Monoazacrown Ether Research Articles

The Synthesis of Hydrobenzoin-Based Monoaza Crown Ethers and Their Application as Recyclable Enantioselective Catalysts

New recyclable monoaza-15-crown ethers have been synthesized starting from (R,R)-(+)- and (S,S)-(−)-hydrobenzoin. These macrocycles proved to be efficient and reusable phase transfer catalysts in a few asymmetric reactions under mild conditions. The asymmetric epoxidation of trans-chalcone took place with up to 81% ee, while using other chalcone derivatives, the products were formed with 68–88% ee. The hydrobenzoin-based lariat ethers were also tested in the cyclopropanation of a few electron deficient olefins using diethyl bromomalonate to afford the product with good enantioselectivities (54–75% ee). The catalysts were recovered by salt formation, followed by extraction, and were reused without the loss of the activity and effect on the enantioselectivity.Graphic The synthesis of hydrobenzoin-based monaza crown ethers and their application as recyclable enantioselective catalysts.

Toward MRI and Optical Detection of Zwitterionic Neurotransmitters: Near-Infrared Luminescent and Magnetic Properties of Macrocyclic Lanthanide(III) Complexes Appended with a Crown Ether and a Benzophenone Chromophore.

Thanks to their versatile magnetic and luminescence features, lanthanide complexes have gained a central position in biomedical imaging as magnetic resonance imaging (MRI) contrast agents and optical imaging probes. In addition, appropriate chemical design allows modification of the magnetic relaxation properties of GdIII complexes and the optical properties of visible- or near-infrared (NIR)-emitting lanthanide chelates upon interaction with various biomarkers, which makes them ideal candidates for the creation of responsive agents. In this Forum Article, we demonstrate such design principles as well as the difficulties encountered in the context of neurotransmitter (NT) detection. Lanthanide(III) complexes of a macrocyclic ligand incorporating a benzophenone chromophore and a monoazacrown ether (LnL3) have been synthesized as responsive probes to monitor amino acid NTs either in MRI (Ln = Gd) or in NIR optical detection (Ln = Nd or Yb). The parameters characterizing the water exchange and rotational dynamics of the gadolinium(III) complex were assessed by 17O NMR and 1H NMRD. In the presence of zwitterionic NTs, the inner-sphere water molecule is replaced by the carboxylate function of the NTs in the gadolinium(III) complex, leading to a decrease of the longitudinal relaxivity from 6.7 to 2-2.5 mM-1 s-1 (300 MHz and 37 °C). The apparent affinity constants range from Ka = 35 for γ-aminobutyric acid (GABA) to 80 M-1 for glycine and glutamate, and there is no selectivity with respect to hydrogen carbonate (Ka = 232; pH 7.4). The gadolinium(III) complex interacts with human serum albumin (HSA), resulting in a 60% increase in the relaxivity (20 MHz, 37 °C) in the absence of NTs. The HSA-bound complex, however, was revealed to be less responsive to NTs because of displacement of the GdIII-bound water by HSA, which was confirmed by the hydration number calculated from luminescence lifetimes of the HSA-bound europium(III) complex. The creation of an imaging agent suitable for NIR detection of NTs for an enhanced sensitivity in biological systems using the benzophenone (BP) moiety as the sensitizer of lanthanide luminescence was also attempted. Upon excitation at 300 nm of the BP chromophore in aqueous solutions of NdL3 and YbL3, characteristic NIR emissions of NdIII and YbIII were observed because of 4F3/2 → 4IJ (J = 9/2-13/2) and 2F5/2 → 2F7/2 transitions, respectively, indicating that this chromophore is a suitable antenna. Despite these promising results, luminescence titrations of NdIII and YbIII complexes with NTs were not conclusive because of chemical conversion of the ligand triggered by light, preventing quantitative analysis. The observed photochemical reaction of the ligand is strongly dependent on the nature of the lanthanide chelated; it is considerably slowed down in the presence of NdIII and EuIII.

Modification of gold surface by electrosynthesized mono aza crown ether substituted catechol-terminated alkane dithiol and its application as a new electrochemical sensor for trace detection of cadmium ions.

Among the toxic metals, cadmium is a very dangerous pollutant because it can extremely damage organs in humans and animals. This toxic metal is introduced into water from different industries such as metal plating, batteries, and alloys. Cadmium bioaccumulates in vital organs and unlike organic pollutants does not show any biological degradation. In this study, an electroactive self-assembled monolayer (SAM) was developed by covalent attachment of a novel mono aza-crown ether substituted catechol-terminated hexane dithiol onto the gold surface. The electrochemical behavior of the fabricated SAM electrode was investigated using voltammetry techniques and electrochemical impedance spectroscopy (EIS). The obtained results from voltammetric experiments revealed that the crown ether moiety of SAM forms a selective complex with cadmium ion. Under optimal conditions, Cd2+ could be detected in the range of 15 μM to 65 μM with a detection limit of 4.5 μM. Selectivity measurements reveal that the sensor is specific for Cd2+ even in the presence of high concentrations of other metal ions. The proposed sensor was applied to the determination of cadmium ion in water samples with high sensitivity and good selectivity.

Clickable complexing agents: functional crown ethers for immobilisation onto polymers and magnetic nanoparticles

A modular library of crown ethers and monoazacrown ethers supported by CuAAC reactions onto magnetic nanoparticles and polymers has been prepared and evaluated as extracting materials for Pb2+ from aqueous and organic solutions.

Potentiometric, spectrophotometric, and AM1d studies of the equilibria between silver(I) ion and monoaza-crown ethers with anthraquinone in various solvents

Complex formation and stability constants between silver(I) and monoaza-12-crown, monoaza-15-crown, and monoaza-18-crown ethers with anthraquinone were determined in acetonitrile, methanol, and propylene carbonate by potentiometric and UV-spectrophotometric methods. Complexes of 1 : 1 and 1 : 2 metal-to-ligand stoichiometry were formed. The solvent composition and the size of the macrocyclic ring affect the stability constants of the complexes. The energetically most favorable structures of the 1 : 1 metal-to-ligand complexes were calculated and visualized by the AM1d method at a semiempirical level of theory.

ChemInform Abstract: Synthesis of Monoazacrown Ethers under Phase‐Transfer Catalysis.

A procedure has been proposed for the synthesis of monoazacrown ethers by reaction of N-benzyldiethanolamine with oligo(ethylene glycol) bis-p-toluenesulfonates in a two-phase system aromatic hydrocarbon-50% aqueous alkali, followed by removal of the benzyl group by catalytic hydrogenolysis. The maximal yields of N-benzylaza-12-crown-4, -18-crown-6, and -21-crown-7 were achieved by adding 4–10 equiv of LiCl, BaBr2, and CsCl, respectively, to the reaction mixture, which probably indicated template effect.

Synthesis of monoazacrown ethers under phase-transfer catalysis

A procedure has been proposed for the synthesis of monoazacrown ethers by reaction of N-benzyldiethanolamine with oligo(ethylene glycol) bis-p-toluenesulfonates in a two-phase system aromatic hydrocarbon-50% aqueous alkali, followed by removal of the benzyl group by catalytic hydrogenolysis. The maximal yields of N-benzylaza-12-crown-4, -18-crown-6, and -21-crown-7 were achieved by adding 4–10 equiv of LiCl, BaBr2, and CsCl, respectively, to the reaction mixture, which probably indicated template effect.

Selective Fluorometric Sensing of Calcium Cation by C-Pivot Lariat Monoaza-crown Ether with Two Pyrene Moieties

Abstract A new type of C-pivot lariat monoaza-crown ether 1b containing a 15-crown-5 ring and two pyrene moieties on the sidearms was found to be a highly sensitive and selective fluorescent chemosensor toward Ca2+ in the presence of Na+, K+, Mg2+, and Ca2+.

ChemInform Abstract: Syntheses and Phase-Transfer Catalytic Activities of Monoazacrown Ethers.

ChemInform Abstract: Syntheses and Phase-Transfer Catalytic Activities of Monoazacrown Ethers.

ChemInform Abstract: Alkylphosphoric Acid Armed Crown Ethers Having a Specific Cation Binding Ability

Abstract The syntheses, transport via a bulk liquid membrane, and cation binding properties of alkylphosphoric acid armed crown ethers are reported. The new armed crown ethers and monoaza crown ether containing 13–19-membered crown rings are synthesized by two methods: (a) the reaction of a hydroxymethyl-substituted crown ether with dichloroalkylphosphate followed by hydrolysis; (b) the one-pot reaction of a hydroxymethyl crown ether with an alkylphosphate in the presence of dicyclohexylcarbodiimide-pyridine. The transport experiments reveal that (i) the alkylphosphoric acid armed crown ethers exhibit specific transport abilities for alkali metal cations which fit the cavity size of their crown rings, (ii) the structure of the bridgehead carbon which bears the pendant arm (trimethylene unit and dimethylene unit) significantly influences the cation selectivity, and (iii) for the zwitterion-type phosphoric acid armed monoaza crown ether the cation selectivities can be controlled by altering the aqueous phase in the liquid membrane transport system. Computer and CPK modelling suggested that the phosphoric acid site is a cooperative coordination site. Spectroscopic data ( 13 C nuclear magnetic resonance and IR) supported the proposed interaction of the cavity complexed crown ether with the side arm.

Rapid and selective lead (II) colorimetric sensor based on azacrown ether-functionalizedgold nanoparticles

A gold nanoparticle (AuNPs)-based simple and fast colorimetric sensor for selectivedetecting of Pb(II) in aqueous solution has been developed. Monodisperse AuNPs(approx. 2.0 nm diameter) has been prepared facilely and further modified with analkanethiol-bearing monoazacrown ether terminus. These AuNPs are shown to selectively sensePb2 + through color change, which is visually discernible by an appearance of the surface plasmonband (SPB) at 520 nm. The recognition mechanism is attributed to the unique structure ofthe monoazacrown ether attached to AuNPs and metal sandwich coordination between twoazacrown ether moieties that are attached to separate nanoparticles. This inter-particlecross-linking results in an aggregation and apparent color change from brownto purple. Additionally, TEM experiments support the optical absorption dataproving the aggregation between azacrown ether-capped gold nanoparticles. ThisAuNP-based colorimetric assay is a facile and robust method and allows fast detection ofPb2 + at ambient temperatures. More importantly, the developed technique does not utilizeenzymatic reactions, light-sensitive dye molecules, lengthy protocols or sophisticatedinstrumentation.

Effects of interactions with the surface on the orientation of the mesogenic monoazacrown-substituted phthalocyanine films

In this paper, the effect of interaction with the substrate surface on the orientation of films' molecules of substituted liquid crystalline phthalocyanines M(II)Pc (M = Cu, Ni, Zn) having monoazacrown ether moieties on the periphery containing long alkyloxyphenyl N-pivotal groups is studied. The phthalocyanine derivatives demonstrate thermotropic mesophase behaviour and show Col h mesophases over a wide temperature range. The preferential orientation of the phthalocyanine films deposited on glass, silicon and NaCl substrates as well as between two of those substrates is studied by polarized Raman spectroscopy at different temperatures. These phthalocyanines form homeotropically aligned films on the surface of NaCl substrate, whereas planar alignment with a random distribution of the column directors occurs on the glass slides.

Synthesis and fluorescence studies of novel bis(azacrown ether) type chemosensors containing an acridinone unit

Three new bis(azacrown ether)s containing an acridinone fluorescent signalling unit were prepared by reacting 9-chloro-4,5-bis(chloromethyl)acridine with monoazacrown ethers with different cavity sizes followed by a hydrolysis step. Their fluorescent characteristics and the complexation properties of the one containing two monoaza-18-crown-6 ether receptors towards selected metal ions were studied. The operation of the latter ligand is based on the photoinduced electron transfer (PET) process, thus it shows fluorescence enhancement in the presence of metal ions. Since the sensor molecule contains two receptor moieties, it is able to form two types of complex with 1:1 and 1:2 ligand to metal ion ratios, which have different emission spectra. The reason for this spectral difference may be that the 1:1 complex is a sandwich type one in which the acridinone unit can undergo structural changes.

Supported Liquid Membrane Transport of Alkali Metal Cations by Monoazacryptand with a Partially Fluorinated Sidearm and the Corresponding Monoazacrown Ethers

Monoazacryptand [20.18.18] (1), monoaza-15-crown-5 (2a), and monoaza-18-crown-6 (2b) with a partially fluorinated sidearm were newly prepared and their transport abilities were estimated in a supported liquid membrane containing a mixture of 2- (perfluorohexyl) ethyl alcohol and 2- (perfluorooctyl) ethyl alcohol. In competitive passive transport of K+, Na+, and Li+ under neutral conditions, the K+ selectivity increased in the order: ionophore 2a<ionophore 2b<ionophore 1; whereas, the transport velocity increased in the order: ionophore 2a<ionophore 1<ionophore 2b. On the other hand, only ionophore 1 successfully transported K+ in the transport from the neutral source phase to the acidic receiving phase. This result was reasonably explained by considering the excellent K+ complexing ability of monoazacryptand (1) in comparison with that of monoazacrown ethers (2a and 2b).

Molecular Dynamics Calculation of Counter Anion Effects on Liquid-Liquid Extraction of Alkali Metal Ions with Spirobenzopyran Derivatives Bearing a Monoazacrown Ether Moiety

Simulations of alkali metal ion extraction ability using spirobenzopyran derivatives bearing a monoazacrown ether moiety were conducted by molecular dynamics calculation. Previously, our simulation studies had revealed the effects of the alkyl chain length in the spirobenzopyran derivatives on extractability towards alkali metal ions. In this research, the counter anion effects on liquid-liquid extraction were investigated by using 1,2-dichloroethane as an organic phase. The results show that the metal ions were more easily extracted into the organic phase when hydrophobic anions such as picrate and phenolate ions were used as counter anions than when hydrophilic anions such as nitrate and chloride ions were used, regardless of the metal ions and the crown ring size. This tendency is theoretically supported as the general anion effect.

Synthesis and optical characterization of novel azacrown ethers containing an acridinone or an N-methylacridinone unit as potential fluorescent chemosensors

Four new achiral and four new chiral monoazacrown ethers containing an acridinone or an N-methylacridinone fluorescent signalling unit were prepared by reacting chloromethyl-substituted acridinone derivatives with achiral monoazacrown ethers with different cavity sizes and enantiopure monoaza-18-crown-6 ethers having two methyl and two isobutyl groups on their chiral centres, respectively. The operation of these chemosensors is based on the photoinduced electron transfer (PET) process, thus they show fluorescence enhancement in the presence of cationic guests. Their fluorescent behaviour as well as their complexation properties towards selected metal ions and the enantiomers of α-(1-naphthyl)ethylammonium perchlorate and potassium mandelate were examined.

The synthesis and characterization of Cu(II) phthalocyanine bearing peripheral monoazacrown ethers and a spectral investigation of its film forming character

Abstract The synthesis, liquid crystalline behavior and self-organizing properties of Cu(II)Pc bearing monoazacrown ether moieties that contain long alkyloxyphenyl N-pivotal groups are described. The Cu(II) phthalocyanine derivative has a hexagonal, columnar structure; optical absorption and vibrational spectroscopy revealed a predominantly co-facial interaction between the chromophores and their orientation parallel to a NaCl surface. It is proposed that such homeotropic alignment is attributable to the ability of the pendant monoazacrown ether groups to coordinate the Na + ions within the NaCl surface.

Absorption‐ and fluorescence‐spectral sensing of alkali metal ions in anionic micelle solutions containing crowned spirobenzopyrans

AbstractSpirobenzopyran derivatives bearing a monoazacrown ether moiety (monoaza‐12‐crown‐4, ‐15‐crown‐5, and ‐18‐crown‐6) and an octadecyl group as a lipophilic moiety, called crowned spirobenzopyrans were synthesized, which can be dissolved in anionic micelle solutions. We examined absorption‐and fluorescence‐spectral changes of micelle solutions containing a crowned spirobenzopyran on addition of alkali metal ions. The crowned spirobenzopyrans are in their merocyanine form in an anionic micelle solution even under dark conditions, showing a significant absorption in the visible region which is attributable to the merocyanine moiety. Crowned spirobenzopyran bearing a monoaza‐12‐crown‐4 moiety exhibited a drastic hypsochromic shift in the absorption and also an enhanced fluorescence on addition of Li+ to the micelle solutions under alkaline conditions. These spectral changes can be attributed to a strong interaction between Li+ bound by the crown ether moiety and a phenolate ion of the merocyanine moiety. Similar absorption and fluorescence‐spectral changes were induced in the anionic micelle solutions containing the other crowned spirobenzopyrans on addition of alkali metal ions. The intensity of the absorption‐spectral changes in the systems of the three crowned spirobenzopyrans, however, differed from each other, depending on the strength of interaction between a metal ion bound to the crown ether moiety and the phenolate ion of the merocyanine moiety. On the other hand, the extent of enhanced relative fluorescence intensity is dependent on the strength of interaction between metal ion and a nitrogen atom of azacrown ether moiety, because the fluorescence spectrum is quenched by photoinduced electron transfer (PET) from the nitrogen atom to the merocyanine moiety. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Synthesis of N-4-vinylbenzyl-monoaza-m-phenylene-34-crown-11 and its copolymerization with styrene

A functional monomer, containing a 34-membered monoazacrown ether unit (VACE) as a pendant group has been synthesized by using resorcinol, tetraethylene glycol, p-tolenesulfonyl chloride and 4-vinylbenzyl chloride as starting materials. The product structure was characterized by means of FT-IR,1H-NMR, EA and MS. Free radical homopolymerized VACE or copolymerized VACE with styrene (ST) by the conventional radical initiator 2,2′-azobis (isobutyronitrile) (AIBN) in toluene solution to afford corresponding polymers. The reactivity ratio of VACE and ST, determined by Fineman-Ross method, gave values 0.6 for VACE, and 1.4 for ST, respectively.

Effect of Crown Ether Ring Size on Binding and Fluorescence Response to Saxitoxin in Anthracylmethyl Monoaza Crown Ether Chemosensors.

Convenient macrocyclization synthetic routes for the preparation of different-sized monoaza anthracylmethyl crown ether chemsensors (15-crown-5, 18-crown-6, 21-crown-7, 24-crown-8 and 27-crown-9) are described. Evaluation of these crowns as chemosensors for saxitoxin revealed that the larger crowns have moderately higher binding constants, with the 27-crown-9 chemosensor having the largest binding constant: 2.29×10(5) M(-1). Fluorescence enhancements of 100% were observed at saxitoxin concentrations of 5 μM, which is close to the detection limit in mouse bioassay.