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.     

Selective binding of unsaturated aliphatic hydrocarbons by a pillar[5]arene

The complexation behavior of unsaturated fatty hydrocarbons,i.e.,1,7-octadiyne and 1,7-octadiene,by a perethylated pillar[5]arene has been investigated,which was compared with that for saturated n-octane. It was found that the host-guest binding strength increased in accordance with the electron-negativity of the terminal carbon atom on the guests:alkyne>alkene>alkane.     

Synthesis of a fully functionalized pillar[5]arene by ‘click chemistry’ and its effective binding toward neutral alkanediamines

A fully functionalized pillar[5]arene was synthesized by ‘click chemistry’ and the possible synthetic strategies have been discussed. The host showed effective binding affinities toward neutral alkanediamines (K_a >10³ M⁻¹), which are much larger than those observed for simple methyl-substituted pillar[5]arene.     

Hybrid vesicles of pillar[5]arene/silica: Host-guest complexation and application in pH-triggered release

Integrating silica with organic nanoparticles can generate unique properties.Here pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes,as well as the catalytic hydrolysis of tetraethoxysilane.Such vesicles exhibited the high strength of silica and unique molecular recognition of pillararenes,both of which could tune the pH-trigge red release behavior.Furthermore,a rhodamine B derivative with hexyl group(RhB-C6) was synthesized,which can form a complex with the pillar[5]arene.Based on the host-guest interaction and high strength of silica,the hybrid vesicles could load more RhB-C6 and the rhodamine B was released more slowly compared with the organic vesicles.     

Synthesis of a water-soluble pillar[6]arene dodecaamine and its selective binding of acidic amino acids in water

A water-soluble pillar[6]arene dodecaamine has been synthesized. ¹H NMR and fluorescence studies indicate that pillar[6]arene dodecaamine could selectively and strongly bind acidic amino acids, i.e. glutamic acid and aspartic acid in water. And the complexation behavior of pillar[6]arene dodecaamine towards acidic tripeptide glutathione and short chain length (C₃ to C₈) dicarboxylic acids in water is also investigated.     

Water-soluble pillar[6]arene stabilized silver nanoparticles: preparation and application in amino acid detection

In the presence of a water-soluble pillar[6]arene WP6 containing 12 imidazolium groups, silver nanoparticles were successfully prepared and investigated in detail by ultraviolet visible spectroscopy, X-ray diffraction, and transmission electron microscopy. Excitingly, these pillar[6]arene stabilized silver nanoparticles were demonstrated to function as a colorimetric sensor to selectively probe glutamic acid in water.     

Preparation of two new [2]rotaxanes based on the pillar[5]arene/alkane recognition motif

Based on the pillar[5]arene/alkane recognition motif, two [2]rotaxanes were successfully prepared. Their formation was confirmed by NMR spectroscopy and ESI mass spectrometry. We also demonstrated that 3,5-dinitrophenyl group and 3,5-bis(trifluoromethyl)phenyl group are big enough to work as stoppers for DPPillar[5]arene, which lays a foundation for the preparation of more complex and functional supramolecular structures.     

Synthesis of a pillar[5]arene dimer by co-oligomerization and its complexation with n-octyltrimethyl ammonium hexafluorophosphate

A pillar[5]arene dimer was successfully prepared by co-oligomerization of 1,4-dimethoxybenzene and 1,6-bis(4-butoxyphenoxy)hexane. It was demonstrated that it forms 1:2 complexes with n-octyltrimethyl ammonium hexafluorophosphate both in chloroform and the gaseous state. A Scatchard plot indicated that the complexation between them is statistical with an average association constant of 6.0 (±0.4) × 10² M⁻¹ in chloroform.     

Effect of gamma-irradiation on the levels of total and cis/trans isomers of beta-carotene in dehydrated parsley

Ionizing radiation is a method for preservation of foods that use the high energy of gamma rays or accelerated electrons, thereby ionizing molecules. The most important precursor of vitamin A is β-carotene, a carotenoid with pro-vitamin A activity. The highly unsaturated chain confers the instability of β-carotene, and some reactions, as isomerisation, can reduce the characteristics of pro-vitamin A. The present study investigated whether increasing doses of 0, 10 and 20 kGy lower the total β-carotene level and if an enhancement of cis-isomers occurred on samples of dehydrated parsley. No differences were observed of either fractions analyzed at doses applied in this study, nor did it contribute to the decrease of vitamin A.     

基于杯芳烃的分子容器的合成及其对有机铵的可逆识别

将三(吡啶基甲基)胺(TPA)引入杯芳烃的下缘, 合成了一种新的具有杯状结构的杯芳烃衍生物, 研究了其对有机铵的分子识别行为.     

New water-soluble iminecalix[4]arene with a deep hydrophobic cavity

We report the synthesis of a new water-soluble iminecalix[4]arene host 4c with a deep hydrophobic cavity. The negatively charged four carboxylate functions on the top of the cavity play a major role in the recognition of charged molecular species. The ¹H NMR titration experiments revealed that host 4c binds with cationic (10-12) and neutral guests (6-9) in water with high binding constants in the order of 10⁴-10⁵ M⁻¹. Cationic guest 9 showed highest binding constant of 2.81 × 10⁵ M⁻¹ with host 4c amongst all tested guests. Selectivity over anionic guests (13-17) is established by the presence of negative charges at the top of the deep hydrophobic cavity, as guests 15 and 17 were not recognized by host 4c. Neutral pyridine derivatives with hydrophobic chains at para positions showed high binding constants of 6.02 × 10⁴-2.23 × 10⁵ M⁻¹. The data obtained for the recognition of the guests by host 4c revealed that the ionic as well as the hydrophobic-hydrophobic interactions are crucial in the molecular recognition in aqueous medium.     

Supramolecular control over LCST behavior of hybrid macrocyclic system based on pillar[5]arene and crown ether

A hybrid system containing a pillar[5]arene unit and ten crown ether moieties was developed. The LCST behavior and thermo-responsiveness were successfully introduced into this pillar[5]arene-crown ether system. Both host–guest interactions and salting-out effect displayed great effects in realizing the supramolecular control over LCST properties and thermo-responsiveness. Compared with the individual macrocycles, this hybrid macrocycle system dramatically amplified the supramolecular control effect over LCST behavior.     

Novel [2]rotaxanes based on the recognition of pillar[5]arenes to an alkane functionalized with triazole moieties

Host-guest complexation between an alkane functionalized with triazole moieties and three pillar[5]arenes was studied. Three pillar[5]arene-based [2]rotaxanes were constructed based on this new recognition motif. The sequence of the yields of these [2]rotaxanes was consistent with the order of association constants between the three corresponding pillar[5]arenes and the alkane. ¹H NMR, electrospray ionization mass spectrometry, and NOESY NMR were employed to characterize these [2]rotaxanes.     

Synthesis and host–guest properties of a calix[6]arene based receptor closed by an internal ion-paired cap

The straightforward synthesis of a C_s symmetrical calix[6]arene possessing carboxylic acid groups as well as an ammonium arm is described. This calixarene can encapsulate ammonium ions through a highly selective recognition process thanks to the presence of an internal ion-paired cap that preorganizes the cavity and constitutes an efficient binding site.     

Reversibly controllable guest binding in precisely defined cavities: selectivity, induced fit, and switching in novel resorcin[4]arene-based container molecules

Two molecular baskets are presented, which were constructed based on a resorcin[4]arene platform. The molecules completely surround suitable guests, such as cyclo- or oxacycloalkanes, and bind them with high strength. The thermodynamic parameters for inclusion complexation were determined as well as the influence of encapsulation on the ring inversion barrier of bound cyclohexane. Two-dimensional NMR spectroscopy clearly shows the existence of a directed attractive interaction between oxacyclohexane and one of the hosts, which constrains the rotation of the bound molecule. Both containers exhibit remarkable binding selectivity as a consequence of their precisely defined structures. They both differentiate between homologous cycloalkanes, and whereas cyclohexane binds best within the larger of the two interior cavities, cyclopentane fits best in the smaller one. The selectivity is governed by ideal filling of space. We have conducted molecular dynamics experiments to understand the thermal fluctuations in the cavity sizes when a guest is bound. The simulations show that within a very narrow range the hosts adapt their binding site to different guests in order to optimize the fraction of occupied space. Once a binding geometry is established, it is characterized by a very low degree of flexibility. The guest-hosting properties of both molecules can be suspended by an external stimulus: addition of acid induces an opening of portals in the structures and immediately releases all bound cargo. Neutralization of the solution completely restores the initial state.     

Supramolecular control over LCST behavior of hybrid macrocyclic system based on pillar[5]arene and crown ether

A hybrid system containing a pillar[5]arene unit and ten crown ether moieties was developed. The LCST behavior and thermo-responsiveness were successfully introduced into this pillar[5]arene-crown ether system. Both host-guest interactions and salting-out effect displayed great effects in realizing the supramolecular control over LCST properties and thermo-responsiveness. Compared with the individual macrocycles, this hybrid macrocycle system dramatically amplified the supramolecular control effect over LCST behavior.     

Synthesis of pillar[7]arene

The first synthesis of pillar[7]arene is reported with two methods.Method A:the FeCl₃-catalyzed condensation reaction of 1,4- dimethoxybenzene（1） with paraformaldehyde in CHCl₃ gave dimethoxypillar[7]arene（3）.Method B:the p-toluenesulfonic acid catalyzed condensation reaction of 2,5-bis（benzyloxymethyl）-1,4-dimethoxybenzene（2） in CH₂Cl₂ gave compound 3.Demethylation of 3 with BBr₃ gave pillar[7]arene（4）.The pillar[7]arene might be a perspective macrocyclic host in host-guest chemistry.     

A pillar[5]arene-based molecular grapple of hexafluorophosphate

A symmetric pillararene-based receptor formed 1:1 complexes instead of 1:2 with different halide anions. The cooperative multivalent hydrogen-bond interactions changed its structure from pillar to conical. By the addition of F, it can work like an excavator grapple selectively grasps a PF₆^- anion.     

Cucurbit[10]uril-based chemistry

With the biggest cavity in the cucurbit[n]urils (CB[n]s) family, CB[10] has shown its unique molecular recognition properties. This review gives a brief summary of the research progresses in the CB[10]-based chemistry, involving its purification and applications in fields such as molecular recognition and molecular assembly.     

Supramolecular polymer materials based on pillar[5]arene: Ultrasensitive detection and efficient removal of cyanide

An ultrasensitive detection and effective removal material was successfully developed by using a pillar[n]arene-based supramolecular polymer gel (MTP5⊃HB). The MTP5⊃HB can ultrasensitively recognize Cu²⁺ and Fe³⁺, and the limits of detection (LODs) for Cu²⁺ and Fe³⁺ are 1.55 and 2.68 nmol/L, respectively. Additionally, the in-situ generated metallogel MTP5⊃HB-Cu can exclusively detect CN⁻, and the LOD for CN⁻ is 1.13 nmol/L. Noticeably, the xerogel of MTP5⊃HB-Cu can effectively remove CN⁻ from aqueous solution with 94.40% removal rate. Test kit based on MTP5⊃HB-Cu is also prepared for convenient detection of CN⁻.