Multinuclear calixarene synthons with covalently linked aryl-palladium(II) complexes

New synthetic procedures have been developed for potentially useful metallacalixarene building blocks. The metal sites were covalently connected to calix[n]arenes (n = 4, 6) by oxidative addition of 4-iodobenzyl precursors to either Pd(PPh(3))(4) or Pd(2)(dba)(3)/tmeda (dba = dibenzylideneacetone) to furnish calixarene-modified aryl-Pd(II)I(L(n)()) complexes [L(n)() = bis-PPh(3) or N,N,N',N'-tetramethylethylenediamine (tmeda)]. Methods were explored for the selective preparation of mono-Pd(II)-calix[4]arene and di-Pd(II)-calix[n]arenes (n = 4 or 6) complexes and also for bifunctional calix[4]arene synthons with two Pd(II) complexes accompanied by 4-pyridylmethyl or 4-cyanobenzyl groups. The properties of the Pd(II)-calix[n]arenes were studied in detail by one- and two-dimensional NMR and mass spectrometric techniques. The X-ray molecular structures of two 4-iodobenzylcalix[4]arene precursors were also determined.     

Arrowroot starch-based films incorporated with a carnauba wax nanoemulsion,cellulose nanocrystals,and essential oils: a new functional material for food packaging applications

Arrowroot starch (AA)-based films incorporated with a carnauba wax nanoemulsion (CWN), cellulose nanocrystals (CNCs), and essential oils (EOs) from Mentha spicata (MEO) and Cymbopogon martinii (CEO) were produced using the casting technique and then characterized in terms of their water barrier, tensile, thermal, optical, and microstructural properties and in vitro antifungal activity against Rhizopus stolonifer and Botrytis cinerea. Whereas the incorporation of CNCs decreased the moisture content and water vapor permeability of the AA/CWN/CNC film, the additional incorporation of either EO decreased the transparency and affected the microstructure of the AA/CWN/CNC/EO nanocomposites. MEO and CEO incorporation improved the thermal stability of the films and provided excellent protection against fruit-spoiling fungi. Because of their excellent barrier properties against fungal growth, water vapor permeability, and ultraviolet and visible light, these AA/CWN/CNC/EO films have promising potential for application as active food packaging or coating materials.

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Fixation of Sulphur Dioxide by Manganese(II)‐Schiff Base Complexes: Thermal Stability of these Adducts and the Possible Conversion of the Coordinated SO2 to Sulphate

A series of manganese(II) complexes of general formula MnLⁿ(H₂O)_m (where H₂Lⁿ are substituted N,N′‐bis(salicylidene)‐1,2‐diimino‐2,2‐dimethylethane) have been prepared by electrochemical synthesis and characterized by analytical and spectroscopic techniques, magnetism and by studying their redox reversibility character by cyclic and normal pulse voltammetry. The reactivity of these complexes with sulphur dioxide has been investigated in the solid state and in toluene slurries at room temperature. The studies of the reversibility of the reaction (desorption studies) by thermogravimetrical analysis (TGD) have shown a different behaviour among the SO₂‐adducts (from irreversible to totally reversible fixing), pointing to different SO₂ binding modes. Thus, adducts 10 , 12 and 14 , kept the SO₂ after TGD, signifying S–bridged SO₂ binding mode, while TGD for 8 , 9 and 13 revealed the lability of their SO₂, attributable to ligand bound SO₂ coordination. The manganese(II) precursor 4 is that one which has the ability of reversily fixing a major quantity of SO₂ and undergoes the sulphato reaction to form 11 also.     

Voltammetric and Spectroscopic Study of Chromium(III)/Picolinate Complexes

The electrochemical properties and the stability of the Cr^III complexes [Cr(pic)₃]·H₂O and [Cr(pic)₂(OH)]₂·5H₂O (Hpic = pyridine‐2‐carboxylic acid = picolinic acid) were investigated in DMF solutions by cyclic voltammetry, and complemented by electronic spectroscopy. The electrochemical results indicate that both compounds undergo a one‐electron reversible reduction process. The mononuclear species has a more accessible reduction potential than the binuclear one. In this last case, the observed one‐electron process can be ascribed to a considerable stabilization of the mixed valence Cr^III/Cr^II species. Both complexes were also characterized by infrared and Raman spectroscopy.     

Protease-catalyzed peptide synthesis on solid support

The direct enzymatic synthesis of peptides from amino acids is widely used as a useful alternative to chemical synthesis. However, good yields of such enzyme-catalyzed reactions require altered reaction conditions to overcome the bias for hydrolysis in aqueous medium. We argue that the synthesis/hydrolysis equilibrium can be shifted toward synthesis in aqueous medium by immobilizing the amine on solid support. In this report, we show the first examples of solid-phase peptide synthesis catalyzed by a protease in bulk aqueous buffer.     

Synthesis and electron-donor ability of the first conjugated pi-extended tetrathiafulvalene dimers

A series of novel conjugated homo (16a,b) and heterodimers (20) of pi-extended tetrathiafulvalenes with p-quinodimethane structures (exTTFs) linked by a conjugative vinyl spacer have been prepared by olefination Wittig-Horner reaction from the corresponding quinones (14, 19) and phosphonates (15a,b). The redox properties, determined by cyclic voltammetry, reveal a strong donor character and the presence of only one four-electron oxidation wave to form the tetracation species at oxidation potential values quite similar to those found for the related monomers. Theoretical calculations (PM3) show a planar central stilbene moiety and highly distorted exTTF units. The electronic spectra support as well as the electrochemical data and theoretical calculation the lack of significant communication between the exTTF units.     

Synthesis of seven-membered oxacycles. Part 2: The furan approach

We describe an efficient new approach for the synthesis of seven-membered oxacycles that is based on the oxidation of a furan ring with singlet oxygen followed by an intramolecular Michael addition.     

Development and evaluation of a GC/FID method for the analysis of free amino acids in quince fruit and jam.

A GC/FID methodology for determination of twenty-one free amino acids in quince fruit (pulp and peel) and jam is described. The sample preparation was simple, involving a SCX Solid-Phase Extraction (SPE) purification step and a fast derivatization with ethyl chloroformate for gas chromatographic analysis. The chromatographic separation was achieved using a CP-Sil 19 CB wcot fused-silica capillary column. Under the chosen conditions, with temperature and pressure programming, this capillary column was able to separate all the amino acids not only in a short time but also with good separation. The GC/FID procedure is rapid, sensitive, reproducible and accurate. The detection limit values for amino acids were low, between 0.004 and 0.115 microg/mL, and the method was precise. As a general rule, the recovery values were high. Due to its rapidity and low cost, this technique can be useful in the quality control of quince products.     

Determination of Se in biological samples by axial view inductively coupled plasma optical emission spectrometry after digestion with aqua regia and on-line chemical vapor generation

A simple and fast method for the determination of Se in biological samples, including food, by axial view inductively coupled plasma optical emission spectrometry using on-line chemical vapor generation (CVG–ICP OES) is proposed. The concentrations of HCl and NaBH₄, used in the chemical vapor generation were optimized by factorial analysis. Six certified materials (non-fat milk powder, lobster hepatopancreas, human hair, whole egg powder, oyster tissue, and lyophilised pig kidney) were treated with 10 mL of aqua regia in a microwave system under reflux for 15 min followed by additional 15 min in an ultrasonic bath. The solutions were transferred to a 100 mL volumetric flask and the final volume was made up with water. The Se was determined directly in these solutions by CVG–ICP OES, using the analytical line at 196.026 nm. Calibration against aqueous standards in 10% v/v aqua regia in the concentration range of 0.5–10.0 µg L^− 1 Se(IV) was used for the analysis. The quantification limit, considering a 0.5 g sample weight in a final volume of 100 mL^− 1 was 0.10 µg g^− 1. The obtained concentration values were in agreement with the total certified concentrations, according to the t-test for a 95% confidence level.