Phase behavior of DNA in the presence of cetyltrimethylammonium bromide / alkyl polyglucoside surfactant mixture

Interaction of DNA with a CTAB/APG mixture was studied by determining its phase behavior. Results showed that, at low DNA concentration, the addition of APG could lead to earlier turbidity, indicating that APG can strengthen the interaction between CTAB and DNA. At high DNA concentration, however, APG had little influence on the turbidity boundary. We found that addition of salt could also lead to such an asymmetry of the phase map. Two mechanisms were presented to account for the asymmetry of the phase behavior. At the lower DNA concentration, it was assumed that the surfactant was bound to DNA in a way similar to that of micelle formation. That is, the binding is dominated by hydrophobic association processes. APG can facilitate this process by forming a surfactant mixture with CTAB, and salt facilitates this process by salting out effects. At high DNA concentrations, surfactants bind to DNA mainly through random electrostatic interaction. Addition of salt screens this interaction and therefore delays the turbidity. APG, however, exerts little influence on this process. Viscosity measurements at low DNA concentration showed that the complex with APG is more compact than that of CTAB alone with DNA.     

Analysis of lipid peroxidation kinetics. 1. Role of recombination of alkyl and peroxyl radicals

The kinetics of the lipid peroxidation reaction is only partly understood. Although the set of reactions constituting the overall reaction are believed to be known, it has not been possible to predict how the reaction will respond to a change of one or more of the parameters, e.g., initial concentrations of reactants or different ways of initiating the reaction, nor has it been possible to predict the time dependence of the products. The reason for these problems is the complicated structure of the kinetic scheme, which includes a chain reaction. In this work we perform an in-depth analysis of the importance of the individual reaction steps, and we introduce a new quasi-stationary concentration method based on the assumption that one or more concentrations vary much slower than the others. We show that it is justified to use a quasi-stationary concentration approximation for the alkyl radical L (*), but not for the peroxyl radicals LO 2 (*) as assumed in previous works. The method allows us to derive manageable analytical expressions. On the basis of literature values of the rate constants, we are able to introduce specific simplifications that allow us to obtain simple analytical expressions for the time dependence of all concentrations involved in the process.     

Analysis of the complex formation of heparin with protamine by light scattering and analytical ultracentrifugation: implications for blood coagulation management

Heparin, a linear glycosaminoglycan, is used in different forms in anticoagulation treatment. Protamine, a highly positive charged peptide containing about 32 amino acids, acts as an antagonist for heparin to restore normal blood coagulation. The complex formation of protamine with heparin was analyzed by a combination of analytical ultracentrifugation and light scattering. Titration of heparin with protamine in blood plasma preparations results in a drastic increase of turbidity, indicating the formation of nanoscale particles. A similar increase of turbidity was observed in physiological saline solution with or without human serum albumin (HSA). Particle size analysis by analytical ultracentrifugation revealed a particle radius of approximately 30 nm for unfractionated heparin and of approximately 60 nm for low molecular weight heparin upon complexation with excess protamine, in agreement with atomic force microscopy data. In the absence of HSA, larger and more heterogeneous particles were observed. The particles obtained were found to be stable for hours. The particle formation kinetics was analyzed by light scattering at different scattering angles and was found to be complete within several minutes. The time course of particle formation suggests a condensation reaction, with sigmoidal traces for low heparin concentrations and quasi-first-order reaction for high heparin concentrations. Under all conditions, the final scattering intensity reached after several minutes was found to be proportional to the amount of heparin in the blood plasma or buffer solution, provided that excess protamine was available and no multiple scattering occurred. On the basis of a direct relation between particle concentration and the heparin concentration present before protaminization, a light scattering assay was developed which permits the quantitative analysis of the heparin concentration in blood plasma and which could complement or even replace the activated clotting time test, which is currently the most commonly used method for blood coagulation management.     

Forced Hydrolysis of In(0H)3– arison of Model with Experiments

This paper presents a theory that links solution complexation equilibria with a model for precipitation predicting the panicle size distribution. This model uses classical nucleation theory and growth rates by various rate limiting steps for the growth of the crystals. This model is compared to forced hydrolysis experiments where dilute Indium nitrate solutions, acidified with nitric acid, were heated to 80°C. The experiments produced cubic particles of Indium hydroxide. The experiments were monitored for temperature, pH. turbidity, indium concentration in solution and particle size distribution, all as a function of lime for comparison with this model. The model gives an accurate prediction of the evolution of the particle size distribution, pH, turbidity, and indium concentration with time.     

Determination of drug and fatty acid binding capacity to pluronic f127 in microemulsions

We propose that one can deduce very insightful information regarding the drug and fatty acid binding capacity of microemulsions through simple turbidity experiments. Pluronic F127-based oil-in-water microemulsions of various compositions were synthesized and titrated to turbidity with concentrated amitriptyline, an antidepressant drug. We observed that, above certain Pluronic F127 concentrations, turbidity was never observed, irrespective of how much amitriptyline was added to the microemulsion. We also observed that whenever sodium caprylate fatty acid was not included in the microemulsion formulation, turbidity never occurred. On the basis of these findings, we were able to determine the point at which all sodium caprylate present in the microemulsion formulation was bound to the F127 in the microemulsion (i.e., no fatty acid was free in the bulk in monomer form). By the same logic we were also able to determine how much amitriptyline was binding to the microemulsions. We also measured the dynamic surface tension, foamability, and fabric wetting time of the microemulsion formulations to further prove the hypothesis that all fatty acid is bound to the F127 in the microemulsion above a critical Pluronic F127 concentration. On the basis of this research, we have concluded that there are approximately 11 molecules of sodium caprylate fatty acid bound per molecule of Pluronic F127 and approximately 12 molecules of amitriptyline bound per molecule of Pluronic F127 in the optimal microemulsion formulation. These findings give us valuable information about the charge density at the oil/water interface and about the mechanism of binding of the drug to the microemulsion.     

基于壳聚糖的浊度法测定超滤膜截留率

研究了以壳聚糖为基准物、浊度法测定超滤膜截留率的方法。以氢氧化钠为沉淀剂,用浊度法分别对6种不同相对分子质量的壳聚糖浓度进行检测,探讨了壳聚糖相对分子质量与氢氧化钠浓度等因素对浊度的影响。结果表明,壳聚糖含量在25~1 000 mg/L范围内与浊度呈现良好的线性关系,线性相关系数r~2≥0.996,检出限在2.1~4.8mg/L之间,样品加标回收率为82.1%~122%。测量结果的相对标准偏差为0.75%~8.7%(n=6)。该法快速、简便,可为超滤膜研究、生产、改性及应用等提供理论指导。     

Structure and function of proteins in hydrated choline dihydrogen phosphate ionic liquid

Ionic liquids are being intensely studied as promising media for the stabilization of proteins and other biomolecules. Choline dihydrogen phosphate (CDHP) has been identified as one of the most promising candidates for this application. In this work we have probed in more detail the effects that CDHP may have on the thermodynamics, structure, and stability of proteins, including one of therapeutic interest. Microcalorimetry and circular dichroism spectropolarimetry (CD) were used to assess the thermal stability of protein solutions in CDHP/water mixtures at various concentrations. Increasing thermal stability of lysozyme and interleukin-2 in proportion to CDHP concentration was observed. Isothermal titration calorimetry (ITC) was used to quantify binding interactions, and indicate that the mechanism for stability does not appear to be dependent upon CDHP binding to protein. CD and small angle X-ray scattering (SAXS) analyses were used to probe for structural changes due to the presence of CDHP. SAXS indicates charge effects on the surface of the protein play a role in protein stability in ionic liquids, and no significant alteration of the overall tertiary conformation of lysozyme was observed at 25 °C. However, after incubation at 37 °C or at higher concentrations of CDHP, small changes in protein structure were seen. Effects on protein activity were monitored using turbidity assays, and CDHP decreases protein activity but does not eliminate it. Protein solubility was also monitored using a turbidity assay and was found to be inversely proportional to the concentration of CDHP in solution.     

Long-chain dicarboxylic acids : II. Precipitation of aqueous 5-(and 6-)carboxy-4-hexyl-2-cyclohexen-1-yl octanoic acid solutions with metal ions

Aqueous dispersions of heavy-metal salts of 5-(and 6-)carboxy-4-hexyl-2-cyclohexen-1-yl octanoic acids, denoted by H₂D, were prepared by direct mixing of solutions of the metal nitrates with solutions of Na₂D. With any particular concentration of D²⁻ ion, it was found that the turbidity increased sharply when the concentration of a metal ion exceeded a certain value. This transition from low to high turbidity defined the boundary between stable and unstable soap suspensions, and the concentration of the added salt at which it occurred was labeled as critical transition concentration (ctc). Complete domains, showing the ctc values for different concentrations of dicarboxylate for thallium(I), magnesium, calcium, and lanthanum counterions, have been given. These transition boundaries are strongly dependent on pH. The mixing of calcium and lanthanum nitrates with a solution of Na₂D gave a suspension of solid particles, whereas immediate spontaneous emulsification occurred when thallium(I) and magnesium nitrates were used.     

Phase separation and structural properties of semidilute aqueous mixtures of ethyl(hydroxyethyl)cellulose and an ionic surfactant

Turbidity and small-angle neutron scattering (SANS) measurements have been carried out over an extended temperature range (10-60 °C) on thermoreversible gelling and non-gelling semidilute aqueous systems of ethyl(hydroxyethyl)cellulose (EHEC) in the presence of various amounts of sodium dodecyl sulfate (SDS). EHEC dissolved in D₂O exhibits a lower consolute solution temperature with an abrupt change of the turbidity upon heating the sample. The turbidity transformation is shifted toward higher temperatures (the cloud point temperature rises) and it becomes gradually gentler as the level of surfactant addition increases. Precision turbidity measurements demonstrate the existence of hysteresis effects when heating and cooling scans are conducted. This effect is reduced with SDS addition and disappears at a sufficiently high SDS concentration where most aggregates are disrupted. It is shown from temperature quench turbidity experiments that it takes a very long time for the temperature-induced complexes to disintegrate. The scattered intensity results from SANS at low values of the scattering vector (q) disclose that elevated temperature and low SDS concentration promote the formation of large-scale associations, and at higher levels of surfactant addition the tendency to form aggregates is suppressed. At high surfactant concentrations (8 and 16 mm), an interaction peak appears in the spectrum at intermediate values of q. For the EHEC sample with 8 mm SDS, the peak disappears at higher temperatures because of enhanced hydrophobicity of the polymer. The analysis of the SANS data for the gelling sample (EHEC with 4 mm SDS) reveals that the inhomogeneity of the gel becomes more pronounced in the post-gel region.     

The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N-isopropylacrylamide) Star Polymers

The thermoresponsive nature of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.     

Effect of thiourea and substituted thioureas on dynein ATPase and on the turbidity response of Tetrahymena cilia.

The effects of thiourea and of several substituted thioureas -- phenylthiourea, alpha-naphtylthiourea, metiamide, and burimamide -- on dynein ATPase have been studied. The substituted thioureas are over 30 times more potent than thiourea in causing enhancement of 30S dynein ATPase activity and inhibition of 14S dynein ATPase activity. The effects of thiourea and phenylthiourea can be prevented by very low concentrations of beta-mercaptoethanol or dithiothreitol. Axonemal ATPase is also enhanced by the thioureas, but the reaction proceeds more slowly than for solubilized 30S dynein. Enhancement of 30S dynein ATPase by metiamide is prevented by low (approximately 1 microM) concentrations of ATP and, less effectively, by AMP-PNP, but not by AMP-PCP even though the latter is a stronger inhibitor of 30S dynein ATPase than is AMP-PNP. The thioureas inhibit the ATP-induced decrease in turbidity (measured as delta A350) of axonemal suspensions. Inhibition of the turbidity response is also prevented by low concentrations of beta-mercaptoethanol, but, in contrast to the irreversible enhancement of ATPase activity, inhibition of the turbidity response is largely reversible. The ability of 30S dynein to rebind onto twice-extracted axonemes is not changed by treatment with phenylthiourea or metiamide. These observations indicate that the thioureas react with at least two sets of SH or S--S groups on axonemes. Reaction with the group(s) on the 30S dynein causes an apparently irreversible enhancement of ATPase activity. Reaction with another group(s) causes a reversible inhibition of the turbidity response.     

Absolute rate of turbulent coagulation from turbidity measurement

Turbidity method has been applied to assess colloid stability. While the method is simple and easy, it is not straightforward in evaluating absolute coagulation rates of colloidal particles. That is, the method requires the evaluation of the extinction cross section of doublets. Recently, the turbidity measurement has been successfully utilized to evaluate the absolute Brownian coagulation rate constant with the T-matrix method, which calculates the extinction cross section of doublets at arbitral size range. The present work was performed to extend the applicability of the method to turbulent coagulation. To this end, we measured the turbidity change of coagulating latex suspensions in a turbulent flow. The measurement was performed as a function of particle size. From the turbidity vs. time relationship, we evaluated turbulent coagulation rate constant using the T-matrix method. Obtained values of the constants agreed well with theoretical ones, demonstrating the usefulness of turbidity method for turbulent coagulation.     

分光光度法测定二氧化钛悬浮体系中甲基橙及光催化降解效果的表征

首次利用三波长分光光度法在二氧化钛（TiO2）悬浮体系中直接测定了甲基橙（AO）并用于光催化降解效果的表征。根据三波长原理，用计算机程序选出的最佳三波长组合为420、476和516nm。在浑浊度不同的二氧化钛悬浮体系中，用三波长法直接测定了标准加入的甲基橙，其回收率为96．7％～101％；同样，在浑浊度一定的悬浮体系中，测定了不同浓度的甲基橙，回收率为99．0％～101％。该法用于表征紫外光照射下的二氧化钛（P25，TiO2纤维）光催化降解甲基橙实际体系，其实际效果与常规测量体系得出的结论完全一致，且不同浑浊度下测量结果的重现性良好。结果表明，三波长分光光度法可以有效地消除悬浮体系中浑浊的干扰，为实现二氧化钛光催化体系的在线监测及光催化降解机理的动力学研究提供了一条可行的途径。     

Effects of pH on dynamics and rheology during association and gelation via the Ugi reaction of aqueous alginate

Effects of solution pH on the physical properties of a semidilute aqueous alginate solution without cross-linker agent and during gelation via the Ugi multicomponent condensation reaction at a fixed cross-linker concentration have been investigated. Both rheology and turbidity results on the alginate solution without cross-linker revealed enhanced associations at low pH. In the course of the cross-linker reaction, the time of gelation is shortest at pH = 3.5 and at pH values above 3.8 no gel is formed but only a viscosification of the solution is observed. The turbidity during the cross-linking reaction rises as the pH increases from 3.5 to 5. Furthermore, the initial change of the turbidity in the course of the cross-linking process is more pronounced at higher pH. The dynamic light scattering (DLS) results of the reaction mixture at pH = 4.0 (ergodic features at this condition) show that the chain relaxation is slowed down as the reaction proceeds. The effect of pH on the kinetics of the Ugi reaction is discussed.     

An automated nephelometric system for evaluation of the growth of bacterial cultures

An automated system comprising sixteen similar, independently controlled bioreactors is described. The operating parameters that can be varied in each bioreactor include pH, aeration, agitation and inlet and outlet liquid flow rates. Automatic turbidity measurements in each bioreactor are possible by employment of a nephelometer mounted on a track such that it aligns with the side arm of each bioreactor. Measurements are plotted automatically on either a linear or a semilogarithmic basis with respect to time. The response of the nephelometer is linear with respect to bacterial concentration throughout its operating range. Results that demonstrate the suitability of the system for studying bacterial oxidation processes where substrate concentrations are very low and where substrate affinity is important are presented.     

Study of flocculation with PONILIT GT-2 anionic polyelectrolyte applied into a chemical wastewater treatment

This paper discusses the applications of synthetic PONILIT GT-2 anionic polyelectrolyte in conjuction with ferric sulfate in a chemical wastewater treatment viz. wastewater from ceramics manufacturing. Synthetic wastewaters with different colloid concentrations were prepared and the coagulation-flocculation process followed by sedimentation and/or filtration was studied. Variables associated with the chemical wastewater composition, mixing time, and the coagulant and flocculant dose are considered in order to appreciate the process efficiency in terms of turbidity, chemical oxygen demand (COD), and color removal. The degrees are higher for turbidity and color (> 80 %) removal respectively, and, satisfactory for COD (< 50 %). An empirical model was elaborated by a third order rotatable design 2³ type, considering ferric sulfate dose, polyelectrolyte dose, and mixing time as independent variables, while the turbidity and color removal efficiencies were chosen as optimization criteria. The empirical model was found adequate for the chemical wastewater treatment. Also, an analysis of the model was performed to find the optimal operating conditions, in order to apply this process for an efficient chemical wastewater treatment using ferric sulfate as coagulation agent and PONILIT GT-2 anionic polyelectrolyte as flocculation agent. The optimal values correspond to a ferric ions concentration of 6.093 mg/L, a polyelectrolyte dose of 0.651 mg/L, and a mixing time of 24.024 minutes for turbidity removal (95.869 %), respectively, and, to a ferric ions concentration of 6.01 mg/L, a polyelectrolyte dose of 0.69 mg/L, and a mixing time of 26 minutes for color removal (98.741 %).      

Effects of surfactant and temperature on rheological and structural properties of semidilute aqueous solutions of unmodified and hydrophobically modified alginate

The dynamic and structural perturbations that result from the interactions between the anionic surfactant sodium dodecyl sulfate (SDS) and the hydrophobically modified biopolymer alginate (HM-alginate) have been studied with the aid of rheological methods, turbidimetry, and small-angle neutron scattering (SANS). The rheological results for a semidilute HM-alginate solution in the presence of SDS disclose strong interactions between HM-alginate and SDS at a low level of surfactant addition, and this feature is accompanied by enhanced turbidity. At higher surfactant concentrations the association complexes are disrupted. A strong temperature effect of the viscosity is observed in HM-alginate solutions at moderate SDS concentrations, where an elevated temperature leads to enhanced chain mobility, which promotes a breakup of the association complexes. The SANS results reveal a pronounced peak in the plot of scattered intensity versus wavevector q at intermediate q values for SDS concentrations above the critical micelle concentration (cmc). With contrast-matching conditions, using deuterated SDS instead of SDS, no interaction peak appears but an "upturn" in the scattered intensity is observed at small q value. The magnitude of this effect decreases with increasing surfactant concentration, showing clearly that SDS is capable of breaking up the large aggregates created.     

Development of novel backwash cleaning technique for reverse osmosis in reclamation of secondary effluent

The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation.     

High-field Overhauser dynamic nuclear polarization in silicon below the metal-insulator transition

Single crystal silicon is an excellent system to explore dynamic nuclear polarization (DNP), as it exhibits a continuum of properties from metallic to insulating as a function of doping concentration and temperature. At low doping concentrations DNP has been observed to occur via the solid effect, while at very high-doping concentrations an Overhauser mechanism is responsible. Here we report the hyperpolarization of (29)Si in n-doped silicon crystals, with doping concentrations in the range of (1-3)?× 10(17) cm(-3). In this regime exchange interactions between donors become extremely important. The sign of the enhancement in our experiments and its frequency dependence suggest that the (29)Si spins are directly polarized by donor electrons via an Overhauser mechanism within exchange-coupled donor clusters. The exchange interaction between donors only needs to be larger than the silicon hyperfine interaction (typically much smaller than the donor hyperfine coupling) to enable this Overhauser mechanism. Nuclear polarization enhancement is observed for a range of donor clusters in which the exchange energy is comparable to the donor hyperfine interaction. The DNP dynamics are characterized by a single exponential time constant that depends on the microwave power, indicating that the Overhauser mechanism is a rate-limiting step. Since only about 2% of the silicon nuclei are located within 1 Bohr radius of the donor electron, nuclear spin diffusion is important in transferring the polarization to all the spins. However, the spin-diffusion time is much shorter than the Overhauser time due to the relatively weak silicon hyperfine coupling strength. In a 2.35 T magnetic field at 1.1 K, we observed a DNP enhancement of 244 ± 84 resulting in a silicon polarization of 10.4 ± 3.4% following 2 h of microwave irradiation.