Preliminary recycling experiments with cellulase enzymes after cotton
treatments at 50°C showed that activity remaining in the treatment liquors
was reduced by about 80% after five recycling steps. The potential problems
of end-product inhibition, thermal and mechanical deactivation, and the
loss of some components of the cellulase complex by preferential and or
irreversible adsorption to cotton substrates were studied. End-product inhibition
studies showed that the build-up of cellobiose and glucose would be
expected to cause no more than 40% activity loss after five textile treatment
cycles. Thermal and mechanical treatments of cellulases suggested that the
enzymes start to be deactivated at 60°C and agitation levels similar to those
used in textile processing did not cause significant enzyme deactivation.
Analysis of cellulase solutions, by fast protein liquid chromatography, before
and after adsorption on cotton fabrics, suggested that the cellobiohydrolase
II (Cel6A) content of the cellulase complex was reduced, relative to the other
components, by preferential adsorption. This would lead to a marked
reduction in activity after several treatment cycles and top-up with pure
cellobiohydrolase II would be necessary unless this component is easily
recoverable from the treated fabric.
Laboratory tests have been carried out in order to assess the influence of groove activation and deactivation on the performance of a twin axial groove steadily loaded hydrodynamic journal bearing. Temperature distribution at the oil–bush interface, oil outlet temperature, total oil flow rate, partial oil flow rate (at each groove), and motor consumption were measured for several journal speeds and loads under constant feeding pressure (pf) and constant feeding temperature (Tf), at five different loading angles ( ). In this study, the corresponding groove was deactivated whenever
negative oil flow rate was observed in it and results were compared. It was found that the groove deactivation strategy has profound influence on the bearing performance when negative flow rate occurs at one groove, preventing such undesirable effects as lubricant starvation at the loaded region of the bearing. Groove deactivation in the event of negative flow rate may be easily implemented by incorporating a check valve to the feeding system of each groove. Such strategy seems to be highly recommended for the safe operation of bearings subjected to high loads and load angles
deviated from 90º.
The deactivation of USY zeolites with different rare earth contents due to the coke formed from n-heptane at 450oC was studied. The results show that the presence of rare earth elements decreases the cracking and coking activities, increasing catalytic stability. However, reaction selectivity was not significantly influenced. The greater the rare earth content, the lower the coking rates and the coke contents. The TPO/DSC profiles suggested that the catalytic effect of the rare earth elements promoted coke oxidation.
n-Heptane cracking on a USY commercial zeolite at 350, 400 and 450ºC was studied. XRF, XRD, 27Al and 29Si-MAS-NMR were used for USY characterization. The nature of the coke was determined by 1H-NMR and infrared spectroscopy. It was observed that temperature influenced the nature of the coke formed, and that an increase in temperature led to a reduction in the solubility of coke in CH2Cl2 and an increase in its aromaticity. Despite these characteristics and the larger amount of coke formed, higher temperatures have less effect on the deactivation process than lower temperatures. Selectivity for C1-C6 fractions was hardly influenced by temperature, and it was that expected for the cracking mechanism of n-paraffins on acid catalysts.
The thermal stability and the energy of deactivation of free invertase and the immobilized enzyme (IE) was measured at temperatures in the range of 35 to 65°C for the hydrolysis of a 5% w/v sucrose solution. The free enzyme at pH 5.0 is stable up to 50°C for a period of 4 h. Invertase immobilized in controlled pore silica by the silane-glutaraldehyde covalent method is stable up to 55ºC, in pH 4.5 for the same period. For higher temperatures the enzyme deactivation follows the exponential decay model and half-lives are 0.53, 1.80, and 13.9 h for free invertase, at 65, 60, and 55ºC, respectively. For the IE half-lives are 0.48, 1.83, and 20.9 h, at 65, 60, and 55ºC, respectively. The IE is more stable than the free invertase; the energy of deactivation being 83.1 kcal/mol for the IE and 72.0 kcal/mol for the free enzyme.
The kinetics of hydrogenation of xylose to xylitol on a sponge nickel catalyst (commonly referred to as Raney Ni catalyst) and of catalyst deactivation were studied. Plausible explanations for the decrease in catalytic activity by means of surface studies, nitrogen adsorption and thermogravimetric analyses of the fresh and spent catalysts are presented. The kinetic parameters of the process were estimated by the use of a semi-competitive model, which allows full competition between the organic species and the hydrogen atoms for the adsorption sites on the catalyst surface (competitive case). In the model, a competitiveness factor (alpha) is introduced to take into account that even after complete coverage of the surface by the organic species, interstitial sites remain for the adsorption of the hydrogen atoms.
In order to produce gasoline directly from syngas, HZSM-5 can be added to the Fischer-Tropsch catalyst. However, this catalytic system shows an important deactivation rate. Aiming at describing this phenomenon, Fe-based catalysts and physical mixtures containing these catalysts and HZSM-5 were employed in this reaction. All these systems were characterized using the following techniques: XRD, XPS, TPR and TPD of CO. This work shows that HZSM-5 interacts with the Fe-based Fischer-Tropsch catalyst during the reduction step, decreasing the Fe concentration on the catalytic surface and thus lowering the activity of the catalytic system in the Fischer-Tropsch Synthesis.
The chemotactic deactivation of human monocytes was studied to provide insight into the mechanism of chemotaxis. Deactivation was dependent on the dose of chemoattractant and time of incubation. A concentration in the cell suspension of 10(-8) M N-formylmethionylleucyl phenylalanine (FMLP) for 45 min at 37 degrees C led to 60% suppression of the subsequent specific chemotactic response. Higher concentrations of FMLP led to almost 100% specific suppression. Deactivation was specific under all conditions used. The response to a nonrelated chemoattractant, human serum-derived C5a, was unaffected by incubation in FMLP. Deactivation was also transient. If cells were deactivated at 37 degrees C with FMLP, they recovered within 6 h at 37 degrees C from this deactivation. Both phenomena, deactivation and recovery from deactivation, were temperature dependent. Monocytes could not be deactivated at 0 degrees C, and they did not recover from deactivation when kept at 0 degrees C. Thus, specific deactivation appears to require cellular metabolism, involving loss of receptors or blocking of a step between receptor occupancy and response.
As shown previously, immune complexes engender in rabbit serum a factor capable of inducing chemotaxis of rabbit polymorphonuclear leukocytes. This chemotactic factor consists of a complex of the fifth, sixth, and seventh components of complement. As demonstrated here, the polymorphonuclear leukocytes incubated with such treated rabbit serum lose their ability to respond chemotactically to the chemotactic factor. They are "deactivated." The process of "deactivation" is a function of the duration of contact of the cells with, and the concentration of, the treated serum. There is a parallelism between the time course of deactivation and of chemotaxis, as well as the dose-response curves for the two processes. Chemotactic factor purified by isoelectric precipitation and ion-exchange chromatography produces deactivation in the same manner as the treated serum. The deactivating activity requires, as does the chemotactic factor, the sixth component of complement; like the chemotactic factor, it is heat-stable and nondialyzable. Deactivation is prevented by the same phosphonate esters shown previously to prevent chemotaxis by the complement-associated chemotactic factor. The profiles of the phosphonates in protecting against deactivation are the same as the profiles for the chemotactic factor-dependent inhibition of chemotaxis. Aromatic amino acid derivatives prevent both chemotaxis and deactivation. We conclude from this evidence that the chemotactic factor is able to deactivate or induce chemotaxis depending upon experimental conditions. The fact that the profiles given by the phosphonates for protection against chemotactic factor-dependent deactivation and for chemotactic factor-dependent inhibition of chemotaxis are the same indicates that the "activatable esterase" is involved in both processes. Acetate esters such as ethyl acetate and others shown previously to prevent chemotaxis by inhibiting the "activated esterase" do not prevent deactivation. This indicates that deactivation can occur without participation of the latter enzyme...
K+ channels encoded by the human ether-à-go-go-related gene (HERG) are distinguished from most other voltage-gated K+ channels by an unusually slow deactivation process that enables cardiac IKr, the corresponding current in ventricular cells, to contribute to the repolarization of the action potential. When the first 16 amino acids are deleted from the amino terminus of HERG, the deactivation rate is much faster (Wang, J., M.C. Trudeau, A.M. Zappia, and G.A. Robertson. 1998. J. Gen. Physiol. 112:637–647). In this study, we determined whether the first 16 amino acids comprise a functional domain capable of slowing deactivation. We also tested whether this “deactivation subdomain” slows deactivation directly by affecting channel open times or indirectly by a blocking mechanism. Using inside-out macropatches excised from Xenopus oocytes, we found that a peptide corresponding to the first 16 amino acids of HERG is sufficient to reconstitute slow deactivation to channels lacking the amino terminus. The peptide acts as a soluble domain in a rapid and readily reversible manner, reflecting a more dynamic regulation of deactivation than the slow modification observed in a previous study with a larger amino-terminal peptide fragment (Morais Cabral...
The outermost charged amino acid of S4 segments in the α subunit of human skeletal muscle sodium channels was mutated to cysteine in domains I (R219C), II (R669C), III (K1126C), and IV (R1448C). Double mutations in DIS4 and DIVS4 (R219C/R1448C), DIIS4 and DIVS4 (R669C/R1448C), and DIIIS4 and DIVS4 (K1126C/R1448C) were introduced in other constructs. Macropatch recordings of mutant and wild-type (hSkM1-wt) skeletal muscle sodium channels expressed in Xenopus oocytes were used to measure deactivation kinetics from open or fast inactivated states.Conductance (voltage) curves (G (V)) derived from current (voltage) (I (V)) relations indicated a right-shifted G (V) relationship for R669C and for R669C/R1448C, but not for other mutations. The apparent valency was decreased for all mutations. Time-to-peak activation at -20 mV was increased for R1448C and for double mutations.Deactivation kinetics from the open state were determined from the monoexponential decay of tail currents. Outermost charge-to-cysteine mutations in the S4 segments of domains III and IV slowed deactivation, with the greatest effect produced by R1448C. The deactivation rate constant was slowed to a greater extent for the DIII/DIV double mutation than that calculated from additive effects of single mutations in each of these two domains. Mutation in DIIS4 accelerated deactivation from the open state...
Human ether á go-go related gene (hERG) potassium channels play a central role in cardiac repolarization where channel closing (deactivation) regulates current density during action potentials. Consequently, mutations in hERG that perturb deactivation are linked to long QT syndrome (LQTS), a catastrophic cardiac arrhythmia. Interactions between an N-terminal domain and the pore-forming “core” of the channel were proposed to regulate deactivation, however, despite its central importance the mechanistic basis for deactivation is unclear. Here, to more directly examine the mechanism for regulation of deactivation, we genetically fused N-terminal domains to fluorescent proteins and tested channel function with electrophysiology and protein interactions with Förster resonance energy transfer (FRET) spectroscopy. Truncation of hERG N-terminal regions markedly sped deactivation, and here we report that reapplication of gene fragments encoding N-terminal residues 1–135 (the “eag domain”) was sufficient to restore regulation of deactivation. We show that fluorophore-tagged eag domains and N-truncated channels were in close proximity at the plasma membrane as determined with FRET. The eag domains with Y43A or R56Q (a LQTS locus) mutations showed less regulation of deactivation and less FRET...
O principal objectivo deste trabalho consistiu no desenvolvimento de novas técnicas de polimerização radicalar por desactivação reversivel (RDRP) catalisada por metais, mais ecológicos do que os existentes, para a polimerização de monómeros com interesse para aplicações biomédicas. Como prova de conceito, este trabalho teve também como objectivo a preparação de novas estruturas poliméricas, para utilização como sequestradores de ácidos biliares (BAS), recorrendo aos métodos RDRP desenvolvidos.
O mecnaismo que rege a RDRP catalisada por metais tem sido alvo de um intenso debate na literatura, existindo a proposta de dois mecanismos distintos: polimerização radicalar viva por transferência de electrão (SET-LRP) e polimerização radicalar por transferência de átomo com activador suplementar e agente redutor (SARA ATRP). Na fase inicial do trabalho pretendeu-se contribuir para a compreensão do mecanismo da polimerização referida, por ser um factor crucial para o desenvolvimento de novos sistemas catalíticos. O rácio ligante/cobre solúvel foi avaliado durante a polimerização do acrilato de metilo (MA) por RDRP catalisada por Cu(0) e os resultados sugeriram que a polimerização é governada pelo mecanismo de SARA ATRP proposto.
Uma das maiores limitações da técnica de ATRP prende-se com o uso de catalisadores metálicos...
Deactivation of the human brain's default mode network (DMN) is regarded as suppression of endogenous activity to support exogenous task-related processes. This phenomenon has important functional relevance and insufficient DMN deactivation has been implicated in several neuropsychiatric disorders. However, the neurochemical mechanism of the DMN′s deactivation remains largely unknown. In the present study, we test the hypothesis that the major excitatory and inhibitory neurotransmitters, glutamate and GABA, respectively, are associated with DMN deactivation. We used magnetic resonance spectroscopy to measure neurotransmitter concentrations in the posterior cingulate cortex/precuneus (PCC/PCu), a key component of the DMN, and functional magnetic resonance imaging to evaluate DMN deactivation induced by an n-back working memory task. Our results demonstrate significant associations of glutamate and GABA with DMN deactivation. Specifically, high regional GABA concentration in the PCC/PCu area is associated with enhanced deactivation induced by the task in the same region, whereas high glutamate concentration is associated with reduced deactivation. Furthermore, the association between GABA and DMN deactivation increases with the cognitive loads. These neurochemical characteristics of DMN deactivation may provide novel insights toward better understanding of the DMN′s functions under normal physiological conditions and dysfunctions in neuropsychiatric disorders.
The deactivation of supported catalysts CsNO3 and LiNO3 for diesel soot combustion is studied in this work. The effect of hydro-treatment at high temperature and presence of CO2 in feed flow were investigated. Catalysts were characterized by means of X ray diffraction, DSC technique and FTIR. A fixed bed reactor was used to measure activity of fresh and deactivated catalysts with NO2/O2 feed. Thermogravimetrical system with air/CO2 feed was used to study the deactivation with CO2. Catalysts with LiNO3 were the most resistant to deactivation by hydro-treatment, and they are not deactivated by CO2. It is postulated that the cesium nitrate solubilizes in water and is eliminated during the hydro-treatment, instead, lithium species interacted more strongly with the support and generate more resistance species.; Fil: Ruiz, Maria Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; Argentina;; Fil: Lick, Ileana Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina;; Fil: Ponzi, Marta Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; Argentina;; Fil: Ponzi...
9th Novel Gas Conversion Symposium, 2010, Lyon. Book of abstracts of 9th Novel Gas Conversion Symposium, 2010. v. cdrom. p. P35-1-P35-2.; Although synthesis gas production through steam reforming (SR) and oxidative steam
reforming (OSR) of ethanol have been extensively studied in the literature [1,2], the design of effective catalysts for these reactions remains a significant challenge. The production of synthesis gas from ethanol involves a complex reaction system. Several reaction pathways take place depending on the catalysts and reaction conditions. Some of these reactions lead to the formation of by-products, which can in turn result in catalyst deactivation. However, the
detailed catalytic surface mechanism for ethanol steam reforming and the deactivation
mechanism are still not entirely understood and represent a formidable challenge to improved catalyst design.
The aim of this work is to provide further insight into the mechanistic pathways of ethanol conversion reactions and to shed light on the deactivation mechanism of SR using a combination of reaction testing, temperature programmed oxidation (TPO) and temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements and scanning transmission electron microscopy (STEM).
Applied Catalysis A: General, 352(2009): 95-113.; The catalyst performance and the deactivation profiles of CeZrO² and Pt/CeZrO² were evaluated for the ethanol decomposition and steam reforming of ethanol reactions at 773 K.
The mecanisms of Co/ceria catalyst deactivation during steam reforming, oxidative steam reforming, and partial oxidation of ethanol were explored by comparing the results from different characterization techniques with those obtained from catalytic testing in a fixed-bed reactor.
This paper studies the effect of space time on the deactivation of a Co/CeO2 catalyst during oxidative steam reforming of ethanol. Increasing space time increased the ethanol conversion and hydrogen selectivity
whereas acetaldehyde formation decreased.
The effect of chemical composition of Mg-Al mixed oxides on both the acid-base properties and the deactivation process during the gas phase self-condensation of acetone was studied. The activity and selectivity for acetone oligomerization depended on the catalyst acid-base properties. Mg-rich catalysts selectively yielded mesityl oxides whereas Al-rich Mg yAlOx oxides produced mainly isophorone. The initial deactivation rate, increased linearly with the density of surface basic sites, thereby suggesting that although Mg yAlOx oxides promote the self-condensation of acetone by both acid- and base-catalyzed mechanisms, the deactivation rate would be closely related to the surface basic properties. The Mg yAlOx activity declines in the acetone oligomerization reaction due to a blockage of both base and acid active sites by a carbonaceous residue formed by secondary reactions. The amount and the nature of the carbon deposits were characterized by temperature-programmed oxidation technique. Mg yAlOx and Al2O3 formed more and heavier coke than pure MgO but the latter deactivates faster. The deactivation rate and coke composition are defined by the nature of the active site involved in the coke-forming reactions at different catalyst compositions rather than by the carbon amount or polymerization degree.