Properties and performance of novel high-resolution/high-permeability ion-exchange media for protein chromatography

There is continued interest in the development of stationary phases for protein chromatography that can provide high resolution at elevated flow rates of the mobile phase. When using porous particles, resolution and dynamic binding capacity decline rapidly as the flow rate is increased. Monolithic columns have been developed to overcome these limitations. However, there are difficulties in manufacturing homogeneous larger scale monoliths. In this paper we investigate the morphology and performance characteristics of columns based on new ion exchangers obtained by mechanically disrupting continuous beds of acrylamido-based polymeric media. Near colloidal suspensions of loose particles obtained with this procedure can be flow-packed in ordinary chromatography columns resulting in beds of unexpectedly high hydraulic permeability. Columns up to 2.2 cm in diameter were studied with both Q and S functionalized media. The hydraulic permeability and interparticle porosity of these columns were rather high. The permeabilities of the S and Q media were 1.5 x 10(-13) and 2.4 x 10(-13) m2, respectively, while the corresponding porosities were 60 and 70%. These porosity values are similar to those of monoliths, suggesting that these particles assemble under flow to give high-porosity bridged structures. The structure of these packed beds was further characterized by embedding small packed columns in resins and obtaining sections for microscopic observation. The sections reveal the presence of small aggregates of non-porous 1-3 microm particles, surrounded by flow channels several micrometers in size. The height equivalent to a theoretical plate under isocratic and gradient elution conditions and the dynamic binding capacity were determined for several proteins and were found to be virtually independent of flow.     

Comparison of permeation resistance of protective gloves to organic solvents with ISO, ASTM and EN standard methods

In this study, the permeation resistance of nitrile and neoprene gloves to benzene and 1,2-dichloroethane was investigated using two permeation cells according to the ISO 6529, ASTM F739, and EN 374-3 standard test methods. The permeability coefficients were found to significantly increase with the flow rate of the collection medium. The appropriate flow rate of nitrogen collection should be higher than 75 and 150 mL/min for the ISO 6529 and ASTM F739 cells, respectively. For an open-loop system, the permeability coefficient of the ISO 6529 cell was obviously greater than that of the ASTM F739 cell, and the difference between these two cells was statistically significant. On the other hand, the breakthrough time was about 20–30 min for either the ISO 6529 or ASTM F739 cell at different flow rates of nitrogen collection. Fick's diffusion coefficient and solubility of permeant in the polymer glove can be specified as alternative test results for standard methods.     

Thermal stability and permeability of microencapsulated n-octadecane and cyclohexane

Microencapsulated phase change materials (MicroPCMs) used as thermal insulating coating and fabrics are usually required to have a prominent thermal stability and a lower permeability. MicroPCMs with a prominent thermal stability and a lower permeability were fabricated by feeding an appropriate content of cyclohexane into n-octadecane followed by heat-treatment at a suitable condition. Microcapsules containing 18-19% reserved expandable space are synthesized at 30-40 wt.% cyclohexane in the oil phase, which have a highest thermal resistant temperature −270 °C, and a lower permeability, less than 1.2%. The weight loss of microcapsules is mainly attributed to the leakage of n-octadecane from some broken capsules, so improving their uniformity can efficiently enhance their thermal stability and lower the permeability.     

双醚二酐型聚醚酰亚胺的透气性能与分子结构之间关系的研究Ⅰ

合成了一系列双醚二酐型聚醚酰亚胺（ＰＥＩ），研究了它们对Ｈ２、ＣＯ２、Ｏ２、Ｎ２和ＣＨ４五种气体的透过性能与分子结构的关系．结果表明，这类聚醚酰亚胺的分子结构对其透气性和透气选择性有很大的影响，聚合物的自由体积和链段活动性是控制透气性和透气选择性的主要因素。三种带有酰亚胺键邻位取代基的聚醚酰亚胺（ＨＱＤＥＡ—ＤＭｏＢＤＡ、ＨＱＤＥＡ—ＤＭＭＤＡ和ＨＱＤＥＡ—ＤＭｏＭＤＡ）具有较大的自由体积和较小的链段活动性、很高的透气性和透气选择性。     

Transport of organic and inorganic solutes through charged mosaic composite membranes

A template pattern with alternating poly(4-vinylpyridine) (P4VP)/poly(vinyl alcohol) (PVA) lamellae was fabricated upon a microporous poly(vinyl chloride) (PVC) membrane by casting of poly[4-vinylpyridine(4VP)-g-vinyl alcohol (VA)] graft copolymer. After a treatment of both binding of microporous membrane with graft copolymer and domain fixing of the PVA matrix, a dilute solution of poly[acrylic acid (AA)-benzyl N,N-dimethyldithiocarbamate (DMTC)]/P4VP or poly[sodium p-styrenesulfonate (SSS)-DMTC]/P4VP binary blend was cast on this template surface. Two types of weak acid/strong base or strong acid/strong base microdomains formed by phase growth were oriented perpendicularly to the membrane surface. After the chemical treatments: introduction of the charge and domain fixing of ion exchange regions, two types of such mosaic microdomains could be constructed on a microporous membrane. We studied the transport behaviors of organic and inorganic solutes through charged mosaic composite membranes. The permeability of inorganic electrolyte, such as KCl was about 20-fold compared to those of organic nonelectrolytes, such as glucose and sucrose. l-Phenylalanine exhibits a low value of permeability at the pH of its isoelectric point.     

Comparison of permeability coefficients of organic vapors through non-porous polymer membranes by two different experimental techniques

The permeability coefficients of saturated and non-saturated vapors of benzene, hexane and cyclohexane through flat polymer membranes (low density polyethylene BRALEN FB2-30 and polyether-block-amide PEBA 4033-PE) by two different experimental techniques at 298.15 K are reported. The permeation data have been obtained using the differential flow permeameter and sorption ones by glass sorption apparatus with McBain’s spiral balance. The so-called stationary (steady) diffusion theory has been applied for evaluating the permeability coefficients from sorption (equilibrium) data and obtained values have been compared with the permeability coefficients from permeation (steady-state) measurements. In the case of relative lower vapors sorption in polymers (hexane and cyclohexane) good agreement between permeability coefficients from sorption and permeation is obtained. Hence, this paper proves the possibility to estimate the permeability coefficients of organic vapors from sorption data without need of performing the permeation experiments.     

Partial volume effect compensation for improved reliability of quantitative blood-brain barrier permeability

INTRODUCTION: Blood-brain barrier (BBB) plays an important role in the pathophysiology of many central nervous system disorders. In the past, a number of laboratory techniques have been proposed to quantify permeability coefficient, k(i), an important index of barrier function. Recently, MRI has been used to estimate k(i) based on the unidirectional tracer kinetics model in one compartment as proposed by Patlak et al. and has been found to be in good agreement with the gold standard quantitative autoradiography technique. Rapid data acquisition, a prerequisite of this MRI-based technique, causes a compromise in spatial resolution resulting in partial volume (PV) averaging, an effect that is seldom explicitly compensated for in quantitative neuroimaging studies. This may have profound effect on the reliability of estimates obtained using quantitative methods. Existing PV compensation techniques that use complex statistical algorithms perform corrections on stationary images. In this proof-of-principle study, the effect of PV averaging on BBB permeability coefficient has been evaluated using a simulation model, and a postprocessing technique that makes use of dynamic information has been proposed for PV compensation in order to improve the reliability of this quantitative method. MATERIALS AND METHODS: A computer simulation model is presented, which evaluates the effect of PV averaging on permeability coefficient estimates. Beginning with a known k(i), a PV compensation technique is proposed, which aims at correcting calculated k(i) to obtain the original estimate. The application of the PV compensation technique is demonstrated in a rat stroke brain model. Magnetic resonance imaging experiments were performed in Wistar rats (n=2) on a 4.7-T scanner. After acquiring localizer, T2-weighted and diffusion-weighted images, a rapid T1 mapping protocol was implemented to acquire one pre-gadolinium-diethylenetriaminepentaacetic acid baseline data set followed by a series of postinjection data sets. The data were postprocessed without and with application of PV compensation technique to obtain a k(i) estimate. RESULTS AND DISCUSSION: The issue of PV averaging as a result of limited spatial resolution is often not addressed in quantitative MRI studies. In this work, simulation experiments have provided useful insight into the PV effects on permeability coefficient estimate. The findings of the simulation experiments agree well with the results obtained from MR experiments. Results from the MR experiments suggest that it may be important to perform PV compensation in order to improve the reliability of permeability coefficient estimates. Future work involves classification of tissue component into gray and white matter and CSF to improve the accuracy of the compensation technique and to investigate repeatability of the technique in a larger group of animals.     

Improved oxygen barrier performance of poly(vinyl alcohol) films through hydrogen bond complex with poly(methyl vinyl ether-co-maleic acid)

Hydrogen bonding between poly(methyl vinyl ether-co-maleic acid) (PMVE-MA) and poly(vinyl alcohol) (PVOH) has resulted in films with lower oxygen transmission rates (OTR) than pure PVOH. In the range 20-30% (w/w) PMVE-MA, complexation between the two polymers in the blend was maximized, as shown by viscometry, Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analysis. OTR measurements have shown that the maximum interpolymer complexation ratio also correlates with the lowest OTR values of the resulting film. The improved oxygen barrier properties are believed to be a combination of the relatively intact PVOH crystalline regions as shown with X-ray diffraction (XRD) and a higher degree of hydrogen bonding in the amorphous regions of the PVOH and PMVE-MA films as indicated by glass transition temperature (T_g) shifts. This leads to denser amorphous regions that reduces the rate of gases diffusing through the polymer film, hence the reduced OTR.     

Uptake and effect of mercury on amino acid losses from the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis

Inorganic mercury (Hg(2+)) and herbicides are important contaminants of world water systems with effects on aquatic organisms and humans. The uptake of Hg(2+) and glycine by the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis was determined. Additionally, the effects of glycine, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4-dinitrophenol (DNP) on the uptake of Hg(2+) were also determined. The loss of primary amines from the excised gills of both species was measured in the presence and absence of Hg(2+) or MeHg(+). The results indicate that (1) the uptake of Hg(2+) is approximately equivalent in both species; (2) comparison of the uptakes with that of inulin, which occupies only extracellular space, shows that Hg(2+) is taken up; (3) the uptake of Hg(2+) is slightly altered by the presence of glycine and herbicides such as 2,4-D and DNP; (4) the rate of loss of primary amines was highly increased relative to the control by the presence of Hg(2+) and to a lesser extent MeHg(+) for both species. These results showed that both inorganic and MeHg(+) are effective in disrupting the permeability of cell membranes, causing leakage of essential amino acids from the cell. This could result in discharge of potential gradients, reduced efficiency of energy coupling, and consequently cell death.     

Physical immobilization of laccase on an electrode by means of poly(ethyleneimine) microcapsules

Microcapsules of poly(ethyleneimine) were used to immobilize laccase on the surface of an electrode and its mediated electron transfer was studied with the redox mediator p-phenylenediamine (PPD). The microcapsules consisted of a cross-linked PEI wall generated from an emulsion of an aqueous phase containing the enzyme. The reaction of encapsulated laccase with PPD was studied by spectrophotometry and oxygen consumption. We found that the encapsulation resulted in a small shift for the optimum pH and a lower K_m value when compared to free laccase. These differences are attributed to the charged micro-environment offered by the microcapsules. The microcapsules were then deposited on a glassy carbon electrode and chronoamperometry was used to evaluate the mediated electron transfer between the enzyme and the electrode. No significant differences in term of optimum pH and K_m occurred upon capsules deposition on the electrode. The response time of the electrode for PPD oxidation was higher than those found in the literature, which suggests that the PEI capsule wall offers some resistance to mediator permeation, an hypothesis that was verified by RDE measurements. The charged nature of the PEI membrane appeared to affect several parameters of the laccase-mediator reaction and the effect of pH and mediator charge on this reaction are reported. The immobilization platform under study can be applied to different enzyme-mediator systems than the laccase-PPD used here and is relevant to the development of bioelectrocatalytic systems.