     

Supramolecular Chemistry In Silico

Computational protocols capable of modelling supramolecular complexes have been evaluated. The complexation of cations by crown ethers and quaternary ammonium ions by an oxacalix[3]arene are presented as examples. In the latter case reliable qualitative results were obtained using the semi-empirical PM3 method where guest LUMO and electrostatic potential energies have been shown to correlate with experimental binding data. The optimal method for more accurate results combines semi-empirical equilibrium geometry and property calculations with single point energy calculations at the HF/6–31G* or BP/6–31G* quantum mechanical level.     

Ammonium Ion Complexes of Tetraethyl Resorcarene: An Ab Initio Study

The complexation of various ammonium ions with a resorcarene host was evaluated by ab initio calculations. The approximations of the binding locations and the interaction energies for each guest are reported. The supramolecular complex formation also affects the conformation of the resorcarene host.     

Study on the Supramolecular System of TAPP and Cyclodextrins by Spectroscopy

The ability of β-cyclodextrin (β-CD), γ-CD, hydroxypropyl-β-CD (HP-β-CD), trimethyl-β-CD (TM-β-CD), sulfurbutylether-β-CD (SBE-β-CD) and carboxymethyl-β-cyclodextrin (CM-β-CD) to break the aggregate of the meso-tetrakis(4-N-trimethylaminobenzyl)porphyrin (TAPP) and to form 2:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. The formation constants are calculated, respectively, by fluorimetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-β-CD (SBE-β-CD and CM-β-CD) is quite different from that of the parent β-CD. At lower pH, the complexation between TM-β-CD and H²TAPP²⁺ (the form of the diprotonated TAPP) hampers the continuous protonation of the pyrrole nitrogen of TAPP and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. ¹HNMR data support the inclusion conformation of the porphyrin–cyclodextrin supramolecular system, indicating the interaction of the meso-phenyl groups of TAPP with the cavity of CDs. For this host–guest inclusion model, cyclodextrin being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for the porphyrin, creating artificial analogues of heme-containing proteins. However, for TAPP, encapsulated within this saccharide-coated barrier, its photophysical and photochemical properties changed strongly.     

pH-Responsive Phase Transition of Supramolecular Hydrogel Consisting of Glycosylated Amino Acetate and Carboxylic Acid Derivative

By addition of a carboxylated amino acetate (2) to a low-molecular-weight hydrogel (1) which has a unique thermally induced volume-phase transition character, a macroscopic pH-responsive feature is newly conferred on the supramolecular hydrogel. The direct observation of temperature-dependent behavior of the mixed hydrogel clearly showed that the thermally induced swelling-shrinkage type of the volume phase transition at pH 4 is shifted to the gel–sol transition at pH 7 by 10?mol% addition of 2 to the hydrogel 1. On the basis of the measurements by TEM, SEM, XRD and FT-IR, it is conceivable that incorporation of the anionic carboxylate of 2 slightly disturbs the packing of the hydrogen bond belt of the mixed hydrogel. Such a slight disturbance greatly leads to the sol–gel transition by elevating temperature, instead of the volume-phase transition. Introduction of dynamic characteristics to supramolecular systems in a macroscopic level may extend the potential of these materials in various fields.     

Metallosupramolecular Chemistry in Two Dimensions

Ultrathin films of metallosupramolecular coordination polyelectrolytes (MEPEs) on planar solid substrates assembled by electrostatic layer-by-layer self-assembly (ELSA) are characterized with UV-vis spectroscopy, optical ellipsometry, and X-ray reflectometry. MEPEs based on different ditopic ligands and transition metal ions are employed and shown to form regular ELSA multilayers. A quantitative analysis is in agreement with a surface coverage of approximately two MEPE monolayers per deposition step. In addition, we demonstrate that multilayers of MEPEs with different transition metal ions can be assembled. Even with kinetically labile metal ions, there is no metal ion exchange in these multilayers. Absorption spectra of multilayers on silicon show a band inversion of the MLCT band, which is rationalized in terms of optical effects.     

Self-assembling Dimeric and Trimeric Aggregates Based on Solvophobic and Charge-pairing Interactions

Self-assembly processes based on shape complementarity and noncovalent binding interactions are widely recognized as a fundamental principle in nature. Besides charge pairing and hydrogen bonding, hydrophobic interactions play a crucial role in water. Here we report the self-assembly of structurally simple monomers to yield defined dimeric and trimeric aggregates in highly polar media, based on ionic and solvophobic interactions. NMR, mass spectrometry and curve fitting were used to characterize these supramolecular assemblies in water–methanol solutions.