Site specific Co(III) sarcophagine binding in multi-component phosphonium and p-sulfonatocalix[4]arene systems

Co(III) sarcophagine-type cage molecules, [Co(diCLsar)](3+) or [Co(HONOsar)](3+), form either 1 : 1 or 1 : 2 host-guest inclusion complexes with mono-phosphonium cations and sodium p-sulfonatocalix[4]arene in the solid state yielding complex I [p-sulfonatocalix[4]arene·Co(diCLsar)·2{benzyltriphenylphosphonium}], complex II [2{p-sulfonatocalix[4]arene}·Co(diCLsar)·3{tetraphenylphosphonium}] and complex III [p-sulfonatocalix[4]arene·Co(HONOsar)·tetraphenylphosphonium]. The diversity of the structural types of these multi-component systems, including the orientation of the Co(III) molecules in the cavities of the calixarenes, depends on the nature of their terminal functional groups. The secondary coordination interactions binding between the Co(III) molecules and p-sulfonatocalix[4]arene have also been investigated in water using NMR techniques.     

磺化杯[4]芳烃与双正电荷季铵盐的键合作用

采用核磁波谱和等温微量热滴定等手段研究了磺化杯[4]芳烃与3个双正电荷季铵盐相互作用的键合比、 键合模式以及热力学参数. 结果表明, 磺化杯[4]芳烃与3个双正电荷季铵盐以不同的键合模式形成1: 1络合物, 其键合常数均超过10⁵ L/mol, 键合作用主要由焓变驱动, 同时伴随着微弱的正负熵变.     

Highly effective binding of methyl viologen dication and its radical cation by p-sulfonatocalix[4,5]arenes

The binding behaviors and thermodynamic origins of p-sulfonatocalix[4]arene (C4AS) and p-sulfonatocalix[5]arene (C5AS) with methyl viologen (MV2+) have been investigated by the methods of isothermal titration calorimetry, NMR, and cyclic voltammetry, showing that the binding abilities of C4AS and C5AS and their host selectivity are dramatically pH-controlled, which is closely discussed from the viewpoint of thermodynamics. Moreover, the radical form of MV+* can also be effectively included by C4AS and C5AS.     

Binding of inorganic cations by p-sulfonatocalix[4]arene monitored through competitive fluorophore displacement in aqueous solution

A new working principle for detecting inorganic cation binding by water-soluble calix[4]arenes involves the displacement of a fluorescent azoalkane as guest. Fluorescence regeneration is observed for various metal ions, and binding of monovalent cations (alkali and ammonium) to p-sulfonatocalix[4]arene is detected and quantified for the first time.     

Interplay of p-sulfonatocalix[4]arene and crown ethers en route to molecular capsules and "Russian dolls"

Diffusion-ordered (1)H NMR spectroscopy techniques have been used to determine the binding strength of p-sulfonatocalix[4]arene (SO(3)[4]) towards a number of charged crown ether species in aqueous conditions. For several (doubly) charged (di)azacrown ethers, all were bound by SO(3)[4] either well or very well with binding constants between 5.1 x 10(2)-9.9 x 10(5) M(-1). These results correlate with, and thus explain the phenomenon of rapid capture of azacrown ethers in molecular capsules based on p-sulfonatocalix[4]arene and lanthanide metals. Similarly, the formation of "Russian doll" superanions in the solution phase is also elucidated. These superanions have been shown to selectively crystallise particular polynuclear aquated metal ions from mixtures in the aqueous phase. Neutral [18]crown-6 is not bound by p-sulfonatocalix[4]arene and displays a binding constant of 0 M(-1). When sodium [18]crown-6 is examined in a similar fashion, binding by SO(3)[4] is observed in solution with K(a) approximately 3.1 x 10(3) M(-1).     

Study on Interaction of L-Tryptophan with p-Sulfonatocalix[4]arene by Spectrofluorometry

A variety of analytical techniques have been employed to investigate the interaction of calixarene with amino acids including 1HNMR1, MALDI-MS2 and calorimetric titration3. Furthermore, spectrofluorometry is another excellent method for its convenience an…     

Lanthanide-induced helical arrays of [{Co(III) sepulchrate} intersection {p-sulfonatocalix[4]arene}] supermolecules

In the presence of lanthanide ions, a Co(III) sepulchrate cation [Co(diHOsar)]3+ and sodium p-sulfonatocalix[4]arene form a 1:1 host-guest complex which is self-assembled into a zeolite-like lattice network comprised of parallel, single stranded helices.     

Calix[4]arene based molecular probe for sensing copper ions

A novel calix[4]arene based molecular probe for metal ions has been designed, synthesized and evaluated. Studies on its binding with different metal ions reveal a noticeable naked eye color change, bathochromic shift in absorption spectrum and remarkable enhancement in fluorescence emission in the presence of Cu²⁺ only. The role of calix[4]arene scaffold for selective recognition of Cu²⁺ has been demonstrated by repeat evaluation and analysis of an appropriate reference molecule. A rational explanation for fluorescence enhancement in 3 on interaction with copper has been suggested.     

The electrochemical behaviour of [Co(sep)]3+ bound with p-sulfonatothiacalix[4]arene and tetracarboxy-p-sulfonatocalix[4]arene in correlation with inclusive and non-inclusive binding modes

The comparative study of the ion-pairing of Co(III) sepulchrate ([Co(sep)]³⁺) with p-sulfonatothiacalix[4]arene and p-sulfonatocalix[4]arene tetracarbonic acid by ¹H NMR and pH-metric data in solution and X-ray data in solid state elucidates pH dependent effect of carboxylate groups on the stoichiometry and the mode of the ion pairing. The electrochemical data of [Co(sep)]³⁺ bound with both calix[4]arenes have been analyzed in the correlation with stoichiometry and the mode of their binding. The pH-dependent effect of tetracarboxy-p-sulfonatocalix[4]arene on the electrochemical behavior of [Co(sep)]³⁺ has been found to correlate with the participation of carboxylate groups in the host?Cguest binding.     

Methodology for the calculation of the potential of mean force for a cation-pi complex in water.

We report potential of mean force (PMF) calculations on the interaction between the p-sulfonatocalix[4]arene and a monovalent cation (Cs(+)). It has been recently shown from microcalorimetry and (133)Cs NMR experiments that the association with Cs(+) is governed by favourable cation-pi interactions and is characterized by the insertion of the cation into the cavity of the macrocycle. We show that the PMF calculation based upon a classical model is not able to reproduce both the thermodynamic properties of association and the insertion of the cation. In order to take into account the different contributions of the cation-pi interactions, we develop a new methodology consisting of changing the standard PMF by an additional contribution resulting from quantum calculations. The calculated thermodynamic properties of association are thus in line with the microcalorimetry and (133)Cs NMR experiments and the structure of the complex at the Gibbs free-energy minimum shows the insertion of the cation into the cavity of the calixarene.     

Capture of di-protonated [2.2.2]cryptand in the cavity of two p-sulfonated calixarenes as part of 2-D bi-layer lanthanide coordination polymers

Treating p-sulfonatocalix[4]arene with lanthanide ions, Ln3+ (Ln = Ce, Nd, Sm and Eu), in the presence of [2.2.2]cryptand results in a 2-D bi-layer coordination polymer with axially elongated diprotonated cryptand in the cavity of two p-sulfonatocalix[4]arenes.     

Thermodynamic origins of selective binding affinity between p-sulfonatocalix[4,5]arenes with biguanidiniums

The binding geometries, abilities and thermodynamic parameters for the intermolecular complexation of two water-soluble calixarenes, p-sulfonatocalix[4]arene (SC4A) and p-sulfonatocalix[5]arene (SC5A), with biguanidinium guests, metformin (MFM) and phenformin (PFM), were investigated by (1)H and 2D NMR spectroscopy, X-ray crystallography, and isothermal titration calorimetry (ITC). The obtained results show that biguanidinium guests are captured by calixarenes with the alkyl or aromatic portion immersed into the cavities and the guanidinium portion fixed at the upper-rims. At both acidic and neutral conditions, SC4A always presents stronger binding affinities to biguanidinium guests than SC5A. Moreover, SC4A prefers to include MFM rather than PFM. As a result, the binding selectivity of MFM is up to 44.7 times for the SC4A/SC5A hosts. The intrinsic relationship between binding structures and selectivities were comprehensively analyzed and discussed from the viewpoint of thermodynamics. Finally, the ITC measurements were further performed in phosphate buffer instead of aqueous solution, to examine the buffer effects, counterion effect, and the differences between thermodynamic and apparent association constants.     

Investigation on the supramolecular recognition behaviour of sulfonatocalix[6]arene with amino benzoic acid isomers

The formation of the complexation behaviour of host molecules water-soluble p-sulfonatocalix[6]arene (C6AS) with amino benzoic acid (ABA) isomers including o-amino benzoic acid (OABA), m-amino benzoic acid (MABA), and p-amino benzoic acid (PABA) – three guest molecules – has been studied by fluorescence spectrophotometric and nuclear magnetic resonance (NMR) spectroscopy. Experimental conditions including the concentration of C6AS and medium acidity were investigated in detail. The results showed that C6AS forms 1:1 complexes with amino benzoic isomers in water. Their stability constants determined by steady-state fluorescence measurement showed that C6AS has stronger recognition with PABA than with OABA or MABA. Moreover, their stability constants of C6AS complexing with three kinds of guest molecules were the largest at pH = 4.0, indicating C6AS has the strongest recognition ability with the dipolar ion of amino benzoic isomers. In addition, to obtain information about the binding model of the interaction, ¹HNMR studies were carried out. The related mechanism is proposed to explain the complexation processes.     

新型杯[4]芳烃氨基苯酚类衍生物的合成及对La3 的选择性识别

设计合成了下缘连有氨基苯氧基结构的杯[4]芳烃衍生物:5,11,17,23-四叔丁基-25-[2-(2-氨基苯氧基)乙氧基]-27-(2-羟基乙氧基)-26,28-二羟基杯[4]芳烃(化合物C),增加了与阳离子的结合位点,有利于通过配位作用对金属离子进行识别。化合物C的结构通过红外光谱、1H NMR、13C NMR和质谱进行了表征。通过紫外可见光谱和荧光发射光谱对化合物C与24种金属阳离子的络合作用进行了研究,结果发现,其对La3+有特殊的识别作用,化合物C与La3+的络合比为1∶1。     

Binding of monovalent metal cations by the p-sulfonatocalix[4]arene: experimental evidence for cation-pi interactions in water

Gibbs free energies, enthalpies and entropies for the binding of Na+, K+, Rb+, Cs+, Ag+, Tl+ and NH4+ by the p-sulfonatocalix[4]arene in water are determined by microcalorimetry. Whereas no significant heat effect is detected with Na+ or Ag+, suggesting that these cations are not complexed, weak but selective binding is observed with the other cations. The whole set of thermodynamic parameters, which demonstrate that the cations bind inside the cavity of the calixarene, evidence the importance of the cation-pi interactions for these complexes in water.     

Exploiting phenyl embraces and pi-stacking in the assembly of arrays of tetraphenylphosphonium p-sulfonatocalix[4]arene

Phenyl embraces involving tetraphenylphosphonium cations feature in complexes of p-sulfonatocalix[4]arene where a phenyl ring of a cation is included in the cavity of the calixarene. The overall structures are based on pseudo-polymorphic supramolecular arrays and their formation is templated or induced by lanthanide ions.     

Determination of Tryptophan using a p-Sulfonated Calix [4,6,8]arene Modified Gold Electrode

The ability of p-sulfonated calix[n]arenes (n = 4, 6, 8) to form complexes with tryptophan was studied. The electrochemical properties of these complexes immobilized on gold surfaces were examined by cyclic voltammetry. Parameters affecting the performance of the modified electrodes including the arene concentration, scan rate, applied potential, and pH were optimized. Under the optimal conditions, the method had a linear response to tryptophan between 1 × 10^?7 M and 1 × 10^?5 M with a detection limit of 3 × 10^?8 M. The interaction of the tryptophan–p-sulfonated calix[4]arene complex was more stable than the tryptophan–p-sulfonated calix[6]arene and p-sulfonated calix[8]arene complexes. Molecular modeling calculations indicated that electrostatic interactions and structural matching effects were predominant stabilizing factors. The modified electrodes demonstrated good reproducibility and high selectivity, illustrating their effectiveness for analytical measurements.     

Design and Synthesis of Calixarene‐Based Bis‐alkynyl‐Bridged Dinuclear AuI Isonitrile Complexes as Luminescent Ion Probes by the Modulation of Au⋅⋅⋅Au Interactions

Two calixarene‐based bis‐alkynyl‐bridged Au^I isonitrile complexes with two different crown ether pendants, [{calix[4]arene‐(OCH₂CONH‐C₆H₄C≡C)₂}{Au(CNR)}₂] (R=benzo[15]crown‐5 ( 1 ); R=benzo[18]crown‐6 ( 2 )), together with their related crown‐free analogue 3 (R=C₆H₃(OMe)₂‐3,4) and a mononuclear gold(I) complex 4 with benzo[15]crown‐5 pendant, have been designed and synthesized, and their photophysical properties have been studied. The X‐ray structure of the ligand, calix[4]arene‐(OCH₂CONH‐C₆H₄C?CH)₂ has been determined. The cation‐binding properties of these complexes with various metal ions have been studied using UV/Vis, emission, ¹H NMR, and ESI‐MS techniques, and DFT calculations. A new low‐energy emission band associated with Au???Au interaction could be switched on upon formation of the metal ion‐bound adduct in a sandwich fashion.     

Synthesis of a functionalised calix[4]arene and its interactions with hemicucurbit[6,7]urils and cucurbit[8]uril

In the present work, we synthesised a functionalised calix[4]arene with 5,11-di(N-methyl-E-(4-pyridylethylene) moiety (CX[4]), and investigated interactions of it with HemiMeQ[6], HemiMeQ[7], and Q[8]) in both water and DMSO using fluorescence spectrophotometry and ¹H NMR spectroscopy. Titration ¹H NMR spectra revealed that Q[n]s prefers to include the N-methyl-E-(4-pyridylethylene) moiety. In particular, the interaction of CX[4] with Q[8] in water resulted in intense fluorescence emission, and this interaction system can respond to compounds such as amantadine.