Thermal behavior of different cocoa powder varieties and their physicochemical,phytochemical and microbiological characteristics

Four cocoa powder varieties processed in different European countries (Germany, Poland, Romania and Bulgaria) were subjected to physicochemical, phytochemical and microbiological analysis. The cocoa powders were extensively characterized by recording their pH and titratable acidity, respectively, the polyphenols and also the methylxantine derivatives content (theobromine and caffeine). The cocoa powders pH ranged between 5.37 and 8.23, while the titratable acidity was 3.2–4.3 miliequivalent (100 g)^?1 of cocoa powder. Their total polyphenols content ranged between 0.986?÷?2.003 g GAE/(100 g)^?1. The methylxanthine derivatives (theobromine and caffeine) were analyzed by the HPLC method and ranges of 0.992–1.174% for theobromine and 0.096–0.369% for caffeine were obtained. Thermal analysis (TG–DTA) combined with mass spectrometry (MS) elucidated the decomposition processes and the volatile substances (CO, CO₂, H₂O, NO, theobromine, caffeine). The thermal analysis revealed transformations in the cocoa powders composition: drying and water loss; decomposition of pectic polysaccharides; lipids, amino acids and proteins, crystalline phase transformations and carbonizations. The microbiological analysis tested the degree of preservation of the cocoa powders across time, specifically immediately after unwrapping and after 14 days.

     

Formation and Characterization of the Boron Dicarbonyl Complex [B(CO)2]−

We report the synthesis and spectroscopic characterization of the boron dicarbonyl complex [B(CO)₂]^?. The bonding situation is analyzed and compared with the aluminum homologue [Al(CO)₂]^? using state‐of‐the‐art quantum chemical methods.     

The effect of a radical scavenger on the propagation of flames in an exothermic-endothermic system

The propagation of a premixed laminar flame supported by an exothermic chemical reaction under adiabatic conditions but subject to inhibition through parallel endothermic chemical processes is considered. These consist of the endothermic decomposition of an inhibitor W leading to the formation of a ‘radical scavenger’ S, which acts as a catalyst for the removal of active radicals X through an additional termination step. The heat loss through the endothermic reaction and the action of the radical scavenger, represented by the parameters α and ρ, both have a strong quenching effect on wave propagation. The dependence of the flame velocity c on α and ρ is determined by numerical integration of the flame equations for a range of values of the other parameters. The (ρ ,c) curve can have at least one turning point, the (α,c) curve can be monotone or it can have one or three turning points, depending on the values of the parameters β, representing the rate at which inhibitor is consumed, μ, the ratio of the activation energies of the reactants and the Lewis numbers. The additional feature caused by the scavenger is that the (α, c) curve has a turning point for any (μ, β) parameter pair if ρ is sufficiently large. A new feature of the model is that, for non-zero values of ρ, there can be four solutions below critical values of α. This behaviour is confirmed by a high activation energy analysis, which also reveals some additional features of the flame structure resulting from the presence of the radical scavenger.AMS subject classification: 80A25, 35K57, 35B32     

Inclusion complexes of Schiff bases as phytogrowth inhibitors

This article details the preparation, characterization and phytotoxic evaluation of several Schiff base inclusion complexes obtained from β-cyclodextrin and p-sulfonic acid calix[6]arene. The inclusion complexes (1:1 molar ratio) were prepared by mixing a 5 mmol L^?1 aqueous solution (containing 1 % DMSO) of Schiff bases (guests) with aqueous solution (containing 1 % DMSO) of 5 mmol L^?1 of β-cyclodextrin or p-sulfonic acid calix[6]arene (hosts). The host–guest systems were characterized via a series of NMR experiments. The ability of the complexes to interfere with the radicle elongation of Sorghum bicolor (dicotyledonous species) and Cucumis sativus (monocotyledonous species) was evaluated. After 48 h, the inclusion complexes inhibited the radicle elongation of both species from 11 to 56 %. The formation of inclusion complexes was also investigated theoretically by molecular dynamics simulations in aqueous solution through implicit approach. Based on the experimental observation, the phytotoxic activity evaluated can be attributed to the formation of host–guest systems. This was supported by the theoretical findings based on stable interaction energy analyses for all the studied supramolecular systems.     

Thermal Cyclization of Phenylallenes That Contain ortho‐1,3‐Dioxolan‐2‐yl Groups: New Cascade Reactions Initiated by 1,5‐Hydride Shifts of Acetalic H Atoms

A series of 2‐(1,3‐dioxolan‐2‐yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1‐(2‐hydroxy)‐ethoxy‐2‐substituted naphthalenes by smooth thermal activation in toluene solution. Electron‐withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride‐like [1,5]‐H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π‐electrocyclic ring‐closure of the resulting reactive ortho‐xylylenes; and 3) a final aromatization step with concomitant ring‐opening of the 1,3‐dioxolane fragment. If the 1,3‐dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2‐disubstituted naphthalenes were converted into their corresponding naphtho‐fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3‐dioxolane fragment on the carbon atom from which the H‐shift took place and also of the electron‐withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π‐electrocyclization step was of lower activation energy than the alternative disrotatory mode.     

Instability,Rupture and Fluctuations in Thin Liquid Films: Theory and Computations

Journal of Statistical Physics - Thin liquid films are ubiquitous in natural phenomena and technological applications. They have been extensively studied via deterministic hydrodynamic equations,...     

Electron–hole symmetry and spin–orbit splitting in IV–VI asymmetric quantum wells

It is shown that, due to the electron–hole symmetry of the fundamental gap of the lead–salts (PbTe, PbSe and PbS), the Rashba spin splitting in their flat band asymmetric quantum wells is much reduced with the usual equal conduction and valence band-offsets. Different from the III–V case, we find that the important structure inversion asymmetry for the Rashba splitting in IV–VI quantum wells with different left and right barriers is not a material property (i.e., barrier height, effective mass or band gap) but results from the band alignment. This is shown by specific envelope function calculations of the spin-dependent subband structure of Pb_1−xEu_xTe/PbTe/Pb_1−yEu_yTe asymmetric quantum wells (x≠y), based on a simple but accurate four-band kp model for the bulk band structure near the gap, which takes into account band anisotropy, nonparabolicity and multi-valley effects.