Alkyl Ammonium Ion Selectivity of Hexahomotrioxacalix[3]arene Triamide Derivative having the Intramolecular Hydrogen-Bonding Group

The lower rim functionalized hexahomotrioxacalix[3]arene triamide 4 with cone-conformation was synthesized from triol 1 by a stepwise reaction. The different extractability for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane is discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups in triamide 4, its affinity to metal cations was weakened. Triamide 4 shows a single selectivity to n-BuNH₃⁺. The anion complexation of triamide 4 was also studied by ¹H NMR titration experiments. Triamide 4 binds halides through the intermolecular hydrogen bonding among the NH hydrogens of amide in a 1:1 fashion in CDCl₃. The association constants calculated from these changes in chemical shifts of the amide protons are K_a = 223 M⁻¹ for Cl⁻ and K_a = 71.7 M⁻¹ for Br⁻. Triamide 4 shows a preference for Cl⁻ complexation than Br⁻ complexation.     

Heteroditopic receptors tris(2-pyridylamide) derivatives derived from hexahomotrioxacalix[3]arene triacetic acid

The lower rim functionalized cone-hexahomotrioxacalix[3]arene tris(2-pyridylamide) derivatives cone- 3 and cone-7 having the hydrogen bonding groups and 2-pyridyl groups were synthesized from triol 1 by a stepwise reaction. Extraction data for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane are discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups, their affinities to metal cations were weakened. The complexation modes of cone-3 and cone -7 with n-BuNH₃Cl and AgSO₃CF₃ were also demonstrated by ¹H NMR titration in CDCl₃. Tris(2-pyridylamide) derivatives cone-3 and cone-7 can complex with n-butyl ammonium ion and silver cation at the same time to form the heteroditopic complexation.     

Synthesis, Conformational Studies and Inclusion Properties of Tetrakis[(2-pyridylmethyl)oxy]thiacalix[4]arenes

An attempted O-alkylation of the flexible macrocycle 1with 2-(chloromethyl)pyridine in the presence of Cs₂CO₃ under THF reflux afforded a mixture of twoconformers of tetra-O-alkylated product 4a in a ratio of 91:9 (cone-4a:1,2-alternate-4a)in 70% yield, while other possible isomers were not observed. In the case of Na₂CO₃, there was no reaction product,only the starting compound 1, whereasonly monoalkylated compound 3 was obtained when usingK₂CO₃ as the base. The distribution of cone conformer decreased in the case of O-alkylation of tetraol 1with 4-(chloromethyl)pyridine or benzyl bromide in the presence of Cs₂CO₃ in comparison with that ofO-alkylation with 2-(chloromethyl)pyridine, while the 1,2-alternate conformer increased in the same sequence. The larger Cs⁺might increase the contribution of the metal template effect, which can hold the 2-pyridylmethyl group(s) and theoxide group(s) on the same side of the tetrathiacalix[4]arene 1 through the cation-O^- and -N-interaction in the caseof O-alkylation of tetraol 1 with 2-(chloromethyl)pyridine.Only when the template metal can hold the 2-pyridyl group(s) andthe oxide group(s) on the same side of the tetrathiacalix[4]arene is the conformation immobilized to thecone. The template effect of the cesium cation plays an important role in this alkylation reaction. The structuralcharacterization of these products is also discussed.The two-phase solvent extraction data indicated thattetrakis[(2-pyridylmethyl)oxy]thiacalix[4]arenes 4a show strong Ag⁺ affinity and a high Ag⁺ selectivity wasobserved for cone-4a. A good Job plot proves 1:1 coordination of cone-4a with Ag⁺ cation.¹H-NMR titration of cone-4a with AgSO₃CF₃ also clearly demonstrates that a 1:1complex is formed with retention of the original symmetry. In contrast, the 1,2-alternate-4a can form a 2:1 metal/thiacalix[4]arene complex and the two metal-binding sites display positive allostericity. The conformational changes ofpyridine moiety from the original outward orientation of the ring nitrogen to the inside orientation toward thethiacalixarene cavity were observed in the processof Ag⁺ complexation.     

Alkyl Ammonium Ion Selectivity of Hexahomotrioxacalix[3]arene Triamide Derivative having the Intramolecular Hydrogen-Bonding Group

The lower rim functionalized hexahomotrioxacalix[3]arene triamide 4 with cone-conformation was synthesized from triol 1 by a stepwise reaction. The different extractability for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane is discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups in triamide 4, its affinity to metal cations was weakened. Triamide 4 shows a single selectivity to n-BuNH ₃ ⁺ . The anion complexation of triamide 4 was also studied by ¹H NMR titration experiments. Triamide 4 binds halides through the intermolecular hydrogen bonding among the NH hydrogens of amide in a 1:1 fashion in CDCl₃. The association constants calculated from these changes in chemical shifts of the amide protons are K _a = 223 M^?1 for Cl^? and K _a = 71.7 M^?1 for Br^?. Triamide 4 shows a preference for Cl^? complexation than Br^? complexation.     

Synthesis and Ion Selectivity of Tetrakis[(N,N-dialkylaminocarbonyl) methoxy]homocalix[4]arenes

An attempted O-alkylation of the flexible macrocycle 1 withN,N-dialkylchloroacetamides in the presence of NaH, K₂CO₃ or Cs₂CO₃ gave only one pure stereoisomer 1,4-alternate-2a–c, while other possible isomers were not observed. In contrast, only an intractable mixture was obtained when Na₂CO₃ was used as base. The structural characterization of these products is discussed. The two-phase solvent extraction data indicated that tetrakis(N,N-dialkylaminocarbonyl) derivatives 2b–c show strong alkali metal cation affinity and the extractabilities are much higher than that for the corresponding calix[4]arene tetraethyl ester 4 and homocalix[4]arene tetraethyl ester 3. High Li⁺ and Na⁺ extractabilities were observed for tetrakis[(N,N-diethylaminocarbonyl) derivative 2b. However, no significant high ion selectivity for alkali metal cations was observed in tetraamide 2b. ¹H-NMR titration of tetraamide 2b with KSCN clearly demonstrates that a 1:1 complex is formed with retention of theoriginal symmetry to be conformationally frozen on the NMR time scale.     

Crown-ether styryl dyes

The surface enhanced Raman scattering (SERS) spectra of styryl dyes containing a crown-ether group and a heteroaromatic residue with sulfoalkyl (1a) or alkyl (1b)N-substituent and of their complexes with Mg²⁺ cations were recorded in the 10^–4–10^–8 mol L^–1 concentration range. A model for the interaction of compoundsla,b with a silver surface during their adsorption on an electrochemically treated electrode was suggested. Fastcis-trans relaxation of the adsorbed molecules1a,b and complexes (1a,b)Mg²⁺ was found. It was shown that at [1a] = 10^–5 mol L^–1 and moderate molar ratios (C _Mg/[1a] = 3/1 to 9/1) in acetonitrile solutions, (trans-1a)Mg²⁺ complexes are joined into head-to-tail type dimers. An excess of Mg²⁺ cations (C_Mg/[1a] > 100) leads to dissociation of the dimers yielding (trans-1a)(Mg²⁺)₂ complexes. The formation of dimers from complexes (trans-1a)Mg²⁺ is accompanied by a substantial distortion of the planar structure oftrans-1a. This may be an important factor influencing the efficiency of photocycloaddition involving dimers of (trans-1a)Mg²⁺.For part 15, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2429–2436, December, 1995.The work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 94-03-08760) and, to some extent, of INTAS (Grant No. 93-1829) and of the International Science Foundation (Grant No. MHAOOO).     

Synthesis and carboxylate anion binding studies on cyclic sugar-amino acid hybrids

Abstract

Here in, the condensation of boc-glycine with 2,6-anhydro-3,4,5-tri-O-benzyl-D-gluco-heptitol followed by its boc-deprotection to form 2,6-anhydro-3,4,5-tri-O-benzyl-D-gluco-heptitolyl bis-glycinate, which in turn on condensation with succinic acid/pyridine-2,6-dicarboxylic acid led to the formation of sugar-amino acid hybrid macrocyclic compounds 4, 6 and debenzylated marocyclic compound 5, having amide bonds that function as efficient host for polar, hydrogen bond acceptors and carboxylate ions. The anion inclusion capability of synthesized macrocylic hosts has been evaluated by the study of their binding with boc-GlyCOOˉ anion as guest through 1H NMR titration studies in CDCl₃. The binding constant (K_a) of boc-GlyCOOˉ guest with macrocyclic hosts 4 and 6 involving succinate and pyridine-2,6-dicarboxylate linkers was found to be 9.201?×?10³ and 1.437?×?10⁴ M^?1, respectively. The higher binding constant was observed in the complex of boc-GlyCOOˉ with pyridine-dicarboxylate containing host may be due to the extra rigidity & suitable conformation attained by the presence of rigid-aromatic dicarboxylate linker.     

New Tetrafunctionalized Cone Calix[4]arenes as Neutral Hosts for Anion Recognition

Abstract

The synthesis and anion binding properties of several new cone calix[4]arenes having different flexibility and tetrafunctionalized at the upper rim with various type of hydrogen bonding donor groups such as thioureas (1–3), trifluoroacetamides (4, 5) and perfluorinated alcohols (6) are reported. The results obtained show that thiourea receptors are the most effective in the complexation of all anions and that the rigid cone compound 2 is more efficient than the mobile cone analog 1 in the binding of spherical anions, whereas the reverse is true for the complexation of tetrahedral H₂PO₄ ^? anion.     

Crown-containing butadienyl dyes 8. Structures and complexation of chromogenic dithia-15(18)-crown-5(6) ethers

The structures of new butadienyl dyes of the benzothiazole series containing the dithia-15-crown-5 (2a) or dithia-18-crown-6 (2b) fragments were established by X-ray diffraction. Complexation of dyes 2a,b with Hg²⁺, Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, and alkaline-earth cations in aqueous-acetonitrile solutions was studied by spectrophotometry. At a high percentage of water in solutions (P _w ≈ 50%), these dyes have a very low ability to bind Pb²⁺ cations (logK < 2) and virtually do not bind Cd²⁺, Zn²⁺, and alkaline-earth cations. At the same time, these dyes form stable 1: 1 complexes with Hg²⁺ and Ag⁺ cations at all P _w. The stability constants of complexes with the Ag⁺ cation increase with increasing P _w because the free energy of hydration of this cation is much lower than the free energy of solvation in acetonitrile. In the P _w range from 0 to 75%, the stability constants of the complexes of dyes 2a,b with the Hg²⁺ cation are larger than those of the corresponding complexes with the Ag⁺ cation by more than four orders of magnitude. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 90–96, January, 2006.     

Synthesis and Complexation Abilities of Novel Multiple-Sites Calix[4]arene Receptors: Calix[4]arene Derivatives with Anthraquinone Groups on Lower Rims and Hydrazone Groups on Upper Rims

By formylation of 1,3-bisubstituted calix[4]arene anthraquinone derivative 1 in hexamethylenetetramine/trifluoroacetic acid system, the corresponding formylated gecalix[4]arene anthraquinone derivative 2 was synthesized in yield of 63%. By further reacting compound 2 with salicylic hydrazide, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, novel calix[4]arene derivatives with anthraquinone and hydrazone groups 3a–3d were obtained in yields of 74–83%. The extracting experiments for series of metallic cations showed that compounds 3a–3d possessed high extracting abilities and extracting selectivity for tested cations. The complexation UV-Vis spectra for a series of anions indicated compounds 3a–3d exhibited the strong complexation abilities for tested anions. The ¹H-NMR titration study showed that compound 3d possessed excellent complexation abilities for ion-pair of NaH₂PO₄ in 1:1 host-guest complex with the association constant of 4.6 × 10⁴ M^?1.     

Synthesis and Conformational Studies of Unnatural Pyrimidine Nucleosides

ABSTRACT

Starting from 3,4-di-O-acetyl-L-rhamnal (6) and thymine (7) the unsaturated nucleosides 1-(2′,3′,6′-trideoxy-4′-O-acetyl-α- and β-L-erythro-hex-2′-enopyranosyl)-thymine (8a and 8b) were prepared in anomerically pure form. In solution 8a was shown to be present in the ⁵ H _o and ⁰ H ₅ conformations, whereas the predominant conformation of 8b was ⁵ H _o. Chemical transformation of 8a and 8b led to the saturated nucleosides 1-(2′,3′,6′-trideoxy-α- and β-L-erythro-hexopyranosyl)thymine (10a and 10b, respectively), which were converted into 1-(4′-azido-2′,3′,4′,6′-tetradeoxy-α- and β-L-threo-hexopyranosyl)thymine (12a and 12b). Preliminary biological studies showed that 9b was inactive against the HIV-1 and HIV-2 viruses.     

A new trans-dioxorhenium(V) complex with 4-aminopyridine: synthesis,structure, electrochemical aspects,DFT, and TD-DFT calculations

The reaction of 1?:?4.4?M proportion of cis-[ReO₂I(PPh₃)₂] and 4-aminopyridine (ampy) in acetone–water gives trans-[ReO₂(ampy)₄]I·2H₂O (1a) in 85% yield. 1a has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, ¹H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of 1a reveals an octahedral trans dioxorhenium(V) complex with a “N₄O₂” coordination for rhenium. 1a has an orthorhombic space group C2221 with a?=?17.576(4), b?=?19.370(4), c?=?15.730(4) Å, V?=?5355(2) ų, and Z?=?8. Geometry optimization of the trans-O,O complex, 1a and its cis-O,O analog, 1b performed at the level of density functional theory reveal that 1a is more stable than 1b by 25?kcal M^–1 in the gas phase. The electronic spectrum of 1a was also analyzed at the level of time-dependent density functional theory. Excitation of 1a in methanol at 450?nm leads to a fluorescent emission at 505?nm with a quantum yield (Ф) of 0.04. Electrochemical studies of 1a in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618?V versus Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621?V versus Ag/AgCl.     

Synthesis and DFT calculations of oxido and phenylimido-rhenium(V) complexes incorporating the N,O donor ligand 2-[(2-hydroxyethylimino)methyl]phenol

The reactions of equimolar amounts of trans-[ReOC1₃(PPh₃)₂] or trans-[Re(NPh)(PPh₃)₂Cl₃] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H₂L) result in the formation of cis-[ReO(HL)PPh₃Cl₂] (1a) and trans-[Re(NPh)(HL)(PPh₃)Cl₂] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10^?4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b.     

Complexation and DFT studies of lanthanide ions by (2-pyridylmethoxy)homooxacalixarene derivatives

The binding of lanthanide cations by 2-pyridylmethoxy derivatives of p-tert-butyldihomooxacalix[4]arene (1b), in the cone conformation, and p-tert-butylhexahomotrioxacalix[3]arene (2b), in both cone and partial cone conformations, was studied. These properties were assessed by extraction studies of the metal picrates from water into dichloromethane and stability constant measurements in methanol and acetonitrile, using spectrophotometric and microcalorimetric techniques. Proton NMR titrations with La³⁺ and Yb³⁺ cations were done in order to get information on the binding sites. Computational methods (density functional theory (DFT) calculations) were also used to complement the NMR data. The p-tert-butylcalix[4]arene analogue (3b) was also studied, and the results of the four ligands were compared. Partial cone-2b is the best extractant for lanthanide ions, showing some preference for the heavy lanthanides. In complexation, all four ligands show the same trend and a high selectivity for Yb³⁺ (ML, log β ≥ 7). Besides the formation of ML complexes, ML₂ species were also obtained. In most cases, these species were corroborated by the proton NMR studies. For partial cone-2b with Pr³⁺ the complexation process is enthalpically driven, whereas for 3b the formation of the ML₂ species with this cation is due to a favourable entropy term. DFT studies indicate that ligand 3b forms the most stable complex with La³⁺, followed by partial cone-2b.     

Synthesis and physiochemical studies on binuclear Cu(II) complexes derived from 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

Preparation of the ligands HL¹ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL² = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL³ = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu₂L(OH)(H₂O)₂](ClO₄)₂.H₂O (L¹=1a, L² =1b, L³ =1c), acetato [Cu₂L(OAc)₂]ClO₄.H₂O (L¹ =2a, L² =2b, L³ =2c) and nitrito [Cu₂L¹(NO₂)₂(H₂O)₂]ClO₄.H₂O (L¹=3a, L² =3b, L³ =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.     

Complexation of fluoride anion and its ion pairs with alkali metal cations by tetra-substituted lower rim calix[4]arene tryptophan derivative

Abstract

Selective binding of fluoride anion and its alkali metal cation ion pairs by a fluorescent calix[4]arene (L) derivative bearing tryptophan moieties was studied in acetonitrile at 25 °C. It was found that LF^? and LF₂^2? complexes were formed and their stability constants were determined by means of UV and ¹H NMR titrations. Both amide and indole NH groups were involved in the stabilisation of the fluoride complexes, i.e. L afforded two anion-binding sites. ¹H NMR titrations provided evidence of simultaneous complexation of both Na⁺ cation and fluoride anion resulting in the formation of a ternary NaLF complex. In this ion pair complex, the Na⁺ cation was most probably bound primarily by the calixarene ether and amide oxygen atoms, whereas the indole NH groups interacted with the fluoride ion. A highly favourable ion pairing between Na⁺ and F^– in acetonitrile was studied using potentiometric measurements. The results pointed out the importance of fluoride pairing with alkali metal cations in aprotic organic solvents and the necessity of taking these reactions into account in the course of speciation studies of such solutions.     

Synthesis and Inclusion Properties of a Novel Thiacalix[4]arene-Based Hard–Soft Receptor with 1,3-Alternate Conformation

A novel ditopic receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with alkali metals and silver ion have been examined by ¹H NMR titration experiment. Although the formation of the heterogeneous dinuclear complexes was not observed, the exclusive formation of mononuclear complexes of 1,3-alternate-3 with metal cations is of particular interest in negative allosteric effect in the thiacalix[4]arene family. These findings demonstrate that preorganization, subtle conformational changes and affinity have a pronounced effect on the complexation process between the two different arms placed at the two edges of the thiacalix[4]arene cavity.     

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by o-, m-, p-amido and o-, m-, p-(amidomethyl)pyridine fragments as receptors for α-hydroxy- and dicarboxylic acids

A series of new p-tert-butyl thiacalix[4]arenes with o-, m-, p-amido and o-, m-, p-(amidomethyl)pyridine substituents at the lower rim in cone, partial cone, and 1,3-alternate conformations were synthesized. The ability of the obtained compounds to recognize the α-hydroxy (glycolic, tartaric) and dicarboxylic (oxalic, malonic, succinic, fumaric, and maleic) acids was investigated by UV-vis spectroscopy. Also, the efficiency and selectivity of binding, the association constants log K_a (10² to 10⁷ M⁻¹) and the stoichiometry were determined for the complexes of p-tert-butyl thiacalix[4]arenes with the acids. The receptors based on p-tert-butyl thiacalix[4]arenes with (amidomethyl)pyridine substitutes are most efficient in complexation in many cases.     

A comparison of the fragmentation pathways of [Cu(II)(Ma)(Mb)]•2+ complexes where Ma and Mb are peptides containing either a tryptophan or a tyrosine residue

[Cu^II(M_a)(M_b)]^?2+ complexes, where M_a and M_b are dipeptides or tripeptides each containing either a tryptophan (W) or tyrosine (Y) residue, have been examined by means of electrospray tandem mass spectrometry. Collision‐induced dissociations (CIDs) of complexes containing identical peptides having a tryptophan residue generated abundant radical cations of the peptides; by contrast, for complexes containing peptides having a tyrosine residue, the main fragmentation channel is dissociative proton transfer to give [M_a + H]⁺ and [Cu^II(M_b – H)]^?+. When there are two different peptides in the complex, each containing a tryptophan residue, radical cations are again the major products, with their relative abundances depending on the locations of the tryptophan residue in the peptides. In the CIDs of mixed complexes, where one peptide contains a tryptophan residue and the other a tyrosine residue, the main fragmentation channel is formation of the radical cation of the tryptophan‐containing peptide and not proton transfer from the tyrosine‐containing peptide to give a protonated peptide. Copyright © 2010 John Wiley & Sons, Ltd.     

Unexplored metallic cation effect in the acidity constants of p-t-butylthiacalix[4]arene,p-t-butylcalix[4]arene and p-t-butylcalix[6]arene in aqueous-organic media

The influence of the metallic cation of the base (Li⁺, Na⁺ or K⁺) was determined on the acid–base constants of p-t-butylthiacalix[4]arene (TC4), p-t-butylcalix[4]arene (CA4) and p-t-butylcalix[6]arene (CA6) in ethanol/water in an large interval of pH values by potentiometry and spectrophotometry. The pK_a values determined by both methods correlate very well and these are characteristic for each macrocycle with influence of the cation of the base without a straight evidence of an effect by the size of the metallic cation. In the case of TC4, pK_a1 and pK_a2 were lower to Li⁺ and Na⁺ than with K⁺. For CA4, an effect of K⁺ on the pK_a2 with respect to Li⁺ was observed. A very different behaviour was observed for CA6 with Li⁺ and K⁺ showing a lower pK_a2 and a higher pK_a3 than with Na⁺. These effects were interpreted on the basis of the interaction/complexation of each cation with each macrocycle.