Synthesis of a Naphthalimide Functionalized Calix[4]arene; A Host Type Fluorophore for Inclusion Compounds in Organic Medium

This article reports the synthesis and the properties of 5,11,17,23-tetra(t-butyl)-25,27-bis-(ethoxy-1,8-naphthalimide)-26,28-hidroxy-calix[4]arene and the formation of an inclusion compound in organic medium. This functionalized calix[4]arene was conceived as the association of a potential host species with a good fluorophore for optical sensoring purposes. Calix[4]-NI as we will call it, maintains its ‘cone-pinched’ configuration and exhibits typical naphthalimide fluorescence bands in non-polar solvents. Its ability to interact with guest species via hydrogen bonding in its endo-hydrophilic cavity to form inclusion compounds was verified with absorption and fluorescence measurements using N-ethanol-1,8-naphthalimide as guest species, which was projected to fit exactly the host cavity and to interact with its naphthalimide π electrons. For this reason, it was possible to follow the formation of the inclusion compound with electronic spectroscopy.in final form: 17 November 2004.This revised version was published online in July 2005 with a corrected issue number.     

A cationic water-soluble pillar[7]arene: Synthesis and its fluorescent host−guest complex in water

The first cationic water-soluble pillar[7]arene CWP7 was prepared. ¹H NMR, ¹³C NMR, and MALDI-TOF-MS were performed to provide converging evidences of the structure of obtained CWP7. Host–guest complexation between this novel pillar[7]arene-based host and sodium pyren-1-olate guest G was fully investigated in aqueous solution. Increased fluorescence intensity was observed during the inclusion complexation. Driven by the cooperativity of electrostatic interactions, π-stacking interactions and hydrophilic/hydrophobic interactions, the guest penetrated into the cavity of CWP7 to form a pseudorotaxane-type inclusion complex with relatively high binding affinity.     

Unique inclusion behaviour of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetraaminothiacalix[4]-arene towards small organic molecules

Tetraaminothiacalixarene 3, bearing four amino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different from those of compound 2 towards small organic molecules upon crystallisation from neat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds.     

Encapsulation of adefovir bis(l-leucine propyl)ester pro-virucide in cucurbit[7]uril and its activity against tobacco mosaic virus

The interaction of cucurbit[7]uril (Q[7]) with a pro-virucide, adefovir bis(l-leucine propyl)ester (PMEA-Leu) in aqueous solutions and in solid state was studied by ¹H NMR, UV absorption spectroscopy, fluorescence and IR spectroscopy. The ¹H NMR revealed that the leucine propyl moiety of the compound could be entrapped in the cavity of the host Q[7], and the other moiety except for leucine propyl moieties, including aminopurine, was probably located at the portal area of Q[7]. Absorption and fluorescence spectroscopy proved that the interaction of Q[7] with PMEA-Leu led to the formation of host–guest inclusion complexes (2:1) that were controlled by the concentration of the host Q[7]. Formation of the inclusion complex between Q[7] and PMEA-Leu was confirmed by IR spectroscopy in solid state. In addition, deliquescent stability studies indicated that the moisture stability of the host–guest complex was significantly enhanced. The phenomenon was explained by the fact that the formation of solid inclusion complexes can prevent the compounds from absorbing water. Finally, bioactivity of PMEA-Leu and its inclusion complex against tobacco mosaic virus (TMV) was tested. The compound PMEA-Leu and its inclusion complexes showed some inhibitory activity against TMV at 500 μg/ml in vivo.     

Host–Guest Complexation Using Pillar[5]arene Crystals: Crystal-Structure Dependent Uptake,Release, and Molecular Dynamics of an Alkane Guest

Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes.     

Amphiphilic Inclusion Spaces for Various Guests and Regulation of Fluorescence Intensity of 1,8‐Bis(4‐aminophenyl)anthracene Crystals

A host framework for inclusion of various guest molecules was investigated by preparation of inclusion crystals of 1,8‐bis(4‐aminophenyl)anthracene (1,8‐BAPA) with organic solvents. X‐ray crystallographic analysis revealed construction of the same inclusion space incorporating 1,8‐BAPA and eight guest molecules including both non‐polar (benzene) and polar guests (N,N‐dimethylformamide, DMF). Fluorescence efficiencies varied depending on guest molecule polarity; DMF inclusion crystals exhibited the highest fluorescence intensity (Φ_F=0.40), four times as high as that of a benzene inclusion crystal (Φ_F=0.10). According to systematic investigations of inclusion phenomena, strong host–guest interactions and filling of the inclusion space led to a high fluorescence intensity. Temperature‐dependent fluorescence spectral measurements revealed these factors effectively immobilised the host framework. Although hydrogen bonding commonly decreases fluorescence intensity, the present study demonstrated that such strong interactions provide excellent conditions for fluorescence enhancement. Thus, this remarkable behaviour has potential application toward sensing of highly polar molecules, such as biogenic compounds.     

Extraction Behavior of Amino Acids by Calix[6]arene Carboxylic Acid Derivatives

A series of calixarene carboxylic acid derivatives were synthesized for the extraction of amino acids. A calix[6]arene carboxylic acid derivative showed the highest extractability to the target tryptophan ester. The main driving forcefor the complexation was the interaction between the ammonium cation of the aminoacid and the oxygen atoms of the host molecule. Stripping of amino acids was alsoaccomplished by contacting the organic solution with a fresh acidic solution. Basedon slope and Job method analyses, it was confirmed that the calix[6]arene formsa 1 : 1 complex with the amino acid ester. The structure of the complex between the calix[6]arene and the amino acid was investigated by ¹H-NMR and CD spectra. The calix[6]arene includes a guest molecule in the cavity, and the inclusion induces the asymmetrization of the host molecule. This host compound functions as a novel recognition tool for amino acids.     

Anchoring of 1,8-naphthalimide derivative into mesoporous MCM-41 molecular sieves

The fluorescent dye molecules, 4-piperidine-1,8-naphthalimide, were successfully fixed into the amino modified pore channel of mesoporous MCM-41 type materials by in situ reaction of 4-piperidinyl-1,8-naphthalic anhydride with the amino group. The formation of amide bonds on the pore surface was verified by infrared spectra. The maximum fluorescence emission peak of this hybrid material has a red shift of 13 nm compared to that of a naphthalimide derivative in ethanol solution. Moreover, the fluorescence intensity of dye molecules grafted into Ce-doped MCM-41 is higher than that in pure silica MCM-41. This phenomenon is attributed to the inhibited internal electron transfer from piperidine to naphthalimide groups by Ce⁴⁺, thus improving the fluorescence intensity of the naphthalimide group. The unique fluorescence behavior of the 1,8-naphthalimide derivative doped hybrid mesoporous material makes it a good candidate for the metal ions microdetection.     

Effect of the size of calixarene macrocycle on the thermodynamic parameters of formation of inclusion compounds in guest vapor—solid host systems

The influence of the calixarene macrocycle size on the thermodynamic parameters of inclusion formation in organic guest vapor—solid host systems was studied in the series of tert-butylcalix[4]arene (1), tert-butylcalix[6]arene (2), and tert-butylcalix[8]arene (3). For this purpose, sorption isotherms of a guest vapor by a solid host were determined using the static method of headspace GC analysis for the systems involving calixarenes 2 and 3 in addition to the earlier obtained data for calixarene 1. Besides, the stoichiometry and decomposition temperatures of saturated clathrates formed in these systems were determined using thermogravimetry. The compositions of some of these clathrates differ substantially from those of clathrates crystallized from a host solution in a liquid guest. For the most guests studied with the thermodynamic activity below 0.6, their uptake by calixarenes 1—3 changes in the series 2 < 1 < 3. As a whole, the trend for each particular parameter of clathrates of hosts 1—3 (stoichiometry, guest activity at 50% saturation of the host) with increasing the size of the calixarene macrocycle is specific for each guest studied. The results obtained are useful for the estimation of receptor properties of calixarenes in quartz microbalance sensors.     

Intermolecular Complexation Between p-Sulfonated Calix[4,6,8]arene Sodium and Neutral Red

The inclusion complexation behavior of the dye guest molecule neutral red with three kinds of water-soluble p-sulfonated calix[n]arene sodium (n=4,6,8) was investigated. p-Sulfonated calix[4,6,8]arene sodium (pSC4, pSC6, pSC8) can react with neutral red to form inclusion complexes, which were confirmed by UV-vis absorption and fluorescence spectroscopy. Fluorescence spectroscopy experiments were performed in pH=4.6 acetic buffer solutions at 25 °C to calculate the stability constants (K _S) for the stoichiometric 1:1 inclusion complexes of pSC4, pSC6 and pSC8 with neutral red. The thermodynamic parameters for the inclusion complexes were determined through a van’t Hoff analysis. Formation of the inclusion complexes of pSC4, pSC6 and pSC8 with neutral red was driven by favorable enthalpic changes with their accompanying negative entropy changes. The complex stability constants monotonically increased with the number of phenolic units in the calixarene ring, which was attributed mainly to electrostatic interactions and hydrogen bonding, rather than to the cavity size.     

Synthesis and fluorescence of N-substituted-1,8-naphthalimides

A number of novel N-substituted-1,8-naphthalimides have been prepared and their fluorescence yields measured in water at pH 7.4. The type of substitutent and the substitution pattern on the naphthalimide nucleus produce markedly different fluorescence yields, (quantum efficiencies, ø varying from ø = 0-0037 for N-(3-N'-morpholino-1-propyl)-4-amino-3-methoxy-1,8-naphthalirnide (7) to ø = 0–77 for N-(3-bromopropyl)-4-acetamido-1,8-naphthalimide (31).     

Recovery of host crystals from inclusion crystals of <Emphasis Type="Italic">p-tert-</Emphasis>butylcalix[4]arene and <Emphasis Type="Italic">p-tert</Emphasis>-butylthiacalix[4]arene by the treatment with a solvent and/or supercritical CO<Subscript>2</Subscript>

Upon stirring inclusion crystals of p-tert-butylthiacalix[4]arene (2) in solvents with heating, guest compounds were efficiently desorbed to yield guest-free crystals. More specifically, upon treatment with methanol, the exchange of guest compounds with methanol in the crystals, followed by the desorption of the methanol afforded metastable host crystals 2β, whereas, upon treatment with heptane, the dissolution of the inclusion crystals and simultaneous crystallization of compound 2 afforded stable host crystals 2α. Further, a host crystal of p-tert-butylcalix[4]arene (1) was recovered by the treatment of 2:1 (host/guest) inclusion crystals of compound 1 with supercritical carbon dioxide (scCO₂), and through the combination of the guest exchange of 1:1 inclusion crystals of compound 1 with hexane and scCO₂ treatment of the resulting 2:1 inclusion crystals 1₂·hexane. Although the recovered host crystal of compound 1 contained a small amount of CO₂, it could be reused for the inclusion of organic compounds.     

Efficient enhancement of fluorescence emission via TPE functionalized cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly

A tetraphenylethene (TPE) functionalized cationic pillar[5]arene (CWP5-TPE) was successfully synthesized, and the intramolecular rotation of the TPE motif was restricted via cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly in water, resulting in the efficient enhancement of fluorescence emission based on the aggregation induced emission (AIE) mechanism. CWP5-TPE self-assembled into nanoribbons while the host–guest inclusion complex formed into supramolecular amphiphile nanoparticles in water.     

Kinetic and thermodynamic inclusion complexes of symmetric teramethyl-substituted cucurbit[6]uril with HCl salts of N,N′-bis(pyridylmethyl)-1,6-hexanediamine

The host–guest interaction of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) with the hydrochloride salts of N,N′-bis(4-pyridylmethyl)-1,6-hexanediamine (P6), N,N′-bis(3-pyridyl-methyl)-1,6-hexanediamine (M6) and N,N′-bis(2-pyridylmethyl)-1,6-hexanediamine (O6) was investigated via single crystal X-ray diffraction, ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy. Single crystal X-ray diffraction showed that the hexyl moiety of P6 or M6 was incorporated in the cavity of TMeQ[6], while the two pyridylmethyl moieties of O6 were incorporated in the TMeQ[6] cavity in the solid state. The ¹H NMR results in aqueous solution revealed that the TMeQ[6]-P6 and TMeQ[6]-M6 host–guest interaction systems produce a kinetic dumbbell-shaped inclusion complex at the initial stage and then an equilibrium pseudorotaxane-shaped inclusion complex as the only product after heating. However, only the pseudorotaxane-shaped inclusion complex was observed for the TMeQ[6]-O6 host–guest interaction system. Aqueous absorption spectrophotometric analysis showed that the dumbbell-shaped inclusion complexes were stable at pH 5.6, had a host–guest ratio of 2:1 and formed quantitatively at ～10¹¹ l²/mol² for the TMeQ[6]-M6 and TMeQ[6]-O6 systems. The transformation from dumbbell to pseudorotaxane-shaped inclusion complexes for the TMeQ[6]-P6 and TMeQ[6]-M6 host–guest systems yielded activation energies of 59.35 ± 1.55 and 78.7 ± 3.45 kJ/mol, respectively. The pseudorotaxane-shaped inclusion complexes were stable at pH 5.6, had a host–guest ratio of 1:1 and formed quantitatively at ～10⁷ l/mol for the TMeQ[6]-M6 and TMeQ[6]-P6 systems.     

Host–guest complexes of some cucurbit[n]urils with the hydrochloride salts of some imidazole derivatives

Interaction between the normal cucurbit[n]urils (n = 6,7,8; Q[6], Q[7], Q[8]) and a sym-tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of some imidazole derivatives N-(4-hydroxylphenyl)imidazole (g1), N-(4-aminophenyl)imidazole (g2), 2-phenylimidazole (g3) in aqueous solution was investigated by using ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by using a single crystal X-ray diffraction determination. The ¹H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 forms for the Q[6]s and Q[7] cases, while with a host:guest ratio of 1:2 form for the Q[8] cases. It was common that the hosts selectively bound the phenyl moiety of the guests. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 5.8 with a host:guest ratio of 1:1 form quantitatively as logK values between 4 and 5 for the smaller hosts Q[6 or 7]s, while with a host:guest ratio of 1:2 form quantitatively as logK values between 11 and 12 for the host Q[8]. Two single crystal X-ray structures of the inclusion complexes TMeQ[6]-g2 · HCl and TMeQ[6]-g3 · HCl showed the phenyl moiety of these two guests inserted into the host cavity, which supported particularly the ¹H NMR spectroscopic study in solution.     

Host–Guest Complexation Behavior of Resorcinarenes with Tetraalkylammonium Ions and N-Methylpyridinium Ions in Methanol: The Effect of Bulky Hydrophobic Substituents at the Extra-Annular Positions

The host–guest interaction of C-methylresorcin[4]arene and its derivative having four tert-butylsulfanylmethyl groups at the extra-annular positions was studied by ¹ H NMR spectroscopy in CD₃OD. Based on the association constants (Ka) and the complexation-induced NMR shifts (CIS), it was concluded that the bulky substituents create a deep cavity with a narrow entrance and improve the size and shape selectivity.     

Spectral and electrochemical investigation of p-sulfonatocalix[4]arene-stabilized vitamin E aggregation

The host–guest interaction of α-tocopherol (vitamin E) with p-sulfonatocalix[4]arene (p-SC4) in solution state is studied using emission and cyclic voltammetric techniques. The lipid soluble α-tocopherol (α-T) forms a solid complex with p-SC4. FTIR and NMR spectral analysis of the solid complex reveals the tight packing of α-T inside the cavity of p-SC4. The structural deformation is confirmed by XRD analysis. SEM images differentiate the highly porous gel like structure of vitamin E aggregate and the solid structure of the host–guest complex prepared. NOESY spectra confirm the tight penetration of α-T within the hydrophobic cavity of p-SC4.     

A novel fluorescent molecule based on 1,8-naphthalimide: synthesis,spectral properties,and application in cell imaging

A novel naphthalimide molecule, 4-(2-methoxyethoxy)-N-butyl-1,8-naphthalimide (MEBN), has been synthesized and characterized. The UV–visible absorption and fluorescence emission spectral properties in n-hexane, toluene, CHCl₃, and CH₃OH were studied. Its optical properties depend on solvent polarity. The application of MEBN in cell imaging was investigated.     

一对含有苯甲醛基修饰的杯芳烃异构体的晶体结构以及它们与铽离子配位的光物理性质

Two calix[4]arene isomers with benzaldehyde moieties, i.e., 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(o-formyl-phenoxy)ethoxy]-26,28-dihydroxycalix[4]arene (3) and 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(p-formylphenoxy)-ethoxy]-26,28-dihydroxycalix[4]arene (4), were synthesized according to a newly designed route in high yields, and their crystal structures have been determined by X-ray crystallographic study. The photophysical behavior on complexation of calix[4]arene derivatives 3 and 4 with terbium(Ⅲ) nitrate was investigated in anhydrous acetonitrile at 25℃ by UV-Vis and fluorescence spectroscopies. The crystallographic structure of 3 indicated that the eight oxygen atoms formed a preorganized ionophoric cavity due to intramolecular π-π stacking, which could encapsulate lanthanide ions tightly. In sharp contrast, the compound 4 formed a linear array by intermolecular π-π stacking, hence the oxygen atoms of pendant arms could not coordinate with metal ions, giving a poor binding ability to Tb^3 . The absorption spectra of 3 with Tb^3 showed clearly a new broad intense absorption at 385nm. Interestingly, the narrow emission line spectrum has also been observed for compound 3 with Tb^3 , and the results obtained were discussed from the viewpoint of energy transfer mechanism between host structures and the properties of lanthanide ions.     

25,27:26,28‐Bis(3,9‐dioxa‐6‐aza­undecane‐1,11‐dioxy)­calix­[4]­arene tetrahydrate

The title compound, C₄₄H₅₄N₂O₈·4H₂O, has twofold crystallographic symmetry and consists of a calix­[4]­arene moiety with four phenyl rings arranged alternately in anti‐orientation fashion and two aza­crown units attached on the lower rims of calix­[4]­arene. This seems to offer a big cavity inside the mol­ecule which might possess a potential for forming host–guest complexes.