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PubMed2007

Isomerization dynamics and control of the eta2/N equilibrium for pyridine complexes.

A series of pyridine complexes are prepared of the general form TpW(NO)(PMe3)(pyr) where pyr is either pyridine or a substituted pyridine. Depending on substitution pattern, the pyridine can be either N- or eta2-coordinated, and the role of the pyridine substituents and metal oxidation state in determining this equilibrium is explored. For eta2-pyridine complexes, the substituent pattern and solubility characteristics also determine the ratio of coordination diastereomers. Rates of both intra- and interfacial linkage isomerizations are explored along with the pyridine rotational barrier. This study is supported by DFT calculations and X-ray data and includes characterization of both eta2-pyridine and eta2-pyridinium complexes.

Crystallography, X-Ray↗
PubMed1998

Characterization of authentic recombinant pea-seed lipoxygenases with distinct properties and reaction mechanisms.

The two major isoforms of lipoxygenase (LOX-2 and LOX-3) from pea (Pisum sativum L. cv. Birte) seeds have been cloned and expressed from full-length cDNAs as soluble, active, non-fusion proteins in Escherichia coli. A comparison of both isoforms purified to apparent homogeneity from E. coli and pea seeds has confirmed the authenticity of the recombinant products and established the properties of the native enzymes. Despite 86% similarity at the amino acid sequence level, the enzymes have distinct properties. They have been characterized in terms of specific activity, Fe content, optimum pH, substrate and product specificity, apparent Km and Vmax for the preferred substrate, linoleic acid, and interfacial behaviour with linoleic acid. We have used this evidence, in addition to EPR spectroscopy of the hydroperoxide-activated enzymes and estimates of kcat/Km, to propose different reaction mechanisms for linoleic acid oxidation for the two isoforms. The differences relate primarily to carbonyl production from linoleic acid for which we propose a mechanism. This implicates the release of a peroxyl radical in an aerobic hydroperoxidase reaction, as the source of the carbonyl compounds formed by dismutation of the liberated peroxyl radical.

Catalysis↗
PubMed1992

Retrieval analyses of a blade implant after 231 months of clinical function.

A blade implant that was retrieved in 1990 after 231 months of clinical function (since 1971) was analyzed with respect to clinical, histological, and biomechanical characteristics. The implant clinical records demonstrated no abnormalities or pathological lesions over the tenure of treatment. The bone to implant interface showed a mixture of interfacial tissue components and conditions with adequate direct bone contact (46.4 to 82.3 percent) for classification as osseointegrated. The abutment fracture leading to removal was characterized as a cyclic fatigue mechanism and the distribution of tissue components along the interface could not be correlated with specific biomechanical loading directions. This report considers the clinical and biomechanical records as they relate to the detailed histological investigation.

Blade Implantation↗
PubMed2005

The role of nonsurface-active species at interfacial molecular recognition by melamine-type monolayers.

The main characteristics of Langmuir monolayers are radically changed by molecular recognition of hydrogen bond nonsurface-active species. The change in the thermodynamic, phase, and structural features by molecular recognition of dissolved uracil or barbituric acid by 2,4-di(n-undecylamino)-6-amino-1,3,5-triazine (2C11H23-melamine) monolayers is characterized by combination of surface pressure studies with Brewster angle microscopy (BAM) imaging and Grazing incidence X-ray diffraction (GIXD) measurements. Phase behavior of the 2C11H23-melamine monolayer and morphology of the condensed phase domains are changed drastically, but in a specific way, by molecular recognition of uracil or barbituric acid. The main characteristics of the interfacial system can be essentially affected by the kinetics of the recognition process. Pure 2C11H23-melamine monolayers show only small compact, but nontextured domains. The monolayers of 2C11H23-melamine-uracil assemblies develop well-shaped circular condensed-phase domains having an inner texture with alkyl chains essentially oriented parallel to the periphery and having a striking tendency to two-dimensional (2D) Ostwald ripening. The 2C11H23-melamine-barbituric acid monolayers form large homogeneous areas of condensed phase that transfer at smaller areas per molecule to a homogeneous condensed monolayer. BAM imaging of corresponding assemblies with ((CH3(CH2)11O(CH2)3)2-melamine having modified alkyl chains demonstrates the specific effect of the monolayer component. GIXD results reveal that molecular recognition of pyrimidine derivatives gives rise only to quantitative changes in the two-dimensional lattice structure. The striking differences in the main characteristics between the supramolecular species are related to their different chemical structures. Quantum chemical calculations using the semiempirical PM3 method provide information about the different nature of the hydrogen-bonding-based supramolecular structures.

Journal Article↗
PubMedDate not supplied

Effect of bonding variables on the shear bond strength and interfacial morphology of a one-bottle adhesive.

This study's objectives were: 1) to determine the combination of bonding procedures (with or without acid etching, moist or dry substrate, one or two applications of primer/adhesive) that would produce the highest shear bond strength of Prime & Bond and Dyract AP and 2) to characterize the resin-dentin/enamel interface produced by these bonding procedures. Ninety-six bovine incisors were randomly assigned to eight groups for shear bond testing to enamel (n = 6) and dentin (n = 6). Prime & Bond and Dyract AP were applied and cured following manufacturers' instructions. Shear bond testing was conducted in a Universal Testing Machine. Thirty-two bovine incisors were sectioned to produce blocks with enamel and dentin, then bonded in pairs for evaluation of interfacial morphology. They were polished and argon ion-etched using a high-speed argon ion-etching machine and examined by SEM. The groups where enamel was etched, kept moist or dry and received a single application of Prime & Bond produced the highest shear bond strength. Dentin bond strengths were high in the groups where dentin was etched and kept moist. The number of Prime & Bond applications had no effect on dentin bond strength. Acid etching results in better adaptation of Prime & Bond to enamel and dentin regardless of whether moisture is present.

Acid Etching, Dental↗
PubMed1986

Physicochemical and morphological characterization of polyisobutyl cyanoacrylate nanocapsules.

Two different polymerization mechanisms of alkyl cyanoacrylates were compared with regard to their morphological and physico-chemical characteristics. Cyanoacrylates were polymerized by simple emulsification into an aqueous medium or by interfacial polymerization in an o/w type emulsion. Suspensions of particles obtained by these two mechanisms show dramatic differences when studied for their turbidity, refractive index, and stability following centrifugation. These observations are consistent with the fact that nanoparticles obtained by emulsion polymerization are known to be formed by a full polymer core, while nanocapsules obtained by interfacial polymerization were thought to consist of an internal oil droplet surrounded by a polymeric wall. This theory was further confirmed by an electron microscopic examination of the internal structures of the two types of polymeric aggregates.

Capsules↗
PubMed2006

Quantifying the physical and chemical mass transfer processes for the fate and transport of Co(II)EDTA in a partially-weathered limestone-shale saprolite.

The objective of the research is to quantify the relative contributions of physical and chemical mass transfer to the movement of Co(II/III)EDTA (chelates of Cobalt and Ethylene Diamine Tetraacetic Acid or EDTA) through a limestone-shale saprolite soil. Saprolite is a collective term referring to partially-weathered bedrock. It exists extensively in the subsurface. Because the parent bedding structures are maintained during the weathering process, saprolite soils are characterized by intensive fractures and secondary deposits of minerals such as Al-, Fe- and Mn-oxides on the fracture surfaces. Movement of reactive species through the soils may be influenced by diffusion into the rock matrix, a physical mass transfer (PMT) process, and interfacial chemical reactions, a chemical mass transfer (CMT) process. The PMT and CMT processes are phenomenologically similar but mechanistically different. In this research, previous laboratory observations from a Br and Co(II)EDTA tracer injection into an undisturbed saprolite soil column were used. Mechanistic reactive transport models were formulated to quantify the PMT and CMT processes. The PMT process was independently characterized by using the non-reactive tracer Br. Model parameters thus obtained were subsequently used as constraints to quantify the CMT processes involving Co(II)EDTA and its oxidation product Co(III)EDTA. Our calculations indicated that the PMT rates of the less reactive Co(III)EDTA were comparable with their theoretical CMT rates. In contrast, for the more reactive species Co(II)EDTA, CMT rates are higher than PMT rates. Evaluations of alternative CMT process models further confirmed one of our hypotheses on the basis of previous experimental understandings. The hypothesis suggested that competition from Fe-oxide for Co(II)EDTA may account for the majority of the decrease of Co(III)EDTA effluent concentrations that resulted in the separation of total Co and Co(III)EDTA breakthrough curves. Because Co(III)EDTA is more mobile than Co(II)EDTA in the subsurface, the results of this research suggest independent quantifications of CoEDTA PMT and CMT processes if laboratory results are to be interpreted correctly and scaled up for field and predictive uses.

Bromine↗
PubMed2000

Polyvinylpyrrolidone Adsorption on Na-Montmorillonite. Effect of the Polymer Interfacial Conformation on the Colloidal Behavior and Binding of Chemicals.

Adsorption behavior of polyvinylpyrrolidone (PVP) on sodium montmorillonite, a swelling clay mineral, was investigated in diluted solutions at an ionic strength of 0.01 M, representative of environmental soil solution conditions. Physicochemical methods such as microcalorimetry, light scattering absorbance, photon correlation spectroscopy, microelectrophoresis, X-ray diffraction, and sedimentation volume measurements were used to characterize the colloidal behavior of montmorillonite particles with various PVP loadings. The extent and properties of the adsorbed PVP train, loop, and end fractions in the particle-stabilizing process have been specified. The interaction study of chemicals such as anionic surfactant sodium dodecyl sulfate and nonionized 4-monochlorophenol as well as their mixture also underlines the importance of the PVP interfacial conformations for the adsorbent capacity of this organoclay. Copyright 2000 Academic Press.

Journal Article↗
PubMed2006

Step-growth synthesis and interfacial friction properties of surface dendron coatings.

We report a new procedure for synthesizing self-assembled two-tiered coatings comprised of a tethered carbosilane dendron canopy layer over an alkylsilane sublayer. The sublayer is anchored to a silicon substrate, and the areal density of the canopy can be controlled by changing the concentration of reactive vinyl groups on the sublayer surface. The structure of the dendron layer is characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS), water contact angle, and ellipsometry. Steric hindrance due to close packing of functional groups has a strong effect on the reaction efficiency, and dendron structure can be obtained only in canopies with low areal densities. Lateral force microscopy (LFM) is used to study interfacial friction and adhesion properties of the coatings. Structural variations in the canopy layer are found to play a crucial role in interfacial friction properties of these coatings.

Adsorption↗
PubMed1992

Hydroxypropyl cellulose/poly(ethylene glycol)-co-poly(propylene glycol) aqueous two-phase systems: system characterization and partition of cells and proteins.

Novel aqueous polymeric two-phase systems are described. These systems are formed by mixing hydroxypropyl cellulose (molecular mass 100,000, trade name Klucel L) with poly(ethylene glycol)-co-poly(propylene glycol) copolymer [molecular mass 6,500, poly(propylene glycol) content 50% w/w, trade name Pluronic P105], in a saline buffer. The phase diagram was measured and the interfacial tensions, phase separation times, and lower phase viscosities of three phase systems having constant Pluronic P105 concentration but varying in Klucel L concentration were determined. The partition behavior of a representative cell, bacterium, and protein and the affinity ligand-mediated alteration in the partition behavior of a protein from a yeast extract protein mixture were also characterized. The results suggest that Klucel L/Pluronic P105 phase systems may be cost-effective substitutes for, or complements to, existing aqueous polymeric phase systems. The physical characterization and representative partition data reported here should facilitate application of these new systems.

Cell Separation↗
PubMed1999

Ideal Mixing of Polymer-Surfactant Complexes of Polyethylene Oxide and Sodium Dodecyl Sulfate Plus Sodium Dodecanoate.

Mixtures of the anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecanoate (SDoD) were investigated regarding their ability to bind to a hydrophilic nonionic polymer, polyethylene oxide (PEO). By electrical conductivity measurements, the parameters with respect to the onsets of surfactant aggregation were determined in the presence of 0.06 M PEO (critical aggregation concentration) and in its absence (critical micelle concentration). It was found that both plots of these parameters for the multicomponent mixtures against molar fraction of SDoD showed an ideal mixing behavior. The same technique was used to estimate the degree of ionization as a fundamental parameter relating to the interfacial composition of mixed aggregates. In addition, in order to monitor changes in polymer-surfactant structures, we used steady-state quenching fluorescence measurements to characterize the sizes of PEO-SDS/SDoD complexes at different compositions of the complex mixture. Copyright 1999 Academic Press.

Journal Article↗
PubMed2005

Membrane activity of the phospholipase C-delta1 pleckstrin homology (PH) domain.

PH-PLCdelta1 [the PH domain (pleckstrin homology domain) of PLCdelta1 (phospholipase C-delta1)] is among the best-characterized phosphoinositide-binding domains. PH-PLCdelta1 binds with high specificity to the headgroup of PtdIns(4,5)P2, but little is known about its interfacial properties. In the present study, we show that PH-PLCdelta1 is also membrane-active and can insert significantly into PtdIns(4,5)P2-containing monolayers at physiological (bilayer-equivalent) surface pressures. However, this membrane activity appears to involve interactions distinct from those that target PH-PLCdelta1 to the PtdIns(4,5)P2 headgroup. Whereas the majority of PtdIns(4,5)P2-bound PH-PLCdelta1 can be displaced by adding excess of soluble headgroup [Ins(1,4,5)P3], membrane activity of PH-PLCdelta1 cannot. PH-PLCdelta1 differs from other phosphoinositide-binding domains in that its membrane insertion does not require that the phosphoinositide-binding site be occupied. Significant monolayer insertion remains when the phosphoinositide-binding site is mutated, and PH-PLCdelta1 can insert into monolayers that contain no PtdIns(4,5)P2 at all. Our results suggest a model in which reversible membrane binding of PH-PLCdelta1, mediated by PtdIns(4,5)P2 or other acidic phospholipids, occurs without membrane insertion. Accumulation of the PH domain at the membrane surface enhances the efficiency of insertion, but does not significantly affect its extent, whereas the presence of phosphatidylethanolamine and cholesterol in the lipid mixture promotes the extent of insertion. This is the first report of membrane activity in an isolated PH domain and has implications for understanding the membrane targeting by this common type of domain.

Animals↗
PubMed2003

Dynamical scaling of surface growth in simple lattice models.

We present extensive simulations of the atomistic Edwards-Wilkinson (EW) and Restricted Edwards-Wilkinson (REW) models in 2+1 dimensions. Dynamic finite-size scaling analyses of the interfacial width and structure factor provide the estimates for the dynamic exponent z=1.65+/-0.05 for the EW model and z=2.0+/-0.1 for the REW model. The stochastic contribution to the interface velocity U due to the deposition and diffusion of particles is characterized for both the models using a blocking procedure. For the EW model the time-displaced temporal correlations in U show nonexponential decay, while the temporal correlations decay exponentially for the REW model. Dynamical scaling of the temporal correlation function for the EW model yields a value of z, which is consistent with the estimate obtained from finite-size scaling of the interfacial width and structure factor.

Journal Article↗
PubMed1998

Ultrastructural and electron diffraction of the bone-ceramic interfacial zone in coral and biphasic CaP implants.

We investigated the influence of natural coral implants used as a bone substitute on the quality of bone ingrowth in rabbits 2, 3, and 6 weeks after implantation. Explants were characterized by transmission electron microscopy and electron diffraction. Bone ingrowth has been previously demonstrated by light microscopy, however, few have been performed in electron microscopy to compare mineralized tissue ingrowth in coral implants which occurs at the expense of calcium carbonate to that of calcium phosphate (CaP) implants. The interface between coral aragonite and mineralized tissue or bone was abrupt, with no invasion of the aragonite structure by newly formed crystals, as occurs in micropores when biphasic CaP (BCP) ceramics were used. The restoring process appears to be different from that induced by BCP implants. Precipitation of needle-like apatite crystals on the CaCO3 implant surface was not observed. Instead, apatitic smooth-shaped crystals formed in aggregates. The coral dissolution process does not release phosphate and so precipitation of apatite does not occur in the micropores of the coral implant, thereby limiting the formation of an apatite layer and hence bone bonding to the outer surface of the implant. In addition, on the outer surface of the implant, close to bone and a phosphorus source, the CaP crystals that do form are in aggregates presumably due to the carbonate and mismatch between the aragonite and the apatite. This seems to result in a delayed bone attachment or weaker bone bonding than CaP implants which encourage an epitaxial biological crystal deposition.

Animals↗
PubMed1998

Characterization of tissue morphology, angiogenesis, and temperature in the adaptive response of muscle tissue to chronic heating.

Previous investigations on the in vivo effects of chronic heat on tissue suggest a response whereby heated tissue temperatures decrease over time. This response occurred in conjunction with localized angiogenesis, which possibly contributed to the temperature decreases by increasing local perfusion and enhancing tissue heat transfer. Our own studies were the first to use a chronic heat source to heat tissue at initial interfacial temperatures between 40 degrees C and 46 degrees C. Initial temperatures above 45.3+/-2.2 degrees C caused necrosis of adjacent tissue. Through an adaptive response, the necrosis was removed by 7 weeks and replaced by a highly vascularized tissue capsule at 41.8+/-0.5 degrees C. The present study sought to characterize the spatial distribution, number of capillaries, and temperatures associated with this adaptive response. Heated and control muscle tissue sections were removed after 2, 4, and 7 weeks of heating at 0.08 W/cm2. Tissue layer thicknesses and capillary densities were measured and correlated with corresponding tissue temperatures. Necrosis was present adjacent to the heat source at 2 and 4 weeks; however by 7 weeks, a highly vascularized fibrous tissue capsule had replaced nearly all necrosis. Capillary densities, particularly near the heat source, were significantly greater at 7 weeks than at either 2 or 4 weeks. Capillary densities in heated tissue capillary fronts tripled from 2 to 7 weeks (106.4+/-14.3 caps/mm2 versus 39.1+/-18.5 caps/mm2). Furthermore, a mean temperature of 41.7+/-0.9 degrees C was measured in heated tissue capillary fronts at all durations, suggesting that this may be a threshold temperature for heat-induced angiogenesis or endothelial cell survival. These findings more completely characterize the perfusion component of the current mathematical model for heat transfer in tissue and will help to establish guidelines for the functional heat loss that an implantable, heat-producing device may allow.

Acclimatization↗
PubMed1992

Interfacial conformation of dipalmitoylglycerol and dipalmitoylphosphatidylcholine in phospholipid bilayers.

Diacylglycerols are minor constituents of membrane lipids, yet are essential in the activation and membrane association of protein kinase C. Solid-state 13C NMR experiments have been used to characterize the orientation of the glycerol backbone of dipalmitoylglycerol (DPG) and dipalmitoylphosphatidylcholine (DPPC) in egg phosphatidylcholine (PC) bilayers. The 13C NMR spectra of both DPG and DPPC specifically 13C-labeled at the sn-2 chain carbonyl exhibit a single narrow resonance (approximately 2 ppm) in liquid-crystalline egg PC bilayers. In contrast, specific 13C-labeling of both the sn-1 and sn-2 chain carbonyls results in an additional broad component (24-32 ppm) with an axially symmetric line shape. These data reveal that DPG has a distinct motionally-averaged structure in PC bilayers that is similar to that of DPPC and is not significantly affected by the absence of the large polar PC headgroup. The NMR line shapes are roughly consistent with the results of previous FTIR and NMR studies that indicate the sn-1 chain extends from the C1 carbon of the glycerol backbone into the hydrophobic interior of the bilayer, while the sn-2 chain first extends parallel to the bilayer surface and incorporates a bend at the ester linkage in order to keep the sn-1 and sn-2 chains parallel. However, the data suggest that the time-averaged orientation of the glycerol backbone is tilted from the bilayer normal, in contrast to the nearly parallel orientation observed in the crystal structures of phosphatidylcholines and phosphatidylethanolamines or the perpendicular orientation observed in the crystal structures of diacylglycerols.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

[Preparation and characterization of nanoemulsion].

AIM: To prepare nanoemulsion-encapsulated BSA-FITC (NEBSA-FITC), study its characteristics, and measure its uptake by dendritic cells (DCs) and peritoneal macrophages. METHODS: NEBSA-FITC was prepared by a method of interfacial polymerization.The encapsulation rate, drug-carrying capacity and stability of the nanoemulsion were determined by Sephadex-G100 chromatography. The shape and size of NEBSA-FITC were observed under electron microscope. The uptake of NEBSA-FITC by DCs and macrophage cells was detected by FACS and laser confocal microscopy. RESULTS: The mean size of NEBSA-FITC was (25+/-10) nm. The encapsulation rate was 91%, the drug-carrying capacity was 0.091 g/L and NEBSA-FITC had a good stability. The FACS analysis showed that DCs and macrophage cells could take in more NEBSA-FITC than free BSA. The observation under laser confocal microscope found that NEBSA-FITC was located in the cytoplasm of DCs. CONCLUSION: Nanoemulsion can be efficiently taken by DCs and macrophage cells, and therefore may be promising efficient carrier of APCs-targeted antitumor vaccine.

Animals↗
PubMedDate not supplied

Membrane formation and characterization of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) for trapping carcinogens.

The membrane characteristics were studied of semi-permeable magnetic polyhexamethyleneterephthalamide microcapsules containing polyethyleneimine (PEI) in order to optimize their use for trapping carcinogens in vivo. The microcapsules were prepared by interfacial polymerization techniques from an aqueous mixture of hexamethylenediamine, PEI and ferrofluid EMG 705 dispersed in an organic phase containing terephthaloyl chloride and trimesoyl chloride. The resulting microcapsule membranes had a complex structure consisting of a polyamide component (70-84 per cent by weight) with chain-terminating carboxy functions and the remainder were PEI incorporated throughout the membrane having residual amine functions. Substantial variation in preparative conditions had little effect upon membrane incorporation of PEI which cross-linked the polyamide chains. However, both TEM and SEM data indicated structural differences when lower concentrations of hexamethylenediamine were used, there being a more uniform formation to give a distinct outer membrane layer (18-45 nm) visible on cross-section and appearing as a smooth outer surface. Magnetite particles appeared to be present throughout the membrane. During membrane formation, no PEI was present in the organic phase, indicating that the microcapsule membrane had formed inwards contrary to the membranes formation reported previously in other systems. The inward transfer of reactive acid chlorides into the aqueous phase resulted in a core of modified PEI. Microcapsule binding of probe substances [14C]N-methyl-N-nitrosourea and eosin varied with the microcapsule preparative conditions used, and appeared to be critically dependent upon the membrane characteristics, especially the incorporation of PEI into the membrane. Characterization of membrane formation and properties allows the optimization of microcapsule binding properties.

Capsules↗