Addition Of Guest Molecules Research Articles

Highly Selective Synthesis of Iridium(III) Metalla[2]catenanes through Component Pre-Orientation by π⋅⋅⋅π Stacking.

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template-free, coordination-driven self-assembly of dinuclear iridium acceptors and 1,5-bis[2-(4-pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich-type π-π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.

Critical Role of Achiral Guest Molecules in Planar Chirality Inversion of Alanine-Appended Pillar[5]arenes.

Planar chirality inversion of pillar[5]arenes bearing d- or l-alanine substituents on both rims was investigated upon addition of guest molecules having pyridinium or imidazole moieties and long alkyl chains. The d- and l-alanine-substituted pillar[5]arenes exhibited pS and pR planar chirality, respectively. However, this planar chirality was inverted upon inclusion of certain achiral molecules, comprising pyridinium or imidazole moieties and long alkyl chains with terminal hydroxyl or methyl groups.

Amphiphilic pillar[n]arenes

Amphiphilic pillar[n]arenes, based on pillar-like macrocyclic frameworks, are a new type of fassionate amphiphilies designed and synthesised by Huang and co-workers in 2012 firstly. A large number of functional amphiphilic pillar[n]arenes can be developed by locating different hydrophilic and hydrophobic groups on the respective sides of the pillar-like frameworks to meet reality requires. In this Review we summarise recent studies in the syntheses, self-assembly and application of amphiphilic pillar[n]arenes. Due to the pillar-like cavities of pillar[n]arenes, they can complex with tremendous guest molecules through host-guest interaction. So it is easy to control the dimensional and morphologic of the assemblies formed from amphiphilic pillar[n]arenes dispersed in water by addition of guest molecules. Moreover, this controllable self-assembly process promote amphiphilic pillar[n]arenes more useful in many areas, such as drug and gene delivery, phase transfer catalysts, bacterial cell agglutination and so on.

Adaptive Building Blocks Consisting of Rigid Triangular Core and Flexible Alkoxy Chains for Self-Assembly at Liquid/Solid Interfaces

Abstract Supramolecular self-assembly in two-dimensional (2D) spaces on solid surfaces is the subject of intense current interest because of perspectives for various applications in nanoscience and nanotechnology. At the liquid/graphite interface, we found by means of scanning tunneling microscopy molecules with a rigid triangular core, a twelve-membered phenylene-ethynylene macrocycle called dehydrobenzo[12]annulene (DBA), substituted by six flexible alkoxy chains self-assembled to form hexagonal porous 2D molecular networks via van der Waals interactions between interdigitated alkyl chains as the directional intermolecular linkages. Factors that affect the formation of the porous 2D molecular networks including alkyl chain length, solvent, solute concentration, and temperature were elucidated through a systematic study. Because DBA molecules are versatile for chemical modification, they turned out to be highly adaptive for on-surface supramolecular chemistry with respect to (i) pore size control by changing the chain length, (ii) study of parity effect due to even or odd number chains, (iii) generation of supramolecular chirality on surfaces by introducing stereocenters, (iv) chemical modification of the pore interior for selective co-adsorption of guest molecules by introducing functional groups. Additionally, formation of superlattice structures on surfaces was incidentally observed by mixing DBAs of different alkoxy chain parity or by addition of guest molecules via an induced-fit mechanism. These results made significant contribution to advancement of supramolecular chemistry in 2D space.

Modulation of the Thermoresponsive Behavior of Poly(N,N‐diethylacrylamide) via Cyclodextrin Host/Guest Interactions

The modulation of the cloud point of aqueous poly(N,N-diethylacrylamide) solutions via the formation of supramolecular cyclodextrin complexes with hydrophobic end groups, namely adamantyl,tert-butyl phenyl and azobenzene, synthesized via RAFT polymerization is described. The dependence of the apparent cloud points after cyclodextrin complexation is investigated with respect to the type and quantity of the guest end group, the polymer chain length and the cyclodextrin/end group ratio. Furthermore, the effect is reversed via the addition of guest molecules or via biocompatible enzymatic degradation of the cyclodextrins entire.

Guest-induced growth of a surface-based supramolecular bilayer

Self-assembly of planar molecules on a surface can result in the formation of a wide variety of close-packed or porous structures. Two-dimensional porous arrays provide host sites for trapping guest species of suitable size. Here we show that a non-planar guest species (C(60)) can play a more complex role by promoting the growth of a second layer of host molecules (p-terphenyl-3,5,3″,5″-tetracarboxylic acid) above and parallel to the surface so that self-assembly is extended into the third dimension. The addition of guest molecules and the formation of the second layer are co-dependent. Adding a planar guest (coronene) can displace the C(60) and cause reversion to a monolayer arrangement. The system provides an example of a reversible transformation between a planar and a non-planar supramolecular network, an important step towards the controlled self-assembly of functional, three-dimensional, surface-based supramolecular architectures.

Carbohydrate-Coated Supramolecular Structures: Transformation of Nanofibers into Spherical Micelles Triggered by Guest Encapsulation

Triblock rigid-flexible dendritic block molecules consisting of a rigid aromatic segment as a stem segment, carbohydrate-branched dendrons as a flexible head, and a hydrophobic alkyl chain were synthesized and characterized. The carbohydrate conjugate molecule based on a methyl group as a hydrophobic tail, in the solid state, self-assembles into a 1D nanostructure, whereas the molecule based on a longer hydrophobic tail self-assembles into 2D nanosheets, as confirmed by X-ray scatterings. In aqueous solution, however, both molecules were observed to self-assemble into carbohydrate-coated cylindrical aggregates with a uniform diameter, as confirmed by dynamic light scatterings and transmission electron microscopic (TEM) investigations. Notably, these cylindrical objects reversibly transformed into spherical objects on addition of guest molecules. Investigation of the interactions of the carbohydrate-coated nanostructures with E. coli cells showed that both nano-objects could immobilize bacterial cells, while the degrees of immobilization were significantly dependent on the shape of nanostructure. These results demonstrated that the supramolecular materials that are responsive to external stimuli can provide novel opportunities to control many biological activities.

Molecular Dynamics Simulations of p‐tert‐Butylcalix[4]arene with Small Guest Molecules

Classical molecular dynamics simulations were used to study p-tert-butylcalix[4]arene inclusion compounds with xenon, nitrogen, hydrogen, methane, and sulfur dioxide guest molecules. The calixarene units were taken to be rigid and the intermolecular molecular interactions were modeled as a sum of the van der Waals interactions with parameters from the AMBER force field and electrostatic interactions. Simulations of the high-density alpha phase and low-density beta0 phase of p-tert-butylcalix[4]arene were used to test the force field. The predicted densities of the two phases were found to agree with experimental measurements at 173 K to within 5 %. Simulations were performed with guests placed inside the calixarene cages of the beta0 phase. Guest-host ratios of 1:1 to 1:4 were considered. Changes in the unit-cell volume and density of the phases with the addition of guest molecules and the inclusion energies for the guests were determined. Finally, the dynamics of the guest motion inside the cages were characterized by determining the root-mean-square displacements and velocity autocorrelation functions of the xenon and nitrogen guests.

Investigation on photophysical properties of a substituted 3H-indole-modified β-cyclodextrin: I. Conformation in water and recognition mechanism as a chemosensor

A substituted 3 H-indole-modified β-cyclodextrin (β-CD), mono-6-deoxy-(2-[( p-amino) phenyl]-3,3-dimethyl-5-carboxyl-3 H-indole)-β-CD (compound A) has been synthesized and characterized by elemental analysis, mass spectrum (MS) and 1H NMR. Induced circular dichroism (ICD), time-resolved fluorescence and computational analysis yield information on the molecular structure that compound A adopts rim-covering conformation in aqueous solution. It forms the 1:1 (guest:host) inclusion complex by addition of native β-CD. Novel recognition behavior of compound A is investigated by means of ICD, time-resolved and steady-state fluorescence. In contrast to the behavior of most conventional CD-based chemosensors with self-inclusion conformation, the fluorescence intensity of this new kind chemosensor is increased upon addition of guest molecules. This new chemosensor exhibits high sensitivity to acyclic and adamantine molecules, but not to the bile acids.

Design of liquid-crystalline foods via field theoretic computer simulations

Abstract Liquid crystalline foods based on self-assembly of lipids and water present rich phase diagrams, in which the hydrophilic and hydrophobic phases are organized in periodic three-dimensional nano-structures of different types, depending on temperature and composition. Since these systems constitute a rare example of food at local thermodynamic equilibrium, their structure can be predicted, in theory, based on the minimization of the total free energy. In the present work, we review past and recent attempts to predict the equilibrium structure of these materials, based on parametric, geometrical and physically inspired approaches. We also summarize our own efforts towards a general predictive simulation tool based on self-consistent field theory. For a specific lipid–water system, this approach allows predicting which liquid crystalline phases are present at equilibrium, but also the relevant topological parameters at a given temperature and composition, such as the radius of water channels or thickness of water lamellae and lipid bi-layers. Furthermore, the addition of guest molecules in either the hydrophobic or hydrophilic phase can also be accounted in the model. This approach should ultimately allow the design of complex liquid crystalline foods based on multiple components and functional molecules.

Redox active macrocyclic receptors for neutral guests.

A novel series of triazine-appended macrocyclic complexes has been investigated as potential hydrogen bonding receptors for complementarily disposed heterocycles. Cocrystallization of a melamine-appended azacyclam complex of Cu(II) has been achieved with barbitone, the barbiturate anion and thymine. In each case, a complementary DAD/ADA hydrogen bonding motif between the melamine group and the heterocycle has been identified by X-ray crystallography. Electrochemical studies of the copper macrocycles in both nonaqueous and aqueous solution show anodic shifts of the Cu(II/)(I) redox couple of more than 60 mV upon addition of guest molecules with matching H-bonding motifs. The Zn(II) analogues have been synthesized via transmetalation of the Cu(II) complex, and their guest binding properties investigated by NMR spectroscopy. (1)H NMR shifts of up to 0.8 ppm were observed upon addition of guest, and stability constants are similar to those obtained electrochemically.

Preparation of fluorescent hyperbranched polymer materials by end-capping approach

Two kinds of novel fluorescent hyperbranched polymers were synthesized by the end-capping approach. The fluorescent hyperbranched polyether (FPEOTM) was obtained by end capping the hyperbranched poly(hydroxyl ether) (PEOTM) with guest molecules N,N-dimethylaminobenzaldehyde (DMABA). In addition, in the presence of triethylamine, the hyperbranched polysulfone-amine with terminal double bonds (HPSA) was synthesized by polyaddition of a new AB2 type monomer (SAP, sulfone amine piperazine) at 40°C for 60 h in chloroform solution. Then the fluorescent hyperbranched polysulfone-amine (FHPSA) was prepared by addition of guest molecules N, N-dimethylaminoanilines (DMAA) with the terminal double bonds of HPSA. The two resulting polymers fluoresce yellow-green color in both solid and solution states. The maximum emission wavelength is (460±10) nm and (470±10) nm, respectively. A novel “complex quenching effect” for hyperbranched polymer was observed. The fluorescence can be quenched by transition metal cations such as Ag+, cu2+ and Fe3+, while alkali and alkaline earth metal cations almost have no influence on the fluorescence intensity.

Design and construction of supramolecular and macromolecular architectures by tandem interactions

AbstractThe self‐assembling behaviour of several molecular building blocks are used to construct a variety of chiral and nonchiral supra‐molecular and macromolecular architectures. These structures can be finely tuned by slight changes in e.g. the shape of the building blocks, the pH and by the addition of guest molecules.

Effects of multiple scattering and Anderson localization of photons in light pulse reflection from a 1D disordered medium with low concentration of impurities

The theory of light pulse reflection from a one-dimensional(1D) disordered scattering medium exemplifying application of the supersymmetry to the solid state physics is developed. It is shown that multiple scattering processes and localization effects lead to a peculiar trapping of light in the medium and, as a result, to a peculiar time evolution of the reflected beam intensity. An addition of guest molecules with a narrow absorption line at low concentrations suppresses the contribution of long trajectories of photons resonating with impurities and, consequently, leads to the appearance of a narrow dip in the spectral decomposition of the reflected light in the long-time asymptotic regime.

CONFORMATIONAL CHANGE OF PHOTORESPONSIVE CAPPED CYCLODEXTRIN DETECTED BY CIRCULAR DICHROISM

Abstract The circular dichroism spectrum of azobenzene-capped β-cyclodextrin (I) was found, in some cases, to show an abrupt change on addition of guest molecules with ionic nature. This nonstoichiometric behavior was regarded as evidence for a conformational transition of the cyclodextrin moiety caused by outside binding of the guest molecules.