Thermal and viscoelastic properties of xanthan gum/chitosan complexes in aqueous solutions

The viscoelasticity and thermal properties of aqueous solutions of blended xanthan gum (XA) with chitosan were investigated in order to study the electrostatic interaction established between two polysaccharides. Storage modulus G’, loss modulus G” and zero shear rate viscosity η_O attain a maximum at a chitosan concentration C _max. The above results indicate that the junction between XA and chitosan is formed in a concentration range lower than C _max and the viscoelasticity of systems increases with increasing concentration. In a concentration range higher than C _max, junction formation may not occur effectively since the excess amount of chitosan completely screens anions of XA. The chain rigidity of XA decreases by the screening of the repulsive interaction between anions on XA chains. The ineffective junction formation and the decrease of XA chain rigidity may cause the decrease of viscoelasticity of systems with increasing concentration. The value of C _max decreases with increasing molecular mass of chitosan. From melting enthalpy of the above system measured by DSC, the amount of non-freezing water (W _nf) was evaluated. W _nf shows a minimum at the concentration C _max. This fact suggests that hydrophobic fields increased by junction structure formation through ion-complexation between XA and chitosan molecules.     

Solution ozonolysis of C<Subscript>70</Subscript>: stable products and chemiluminescence

For the first time the total and relative contents of the stable ozonolysis products of fullerene C₇₀ solutions were identified by IR spectroscopy and elemental and chemical analyses. At the 100% conversion of C₇₀ a mixture of products corresponding to the empirical formula C₇₀O_14.3H_0.21 (epoxides: polyketones: polyesters: secondary fullerene ozonides (SFOZ): acids = 1.07: 6: 6: 0.21: 1.02) is formed. The content of polyketones, polyesters, acids, and SFOZ increases during the whole ozonolysis time (1 h). The number of oxygen atoms in epoxides C₇₀O _n (n = 1–4) is lower than that in epoxides C₆₀O _n (n = 1–6) formed by the ozonolysis of fullerene C₆₀. The kinetic curve of accumulation of epoxides C₇₀O _n (n = 1–4) passes through a maximum, which is observed 0.5 min after the beginning of ozonolysis. No epoxides were identified among the products 3.5 min after the ozonolysis. The photoluminescence (PL) (λ_max = 645 and 685 nm) of fullerene polyketones in glassy EtO₂/EtOH solutions frozen at 77 K was observed. This PL is much brighter, than that of polyketones formed upon the ozonolysis of fullerenes C₆₀. For the first time the chemiluminescence (CL) was detected and studied upon the ozonolysis of C₇₀ solutions at 300 K. The CL emitters are excited states of fullerene polyketones. The CL spectrum is partially overlapped with the known CL spectrum appeared upon the ozonolysis of C₆₀ (λ_max = 685 nm) but contains the greater number of maxima (λ_max = 645 and 685 nm), which is related to a lower symmetry of the C₇₀ oxidation products.     

Performance evaluation of the GastroPlusTM software tool for prediction of the toxicokinetic parameters of chemicals

ABSTRACT

The accurate prediction of toxicokinetic parameters arising from oral, dermal and inhalation routes of chemical exposure is a key element in chemical safety assessments. In this research, the physiologically based pharmacokinetic (PBPK) GastroPlus^TM software was evaluated against a series of chemicals for the prediction of toxicokinetic parameters. Overall, 67% of predicted intrinsic clearance (Clint) values were within 1- to 10-fold of empirical data for 463 compounds, and 87% of the predicted fraction unbounded in plasma (Fup) values were 1- to 3-fold of empirical data for 441 compounds. The r² (coefficient of determination) of predicted C_max (maximum plasma concentration) and AUC (Area Under Curve) values versus the corresponding empirical values from oral, inhalation and dermal exposures ranged from 0.04 to 0.92. Among the three exposures, the highest r² values, ranging from 0.80 to 0.92, were observed for oral exposure predictions, where 88% of the compounds had 1- to 10-fold differences between predicted and empirical values for C_max and AUC. The predicted plasma C_ss (steady-state plasma concentration) values were consistent with those C_ss values calculated by in vitro-to-in vivo extrapolation (IVIVE) approaches using experimental parameters. Based on the evaluation results, GastroPlus? can be used as a QSAR/PBPK tool for toxicokinetic parameter predictions.     

Study of the physicochemical characteristics of dispersions of n-alkanes C23H48 and C28H58 in water: zeta potential and temperatures of phase transitions

The effect of pH on the zeta potential of dispersions of individual n-alkanes C₂₃H₄₈ and C₂₈H₅₈ with particle sizes of the order of 100 nm, which were prepared by ultrasonic dispersion without the addition of surfactants, was studied. It is shown that at pH ranged from 4 to 12, the investigated n-alkanes form stable dispersions in water. They are characterized by a high zeta potential varying from ?30 to ?50 mV. The phase transition temperatures (melting point, crystallization temperature, formation of rotator phases) were determined for the dispersions using an optical method.

     

Quantitative temperature gradient focusing performed using background electrolytes at various pH values

Temperature gradient focusing (TGF) has previously been shown to be a practical technique for simultaneous concentration and separation of a variety of samples. In this paper, we demonstrate that TGF can be conducted at a wide range of pH values. Techniques for first-order prediction of the suitability of a given BGE for focusing are discussed. Buffer suitability for TGF is assessed experimentally by simultaneously concentrating and separating a pair of fluorescent analytes. One analyte is held at constant concentration for use as an internal standard while the concentration of the other dye is varied. Peak area is shown to vary linearly with the input dye concentration. A high degree of resolution (R(s) >3) of fluorescein and carboxyfluorescein, as well as for two LysoSensor-based dyes, is also observed. Foucusing and separation by TGF was successfully conducted quantitatively in BGE solutions of pH from 3.0 to 10.5.     

Controlled protein adsorption on a silica microparticle

In the present study, controlled protein adsorption on a rigid silica microparticle is investigated numerically using classical Langmuir and two-state models under electrokinetic flow conditions. The instantaneous particle locations are simulated along a straight microchannel using an arbitrary Lagrangian−Eulerian framework in the finite element method for the electrophoretic motion of the charged particle. Within the scope of the parametric study, the strength of the external electric field (E), particle diameter (D_p), the zeta potential of the particle (ζ_p), and the location of the microparticle away from the channel wall (H) are systematically varied. The results are also compared to the data of pressure-driven flow having a parabolic flow profile at the inlet whose maximum magnitude is set to the particle's electrophoretic velocity magnitude. The validation studies reveal that the code developed for the particle motion in the present simulations agrees well with the experimental results. It is observed that protein adsorption can be controlled using electrokinetic phenomena. The plug-like flow profile in electrokinetics is beneficial for a microparticle at every spatial location in the microchannel, whereas it is not valid for the pressure-driven flow. The electric field strength and the zeta potential of the particle accelerate the protein adsorption. The wall shear stress and shear rate are good indicators to predict the adsorption process for electrokinetic flow.     

The effect of column characteristics on the minimum analyte concentration and the minimum detectable amount in capillary gas chromatography. Part II: The stationary phase film thickness

For a typical narrow bore (50 μm) and wide bore (320 μm) capillary column the effects of increased stationary phase film thickness (d_f) on the minimum detectable amount, Q_o, as well as on the minimum analyte concentration, C_o, are described. In treating the effect of an increased film thickness, two approaches can be followed; either the separation temperature is kept constant, resulting in larger values of the capacity ratio, k, or the column temperature is increased such as to keep k constant. For normalized chromatographic conditions the effects of both approaches on the minimum plate height, optimum carrier gas velocity, and required plate number are described, finally yielding expressions for Q_o and C_o for both mass flow and concentration sensitive detectors. At constant temperature, C_o always increases with the film thickness for mass flow sensitive detectors (e.g. FID). Wide bore thin film columns offer the lowest value of C_o attainable. For concentration sensitive detectors (e.g. TCD), C_o is affected neither by column diameter nor by film thickness. The Q_o–d_f plot for constant temperature shows a minimum, suggesting an optimum film thickness for mass flow sensitive as well as concentration sensitive detectors. The corresponding capacity ratio has a value between 0.5 and 1.5. At elevated temperatures (k constant) in combination with mass flow sensitive detectors, again an optimum film thickness exists, corresponding to a minimum value of C_o. For constant capacity ratio Q_o always increases with the film thickness for both types of detectors. As indicated above, in some situations the lowest values of C_o and Q_o are obtained at an increased film thickness, the effect being marginal. As an initial guideline, for the daily practice of capillary gas chromatography with respect to minimum values of C_o and Q_o, the use of thin film columns is to be preferred.     

Synergistic enantioseparation systems with either cyclodextrins or cyclofructans and L‐alanine Tert butyl ester lactate

The combined use of chiral ionic liquids (CILs) and conventional chiral selectors (CSs) in CE, to establish a synergistic system, has proven to be an effective approach for the separation of enantiomeric pairs. In this study, a new CE method was developed, employing a binary system of a CS, either a cyclodextrin (CD) or a cyclofructan (CF), and a chiral amino acid ester‐based ionic liquid (AAIL), for the chiral separation of four basic, acidic and zwitterionic drug compounds. In particular, the enantioseparation of two anticoagulants, warfarin (WAR) and coumachlor (COU), a non‐opioid analgesic, nefopam (NEF) and a third‐generation antihistamine, fexofenadine (FXD), was examined, by supporting the BGE with a CS and the chiral AAIL L‐alanine tert butyl ester lactate (L‐AlaC₄Lac). Parameters, such as the type of the CS, the concentration of both the CS and L‐AlaC₄Lac, and the BGE pH, were methodically examined in order to optimize the chiral separation of each analyte. It was observed that, in some cases, the addition of the AAIL into the BGE improved both resolution (R_s) and efficiency (N) significantly. In other cases, the synergistic effect enabled baseline separation of analyte enantiomers, at a much lower concentration of the CS. Finally, after optimization of separation conditions, baseline separations (R_s>1.5) of all four analytes were achieved in less than 5 min.     

Liquid chromatography tandem mass spectrometry method for the quantification of sarpogrelate, a selective 5-HT(₂A) receptor antagonist, in plasma: application to a pre-clinical pharmacokinetic study

A simple LC‐MS/MS method was developed and validated for the estimation of sarpogrelate in 50 µL of rat plasma. The analyte and internal standard (IS) were extracted from rat plasma by acetonitrile precipitation and they were separated on a reversed‐phase C₈ column with gradient program. The MS acquisition was performed with multiple reaction monitoring mode using m/z 430.2 to m/z 135.0 for analyte and m/z 448.2 to m/z 285.3 for IS. The calibration curves were linear over the range of 1–1000 ng/mL with the correlation coefficient greater than 0.999. With dilution integrity up to 20‐fold, the upper limit of quantification was extendable up to 15,000 ng/mL. The method was successfully applied to the analysis of rat plasma samples after single dose oral administration of sarpogrelate at 5 mg/kg to rats for the determination of its pharmacokinetics. Following oral administration the maximum mean concentration in plasma (C_max, 11514 ng/mL) was achieved at 0.25 h (T_max) and the area under curve (AUC_0–24) was 11051 ± 3315 ng h/mL. The half‐life (t_1/2) and clearance (Cl) were 2.9 ± 1.1 h and 490 ± 171 mL/h/kg, respectively. We believe that development of a method in rodent plasma would facilitate the ease of adaptability of sarpogrelate in human plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

Interaction Between GMAC-m-CS and Surfactants: Surface Tension and Conductivity Methods

Glycidyl trimethyl ammonium chloride-modified chitosan (GMAC-m-CS) was synthesized through nucleophilic substitution of GMAC on CS in isopropanol dispersed system, which was characterized by FTIR and ¹H NMR methods. The interaction between GMAC-m-CS and surface active ILs ?1-dodecyl (tetradecyl and hexadecyl)-3-methylimidazolium bromide (C_nmimBr, n = 12, 14, 16) was studied by surface tension and conductivity methods. The amount of C_nmimBr adsorbed on GMAC-m-CS increases first with raising temperature, and then decreases, which reaches the largest amount at 30°C. The amount increases with the increase of alkyl chain length. The surface tension reducing capabilities of GMAC-m-CS/C_nmimBr systems increase with temperature, however, decrease with the increase of GMAC-m-CS concentration. The aggregation processes of C₁₄mimBr in solutions without GMAC-m-CS and with high concentration of GMAC-m-CS were entropy driven; however, it is enthalpy driven in solutions with low concentration of GMAC-m-CS. Based on the analysis of properties of GMAC-m-CS/C_nmimBr, the interaction model of GMAC-m-CS/ILs was proposed.     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(C_nTAB)对其进行插层处理;通过改变C_nTAB的链长、浓度,得到系列C_nTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及C_nTAB插入量进行表征。结果表明,随着C_nTAB链长的增长、C_nTAB浓度的增大,C_nTAB/GO插层复合物的最大底面间距逐渐增大。C_nTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即C_nTAB以单分子层吸附在GO片层上。根据C_nTAB/GO插层复合物最大底面间距及C_nTAB插入量的变化规律分析,得出C_nTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

Transport properties of alkyltrimethylammonium bromide surfactants in aqueous solutions

Differential mutual diffusion coefficients of n-alkyltrimethylammonium bromides [CH₃(CH₂)_n–1N(CH₃)₃Br, C_nTAB] (n=10, 12, 14, 16) have been measured in aqueous solutions at 298.15 K using a conductimetric cell and an automatic apparatus to follow diffusion. The cell is based on an open-ended capillary, and the technique follows the diffusion process by measuring the resistance of a solution inside the capillaries at various times. The electrical conductances of those solutions have also been measured to calculate the critical micellar concentration (cmc). Thermodynamic analysis of the data suggests that the free ion concentration decreases at concentrations above the cmc, in agreement with theoretical predictions. The obtained values of the micellization parameters were used to model the mutual diffusion coefficients of C_nTAB aqueous solutions.     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(CnTAB)对其进行插层处理;通过改变CnTAB的链长、浓度,得到系列CnTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及CnTAB插入量进行表征。结果表明,随着Cn TAB链长的增长、CnTAB浓度的增大,CnTAB/GO插层复合物的最大底面间距逐渐增大。CnTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即CnTAB以单分子层吸附在GO片层上。根据CnTAB/GO插层复合物最大底面间距及CnTAB插入量的变化规律分析,得出CnTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

Radiation telomerization of tetrafluoroethylene in butyl chloride solution

The kinetics of the radiation-initiated polymerization of tetrafluoroethylene (TFE) in butyl chloride has been studied. The rate of the process, the properties and yield of telomers obtained depend on the initial concentration of TFE (2.6–22 wt %) in the solution and the dose of γ-irradiation. The analysis of the measured IR absorption spectra and a possible scheme of the process allow to suggest that the main product of the reaction is C₄H₈Cl(C₂F₄) _n−1CF₂CF₂H with the formation of small amounts of C₄H₉(C₂F₄) _n−1CF₂CF₂H and Cl(C₂F₄) _n−1CF₂CF₂H. The average number of links in the telomer (n) increases from 7.6 to 16.1 when the concentration of the monomer in the solution varies in the range of 7–22 wt %. The length of the chain of the soluble telomers (n) does not depend on the initial concentration of TFE and makes ∼7.     

A comparison of experimental measurements and theoretical predictions regarding the behavior of a turbulent argon plasma jet discharging into air

Computed results are presented describing the temperature and concentration fields obtained when an argon plasma jet is being discharged into ambient air. A previously published mathematical model for turbulent plasma plumes is used for the calculations. These predictions are compared with recent), published experimental measurements by Brossa and Pfender, performed with an enthalpy probe. The theoretical predictions appear to agree reasonably well with the measurements of both the temperature and concentration profiles, with a maximum deviation in the 10–20% range.Notation A _max maximum temperature or velocity in the torch exit profile - C ₁ C ₂ C _D constants inK- model - h enthalpy - I torch current - K turbulent kinetic energy per unit mass - m mass concentration of plasma p pressure - Q How rate of argon through the torch - r radial coordinate - r _n nozzle radius (inside) - S source term for dependent variable      

Aggregate morphology and flow behaviour of micellar alkylglycoside solutions

Solutions of n-nonyl-β-D-glucoside (C₉G₁), n-decyl-β-D-glucoside (C₁₀G₁), n-dodecyl-β-D-maltoside (C₁₂G₂), n-tetradecyl-β-D-maltoside (C₁₄G₂) and C₉G₁/C₁₀G₁ mixtures have been characterised by capillary viscometry and rheology in H₂O and D₂O, in order to map the influence of surfactant characteristics on micellisation over a wide concentration range. For the maltosides, the micellar solutions are shear thinning with a zero-shear viscosity that scales with concentration according to a power law with an exponent of about 5.8. In contrast, solutions of the glucosides C₉G₁, C₁₀G₁ and their mixtures show Newtonian flow behaviour and a much lower scaling exponent (<2.4). In C₉G₁/C₁₀G₁ mixtures, the scaling exponent decreases monotonously with increasing C₁₀G₁ content. The flow behaviour correlates with the packing requirements of the various surfactants, and are compatible with the idea that the maltosides form worm-like micelles, whereas the glucosides form branched, interconnected micelles (C₉G₁) and space-filling micellar networks (C₁₀G₁).     

Randomized two‐way cross‐over bioequivalence study of two amoxicillin formulations and inter‐ethnicity pharmacokinetic variation in healthy Malay volunteers

The objectives of this study were to develop a new deproteinization method to extract amoxicillin from human plasma and evaluate the inter‐ethnic variation of amoxicillin pharmacokinetics in healthy Malay volunteers. A single‐dose, randomized, fasting, two‐period, two‐treatment, two‐sequence crossover, open‐label bioequivalence study was conducted in 18 healthy Malay adult male volunteers, with one week washout period. The drug concentration in the sample was analyzed using high‐performance liquid chromatography (UV–vis HPLC). The mean (standard deviation) pharmacokinetic parameter results of Moxilen® were: peak concentration (C_max), 6.72 (1.56) µg/mL; area under the concentration–time graph (AUC_0–8), 17.79 (4.29) µg/mL h; AUC_0–∞, 18.84 (4.62) µg/mL h. Those of YSP Amoxicillin® capsule were: C_max, 6.69 (1.44) µg/mL; AUC_0–8, 18.69 (3.78) µg/mL h; AUC0_0–∞, 19.95 (3.81) µg/mL h. The 90% confidence intervals for the logarithmic transformed C_max, AUC_0–8 and AUC_0–∞ of Moxilen® vs YSP Amoxicillin® capsule was between 0.80 and 1.25. Both C_max and AUC met the predetermined criteria for assuming bioequivalence. Both formulations were well tolerated. The results showed significant inter‐ethnicity variation in pharmacokinetics of amoxicillin. The C_max and AUC of amoxicillin in Malay population were slightly lower compared with other populations. Copyright © 2014 John Wiley & Sons, Ltd.     

Detector Systems in Capillary Gas Chromatography

Expressions for the minimum detectable amount Q_o and the minimum analyte concentration C_o as functions of the chromatographic parameters are derived for both mass and concentration sensitive detectors. The effects of pressure drop, column inner diameter, and film thickness are given. The minimum analyte concentration for mass flow sensitive detectors, C_o^m, can be reduced considerably by selecting the carrier gas velocity well above its optimum value (related to H_min), however, at the cost of long columns and long analysis times. For Q_o the improvements can be neglected, and so the analysis can best be performed at u_opt. When the flow rate in the detector, F_d, is equal to the column flow rate F_c, the maximum permissible detector volume of concentration sensitive detectors is proportional to d_c² up to d_c³, and so narrow bore columns require detectors of extremely small volume. Make-up gas has to be added when the actual volume is too large, thus worsening the detectability. Another approach, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in combination with small volume concentration sensitive detectors, very small values of Q_o^c and C_o^c are obtainable when the abundant carrier gas can be removed before entering the detector cell. Digital noise filtering can further reduce the obtainable Q_o and C_o values, especially for broad peaks and thus for wide bore columns.     

Effect of the reaction temperature on the morphology of nanosized HAp

The main purpose of this study is numerically investigating the flow and heat transfer of nanofluid flow inside a microchannel with L-shaped porous ribs as well as studying the effect of porous media properties on the performance evaluation criterion (PEC) of the fluid. In the present paper, in addition to the pure water fluid, the effect of using water/CuO nanofluid on the PEC of microchannel was investigated. The flow was simulated in four Reynolds numbers and two different volume fractions of nanoparticles in laminar flow regime. The investigated parameters are the thermal conductivity and the porosity rate of porous medium. The results indicate that with the existence of porous ribs, the nanofluid does not have a significant effect on heat transfer increase. By using porous ribs in flow with Reynolds number of 1200, the heat transfer rate increases up to 42% and in flow with Reynolds number of 100, this rate increases by 25%.

     

Charge exchange and charge separation processes of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications

The charge exchange and charge separation processes of a series of [C₃H_n]²⁺ and [C₃D_n]²⁺ (n = 1–6) dications have been investigated experimentally in a mass spectrometer of reversed geometry. The relative reaction cross-sections for charge exchange with nitrogen exhibited a 20-fold variation which has implications for the interpretation of 2E spectra with respect to dication relative intensities. Charge separation resulting in deprotonation was observed for all [C₃D_n]²⁺ species investigated, while de-deuteronation was observed for [C₃D_n]²⁺ (n = 1–4) only. Intercharge separations calculated from the observed ion kinetic energies released upon charge separation suggest linear structures for [C₃D_n]²⁺ and [C₃D_n]²⁺ (n = 1–2) and cyclic structures for [C₃D_n]²⁺ (n = 3–6) and [C₃D_n]²⁺ (n = 3–4).