Analysis of the kinetics of phase and amplitude gratings recorded in azopolymer films

In this work we use a stabilized holographic technique to study both refractive index and absorption gratings recorded in thin films made of Disperse Red 1 (DR1) embedded in an organic polymer matrix (PMMA) deposited on glass substrate. Gratings are recorded by linearly polarized illumination with the interference pattern of two crossing beams. One of the beams is phase modulated and the interference signals between the transmitted and diffracted waves are detected by a tuned lock-in amplifier. The technique allows measuring separately changes of the refractive index and the absorption coefficient during the course of the photoreaction process. The time evolution of the diffraction efficiencies during recording has shown bi-exponential kinetics for both gratings. © 2008 American Institute of Physics.

Kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions

The study of the kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with Ag additions showed that the presence of Ag retarded the eutectoid decomposition reaction and enhanced martensite stabilization. This stabilization effect was attributed to Ag atoms redistribution as structure defects, increase in the numbers of Cu-Al pairs due to Ag-Al interaction and the Al atoms redistribution around one Cu atom at the sub-lattice of the martensitic crystal. © 2008 Trans Tech Publications.

Analytical model for heterogeneous crystallization kinetics of spherical glass particles

An analytical model developed to describe the crystallization kinetics of spherical glass particles has been derived in this work. A continuous phase transition from three-dimensional (3D)-like to 1D-like crystal growth has been considered and a procedure for the quantitative evaluation of the critical time for this 3D-1D transition is proposed. This model also allows straightforward determination of the density of surface nucleation sites on glass powders using differential scanning calorimetry data obtained under different thermal conditions. © 2009 The American Ceramic Society.

Study of biosorption of rare earth metals (La, Nd, Eu, Gd) by Sargassum sp. biomass in batch systems: Physicochemical evaluation of kinetics and adsorption models

This work evaluated kinetic and adsorption physicochemical models for the biosorption process of lanthanum, neodymium, europium, and gadolinium by Sargassum sp. in batch systems. The results showed: (a) the pseudo-second order kinetic model was the best approximation for the experimental data with the metal adsorption initial velocity parameter in 0.042-0.055 mmol.g -1.min-1 (La < Nd < Gd < Eu); (b) the Langmuir adsorption model presented adequate correlation with maximum metal uptake at 0.60-0.70 mmol g-1 (Eu < La < Gd < Nd) and the metal-biomass affinity parameter showed distinct values (Gd < Nd < Eu < La: 183.1, 192.5, 678.3, and 837.3 L g-1, respectively); and (c) preliminarily, the kinetics and adsorption evaluation did not reveal a well-defined metal selectivity behavior for the RE biosorption in Sargassum sp., but they indicate a possible partition among RE studied. © (2009) Trans Tech Publications.

Analysis of polymerization time on abrasive wear of dental resins

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Temperature rise during adhesive and composite polymerization with different light-curing sources

AIM: This study evaluated the temperature rise of the adhesive system Single Bond (SB) and the composite resins Filtek Z350 flow (Z) and Filtek Supreme (S), when polymerized by light-emitting diode (LED XL 3000) and quartz-tungsten halogen (QTH Biolux). METHODS: Class V cavities (3 yen2 mm) were prepared in 80 bovine incisors under standardized conditions. The patients were divided as follows: G1: Control; G2: SB; G3: SB + Z; G4: SB + S. The groups were subdivided into two groups for polymerization (A: QTH, B: LED). Light curing was performed for 40 s and measurement of temperature changes during polymerization was performed with a thermocouple positioned inside the pulp chamber. Data were statistically analyzed using ANOVA and Tukey tests. RESULTS: The factors material (P<0.00001) and curing unit (P<0.00001) had significant influence on temperature rise. The lowest temperature increase (0.15 degrees C) was recorded in G2 B and the highest was induced in G1 A (0.75 degrees C, P<0.05). In all groups, lower pulp chamber temperature measurements were obtained when using LED compared to QTH (P<0.05). CONCLUSION: QTH caused greater increases in tooth temperature than LED. However, both sources did not increase pulpal temperature above the critical value that may cause pulpal damage.

Conductive nanocomposites based on cellulose nanofibrils coated with polyaniline-DBSA via in situ polymerization

Cellulose nanofibrils (CNF) were extracted by acid hydrolysis from cotton microfibrils and nanocomposites with polyaniline doped with dodecyl benzenesulphonic acid (PANI-DBSA) were obtained by in situ polymerization of aniline onto CNF. The ratios between DBSA to aniline and aniline to oxidant were varied in situ and the nanocomposites characterized by four probe DC electrical conductivity, ultraviolet-visible-near infrared (UV-Vis - NIR) and Fourier-transform infrared (FTIR) spectroscopies and X-ray diffraction (XRD). FTIR and UV-Vis/NIR characterization confirmed the polymerization of PANI onto CNF surfaces. Electrical conductivity of about 10 -1 S/cm was achieved for the composites; conductivity was mostly independent of DBSA/aniline (between 2 and 4) and aniline/oxidant (between 1 and 5) molar ratios. X-ray patterns of the samples showed crystalline peaks characteristic of cellulose I for CNF samples, and a mixture of both characteristic peaks of PANI and CNF for the nanocomposites. Field emission scanning electron microscopy (FESEM) characterization corroborated the abovementioned results showing that PANI coated the surface of the nanofibrils. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetic parameters for thermal decomposition of supramolecular polymers derived from diclofenac-meglumine supramolecular adducts

Meglumine is an aminocarbohydrate able to form supramolecular adducts with organic acids. The recognition is based on hydrogen bonds and the structures resulting from the complexation have high solubility in water. This property has been exploited by the pharmaceutical industry in the improvement of existing drugs, and the successful example of this approach involves the poorly soluble non-steroidal anti-inflammatory drugs (NSAIDs). Investigation of the thermal behavior of adduct obtained from meglumine and the NSAID diclofenac revealed that a polymer-like material is formed from the self-assembly of diclofenac-meglumine adducts in the melt. This polymer showed a high molecular weight around 2.0×105kDa. The kinetic parameters for the thermal decomposition step of the polymer were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15 and 20°Cmin-1, the Eα and Bα terms could be determined, and consequently the pre-exponential factor, Aα, as well as the kinetic model, g(α). © 2012 Elsevier B.V.

Cooperative RNA Polymerase Molecules Behavior on a Stochastic Sequence-Dependent Model for Transcription Elongation

The transcription process is crucial to life and the enzyme RNA polymerase (RNAP) is the major component of the transcription machinery. The development of single-molecule techniques, such as magnetic and optical tweezers, atomic-force microscopy and single-molecule fluorescence, increased our understanding of the transcription process and complements traditional biochemical studies. Based on these studies, theoretical models have been proposed to explain and predict the kinetics of the RNAP during the polymerization, highlighting the results achieved by models based on the thermodynamic stability of the transcription elongation complex. However, experiments showed that if more than one RNAP initiates from the same promoter, the transcription behavior slightly changes and new phenomenona are observed. We proposed and implemented a theoretical model that considers collisions between RNAPs and predicts their cooperative behavior during multi-round transcription generalizing the Bai et al. stochastic sequence-dependent model. In our approach, collisions between elongating enzymes modify their transcription rate values. We performed the simulations in Mathematica® and compared the results of the single and the multiple-molecule transcription with experimental results and other theoretical models. Our multi-round approach can recover several expected behaviors, showing that the transcription process for the studied sequences can be accelerated up to 48% when collisions are allowed: the dwell times on pause sites are reduced as well as the distance that the RNAPs backtracked from backtracking sites. © 2013 Costa et al.

Evaluation of Sperm Kinetics and Plasma Membrane Integrity of Frozen Equine Semen in Different Storage Volumes and Freezing Conditions

In the present study, different freezing systems (Styrofoam box and Mini Digitcool ZH 400) and storage volumes (0.5- and 0.25-mL straws) were compared with regard to sperm kinetics and plasma membrane integrity of frozen and thawed semen. For that, three ejaculates from four animals were frozen in Styrofoam box and Mini Digitcool ZH 400 machine. The 0.5-mL straws were thawed at 46°C for 20 seconds, and the 0.25-mL straws were thawed at 46°C for 12 seconds. Statistical analysis was performed using program R of descriptive analysis box plot, followed by analysis of variance using PROC MIXED of SAS 9.1 package. Variances of 5% were considered as different. There was no interaction between the straw sizes and volumes; however, statistical differences were observed between the semen storage volumes. The 0.5-mL straws had higher total motility (%), progressive motility (%), average path velocity (μm/s), straight-line velocity (μm/s), curvilinear velocity (μm/s), and rapid sperm percentage (%) than the 0.25-mL straws. However, plasma membrane integrity analysis did not differ between the two straws. Thus, it is possible to conclude that equine sperm cryopreserved in 0.5-mL straws has better sperm kinetics than when stored in 0.25-mL straws. Additionally, it is possible to conclude that automated systems that enable faster freezing rates result in a seminal quality that is similar to the one obtained by the conventional system using Styrofoam boxes. © 2013 Elsevier Inc.

Durability of Adhesion between Feldspathic Ceramic and Resin Cements: Effect of Adhesive Resin, Polymerization Mode of Resin Cement, and Aging

Purpose: Adhesive cementation is an important step for restorations made of feldspathic ceramic as it increases the strength of such materials. Incorrect selection of the adhesive resin and the resin cement to adhere to the ceramic surface and their durability against aging can affect the adhesion between these materials and the clinical performance. This study evaluated the effect of adhesive resins with different pHs, resin cements with different polymerization modes, and aging on the bond strength to feldspathic ceramic. Materials and Methods: One surface of feldspathic ceramic blocks (VM7) (N = 90) (6.4 × 6.4 × 4.8 mm3) was conditioned with 10% hydrofluoric acid for 20 seconds, washed/dried, and silanized. Three adhesive resins (Scotchbond Multi-Purpose Plus [SBMP], pH: 5.6; Single Bond [SB], pH: 3.4; and Prime&Bond NT [NT], pH: 1.7) were applied on the ceramic surfaces (n = 30 per adhesive). For each adhesive group, three resin cements with different polymerization modes were applied (n = 10 per cement): photo-polymerized (Variolink II base), dual polymerized (Variolink II base + catalyst), and chemically polymerized (C&B). The bonded ceramic blocks were stored in water (37°C) for 24 hours and sectioned to produce beam specimens (cross-sectional bonded area: 1 ± 0.1 mm2). The beams of each block were randomly divided into two conditions: Dry, microtensile test immediately after cutting; TC, test was performed after thermocycling (12,000×, 5°C to 55°C) and water storage at 37°C for 150 days. Considering the three factors of the study (adhesive [3 levels], resin cement [3 levels], aging [2 levels]), 18 groups were studied. The microtensile bond strength data were analyzed using 3-way ANOVA and Tukey's post hoc test (α= 0.05). Results: Adhesive resin type (p < 0.001) and the resin cement affected the mean bond strength (p= 0.0003) (3-way ANOVA). The NT adhesive associated with the chemically polymerized resin cement in both dry (8.8 ± 6.8 MPa) and aged conditions (6.9 ± 5.9 MPa) presented statistically lower bond strength results, while the SBMP adhesive resin, regardless of the resin cement type, presented the highest results (15.4 to 18.5 and 14.3 to 18.9 MPa) in both dry and aged conditions, respectively (Tukey's test). Conclusion: Application of a low-pH adhesive resin onto a hydrofluoric acid etched and silanized feldspathic ceramic surface in combination with chemically polymerized resin cement did not deliver favorable results. The use of adhesive resin with high pH could be clinically advised for the photo-, dual-, and chemically polymerized resin cements tested. © 2012 by the American College of Prosthodontists.

Photo-Fenton degradation kinetics of low ciprofloxacin concentration using different iron sources and pH

The aim of the present study was to compare the degradation kinetics of low (1 mg L-1) and high (25 mg L-1) concentrations of ciprofloxacin (CIP) aiming to decrease the concentration of additives and evaluate the pH limitation by the use of low iron concentrations and organic ligands. A parameterized kinetic model was satisfactorily fitted to the experimental data in order to study the performance of photo-Fenton process with specific iron sources (iron citrate, iron oxalate, iron nitrate) under different pH medium (2.5, 4.5, 6.5). The process modeling allowed selecting those process conditions (iron source, additives concentrations and pH medium) which maximize the two performance parameters related to the global equilibrium conversion and kinetic rate of the process. For the high CIP concentration, degradation was very influenced by the iron source, resulting in much lower efficiency with iron nitrate. At pH 4.5, highest TOC removal (0.87) was achieved in the presence of iron citrate, while similar CIP conversions were obtained with oxalate and citrate (0.98 after 10 min). For the low CIP concentration, much higher conversion was observed in the presence of citrate or oxalate in relation to iron nitrate up to pH 4.5. This behavior denotes the importance of complexation also at low dosages. Appropriate additives load (320 μM H 2O2; 6 μM Fe) resulted in a CIP conversion of 0.96 after10 min reaction with citrate up to pH 4.5. © 2013 Elsevier B.V. All rights reserved.

The Mode of Action of Recombinant Mycobacterium tuberculosis Shikimate Kinase: Kinetics and Thermodynamics Analyses

Tuberculosis remains as one of the main cause of mortality worldwide due to a single infectious agent, Mycobacterium tuberculosis. The aroK-encoded M. tuberculosis Shikimate Kinase (MtSK), shown to be essential for survival of bacilli, catalyzes the phosphoryl transfer from ATP to the carbon-3 hydroxyl group of shikimate (SKH), yielding shikimate-3-phosphate and ADP. Here we present purification to homogeneity, and oligomeric state determination of recombinant MtSK. Biochemical and biophysical data suggest that the chemical reaction catalyzed by monomeric MtSK follows a rapid-equilibrium random order of substrate binding, and ordered product release. Isothermal titration calorimetry (ITC) for binding of ligands to MtSK provided thermodynamic signatures of non-covalent interactions to each process. A comparison of steady-state kinetics parameters and equilibrium dissociation constant value determined by ITC showed that ATP binding does not increase the affinity of MtSK for SKH. We suggest that MtSK would more appropriately be described as an aroL-encoded type II shikimate kinase. Our manuscript also gives thermodynamic description of SKH binding to MtSK and data for the number of protons exchanged during this bimolecular interaction. The negative value for the change in constant pressure heat capacity (ΔCp) and molecular homology model building suggest a pronounced contribution of desolvation of non-polar groups upon binary complex formation. Thermodynamic parameters were deconvoluted into hydrophobic and vibrational contributions upon MtSK:SKH binary complex formation. Data for the number of protons exchanged during this bimolecular interaction are interpreted in light of a structural model to try to propose the likely amino acid side chains that are the proton donors to bulk solvent following MtSK:SKH complex formation. © 2013 Rosado et al.

Sleeving nanocelluloses by admicellar polymerization

This investigation reports the first application of admicellar polymerization to cellulose nanofibers in the form of bacterial cellulose, microfibrillated cellulose, and cellulose nanowhiskers using styrene and ethyl acrylate. The success of this physical sleeving was assessed by SEM, FTIR, and contact angle measurements, providing an original and simple approach to the modification of cellulose nanofibers in their pristine aqueous environment. © 2013 The Authors. Published by Elsevier Inc.