Página 1 dos resultados de 5830 itens digitais encontrados em 0.009 segundos

Study of the pozzolanic reaction kinetics in sugar cane bagasse-clay ash/calcium hydroxide system: kinetic parameters and pozzolanic activity

VILLAR-COCINA, E.; ROJAS, M. Frias; MORALES, E. Valencia; SAVASTANO JR., H.
Fonte: THOMAS TELFORD PUBLISHING Publicador: THOMAS TELFORD PUBLISHING
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
57.114873%
This paper presents a study of the pozzolanic reaction kinetics between calcium hydroxide and a mixture of sugar cane bagasse with 20 and 30% of clay, burned at 800 and 1000 degrees C (SCBCA) by electrical conductivity measurements. A kinetic-diffusive model produced in previous studies by some of the authors was used. The model was fitted to the experimental data, which allowed the computation of the kinetic parameters of the pozzolanic reaction (reaction rate constant and free energy of activation) that rigorously characterised the pozzolanic activity of the materials. The results show that SCBCA demonstrated reactivity and good pozzolanic qualities in the range 800-1000 degrees C.

Parâmetros relacionados à cinética de reação e tensão de polimerização de compósitos restauradores; PARAMETERS RELATED TO REACTION KINETICS AND POLYMERIZATION STRESS OF RESTORATIVE COMPOSITES

Pfeifer, Carmem Silvia Costa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/06/2007 PT
Relevância na Pesquisa
56.99196%
Proposição: O objetivo deste estudo foi avaliar como a contração volumétrica (CV), o grau de conversão (GC), a taxa máxima de polimerização (RPmax) e a tensão de polimerização (TPmax) de dois compósitos experimentais são influenciados pela concentração de fotoiniciadores na matriz e pela irradiância aplicada na fotopolimerização. Material e métodos: Duas séries de monômeros foram formuladas, com partes iguais em peso dos seguintes monômeros: série B= Bis-GMA/ TEGDMA; série U= Bis-GMA/ UDMA / TEGDMA. Essas séries foram combinadas a três níveis de fotoiniciadores, num total de seis materiais experimentais, com a concentração em porcentagem de peso de uma amina terciária (EDMAB) e canforoquinona (CQ), respectivamente: alta (H)= 0,8 / 1,6; intermediária (M)= 0,4 / 0,8 e baixa (L)= 0,2 / 0,4. A todas as misturas, 75% e peso de vidro de estrôncio e 5% em peso de OX-50 (sílica coloidal) foram adicionados. O estudo foi dividido em três módulos: no primeiro, os seis compósitos foram testados quanto aos parâmetros descritos acima para a mesma dose de energia aplicada. No segundo, os mesmos materiais foram testados com a dose de energia ajustada de acordo com a concentração de fotoiniciadores de modo que todos os níveis atingissem graus de conversão semelhantes. No terceiro módulo...

Styrene photocatalytic degradation reaction kinetics

Taffarel, Silvio Roberto; Lansarin, Marla Azario; Moro, Celso Camilo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
Relevância na Pesquisa
57.29921%
A reação de degradação fotocatalítica do estireno foi estudada utilizando-se TiO2 P-25 (Degussa) como catalisador. Os experimentos foram realizados em um reator “slurry” em bateladas, com controle de temperatura, empregando-se uma lâmpada UV. Foram estudados os efeitos do pH, da concentração inicial de estireno, da concentração do catalisador e da adição de H2O2 sobre a velocidade da reação. Os resultados mostraram que, em 90 min, cerca de 95% da quantidade inicial da molécula foi consumida por fotocatálise. Verificou-se também que a reação segue uma cinética de primeira ordem para concentrações iniciais de estireno, entre 15,27 e 57,25 ppm, a 30 °C. A análise cromatográfica das amostras coletadas durante os experimentos de fotodegradação identificou o benzaldeído como um dos intermediários dessa reação. Além disso, a adição de H2O2 aumentou a velocidade de degradação.; The aqueous styrene photocatalytic degradation reaction was evaluated using TiO2 P-25 (Degussa) as a catalyst. These experiments were accomplished in a batch slurry reactor with temperature control and a UV lamp. The effects of the initial styrene concentration, the catalyst concentration, the hydrogen peroxide addition and the initial pH of the solution on the reaction were evaluated. The experimental results showed that in 90 min...

Cimento de Alfa-TCP com diferentes aditivos : cinética da reação de cura, propriedades mecânicas e avaliação da citotoxicidade; Alpha-TCP cement with different additives : kinetics of curing reaction, mechanical properties and evaluation of cytotoxicity

Hugo Ananias Inácio Cardoso
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/02/2010 PT
Relevância na Pesquisa
47.36699%
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...

Reaction Kinetics Analysis of Chemical Changes in Pressure-Assisted Thermal Processing

Ramirez, Rosario; Saraiva, Jorge; Pérez Lamela, Concepción; Torres, J. Antonio
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
67.35473%
Pressure-assisted thermal processing (PATP) at T < 100°C can be used when enzyme inactivation and pasteurization by high pressure processing (HPP) is not feasible due to long processing times while PATP at T > 100°C can be used when bacterial spores inactivation is necessary. In PATP, the adiabatic compression/decompression heat increases/decreases temperature almost instantaneously, and the simultaneous application of high pressure (~600–700 MPa) and temperature (~100–120°C) accelerates spore inactivation. PATP effects on chemical changes are analyzed using a reaction kinetics approach including activation volume (V a) and activation energy (E a) values. Reaction rates increase or decrease with pressure for negative or positive V a values, respectively, while rate temperature and pressure sensitivity depends on the magnitude of E a and V a values, respectively. The complex effects of food matrix, pH, dissolved oxygen, and presence of antioxidants show that optimization of vitamin, pigment and flavor retention while ensuring PATP microbial and enzyme inactivation will require substantially more chemical reaction kinetics research.

Styrene photocatalytic degradation reaction kinetics

Taffarel,Silvio R.; Lansarin,Marla A.; Moro,Celso C.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 EN
Relevância na Pesquisa
57.29921%
The aqueous styrene photocatalytic degradation reaction was evaluated using TiO2 P-25 (Degussa) as a catalyst. These experiments were accomplished in a batch slurry reactor with temperature control and a UV lamp. The effects of the initial styrene concentration, the catalyst concentration, the hydrogen peroxide addition and the initial pH of the solution on the reaction were evaluated. The experimental results showed that in 90 min, 95% of the initial styrene was degraded by photocatalysis. It was verified that the styrene degradation rate fits a pseudo-first-order kinetics for initial styrene concentrations between 15.27 and 57.25 ppm, at 30ºC. The chromatographic analysis of the samples collected during the photocatalytic degradation revealed benzaldehyde as one of the intermediates. The addition of H2O2 accelerated the degradation reaction until the system reached a certain optimum peroxide concentration in the reactor. Further H2O2 additions resulted in a reaction rate reduction.

Reaction kinetics of some important site-specific endonucleases.

Hinsch, B; Kula, M R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 10/07/1981 EN
Relevância na Pesquisa
47.305093%
Reaction kinetics of the site-specific endonucleases BamHI, BgIII, C1aI, EcoRI, HpaII, PstI, SaII, SmaI, and XorII were investigated employing some frequently used substrates. Six of these enzymes could be analyzed under steady-state conditions. Kinetic data were obtained from progress curves applying an integrated Michaelis-Menten equation. KM ranged from 4 x 10(-9) M to 4 x 10(-11) M. Activities also spanned two orders of magnitude. In the case of C1aI the analysis of the pre-steady-state kinetics ("burst reaction") allowed the assessment of several rate constants. The rate-limiting step is the very slow dissociation of the enzyme-product complex (0.22 min(-1)). This complex is formed from the enzyme-bound nicked intermediate at a rate of 1.7 min(-1). The introduction of the first cut is again faster by a factor of about 6. SmaI and XorII resembled C1aI in their kinetics. The burst reaction can be used for the easy and unambiguous determination of molar concentrations of site-specific endonucleases in any preparation, which is free of non-specific DNases.

An analysis of the reaction kinetics of the hexahaem nitrite reductase of the anaerobic rumen bacterium Wolinella succinogenes.

Blackmore, R S; Brittain, T; Greenwood, C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/10/1990 EN
Relevância na Pesquisa
47.293716%
The reduction kinetics of both the resting and redox-cycled forms of the nitrite reductase from the anaerobic rumen bacterium Wolinella succinogenes were studied by stopped-flow reaction techniques. Single-turnover reduction of the enzyme by dithionite occurs in two kinetic phases for both forms of the enzyme. When the resting form of the enzyme is subjected to a single-turnover reduction by dithionite, the slower of the two kinetic phases exhibits a hyperbolic dependence of the rate constant on the square root of the reductant concentration, the limiting value of which (approximately 4 s-1) is assigned to a slow internal electron-transfer process. In contrast, when the redox-cycled form of the enzyme is reduced by dithionite in a single-turnover experiment, both kinetic phases exhibit linear dependences of the rate on the square root of dithionite concentration, with associated rate constants of 150 M-1/2.s-1 and 6 M-1/2.s-1. Computer simulations of both the reduction processes shows that no unique set of rate constants can account for the kinetics of both forms, although the kinetics of the redox-cycled species is consistent with a much enhanced rate of internal electron transfer. Under turnover conditions the time course for reduction of the enzyme...

Analysis of coupled bimolecular reaction kinetics and diffusion by two-color fluorescence correlation spectroscopy: enhanced resolution of kinetics by resonance energy transfer.

Hom, Erik F Y; Verkman, A S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/2002 EN
Relevância na Pesquisa
47.524287%
In two-color fluorescence correlation spectroscopy (TCFCS), the fluorescence intensities of two fluorescently-labeled species are cross-correlated over time and can be used to identify static and dynamic interactions. Generally, fluorophore labels are chosen that do not undergo Förster resonance energy transfer (FRET). Here, a general TCFCS theory is presented that accounts for the possibility of FRET between reactants in the reversible bimolecular reaction, [reaction: see text] where k(f) and k(b) are forward and reverse rate constants, respectively (dissociation constant K(d) = k(b)/k(f)). Using this theory, we systematically investigated the influence on the correlation function of FRET, reaction rates, reactant concentrations, diffusion, and component visibility. For reactants of comparable size and an energy-transfer efficiency of approximately 90%, experimentally measurable cross-correlation functions should be sensitive to reaction kinetics for K(d) > 10(-8) M and k(f) >or= approximately 10(7) M(-1)s(-1). Measured auto-correlation functions corresponding to donor and acceptor labels are generally less sensitive to reaction kinetics, although for the acceptor, this sensitivity increases as the visibility of the donor increases relative to the acceptor. In the absence of FRET or a significant hydrodynamic difference between reactant species...

Use of Fiber Optic Technology to Measure the Effects of Anesthesia on Luciferase Reaction Kinetics

Semprini, Sabrina; Saunter, Christopher D; Ludwig, Mike; Girkin, John M; Mullins, John J
Fonte: American Association for Laboratory Animal Science Publicador: American Association for Laboratory Animal Science
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
47.39058%
In vivo bioluminescent imaging (BLI) is a sensitive and reliable technique for studying gene expression, although experiments must be controlled tightly to obtain reproducible and quantitative measurements. The luciferase reaction depends on the availability of the reaction substrate, oxygen, and ATP, the distribution of which can vary markedly in different tissues. Here we used in vivo fiber optic technology, combined with stereotaxis-assisted surgery, to assess luciferase reaction kinetics in response to 2 anesthetic regimens, isoflurane and ketamine–xylazine. Transgenic rats that expressed luciferase under the control of the human prolactin promoter were used as a model organism. Anesthesia had a marked effect on luciferase reaction kinetics. The rise time to peak emission differed by 20 min between isoflurane and ketamine–xylazine. Optical imaging using a charge-coupled–device camera confirmed this delay. These results demonstrate that different anesthetics can have substantial effects on luciferase reaction kinetics and suggest that the timing of image acquisition after substrate injection should be optimized in regard to experimental conditions and the tissues of interest.

Reaction Kinetics for the Biocatalytic Conversion of Phenazine-1-Carboxylic Acid to 2-Hydroxyphenazine

Chen, Mingmin; Cao, Hongxia; Peng, Huasong; Hu, Hongbo; Wang, Wei; Zhang, Xuehong
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 06/06/2014 EN
Relevância na Pesquisa
47.45248%
The phenazine derivative 2-hydroxyphenazine (2-OH-PHZ) plays an important role in the biocontrol of plant diseases, and exhibits stronger bacteriostatic and fungistatic activity than phenazine-1-carboxylic acid (PCA) toward some pathogens. PhzO has been shown to be responsible for the conversion of PCA to 2-OH-PHZ, however the kinetics of the reaction have not been systematically studied. Further, the yield of 2-OH-PHZ in fermentation culture is quite low and enhancement in our understanding of the reaction kinetics may contribute to improvements in large-scale, high-yield production of 2-OH-PHZ for biological control and other applications. In this study we confirmed previous reports that free PCA is converted to 2-hydroxy-phenazine-1-carboxylic acid (2-OH-PCA) by the action of a single enzyme PhzO, and particularly demonstrate that this reaction is dependent on NADP(H) and Fe3+. Fe3+ enhanced the conversion from PCA to 2-OH-PHZ and 28°C was a optimum temperature for the conversion. However, PCA added in excess to the culture inhibited the production of 2-OH-PHZ. 2-OH-PCA was extracted and purified from the broth, and it was confirmed that the decarboxylation of 2-OH-PCA could occur without the involvement of any enzyme. A kinetic analysis of the conversion of 2-OH-PCA to 2-OH-PHZ in the absence of enzyme and under different temperatures and pHs in vitro...

Refolded scFv Antibody Fragment against Myoglobin Shows Rapid Reaction Kinetics

Song, Hyung-Nam; Jang, Jun-Hyuck; Kim, Young-Wan; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 18/12/2014 EN
Relevância na Pesquisa
47.305093%
Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the VH–VL sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10−4 M−1·s−1 and 6.29 × 10−3 s−1, respectively, with an affinity value exceeding 107 M−1 (kon/koff), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor.

A study of oxidation reaction kinetics during an air injection process.

Das, Shyamol Chandra
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
67.140444%
Air injection is an enhanced oil recovery (EOR) process in which compressed air is injected into a high temperature, light-oil reservoir. The oxygen in injected air is intended to react with a fraction of reservoir oil at elevated temperature resulting in in-situ generation of flue gases and steam, which, in turn, mobilize and drive the oil ahead towards the producing wells. To understand and determine the feasibility of the air injection process application to a given reservoir, it is necessary to understand the oxidation behaviour of the crude oil. The aim of this study is to screen two Australian light-oil reservoirs; Kenmore Oilfield, Eromanga Basin, and another Australian onshore oil and gas field “B”* for air injection EOR process, and to understand the oxidation reaction kinetics during air injection. It is carried out by the thermogravimetric and differential scanning calorimetric (TGA/DSC) studies to investigate the oxidation mechanism during an air injection process. There has not been any TGA/DSC evaluation conducted to date with regard to air injection for Australian light-oil reservoirs. A series of thermal tests was performed to investigate the oxidation behaviour of two selected reservoirs in both air and oxygen environments. The first step undertaken in this study is thermogravimetric and calorimetric characterization of crude oils to (i) identify the temperature range over which the oil reacts with oxygen...

The mechanism and kinetics of α-NiS oxidation in the temperature range 670–700 °C; The mechanism and kinetics of alpha-NiS oxidation in the temperature range 670-700 degrees C

Wang, H.; Pring, A.; Ngothai, Y.; O'Neill, B.
Fonte: Mineralogical Soc Amer Publicador: Mineralogical Soc Amer
Tipo: Artigo de Revista Científica
Publicado em //2006 EN
Relevância na Pesquisa
47.35473%
The oxidation behavior of synthetic α-NiS in air has been investigated over the temperature range 670-700 °C. The α-NiS was ground and sieved to give a particle size ranging from 53 to 90 μm. Three oxidation paths were observed: (i) α-NiS + 3/2 O2 → NiO + SO2 (ii) 3α-NiS +O2 → Ni3S2 + SO2 (iii) Ni3S2 + 7/2 O2 → 3NiO + 2SO2 No Ni3S2 (heazlewoodite) was observed over the course of α-NiS oxidation at 670 and 680 °C. The dominant oxidation path at this temperature is path i. At 700 °C, however, all three oxidation paths were observed. As an intermediate oxidation product, Ni3S2 steadily exsolved from α-NiS, reaching a maximum quantity after about 80 min of oxidation, declining afterward, and approaching annihilation at 160 min of oxidation. Experimental results show that the exsolution of Ni3S2 is likely triggered by the loss of one third of S in the α-NiS structure with the release of SO2 rather than by an intrinsic thermal decomposition of α-NiS to α-Ni1.xS + Ni3S2. The eventual annihilation of Ni3S2 was caused by a further oxidation of Ni3S2 to NiO. Oxidation paths 2 and 3 form a typical single chain reaction: α-NiS →k1→ Ni3S2 →k2→ NiO The approximate values of k1 are k2 are 3 x 10-4s-1 and 5 x 10-4s-1 respectively. Oxidation temperature was found to play important roles both in the oxidation kinetics and the oxidation mechanism. By decreasing 10 °C from 680 to 670 °C...

Mathematical Modeling of PEM Fuel Cell Cathodes: Comparison of First-order and Half-order Reaction Kinetics

Castagne, DAVID
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1040075 bytes; application/pdf
EN; EN
Relevância na Pesquisa
57.29921%
Mathematical modeling helps researchers to understand the transport and kinetic phenomena within fuel cells and their effects on fuel cell performance that may not be evident from experimental work. In this thesis, a 2-D steady-state cathode model of a proton-exchange-membrane fuel cell (PEMFC) is developed. The kinetics of the cathode half-reaction were investigated, specifically the reaction order with respect to oxygen concentration. It is unknown whether this reaction order is one or one half. First- and half-order reaction models were simulated and their influence on the predicted fuel cell performance was examined. At low overpotentials near 0.3 V, the half-order model predicted smaller current densities (approximately half that of the first-order model). At higher overpotentials above 0.5 V, the predicted current density of the half-order model is slightly higher than that of the first-order model. The effect of oxygen concentration at the channel/porous transport layer boundary was also simulated and it was shown the predicted current density of the first-order model experienced a larger decrease (~10-15% difference at low overpotentials) than the half-order model. Several other phenomena in the cathode model were also examined. The kinetic parameters (exchange current density and cathode transfer coefficient) were adjusted to assume a single Tafel slope...

Reversibly Switching Silver Hierarchical Structures via Reaction Kinetics

Liu, Jianmei; Yang, Tao; Li, Chengxiang; Dai, Jinhui; Han, Yongsheng
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 07/10/2015 EN
Relevância na Pesquisa
47.417686%
Here we report a study on controllable synthesis of hierarchical silver structures via regulating reaction kinetics. Silver particles with various morphologies are synthesized by a solution-based reduction approach at the addition of amino acids. The amino acid is used to coordinate with silver ions to slow down the reduction of silver ions. With the increase of glycine concentration, the morphologies of silver particles switch from dendrites, to flowers and to compacted spheres, which is attributed to the decrease of reaction rate as a result of the coordination. Three more amino acids are examined and confirms the role of reaction kinetic in shaping silver particles. Furthermore, by increasing the concentration of the reductant, the silver morphologies change from compact spheres to loose flowers as a result of the increase of reaction rate. Therefore the silver hierarchical structure can be reversibly switched by reaction kinetics. The silver particles synthesized are tested for surface enhanced Raman scattering (SERS) property and the dendritic particles present a remarkable SERS activity. This study shows that reaction kinetics is a powerful tool to tune hierarchical structures of silver particles, which is expected to be transferable to other material systems.

Jarosite dissolution II - Reaction kinetics, stoichiometry and acid flux

Welch, Susan; Kirste, Dirk; Christy, Andrew; Beavis, Fern; Beavis, Sara
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
57.021367%
A study was undertaken to characterize a natural jarosite sample from an acid sulfate soils site and to experimentally determine the kinetics of dissolution and major ion release from jarosite under a range of different conditions. The jarosite was source

Reaction-kinetics of organo-clay hybrid films: in-situ IRRAS and AFM studies

Hussain, Syed Arshad; Islam, Md N.; Bhattacharjee, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/06/2011
Relevância na Pesquisa
47.41663%
In this paper we have reported the reaction kinetics of nano dimensional clay saponite and hectorite with an amphiphilic cation octadecyl rhodamine B (RhB) in hybrid Langmuir monolayer at the air-water interface. The surface pressure-molecular area (pi-A) isotherms were strongly influenced by the presence of clay with the lift-off area of the cationic amphiphile shifted to progressively larger area. In-situ infrared reflection absorption spectroscopy (IRRAS) was used to demonstrate the reaction kinetics. Time taken to complete the reaction kinetics for RhB-hectorite hybrid films is larger than RhB-saponite hybrid films. Atomic force microscopic images of hybrid Langmuir-Blodgett films give compelling visual evidence of the incorporation of clay platelets into the hybrid films and density of which increases with the progress of reaction kinetics.; Comment: 11 pages, 5 figures

Non-Markovian polymer reaction kinetics

Guérin, Thomas; Bénichou, Olivier; Voituriez, Raphaël
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/09/2012
Relevância na Pesquisa
47.29921%
Describing the kinetics of polymer reactions, such as the formation of loops and hairpins in nucleic acids or polypeptides, is complicated by the structural dynamics of their chains. Although both intramolecular reactions, such as cyclization, and intermolecular reactions have been studied extensively, both experimentally and theoretically, there is to date no exact explicit analytical treatment of transport-limited polymer reaction kinetics, even in the case of the simplest (Rouse) model of monomers connected by linear springs. We introduce a new analytical approach to calculate the mean reaction time of polymer reactions that encompasses the non-Markovian dynamics of monomer motion. This requires that the conformational statistics of the polymer at the very instant of reaction be determined, which provides, as a by-product, new information on the reaction path. We show that the typical reactive conformation of the polymer is more extended than the equilibrium conformation, which leads to reaction times significantly shorter than predicted by the existing classical Markovian theory.; Comment: Main text (7 pages, 5 figures) + Supplemantary Information (13 pages, 2 figures)

Magnesium Monocationic Complexes: A Theoretical Study of Metal Ion Binding Energies and Gas-Phase Association Kinetics

Dunbar, Robert C.; Petrie, Simon
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
57.021367%
Bond dissociation energies (BDEs) for complexes of ground state Mg+ (2S) with several small oxygen- and nitrogen-containing ligands (H2O, CO, CO2, H2CO, CH3OH, HCOOH, H2CCO, CH3CHO, c-C2H4O, H2CCHOH, CH3CH2OH, CH3OCH3, NH3, HCN, H2CNH, CH3NH2, CH3CN, CH3CH2NH2, (CH3)2NH, H2NCN, and HCONH2) have been calculated at the CP-dG2thaw level of theory. These BDE values, as well as counterpoise-corrected MP2(thaw)/6-311+G(2df,p) calculations on the Mg+ complexes of several larger ligands, augment and complement existing experimental or theoretical determinations of gas-phase Mg+/ligand bond strengths. The reaction kinetics of complex formation are also investigated via variational transition state theory (VTST) calculations using the computed ligand and molecular ion parameters. Radiative association rate coefficients for most of these systems increase by approximately 1 order of magnitude with every 3-fold reduction in temperature from 300 to 10 K. Several of the largest molecules surveyed-notably, CH3COOH, (CH3)2CO, and CH3CH2CN - exhibit comparatively efficient radiative association with Mg+ (kRA ≥ 1.0 × 10-10 cm3 molecule-1 s-1) at temperatures as high as 100 K, implying that these processes may have a considerable influence on the metal ion chemistry of warm molecular astrophysical environments known to contain these potential ligands. Our calculations also identify the infrared chromophoric brightness of various functional groups as a significant factor influencing the efficiency of the radiative association process.