Contaminant(s) in phase-separating papers.
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Chromatography, Gas↗
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High-performance liquid chromatography of eburnane alkaloids. I. Separation on reversed phases.
Separation of eburnane alkaloids using reversed-phase high-performance liquid chromatography was investigated on muBondapak C18 in LiChrosorb RP-8 columns with acetonitrile-aqueous 0.01 M ammonium carbonate as eluent. The method can be successfully applied for the group separation of eburnane alkaloids as well as for the separation of stereoisomers and of ester homologues.
Alkaloids↗
A multinuclear solid state NMR study of the sol-gel formation of amorphous Nb2O5-SiO2 materials.
Multinuclear 1H, 13C, 17O, 29Si MAS and 93Nb static NMR is reported from a series of sol-gel prepared (Nb2O5)x(SiO2)(1-x) materials with x=0.03, 0.075 or 0.30. 13C NMR shows that by 500 degrees C the organic precursor fragments have been removed although some residual carbon remains as a separate phase. The 29Si NMR typically shows three Q-species (Q2,3,4) in the initial gels, and that with increasing heat treatment the average n of the Qn-species increases as the organic fragments and hydroxyl groups are removed. 17O shows unequivocally that the x=0.03 and 0.075 samples are not phase separated, while at the much higher niobia-content of x=0.30 Nb-O-Nb signals are readily detected, a definite indication of the atomic scale phase separation of Nb2O5. The x=0.03 and 0.075 samples heated to 750 degrees C are thus representative of amorphous niobium silicates. Comparison is made to other sol-gel prepared metal silicates especially with another Group Va metal tantalum. The effects of tantalum and niobium on the silica network are very different and it is suggested here that most of the niobium is present as NbO4, forming part of the silicate network.
Journal Article↗
Children in divorce: intervention in the phase of separation.
Divorce of their parents can create difficulties for the development of young children. The ability of children to integrate the various losses involved in the breaking up of a family is impeded by limitations of their cognitive understanding of events taking place during the separation phase. Because their thinking process is as yet immature, children often feel responsible for the divorce, and they otherwise distort the meaning of the events about them. The pediatrician can often guide and encourage parents to facilitate their children's understanding and acceptance of the changes in their lives.
Anxiety, Separation↗
L-DOPA decarboxylase association with membranes in mouse brain.
This work presents evidence on the association of active DDC molecules with membranes in mammalian brain. L-DOPA decarboxylase (DDC) is generally considered to be a cytosolic enzyme. Membrane-associated DDC was detected by immunoblotting and enzymatic assay experiments. DDC activity and immunoreactivity could be partially extracted from mammalian brain membranes by detergent. Fractionation of membranes by temperature-induced phase separation in Triton X-114, resulted in the recovery of membrane-associated DDC in separation phases where integral and hydrophobic membrane proteins separate. Treatment of membranes with phosphatidylinositol-specific phospholipase C or proteinase K, did not elute membrane-associated DDC activity, suggesting that a population of DDC molecules exist embedded within membranes. The elucidation of the functional significance of the enzyme's association with membranes could provide us with new information leading to the better understanding of the biological pathways that DDC is involved in.
Animals↗
Effects of D-amphetamine and ethanol on variable and repetitive key-peck sequences in pigeons.
This experiment assessed the effects of d-amphetamine and ethanol on reinforced variable and repetitive key-peck sequences in pigeons. Pigeons responded on two keys under a multiple schedule of Repeat and Vary components. In the Repeat component, completion of a target sequence of right, right, left, left resulted in food. In the Vary component, 4-peck sequences differing from the previous 10 produced food. d-Amphetamine (0.1-3.0 mg/kg, i.m.) was administered in two separate phases, separated by ethanol administration (1.0-2.0 g/kg, i.g.). Under control conditions, measures of variability were high in the Vary component, and lower in the Repeat component. Following administration of the highest dose of d-amphetamine, but not ethanol, response rates decreased in both components. d-Amphetamine and ethanol tended to increase overall sequence variability in the Repeat component, and had less of an effect in the Vary component. Performance in the Repeat component during Phase 2 of d-amphetamine administration was more disrupted than during Phase 1. Measures of variability and repetition based on shifts in the relative frequency distributions of the 16 possible keypeck sequences differed from those based on the overall measure of variability, highlighting the importance of considering both molar and molecular measures when assessing the effects of drugs on reinforced variability and repetition. In addition, the shifts in the relative frequency distribution of response sequences suggest that d-amphetamine produced decrements in repeat performance by decreasing discriminative control within response sequences, whereas ethanol decreased repeat performance by decreasing discriminability between components as well as discriminative control within response sequences.
Animals↗
Crystallinity and morphology in films of starch, amylose and amylopectin blends.
Films of potato starch, amylose, and amylopectin and blends thereof were prepared by solution casting and examined using X-ray diffraction, light microscopy, transmission electron microscopy, and differential scanning calorimetry. Amylose films had a relative crystallinity of about 30% whereas amylopectin films were entirely amorphous. Blending of amylose and amylopectin resulted in films with a considerably higher degree of crystallinity than could be predicted. This is explained by cocrystallization between amylose and amylopectin and possibly by crystallization of amylopectin. The crystallized material gave rise to an endotherm detected with differential scanning calorimetry. The enthalpy and peak temperature of the transition also increased as the water content decreased. When the amylose proportion in the blends was low, separate phases of amylose and amylopectin were observed by light microscopy. At higher amylose proportions, however, the phase separation was apparently prevented by amylose gelation and the formation of a continuous amylose network. The amylose network in the films, observed with transmission electron microscopy, consisted of stiff strands and open pores and became less visible as the amylose proportion decreased. The water content of the films was dependent on the microstructure and the crystallinity.
Amylopectin↗
Lipase-catalyzed biodegradation of poly(epsilon-caprolactone) blended with various polylactide-based polymers.
Poly(epsilon-caprolactone) was blended with various polylactide-based polymers and processed to films by the solution casting method. Blends of 25/75, 50/50, 75/25, 90/10, and 95/5 (w/w) poly(epsilon-caprolactone)/poly(l-lactide), a 95/5 (w/w) blend of poly(epsilon-caprolactone) with a poly(d-lactide), a 50/50 (w/w) poly(l-lactide)-poly(d-lactide) mixture, and a poly(l-lactide-co-epsilon-caprolactone) copolymer were considered comparatively. The various phase-separated films were allowed to degrade in the presence of Pseudomonas lipase, biodegradation being monitored by proton nuclear magnetic resonance, size exclusion chromatography, differential scanning calorimetry, X-ray diffraction, and environmental scanning electron microscopy. The formation of separated phases during solvent evaporation and their morphologies are discussed. The introduction of poly(l-lactide) dramatically decreased the degradation rate of poly(epsilon-caprolactone)/poly(l-lactide) blends. The higher the percentage of poly(l-lactide), the slower the degradation, while the presence of cracks and increasing the lipase concentration acted in favor of the enzymatic degradation. Long-term enzymatic degradation of the various 95/5 blends was investigated over 480 h. The poly(epsilon-caprolactone) phase was enzymatically degraded by the lipase regardless of the blend type, the degradation rate depending on the nature of the co-components.
Biodegradation, Environmental↗
Ion adsorption and lamellar-lamellar transitions in charged bilayer systems.
Using a primitive model approach, we analyze the influence of ion specific adsorption on the phase behavior of charged lamellar systems. The presence of a weak short-ranged surface potential, attracting monovalent counterions, induces a phase separation, where the separate phases have different repeat distance. If the adsorption potential is very weak, the more narrow phase never forms. An opposite behavior is found for strong surface affinities. Both Monte Carlo simulations and a recently developed correlation-corrected Poisson-Boltzmann theory are adopted, with a nearly quantitative agreement between the approaches. Different counterions are discriminated by the adsorption potential strength, and with physically reasonable values, experimental observations on these systems are well reproduced. The study highlights the importance of electrostatic correlations, even though only monovalent ions are present.
Journal Article↗
Metal ion determination by flame atomic absorption spectrometry through reagentless coacervate phase separation-extraction into lamellar vesicles.
The phase separation of lamellar vesicles of anionic surfactants in aqueous solutions and its application as a novel liquid coacervate extraction procedure was examined. Solutions of lauric acid sodium salt separate into two phases in the presence of alkaline earth metals and a water miscible cosurfactant. It is proven that the surfactant phase is built of a perplexed network of multilamellar vesicles consisting of densely packed bilayers. Several factors affecting the formation of this new phase as well as its analytical utility in the preconcentration of metallic ions were assessed on the basis of better exploitation of this new nonspecific extraction technique. In essence, although the procedure to arrive at the optimum conditions seems laborious, the delivered method is straightforward, alleviating the requirement for prereaction with a complexing agent and highly reproducible under the optimum experimental conditions. As an analytical demonstration, the method was successfully applied to the determination of Cd(2+) and Zn(2+) in natural waters. Recoveries were higher than 95%, and detection limits as low as 3 microg L(-)(1) were accomplished by preconcentrating only 10 mL of sample volume in the presence of 0.45% (w/v) anionic surfactant.
Journal Article↗
Macromolecular crowding and its consequences.
Incompatible pairs of polymers separate into two phases in aqueous solution above a few percentage points total concentration. Protein pairs can also produce phase separation, but at somewhat higher concentrations. In this chapter, we explore the effect of high background concentrations of macromolecules on phase separation of pairs of species which would not be at sufficiently high concentration to separate in the absence of the uninvolved species. Effects produced by such high background concentrations are known as macromolecular crowding. Dramatic enhancements in various association reactions due to crowding have been predicted and observed but its effects on phase separation in biological mixtures typical of the cytoplasm have not been examined. Here, we describe a calculation based on the Flory-Huggins treatment of concentrated polymer solutions that sheds some light on this issue. We find that a background of 20 wt % of a high molecular weight species greatly reduces the concentrations needed to produce phase separation in a mixture of two incompatible macromolecules if one is more hydrophobic than the other. Given the high total concentration of macromolecules in cytoplasm, it is perhaps surprising that phases have not been observed. This issue is discussed and some explanations offered.
Bacterial Proteins↗
Microdomain structure in polylactide-block-poly(ethylene oxide) copolymer films.
Structured surface is an important property of polymer biomaterials for tissue engineering, for its capacity to expose domains with different surface energy and functional groups. For this purpose, amphiphilic A-B-A block copolymers with polylactide (PLA) as A blocks and poly(ethylene oxide) (PEO 3, Mn = 3090; PEO6, Mn = 6110) as B block were synthesized by ring-opening polymerization of either L-lactide (L-LA) or DL-lactide (DL-LA), using poly(ethylene glycol)s as macroinitiators and tin(II) octanoate (Sn(Oct)2) as a catalyst. Differential scanning calorimetry (DSC) and electron microscopy were used to study the phase separation of the hydrophobic (PLA) and hydrophilic (PEO) segments in films made of the copolymers and their blends with high-molecular-weight PLA homopolymers. Hydrophilic (PEO) and hydrophobic (PLA) domains were formed at the polymer film surface due to the separation of phases. The phase separation was affected by the copolymer composition and the stereoregularity of PLA blocks in the copolymers.
Biocompatible Materials↗
X-ray diffraction analysis of isolated skin lipids: reconstitution of intercellular lipid domains.
Low- and wide-angle X-ray diffraction were used to determine the structural organization of lipids isolated from the stratum corneum extracellular matrix that forms the major water permeability barrier in mammalian epidermis. Hydrated pig skin ceramides gave a single low-angle reflection of about 62 angstroms and a wide-angle-reflection at 4.15 angstroms. The addition of either cholesterol or fatty acid, the other major lipid components of the skin stratum corneum extracellular matrix, modified this diffraction pattern, depending on the lipid mole ratios. In the absence of water, lipid mixtures exhibited lipid phase separation, as shown by low- and wide-angle reflections typical of a separate cholesterol phase. However, a hydrated 2:1:1 mole ratio of ceramide:cholesterol:palmitic acid (similar to that found in stratum corneum) produced a diffraction pattern with a single sharp wide-angle reflection at 4.10 angstroms and low-angle reflections which indexed as the first eight orders of a single repeat period of 130 angstroms. The repeat period and intensity distribution of the low-angle data were similar to those found in intact stratum corneum [White et al. (1988) Biochemistry 27, 3725-3732; Bouwstra et al. (1994) Biochim. Biophys. Acta 1212, 183-192]. Higher concentrations of cholesterol or palmitic acid resulted in lipid phase separations. The 130 angstrom repeat period decreased only about 3 angstroms as water was removed by incubation in low-relative humidity atmospheres. The 130 angstrom repeat period depended on the presence of a particular ceramide, N-(omega-acyloxy)-acylsphingosine, which is found only in the epidermis. In contrast, 2:1:1 mixtures of brain ceramide:cholesterol:palmitic acid gave reflections of 56 and 34 angstroms. These results indicate that a structure with dimensions similar to those of the lamellar repeating unit found in skin stratum corneum does not depend on the presence of protein but does depend on the presence of specific skin ceramides and appropriate concentrations of cholesterol and fatty acid.
Animals↗
Purification and characterization of the bovine pituitary luteinizing hormone releasing hormone M(r) 60,000 binding protein.
Luteinizing hormone releasing hormone (LHRH) regulates the release of luteinizing hormone and follicle stimulating hormone from the pituitary. This process takes place through interaction with high affinity membrane receptors. In addition LHRH inhibits the growth of several cancer cell lines through the interaction with M(r) 60,000 LHRH receptors. Here we describe the purification to homogeneity of the M(r) 60,000 bovine pituitary LHRH binding protein in amounts allowing N-terminal sequencing and peptide mapping. The procedure describes solubilization of luteinizing hormone releasing hormone receptors from homogenized bovine pituitaries in an active form by using the detergent Triton X-114. The receptors were retained in the Triton X-114 phase during temperature-dependent phase separation. Preparative phase separations were performed directly on solubilized bovine pituitary extracts. SDS-PAGE of the purified LHRH receptor after LHRH-immobilized affinity chromatography showed the presence of a single band with M(r) 60,000. Partial sequencing of this band after trypsin digestion of gel pieces revealed unknown sequences with a possible homology to other receptors including some G-protein coupled receptors.
Amino Acid Sequence↗
Sterol structure determines the separation of phases and the curvature of the liquid-ordered phase in model membranes.
The existence of lipid rafts in biological membranes in vivo is still debated. In contrast, the formation of domains in model systems has been well documented. In giant unilamellar vesicles (GUVs) prepared from ternary mixtures of dioleoyl-phosphatidylcholine/sphingomyelin/cholesterol, a clear separation of liquid-disordered and sphingomyelin-enriched, liquid-ordered phases could be observed. This phase separation can lead to the fission of the liquid-ordered phase from the vesicle. Here we show that in cholesterol-containing GUVs, the phase separation can involve dynamic redistribution of lipids from one phase into another as a result of a cross-linking perturbation. We found that the molecular structure of a sterol used for the preparation of GUVs determines (i) its ability to induce phase separation and (ii) the curvature (positive or negative) of the formed liquid-ordered phase. As a consequence, the latter can pinch off to the outside or inside of the vesicle. Remarkably, some mixtures of sterols induce liquid-ordered domains exhibiting both positive and negative curvature, which can lead to a new type of budding behavior in GUVs. Our findings could have implications for the role of sterols in various cell-biological processes such as budding of secretory vesicles, endocytosis, or formation of multivesicular bodies.
Cholera Toxin↗
Aqueous two-phase systems for protein separation. Studies on phase inversion.
Phase equilibrium studies were done with the PEG 400-phosphate system, obtaining equilibrium binodal lines, tie lines and phase inversion points. A method of calculation of the critical point on the binodal curve is described. The influence of the presence of NaCl in solution was studied, and the comparative results are presented. It was found that in some range of concentration the shift produced in the binodal line can be important. The rate of phase separation can be used as an indication of which of the phases is continuous. Using this method the phase inversion point can be determined in the system for each tie line. A range of ambiguity was found, where the continuity of the phases is affected not only by the composition of the mixture, but also by the fluid dynamics. Within this range, gentle agitation produces a bottom-continuous suspension. while strong agitation produces a top-continuous suspension. Two inversion points exist therefore on each tie line, delimiting on the phase equilibrium plane a region where the phase continuity depends on fluid dynamics. The convergence of this region towards the critical point can be used to control of the consistency of the experimental data.
Chemistry Techniques, Analytical↗
Suppression of ionization and optimization of assay for 3-hydroxy fatty acids in house dust using ion-trap mass spectrometry.
BACKGROUND: 3-Hydroxy fatty acids (3-OHFAs), components of lipid A of gram-negative bacteria are useful chemical markers of endotoxin. METHODS: We analyzed 3-OHFAs in house dust as trimethylsilyl (TMS) methyl ester derivatives in the electron impact ionization mode using gas chromatography ion-trap mass spectrometry. Linear calibrations with r > 0.995 were observed for all the 3-OHFA methyl ester external standards. RESULTS: Recovery efficiency experiments with house dust demonstrated that accurate quantification requires calibration curves to be subjected to phase separation and solid phase extraction (SPE) because of differing clean-up losses according to chain length of 3-OHFAs. Recovery experiments also demonstrated interference with detection of C16:0 by the ion trap, which may be due to suppression of ionization by a constituent in house dust. Interference was overcome by injecting 1:4 dilutions of derivatized samples. The range of recoveries was 89.3%-111.5% for 3-OHFAs added to house dust. The reproducibility of injections was high (CV for C14:0 = 2.36%). The limit of detection (LOD) was 0.15 ng/mg for each 3-OHFA. CONCLUSIONS: The modifications we made included: use of 3-hydroxy C11:0 and C13:0 methyl esters as internal standards, subjecting calibration standards to phase separation and SPE; addition of water to phase separation; addition of 1-pentadecanol as a carrier; injecting 1:4 diluted TMS derivatives of 3-OHFAs; and monitoring both m/z 131 and 133 ions to improve stability of area measurements for product ions. This method of optimization establishes an appropriate technique for quantification of 3-OHFAs in house dust.
Air Microbiology↗
Detection of lipid domains in docasahexaenoic acid-rich bilayers by acyl chain-specific FRET probes.
A major problem in defining biological membrane structure is deducing the nature and even existence of lipid microdomains. Lipid microdomains have been defined operationally as heterogeneities in the behavior of fluorescent membrane probes, particularly the fluorescence resonance energy transfer (FRET) probes 7-nitrobenz-2-oxa-1,3-diazol-4-yl-diacyl-sn-glycero-3-phosphoethan olamine (N-NBD-PE) and (N-lissamine rhodamine B sulfonyl)-diacyl-snglycero-3-phosphoethanolamine (N-Rh-PE). Here we test a variety of N-NBD-PEs and N-Rh-PEs containing: (a) undefined acyl chains, (b) liquid crystalline- and gel-state acyl chains, and (c) defined acyl chains matching those of phase separated membrane lipids. The phospholipid bilayer systems employed represent a liquid crystalline/gel phase separation and a cholesterol-driven fluid/fluid phase separation; phase separation is confirmed by differential scanning calorimetry. We tested the hypothesis that acyl chain affinities may dictate the phase into which N-NBD-PE and N-Rh-PE FRET probes partition. While these FRET probes were largely successful at tracking liquid crystalline/gel phase separations, they were less useful in following fluid/fluid separations and appeared to preferentially partition into the liquid-disordered phase. Additionally, partition measurements indicate that the rhodamine-containing probes are substantially less hydrophobic than the analogous NBD probes. These experiments indicate that acyl chain affinities may not be sufficient to employ acyl chain-specific N-NBD-PE/N-Rh-PE FRET probes to investigate phase separations into biologically relevant fluid/fluid lipid microdomains.
Calorimetry, Differential Scanning↗