Synthesis, 1H-NMR conformational analysis and complexation studies of two di-imidazolyl acetamido p-tert-butylcalix[4]arenes

The synthesis of a new di-imidazolyl-di-methoxy acetamido p-tert-butylcalix[4]arene 4 is reported. 4 has been prepared by reacting the corresponding di-methyl ester di-methoxy derivative with histamine in 1:1 mixture of methanol: toluene. The binding properties of 4 towards alkali, alkaline earth, transition (Zn²⁺, Co²⁺) and heavy (Pb²⁺, Cd²⁺) metals have been investigated along with the complexes stoichiometries. The ¹H-NMR spectra of complexes show the location of cations in receptor 4. Partial cone conformation is observed only with strontium and calcium whereas the cone conformation is detected with most of the cations. Comparison of the complexation results with those obtained for di-imidazolyl acetamido p-tert-butylcalix[4]arene 3 missing the methyl groups is also reported.     

Determination of Ni2+ using an equilibrium ion exchange technique: Important chemical factors and applicability to environmental samples

The main purpose of this study was to investigate the relationship between some coffee roasting variables (weight loss, density and moisture) with near infrared (NIR) spectra of original green (i.e. raw) and differently roasted coffee samples, in order to test the availability of non-destructive NIR technique to predict coffee roasting degree. Separate calibration and validation models, based on partial least square (PLS) regression, correlating NIR spectral data of 168 representatives and suitable green and roasted coffee samples with each roasting variable, were developed. Using PLS regression, a prediction of the three modelled roasting responses was performed. High accuracy results were obtained, whose root mean square errors of the residuals in prediction (RMSEP) ranged from 0.02 to 1.23%. Obtained data allowed to construct robust and reliable models for the prediction of roasting variables of unknown roasted coffee samples, considering that measured vs. predicted values showed high correlation coefficients (r from 0.92 to 0.98). Results provided by calibration models proposed were comparable in terms of accuracy to the conventional analyses, revealing a promising feasibility of NIR methodology for on-line or routine applications to predict and/or control coffee roasting degree via NIR spectra.     

Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes

New liquid‐crystalline pillar[5]arene derivatives have been prepared by grafting first‐generation Percec‐type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc‐shaped structure perfectly suited for self‐organization into a columnar liquid‐crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6‐dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Col_h mesophase has been deduced from X‐ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4‐dimethoxypillar[5]arene and 1,6‐dicyanohexane.     

Extraction behaviour of amino acid esters by functionalised calix[4]arenes

Calixarenes 2–4, 6 and 7 in the cone conformation variously substituted by acid or amido functions, glycolic chains and hydroxyl groups were synthesised. They have been used in extraction of native amino acid and amino acid esters.     

Silica supported sulfated zirconia prepared by a sol-gel process: Effect of solvent evacuation procedure on the structural, textural and catalytic properties

Sol-gel process was used to prepare silica supported sulfated zirconia catalysts. The main parameter studied in this work was the gel drying method through four different ways of solvent evacuation. Textural, structural as well as the acidic properties of the four samples were studied using N₂ physisorption, X-ray diffraction, mass spectrometry, sulfur chemical analysis and adsorption-desorption of pyridine. The isomerization of n-hexane was used as a catalytic test. The surface areas and the pore distributions are highly affected by the drying mode. One of the four drying methods leads to a solid having improved textural properties and presenting both the crystalline ZrO₂ tetragonal phase and a particular type of sulfate mode bond. It seems that these three conditions are necessary for achieving high catalytic activity.     

Self‐inclusion in 5,11,17,23‐tetra‐tert‐butyl‐26,27,28‐tri­hydroxy­‐25‐(methoxy­carbonyl­methoxy)calix­[4]­arene chloro­form trisolvate

The title compound, C₄₇H₆₀O₆·3CHCl₃, is the first example of a lower‐rim mono‐ester calixarene derivative to be crystallographically characterized. The cone conformation adopted by the macrocycle is stabilized by three intramolecular hydrogen bonds. Self‐inclusion of the methyl ester chain in the cavity of an adjacent mol­ecule gives rise to infinite chains parallel to the c axis. C—H⋯π interactions involving the methyl group most imbedded in the cavity contribute to the stabilization of the system.     

Spectral analysis and generation of certain highly oscillatory curves related to chaos,part 2: Calculation aspects

The Fourier spectrum of a curve on a given interval, as represented by the Fourier series, is very reflective of the oscillatory behavior of the curve as the “weights” of the Fourier coefficients can indicate the individual prominence of frequencies of oscillations. But, unfortunately, the calculations of the Fourier coefficients can often get quite cumbersome.     

Umsetzungen von 1-Aminoalkan-1,1-diphosphonsäuren mit salpetriger Säure

Reactions of 1-Aminoalkane-1,1-diphosphonic Acids with Nitrous Acid Compounds of the structure RC(NH₂)(PO₃H₂)₂ 1 give products RC(OH)(PO₃H₂)₂ 2 in high yields by the reaction with nitrous acid. In contrast, when R = Aryl the reaction of 1 often gives in concentrated hydrochloric acid RCCl(PO₃H₂)₂ 3 . Exceptions to the above reaction are described.     

Hyperbranched molecules based on calixarenes

Synthesis of the diamide 2 derived from tris(2-aminoethyl)amine and monocarboxymethylcalix[4]arene provides a starting material useful for the preparation of a variety of hyperbranched molecules. Metal ion binding is one of the potentially useful properties of these new materials.