calixarenes and acetonitrile

In this manuscript we consider from a theoretical point of view the recently reported experimental quantification of anion-π interactions (the attractive force between electron deficient aromatic rings and anions) in solution using aryl extended calix[4]pyrrole receptors as model systems. Experimentally, two series of calix[4]pyrrole receptors functionalized, respectively, with two and four aryl rings at the meso positions, were used to assess the strength of chloride-π interactions in acetonitrile solution. As a result of these studies the contribution of each individual chloride-π interaction was quantified to be very small (<1 kcal/mol). This result is in contrast with the values derived from most theoretical calculations. Herein we report a theoretical study using high-level density functional theory (DFT) calculations that provides a plausible explanation for the observed disagreement between theory and experiment. The study reveals the existence of molecular interactions between solvent molecules and the aromatic walls of the receptors that strongly modulate the chloride-π interaction. In addition, the obtained theoretical results also suggest that the chloride-calix[4]pyrrole complex used as reference to dissect experimentally the contribution of the chloride-π interactions to the total binding energy for both the two and four-wall aryl-extended calix[4]pyrrole model systems is probably not ideal.

Topics: Acetonitriles; Calixarenes; Chlorides; Hydrogen Bonding; Models, Chemical; Porphyrins; Quantum Theory; Solutions; Thermodynamics

A innovative 5-Cl-8-oxyquinolinepropoxycalix[4]arene ligand (2) have been prepared, exhibiting, at room temperature, blue fluorescent light emission and resulting in shift band to green fluorescent light (fluorescence mode) in the presence of coordinated Eu(III) and Tb(III) ions. Terbium complex presented phosphorescence emission as noted by typical bands at 490 nm, 545 nm and 585 nm. TG/DTG data exhibited typical thermal behavior for these compounds, however DSC curves showed the melting temperature near 300 °C for the samples, demonstrating an unusual thermal stability when quinoline derivatives are attached to calix[4]arene matrix. This fact strongly suggests an effective approach to preparing the photoluminescent compound associating high chemical and thermal stability.

Topics: Acetonitriles; Calixarenes; Calorimetry, Differential Scanning; Chloroquinolinols; Europium; Ligands; Luminescence; Magnetic Resonance Spectroscopy; Spectrometry, Fluorescence; Spectrophotometry, Infrared; Spectrophotometry, Ultraviolet; Temperature; Terbium; Thermogravimetry

Calixresorcinarenes have proved to be unique molecules for molecular recognition via hydrogen bonding, hydrophobic and ionic interactions with suitable substrates such as cations. The study of the interactions involved in the complexation of different cations with calixresorcinarenes in solvent mixtures is important for a better understanding of the mechanism of biological transport, molecular recognition, and other analytical applications. This article summarizes different aspects of the complexes of the Ti(3+) metal cation with c-methylcalix[4]resorcinarene (CMCR) as studied by conductometry in acetonitrile (AN)-water (H₂O) binary mixtures at different temperatures. Conductance data show that the metal cation/ligand (ML) stoichiometry of the complexes in solution is 1:1 in all cases. Non-linear behaviour was observed for the variation of logKf of the complexes vs. the composition of the binary solvent mixtures. Selectivity of CMCR for the Ti(3+) cation is sensitive to solvent composition; in some cases and at certain compositions of the mixed solvent systems, the selectivity order is changed. Values of thermodynamic parameters (ΔH(c)(0), ΔS(c)(0)) for formation of the CMCR-Ti(3+) complexes in AN-H₂O binary systems were obtained from the temperature dependence of stability constants, and the results show that the thermodynamics of complexation reactions are affected by the nature and composition of the mixed solvents.

Topics: Acetonitriles; Calixarenes; Coordination Complexes; Electric Conductivity; Phenylalanine; Solutions; Solvents; Thermodynamics; Titanium; Water

The calix[4]arene secondary-amide derivative L was synthesized, and its complexation with alkali-metal cations in acetonitrile (MeCN) was studied by means of spectrophotometric, NMR, conductometric, and microcalorimetric titrations at 25 °C. The stability constants of the 1:1 (metal/ligand) complexes determined by different methods were in excellent agreement. For the complexation of M(+) (M = Li, Na, K) with L, both enthalpic and entropic contributions were favorable, with their values and mutual relations being quite strongly dependent on the cation. The enthalpic and overall stability was the largest in the case of the sodium complex. Molecular and crystal structures of free L, its methanol and MeCN solvates, the sodium complex, and its MeCN solvate were determined by single-crystal X-ray diffraction. The inclusion of a MeCN molecule in the calixarene hydrophobic cavity was observed both in solution and in the solid state. This specific interaction was found to be stronger in the case of metal complexes compared to the free ligand because of the better preorganization of the hydrophobic cone to accept the solvent molecule. Density functional theory calculations showed that the flattened cone conformation (C(2) point group) of L was generally more favorable than the square cone conformation (C(4) point group). In the complex with Na(+), L was in square cone conformation, whereas in its adduct with MeCN, the conformation was slightly distorted from the full symmetry. These conformations were in agreement with those observed in the solid state. The classical molecular dynamics simulations indicated that the MeCN molecule enters the L hydrophobic cavity of both the free ligand and its alkali-metal complexes. The inclusion of MeCN in the cone of free L was accompanied by the conformational change from C(2) to C(4) symmetry. As in solution studies, in the case of ML(+) complexes, an allosteric effect was observed: the ligand was already in the appropriate square cone conformation to bind the solvent molecule, allowing it to more easily and faster enter the calixarene cavity.

Topics: Acetonitriles; Amides; Calixarenes; Calorimetry; Cations; Coordination Complexes; Crystallography, X-Ray; Magnetic Resonance Spectroscopy; Metals, Alkali; Models, Molecular; Phenols; Spectrophotometry; Thermodynamics

The complexation reactions between the macrocyclic ionophore, p-isopropylcalix[6]arene and Cs+ cation were studied in dimethylsulfoxide-acetonitrile (DMSO-AN) binary non-aqueous solvents at different temperatures using a conductometry method. The conductance data show that the stoichiometry of the (p-isopropylcalix[6]-arene·Cs)+ complex in all binary mixed solvents is 1:1. The stability of the complexes is affected by the composition of the binary solvent media and a non-linear behavior was observed for changes of log K(f) of the complex versus the composition of the binary mixed solvents. The thermodynamic parameters (DH°(c) and DS°(c)) for formation of (p-isopropyl-calix[6]arene·Cs)+ complex were obtained from temperature dependence of the stability constant and the obtained results show that the (p-isopropylcalix[6]arene·Cs)+ complex is enthalpy destabilized, but entropy stabilized, and the values of the mentioned parameters are affected strongly by the nature and composition of the binary mixed solvents.

Topics: Acetonitriles; Calixarenes; Cations; Cesium; Chelating Agents; Chlorides; Conductometry; Coordination Complexes; Dimethyl Sulfoxide; Solvents; Thermodynamics

Not one but two: The title reaction proceeds through the dual C-H bond cleavage of both aniline and acetonitrile. The reaction affords a variety of cyano-bearing indolinones in excellent yield. Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile.

Topics: Acetonitriles; Alkanes; Alkenes; Alkylation; Calixarenes; Catalysis; Molecular Structure; Oxidation-Reduction; Palladium

Following the synthesis and characterization of meso-tetramethyl tetrakis (4-phenoxy acetone) calix[4]pyrrole, 1, the solution properties of this receptor in various solvents were investigated. Particular emphasis is placed on the selection of the solvent in assessing thermodynamic selectivity in ion complexation studies involving calixpyrrole receptors. Thus, statements recently made in the literature are addressed.The interaction of 1 with anions and cations was assessed through (1)H NMR in CD(3)CN at 298 K. Among anions, significant chemical shift changes were observed in the pyrrolic protons by the addition of halide salts to 1 in the deuterated solvent. The sequence observed in the Deltadelta values is that observed in the transfer Gibbs energies of these anions from a dipolar aprotic (acetonitrile) to a protic medium (representative of 1) based on the Ph(4)AsPh(4)B convention. As far as metal cations in CD(3)CN are concerned, the most significant changes are observed (relative to those of the ligand) in the protons of the phenoxy acetone functionality upon the addition of the mercury(ii) salt to 1. Conductance measurements reveal the formation of 1 : 1 complexes with these ions. Thermodynamic data derived from titration calorimetry are reported and compared with available data for analogous ligands. A quantitative evaluation of the thermodynamic stability was carried out. The applications of these ligands as anchor groups in oligomeric frameworks are discussed. Final conclusions are given.

Topics: Acetonitriles; Calixarenes; Conductometry; Isomerism; Magnetic Resonance Spectroscopy; Porphyrins; Solubility; Solutions; Substrate Specificity; Thermodynamics

Solid C-methylcalix[4]resorcinarene solvated by acetonitrile and water (CAL-Me) and then modified by slow solvent evaporation (CAL-Me*) was studied using single-crystal and powder X-ray diffraction, FT-IR, and (13)C CP/MAS NMR. The CAL-Me solvate crystallizes in the monoclinic P2(1)/n space group with three CH(3)CN and two H(2)O molecules in the asymmetric part of the unit cell. The CAL-Me molecules adopt a typical crown conformation with all of the hydroxyl groups of the aryl rings oriented up and all of the methyl groups disposed down (the rccc isomeric form). The crystalline network is formed by resorcinarene, CH(3)CN, and H(2)O molecules and assembled by intermolecular hydrogen bonds and weak C-H...A or C-H...pi interactions. The desolvated CAL-Me* loses its crystalline character and becomes partly amorphous. It is devoid of CH(3)CN and deficient in water. However, the resorcinarene molecules still remain in the crown conformation supported by intramolecular hydrogen bonds, while intermolecular hydrogen bonds are considerably disintegrated. The work directs general attention to the problem of stability and polymorphism of resorcinarene solvates. It shows that the joint use of diffractometric and spectroscopic methods is advantageous in the structural studies of complex crystalline macromolecular systems. On the other hand, the solid-state IR and NMR spectroscopic analyses applied in tandem have been found highly beneficial to elucidate the disordered structure of poorly crystalline, desolvated resorcinarene.

Topics: Acetonitriles; Calixarenes; Crystallography, X-Ray; Hydrogen Bonding; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Phenylalanine; Solvents; Spectroscopy, Fourier Transform Infrared; X-Ray Diffraction

A series of three di-ionizable calix[4]arenes with two pendant dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims was synthesized. Structures of the three ligands were identical except for the length of the spacers which connected the two dansyl groups to the calix[4]arene scaffold. Following conversion of the ligands into their di-ionized di(tetramethylammonium) salts, absorption and emission spectrophotometry were utilized to probe the influence of metal cation (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Ag+, Cd2+, Co2+, Fe2+, Hg2+, Mn2+, Pb2+, Zn2+ and Fe3+) complexation in acetonitrile. Upon complexation with these metal cations, emission spectra underwent marked red shifts and quenching of the dansyl group fluorescence for the di-ionized ligand with the shortest spacer. A similar effect was noted for the di-ionized ligand with an intermediate spacer for all of the metal ions, except Ba2+. For the di-ionized ligand with the longest spacer, the metal cations showed different effects on the emission spectrum. Li+, Mg2+, Ca2+ and Ba2+ caused enhancement of emission intensity with a red shift. Other metal cations produce quenching with red shifts in the emission spectra. Transition metal cations interacted strongly with all three di-ionized ligands. In particular, Fe3+ and Hg2+ caused greater than 99% quenching of the dansyl fluorescence in the di-ionized ligands.

Topics: Acetonitriles; Calixarenes; Dansyl Compounds; Fluorescence; Ions; Metals; Phenols; Spectrophotometry

Retention profiles in series of the neutral and highly hydrophobic 1,3,4-oxadiazoles containing chlorophenylurea and halogenobenzamide moiety and indicating analgesic activity were determined in the isocratic standard- and narrow-bore HPLC systems employing, respectively, various octadecylsilica and different calixarene bonded stationary phases. When acetonitrile - 2.65 mM phosphoric acid (55 : 45, %, v/v), pH* 3.25, mobile phase was applied retention of these compounds increased with decline of their overall hydrophobicity according to the general preference of more polar compounds by calixarene cavity in time of its non-specific host-guest supramolecular interactions with halogenated substances. The size of calixarene nanocavity and its upper-rim substitution did not change the observed retention order, resolution and selectivity of separation for oxadiazoles. Compared to the retention on the non-end-capped and the highly-end-capped octadecylsilica HPLC column a most improved separation of some regioisomers of halogenated 1,3,4-oxadiazoles were observed on both used calixarene-type HPLC supports. In addition, preliminary data on the self-assembled supramolecular crystal structure of exemplary 1,3,4-oxadiazolchlorophenylurea with cis-elongated conformation was reported and formation of the monovalent inclusion host-guest complexes between 1,3,4-oxadiazoles and each calixarene-type stationary phase was studied with molecular modelling MM+ and AM1 methods. The structural, isomeric and energetic factors leading to the hydrogen bond stabilized inclusion complexes between these species were considered and used for explanation of observed retention sequence and selectivity of 1,3,4-oxadiazoles separation in applied calixarene-based HPLC systems. All these data would be useful in future development of optimized procedures enabling encapsulation of 1,3,4-oxadiazolurea-type drugs with calixarenes.

Topics: Acetonitriles; Analgesics; Benzamides; Calixarenes; Chromatography, High Pressure Liquid; Crystallography; Halogenation; Hydrogen Bonding; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Models, Molecular; Molecular Structure; Oxadiazoles; Phenylurea Compounds; Phosphoric Acids; Silicon Dioxide; Technology, Pharmaceutical

The migration behavior of three calix[4]pyrroles (C4Ps) in acetonitrile (ACN) and in the mixtures of ACN/ethanol (EtOH) (95:5; v/v)with tetraalkylammonium chloride as background electrolyte (BGE) was studied. Electroosmotic flow (EOF) mobilities and absolute mobilities in ACN and mixture of ACN/EtOH (95:5; v/v) were investigated. A decrease of EOF mobilities in EtOH/ACN was observed compared with that of in pure ACN. Variation of the C4Ps effective mobilities as a function of the square root of concentration of tetraakylammonium chloride salts such as tetramethylammonium chloride (Me4NCl), tetraethylammonium chloride (Et4NCl) and tetrabutylammonium chloride (Bu4NCl) in both solvents was plotted, and straight lines were exhibited when Bu(4)NCl was used as BGE. Absolute mobilities of C4Ps were obtained by extrapolation from the mentioned plots. It was found that the absolute mobilities of C4Ps is independent of the nature of BGE and the values are: meso-octamethylcalix[4]pyrrole (OMCP)>meso-tetracyclopentylcalix[4]pyrrole (TPCP)>meso-tetracyclohexylcalix[4]pyrrole (THCP). The ion-pairing constants follow the order under given solvent: Me4N+>Et4N+>Bu4N+, and ion-pairing constant of C4P follows the order: THCP>TPCP>OMCP. As though, ion-pairing association is intensified by steric hindrance.

Topics: Acetonitriles; Calixarenes; Cations; Electrolytes; Electroosmosis; Electrophoresis, Capillary; Porphyrins; Quaternary Ammonium Compounds

The interaction of calix[3]thieno[1]pyrrole, 1, and halide and dihydrogen phosphate anions in a variety of solvents (acetonitrile, propylene carbonate, N,N-dimethylformamide, and dimethyl sulfoxide) has been investigated through 1H NMR, conductance measurements, and titration calorimetry. 1H NMR measurements reveal the sites of interaction of the ligand with the anions in CD3CN while the composition of the complex was determined through conductance measurements. A quantitative assessment of anion-ligand interactions is provided. Thus the thermodynamics of complexation of 1 with halide and dihydrogen phosphate anions in dipolar aprotic media at 298.15 K is reported. These data are interpreted in terms of the thermodynamics of transfer of reactants and product from a reference solvent (acetonitrile) to other solvents. The crucial role played by the solvent on the ability of the ligand to interact with anions and on the composition of the complex is demonstrated.

Topics: Acetonitriles; Anions; Calixarenes; Conductometry; Dimethyl Sulfoxide; Dimethylformamide; Formamides; Hydrocarbons, Halogenated; Ligands; Magnetic Resonance Spectroscopy; Molecular Structure; Phosphates; Propane; Pyrroles; Solvents; Thermodynamics; Thiophenes

Standard solution Gibbs energies, DeltasG degrees, of the resorcarene-based receptor 5,11,17,23-ethylthiomethylated calix[4]resorcarene, (characterized by 1H NMR and X-ray diffraction studies) in its monomeric state (established through partition experiments) in various solvents are for the first time reported in the area of resorcarene chemistry. Transfer Gibbs energies of from hexane (reference solvent) to other medium are calculated. Agreement between DeltatG degrees (referred to the pure solvents) and standard partition Gibbs energies, DeltapG degrees (solvent mutually saturated) is found. Cation-ligand interactions were investigated through 1H NMR (CD3CN and CD3OD) and conductometric titrations in acetonitrile and methanol. 1H NMR data revealed the sites of interaction of with the metal cation. The composition of the metal-ion complexes (Ag+ and Pb2+ in acetonitrile and Ag+ and Cu2+ in methanol) was established through conductometric titrations. Thus, complexes of 1:1 stoichiometry were formed between and Ag+ and Pb2+ in acetonitrile and Cu2+ in methanol. However, in moving from acetonitrile to methanol, the composition of the silver complex was altered. Thus, two metal cations are hosted by a unit of the ligand. As far as Cu2+ and in acetonitrile is concerned, conductance data suggest that metalates are formed in which up to four units of Cu2+ are taken up per unit of resorcarene. The contrasting behavior of with Cu2+ in acetonitrile relative to methanol is discussed. As far as mercury (II) is concerned, the unusual jump in conductance observed in the titration of Hg2+ with in acetonitrile and methanol after the formation of a multicharged complex (undefined composition) is attributed to the presence of highly charged smaller units (higher mobility) resulting from the departure of pendant arms from the resorcarene backbone. Isolation of these species followed by X-ray diffraction studies corroborated this statement. The thermodynamic characterization of metal-ion complexes of Ag+ and Pb2+ in acetonitrile and Cu2+ and Ag+ in methanol is reported. Final conclusions are given.

Topics: Acetonitriles; Calixarenes; Cations; Conductometry; Copper; Macrocyclic Compounds; Magnetic Resonance Spectroscopy; Metals; Methanol; Models, Molecular; Molecular Conformation; Silver; X-Ray Diffraction

The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent-ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1-CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 x 10(3). In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 x 10(3) higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in propylene carbonate the ability of 1 to interact with these cations is lost. An outstanding feature of thermodynamics emerges when an assessment is made of the ligand effect on the complexation of these cations and analogues calix(4)arene derivatives. Thus, in acetonitrile the thermodynamics of cation complexation by the hydrophilic cavity of a calix(4)arene containing mixed pendant groups is built up from thermodynamic data for the same process involving derivatives with common functionalities at the narrow rim. This is a unique example of the additive contribution of pendant arms in the field of thermodynamics of calixarene chemistry.

Topics: Acetonitriles; Calixarenes; Ligands; Magnetic Resonance Spectroscopy; Mercury; Methanol; Molecular Structure; Organometallic Compounds; Phenols; Silver; Solvents; Thermodynamics

A calix[4]arene derivative containing ethoxycarbonylmethoxy groups in the coordination sphere and an iminopyridinium indicator group was studied by FT-IR spectroscopy in acetonitrile solution. The characteristic changes of v(C=O) stretching vibration offered an opportunity for the improvement on selectivity of the ion recognition process of this ligand. The shift of the carbonyl stretching vibration band depended on complex formation as well as on the equilibrium constants of complex formation. In the case of sodium complex, a well-defined isobestic point was detected in the v(C=O) region while altering the sodium concentration. The affinity of thallium(III) to form complex with calixarene 1 was found comparable with those of lithium, sodium or calcium. The complex was found to be an M2L type supramolecule, whereas one molecule of triethylamine was necessary for the formation of each complex.

Topics: Acetonitriles; Calcium; Calixarenes; Ethylamines; Ions; Lithium; Models, Chemical; Phenols; Sodium; Spectrophotometry; Spectroscopy, Fourier Transform Infrared; Thallium; Time Factors

The complexation spectroscopic behavior of three p-tert-butylcalix[4]arene Schiff bases i.e. 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(3-nitrobenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (1), 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(2-hydroxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (2), and 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(2-hydroxy-3-methoxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (3) with lanthanoid nitrates (Tb3+ and Eu3+) has been investigated in anhydrous acetonitrile at 25 degrees C by using UV-vis and FT-IR as well as fluorescence spectra. The results obtained indicated that the spectroscopic behavior of compounds 1-2 upon complexation with lanthanoid ions did not show any significant larger difference in comparison with free compounds 1 and 2, which may be contributed to the poor binding ability. Contrary to compounds 1 and 2, the lower rim functional groups in compound 3 can form two large pi electron conjugate system with lanthanide ion and encapsulate lanthanide ions tightly, displaying the novel spectroscopic behavior upon complexation with lanthanide ions. As compared with compound 3, the formation complexes of compound 3 with Tb3+ and Eu3+ showed new broad intense absorption at 398 nm, respectively, and IR spectra showed that O-H stretching vibration at 3413.40 cm(-1) displayed a large drop. It is interestingly noted that the narrow emission line spectra were observed only for 3 complex with Tb3+, but did not for 3-Eu3+ complex. In the 3-Eu3+ complex, the broad-band emission at lambda(max) = 534 nm was obtained at the excitation of 398 nm. The spectroscopic behavior of three calix[4]arene derivatives upon complexation with lanthanoids was discussed from the relationship between the host structure and the properties of guest lanthanide ions.

Topics: Acetonitriles; Calixarenes; Lanthanoid Series Elements; Light; Nitrates; Phenols; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Spectroscopy, Fourier Transform Infrared