Ditopic Guest Research Articles

Supramolecular Copolymerization by Sequence Reorganization of a Supramolecular Homopolymer.

The homopolymeric sequence formed by the head-to-head association of tetrakisporphyrin 1 is completely dissociated by the competitive association of the ditopic guest G2, resulting in the supramolecular copolymer poly-1⋅G2 with an alternatingly repeating host-guest sequence. The 1:1 stoichiometry of 1 and G2 is confirmed by a Job plot using UV/Vis titration and diffusion-ordered NMR spectroscopy (DOSY). The solution viscometry for poly-1 and poly-1⋅G2 suggests that the supramolecular chain of poly-1 behaves like a rod, whereas the supramolecular copolymer chain of poly-1⋅G2 behaves like a swelled fat chain, which is entangled in the semi-dilute regime. Atomic force microscopy shows that the supramolecular polymer poly-1⋅G2 is highly oriented through the interdigitation of the long alkyl chains.

Supramolecular Copolymerization by Sequence Reorganization of a Supramolecular Homopolymer

AbstractThe homopolymeric sequence formed by the head‐to‐head association of tetrakisporphyrin 1 is completely dissociated by the competitive association of the ditopic guest G2, resulting in the supramolecular copolymer poly‐1⋅G2 with an alternatingly repeating host–guest sequence. The 1:1 stoichiometry of 1 and G2 is confirmed by a Job plot using UV/Vis titration and diffusion‐ordered NMR spectroscopy (DOSY). The solution viscometry for poly‐1 and poly‐1⋅G2 suggests that the supramolecular chain of poly‐1 behaves like a rod, whereas the supramolecular copolymer chain of poly‐1⋅G2 behaves like a swelled fat chain, which is entangled in the semi‐dilute regime. Atomic force microscopy shows that the supramolecular polymer poly‐1⋅G2 is highly oriented through the interdigitation of the long alkyl chains.

Differences between the Interactions of Linear and Tetrahedron-like Ditopic Guests with Cucurbit[8]uril: Steric Hindrance and Molecular Structure Play Dominant Roles.

A tetrahedron-like guest molecule (THV) with four ditopic arms, consisting of viologen (V) and hexylene moieties, was synthesized, and its interaction with cucurbit[8]uril (CB[8]) was investigated. As a reference, the interaction between CB[8] and an analogue of the arm of the linear ditopic guest (LHV) was first explored by 1 H NMR and UV/Vis spectroscopy. In this case, CB[8] was located on the hexylene moiety and resulted in the formation of a binary complex. However, when THV interacted with CB[8], despite having four arms with four hexylene moieties, only two CB[8] molecules were identified as located on the hexylene moieties; the other two CB[8] molecules resided on the V moieties. Great steric hindrance among the arms played a dominant role in the interaction between THV and CB[8]. Regardless of whether the guest molecule was THV or LHV, CB[8] moved to its V moiety (electron-deficient part) to form the charge-transfer complex upon the addition of a stopper containing a naphthol residue (electron-rich part). Guests LHV and THV were reduced to LHV+(+.) and THV+4(+.) upon the addition of sodium dithionite. Dimerization of LHV+(+.) was enhanced when CB[8] was present in less than 0.5 equivalents. In contrast, dimerization was suppressed when CB[8] was present in more than 0.5 equivalents. However, the V+. units of THV+4(+.) stacked intramolecularly because of the tetrahedron-like molecular structure of THV. The influence of CB[8] on the dimerization of THV+4(+.) was weaker than that on LHV+(+.) .

Intramolecular chirality induction and intermolecular chirality modulation in BINOL bridged bisporphyrin hosts

We have studied the intra- and inter-molecular chirogenesis events on a family of chiral bisporphyrin hosts H1-H3. The three pairs of enantiomers for H1-H3 were constructed by connecting two zinc(II) porphyrinates to a homochiral (R)-(+)- or (S)-(−)-1,1′-bi-2-naphthol (BINOL) with ester or ether linkages. Split Cotton effects were observed for all of the bisporphyrin hosts. For each enantiomer, the sign of the bisignate CD couplets directly correlates to the stereostructure of the BINOL linker, namely a (R)-BINOL linker leads to a negative CD couplet and vise versa. The CD intensities of the hosts are decreasing from H1 to H3 along with the increasing of the length and flexibility of the chemical linkages between BINOL and porphyrin subunits. The predictable CD signs and regularly changed CD intensities demonstrate the defined intramolecular asymmetric information transfer, by which the chirality of a BINOL linker is translated to a preferred chiral twist in the inter-porphyrin arrangement with tunable efficiency. Furthermore, the intermolecular binding of 4,4′-BiPyridyl (BiPy), as a typical achiral ditopic guest, to the series of hosts were detected by UV–Vis, 1H NMR and CD spectroscopic titrations. The results indicate a convergent and complementary 1:1 binding mode, in which a BiPy ligand binds to a host molecule by ditopic ZnN coordination forming a stable cyclic supramolecular complex. In particular, the intensity of CD signals decreases significantly for all of the supramolecular complexes in comparison with the chiral bisporphyrin hosts alone, though the CD sign does not change. The observation is rationalized by DFT molecular modeling, which suggests that upon the formation of 1:1 cyclic supramolecular complexes the chiral twist direction of the two porphyrin moieties does not change, while the ZnZn distance increases remarkably. The present results highlight the effects of intramolecular chirality induction and intermolecular chirality modulation in BINOL bridged porphyrin tweezer systems.

Stepwise Motion in a Multivalent [2](3)Catenane.

The motions of biomolecular machines are usually multistep processes, and are involved in a series of conformational changes. In this paper, a novel triply interlocked [2](3)catenane composed of a tris(crown ether) host eTC and a circular ditopic guest with three dibenzyl ammonium (DBA) sites and three N-methyltriazolium (MTA) sites was reported. Due to the multivalency nature of the catenane, the acid-base triggered motion was performed by a stepwise manner. The coconformations of the four related stable states have been directly identified and quantified which confirmed the multistep process. In order to quantify the dynamics with environmental acidity changes, the values of the three levels of dissociation constant pKa have been determined. The special interlocked topology of the [2](3)catenane also endows the motion of each crown ether ring in the host with unexpected selectivity for the MTA sites. This study provides clues to comprehend the underlying motion mechanism of intricate biological molecular machines, and further design artificial molecular machine with excellent mechanochemistry properties.

Multilayered inclusion nanocycles of anionic spiroborates.

Multilayered spiroborate nanocycles were prepared from tris- or tetrakis(dihydroxynaphthalene) and tetrahydroxyanthraquinone as pillar and crossbar units via the reversible formation of a spiroborate linkage. The four-layered spiroborate nanocycle recognized two cationic aromatic guests simultaneously and exhibited the ability to form a supramolecular one-dimensional array by combining with methyl viologen dimer as the ditopic guest.

A foldable cyclic oligomer: chiroptical modulation through molecular folding upon complexation and a change in temperature.

A foldable cyclic oligomer 1 consisting of three terephthalamide units spaced with a 3-fold o-phenylene unit presented a dynamic pair of enantiomeric forms through molecular folding, to which the external chirality on a ditopic guest [(S,S)-2 or (R,R)-2] was supramolecularly transferred to prefer a particular sense of dynamic helicity [(M,M)-/(P,P)-1 and (M,M,P)-/(P,P,M)-1]. In the macrocycle, the terephthalamide units acted as exotopic binding sites to fold into helical forms upon complexation. The internal chirality associated with a host [(R,R,R,R,R,R)-1b] had no preference in a helical sense in the absence of a guest. Instead, the internal chirality was responsible for the signal modulation that it was cooperatively or competitively transferred in response to the external chirality on a guest (S,S)-2 or (R,R)-2. During the diastereomeric complexation, a particular sense of dynamic helicity was favored due to cooperative transmission of chirality when the helical preference was matched between the host and guest. Alternatively, the host complexed with an antipodal guest underwent a drastic change in conformation upon a change in temperature.

Controlled dynamic helicity of a folded macrocycle based on a bisterephthalamide with a twofold Z-shaped structure.

Dynamic helicity in a folded macrocycle and control of the helical preference are described. We designed macrocycle 1 with a dual mode of folding through the integration of two flexible units that are arranged twice to form a cyclic structure. As a folding unit, we used a terephthalamide skeleton and a Z-shaped hydrocarbon: the former acted as a control unit to induce a preference of a particular sense of dynamic helicity and the latter was just a spacer. A terephthalamide unit provided a binding site for capturing a ditopic hydrogen-bonding guest when it adopted helically folded syn forms (M/P). Thus, only the terephthalamide unit controlled the helical sense of dynamic helicity in a folded macrocycle through the supramolecular transmission of chirality upon complexation with a chiral ditopic guest. In addition, chirality on a host could also contribute to the control of the helical preference in a folded macrocycle, which led to exceptionally enhanced chiroptical signals.

Toward Reversible Control of Cucurbit[n]uril Complexes

CONSPECTUS: The cucurbit[n]uril (CBn) host family consists of a group of rigid macrocyclic hosts with barrel-like shapes and limited solubility in aqueous media. These hosts are capable of reaching high binding affinities with positively charged hydrophobic guests. In optimum cases, equilibrium association constant (K) values as high as 10(17) M(-1) have been reported, exceeding the binding affinity of the avidin-biotin host-guest pair. The synthetic CBn receptors have shattered the notion that highly stable noncovalent complexes can form only when one of the partners is a molecule of biological origin. The work described in this Account is concerned with the development of methods geared toward the reversible modulation of the binding affinity of CBn inclusion complexes under mild conditions. A good fraction of the research work has dealt with redox active guests, such as 4,4'-bipyridinium (viologen), ferrocene, and cobaltocenium derivatives. Our experimental results show that the thermodynamics and kinetics of the electron transfer reactions of these compounds can be substantially altered by complexation with CBn hosts, and therefore, electron transfer reactions can be used to exert a measure of control on the overall binding affinity of the CBn complexes. We have also developed systems in which proton transfer reactions have a strong effect on the binding affinity. With more structurally elaborate guests containing more than one adjacent binding sites, proton transfer reactions may affect the average location of the CBn host within the complexes. A series of guest compounds containing paramagnetic 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residues also exhibit interesting binding properties with CB7 and CB8. The latter host forms a very stable host-guest pair with TEMPO subunits, in which the nitroxide group resides inside the host cavity. Finally, with suitable ditopic guests, we have detected distinct microscopic complexes using experimental techniques with relatively slow time scales, such as NMR spectroscopy. These unusual findings are the result of the considerable thermodynamic and kinetic stability of CBn inclusion complexes.

Porphyrin-Based Supramolecular Alternating Block Copolymer

S-shaped tetrakisporphyrin 1 forms supramolecular polymeric assemblies via a complementary affinity1,2 of its bisporphyrin units in solution.3 The self-association constant determined by applying the isodesmic model is more than 106 L mol–1, which suggests that a sizable polymer forms at millimolar concentrations at room temperature. Trinitrofluorenone (TNF) binds within the molecular clefts provided by the bisporphyrin units via a charge transfer interaction. Thus, bisTNF guest can connect the tetrakisporphyrin via host-guest interaction to form an alternating block copolymer. In this presentation, we will discuss the structure transition from the tetrakisporphyrin-based supramolecular homopolymer to an alternating AB type block copolymer through competitive ditopic guest complexation.1) Haino, T. et al., Y. Tetrahedron Lett. 2005, 46, 257.2) Haino, T. et al., Y. J. Org. Chem. 2006, 71, 2572.3) Haino, T. et al., U. Proc. Natl. Acad. Sci. USA 2009, 106, 10477.

Cross-Linked Supramolecular Polymer Gels Constructed from Discrete Multi-pillar[5]arene Metallacycles and Their Multiple Stimuli-Responsive Behavior

A new family of discrete hexakis-pillar[5]arene metallacycles with different sizes have been successfully prepared via coordination-driven self-assembly, which presented very few successful examples of preparation of discrete multiple pillar[n]arene derivatives. These newly designed hexakis-pillar[5]arene metallacycles were well characterized with one-dimensional (1-D) multinuclear NMR ((1)H and (31) P NMR), two-dimensional (2-D) (1)H-(1)H COSY and NOESY, ESI-TOF-MS, elemental analysis, and PM6 semiempirical molecular orbital methods. Furthermore, the host-guest complexation of such hexakis-pillar[5]arene hosts with a series of different neutral ditopic guests G1-6 were well investigated. Through host-guest interactions of hexakis-pillar[5]arene metallacycles H2 or H3 with the neutral dinitrile guest G5, the cross-linked supramolecular polymers H2⊃(G5)3 or H3⊃(G5)3 were successfully constructed at the high-concentration region, respectively. Interestingly, these cross-linked supramolecular polymers transformed into the stable supramolecular gels upon increasing the concentrations to a relatively high level. More importantly, by taking advantage of the dynamic nature of metal-ligand bonds and host-guest interactions, the reversible multiple stimuli-responsive gel-sol phase transitions of such polymer gels were successfully realized under different stimuli, such as temperature, halide, and competitive guest, etc. The mechanism of such multiple stimuli-responsive processes was well illustrated by in situ multinuclear NMR investigation. This research not only provides a highly efficient approach to the preparation of discrete multiple pillar[n]arene derivatives but also presents a new family of multiple stimuli-responsive "smart" soft matters.

Cyclic [4]Rotaxanes Containing Two Parallel Porphyrinic Plates: Toward Switchable Molecular Receptors and Compressors

Twenty years ago, researchers considered the synthesis of simple rotaxanes a challenging task, but with the rapid development of this field, chemists now view these interlocking molecules as accessible synthetic targets. In a major advance for the field, researchers have developed transition metals or organic molecules as templating structures, making it easier to construct these molecular systems. In addition, chemists have found ways to introduce new functional groups, which have given these compounds new properties. Today researchers can also construct multirotaxanes consisting of several individual components, but the synthesis of the most complex structures remains challenging. This Account primarily discusses the cyclic [4]rotaxanes incorporating porphyrins that the Strasbourg group has synthesized and studied during the past few years. These cyclic [4]rotaxanes consist of two rigid rods threaded through the four rings of two molecules of a bis-macrocycle, and the synthetic strategy used for making them relies on the copper(I)-driven "gathering-and-threading" reaction. The formation of the threaded precursors was mostly quantitative, and the quadruple stoppering reaction leading to the target compound produces high yields because of the efficient copper-catalyzed azide-alkyne cycloaddition (CuAAC) or click chemistry reaction. These rotaxanes behave as receptors for various ditopic guests. We prepared and studied two types of molecules: (i) a rigid compound whose copper(I) complex has a well-defined shape, with high selectivity for the guest geometry and (ii) a much more flexible [4]rotaxane host that could act as a distensible receptor. The rigid [4]rotaxane was crystallized, affording a spectacular X-ray structure that matched the expected chemical structure. In addition, metalation or demetalation of the rigid [4]rotaxane induces a drastic geometric rearrangement. The metal-free compound is flat without a binding pocket, while the copper-complexed species forms a rectangle-like structure. The removal of copper(I) also expels any complexed guest molecule, and this process is reversible, making the rigid porphyrinic [4]rotaxane a switchable receptor. The rigid [4]rotaxane was highly selective for short, ditopic guests in its copper(I)-complexed form, but the flexible copper(I)-complexed [4]rotaxane proved to be a versatile receptor. Its conformation can adjust to the size of the guest molecule similar to the induced fit mechanism that some enzymes employ with substrates.

Complexation-induced inversion of helicity by an organic guest in a dynamic molecular propeller based on a tristerephthalamide host with a two-layer structure

A tristerephthalamide host exhibited two helical geometries with (M)- and (P)-helicity, respectively, in terms of the twisting direction of a two-layer structure, and the helical preference switched upon complexation with a ditopic guest. In both uncomplexed and complexed states, the intramolecular transmission of chirality was responsible for the control of helicity.

(24-Сrown-8)-Linked Dimeric Phthalocyanines and Their Metal Complexes

A convenient synthetic approach towards alkyloxy substituted (24-crown-8)-linked dimeric phthalocyanines is developed. The influence of the alteration of the reaction conditions and the origin of the precursors onto the yield of the target compounds is revealed. The Mg-templated statistical condensation of the mixture of phthalonitriles is found to be the most efficient and versatile pathway. The developed demetallation procedure of obtained Mg-phthalocyanines allows to prepare metal-free (24-crown-8)-linked dimeric phthalocyanines, which are versatile precursors for preparation of other metal complexes. The preliminary AM1 semi-empirical calculations have demonstrated that the dimeric linked phthalocyanine metal complexes may become convenient receptors for recognition of ditopic guests.

Multistate self-assembled micro-morphology transitions controlled by host–guest interactions

The multistate micro-morphology of aggregates in aqueous solution can be manipulated by host-guest interactions between bis-sulfonatocalix[4]arene, γ-CD and a ditopic guest possessing viologen and coumarin moieties.

Assembly of Gold Nanoparticles on Functionalized Si(100) Surfaces through Pseudorotaxane Formation

The assembly of gold nanoparticles (AuNPs) on a hydrogenated Si(100) surface, mediated by a series of hierarchical and reversible complexation processes, is reported. The proposed multi-step sequence involves a redox-active ditopic guest and suitable calix[n]arene-based hosts, used as functional organic monolayers of the two inorganic components. Surface reactions and controlled release of AuNPs have been monitored by application of XPS, atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM) and electrochemistry.

Supramolecular ternary polymer mediated by cucurbituril and cyclodextrin

A novel supramolecular ternary polymer mediated by macrocyclic molecules cucurbit[8]uril (CB[8]) and cyclodextrin was successfully constructed, based on the CB[8]-stabilized charge-transfer (CT) interaction and cyclodextrin–adamantane host–guest interaction. Herein, we synthesized a naphthol-modified β-cyclodextrin (Np-β-CD) and an adamantane–viologen ditopic guest to obtain a ditopic host–guest complex with a preorientational donor–acceptor pair. Furthermore, after addition of CB[8] to the complex, the donor–acceptor pair of naphthol–viologen was encapsulated into the cavity of CB[8] leading to a linear supramolecular polymer which was well characterized by various methods, including DOSY, DLS, SEM, TEM and AFM. This work enriches the field of supramolecular polymers and provides a novel method to fabricate supramolecular architectures with multiple macrocyclic host molecules.

A Flexible Copper(I)‐Complexed [4]Rotaxane Containing Two Face‐to‐Face Porphyrinic Plates that Behaves as a Distensible Receptor

A new cyclic [4]rotaxane composed of two flexible bis-macrocycles and two rigid axles is described. Each bis-macrocycle consists of two rings attached to antipodal meso positions of a central Zn porphyrin through single C-C bonds. Each ring incorporates a 2,9-diphenyl-1,10-phenanthroline chelation site. The axles contain two coplanar bidentate sites derived from the 2,2'-bipyridine motif. The building blocks were assembled by using a one-pot threading-and-stoppering reaction, which afforded the [4]rotaxane in 50% yield. The "gathering-and-threading" effect of copper(I) was utilised in the formation of a [4]pseudorotaxane, which was immediately converted to the corresponding [4]rotaxane by a quadruple CuAAC stoppering reaction. The rotaxane contains two face-to-face zinc porphyrins, which allowed the coordination of ditopic guest substrates. The rotaxane host showed remarkable flexibility and was able to adjust its conformation to the guest size. It can be distended and accommodate rod-like guests of 2.6 to 15.8 Å in length.

Molecular Recognition with Ditopic Cavitand Re Complexes

AbstractThe synthesis of a series of cavitand receptors bearing increasing numbers of phosphonate groups at their upper rims and of the corresponding Re‐based ditopic complexes is reported. The molecular recognition properties of these phosphonate cavitands towards both monotopic and ditopic N‐methylpyridinium salts were investigated. The numbers and spatial dispositions of P=O units are pivotal for the complexation of guest ions. The removal of a single P=O bridge from the parent tetraphosphonate cavitand was sufficient to reduce the association constant by almost three orders of magnitude. Elimination of a second P=O unit completely abolished complexation in the AC distal isomer, both in monotopic and in ditopic hosts. The preorganised structure obtained by interconnection of two triphosphonate cavitands through a Re system showed moderate positive self‐assembly cooperativity in the inclusion of ditopic N‐methylpyridinium salts in both polar and nonpolar solvents. The speciation profile in ethanol indicates that the clamshell 1:1 complex is dominant at low concentrations (< 10–4 M) whereas the 1:2 complex is preferred at higher concentrations of ditopic guest.

Guest-controlled aggregation of cavitand gold nanoparticles and N-methyl pyridinium-terminated PEG

The introduction of a disulfide functionalized tetraphosphonate cavitand on Au nanoparticles promotes the reversible self-assembly of a hybrid network upon addition of a polymeric ditopic guest.