Paraquat guest induced hydrogen-bonding modes of a hydrazide-derived bis(meta-phenylene)-32-crown-10 host in the solid state

A hydrazide-derived bis(meta-phenylene)-32-crown-10 host showed a dimeric structure via quadruple N-H?O hydrogen bonds, but a polymeric structure via two N-H?O hydrogen bonds and two C-H?O hydrogen bonds at each knot in the presence of paraquat in the solid state, which led to a novel poly(taco complex) and ordering arrangement of the guest molecules indirectly.     

ZrOCl2·8H2O: an efficient Lewis acid catalyst for the one-pot multicomponent synthesis of β-acetamido ketones

Aromatic aldehydes were reacted in one-pot with enolisable ketones, acetonitrile and acetyl chloride at ambient temperature in the presence of ZrOCl₂·8H₂O to furnish the corresponding β-acetamido ketones in very good to excellent yields. X-ray crystallographic analysis of one anti-β-acetamido ketone exhibited a two-dimensional supramolecular framework by a combination of N-H?O, C-H?O and C-H?π (arene) hydrogen bonds.     

Aminopyridyl derivative of thiacalix[4]arene-carboxylic acid as ionizable highly selective Ag+ ionophore

A novel mono-ionizable receptor 2 possessing three aminopyridyl and one carboxylic group in 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. For competitive solvent extraction of alkali metal (Na⁺, K⁺ and Cs⁺) and some transition metal (Cu²⁺, Zn²⁺, TI⁺, Ag⁺) cations from aqueous solutions into chloroform, it was found that the introduction of proton-ionizable group (carboxylic acid moiety) into the aminopyridyl-thiacalix[4]arene derivative could further improve its Ag⁺ extractability with high selectivity.     

Anion binding by meta ureido-substituted thiacalix[4]arenes

The regioselective nitration of 25,26,27,28-tetrapropoxythiacalix[4]arene (1,3-alternate) led to the formation of mono- and dinitro derivatives bearing NO₂ groups in the meta positions at the same side of the molecule. Their reduction and subsequent condensation with arylisocyanates gave the new types of anion receptors with a so far unknown meta-substitution pattern. In a highly HB-competitive solvent like DMSO, the novel ligands showed good complexation abilities. Moreover, as can be documented by higher complexation constants, achiral receptors 9a, 9b are better preorganized for anion binding than corresponding stereoisomers 10a, 10b. Our results indicate that anion receptors based on meta-substituted thiacalixarenes possess complexation abilities fully comparable with common para-substituted analogues.     

Dimeric water embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene

X-ray crystallographic analysis and density functional B3LYP/6-31G(d) calculation confirm that dimeric water is embedded within a hydrophobic cavity of tetra-(p-tert-butyl)thiacalix[4]arene and stabilized by hydrogen bondings of aromatic π?H₂O(1) and methyl?H₂O(2) in the dimeric water inclusion complex with binding energies of 1.4 and 0.9 kcal mol⁻¹ respectively, and by hydrogen bonding formed between H₂O(2) and four phenolic OH groups from an adjacent tetra-(p-tert-butyl)thiacalix[4]arene, with binding energy of 3.8-4.2 kcal mol⁻¹.     

Evaluation and solubility improvement of Carvedilol: PSC[n]arene inclusion complexes with acute oral toxicity studies

The aqua phobic molecules that are practically insoluble in aqueous media demonstrate a staggeringly slow intrinsic dissolution rate. In this work, we exemplify the utility of calixarenes as a tool to form inclusion complexes with Carvedilol (CDL). It is poorly water soluble drug. CDL is a Biopharmaceutical Classification System (BCS) Class II drug and it is a nonselective β-adrenegenic blocking agent with α1-blocking activity. It is mainly used in the management of hypertension. The maximum complexation of the drug was accomplished after 48?h of stirring with para sulphonato calix[4]arene (PSC[4]arene) and para sulphonato calix[6]arene (PSC[6]arene) in water and evaporation of water to acquire solid complexes. The study includes characterisation of both the complexes—physical mixtures of drug and PSC[4]arene and PSC[6]arenes by different methods like Fourier-transform infra red spectroscopy, differential scanning calorimetry and powder X-ray diffraction, proton nuclear magnetic resonance. This studies shows that there is electrostatic interaction between drug and PSC[n]arenes. The complexation was determined by phase solubility study. The prepared complexes exhibited improved in vitro dissolution profile and decreased in vivo acute oral toxicity compared to the pure drug.     

Synthesis, structure and inclusion properties of cone-tris{[(5′-methyl-2,2′-bipyridyl)-5-yl]oxycarbonylmethoxy}hexahomotrioxacalix[3]arene

Hexahomotrioxacalix[3]arene having [(5′-methyl-2,2′-bipyridyl)-5-yl]oxycarbonylmethoxy group with cone conformation was prepared, which shows strong Ag⁺ affinity and acts as a ditopic receptor for Ag⁺ and nBuNH₃ ⁺. A conformational change of 2,2′-bipyridyl moiety from the original outward orientation of the ring nitrogen to the inside orientation toward the thiacalixarene cavity was observed in the process of Ag⁺ complexation.     

Synthesis and characterization of a new pillar[5]arene-based [1]rotaxane

In this study, we reported the synthesis of three kinds of mono-functional pillar[5]arene derivatives PRI, PRII and R and their structures were studied by 1D and 2D NMR spectra and mass spectra. The 2D NMR spectra including ¹H-¹³C HSQC, ¹H-¹H COSY and NOESY spectra indicated that PRI and PRII are both stable self-included pseudo[1]rotaxanes in CDCl₃. These original structures are promising compounds for the design of pillar[5]-based [1]rotaxane. And the results showed that R could exist stable in CDCl₃ and DMSO because of the coordination of N-H?O hydrogen bonding interaction and C-H?π interaction.     

Synthesis,crystal structure and complexation behaviour of a thiacalix[4]arene bearing 1,2,3-triazole groups

The structure and complexation behaviour of 1,3-alternate-1,2,3-triazole based on thiacalix[4]arene,1,3-alternate-1 and 2 have been determined by means of X-ray analysis, fluorescence and ¹H NMR spectroscopy. The X-ray results suggested that the nitrogen atom N3 on triazole ring can act as hydrogen bond acceptors in the self-assembly of a supramolecular structure. The fluorescence spectra changes indicated that the thiacalix[4]arene bearing 1,2,3-triazole groups were highly selective for Ag⁺ in comparison with other tested metal ions by enhancement of the monomer emission of pyrene. The ¹H NMR results suggested that Ag⁺ can be strongly bonded by the triazole groups with the cooperation of the ionophoric cavity formed by the two inverted benzene rings and the sulfur atoms of the thiacalix[4]arene.     

Excellent Ag+ selective receptors: Syntheses and complexation properties of novel biscalix[4]arene with benzalazine groups

By reacting mono-substituted or 1,3-bi-substituted [2-(p-formylphenyloxy)ethyloxy]-p-tert-butylcalix[4]arene (3 or 4) with hydrazine hydrate in ‘1+2’ or ‘2+2’ condensation mode, novel benzalazine-bridging biscalix[4]arenes 5 and 7 were conveniently obtained in the yields of 76 and 81%, respectively. Condensation of compound 4 and salicylide hydrazone gave a novel calix[4]arene benzalazine derivative 6 in the yield of 85%. The structures and conformations of all new compounds were characterised by elemental analyses, ESI-MS, ¹H NMR and ¹H–¹H COSY techniques. Biscalix[4]arene 7 adopts a symmetrical cone conformation with tube cavity. The liquid–liquid extraction experiment showed that all new hosts possessed excellent complexation abilities towards soft metal cations. Compound 7 exhibited high complexation selectivity towards Ag⁺. The Ag⁺/Na⁺ and Ag⁺/Hg²⁺ extraction percentages of host 7 were as high as 73.1 and 54.9, respectively. The UV–vis spectra complexation experiments revealed that the complexation constant of receptor 7 with Ag⁺ was 1.9 × 10⁵ M^? 1 and the 1:1 stoichiometry of receptor 7–Ag⁺ complex was formed. The ¹H NMR spectra complexation experiments suggested that Ag⁺ was bound in a cavity composed of two benzalazine groups on bridging chains.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group

Proton NMR data at 100 MHz are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, XC₆H₄Sn(CH₃)₃, where X = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon [¹J(¹³C¹H)] and tin [²J(SnC¹H)]. Solvent effects and other extraneous factors invalidate comparisons of ? values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ?[C(1)Sn] > ? [SnC] > ? [CH]. Satisfactory correlations (r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, ²J(SnC¹H) and the constituent, one-bond ¹J (Sn¹³C) and J(¹³C¹H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, ¹J(Sn¹³C) and ¹J(¹³C¹H) is lower (r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and ¹¹⁹Sn Mössbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para-trimethyltin group of ?0.14, and the significance of this value is discussed.     

(1+1) or (2+2) Coupling for bis(tosyloxyethoxy)benzenes with calix[4]arene and thiacalix[4]arene

As bifunctional reagents, bis(tosyloxyethoxy)benzenes can react with p-tert-butylcalix[4]arene or p-tert-butylthiacalix[4]arene to afford intramolecularly bridged (1+1) or intermolecularly bridged (2+2) products. It was found that the bridging pattern strongly depended on the structure of bis(tosyloxyethoxy)benzene and the kind of calixarene. For the ortho-isomer of bis(tosyloxyethoxy)benzene, intramolecularly bridged calix[4]arene and thiacalix[4]arene were the main products. For the para-isomer, the bridging reaction was in a (2+2) fashion. As for the meta-isomer, double thiacalix[4]arene and intramolecularly bridged calix[4]crown were synthesized.     

Variational RRKM theory calculation of thermal rate constant for carbon—hydrogen bond fission reaction of nitro benzene

The present work provides quantitative results for the rate of unimolecular carbon-hydrogen bond fission reaction of benzene and nitro benzene at elevated temperatures up to 2000 K. The potential energy surface for each C-H (in the ortho, meta, and para sites) bond fission reaction of nitro benzene was investigated by ab initio calculations. The geometry and vibrational frequencies of the species involved in this process were optimized at the MP2 level of theory, using the cc-pvdz basis set. Since C-H bond fission channel is barrier less reaction, we have used variational RRKM theory to predict rate constants. By means of calculated rate constant at the different temperatures, the activation energy and exponential factor were determined. The Arrhenius expression for C-H bond fission reaction of nitro benzene on the ortho, meta and para sites are k(T) = 2.1 × 10¹⁷exp(?56575.98/T), k(T) = 2.1 × 10¹⁷exp(?57587.45/T), and k(T) = 3.3 × 10¹⁶exp(?57594.79/T) respectively. The Arrhenius expression for C-H bond fission reaction of benzene is k(T) = 2 × 10¹⁸exp(?59343.48.18/T). The effect of NO₂ group, location of hydrogen atoms on the substituted benzene ring, reaction degeneracy, benzene ring resonance and tunneling effect on the rate expression have been discussed.     

Synthesis of a Tweezer—like Bis（Phenylthiapropoxy）calix[4]—arene as a Cation／π Enhanced Sensor for Ion—Selective Electrodes

Two novel 25,27-dihydroxy-26,28-bis(3-phenylthiapropxy)-calix[4]arene(3) and 25,27-dihydroxy-26,28-bis(3-phenylthiapropoxy)-5,11,17,23-tetra-tert-butylcalix[4] arene (4) were synthesized for the evaluation of their ion-selectivity in ion-selective electrodes(ISEs).ISEs based on 3 and 4 as neutral ionophores were prepared,and their selectivity coefficients for Ag^ (lg KAg,M^pot)were investigated against other alkali metal,alkaline-earth metal,aluminum,thallium(Ⅰ）,Lead and some transition metal ions using the separate solution method (SSM).These ISEs showed excellent Ag^ seletivity over most of the interfering cations examined,except for Hg^2 and Fe^2 having relative smaller interference(lg KAg,M^pot≤-2.1).     

Allosteric bindings of thiacalix[4]arene-based receptors with 1,3-alternate conformation having two different side arms

A novel ditopic receptor possessing two complexation sites such as crown ether and 2-pyridylmethyl groups bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with Li⁺ and Ag⁺ have been examined by ¹H NMR titration experiment. The exclusive formation of mononuclear complexes of 1,3-alternate-5 with Li⁺ and Ag⁺ was observed even though the formation of the heterogeneous dinuclear complexes was expected. The decomplexation of Li⁺ from the crown moiety of 1:1 complex 1,3-alternate-5?Li⁺ to form the Ag⁺?1,3-alternate-5 complex by addition of AgSO₃CF₃ clearly shows that pyridyl moiety works as an efficient switch-off of the recognition ability of the crown moiety. We have also developed the construction of hydrogen-bonding self-assembly heterodimeric systems based on bis(4-pyridyl) and dicarboxylic acid thiacalix[4]arene derivatives in 1,3-alternate conformation. Their supramolecular behaviors are studied by ¹H NMR titration experiments with K⁺ and Ag⁺ ions. Although the values of the dimerization constants are relatively small, the stability of the dimers is strong enough to overcome only small conformational changes upon complex formation.     

一种基于硫杂杯[4]芳烃的高效银离子载体

合成了基于下缘含有酰肼基团的硫杂杯芳烃衍生物的银离子载体1,其核磁研究证实硫杂杯芳烃以1,3-交替构象存在,并且通过非竞争萃取实验和竞争萃取实验研究了它对碱金属和过渡金属离子（Li⁺, Na⁺, K⁺, Cs⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Ag⁺）的键合能力和选择性。实验结果表明：将酰肼基团引入1,3-交替构象的硫杂杯芳烃骨架的下缘可以提高其对Ag⁺的键合能力和选择性,同时,对Cu²⁺的萃取能力较弱,对碱金属离子和其它的重金属离子几乎没有萃取能力。进一步的核磁滴定和电喷雾质谱实验显示化合物1与银离子形成配合物的配合计量比为1：1,由此推断主要由“N-Ag⁺”配位键以及硫杂杯芳烃骨架的协同作用构成了化合物1与银离子的配合模式。     

Structural studies on (3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellanes (DDDP)

The methyl and nitro derivatives of (3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellanes P2, P3, P7 and P9 were synthesized. The X-ray diffraction studies showed that 16,20-dinitro derivative (P7) crystallizes in non-centrosymmetric Pcn2 space group making this crystal to be promising in non-linear optics. The geometry of molecules is discussed in relation to the intramolecular interaction and charge distribution. Very helpful appeared from this point of view the ¹³C NMR spectra. In packing of molecules an important role play the N-H?O and C-H?O hydrogen bonds reflected both in the crystal structures and IR spectra.     

Cytosine: para-sulphonato-calix[4]arene assemblies: in solution, in the solid-state and on the surface of hybrid silver nanoparticles

The molecular recognition by para-sulphonato-calix[4]arene of cytosine, occurs in solution, in the solid-state and by assembly on the surface of para-sulphonato-calix[4]arene capped silver nanoparticles. Each of these states shows different modes of assembly; in solution a 1:1 complex is formed; in the solid state a 4:1 assembly exists, however some of the cytosine molecules are present as space fillers and do not participate in the host (guest complexes, finally on the surface of the hybrid silver/para-sulphonato-calix[4]arene nanoparticles a 2:1 cytosine/para-sulphonato-calix[4]arene assembly is observed. The assembly processes have been studied by DOSY NMR, fluorescence spectroscopy, Dynamic Light Scattering (DLS), Single Crystal Solid State Diffraction, Visible Spectroscopy and Electron Microscopy. The results demonstrate how cytosine initiates the aggregation of the hybrid silver/para-sulphonato-calix[4]arene hybrid nanoparticles.     

Weak interactions involving organic fluorine: a comparative study of the crystal packing in substituted isoquinolines

Weak interactions involving fluorine have been analyzed in the structure of 6-methoxy-1,2-diphenyl-1,2,3,4-tetrahydroisoquinoline with fluorine substitution at para-, meta- and ortho- positions, respectively, on the 1-phenyl ring. The packing modes in the crystalline lattice as determined by X-ray diffraction techniques generate motifs via F?F, C-H?F and C-F?π interactions. The three structures as compared to the parent compound depict conformational changes in the saturated tetrahydroisoquinoline moiety. The salient features of the four structures in terms of weak interactions involving fluorine suggest that organic fluorine does resemble the other halogens.     

Binding of fluorine containing anions by new cationic Co(III) complex: Competitive interaction of chloride and hexafluorophosphate with [Co(phen)(H2biim)2]

A new mixed ligand cobalt(III) complex salt [Co(phen)(H₂biim)₂]Cl₃ (1) (where phen = 1,10-phenanthroline, H₂biim = 2,2′-biimidazole) has been synthesized for the first time. In an effort to explore this new cationic complex [Co(phen)(H₂biim)₂]³⁺ as binding agent for fluoroanions, complex salt [Co(phen)(H₂biim)₂](PF₆)₂Cl·2H₂O(2) has been synthesized and characterized. Single crystal X-ray structure determination has revealed that complex salt 2 crystallizes in monoclinic crystal system with space group P2₁/c and consist of one complex cation, one chloride, two hexafluorophosphate anions and two water molecules of crystallization. The packing analyses revealed that the complex cations are arranged in such a way that N-H groups of biimidazole moiety are involved in N-H?Cl interaction with chloride ion while C-H groups of phen/H₂biim are involved in C-H?F interaction with hexafluorophosphate to keep these groups in close proximity. A strong network of hydrogen bond interactions C-H?F, N-H?O, N-H?Cl, C-H?O (water) and O-H?O (water) are responsible for the stabilization of 3D supramolecular architecture. To the best of our knowledge, this is the first crystal structure of any salt containing the cation [Co(phen)(H₂biim)₂]³⁺.