Espectrometria de massas com ionização por "electrospray" aplicada ao estudo de espécies inorgânicas e organometálicas

Although electrospray ionization mass spectrometry (ES-MS) has been extensively applied to study organic and biochemical species, it is also specially suitable to study inorganic and organo-metallic species. Such species, even those that are low-volatile or thermo-unstable, can be easily ionized or simply transferred from liquid to gas phase by electrospray. However, chemical transformations frequently occur during the process. This paper discusses the fundamental aspects of electrospray ionization as well as its analytical applicability to inorganic and organo-metallic species in order to spread the technique and make its characteristics more familiar to potential users.

Síntese de novos herbicidas derivados do 1,2alfa,4alfa,5-tetrametil-8-oxabiciclo[3.2.1]oct-6-en-3-ona

In this paper we report the synthesis of biologically active compounds through a [3+4] cycloaddition reaction to produce the main frame structure, followed by several conventional transformations. The 1,2alpha,4alpha,5-tetramethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (11) obtained from a [3+4] cycloaddition reaction was converted into 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3-one (13) in 46% yield. This was further converted into the alcohols 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (14), 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3beta-ol (15), 1,2alpha,4alpha,5-tetramethyl-3-butyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (17), 1,2alpha,4alpha,5-tetramethyl-3-hexyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (18) and 1,2alpha,4alpha,5-tetramethyl-3-decyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (19). Dehydration of 17, 18 and 19 with thionyl chloride in pyridine resulted in the alkenes 20, 21 and 22 in ca. 82% - 89% yields from starting alcohols. The herbicidal activity of the compounds synthesized was evaluated at a concentration of 100 µg g-1. The most active compound was 21 causing 42,7% inhibition against Cucumis sativus L.

The Transformation of Practical Teaching Focusing on Dialogic Learning

This study investigates the transformation of practical teaching in a Catalan school, connected to the design, implementation and development of project-based learning, and focusing on dialogic learning to investigate its limits and possibilities. Qualitative and design-based research (DBR) methods are applied. These methods are based on empirical educational research with the theory-driven of learning environments. DBR is proposed and applied using practical guidance for the teachers of the school. It can be associated with the current proposals for Embedding Social Sciences and Humanities in the Horizon 2020 Societal Challenges. This position statement defends the social sciences and the humanities as the most fundamental and important ideas to face all societal challenges. The results of this study show that before the training process, teachers apply dialogic learning in specific moments (for example, when they speak about the weekend); however, during the process and after the process, they work systematically with dialogic learning through the PEPT: they start and finish every activity with a individual and group reflection about their own processes, favouring motivation, reasoning and the implication of all the participants. These results prove that progressive transformations of teaching practice benefit cooperative work in class

Transformation of a Rural Landscape in the Eastern Pyrenees Between 1953 and 2000

In the mid-20th century, the southern parts of the Madres and Mont Coronat massif (Eastern Pyrenees, France) were characterized by a Mediterranean landscape shaped by human activity. Long-term use of these mountains for crops, livestock, and forestry led to an increase in grassland areas at the expense of forest. However, socioeconomic transformation (abandonment of agriculture and a decrease in the rural population) in recent decades has caused profound changes in this massif. Interpretation of aerial photographs (1953, 1969, 1988, and 2000) made it possible to detect and analyze the changes produced in the study area (6787 ha) during this period. In 1953 most of the massif landscape consisted of grasslands (38%) and open forests (18%), with some areas of dense forest (15%). By 2000, dense forest cover had doubled in size (31%), and grassland had decreased considerably (by 73% of the initial area). Since 1953, the study area has become more homogeneous, with a few local exceptions. The results of this study suggest that socioeconomic factors might be the main cause of landscape transformations in this period of approximately 50 years.

N-halossacarinas: reagentes úteis (e alternativos) em síntese orgânica

N-halosaccharins proved to be useful and alternative reagents for diverse organic transformations, such as halogenation of aromatic compounds, benzylic and alpha-carbonylic positions, cohalogenation of alkenes, oxidation of secondary alcohols, etc. Their preparation from saccharin, a cheap and readly available starting material, is simple.

Sensores eletroquímicos: considerações sobre mecanismos de funcionamento e aplicações no monitoramento de espécies químicas em ambientes microscópicos

Electrochemical sensors have attracted considerable attention in recent years because they provide data about the chemical state of our surroundings and the dynamics of the chemical transformations in the form a spatially resolved image. Particular interest has been directed to measurements in restricted-volume samples as new technologies enable the fabrication of miniaturized versions of sensors with reproducible characteristics. Taking these aspects into consideration, this review focuses on the use of electrodes of micrometer dimensions to acquire chemical information in microdomains in which concentrations may not be spatially homogeneous. This is possible because microelectrodes allow fast-response measurements with micrometer resolution to be performed. On the other hand, the use of microelectrodes as amperometric sensors presents an inherent drawback owing to the insufficient specificity toward the substrate of interest. Hence, some comments on strategies to enhance the selectivity of amperometric sensors are also made. Finally, recent applications of structurally microscopic electrodes as in vivo sensors are shown, as well as a prospect of the future trend in this field.

Critical behavior in nonequilibrium phase transitions

The nonequilibrium phase transitions occurring in a fast-ionic-conductor model and in a reaction-diffusion Ising model are studied by Monte Carlo finite-size scaling to reveal nonclassical critical behavior; our results are compared with those in related models.

Critical behavior of a water monolayer under hydrophobic confinement

The properties of water can have a strong dependence on the confinement. Here, we consider a water monolayer nanoconfined between hydrophobic parallel walls under conditions that prevent its crystallization. We investigate, by simulations of a many-body coarse-grained water model, how the properties of the liquid are affected by the confinement. We show, by studying the response functions and the correlation length and by performing finite-size scaling of the appropriate order parameter, that at low temperature the monolayer undergoes a liquid-liquid phase transition ending in a critical point in the universality class of the two-dimensional (2D) Ising model. Surprisingly, by reducing the linear size L of the walls, keeping the walls separation h constant, we find a 2D-3D crossover for the universality class of the liquid-liquid critical point for L/h=~50, i.e. for a monolayer thickness that is small compared to its extension. This result is drastically different from what is reported for simple liquids, where the crossover occurs for , and is consistent with experimental results and atomistic simulations. We shed light on these findings showing that they are a consequence of the strong cooperativity and the low coordination number of the hydrogen bond network that characterizes water.

Preparo da para-cloroanilina: um experimento simples, rápido e barato

Experiments simple, short and efficient for experimental disciplines in undergraduate courses in Chemistry are an excellent opportunity for students to consolidate the learning of theoretical concepts in classical chemical transformations. The use of a safe reagent, of low cost and easy access is the motivation for this communication, that describes the use of trichloroisocyanuric acid - a chlorinating agent used in the treatment of swimming pool water - for the chlorination of acetanilide, an intermediate in the preparation of para-chloroaniline.

Metátese de olefinas aplicada ao fechamento de anéis: uma ferramenta poderosa para a síntese de macrociclos naturais

For a quarter of a century, metathesis has become indispensable for the synthesis of natural and non-natural products, particularly of biologically active compounds. This review illustrates through a maximum of appropriate examples the power and the versatility of the metathesis ring-closure (RCM) reaction as a key ring-closure methodology for the synthesis of natural macrocycles. Its high functional group compatibility as well as the possibility of further transformations makes this reaction a powerful tool in the cases where the structural framework and function requirements are difficult to meet.

Energian käyttö sahatavaran kuivauksessa

Sahatavaran tuotannossa käytetään runsaasti lämpöä ja sähköä. Sähköä käytetään pääasiassa sahausvaiheessa ja lämpöä kuivausvaiheessa. Sahatavarakuutiosta haihdutetaan vettä kuivaamoissa noin 230-600 kiloa. Sahatavara kuivataan, koska kuivattu sahatavara säilyy paremmin ja on lisäksi kevyempää, kestävämpää ja sen muodonmuutokset ovat pienempiä. Työssä käsiteltävällä sahalla on erääseen kanavakuivaamoon tehty koerakennelma, jonka avulla kuivaamosta poistettavan ilman sisältämää lämpöä hyödynnetään sahatavaran lämmittämisessä kuivauslämpötilaan kuormanvaihdon jälkeen. Energiansäästön lisäksi rakennelman toivotaan ehkäisevän kuormanvaihdosta aiheutuvia olosuhdemuutoksia kuivausprosessin muissa vaiheissa. Poistoilman sisältämä höyry lauhtuu lämmittäessään kylmää sahatavaraa. Lauhtumisen yhteydessä vapautuu runsaasti energiaa. Tehtyjen kokeiden perusteella koerakennelma vähensi lämmönkulutusta selvästi. Lämmönkulutuksen alenema oli jopa teorialaskelmaa suurempi, mistä syystä kokeellisessa osassa tehtyihin mittaustuloksiin on syytä suhtautua varauksella. Perinteisessä kuivaamossa kosteus poistuu pääasiassa vesihöyrynä, mutta koerakennelman avulla saadaan noin puolet puusta haihdutetusta vedestä lauhtumaan takaisin vedeksi.

Reações de organocatálise com aminas quirais: aspectos mecanísticos e aplicações em síntese orgânica

The philosophy of organocatalysis is based on the utilization of organic compounds to catalyze organic transformations without the intervention of metals. This area has attracted much attention of the synthetic chemistry community on the last years, which can be confirmed by the explosion of published papers dealing with this subject. Phosphorus compounds, urea and thiourea derivatives, alkaloids, guanidine derivatives, for example, have already been used as organocatalysts. In this review we have focused on the use of chiral amines as organocatalyst. We have also chosen some outstanding examples to demonstrate the potentiality of this strategy in the synthesis of natural products and biologically active compounds.

Gliceroquímica: novos produtos e processos a partir da glicerina de produção de biodiesel

Glycerol is a byproduct of biodiesel production through transesterification of oils and fat. This article discusses the chemical transformation of glycerol in ethers, acetals and esters of high technological applications, especially in the fuel sector. Glycerol hydrogenolysis, dehydration to acrolein and oxidation are discussed as well, to show the potential use of glycerol for production of plastic monomers. Finally, the article shows other transformations, such as syn gas production, epichloridrin and glycerin carbonate.

Transformações biológicas: contribuições e perspectivas

In a moment that amazingly advances are being reached on the development of technologies to obtain high value chemical compounds as polymers, fine chemicals, pharmaceutical industry intermediates and chemical entities, we cannot refuse that a meaningful progress is due to the maturing in knowledge of biological transformations. Biocatalysis and biotransformations are being widespread applied to generate processes and products with incredible success. In this review article we present the main contributions of biotechnology and biological catalytic processes to Chemistry, the most important evolution steps on enzymatic transformations, how it has being applied and which are the perspectives to academic and industrial environments. We also would like to stimulate the community to step out research in biotechnology applicable to chemical and pharmaceutical industries, trying to achieve what we believe to be the ideal layout: integrating chemical transformations, enzymatic conversions and fermentation processes.

O ressurgimento da química de benzino com sililaril triflatos no contexto das reações de inserção em ligações sigma

In this paper we gathered articles concerning insertion reactions of arynes, exclusively generated from 2-(trimethylsilyl)aryl triflates in the presence of fluoride ions, in substrates bearing nucleophilic and electrophilic portions separated by sigma bonds. Accordingly, we stand out the great importance and versatility of such transformations in the preparation of highly functionalized aromatic systems, which are hardly synthesized in just one step for other methods.