共查询到20条相似文献,搜索用时 546 毫秒
1.
Na'il Saleh Mohammed A. Meetani Leena Al-Kaabi Indrajit Ghosh 《Supramolecular chemistry》2013,25(9):650-656
The supramolecular interactions of the ocular drug tropicamide (TR) with cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solutions by using 1H NMR, ESI-MS and UV–vis spectroscopic techniques. The results indicate a 1:1 binding stoichiometry of TR with CB7 and CB8. The binding constants of TR in its protonated form were higher (e.g. K = 4 × 106 M? 1 with CB8) than in its neutral form (e.g. K = 1.4 × 104 M? 1 with CB8), which led to a complexation-induced increase in its pK a value of ca. 0.5 and 2 units with CB7 and CB8, respectively. In the presence of about 1% (w/v) CB8, the ionisation degree of 0.1% (w/v) TR was increased from 2% to 62% at neutral pH. The increase in the pK a value and thus stabilisation of the protonated TR species at neutral pH is discussed in the context of supramolecular drug delivery of ophthalmologic drugs. 相似文献
2.
Jing Wu Lyle Isaacs Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11675-11680
Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the formation of purple‐colored CB[7] ? cis‐ 1? 2 H+ and CB[7] ? cis‐ 3? 2 H+ complexes, respectively. The high binding affinity and selectivity displayed by CB[7] toward 1 and 3 pays the >10 kcal mol?1 thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large pKa shifts and high pH responsiveness, which are characteristic of cucurbit[n]uril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4 – 10 . This indicator displacement assay is capable of quantifying the pseudoephedrine ( 5 ) content in Sudafed tablets over the 5–350 μM range. 相似文献
3.
André Seco Dr. Shilin Yu Dr. Arnaud Tron Dr. Nathan D. McClenaghan Prof. Fernando Pina Prof. A. Jorge Parola Dr. Nuno Basílio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16512-16522
A linear double pyridinium-terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV-Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensitive. Switching from the neutral chalcone to the cationic flavylium form upon irradiation at 365 nm under acidic conditions provided an enhanced CB7 association (K1:1 increases from 1.2×105 M−1 to 1.5×108 M−1), limiting spontaneous on-thread cucurbituril shuttling. This co-conformational change in the [2]pseudorotaxane is reversible in the dark with kobs=4.1×10−4 s−1. Threading the flavylium moiety into CB7 leads to a dramatic increase in the fluorescence quantum yield, from 0.29 in the free axle to 0.97 in the [2]pseudorotaxane and 1.0 in the [3]pseudorotaxane. 相似文献
4.
Controlling the Reactivity of the SeSe Bond by the Supramolecular Chemistry of Cucurbituril 下载免费PDF全文
Huifeng Ren Zehuan Huang Dr. Hui Yang Prof. Huaping Xu Prof. Xi Zhang 《Chemphyschem》2015,16(3):523-527
We describe a new strategy to control the reactivity of Se?Se bond by using supramolecular chemistry of cucurbituril. We have demonstrated that selenocystamine (SeCy) and cucurbit[6]uril (CB[6]) can form a stable supramolecular complex (Ka=5.5×106 M ?1). Before complexation, the free Se?Se bond in SeCy is rather sensitive to redox stimuli and gets disrupted quickly with addition of reductant or oxidant. However, after binding with CB[6], the Se?Se bond becomes quite inert and hardly reacts with reductant or oxidant. One advantage of this supramolecular protection is that it can be applied in a wide pH range from weakly acidic to basic. Additionally, the supramolecular complex formed by SeCy and CB[6] can be reversibly dissociated simply with addition of Ba2+. 相似文献
5.
The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method. Titration of CB[8] into a solution of Proflavine results in a 95% decrease in fluorescence up to a CB[8] to Proflavine ratio of 2:1. From the induced fluorescence spectra a binding constant of 1.9 × 107 M? 1 was determined. When Proflavine is titrated into a solution of CB[8] a similar binding constant is calculated (1.3 × 107 M? 1). Titration of CB[6] into a solution of Proflavine yields a decrease in fluorescence of 18–20%, but no binding is observed beyond what is seen within experimental error. Finally, titration of CB[7] into a solution of Proflavine results in an increase in fluorescence (32%) and a blue-shift of the emission wavelength from 509 nm to 485 nm. From the induced fluorescence spectra a binding constant of 1.65 × 107 M? 1 was determined. From 1H NMR it appears that the decrease in fluorescence for Proflavine with CB[6] and CB[8] is due to collisional quenching, whereas the increase in fluorescence with CB[7] may be due to rotational restriction. 相似文献
6.
The complexation behaviors of acridine red (AR), neutral red (NR) and rhodamine B (RhB) dye guest molecules by three kinds of supramolecular hosts, including β-cyclodextrin (β-CD), calix[4]arene tetrasulfonate (C4AS) and cucurbit[7]uril (CB[7]), have been investigated by means of fluorescence spectra in aqueous citrate buffer solution (pH 6.0). The results obtained show that the three hosts, possessing different types of cavity, lead to various complexation-induced fluorescence of dye guests, and present different binding ability and molecular selectivity. The complexation stability constants decrease in the order of NR > AR > RhB for C4AS and CB[7] hosts, while in the order of RhB > AR > NR for β-CD host. Particularly, CB[7] displays the strongest binding ability with NR (K S = 33300 M? 1), and provides the molecular selectivity of 4.8 for NR/AR pairs. Although the binding ability of C4AS for present dye guests is weaker than CB[7], but the molecular selectivity of the two hosts are nearly equivalent. β-CD shows stronger binding ability with RhB (K S = 5880 M? 1) as comparison with CB[7] and C4AS. Furthermore, the solvent effects and salt effects during the course of complexation have also been investigated. 相似文献
7.
Nial J. Wheate Virendra Vora Nahoum G. Anthony Fiona J. McInnes 《Journal of inclusion phenomena and macrocyclic chemistry》2010,68(3-4):359-367
The potential use of cucurbit[7]uril (CB[7]) as an excipient in oral formulations for improved drug physical stability or for improved drug delivery was examined with the antituberculosis drugs pyrazinamide (pyrazine-2-carboxamide) and isoniazid (isonicotinohydrazide). Both drugs form 1:1 host–guest complexes with CB[7] as determined by 1H nuclear magnetic resonance spectrometry, electrospray ionisation mass spectrometry and molecular modelling. Drug binding is stabilised by hydrophobic effects between the pyridine and pyrazine rings of isoniazid and pyrazinamide, respectively, to the inside cavity of the CB[7] macrocycle as well as hydrogen bonds between the hydrazide and amide groups of each drug to the CB[7] carbonyl portals. At pH 1.5, isoniazid binds CB[7] with a binding constant of 5.6 × 105 M?1, whilst pyrazinamide binds CB[7] at pH 7 with a much smaller binding constant (4.8 × 103 M?1). Finally, CB[7] prevents drug melting through encapsulation. Where previously pyrazinamide displays a typical melting point of 189 °C and isoniazid 171 °C, by differential scanning calorimetry, no melting or degradation at temperatures up to 280 °C is observed for either drug once bound by CB[7]. 相似文献
8.
Dr. Liping Cao Dr. Marina Šekutor Dr. Peter Y. Zavalij Prof. Dr. Kata Mlinarić‐Majerski Prof. Dr. Robert Glaser Prof. Dr. Lyle Isaacs 《Angewandte Chemie (International ed. in English)》2014,53(4):988-993
Host?guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by 1H NMR spectroscopy and X‐ray crystallography. 1H NMR competition experiments revealed that CB[7]? 6 is among the tightest monovalent non‐covalent complexes ever reported in water with Ka=7.2×1017 M ?1 in pure D2O and 1.9×1015 M ?1 in D2O buffered with NaO2CCD3 (50 mM ). The crystal structure of CB[7]? 6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe3+ groups of 6 (7.78 Å), which allows it to establish 14 optimal ion‐dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the C?O portals within the CB[7]? 6 complex, and the co‐linearity of the C7 axis of CB[7] with the N+???N+ line in 6 . This work further blurs the lines of distinction between natural and synthetic receptors. 相似文献
9.
Cucurbit[7]uril: A High‐Affinity Host for Encapsulation of Amino Saccharides and Supramolecular Stabilization of Their α‐Anomers in Water 下载免费PDF全文
Yoonjung Jang Dr. Ramalingam Natarajan Dr. Young Ho Ko Prof. Dr. Kimoon Kim 《Angewandte Chemie (International ed. in English)》2014,53(4):1003-1007
Cucurbit[7]uril (CB[7]), an uncharged and water‐soluble macrocyclic host, binds protonated amino saccharides (D ‐glucosamine, D ‐galactosamine, D ‐mannosamine and 6‐amino‐6‐deoxy‐D ‐glucose) with excellent affinity (Ka=103 to 104 M ?1). The host–guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI‐TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D ‐mannosamine, are bound as α‐anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D ‐galactosamine hydrochloride (Ka=1.6×104 M ?1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α‐anomer by the host. 相似文献
10.
Mhejabeen Shaikh Sharmistha Dutta Choudhury Dr. Jyotirmayee Mohanty Dr. Achikanath C. Bhasikuttan Dr. Werner M. Nau Prof. Haridas Pal Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12362-12370
The effect of the macrocyclic host, cucurbit[7]uril (CB7), on the photophysical properties of the 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI) dye have been investigated in aqueous solution by using ground‐state absorption and steady‐state and time‐resolved fluorescence measurements. All three prototropic forms of the dye (cationic, neutral, and anionic) form inclusion complexes with CB7, with the largest binding constant found for the cationic form (K≈2.4×106 M ?1). At pH≈4, the appearance of a blue emission band upon excitation of the HPBI cation in the presence of CB7 indicates that encapsulation into the CB7 cavity retards the deprotonation process of the excited cation, and hence reduces its subsequent conversion to the keto form. Excitation of the neutral form (pH≈8.5), however, leads to an increase in the keto form fluorescence, indicating an enhanced excited‐state intramolecular proton‐transfer process for the encapsulated dye. In both the ground and excited states, the two pKa values of the HPBI dye show upward shifts in the presence of CB7. The prototropic equilibrium of the CB7‐complexed dye is represented by a six‐state model, and the pH‐dependent changes in the binding constants have been analyzed accordingly. It has been observed that the calculated pKa values using this six‐state model match well with the values obtained experimentally. The changes in the pKa values in the presence of CB7 have been corroborated with the modulation of the proton‐transfer process of the dye within the host cavity. 相似文献
11.
Hui Yang Yebang Tan Jingcheng Hao Huabiao Yang Fawen Liu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(10):2135-2142
A novel side‐chain polypseudorotaxanes P4VBVBu/CB[7] was synthesized from poly‐N‐n‐butyl‐N′‐(4‐vinylbenzyl)‐4,4′‐bipyridinium bromide chloride (P4VBVBu) and cucurbit [7]uril (CB[7]) in water by simple stirring at room temperature. CB[7] beads are localized on viologen units in side chains of polypseudorotaxanes as shown by 1H NMR, IR, XRD, and UV–vis studies, and it is considered that the hydrophobic and charge‐dipole interactions are the driving forces. TGA data show that thermal stability of the polypseudorotaxanes increases with the adding of CB[7] threaded. DLS data show that P4VBVBu and CB[7] could form polypseudorotaxanes, and the average hydrodynamic radius of the polypseudorotaxanes increases with increasing the concentration of CB[7]. The typical cyclic voltammograms indicate that the oxidation reduction characteristic of P4VBVBu is remarkably affected by the addition of CB[7] because of the formation of polypseudorotaxanes and the shielding effects of CB[7] threaded on the viologen units of polypseudorotaxanes. With the increase of the concentration of KBr or K2SO4, the formation of the polypseudorotaxanes was inhibited due to the shielding effects of both Br? or SO to viologen ion and K+ to CB[7] by UV–vis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2135–2142, 2010 相似文献
12.
Jinglin Tan Zhiman Liao Cuiping Tian Jufang Shao 《Journal of inclusion phenomena and macrocyclic chemistry》2018,90(1-2):143-147
Inclusion complexes of α,ω-bisimidazolium oligosiloxane (Im-PDMS) and cucurbit[7]uril (CB[7]) in aqueous solution were studied. The binding interactions were monitored by 1H NMR. Their annular aggregate morphologies were confirmed by TEM. The aggregation behavior of free Im-PDMS and Im-PDMS in 10?4 CB[7] were investigated using surface tension measurement. 相似文献
13.
The effect of cucurbit[7]uril (CB7) on the spiropyran‐merocyanine photochromic interconversion was studied in acidic and alkaline aqueous solutions. The merocyanine (MC) isomer was found to be the thermodynamically most stable form both in water and in the presence of CB7. A preferential binding of the protonated merocyanine (MCH+) to CB7 was observed with an equilibrium constant of 7.4 × 104 m ?1, and the complex formation led to significant diminution of acidity of the guest. The photoinduced transformation of MCH+ to the spiropyran isomer was accelerated 2.3‐fold upon addition of CB7, whereas the rates of the other photochromic processes were not affected. The partial inclusion of MCH+ in CB7 led to dual fluorescence due to the incomplete deprotonation in the singlet‐excited state. 相似文献
14.
Xuzhuo Sun Bo Li Jin Cao Jing Chen Ning Wang Dongjin Wan Haibo Zhang Xiaohai Zhou 《中国化学》2012,30(4):941-946
A pseudorotaxane of cucurbit[6]uril (CB[6]) with guest molecule N,N′‐hexamethylenebis (pyrazinyl perchlorate) (BPHP) was synthesized and characterized by 1H NMR spectra, IR, single crystal X‐ray diffraction analysis and thermogravimetric analysis. The structure of the pseudorotaxane (CB[6]·BPHP) is stabilized by host‐guest hydrogen bonds. Self‐assembly of the pseudorotaxane produces infinite one‐dimensional and two‐dimensional networks with intermolecular hydrogen bonds. In the molecular packing of the CB[6]·BPHP, ClO4?(H2O)2 water clusters serve as bridges to associate these pseudorotaxanes and form three‐dimensional networked pseudopolyrotaxane. 相似文献
15.
Liping Cao 《Supramolecular chemistry》2014,26(3-4):251-258
We determined the relative binding constants (Krel) for guests 1–19 towards cucurbit[7]uril by 1H NMR competition experiments in 100 mM Na3PO4-buffered D2O. In these experiments, we use guest 11 as the reference guest because of its strong binding towards CB[7] and its advantageous spectroscopic properties (e.g. slow exchange on NMR timescale and distinct resonances for key protons). To convert the determined Krel values to absolute binding constants, we performed a direct UV–vis titration of 1 with CB[7] to determine Ka for CB[7]√1. The trends in the determined values of Krel and Ka are discussed with respect to the importance of the concentration of metal ions in the buffer, the influence of hydroxyl groups located at the portals or inside the CB[7] cavity, geometry of the guest (e.g. regioisomers), the number of guest C atoms and secondary electrostatic interactions. 相似文献
16.
In the presence of cucurbit[7]uril (CB[7]), the CB[7] could react with palmatine, which served as a sensitive fluorescence probe, to form host‐guest stable complexes and the fluorescence intensity of the complexes was greatly enhanced. The fluorescence intensity decreased linearly with an increasing number of L‐cystine in the inclusion system. The experimental results show that there exists a competition between L‐cystine and palmatine for the CB[7] hydrophobic cavity and L‐cystine occupies the space of CB[7] cavity, leading palmatine molecules to be forced to reside in the aqueous environment. Based on the fluorescence quenching of the CB[7]/palmatine complexes resulting from complex formation between CB[7] and L‐cystine, a spectrofluorimetric method for the determination of L‐cystine in aqueous solution in the presence of CB[7] was developed. The linear relationship between the corresponding values of the fluorescence quenching ΔF and L‐cystine concentration was obtained in the range of 6.0 to 1.5×103 ng·mL?1, with a correlation coefficient (r) of 0.9996. The detection limit was 2.0 ng·mL?1. The application of the present method to the determination of L‐cystine in tablets gave satisfactory results. This paper also discussed the mechanism of the fluorescence indicator probe. 相似文献
17.
Wanhua Lei Dr. Guoyu Jiang Dr. Qianxiong Zhou Dr. Yuanjun Hou Prof. Baowen Zhang Prof. Xuexin Cheng Prof. Xuesong Wang 《Chemphyschem》2013,14(5):1003-1008
Nanoscaled coordination polymers based on biologically prevalent ions have potential applications in drug delivery and biomedical imaging. Herein, coordination polymer nanoparticles of anionic porphyrins, including meso‐tetra(4‐carboxyphenyl)‐porphyrin (H2TCPP4?) and meso‐tetra(4‐sulfonatophenyl)‐porphyrin (H2TPPS4?), and alkaline or alkaline earth metal cations, such as K+ and Ca2+, were constructed in aqueous solution in the presence of cucurbit[7]uril (CB7) or cucurbit[8]uril (CB8). UV/Vis absorption and fluorescence spectroscopy, dynamic light scattering (DLS), scanning electron spectroscopy (SEM), and atomic force microscopy (AFM) were applied to explore the assembly and particle formation of porphyrin anions and metal cations mediated by CBn. The particle size depends on the kinds of CBn and metal cations and their concentrations. The uptake of H2TPPS4? particles by tumor cells (A549 cells) was found to be more efficient than H2TPPS4? at 37 °C, showing the application potential of such assembled particles in biology and medicine. 相似文献
18.
Guest–host inclusion complexes between 6-benzyladenine (6-BA), cucurbit[7]uril (Q[7]), symmetrical tetramethylcucurbit[6]uril (TMeQ[6]) and meta-hexamethyl-substituted cucurbit[6]uril (HMeQ[6]) in aqueous solution were investigated by 1H NMR, UV absorption spectroscopy and phase solubility studies. The 1H NMR spectra analysis revealed that the hosts selectively bound the phenyl moiety of the guests. Absorption spectroscopic analysis defined the stability of the host–guest inclusion complexes. A host:guest ratio of 1:1 was measured quantitatively as (5.63 ± 0.26) × 104, (1.94 ± 0.17) × 103 and (2.89 ± 0.23) × 103 mol L? 1 for the Q[7]-6-BA, TMeQ[6]-6-BA and HMeQ[6]-6-BA systems, respectively. Phase solubility diagrams were analysed through rigorous procedures to obtain estimates of the complex formation constants for Q[n]-6-BA complexation. The formation constants were (1.29 ± 0.24) × 104 L mol? 1 for Q[7]-6-BA, (3.20 ± 0.17) × 103 L mol? 1 for TMeQ[6]-6-BA and (3.52 ± 1.01) × 103 L mol? 1 for TMeQ[6]-6-BA. Furthermore, phase solubility studies showed that 6-BA solubility increased as a function of Q[7], TMeQ[6] and HMeQ[6] concentrations. The thermodynamic parameters of the complex formation were also determined. The formation of inclusion complexes between 6-BA and Q[7] was enthalpy controlled, suggesting that hydrophobic and van der Waals interactions were the main driving forces. Our results demonstrated that the complexation of 6-BA with Q[n] could be used to improve the solubility of 6-BA. 相似文献
19.
Ruibing Wang Ian W. Wyman Shihao Wang Donal H. Macartney 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(3-4):233-237
Inclusion of a biological photosensitizer and prototype of β-carbolines, norharmane (NHM), into the cavity of cucurbit[7]uril (CB[7]) has been investigated for the first time, by using 1H NMR and UV–visible spectroscopy, and ab initio calculations. Protonated NHM forms a very stable host–guest complex with CB[7] in aqueous solution, with a binding constant of (9.0 ± 0.5) × 104 M?1. The encapsulation of NHM into CB[7] has driven the prototropic equilibrium of NHM to protonated NHM (NHMH+) at neutral pH. A pH titration for the host–guest complex revealed a moderate shift of the acid–base equilibrium in the ground-state (from 7.2 to 7.9), which may be caused by the low polarity microenvironment of the CB[7] cavity. The CB[7] provides a binding pocket for the hydrophobic molecule, and the polar, carbonyl-lined portals offering an anchoring site for the positive charge of the cationic species NHMH+. 相似文献
20.
Suhang He Chan Zhou Haibo Zhang Xiaohai Zhou 《Journal of inclusion phenomena and macrocyclic chemistry》2013,76(3-4):333-344
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]. 相似文献