Biquinolino-modified beta-cyclodextrin dimers and their metal complexes as efficient fluorescent sensors for the molecular recognition of steroids

A series of bridged beta-cyclodextrin (beta-CyD) dimers possessing functional tethers of various lengths was synthesized in moderate yield by the treatment of 2,2'-biquinoline- 4,4'-dicarboxylic dichloride with beta-CyD or mono[6-oligo(ethylenediamino)-6-deoxy]-beta-CyDs. The products were 2,2'-biquinoline-4,4'-dicarboxy-bridged bis(6-O-beta-CyD) (8), N,N'-bis(2-aminoethyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (9), and N,N'-bis(5-amino-3-azapentyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (10). The reaction of 8-10 with copper perchlorate give their copper(II) complexes 11-13 in satisfactory yields of over 77 %. All the bis(beta-CyD)s 8-13 act as efficient fluorescent sensors and display remarkable fluorescence enhancement upon addition of optically inert steroids. The inclusion complexation behaviors of 8-13 when treated with the representative steroids cholate (14), deoxycholate (15), and glycocholate (16) in aqueous solution at 25 degrees C were investigated by means of UV/Vis spectroscopy, conductivity and fluorescence measurements, circular dichroism spectroscopy, and 2D NMR spectroscopy. The tether length of bis(beta-CyD) 9 allows it to adopt a cooperative host-tether-guest binding mode in which the spacer and guest are co-included in the two CyD cavities. As a result of this cooperation, 9 has a stability constant (K(s)) about 2x10(2) times higher than that of monomodified beta-CyD 4 for inclusion complexation with cholate. Metallooligo(beta-CyD)s with four beta-CyD units have enhanced binding abilities compared with monomodified beta-CyDs. These metallo compounds have binding affinities for guest steroids that are up to 50-4.1x10(3) times higher than those of CyDs 2-4. The guest-induced fluorescence enhancement of bis(CyD)s opens a new channel for the design of sensor materials. The complex stability constants of these compounds are discussed from the viewpoint of induced-fit interaction and cooperative multiple binding between host and guest.     

Thermodynamics of molecular recognition of bile salts by 3,6'-(oligoethylenediamino-bridged) beta-cyclodextrin dimers

The molecular recognition behaviors of some representative bile salts by three 3,6'-bridged beta-cyclodextrin dimers with oligo(ethylenediamino) linkers in different lengths, i.e. 3,6'-(ethylenediamino-bridged) beta-cyclodextrin dimer (1), 3,6'-(diethylenetriamino-bridged) beta-cyclodextrin dimer (2), and 3,6'-(triethylenetetraamino-bridged) beta-cyclodextrin dimer (3), were investigated in aqueous phosphate buffer solution (pH 7.20) at 25 degrees C by means of 2D NMR spectroscopy and isothermal titration microcalorimetry. Owing to the cooperative host-linker-guest binding mode between host and guest, these 3,6'-bridged beta-cyclodextrin dimers showed significantly enhanced binding abilities and molecular selectivities as compared with native beta-cyclodextrin through the simultaneous contributions of hydrophobic, hydrogen bond, and electrostatic interactions. Thermodynamically, the inclusion complexations of these beta-cyclodextrin dimers with bile salts were mainly driven by large enthalpic gain, accompanied by slight to moderate entropic loss. An enthalpy-entropy compensation analysis demonstrated that these beta-cyclodextrin dimers experienced large conformational changes and extensive desolvation effect upon inclusion complexation with guest molecules.     

Dipyrrolyl quinoxalines with extended chromophores are efficient fluorimetric sensors for pyrophosphate

2,3-Di(pyrrole-2-yl)quinoxaline anion sensors with extended chromophores display dramatic enhancement in fluorescence intensity (sensing output), increased affinity for inorganic anions as well as strong selectivity for pyrophosphate over phosphate anion.     

Molecularly imprinted polymer using beta-cyclodextrin as functional monomer for the efficient recognition of bilirubin

Bilirubin (BR) imprinted polymer was successfully prepared using supramolecular host compound β-cyclodextrin (β-CD) as functional monomer. The adsorption equilibrium was attained in about 4 h, which indicated that the adsorption kinetics was comparatively fast. The results of adsorption and selectivity experiments indicated that BR-imprinted β-CD polymer was able to bind BR specifically and reversibly. The specific recognition of BR-imprinted β-CD polymer for BR may be due to the cooperative effects of inclusion interaction and hydrogen bonding. This BR-imprinted β-CD polymer was further applied to eliminate BR in human serum sample. It was verified that the binding specificity of the BR-imprinted polymer for BR was essentially sufficient in the presence of other compounds coexisting in serum sample. Therefore, as a reusable material possessing high affinity and selectivity, BR-imprinted β-CD polymer has a potential application perspective as a clinical hemoperfusion material.     

8-hydroxyquinoline derivatives as fluorescent sensors for magnesium in living cells

Despite the key role of magnesium in many fundamental biological processes, knowledge about its intracellular regulation is still scarce, due to the lack of appropriate detection methods. Here, we report the spectroscopic and photochemical characterization of two diaza-18-crown-6 hydroxyquinoline derivatives (DCHQ) and we propose their application in total Mg(2+) assessment and in confocal imaging as effective Mg(2+) indicators. DCHQ derivatives 1 and 2 bind Mg(2+) with much higher affinity than other available probes (K(d) = 44 and 73 microM, respectively) and show a strong fluorescence increase upon binding. Remarkably, fluorescence output is not significantly affected by other divalent cations, most importantly Ca(2+), or by pH changes within the physiological range. Evidence is provided on the use of fluorometric data to derive total cellular Mg(2+) content, which is consistent with atomic absorption data. Furthermore, we show that DCHQ compounds can be effectively employed to map intracellular ion distribution and movements in live cells by confocal microscopy. A clear staining pattern consistent with known affinities of Mg(2+) for biological ligands is shown; moreover, changes in the fluorescence signal could be tracked following stimuli known to modify intracellular Mg(2+) concentration. These findings suggest that DCHQ derivatives may serve as new tools for the study of Mg(2+) regulation, allowing sensitive and straightforward detection of both static and dynamic signals.     

Highly enantioselective fluorescent recognition of amino acid derivatives by unsymmetrical salan sensors

Novel unsymmetrical salan fluorescent sensors 2a and 2b have been designed and synthesized. The chiral recognition of N-Boc-protected amino acids by 2a and 2b has been investigated. Sensor 2a possesses higher sensitivity and enantioselectivity than sensor 2b does. Job analysis and nonlinear regression results show that 2a can form a 1:1 stoichiometric complex with a N-Boc-protected amino acid. The obtained response selectivities and the association constants indicate that 2a is a highly enantioselective and sensitive fluorescent sensor toward N-Boc-protected amino acids.     

Molecular recognition thermodynamics of bile salts by beta-cyclodextrin dimers: Factors governing the cooperative binding of cyclodextrin dimers

The complex stability constants (K(S)), standard molar enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the inclusion complexation of two families of beta-cyclodextrin (beta-CD) dimers, i.e. beta-CD dimers Se1-Se4 bearing 2,2'-diselenobis(benzoyl) tether (Se-dimers) and beta-CD dimers Py1-Py4 bearing 2,2'-bipyridine-4,4'-dicarboxy tether (Py-dimers), with four bile salt guests, i.e. sodium cholate (CA), sodium deoxycholate (DCA), sodium glycocholate (GCA), and sodium taurocholate (TCA), were determined at 25 degrees C in Tris buffer solution (pH 7.4) at 298.15 K by means of isothermal titration microcalorimetry. The thermodynamic parameters obtained, together with the ROESY spectra of interactions between beta-CD dimers and bile salts, consistently suggest that the length, flexibility, and structure of spacers linking the two beta-CD cavities not only determine the binding modes but also significantly alter the molecular selectivity of beta-CD dimers.     

Effect of beta-cyclodextrin charge type on the molecular recognition thermodynamics of reactions with (ferrocenylmethyl)dimethylaminium derivatives

Complex stability constants (KS), standard molar enthalpic changes (DeltaH degrees ), and entropic changes (TDeltaS degrees ) for the inclusion complexations of native beta-cyclodextrin (1) and two oppositely charged beta-cyclodextrins, i.e., mono(6-amino-6-deoxy)- beta-cyclodextrin (2) and mono[6-O-6-(4-carboxylphenyl)]- beta-cyclodextrin (3), with two (ferrocenylmethyl)dimethylaminium derivatives, i.e., FC4+Br(-) and FC8+Br(-), were determined at 25 degrees C in aqueous phosphate buffer solution (pH 7.20) by means of isothermal titration microcalorimetry (ITC). Cyclic voltammetry studies showed that the ferrocene groups of the guests were included in the beta-cyclodextrin cavity to form host-guest complexes. As compared with neutral beta-cyclodextrin, the positively charged host 2 showed decreased binding toward (ferrocenylmethyl)dimethylaminium guests. This was attributed to electrostatic repulsion, while the negatively charged host 3 displayed increased binding due to electrostatic attractions. Thermodynamically, the ionization of host CDs affects both enthalpic and entropic changes of host-guest complexations presumably by changing the hydrophobicity and the desolvation effect of hosts upon inclusion complexation. Moreover, the solvent effect was also discussed from the viewpoint of thermodynamics.     

选择性识别儿茶酚胺的长波长二硼酸荧光探针

儿茶酚胺是人体中重要的神经递质.选择性识别儿茶酚胺对帕金森氏综合症、嗜铬细胞瘤、神经母细胞瘤等疾病临床诊断及病理学研究具有重要意义.2-(4-二羟基硼烷)苯基喹啉-4-羧酸(PBAQA)与糖结合后荧光强度增强,与儿茶酚胺结合后荧光强度下降,可以作为选择性识别儿茶酚胺的荧光探针.但由于发射波长较短,PBAQA及其衍生物在荧光成像方面存在诸多限制.本文作者采用廉价易得的原料制备中间体PBAQA,然后经酰胺缩合、脱保护,制备氨基中间体,再与3-羧基硼酸缩合合成二硼酸.目标化合物的发射波长明显红移至500 nm左右,斯托克位移超过100 nm.初步活性测试发现,目标化合物与儿茶酚胺结合后荧光强度明显降低,且荧光强度改变与儿茶酚胺浓度存在线性关系,可作为选择性识别儿茶酚胺的长波长荧光探针.     

Synthesis of bridged and metallobridged bis(beta-cyclodextrin)s containing fluorescent oxamidobisbenzoyl linkers and their selective binding towards bile salts

A series of beta-cyclodextrin (beta-CD) dimers containing fluorescent 2,2'-oxamidobisbenzoyl and 4,4'-oxamidobisbenzoyl linkers--that is, 6,6'-[2,2'-oxamidobis(benzoylamino)]ethyleneamino-6,6'-deoxy-bis(beta-CD) (2), 6,6'-[2,2'-oxamidobis(benzoylamino)]diethylenediamino-6,6'-deoxy-bis(beta-CD) (3), 6,6'-[4,4'-oxamidobis(benzoylamino)]ethyleneamino-6,6'-deoxy-bis(beta-CD) (4), and 6,6'-[4,4'-oxamidobis(benzoylamino)]diethylenediamino-6,6'-deoxy- bis(beta-CD) (5)--were synthesized from the corresponding oxamidobis(benzoic acid)s through treatment with mono[6-aminoethyleneamino-6-deoxy]-beta-CD or mono[6-diethylenetriamino-6-deoxy]-beta-CD. Further treatment of 2-5 with copper perchlorate gave their Cu(II) complexes 6-9 in satisfactory yields. The conformation and binding behavior of 2-9 towards two bile salt guests--sodium cholate (CA) and sodium deoxycholate (DCA)--was comprehensively investigated by circular dichroism, 2D NMR spectroscopy, and fluorescence spectroscopy in Tris-HCl buffer solution (pH 7.2) at 25 degrees C. Thanks to the cooperative host-linker-guest binding mode, the stoichiometric 1:1 complexes formed by bis(beta-CD)s 2-5 with bile salts gave high stability constants (KS values) of up to 10(3)-10(4) M(-1). Significantly, benefiting from the intramolecular 1:2 or 2:4 binding stoichiometry, the resulting complexes of metallobis(beta-CD)s 6-9 with bile salts gave much higher KS values of up to 10(6)-10(7) M(-2). The enhanced binding abilities of bis(beta-CD)s and metallobridged bis(beta-CD)s are discussed from the viewpoints of induced-fit interactions and multiple recognition between host and guest.     

Synthesis of bispyrenyl sugar-aza-crown ethers as new fluorescent molecular sensors for Cu(II)

Two N-pyrenylacetamide-substituted sugar-aza-crown ethers have been synthesized as new fluorescent chemosensors. The designed ligands 1 and 2 exhibit fluorescence characteristics of a pyrene monomer and a dynamic excimer emission when compared to N-pyrenylacetamide as a model compound. Both ligands displayed a Cu2+-sensitive fluorescence quenching with a 1:1 stoichiometry and high stability constants (log K = 6.7 for 1 and 7.8 for 2). The quenching effect was rationalized on the basis of photoinduced electron transfer from the excited pyrene to the complexed Cu2+ cation, while the changes in excimer-to-monomer ratio were explained by a conformational analysis through DFT calculations. The predicted structure suggests that the Cu2+ cation is coordinated with the two carbonyl groups and the sugar-aza-crown ethers which rigidified the complex structure and placed the two pyrene moieties far apart.     

Triple molecular recognition as a directing element in the formation of host-guest complexes with p-sulfonatocalix[4]arene and beta-cyclodextrin

We have investigated a mixture consisting of p-sulfonatocalix[4]arene (CX4), beta-cyclodextrin (beta-CD), and 2,3-diazabicyclo[2.2.2]oct-2-ene (1) and its bridgehead-substituted derivative (2) in the absence and presence of Zn(2+). In the absence of Zn(2+), four equally populated host-guest complexes exist in solution, as projected from their comparable binding constants (ca. 1000 M(-1)). However, upon the addition of Zn(2+), the formation of a ternary complex, CX4 x 1 x Zn(2+), is induced by a synergy of three supramolecular interactions (Coulombic, hydrophobic, and weak metal-ligand bonding). Concomitantly, the CX4 x 2 complex is destabilized by competitive binding, which drives the system toward a state where only two complexes predominate: namely, CX4 x 1 x Zn(2+) and beta-CD x 2. Known binding constants for the multiple equilibria were used to model the complex system, and the results were consistent with experimental data obtained from 1D and 2D NMR as well as induced circular dichroism (ICD) spectroscopy. The combined results demonstrate how a subtle interplay between cooperative and competitive binding can be exploited to design a complex multicomponent sorting system.     

Assembly of bionanostructures onto beta-cyclodextrin molecular printboards for antibody recognition and lymphocyte cell counting

The assembly of complex bionanostructures onto beta-cyclodextrin (betaCD) monolayers has been investigated with the aims of antibody recognition and cell adhesion. The formation of these assemblies relies on host-guest, protein-ligand, and protein-protein interactions. The buildup of a structure consisting of a divalent bis(adamantyl)-biotin linker, streptavidin (SAv), biotinylated protein A (bt-PA), and an Fc fragment of a human immunoglobin G (IgG-Fc) was studied with surface plasmon resonance (SPR) spectroscopy. Patterns of this bionanostructure were obtained via microcontact printing of the divalent linker at the molecular printboard, followed by the subsequent attachment of the proteins. Fluorescence microscopy showed that the buildup of these bionanostructures on the betaCD monolayers is highly specific. On the basis of these results, bionanostructures were made in which whole antibodies (ABs) were used instead of the IgG-Fc. These ABs were bound to the SAv layer via biotinylated protein G (bt-PG) or via a biotinylated AB. These constructions yielded specifically bound ABs with a less than maximal density, as shown by SPR spectroscopy and atomic force microscopy (AFM). Finally, the immobilization of ABs to the molecular printboard was used to create platforms for lymphocyte cell count purposes. Monoclonal ABs (MABs) were attached to the SAv layer using bt-PG, an engineered biotin functionality, or through nonspecific adsorption. The binding specificity of the immobilized cells was the highest on the buildup made from bt-PG, which is attributed to an optimized orientation of the antibodies. An approximately linear relationship between the numbers of seeded cells and counted cells was demonstrated, rendering the platform potentially suitable for lymphocyte cell counting.     

A novel chiral terpyridine macrocycle as a fluorescent sensor for enantioselective recognition of amino acid derivatives

Terpyridine macrocycle 1 is shown to be a strong chelating agent for organic ammonium salts and also a useful chromophore in fluorescent sensing. It exhibits very good enantioselectivity (K(obs)(S)/K(obs)(R)= 3.8) in chiral discrimination of alpha-phenylglycine methyl ester hydrochloride (PhEtOMe).     

Highly enantioselective fluorescent sensor for chiral recognition of amino acid derivatives

A highly enantioselective fluorescent sensor, containing benzylaminomethyl groups at 3,3′-position of 1,1′-bi-2-naphthol (BINOL), has been used to conduct the chiral recognition of α-amino acid derivatives. It is observed that one enantiomer of N-Boc-proline can increase the fluorescence intensity of the binaphthyl fluorophores by over 57-fold, while the other enantiomer can cause only sixfold fluorescence enhancement. Such unusually highly enantioselective response demonstrates that this sensor is potentially useful in the enantioselective recognition of amino acid derivatives.     

Covalently immobilized aminonaphthalimide as fluorescent carrier for the preparation of optical sensors

By replacing the hydrogen of the 4-amino group of a 4-amino-1,8-naphthalimide derivative with an N-acryloxyethyl group, the fluorophore has been covalently immobilized on an optical sensor surface by UV photopolymerization. The optical sensor obtained can be used for the determination of picric acid. The linear range and detection limit of the sensor are 9.80x10(-7)-1.96x10(-4) mol L(-1) and 7.1x10(-7) mol L(-1), respectively. Leaching of the fluorophore from the membrane is effectively prevented by covalent immobilization, resulting in a sensor with a relatively long lifetime. The response time of the sensor is short, and the reproducibility and reversibility are good. The sensor has been used for the indirect determination of the chloroquine content of pharmaceutical tablets.     

Novel and highly efficient bifunctional calixarene thiourea derivatives as organocatalysts for enantioselective Michael reaction of nitroolefins with diketones

New bifunctional calixarene thiourea organocatalysts were synthesized and applied in catalytic asymmetric Michael addition of acetylacetone to various nitroolefins at room temperature. The corresponding adducts were obtained in good to excellent yields with excellent enantioselectivities (up to 92% ee). The present research demonstrates the advantages of incorporating two stereocontrolling structures into a single catalyst. Notably, it offers a simple and convenient doubly stereocontrolled approach for the catalytic asymmetric synthesis of a chiral organic molecule.     

Optimization of the molecular orbital energies of conjugated polymers for optical amplification of fluorescent sensors

Cationic water-soluble poly(fluorene-co-phenylene)s with electron withdrawing or donating substituents on the conjugated backbone were designed and synthesized. Fluorescence resonance energy transfer (FRET) experiments between these conjugated polymers and dye-labeled single-stranded DNA (ssDNA-C*) reveal the importance of matching donor and acceptor orbital energy levels to improve the sensitization of C* emission. Quenching of polymer fluorescence with ssDNA-C* and differences in C* emission suggest involvement of photoinduced charge transfer (PCT) as an energy wasting mechanism. The HOMO and LUMO energy levels of the conjugated polymers and C serve as a preliminary basis to understand the competition between FRET and PCT. Dilution of C in polymer/ssDNA-C complexes by addition of ssDNA yields insight into C*...C self-quenching. Under optimized conditions, where there is no probe self-quenching and minimum PCT, efficient signal amplification is demonstrated despite poor spectral overlap between polymer and C.