The unconstrained local hardness: an intriguing quantity, beset by problems

Developing a mathematical approach to the local hard/soft acid/base principle requires an unambiguous definition for the local hardness. One such quantity, which has aroused significant interest in recent years, is the unconstrained local hardness. Key identities are derived for the unconstrained local hardness, δμ/δρ(r). Several identities are presented which allow one to determine the unconstrained local hardness either explicitly using the hardness kernel and the inverse-linear response function, or implicitly by solving a system of linear equations. One result of this analysis is that the problem of determining the unconstrained local hardness is infinitely ill-conditioned because arbitrarily small changes in electron density can cause enormous changes in the chemical potential. This is manifest in the exponential divergence of the unconstrained local hardness as one moves away from the system. This suggests that one should be very careful when using the unconstrained local hardness for chemical interpretation.     

Stereo- and regioselective synthesis of β-amino-β-tetrazolylvinylphosphonates

Addition of 5-substituted tetrazoles to dimethyl [(N,N-diisopropylamino)ethynyl]phosphonate proceeds regio- and stereoselectively to yield (Z)-[2-diisopropylamino-2-(tetrazolyl)vinyl]phosphonic acid dimethyl esters. The Z-configuration of the products was confirmed by ¹Н NMR spectroscopy and single-crystal X-ray diffraction. The reactions occur via nucleophilic attack of tetrazole involving predominantly the N-1 atom of the tetrazole ring.     

Regiospecificity in the reaction of 2,3-dichloronaphthazarins with azide anions. Synthesis of echinamine A—a metabolite produced by the sea urchin Scaphechinus mirabilis

It was found that 6-hydroxy- and 6-alkoxy-2,3-dichloronaphthazarins react smoothly with sodium azide in methanol to produce the corresponding 2-azido derivatives as single regioisomers. We have explored the utility of this reaction for the synthesis of echinamine A (3-amino-7-ethyl-2,5,6,8-tetrahydroxy-1,4-naphthoquinone)—the first marine aminated hydroxynaphthazarin, a metabolite of the sea urchin Scaphechinus mirabilis (Agassiz).     

Ionic Liquids as Unique Solvents in One‐Pot Synthesis of 4‐(N,2,2,2‐Tetranitroethylamino)‐3‐R‐Furazans

An efficient two‐step one‐pot protocol for the synthesis of N‐nitrated trinitroethylamino furazans in an ionic liquid has been developed involving the condensation of aminofurazans with trinitroethanol and the N‐nitration of an intermediate Mannich base. Trinitroethylnitramino derivatives have been synthesized and characterized by multinuclear NMR spectroscopy and X‐ray crystallography. A role of the N,2,2,2‐tetranitroethylamino group for stabilization of the high‐density crystal‐packing motif is described. The performance calculations gave detonation pressures and velocities for the furazan derivatives in a range of about 31–36 GPa and 8330–8745 ms^?1, respectively, which makes them competitive energetic materials. Furthermore, due to the positive oxygen balance, the compounds could be potential oxidizers for energetic formulations.     

Mixed sorbents and their use in continuous flow analysis

The new approach to enhancing the selectivity of sorption separation of metal ions was suggested. The approach is based on using mixed sorbents, which may be obtained, e.g. by simultaneous immobilization of complexing reagents on silica gel and reverse-phase silica gel (C₁₆, Ph). The methods are developed for the simultaneous determination of two (Co-Fe, Co-Zn, Al-Mn) or three (Al, Mn and Fe) elements in the concentration range 2.10^–6–7.10^–4 M with the performance of 21–36 samples per hour.     

Thermogravimetric and calorimetric evaluation of babassu biodiesel obtained by the methanol route

The growing petroleum deficit requires the development of alternative fuel sources. Biodiesel is a good alternative, as it is a biodegradable and renewable product, which obeys the carbon cycle. In this work, the biodiesel from babassu was synthesized using the methanol route, and characterized by physico-chemical analyses in order to make able the investigated biodiesel to fulfill with its properties the requirements of Brazilian National Agency for Petroleum, Natural Gas and Biofuel (ANP). Besides gas chromatography, IR spectroscopy experiments and thermoanalytical measurements in air and in nitrogen were done to determine the main thermal decomposition processes and calorimetric events. The evaporation temperature of babassu biodiesel was similar in both atmospheres, started around 52 in air and around 60°C in nitrogen.     

Characterization of Collagen from Three Genetic Lines (Gray,Red and F1) of Oreochromis niloticus (Tilapia) Skin in Young and Old Adults

From tilapia (Oreochromis niloticus) farming, the by-products have been identified as a source of collagen that could be used for the development of dermocosmetics or pharmaceutical products. However, the characteristics of collagen related to a specific strain or culture must be well defined prior to its application. Collagen was extracted from the skin of three strains of tilapia: red YY males (YY: two Y-type sex chromosomes), XX gray females, and the F1: offspring of crossing red YY males with XX gray females; at different ages in the adult phase, using acetic acid and pepsin enzyme. The characteristics of acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were shown by SDS-PAGE band profiles to be similar to bovine collagen type I (SIGMA), the PSC of gray tilapia being more fragile to temperature changes, consistent with the results of fractional viscosity. The characteristics of the F1 progeny were prioritized for being a commercially productive and sustainable source for the extraction of collagen, and the ASC form, being the one with the greatest stability and advantage over PSC, of importance to our investigations, leads to a controlled digestion as in the case of peptide induction, and also in the development of natural products in the pharmaceutical and/or dermocosmetic industry. Evaluations of the triple helix structure by FT-IR, X-ray diffraction and UV–visible spectroscopy give similar results between the strains: red, gray, and F1, and between ages in the adult form F1 (15, 24, and 36 months of age). Consequently, the skin of tilapia in adult form is recommended sustainably for up to 24 months of age where the collagen is obtained with the use of acetic acid without enzymatic treatment.     

Formation of Nanostructures in Multi Component Systems Based on Organic Polymer and Coordination Metal Compound

Structuring of polyurethane (PU) networks is analyzed under influence of transition metal coordination compounds: mono-ionic β-diketonates and polyheteronuclear metal-organic complexes. Formed in situ nanostructures both organic and inorganic were found in organic polymer modified with coordination metal compound. Influence of coordination junction point spatial symmetry and content of metal ion in modifier on structure and dielectric characteristics of modified PUs is analyzed using X-ray, EPR, SEM and transmission optical microscopy, DRS and DSC methods.