Cryo-negative staining: advantages and applications for three-dimensional electron microscopy of biological macromolecules

Les échantillons biologiques ne s?arrangent pas toujours en objets ordonnés (cristaux 2D ou hélices) nécessaires pour la microscopie électronique ni en cristaux 3D parfaitement ordonnés pour la cristallographie rayons X alors que de nombreux spécimens sont tout simplement trop << gros D pour la spectroscopie NMR. C?est pour ces raisons que l?analyse de particules isolées par la cryo-microscopie électronique est devenue une technique de plus en plus importante pour déterminer la structure de macromolécules. Néanmoins, le faible rapport signal-sur-bruit ainsi que la forte sensibilité des échantillons biologiques natifs face au faisceau électronique restent deux parmi les facteurs limitant la résolution. La cryo-coloration négative est une technique récemment développée permettant l?observation des échantillons biologiques avec le microscope électronique. Ils sont observés à l?état vitrifié et à basse température, en présence d?un colorant (molybdate d?ammonium). Les avantages de la cryo-coloration négative sont étudiés dans ce travail. Les résultats obtenus révèlent que les problèmes majeurs peuvent êtres évités par l?utilisation de cette nouvelle technique. Les échantillons sont représentés fidèlement avec un SNR 10 fois plus important que dans le cas des échantillons dans l?eau. De plus, la comparaison de données obtenues après de multiples expositions montre que les dégâts liés au faisceau électronique sont réduits considérablement. D?autre part, les résultats exposés mettent en évidence que la technique est idéale pour l?analyse à haute résolution de macromolécules biologiques. La solution vitrifiée de molybdate d?ammonium entourant l?échantillon n?empêche pas l?accès à la structure interne de la protéine. Finalement, plusieurs exemples d?application démontrent les avantages de cette technique nouvellement développée.<br/><br/>Many biological specimens do not arrange themselves in ordered assemblies (tubular or flat 2D crystals) suitable for electron crystallography, nor in perfectly ordered 3D crystals for X-ray diffraction; many other are simply too large to be approached by NMR spectroscopy. Therefore, single-particles analysis has become a progressively more important technique for structural determination of large isolated macromolecules by cryo-electron microscopy. Nevertheless, the low signal-to-noise ratio and the high electron-beam sensitivity of biological samples remain two main resolution-limiting factors, when the specimens are observed in their native state. Cryo-negative staining is a recently developed technique that allows the study of biological samples with the electron microscope. The samples are observed at low temperature, in the vitrified state, but in presence of a stain (ammonium molybdate). In the present work, the advantages of this novel technique are investigated: it is shown that cryo-negative staining can generally overcome most of the problems encountered with cryo-electron microscopy of vitrified native suspension of biological particles. The specimens are faithfully represented with a 10-times higher SNR than in the case of unstained samples. Beam-damage is found to be considerably reduced by comparison of multiple-exposure series of both stained and unstained samples. The present report also demonstrates that cryo-negative staining is capable of high- resolution analysis of biological macromolecules. The vitrified stain solution surrounding the sample does not forbid the access to the interna1 features (ie. the secondary structure) of a protein. This finding is of direct interest for the structural biologist trying to combine electron microscopy and X-ray data. developed electron microscopy technique. Finally, several application examples demonstrate the advantages of this newly

Selective catalytic reduction of nitrogen oxides with ammonia in forced unsteady state reactors - Case based reasoning and mathematical model simulation reasoning

The application of forced unsteady-state reactors in case of selective catalytic reduction of nitrogen oxides (NOx) with ammonia (NH3) is sustained by the fact that favorable temperature and composition distributions which cannot be achieved in any steady-state regime can be obtained by means of unsteady-state operations. In a normal way of operation the low exothermicity of the selective catalytic reduction (SCR) reaction (usually carried out in the range of 280-350°C) is not enough to maintain by itself the chemical reaction. A normal mode of operation usually requires supply of supplementary heat increasing in this way the overall process operation cost. Through forced unsteady-state operation, the main advantage that can be obtained when exothermic reactions take place is the possibility of trapping, beside the ammonia, the moving heat wave inside the catalytic bed. The unsteady state-operation enables the exploitation of the thermal storage capacity of the catalyticbed. The catalytic bed acts as a regenerative heat exchanger allowing auto-thermal behaviour when the adiabatic temperature rise is low. Finding the optimum reactor configuration, employing the most suitable operation model and identifying the reactor behavior are highly important steps in order to configure a proper device for industrial applications. The Reverse Flow Reactor (RFR) - a forced unsteady state reactor - corresponds to the above mentioned characteristics and may be employed as an efficient device for the treatment of dilute pollutant mixtures. As a main disadvantage, beside its advantages, the RFR presents the 'wash out' phenomena. This phenomenon represents emissions of unconverted reactants at every switch of the flow direction. As a consequence our attention was focused on finding an alternative reactor configuration for RFR which is not affected by the incontrollable emissions of unconverted reactants. In this respect the Reactor Network (RN) was investigated. Its configuration consists of several reactors connected in a closed sequence, simulating a moving bed by changing the reactants feeding position. In the RN the flow direction is maintained in the same way ensuring uniformcatalyst exploitation and in the same time the 'wash out' phenomena is annulated. The simulated moving bed (SMB) can operate in transient mode giving practically constant exit concentration and high conversion levels. The main advantage of the reactor network operation is emphasizedby the possibility to obtain auto-thermal behavior with nearly uniformcatalyst utilization. However, the reactor network presents only a small range of switching times which allow to reach and to maintain an ignited state. Even so a proper study of the complex behavior of the RN may give the necessary information to overcome all the difficulties that can appear in the RN operation. The unsteady-state reactors complexity arises from the fact that these reactor types are characterized by short contact times and complex interaction between heat and mass transportphenomena. Such complex interactions can give rise to a remarkable complex dynamic behavior characterized by a set of spatial-temporal patterns, chaotic changes in concentration and traveling waves of heat or chemical reactivity. The main efforts of the current research studies concern the improvement of contact modalities between reactants, the possibility of thermal wave storage inside the reactor and the improvement of the kinetic activity of the catalyst used. Paying attention to the above mentioned aspects is important when higher activity even at low feeding temperatures and low emissions of unconverted reactants are the main operation concerns. Also, the prediction of the reactor pseudo or steady-state performance (regarding the conversion, selectivity and thermal behavior) and the dynamicreactor response during exploitation are important aspects in finding the optimal control strategy for the forced unsteady state catalytic tubular reactors. The design of an adapted reactor requires knowledge about the influence of its operating conditions on the overall process performance and a precise evaluation of the operating parameters rage for which a sustained dynamic behavior is obtained. An apriori estimation of the system parameters result in diminution of the computational efforts. Usually the convergence of unsteady state reactor systems requires integration over hundreds of cycles depending on the initial guess of the parameter values. The investigation of various operation models and thermal transfer strategies give reliable means to obtain recuperative and regenerative devices which are capable to maintain an auto-thermal behavior in case of low exothermic reactions. In the present research work a gradual analysis of the SCR of NOx with ammonia process in forced unsteady-state reactors was realized. The investigation covers the presentationof the general problematic related to the effect of noxious emissions in the environment, the analysis of the suitable catalysts types for the process, the mathematical analysis approach for modeling and finding the system solutions and the experimental investigation of the device found to be more suitable for the present process. In order to gain information about the forced unsteady state reactor design, operation, important system parameters and their values, mathematical description, mathematicalmethod for solving systems of partial differential equations and other specific aspects, in a fast and easy way, and a case based reasoning (CBR) approach has been used. This approach, using the experience of past similarproblems and their adapted solutions, may provide a method for gaining informations and solutions for new problems related to the forced unsteady state reactors technology. As a consequence a CBR system was implemented and a corresponding tool was developed. Further on, grooving up the hypothesis of isothermal operation, the investigation by means of numerical simulation of the feasibility of the SCR of NOx with ammonia in the RFRand in the RN with variable feeding position was realized. The hypothesis of non-isothermal operation was taken into account because in our opinion ifa commercial catalyst is considered, is not possible to modify the chemical activity and its adsorptive capacity to improve the operation butis possible to change the operation regime. In order to identify the most suitable device for the unsteady state reduction of NOx with ammonia, considering the perspective of recuperative and regenerative devices, a comparative analysis of the above mentioned two devices performance was realized. The assumption of isothermal conditions in the beginningof the forced unsteadystate investigation allowed the simplification of the analysis enabling to focus on the impact of the conditions and mode of operation on the dynamic features caused by the trapping of one reactant in the reactor, without considering the impact of thermal effect on overall reactor performance. The non-isothermal system approach has been investigated in order to point out the important influence of the thermal effect on overall reactor performance, studying the possibility of RFR and RN utilization as recuperative and regenerative devices and the possibility of achieving a sustained auto-thermal behavior in case of lowexothermic reaction of SCR of NOx with ammonia and low temperature gasfeeding. Beside the influence of the thermal effect, the influence of the principal operating parameters, as switching time, inlet flow rate and initial catalyst temperature have been stressed. This analysis is important not only because it allows a comparison between the two devices and optimisation of the operation, but also the switching time is the main operating parameter. An appropriate choice of this parameter enables the fulfilment of the process constraints. The level of the conversions achieved, the more uniform temperature profiles, the uniformity ofcatalyst exploitation and the much simpler mode of operation imposed the RN as a much more suitable device for SCR of NOx with ammonia, in usual operation and also in the perspective of control strategy implementation. Theoretical simplified models have also been proposed in order to describe the forced unsteady state reactors performance and to estimate their internal temperature and concentration profiles. The general idea was to extend the study of catalytic reactor dynamics taking into account the perspectives that haven't been analyzed yet. The experimental investigation ofRN revealed a good agreement between the data obtained by model simulation and the ones obtained experimentally.

Sisäisten donorien vaikutus Polypropeeni Ziegler-Natta katalyytissä

Tässä työssä tutkittiin erilaisten sisäisten donorien vaikutusta polypropeenin ominaisuuksiin käytettäessä Ziegler-Natta-katalyyttiä, joka valmistettiin Borealiksen aiemmin kehittämällä kaksifaasimenetelmällä. Tällä uudella menetelmällä katalyytti voidaan valmistaa ilman lisättyä sisäistä donoria ja kantajaa. Katalyyttihiukkaset saadaan kaksifaasisysteemin ansiosta muodoltaan pyöreiksi. Työn kokeellisessa osassa valmistettiin erilaisia Mg-komplekseja, jossa sisäinen donori muodostuu in-situ alkoholin ja karboksyylihappokloridin reagoidessa keskenään. Katalyyttisynteesissä Mg-kompleksi reagoi TiCl4:n kanssa. Saatujen katalyyttien ominaisuuksia testattiin polymeroimalla niillä propeenia 70 °C:ssa tunnin ajan. Polymeerien ominaisuuksia tutkittiin useiden eri karakterisointimenetelmien avulla. Lisäksi tutkittiin mahdollisuutta valmistaa katalyytti, joka ei sisältäisi ftalaattia. Työssä havaittiin, että katalyytin valmistusmenetelmä on käyttökelpoinen myös muilla sisäisillä donoreilla kuin referenssinä käytetyllä DOP:lla. Kaksiliuosfaasi-systeemi saatiin aikaan myös kahdella muulla työssä tutkitulla sisäisellä donorilla. Lisäksi faasitasapainokokeissa kahden liuosfaasin systeemi saatiin aikaan sisäisellä donorilla, joka ei sisältänyt ftalaattia. Kyseisellä katalyytillä havaittiin olevan muista katalyyteistä poikkeavia ominaisuuksia. Esimerkiksi se antoi matalamman isotaktisuuden kuin referenssikatalyytti ja se saattaisikin soveltua matalan isotaktisuuden pehmeille tuotteille. Työssä kokeiltiin yhdellä uudella katalyytillä myös eteenin polymerointia, sillä katalyytin donoripitoisuus oli hyvin matala. Katalyytin aktiivisuus eteenipolymeroinnissa oli varsin hyvä.

Kaasutuskaasun puhdistus

Tässä diplomityössä on selvitetty hiilestä, jätteestä tai biopolttoaineesta kaasutetun kaasun märkä- ja kuivapuhdistusta. Kaasutuskaasun puhdistuksella voidaan likainen ja jopa ongelmallinen aines muuttaa tai puhdistaa sellaiseksi ympäristökelpoiseksi polttoaineeksi, että sitä voidaan käyttää nykyisissä kulutuskohteissa ongelmitta. Lisäkannustusta kaasutuskaasun puhdistus saa uusista EU-direktiiveistä, jotka tulevat rajoittamaan jätteiden läjittämistä kaatopaikoille. Loppusijoitukseen meneviä jätevirtoja voidaan energiakäytöllä pienentää huomattavasti.Työ on tehty PVO-Engineering Oy:n voimalaitostekniikan osastolle kevään 2001 aikana. Työn tavoitteena oli kasvattaa yrityksen tietomäärää kaasutuskaasun puhdistuksen osalta. Lisäksi pyrittiin selvittämään uuden keraamisen pussisuodatinmateriaalin käyttöä kaasutuskaasun kuumakuivasuodatuksessa. Työn ensimmäisessä osassa esitetään kaasutuskaasun koostumuksen ja syntymisen lisäksi tämän työn lähtökohdat ja tavoitteet. Toisessa osassa selvitetään kaasulle asetettavia vaatimuksia eri käyttötapojen mukaan. Kolmannessa ja neljännessä osassa selvitetään puhdistettavien komponenttien käyttäytymistä ja sopivia puhdistusmenetelmiä.Kaasutuskaasun puhdistustekniikka vaihtelee paljonkin riippuen kaasun käyttökohteesta. Eroja syntyy käyttökohteen asetettamista vaatimuksista polttoaineelle, kaasutettavan polttoaineen koostumuksesta ja laadun vaihtelusta. Puhdistuksessa keskitytään kloori -, rikki -, typpi - ja metalliyhdisteiden poistamiseen kaasuvirrasta. Erotuskyvyllä arvioituna eri puhdistusmenetelmistä tehokkaimpia ovat pesurisähkösuodatinyhdistelmät. Niiden suuret jätemäärät ovat kuitenkin iso ongelma. Kuumakuivapuhdistuksessa pyritään kehittämään menetelmä, jossa syntyvät jätemäärät ovat pieniä ja puhdistustulos on riittävä. Puhdistuksen apukeinona käytetään usein erilaisia katalyyttejä. Tunnetuimpia ovat erilaiset kalsiumpohjaiset materiaalit ja mineraalit. Katalyyteillä voidaan tehostaa tarpeellisia kemiallisia reaktioita puhdistusprosessissa. Kaikki puhdistukseen liittyvät ongelmat ovat kooltaan niin suuria, että niiden ratkaisemiseksi on tulevaisuudessa tehtävä lujasti töitä. Markkinanäkymät toimivalle puhdistustekniikalle ovat nykymaailmassa hyvät. Niinpä tuotekehitykseen laitetut panokset voivat tulevaisuudessa olla yritykselle kullan arvoisia.

Kationinvaihtohartsien hapetuskestävyys

Hyvin puhdasta vettä vaativissa sovelluksissa käytettävät kationinvaihtohartsit eivät saisi vuotaa puhdistettavaan veteen mitään vieraita aineita. Todellisuudessa hartsit kuitenkin vuotavat hyvin pieniä määriä erilaisia yhdisteitä käytön aikana. Aineet, joita kationinvaihtohartsi päästää veteen, ovat osaksi hartsin polymerointireaktion aikana sen rungon sisään jääneitä yhdisteitä. Nämä voidaan suurimmaksi osaksi poistaa pesemällä hartsia. Osittain niitä syntyy myös hartsin polystyreenidivinyylibentseenirungon (PS-DVB) hapettuessa. Hapettumisen seurauksena syntyneet yhdisteet ovat pääosin orgaanisia sulfonaatteja. Tämä työ koskee ydinvoimalaitoksissa käytettäviä pulverihartseja, joita käytetään primääripiirissä kiertävän lauhdeveden puhdistukseen ja jotka joutuvat siellä alttiiksi hapettumiselle. Yleensä hapettuminen on hidasta ja se johtuu veteen liuenneesta hapesta. Hapettuminen nopeutuu huomattavasti, jos vedessä on läsnä hapettimia tai siirtymämetalli-ioneja. Tällaisia hapettimia ovat esimerkiksi vetyperoksidi, otsoni, vapaa kloori, typpihappo ja kromi. Vetyperoksidin vaikutuksesta hartsin runkoon muodostuu hydroperoksidiryhmä, jonka hajoamisesta alkaa reaktioiden sarja, joka lopulta johtaa hartsin polymeerirungon katkeamiseen. Siirtymämetalli-ionit katalysoivat peroksidien hajoamista. Tavallisimpia hapetusta katalysoivia metalli-ioneja ovat rauta ja kupari, joiden katalyyttinen aktiivisuus on suuri. Tässä työssä pyrittiin selvittämään, onko mahdollista valmistaa hartseja, jotka kestävät hapettumista paremmin kuin nykyisin käytössä olevat hartsit. Sen tutkimiseksi tehtiin kiihdytettyjä hapetuskokeita käyttäen hapettimena vetyperoksidia ilman siirtymämetalli-ioni katalyyttejä. Hapetuskokeet tehtiin kaupallisesti saatavilla hartseilla ja uusilla työtä varten syntetisoiduilla koehartseilla. Hapetuskokeiden etenemistä seurattiin mittaamalla veteen liuenneiden orgaanisten aineiden kokonaismäärää (TOC-analyysi) ja liuoksessa esiintyvien orgaanisten sulfonaattien määrää johtokykymittauksin. Saadut tulokset antoivat viitteitä siitä, että hartsin synteesiolosuhteilla voi olla suurempi vaikutus sen hapetuskestävyyteen kuin synteesissä käytetyillä raaka-aineilla.

Removal of Lipophilic Wood Extractives from TMP Process Waters by Wet Oxidation

Työssä tutkittiin kokeellisesti rasvaliukoisten uuteaineiden poistamista TMP -prosessin vesikierroista märkähapetuksen avulla. Työn tavoitteena oli tutkia mahdollisuudet hyödyntää TMP -prosessissa vallitsevaa korkeaa lämpötilaa rasvaliukoisten uuteaineiden poistamiseen hapettamalla niitä puhtaalla hapella. Kirjallisuusosassa tarkasteltiin märkähapetuksen teknologiaa, reaktiomekanismia, käytettyjä katalyyttejä, käyttökohteita sekä kustannuksia. Kokeita suoritettiin autoklaavireaktorissa lämpötiloissa 140 °C, 160 °C ja 180 °C. Vetyperoksidia käytettiin katalyyttinä lisätyn vetyperoksidin määrän ollessa 100 - 1800 mg/l ja hapen osapaineen ollessa 0 ( typpiatmosfääri) - 15 baria. Kokeissa tarkasteltiin kemiallisen hapenkulutuksen (COD), rasvaliukoisten uuteaineiden konsentraation, orgaanisen kokonaishiilen (TOC) ja värin muutoksia kokeiden aikana eri lämpötiloilla, hapen osapaineilla ja lisätyn vetyperoksidin määrillä. Kokeissa saavutettiin 30 %:n COD:n vähenemä sekä 90 %:n vähenemä rasvaliukoisissa uuteaineissa lämpötiloissa 160 °C ja 180 °C. Lisäämällä vetyperoksidia katalyyttinä saavutettiin lähes sama tulos lämpötilassa 140 °C. Suurin tässä työssä havaittu ongelma oli lisääntynyt värinmuodostus vedessä olevassa hienojakoisessa kiintoaineessa hapetuksen aikana. Tämän vuoksi lisätutkimukset ovat tarpeellisia sen seikan selvittämiseksi, voidaanko muodostunut väri mahdollisesti poistaa massan valkaisussa.

Lipase Improvement: Goals and strategies

Lipases have received great attention as industrial biocatalysts in areas like oils and fats processing, detergents, baking, cheese making, surface cleaning, or fine chemistry . They can catalyse reactions of insoluble substrates at the lipid-water interface, preserving their catalytic activity in organic solvents. This makes of lipases powerful tools for catalysing not only hydrolysis, but also various reverse reactions such as esterification, transesterification, aminolysis, or thiotransesterifications in anhydrous organic solvents. Moreover, lipases catalyse reactions with high specificity, regio and enantioselectivity, becoming the most used enzymes in synthetic organic chemistry. Therefore, they display important advantages over classical catalysts, as they can catalyse reactions with reduced side products, lowered waste treatment costs, and under mild temperature and pressure conditions. Accordingly, the use of lipases holds a great promise for green and economical process chemistry.

The initial oxidation of transition metal surfaces

Due to their numerous novel technological applications ranging from the example of exhaust catalysts in the automotive industry to the catalytic production of hydro- gen, surface reactions on transition metal substrates have become to be one of the most essential subjects within the surface science community. Although numerous applications exist, there are many details in the different processes that, after many decades of research, remain unknown. There are perhaps as many applications for the corrosion resistant materials such as stainless steels. A thorough knowledge of the details of the simplest reactions occuring on the surfaces, such as oxidation, play a key role in the design of better catalysts, or corrosion resistant materials in the future. This thesis examines the oxidation of metal surfaces from a computational point of view mostly concentrating on copper as a model material. Oxidation is studied from the initial oxidation to the oxygen precovered surface. Important parameters for the initial sticking and dissociation are obtained. The saturation layer is thoroughly studied and the calculated results arecompared with available experimental results. On the saturated surface, some open questions still remain. The present calculations demonstrate, that the saturated part of the surface is excluded from being chemically reactive towards the oxygen molecules. The results suggest, that the reason for the chemical activity of the saturated surface is due to a strain effect occuring between the saturated areas of the surface.

Síntese de catalisadores Ziegler-Natta: algumas rotas e suas dificuldades

The Ziegler-Natta catalyst and the polymerization thereof are systems which require careful handling and special treatment of chemicals. In spite of the use of inert atmosphere and dry chemicals, some Ziegler-Natta systems may present low activities or even may deactivate because of unsuitable handling. Some features of the TiCl3 synthesis and its characterization when related to the presence of impurities are described. Evidences of poor handling of chemicals and/or laboratory devices while in synthesis of the catalyst are emphasized. The problems arising from butadiene polymerization and some relevant details in propylene polymerization are also presented with teaching objectives.

Recuperação de metais de catalisadores usados de hidrotratamento (NiMo E CoMo/AL2O3)

This work presents a detailed study of the leaching behavior of deactivated hydrotreating catalysts (CoMo, NiMo/Al2O3) in presence of oxalate and NH4+ ions in various media. The yield of metals recovery may be optimized by adjusting several experimental parameters (time, temperature, etc). Leaching is limited by physical factors (diffusional effects caused by coke) and by the existence of silicate/spinel-like species which are poorly soluble in leaching solutions. Coke may be eliminated by an oxidation step at temperatures between 300-400ºC. Above 400ºC, solubilization of Ni and Co is drastically reduced. 50-90% wt of sulphate species and 15-30% wt of phosphate ions are solubilized during leaching. Silicon (as SiO2) is not solubilized. The best Ni-Co-Mo recoveries are in the 70-90% wt range; Fe recovery may be quantitative, whereas Al leaching may be lower than 5% wt.

Ação promotora do berílio em catalisadores da síntese do estireno

The catalytic dehydrogenation of ethylbenzene in presence of steam is the main commercial route to produce styrene. The industrial catalysts are potassium- and chromia-doped hematite which show low surface areas leading to bad performance and short life. In order to develop catalysts with high areas, the effect of beryllium on the textural properties and on the catalytic performance of this iron oxide was studied. The influence of the amount of the dopant, the starting material and the calcination temperature were also studied. In sample preparations, iron and beryllium salts (nitrate or sulfate) were hydrolyzed with ammonia and then calcinated. The experiments followed a factorial design with two variables in two levels (Fe/Be= 3 and 7; calcination temperature= 500 and 700ºC). Solids without any dopant were also prepared. Samples were characterized by elemental analysis, infrared spectroscopy, surface area and porosity measurements, X-ray diffraction, DSC and TG. The catalysts were tested in a microreactor at 524ºC and 1 atm, by using a mole ratio of steam/ ethylbenzene=10. The selectivity was measured by monitoring styrene, benzene and toluene formation. It was found that the effect of beryllium on the characteristics of hematite and on its catalytic performance depends on the starting material and on the amount of dopant. Surface areas increased due to the dopant as well as the nature of the precursor; samples produced by beryllium sulfate showed higher areas. Beryllium-doped solids showed a higher catalytic activity when compared to pure hematite, but no significant influence of the anion of starting material was noted. It can be concluded that beryllium acts as both textural and structural promoter. Samples with Fe/Be= 3, heated at 500ºC, lead to the highest conversion and were the most selective. However, catalysts prepared from beryllium sulfate are the most promising to ethylbenzene dehydrogenation due to their high surface area which could lead to a longer life.

Anticorpos catalíticos: expandindo o alcance da catálise enzimática

The vast binding repertoire of the immune system has been exploited for the generation of tailor-made selective catalysts. Since the first reports of chemical reactions catalyzed by antibodies were published, research in this field, which borders chemistry and biology, has been rapidly established and a number of catalytic antibodies that carry out a wide range of reactions, have been developed. Recent advances have led to antibodies that catalyse complex, multi-step reactions and difficult chemical transformations, as well as reactions that do not have an organic equivalent at all. Current research in this field has been devoted to practical applications of this technology.

Troca iônica no estado sólido de európio3+ em zeólita Y: influência do tempo de reação

Rare earth elements supported in zeolites are the most important catalysts in the fluid cracking of petroleum. The solid state ion exchange of Eu3+ in Y zeolite was investigated. First of all, the hydrated EuCl3 was well mixed in a ball mill and was then heated at 300ºC for different times. The quantitative determination of Eu3+ showed that the degree of ion exchange depends on the reaction time at constant temperature, being ~95% in 4 h. The X-ray study showed that the crystallinity of the zeolite is little affected by the exchange procedure. The study of spectroscopic properties of Eu3+, emission spectra and lifetime, give information about the migration and position of the ion in the zeolite cages.

Hidróxidos duplos lamelares: síntese, estrutura, propriedades e aplicações

The layered double hydroxides, known as anionic clays and represented by the general formula [M2+1-x M3+x (OH) 2]x+ Am-x/m·nH 2O, are a group of materials which are of much interest currently. They present a variety of potential applications as adsorbents, catalysts and catalyst support, ion-exchangers, antacids and as a polymer stabilizer. It is possible to obtain a broad variety of layered double hydroxides (LDHs), depending on the identity and ratio of the cations M2+ and M3+, as well as the interlamelar anion. The aim of this review is to give out some information about this class of materials, concerning to the synthesis, characterization, properties and applications.

Propriedades texturais e catalíticas de óxidos de ferro contendo cromo e cobre

Chromium and copper-doped hematites were prepared with the aim of studying the synergistic effect of these dopants on the textural and on the catalytic properties of the iron oxides towards the high temperature shift reaction. It was found that the most active catalysts were those with the highest amount of copper. They had the Fe(II)/Fe(III) ratio near the stoichiometric value of magnetite, the highest surface areas under the reactional atmosphere and the greatest tendency to produce the active form; they also were poorly crystalline solids. The best performance was shown by the catalyst with Fe/Cu=10, heated at 300ºC. It can thus be concluded that copper acts both as textural and structural promoter in these catalysts.