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At least 703 records · Page 39Linked to original sources
PubMed1993

Characterization of 5-fluorouracil loaded liposomes prepared by reverse-phase evaporation or freezing-thawing extrusion methods: study of drug release.

Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by freeze-thawing extrusion technique (FATVET) and the reverse-phase evaporation method (REV) from natural (bovine brain) sphingomyelin (SM) and synthetic distearoylphosphatidylcholine (DSPC) phospholipids was studied. Reverse-phase evaporation vesicles obtained from DSPC sized through polycarbonate membranes of 0.2 micron pore size were found to entrap roughly double amounts of drug than did extruded liposomes (0.1 micron pore size); however, s-REV in these preparations were more heterogenous in vesicle size than FATVET. The rate of in vitro drug release from the liposomes was found to be dependent of the bilayer composition and the method used to prepare the vesicles. The permeability coefficient P obtained was approx. 10(-11) m/s. The results suggest that 5-FU release is kinetically controlled by an interfacial process seemingly dependent on the surface activity of the drug. Also, the physical state of the bilayer determines the retention capacity of the vesicles. Thus, liposomes consisting of distearoylphosphatidylcholine whose acyl chains were in a gel state at the working temperature (37 degrees C) retained 70% of encapsulated 5-FU after 1 h, whereas liposomes composed of natural bovine brain sphingomyelin retained only 15% over the same period.

Animals↗
PubMed2004

Dynamic in situ characterization of organic monolayer formation via a Novel substrate-mediated mechanism.

Ultrahigh vacuum scanning tunneling microscopy data investigating octylsilane (C8H17SiH3) monolayer pattern formation on Au(111) are presented. The irregular monolayer pattern exhibits a 60 A length scale. Formation of the octylsilane monolayer relaxes the Au(111) 23 x square root3 surface reconstruction and ejects surface Au atoms. Au adatom diffusion epitaxially extends the Au(111) crystal lattice via step edge growth and island formation. The chemisorbed monolayer covers the entire Au surface at saturation exposure. Theoretical and experimental data suggest the presence of two octylsilane molecular adsorption phases: an atop site yielding a pentacoordinate Si atom and a surface vacancy site yielding a tetracoordinate Si atom. Theoretical simulations investigating two-phase monolayer self-assembly dynamics on a solid surface suggest pattern formation results from strain-induced spinodal decomposition of the two adsorption phases. Collectively, the theoretical and experimental data indicate octylsilane monolayer pattern formation is a result of interfacial Au-Si interactions and the alkyl chains play a negligible role in the monolayer pattern formation mechanism.

Journal Article↗
PubMed1997

Purification and characterization of three distinct types of phospholipase A2 inhibitors from the blood plasma of the Chinese mamushi, Agkistrodon blomhoffii siniticus.

Three distinct types of phospholipase A2 (PLA2) inhibitory proteins (PLIalpha, PLIbeta, and PLIgamma) were isolated from the blood plasma of the Chinese mamushi, Agkistrodon blomhoffii siniticus. PLIalpha is an inhibitor that we have already purified and whose amino acid sequence we have already determined [Ohkura, Inoue, Ikeda and Hayashi (1993) J. Biochem. (Tokyo) 113, 413-419]. It inhibited selectively the group-II acidic PLA2s from Crotalidae venom. PLIbeta was a 160-kDa glycoprotein having a trimeric structure composed of 50-kDa subunits. The amino acid sequence of the first 30 amino acids of the N-terminal part of the 50-kDa subunit was determined and found to have no significant homology to that of known proteins. PLIbeta was a selective inhibitor against the group-II basic PLA2s from Crotalidae venom. Some amino acid residues located in or close to the interfacial binding surface of the group-II basic PLA2s were suggested to be involved in selective binding to PLIbeta. PLIgamma was a 100-kDa glycoprotein containing 25-kDa and 20-kDa subunits and inhibited all of the PLA2s investigated equally, including Elapidae venom PLA2s (group I), Crotalidae and Viperidae venom PLA2s (group II) and honey-bee PLA2 (group III). From the N-terminal sequences of the two subunits, PLIgamma was found to be the same type of PLI that had been purified from Thailand cobra plasma.

Agkistrodon↗
PubMed1994

Structural and immunological characterization of a biosurfactant produced by Bacillus licheniformis JF-2.

Bacillus licheniformis JF-2 produces a very active biosurfactant under both aerobic and anaerobic conditions. We purified the surface-active compound to homogeneity by reverse-phase C18 high-performance liquid chromatography and showed that it is a lipopeptide with a molecular weight of 1,035. Amino acid analysis, fast atom mass and infrared spectroscopy, and, finally, 1H, 13C, and two-dimensional nuclear magnetic resonance demonstrated that the biosurfactant consists of a heterogeneous C15 fatty acid tail linked to a peptide moiety very similar to that of surfactin, a lipopeptide produced by Bacillus subtilis. Polyclonal antibodies were raised against surfactin and shown to exhibit identical reactivity towards purified JF-2 lipopeptide in competition enzyme-linked immunosorbent assays, thus providing further evidence for the structural similarity of these two compounds. Under optimal conditions, the B. licheniformis JF-2 biosurfactant exhibits a critical micelle concentration of 10 mg/liter and reduces the interfacial tension against decane to 6 x 10(-3) dyne/cm, which is one of the lowest interfacial tensions ever reported for a microbial surfactant.

Amino Acid Sequence↗
PubMed2003

Effects of interfacial variables on ceramic adherence to cast and machined commercially pure titanium.

STATEMENT OF THE PROBLEM: Titanium-ceramic bonding is less optimal than conventional metal-ceramic bonding, due to excessive oxidation of titanium during porcelain firing. PURPOSE: This in vitro study evaluated the effects of porcelain firing atmosphere and gold sputter coating on titanium surfaces on porcelain bonding to machined and as-cast titanium substrates. Material and methods Eight groups of ASTM grade 2 commercially pure (CP) titanium specimens (13 mm x13 mm x1 mm) were prepared (n=10). A conventional Au-Pd-In metal-ceramic alloy (Orion) and an ultra low-fusing porcelain (Finesse) served as the control (n=10). Forty machined titanium specimens were prepared from 1.00-mm thick titanium sheets with a diamond band saw. Forty titanium specimens were produced in a centrifugal dental titanium casting machine. All titanium specimens were airborne particle abraded with 110-microm alumina particles, whereas the control specimens were airborne particle abraded with 50-microm alumina particles. Forty titanium specimens (20 specimens each of as-cast and machined titanium) were randomly selected for gold sputter coating before ceramic firing. An ultra low-fusing porcelain (Vita Titankeramik) was fused on the central 6-mm diameter circular area on each titanium specimen. Porcelain firing environments for the titanium specimens consisted of vacuum and a reduced argon atmosphere. Porcelain was debonded by a biaxial flexure, constant strain test at a cross-head speed of 0.25 mm/min. Specimens were analyzed by standardized SEM/EDS analysis 3 times throughout the study to determine the silicon atomic percentage (Si at %): (1) after airborne particle abrasion, before porcelain application; (2) after the application of the first layer of porcelain; and (3) after the fracture of porcelain from the metal substrate. The titanium-ceramic adhesion was characterized by determining the area fraction of adherent porcelain (AFAP). Results were analyzed by analysis of variance and the Student-Newman-Keuls test (alpha=.05). RESULTS: Statistical analysis showed a significant difference in the AFAP values among all the groups. AFAP value of the control group was significantly higher (135.35 +/- 23.68) than those of the experimental groups (P<.001). For the machined titanium, AFAP value of gold sputter-coated/argon group (91.38 +/- 7.93) was significantly higher than the rest of the groups (P<.001). For the as-cast titanium fired in vacuum, significantly lower AFAP values (P<.001) were found in the gold sputter-coated group (50.2 +/- 11.26 vs 66.15 +/- 10.41). AFAP values between the argon groups with or without the gold coating were not significantly different (P=.303); however, both argon groups (93.83 +/- 4.65 and 98.09 +/- 6.35) showed significantly higher AFAP values compared with the vacuum groups (P<.001). CONCLUSION: Firing porcelain in a reduced argon atmosphere significantly improved titanium-ceramic bonding for machined and as-cast titanium. The sputter-coated gold layer on titanium provided improved titanium-ceramic bonding only when combined with firing porcelain in reduced argon atmosphere. When porcelain was fired in vacuum in the presence of the gold layer, the titanium-ceramic bonding was weakened in as-cast titanium and was not affected in machined titanium. Conventional noble metal-ceramic bonding was superior to titanium-ceramic bonding regardless of the interfacial variables examined in this study.

Aluminum Oxide↗
PubMed1982

Mechanical properties of the fibrous tissue found at the bone-cement interface following total joint replacement.

A long-term problem associated with total joint replacements is the formation of a fibrous tissue at the bone-cement interface which may compromise the fixation of the prosthesis. In this study, harvestable amounts of interfacial fibrous tissue were generated using a prosthetic replacement of the canine stifle joint as an animal model. The collected tissues were examined histologically and by uniaxial, unconfined compression tests. The fibrous tissue had a matlike structure. The heavy collagen fibers were distributed at random in sheets and the sheets themselves were layered to form a mat. Such a structure may be able to resist compressive stresses normal to the plane of the mat but is probably not well suited to resist shearing stresses. The fibrous tissue proved to be a very compliant, deformable material and to undergo very large strains with load. The stress-strain curve for the tissue was nonlinear and was characterized by large deformations at low loads. But with increasing loads, the material became stiffer, and at high loads, the stress-strain curve became linear with a short-term tangent modulus of 1.9 MPa at a stress level of 0.5 MPa and a compressive strain level of 50%. With regard to total joint replacement systems which consist of an outer bone shell followed by a thin layer of fibrous tissue, a mantle of PMMA cement and a central core of metal or UHMW polyethylene, the fibrous tissue is substantially more yielding and deformable than the other elements of the structure and may have a significant effect on the structural behavior of the system.

Animals↗
PubMed2001

Interfacial mass transfer in randomly packed towers: a confident correlation for environmental applications.

Volumetric mass-transfer coefficients (kLa(w), KLa(w), kGa(w), kGa(w)) required for randomly dumped packed tower design were gathered from the literature to generate a working database comprehending 2675 measurements relevant to water and air pollution abatement processes. The cross-examination of two important correlations predicting mass-transfer coefficients was achieved through this database (Onda correlation, 1968; Billet and Schultes correlation, 1993). Some limitations regarding either the level of accuracy or the application range came to light with this investigation. Artificial neural network (ANN) modeling is then proposed allowing all four mass-transfer coefficients predictions. A single ANN correlation was built to predict the dimensionless gas (or liquid) film Sherwood number (ShL/G) as a function of six dimensionless groups, namely, the liquid Reynolds (ReL), Froude (FrL), Eotvös (EoL) numbers, the gas (or liquid) Schmidt number (ScL/G), the Lockhart-Martinelli parameter (chi), and a bed-characterizing number (K). Using the ANN correlation and the two-film theory, a reconciliation procedure was further implemented resulting in better predictions of the gas (or liquid) overall volumetric mass-transfer coefficients. The resulting correlation yielded an absolute average relative error of 22.1% and a standard deviation of 21.1% based on whole database while the ANN predictions remain in accordance with the physical evidence reported in the literature.

Air Pollutants↗
PubMed2026

Operando X-ray Spectroscopy Unveils Light-Driven Redox Selectivity for Photo-Assisted Li-S Batteries.

Photo-assisted lithium-sulfur batteries (PALSBs) can accelerate the sluggish redox kinetics of sulfur cathodes. However, the introduced light field inevitably complicates interfacial reactions, necessitating in situ evidence under realistic operating conditions. Here, we construct a TiO2/FePS3 (TF) p-n junction bifunctional photoelectrode and employ a multiphysics-coupled in situ x-ray spectroscopic technique to elucidate light-regulated catalysis from the interface into the bulk. Operando low-energy XPS identifies potential interfacial catalytic sites. High-energy operando XAFS is, for the first time, applied in PALSBs to track the K-edge position of catalytic centers throughout cycling. The results show that the reversible dynamic valence evolution synchronizes with the stepwise sulfur redox process, revealing that photogenerated carriers and electrocatalytic electrons act cooperatively to promote polysulfide conversion. DFT calculations corroborate, from thermodynamic and kinetic perspectives, that illumination strengthens polysulfide anchoring and lowers the energy barriers of key conversion steps, consistent with the operando spectroscopic observations. Benefiting from this photoelectrochemical co-regulation, the TF-based PALSB maintains excellent reversible capacity and cycling stability under high sulfur loading and low electrolyte content. This work establishes a characterization paradigm for the rational design of high-performance photo-assisted Li-S cathodes.

operando x&#x2010;ray spectroscopy↗
PubMed2026

Micro- and nanoplastics-induced neurotoxicity: a CNS-centered, evidence-graded adverse outcome pathway framework based on systematic weight-of-evidence assessment.

Micro- and nanoplastics (MPs/NPs) are ubiquitous anthropogenic particulate pollutants posing emerging threats to human neurological health. Severe heterogeneity in particle physicochemical properties, environmental aging status, exposure paradigms and experimental platforms has created persistent mechanistic uncertainties in MP/NP neurotoxicology, hindering reliable hazard characterization and risk translation. Here, we systematically consolidate empirical toxicological evidence and construct a dedicated central nervous system (CNS)-targeted adverse outcome pathway (AOP) network integrated with rigorous weight-of-evidence (WoE) grading to elucidate the hierarchical, particle-specific toxic cascades underlying MP/NP-induced neural injury. Our synthesis overturns the conventional linear toxicity paradigm, demonstrating that MPs/NPs trigger neurotoxicity via a complex multi-input mechanistic network. We definitively establish oxidative stress as a robust early convergent key event-rather than a universal molecular initiating event-orchestrating ROS overproduction, lipid peroxidation, mitochondrial dysfunction, and neuroinflammation to propagate neuronal damage. This core module is driven by five distinct particulate upstream triggers: particle-biomolecule interfacial perturbation, corona-facilitated cellular internalization, plastic-associated chemical leaching, aging-derived free radical reactivity, and gut-borne systemic neurotoxic signaling. Downstream pathogenic outcomes encompass glial overactivation, neurotransmitter dyshomeostasis, autophagy-lysosome dysfunction, metabolic reprogramming, regulated neuronal cell death, and behavioral impairments. Tiered WoE analysis confirms strong validation for early oxidative/inflammatory cascades, moderate support for gut-brain axis crosstalk and intracellular trafficking disruption, and nascent evidence for synaptic dysfunction and neurodegeneration-linked proteostatic defects. Extrapolation to human health risk remains constrained by the frequent use of high-dose exposure paradigms, limited validated data on internal dosimetry in the human brain, discrepancies between effective concentrations in experimental models and environmentally relevant human tissue burdens, and insufficient causal validation of distal adverse outcomes. We highlight key research priorities including aged mixed-particle exposure systems, leachate-controlled assays, quantitative internal dose evaluation, and mechanistic intervention verification. This evidence-stratified AOP framework resolves longstanding mechanistic ambiguities in particulate neurotoxicity, providing a standardized, causality-based foundation for future mechanistic exploration and health risk assessment of global plastic pollution.

Adverse outcome pathway↗
PubMed1993

One-step purification and characterization of human pancreatic lipase expressed in insect cells.

A cDNA clone encoding the sequence of human pancreatic lipase (HPL) was subcloned into the baculovirus transfer vector pVL1392 and used in co-transfection of Spodoptera frugiperda (Sf9) insect cells with wild-type Autographa californica nuclear polyhedrosis virus (AcNPV) DNA. A single recombinant protein (50 kDa) secreted by Sf9 cells was detectable in the culture medium 24 h post-infection using both anti-HPL polyclonal antibodies and potentiometric measurements of lipolytic activity. The expression level reached 40 mg/l of enzyme at 6 days. A single cation-exchange chromatography was sufficient to obtain a highly pure recombinant HPL as demonstrated by N-terminal sequencing, amino acid composition and carbohydrate analysis, as well as by mass spectrometry. These analyses revealed the production of mature protein with the correct processing of signal peptide and an homogenous glycosylation pattern. The kinetic properties of recombinant and native HPL were compared. Both enzymes showed similar profiles of interfacial activation, inhibition by bile salts and re-activation by colipase.

Amino Acid Sequence↗
PubMed2005

Two-phase flow in porous media: Crossover from capillary fingering to compact invasion for drainage.

It had been predicted that the capillary fingering observed at small capillary numbers should change or cross over to compact invasion at larger capillary numbers or longer times [D. Wilkinson, Phys. Rev. A 34, 1380 (1986)]. We present results from pore-level modeling in two dimensions for the average position (related to the position of the interface) of the injected fluid as well as the width of the interface between the injected, nonwetting fluid and the defending, wetting fluid. These results are entirely consistent with the predicted crossover from the fractal flow characterized by invasion percolation with trapping (IPWT) to compact/linear/stable flow, where the position of the injected fluid advances linearly with time and where the width of the interface is constant. Furthermore, our results for the characteristic time, at which the crossover occurs, agree with the predictions of Wilkinson. To focus on the effect of capillary number, we are considering only viscosity-matched flows where both fluids have the same viscosities. To our knowledge, these are the first pore-level modeling results that quantitatively test the general predictions of Wilkinson for this capillary crossover in the case of drainage. Our modeling results are used to provide closed form expressions predicting the dependence of average position and interfacial width upon capillary number and time, regardless of the size of the system. The size scaling inherent in the crossover combined with our results locating the upper and lower bounds of the crossover regime enable us to predict the location of the crossover for two-dimensional systems of different size. These predictions are compared with flow patterns from experiments in the literature. The agreement between our predictions and the experimental flow patterns indicates that the experiments exhibit the same IPWT to compact crossover observed in our modeling.

Journal Article↗
PubMed2004

Calcium phosphate sol-gel-derived thin films on porous-surfaced implants for enhanced osteoconductivity. Part I: Synthesis and characterization.

Thin sol-gel-formed calcium phosphate (Ca-P) films were formed on sintered porous-surfaced implants as an approach to increasing the rate of bone ingrowth. The films were prepared using either an inorganic precursor solution (with calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) or an organic precursor solution (with calcium nitrate tetrahydrate and triethyl phosphite). We report on the formation and characteristics of the films so formed. Film characteristics were assessed by thin film X-ray diffraction, diffuse-reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. In addition, thin sections were prepared either across or parallel to the Ca-P/Ti6Al4V interface and examined by transmission electron microscopy. Both approaches resulted in the formation of nanocrystalline carbonated hydroxyapatite films but with different Ca/P ratios and structures, the Inorganic Route-formed film having a lower Ca/P ratio (1.46 cf 2.10 for the Organic Route-formed film) and having a more irregular topography. An interfacial reaction product (CaTi(2)O(5)) was identified by selected area electron diffraction with the Inorganic Route-formed film only.

Absorptiometry, Photon↗
PubMed2006

Water-hydrocarbon interfaces: effect of hydrocarbon branching on interfacial structure.

Molecular dynamics simulation are performed for the water/hydrocarbon system to study the effect of hydrocarbon branching on interfacial properties. The following two series of hydrocarbons are considered: (1) n-pentane, 2-methyl pentane, and 2,2,4-trimethyl pentane (constant chain length) and (2) n-octane, 2-methyl heptane, and 2,2,4-trimethyl pentane (constant molecular mass). With a simple algorithm for identification of surface sites and mapping nonsurface sites to these surface sites, intrinsic profiles were constructed with respect to the surface layer. Intrinsic density profiles for water and hydrocarbons with respect to the hydrocarbon and water surface, respectively, resemble density profiles of liquids in the presence of a wall. Order parameters were used to study orientation of molecules with respect to the surface normal and the hydrogen bond network was characterized in terms of the number of hydrogen bonds per water molecule and percentage of hydrogen bonded molecules in the first coordination shell. The corresponding intrinsic profiles were obtained. The O-H bond for surface water was found to have two preferential orientations, pointing toward the hydrocarbon phase and parallel to the interface. Hydrocarbon molecules in series 1 orient along the interface with the more branched molecule better aligned. For molecules in series 2, the larger molecular length reduces the alignment of molecules along the interface.

Journal Article↗
PubMed2005

Lipopolymers from new 2-substituted-2-oxazolines for artificial cell membrane constructs.

We present the synthesis of novel 2-oxazoline monomers with different 2-substituents and their consecutive conversion into lipopolymers by living cationic polymerization. The side functions of these monomers were varied to realize different steric needs and hydrogen bonding interactions of the polymer side chains. 2-(2'-N-pyrrolidonyl-ethyl)-2-oxazoline, 2-(3'-methoxymonoethyleneglycol)propyl-2-oxazoline, and 2-(3'-methoxytriethyleneglycol)propyl-2-oxazoline were synthesized. All of the monomers could be converted into the corresponding lipopolymers by living cationic polymerization using 2,3-di-O-octadecyl-1-trifluormethansulfonyl-sn-glycerol as the initiator. The characterization of the 2,3-di-O-octadecyl-glycerol-poly(2-oxazoline) lipopolymers by NMR spectroscopy, IR spectroscopy, and gel permeation chromatography revealed that the targeted molar masses and compositions can be controlled by the initial initiator/monomer ([M](0)/[I](0)) ratio for all the synthesized lipopolymers. The polydispersities were found to be narrow (polydispersity indices from 1.06-1.3). The amphiphilic lipopolymers were spread at the air-water interface (Langmuir-Blodgett film balance) and the effect of the polymer side groups and chain lengths upon the Pi-area (A) isotherms of the corresponding lipopolymer monolayers were compared and analyzed. The impact of the polymer side functionalities on a 2D gel formation was examined using an interfacial rheometer operated in an oscillating stress-strain mode. Interestingly enough, none of the newly synthesized lipopolymers showed a rheological transition. This somewhat surprising result not only verified that these 2D gels are not established by hydrogen bonding among hydrophilic polymer moieties, as earlier proposed, but also supported the concept of jammed surface micelles as the more likely origin for the gelation phenomenon. [Diagram: see text]

Membranes, Artificial↗
PubMed2003

Immobilization of Chinese herbal medicine onto the surface-modified calcium hydrogenphosphate.

To accelerate the healing of bone defects or for healing to take place, it is often necessary to fill them with suitable substance. Various artificial materials defects have been developed. Among these, calcium phosphates and bioactive glass have been proven to be biocompatibile and bioactive materials that can chemically bond with bone, and have been successfully used clinically for repair of bone defects and augmentation of osseous tissue. However, those bioceramics have only the property of osteoconduction without any osteoinduction. Many ligands have been physicochemically absorbed onto substrates to enhance cell-substrate interactions. Although widely developed, they are still limited to use in long-term implantation because of their half-life period. Thus, some interfacial modification will be required for enhancing the efficacy of the delivery system. These models involve the immobilization of biologically active ligands of natural and synthetic origin onto various substrates to produce an interface with stronger chemical bond between ligand and substrate. The advantage of covalently immobilizing a ligand is that a chemical bond is present to prevent ligand or medicine from desorption. In our study, a two-step chemical immobilization was performed to surface-modified calcium hydrogenphosphate powders. The first was to modify the surface of calcium hydrogen-phosphate (CHP) with a coupling agent of hexanmethylene diisocyanate (HMDI). CHP surface modified by HMDI is abbreviated as MCHP. The linkage between CHP and HMDI will be characterized by FTIR. The second step was to immobilize chemically Gusuibu onto MCHP. Moreover, the sorption and desorption of Gusuibu was evaluated and quantitatively analyzed by spectrophotometer and HPLC. Bioceramic CHP was surface-modified by a two-step chemical immobilization. First, the surface of calcium hydrogen-phosphate (CHP) was successfully modified with coupling agent of hexanmethylene diisocyanate (HMDI). The first step was also activated the surface of CHP to induce primary amine terminator. The reaction of this functional group with Gusuibu was the second step. We confirmed simultaneously that Gusuibu could be immobilized chemically onto the surface of MCHP. Although some immobilized Gusuibu was also released rapidly at the first 12h, the degree of the released Gusuibu was lower than both by Gusuibu-adsorbing MCHP and Gusuibu-adsorbing CHP.

Adsorption↗
PubMed2005

Supramolecular assemblies and molecular recognition of amphiphilic schiff bases with barbituric acid in organized molecular films.

A bolaform Schiff base, N,N'-bis(salicylidene)-1,10-decanediamine (BSC10), has been synthesized and its interfacial hydrogen bond formation or molecular recognition with barbituric acid was investigated in comparison with that of a single chain Schiff base, 2-hydroxybenzaldehyde-octadecylamine (HBOA). It has been found that while HBOA formed a monolayer at the air/water interface, the bolaform Schiff base formed a multilayer film with ordered layer structure on water surface. When the Schiff bases were spread on the subphase containing barbituric acid, both of the Schiff bases could form hydrogen bonds with barbituric acid in situ in the spreading films. As a result, an increase of the molecular areas in the isotherms was observed. The in situ H-bonded films could be transferred onto solid substrates, and the transferred multilayer films were characterized by various methods such as UV-vis and FT-IR spectrosopies. Spectral changes were observed for the films deposited from the barbituric acid subphase, which supported the hydrogen bond formation between the Schiff bases and barbituric acid. By measuring the MS-TOF of the deposited films dissolved in CHCl3 solution, it was concluded that a 2:1 complex of HBOA with barbituric acid and a 1:2 complex of BSC10 with barbituric acid were formed. On the other hand, when the multilayer films of both Schiff bases were immersed in an aqueous solution of barbituric acid, a similar molecular recognition through the hydrogen bond occurred. A clear conformational change of the alkyl spacer in the bolaform Schiff base was observed during the complex formation with the barbituric acid.

Journal Article↗
PubMed2005

Use of block copolymer-stabilized cadmium sulfide quantum dots as novel tracers for laser scanning confocal fluorescence imaging of blend morphology in polystyrene/poly(methyl methacrylate) films.

This paper describes the first use of polymer-coated quantum dots (QDs) as fluorescent tracers for LSCFM imaging of phase morphology in polymer blends. Cadmium sulfide (CdS) QDs stabilized at the surface with a PS-b-PAA block copolymer are shown to be well dispersed via their polystyrene (PS) brush layer in the PS phase of solvent-cast 40/60 (w/w) PS/PMMA blends. The QDs are excluded from the PMMA phase, providing excellent fluorescence contrast for LSCFM imaging of the phase-separated blends. The presence of PS-b-PAA-stabilized QDs does not appear to affect the blend morphology, since the observed morphologies are the same when the percentage of QDs within the PS phase is varied from 10 to 50 wt %. These QD fluorescent tracers are used to characterize several aspects of blend morphology in solvent-cast 40/60 PS/PMMA blends containing PS homopolymer with either 100 (low molecular weight) or 1250 (high molecular weight) repeat units. In the PS(1250)/PMMA blends, a percolating distribution of PMMA droplets (2-25 mum) in a PS matrix is observed in the bulk, and a distinct inversion in the continuous phase is found near the glass substrate. In the PS(100)/PMMA blends, a "phase-in-phase" morphology is found, consisting of large PS domains (20-100 mum) dispersed in a PMMA continuous phase and small PMMA domains (1-2 mum) scattered throughout the larger PS droplets. The observed change in blend structure is attributed to a lower interfacial tension for the lower molecular weight PS.

Journal Article↗
PubMed1994

Interactions of plasma proteins with a novel polysaccharide surfactant physisorbed to polyethylene.

A polysaccharide surfactant, dextran-[1,6 bis(2-hydroxypropyl-1-amine)hexane]-dextran, (D-H-D) was prepared by reacting dextran (Mw = 8200) with epichlorohydrin followed by reaction with 1,6-hexanediamine. The D-H-D polymer product was characterized by gel permeation chromatography (GPC), and 13C-nuclear magnetic resonance spectroscopy (13C-NMR). D-H-D was physisorbed on polyethylene (PE) from aqueous solution, and the adhesion stability and resistance to protein adsorption was examined under static and dynamic flow conditions, using a modified rotating disk system. Modified surfaces were characterized by attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA) and by water contact angles. Under applied shear stresses of up to 73 dyn cm-2, the adhesion of D-H-D on PE was sufficient to inhibit desorption by water (> 90% D-H-D on PE was retained) and 5% SDS surfactant solution (approximately 83% D-H-D retained), as determined by ATR-FTIR. Under similar shear stress conditions, albumin adsorption on D-H-D modified PE was reduced by over 90%, and protein adsorption from fresh human plasma was reduced by approximately 70% compared with unmodified PE. The results are discussed in terms of interfacial forces, and the suitability of this approach for studying protein-surface interactions and for developing a novel class of protein-resistant biomaterials.

Adsorption↗