Batch cooling crystallization of xylitol produced by biotechnological route

BACKGROUND: This work deals with the xylitol production by biotechnological routes emphasizing the purification process using crystallization. RESULTS: Xylitol volumetric productivity of 0.665 g L(-1) h(-1) and yield of 0.7024 g g(-1) were obtained after 92 h fermentation. The fermented broth (61.3 g L(-1) xylitol) was centrifuged, treated and concentrated obtain a syrup (745.3 g L(-1) xylitol) which was crystallized twice, xylitol crystals with 98.5-99.2% purity being obtained. CONCLUSION: The hypothetical distribution obtained permits the determination of modeling parameters, which make possible the estimation of crystal dominant size from different initial experimental conditions. (C) 2008 Society of Chemical Industry

Niobium hydrogenation process Effect of temperature and cooling rate from the hydrogenation temperature

High-purity niobium powder can be produced via the hydrogenation and dehydrogenation processes The present work aimed at the effect of temperature and cooling rate conditions on the niobium hydrogenation process using hydrogen gas The hydrogen contents of the materials were evaluated by weight change and chemical analysis X ray diffraction (XRD) was performed to identify and determine the lattice parameters of the formed hydride phases No hydrogenation took place under isothermal conditions only during cooling of the materials Significant hydrogenation occurred in the 500 C and 700 C experiments leading to the formation of a beta NbH(x) single phase material (C) 2010 Elsevier Ltd All rights reserved

Vegetable Oil Quenchants: Calculation and Comparison of The Cooling Properties of a Series of Vegetable Oils

The compositions of canola, soybean, corn, cottonseed and sunflower oils suggest that they exhibit substantially different propensity for oxidation following the order of Canola < corn < cottonseed < sunflower approximate to soybean. These data suggest that any of the vegetable oils evaluated could be blended with minimal impact on viscosity although compositional differences would surely affect oxidative stability. Cooling curve analysis showed that similar cooling profiles were obtained for different vegetable oils. Interestingly, no film boiling or transition nucleate boiling was observed with any of the vegetable oils and heat transfer occurs only by pure nucleate boiling and convection. High-temperature cooling properties of vegetable oils are considerable faster than those observed for petroleum oil-based quenchants. (C)2010 Journal of Mechanical Engineering. All rights reserved.

Influence of Microstructures on Polarization Resistance and Hydrogen-Induced Cracking of a Micro-Alloyed Steel Submitted to Different Cooling Rates

The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied. Samples 19.1 x 6 x 2 mm, containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer, were submitted to Rp and HIC corrosion tests. Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003, in this case, modified only with regard to the size of the samples. Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5 degrees C.s(-1)) showed higher susceptibility to hydrogen-induced cracking, with large cracks in the middle of the sample propagating along segregation bands, corresponding to the centerline of the plate thickness. For cooling rates of 10 degrees C.s(-1), only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions. For higher cooling rates (40 degrees C.s(-1)) very few small cracks were detected, linked to non-metallic inclusions. This result suggests that structures formed by polygonal structures and segregation bands (were cutectoid microconstituents predominate) have higher susceptibility to HIC. Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals. Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation; segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks, frequently associated to non-metallic inclusions. Polarization resistance essays performed on the steel in theas received condition, prior to any heat treatment, showed larger differences between the regions of the plate, with a considerably lower Rp in the centerline. The austenitization heat treatments followed by cooling rates of 0.5 e 10 degrees C.s(-1) made more uniform the corrosion resistance along the thickness of the plate. The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed, allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.

Integrated analysis of cooling water systems: Modeling and experimental validation

Cooling towers are widely used in many industrial and utility plants as a cooling medium, whose thermal performance is of vital importance. Despite the wide interest in cooling tower design, rating and its importance in energy conservation, there are few investigations concerning the integrated analysis of cooling systems. This work presents an approach for the systemic performance analysis of a cooling water system. The approach combines experimental design with mathematical modeling. An experimental investigation was carried out to characterize the mass transfer in the packing of the cooling tower as a function of the liquid and gas flow rates, whose results were within the range of the measurement accuracy. Then, an integrated model was developed that relies on the mass and heat transfer of the cooling tower, as well as on the hydraulic and thermal interactions with a heat exchanger network. The integrated model for the cooling water system was simulated and the temperature results agree with the experimental data of the real operation of the pilot plant. A case study illustrates the interaction in the system and the need for a systemic analysis of cooling water system. The proposed mathematical and experimental analysis should be useful for performance analysis of real-world cooling water systems. (C) 2009 Elsevier Ltd. All rights reserved.

A systemic approach for optimal cooling tower operation

The thermal performance of a cooling tower and its cooling water system is critical for industrial plants, and small deviations from the design conditions may cause severe instability in the operation and economics of the process. External disturbances such as variation in the thermal demand of the process or oscillations in atmospheric conditions may be suppressed in multiple ways. Nevertheless, such alternatives are hardly ever implemented in the industrial operation due to the poor coordination between the utility and process sectors. The complexity of the operation increases because of the strong interaction among the process variables. In the present work, an integrated model for the minimization of the operating costs of a cooling water system is developed. The system is composed of a cooling tower as well as a network of heat exchangers. After the model is verified, several cases are studied with the objective of determining the optimal operation. It is observed that the most important operational resources to mitigate disturbances in the thermal demand of the process are, in this order: the increase in recycle water flow rate, the increase in air flow rate and finally the forced removal of a portion of the water flow rate that enters the cooling tower with the corresponding make-up flow rate. (C) 2009 Elsevier Ltd. All rights reserved.

Influence of storage temperature on cooling intensity of topical emulsions containing encapsulated menthol

The cooling intensity of topical emulsions added with encapsulated or free menthol was evaluated by a screened and trained panel recruited based on the American Society for Testing and Materials method. A sensory panel composed of 10 trained judges performed the evaluation of samples stored at 22 +/- 2C for 24 h and, after 28 days of storage, at 37.0 +/- 0.5C. The obtained data were analyzed by analysis of variance and Tukey`s test. The results showed an increase of cooling intensity as a function of encapsulated menthol concentration. The opposite was observed in samples added with free menthol, which may have caused sensory fatigue. Storage at 37 +/- 0.5C for 28 days had no impact on the cooling intensity of emulsions containing encapsulated menthol, demonstrating high stability and suggesting its application in cooling skin care products. In contrast, emulsions added with free menthol showed a drastic decrease of cooling intensity at 37 +/- 0.5C..

Reduced pH induces an inactive non-native conformation of the monomeric bothropstoxin-I (Lys49-PLA(2))

Bothropstoxin-I (BthTx-I), a Lys49-PLA(2) from Bothrops jararacussu venom, permeabilizes membranes by a non-hydrolytic Ca(2+)-independent mechanism. The BthTx-I showed activity against liposomes including 10% and 50% negatively charged lipids at pH 7.0, but not at pH 5.0. Nevertheless, ultracentrifugation and FRET demonstrated that at pH 5.0 the BthTx-I is bound to 50% negatively charged membranes. ANS binding identified a non-native monomeric conformation at pH 5.0, suggesting that tertiary structure alterations result in activity loss of the BthTx-I at low pH. (C) 2009 Elsevier Ltd. All rights reserved.

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser

Objectives: The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization. Methods: 84 enamel blocks were randomly assigned to seven groups (n = 12): G1: control group - no treatment, G2-G7: experimental groups treated with Er:YAG laser (80 mJ/2 Hz) at different irradiation distances with or without cooling: G2: 4 mm/2 mL; G3: 4 mm/no cooling; G4: 8 mm/2 mL; G5: 8 mm/no cooling; G6: 16 mm/2 mL; G7: 16 mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100 mu m in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha = 5%). Results: The control group (CLDM = 0.67 mm) was statistically different from group 2 (CLDM = 0.42 mm), which presented a smaller lesion depth, and group 6 (0.91 mm), which presented a greater lesion depth. The results of groups 3 (CLDM = 0.74 mm), 4 (CLDM = 0.70 mm), 5 (CLDM = 0.67 mm) and 7 (CLDM = 0.89 mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2. Conclusions: It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling. (C) 2010 Elsevier Ltd. All rights reserved.

An alternative method to study the cooling of glasses from melt to solid phase

The aim of this preliminary work was to present a novel method, suitable to investigate the glass cooling, from melt to solid state, based on a fast, non-usual and easy microwave method. The following glass system xBaO . (100-x)B(2)O(3) (x = 0% and 40%) was selected as an example for this study. The melt was poured inside a piece of waveguide and then, its cooling was monitored by the microwave signal as a function of time. The variations in the signal can provide valuable informations about some structural changes that take place during the cooling stages, such as relaxation processes. This method can be useful to investigate the cooling and heating of other materials, opening new possibilities for investigation of dielectric behavior of materials under high temperatures. (C) 2008 Elsevier Inc. All rights reserved.

Molecular conformation of the racemic indan derivative (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide

This paper presents the structural characterization of the indan derivative (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxamide, which was unambiguously determined by X-ray diffraction (XRD) to be a racemate (R/S: 50/50) crystallizing in an achiral crystal structure (P2(1)/c, a = 9.3180(1) , b = 7.9070(2) , c = 19.7550(4) , beta = 103.250(1)A degrees, V = 1416.75(5) (3) and Z = 4). The diastereomers are related by the inversion symmetry and linked by H bond forming a dimer. The crystal packing is stabilized by hydrogen bonds, including the classical one responsible for the formation of centrosymmetric dimers, and non-classical ones involving C-H center dot center dot center dot O and C-H center dot center dot center dot pi-aryl interactions. The intra and intermolecular geometry of the title compound is compared to the (+/-)-1-trans-3-(3,4-dichlorophenyl)-2,3-dihydro-1H-indene-1-carboxylic acid one, which also present an achiral crystal structure from racemates (R/S: 50/50). The two indan derivatives crystallize in a very similar unit cell.

Analysis of Agonist and Antagonist Effects on Thyroid Hormone Receptor Conformation by Hydrogen/Deuterium Exchange

Thyroid hormone receptors (TRs) are ligand-gated transcription factors with critical roles in development and metabolism. Although x-ray structures of TR ligand-binding domains (LBDs) with agonists are available, comparable structures without ligand (apo-TR) or with antagonists are not. It remains important to understand apo-LBD conformation and the way that it rearranges with ligands to develop better TR pharmaceuticals. In this study, we conducted hydrogen/deuterium exchange on TR LBDs with or without agonist (T(3)) or antagonist (NH(3)). Both ligands reduce deuterium incorporation into LBD amide hydrogens, implying tighter overall folding of the domain. As predicted, mass spectroscopic analysis of individual proteolytic peptides after hydrogen/deuterium exchange reveals that ligand increases the degree of solvent protection of regions close to the buried ligand-binding pocket. However, there is also extensive ligand protection of other regions, including the dimer surface at H10-H11, providing evidence for allosteric communication between the ligand-binding pocket and distant interaction surfaces. Surprisingly, C-terminal activation helix H12, which is known to alter position with ligand, remains relatively protected from solvent in all conditions suggesting that it is packed against the LBD irrespective of the presence or type of ligand. T(3), but not NH(3), increases accessibility of the upper part of H3-H5 to solvent, and we propose that TR H12 interacts with this region in apo-TR and that this interaction is blocked by T(3) but not NH(3.) We present data from site-directed mutagenesis experiments and molecular dynamics simulations that lend support to this structural model of apo-TR and its ligand-dependent conformational changes. (Molecular Endocrinology 25: 15-31, 2011)

Experimental and theoretical investigation of molecular structure and conformation of the 4-isopropylthioxanthone

In this study, the molecular structure and conformational analyses of the 4-isopropylthioxanthone (4-ITX) are reported according to experimental and theoretical results. The compound crystallizes in the centrosymmetric P (1) over bar space group with only one molecule in the asymmetric unit, presenting the most stable conformation, in which the three fused-rings adopt a planar geometry, and the isopropyl group assumes a torsional angle with less sterical hindrance. The structural and conformational analyses were performed using theoretical calculations such as Hartree-Fock (HF), DFT method in combination with 6-311G(d,p) and 6-31++G(d,p) and the results were compared with infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The supramolecular assembly of 4-ITX is kept by non-classical C-H center dot center dot center dot O hydrogen bonds and weak interactions such as pi-pi stacking. 4-ITX was also studied by (1)H and (13)C NMR spectroscopy. UV-Vis absorption spectroscopic properties of the 4-ITX showed the long-wavelength maximum shifts towards high energy when the solvent polarity increases. (C) 2011 Elsevier B.V. All rights reserved.

Studies towards the identification of putative bioactive conformation of potent vasodilator arylidene N-acylhydrazone derivatives

In this report we disclose the synthesis, vasodilatory activity, and identification of bioactive conformation of new N-acylhydrazone and N-methyl-N-acylhydrazone derivatives, structurally designed by bioisosteric replacements of previously described cardioactive compounds LASSBio-294 and its N-methyl derivative LASSBio-785. Some of these novel derivatives presented improved vasorelaxant properties, being new cardiovascular drug candidates. (C) 2009 Elsevier Masson SAS. All rights reserved.

Conflicting structural and geochronological data from the Ibituruna quartz-syenite (SE Brazil): Effect of protracted ""hot"" orogeny and slow cooling rate?

The Ibituruna quartz-syenite was emplaced as a sill in the Ribeira-Aracuai Neoproterozoic belt (Southeastern Brazil) during the last stages of the Gondwana supercontinent amalgamation. We have measured the Anisotropy of Magnetic Susceptibility (AMS) in samples from the Ibituruna sill to unravel its magnetic fabric that is regarded as a proxy for its magmatic fabric. A large magnetic anisotropy, dominantly due to magnetite, and a consistent magnetic fabric have been determined over the entire Ibituruna massif. The magmatic foliation and lineation are strikingly parallel to the solid-state mylonitic foliation and lineation measured in the country-rock. Altogether, these observations suggest that the Ibituruna sill was emplaced during the high temperature (similar to 750 degrees C) regional deformation and was deformed before full solidification coherently with its country-rock. Unexpectedly, geochronological data suggest a rather different conclusion. LA-ICP-MS and SHRIMP ages of zircons from the Ibituruna quartz-syenite are in the range 530-535 Ma and LA-ICP-MS ages of zircons and monazites from synkinematic leucocratic veins in the country-rocks suggest a crystallization at similar to 570-580 Ma, i.e., an HT deformation >35My older than the emplacement of the Ibituruna quartz-syenite. Conclusions from the structural and the geochronological studies are therefore conflicting. A possible explanation arises from (40)Ar-(39)Ar thermochronology. We have dated amphiboles from the quartz-syenite, and amphiboles and biotites from the country-rock. Together with the ages of monazites and zircons in the country-rock, (40)Ar-(39)Ar mineral ages suggest a very low cooling rate: <3 degrees C/My between 570 and similar to 500 Ma and similar to 5 degrees C/My between 500 and 460 Ma. Assuming a protracted regional deformation consistent over tens of My, under such stable thermal conditions the fabric and microstructure of deformed rocks may remain almost unchanged even if they underwent and recorded strain pulses separated by long periods of time. This may be a characteristic of slow cooling ""hot orogens"" that rocks deformed at significantly different periods during the orogeny, but under roughly unchanged temperature conditions, may display almost indiscernible microstructure and fabric. (C) 2009 Elsevier B.V. All rights reserved.