Theoretical analyses of the host–guest interaction within chlorine hydrate

The host–guest interaction is necessary for the stabilization of hydrates. Using Density Function Theory methods, the host–guest interaction within an unconventional chlorine hydrate was investigated, in combination with typical noncovalent analyses. The host–guest interaction energy was predicted to be as high as 17.51 kcal/mol, which was stronger than the typical van der Waals (vdW) interaction, due to an involvement of up to 20 Cl…O interactions. Polarization and dispersion energies made up the main contribution to the total interaction energy. Further visualization of the host–guest interaction validated, together with the general Cl…O interaction, another vdW interaction between the guest‐Cl atom and the five‐membered H₂O cluster. Isosurfaces associated with two patterns of vdW interactions yielded a better “fit” in shape, suggesting their cooperativity in stabilizing the steric configuration. The σ‐region on the guest‐Cl atom was verified to regulate the electron redistribution over the molecular space. These results are useful for understanding specific halogen behavior, and the origin and nature of host–guest interaction in hydrates. © 2013 Wiley Periodicals, Inc.     

Construction of different supramolecular polymer systems by combining the host–guest and hydrogen‐bonding interactions

Poly(ethylene glycol) (PEG) can form either the inclusion complex with α‐cyclodextrins (α‐CDs) through host–guest interactions or the interpolymer complex with poly(acrylic acid) (PAA) through hydrogen‐bonding interaction. Mixing α‐CD, PEG, and PAA ternary components in an aqueous solution, the competition between host–guest and hydrogen‐bonding interactions occurs. Increasing feed ratio of α‐CD:EG:AA from 0:1:1 to 0.2:1:1 (molar ratio), various interesting supramolecular polymer systems, such as hydrogen‐bonding complex, dynamic polyrotaxane, crystalline inclusion complex, and thermoresponsive hydrogel, are successively obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1114–1120, 2008     

Dendronized copolymers functionalized with crown ethers and their reversible modification through host–guest interaction

Crown ether‐functionalized dendronized copolymers with an alternating structure were synthesized by free radical copolymerization of styrene derivatives pendent with Percec‐type polyether dendron of two generations and maleimide pendent with dibenzo[24]crown‐8 (24C8). Novel dendronized copolymers bearing tremendous host molecular cavities have been characterized by ¹H NMR, ¹³C NMR spectroscopy, static light scattering (SLS), and differential scanning calorimetry (DSC) analysis as well as atomic force microscopy (AFM) techniques. Host–guest interactions between 24C8 units dispersed along the dendronized copolymers and organic ammonium salts of pyrene, anthracene, and phenol have been explored. These molecular recognition processes can be monitored by ¹H NMR spectroscopy and fluorescence excitation spectroscopy. These results showed that the supramolecular polymer systems are acid–base controllable, demonstrating that dendronized copolymers may be modified reversibly via host–guest interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Supramolecular hydrogen-bonded liquid–crystalline polymer complexes. Design of side-chain polymers and a host–guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.     

Theoretical investigation of enantioselectivity of cage‐like supramolecular assembly: The insights into the shape complementarity and host–guest interaction

Enantioselectivity in the aza‐Cope rearrangement of a guest molecule encapsulated in a cage‐like supramolecular assembly [Ga₄L₆]^12? [L = 1,5‐bis(2',3'‐dihydroxybenzamido)naphthalene] is investigated using density functional theory and ab initio molecular orbital calculations. Reaction pathways leading to R‐ and S‐enantiomers encapsulated in the [Ga₄L₆]^12? are explored. The reaction barriers and the stabilities of the prochiral structures differed in the [Ga₄L₆]^12?, resulting that the product with an R structure is favorably produced in the Δ‐structure [Ga₄L₆]^12?. The large energy difference in the prochiral structures in the [Ga₄L₆]^12? was attributed to the deformation of the bulky substituent. The host–guest interaction energy raises the reaction barrier for the product with an S structure. The previous study suggested that the different stability of the prochiral substrates in the assembly was the origin of the enantioselectivity, and the suggestion is supported by our computational finding. In addition, our results show that the difference in the reaction barriers also importantly contributes to the enantioselectivity. © 2015 Wiley Periodicals, Inc.     

Design and synthesis of triptycene based fluorescent polymer with pendent triazole: Effect of functionality on host–guest interaction

Fluorescent materials have emerged as one of the promising candidates for chemical sensing due to their high sensitivity towards analytes that are relatively electron deficient such as nitroaromatics (NACs). Herein, four new 1,2,3‐triazole functionalized dibromo monomers ( 2‐5 ) have been synthesized. These dibromo monomers ( 2‐5 ) have been subsequently polymerized with 2,6‐diethynyltriptycene ( DET ) to yield four new ethynyl linked polymers ( P2‐P5 ) with 1,2,3‐triazole pendent. These polymers are organosoluble, amorphous in nature and have high thermal stability [T_d > 289 °C and high char yield (>73%) at 800 °C]. Interestingly these new polymers ( P2‐P5 ) are highly fluorescent in solution (Φ = 0.37–0.43 in DCM) relative to the polymer ( P1 ) that does not have the 1,2,3‐triazole motif as a pendent. The host–guest interaction between these polymers ( P1‐P5 ) and electron deficient molecules (PA and C₆₀) has been investigated. The Stern–Volmer quenching constant (K_SV) data suggest that the interaction of picric acid and polymers increases significantly in presence of 1,2,3‐triazole linked pendent group whereas in case of C₆₀, the K_SV value decrease considerably in presence of 1,2,3‐triazole linked pendent. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3725–3735     

Host–guest interactions between octa acid and cations/nucleobases

The nature of host–guest interaction in between octa acid cavitand (OA) and some representative cationic guests (Li⁺, Na⁺, K⁺, Be⁺², Mg⁺², Ca⁺², Li₃O⁺, Na₃O⁺, K₃O⁺) as well as heterocyclic moieties like [adenine (A), guanine (G), cytosine (C), thymine (T), uracil (U), and tetrathiafulvalene (TTF)] has been examined with the aid of density functional theory (DFT)‐based computations. Thermochemical results indicate that all the guests bind with OA in a thermodynamically favorable fashion at 298.15 K temperature and one atmospheric pressure. OA exhibits high selectivity in binding the lighter cations/metal cluster cations as compared to the heavier congeners along each given series. Moreover, OA exhibits enhanced affinity as well as selectivity in binding A/G/TTF molecules as compared to C/T/U. Noncovalent interaction and energy decomposition analyses reveal that in addition to the van der Waals interaction, significant contribution from electrostatic as well as orbital interactions dictate the outcome in all the host–guest complexes. Time dependent DFT calculations have been carried out to assess the role of the guests in tuning the electronic properties as well as absorption spectrum of OA. © 2017 Wiley Periodicals, Inc.     

Photoswitching of the third-order nonlinear optical properties of azobenzene-containing phthalocyanines based on reversible host–guest interactions

Two water soluble azobenzene and phthalocyanine dyads with D–π–A alignment were synthesized. It was found that both compounds showed very large molecular cubic hyperpolarizabilities which are at the order of 10⁻³⁰ esu as the result of their unique chemical structure. The azobenzene moieties of these compounds, upon alternating illumination of UV and visible light, could reversibly associate with α-CD to form inclusion complexes through host–guest interaction in aqueous media, resulting in apparent influences to the 3rd NLO properties of these compounds. This influence is especially significant for the phthalocyanine whose central metal atom is copper (II). The molecular cubic hyperpolarizability γ of the inclusion complex for the copper phthalocyanine is 2.1 × 10⁻³⁰ esu. When the inclusion complex dissociated under the illumination of 365 nm light, γ value increased to 4.2 × 10⁻³⁰ esu, which is a 100% enhancement. Taking account of the large molecular cubic hyperpolarizabilities of these compounds, the present materials are potential as ideal 3rd NLO photoswitching systems.     

In situ synthesis of metallophthalocyanines into pores of MIL‐101: A novel and green strategy for preparation of host–guest catalysts

A novel strategy is developed to encapsulate metallophthalocyanines (MPcs, M = Cu, Ni and Co) into MIL‐101 to give MPcs@MIL‐101 via in situ synthesis of MPcs from component fragments in 1‐butyl‐3‐methylimidazolium bromide as an ionic liquid. This strategy overcomes some drawbacks of existing methods for encapsulation of MPcs into metal–organic frameworks. The chemical and structural properties of MPcs@MIL‐101 were determined using scanning electron microscopy, powder X‐ray diffraction, and Fourier transformation infrared and flame atomic absorption spectroscopies. The results showed that CuPc@MIL‐101, which was used as a ‘ship‐in‐a‐bottle’ catalyst, demonstrates excellent catalytic performance in the oxidative amidation of aldehydes with amine salts. It is confirmed that CuPc@MIL‐101 can be reused up to five times without significant loss of its activity.     

Optosensing of cationic surfactants based on host–guest chemistry

An optode membrane for cationic surfactants is presented. Plasticized poly(vinyl chloride) (PVC) membranes incorporating the hexaester of calix[6]arene and the neutral H⁺-selective chromo-ionophore (ETH5294) have proved to be excellent reversible sensing devices for cationic surfactants as exemplified by cetyltrimethylammonium bromide (CTMAB). Based on host–guest chemistry, the guest molecule CTMAB was extracted into the PVC membrane, forming a host–guest adduct with the host molecule calix[6]arene ionophore and causing a concomitant release of a proton from the protonated ETH5294 into the solution. Upon deprotonation, ETH5294 undergoes a color change which can be used as a means for the quantitation of CTMAB. Unlike small inorganic cations, such as K⁺ and Na⁺, the experimental results show that the membrane response depends to a great extent on the migration process of CTMAB from the bulk of the solution to the membrane interface. A modified theoretical equation describing the membrane response on the CTMAB concentrations has been derived and shown to be in conformity with the experimental results.     

Modulating the Binding of Polycyclic Aromatic Hydrocarbons Inside a Hexacationic Cage by Anion–π Interactions

We report the template‐directed synthesis of BlueCage⁶⁺, a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units. These moieties endow the cage with a remarkably electron‐poor cavity, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs). Upon forming a 1:1 complex with pyrene in acetonitrile, however, BlueCage?6 PF₆ exhibits a lower association constant K_a than its progenitor ExCage?6 PF₆. A close inspection reveals that the six PF₆^? counterions of BlueCage⁶⁺ occupy the cavity in a fleeting manner as a consequence of anion–π interactions and, as a result, compete with the PAH guests. This conclusion is supported by a one order of magnitude increase in the K_a value for pyrene in BlueCage⁶⁺ when the PF₆^? counterions are replaced by much bulkier anions. The presence of anion–π interactions is supported by X‐ray crystallography, and confirms the presence of a PF₆^? counterion inside its cavity.     

An enhanced host–guest electro‐optical polymer system using poly(norbornene‐dicarboximides) via ROMP

High glass transition temperature poly(N‐cyclohexyl‐5‐norbornene‐2,3‐dicarboximide)s (NDI)s prepared by ring opening metathesis polymerization yielded polymers with a narrow polydispersity and well‐controlled molecular weight materials when using the Grubbs first generation initiator. Polymers produced using the Grubbs second generation initiator could not be controlled easily. By initiator selection it was also possible to synthesize polymers with either 98 or 52% trans microstructures. These materials were employed as electro‐optic (EO) polymer hosts for high molecular hyperpolarizability (β) phenyl vinylene thiophene vinylene bridge chromophores. This chromophore was modified by the incorporation of a tert‐butyldiphenylsilane group. The addition was able to further increase its EO coefficient (r₃₃) to reach 93 pm/V in a trans rich poly(NDI) produced by the Grubbs first generation initiator, compared to a benchmark chromophore / polymer combination. We investigated in detail the relationship between polymer microstructure and their absolute molecular weight on forming the best host–guest with the high β chromophore. Our results indicate that by utilizing a very simple host–guest system a high r₃₃ can be realized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Fluorescent Cross‐Linked Supramolecular Polymer Constructed by Orthogonal Self‐Assembly of Metal–Ligand Coordination and Host–Guest Interaction

A new host molecule consists of four terpyridine groups as the binding sites with zinc(II) ion and a copillar[5]arene incorporated in the center as a spacer to interact with guest molecule was designed and synthesized. Due to the 120 ° angle of the rigid aromatic segment, a cross‐linked dimeric hexagonal supramolecular polymer was therefore generated as the result of the orthogonal self‐assembly of metal–ligand coordination and host–guest interaction. UV/Vis spectroscopy, ¹H NMR spectroscopy, viscosity and dynamic light‐scattering techniques were employed to characterize and understand the cross‐linking process with the introduction of zinc(II) ion and guest molecule. More importantly, well‐defined morphology of the self‐assembled supramolecular structure can be tuned by altering the adding sequence of the two components, that is, the zinc(II) ion and the guest molecule. In addition, introduction of a competitive ligand suggested the dynamic nature of the supramolecular structure.     

Theoretical prediction of the host–guest interactions between novel photoresponsive nanorings and C60: A strategy for facile encapsulation and release of fullerene

A series of photoresponsive‐group‐containing nanorings hosts with 12～14 Å in diameter is designed by introducing different number of azo groups as the structural composition units. And the host–guest interactions between fullerene C₆₀ and those nanoring hosts were investigated theoretically at M06‐2X/6‐31G(d)//M06‐L/MIDI! and wB97X‐D/6‐31G(d) levels. Analysis on geometrical characteristics and host–guest binding energies revealed that the designed nanoring molecule (labeled as 7 ) which is composed by seven azo groups and seven phenyls is the most feasible host for encapsulation of C₆₀ guest among all candidates. Moreover, inferring from the simulated UV‐vis‐NIR spectroscopy, the C₆₀ guest could be facilely released from the cavity of the host 7 via configuration transformation between trans‐form and cis‐form of the host under the 563 nm photoirradiation. Additionally, the frontier orbital features, weak interaction regions, infrared, and NMR spectra of the C₆₀@7 host–guest complex have also been investigated theoretically. © 2015 Wiley Periodicals, Inc.     

Tunable Water‐Soluble Supramolecular Polymers by Visible‐Light‐Regulated Host–Guest Interactions

The development of artificial self‐assembling systems with dynamic photo‐regulation features in aqueous solutions has drawn great attention owing to the potential applications in fabricating elaborate biological materials. Here we demonstrate the fabrication of water‐soluble cucurbit[8]uril (CB[8])‐mediated supramolecular polymers by connecting the fluorinated azobenzene (FAB) containing monomers through host‐enhanced heteroternary π–π stacking interactions. Benefiting from the unique visible‐light‐induced E→Z photoisomerization of the FAB photochromophores, the encapsulation behaviors between the CB[8] macrocycle and the monomers could be regulated upon visible light irradiation, resulting in the depolymerization of such CB[8]‐mediated supramolecular polymers.     

Perturbation of Spin Crossover Behavior by Covalent Post‐Synthetic Modification of a Porous Metal–Organic Framework

Covalent post‐synthetic modification is a versatile method for gaining high‐level synthetic control over functionality within porous metal–organic frameworks and for generating new materials not accessible through one‐step framework syntheses. Here we apply this topotactic synthetic approach to a porous spin crossover framework and show through detailed comparison of the structures and properties of the as‐synthesised and covalently modified phases that the modification reaction proceeds quantitatively by a thermally activated single‐crystal‐to‐single‐crystal transformation to yield a material with lowered spin‐switching temperature, decreased lattice cooperativity, and altered color. Structure–function relationships to emerge from this comparison show that the approach provides a new route for tuning spin crossover through control over both outer‐sphere and steric interactions.     

Capsule–Capsule Conversion by Guest Encapsulation

Guest‐induced M₁₈L₆–M₂₄L₈ capsule–capsule conversion is reported. Both capsules are composed of Pd^II ethylenediamine units (M) and 1,3,5‐tris(3,5‐pyrimidyl)pyrimidine (L), and form trigonal bipyramidal (M₁₈L₆) and octahedral (M₂₄L₈) closed‐shell structures with huge hydrophobic inner spaces. The M₁₈L₆ trigonal bipyramid is converted to the M₂₄L₈ octahedron through encapsulation of large aromatic guests, with the latter capsule possessing a cavity volume three times larger than the former. Despite the dynamic properties of the capsule host, the encapsulated guests are difficult to extract and are thus isolated from the external environment.     

Modulation of Protein Dimerization by a Supramolecular Host–Guest System

Two sets of cyan and yellow fluorescent proteins, monomeric analogues, and analogues with a weak affinity for dimerization were functionalized with supramolecular host–guest molecules by expressed protein ligation. The host–guest elements induce selective assembly of the monomeric variants into a supramolecular heterodimer. For the second set of analogues, the supramolecular host–guest system acts in cooperation with the intrinsic affinity between the two proteins, resulting in the induction of a selective protein–protein heterodimerization at a more dilute concentration. Additionally, the supramolecular host–guest system allows locking of the two proteins in a covalent heterodimer through the facilitated and selective formation of a reversible disulfide linkage. For the monomeric analogues this results in a strong increase of the energy transfer between the proteins. The protein heterodimerization can be reversed in a stepwise fashion. The trajectory of the disassembly process differs for the monomeric and dimerizing set of proteins. The results highlight that supramolecular elements connected to proteins can both be used to facilitate the interaction between two proteins without intrinsic affinity and to stabilize weak protein–protein interactions at concentrations below those determined by the actual affinity of the proteins alone. The subsequent covalent linkage between the proteins generates a stable protein dimer as a single species. The action of the supramolecular elements in concert with the proteins thus allows the generation of protein architectures with specific properties and compositions.