Adsorption of Binary Mixtures in a Zeolite Micropore

Abstract

We investigate the selective adsorption of xenon, argon, and methane in zeolite NaA by applying the grand canonical ensemble Monte Carlo simulation technique to an adsorbed binary mixture and to two reference systems: i) an adsorbed single component system and ii) a bulk mixture. We define and calculate selectivities and excess densities due to i) mixing and ii) adsorption in terms of differences between the binary adsorbed system and these reference systems. We observe that xenon selectively adsorbs in both xenon-argon and xenon-methane mixtures at low chemical potential (low pressure) due to its greater energetic interaction with the zeolite. However, a reversal in selectivity occurs at higher chemical potential in both of these mixtures. This is due in large part to the greater efficiency in which the smaller component “packs” in the pore as compared to the bulk. We show that the crossover in selectivity occurs at a lower chemical potential for a mixture where one component can occupy regions of the porespace inaccessible to the other. We suggest that this crossover in selectivity may be a general feature of microporous adsorption.     

Phase Separations in Binary and Ternary Cholesterol-Phospholipid Mixtures

A pair of recent studies has reopened debate on the subject of phase separations in model bilayer mixtures of cholesterol (Chol) and dipalmitoyl-phosphatidylcholine (DPPC). Fluorescence microscopy methods have not been able to detect phase separations in binary DPPC-Chol mixtures that have been inferred from NMR studies. However, micron-scale phase-separated liquid domains are observed by fluorescence in ternary mixtures of DPPC, Chol, and diphytanoyl-phosphatidylcholine (DiPhyPC). Here, a model of condensed complexes of Chol and DPPC is used to account for these results. In particular, it is shown that the orientation of tie-lines in ternary mixtures of DiPhyPC/DPPC/Chol is compatible with phase separation in binary DPPC/Chol mixtures.     

Quantitation of pH-induced Aggregation in Binary Protein Mixtures by Dielectric Spectroscopy

This paper presents a quantitative approach for measuring pH-controlled protein aggregation using dielectric spectroscopy. The technique is demonstrated through two aggregation experiments, the first between ??-lactoglobulin (??-Lg) and hen lysozyme (HENL) and the second between bovine serum albumin (BSA) and HENL. In both experiments, the formation of aggregates is strongly dependent on the solution pH and is clearly indicated by a decrease in the measured permittivity when the second protein is added. A quantifiable lower-bound on the ratio of proteins involved in the aggregation process is obtained from the permittivity spectra. Lower-bound aggregation ratios of 83?% for ??-Lg/HENL at pH?6.0 and 48?% for BSA/HENL at pH?9.2 were consistent with turbidity measurements made on the same solutions.     

Membrane Protein Frustration: Protein Incorporation into Hydrophobic Mismatched Binary Lipid Mixtures

Bacteriophage M13 major coat protein was reconstituted in different nonmatching binary lipid mixtures composed of 14:1PC and 22:1PC lipid bilayers. Challenged by this lose-lose situation of hydrophobic mismatch, the protein-lipid interactions are monitored by CD and site-directed spin-label electron spin resonance spectroscopy of spin-labeled site-specific single cysteine mutants located in the C-terminal protein domain embedded in the hydrophobic core of the membrane (I39C) and at the lipid-water interface (T46C). The CD spectra indicate an overall α-helical conformation irrespective of the composition of the binary lipid mixture. Spin-labeled protein mutant I39C senses the phase transition in 22:1PC, in contrast to spin-labeled protein mutant T46C, which is not affected by the transition. The results of both CD and electron spin resonance spectroscopy clearly indicate that the protein preferentially partitions into the shorter 14:1PC both above and below the gel-to-liquid crystalline phase transition temperature of 22:1PC. This preference is related to the protein tilt angle and energy penalty the protein has to pay in the thicker 22:1PC. Given the fact that in Escherichia coli, which is the host for M13 bacteriophage, it is easier to find shorter 14 carbon acyl chains than longer 22 carbon acyl chains, the choice the M13 coat protein makes seems to be evolutionary justified.     

Chirality Driven Twisting as a Driving Force of Primitive Folding in Binary Mixtures

Origins of Life and Evolution of Biospheres - The N-trifluoroacetylated α-aminoalcohols (TFAAAs) are able to form quasi-one-dimensional supramolecular fibers (strings) when chirally pure, and...     

Study of the Transformations of Micro/Nano-crystalline Acetaminophen Polymorphs in Drug-Polymer Binary Mixtures

This study elucidates the physical properties of sono-crystallised micro/nano-sized acetaminophen/paracetamol (PMOL) and monitors its possible transformation from polymorphic form I (monoclinic) to form II (orthorhombic). Hydrophilic Plasdone® S630 copovidone (S630), N-vinyl-2-pyrrolidone and vinyl acetate copolymer, and methacrylate-based cationic copolymer, Eudragit® EPO (EPO), were used as polymeric carriers to prepare drug/polymer binary mixtures. Commercially available PMOL was crystallised under ultra sound sonication to produce micro/nano-sized (0.2–10 microns) crystals in monoclinic form. Homogeneous binary blends of drug-polymer mixtures at various drug concentrations were obtained via a thorough mixing. The analysis conducted via the single X-ray crystallography determined the detailed structure of the crystallised PMOL in its monoclinic form. The solid state and the morphology analyses of the PMOL in the binary blends evaluated via differential scanning calorimetry (DSC), modulated temperature DSC (MTDSC), scanning electron microscopy (SEM) and hot stage microscopy (HSM) revealed the crystalline existence of the drug within the amorphous polymeric matrices. The application of temperature controlled X-ray diffraction (VTXRPD) to study the polymorphism of PMOL showed that the most stable form I (monoclinic) was altered to its less stable form II (orthorhombic) at high temperature (>112°C) in the binary blends regardless of the drug amount. Thus, VTXRD was used as a useful tool to monitor polymorphic transformations of crystalline drug (e.g. PMOL) to assess their thermal stability in terms of pharmaceutical product development and research.     

Taste Responses to Binary Mixtures of Amino Acids in the sea catfish, Arius felis

In vivo electrophysiological recordings in the sea catfish,Arius felis, showed that the magnitude of the integrated facialtaste responses to binary mixtures of amino acids was predictablewith knowledge obtained from previous cross-adaptation studiesof the relative independence of the respective binding sitesof the component stimuli. Each component from which equal aliquotswere drawn to form the mixtures was adjusted in concentrationto provide for approximately equal reponse magnitudes. The magnitudeof the taste responses to binary mixtures whose component aminoacids showed minimal cross-adaptation was significantly greaterthan that to binary mixtures whose components exhibited considerablecross-reactivity. There was no evidence for mixture suppression.The relative magnitude of the taste responses in the sea catfishto stimulus mixtures is similar to that previously reportedfor olfactory receptor responses in the freshwater channel catfishand chorda tympani taste responses in the hamster. Chem. Senses21: 45–53, 1996.     

The Effect of Sweeteners on Perceived Viscosity

Two different sweeteners, sucrose and aspartame, were matchedin perceived sweetness intensity. These solutions were thickenedwith carboxymethylcellulose to six different viscosity levels.Sucrose and aspartame appeared to decrease perceived viscosityof the solutions at a specific sweetener concentration, at allviscosity levels. However, in a second similar experiment withthree viscosity levels and seven sucrose concentrations no effectof sucrose concentration on perceived viscosity was found. Reasonsfor these conflicting results are discussed. No definite conclusionsabout the effect of sweeteners on perceived viscosity can asyet be drawn. Chem. Senses 20: 441–450, 1995.     

An Alternative Ionic Conductivity Mechanism for Plastic Crystalline Salt–Lithium Salt Electrolyte Mixtures

The phase behavior and ionic conductivity of tetraethylammonium bis(trifluoromethane‐sulfonyl)imide (Et₄NTFSI) salt mixtures with LiTFSI have been examined. In addition, the phase behavior and crystal structure of neat LiTFSI is also reported. Two (1‐x) Et₄NTFSI‐(x) LiTFSI (x = 0.50 and 0.67, where x is the mol fraction) mixed‐salt crystalline phases form. Large variations in ionic conductivity are observed; these are attributed to solid‐solid phase transitions of the neat Et₄NTFSI salt creating disordered plastic crystalline phases and the formation of a low‐melting eutectic composition between the neat Et₄NTFSI salt and the 1/1 Et₄NTFSI/LiTFSI (x = 0.50) phase. Although Et₄NTFSI and LiTFSI melt at 102 and 234 °C, respectively, the two salts form a eutectic system with a melting temperature of 32 °C. Based upon the findings reported, a new conductivity mechanism is proposed for plastic crystalline salt‐lithium salt electrolytes which is not ascribed to solid‐state diffusion/conduction.     

Toxicity of Binary Mixtures of Enantiomers in Chiral Organophosphorus Insecticides: The Significance of Joint Effects Between Enantiomers

The existence of enantiomer‐enriched mixtures of chiral pesticides in the environment is overwhelmingly positive. However, interactions between enantiomers have not been considered so far in risk assessments. Here, we chose three organophosphorus pesticides as representative chiral pesticides to investigate the possible interaction mode between each pair of enantiomers both in in vivo and in vitro. Data show that the enantiomers of methamidophos and profenofos have a simple additive effect, <zaq;1> whereas fensulfothion acts as an antagonist in AChE‐inhibition model. In contrast, enantiomers of methamidophos and fensulfothion had an additive effect in an acute toxicity test against Daphnia magna. A synergistic effect was observed in the joint toxicity of the profenofos enantiomers. The ability for enantiospecific biodegradation in the in vivo model contributed to the different interaction observed between the in vitro and in vivo models. Moreover, binding affinities were suspected as another reason for the different mode of action of mixture enantiomers. Our study recommends using a joint research model to treat chiral compounds in the real environment. Chirality 25:787–792, 2013. © 2013 Wiley Periodicals, Inc.     

Psycho-Socioeconomic Factors Affecting Complementary and Alternative Medicine Use among Selected Rural Communities in Malaysia: A Cross-Sectional Study

Introduction

The use of complementary and alternative medicine (CAM) as a source of cure has gained much spectrum worldwide, despite skeptics and advocates of evidence-based practice conceptualized such therapies as human nostrum.

Objective

This study aimed to explore the factors affecting CAM use among rural communities in Malaysia.

Methods

A cross-sectional study was carried out on 288 occupants across four rural villages within the District of Selama, Perak, Malaysia. A survey that consisted of socio-economic characteristics, history of CAM use and the validated Holistic Complementary and Alternative Medicine Questionnaire (HCAMQ) were used.

Results

The prevalence of self-reported CAM use over the past one year was 53.1%. Multiple logistic regression analyses yielded three significant predictors of CAM use: monthly household income of less than MYR 2500, higher education level, and positive attitude towards CAM.

Conclusion

Psycho-socioeconomic factors were significantly associated with CAM use among rural communities in Malaysia.     

Enhancement of Synthetic Trichoderma-Based Enzyme Mixtures for Biomass Conversion with an Alternative Family 5 Glycosyl Hydrolase from Sporotrichum thermophile

Enzymatic conversion of lignocellulosic materials to fermentable sugars is a limiting step in the production of biofuels from biomass. We show here that combining enzymes from different microbial sources is one way to identify superior enzymes. Extracts of the thermophilic fungus Sporotrichum thermophile (synonym Myceliophthora thermophila) gave synergistic release of glucose (Glc) and xylose (Xyl) from pretreated corn stover when combined with an 8-component synthetic cocktail of enzymes from Trichoderma reesei. The S. thermophile extracts were fractionated and an enhancing factor identified as endo-β1,4- glucanase (StCel5A or EG2) of subfamily 5 of Glycosyl Hydrolase family 5 (GH5_5). In multi-component optimization experiments using a standard set of enzymes and either StCel5A or the ortholog from T. reesei (TrCel5A), reactions containing StCel5A yielded more Glc and Xyl. In a five-component optimization experiment (i.e., varying four core enzymes and the source of Cel5A), the optimal proportions for TrCel5A vs. StCel5A were similar for Glc yields, but markedly different for Xyl yields. Both enzymes were active on lichenan, glucomannan, and oat β-glucan; however, StCel5A but not TrCel5A was also active on β1,4-mannan, two types of galactomannan, and β1,4-xylan. Phylogenetically, fungal enzymes in GH5_5 sorted into two clades, with StCel5A and TrCel5A belonging to different clades. Structural differences with the potential to account for the differences in performance were deduced based on the known structure of TrCel5A and a homology-based model of StCel5A, including a loop near the active site of TrCel5A and the presence of four additional Trp residues in the active cleft of StCel5A. The results indicate that superior biomass-degrading enzymes can be identified by exploring taxonomic diversity combined with assays in the context of realistic enzyme combinations and realistic substrates. Substrate range may be a key factor contributing to superior performance within GH5_5.     

利用毛细管电泳法分析甜菊糖苷的含量

本文介绍了一种用毛细管区带电泳法筛选甜菊糖苷突变体的有效方法。根据实验结果,优化的电泳条件为60mmol/LTris-硼酸缓冲液(pH8.0),柱温30℃,工作电压25kV。优化条件下,甜菊苷(Stevioside)迁移时间的R.S.D为0.45%(15次),且在7.45×10