Calix[4]arene-based, Hg2+ -induced intramolecular fluorescence resonance energy transfer chemosensor

A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ to a CH3CN solution of 1 gave a significantly enhanced fluorescence at approximately 575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al3+ induced a distinct increase of pyrenyl excimer emission ( approximately 475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg2+ and Al3+ were also proposed for the interesting observation.     

A novel pyrenyl-appended tricalix[4]arene for fluorescence-sensing of Al(III)

In acetonitrile, the tren-N-tricalix[4]arene 4 with three appended pyrenyl groups showed an enhanced fluorescence in the presence of Al³⁺ and, to a lesser extent, of In³⁺. Compound 4 was shown to form a 1:1 complex with Al³⁺, the metal cation being located in the tren part. The association constant (K_a) of 4 for the Al³⁺ cation was calculated to be 8.7×10³ M⁻¹ in acetonitrile.     

An agent-based approach to the two-dimensional guillotine bin packing problem

The two-dimensional guillotine bin packing problem consists of packing, without overlap, small rectangular items into the smallest number of large rectangular bins where items are obtained via guillotine cuts. This problem is solved using a new guillotine bottom left (GBL) constructive heuristic and its agent-based (A–B) implementation. GBL, which is sequential, successively packs items into a bin and creates a new bin every time it can no longer fit any unpacked item into the current one. A–B, which is pseudo-parallel, uses the simplest system of artificial life. This system consists of active agents dynamically interacting in real time to jointly fill the bins while each agent is driven by its own parameters, decision process, and fitness assessment. A–B is particularly fast and yields near-optimal solutions. Its modularity makes it easily adaptable to knapsack related problems.     

New estimators of the extreme value index under random right censoring,for heavy-tailed distributions

This paper presents new approaches for the estimation of the extreme value index in the framework of randomly censored samples, based on the ideas of Kaplan-Meier integration and the synthetic data approach of Leurgans (1987). These ideas are developed here in the heavy-tailed case, and lead to modifications of the Hill estimator, for which the consistency is proved under first order conditions. Simulations exhibit good performances of the two approaches, compared to the only existing adaptation of the Hill estimator in this context     

Thin‐layer chromatography‐bioautographic method for the detection of arginase inhibitors

Arginase represents a promising therapeutic target for various pathologies including inflammatory, cardiovascular, and parasitic diseases or cancers. In the current work, we report, for the first time, about the development of a thin‐layer chromatography‐based bioautography which can be used to rapidly detect arginase inhibitors in complex matrices such as plant extracts. The assay is based on the detection of urea produced by arginase using the coloring reagent α‐isonitrosopropiophenone, resulting in the formation of a pink background on thin‐layer chromatography plates. The assay conditions were optimized in order to provide sufficient contrast between the pink colored thin‐layer chromatography plate and the clearer zones generated by the presence of arginase inhibitors. Different parameters were tested, such as incubation time and temperature, atmospheric conditions, as well as substrate and enzyme concentrations. This technique makes it possible to detect 0.1 μg of a known arginase inhibitor, N^ω‐hydroxy‐nor‐Arginine, after it has been spotted, either pure or mixed with a Myrtus communis methanolic fruit extract, and the plate has been developed in an appropriate solvent. The newly developed method was used to reveal the presence of an inhibitor in hempseed cakes (Cannabis sativa L.).     

Synthesis and binding properties of calix[4]arenes with [2 + 2'] mixed ligating functional groups

A series of mixed [2 + 2'] p-tert-butylcalix[4]arene have been synthesised by selective 1,3-dialkylation of phenolic groups using various alkylating agents such as benzyl bromide, methyl iodide, ethyl bromoacetate, and 2-methoxyethyl tosylate. The extraction and complexation properties of the synthesized calixarenes towards alkali and alkaline earth metal cations have been investigated in acetonitrile by means of UV spectrophotometry and 1H NMR spectroscopy. The results show the formation of ML and/or ML2 species depending on the ligand and the cation. The enthalpies and entropies of complexation of alkali metal cations by a tetraglycol, diglycol-dibenzyl and diglycol-diester derivatives have been obtained from calorimetric measurements. The results revealed that the formation of ML species is controlled by enthalpy while the formation of ML2 from ML is entropy driven.     

Cyclische intramolekulare Ester von Äthanolamin-N-methylenphosphonsäuren

The reaction of monoethanolamine with formaldehyde and phosphorous acid gives a mixture of 2-hydroxy-2-oxo-4-phosphonylmethyl-1.4.2-oxazaphospha(V)-cyclohexane and monoethanolamine-N,N-dimethylenephosphonic acid; similarly, diethanolamine, formaldehyde and phosphorous acid yield 2-hydroxy-2-oxo-4-(β-hydroxy-ethyl)-1.4.2-oxazaphospha(V)-cyclohexane along with diethanolamine-N-methylenephosphonic acid.     

Alkali metal ion complexes of functionalised calixarenes--competition between pendent arm and anion bonding to sodium

Determination of the crystal structure of the acetonitrile inclusate of the complex formed between sodium trifluoromethanesulfonate (triflate, CF3SO3-) and the narrow-rim functionalised calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,27-di(phenylmethoxy)-26,28-di(2'-methoxyethoxy)calix[4]arene, has shown, somewhat unexpectedly, that the diether pendent arms do not chelate the sodium cation, although coordination of all four phenolic oxygen atoms does draw the calixarene into a nearly symmetrical cone form, consistent with conclusions drawn earlier from solution 1H NMR data. Crystals of C64H80O6.NaO3S.CF3.CH3CN obtained from acetonitrile solvent are monoclinic, C2/c, a structure determination at 'low' temperature (153 K) resolving several difficulties encountered in earlier attempts to analyse data acquired at approximately 295 K, and indicative of an interesting temperature dependence of substituent and anion orientations.     

Synthesis and Complexing Properties of Four New Tetraamido-type p-tert-Butyl Calix[4]arenes Presenting Two Proximal Binding Subunits

The synthesis of four new tetraamido-type p-tert-butylcalix[4]arenes presenting two proximal binding subunits is reported. Complexation of alkalimetals and zinc picrates with these ligands have been carried out and monitored by ¹H-NMR inCDCl₃. It is shown that hard cations are included in the tetraamido cavity while thezinc cation is chelated to the pyridine rings of one of the ligands. The formation of a 1:1:1heterobinuclear complex is also described     

Synthesis and complexing properties of four imidazolyl acetamido p-tert-butylcalix[4]arenes

Four imidazolyl acetamido p-tert-butylcalix[4]arenes 5–8 have been prepared by reacting the corresponding methyl esters derivatives 1–4 with histamine in 1:1 mixture of methanol:toluene. The yields ranged from 56 to 68%. 5–8 have been shown to be in cone conformation. The complexation behaviour of 5–8 towards monovalent metal picrates M⁺Pic⁻ with M⁺ = Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ and divalent metal picrates M²⁺(Pic⁻)₂ with M²⁺ = Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Zn²⁺ and Co²⁺ are given. Tentative localisation of the metal cations in the receptors is given. The binding properties towards these cations have been determined along with stoichiometries of the complexes.