Thermal and kinetic study of the ferroelectric phase transition in deuterated triglycine selenate

The specific heat and the enthalpy variation of a highly deuterated crystal of ferroelectric triglycine selenate have been measured around its first-order phase transition using the technique square modulated differential thermal analysis (SMDTA). The low temperature variation rate has allowed analyzing the kinetics of the phase transition. Due to an internal crack in the sample, the transition is carried out in two steps and an intermediate region where the transition is blocked and both phases coexist without transformation has been found. The latent heat on cooling (L _c=1.32±0.02 J g^–1) is higher than on heating (L _h=1.08±0.02 J g^–1) due to the thermal hysteresis and the great difference between the specific heat in both phases. Nevertheless, the enthalpy balance is fulfilled on heating and on cooling.     

Complex Tellurium Salts with Supramolecular Bidimensional Lattices: Synthesis and X‐ray Characterization of (2‐Br‐C5NH5)2[TeX6] (X = Cl,Br)

The reaction of tellurium(IV) tetrahalides with hydrochloric and hydrobromic acid leads to the formation of (H₃O)₂[TeX₆], which reacts subsequently with (2‐Br‐C₅NH₅)⁺X^‐ to afford (2‐Br‐C₅NH₅)₂[TeCl₆] ( 1 ) and (2‐Br‐C₅NH₅)₂[TeBr₆] ( 2 ). The structure of the complex salts were analysed by X‐ray diffractometry affording the centrosymmetric space groups P2₁/n (monoclinic, 1 ) and P1¯ (triclinic, 2 ). Interionic hydrogen bondings hold their lattices in bidimensional supramolecular arrays not yet described in the literature. The lone electron pair of the AX₆E‐system of the hexahalotellurates [TeX₆]^2‐ (X = Cl, Br) seems to be fully delocalized since only small octahedral deviations were observed for the anionic species. The structures of the title compounds were refined with the Te atoms occupying sites with full point symmetry, approximately m3¯m. In both cases the Te atoms enclose centers of inversion and the octahedrally dynamic structures are enforced and stabilized along the supramolecular lattices by the crystal field of the 2‐Br‐pyridinium cations.     

Phenomenological rules for the computation of magneto-electric susceptibilities

Applying the model of the anharmonic oscillator, phenomenological expressions were derived, allowing calculation of the components of tensors describing non-linear magneto-electric susceptibilities. Detailed calculations were carried out for the pseudo-tensor of fourth order ^eeem in terms of which magneto-optical birefringence and rotation are expressed for the monocrystals KDP, DKDP, ADP, KDA, LiNbO₃, LiTaO₃ and NaClO₃. From the results obtained it follows that non-linear magneto-electric susceptibilities, which are described by the pseudo-tensor ^eeem are of the order of 10^–16 m V^–1T^–1.Part of this work was carried out under Research Project MR 15.     

Supramolecular Assembling of Complex Tellurium Salts: Synthesis and Crystal Structures of {Cs[PhTeCl4]·CH3OH} and Cs[PhTeBr4]

The direct reaction between PhTeCl₃ and CsCl in methanol affords {Cs[PhTeCl₄]·CH₃OH}. Cs[PhTeBr₄] was prepared by refluxing [2‐Br‐C₅NH₅][PhTeBr₄] and CsCl in ethanol in the presence of an excess of HBr. In {Cs[PhTeCl₄]·CH₃OH} the [PhTeCl₄]^— units form dimers by secondary Te···Cl bonds with methanol molecules bridging adjacent Cs⁺ cations. In both compounds, the alkali metal cation interacts secondarily with the chlorine and bromine Te‐ligands, achieving singular coordination polyhedrons and holding the lattices in supramolecular tridimensional assemblies. The new complexes, {Cs[PhTeCl₄]·CH₃OH} and Cs[PhTeBr₄], crystallize in the space groups P2₁/c and P2₁/n, respectively. Only one such structure has been reported before.     

Synthesis of Fructooligosaccharides from Aspergillus niger Commercial Inulinase Immobilized in Montmorillonite Pretreated in Pressurized Propane and LPG

Commercial inulinase from Aspergillus niger was immobilized in montmorillonite and then treated in pressurized propane and liquefied petroleum gas (LPG). Firstly, the effects of system pressure, exposure time, and depressurization rate, using propane and LPG, on enzymatic activity were evaluated through central composite design 2³. Residual activities of 145.1 and 148.5 % were observed for LPG (30 bar, 6 h, and depressurization rate of 20 bar?min^?1) and propane (270 bar, 1 h, and depressurization rate of 100 bar?min^?1), respectively. The catalysts treated at these conditions in both fluids were then used for the production of fructooligosaccharides (FOS) using sucrose and inulin as substrates in aqueous and organic systems. The main objective of this step was to evaluate the yield and productivity in FOS, using alternatives for enhancing enzyme activity by means of pressurized fluids and also using low-cost supports for enzyme immobilization, aiming at obtaining a stable biocatalyst to be used for synthesis reactions. Yields of 18 % were achieved using sucrose as substrate in aqueous medium, showing the potential of this procedure, hence suggesting a further optimization step to increase the process yield.     

Double Carbonyl Substitution in [BrMn(CO)5]: Reaction with Benzoylhydrazine and Synthesis of fac‐[Mn(Br)(CO)3(BHD)]·2THF (BHD = OC(Ph)—NH—NH2)

[BrMn(CO)₅] reacts with benzoylhydrazine in THF occurring substitution of two CO groups by a Metal‐ligand ring to give fac‐[Mn(Br)(CO)₃(BHD)]·2THF (BHD = C₆H₅CONHNH₂). The novel compound shows a distorted octahedral arrangement at the manganese atom, with three nearly linear carbonyl ligands in a fac arrangement, illustrating another example that the CO group in position trans to the bromine ligand in [BrMn(CO)₅] presents the most intensive metal‐CO backbonding effect of all the CO groups of the parent complex, leading to the formation of a facial (and not meridional) isomer, even in the presence of a bidentate ligand like benzydrazide. X‐ray measures of yellow crystals showed that the title complex belong to space group P2₁/c, with the asymmetric unit containing one crystallographically independent [Mn(Br)(CO)₃(BHD)] complex and two tetrahydrofurane solvate molecules. The new compound represents heretofore the unique occurrence of the complexing single bidentate ligand ‐O=C(Ph)‐N(H)‐N(H)₂‐ with an octahedral coordination at the Mn^I atom supported chiefly by carbonyl groups.     

Partial Characterization of Inulinases Obtained by Submerged and Solid-State Fermentation Using Agroindustrial Residues as Substrates: A Comparative Study

Inulinase belongs to an important class of enzymes as it can be used to produce high-fructose syrups by enzymatic hydrolysis of inulin and fructooligosaccharides, which has been used as functional food. This work aimed to carry out a partial characterization of the crude enzymatic extract of two different inulinases, obtained by solid-state fermentation (SSF) and submerged fermentation (SmF), using agroindustrial residues as substrates. The crude enzymatic extract obtained by SmF showed an optimal pH and temperature for hydrolytic activity of 4.5 and 55?°C, respectively; and that obtained by SSF conducted to optimal pH and temperature of 5.0 and 55?°C, respectively. Both enzymes presented high thermostability, with a D value of 230.4 h and 123.1 h for SmF and SSF, respectively. The inulinase produced by SmF showed highest stability at pH?4.4, while inulinase obtained by SSF was more stable at pH?4.8. The results showed that inulinase obtained by SmF is less susceptible to pH effect and the inulinase obtained by SSF is more resistant to higher temperatures.     

Observation of the ferroelectric phase transition in Pb5Ge3O11 by the chemical potential changes

We observed the transition from the ferroelectric (FE) to paraelectric (PE) phase in the semiconducting, ferroelectric Pb₅Ge₃O₁₁ single crystal with the use of the contact electrode method. To this purpose a thin, metallic layer was placed onto the Pb₅Ge₃O₁₁ crystal surface, forming the contact electrode. At opposite ends of the contact electrode, silver wires were glued and a voltage was applied to the contact electrode in such a way that the electric current could flow only through the attached electrode. The electric resistance R(T) of the electrode was measured as a function of temperature. Two series of measurements were performed. In one of them the ferroelectric c-axis of the investigated crystal was perpendicular to the contact electrode. In the second one the c-axis was parallel to the attached electrode. We used gold as the contact electrode material. The anomaly in the R(T) in a form of a kink at T _kink?=?452?K was found for both c-axis orientations. The measured value of T _kink, appearing in the temperature dependence of contact electrode resistance, corresponds exactly to the phase transition temperature T _C from the FE to PE phase of the investigated Pb₅Ge₃O₁₁ material. This result demonstrates that the contact electrode method, primarily proposed exclusively to find critical temperatures of metallic samples, also works well in the case of ferroelectric and semiconducting materials like Pb₅Ge₃O₁₁. We ascribe the effect of the resistance kink in the temperature dependence of the contact electrode R(T) to thermal excitations of the electrons with different rates below and above T _C due to different electronic activation energies in the FE and PE phases of the investigated Pb₅Ge₃O₁₁ crystal. It, however, means that the phase transition in the electronic subsystem of the Pb₅Ge₃O₁₁ transfers into the electron gas of the contact electrode via the chemical potential relation µ _sample?=?µ _electrode due to the contact between the sample and the electrode. The magnitude of the kink, observed in the R(T) dependence, was higher on heating than on cooling. The additional measurement of the thermally stimulated current (TSC) was carried out on the non-polarised Pb₅Ge₃O₁₁ sample. In this series of measurements, the sample was covered with gold layers sputtered on the two opposite surfaces of the crystal. The TSC anomaly occurred, related to the residual pyroelectric effect, several degrees below the Curie temperature, T _C, and does not disturb the detection of the critical point with the use of the contact electrode method.     

Concentration,Partial Characterization,and Immobilization of Lipase Extract from <Emphasis Type="Italic">P. brevicompactum</Emphasis> by Solid-State Fermentation of Babassu Cake and Castor Bean Cake

One relevant limitation hindering the industrial application of microbial lipases has been attributed to their production cost, which is determined by the production yield, enzyme stability among other. The objective of this work was to evaluate the concentration and immobilization of lipase extracts from Penicillium brevicompactum obtained by solid-state fermentation of babassu cake and castor bean cake. The precipitation with ammonium sulfate 60% of saturation of crude extract obtained with babassu cake as raw material showed an enhancement in hydrolytic and esterification activities from 31.82 to 227.57 U/g and from 170.92 to 207.40 U/g, respectively. Concentrated lipase extracts showed preference to medium-chain triglycerides and fatty acids. It is shown that the enzyme activity is maintained during storage at low temperatures (4 and −10°C) for up to 30 days. Higher esterification activities were achieved when the lipase extract was immobilized in sodium alginate and activated coal.