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PubMed1999

Development and validation of a high-performance liquid chromatographic stability-indicating method for the analysis of Synercid in quality control, stability and compatibility studies.

A gradient high-performance liquid chromatographic (HPLC) method was developed for the analysis of Synercid freeze-dried powder in routine quality control, stability and compatibility studies. This method is suited for a simultaneous assay of drug substances and impurities. The method was validated for precision, reproducibility, linearity, accuracy and limits of detection. The robustness study that was performed according to an experimental design is described.

Anti-Bacterial Agents↗
PubMed2005

Structural and compositional characterization of yttria-stabilized zirconia: evidence of surface-stabilized, low-valence metal species.

The structural properties of polycrystalline yttria-stabilized zirconia (YSZ) have been studied using FT-Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Yttria content was varied between 8 and 15% (by mole fraction) to determine compositional effects on YSZ phonon structure, lattice parameter, and oxidation state. The dominant feature in the low-frequency Raman spectrum correlates quite closely with the material's sole (cubic) lattice parameter. XPS measurements of typical YSZ samples show only a single species of both Y and Zr. After exposing YSZ to a reducing environment (H2) at elevated temperatures (1000 degrees C), however, the XPS spectra of YSZ show new features at lower binding energy for both Y and Zr. Angle-resolved XPS measurements suggest that these reduced forms of Y and Zr exist only within the first few molecular layers of the sample. This treatment does not effect the XRD pattern, nor does it change the low-frequency phonon structure observed in the Raman spectrum, although the Raman spectrum does experience approximately 50% reduction in overall signal intensity. These disparities are reconciled with each other based on differences in each technique's sampling depth. The impact that surface-reduced YSZ may have on the chemistry occurring within solid oxide fuel cells is discussed briefly.

Journal Article↗
PubMed1994

Role of disulfide linkage and putative intermolecular binding residues in the stability and binding of the extrinsic manganese-stabilizing protein to the photosystem II reaction center.

Site-directed mutations were produced at three highly conserved amino acid positions of MSP of the photosystem II (PSII) reaction center in the transformable cyanobacterium Synechocystis sp. PCC6803. The highly conserved aspartate at position 9 of the mature MSP was changed to a lysine (strain MSP-D9K) to assess its role in the proposed N-terminal binding region (Eaton-Rye & Murata, 1989; Odom & Bricker, 1992). This strain accumulates normal levels of MSP, and the properties of the H2O-splitting enzyme are only slightly altered relative to the wild-type. In contrast, replacement of cysteine 20 with a serine, which is proposed to disrupt the intramolecular disulfide bridge (Tanaka et al., 1989), produces a phenotype with no detectable accumulation of MSP, despite normal levels of mRNA transcripts. Like the psbO deletion strain, the MSP-C20S mutant exhibits impaired O2 evolution activity and a greater stability of the S2 state as measured by thermoluminescence. Mutation of strictly conserved aspartate 159 to asparagine (MSP-D159N) does not affect the accumulation of MSP, but causes a reduction in the H2O-oxidation activity and thermoluminescence properties intermediate between the wild-type and the psbO deletion strain. In addition, we report upon improved methods for obtaining oxygen-evolving membranes from mutant cells.

Aspartic Acid↗
PubMed1996

Specific Sequestering Agents for the Actinides. 29. Stability of the Thorium(IV) Complexes of Desferrioxamine B (DFO) and Three Octadentate Catecholate or Hydroxypyridinonate DFO Derivatives: DFOMTA, DFOCAMC, and DFO-1,2-HOPO. Comparative Stability of the Plutonium(IV) DFOMTA Complex(1).

The metal complex stability constants of Th(IV) with desferrioxamine B (DFO) and three octadentate derivatives [N-(2,3-dihydroxy-4-carboxybenzoyl)desferrioxamine B (DFOCAMC), N-(1,2-dihydro-1-hydroxy-2-oxopyridin-6-yl)carbonyl)desferrioxamine B (DFO-1,2-HOPO) and N-(2,3-dihydroxy-4-(methylamido)benzoyl)desferrioxamine B (DFOMTA)] have been determined. The formation constant of the Pu(IV)/DFOMTA complex has also been determined, and the formation constants have been estimated for the other Pu(IV) complexes of octadentate DFO derivatives. The DFO derivatives form 1:1 complexes with Th(IV) in aqueous solution. The solution chemistry of the Th(IV) complexes has been studied by spectrophotometric, potentiometric and proton NMR titrations. The Th(IV) formation constants are as follows (log K(f) values and esd's): DFO, 26.6(1); DFOMTA, 38.55(5); DFOCAMC, 37.2(3); DFO-1,2-HOPO, 33.7(4). The Pu(IV)/DFOMTA formation constant, determined by competitive spectrophotometric titration is (log K(f) value) 41.7(2). The estimation of the other Pu(IV) formation constants are as follows (log K(f) values): DFOCAMC, 40.4; DFO-1,2-HOPO, 36.9. The selectivity of DFO and the three derivatives for actinide(IV) ions is discussed.

Journal Article↗
PubMed2002

Relationships between carbocation stabilities and electrophilic reactivity parameters, E: quantum mechanical studies of benzhydryl cation structures and stabilities.

Quantum chemical calculations of the affinities of benzhydryl cations (XC(6)H(4))(2)CH(+) for the methyl anion, hydroxide, and hydride anion have been performed up to the B3LYP/6-311++G(3df,2pd)//B3LYP/6-31G(d,p) level and compared with rate and equilibrium constants in solution. An excellent linear correlation between the empirical electrophilicity parameter E (by log k = s(N + E); Mayr, H.; Bug, T.; Gotta, M. F.; Hering, N.; Irrgang, B.; Janker, B.; Kempf, B.; Loos, R.; Ofial, A. R.; Remennikov, R.; Schimmel, H. J. Am. Chem. Soc. 2001, 123, 9500-9512) and the calculated methyl anion affinities ranging over 46.5 kcal mol(-1) is found that reproduces the electrophilicity parameters E which range from -10 to +6 with a standard deviation of +/-0.26 (11 points). The calculated OH(-) and H(-) affinities correlate with the calculated CH(3)(-) affinities with a slope of 1.00, indicating that the relative anion affinities of benzhydrylium ions are independent of the nature of the reference base. Linear correlations of the experimental pK((R)(+)) values and chloride ion affinities in solution with the calculated anion affinities in the gas phase indicate that solvation attenuates the differences of carbocation stabilization in the gas phase but does not affect the relative differences. Application of Marcus theory shows that only reaction series with alpha = partial differential DeltaG(++)/ partial differential Delta(r)G degrees = 0.5 corresponding to a slope parameter of s = 0.67 can have constant intrinsic barriers. The slope parameters s found for pi-nucleophiles and C-H hydride donors (s approximately equal 1) are interpreted by a decrease of the intrinsic barriers with increasing electrophilicities of the carbocations. On the other hand, a value of s < or = 0.67 as found for many n-nucleophiles as well as for Si-H, Ge-H, or Sn-H hydride donors is indicative of intrinsic barriers which are constant or slightly increase with increasing electrophilicity of the carbocation.

Journal Article↗
PubMed2007

Synthesis, stabilities, and redox behavior of mono-, di-, and tetracations composed of di(1-azulenyl)methylium units connected to a benzene ring by phenyl- and 2-thienylacetylene spacers. A concept of a cyanine-cyanine hybrid as a stabilized electrochromic system.

This paper describes the preparation of two tetracations 4a(4+) and 4b(4+) composed of di(1-azulenyl)methylium units based on a new structural principle of a cyanine-cyanine hybrid for the design of electrochromic materials with two color changes. Di- and monocations 5a(2+), 5b(2+) and 6a+, 6b+ composed of di(1-azulenyl)methylium units were also prepared for the purpose of comparison. The pKR+ values of the tetracations are rather high despite their tetracationic structure, although the stability of these cations decreases with the increase of the number of the existing cation units. The cyclic voltammetry (CV) of these cations revealed the presumed multielectron redox properties. However, the tetracations did not exhibit the idealized electrochemical behavior, in which subsequent two-electron reduction was presumed as the cyanine-cyanine hybrid, probably due to the less effective electrochemical interaction among the positive charges. The scope of the creation of the novel polyelectrochromic materials taking the new structural principle is demonstrated by these examples.

Journal Article↗
PubMed2007

Foiled carbenes revisited: When sigma-stabilization surpasses pi-stabilization.

The bicyclic alkenylidenes 9 (bicyclo[3.2.1]oct-2-en-8-ylidene) and 17 (bicyclo[3.3.1]non-2-en-9-ylidene) were claimed to be stabilized foiled carbenes. Our B3LYP and MP2 computations confirm previous experimental data. Moreover, they show that these carbenes are very reactive and rearrange rapidly, mainly through a 1,2-vinyl shift by overcoming a low barrier (1.2 to 5.4 kcal/mol). This is in contrast to the high barriers (up to 30 kcal/mol) predicted for the same type of rearrangements in norborn-2-en-7-ylidene derivatives. In 17 and bicyclo[4.1.1]oct-2-en-7-ylidene (23), the divalent carbon atom is even bent away from the double bond!

Journal Article↗
PubMed2005

Simulation of energetic stability of facetted l-glutamic acid nanocrystalline clusters in relation to their polymorphic phase stability as a function of crystal size.

A molecular modeling approach is used to study the stability of different polymorphic forms of l-glutamic acid through building and optimizing molecular clusters of different sizes and shapes with the latter corresponding to the predicted crystal growth morphologies. The results reveal that the initially nucleating (according to Oswald rule) metastable (alpha) form is the more energetically stable form at small cluster sizes of ca. 200 molecular units, whereas the stable (beta) form is more stable when the cluster size is larger.

Algorithms↗
PubMed2006

On the morphology and stability of Au nanoparticles on TiO2(110) prepared from micelle-stabilized precursors.

The morphology and stability of well-ordered, nanostructured Au/TiO2(110) surfaces, prepared by deposition of Au loaded micelles on TiO2(110) substrates and subsequent oxidative removal of the polymer shell in an oxygen plasma, was investigated by noncontact AFM, SEM and XPS. The resulting arrays of Au nanoparticles (particle sizes 1-5 nm) form a nearly hexagonal pattern with well-defined interparticle distances and a narrow particle size distribution. Particle size and particle separation can be controlled independently by varying the Au loading and the block-copolymers in the micelle shell. The oxygen plasma treatment does not affect the size and distance of the Au nanoparticles; the latter are fully metallic after subsequent UHV annealing (400 degrees C). The particles are stable under typical CO oxidation reaction conditions, up to at least 200 degrees C, making these surfaces ideally suited as defined model systems for catalytic studies. Significant changes in the height distributions of the Au nanoparticles are found upon 400 degrees C annealing in O2. For adlayers with small interparticle distances, this leads to a bimodal particle size distribution, which together with the preservation of the lateral order points to Ostwald ripening.

Journal Article↗
PubMed2005

Multiple high-level QM/MM reaction paths demonstrate transition-state stabilization in chorismate mutase: correlation of barrier height with transition-state stabilization.

Multiple profiles for the reaction from chorismate to prephenate in the enzyme chorismate mutase calculated with hybrid density functional combined quantum mechanics/molecular mechanics methods (B3LYP/6-31G(d)-CHARMM27) agree well with experiment, and provide direct evidence of transition-state stabilization by this important enzyme, which is at the centre of current debates about the nature of enzyme catalysis.

Chorismate Mutase↗
PubMed2001

Transition state complexes of the Klebsiella pneumoniae nitrogenase proteins. Spectroscopic properties of aluminium fluoride-stabilized and beryllium fluoride-stabilized MgADP complexes reveal conformational differences of the Fe protein.

Stable inactive 2 : 1 complexes of the Klebsiella pneumoniae nitrogenase components (Kp2/Kp1) were prepared with ADP or the fluorescent ADP analogue, 2'(3')-O-[N-methylanthraniloyl] ADP and AlF(4)(-) or BeF(3)(-) ions. By analogy with published crystallographic data [Schindelin et al. (1997) Nature 387, 370-376)], we suggest that the metal fluoride ions replaced phosphate at the two ATP-binding sites of the iron protein, Kp2. The beryllium (BeF(x)) and aluminium (AlF(4)(-)) containing complexes are proposed to correspond to the ATP-bound state and the hydrolytic transition states, respectively, by analogy with the equivalent complexes of myosin [Fisher et al. (1995) Biochemistry 34, 8960-8972]. (31)P NMR spectroscopy showed that during the initial stages of complex formation, MgADP bound to the complexed Kp2 in a manner similar to that reported for isolated Kp2. This process was followed by a second step that caused broadening of the (31)P NMR signals and, in the case of the AlF4- complex, slow hydrolysis of some of the excess ADP to AMP and inorganic phosphate. The purified BeFx complex contained 3.8 +/- 0.1 MgADP per mol Kp1. With the AlF(4)(-) complex, MgAMP and adenosine (from MgAMP hydrolysis) replaced part of the bound MgADP although four AlF(4)(-) ions were retained, demonstrating that full occupancy by MgADP is not required for the stability of the complex. The fluorescence emission maximum of 2'(3')-O-[N-methylanthraniloyl] ADP was blue-shifted by 6-8 nm in both metal fluoride complexes and polarization was 6-9 times that of the free analogue. The fluorescence yield of bound 2'(3')-O-[N-methylanthraniloyl] ADP was enhanced by 40% in the AlF(4)(-) complex relative to the solvent but no increase in fluorescence was observed in the BeFx complex. Resonance energy transfer from conserved tyrosine residues located in proximity to the Kp2 nucleotide-binding pocket was marked in the AlF(4)(-) complex but minimal in the BeFx fluoride complex, illustrating a clear conformational difference in the Fe protein of the two complexes. Our data indicate that complex formation during the nitrogenase catalytic cycle is a multistep process involving at least four conformational states of Kp2: similar to the free Fe protein; as initially complexed with detectable (31)P NMR; as detected in mature complexes with no detectable (31)P NMR; in the AlF(4)(-) complex in which an altered tyrosine interaction permits resonance energy transfer with 2'(3')-O-[N-methylanthraniloyl] ADP.

Adenosine Diphosphate↗
PubMedDate not supplied

A metacarpophalangeal joint stabilization splint: the Galindo-Lim thumb metacarpophalangeal joint stabilization splint.

Creation of a splint should allow for maximal functional use of the hand as well as comfort. The design of the Galindo-Lim splint enhances functional use of the hand not only because it stabilizes the MCP joint but also because it does not cross the wrist crease, thus allowing full wrist motion. Independence in the performance of daily activities is easily achieved with the Galindo-Lim splint (Figure 5). The splint is appropriate for patients with a variety of diagnoses, including MCP joint volar plate injuries, collateral ligament injuries, joint hypermobility, and arthritic conditions.

Equipment Design↗
PubMed1991

On the stability of dispensable constituents of the eukaryotic genome: stability of coding sequences versus truly hypervariable sequences in a clonal vertebrate, the amazon molly, Poecilia formosa.

In clonal unisexual vertebrates, the genes specifying the males become dispensable. To study the fate of such genes the gynogenetic all-female fish Poecilia formosa was treated with androgens. Phenotypic males were obtained that exhibited the complete set of male characteristics of closely related gonochoristic species, including body proportions, pigmentation, the extremely complex insemination apparatus of poeciliid fish, sexual behavior, and spermatogenesis. The apparent stability of such genic structures, including those involved in androgen regulation, is contrasted by high instability of noncoding sequences. Frequent mutations, their clonal transmission, and at least two truly hypervariable loci leading to individual differences between these otherwise clonal organisms were detected by DNA fingerprinting. These observations substantiate the concept that also in "ameiotic" vertebrates certain compartments of the genome are more prone to mutational alterations than others.

Journal Article↗
PubMed2002

Stabilization of telomere length and karyotypic stability are directly correlated with the level of hTERT gene expression in primary fibroblasts.

Telomere shortening and lack of telomerase activity have been implicated in cellular senescence in human fibroblasts. Expression of the human telomerase (hTERT) gene in sheep fibroblasts reconstitutes telomerase activity and extends their lifespan. However, telomere length is not maintained in all cell lines, even though in vitro telomerase activity is restored in all of them. Cell lines expressing higher levels of hTERT mRNA do not exhibit telomere erosion or genomic instability. By contrast, fibroblasts expressing lower levels of hTERT do exhibit telomere shortening, although the telomeres eventually stabilize at a shorter length. The shorter telomere lengths and the extent of karyotypic abnormalities are both functions of hTERT expression level. We conclude that telomerase activity is required to bypass senescence but is not sufficient to prevent telomere erosion and genomic instability at lower levels of expression.

Animals↗
PubMed1985

Probing stability and dynamics of proteins by protease digestion. I: Comparison of protease susceptibility and thermal stability of cytochromes c.

Protease susceptibility of homologous proteins in their native conformations was studied. This work aims to establish a broad and quantitative basis for the utilization of protease digestion to analyze the local stability of native proteins. Using high-performance liquid chromatography (HPLC) the time course of the proteolytic degradation of intact proteins was quantitatively traced. Rapid separation of peptide fragments with HPLC made possible the elucidation of sequential digestion originating from the cleavage at a very few sites which are locally unstable in the protein structure. Using four serine proteases, chymotrypsin, trypsin, elastase and subtilisin BPN', we found some common trends in proteolysis for a group of proteins of the cytochrome c family. By comparing of the proteolysis and thermal denaturation with ten homologous cytochromes c extracted from horse, beef, Candida krusei, Saccharomyces cerevisiae, chicken, tuna, pigeon, rabbit, dog and rat, protease susceptibility was related to locally unfolding states intrinsic to the native conformation.

Animals↗
PubMed2002

Meiotic spindle stability depends on MAPK-interacting and spindle-stabilizing protein (MISS), a new MAPK substrate.

Vertebrate oocytes arrest in the second metaphase of meiosis (metaphase II [MII]) by an activity called cytostatic factor (CSF), with aligned chromosomes and stable spindles. Segregation of chromosomes occurs after fertilization. The Mos/.../MAPK (mitogen-activated protein kinases) pathway mediates this MII arrest. Using a two-hybrid screen, we identified a new MAPK partner from a mouse oocyte cDNA library. This protein is unstable during the first meiotic division and accumulates only in MII, where it localizes to the spindle. It is a substrate of the Mos/.../MAPK pathway. The depletion of endogenous RNA coding for this protein by three different means (antisense RNA, double-stranded [ds] RNA, or morpholino oligonucleotides) induces severe spindle defects specific to MII oocytes. Overexpressing the protein from an RNA not targeted by the morpholino rescues spindle destabilization. However, dsRNA has no effect on the first two mitotic divisions. We therefore have discovered a new MAPK substrate involved in maintaining spindle integrity during the CSF arrest of mouse oocytes, called MISS (for MAP kinase-interacting and spindle-stabilizing protein).

Amino Acid Sequence↗
PubMed1995

Helix-stabilizing compounds CC-1065 and U-71,184 bind to RNA-DNA and DNA-DNA duplexes containing modified internucleotide linkages and stabilize duplexes against thermal melting.

CC-1065 and U-71,184 bind and hyperstabilize DNA duplexes, but little is known about their effects on nucleic acid duplexes of different structure. A 20 mer DNA sequence (5'-TTACTTCAGTTATGAGACCA) containing a drug binding sequence (5'-AGTTA) was selected as the target sequence, and this was duplexed with complementary antisense sequences containing phosphodiester (PO), phosphorothioate (PS), and methylphosphonate (MP) bonds. The duplexes containing PO or PS bound 2 CC-1065 molecules per duplex, presumably at both the target site and at a lower affinity site (5'-AGTAA) on the antisense strand. The duplex containing MP bound only 1 CC-1065, and all duplexes bound only 1 U-71,184. Both CC-1065 and U-71,184 bound to 20 mer duplexes comprised of oligo(dA)-oligo(dT) (2.5 and 2 drugs per duplex, respectively) and poly(rA)-oligo(dT) (1 drug per 20 base pairs). CC-1065 also bound to duplexes between the PO- or PS-based antisense structures and a complementary synthetic 20 mer RNA sequence, with about 1 drug per duplex in each case. CC-1065 increased the Tm for the 20 mer DNA duplexes 17 to 29 degrees C, and the corresponding values for U-71,184 ranged from 7 to 19 degrees C. CC-1065 raised the Tm of oligo(dA)-oligo(dT) and poly(rA)-oligo(dT) 29 degrees C. U71,184 increased the Tm for oligo(dA)-oligo(dT) 30 degrees C but did not significantly elevate the Tm for the corresponding RNA-DNA duplex. The results show that CC-1065 and U-71,184 are capable of binding and stabilizing a variety of nucleic acid duplexes. These agents or their analogs may become useful ligands for antisense oligonucleotide applications.

Antineoplastic Agents↗
PubMed2003

Bifurcation and stability analysis of rotating chemical spirals in circular domains: boundary-induced meandering and stabilization.

Recent experimental and model studies have revealed that the domain size may strongly influence the dynamics of rotating spirals in two-dimensional pattern forming chemical reactions. Hartmann et al. [Phys. Rev. Lett. 76, 1384 (1996)], report a frequency increase of spirals in circular domains with diameters substantially smaller than the spiral wavelength in a large domain for the catalytic NO+CO reaction on a microstructured platinum surface. Accompanying simulations with a simple reaction-diffusion system reproduced the behavior. Here, we supplement these studies by a numerical bifurcation and stability analysis of rotating spirals in a simple activator-inhibitor model. The problem is solved in a co-rotating frame of reference. No-flux conditions are imposed at the boundary of the circular domain. At large domain sizes, eigenvalues and eigenvectors very close to those corresponding to infinite medium translational invariance are observed. Upon decrease of domain size, we observe a simultaneous change in the rotation frequency and a deviation of these eigenvalues from being neutrally stable (zero real part). The latter phenomenon indicates that the translation symmetry of the spiral solution is appreciably broken due to the interaction with the (now nearby) wall. Various dynamical regimes are found: first, the spiral simply tries to avoid the boundary and its tip moves towards the center of the circular domain corresponding to a negative real part of the "translational" eigenvalues. This effect is noticeable at a domain radius of R<R(cr,1). The spiral subsequently exhibits an oscillatory instability: the tip trajectory displays a meandering motion, which may be characterized as boundary-induced spiral meandering. A systematic study of the spiral rotation as a function of a control parameter and the domain size reveals that the meandering instability in large domains becomes suppressed, and the spiral rotation becomes rigid, at a critical radius R(cr,0). Boundary-induced meandering arises below a second critical radius R(cr,2)<R(cr,0).

Journal Article↗