Four-dimensional description of the structure and phase transitions of KFeF4 (phase II and superstructure phase III).
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Journal Article↗
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Dynamics of phase separation between a lyotropic dilute lamellar phase and an isotropic phase.
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Journal Article↗
[On clinical significance of the determination of the mechanical systole and of its phases (the phase of contraction and the phase of ejection)].
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Heart↗
Reversed phase ion pair chromatography with an adsorbing stationary phase and a hydrophobic quaternary ammonium ion in the mobile phase. Part II: quantitative analysis of multi-component analgesic pharmaceutical preparations.
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Analgesics↗
Combined reversed phase and anion exchange solid phase extraction for the assay of the neuroprotectant NBQX in human plasma and urine.
A combination of reversed phase and anion exchange solid phase extraction (SPE) was investigated for the liquid chromatographic assay of the neuroprotectant agent NBQX in human plasma and urine. Reversed phase SPE alone using a variety of phases failed to yield sufficiently pure extracts for the assay of plasma in the low ng/mL concentration range using UV detection. However, using Bond Elut Certify II SPE columns containing a mixture of reversed phase and anion exchange functionalities markedly improved the purity of plasma extracts. Furthermore, a change of detector wavelength from UV (294 nm) to the visible region (380 nm) removed some minor interfering peaks originating from plasma. Using optimized SPE conditions with an extraction recovery of 92.3% and a high performance liquid chromatographic procedure with Lichrospher C18 as the stationary phase, the lower limit of quantitation in human plasma was 2 ng/mL (corresponding to 0.75 ng injected on-column). Intra-assay coefficients of variation ranged from 9.6% at 2 ng/mL to 1.3% at 10 ng/mL. A similar SPE procedure was applied to human urine with acceptable recovery (88.3%), but an analytical column of different selectivity (Chromspher B C18) was necessary in order to avoid interference from the urine. The limit of quantitation for the urine assay was 25 ng/mL and the intra-assay precision ranged from 4.6% at 25 ng/mL to 2.2% at 500 ng/mL.
Chromatography, High Pressure Liquid↗
Semiautomated method for noise reduction and background phase error correction in MR phase velocity data.
Background phase distortion and random noise can adversely affect the quality of magnetic resonance (MR) phase velocity measurements. A semiautomated method has been developed that substantially reduces both effects. To remove the background phase distortion, the following steps were taken: The time standard deviations of the phase velocity images over a cardiac cycle were calculated. Static regions were identified as those in which the standard deviation was low. A flat surface representing an approximation to the background distortion was fitted to the static regions and subtracted from the phase velocity images to give corrected phase images. Random noise was removed by setting to zero those regions in which the standard deviation was high. The technique is demonstrated with a sample set of data in which the in-plane velocities have been measured in an imaging section showing the left ventricular outflow tract of a human left ventricle. The results are presented in vector and contour form, superimposed on the conventional MR angiographic images.
Blood Flow Velocity↗
The influence of the mobile phase pH and the stationary phase type on the selectivity tuning in high performance liquid chromatography nucleosides separation.
Analysis of the modified nucleosides is particularly important in the medical area because of a possibility of cancerogenic processes studies. The aim of this work was to study the selectivity tuning of modified nucleosides through the investigations of interactions analyte (modified nucleoside) <==> stationary phase <==> mobile phase. A series of homemade stationary phases with different surface properties has been utilized. All of them contain various interaction sites such as: cholesterol (SG-CHOL); n-acylamide (SG-CHOL, SG-AP); aminopropyl (SG-CHOL, SG-AP, SG-NH2, SG-MIX); cyanopropyl, phenyl, octyl (SG-MIX), octadecyl (SG-MIX, SG-C18) and silanols localized on the silica gel surface of all packings. The attempt to predict the main interactions responsible for the retention between nucleosides and stationary phase ligands was done on the basis of the elemental analysis, and proportional part of an individual ligand bonded to silica surface results. In order to study the influence of different packing types on the analyzed nucleosides retention, the relationship between pH of the mobile phase buffer and the selectivity of a stationary phase was investigated.
Chromatography, High Pressure Liquid↗
Generalized theory for two-phase ion-pair and complexometric titrations. II. Two-phase titrations with side reactions.
For the two-phase titration based on ion-pair and metal-complex formation full attention is given to side reactions in both phases. Their significance for the applicability of this type of titration is evaluated. Side reactions in the aqueous phase diminish and in the organic phase promote the 'titratability'. Equations for the calculation of the side reaction coefficients, the titration curve and the selection of the optimal pH and minimal side reaction interference (in the aqueous phase) are presented. Finally a full description is given of the two-phase titration including all parameters determining the 'titratability'. The merits of the developed theory are illustrated by literature examples.
Chemical Phenomena↗
High-frequency transcranial magnetic stimulation of the supplementary motor area reduces bimanual coupling during anti-phase but not in-phase movements.
Previous electrophysiological and neuroimaging studies have provided evidence that the supplementary motor area (SMA) has an important role in the control of bimanual coordination. The present experiment investigated the effects of high-frequency repetitive transcranial magnetic stimulation (rTMS) over the SMA region on kinematic variables during cyclical bimanual coordination, with a particular focus on the quality of coordination. Subjects performed metronome-paced trials of in-phase and anti-phase bimanual index-finger movements at near-maximal cycling frequency. During movement execution, rTMS (20 Hz, 0.5 s, 120% hand motor threshold) was applied over one of three positions in the sagittal midline 2.0, 4.0 and 6.0 cm anterior to the primary motor leg area. Sham rTMS was included as a control condition. After rTMS, the mean relative phase error between hands increased, but only in the anti-phase trials. The maximum increase in phase error occurred immediately after rather than during the rTMS train. The effect was largest after stimulation 4 or 6 cm anterior to the leg area of the primary motor cortex. We did not observe any changes in the variability of relative phase or in cycle duration or movement amplitude. Findings are discussed in light of recent functional models on the role of the SMA in bimanual movement control.
Adult↗
Detection of liver metastases: gadobenate dimeglumine-enhanced three-dimensional dynamic phases and one-hour delayed phase MR imaging versus superparamagnetic iron oxide-enhanced MR imaging.
The aim of this study was to compare the diagnostic performance of gadobenate dimeglumine (Gd-BOPTA)-enhanced MR imaging, including dynamic phases and one-hour delayed phase, versus superparamagnetic iron oxide (SPIO)-enhanced imaging for detection of liver metastases. Twenty-three patients with 59 liver metastases underwent Gd-BOPTA-enhanced MR imaging (unenhanced, arterial, portal, equilibrium and one-hour delayed phase) using three-dimensional volumetric interpolated imaging and SPIO-enhanced T2-weighted turbo spin-echo and T2*-weighted gradient-echo sequences on a 1.5-T unit. Three observers independently interpreted the three sets of images, i.e. Gd-BOPTA-enhanced dynamic MRI (set 1), delayed phase imaging (set 2) and SPIO-enhanced MRI (set 3). Diagnostic accuracy was evaluated using the alternative-free response receiver operating chracteristic (ROC) analysis. Sensitivity and positive predictive value were also evaluated. The mean accuracy (Az values) and sensitivity of Gd-BOPTA-enhanced delayed phase imaging (0.982, 95.5%) were comparable to those of SPIO-enhanced imaging (0.984, 97.2%). In addition, Az values and sensitivities of both imaging sets were significantly higher than those of Gd-BOPTA-enhanced dynamic images (0.826, 77.4%: p<0.05). There was no significant difference in the positive predictive value among the three image sets. Gd-BOPTA-enhanced delayed phase imaging showed comparable diagnostic performance to SPIO-enhanced imaging for the detection of liver metastases, and had a better diagnostic performance than Gd-BOPTA-enhanced dynamic images.
Adult↗
Distribution of platelet glycoproteins and phosphoproteins in hydrophobic and hydrophilic phases in Triton X-114 phase partition.
Platelets, either unlabelled, surface-labelled by the periodate NaB3H4 method or metabolically labelled with 32P were solubilized in Triton X-114 and partitioned into aqueous and detergent phases. The phases were analysed by two-dimensional polyacrylamide gel electrophoresis followed by silver-staining, fluorography or indirect autoradiography. Each of the phases contains a distinct set of proteins. The surface-labelled glycoproteins partition into the hydrophobic phase with the notable exceptions of glycoproteins Ib and GP17(5.8-6.5) and minor amounts of a few others. The phosphoproteins which undergo increased phosphorylation on platelet activation in general separate in the hydrophobic phase, while higher molecular weight phosphoproteins were principally in the hydrophilic phase. This method might be used as a first step in purifying many platelet components.
Blood Platelets↗
Inhibitor of protein synthesis phase-shifts the circadian oscillator and inhibits the light induced-phase shift of the melatonin rhythm in pigeon pineal cells.
Our recent study showed that dissociated pigeon pineal cells expressed a circadian oscillation of melatonin release which entrained to light-dark cycle and persisted under constant darkness in vitro, suggesting that pigeon pineal cells contain the circadian oscillator and photoreceptors. Six-hour pulses of anisomycin, an inhibitor of protein synthesis that acts at hte 80S ribosomal subunit, induced steady state and phase depended phase shifts of the circadian oscillation of melatonin release. The phase advances and delays were produced at CT 7.9 h and between CT 18.6 h and CT 4.5 h, respectively. The magnitudes of phase shifts were dose dependent and correlated with the magnitudes of inhibition of protein synthesis determined at CT 4.5 h. Furthermore, anisomycin blocked the light-induced phase advance. Two dimensional electrophoresis revealed that synthesis of two proteins with Mr of 17,600 and less than 5000 are stimulated by a 3-h light pulse at CT 18.6 h which corresponds to the light-induced phase advance region. These results suggest that 80S ribosomal protein synthesis is involved in normal or light-entrainment functions of the circadian oscillator in pigeon pineal cells.
Animals↗
Implications of a non-lamellar lipid phase for the tight junction stability. Part I: Influence of basic amino acids, pH and protamine on the bilayer-hexagonal II phase behaviour of PS-containing PE membranes.
Inverted lipid micelles have been proposed, among other biological functions, to constitute the structural basis of the so-called tight junctions, a special cell cell contact found in epithelia and endothelial, which act as a barrier for the paracellular solute passage. As a model system for the opening and closing of this gate, we investigated the formation of the inverted hexagonal phase (HII phase) in lipid bilayer systems consisting of egg phosphatidylethanolamine (egg PE) and mixed egg PE/bovine brain phosphatidylserine (BBPS) membranes. The formation of the HII phase was modulated by Ca2+ ions, pH, basic amino acids and protamine. The lamellar-HII phase transition temperature TH of pure egg PE membranes at pH 7.0 was lowered with increasing Ca2+ concentration. This effect was attenuated by the presence of 50 mM lysine methyl ester. In the mixed lipid system, this effect was also observed, but even more pronounced. However this effect could be compensated for by raising the Ca2+ concentration from 2 to 10 mM. This was not observed in the pure PE system. In the absence of Ca2+, lysine methyl ester and protamine lowered TH in both monocomponent and mixed lipid systems, whereas lysine caused the opposite effect. The pH-dependence of mixed lipid systems, which were investigated up to a BBPS content of 20 mol%, clearly shows that increasing PS content stabilizes the lamellar phase even at low pH. The results obtained with model membranes are discussed with respect to biological implications of the lamellar-HII phase transition for the modulation of tight junction stability.
Amino Acids↗
20-Hydroxyecdysone accelerates the flow of cells into the G1 phase and the S phase in a male accessory gland of the mealworm pupa (Tenebrio molitor).
The cells of the bean-shaped accessory glands of mealworms proliferate through the first 7 days of the 9-day pupal stage. Immediately after larval-pupal ecdysis, 25-27% of the cells were in the G1 phase, 60-65% were in the G2 phase, and the balance were in S phase. Over the first 4 days of normal development, the S fraction gradually increased, to reach its highest level in the mid-pupa at the time of the major ecdysteroid peak (Delbecque et al., 1978). Thereafter, the S fraction declined until over 95% of the cells had accumulated in G2 on Day 8. When 0-day pupal glands were explanted into Landureau's S-20 medium for 6 days, the G1 fraction remained fairly constant (25-30%) while S and the G2 fractions fluctuated. On the first day in vitro, the G2 fraction declined and the S fraction rose. On the second day in basal media, the S fraction fell and G2 rose correspondingly until 70% of the cells reached G2 when cycling stopped on the third day. With addition of 20-hydroxyecdysone to 0-day cultures, the S fraction increased quite sharply. It remained large for all 6 days of the experiment in the continuing presence of hormone. A 1-day pulse of hormone produced a transient increase in S. We blocked cell cycling with hydroxyurea in a stathmokinetic experiment and showed that 20-hydroxyecdysone accelerated the flow of cells from the G2 phase to the G1 phase by 2.5-fold. An increase in the G1 fraction was detected within 10 hr of hormone administration and the effect was dose-dependent with an ED50 of 5 X 10(-7) M for 20-hydroxyecdysone. We conclude that 20-hydroxyecdysone acts at a control point in the G2 phase. Incubation of the glands with 20-hydroxyecdysone for only 30-60 min followed by washout stimulated the flow from G2 to G1 and the effect persisted after transfer of the tissues to hormone-free media. Dose-dependent stimulation also occurred with ponasterone A (ED50 3 X 10(-9] but not with cholesterol.
Animals↗
Solid phase disruption of fluid phase equilibrium in affinity assays with ELISA.
Quantitation of antibody affinity for antigen can provide important information in assessment of the human immune response. Enzyme-linked immunosorbent assay (ELISA) methods are sufficiently sensitive to permit affinity measurements of low affinity, low titer antibody. The major assumption in using this method, that the solid phase does not influence the equilibrium of the fluid phase antibody-antigen interaction, is not strictly true. Hence, conditions must be chosen to minimize such interference, which can result in spuriously low values of affinity. The degree of solid phase interference was therefore quantitated for an ELISA that measures the affinity between antibody directed against the capsular polysaccharide of Haemophilus influenzae type b, using a monovalent 3-unit oligosaccharide prepared from polysaccharide. The solid phase antigen density had the greatest effect upon disruption of the fluid phase. The concentration of antibody chosen had a measurable but modest effect on the outcome of ELISA, whereas the time of incubation of the antibody and oligosaccharide had no demonstrable effect. By choosing the conditions of the assay carefully, it was possible to minimize interference from the solid phase, so that the measured affinity of anticapsular polysaccharide antibody for monovalent antigen was similar to that obtained with the more traditional precipitation method.
Antibody Affinity↗
Microemboli reduce phase III slopes of CO2 and invert phase III slopes of infused SF6.
We investigated the effect of increasing doses of intravenously infused glass microspheres (mean diameter 125 microns) on gas exchange in anesthetized, heparinized, mechanically ventilated goats (VT = 16-18 ml/kg). Breath-by-breath CO2 expirograms were collected using a computerized system (Study A) during the infusion of a total of 15 g of microspheres. We found a 50% decrease in extravascular lung water by indicator dilution with a corresponding doubling of alveolar dead space (VDalv). Airways deadspace (VDaw) decreased by 13 ml (10%) and mean normalized phase III slope for CO2 decreased from 0.23 to -0.08 L-1 becoming negative in 3 of 5 animals. In a second study (Study B), simultaneous breath-by-breath CO2 and infused SF6 expirograms were collected using an infrared CO2 analyzer and a mass spectrometer. Under baseline conditions VDaw for CO2 was smaller than for SF6 and the ratio of the phase III slope for SF6 to the phase III slope for CO2 was 1.39. Following embolization there were no differences in VDaw between the two gases, however, the phase III slope for CO2 became either slightly negative or extremely flat, while the phase III slope for SF6 became negative in 73% of the breaths (-0.17 L-1, P < 0.05). Negative phase III slopes have been predicted by a single path model when blood flow is confined to the most mouthward generations of the acinus (Schwardt et al., Ann. Biomed. Engin, 19: 679-697, 1991). The agreement between the numerical model and the experimental data is consistent with a serial distribution of blood flow within the acinus.
Animals↗
Comparison between aqueous-phase and gas-phase exposure protocols for determining the mutagenic potential of nitrogen dioxide and the gas fraction of welding fumes.
Nitrogen dioxide and the gas fraction of welding fumes, a complex gas mixture which contains high concentrations of nitrogen dioxide, were tested for mutagenicity in Salmonella typhimurium tester strains, TA1535 and TA1538. A comparison between 2 exposure protocols, aqueous phase and gas phase, was made to evaluate the sensitivity of each in measuring the mutagenic potential of the gases. In the aqueous-phase exposure, a suspension of cells in an isotonic salt solution was exposed by bubbling the gas through the culture. In the gas-phase exposure, the plated cells were exposed to the gas in a chamber. For both gases tested, the gas-phase exposure resulted in a higher reversion frequency than the aqueous-phase exposure. Furthermore, we found that nitrogen dioxide accounted for only a fraction of the mutagenicity observed for the gas fraction of welding fumes.
Filtration↗
A design for phase II testing of anticancer agents within a phase III clinical trial.
A design for testing new anticancer agents is proposed such that the initial testing of new agents (phase II trials) is included within the framework of a comparative clinical trial (phase III). Randomization between phase II trials and the treatment groups of the phase III trial enforces consistency of patient selection and evaluation of response criteria. Patients who progress on the phase II trials of the new agents are randomized to one of the treatments of the phase III trial. Design issues, such as sample size and power, and analysis of the proposed design, are discussed. Advantages and disadvantages of the design are illustrated by sample size calculations for a current clinical trial in advanced breast cancer.
Antineoplastic Agents↗