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At least 1,729 records · Page 96Linked to original sources
PubMed2005

Lifting the Pt[100] surface reconstruction through oxygen adsorption: a density functional theory analysis.

The adsorption of atomic oxygen on unreconstructed Pt[100]-(1 x 1) and reconstructed Pt[100]-(5 x 1) was modeled using density-functional theory in an attempt to understand the relative stability of the unreconstructed phase as a function of oxygen coverage. Our calculations showed that at zero temperature the (5 x 1) is more stable than the unreconstructed (1 x 1) phase at zero oxygen coverage. However, oxygen absorption on the Pt[100]-(5 x 1) phase removed the reconstruction, reversing the phase stability. Using thermochemical analysis, we show desorption of oxygen corresponding to a temperature near 730 K, consistent with experimentally observed desorption peaks for oxygen covered (1 x 1) surfaces. These results have ramifications for understanding the full Pt[100](1 x 1)-->Pt[100]hex-R0.7 degrees surface phase transition.

Journal Article↗
PubMed1996

Influence of fluorescent antibody probe specificity on flow cytometric analysis of antibody-producing cells.

In the flow cytometric analysis of the stability of antibody-producing cells, fluorescent antibody probes specific for immunoglobulin heavy chains have been widely utilized to quantify intracellular antibodies. To investigate the effect of the specificity of antibody probes on flow cytometric analysis, non-producing subclones of the 6-31 transfectoma were stained with fluorescein isothiocyanate (FITC)-conjugated anti-human IgGs specific for heavy chain and light chain, respectively. The use of heavy chain-specific probe identified heavy chain-only producers as producers, whereas the use of light chain-specific probe identified light chain-only producers as producers. Thus, both heavy chain-specific and light chain-specific antibody probes should be used for the accurate evaluation of heterogeneous non-producing population. Furthermore, the results of the flow cytometric analysis were confirmed by immunoblotting, suggesting that flow cytometry is a useful technique for the rapid evaluation of the stability of transfectomas producing chimeric antibody.

Animals↗
PubMed2006

Femoral rollback of cruciate-retaining and posterior-stabilized total knee replacements: in vivo fluoroscopic analysis during activities of daily living.

Restoration of the physiological flexor/extensor mechanism at the knee in terms of appropriate muscular lever arms, proper required quadriceps force, and suitable patellofemoral compressive force, is fundamental for the success of total knee replacement. Therefore, measurements of anteroposterior translation of the femoral component over the tibial base-plate against joint flexion during daily living activities are essential for the assessment of the in vivo performance of current prosthesis designs. Patients treated with posterior stabilized and cruciate retaining prostheses with excellent clinical scores were evaluated during stair climbing, sitting and rising from a chair, and step up and down, using a three-dimensional pose reconstruction technique based on videofluoroscopy. The posterior stabilized patients experienced a fairly consistent and physiological rollback specific of each motor task, demonstrating proper function of the spine-cam mechanism. Rollback was somehow inconsistent among subjects in the cruciate retaining group, accompanied with a smaller range of knee flexion. In this group, more posterior locations of the condyles correlated significantly with higher clinical and functional scores. Articular surface conformity restores physiological rollback in the presence of a spine-cam mechanism, but not coherently in the presence of the posterior cruciate ligament.

Activities of Daily Living↗
PubMed1979

Modified USP assay for simultaneous determination of aspirin and nonaspirin salicylates in aspirin and buffered aspirin tablets.

Modified USP procedures are described for the simultaneous determination of nonaspirin salicylates and aspirin in aspirin and buffered aspirin tablets. The existing USP procedures are not stability indicating for intact aspirin when significant levels of nonaspirin salicylates are present, as is often the case in short-term, high temperature stability programs. The modified procedures yeld considerably shorter analysis times and stability-indicating assays for intact aspirin without the need for sophisticated equipment other than that presently required by USP XIX.

Aspirin↗
PubMed2002

Stable drop shapes under disjoining pressure. I. A hierarchical approach and application.

The contact line region as affected by the disjoining pressure has been analyzed under the assumption that it can sustain only two types of profiles. Disjoining pressure represents the extra potential in thin films that always exists in the contact angle region where a liquid drop or a wedge thins to meet the solid substrate and in turn affects the contact angle as well as the film profile. It is shown here that the integration of the augmented Young-Laplace equation to yield the above types of drop profiles under the action of disjoining pressure leads to the usual conditions of equilibrium as well as the condition of stability in the same analysis. Other inequality constraints are obtained where the stability condition does not apply. The fact that stability condition coexists with the conditions of equilibrium is pursued to show in one case that the stability modifies half of the predicted outcomes in the drop shapes. In addition, exceptions to the rule are found, which are physically meaningful, and a scale-dependent equilibrium is reported for the first time.

Journal Article↗
PubMed2002

Mass movements and conservation management in Malta.

Mass movements at an environmentally sensitive but very popular leisure site in Malta were investigated in order to establish whether they were naturally occurring or whether they might in some way have resulted from the chronic long-term degradation of the site. Field surveys of the slopes were undertaken and physical and geotechnical properties of the Maltese Blue Clay Formation, which forms the slopes, were determined from laboratory analysis of samples. Slope stability was analysed using the infinite slope model; analysis of two 1996 mudflows indicates that these mass movements are natural processes. A landslide hazard analysis based on this finding suggested that whilst future mudflows constitute a small hazard, the risk of harm arising from them is even smaller. The implications of this for conservation management of the site are important, given the objective of restoring and then maintaining a natural ecological environment at the site. The mudflows are integral components of this natural environment, shaping the landscape and the ecological communities. The provision of information to visitors constitutes a valuable education and management tool that should further reduce the risk of harm and promote responsible recreational use of the site. However, it is essential that managers understand the nature of all relevant components of an environmentally sensitive site, in order that appropriate management strategies are devised. In the case discussed, these might include avoiding unnecessary future intervention on the clay slopes.

Conservation of Natural Resources↗
PubMed2005

Multiple ligand-binding modes in bacterial R67 dihydrofolate reductase.

R67 dihydrofolate reductase (DHFR), a bacterial plasmid-encoded enzyme associated with resistance to the drug trimethoprim, shows neither sequence nor structural homology with the chromosomal DHFR. It presents a highly symmetrical toroidal structure, where four identical monomers contribute to the unique central active-site pore. Two reactants (dihydrofolate, DHF), two cofactors (NADPH) or one of each (R67*DHF*NADPH) can be found simultaneously within the active site, the last one being the reactive ternary complex. As the positioning of the ligands has proven elusive to empirical determination, we addressed the problem from a theoretical perspective. Several potential structures of the ternary complex were generated using the docking programs AutoDock and FlexX. The variability among the final poses, many of which conformed to experimental data, prompted us to perform a comparative scoring analysis and molecular dynamics simulations to assess the stability of the complexes. Analysis of ligand-ligand and ligand-protein interactions along the 4 ns trajectories of eight different structures allowed us to identify important inter-ligand contacts and key protein residues. Our results, combined with published empirical data, clearly suggest that multipe binding modes of the ligands are possible within R67 DHFR. While the pterin ring of DHF and the nicotinamide ring of NADPH assume a stacked endo-conformation at the centre of the pore, probably assisted by V66, Q67 and I68, the tails of the molecules extend towards opposite ends of the cavity, adopting multiple configurations in a solvent rich-environment where hydrogen-bond interactions with K32 and Y69 may play important roles.

Binding Sites↗
PubMed2005

A new approach to evaluate stability of amodiaquine and its metabolite in blood and plasma.

A stability study for amodiaquine (AQ) and desethylamodiaquine (AQm) in whole blood and plasma is reported. AQ, AQm and chloroquine (CQ) were simultaneously analysed and the ratios AQ/CQ and AQm/CQ were used to ensure correct interpretation of the stability results. CQ was stable in whole blood and plasma at all tested temperatures enabling it to be a stability marker in stability studies. Simultaneous analysis of compounds, of which at least one is already known to be stable, permits a within sample ratio to be used as a stability indicator. The new approach significantly reduced bias when compared to the traditional approach. AQ and AQm were stable in plasma at -86 degrees C and -20 degrees C for 35 days, at 4 degrees C for 14 days and at 22 degrees C for 1 day. AQ and AQm were stable in blood at -86 degrees C and 4 degrees C for 35 days, at -20 degrees C and 22 degrees C for 7 days and at 37 degrees C for 1 day.

Amodiaquine↗
PubMed2002

Isolation and characterization of a family of stable RNA tetraloops with the motif YNMG that participate in tertiary interactions.

RNA is known to fold into a variety of structural elements, many of which have sufficient sequence complexity to make the thermodynamic study of each possible variant impractical. We previously reported a method for isolating stable and unstable RNA sequences from combinatorial libraries using temperature gradient gel electrophoresis (TGGE). This method was used herein to analyze a six-nucleotide RNA hairpin loop library. Three rounds of in vitro selection were performed using TGGE, and unusually stable RNAs were identified by cloning and sequencing. Known stable tetraloops were found, including sequences belonging to the UNCG motif closed by a CG base pair, and the CUUG motif closed by a GC base pair. In addition, unknown tetraloops were found that were nearly as stable as cUNCGg, including sequences related through substitution of the U with a C (Y), the C with an A (M), or both. These substitutions allow hydrogen bonding and stacking interactions in the UNCG loop to be maintained. Thermodynamic analysis of YNMG and variant loops confirmed optimal stability with Y at position 1 and M at position 3. Similarity in structure and stability among YNMG loops was further supported by deoxyribose substitution, CD, and NMR experiments. A conserved tertiary interaction in 16S rRNA exists between a YAMG loop at position 343 and two adenines in the loop at position 159 (Escherichia coli numbering). NMR and functional group substitution experiments suggest that YNAG loops in particular have enhanced flexibility, which allows the tertiary interaction to be maintained with diverse loop sequences at position 159. Taken together, these results support the existence of an extended family of UNCG-like tetraloops with the motif cYNMGg that are thermodynamically stable and structurally similar and can engage in tertiary interactions in large RNA molecules.

Circular Dichroism↗
PubMed2003

Higher correlations, universal distributions, and finite size scaling in the field theory of depinning.

Recently we constructed a renormalizable field theory up to two loops for the quasistatic depinning of elastic manifolds in a disordered environment. Here we explore further properties of the theory. We show how higher correlation functions of the displacement field can be computed. Drastic simplifications occur, unveiling much simpler diagrammatic rules than anticipated. This is applied to the universal scaled width distribution. The expansion in d=4-epsilon predicts that the scaled distribution coincides to the lowest orders with the one for a Gaussian theory with propagator G(q)=1/q(d+2 zeta), zeta being the roughness exponent. The deviations from this Gaussian result are small and involve higher correlation functions, which are computed here for different boundary conditions. Other universal quantities are defined and evaluated: We perform a general analysis of the stability of the fixed point. We find that the correction-to-scaling exponent is omega=-epsilon and not -epsilon/3 as used in the analysis of some simulations. A more detailed study of the upper critical dimension is given, where the roughness of interfaces grows as a power of a logarithm instead of a pure power.

Journal Article↗
PubMed1985

Stability of azure B-eosin Y staining solutions.

The stability of azure B-eosin Y staining solutions of varying composition and of a routine May Grunwald Giemsa (MGG) stain were studied by analysis of the density histogram of white blood cells obtained by an image analysis computer. The stability appeared to be variable and depended on the concentration of the dyes, the molarity of the buffer solutions and the presence of dimethylsulfoxide (DMSO) as a stabilizer. Although most staining solutions including the routine MGG stain showed marked loss of staining capacity soon after preparation, it was possible to obtain an azure B-eosin Y mixture with very satisfactory staining properties which did not decrease during 8 h after its preparation.

Azure Stains↗
PubMedDate not supplied

[Study of Beck's hopelessness scale. Validation and factor analysis].

The validation study and factorial analysis of the Beck's hopelessness scale is presented. Two groups were compared including patients suffering from depression (n = 100) and a control group (n = 93). Age and sex were comparable in the two groups. The hopelessness scale is valid, and differentiates depressive patients from control subjects. The scale has a good reliability (test-retest, r = .81) and a good internal consistency (alpha = .97) for depressive subjects and alpha = .79 for control subjects). It also shows a good concurrent validity with other scales assessing depressive cognitions, the automatic thoughts questionnaire, the dysfunctional attitudes scale (form A) and a scale assessing the suicidal risk (ERSD). No concurrent validity is found with scales assessing the intensity of depression, the Beck depression inventory and the Hamilton scale. The factorial analysis elicits a general factor, accounting for 38.15% of the variance, and reflecting negative feelings about the future. The study of all the factorial analysis shows the stability of the factorial structure.

Adult↗
PubMed1997

Engineering the independent folding of the subtilisin BPN' prodomain: analysis of two-state folding versus protein stability.

In complex with subtilisin BPN', the 77 amino acid prodomain folds into a stable compact structure comprising a four-stranded antiparallel beta-sheet and two three-turn alpha-helices. When isolated from subtilisin, the prodomain is 97% unfolded even under optimal folding conditions. Traditionally, to study stable proteins, denaturing cosolvents or temperatures are used to shift the equilibrium from folded to unfolded. Here we manipulate the folding equilibrium of the unstable prodomain by introducing stabilizing mutations generated by design. By sequentially introducing three stabilizing mutations into the prodomain we are able to shift the equilibrium for independent folding from 97% unfolded to 65% folded. Spectroscopic and thermodynamic analysis of the folding reaction was carried out to assess the effect of stability on two-state behavior and the denatured state. The denatured states of single and combination mutants are not discernably different in spite of a range of DeltaGunfolding from -2.1 to 0.4 kcal/mol. Conclusions about the nature of the denatured state of the prodomain are based on CD spectral data and calorimetric data. Two state folding is observed for a combination mutant of marginal stability (DeltaG = 0). Evidence for its two-state folding is based on the observed additivity of individual mutations to the overall DeltaGunfolding and the conformity of DeltaGunfolding vs T to two-state assumptions as embodied in the Gibbs-Helmholz equation. We believe our success in stabilizing the two-state folding reaction of the prodomain originates from the selection of mutations with improved ability to fold subtilisin rather than selection for increase in secondary structure content. The fact that a small number of mutations can stabilize the independent folding of the prodomain implies that most of the folding information already exists in the wild-type amino acid sequence in spite of the fact that the unfolded state predominates.

Bacillus subtilis↗
PubMed2002

Stability of the lactose permease in detergent solutions.

Protein stability, as measured by irreversible protein aggregation, is one of the central difficulties in the handling of detergent-solubilized membrane proteins. We present a quantitative analysis of the stability of the Escherichia coli lactose (lac) permease and a series of lac permease fusion proteins containing an insertion of cytochrome(b562), T4 lysozyme or beta-lactamase in the central hydrophilic loop of the permease. The stability of the proteins was evaluated under a variety of storage conditions by both a qualitative SDS-PAGE assay and by a quantitative hplc assay. Long-chain maltoside detergents were more effective at maintaining purified protein in solution than detergents with smaller head groups and/or shorter alkyl tails. A full factorial experiment established that the proteins were insensitive to sodium chloride concentrations, but greatly stabilized by glycerol, low temperature and the combination of glycerol and low temperature. The accurate quantitation of the protein by absorbance spectroscopy required exclusion of all contact with clarified polypropylene or polyvinyl chloride (PVC) materials. Although some of the fusion proteins were more prone to aggregation than the wild-type permease, the stability of a fusion protein containing a cytochrome(b562) insertion was indistinguishable from that of native lac permease.

Chromatography, High Pressure Liquid↗
PubMed2006

The stability of herpes simplex virus type I genomes in infected Vero cells undergoing viral induced apoptosis.

Maintaining the viral genome intact following infection and prior to replication is critical to the virus life cycle. Here we report an analysis of the stability of herpes simplex virus type 1 (HSV-1) genomes, relative to host chromosomal DNA, in infected cells as a function of viral induced apoptosis. The results show that, in the absence of DNA replication, the input genomes of wild-type (KOS), and replication compromised ICP27 deleted (d27-1) virus are remarkably stable. Intracellular half-lives of their genomes exceeded 24 hours. In contrast, the half-life of replication incompetent ICP4 deleted (d120) viral genomes were significantly less (approximately 8 hours). Interestingly, it was also noted that in cells infected under conditions permissible for replication, viral DNA replication occurs, even in cells undergoing apoptosis. The possibility that the genome structure and replication compartment formation provide protection to the HSV-1 genome from degradation is discussed.

Animals↗