Azacrown Derivatives Research Articles

In-depth Study of a Novel Class of Ditopic Gadolinium(III)-based MRI Probes Sensitive to Zwitterionic Neurotransmitters.

The efficacy of Gd-based low-molecular weight ditopic MRI probes on binding zwitterionic neurotransmitters (ZNTs) relies on their structural compatibility. ZNTs are challenging biomarkers for monitoring chemical neurotransmission due to their intrinsic complexity as target molecules. In this work, we focus on tuning the cyclen- and azacrown ether-based binding sites properties to increase the affinity toward ZNTs. Our approach consisted in performing structural modifications on the binding sites in terms of charge and size, followed by the affinity evaluation through T1-weighted relaxometric titrations. We prepared and investigated six Gd3+ complexes with different structures and thus properties, which were found to be acetylcholine insensitive; moreover, two of them displayed considerably stronger affinity toward glutamate and glycine over hydrogencarbonate and other ZNTs. Complexes with small and non-charged or no substituents on the azacrown moiety displayed the highest affinities toward ZNTs, followed by strong decrease in longitudinal relaxivity r1 of around 70%. In contrast, hosts with negatively charged substituents exhibited lower decrease in r1 of nearly 30%. The thorough investigations involving relaxometric titrations, luminescence, and NMR diffusion experiments, as well as theoretical density functional theory calculations, revealed that the affinity of reported hosts toward ZNTs is greatly affected by the remote pendant on the azacrown derivative.

Conformational search and spectroscopic analysis of bis-β-d-glucopyranosyl azacrown derivative

1,10-N,N′-bis-(β-d-ureidoglucopyranosyl)-4,7,13-trioxa-1,10-diazacyclopentadecane is a new, recently synthesized compound, which exhibits complexation ability towards drugs. In the present study various theoretical methods, including molecular mechanics, computer simulations, semiempirical and DFT calculations, are applied to find the lowest energy conformers of this molecule in vacuo and in aqueous solution. For the most stable structures the vibrational frequencies as well as the C and H chemical shifts were computed. Along with the theoretical investigation the IR in the KBr discs and the NMR spectra in water and in pyridine were experimentally recorded. It is shown that in the lowest energy structures the two glucosyl units are placed on the same side of the diazacrown ring with their mutual orientations favoring formation of hydrogen bonds. The “open” structure, in which no such hydrogen bonds can be formed, is found to have much higher energy. The computed and measured IR spectra and NMR chemical shifts are compared and discussed in detail. The most stable structures are analyzed with respect to the possible mechanism of complexation of drugs.

2]Pseudorotaxane Formation with FRET Based Luminescence Response: Demonstration of Boolean Operations through Self-Sorting on Solid Surface.

Binary pseudorotaxane formation between an aza crown derivative as host (H) and two different imidazolium derivatives as guests (G1 and G2) have been studied in detail by NMR (1H NMR, 2D NOESY), optical (steady state electronic and emission spectroscopy), and mass spectroscopy. Binding stoichiometry (1:1), association constant for the respective [2]pseudorotaxane formation (KaH.G1 = (2.61 ± 0.015) × 103 M-1 and KaH.G2 = (1.27 ± 0.16) × 103 M-1), and associated thermodynamic parameters are also evaluated based on isothermal titration calorimetric (ITC) studies. FRET based luminescence ON responses are observed on formation of the binary pseudorotaxane (H.G1 and H.G2) in a nonpolar medium like dichloromethane. The thermodynamic feasibility of such an energy transfer process is also examined. The higher affinity of H and 18-crown-6 toward K+, as compared to those toward G1 or G2, and the reversibility in the host-guest binding process are utilized in demonstrating the self-sorting phenomena with associated changes in luminescence responses that could be correlated for Boolean operators like YES, INHIBIT, OR, and AND gates.

The Reaction of Phenyldichlorophosphine with Bis(Salicylidene)Ethanediamine—A New Approach to Aza-Crown Derivatives

GRAPHICAL ABSTRACT

Synthesis of bis-cellobiose and bis-glucose derivatives of azacrown macrocycles as hosts in complexes with acetylsalicylic acid and 4-acetamidophenol

Two new C2 symmetric bis-cellobiose and bis-glucose azacrown derivatives were prepared according to the one-step procedure using azacrown ethers and azidosaccharides. Their complexes with aspirin and paracetamol were studied with the use of proton NMR spectroscopy. It was found that these pseudocryptands bind aspirin and paracetamol but each one in a different manner.

A new calix[4]azacrown ether based boradiazaindacene (Bodipy): Selective fluorescence changes towards trivalent lanthanide ions

We report on the synthesis and photophysical properties of a new calix[4]azacrown derivative, capped with two amide bridges, in the cone conformation bearing two boradiazaindacene (Bodipy) groups at the narrow rim. Its binding properties towards trivalent lanthanide ions such as La3+, Gd3+, Tb3+, Dy3+, Er3+ and Yb3+ were investigated by using spectroscopic techniques. With respect to fluorescence intensity changes upon trivalent lanthanide ion complexation, calix[4]azacrown ether based Bodipy showed higher selectivity towards Yb3+ ion over other ions. Presence of proximal two amide groups in calix[4]azacrown ether based Bodipy were observed to play an important role in exhibiting its lanthanide ion binding.

Chlorophyll tailored 20-trifluoroacetamide and its azacrown derivative as pH sensitive colorimetric sensor probe with response to AcO−, F− and CN− ions

Chlorophyll derivatives were functionalized with a trifluoroamide (TFA) group to obtain colorimetric ion sensors. Prior to this, a NO2BF4*pyridine based, chlorin nitration method was developed. The base strength dependent sensing of AcO−, F− and CN− ions was detected in aqueous media, which was enhanced in nonprotic solvents by an integration of the ditopic chelation capable amine crown-6 moiety.

Synthesis of a novel calix[4]azacrown ionophore and its extraction ability toward Cr(VI)

The present study describes the synthesis of a novel extractant p-tert-butyl-calix[4]azacrown ionophore (5) and evaluation of its extraction capability toward dichromate ion from aqueous solution. At first, p-tert-butyl-calix[4]azacrown ionophore (5) has been synthesized from the condensation of p-tert-butyl-calix[4]arene diamine (3) with N-(4-formylphenyl)-aza-15-crown-5 (4). The studies regarding the removal of dichromate ion from the aqueous solutions have been carried out in the liquid–liquid extraction systems. The extraction results showed that p-tert-butyl-calix[4]azacrown derivative (5) exhibited generally higher affinity towards dichromate ion than both 3 and 4 at all studied pHs.

Synthesis and Characterisation of 4-Aminophthalimido-N-Alkyl-Calix[4]Azacrown Derivatives

Two 4-amino-N-bromoalkylphthalimide derivatives were prepared by the reduction of 4-nitro-N-bromoalkylphthal-imides and SnCl2 and reacted with calix[4]azacrown to give two new 4-aminophthalimido-N-alkyl-calix[4]azacrown derivatives. They were characterised by IR, 1H NMR, 13C NMR and HRMS and shown to adopt a cone conformation, 4-aminophthalimido-N-alkyl-calix[4]azacrown may provide a potential fluorescent probe for Cu2+.

Synthesis and extraction abilities of mono-formylated calix[4]-1,3-aza-crown and its hydrazone derivatives

By formylation of calix[4]-1,3-aza-crown in hexamethylenetetramine/trifluoroacetic acid system, the first formylated calix[4]-aza-crown derivative 6 was synthesized in yield of 61%. Reacting compound 6 with salicyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarbazide afforded four novel calix[4]crown hydrazone derivatives 7a–d in yields of 70–90%. By condensating compound 6 with series of bifunctional reagents, the novel mono-bridged biscalix[4]-aza-crown hydrazone derivatives 8a–c were prepared in high yields. The extraction experiments showed that all new compounds were good receptors for metal cations, especially, for soft metal cations. The extraction results suggested that the hydrazone groups produced favorable influences for binding soft cations. The two calix[4]arene units in compounds 8a–c could bind metal cations concurrently.

Synthesis of some azacrown derivatives and fabrication of their nanofilms on the glassy carbon surface

The modification of N-phenyl-aza-15-crown-5 (PA15C5) and N-(4-aminophenyl)-aza-15-crown-5 (4APA15C5) on glassy carbon (GC) electrode was performed by the electrochemical oxidation of the corresponding azacrown derivatives in anhydrous acetonitrile media. The electrochemical behavior of the resulting modified GC electrode was investigated in the presence of electroactive redox probes and these results, together with the X-ray photoelectron spectroscopy (XPS) and reflection-absorption infrared spectroscopy were used to confirm the attachment of these molecules onto the GC surface. The ellipsometric thicknesses of PA15C5 and 4APA15C5 films at the GC surface was obtained around 9.28 ± 0.40 and 10.50 ± 1.10 nm, respectively. Azacrown modified nanoscale surfaces serve as alkali metal sensor specific for their cavity in the crown ring.

Chiral Moieties-Oriented Single-Stranded Helical Assembly of Calix[4]azacrown Derivatives

Bridging of calix[4]arene derivatives with optically active subunits derived from chiral l/d-amino alcohols has resulted in two novel calix[4]azacrowns enantiomers S-C51H64NO7·CH3OH·H2O (S-1) and R-C51H64NO7·CH3OH·H2O (R-1), which were crystallized separately. Single crystal X-ray diffraction studies revealed that they each encapsulate a methanol molecule by weak interactions and that they form supramolecular enantiomeric helical arrangements along the crystallographic axis, which are constructed via C–H···O hydrogen bonds involving bridging water molecules. A similar helical arrangement was also found in the crystal structure of a previously reported calix[4]azacrown compound S-C108H146N2O16 (S-2).

Studies on [3]pseudorotaxane formation from a bis-azacrown derivative as host and imidazolium ion-derivatives as guest

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying π-π/donor-acceptor interaction. The mechanism for the naphthalene-based luminescence quenching by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with static quenching as the dominant one.

Novel Synthesis and Characterisation of N-Substituted-Calix[4](aza)Crown Derivatives

A novel series of calix[4](aza)crown derivatives is prepared by the reaction between calix[4](aza)crown and 4-bromoacetamido-N-alkyl-1, 8-naphthalimide derivatives. They may be useful fluorescent chemosensors, and have been structurally characterised by IR, 1H NMR, 13C NMR, MS and elemental analyses. From the analytical data, it was found those compounds adopted a cone conformation.

Novel synthesis of N-substituted-calix[4]azacrown derivatives

A novel series of calix[4]azacrown derivatives with the reaction between calix[4]azacrown and the different fluorophore derivatives, which may be useful fluorescent receptors, have been synthesized and structurally characterized by IR, 1H NMR, 13C NMR and MS. From their analysis data, it was found those compounds adopted a cone conformation.

Chiral calix[4]azacrowns for enantiomeric recognition of amino acid derivatives

In this study the synthesis of novel chiral calix[4]azacrown derivatives has been reported. The enantioselectivity of chiral receptors was investigated by using UV–vis spectroscopy. All the chiral calix[4]arene derivatives exhibited certain chiral recognition toward the enantiomers of phenylalanine (Phe-OMe·HCl) and alanine methyl ester hydrochlorides (Ala-OMe·HCl). As a chiral receptor, the furfuryl-armed calix[4]azacrown ether 7 has the best enantiomeric discriminating ability for α-amino acid ester hydrochlorides (up to K L/ K D=2.08, ΔΔ G 0=−1.82 kJ mol −1) in CHCl 3. The enantiomeric recognition abilities for guests are also discussed from a thermodynamic point of view.

ChemInform Abstract: Novel Synthesis and Characterization of N‐Substituted‐calix[4]azacrown Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Novel Synthesis and Characterization of N‐Substituted‐calix[4]azacrown Derivatives

Novel calix[4]azacrown derivatives from the reaction between calix[4]amidocrown and the different N‐(4‐bromoacetamidephthalimido)alkanes derivatives, which may be useful intemediate compounds of pseudorotaxane, have been synthesized and structurally characterized by IR, 1H NMR, 13C NMR, MS, and elemental analyses. From their analysis data, it was found that compounds 6a–d adopted a cone conformation.

Two electroactive ferrocenyl chalcones as original optical chemosensors for Ca 2+ and Ba 2+ cations in CH 3CN

The optical study of ferrocenyl ligands 1– 2 is presented, and reveals several interesting points. Contrary to their monosubstituted counterparts, these ligands exhibit fluorescence properties in acetonitrile. They can detect calcium, and also barium, by four different techniques: NMR, electrochemistry, UV–Vis absorption spectroscopy and fluorimetry in the same solvent. Each ligand detects both salts in the same manner by UV–Vis absorption and by fluorimetry. The response depends on the nature of the N terminal groups of the ligand. In each case, the ligand–calcium interaction is complex and involves 3–5 species in equilibrium in solution. Their association constants have been determined by fitting the UV–Vis data. Remarkably, for 2 and the calcium salts, nearly the same set of association constants can be used to fit not only the UV–Vis data obtained with calcium triflate (in a restricted range of concentration) or with calcium perchlorate, but also the NMR data obtained with calcium triflate. Interestingly, these results strengthen the fact that, in this family of compounds, the azacrown derivatives are less sensitive to high calcium triflate concentrations than their simple N-alkyl homologues. It is noteworthy that the complex non-monotonous fluorescence behaviour of compounds 1 and 2 upon Ca 2+ or Ba 2+ addition is quite original for ferrocenyl chalcones. These ligands constitute scarce examples of multi-signalling fluorescent ferrocenyl chemosensors for Ca 2+ and Ba 2+ cations in CH 3CN.

Potentiometric liquid membrane pH sensors based on calix[4]-aza-crowns

The calix[4]-aza-crown derivatives have been used in polymeric ion selective electrodes (ISEs) for pH sensing. The membranes containing ionophores and cation exchangers showed near Nernstian response to hydrogen ions and wide dynamic range. New carrier based electrodes exhibited high selectivity over alkali metal ions. The binding properties of ionophores with hydrogen ions (acidity constants pKa) in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. The influence of membrane solvents (plasticizers) and the types of the ion exchangers were studied.