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PubMed1999

Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts.

Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)]1-x[M(III)]x(OH)2][Cl]x yH2O, by way of M(III) hydroxide/hydrous oxide intermediates. Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximately Ni < Zn for M(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.

Aluminum↗
PubMed2006

Natural bond orbital analyses of persulfoxide stabilization by remote functional groups. The conformationally induced electrostatic stabilization sulfide photooxygenation mechanism.

The conformationally induced electrostatic stabilization (CIES) sulfide photooxygenation mechanism was computationally examined using an ab initio model and extended to the study of new donor atoms. The MP2/6-31G(d) geometries and a natural population analysis of natural lone-pair orbitals on the donor atoms support the mechanism and reveal that oxygen and nitrogen donor groups are more stabilizing than sulfur.

Journal Article↗
PubMed1999

Optical Resolution and Configurational Stability of Selenoxides Stabilized by Intramolecular Coordination.

2-((Dimethylamino)methyl)phenyl alkyl (or aryl) selenoxides, configurationally stabilized by intramolecular coordination of an amino group to the selenium atom, were optically resolved into their enantiomeric isomers by means of high-performance liquid chromatography using an optically active column packed with amylosecarbamate derivative/silica gel. This is the first example of the isolation of optically pure selenoxides without bulky substituents and also the first isolation of optically pure alkyl aryl selenoxides. The absolute configuration of the (-)-isomers could be assigned to be the S-form by comparison of their specific rotations, circular dichroism spectra, and behavior on the optically active column with those of the sulfur analogue, prepared by Andersen's method. Racemization of the optically active selenoxides was accelerated not only in acidic solution but also in basic media. This result indicates there are two different mechanisms for their racemization in acidic and basic media. The stabilization energy of the selenoxides by the intramolecular coordination of an amino group to the selenium atom was estimated to be ca. 3 kcal mol(-)(1) on the basis of variable-temperature (1)H NMR measurements.

Journal Article↗
PubMed2005

On the stability of IrCl6(3-) and other triply charged anions: solvent stabilization versus ionic fragmentation and electron detachment for the IrCl6(3-).(H2O)n n = 0-10 microsolvated clusters.

The intrinsic gas-phase stability of the IrCl(6)(3-) trianion and its microsolvated clusters, IrCl(6)(3-).(H(2)O)(n) n = 1-10, have been investigated using density functional theory (DFT) calculations. Although IrCl(6)(3-) is known to exist as a stable complex ion in bulk solutions, our calculations indicate that the bare trianion is metastable with respect to decay via both electron detachment and ionic fragmentation. To estimate the lifetime of IrCl(6)(3-), we have computed the electron tunneling probability using an adaption of the Wentzel-Kramer-Brillouin theory and predict that the trianion will decay spontaneously via electron tunneling on a time scale of 2.4 x 10(-13) s. The global minimum structure for IrCl(6)(3-).H(2)O was found to contain a bifurcated hydrogen bond, whereas for IrCl(6)(3-).(H(2)O)(2), two low energy minima were identified; one involving two bifurcated water-ion hydrogen bonds and a second combining a bifurcated hydrogen bond with a water-water hydrogen bond. Clusters based on each of these structural motifs were obtained for all of the n = 3-10 systems, and the effect of solvation on the possible decay pathways was explored. The calculations reveal that solvation stabilizes IrCl(6)(3-) with respect to both electron detachment decay and ionic fragmentation, with the magnitude of the repulsive Coulomb barrier for ionic fragmentation increasing smoothly with sequential solvation. This study is the first to compare the propensity for electron detachment versus ionic fragmentation decay for a sequentially solvated triply charged anion.

Journal Article↗
PubMed2005

Stability of a flat gas-liquid interface containing nonidentical spheres to gas transport: toward an explanation of particle stabilization of gas bubbles.

It is shown that a flat interface between a soluble gas and a liquid that contains an arbitrary number of partially wetting nonidentical spheres is linearly stable to slight perturbations caused by fluctuations in the gas volume. Stability is proved by showing that the rate of change of the volume of the gas with curvature of the interface is positive in the neighborhood of the equilibrium state of zero interface curvature. Physically, the volume fluctuations induce fluctuations in the curvature of the interface that would naturally lead to dissolution of gas into the liquid in the case of positive curvature and entry of gas into the bubble in the case of negative curvature, either of which restores equilibrium. This result may possibly explain the unusual long-term stability of gas bubbles covered by colloidal particles in the recent experiments of Du et al. (Du, Z.; Bilbao-Montoya, M. P.; Binks, B. P.; Dickinson, E.; Ettelaie, R.; Murray, B. S. Langmuir 2003, 19, 3106).

Journal Article↗
PubMed2005

Sterically stabilized cyclopropenonophanes and an electronically stabilized cyclopropenethionophane: syntheses, structural properties, and reactivity.

The syntheses of sterically stabilized cyclopropenonophanes as well as an electronically stabilized cyclopropenethionophane are reported, and their molecular structures in the solid state are elucidated. The sulfur of the CS moiety in cyclopropenethiones was shown to react as a nucleophile. Temperatures of more than 240 degrees C favor the extrusion of CO in the cyclopropenonophane to afford an alpha,alpha'-tetramethyl-substituted cyclodiyne. [reaction: see text]

Journal Article↗
PubMed1994

[The effect of proprioception on functional stability of the upper ankle joint with special reference to stabilizing aids].

Both ankle joints of 14 uninjured volunteers and 16 patients with unstable ankle joints were tested regarding their proprioceptive capabilities. Three tests were used for the study: single-leg stance test, single-leg jumping course test, angle-reproduction test. The influence of three stabilization devices (lace-on-brace, stirrup-brace, taping) on the proprioceptivity of stable and unstable ankle joints were evaluated as well. The scores of the single-leg jumping course test without any stabilizing device (category "standard") ranged between 8.06 and 13.68 (10.65 +/- 1.29). In the categories "mikros" (9.85 +/- 0.99), "aircast" (9.99 +/- 1.14) and with the tape bandage (category "taping") (10.27 +/- 0.81) the scores were lower. In general, the scores of all trials with orthoses were lower compared to the category "standard". The differences of the categories "standard-mikros" and "standard-aircast" revealed a significant reduction of the scores when applicating these orthoses (p < 0.01). The differences of the category "standard-taping" as well as the single scores between the categories "mikros" and "aircast" were not statistically significant. According to the results of the single-leg stance test the error rate was within the range of 0-16 (5.12 +/- 2.85) for the category "standard", it was lower for the categories "mikros" (3.65 +/- 2.65) and "aircast" (4.17 +/- 2.59). The error rate was highest in the group with applicated tape bandage (5.79 +/- 3.53). The differences between the categories "standard"-"mikros" as well as "standard"-"aircast" were statistically significant (p < 0.01). There was also a significant difference between these categories regarding injured and uninjured ankle joints (p < 0.01). The pair differences of the categories "standard" and "taping" were below the significance level as well as the error rates of the categories "mikros" and "aircast". The ankle-reproduction-test showed higher values for the category "standard" (2.36 degrees +/- 0.97) in comparison to the categories "mikros" (1.46 degrees +/- 0.72). "aircast" (1.62 degrees +/- 0.91) and "taping" (1.84 degrees +/- 0.41). In the category "standard" the reproduction error of the uninjured ankle joints was lower (2.30 degrees +/- 1.04) compared to the group of unstable ankle joints (2.44 degrees +/- 0.81), whereas in all other categories the reproduction error was higher in the group of uninjured joints. The differences in all findings between the categories "standard"-"mikros" and "standard"-"aircast" were statistically significant (p < 0.01). The results of the three tests showed a statistically highly significant difference between injured and uninjured ankle joints (p < 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Ankle Injuries↗
PubMed2006

Structure and stability of Al13H(n) (n=1-13) clusters: exceptional stability of Al13H13.

We have performed density functional calculations for the structure and stability of Al(13)H(n) (n=1-13) clusters. Population analysis has shown significant charge transfer occurring from the Al cluster to the H atoms. The population for Al(13) varies from 0.24 (Al(13)H) to 2.83 (Al(13)H(13)). The shape of Al(13) moieties in the Al(13)H(n) (n>/=8) clusters is significantly distorted from the icosahedral structure of Al(13) and is a "cagelike" form. Al(13)H(13) has a capped icosahedron as the ground-state structure, similar to B(13)H(13), while the shape of B(13) (planar) is different from Al(13) (icosahedral). The Al(13)H(13) cluster is predicted to be exceptionally stable on the basis of the high stabilization energy and the negative nucleus independent chemical shift value.

Journal Article↗
PubMed1995

Role of aromatic residues in stabilization of the [Fe4S4] cluster in high-potential iron proteins (HiPIPs): physical characterization and stability studies of Tyr-19 mutants of Chromatium vinosum HiPIP.

The functional role of residue Tyr-19 of Chromatium vinosum HiPIP has been evaluated by site-directed mutagenesis experiments. The stability of the [Fe4S4] cluster prosthetic center is sensitive to side-chain replacements. Polar residues result in significant instability, while nonpolar residues (especially with aromatic side chains) maintain cluster stability. Two-dimensional NMR data of native and mutant HiPIPs are consistent with a model where Tyr-19 serves to preserve the structural rigidity of the polypeptide backbone, thereby maintaining a hydrophobic barrier for exclusion of water from the cluster cavity. Solvent accessibility results in more facile oxidation of the cluster by atmospheric oxygen, with subsequent rapid hydrolysis of the [Fe4S4]3+ core.

Aerobiosis↗
PubMed2000

Glycosylation/Hydroxylation-induced stabilization of the collagen triple helix. 4-trans-hydroxyproline in the Xaa position can stabilize the triple helix.

We have shown recently that glycosylation of threonine in the peptide Ac-(Gly-Pro-Thr)(10)-NH(2) with beta-d-galactose induces the formation of a collagen triple helix, whereas the nonglycosylated peptide does not. In this report, we present evidence that a collagen triple helix can also be formed in the Ac-(Gly-Pro-Thr)(10)-NH(2) peptide, if the proline (Pro) in the Xaa position is replaced with 4-trans-hydroxyproline (Hyp). Furthermore, replacement of Pro with Hyp in the sequence Ac-(Gly-Pro-Thr(beta-d-Gal))(10)-NH(2) increases the T(m) of the triple helix by 15.7 degrees C. It is generally believed that Hyp in the Xaa position destabilizes the triple helix because (Pro-Pro-Gly)(10) and (Pro-Hyp-Gly)(10) form stable triple helices but the peptide (Hyp-Pro-Gly)(10) does not. Our data suggest that the destabilizing effect of Hyp relative to Pro in the Xaa position is only true in the case of (Hyp-Pro-Gly)(10). Increasing concentrations of galactose in the solvent stabilize the triple helix of Ac-(Gly-Hyp-Thr)(10)-NH(2) but to a much lesser extent than that achieved by covalently linked galactose. The data explain some of the forces governing the stability of the annelid/vestimentiferan cuticle collagens.

Amino Acid Sequence↗
PubMed2000

The effect of particle morphology on the physical stability of pharmaceutical powder mixtures: the effect of surface roughness of the carrier on the stability of ordered mixtures.

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.

Chemistry, Pharmaceutical↗
PubMed2003

Sterically stabilized etoposide liposomes: evaluation of antimetastatic activity and its potentiation by combination with sterically stabilized pentoxifylline liposomes in mice.

Cytotoxic activity of chemotherapeutic agents can be enhanced by site-specific delivery or by combination with other less toxic agents. In the present study, enhancement in the antimetastatic activity of etoposide (ETP) by encapsulation in sterically stabilized liposomes was evaluated in the murine experimental B16F10 melanoma model. Further, potentiation of its antimetastatic activity by combination with pentoxifylline (PTX) solution or sterically stabilized PTX liposomes was evaluated in the same animal model. Upon intravenous administration, ETP solution and ETP liposomes inhibited pulmonary tumor nodule formation in a dose-dependent manner. Encapsulation of ETP in liposomes resulted in significant enhancement in its antimetastatic activity at doses of 0.5 mg/kg and 0.75 mg/kg as compared to ETP solution at similar doses. In combination therapy, the effect of sequence of administration of the drugs, ETP and PTX, was evaluated. Enhancement of antimetastatic activity of ETP solution when used in combination with PTX solution was effected by the sequence in which the solutions were administered. However, a combination of ETP liposomes and PTX liposomes led to potentiation of antimetastatic activity in a sequence-independent manner. The results indicate that antimetastatic activity of ETP is significantly enhanced by encapsulation in liposomes. Administration of ETP liposomes with PTX liposomes further potentiated the activity, suggesting the usefulness of this combination in clinical practice for reducing the dose-limiting toxic effects of ETP.

Animals↗
PubMed1997

The ups and downs of nucleic acid duplex stability: structure-stability studies on chemically-modified DNA:RNA duplexes.

In an effort to discover novel oligonucleotide modifications for antisense therapeutics, we have prepared oligodeoxyribonucleotides containing more than 200 different modifications and measured their affinities for complementary RNA. These include modifications to the heterocyclic bases, the deoxy-ribose sugar and the phosphodiester linkage. From these results, we have been able to determine structure-activity relationships that correlate hybridization affinity with changes in oligonucleotide structure. Data for oligonucleotides containing modified pyrimidine nucleotides are presented. In general, modifications that resulted in the most stable duplexes contained a heteroatom at the 2'-position of the sugar. Other sugar modifications usually led to diminished hybrid stability. Most backbone modifications that led to improved hybridization restricted backbone mobility and resulted in an A-type sugar pucker for the residue 5'to the modified internucleotide linkage. Among the heterocycles, C-5-substituted pyrimidines stood out as substantially increasing duplex stability.

DNA↗
PubMed1996

Assessment of pelvic ring stability after injury. Indications for surgical stabilization.

The indications for surgical stabilization of pelvic ring injuries are based on an assessment of the extent of disruption of the pelvic ring and the associated deformity of the bony pelvis. The relevant anatomy and biomechanics or the pelvis, pelvic ring injury classifications, initial assessment, and emergent treatment of patients with pelvic ring injuries is reviewed, and a discussion or indications for surgical stabilization of pelvic ring disruptions is presented.

Biomechanical Phenomena↗
PubMed2004

Preliminary stabilization of the less invasive stabilization system.

We describe the use of a universal T-handle chuck to provide preliminary stabilization of the Less Invasive Stabilization System supracondylar femur implant and aiming device. This technique is helpful to maintain the position of the plate against the bone during intraoperative radiographs and initial screw insertion. Use of this simple technique may help avoid the problems that occur when the plate is positioned too far away from the lateral femoral cortex.

Bone Plates↗
PubMed1986

Stability of the hexagonal lattice structure formed by an R-form lipopolysaccharide of Klebsiella: study of long-range stability.

The R-form lipopolysaccharide (LPS) from Klebsiella strain LEN-111 (O3-:K1-) forms a hexagonal lattice structure with a lattice constant of 14 to 15 nm when it is precipitated by addition of two volumes of 10 mM MgCl2-ethanol. The stability of this hexagonal lattice structure in long-term incubation at 4 C was investigated. The hexagonal lattice structure was stable for at least 220 days when the LPS was suspended in distilled water, but it had been disintegrated into a rough mesh-like structure when the LPS was suspended in 50 mM tris(hydroxymethyl)aminomethane (Tris) buffer, pH 8.5, at 4 C for 60 days. Half of the Mg bound to the LPS was released when the LPS was suspended in Tris buffer for 60 days, whereas Mg was not released when it was suspended in distilled water even for 220 days. By contrast, it was stable for at least 220 days in Tris buffer containing 5 mM MgCl2. The LPS suspended in Tris buffer for 60 days, at which time the structure had been disintegrated, could be restored to the original hexagonal lattice structure within 24 hr by addition of 5 mM MgCl2. From these results it is concluded that the hexagonal lattice structure of the LPS retains long-range stability if Mg bound to the LPS is not released from the LPS.

Chemical Phenomena↗
PubMed1987

What is psychophysically perfect image stabilization? Do perfectly stabilized images always disappear?: comment.

This Communication calls attention to an earlier paper [L. E. Arend and G. T. Timberlake, J. Opt. Soc. Am. A 3, 235 (1986)] in which direct measurements have shown that retinal-image movements less than 1 arc min are required for perfect stabilization. It also cites papers that show that stabilized images of targets that contain no sharp structure in the foveal region disappear completely and permanently. Other targets disappear and reappear as a whole or as fragments intermittently.

Humans↗
PubMed1987

What is psychophysically perfect stabilization? Do perfectly stabilized images always disappear?: reply to comment.

We acknowledge the earlier work cited by Ditchburn in his comment [R. W. Ditchburn, J. Opt. Soc. Am. A 4, 405-406 (1987).] and point out a crucial difference between that work and our novel approach [L. E. Arend and G. T. Timberlake, J. Opt. Soc. Am. A 3, 235 (1986)]. Our procedure provides measurements uncontaminated by residual errors of stabilization. The visual system's extreme sensitivity to small temporal changes and the indirectness of the evidence cited by Ditchburn leave the meaning of stabilized-image reappearance unclear.

Humans↗