One of the major challenges in the field of biophysical chemistry is the study of the mechanisms of protein folding, i.e., how an unstructured polypeptide chain can rapidly adopt an unique, densely packed, three-dimensional structure. Modifications in the folding kinetics and transitions to “misfolded” states are thought to be involved in the pathogenesis of many diseases commonly known as conformational disorders, including cystic fibrosis, type II diabetes, Alzheimer’s and Parkinson’s diseases. The global folding of proteins typically occurs in the millisecond to second time scale, but the underlying fundamental molecular events such as beta-hairpin or alpha-helix folding occur in the microsecond or faster time scale. The methods generally employed for studying folding or unfolding kinetics are typically limited to the time range of milliseconds or slower because the process usually involves mixing buffers in stopped-flow apparatus. A new generation of kinetic experiments has emerged to investigate the mechanisms of protein folding on the previously inaccessible sub-millisecond time scale. As a result, the earliest conformational events related to folding, occurring within microseconds or less may now be measured experimentally and interpreted. Laser-triggered fast initiation of the folding/unfolding reaction coupled with fast detection techniques provides the tools to probe these events in detail.; As the native conformations of peptides and proteins are normally sensitive to pH...

OBJETIVO: caracterizar a interação entre tensão e cinética de polimerização e seus parâmetros determinantes, e avaliar a qualidade da rede polimérica e propriedades mecânicas de compósitos comerciais para dentes posteriores a base de dimetacrilato ou de silorano. A cinética de polimerização foi avaliada sob influência da intensidade da fonte de luz, da temperatura e da umidade. Por fim, o grau de conversão (GC) do compósito a base de silorano foi avaliado por espectroscopia e titulação. MÉTODOS: foram utilizados três compósitos de baixa contração: Kalore (KAL - GC America) e N´Durance (NDUR Septodont), a base de dimetacrilatos; e Filtek P90 (P90 - 3MESPE), a base de silorano. O EsthetX HD (EHD - Dentsply) foi utilizado como controle. A tensão de polimerização (TP) dos espécimes (n = 5; Ø = 5 mm; h = 1 mm, 10 min) foi obtida em máquina universal de ensaios mecânicos. A contração volumétrica (CVol) foi determinada em linômetro (n = 3; Ø = 6 mm; h = 1,5 mm; 10 min). O módulo de elasticidade em flexão (MeFlex) e a resistência à flexão (RFlex) (n = 10; 10 x 2 x 1 mm) foram obtidos através do teste de dobramento em três pontos (8 mm entre apoios; 0.5 mm/min). O GC e a taxa de polimerização (Rp) dos espécimes (n = 3; Ø = 6...

Atualmente, no ensino médio brasileiro, o tema cinética química tem sido apontado por professores do ensino médio como sendo de difícil abordagem devido ao caráter empírico como também abstrato dos conhecimentos envolvidos. Levando em consideração essas dificuldades, o objetivo desta pesquisa foi o de identificar como uma abordagem com foco na história da ciência pode contribuir para uma transição progressiva de professores de química do ensino médio no que se refere ao modelo de ensino de cinética química, considerando os conteúdos e as estratégias de ensino utilizadas. Para alcançar esse objetivo foi oferecido um curso de formação continuada para 20 professores de química, em que foi apresentado o tema cinética química na perspectiva do desenvolvimento histórico desse tema (reconstrução histórica), permitindo assim uma melhor compreensão do contexto no qual esses conceitos foram desenvolvidos. Baseando-se na perspectiva de Lakatos, foram construídos modelos de ensino de cinética química a partir das ideias dos professores, procurando-se verificar se esses modelos formam sequências de transição progressiva, similares ao que Lakatos, na História da Ciência, se refere a "problemática" que aumenta o poder explanatório/heurístico do modelo. A evolução dos modelos...

O objetivo central deste trabalho foi investigar como a Cinética Química foi sendo apropriada pelos livros didáticos destinados ao Ensino Médio, em um determinado período de tempo (1929-2004), através do estudo do desenvolvimento histórico dos conceitos químicos envolvidos neste tema. Outro objetivo foi o de identificar as concepções sobre ciência veiculadas pelos livros didáticos ao tratarem o tema Cinética Química. O modelo adotado para a análise dos livros didáticos está baseado na linha de pesquisa desenvolvida por Níaz (2001) e Justi (1997; 1999), que se baseia na história e filosofia da ciência para entender o tratamento dado aos conceitos químicos pelo livro didático. Para isso, foi utilizada a metodologia de Imre Lakatos, da reconstrução racional do conhecimento científico, para analisar a evolução histórica das idéias sobre Cinética Química. A reconstrução histórica foi feita a partir de pesquisas de historiadores da ciência, artigos de pesquisadores e artigos originais dos cientistas que estiveram envolvidos no estudo da cinética química. Foram propostos quatro Programas de Investigação Científica que representam o conhecimento científico sobre a Cinética Química no período de 1850 até 1935...

Introdução: A reabilitação cardiopulmonar e metabólica (RCPM) é uma importante estratégia no tratamento da insuficiência cardíaca isquêmica. Entretanto, os seus principais mecanismos de melhora e as correlações com aumento na capacidade de exercício e menos sintomas ainda não estão totalmente esclarecidos. Objetivos: Investigar os efeitos de um programa multidisciplinar de RCPM sobre o tempo de tolerância ao esforço (TLim) e a resposta da fase rápida (fase II) da cinética do consumo de oxigênio (variável relacionada ao desempenho oxidativo muscular) em cardiopatas isquêmicos. Adicionalmente, avaliar as variáveis cardiovasculares, ventilatórias e metabólicas nos TCPE máximo (TRIM) e de endurance (TSCC), além da composição corporal pela bioimpedância elétrica, fração de ejeção (FE) e qualidade de vida. Métodos: Cento e seis pacientes com cardiopatia isquêmica encaminhados ao PRCPM foram submetidos ao TRIM em esteira rolante e, após intervalo de 1 a 7 dias, ao TSCC, com 80% da carga atingida no TRIM. Trinta e sete (37) pacientes foram excluídos, 31 por adesão < 50% às sessões de treinamento, 3 com IMC> 35kg.m-2 e 3 com FE<35%. Após 12 semanas de RCPM, 69 pacientes foram ressubmetidos aos mesmos testes e analisados os efeitos sobre o TLim...

O objetivo deste trabalho é realizar uma análise sobre a cinética de nêutrons utilizando um modelo fracionário, recente na literatura. Este novo modelo envolve uma nova relação constitutiva entre a corrente de nêutrons e o fluxo escalar de nêutrons, em que uma das suposições realizada para a relação constitutiva clássica (lei de Fick) não é feita: a densidade de corrente não mais é irrelevante se comparada `a taxa de colisão. Ao considerar esta hipótese, este novo modelo aqui apresentado se torna mais abrangente que o modelo fickiano clássico. Para manter o caráter geral do modelo é considerado um operador diferencial de ordem fracionaria em sua dedução, o que acresce ao modelo dois novos parâmetros: o tempo de relaxação e a ordem da derivada fracionária. Considerando este modelo, é realizada a dedução das equações de cinética de nêutrons, com ênfase na cinética pontual de nêutrons. A equação fracionária de cinética pontual de nêutrons é resolvida analiticamente através do método da decomposição, a fim de estudar o novo modelo minimizando os erros numéricos. Os resultados obtidos através desta metodologia são comparados com os resultados clássicos em diversos casos, com a finalidade de analisar a influência dos parâmetros fracionários no modelo.; The objective of this work is to make an analysis about the neutron kinetics using a recent model on the literature. This new model involves a new constitutive relation between the neutron current and the neutron scalar flux...

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Dynamics of the environments of complex systems such as biomolecules, polar solvents, and glass plays an important role in controlling electron transfer reactions. The kinetics is determined by the nature of a complex multidimensional landscape. By quantifying the mean and high-order statistics of the first-passage time and the associated ratios, the dynamics in electron transfer reactions controlled by the environments can be revealed. We consider real experimental conditions with finite observation time windows. At high temperatures, exponential kinetics is observed and there are multiple kinetic paths leading to the product state. At and below an intermediate temperature, nonexponential kinetics starts to appear, revealing the nature of the distribution of local traps on the landscape. Discrete kinetic paths emerge. At very low temperatures, nonexponential kinetics continues to be observed. We point out that the size of the observational time window is crucial in revealing the intrinsic nature of the real kinetics. The mean first-passage time is defined as a characteristic time. Only when the observational time window is significantly larger than this characteristic time does one have the opportunity to collect enough statistics to capture rare statistical fluctuations and characterize the kinetics accurately.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); The aggregation kinetics of solutions of vinyltriethoxysilane-derived organic/silica hybrid species were studied by small-angle X-ray scattering (SAXS) in a strongly basic medium. The SAXS intensity was analysed by a modified Sharp-Bloomfield (SB) global function and its evolution was found to be compatible with the growth, coiling and branching of the polymeric macromolecules in solution. A form factor valid for randomly and nonrandomly branched polycondensates and for polydisperse coils of linear chains was used in the modified SB model, instead of the Debye function valid for monodisperse coils of linear chains. The aggregation kinetics are accelerated with increasing base concentration in the studied range, but all the kinetics curves can be matched to a unique curve using an appropriate time scaling factor. The aggregation kinetics suggest that physical forces (hydrothermal forces) associated with phase coarsening could be active in the aggregation process, together with diffusion mechanisms.

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO(2)max), work-rate associated to VO(2)max (IVO(2)max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty-five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO(2)max of LF, IF and HF groups were, respectively, 36.0 +/- 3.1, 51.1 +/- 4.5 and 68.1 +/- 3.9 ml . kg . min(-1) (p <= 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p <= 0.05) in HF (Mod, 27.5 +/- 5.5 s; Max, 32.6 +/- 8.3 s) and IF (Mod, 25.0 +/- 3.1 s; Max, 42.6 +/- 10.4 s) when compared to LF (Mod, 35.7 +/- 7.9 s; Max: 57.8 +/- 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high.

The objective of the present study was to compare pulmonary gas exchange kinetics (VO 2 kinetics) and time to exhaustion (Tlim) between trained and untrained individuals during severe exercise performed on a cycle ergometer and treadmill. Eleven untrained males in running (UR) and cycling (UC), nine endurance cyclists (EC), and seven endurance runners (ER) were submitted to the following tests on separate days: (i) incremental test for determination of maximal oxygen uptake (VO 2max) and the intensity associated with the achievement of VO 2max (IVO 2max) on a mechanical braked cycle ergometer (EC and UC) and on a treadmill (ER and UR); (ii) all-out exercise bout performed at IVO 2max to determine the time to exhaustion at IVO 2max (Tlim) and the time constant of oxygen uptake kinetics (τ). The τ was significantly faster in trained group, both in cycling (EC = 28.2 ± 4.7 s; UC = 63.8 ± 25.0 s) and in running (ER = 28.5 ± 8.5 s; UR = 59.3 ± 12.0 s). Tlim of untrained was significantly lower in cycling (EC = 384.4 ± 66.6 s vs. UC; 311.1 ± 105.7 s) and higher in running (ER = 309.2 ± 176.6 s vs. UR = 439.8 ± 104.2 s). We conclude that the VO 2 kinetic response at the onset of severe exercise, carried out at the same relative intensity is sensitive to endurance training...

Os cimentos ósseos à base de fosfato de cálcio são biomateriais cerâmicos biorreabsorvíveis utilizados na substituição e no reparo de tecido ósseo danificado. Apresentam uma série de atrativos, como excelente biocompatibilidade e capacidade de serem moldados em cavidades pequenas e complexas. Porém, sua aplicação é restringida pela sua baixa resistência mecânica e sua cinética da reação lenta. O objetivo principal deste trabalho foi desenvolver cimentos de fosfato de cálcio, baseado no sistema do alfa-fosfato tricálcico, com melhores propriedades mecânicas e cinética da reação acelerada. Para isso, obteve-se o pó de alfa-fosfato tricálcico a partir de reagentes sintetizados em laboratório a fim de se obter pureza elevada; utilizou-se hidrogeno fosfato de sódio, ácido cítrico e ácido tânico como aditivos na solução de pega a fim de melhorar suas propriedades. O método de obtenção dos reagentes mostrou-se eficaz, obtendo-se pó de alfa-fosfato tricálcico com pureza elevada. Todas as combinações de aditivos utilizadas aceleraram a cinética da reação e aumentaram a resistência mecânica do cimento de fosfato de cálcio, obtendo-se valores superiores aos reportados na literatura; The calcium phosphate bone cements are resorbable bioceramics used for replacement and repair of damaged bone tissue. Such material has many benefits...

Food thermal processing conditions can be optimized in terms of final product quality retention. This optimization is possible due to the difference between the temperature dependence of quality factors and microorganisms or enzymes kinetics of thermal degradation or inactivation, respectively. All the available research in this field assume first order degradation kinetics for the quality parameters. In this work the effect of reaction type kinetics on optimal thermal processing conditions and final quality retention is analyzed. Zero, second and reversible first order kinetics are taken into consideration. Assuming that the Arrhenius model is applicable, the main conclusion is that the reaction type kinetics does not have influence on constant optimal thermal processing temperatures for maximizing the final surface product quality retention. Optimal conditions for maximizing volume average quality retention are affected by the reaction quality thermal degradation kinetics and the differences between optimal constant temperatures depend on the kinetic parameters values and processing conditions and requirements. For reversible first order degradation kinetics, final quality retentions are analyzed as a function of processing conditions and kinetic parameters and the calculation of optimal processing conditions is discussed.

In this paper we address some aspects of the kinetics of hydrogen absorption and desorption of Mg2FeH6 nanocomposite powder. The Mg2FeH6 material was prepared from a 2Mg-Fe composition by reactive milling under H2 pressure at room temperature. After mechano-chemical processing, the material was mainly constituted of Mg2FeH6 having a hydrogen gravimetric capacity corresponding to 94% of the theoretical capacity. The kinetics of hydrogen absorption at constant temperature and the transformation of phases during this process were studied. The kinetics of hydrogen absorption presented a two-step behaviour. First, β-MgH2 was formed with faster kinetics than Mg2FeH6 under constant temperature and H2 pressure. Then, β-MgH2 reacted with α-Fe forming Mg2FeH6 in a much slower reaction. Unexpectedly, reaction of hydrogen desorption showed an one-step kinetics, even if Mg2FeH6 and β-MgH2 phases were previously present in the powder.

GABAergic inhibition displays rich functional diversity throughout the CNS, which arises from variations in the nature of inputs, subunit composition, subcellular localization of receptors and synapse geometry, or reuptake mechanisms. In the spinal dorsal horn (SDH), GABAA and glycine receptors play a major role in the control of excitability and accuracy of nociceptive processing. Identifying which components shape the properties of the inhibitory synapses in different cell types is necessary to understand how nociceptive information is integrated. To address this, we used transgenic mice where inhibitory interneurons express GAD65-EGFP. We found that GABAA, but not glycine receptor-mediated evoked IPSCs displayed slower kinetics in EGFP+ vs. EGFP− interneurons. GABAA miniature IPSC decay kinetics showed a large variability in both populations, however the distribution of decays differed between EGFP+ and EGFP− interneurons. The range of mIPSC decay kinetics observed was replicated in experiments using rapid application of GABA on outside-out patches taken from SDH neurons in slices. Furthermore, GABAA decay kinetics were not affected by uptake blockers and were not different in mice lacking δ or α5 subunits, indicating that intrinsic channel properties likely underlie the heterogeneity. To identify whether other α subunits shape the various kinetic properties observed we took advantage of knock-in mice carrying point mutations in either the α1...

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2012.; The amount and timing of effector molecule secretion are tightly regulated in CD4 T cells during the immune response. T cell cytokine profiles have been studied extensively, but how chemokines are expressed during activation is less clear. This study showed that human CD4 T cells, activated with either influenza antigen or polyclonal stimulation, produce chemokines and cytokines with different kinetics. IL-2, IFNγ and TNFα were quickly induced, while chemokines CCL1, CCL3 and CCL4 were secreted later. Further analysis of sorted early cytokine positive cells showed that even though the IFNγ and IL-2 secreting cells have a preference to subsequently produce chemokines, the majority of chemokine producing cells did not secrete cytokines at early times. In addition to analyzing expression kinetics in individual cells, the kinetics of expansion of cytokine/chemokine-secreting cells during the human immune response to influenza vaccination were measured. The numbers of influenza-responsive CD4 T cells able to secrete chemokines increased transiently, 7 days after influenza vaccination, while the cytokine response did not change significantly. The response was then tracked more precisely by daily sampling...

Biodiesel is considered as an attractive alternative to petrodiesel for transportation applications. Substituting petrodiesel with domestically produced biodiesel increases energy independence, reduces the carbon footprint, and offers a viable path toward biomass utilisation. It has been found that biodiesel-fuelled engines emit up to 70% lower particulate matter (PM) compared to petrodiesel-fuelled engines, although they emit up to 20% more nitric oxides (NOx). In this study, simulations are employed to improve the fundamental understanding of biodiesel and petrodiesel combustion under pressure and temperature conditions in engines. n-Heptane is used as the surrogate for petrodiesel fuel and a ternary mixture of methyl decanoate, methyl-9-decenoate, and n-heptane as the surrogate for biodiesel fuel. The choice of chemical kinetic mechanism is a compromise between computational time and accuracy. Four mechanisms are evaluated and a 160-species skeletal chemical kinetic mechanism is employed to model the oxidation of n-heptane. The computational time is shown to increase dramatically as the complexity of the mechanism increases. Soot kinetics is represented using a chemical mechanism that models the growth of soot precursors starting from a single aromatic ring and growing by hydrogen abstraction and carbon (acetylene) addition. NOx kinetics is represented using the thermal...

Eine Vielzahl der heute bekannten Untergrundverunreinigungen in SW-Deutschland befindet sich in den Lockersedimenten der Talaquifere. Diese sind durch die bevorzugte Nutzung der Flusstäler für urbane und industrielle Ansiedlungen in besonderem Maße einem Eintrag von Schadstoffen ausgesetzt. Zur Beurteilung möglicher Sanierungsmethoden oder zur Gefahrenbeurteilung z.B. für das Grundwasser kommt einer möglichst genauen Kenntnis der Transportvorgänge hier eine große Bedeutung zu. Der Transport gelöster organischer Schadstoffe im Grundwasser unterliegt in großem Ausmaß den Wechselwirkungen mit den verschiedenen Bestandteilen des heterogenen Aquifermaterials. Ziel dieser Arbeit war es, die Sorption und Sorptionskinetik hydrophober organischer Verbindungen (PHE und TCE) innerhalb der petrographisch unterschiedlichen Komponenten (Lithokomponenten) der heterogenen Aquifersedimente des Neckartals und von Festgesteinen aus deren Liefergebiet zu untersuchen. Neben verschiedenen sedimentpetrographischen Methoden kamen dabei vor allem Laborversuche zur Gleichgewichtssorption und zur Sorptionskinetik zum Einsatz. Die Sorption im Gleichgewicht lässt sich für alle untersuchten Komponenten mittels dem nichtlinearen Freundlich-Sorptionsmodell beschreiben. Innerhalb der Aquifersedimente des Neckartals wird die Sorption eindeutig durch die Muschelkalke und Jurakalke dominiert...

The autolysis of trypsin and α-chymotrypsin is accelerated in the presence of colloidal silica and glass surfaces. It is proposed that adsorption of the enzymes (favoured by electrostatic factors) results in a conformational change that renders the adsorbed enzyme more susceptible to proteolytic attack. Although the adsorbed enzymes are more susceptible to proteolysis, their activity towards low-molecular-weight substrates is not affected, indicating a relatively minor conformational change on adsorption. The rates of autolysis in solution (i.e. in `inert' vessels) are second-order for both trypsin and α -chymotrypsin, with rate constants of 13.0mol−1·dm3·s−1 for trypsin (in 50mm-NaCl at pH8.0 at 25°C) and 10.2mol−1·dm3·s−1 for α-chymotrypsin (in 0.1m-glycine at pH9.2 at 30°C). In glass vessels or in the presence of small areas of silica surface (as colloidal silica particles), the autolysis of both trypsin and α-chymotrypsin can show first-order kinetics. Under these conditions, saturation of the surface occurs and the fast surface proteolytic reaction controls the overall kinetic order. However, when greater areas of silica surface are present, saturation of the surface does not occur, and, since for a considerable portion of the adsorption isotherm the amount adsorbed is approximately proportional to the concentration in solution...

OBJECTIVES: To assess whether there is a correlation between oxygen uptake (VO2) and heart rate (HR) on-kinetics in the constant-load cycle-ergometer test (CLT) and the BODE index and its isolated variables in patients with chronic obstructive pulmonary disease (COPD). METHOD: Fourteen male patients between 55 and 78 years of age with moderate to severe COPD were evaluated. Each patient underwent spirometry, the six-minute walk test (6MWT), the cycle-ergometer incremental test (IT) and CLT on alternate days. The exhaled gases were collected, and the VO2 and HR on-kinetics were analyzed. The BODE index was calculated. RESULTS: It was noted that the VO2 tau (τ) and mean response time (MRT) were significantly higher than HR τ and MRT. Moderate and strong correlations between τ and MRT of the VO2 and HR and the BODE index was noted (r=0.75 and r=0.78; r=0.62 and r=0.63, respectively), and there were correlations between the VO2 τ and MRT and the forced expiratory volume in one second (FEV1) (r=-0.60; r=-0.53) and the distance traveled at 6MWT (DT-6MWT) (r=-0.61; r=-0.44) and DT-6MWT % predicted (r=-0.62; r=-0.46). The HR τ and MRT were correlated with DT-6MWT (r=-0.59; r=-0.58) and DT-6MWT % predicted (r=-0.62; r=-0.62). CONCLUSION: The slowing of cycle-ergometer VO2...

Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kinetics. The estimation of kinetic parameters is performed by gPROMS (general PRocess Modeling System) parameter estimation tool. The reaction kinetics differs from low to highly-concentrated NaOH solutions. In highly-basic (.10 wt% NaOH), aqueous solutions of NaBH4, the rate is independent of NaOH concentration, while for lower-basic (< 10 wt% NaOH) solutions, the dependence is -0.57, confirming the inhibition of hydrolysis kinetics by NaOH.