An automated microreactor for semi-continuous biosensor measurements.

Living bacteria or yeast cells are frequently used as bioreporters for the detection of specific chemical analytes or conditions of sample toxicity. In particular, bacteria or yeast equipped with synthetic gene circuitry that allows the production of a reliable non-cognate signal (e.g., fluorescent protein or bioluminescence) in response to a defined target make robust and flexible analytical platforms. We report here how bacterial cells expressing a fluorescence reporter ("bactosensors"), which are mostly used for batch sample analysis, can be deployed for automated semi-continuous target analysis in a single concise biochip. Escherichia coli-based bactosensor cells were continuously grown in a 13 or 50 nanoliter-volume reactor on a two-layered polydimethylsiloxane-on-glass microfluidic chip. Physiologically active cells were directed from the nl-reactor to a dedicated sample exposure area, where they were concentrated and reacted in 40 minutes with the target chemical by localized emission of the fluorescent reporter signal. We demonstrate the functioning of the bactosensor-chip by the automated detection of 50 μgarsenite-As l(-1) in water on consecutive days and after a one-week constant operation. Best induction of the bactosensors of 6-9-fold to 50 μg l(-1) was found at an apparent dilution rate of 0.12 h(-1) in the 50 nl microreactor. The bactosensor chip principle could be widely applicable to construct automated monitoring devices for a variety of targets in different environments.

Algumas Considerações sobre a Regra de Hund e a Estrutura Eletrônica de Átomos no Ensino de Química

Hund's maximum multiplicity rule as stated in most elementary and intermediate level textbooks on general and inorganic chemistry and usually taught at the college and undergraduate level is incorrect. It is true that electrons entering a subshell of an atom tend to occupy the orbitals singly as far as possible but not necessarily with parallel spins. Also, proper definitions and correct use of terms like configuration, microstate, spectroscopic term, level and state are essential if confusion on the part of the student, especially the beginner, is to be avoided.

A Eterna Busca do Indivisível: do Átomo Filosófico aos Quarks e Léptons

The fascinating search of the inner boundaries of the Universe, has been entangled, since the birth of greek philosophy 25 centuries ago, with the main epistemological changes in the History of Science. This paper does not intend to present a systematic description of the discovery of the elementary particles. By stressing the main achievements of the knowledge of matter's structure and their dependence on symmetry arguments, it is argued that even considering profound differences in each historical period, there is a paradgima of atom shared by Chemistry and Particle Physics. This text could help High School Teachers of Chemistry and Physics, as well as motivate them, in the challenge of explaining to their pupils how the idea of atom evolved.

Síntese e caracterização estrutural de complexos mono e bimetálicos de paládio e platina com ligantes contendo nitrogênio e enxofre

The synthesis of several mono- and bimetallic platinum and palladium complexes are reported. The monometallic complexes are of the type MCl2(PEt3)2L (L=2-aminothiazol; benzothiazol; 2-imidazolidithione; M=Pt; Pd), and the bimetallic complexes (M2Cl4(PEt3) 2L) are derived from them. Infrared spectroscopic characterization of the monometallic complexes shows that the metal centre are coordinated through the N-endocyclic (L=2-aminothiazol; benzothiazol) and through the sulphur when L=2-imidazolidithione. Coordination of a second metal fragment occurs via the sulphur atom (L=2-aminothiazol; benzothiazol) according to infrared studies. 31P{¹H} NMR spectroscopy suggest that the complexes have a cis- configuration since the ¹J Pt-P are around the value found for this type of compound.

Conforma: a program for determining ring conformations and puckering coordinates

A program (CONFORMA) was developed to calculate ring puckering coordinates using Cremer and Pople's (J. Am. Chem. Soc. 1975, 97, 1354) methodology, which quantifies the conformation of five or more atom rings. The program performs, also, a conformational analysis based on these results.

Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 1: CF4 / O2

The plasma etching of semiconductor surfaces with fluorine-containing compounds has technological interest. Presently, considerable effort is being devoted to understand the chemistry involved. In this work, a numerical modeling analysis of the gas-phase decomposition of CF4/O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes was determined as well as the effect of the parameters' uncertainties. The results were compared with experimental data. The main etching agent in the system is the fluorine atom. The concentration of the main species, SiF4, CO, CO2 and COF2 depend on the composition of the mixture.

Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 2: SF6 / O2

In this work, a numerical modeling analysis of the gas-phase decomposition of SF6 / O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes and the effect of the parameters' uncertainties were determined. The model was compared with experimental data for the plasma etching of silicon and with the calculated results for the CF4 / O2 system. In both systems the main etching agent is the fluorine atom and the concentration of the major species depends on the composition of the mixture. The etching rate is greater for SF6 / O2.

Modelos para o carbono sp³: quatro pirâmides no tetraedro

We describe a paper model for the sp³ carbon atom, consisting of four pyramids that can be assembled to produce a tetrahedron. The main feature of this model is that, when two of the pyramids are properly put together, the solid thus formed is an "open" tetrahedron, containing edges connecting the center of the tetrahedron to its vertices. The student can easily imagine the whole tetrahedron and, at the same time, he can observe its center and the lines corresponding to the directions of sp³ orbitals.

Metsäpolttoaineiden vesitiekuljetus proomukalustolla

Metsäpolttoaineiden käyttö kasvaa lämpö- ja voimalaitoksissa ja mahdollisissa biojalostamoissa. Metsäpolttoaineilla voidaan saavuttaa päästövähennyksiä korvaamalla päästöintensiivisempiä polttoaineita. Metsäpolttoaineen kysynnän kasvu suurkäyttöpaikoilla luo uusia vaatimuksia metsäbiomassan hankintaan. Metsäpolttoaineiden vesitiekuljetuksen sisältämiä logistiikkajärjestelmiä kehittämällä toimitusvarmuutta pystytään parantamaan ja hankintaa laajentamaan kustannustehokkaasti ja ympäristöystävällisesti. Kuljetuskokeilut antoivat uutta tietoa vesitiekuljetuksen sisältämästä hankinnasta. Lastikapasiteetti nykyisen kaltaisessa Eurooppa IIa -suurproomussa vaihtelee 1200 tonnista jopa 1800 tonniin (kosteus 40 %) riippuen tiivistymisestä ja proomun modifiointiasteesta. Metsähakkeen energiatiheys oli suurproomukuljetuksissa keskimäärin 1 MWh/i-m3, joka oli 25 % parempi kuin vertailun hakerekkakuljetuksissa. Vesitiekuljetuksen kustannukset olivat kuljetuskokeiluissa lastauksineen ja purkuineen 0,02 €/MWh/km, ollen noin 20 % ketjun kokonaiskustannuksista. Simuloinnin edullisimpien vesitiekuljetusvaihtoehtojen vaihteluvälin kustannukset olivat vastaavasti 0,013 - 0,026 €/MWh/km. Lastauksen ja purun kustannus oli 0,4 - 0,6 €/MWh ja vesitiekuljetus 0,9 - 2,0 €/MWh (100 km). Ketjun kokonaiskustannukset hakkuutähdehakkeelle vaihtelivat simuloinnin edullisimpien vaihtoehtojen perusteella välillä 10,8 - 12,1 €/MWh (30 km rekka, 100 km proomu). Kuljetusketjujen simuloinnin kustannukset osoittivat proomukuljetusketjun olevan kilpailukykyinen vaihtoehto hakerekkakuljetusketjulle kalustosta ja vuosittaisista käyttötunneista riippuen kuljetusetäisyyden ylittäessä 100 km. Kustannustehokkain ratkaisu vesitiekuljetuksessa saavutettiin pienen aluksen ja suuren kokoluokan proomuyksikön kytkyeellä. Haketus kannattaa toteuttaa ennen proomukuljetuksen osuutta metsähakkeen paremman tiiviyden ja käsiteltävyyden perusteella. Logistiikkajärjestelmiä pitää kehittää tapauskohtaisesti käyttöpaikan tarpeet ja olosuhteet huomioon ottaen. Metsäpolttoaineiden vesitiekuljetuksen sisältämän logistiikan liiketoimintamallien vertailussa arvioitiin vaihtoehtoiset ulkoistetut toimintamallit paremmaksi kuin nykyinen urakointimalli. Tämä mahdollistaa paremman metsähakkeen saatavuuden ja logistiikan tehokkuuden lastausterminaaleissa. Terminaalitoiminnot ja proomukuljetukset lisäävät uusia liiketoimintamahdollisuuksia ja mahdollistavat metsäpolttoaineiden

Vacancy-assisted domain-growth in asymmetric binary alloys: A Monte Carlo Study

A Monte Carlo simulation study of the vacancy-assisted domain growth in asymmetric binary alloys is presented. The system is modeled using a three-state ABV Hamiltonian which includes an asymmetry term. Our simulated system is a stoichiometric two-dimensional binary alloy with a single vacancy which evolves according to the vacancy-atom exchange mechanism. We obtain that, compared to the symmetric case, the ordering process slows down dramatically. Concerning the asymptotic behavior it is algebraic and characterized by the Allen-Cahn growth exponent x51/2. The late stages of the evolution are preceded by a transient regime strongly affected by both the temperature and the degree of asymmetry of the alloy. The results are discussed and compared to those obtained for the symmetric case.

LWC-paperin opasiteetin parantaminen

LWC-syväpainopaperilta vaaditaan hyvän ajettavuuden, kiillon ja sileyden ohella hyvää opasiteettia. Tämä on asettanut haasteita LWC-paperin valmistajille paperin neliömassojen laskiessa. Tässä diplomityössä etsittiin keinoja parantaa kevyiden LWC-syväpainolajien opasiteettia heikentämättä oleellisesti muita tärkeitä paperin ominaisuuksia. Tavoitteena oli nostaa CR48-lajin opasiteetti tavoitearvoon 90 %. Työn kirjallisuusosassa perehdyttiin paperin optisten ominaisuuksien teoriaan sekä raaka-aineisiin ja prosessin osiin, joilla on vaikutusta paperin opasiteettiin. Työn kokeellisessa osassa tutkittiin olemassa olevan aineiston perusteella tekijöitä, joilla uskottiin olevan vaikutusta CR48-lajin opasiteettiin. Tutkimuksen ja kirjallisuuden perusteella ajettiin tehdaskoeajoa, joiden avulla pyrittiin parantamaan paperin opasiteettia. CR48-lajin opasiteettitavoite saavutettiin kolmella eri tavalla. Opasiteettitavoite saavutettiin, kun paperin vaaleus säädettiin tavoitearvoon pigmenttivärin avulla tumman hierteen sijasta. Tällöin väripigmentin määrää päällystyspastassa nostettiin 0,01 osaa ja valkaistun hierteen osuus kokonaishierteen määrästä oli 100 %. Vaaleuden säätö pastavärillä oli käytännössä hidasta ja hankalaa. Opasiteettitavoite saavutettiin myös, kun hierre jauhettiin täysin koeterillä. Koeterillä tapahtuva jauhatus oli rajumpaa ja katkovampaa kuin perinteisillä terillä, joten hienoaineen lisääntyminen ja kuidun lyheneminen paransivat paperin opasiteettia, mutta lujuudet huononivat. Lisäksi tavoiteopasiteetti saavutettiin, kun sellun osuutta vähennettiin 8 %-yksikköä. Lujuuden säilymisen kannalta sellun vähennys oli parempi keino opasiteetin parantamiseksi kuin hierteen jauhaminen koeterillä. Koeajojen perusteella pohjapaperin tuhkapitoisuuden nostolla ja hierteen CSF-luvun alentamisella ei ollut vaikutusta paperin opasiteettiin. Lisäksi 100 %:nen koeterillä jauhettu sahahakehierre antoi paperille huonomman opasiteetin kuin hierre, josta puolet oli jauhettu koeterillä ja raaka-aineesta 25 % oli sahahaketta.

Investigação espectroscópica dos carbonilos heterobimetálicos cis-[Fe(CO)4(HgX)2], X = Cl, Br,I

The series of compounds cis-[Fe(CO)4(HgX)2], X=Cl,Br,I shows an octahedral geometry around the iron atom with the two HgX groups cis to each other. In this paper the assignment for the carbonyl stretching modes and the calculation of their force constants were performed on the basis of the Cotton-Krainhanzel model. Taking into account all the data from the IR, 199Hg NMR and UV-vis spectra it is possible to verify the influence of X on the electronic densities at the metallic centers.

Síntese orgânica limpa

An introduction to the fundamental concepts and main aspects of organic clean synthesis is given, and relevant industrial examples which have implemented the philosophy of cleaner synthesis are also presented. Recent trends in organic synthesis which are environmentally friendly are also discussed.

Íons carbônio

Carbonium ions are carbocations with a pentacoordinated carbon atom, where the electronic octet is maintained. They possess a three center two electron bond in order to keep the tetravalence of the carbon atom. This paper reviews the concept of carbonium ions, their formation, stability and reactions.

Economia de átomos, engenharia molecular e catálise organometálica bifásica: conceitos moleculares para tecnologias limpas

For economical and ecological reasons, synthetic chemists are confronted with the increasing obligation of optimizing their synthetic methods. Maximizing efficiency and minimizing costs in the production of molecules and macromolecules constitutes, therefore, one of the most exciting challenges of synthetic chemistry. The ideal synthesis should produce the desired product in 100% yield and selectivity, in a safe and environmentally acceptable process. In this highlight the concepts of atom economy, molecular engineering and biphasic organometallic catalysis, which address these issues at the molecular level for the generation of "green" technologies, are introduced and discussed.