Linear viscoelastic studies on a transient network formed by host–guest interaction

A host–guest (HG) polymer was prepared through the radical polymerization of acrylamide monomers (AAm) with a small amount of host‐guest linkers, β‐cyclodextrin‐attached AAm (βCD‐AAm) and adamantane‐attached AAm (Ad‐AAm). The linear viscoelastic and swelling measurements indicated that the resulting HG polymer swollen in water was gel‐like, although the HG polymer is conceptually a linear chain having only temporary crosslinkings. NMR measurements indicated that half of the βCD units incorporated in the HG polymer do not form the inclusion complex with Ad. Rheological analysis of the HG polymer revealed that HG interaction retarded the Rouse modes of networks but did not affect the level of the plateau modulus, which was simply described by the entanglements of AAm chains. This result was confirmed with the reference experiment, in which Ad were capped by competitive βCD molecules. Furthermore, the PAAm polymer with only βCD units (no Ad) was found to exhibit gel‐like behavior. This behavior was attributed to the formation of a small amount of rotaxane structure, which act as permanent crosslinkings, based on 2D NMR data. The HG polymer is basically an entanglement network with temporary sticky points due to the HG interaction, and a few permanent branching points. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1109–1117     

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     

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.     

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     

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     

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     

Synthesis and characterization of rigid‐chain liquid–crystalline polymers containing laterally attached side rods

A series of rigid‐chain polymers containing different concentrations of laterally attached side rods was synthesized. These polymers exhibited liquid crystallinity even up to a maximum side rod concentration of 20 mol %. The crystallinity of the polymers, however, decreased with an increase in the side‐rod concentration. These polymers had lower dielectric constants compared with their parent polymers, that is, similar polymers, but without laterally attached side rods. A dielectric constant of 2.6 can be achieved by incorporating 10 mol % of laterally attached side rods, which is 0.5 lower than that of its parent polymer. The reduction of dielectric constant may be attributed to low crystallinity as well as the less dense packing structure of the polymers induced by the incorporation of laterally attached side rods. This series of polymers also had good thermal stability. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1288–1294, 2001     

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.     

Kinetics of orientation of a side-chain liquid–crystal polymer as measured by a high-temperature SQUID-magnetometer

A superconducting quantum interference device (SQUID) magnetometer suitable for measurements of the magnetic susceptibility up to 600 K has been used to follow the kinetics of realignment in the nematic phase of a side-chain liquid–crystal polymer. Experiments are performed using monodomain and polydomain samples. Results obtained in monodomain samples are in quantitative agreement with the prediction of the continuum theory up to an angle of approximately 60°. Experiments conducted at higher starting angles give clear indication of backflow effects. Data obtained from experiments on polydomain samples have been compared with model calculations using the data on the monodomain samples. This comparison leads to the conclusion that in this case backflow effects play an important role, too. All results show that SQUID magnetometry allows monitoring of the kinetics of realignment with highest precision. © 1992 John Wiley & Sons, Inc.     

Mechanistic study of trans⇆cis isomerization of the substituted azobenzene moiety bound on a liquid‐crystalline polymer

A mechanistic study of the trans?cis isomerization of the azobenzene moiety in a side‐chain liquid‐crystal polymer system was carried out with six liquid‐crystalline polymethacrylates in which different electron‐withdrawing substituents were attached to the para‐positions of the azobenzene chromophores. Compared to the non‐nitro‐substituted azo polymers, the nitro‐substituted azo polymers exhibited two quite different behaviors: an extraordinarily high reaction rate of the thermal cis–trans isomerization and an unexpected composition of cis–trans isomers obtained from the photochemical trans–cis isomerization process. A potential energy profile for the isomerization process was established on basis of the structures of the proposed transition states and was employed to elucidate the reaction mechanism. The results confirmed that the nitro‐substituted azo polymer system proceeded via a rotation mechanism in either direction of the trans?cis isomerization reaction, whereas the non‐nitro‐substituted species were more likely to follow an inversion mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2296–2307, 2001     

Exploiting Host–Guest Interactions for the Synthesis of a Rod–Rod Block Copolymer with Crystalline and Liquid‐Crystalline Blocks

By making use of the host–guest interactions between the host molecule tris‐o‐phenylenedioxycyclotriphosphazene (TPP) and the rod–coil block copolymer (BCP) poly(ethylene oxide)‐block‐poly(octyl 4′‐octyloxy‐2‐vinylbiphenyl‐4‐carboxylate) (PEO‐b‐PVBP), the supramolecular rod–rod block copolymer P(EO@TPP)‐b‐PVBP was constructed. It consists of a crystalline segment P(EO@TPP) with a hexagonal crystalline structure and a columnar nematic liquid‐crystalline segment (PVBP). As the PVBP segments arrange themselves as columnar nematic phases, the crystalline structure of the inclusion complex P(EO@TPP), which has a smaller diameter, is destroyed. The self‐assembled nanostructure is thus clearly affected by the interplay between the two blocks. On the basis of wide‐ and small‐angle X‐ray scattering analysis, we conclude that the supramolecular rod–rod BCP can self‐assemble into a cylinder‐in‐cylinder double hexagonal structure.     

Effects of monomer structures on the evolution of liquid–crystal texture and crystallization during thin-film polymerization

We investigated in situ the effects of monomer structures on the formation and evolution of liquid–crystal texture and crystallization during thin-film polymerization of a series of liquid–crystalline and crystalline polymers. The monomers used in this study consisted of 2,6-acetoxynaphthoic acid (ANA), p-acetoxybenzoic acid (ABA), acetoxy acetanilide (AAA), and isophthalic acid (IA). The polycondensation reactions were conducted on the heating stage of a polarizing microscope. The formation of liquid crystallinity was found to be strongly dependent on the straight-monomer structures of ANA and ABA and their percentages as well as the reaction temperature. For the ANA/AAA/IA and ABA/AAA/IA reaction systems, the critical straight-monomer content (ANA or ABA) existed to form the liquid–crystalline (LC) state. Interestingly, the critical content to form liquid crystallinity decreased with an increase in the reaction temperature. Above the critical content, the appearance of a defective LC phase and the annihilation of disclinations were observed during the polycondensation reactions. The number of defects decreased with increasing reaction time through annihilation. The annihilation rate increased whereas the defect density decreased with increasing straight-monomer content. For the same molar ratio, the reaction system containing ANA had a faster annihilation rate than that containing ABA. Below the critical content, crystalline polymers were formed. Nucleation and crystal growth were observed during the reactions, and the rate of crystal growth decreased with increasing ANA or ABA content. For the systems having the same molar ratio of ANA or ABA, the ANA/AAA/IA system had a higher tendency to yield the LC phase than the ABA/AAA/IA system because ANA has a longer mesogenic unit. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3084–3096, 1999     

Liquid crystalline supramolecular crosslinked polymer complexes of ditopic rylenebisimides and P4VP

Perylenebisimide and naphthalenebisimide (PBI‐PDP and NBI‐PDP) end functionalized with pentadecyl phenol is designed as ditopic hydrogen bonding acceptors to form supramolecular crosslinked network with poly(4‐vinyl pyridine) (P4VP). The pristine PBI‐PDP has been grown as single crystals from DCM‐MeOH (dichloromethane‐methanol) mixture at room temperature, which revealed a P21 space group. Noticeably, the pentadecyl alkyl chain shields the aromatic perylene core on both sides resulting in the absence of π–π interaction in single‐crystal assembly. The naphthalenebisimide derivative exhibits thermotropic liquid crystalline behavior, while both the molecules exhibits lyotropic liquid crystalline phases in tetrahydrofuran (THF), which were characterized using a combination of differential scanning calorimeter, X‐ray diffraction, and polarized light microscopy. The hydrogen‐bonded complex of both the rylenebisimides with P4VP preserves the mesomorphic properties in THF. The electron transport mobility measured by space charge limited current measurements reveals a two orders of magnitude increase in the charge transport in the P4VP complex compared to that of the pristine molecule. The average electron mobility obtained is μ _e,avg: 10^?3 cm²/Vs for P4VP‐PBI compared to μ _e,avg: 10^?5 cm²/Vs for pristine PBI derivative. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 951–959     

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.     

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.     

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.     

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.     

Coupling of homogeneous liquid–liquid extraction and dispersive liquid–liquid microextraction for the extraction and preconcentration of polycyclic aromatic hydrocarbons from aqueous samples followed by GC with flame ionization detection

In the present study, a simple and rapid method for the extraction and preconcentration of some polycyclic aromatic hydrocarbons in water samples has been developed. In this method, two sample preparation methods were combined to obtain high extraction recoveries and enrichment factors for sensitive analysis of the selected analytes. In the first stage of the method, a homogeneous solution containing an aqueous solution and cyclohexyl amine is broken by the addition of a salt. After centrifugation, the upper collected phase containing the extracted analytes is subjected to the following dispersive liquid–liquid microextraction method. Rapid injection of the mixture of cyclohexyl amine resulted from the first stage and 1,1,2‐trichloroethane (as an extraction solvent) into an acetic acid solution is led to form a cloudy solution. After centrifuging, the fine droplets of the extraction solvent are settled down in the bottom of the test tube, and an aliquot of it is analyzed by gas chromatography. Under the optimum extraction conditions, enrichment factors and limits of detection for the studied analytes were obtained in the ranges of 616–752 and 0.08–0.20 μg/L, respectively. The simplicity, high extraction efficiency, short sample preparation time, low cost, and safety demonstrated the efficiency of this method relative to other approaches.