Synthesis of Eight Nitrogen‐Pivot Benzo‐aza‐lariat Crown Ethers

A short and convenient synthesis of two series of eight totally new lariat crown ethers is reported in this article. These lariat ethers are derived from triaza‐dibenzo‐27‐crown‐7 and diaza‐dibenzo‐27‐crown‐7 through condensation of appropriate aza‐crown ethers with appropriate substituted compounds in chloroform. The substituted reagents are acetic anhydride, benzoyl chloride, phthalic anhydride, and butanedioic anhydride, respectively.     

Synthesis and recognition of amino acids by binaphthyl-crown receptors

Two binaphthyl crown receptors containing phenylboric acid 2 and 2,4-dinitrophenylurea 3 as lariat parts were prepared from the optically active binaphthyl crown alcohol 1 in two and four steps, respectively. Host 2 showed a 30% extraction efficiency for GABA by a solid-liquid extraction method in DMSO. Chromogenic Host 3 discriminated the guest linear amino acid by molecular length and the information was revealed through color changes.     

Synthesis of redox active large macrocyclic hosts and the recognition of secondary ammonium salts

Interconvertible macrocyclic hosts containing thiol groups or a disulfide linkage in the binding cavity have been synthesized. The binding affinities of the reduced and oxidized forms toward benzylammoium derivatives are completely reverse. Formation of pseudorotaxane is suggested upon the host-guest complexation.     

Molecular structures of benzoylbenzo-12-crown-4 and diphenylacetylbenzo-12-crown-4 and possible reasons for different conformational states of their macrocycles

The molecular structures of (benzoyl)benzo-12-crown-4 (a=22.387,b=4.503,c=16.167 Å,d _calc=1.34 g cm^–3,Z=4, space groupP2₁ nc, DAR-UM, Cu-K,R=0.056) and (diphenylacetyl)benzo-12-crown-4 (a=8.866,b=23.337,c=10.737 Å;d _calc=1.25 g cm^–3,Z=4, space groupP2₁2₁2₁, DAR-UM, Cu-K, R=0.056) have been investigated. The differences in the conformations of the macrocycles and the degree of conjugation between the benzene ring orbitals and the lone pairs on the adjacent oxygen atoms in the macrocycle are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1906–1911, November, 1993.     

Bis(crown ether) and Azobenzocrown Derivatives of Calix[4]arene. A Review of Structural Information from Crystallographic and Modelling Studies

The association within one molecule ofcalix[4]arene and crown ether moieties leads toligands with new complexing properties. In particular,calix[4]arene bis(crown-6) and some of itsderivatives have been shown to be highly selectiveextractants for caesium ions. This review presents thebackground of the study and the results of crystalstructure determinations and molecular modellingcalculations performed during the investigation of twomolecular families, the bis(crown ether) and theazobenzocrown derivatives of calix[4]arene.     

Crown Ether Host-Guest Molecular Ferroelectrics

In recent years, molecular ferroelectrics have received great attention due to their low weight, mechanical flexibility, easy preparation and excellent ferroelectric properties. Among them, crown-ether-based molecular ferroelectrics, which are typically composed of the host crown ethers, the guest cations anchored in the crown ethers, and the counterions, are of great interest because of the host-guest structure. Such a structure allows the components to occur order-disorder transition easily, which is beneficial for inducing ferroelectric phase transition. Herein, we summarized the research progress of crown ether host-guest molecular ferroelectrics, focusing on their crystal structure, phase transition, ferroelectric-related properties. In view of the small spontaneous polarization and uniaxial nature, we outlook the chemical design strategies for obtaining high-performance crown-ether-based molecular ferroelectrics. This minireview will be of guiding significance for the future exploration of crown ether host-guest molecular ferroelectrics.     

A Molecular Cable Car for Transmembrane Ion Transport

The controlled transport of molecular and ionic substrates across bilayer membranes is a fundamental task for the operation of living organisms. It is also a highly fascinating and demanding challenge for artificial molecular machines. The recent report of a synthetic transmembrane molecular shuttle that can transport potassium ions selectively down a gradient in a liposomal system makes a small but significant step towards this goal.     

Macrocyclic thioether design by molecular modelling

Abstract

Two trithiamacrocycles have been designed by molecular modelling to have preorganised endodentate sulfur donor atoms. These new macrocycles have five- and six-membered saturated heterocycles inserted into 2,5,8-trithia[9]-m-benzenophane; molecular dynamics simulations suggest that the endo forms will be rigid on a nanosecond timescale. Optimum metal-sulfur distances which the new ligands will accommodate lie between 2.76 Å and 2.95 Å, suggesting they will be particularly suitable for a large soft metal ion such as silver(I).     

Molecular Modeling Studies on Molecular Recognition: Crown Ethers,Cryptands and Cryptates. From Static Models in vacuo to Dynamical Models in Solution

Abstract

Molecular Mechanics, Monte Carlo and Molecular Dynamics simulations on free and complexed crown ethers, on bicyclic cryptands and cryptates provide deeper insights into their conformational and recognition properties and allow to address the questions of preorganisation, complementarity, and binding selectivity. Alternatively, references to experimental data allow to outline present theoretical and computational limitations. Of particular interest are the microscopic pictures obtained in solution, which demonstrate the importance of solvent and environment effects on the precise structure of free and complexed receptors, and on their dynamics. Quantitative insights into relative free energies in solution represents a most promising breakthrough for computational studies in molecular recognition.     

A Convenient and Efficient Method for the Preparation of Unique Fluorophores of Lariat Naphtho‐Aza‐Crown Ethers

New naphtho‐aza‐crown ethers containing different phenolic side‐arms attached through the ortho‐position of the phenol have been prepared under solvent‐free conditions. The starting macrocyclic naphtho‐aza‐crown ether 2 was obtained by treatment of naphthalene dicarboxylic acid diester 1 with diethylenetriamine in EtOH at room temperature for two days without stirring in 77% yield (Scheme 1). Phenolic ligands ( 3 – 14 ) were synthesized by the Mannich reaction of the secondary macrocyclic amine 2 with the substituted phenols using nontoxic and inexpensive CaCl₂. This procedure was applied successfully for the synthesis of Mannich bases from simple secondary amines. The CaCl₂ powder can be reused up to three times after simple washing with dry acetone.     

Molecular design of crown ethers .18.~1 Cationextractability and selectivities of selena-13- to 14-crown-4

Three selena-crown-4 derivatives have been prepared and their cation binding abilities and selectivities with alkali and heavy metal ions have been evaluated by solvent extraction of aqueous metal picrates to show the highest Ag extractability for novel benzo-selena-14-crown-4 (2,3-benzo-7,12-diselena-1, 4-dioxacyclotetradecane-2-ene) over any other crown ethers.     

Crystalline complexes of N,N'-ditritylurea (DTU) and N-tritylurea (NTU) hosts with molecular guests

This paper reports crystalline complexes of the new hosts N,N'-ditritylurea (DTU) and N-tritylurea (NTU) with various uncharged molecular guests. The crystal structures of the following complexes were elucidated by single crystal X-ray diffraction analysis at 115^oK: (I) 1:1 DTU-propanamide — space group C2/c, a=15.839Å, b=9.088Å, c=24.584Å, =111.05^o, Z=4; (II) 1:1 DTU-ethyl N-acetylglycinate — space group P1, a=9.010Å, b=10.800Å, c=19.810 Å, =105.29^o =94.33^o, =93.03^o, Z=2; (III) 2:1 NTU-N, N-dimethylformamide — space group Cc, a=29.614Å, b=8.906Å, c=16.127Å, =121.04^o, Z=4. The three crystal structures are stabilized mainly by a cooperative effect of hydrogen bonding between amide fragments displaced along the shortest axis of each crystal. This interaction occurs between host and guest in complexes I and II, and between host and host in complex III. The latter also represents a cage-type clathrate in which the guest molecules are accommodated in voids between the hydrophobic fragments of four neighboring NTU hosts. On the other hand, complexes of DTU are characterized by a more specific interaction between the two components, each guest molecule being inserted between two adjacent hosts (related by translation) and strongly bound to them via hydrogen bridges. These results illustrate a useful concept in the design of molecular species which can be potential hosts upon crystallization with neutral molecular guests. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82022 (7 pages).     

Crystal Structure and Properties of a New Copper(II) Complex of Dioxocyclam Appended with 8-Methylquinoline (Dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione)

The IR spectra of the crystalline complexes of 3-and 4-nitrophenol with crown ethers were studied, viz.,18-crown-6 (18C6), benzo-18-crown-6 (B18C6),dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-24-crown-8 (DB24C8). The spectra of uncomplexed crown ethers showed water absorption bands which indicate the presence of two types of bound water molecules, viz., cavitant water enclosed by the strong ether-cavity field and outer-layer hydrogen-bonded water molecules. Upon complexation with 3- and 4-nitrophenol, the bands attributed to cavitant water disappeared, leaving the outer layer water to act as a bridge between the host crown ether and the guest phenols. The results further showed that of the crown ethers and of the phenols, B18C6 and DC18C6 and 3-nitrophenol, have the strongest interaction. The behaviour of the phenols was explained by the increased contribution of the inductive-moment over the resonance -moment in thecomplexes.     

Complex formation of D-mannonaphto-18-crown-6-ether and enantiomers of phenylalanine in water studied by different physochemical methods

Complex formation of D-mannonaphto-18-crown-6-ether 1 with D- and L-phenylalanine (Phe) and their derivatives was studied using conduction and titration microcalorimetry in aqueous solution, and solvent–solvent (water–chloroform) extraction. The thermal effects accompanying the complexation process were determined, but the chiral recognition effects were very small. The chiral differentiation of amino acid was observed in the experiments of the extraction from water to chloroform phase containing chiral receptor.     

NMR Studies of Mixed-Ligand Lanthanide (III) Complexes. Peculiarities of Molecular Structure, Dynamics and Paramagnetic Properties for Cerium Subgroup Chelates with Crown Ethers

The molecular structure, dynamics and paramagnetic properties of the complex cations [Ln(ptfa)₂ (18-crown-6)]⁺ in deuterated toluene were studied for Ln = La, Ce, Pr and Nd. The activation enthalpy values of 68 ± 5, 55 ± 15 and 60 ± 13 kJ mol^-1 for the 18-crown-6 conformationalinversion processes for the complexcations of Ce, Pr and Nd, respectively,were obtained. Quantitativeinvestigation of the lanthanide-induced chemical shifts shows a monotonic change of a spatial structure and magnetic susceptibility in comparison with the Bleaney predicted dependence. The free energy of molecular inversion activation for 18-crown-6 molecules in the complex cation [Ln(fod)₂(18-crown-6)]⁺ is 74 ± 9 kJ mol^-1 at 363 K, which is a little more than the value of the free energy of activation 64 ± 9 kJ mol^-1 at 363 K in the complex cation [Ln(ptfa)₂(18-crown-6)]⁺.     

Intramolecular Dynamics and Molecular Structure of Europium(III) Chelate Complexes with Crown Ethers as Studied by NMR Spectroscopy

Earlier the intramolecular inversion of the 18-crown-6 molecules was found in the complex ion pairs [Ln(ptfa)₂ (18-crown-6)]⁺ [Ln(ptfa)₄]⁻ (H₂O)₄ where Ln = La(1), Ce (2), Pr (3), Nd (4), and ptfa is 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione. In this work the peculiarities of the molecular structure and dynamics were studied for [Eu(ptfa)₂ (18-crown-6)]⁺ [Eu(ptfa)₄]⁻ (H₂O)₄ (5) by NMR spectroscopy techniques. Through VT-NMR spectra analysis the temperature dependence was obtained for the rate constant. The free energy ΔG^‡(320) of 18-crown-6 ring inversion activation was found to be 65 ± 5 kJ mol⁻¹ for 5 in CDCl₃. This result is comparable with the earlier data [S.P. Babailov and D.A. Mainichev: J. Inclusion Phenom. Macrocyclic Chem. 43, 187–193 (2002)] for complexes 2, 3, 4 in deuterated toluene (ΔG^‡(320)=65 ± 9, 64 ± 9, 64 ± 9 kJ mol⁻¹ respectively). It was found by relaxation NMR spectroscopy that the effective distance between Ln and protons of the crown molecule is 4.5 ± 0.2 Å. The analysis of structural parameters testifies that the crown ether and chelated anions are in the first coordination sphere of a Ln cation. Obtained geometrical parameters show that the complex cations of Eu, Ce and Pr have similar spatial structures.This revised version was published online in July 2005 with a corrected issue number.     

The structure of a 1:4 adduct between 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) and thiourea

The structure of 18-crown-6·4 thiourea has been determined by single crystal X-ray methods. The unit cell is monoclinic and the space group isP2₁, witha=9.251(3),b=19.285(8),c=16.556(7) Å and =90.85(6)°. There are two formula units, C₁₂H₂₄O₆·4CH₄N₂S, in the asymmetric unit; finalR=0.086. One thiourea is attached at either side of the macrocycle (biangular conformation) via N–N...O bonds and the patterns in the two crystallographically-independent adductsA andB differ slightly, involving two bifurcated hydrogen bonds inA. Core adducts are linked by additional thiourea molecules via N–H...S bonds. As compared to the analogous 18-crown-6·5 urea, the present 1:4 stoichiometry might be attributed to the longer S...N hydrogen bonding distance, i.e., to the bigger van der Waals radius of sulphur. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82004 (31 pages). To obtain copies, see p. ii of this issue.