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At least 145 records · Page 8Linked to original sources
PubMed1985

Simultaneous high-performance liquid chromatographic stability-indicating analysis of acetaminophen and codeine phosphate in tablets and capsules.

A high-performance liquid chromatographic method has been developed for the simultaneous determination of acetaminophen and codeine phosphate for product stability studies, and release and dissolution testing of tablets and capsules. The reversed-phase method utilizes UV detection at 214 nm, a C18 column and requires a maximum of 10 min per analysis. The method has been validated for use with products containing as much as 500 mg of acetaminophen and as little as 7.5 mg of codeine phosphate. The known potential degradation products, p-aminophenol, codeine N-oxide, and codeinone are separated for quantitation simultaneous with the parent compounds. The method has been shown to be linear, reproducible, specific, sensitive and rugged.

Acetaminophen↗
PubMed1986

Three adenovirus type 8 genome types defined by restriction enzyme analysis: prototype stability in geographically separated populations.

Adenovirus type 8 strains were collected over a 19-year period from eye specimens from patients with keratoconjunctivitis. These strains were divided by restriction enzyme analysis with the endonucleases SalI, HindIII, SacI, KpnI, and SmaI into three genotypic subgroups. The prototype strain (Trim) was found throughout the United States from 1966 through 1985 and also in Taiwan and Greece in the early 1980s. Genotype 8C was identified in an arc from Maryland to Missouri to Alabama from 1971 through 1974. Genotype 8D was found only in an epidemic of eye disease among Vietnamese refugees being resettled in northwest Florida in 1975. Genotypes 8C and D were distinct from genotypes 8A and B described from Japan in 1975 through 1981. Hemagglutination tests with a battery of avian and mammalian erythrocytes did not distinguish between the genotypic subgroups. Similarly, the genotypes could not be differentiated by hemagglutination inhibition or serum neutralization tests with reference prototype antisera. The long-term prevalence of the Trim strain suggests that adenovirus type 8 has greater genetic stability than the other adenovirus types studied to date.

Adenoviridae Infections↗
PubMed1975

Immobilized glutamate oxaloacetate transaminase. Steady state kinetic analysis and stability studies.

1. Glutamate oxaloacetate transaminase (L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1) was immobilized on amino ethyl cellulose using the bifunctional reagent diethyl adipimidate. 2. The steady state kinetic analysis was performed for the particulate and the free enzyme, and the Michaelis constants measured for the amino ethyl cellulose derivative were not greatly different from those measured for the free glutamate oxaloacetate transaminase, while the latter were in good agreement with values in the literature. 3. The amino ethyl cellulose-glutamate oxaloacetate transaminase was slightly more stable than the free enzyme at 65 degrees C, but was stabilised less by polyethylene glycol than the free enzyme.

Adipates↗
PubMed1996

Environmental fluctuations and the maintenance of genetic diversity in age or stage-structured populations.

The ability of random fluctuations in selection to maintain genetic diversity is greatly increased when generations overlap. This result has been derived previously using genetic models with very special assumptions about the population age structure. Here we explore its robustness in more realistic population models, with very general age structure or physiological structure. For a range of genetic models (haploid, diploid, single and multi-locus) we find that the condition for maintaining genetic diversity generalizes almost without change. Genetic diversity is maintained by selection if a product of the form (generation overlap) x (selection intensity) x (variability in the selection regime) is sufficiently large, where the generation overlap is measured in units of Fisher's reproductive value. This conclusion is based on a local evolutionary stability analysis, which differs from the standard "protected polymorphism" criterion for the maintenance of genetic diversity. Simulation results match the predictions from the local stability analysis, but not those from the protected polymorphism criterion. The condition obtained here for maintaining genetic diversity requires fitness fluctuations that are substantial but well within the range observed in many studies of natural populations.

Aging↗
PubMed2000

A new explicit stability criterion for human periodic breathing.

The aim of this paper is to carry out a stability analysis for periodic breathing in humans that incorporates the dynamic characteristics of ventilation control. A simple CO2 model that takes into account the main elements of the respiratory system, i.e. the lungs and the ventilatory controller with its dynamic properties, is presented. This model results in a three-dimensional non-linear delay differential system for which there exists a unique equilibrium point. Our stability analysis of this equilibrium point leads to the definition of a new explicit stability criterion and to the demonstration of the existence of a Hopf bifurcation. Numericall simulations illustrate the influence of physiological parameters on the stability of ventilation. and particularly the major role of the dynamic characteristics of the respiratory controller.

Carbon Dioxide↗
PubMed1991

Size analysis and stability study of lipid vesicles by high-performance gel exclusion chromatography, turbidity, and dynamic light scattering.

Vesicles of egg phosphatidylcholine (EPC) and phosphatidic acid (EPA) were prepared by reverse-phase evaporation (REV) followed either by sequential extrusion through polycarbonate membranes with pore diameters of 0.8, 0.4, 0.2, 0.1, and 0.05 micron or by filtration through 0.8-micron cellulosic or 0.22-micron polyvinylidene fluoride (PVF) membranes. The resulting vesicles ranging from 130 to 640 nm in mean diameter (REVs) were characterized by high-performance liquid chromatography (HPLC) using a TSK G6000 PW gel exclusion column. The efficiency of this technique to determine vesicle size parameters was studied by the analysis of the chromatograms in combination with dynamic light scattering (DLS) determination of the mean diameters (MD) of the fractionated vesicles in the region of the elution profile maxima. The HPLC TSK G6000 PW gel exclusion provides a reproducible and fast method of size characterization for lipid vesicles having MD up to 1 micron, the best selectivity being obtained in the 20- to 500-nm MD range. HPLC analysis of REV's demonstrates that: (i) both the average size and polydispersity of the vesicles decrease with decreasing pore size of the membranes, cellulosic or PVF "tortuous" ones being less efficient than "straight bores" polycarbonate ones; (ii) mixed EPC/EPA REVs sequentially extruded down through 0.2-micron polycarbonate membranes are highly deformable without rupture of the bilayer; and (iii) the mean size of extruded REV's is stable for at least 1 week. The role of EPA on the size stability of mixed EPC/EPA vesicles was studied by coupling HPLC gel exclusion and turbidity analysis of pure EPC and EPC/EPA (mole ratio: 91/9) sonicated small unilamellar vesicles as a function of time. The apparent size variation of EPC vesicles observed over a week, is mainly due to their aggregation which is significantly reduced by the introduction of a small amount of EPA in the vesicle membrane.

Chromatography, High Pressure Liquid↗
PubMed1993

Analysis of stability of human upright posture based upon the measurement of the head sway.

The paper is dealing with the description of a simple and inexpensive technique for recording and measuring of the head sway during upright stance. In particular the recording system and the evaluation of the body sway data are highlighted. The objectives of the head sway signal analysis are the determination of sway components in the side-to-side (lateral) direction and forward-backward (anteroposterior) direction. It is anticipated that it will be possible to extract from the digitized data some information about the transfer characteristic and stability margin of the neuromuscular control system concerned with the maintenance of equilibrium. Additional information of potential clinical significance could be obtained by correlating the measured sway data with electromyographically determined changes in the activity of the main postural muscles. The information obtained is comparable to that gathered by more sophisticated, and more expensive conventional devices. A special feature is the easy portability of the system which permits collection of stabilometric data even in remote locations, while the analysis on which the diagnostic assessment is based can be performed at a later date in a central facility equipped with the necessary instrumentation.

Head↗
PubMed1997

Stability and analysis of 2-chloro-2'-deoxyadenosine, 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine and 2-chloroadenine in human blood plasma.

Cladribine (2-chloro-2'-deoxyadenosine, CdA) is a purine nucleoside analog with activity against lymphoproliferative and autoimmune disorders. 2-Chloro-2'-arabino-fluoro-2'-deoxyadenosine (CAFdA), a derivative of CdA with better acid stability, shows a similar in vitro spectrum of activity as CdA. 2-Chloroadenine (CAde) is the major catabolite of both CdA and CAFdA. We have developed a high performance liquid chromatography method to measure CdA, CAFdA and their metabolite CAde in plasma. This method employees an internal standard, chloroadenosine (CAdo), and a C8 solid-phase extraction to isolate and concentrate the substances. Chromatographic separation was achieved using a C8 reverse-phase column, with UV detection at 265 nm, which gives a limit of detection of 1 nmol/l for all substances. The method was reproducible with intra- and inter-assay coefficients of variations below 6% at 50 nmol/l and at 5 nmol/l below 23%. The average recoveries of CdA, CAde, CAFdA and the internal standard were higher than 70%. Stability studies of authentic patient samples show that samples containing CdA should be kept in a refrigerator or on ice to prevent degradation. Plasma containing CAde should not be kept at -20 degrees C for longer than 10 weeks before analysis. CdA and CAFdA remain almost stable during storage at -20 degrees C for 12 weeks.

Adenine↗
PubMed2001

Shape stability of sonoluminescence bubbles: comparison of theory to experiments.

Single bubble sonoluminescence (SBSL) is the brief flash of light emitted from a single, stable, acoustically forced bubble. In experiments, the maximum pressure amplitude with which a bubble may be forced is limited by considerations of spherical stability. The traditional linear stability analysis predicts a threshold for SBSL at a much lower pressure amplitude than experimental observations. This work shows that if one constructs an accurate model of the radial dynamics, the traditional linear stability analysis predicts a boundary that is in excellent agreement with experimental data.

Journal Article↗
PubMed2000

Analysis and stability study of retinoids in pharmaceuticals by LC with fluorescence detection.

Liquid chromatographic (HPLC) methods with fluorescence detection at different wavelengths were developed for measurements of retinoic acids (13-cis and all-trans) in pharmaceutical dosage forms and components of 'retinoid solution' (all-trans retinoic acid, vitamin A palmitate and beta-carotene), a galenical of 'Di Bella therapy', using reversed phase columns under isocratic conditions. The stability of all-trans retinoic acid in cream and all-trans retinoic acid and vitamin A palmitate in 'retinoid solution' was investigated. Solid-phase extraction (SPE), using C18 sorbent was applied to the analysis of retinoic acids (9-cis, 13-cis and all-trans) in the 'retinoid solution' to obtain a practical and reliable sample clean-up. The results showed that these preparations (cream and solution) can be conveniently stored in the dark (t.a. or 2-8 degrees C): under these conditions about 86-87% of the all-trans retinoic acid initial concentration in both formulations and about 73-78% of vitamin A palmitate in the 'retinoid solution' remained after 90 days, while under sunlight exposure rapid degradation of the drugs was observed.

Chromatography, High Pressure Liquid↗
PubMed1993

Analysis and stability of phenylglyoxylic and mandelic acids in the urine of styrene-exposed people.

In this work a high-performance liquid chromatographic method is described that is reliable and practical for use in routine biological monitoring of exposure to styrene. The method uses a modern diode array detection technique by which mandelic and phenylglyoxylic acids can be measured simultaneously using different wavelengths. The liquid chromatographic method was compared to a gas chromatographic method developed for the analysis of mandelic, phenylglyoxylic and para-hydroxymandelic acids. The methods gave results consistent with each other. These two methods were then used to check the stability of the main metabolites of styrene, especially of phenylglyoxylic acid, in urine samples stored at +6 degrees C or at -18 degrees C for periods up to 70 days. None of the frozen samples showed any significant decrease in the phenylglyoxylic acid concentration, whereas at 6 degrees C one of the samples showed a reduction of 46% after 1 month.

Chromatography, Gas↗
PubMed1992

The folding of an enzyme. I. Theory of protein engineering analysis of stability and pathway of protein folding.

The theory, assumptions and limitations are outlined for a simple protein engineering approach to the problem of the stability and pathway of protein folding. It is a general procedure for analysing structure-activity relationships in non-covalent bonding, including enzyme catalysis, that relates experimentally accessible data to changes in non-covalent bonding. Kinetic and equilibrium measurements on the unfolding and refolding of mutant proteins can be used to map the formation of structure in transition states and folding intermediates. For example, the ratio of the changes in the activation energy of unfolding and the free energy of unfolding on mutation is measured to give a parameter phi. There are two extreme values of phi that are often found in practice and may be interpreted in a simple manner. A value of phi = 0 implies that the structure at the site of mutation is as folded in the transition state as it is in the folded state. Conversely, phi = 1 shows that the structure at the site of mutation is as unfolded in the transition state as it is in the unfolded structure. Fractional values of phi are more difficult to interpret and require a more sophisticated approach. The most suitable mutations involve truncation of side-chains to remove moieties that preferably make few interactions with the rest of the protein and do not pair with buried charges. Fractional values of phi found for this type of mutation may imply that there is partial non-covalent bond formation or a mixture of states. The major assumptions of the method are: (1) mutation does not alter the pathway of folding; (2) mutation does not significantly change the structure of the folded state; (3) mutation does not perturb the structure of the unfolded state; and (4) the target groups do not make new interactions with new partners during the course of reaction energy. Assumptions (2) and (3) are not necessarily essential for the simple cases of phi = 0 or 1, the most common values, since effects of disruption of structure can cancel out. Assumption (4) may be checked by the double-mutant cycle procedure, which may be analysed to isolate the effects of just a pair of interactions against a complicated background. This analysis provides the formal basis of the accompanying studies on the stability and pathway of folding of barnase, where it is seen that the theory holds very well in practice.

Bacterial Proteins↗
PubMed2001

Global stability, local stability and permanence in model food webs.

The dynamical theory of food webs has been based typically on local stability analysis. The relevance of local stability to food web properties has been questioned because local stability holds only in the immediate vicinity of the equilibrium and provides no information about the size of the basin of attraction. Local stability does not guarantee persistence of food webs in stochastic environments. Moreover, local stability excludes more complex dynamics such as periodic and chaotic behaviors, which may allow persistence. Global stability and permanence could be better criteria of community persistence. Our simulation analysis suggests that these three stability measures are qualitatively consistent in that all three predict decreasing stability with increasing complexity. Some new predictions on how stability depends on food web configurations are generated here: a consumer-victim link has a smaller effect on the probabilities of stability, as measured by all three stability criteria, than a pair of recipient-controlled and donor-controlled links; a recipient-controlled link has a larger effect on the probabilities of local stability and permanence than a donor-controlled link, while they have the same effect on the probability of global stability; food webs with equal proportions of donor-controlled and recipient-controlled links are less stable than those with different proportions.

Animals↗
PubMed2026

Pattern Formation in a Spatial Public Goods Dilemma due to Diffusive or Directed Motion.

The costly provision of public goods serves as a model problem for the evolution of cooperative behavior, presenting a social dilemma between the collective benefits of shared resources and the individual incentive to free-ride in resource production. The spatial structure of populations can also impact cooperation over public goods, as diffusion of public goods and intentional motion of individuals towards regions with greater resources can interact with population and public goods dynamics to produce heterogeneous patterns in the spatial distribution of strategies and resources. In this paper, we build off a model introduced by Young and Belmonte for the reaction dynamics of interacting individuals and an explicit public good, deriving a system of PDEs that describes the spatial profiles of strategies and the public good in the presence of both diffusive motion of individuals and resources and chemotaxis-like directed motion of individuals in response to gradients in the concentration of public goods. Through linear stability analysis, we show that spatial patterns in strategic and public goods profiles can emerge due to either Turing instability with high defector diffusivity or a directed-motion instability through strong sensitivity of cooperators towards increasing resource concentration. We further explore the emergent spatial patterns with a mix of weakly nonlinear stability analysis and numerical simulation, showing that, for a wide range of reaction parameters, diffusion-driven instability appears to increase cooperation and public goods across the spatial domain, while directed motion of cooperators towards public goods tends to decrease cooperation and environmental quality across the environment.

Models, Biological↗