Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “phasing”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed2002

On-line coupling of miniaturized solid-phase extraction and microcolumn liquid-phase separations.

On-line coupling of miniaturized solid-phase extraction methods and microcolumn separation techniques are reviewed. A conventional solid-phase micro-extraction device and fiber-in-tube solid-phase extraction was employed as the sample preparation method. In the fiber-in-tube technique, a novel fibrous polymeric material was introduced as the extraction medium for the microscale sample preparation step which could be directly coupled with microcolumn liquid-phase separation systems, such as microcolumn liquid chromatography, capillary electrophoresis, and capillary electrochromatography. The applications of these hyphenated systems, consisting of the sample preparation and separation processes, are also reviewed.

Capillary Action↗
PubMed2004

Selectivity of long chain stationary phases in reversed phase liquid chromatography.

A series of commercial monomeric and polymeric C(18), C(27), and C(30) stationary phases were compared with immobilized poly(ethylene-co-acrylic acid) stationary phases synthesized in-house. The columns were characterized on the basis of methylene selectivity, silanol activity, metal activity, pore size, shape selectivity, and the ability to separate tocopherol isomers and carotenoid isomers. Monomeric and polymeric C(30) phases were shown to yield excellent separations of the tocopherol isomers while the polymeric C(30) and polyethylene phases were more appropriate to the separation of carotenoids.

Acrylic Resins↗
PubMed2003

The facile HPLC enantioresolution of amino acids, peptides on naphthylethylcarbamate-beta-cyclodextrin bonded phases using the acetonitrile-based mobile phase after their pre-column derivatization with phenyl isothiocyanate: factors that affect the resolution.

A variety of alpha-amino acids are enantioresolved for the first time on naphthylethylcarbamate-beta-cyclodextrin bonded phases (i.e., SN- and RN-beta-CD) using the acetonitrile-based mobile phase after their pre-column derivatization with phenyl isothiocyanate in alkaline medium. The resolution is better obtained on RN-beta-CD phase and fails to reproduce if the amino acid is N-benzoylated or N-carbobenzyloxylated under the same chromatographic conditions. The enhanced resolution is believed to be due to the re-location of the hydrogen receptor site from sulfur to nitrogen on the isothiocyanyl fragment of derivatizing reagent, which in turn changes the enantioselectivity. Also, the sulfur atom is larger in size and subject to steric hindrance more significantly in comparison with oxygen. The carboxyl group of amino acid is essential toward a satisfactory resolution. The position of the amino group on the backbone affects the resolution as well. Finally, the resolution is either not observed or unsatisfactory in the reversed- or normal phase mode for most of the amino acids examined in this study.

Acetonitriles↗
PubMed2004

The HPLC resolution of N-2,4-dinitrophenylated amino acids and peptides stereoisomers on naphthylethylcarbamate-beta-cyclodextrin bonded phase using the acetonitrile-based mobile phase: evidence for the chiral recognition pattern.

A facile method of enantioresolving a variety of alpha-amino acids and peptides on naphthylethylcarbamate-beta-cyclodextrin bonded phases (i.e., SN- and RN-beta-CDs) under the elution of acetonitrile-based mobile phase makes use of 2,4-dinitrofluorobenzene (DNFB) as the tagging reagent, which undergoes nucleophilic substitution by the free amino group in alkaline medium to give a N-2,4-dinitrophenyl (DNP) derivative. The resolution is better obtained on RN-beta-CD phase and fails to reproduce on the intact beta-cyclodextrin bonded phase under the same chromatographic conditions, which strongly suggests that the observed resolution should be due to the interaction of analyte with naphthylethylcarbamate moiety, not with the residual secondary hydroxyl groups on the beta-cyclodextrin.

Acetonitriles↗
PubMed1986

Solid-phase sequencing on the gas-phase sequencer.

Automated Edman degradation has been successfully used for determining the primary structure of numerous peptides and proteins. Quantitative solid-phase Edman degradation has great potential use for amino acid sequence analysis of synthetic peptides assembled on resin support by the Merrifield procedure. We report here the combined use of a modified gas-phase sequencer program and our improved reversed-phase HPLC analysis for PTH-amino acids to carry out the sequence analysis on synthesized peptide resins. This approach is far more sensitive than using glass beads on the conventional solid-phase sequencer. The peptide was assembled on copoly (styrene-1% divinylbenzene) resin beads at an initial substitution of 0.54 mmol/g. On a routine basis, 10-15 resin beads are used, and a repetitive yield of 94% is obtained: as few as 4 beads can be successfully sequenced. The HPLC PTH-amino acid analysis is sensitive down to subpicomole quantities. This procedure offers a sensitive and rapid analytical tool for checking the purity of peptides as they are being assembled on solid support.

Amino Acid Sequence↗
PubMed1975

Identification of the 120 mus phase in the decay of delayed fluorescence in spinach chloroplasts and subchloroplast particles as the intrinsic back reaction. The dependence of the level of this phase on the thylakoids internal pH.

After a 500 mus laser flash a 120 mus phase in the decay of delayed fluorescence is visible under a variety of circumstances in spinach chloroplasts and subchloroplast particles enriched in Photosystem II prepared by means of digitonin. The level of this phase is high in the case of inhibition of oxygen evolution at the donor side of Photosystem II. Comparison with the results of Babcock and Sauer (1975) Biochim. Bio-phys. Acta 376, 329-344, indicates that their EPR signal IIf which they suppose to be due to Z+, the oxidized first secondary donor of Photosystem II, is well correlated with a large amplitude of our 120 mus phase. We explain our 120 mus phase by the intrinsic back reaction of the excited reaction center in the presence of Z+, as predicted by Van Gorkom and Donze (1973) Photochem. Photobiol. 17, 333-342. The redox state of Z+ is dependent on the internal pH of the thylakoids. The results on the effect of pH in the mus region are compared with those obtained in the ms region.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1983

Polymorphic phase behaviour of dilinoleoylphosphatidylethanolamine and palmitoyloleoylphosphatidylcholine mixtures. Structural changes between hexagonal, cubic and bilayer phases.

The polymorphic phase behaviour of dilinoleoylphosphatidyethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) is investigated by freeze-fracture electron microscopy, X-ray diffraction and 31P-NMR. The structures at 5% or less POPC are predominantly inverted hexagonal (HII), whereas at 15% or more POPC, the structure is mostly bilayer (L), interrupted by defects (lipidic particles). A cubic phase structure is observed in the transition range between H and L phases; the cubic arrangement deteriorates at higher temperatures into an amorphous aggregate of spherical units. Both cubic and amorphous structures contribute to the isotropic 31P resonance, with no preference for PC or PE partitioning in the isotropic motion as observed by high resolution NMR. The existence of the cubic phase seems to depend cirtically on the homogeneity and the degree unsaturation of the phospholipids.

Freeze Fracturing↗
PubMed1985

Activities of several phase I and phase II xenobiotic biotransformation enzymes in cultured hepatocytes from male and female rats.

Hepatocytes were isolated from adult male and female rats and maintained in monolayer culture for up to 24 hr. The degree of preservation of representative phase I and phase II xenobiotic biotransformation enzymes was studied in these cells immediately after isolation, after attachment in culture, and after 24 hr in culture. Regarding phase I pathways, hepatocytes during 24 hr lost 50% of cytochrome P-450, but maintained high mixed function oxidase activities; 75% of aryl hydrocarbon hydroxylase and 65% of benzphetamine demethylase activities were preserved in hepatocytes from males, whereas in hepatocytes from females 70 and 50% of these activities, respectively, were maintained. Of phase II pathways, glutathione transferase activity after 24 hr, tested toward 1,2-dichloro-4-nitrobenzene as substrate, was diminished in male hepatocytes to 20% of the initial liver activity and in female cells, to 35%, whereas the activity tested toward 1-chloro-2,4-dinitrobenzene as substrate was stable. UDP-glucuronosyltransferase activities, tested toward p-nitrophenol and phenolphthalein as substrates, were slightly increased during 24 hr of culture of hepatocytes to levels higher than in liver before perfusion. The level of UDP-glucuronic acid, the endogenous substrate for the enzyme, was reduced after isolation to only 6% of the initial liver value, and then increased during culture to a level approximately 60% of normal. Thus, the changes in xenobiotic biotransformation enzymes and associated constituents in cultured hepatocytes were not uniform, although biotransformation capability remained reasonably intact.

Animals↗
PubMed1990

Phase I and phase II xenobiotic biotransformation in cultures and co-cultures of adult rat hepatocytes.

The aim of this study was to measure the activity of phase I and II key enzymes in the biotransformation of xenobiotics and their inducibility by phenobarbital (2 mM) in two currently used in vitro models, namely adult rat hepatocytes, conventionally cultured or co-cultured with rat epithelial cells derived from primitive biliary duct cells. For phase I, the cytochrome P450 content and the enzymic activities of 7-ethoxycoumarin O-deethylase and aldrin epoxidase have been determined, for phase II glutathione S-transferase activity was measured. In conventional cultures, all phase I parameters investigated declined continuously as a function of culture time. Two mM phenobarbital had inducing effects on 7-ethoxycoumarin O-deethylase and glutathione S-transferases but not on aldrin epoxidase. In co-cultures, after an initial decrease, a steady state situation developed for all the parameters measured, lasting for at least 10 days. The cytochrome P450 content, the 7-ethoxycoumarin O-deethylase, aldrin epoxidase and glutathione S-transferase activities were maintained from 3 to 4 days on at 25, 100, 15 and 50%, respectively, of their corresponding value obtained for freshly isolated hepatocytes. After phenobarbital treatment, the parameters mentioned were significantly increased with the exception of the aldrin epoxidase activity of which the inducibility was nearly completely lost.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1994

Phases and phase transitions of the hydrated phosphatidylethanolamines.

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset referring to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38-year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.

Chemical Phenomena↗
PubMed1976

Differences in the mode of exucative reaction between early phase and late phase of carrageenin-induced inflammation in rats.

Differences in the mode of vascular permeability change induced by some stimulants such as chemical mediators between the early phase and the late phase of the carrageenin-induced granulomatous inflammation were investigated with the aid of 131I-human serum albumin as an indicator for the measurement of vascular permeability. In the early pregranulomatous phase of the inflammation, histamine injection into the inflammation locus markedly elevated local vascular permeability, while prostaglandins E1 and E2 showed no effect. On the other hand, in the late phase of the inflammation, where permanent granuloma tissue had been formed, prostaglandins E1 and E2 significantly enhanced the local vascular permeability, while histamine was inert.

Animals↗
PubMed1993

Studies on a new cross-axis coil planet centrifuge for performing counter-current chromatography. I. Design of the apparatus, retention of the stationary phase, and efficiency in the separation of proteins with polymer phase systems.

An improved model of the cross-axis synchronous flow-through coil planet centrifuge has been designed in light of previous studies. The apparatus has a versatile feature in that both analytical and preparative columns can be accommodated in both off-center and central positions. Each has merit in separations. Retention of stationary phase was examined with various two-phase solvent systems used for the separation of biopolymers. Both analytical and preparative columns showed satisfactory retention of the stationary phase under optimum conditions. The apparatus was evaluated in separation of a set of protein samples using a polyethylene glycol-potassium phosphate biphasic system. In both types of columns all proteins were resolved with partition efficiencies of 260 to 670 theoretical plates. Further studies indicated that the relatively low partition efficiency of proteins is mainly attributed to their high molecular mass or molecular heterogeneity within each species rather than due to the high viscosity of the polymer phase system.

Centrifugation↗
PubMed1994

Spatial scale dependent in-phase and anti-phase directional biases in the perception of self-organized motion patterns.

A long row of evenly spaced dots is displaced on successive frames by half the distance between the dots. Although these stimuli are directionally ambiguous, spatially and temporally coherent unidirectional and oscillatory motion patterns are perceived as a result of the temporal persistence of competing in-phase and anti-phase directional biases, respectively. The perceiver's spatial scale is critical is determining whether dots are near enough to favor an in-phase bias or far enough apart to favor an anti-phase bias. The results are explained by a differential-gradient model of cooperative interaction, which specifies that the strength of facilitating (excitatory) interactions among motion detectors with similar directional selectivity falls off with distance at a greater rate than the strength of competing inhibiting interactions.

Distance Perception↗
PubMed1991

Progress report of a phase II and a phase III trial with etanidazole (SR-2508): a multicentre European study.

A group of 6 European cancer centers, coordinated by the Institut Gustave-Roussy, began a phase II trial of the radiosensitizing drug, etanidazole, in November 1986. The trial was designed to study the toxicity of the drug and the feasibility of a phase III trial on the combination of etanidazole with radiotherapy for treating head and neck squamous cell carcinomas. Thirty-one patients were included in the phase II trial between November 1986 and June 1987; 25 completed the whole course of treatment. Most of the neuropathies occurred during the two weeks following radiotherapy, but had no major effect on radiotherapy itself. The area under the curve (AUC) was measured in 22 patients; there was no correlation between total AUC and the incidence of neuropathy, although there was a trend towards more neuropathies at high total AUC. The toxicity of Eta did not appear excessive. A phase III trial was therefore begun in July 1987. Twenty-nine centers in 5 European countries (France, Italy, Germany, Austria and the UK) took part. A total of 330 patients had been enrolled by the end of November 1989. This report presents the results available to date. 15% of the patients treated with Eta plus radiotherapy have received less than 15 Eta injections, mainly because of skin rashes (5%), peripheral neuropathies (3%) or patient refusal (3%). The overall frequency of neuropathies was 27%, but most were grade I and occur mainly after treatment. There were similar percentages of radiotherapy-related toxicities, mainly acute reactions in irradiated normal tissues, in both Eta and control arms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Analysis of benzodiazepines and tricyclic antidepressants in serum using a common solid-phase clean-up and a common mobile phase.

A single, rapid and specific solid-phase clean-up procedure was developed for the analysis of benzodiazepines and tricyclic antidepressants using a carefully selected wash step and specific sequential elution. Benzodiazepines were eluted from the solid-phase column using as mixture of water-methanol-acetonitrile (2:3:3) followed by the elution of tricyclic antidepressants with methanol containing 0.6% diethylamine. A 30% solution of acetonitrile in phosphate buffer containing dimethyloctylamine was used as a common isocratic mobile phase for the analysis of benzodiazepines and tricyclic antidepressants on a reversed-phase column and detection was carried out at 242 nm. The sensitivity limit of the assay for benzodiazepines and tricyclic antidepressants was 25 ng/ml in serum with recoveries of 95-105% for benzodiazepines and 76-95% for tricyclic antidepressants. The results were linear for benzodiazepines over the range 50-2000 ng/ml and for tricyclic antidepressants over the range 25-500 ng/ml. Analysis for benzodiazepines and tricyclic antidepressants gave good precision, with a coefficient of variation of less than 5.0%. The method described here will be suitable for use in a clinical setting, where there is a concomitant use of benzodiazepines and tricyclic antidepressants.

Anti-Anxiety Agents↗
PubMed1996

Protein partition between the different phases comprising poly(ethylene glycol)-salt aqueous two-phase systems, hydrophobic interaction chromatography and precipitation: a generic description in terms of salting-out effects.

The solution behaviour of selected proteins has been studied under conditions promoting precipitation, binding to mildly hydrophobic adsorbents or partition. Solvophobic theory may be used to describe these forms of protein partition. The tendency of a protein to partition therein is dependent upon surface properties of the protein solute mediated by the concentration and nature of added salts. As applied to partitioning in poly(ethylene glycol) (PEG)-salt systems this implies that linear (Brönsted) relationships apply only to proteins partitioned close to the critical point. At longer tie-line lengths protein partitioning is increasingly influenced by salting-out forces. This is confirmed by the observed behaviour of the proteins. The point at which this behaviour changes has been unambiguously defined enabling the direct comparison of phase transition of proteins during partition in all systems. The results obtained show that phase transition during adsorption and partition occur at similar concentrations of salt. This is less than that required to promote precipitation. It appears, from these limited studies, that top-phase preferring proteins are partitioned at salt concentrations above those required to cause adsorption. Proteins preferring the lower phase are partitioned at salt concentrations close to or below those required for adsorption. This raises questions regarding the solvated molecular form of the partitioned proteins and the definition of the partition coefficient.

Chemical Precipitation↗
PubMed1996

Aqueous two-phase systems with a liquid protein (bovine serum albumin) phase for partitioning of enzymes.

New aqueous liquid-liquid two-phase systems based on bovine serum albumin and sodium thiocyanate in combination with either poly(vinyl alcohol) or poly(ethylene glycol) were investigated. Phase diagrams are presented. Lactate dehydrogenase and some mitochondrial enzymes were partitioned in the systems. All the phase components used influenced, either positively or negatively, the activity of lactate dehydrogenase. The enzymes showed a strong preference for the albumin phase. Possible scientific and biotechnological uses are discussed.

Animals↗
PubMed1993

Properties of the phase-alternating phase-shift (PHAPS) multiple spin-echo protocol in MRI: a study of the effects of imperfect RF pulses.

The effects of imperfect radiofrequency (RF) pulses on the echo amplitudes from the Carr-Purcell (CP), Carr-Purcell-Meiboom-Gill (CPMG), and the PHase-Alternating Phase-Shift (PHAPS; combination of CP and CPMG) multiple spin-echo schemes were studied. Properties of the PHAPS scheme for transverse relaxation time measurements was emphasized. Numerical simulations on non-relaxing spin systems were performed to assess the properties of selective (damped sinc shaped) and nonselective refocusing pulses in terms of effective spatial selectivity and generation of secondary echo signal. Analytical solutions of the Bloch equations were applied to study the generation and propagation of stimulated echo signal caused by nonideal 180 degrees phase reversals, and the results were used to analyse the numerical simulations in terms of primary and stimulated echo components. Finally, the simulated echo train patterns from the different MSE schemes were compared with MR imaging measurements. It was found that the underestimation of T2 values by the PHAPS protocol with selective refocusing pulses is mainly an effect of an "artificial" echo amplitude decay in the CP scheme, while the CPMG scheme produces a typical even-odd echo pattern (different from corresponding echo patterns in conventional high resolution NMR). Both effects are related to the flip angle error and phase dispersion along the slice selection direction from selective RF pulses, and are not significantly influenced by stimulated echo interference for nonrelaxing spin systems. However, the presence of stimulated echoes at the time of the primary echoes implies a dependence on T1 of the PHAPS echo amplitudes. In the CPMG protocol, different gradient schemes have been implemented to defocus stimulated echoes. However, the results indicate that there exists stimulated components that will not be affected by such gradients, and that the optimization of the RF refocusing pulses then remain the main objective.

Artifacts↗