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Abstract
Supramolecule chemistry is an advanced research topic in current chemistry, and the selective synthesis of the host compound is an important aspect. Cyclodextrins and crownethers, which have their own special characters and disadvantages, are both widely used in supramolecular chemistry. The cyclodextrin-crownether coupling system which has two or more recognition sites will expand their applications greatly in the area of molecular recognition, enzyme mimic, chromatography, etc. through synergistic effection with fine results. Here, the recent development of cyclodextrincrownether coupling system is reviewed. Firstly, the synthesis of different kinds of cyclodextrin- crownether coupling systems is introduced, including the synthesis clues, approaches and methods. Then, the application of the system is emphatically described, including in the field of molecule recognition, mimetic enzyme, isolation of isomers and energy transfer of light. At last, the disadvantages in recent study and prospects are pointed out.
... Cooperative separation processes employing ionic liquids and CDs have been recently reviewed [214]. Application and potentialities of CD-crown ether coupling system in supramolecular chemistry has been reviewed by Sun et al. [215]. The authors, in particular, focus on recent developments and applications of these coupling systems in fields such as molecule recognition, mimetic enzyme, isolation of isomers and energy transfer of light. ...
The most important and broadly used chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC) are reviewed. After a short description of the state of the art, for each kind of CSP the most important contributions published in the last couple of years are summarized. For the sake of classification, these works have been divided into studies on enantiorecognition mechanisms, new materials, and new applications. Emphasis is given to new, emerging CSPs that seem to possess all requisites to be considered potentially successful chiral separation media in the next future.
Supramolecular chemistry is a hot research topic in current chemistry. It is more attractive to build machines in a nanometer scale by mimicking the macro-scale processes through supramolecular way. Being different from the traditional "motile" molecular machines, the novel "processing" molecular machines based on the cyclodextrin-fullerene coupling system focus on a "recognition-capture-processing-release" procedure, but not on the position changes in and between molecules. This new molecular machine will supply a new approach in the area of enzyme mimic, biological process research, photo-immobilization, etc. Here, the development of cyclodextrinfullerene coupling system is reviewed. Firstly, the synthesis of different kinds of cyclodextrin-fullerene coupling systems, including the synthesis clues, approaches and characterization, is introduced. Then, the application of the system is emphatically described, including molecular recognition, DNA cleavage and electron transfer, etc. Finally, based on current developments of the system, the prospects are pointed out.
The synthesis and properties of cyclodextrin-calix[n]arene are reviewed. Cyclodextrin-calix[n]arene is a kind of powerful macromolecule which could be applied to the fields such as molecular recognition, host-guest chemistry, organic chemistry in water and molecular catalysis reaction etc.
The selective HNO3 nitration of di-n-octylcrown-6 calix[4]arene using different conditions, studied with LCMS and NMR (1H and 13C) spectroscopic techniques, lead to the identification of most of the expected nitro derivative isomeric compounds. The formation of these isomers under acidic and radiolytic conditions is discussed with the help of molecular modelling.Key words: calix crown compounds, nitration of calixarenes, NMR of isomeric nitrocalixarenes, LC-ESI-MS.
Some fundamental aspects of capillary electrochromatography (CEC) (electroosmotic flow, capacity factor, plate height) were studied by carrying out the separation of some neutral compounds with capillaries packed with octadecylsilica particles (ODS). No loss of efficiency up to a linear electroosmotic velocity of 1.3 mm/s was observed for retained analytes (capacity factors varying from 0.7 to 2.5). The extra-column dispersions caused by the frit and the unpacked section separating the frit from the detection window were estimated. Chiral separations of the neutral enantiomers of chlorthalidone by packed capillary electrochromatography was successfully achieved using two approaches: (a) use of the chiral agent, hydroxypropyl-β-cyclodextrin (HPβCD) directly in the mobile phase with an achiral stationary phase (3 μm ODS); (b) use of a chiral stationary phase (5 μm HPβCD-bonded silica particles) with an achiral mobile phase. As with liquid chromatography, the second method achieves higher selectivity and resolution in a shorter analysis time.
β-Cyclodextrin derivatives connected with diaza-18-crown-6 through flexible bridges (R) at the secondary face 1a-c (1a: R = -(CH2)4-; 1b: R = -CH2CH2OCH2CH2-; 1c: R = -(CH2)8-) have been prepared. The association constants of 1 with (2-naphthoxy)alkylammonium ions (2a: alkyl = butyl; 2b: alkyl = octyl) were determined by induced circular dichroism (ICD) spectroscopy and it was found that the derivatization of β-CD with the diazacrown resulted in enhanced binding with 2, compared to the native β-CD. ICD Characteristics of the host-guest complexes indicate that a part of the alkylammonium moiety of 2 is protruded from the secondary side of the β-CD cavity, and the guest molecules 2a and 2b move to the secondary and primary side, respectively, to make the binding of the ammonium group with the diaza-18-crown-6 moiety more feasible. The energy accompanied by the relocation of the guest molecules inside β-CD moiety is compensated by the interaction energy between the ammonium ion and diazacrown ether.
Cyclodextrins, widely applied in green organic synthesis, can transfer hydrophobic molecules into water by the supramolecular interaction. As an important kind of host molecules, they can also influence the microenvironment of hydrophobic molecules by the host-guest interaction and change traditional reaction conditions to obtain good yield without byproduct. The recent developments of application of cyclodextrins in green organic reactions such as oxidation reaction, addition reaction, ring opening reaction, deprotection reaction, coupling reaction, substitution reaction, etc. are reviewed. The catalytic mechanisms are also discussed in this article.
This paper summarizes the main research of azacrown ether compounds and macrocyclic polyamines in our group from 1985 to 2000. It consists four parts: (1) Research of synthetic method of a series new macrocyclic compounds; benzoazacrown ether, azacrown ethers containing central functional group and their N-pivot lariat derivatives, Schiff's azacrown ethers and macrocyclic polyamines containing pyridine or bipyridine ring etc. (2) Application of NMR in the complexation of N-substituted benzocrown ethers with p-toluene diazonium fluoroborate, conformation of azacrown ether containing central group, and research of dilution shift effect. (3) Research of synthesis and photochromism of crowned indolinospiropyrans as artifical signaling recepter. (4) Synthesis and molecular recognition of cyclodextrin dimers.
Azametallacrowns (azaMCs) with the M-N-N repeating units can be assembled by the trianionic pentadentate N-acylhydrazide ligands with different metal ions and their ring sizes have been enlarged from aza18-MC-6 to aza60-MC-20. Azametallacrowns not only exhibit uniquely physical and biologic properties, but also can be used as second building units (SBUs) to construct a series of azametallacrown supmmolecular polymers. This review summarizes the structural characters, categories and properties of azametallacrowns.
Thirty-three cyclic polyethers, derived from aromatic vicinal diols and containing from 9 to 60 atoms including 3 to 20 oxygen atoms in the ring, have been synthesized. Some of these have been prepared in good yields without the use of a high-dilution technique. Fifteen of the compounds have been catalytically hydrogenated to the corresponding saturated cyclic polyethers. Many of those containing five to ten oxygen atoms form stable complexes with some or all of the cations of: Li, Na, NH 4, RNH 3, K, Rb, Cs, Ag(I), Au(I), Ca, Sr, Ba, Cd, Hg(I), Hg(II), La(III), Tl(I), Ce(III), and Pb(II). Many of these complexes can be isolated in the crystalline form depending on the anion. They appear to be salt-polyether complexes formed by ion-dipole interaction between the cation and the negatively charged oxygen atoms of the polyether ring. The stoichiometry of the complexes is one molecule of polyether per single ion regardless of the valence. Some of the polyethers, by complexing, solubilize inorganic compounds, such as potassium hydroxide and permanganate, in aromatic hydrocarbons.
A series of crown ether-capped 3-(2-O-β-cyclodextrin)-2-hydroxypropylsilyl silica particles have been prepared for use as novel bonded chiral stationary phases (CSP) for liquid chromatography. These materials were prepared using a successive multiple-step liquid-solid phase reaction on the silica gel surface. First, β-cyclodextrin (β-CD) was anchored at its C(2) position (on the larger rim of the β-CD torus) onto the silica surface. This material was then derivatized by treatment with bromoacetyl bromide. The bromoacetate-containing CD-silica was finally treated with four amine-containing crown ethers in acetonitrile in the presence of potassium carbonate. These bonded phases were characterized by means of elemental analysis and Fourier-transform infrared spectroscopy. Since these CSPs have a chiral selector with two recognition sites, i.e., crown ether and substituted β-cyclodextrin, they provide excellent selectivity for the separation of enantiomers and positional isomers. These CSPs exhibit excellent selectivities for a wide variety of chiral separations in ultrahigh pressure capillary liquid chromatography (UHPLC) and capillary electro-chromatography (CEC) due to the cooperative functioning of the crown ether and β-CD.
A novel β-cyclodextrin derivative 6 bearing a crown ether moiety has been synthesized by a convenient method in 9.4% yield. Its self-assembled monolayer (SAM) was fabricated on the gold surface, which was characterized by using surface-enhanced Raman spectra. A number of cyclodextrin (CD) derivatives and crown ethers have been designed and synthesized in order to examine their molecular/ions recognition mechanics and control molecular assembly and self-assembly. However, CD derivatives linked by crown ether have rarely been synthesized and their molecular assembly has not been extensively investigated 1 . In the present communication, we report the synthesis of 4', 5' -dimercap -tomethylene-benzo-15-crown-5 tethered β-cyclodextrin and its self-assembled monolay-er (SAM) was fabricated on the gold surface. The crown ether modified β-CD 6 was synthesized according to Scheme 1 . In this synthetic route, 4', 5'-bis(bromomethyl)-benzo-15-crown-5 2 2 and thiourea were stirred for 24 h in EtOH at 50°C, then the mixture was hydrolyzed with aqueous NaOH (10%). After acidification, it is extracted with ether. Finally, the crude product was recrystallized from cyclohexane to give pure sample 3. Moreover, 3 and the mono-[6-O-(p-toluenesulfonyl)]-β-CD 5 3 was stirred in DMF for 10 days under N 2 at 70°C. After evaporation of DMF, the residue was dissolved in hot water, then poured into acetone with vigorous stirring. The brown precipitate formed was purified by the column of Sephadex G-25 with the elution of water two times to give pure 6 in 9.4% yield. These samples are confirmed by elemental analysis and spectroscopic data 4 . The Au-foil was immersed in a solution of 6 (0.1 mol/L) at room temperature for 24 h, then washed with water. The SAM was obtained. In the surface-enhanced Raman spectra of the SAM, the characteristic frequency of S-C at 713 cm -1 was shown, but the characteristic vibration of S-H at 2574 cm -1 does not exist 5 . Meanwhile, the vibration of the modified CD 6 can be observed at 2890, 1577, 1488, 1291, 1002 cm -1 . These results indicate the formation of the SAM on the gold surface.
The direct coupling via succinyl-diamide links of a difunctionalised cyclodextrin (CD) to di- and tetra-functionalised calix[4]arene-crown-6 (CAL) leads to tubular calixarene–cyclodextrin species. The product structures were characterised by high resolution 1H and 13C NMR and MALDI-TOF spectroscopies.
Two novel types of crown ether capped β-cyclodextrin (β-CD) bonded silica, namely, 4'-aminobenzo-X-crown-Y (X=15, 18 and Y=5, 6, resp.) capped [3-(2-O-β-cyclodextrin)-2-hydroxypropoxyl propylsilyl-appended silica, have been prepared and used as stationary phases in capillary electrochromatography (CEC) to separate chiral compounds. The two stationary phases have a chiral selector with two recognition sites: crown ether and β-CD. They exhibit excellent enantioselectivity in CEC for a wide range of compounds. After inclusion of metal ions (Na- or K-) from the running buffer into the crown ether units, the stationary phases become positively charged and can provide extra electrostatic interaction with ionizable solutes and enhance the dipolar interaction with polar neutral solutes. This enhances the host-guest interaction with the solute and improves chiral recognition and enantioselectivity. Due to the cooperation of the anchored β-CD and the crown ether, this kind of crown ether capped β-CD bonded phase shows better enantioselectivity than either β-CD-or crown ether bonded phases only. These new types of stationary phases have good potential for fast chiral separation with CEC.
α-, β-, and γ-Cyclodextrins are cyclic oligosaccharides consisting of six, seven, or eight glucose units, which can be obtained on a large scale from starch. They form inclusion compounds with smaller molecules which fit into their 5—8 Å cavity. These (crystalline) complexes are of interest for scientific research as, contrary to the classical clathrates, they exist in aqueous solution and can be used to study the hydrophobic interactions which are so important in biological systems. Cyclodextrins also serve as models both for polymeric starch and, in the form of their polyiodide complexes, for “blue iodine-starch”. As cyclodextrins catalyze several chemical reactions they and their functionalized derivatives provide useful enzyme models. Cyclodextrins can be used to advantage in the production of pharmaceuticals, pesticides, foodstuffs, and toilet articles—the (micro-encapsulated) active and aromatic substances enclosed within them are protected from the effects of light and atmosphere and can be easily handled and stored in powder from. Substances which are not very soluble in water become more soluble in the presence of cyclodextrins—creams and emulsions can be stabilized, and the growth and yield of grain harvests can be increased. Cyclodextrins can be chemically modified for many different purposes; polymerized cyclodextrin or cyclodextrin bound to a polymer carrier have already been employed in gel inclusion and affinity chromatography.
The tetraoxadiazacyclo-octadecanyl-β-cyclodextrin (1) provides a molecular assembly with two recognition receptor sites, which co-operate in the association of alkali-metal p-nitrophenolates as substrates.
The coupling of two or four mono-6-amino β-cyclodextrin (amino-CD) units, (unprotected or permethylated hydroxyls), to diisopropoxycalix[4]arene crown-6 (CAL) was realised using the N,N′-succinyldiamide linker. The resulting molecules in two series were characterised with the help of mass and NMR spectroscopies. The yields of all coupling products were improved for permethylated sugar series compared to the hydroxylated CD series or to our previous studies. The two β-cyclodextrin (β-CD) residues coupled to disubstituted CAL were orientated from the same side of the crown ether.
A series of β-cyclodextrin derivatives, carrying pyridinio (4−6), phosphonyl (7, 8), seleno (9−11), m- and p-picolinyl (12, 13), o-chloroanilino (16), 8-quinolyl (17), furfuryl (18), and 9-fluorenyl (19) moieties in the side chain, were newly synthesized, and their complexation behavior was assessed and discussed thermodynamically, using l-tryptophan and a few naphthalene derivatives as representative guests. Calorimetric titrations have been performed at 25.0 °C in buffered aqueous solution (pH 7.20) to give the complex stability constants and thermodynamic parameters for the 1:1 inclusion complexation of these guests with the native and modified α-, β-, and/or γ-cyclodextrins (1−20). All of the chemical modifications to the primary side of cyclodextrins examined led to significant changes in complex stability and thermodynamic parameters, which are elucidated in terms of the conformational, electrostatic, hydrogen-bonding, and hydration effects. Thermodynamically, the inclusion complexation is mainly enthalpy-driven with a negative or minor positive entropic contribution, which in some cases determines the complex stability. The induced circular dichroism spectral analyses of these cyclodextrin derivatives indicated that the aromatic moiety in modified β-cyclodextrins (4−6, 9−19) only shallowly penetrates into the hydrophobic cavity of β-cyclodextrin, while the phenyl phosphate and fluorenyl moieties in 7 and 20 are embedded into the hydrophobic cavity of β-cyclodextrin because of the longer linking chain. Using all the thermodynamic data for a wide variety of cyclodextrin derivatives obtained in this and previous studies, the entropy changes (TΔS) were plotted against the enthalpy changes (ΔH) to give an excellent linear relationship. The slope (α) of 1.02 and an intercept (TΔS0) of 4.3 of the regression line indicate substantial conformational changes and extensive desolvation caused upon complexation, respectively.
beta-Cyclodextrin (beta-CD) functionalized with diaza-18-crown-6 at primary face shows 7-10 fold greater binding constants for aromatic ammonium ions in aqueous media than the unmodified beta-CD by the cooperative binding of the aromatic group to beta-CD and ammonium group to crown ether moiety.
A new photoactive supramolecular assembly featuring a cyclodextrin modified with a Eu{sup 3+} {contained in} aza crown ether has been prepared. The authors report the complete characterization of the crown-modified cyclodextrin as well as the synthesis and photophysical properties when Eu{sup 3+} occupies the aza receptor site. The luminescence properties of the cyclodextrin appended with Eu{sup 3+} {contained in} aza mimic that of the simple Eu{sup 3+} {contained in} aza complex. However, enhanced europium emission is observed upon the introduction of benzene to solutions of the supramolecular assembly. They attribute this enhancement to an absorption-energy-transfer-emission process from benzene in the cavity of cyclodextrin to Eu{sup 3+} ion residing in the appended aza macrocycle.
Fused-silica capillaries of 50-mum internal diameter were packed with an alpha1-acid glycoprotein chiral stationary phase. The properties of electroosmosis in these packed capillaries were studied by investigating the influence of field strength, pH, and solvent composition on the velocity of electroosmotic flow. Direct enantiomeric separation by capillary electrochromatography was investigated with the use of these packed capillaries. Chiral resolution was achieved for the enantiomers of benzoin, hexobarbital, pentobarbital, ifosfamide, cyclophosphamide, disopyramide, metoprolol, oxprenolol, alprenolol, and propranolol. The effects of pH, electrolyte concentration, and concentration of organic solvents in the mobile phase on the retention and the enantioselectivity were studied.
The synthesis and full spectroscopic characterization (IR, 1D and 2D TOCSY and ROESY NMR, MS) of a novel capped β-cyclodextrin bearing a 6A,6D-dideoxy-N,N′-3,6,9-trioxa-undecanoyl-(L,L)-bis-alanyl bridge are described. The chiral recognition properties of the product towards Dns-amino acids have been examined by capillary electrophoresis.
Two novel benzo-15-crown-5 tethered -cyclodextrins 1 and 2have been synthesized by coupling substituted benzo-15-crown-5 with corresponding-cyclodextrin derivatives. Their inclusion complexation behavior withrepresentative guests, such as cyclohexanol, cyclohexane carboxylic acid, cyclohexaneacetic acid, sodium cyclohexane carboxylate, and potassium cyclohexane carboxylate,was investigated in aqueous solution by means of fluorescence spectrometry. As compared with parent -cyclodextrin, benzo-15-crown-5 tethered -cyclodextrins 1–2 display significantly enhanced molecular binding abilities and selectivities towards model substrates, especially towards substrates containing alkali-metal cations. These results indicate that, bearing two recognition sites in a single molecule, these supramolecular architectures can strongly enhance the molecular binding ability of parent -cyclodextrin by the cooperative binding of the -cyclodextrin cavity and the crown ether moiety. Possessing a shorter linker, crown ether--cyclodextrin 2 shows much higher binding affinity with guest molecules than crown ether--cyclodextrin 1, which may be attributed to the binding size and molecular multiple recognition behavior between host and guest.
The solution of a new synthesized compound, mono-6-(1'-benzo-aza-15-crown-5)-2, 3, 6- permethyl-β-cyclodextrin, in the moderately
polar polysiloxane OV-1701 was coated onto fused silica capillary column. The chromatographic characteristics including column
efficiency, polarity and selectivity were studied. Excellent selectivity for the separation of enantiomers and positional
isomers was obtained. The results show that the combined effect between the special caves of β-cyclodextrin and crown ether
plays a significant role in the separation.
a b s t r a c t Azophenol dyes 1–5 having the permethylated cyclodextrin and/or crown moieties have been synthe-sized. Compounds 1 and 2 provide critical information for discrimination among 1 –3 amines by unique color changes. Addition of 1 and 2 amines to solutions of 1 or 2 in chloroform shifts the absorbance maximum of the initial solutions from 380 nm to w580 nm and w530 nm, respectively, but no change is observed with 3 amines. The high selectivity of 1 is mainly due to H-bonding between the ammonium H atoms of the amine and oxygen atoms of the crown-6. The selectivity of 1 possessing the b-cyclodextrin moiety toward amines was higher than that of 2 possessing the a-cyclodextrin moiety. On the other hand, chloroform solutions of 3 or 4, which lack the crown ether moiety, changed from yellow (380 nm) to pink (500 nm) with the addition of 1 and 2 amines, but with no selectivity. These results indicate that the crown unit in 1 or 2 plays an important role in discriminating among the types of amines.
The addition of an achiral crown ether (18-crown-6) to a cyclodextrin-based separation can significantly affect the capillary electrophoresis (CE) enantioresolution of organic racemates that contain a primary amine functional group. In most cases an enhancement of the enantioseparation was observed. However, there are also cases where the addition of 18-crown-6 was detrimental to a cyclodextrin-based CE enantioseparation. The effect of concentration of the two complexing additives as well as the effect of pH and added potassium ion were examined. A specific three-body complex involving simultaneous, dual inclusion complex formation can be used to explain both the enhanced and diminished enantioselectivities observed when 18-crown-6 is added to the run buffer.
Enantiomer separation by electrochromatography employing modified cyclodextrins as stationary phases is performed in two ways. (i) Polysiloxane-linked permethylated beta-cyclodextrin (Chirasil-Dex 1) or related selectors are coated and immobilized onto the inner surface of a capillary column. Enantiomer separation is performed in the open tube and the method is referred to as open-tubular capillary electrochromatography (o-CEC). (ii) Silica-linked native beta-cyclodextrin, permethylated beta-cyclodextrin (Chira-Dex 2) or hydroxypropyl-beta-cyclodextrin are filled into a capillary column and the bed is secured by two frits. Enantiomer separation is performed in a packed column and the method is referred to as packed capillary electrochromatography (p-CEC). In a unified instrumental approach, method (i) as well as method (ii) can be operated both in the electro- and pressure-driven modes (o-CEC vs. open-tubular liquid chromatography (o-LC) and p-CEC vs. p-LC). It is demonstrated that the electro-driven variant affords higher efficiencies at comparable elution times. Employing a single open-tubular column coated with Chirasil-Dex 1, a unified enantioselective approach can be realized in which the same selectand is separated using all existing chromatographic modes for enantiomers, i.e., gas chromatography (GC), super-critical fluid chromatography (SFC), o-LC and o-CEC. As the chiral selector is utilized as a stationary phase, an additional chiral selector may be added to the mobile phase. In the resulting dual chiral recognition systems, enhancement of enantioselectivity (matched case) or compensation of enantioselectivity (mismatched case) may be observed. The overall enantioselectivity is dependent on the sense of enantioselectivity of the selectors chosen and their influence on the electrophoretic and electroosmotic migration of the enantiomers of a selectand.
IntroductionThe Inclusion Phenomena of CyclodextrinsOrigin of Microvessels as Molecular FlasksOrganic Reactions Mediated by CD in WaterConclusion
References
The extraction of (135)Cs from high activity waste arising from reprocessing of spent fuel can be achieved by using calix[4]arene crown compounds. The radiolytic degradation of calix[4]arene crowns as well as their solvent, o-nitrophenyloctyl ether (NPOE), was studied using electrospray ionization mass spectrometry (ESI-MS) (that formed Cs(+) or Na(+) adducts) in nitric acid, as well as by chemical ionization tandem mass spectrometry (MS/MS) experiments. The structures of major degradation products were identified with MS and specifically labelled nitric acid. Although NPOE and calix[4]arene crowns alone are relatively stable, under simulated conditions resembling the real industrial processes involving radiolysis in the presence of nitric acid, several products resulting from nitration and oxidation were observed.
Two bonded chiral stationary phases (CSPs), 8-aminoquinoline-2-ylmethyl- and 8-aminoquinoline-7-ylmethyl-diaza-18-crown-6-capped [3-(2-O-beta-cyclodextrin)-2-hydroxypropoxy]propylsilyl silica particles (non-porous, 1.5 microm), have been prepared and evaluated using capillary liquid chromatography at high pressures (> or = 8000 p.s.i.). High column efficiency (up to 400 000 plates m(-1)) was achieved for chiral separations. These CSPs with two recognition sites, i.e. substituted-diaza-18-crown-6 and beta-cyclodextrin combined with high chromatographic efficiency provide good resolution of a variety of enantiomers and positional isomers in relatively short times under reversed-phase conditions. After inclusion of a Ni (II) ion from the mobile phase, the positively charged crown ether-capped beta-cyclodextrin facilitates specific static, dipolar, and host-guest complexation interactions with solutes.
In order to quantitatively investigate their molecular binding ability, a series of cyclodextrin-crown ether conjugates containing beta-cyclodextrin (beta-CyD) and crown ether units, i.e.N-(benzoaza-15-crown-5)acylaminomethylene tethered 6-diethylenetriamino-6-deoxy-beta-CyD, N-(benzoaza-15-crown-5)acylaminomethylene tethered 6-triethylenetetraamino-6-deoxy-beta-CyD and 4',5'-dimethylene-benzo-15-crown-5 tethered 6-diethylenetriamino-6-deoxy-beta-CyD, have been prepared as ditopic molecular receptors. Their inclusion complexation behavior with four representative fluorescent dyes, i.e. ammonium 8-anilino-1-naphthalenesulfonate (ANS), sodium 6-toluidino-2-naphthalenesulfonate (TNS), acridine red (AR) and rhodamine B (RhB), has been comprehensively investigated in aqueous NaH2PO4/Na2HPO4 or KH2PO4/K2HPO4 buffer solution (pH 7.20) by means of circular dichroism, fluorescence, and 2D NMR spectra. The results indicate that the self-assembly of crown ether modified beta-CyD mediated by potassium ion exhibits a dimeric structure, which significantly enhances the original binding ability and molecular selectivity of parent beta-CyD and its derivatives towards guest molecules through the cooperative binding of two hydrophobic CyD cavities with one guest. This cooperative binding mode of K+/CyD-crown ether systems are further confirmed by Job's experiments and 2D NMR investigations. Attributed to the positive contributions from the metal-ligated crown ether cap and K+-mediated dimerization of CyDs, the binding constant (Ks) values of CyD-crown ether conjugates toward ANS are 10-83 times higher than that of beta-CyD. The increased binding ability and molecular selectivity of CyD-crown ether conjugates are discussed from the viewpoints of size/shape-fit and multiple recognition mechanism.
[reaction: see text] Azophenol dyes having the permethylated cyclodextrin and/or crown moieties have been synthesized. Compound 1 provides critical information on discriminating 1-3 degrees amines with unique color changes. Addition of 1 degrees and 2 degrees amines to 1 shifts the absorbance maximum of 1 from 380 to approximately 580 and approximately 530 nm, respectively, but no change is observed with 3 degrees amines. The high selectivity of 1 is mainly due to H-bonding between the ammonium H atoms of the amine and oxygen atoms of the crown-6.