Binary and Ternary Copper(II) Complexes with NIPAAm/IA Copolymers and Aminoacids: Interpretation of UV‐Visible Spectra and Cyclic Voltammograms

The complex formations of homopolymers and copolymers of poly(N‐isopropyl acrylamide) (PNIPAAm), polyacrylamide (PAAm) and poly(itaconic acid) (PIA) with Cu(II) ions in aqueous solutions were studied by using UV‐visible spectra in the region of 200–1100 nm and cyclic voltammograms between ?0.800 V and 0.600 V. According to the optical and electrochemical spectra of the polymer‐ and copolymer‐Cu(II) complexes and their ternary complexes with alanine, i.e., absorptions and the shifts in the wavelength of the maximum absorptions, currents and potentials of the peaks in the pH range of 3–12, the intensities of anodic and cathodic peak currents of polymers containing IA groups decrease with increasing pH and they show maximum absorptions at lower wavelengths than do the homopolymers used in this work. The peak point of the visible band shifts from 800 to 650 nm, with increasing pH, while the intensity of the third anodic peak observed after pH=4 increases in the case of both Ala‐Cu(II) and its ternary solution with P(NIPAAm‐co‐IA, 9.8 mol%). Both the pH‐dependent shifts of maximum absorptions and the appearence of the third anodic peaks as the pH raised were interpreted as a presence of tetracoordinated Cu(II) complexes in the solution and on the electrode surface, involving combined carboxyl, amide and amine interaction.     

Metal ion complexation in acetonitrile by cone,di-ionised calix[4]arene-1,2-crown ethers with two pendant dansyl fluorophores

Four cone calix[4]arene-1,2-crown ethers each with two ionisable side arms containing dansyl groups are synthesised. The crown ether ring on the lower rim is varied from crown-4 to crown-5 with hydrogen or tert-butyl groups on the para position of the upper rim. Di(tetramethylammonium) salts of the di-ionised ligands are utilised for spectrofluorimetric titration experiments in MeCN. The influence of alkali metal, alkaline earth metal and selected transition and heavy metal (Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) cations on the spectroscopic properties of the two dansyl groups linked to the lower rim of the conformationally locked, di-ionised calix[4]arene-1,2-crown ether frameworks is investigated by emission spectrophotometry. All of the metal cations induce red shifts in the emission spectra of the di-ionised ligands. The metal cations produce enhancement or quenching of the fluorescence emissions. Changes in the fluorescence emission as a function of the metal cation identity, the lower rim crown ether ring size and the absence or presence of upper rim tert-butyl groups are investigated.     

Molecular Chirality Recognized by Achiral Compounds

Abstract

Three cases are described where chirality is recognized by achiral molecules, where chirality is induced into achiral compounds through interactions with chiral compounds, and lastly where induced chirality in the solid-state is utilized for an enantio-selective photoreaction. In the first instance, the thermodynamically and kinetically preferred diastereoisomer of an optically labile chromium complex depended on the nature of the achiral solvent. In the second case, for the first time 1,2-chloroethane was trapped and observed in a chiral near-eclipsed form and 1-chloropropane in the truly eclipsed form at room temperature in a 1:1 inclusion complex with an optically active host molecule. Finally, induced chirality in a prochiral compound in the solid-state was successfully employed in an enantio-selective photoreaction. In the two cases, solid-state CD provided valuable information.     

Influence of amidoammonium calix[4]resorcinarenes on methyl orange protolytic equilibrium: supramolecular indicator systems

Here, we report on the study of cationic amidoammonium calix[4]resorcinarenes 1–5 of various lipophilicity capable of binding acid–base indicator methyl orange (MO). We identified the contributions of macrocycle aggregation and conformational mobility in the binding of MO. The effective pK_a values of bound MO systematically decrease as the size and the packing density of the aggregates increase with an increase in calixresorcinarene lipophilicity. Consideration of a series of macrocycles clearly shows that large aggregates form most stable complexes, binding guests not on individual level but as aggregates. It was found that the most stable MO complex with 5 is formed due to electrostatic binding with ammonium groups of the macrocycle and incapsulation of MO in a hydrophobic layer of the aggregates. We have shown that competitive binding of MO and cationic surfactants by aggregates of 5 is suitable for visual/spectrophotometric detection of colourless anionic substrates.     

Inclusion Interactions of Cucurbit[7]uril with Adenine and its Derivatives

Interactions of cucurbit[7]uril (Q[7] host) with guest adenine (g1), adenosine (g2) and 2′,3′-o-isopropylideneadenosine (g3) were studied in details by ¹H NMR, UV absorption spectroscopy, fluorescence spectroscopy and high performance liquid chromatography (HPLC) methods. We found that the suitable pH range for interaction was between 1 and 7, and the optimal pH range was between 2 and 4. The ¹H NMR analysis indicated that Q[7] selectively interacted with the adenine moiety of the guests g1 and g2, while Q[7] selectively interacted with the D-ribose sugar ring moiety of the guest g3. Moreover, ¹H NMR spectra showed that the exchange between the bound guest and the free guest was fast on the NMR time scale for the Q[7]-g1 and Q[7]-g2 systems. However, an obvious equilibrium between the bound host/guest and the unbound host/guest were observed in the Q[7]-g3 complex. Several methods were used to determine quantitatively the stability of the three host–guest inclusion complexes formed between Q[7] and the guests. The formation constants by UV and fluorescence were 1.90 × 10⁵ L mol^? 1 and 1.34 × 10⁵ L mol^? 1 for Q[7]-g1, 9.41 × 10⁴ L mol^? 1 and 4.24 × 10⁴ L mol^? 1 for Q[7]-g2, 4.50 × 10⁴ L mol^? 1 and 3.62 × 10⁴ L mol^? 1 for Q[7]-g3, respectively. HPLC method was also introduced to explore the interactions between Q[7] and the adenine and its derivatives. The formation constants of the host–guest inclusion complexes, as determined by HPLC, were 6.76 × 10⁴ L mol^? 1 for Q[7]-g1, 1.80 × 10⁴ L mol^? 1 for Q[7]-g2, 3.01 × 10⁴ L mol^? 1 for Q[7]-g3 respectively. Our study suggested that Q[7] could be a suitable host for the delivery of bioactive molecules, such as the adenine and its derivatives.     

Dimerisation and complexation of 6-(4′-t-butylphenylamino)naphthalene-2-sulphonate by β-cyclodextrin and linked β-cyclodextrin dimers

This study shows that stereochemical factors largely determine the extent to which 6-(4′-t-butylphenylamino)-naphthalene-2-sulphonate, BNS^?  and its dimer, (BNS^? )₂, are complexed by β-cyclodextrin, βCD, and a range of linked βCD dimers. Fluorescence and ¹H NMR studies, respectively, show that BNS^?  and (BNS^? )₂ form host–guest complexes with βCD of the stoichiometry βCD.BNS^?  (10^? 4 K ₁ = 4.67 dm³ mol^? 1) and βCD.BNS₂ ^2 ?  (10^? 2 K ₂′ = 2.31 dm³ mol^? 1), where the complexation constant K ₁ = [βCD.BNS^? ]/([βCD][BNS^? ]) and K ₂′ = [βCD. (BNS^? )₂]/([βCD.BNS^? ][BNS^? ]) in aqueous phosphate buffer at pH 7.0, I = 0.10 mol dm³ at 298.2 K. (The dimerisation of BNS^?  is characterised by 10^? 2 K _d = 2.65 dm³ mol^? 1.) For N,N-bis((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)succinamide, 33βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂su, N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)succinamide, 66βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂ur, and N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)urea, 66βCD₂ur, the analogous 10^? 4 K ₁ = 11.0, 101, 330, 29.6 and 435 dm³ mol^? 1 and 10^? 2 K ₂′ = 2.56, 2.31, 2.59, 1.82 and 1.72 dm³ mol^? 1, respectively. A similar variation occurs in K ₁ derived by UV–vis methods. The factors causing the variations in K ₁ and K ₂ are discussed in conjunction with ¹H ROESY NMR and molecular modelling studies.     

Synthesis and anion binding of 2-arylazo-meso-octamethylcalix[4]pyrroles

2-Arylazo-5,5,10,10,15,15,20,20-octamethylcalix[4]pyrroles (azo-OMCPs) have been synthesised by the reaction of calix[4]pyrrole with aryldiazonium chloride in 15–45% yields. The solution-state binding studies of the synthesised hosts were investigated by absorption spectroscopy and ¹H NMR in DMSO and CDCl₃, respectively. These receptors, appended with electron-donating and electron-withdrawing groups, displayed enhanced affinity and selectivity for fluoride anion. Well-defined colour change in the visible region of the spectrum was observed upon addition of fluoride ion in DMSO solution of azo-OMCPs. Detailed NMR studies in CDCl₃ revealed that azo-OMCPs with nitro and chloro groups have higher binding affinity for fluoride ion.

     

Chromogenic amides of pyridine-2,6-dicarboxylic acid as anion receptors

The synthesis of simple, chromogenic pyridine-2,6-dicarboxylic acid amides, derivatives of isomeric nitroanilines and aminonitrophenols, and their ion binding properties are described. The ligands' response to ionic species was examined by naked eye and was studied with the use of UV–vis spectroscopy in DMSO and its mixture with water. The effect of the localisation and the type of the substituents in aromatic rings were discussed. ¹H NMR experiments were carried out to probe the mechanism of anion recognition, i.e. complexation via hydrogen bond formation versus ligand deprotonation. A selective response of N,N′-bis(2-hydroxy-4-nitrophenyl)pyridine-2,6-dicarboxamide (L5) towards dihydrogen phosphate was found in both DMSO and DMSO–water (95:5) solvent mixture. The structure of N,N′-bis(2-hydroxy-5-nitrophenyl)pyridine-2,6-dicarboxamide (L4) was confirmed by X-ray crystallography.