Cyclen Research Articles

Enthalpies and entropies of sublimation and vaporization of aza crown ethers and cryptands measured by TGA

AbstractIn this work, the solid–gas and liquid–gas change of phase enthalpies of three aza crown ethers and two cryptands are derived from thermogravimetric data. For each of the compounds under study, the mass loss rate, dm/dt, was measured by isothermal thermogravimetry, then Pieterse and Focke equation combined with that of Clausius–Clapeyron was applied to correlate mass loss rate with temperature and to derive the respective vaporization or sublimation enthalpies at the experimental temperature and at 298.15 K. Such enthalpies are reported with the derived entropies and Gibbs energies of change of phase for the analyzed compounds. The results show a general trend of increasing value of the thermodynamic property as the number of the nitrogen atoms increases in the molecular structure of the macrocycle.

Azacrown-calixpyrrole isosteres: receptors and sensors for anions.

Calix[4]pyrroles (CPs) and polyammonium azacrowns (ACs) are well-known receptors for anions. CPs bind anions by directional hydrogen bonds that do not always work well for aqueous analytes. The positive charge in polyammonium ACs allows for a stronger but non-directional anion-ammonium electrostatic attraction but lack selectivity. Bridging the gap between CPs and ACs could increase affinity and potentially preserve the selectivity of anion binding. We have synthesized a flexible calixpyrrole-azacrown near isosteric receptor and incorporated an environmentally sensitive dansyl fluorophore to enable fluorescence measurements. Anion binding was evaluated using NMR and fluorescence titrations. The isosteric receptor shows a strong affinity for aqueous phosphates and phosphonates (Na+ salts) in the order HAsO42- > H2PO4- > H2P2O72- > glyphosate2- > AMP- > methylphosphonate- ≫ ADP2- or ATP3- but does not bind halides. This is in stark contrast to CP which shows a strong preference for halides over oxyanions. The anion binding by the new receptor was accompanied by analyte-specific changes in fluorescence intensity and spectral width and by a wavelength shift. These parameters were used in qualitative and quantitative sensing of aqueous anions. By applying machine-learning algorithms, such as linear discriminant analysis and support vector machine linear regression, this one sensor can differentiate between 10 different analytes and accurately quantify herbicide glyphosate and methylphosphonate, a product of sarin, soman or cyclosarin hydrolysis. In fact, glyphosate can be quantified even in the presence of competing anions such as orthophosphate (LODs were ≤ 1 μM).

Synthesis and chelation study of a fluoroionophore and a glycopeptide based on an aza crown iminosugar structure

Capitalizing on a recently reported iminosugar-based aza-crown (ISAC) accessed by a double Staudinger azaWittig coupling reaction, we have expanded the structural diversity of this new family of sweet cyclam analogs. Replacement of the two secondary amines linking the iminosugar units by two amide bonds obtained a cyclodimerization by with BOP and DIPEA led to a macrocycle that did not demonstrate efficient Zn2+ chelation unlike the parent ISAC. Introduction of two pyrene moieties on the secondary amines of the parent ISAC yielded a new fluoroionophore that selectively binds Hg2+ in methanol.

Further Approaches in the Design of Antitumor Agents with Response to Cell Resistance: Looking toward Aza Crown Ether-dtc Complexes.

The dianionic aza crown ether-dtc N,N'-bis(dithiocarbamate)-1,10-diaza-18-crown-6 (L2-) is a versatile ligand capable of yielding binuclear complexes with group 10 elements, also known as Ni-triade, [μ-(κ2-S,-S'-L)M2(PPh3)4]Cl2 (M = Pd (1), Pt (2)), [μ-(κ2-S,-S'-L)M2(PPh3)4](BPh4)2 (M = Pd (3), Pt (4)), and μ-(κ-S,-S'-L)Ni2(PPh3)2Cl2 (5), and has proven to be an excellent option to the design of metal-based drugs able to provide multiple response to cell resistance. Palladium and platinum complexes, 1 and 2, were tested for cytotoxicity in the human cervix carcinoma cell line HeLa-229, the human ovarian carcinoma cell line A2780, and the cisplatin-resistant mutant A2780cis, finding significant activity toward all three cancer cell lines, with low micromolar IC50 values, comparable to cisplatin. Markedly, against the cisplatin resistant cell line A2780cis, compound 2 exhibits better cytotoxic activity than the clinical drug (IC50 = 2.3 ± 0.2 μM for 2 versus 3.6 ± 0.5 μM for cisplatin). Moreover, an enhancement of the antitumor response is achieved when adding an equimolar amount of alkali metal chloride (NaCl or KCl) to the medium, for instance, testing compound 1 against the cisplatin-resistant A2780cis cells, the IC50 decreases from 9.3 ± 0.4 to 7.4 ± 0.3 and 5.4 ± 0.1 μM, respectively, after addition of the salt solution. For the platinum derivative 2, the IC50 improves by ca. 40% reaching 1.3 ± 0.1 μM when potassium chloride is added. Likewise, the resistant factor found for 2 (RF = 1) confirms that this complex circumvents cisplatin-resistance in A2780cis and is improved with the addition of potassium chloride (RF = 0.65). The presence of the aza crown ether moiety as linker in the systems studied herein is a key point since, in addition to allowing and facilitating interaction with alkali metal ions, this unit is flexible enough to adapt to a variety of environments, as confirmed by the X-ray crystal structures described, where different conformations and ways to fold in are found. In order to gain insight into the electronic and structural facts involved in the interaction of complex 2 with the alkali metal ions, a DFT study was performed, and the description of the molecular electrostatic potentials (MEPs) is also presented.

One-step electrochemically driven production of aza macrocycle-based pseudo-cryptand: An accessible route for creating of diverse cryptand-resembles compounds

Cryptands (CPs) are appeal architectures because they offer better selectivity and binding properties to alkali metals than crown ethers, although their synthesis is harsh and costly. We report here using an accessible and easy to use method for synthesis of a pseudo-cryptand structure by taking advantage of two homologues of “aza-crown ethers” and of in-situ generated “ortho-quinone” (OQ). The procedure relies on the in-situ production of three different 3-R-substituted (R = H, CH3, and OCH3) quinones, playing the role of electrophiles, which are electrochemically produced from their equivalent catechols in the presence of two studied azacrowns (ACs), in the role of the nucleophile, in aqueous buffered solutions. The advancement of electrochemically-triggered process is followed by cyclic voltammetry, controlled potential coulometry and UV–Vis techniques. The corresponding results infer a 1,4-Michael addition of ACs via their amine moieties to the electrochemically derived o-quinones. DFT calculation was employed to evaluate the diverse aspects of the process including the ability of thermodynamic proceeding of the reactions during different steps of processes, the effect of different substituted pendant groups on the ΔG and the HOMO-LUMO energy levels in either of OQs that directly introduce reactivity of them. Two different mechanisms ECE and ECECE were proposed for either of the nucleophiles. The NMR, FTIR, and mass-spectroscopy (MS) were exploited to characterize the possible structures formed. The binding affinities for the prepared compounds were shown by spectrophotometry using the respective solution of metallic cations.

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.

ANODIC STRIPPING VOLTAMMETRIC DETERMINATION OF LEAD USING A CHEMICALLY MODIFIED ELECTRODE BASED ON AZA CROWN ETHER

A glassy carbon electrode was modified by drop-coating technique using 1,4,10,13-Tetraoxa-7,16-diazaciclooctadecano (diaza-18 -crown-6 or DA18C6) and Nafion (NF) for the determination of Pb (II) by square wave anodic stripping voltammetric (SWASV). The new electrode exhibits an increase in due to major pre-concentration of aza crown ether and ionic exchange of NF with metal cations. Optimal conditions were: 3 mmol L-1 DA18C6, 3 wt % NF, 10 mmol L-1 HCl as supporting electrolyte, a frequency of 15 Hz , an accumulation time of 300 s and an accumulation potential of -0.80 V. The detection limit was 0.09 μg L-1 and linear range was 10-50 μg L-1. Interference from metal ions such us Fe (II), Pb (II), Cd (II) and Cu (II) was also studied. The method is sensitive, selective and simple with a relative standard deviation of 11%.

Electrochemical Reduction of α-Diketones and α-Diimines in the Presence of a Bielectrophilic Substrate: Synthesis of New Aza-Crown Compounds

The electrochemical reduction of α-diketones and α-diimines with the tritosylate of diethanolamine produces the corresponding aza crown compounds. This study was conducted using cyclic voltammetry in an aprotic medium and by preparative electrolysis on a stirred mercury pool. The obtained products were fully characterized by spectroscopic IR, NMR and HRMS methods and by elementary analysis.

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.

PREDICTIONS OF STRESS-STRAIN CURVE AND FATIGUE LIFE FOR AISI 316 STAINLESS STEEL IN CYCLIC STRAINING

In this study, experimental observations have been performed to understand the cyclic stress-amplitude response, the cyclic hardening/softening characteristics and the cyclic fatigue properties of AISI 316 stainless steel. Based on the experimental observations, these results are found so that the tested AISI 316 stainless steel possesses cyclic hardening characteristics. The shape of the stable hysteresis loop is symmetrical in tension and compression. The Massing cyclic stress-strain behavior is obviously absent. For the case of the absence of the Massing behavior, the power-law type equation is successfully applied to simulate the shape of the stable hysteresis loop at all applied levels of fully-reversed cyclic straining. For the �������� -based and ���������������� �������� -based fatigue life curves, the typical expressions are developed via cyclic fatigue properties. Besides, a power-law type relationship is also used to develop the fatigue life curve. In contrast to the typical expression, it is found that the power-law relationship is a viable and valid expression in fatigue life predictions. Similarly, the power-law relationship is also used to describe the correlation between the cumulative plastic strain energy W_f with the corresponding the fatigue life cycle N_f. Based on the comparison between the predicted and experiment cycles, it is confirmed that the predicted value of W_f calculated on the basis of the simulated hysteresis loop is capable of yielding reasonable life predictions via the W_f- N_f curve.

Intercalation/De-Intercalation Reactions of Lithium Ion at Graphite in Electrolyte Solutions Containing 3D-Transition-Metal Ions and Cyclic Ethers

The effects of 3d-transition-metal ions in the electrolyte on the intercalation/de-intercalation reactions of Li+ at graphite negative-electrodes were investigated. The edge plane of highly oriented pyrolytic graphite (HOPG) was used as a model electrode, and electrochemical properties were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. A drastic decrease in redox current due to intercalation/de-intercalation reactions of Li+ was observed in electrolyte solutions containing Fe, Co, Ni, and Mn ions. In addition, interfacial resistance between the edge plane HOPG electrode and the electrolyte increased significantly. The effects of cyclic ethers, such as crown ether, aza crown ether, and cryptand, as electrolyte additives were applied to suppress the degradation of graphite negative-electrodes. As a result, specific cyclic ethers greatly suppressed the degradation of edge plane HOPG negative-electrodes in electrolyte solutions containing the above transition-metal ions.

Rapid, Eco‐friendly, and One‐pot Synthesis of New Lariat Ethers Based on Anthraquinone by Using ZnO Nanoparticles via “Mannich” Reaction under Solvent‐free Condition

High yielding preparation of structurally different anthraquinone lariat ethers from the reaction of a novel anthraquinone aza crown ether 3 with a variety of substituted phenols and paraformaldehyde in the presence of zinc oxide nanoparticles at 100°C in a solvent‐free condition has been described. The procedure of these reactions is very simple, the yields are generally high to excellent, and the method is applicable to large scale operation without any problem. Furthermore, the zinc oxide nanoparticles could be recovered and recycled up to five times by simple filtration of the reaction mixture.

Macrobicyclic and Macrotricyclic Derivatives of N,N’,N’’,N’’’-Tetrasubstituted Cyclen and Cyclam

Macrobicyclic and Macrotricyclic Derivatives of N,N’,N’’,N’’’-Tetrasubstituted Cyclen and Cyclam

Synthesis, O2-binding ability and catalytic oxidation performance of cobalt(II) complexes with dihydroxamic acid functionalized N-pivot lariat ethers

Abstract Novel Co(II) complexes with dihydroxamic acids functionalized N -pivot lariat ether CoL 1 –CoL 4 were synthesized and characterized. Their oxygenation constants (ln K O2 ) and thermodynamic parameters (ΔH°, ΔS°) were measured. And their catalytic performance in oxidation of p -xylene to p -toluic acid (PTA) was investigated. The enhancement of O 2 -binding and catalytic oxidation activity by the oxa aza crown ether ring of the cobalt complexes were discussed.

A Study of Fracture in a Rotating Disc

This investigation deals with the fracture produced in a disc by simple rotation cycles as well as rotation cycles under an imposed hydrostatic pressure. In both the cases, relations are obtained between the critical angular speed omega and the number of cycles N, required to cause fracture.

Determination of log P values of new cyclen based antimalarial drug leads using RP-HPLC.

Lipophilicity, expressed by log P, is an important physicochemical property of drugs that affects many biological processes, including drug absorption and distribution. The main purpose of this study to determine the log P values of newly discovered drug leads using reversed-phase high-performance liquid chromatography (RP-HPLC). The reference standards, with varying polarity ranges, were dissolved in methanol and analyzed by RP-HPLC using a C18 column. The mobile phase consisted of a mixture of acetonitrile, methanol and water in a gradient elution mode. A calibration curve was plotted between the experimental log P values and obtained log k values of the reference standard compounds and a best fit line was obtained. The log k values of the new drug leads were determined in the same solvent system and were used to calculate the respective log P values by using the best fit equation. The log P vs. log k data gave a best fit linear curve that had an R2 of 0.9786 with Pvalues of the intercept and slope of 1.19 x 10(-6) and 1.56 x 10(-10), respectively, at 0.05 level of significance. Log P values of 15 new drug leads and related compounds, all of which are derivatives of macrocyclic polyamines and their metal complexes, were determined. The values obtained are closely related to the calculated log P (Clog P) values using ChemDraw Ultra 12.0. This experiment provided efficient, fast and reasonable estimates of log P values of the new drug leads by using RP-HPLC.

Aza-crown-ether-appended xanthene: selective ratiometric fluorescent probe for silver(I) ion based on arene-metal ion interaction.

In this Communication, we report on the development of a ratiometric fluorescent probe for silver(I) ions (Ag(I)) based on an arene-metal ion interaction. The probe selectively senses Ag(I) among various metal ions with a large-emission red shift under aqueous conditions, enabling the selective ratiometric detection of Ag(I). X-ray crystallography and NMR analyses reveal that Ag(I) comes into close contact with the fluorophore, which induces a large-emission red shift. The high sensing selectivity of the probe toward Ag(I) might be attributable to the restricted rigid conformation of the cyclic aza crown ether, which exclusively binds Ag(I). In addition to Ag(I) sensing, the Ag(I) complex of the probe is also used for the ratiometric sensing of a cyanide anion (CN(-)), highlighting the utility of the reported probe in fluorescence sensing.

Guest–host interaction in an aza crown analog

Host–guest interactions in a new aza crown analog with alkali and alkaline earth metal ions are studied at different levels of theory. All the compounds are optimized at B3LYP/6‐311+G(d) level of theory. To build the general idea about the consequence of methods of computation on the interaction energy of metal ions with the ligand, geometry optimization of some selected planar systems are carried out at the M05‐2X, PBE0, wB97XD, and B3LYP‐D levels. Calculated geometrical parameters, interaction energies, nucleus‐independent chemical shift values, and thermodynamic properties highlight the selectivity associated with these interactions. Further insights into the nature of the bonding in these ion‐macrocyclic supramolecular units are obtained through the natural bond orbital, atoms‐in‐molecules, bond energy decomposition, and electron localization function analyses. © 2014 Wiley Periodicals, Inc.

Complexation and transport of amino acid esters and their salts with synthesised chiral novel aza crown ether derivatives

The syntheses of four aza-15-crown-5 ethers bearing phenyl and phenoxymethyl moieties attached to a stereogenic centre on the crown ring were achieved. Macrocycles have exhibited strong binding ability (Ka = 5364–12,969 M− 1) and modest enantiomeric discrimination towards the enantiomers of amino acid methyl ester salts by UV titration method in CHCl3 at 25°C. Computer modelling results supported experimental data providing a detailed understanding of the molecular recognition mode between hosts and guests and the likely binding sites involved. Macrocycles were used for chiral discrimination of amino acids in their zwitterionic forms or as potassium and sodium salts in transport experiments across a bulk chloroform membrane with satisfactory selectivity.

ChemInform Abstract: Liquid Crystalline Crown Ethers

AbstractReview: 149 refs.