Selective functionalization at the small rim of calix[6]arene. Synthesis of novel non-symmetrical N3, N4 and N3ArO biomimetic ligands

Eight novel calix[6]arene-based biomimetic ligands for transition metal ions have been synthesized. They display a non-symmetrical N₃, N₄ or N₃ArO binding core that mimics enzyme active sites presenting histidine and tyrosine residues. The key step for their synthesis is the mono-alkylation at the small rim of the C_3v symmetrical trimethyl ether derivative of tBu-calix[6]arene with N-Boc-2-chloroethylamine to yield a novel calix[6]arene synthon. Its combined O-alkylation with a chloromethyl aromatic amine and N-deprotection or alkylation or reductive alkylation with a salicylaldehyde derivative yielded the calix[6]arene-based ligands with mixed N/O donors.     

Synthesis and binding properties of carboxylphenyl-modified calix[4]arenes and cytochrome c

Two novel carboxylphenyl-modified calix[4]arenes, tetrakis-carboxylphenylcalix[4]arene (TCPC) and 1,3-bis-carboxylphenylcalix[4]arene (BCPC), as well as a corresponding analogue for comparison, tetrakis-phenylcalix[4]arene (TPC), have been synthesized by palladium-catalyzed Suzuki cross-coupling of arylboronic acid and tetrabromocalix[4]arene as a key step. The binding properties of these calix[4]arene derivatives with bovine heart cytochrome c (cyt c) in dimethylformamide (DMF) was investigated by fluorescence spectroscopy. The binding affinity in the order of TCPC > BCPC ? TPC reflects a clear dependence on the number of carboxyl ligating groups attached onto a receptor and suggests the electrostatic force may be the predominant factor driving the complexing process. The stable 1:1 complexes of TCPC and BCPC with cyt c were evidenced with the binding constants of 3.15 × 10⁶ and 5.85 × 10⁵ L mol⁻¹, respectively. Due to a large overlap between the emission spectrum of TCPC and the absorption spectrum of cyt c, and a short interaction distance (estimated to be 5.6 nm) between them, the fluorescence quenching of TCPC upon complexation with cyt c is attributed to an efficient energy transfer.     

An efficient synthetic route to substituted tetrahydropyrimidines by Cu(OTf)2-mediated nucleophilic ring-opening followed by the [4+2] cycloaddition of N-tosylazetidines with nitriles

A highly efficient strategy for Cu(OTf)₂-mediated S_N2 type nucleophilic ring-opening followed by the [4+2] cycloaddition reactions of a number of 2-aryl-N-tosylazetidines with nitriles to afford a variety of substituted tetrahydropyrimidines in excellent yields is reported. The resulting tetrahydropyrimidines could easily be transformed into synthetically important 1,3-diamines by acid-catalyzed hydrolysis. The strategy has been extended to the synthesis of enantiomerically pure tetrahydropyrimidines from enantiopure disubstituted azetidines. The reaction proceeds through an S_N2 type mechanism as proposed by us earlier.     

Reaction of trimethylaluminum with calixarenes. I. Synthesis and structure of [Calix[8]arene methyl ether] [AlMe3]6·2 toluene and of [p-tert-butylcalix[8]arene methyl ether] [AlMe3]6·4 benzene

Reaction of the methyl ether of calix[8]arene with AlMe₃ yields [calix[8]arene methyl ether] [AlMe₃]₆·2 toluene,1, while that ofp-tert-butylcalix[8]arene gives [p-tert-butylcalix[8]arene methyl ether] [AlMe₃]₆·4 benzene,2. Both compounds1 and2 fail to react with alkali metal salts, MX. In1, the absence of a butylpara-substituent affords greater flexibility than is the case for thetert-butyl compound2. Thus, all six of the AlMe₃ groups are located on the outside of the macrocyclic ring (in projection) in1, but two AlMe₃ units are found on the inside in2. Colorless, air-sensitive crystals of1 belong to the triclinic space group witha=13.690(8),b=14.317(4),c=14.738(6) Å, =76.11(3), =62.36(4), =82.41(4)^o, andD _c =1.06 g cm^–3 forZ=1. Refinement led toR=0.101 for 1154 observed reflections.2 crystallizes in with =12.400(6),b=16.229(8),c=19.251(5) Å, =96.17(3), =107.25(3), =101.54(3)^o, andD _c =1.01 g cm^–3 forZ=1. Refinement of2 gaveR=0.128 for 4351 observed reflections. The macrocyclic array in both1 and2 lies about a crystallographic center of inversion. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82049 (48 pages).     

A novel method for the upper rim alkoxy-substitution of calix[4]arene via a bis(spirodienone) route

A mild and efficient one-step procedure for the upper rim modification of calix[4]arene via a bis(spirodienone) is described. The bis(spirodienone) on reaction with alcohols in the presence of p-TSA affords mono- and 1,3-disubstituted alkoxy derivatives in moderate to good yields.     

Synthesis and evaluation of multitopic bisbenzothiazolyl calix[4]arenes for ionic toxicants

Abstract

Two new benzothiazolyl calix[4]arene-based multitopic molecular receptors L-1 and L-2 have been synthesised and evaluated for recognition of ionic toxicants. The receptors selectively interact with copper, silver and fluoride ion toxicants as assessed through UV-visible, NMR and colorimetric techniques. The stability of L-1:Cu⁺² and L-2:Cu⁺² complexes was found to be higher than that of complexes formed with Ag⁺ and F^– complexes in the presence of trifluoroacetic acid. Superiority of L-1 over L-2 for analysis of identified toxicants has been determined by measurement of binding constants.     

(C70)2- -tert-butylcalix[6]arene complex films on electrodes catalyze the reduction of nitrite ions

(C₇₀)₂- -tert-butylcalix[6]arene complex films on GC electrode surface showed two couples of redox reactions in mixed solvent of (1:1, v:v) acetonitrile and water containing tetra-butylammonium perchlorate. The electrocatalytic reduction for nitrite by these films was observed, indicating that (C₇₀)₂- -tert-butylcalix[6]arene is capable of mediating the electron transfer to nitrite.     

A selective fluorescent probe for La and Y based on calix[6]arene

A new fluorescent probe based on calix[6]arene functionalized with three naphthoic acid groups was synthesized and showed selective fluorescence enhancement in the presence of La³⁺ and Y³⁺. In addition, the fluorescence enhancement behaviors depended on the pH values of the solution.     

Di-μ-hydroxy-bis(N,N,N′,N′-tetramethylenediamine)-copper(II) chloride [Cu(OH)·TMEDA]2Cl2: an efficient, practical catalyst for benzylation and allylation of amides

An efficient protocol for the benzylation or allylation of amides using the corresponding benzyl or allyl chlorides as electrophiles under basic conditions with commercially available 5 mol % of [Cu(OH)TMEDA]₂Cl₂ as catalyst was developed. Under these conditions, unprotected amino acids were benzylated without any racemization.     

An efficient synthesis of 5-substituted 1H-tetrazoles via B(C6F5)3 catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazole derivatives from various nitriles and sodium azide (NaN₃) via [3+2] cycloaddition reaction using B(C₆F₅)₃ as a catalyst. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, low toxicity, easy work-up, high yields, and compatibility with other functional groups.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

Synthesis of substituted imidazolines via [3+2]-cycloaddition of aziridines with nitriles

An efficient synthesis of 2,4-disubstituted 1H-imidazolines from aziridines and nitriles in the presence of BF₃-Et₂O or triethyloxonium tetrafluoroborate has been described. The reaction proceeds via a [3+2]-cycloaddition reaction. Most of the nitriles successfully underwent cycloaddition reactions with aziridines even at room temperature in a very short time.     

Mo(CO)6-mediated synthesis of calix[4]arenes carrying β-hydroxy ketones or α,β-unsaturated-β-amino ketones

Mo(CO)₆-mediated ring opening reactions of calix[4]arene isoxazolines/isoxazoles provide a new synthetic methodology for calix[4]arenes carrying bifunctional β-hydroxy ketones or α,β-unsaturated-β-amino ketones. Mo(CO)₆ is a highly selective and convenient reagent for the ring opening process of these supramolecular isoxazolines/isoxazoles.     

A new fluorogenic calix[4]arene N-dansylcarboxamide in the cone conformation for selective optical recognition of mercury(II)

A novel fluorogenic calix[4]arene dansylcarboxamide in the cone conformation has been synthesized as the disodium salt and employed in optical recognition of mercury(II). In extraction from aqueous solutions with high content of competing Na⁺ (C_Na+ ∼0.1 M; pH 5.0, acetate buffer) into CHCl₃, the fluoroionophore allowed for detection of 8.0 × 10⁻⁷ M Hg²⁺ (1:1 complex; ) with high selectivity over many other relevant metal ions.     

Bi2WO6/g-C3N4复合型催化剂的制备及其可见光光催化性能

利用溶剂热法,把Bi2WO6纳米颗粒植入g-C3N4层间和表面成功地制备了Bi2WO6/g-C3N4复合型光催化剂。通过XRD、SEM、TEM、BET和UV-Vis分别对样品的结构、组成、形貌、比表面积、光学性能进行了表征。结果表明,g-C3N4层状结构被部分剥离成碎片且与Bi2WO6纳米颗粒形成了复合物。Bi2WO6/g-C3N4复合型光催化剂与单一Bi2WO6相比不仅扩展了可见光的响应范围、增大了比表面还加速了光生电子与空穴的分离。结果表明,Bi2WO6的最佳负载量为60wt%时,复合型光催化剂具有最高的可见光催化活性且性能稳定、易回收。     

一维双核锌配合物[Zn2(SHSH)2(2-Me-py)2]的合成、晶体结构及理论研究

The crystal of one-dimensional binuclear zinc complex [Zn₂(SHSH)₂(2-Me-py)₂] was obtained in DMF and 2-methylpyridine, where SHSH is salicylaldehyde salicylhydrazone. It has been characterized by IR, UV, element analysis and X-ray diffraction analysis. The crystallographic data were as follows: monoclinic system, space group P2₁/c, a=1.144 49 nm, b=1.206 69 nm, c=1.379 39 nm, β=97.039°, Z=2, V=1.890 6 nm³, M_r=825.47, D_c=1.450 g·cm^-3, μ=1.324 mm-1, F(000)=848 and the final R=0.033 6 and wR=0.094 7 for 3 752 observed reflections with I≥2σ(I). The theoretical investigation of title complex as a structure unit was carried out at B3LYP/6-31G and HF/6-31G levels with Guassian 03W program, and the atomic charges, natural bond orbital analysis and bond energies were also discussed. CCDC: 260920.     

Bi2WO6/g-C3N4复合型催化剂的制备及其可见光光催化性能

利用溶剂热法, 把Bi₂WO₆纳米颗粒植入g-C₃N₄层间和表面成功地制备了Bi₂WO₆/g-C₃N₄复合型光催化剂。通过XRD、SEM、TEM、BET和UV-Vis分别对样品的结构、组成、形貌、比表面积、光学性能进行了表征。结果表明, g-C₃N₄层状结构被部分剥离成碎片且与Bi₂WO₆纳米颗粒形成了复合物。Bi₂WO₆/g-C₃N₄复合型光催化剂与单一Bi₂WO₆相比不仅扩展了可见光的响应范围、增大了比表面还加速了光生电子与空穴的分离。结果表明, Bi₂WO₆的最佳负载量为60wt%时, 复合型光催化剂具有最高的可见光催化活性且性能稳定、易回收。     

A mild and efficient chemoselective protection of amines as N-benzyloxycarbonyl derivatives in the presence of La(NO3)3·6H2O under solvent-free conditions

A facile and versatile method for the chemoselective N-benzyloxycarbonylation of amines has been developed by treatment with benzyloxycarbonyl chloride (Cbz-Cl) in the presence of lanthanum(III) nitrate hexahydrate under solvent-free conditions. The method is general for the preparation of N-Cbz derivatives of aliphatic (acyclic and cyclic) and aromatic amines.     

Syntheses, structures, and magnetic and optical properties of the compounds [Hg3Te2][UCl6] and [Hg4As2][UCl6]

Two new quaternary salts, [Hg₃Te₂][UCl₆] and [Hg₄As₂][UCl₆], have been synthesized and their structures determined by single-crystal X-ray diffraction analysis. [Hg₃Te₂][UCl₆] is the product of a reaction involving UCl₄, HgCl₂, and HgTe at 873 K. The compound crystallizes in space group P2₁/c of the monoclinic system. [Hg₄As₂][UCl₆] results from the reaction of U, Hg₂Cl₂, and As at 788 K. It crystallizes in space group Pbca of the orthorhombic system. [Hg₃Te₂][UCl₆] has a two-dimensional framework of layers, whereas [Hg₄As₂][UCl₆] has a three-dimensional framework of layers interconnected by Hg atoms linearly bonded to As atoms. Both framework structures contain discrete [UCl₆]²⁻ anions between the layers. [Hg₃Te₂][UCl₆] exhibits temperature-independent paramagnetism. The optical absorption spectra of these compounds display f-f transitions.     

TEMPO-catalyzed oxidation of benzylic alcohols to aldehydes with the H2O2/HBr/ionic liquid [bmim]PF6 system

A selective oxidation of benzylic alcohols to the corresponding aldehydes in room temperature ionic liquid was achieved by using TEMPO/HBr/H₂O₂ system, and both ether-insoluble acetamido-TEMPO and ionic liquid [bmim]PF₆ can be successfully recovered and reused for the oxidation of the same (different) substrate.