Guest induced morphology transitions of star shaped pillar[5]arene trimer via endo host-guest and "exo-wall" electron-transfer interactions

Star shape bridged pillar[5]arene trimer(C3-PLT) based on benzene-1,3,5-tricarboxamide(BTAs) was successfully synthesized,which exhibited outstanding guest responsive morphology transition properties.The morphology tining studies was efficiently achieved with the addition of competitive guest molecules G1 and G2 by various self-assembly mechanisms.C3-PLT itself displays nanofiber morphology through H-type π-π stacking,and this nanofiber morphology can be completely transformed into spherical vesicles by host-guest interaction Gl,while upon addition of G2 into C3-PLT by means of "exo-wall" electron-transfer interactions,sheet superstructures can be observed.SEM,~1 H NMR,DOSY,fluorescence spectroscopy,and viscosity have verified the formation of supramolecular polymers and morphological transitions between C3-PLT with both guests.     

Pillar[5]arene based conjugated macrocycle polymers with unique photocatalytic selectivity

The development of heterogeneous catalysts with substrate shape, size or electronic constitution selectivity is a huge challenge in photocatalysis. Reported herein is a host-guest interaction strategy to endow photocatalysts with special selectivity. By adjusting the precursors, conjugated macrocycle polymers (CMPs) with pillar[5]arene struts (CMP-1 and CMP-2) and a corresponding non-pillar[5]arene-contained conjugated organic polymer (COP-1) were prepared and the photocatalytic activities toward sulfide derivatives were investigated. The sulfides showed similar conversions when COP-1 was used as a photocatalyst, but exhibited significant differences when it turned to the CMPs. Remarkably, the conversion yield of S-1 achieved near 18 folds over the one of S-2 when CMP-2 was used as a catalyst. Mechanism studies confirmed that the “host-guest” effect of pillar[5]arene struts in CMPs was the main cause of the difference. The present work establishes CMPs as novel heterogeneous photocatalysts with substrate selectivity, and such a method will inspire the researchers concerning preparation of heterogeneous catalysts with excellent selectivity.     

Binding modes of cucurbit[6]uril and cucurbit[7]uril with a series of bis-pyridinium compounds

Binding behaviors of cucurbit[6]uril (CB[6]) and cucurbit[7]uril (CB[7]) with a series of bis-pyridinium compounds N, N’-hexamethylenebis(1-alkyl-4-carbamoyl pyridinium bromide) (HBPB-n) (alkyl chain length, n = 6, 8 and 10) guests were investigated using ¹H-NMR, ESI–MS and single crystal X-ray diffraction methods. The results show that CB[6] and CB[7] can form [2]pseudorotaxanes with HBPB-n easily. When increasing the length of tail alkyl chain, the binding site of CB[6] at guest molecules changed from the tail to the middle part, while CB[7] remained located over the tail chain. As CB[6] and CB[7] were added in HBPB-8 aqueous solution, a [3]pseudorotaxane was formed by the inclusion of the internal middle site in CB[6] and the tail chain in CB[7].     

Interaction between tetramethylcucurbit[6]uril and some pyridine derivates

Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) with hydrochloride salts of 2-phenylpridine (G1), 2-benzylpyridine (G2), and 4-benzylpyridine (G3) (guests) have been investigated by using 1H NMR spectroscopy and electronic absorption spectroscopy and theoretical calculations. The 1H NMR spectra analysis established an interaction model in which the host selectively included the phenyl moiety of the HCl salt of the above three guests, and formed inclusion complexes with a host-guest ratio of 1:1. Absorption spectrophotometric analysis allowed quantitative measurement of the stability of these host-guest inclusion complexes. Particularly, we have established a competitive interaction in which one host-guest inclusion complex pair is much more stable than another host-guest inclusion complex pair. The stability constants for the three host-guest inclusion complexes of TMeQ[6]-G1, TMeQ[6]-G2, and TMeQ[6]-G3 are approximately 2x10(6), 60.7, and 19.9 mol-1.L, respectively. To understand how subtle differences in the structure of the title guests lead to a significant difference in the stability of the corresponding host-guest inclusion complexes with the TMeQ[6], ab initio theoretical calculations have been performed, not only for the gas phase but also the solution phase (water as solvent) in all cases. The calculation results revealed that when the phenyl moiety of the three pyridine derivate guests was included, the host-guest complexation reached the minimum, and the corresponding energy differences for the formation of the title host-guest inclusion complexes are qualitatively consistent with the experimental results.     

六元和七元瓜环与两类端邻苯二甲酰亚胺基紫精轮烷的组装及性质

设计合成了2种不同碳链长度的客体分子1,1'-二甲基邻苯二甲酰亚胺基-4,4'-联吡啶溴化物 (G1)和1,1'-二丁基邻苯二甲酰亚胺基-4,4'-联吡啶溴化物(G2). 利用紫外-可见吸收光谱、 核磁共振波谱和等温滴定量热等方法研究了客体分子G1和G2与六元(Q[6])和七元瓜环(Q[7])的超分子自组装方式. 结果表明, 在加热回流情况下G1与Q[6]利用滑移法能与紫精基团包结形成[2]轮烷结构, 而Q[7]在常温下就能滑过封端基团邻苯二甲酰亚胺与紫精基团包结形成[2]准轮烷结构.     

Effect of Alkylpyrazinium Counterions on the Host-guest Recognition Based on Dimethoxypillar[5]arenes

In this work, we synthesized n-octylpyrazinium bromide(G-Br) and n-octylpyrazinium hexafluorophosphate(G-PF₆) as model guests and studied their host-guest complexation with 1,4-dimethoxypillar[5]arene(DMP5A). Effect of alkylpyrazinium counterions on the host-guest recognition was investigated. Based on the ¹H NOESY spectra, the binding site of DMP5A with G-PF₆ is the same as that of DMP5A with G-Br. However, G-PF₆ forms a stronger complex with DMP5A than G-Br, owing to that hexafluorophosphate forms weaker doubly inonic H-bonds with ammonium cation than bromide ion in chloroform, which leads to some aggregates that could be dissociated with the addition of DMP5A.     

七、八元瓜环与二溴化1,n-亚烷基-二-2-甲基吡啶的超分子自组装

合成和表征了4个碳链长度不同二溴化1,n-亚烷基-二-2-甲基吡啶(客体,n=6,8,10,12),利用1H NMR技术、热重分析及紫外吸收光谱法考察了这些客体与七、八元瓜环(主体)的相互作用,以及形成的主客体包结物的结构特征.研究结果表明4个客体与七、八元瓜环形成不同的主客体包合物.七元瓜环可穿梭在线性客体分子上形成类轮烷型或哑铃型主客体包合物;而由于具有较大的空腔,八元瓜环可包容弯曲状的整个客体分子.     

Characterization of self-assembled supramolecular [Ga4L6] host-guest complexes by electrospray ionization mass spectrometry

Self-assembled supramolecular host-guest complexes have been characterized by electrospray ionization mass spectrometry. The spectra obtained by use of a Q-TOF instrument equipped with a Z-spray ion source show primarily the 3- and 4- charge states of the assemblies. The assemblies have the general formula [guest subset Ga4L6]11- where L represents the chelating bidentate catechol ligand 1,5-bis(2',3'-dihydroxy-benzamido)naphthalene and guests are tetramethyl ammonium (Me4N+), tetraethyl ammonium (Et4N+), tetra-n-propyl ammonium (Pr4N+) and decamethylcobaltocenium (Cp*2Co+) cations. For the first time, the mass spectrum of the empty assembly [Ga4L6]12- is reported. This article also reports that provided the electrospray ion source is capable of preserving noncovalent interactions, it is possible to observe host-guest complexes containing both weak binding guests as well as sterically demanding guests in the mass spectra. The present data suggest that electrospray mass spectrometry is a powerful tool for characterization of supramolecular host-guest complexes.     

Binding selectivity of cucurbit[7]uril: bis(pyridinium)-1,4-xylylene versus 4,4'-bipyridinium guest sites

The binding interactions between the host cucurbit[7]uril (CB7) and a series of linear guests containing bis(pyridinium)-1,4-xylylene and/or 4,4'-bipyridinium residues were investigated by (1)H NMR spectroscopy. CB7 was found to exhibit considerable binding selectivity for bis(pyridinium)-1,4-xylylene over 4,4'-bipyridinium sites. New pseudo-rotaxane and rotaxane compounds were synthesized utilizing the host-guest interactions between CB7 and the surveyed guests. [structure: see text]     

Dinuclear molybdenum complexes derived from diphenols: electrochemical interactions and reduced species

The new diphenolato complexes [{Mo(NO){HB(dmpz)₃}Cl}₂Q] where dmpz = 3,5-dimethylpyrazolyl and Q = OC₆H₄(C₆H₄O (n = 1 or 2), OC₆H₄CR=CRC₆H₄O (R = H or Et), and OC₆H₄CH=CHC₆H₄CH=CHC₆H₄O have been prepared and their electrochemical properties (cyclic and differential pulse voltammetry) compared with previously reported analogues where Q = OC₆H₄O, OC₆H₄EC₆H₄O (E = SO₂, CO and S), OC₆H₄ (CO)C₆H₄ C₆H₄(CO)C₆H₄O and 1,5- and 2,7-O₂C₁₀H₆. The electrochemical interaction between the redox centres in the new complexes is very weak, in contrast to that in the 1,4-benzenediolato and naphthalendiolato species. The EPR spectra of the reduced mixed-valence species [{Mo(NO){HB(dmpz)₃}Cl}₂Q]⁻ where Q = 1,3- and 1,4-OC₆H₄O and OC₆H₄SC₆H₄O shows that they are valence-trapped at room temperature, whereas those of the dianions [{Mo(NO){HB(dmpz)₃}Cl}₂Q]²⁻ where Q = 1,4-OC₆H₄O, OC₆H₄EC₆H₄O (E = CO or S) and OC₆H₄CH=CHC₆H₄CH=CHC₆H₄O shows that the unpaired spins on each molybdenum centre are strongly correlated (J, the spin exchange integral A_Mo, the metal-hyperfine coupling constant). The electrochemical properties and the comproportionation constants for the reaction [{Mo(NO){HB(dmpz)₃} Cl}₂Q] + [{Mo(NO){HB(dmpz)₃}Cl}O]₂]²⁻2[{Mo(NO) {HB(dmpz)₃}Cl}₂Q]⁻ where Q = diphenolato bridge, are compared with related compounds containing benzenediamido and dianilido bridges.     

Polysaccharide-based supramolecular drug delivery systems mediated via host-guest interactions of cucurbiturils

With excellent biocompatibility and biodegradability,natural polysaccharides and their derivative s have exhibited great potential in constructing drug delivery ve hicles for tissue engineering and therapeutics.Cucurbit[n]uril(CB [n])-mediated reversible crosslinking of polysaccharides possess intrinsic stimuliresponsiveness towards competitive guests and have been extensively investigated to fabricate various particles and hydrogels for multiple stimuli-re sponsive drug release by incorpo ration with other stimuli including photo,redox,and enzyme.Through host-guest interactions between CB[6] and aliphatic diamines,functional tags covalently connected with CB[6] can be readily anchored into polysaccharidebased hydrogels,realizing multiple functionalization.The rheological prope rty and drug release profile of polysaccharide-based supramolecular hydrogels can be facilely tuned through CB [8]-mediated dyna mic homo or hetero crosslinking of polysaccharides and/or other polymers.In this review,we introduce and summarize recent progress regarding polysaccharide-based supramolecular drug delivery systems mediated via host-guest interactions of CB[6] and CB[8],covering both bulk hydrogels and particular systems.At the end,possible utilization of CB[7]-based host-guest interactions in constructing polysaccharide-based drug delivery systems and future perspectives of this research direction are also discussed.     

Cucurbit[7]uril host-guest complexes with small polar organic guests in aqueous solution

The host-guest stability constants for the inclusion of a series of small neutral polar organic guests in cucurbit[7]uril (CB[7]) have been determined in aqueous solution by (1)H NMR titrations. The dependence of the stability constant on the nature of the guests indicates that hydrophobic and dipole-quadrupole interactions are responsible for the binding. The complexation-induced chemical shift changes in the guest proton resonances, coupled with energy-minimization calculations, suggest that the guests are located such that their dipole moment is aligned perpendicular with the quadrupole moment of the CB[7] host. The stability constants for acetone and acetophenone decrease in the presence of Na(+) or K(+) cations as a result of cation capping of the CB[7] portals.     

A comparison of mesogenic properties of p-carborane-1,12-dicarbaldehyde schiff's bases with their terephthaldehyde analogues

A homologous series of carborane-containing Schiff's bases 1A[n] (n = 1-10) was prepared and compared with the analogous series 1B[n] derived from terephthaldehyde. An exponential fit of the T _NI values for both series yielded a quantitative assessment of the effect of ring structure on mesophase stability. This includes the T _NI value for n→∞ (86°C for 1A[n] and 209°C for 1B[n]) and steepness of descent (0.135 for 1A[n] and 0.095 for 1B[n]). The difference in behaviour of the two series was attributed, largely, to conformational properties of the central rings A and B. Electronic interactions between the central rings and the π-substituents were investigated by UV spectroscopy and by quantum-mechanical calculations. The effect of replacement of O with CH₂ in the terminal chain of 1[n] on the namatic phase stability was assessed for n = 5-7.     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Liquid crystalline hexa-amides and side chain polysiloxanes of azacrown [18]-N6

The hexa-4-dodecyloxybenzoyl derivative 1 of azacrown [18]-N₆ was originally reported to have a 'tubular' mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of 1 under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of 1 is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative 2 of azacrown [18]-N₆ has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH₂)₁₁ spacer and 75-84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N₆ mesogen. The polysiloxanes also display a liquid crystalline phase.     

Interaction of host-guest complexes of cucurbit[n]urils with double probe guests

Since the structure of cucurbituril(Q[6]) has been determined in 1981[1] and its homologues cucurbit [n = 5,7,8 and 10]uril(Q[5], Q[7], Q[8] and Q[10]) have been reported in 2000[2,3], 2002[4], a series of host-guest complexes[5—7], novel supramolecular as-semblies[8—10], molecular encapsulates[11,12] and mo-lecular containers[13,14] based on Q[n] have been stud-ied extensively. All cucurbituril homologues have common char-acteristic features, i.e. hydrophobic cavity, and polar carbonyl gr…     

Crystal-smectic E mesophases in a series of 2-(4-n-alkylphenyl)indenes

A series of 2-(4-n-alkylphenyl)indenes (3) with different alkyl substituents (CH₃ to C₁₀H₂₁) were synthesized and systematically characterized using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction compared with 2-phenylindene (3a). Depending on the alkyl chain length, highly ordered crystal-smectic E mesophases were observed and confirmed by X-ray diffraction for the derivatives 3h-3k with heptyl to decyl chains (n = 6-9). For 3f with a pentyl side chain (n = 4), an X-ray crystal structure analysis was carried out.     

Interaction of host-guest complexes of cucurbit[<Emphasis Type="Italic">n</Emphasis>] urils with double probe guests

Three guests with two moiety probes for different Cucurbit[n = 6-8]urils have been synthesized. They are N-(2-methylenethiophen)-adamataneamine, N-(2-methylene pyrrole)-adamataneamine and N-(2-methylenefurfuran)-adamataneamine. The probes are methyle-nepyridyl typically for Q[6] and adamataneamine typically for Q[7]. The host-guest complexes of Cucurbit[n = 6-8]urils with these guests have been investigated by using NMR techniques and ESMS method. Also, thermoanalysis has been used for exploring relationship of enthalpy and stability of the host-guest complexes.     

Equilibrium isotope effects on noncovalent interactions in a supramolecular host-guest system

The self-assembled supramolecular complex [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) can act as a molecular host in aqueous solution and bind cationic guest molecules to its highly charged exterior surface or within its hydrophobic interior cavity. The distinct internal cavity of host 1 modifies the physical properties and reactivity of bound guest molecules and can be used to catalyze a variety of chemical transformations. Noncovalent host-guest interactions in large part control guest binding, molecular recognition and the chemical reactivity of bound guests. Herein we examine equilibrium isotope effects (EIEs) on both exterior and interior guest binding to host 1 and use these effects to probe the details of noncovalent host-guest interactions. For both interior and exterior binding of a benzylphosphonium guest in aqueous solution, protiated guests are found to bind more strongly to host 1 (K(H)/K(D) > 1) and the preferred association of protiated guests is driven by enthalpy and opposed by entropy. Deuteration of guest methyl and benzyl C-H bonds results in a larger EIE than deuteration of guest aromatic C-H bonds. The observed EIEs can be well explained by considering changes in guest vibrational force constants and zero-point energies. DFT calculations further confirm the origins of these EIEs and suggest that changes in low-frequency guest C-H/D vibrational motions (bends, wags, etc.) are primarily responsible for the observed EIEs.     

Modes of binding interaction between viologen guests and the cucurbit[7]uril host

[structure: see text] Host-guest interactions between cucurbit[7]uril (CB7) and a series of dialkyl-4,4'-bipyridinium (viologen) dicationic guests were investigated by NMR spectroscopy. CB7 includes the aromatic nucleus of short chain viologens, but the mode of interaction is different with longer chain viologens due to the favorable hydrophobic interactions between the terminal alkyl substituents and the inner cavity of the host. A new pseudorotaxane was designed and synthesized on the basis of viologen-CB7 binding interactions.