Supramolecular Control Research Articles

Guest-Triggered ZnII Translocation and Supramolecular Nuclearity Control in Calix[6]arene-Based Complexes

Two new polytopic ligands based on a calix[6]arene scaffold were synthesized. The truncated cone-shaped calixarene was functionalized at its small rim by a tris-imidazole site, aimed at generating a tetrahedral Zn(II) complex, where a fourth labile site inside the cavity is accessible through the funnel provided by its large rim. Tridentate aza ligands (either two or three) were then grafted at this large rim (the entrance of the cavity). Zn(II) coordination studies, monitored by (1)H NMR spectroscopy, showed unprecedented behavior in this family of heteropolytopic ligands. Indeed, it gives access to complexes of various nuclearities in acetonitrile, where zinc binding is under the supramolecular control of the guest. It is first shown that, in the absence of a good guest donor (a primary amine), Zn(II) binding is favored at the large rim where two tridentate nitrogenous groups can form an octahedral complex. The addition of a long guest such as heptylamine induces the quantitative translocation of the Zn(II) ion from the large rim octahedral (O(h)) site to the small rim tetrahedral (T(d)) site provided by the trisimidazole core and the guest ligand. With 2 equiv of Zn(II), well-defined dinuclear complexes were obtained and isolated, with one Zn(II) ion bound at each rim. Interestingly, it is shown that the binding mode at the large rim is under the supramolecular control of the guest bound at the small rim (with short guests, the O(h) environment is obtained at the large rim, whereas long guests disrupt this core through an induced-fit process); the partially included and dangling alkyl chain opens the large rim (entrance of the cavity) and pushes apart the tridentate moieties. As a result, a guest-induced switch of Zn(II) binding mode occurs and frees one of the tridentate groups from coordination, allowing further extension of the complex nuclearity.

Supramolecular Control of Selectivity in Hydroformylation of Vinyl Arenes: Easy Access to Valuable β‐Aldehyde Intermediates

A rationally designed regioselective formylation catalyst, in which noncovalent ligand-​substrate interactions allow the unprecedented reversal of selectivity from the typical α-​aldehyde to the otherwise unfavored β-​aldehyde, is reported. Thus, hydroformylation of o-​vinyl arene(or heteroarene)​carboxylic acids, e.g. I (R = 4-​Me, 6-​Me, 5-​O2N, 3,​4-​benzo, 5,​6-​OCH2O, etc.)​, with syngas in dichloromethane in the presence of this newly developed catalytic system and a base afforded the corresponding aldehydes, e.g. II, with excellent regioselectivity and high chemoselectivity towards aldehydes.

Supramolecular Control of Selectivity in Hydroformylation of Vinyl Arenes: Easy Access to Valuable β‐Aldehyde Intermediates

Gegen den Strom! In einem rational entworfenen regioselektiven Hydroformylierungskatalysator, [Rh/L], treten nichtkovalente Ligand-Substrat-Wechselwirkungen auf, die eine ungewöhnliche Selektivitätsumkehrung weg vom α-Aldehyd zum normalerweise nicht gebildeten β-Aldehyd bewirken. Dieses katalytische System eröffnet neuartige und nachhaltige Zugänge zu wichtigen Zwischenstufen der Feinchemikalienindustrie. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Supramolecular control of cell adhesion via ferrocene–cucurbit[7]uril host–guest binding on gold surfaces

Supramolecular control of adhesion of cells is demonstrated using synthetic integrin binding RGD peptide-ferrocene conjugates that were immobilized via host-guest chemistry onto cucurbit[7]uril coated gold surfaces.

Supramolecular control during triplet sensitized geometric isomerization of stilbenes encapsulated in a water soluble organic capsule

Triplet sensitized photoisomerization of several stilbenes included within a water-soluble organic capsule has been investigated. In this study octa acid that self assembles in the presence of hydrophobic guest molecules to form a host-guest complex is utilized to solubilize hydrophobic stilbenes and triplet sensitizers in water, and to provide confinement during the geometric isomerization of included olefins. By monitoring the steady state and time resolved room temperature phosphorescence from 4,4'-dimethylbenzil in the presence of acceptor stilbenes and their nitrogen analogues (stilbazole and bispyridyl ethylene) we have been able to establish that triplet-triplet energy transfer occurs between encapsulated donors and encapsulated (or free) acceptors. The mechanism of the energy transfer process is yet to be fully understood although a similar phenomenon has been reported earlier in the literature with Cram's hemicarcerand as the host. The photostationary state composition of cis and trans isomers within the OA capsule is dependent on the relative binding strength of the two isomers with the OA capsule. Further investigation is needed to fully exploit the interesting observations made here to steer the photoisomerization towards a single isomer.

Emission Color Trajectory and White Electroluminescence Through Supramolecular Control of Energy Transfer and Exciplex Formation in Binary Blends of Conjugated Polyrotaxanes

AbstractWhite electroluminescence and fine‐tuning of the emission color from binary blends of a blue‐emitting polymer and a green/yellow‐emitting threaded molecular wire consisting of a conjugated polymer supramolecularly encapsulated by functionalized cyclodextrins are demonstrated. Encapsulation controls the minimum intermolecular distance on the nanoscale, resulting in suppressed energy‐transfer between the blend constituents and reduced formation of interchain charge‐transfer complexes. The use of a green‐emitting polyrotaxane significantly improves the electrical properties with respect to blends of a blue electroluminescent polyrotaxane and leads to a significant reduction in the turn‐on voltage required for achieving white electroluminescence (VON = 3 V), with only 20% by weight of the encapsulated material.

Highly Fluorescent Slipped-Cofacial Phthalocyanine Dimer as a Shallow Inclusion Complex with α-Cyclodextrin

Supramolecular control of the π-stacked configuration of aqueous phthalocyanine (Zn[Pc(SO(3))(4)]) was achieved, allowing organization of a J-type slipped-cofacial dimer with per-O-methylated α-cyclodextrin (TMe-α-CDx) by the aid of host-guest interactions. Pristine Zn[Pc(SO(3))(4)] forms nonfluorescent face-to-face aggregates in water. The π-stacked configuration was controlled in the slipped-cofacial dimer, which was formed as a shallow inclusion complex with TMe-α-CDx, giving remarkably enhanced fluorescence with a very small Stokes shift. Organization of the J-type slipped-cofacial dimer as a 2:2 Zn[Pc(SO(3))(4)]-TMe-α-CDx complex was achieved through π-stacking of the unencapsulated segment of Zn[Pc(SO(3))(4)] shallowly encapsulated by a small TMe-α-CDx cavity.

Tunable Self-Assembled Elastomers Using Triply Hydrogen-Bonded Arrays

This article describes the synthesis and surpamolecular assembly of polyurethane-based elastomers. Triple hydrogen bonding between novel amidoisocytosine (AIC) and ureidoimidazole (UIM) motifs is used to promote assembly of the material. The material comprises an amorphous phase derived from a telechelic diol and a hard crystalline phase that comprises the supramolecular end groups. The use of a heterocomplementary hydrogen bonding interaction results in two unique features: (1) assembly of the elastomer occurs only in the presence of both components, and (2) different feed ratios used during synthesis allow the materials properties to be tuned as the stoichiometries of the components found in the amorphous and crystalline phases of the material are varied. The approach hence offers supramolecular control over materials properties and results in materials that can be melted and therefore processed at lower temperature compared to standard covalent elastomers.

Supramolecular Control of Photochemical and Electrochemical Properties of Two Oligothiophene Derivatives at the Air/Water Interface

Two geometric isomers of oligothiophene derivatives containing two crowned styryl fragments in 2- or 3-positions of thiophene rings are able to form stable monolayers on the water subphase. The organizing of crown-containing oligothiophenes in monolayers is guided by the π-stacking interaction of hydrophobic styrylthiophene fragments and interaction of hydrophilic macrocycles with the water subphase. The difference in structure of oligothiophene molecules leads to the formation of distinct monolayer architectures with various electrochemical and optical characteristics.

Selective oxidation of unactivated C–H bonds by supramolecular control

Efficient methods for dioxirane-based selective C-H bond oxidation by supramolecular control in H(2)O have been developed. With β-cyclodextrin as the supramolecular host, site-selective oxidation of the terminal over the internal tertiary C-H bond of 3,7-dimethyloctyl esters 3a-c was achieved. In addition, β-cyclodextrin selectively enhanced the C-H bond oxidation of cumene in a mixture of cumene and ethyl benzene in H(2)O. Through (1)H NMR studies, the selectivity in C-H bond oxidation could be attributed to the inclusion complex formation between β-cyclodextrin and the substrates.

Supramolecular control over Diels–Alder reactivity by encapsulation and competitive displacement

A water-soluble M4L6 coordination cage was used as a supramolecular protecting group in the Diels–Alder reaction between furan and maleimide. Encapsulation of furan in the cage prevents the Diels–Alder reaction, while subsequent addition of a competing guest will initiate the reaction.

Supramolecular control of self-assembling terthiophene–peptide conjugates through the amino acid side chain

The self-assembly of oligothiophene-peptide conjugates can be directed through the systematic variation of the peptide sequence into different nanostructures, including flat spicules, nanotubes, spiral sheets, and giant, flat sheets. Furthermore, the assembly of these molecules is not controlled by steric interactions between the amino acid side chains.

Molecular and Supramolecular Control of the Work Function of an Inorganic Electrode with Self-Assembled Monolayer of Umbrella-Shaped Fullerene Derivatives

The surface properties of inorganic substrates can be altered by coating with organic molecules, which may result in the improvement of the properties suitable for electronic or biological applications. This article reports a systematic experimental study on the influence of the molecular and supramolecular properties of umbrella-shaped penta(organo)[60]fullerene derivatives, and on the work function and the water contact angle of indium-tin oxide (ITO) and gold surfaces. We could relate these macroscopic characteristics to single-molecular level properties, such as ionization potential and molecular dipole. The results led us to conclude that the formation of a SAM of a polar compound generates an electronic field through intermolecular interaction of the molecular charges, and this field makes the overall dipole of the SAM much smaller than the one expected from the simple sum of the dipoles of all molecules in the SAM. This effect, which was called depolarization and previously discussed theoretically, is now quantitatively probed by experiments. The important physical properties in surface science such as work function, ionization potential, and water contact angles have been mutually correlated at the level of molecular structures and molecular orientations on the substrate surface. We also found that the SAMs on ITO and gold operate under the same principle except that the "push-back" effect operates specifically for gold. The study also illustrates the ability of the photoelectron yield spectroscopy technique to rapidly measure the work function of a SAM-covered substrate and the ionization potential value of a molecule on the surface.

Supramolecular Control on Chemo- and Regioselectivity via Encapsulation of (NHC)-Au Catalyst within a Hexameric Self-Assembled Host

The encapsulation of a Au(I) catalyst within a self-assembled, hydrogen bonded, hexameric capsule dramatically changes its catalytic activity, leading to unusual products due to the steric requirements of the host's cavity.

In situ synthesis of fluorescent poly(norbornene)/oxazine-1 dye loaded fluoromica hybrids: supramolecular control over dye arrangement

We report on the in situ synthesis of fluorescent poly(norbornene)/oxazine-1 (Ox1) dye loaded fluoromica mineral Somasif (SME) hybrid materials. SME acts as host for supramolecular arrangement of Ox1 molecules in their 2D interlayer region. The dye arrangement is easily tuned by modulating the dye loading as well as by competitive intercalation with an ammonium surfactant. The dye molecules bend at most by 30° with respect to the SME layer surface increasing the dye loading up to 69% of the clay cation exchange capacity (CEC). This Ox1 state provides accessible interlayer voids which in turn facilitate the entry of polymerizable monomers (i.e., norbornene and ethylene) and the in situgrowth of the polymer. In this way a highly processable polymer hybrid, in which the dye molecules are highly oriented in the inorganic framework, is formed. The optical spectroscopy shows unique J-band characteristics along with the Ox1 monomer features. The formation of the J-aggregates is likely induced by the interlayer segregated poorly polar norbornene phase that forces the Ox1 molecules to increase the head-to-tail interaction between them. These features strongly encourage the technical application of these materials for fabricating functional devices with unique photoluminescence properties.

Strong supramolecular control over protein self-assembly using a polyamine decorated β-cyclodextrin as synthetic recognition element

The supramolecular host molecule heptakis-[6-deoxy-6-(2-aminoethylsulfanyl)]-β-cyclodextrin provides strong control over protein self-assembly in synthetic supramolecular protein constructs. Mono-functionalization of this modified β-cyclodextrin with a cysteine residue allows for site-selective synthetic conjugation to a protein and formation of a highly stable synthetic protein complex with a lithocholic acid conjugated protein as the interaction partner.

ChemInform Abstract: Metal—Salophen‐Based Receptors for Anions

AbstractReview: 112 refs.

Supramolecular control of photochromism in a β-cyclodextrin/Schiff base system

The inclusion complex of a salicylaldehyde Schiff base (anil) in β-cyclodextrin (βCD) is reported for the first time. UV–vis spectroscopic and fluorescence studies show that N-(1-adamantyl)salicylaldimine (ASA), which is thermochromic as a free crystalline compound, becomes photochromic upon encapsulation into βCD. Characterisation of the complex has been performed by NMR spectroscopy in aqueous solution and by UV and fluorescence spectroscopy and powder X-ray diffraction in the crystalline state. The NMR studies indicate host:guest ratio of 1:1 and prove that only the adamantyl moiety of the guest is enclosed into the host cavity, whereas the hydroxyphenyl part is outside. Trials to grow single crystals of the complex produced a novel βCD lattice, which can be rationalized by applying the inclusion mode suggested by NMR spectroscopy. βCD in the crystal lattice seems to act as a medium allowing the cis to trans isomerisation of ASA, a volume-demanding process necessary for the expression of photochromism in this class of molecules. The study demonstrates that βCD nanocavities can lead to supramolecular control of the photochemical behaviour of appropriately designed anils, a property with many potential applications.

Allosteric Supramolecular Triple-Layer Catalysts

Allosteric regulation of organometallic catalysts could allow for greater control over reactions. We report an allosteric supramolecular structure in which a monometallic catalytic site has been buried in the middle layer of a triple-layer complex. Small molecules and elemental anions can open and close this complex and reversibly expose and conceal the catalytic center. The ring-opening polymerization of ε-caprolactone can be turned on by the in situ opening of the triple-layer complex and then completely turned off by reforming it through the abstraction of Cl(-), the allosteric effector agent, without appreciable loss of catalytic activity. This process can regulate the molecular weights of the resulting polymers.

Supramolecular Control of Stiffness and Strength in Lightweight High‐Performance Nacre‐Mimetic Paper with Fire‐Shielding Properties

Taking the heat: Hard/soft core/shell colloidal building blocks allow large-scale self-assembly to form nacre-mimetic paper. The strength and stiffness of this material can be tailored by supramolecular ionic bonds. These lightweight biomimetic materials show excellent and tunable mechanical properties and heat and fire-shielding capabilities.