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PubMedDate not supplied

Stereochemistry of the major rat liver microsomal metabolites of the carcinogen 7-methylbenz[c]acridine.

The major metabolites of the carcinogen 7-methylbenz[c]acridine (7MBAC), trans-5,6-dihydro-5,6-dihydroxy-7-methylbenz[c]acridine (7MBAC-5,6-DHD), and trans-8,9-dihydro-8,9-dihydroxy-7-methylbenz[c]acridine (7MBAC-8,9-DHD) were characterized as their enantiomers after separation of their bis-(+)-(1R,2S,4S)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5 -ene-2-carboxylic acid [(+)-HCA] esters and hydrolysis. The synthetic precursor, trans-3,4-dihydroxy-7-methyl-1,2,3,4-tetrahydrobenz[c]acridine (7MBAC-3,4-THD), was similarly separated into enantiomers, and the dihydrodiol trans-3(S),4(S)-dihydro-3,4-dihydroxy-7-methylbenz[c]acridine (7MBAC-3,4-DHD) was prepared from 7MBAC-3(S),4(S)-THD. Absolute configurations were assigned by the chiral exciton coupling of the bis-p-(dimethylamino)benzoate of 7MBAC-3(R),4(R)-THD, and by the semiempirical methods based on the biaryl chromophores of the enantiomers of 7MBAC-5,6-DHD and of the methanolysis products of the 5,6-oxide of 7MBAC which were resolved as their (+)-HCA esters. X-ray crystallography was used for 7MBAC-8(S),9(S)-DHD bis-(+)-HCA ester, and assignments were correlated with chiral exciton coupling of the bis-4-(dimethylamino)cinnamates of 7MBAC-5(R),6(R)-DHD and 7MBAC-8(S),9(S)-DHD. The stereochemical compositions of four metabolites (three dihydrodiols and 7MBAC-5,6-oxide) formed in incubations with rat liver microsomes from control and induced liver were determined by normal-phase separations of bis-(+)-HCA esters, and by chiral stationary-phase separation of the 5,6-oxide methanolysis products. The 3(R),4(R)-enantiomer of 7MBAC-3,4-dihydrodiol predominated, 74-98% enantiomeric purity, and purity for the oxide varied from about 71% 5(R),6(S)-oxide for control microsomes to about 28% 5(R),6(S)-oxide for liver microsomes obtained from 3-methylcholanthrene-pretreated rats.

Acridines↗

PubMed2002

Application of complex macromolecular architectures for advanced microelectronic materials.

The distinctive features of well-defined, three-dimensional macromolecules with topologies designed to enhance solubility and amplify end-group functionality facilitated nanophase morphologies in mixtures with organosilicates and ultimately nanoporous organosilicate networks. Novel macromolecular architectures including dendritic and star-shaped polymers and organic nanoparticles were prepared by a modular approach from several libraries of building blocks including various generations of dendritic initiators and dendrons, selectively placed to amplify functionality and/or arm number, coupled with living polymerization techniques. Mixtures of an organosilicate and the macromolecular template were deposited, cured, and the phase separation of the organic component, organized the vitrifying organosilicate into nanostructures. Removal of the sacrificial macromolecular template, also denoted as porogen, by thermolysis, yielded the desired nanoporous organosilicate, and the size scale of phase separation was strongly dependent on the chain topology. These materials were designed for use as interlayer, ultra-low dielectric insulators for on-chip applications with dielectric constant values as low as 1.5. The porogen design, chemistry and role of polymer architecture on hybrid and pore morphology will be emphasized.

Electronics↗

PubMed1982

Temperature-induced vertical shift of proteins in membranes.

Thermotropic changes in the transverse order of microsomal membranes isolated from Tetrahymena are revealed by low-angle X-ray diffraction. These are correlated with the lateral order of the membrane lipids by wide-angle X-ray diffraction. Upon lowering the temperature from 28 degrees C to 2 degrees C, the Bragg period of the membrane stack reveals an abrupt increase of approximately 3.1 nm at approximately 19 degrees C, which is reversible upon reheating to 28 degrees C. This is coupled with an alteration in the electron density profile, revealing a shift of mass from the hydrophobic core towards one of the two hydrophilic surfaces. Between 35 degrees C and 0 degrees C, the membrane lipids undergo a broad, thermotropic "two-stage" liquid crystalline in equilibrium crystalline phase separation with a "breakpoint" at approximately 18 degrees C. This breakpoint signals an abrupt lipid redistribution, presumably due to a change in the composition of the two coexisting liquid crystalline and crystalline lipid phases. We conclude: (1) the temperature-induced mass shift reflects a shift in the transverse partition of proteins in membranes; (2) this is triggered by an abrupt lipid redistribution occurring during a broad liquid crystalline in equilibrium crystalline phase separation.

Fatty Acids↗

PubMed2006

Effect of polycation length on its complexation with DNA and with poly(oxyethylene-block-sodium methacrylate).

Polyelectrolyte complexes of a synthetic polycation with either a genomic DNA or a synthetic poly(oxyethylene-block-sodium methacrylate), POE-b-PMANa, have been studied in aqueous solutions as a function of cation:anion ratio, the degree of polymerization of the polycation, the ionic strength, and temperature using dynamic light scattering and turbidity measurements. The polycation was a copolymer of methacryl oxyethyl trimethylammonium chloride and poly(oxyethylene) monomethyl ether monomethacrylate with 4-5 oxyethylene repeating units, PMOTAC-g-POE. The molar masses of the polycations in a homological series were 0.3, 0.9, and 2.1 x 10(6) g/ mol. The amount of comonomers with poly(oxyethylene) tails in the copolymers was 15 mol %. The molar mass of the POE-b-PMANa was 75000 g/mol and that of the POE-block was 5000 g/mol. The molar mass of the polycation was shown to have a dramatic effect on the stability and size of the complexes formed by either of the polyanions. An increase in the polycation molar mass shifts the cloud point toward the lower polycation content in the complexes, and a macro phase separation occurs in the solutions with the cation to anion molar ratios much below than 1:1. Increasing the ionic strength has a similar effect. Further addition of salt to turbid and phase-separated solutions results in dissociation of the complexes, and the polyions dissolve as individual macromolecules. The effect of POE on the stability of polyelectrolyte complexes is discussed as well.

Cations↗

PubMed2004

Rheology of mixed beta-casein/beta-lactoglobulin films at the air-water interface.

The adsorption of dilute mixtures of beta-casein/beta-lactoglobulin to the air-water interface was investigated using surface dilatation and surface shear rheology. The data were fitted to simple rheological models to try to gain further information regarding the composition and nature of the interface. The dilatational measurements suggested that the composition of the interface could be determined using these models and that the surface concentration was dominated by the beta-casein in the early stages of adsorption but that high levels of beta-lactoglobulin were present in the final stages. Surface shear rheological measurements showed a similar trend. However, the shear measurements appeared to be more sensitive to the strength of the network than to the composition of the interface. Fluorescence microscopy supported the findings and demonstrated that any "phase separation" capable of affecting the surface rheological measurements occurred at the sub-micrometer scale. The results also demonstrated that the heterogeneity of the interface, once formed, is kinetically trapped, and no further phase separation occurs over the time span of the experiments.

Adsorption↗

PubMed2000

Simple views on critical binary liquid mixtures in porous glass

A simple scenario, different from previous attempts, is proposed to resolve the problem of the slow phase separation dynamics of binary liquid mixtures confined in porous Vycor glass. We demonstrate that simply mutual diffusion, renormalized by critical composition fluctuations and geometrical hindrance of the porous glass, accounts for the slow phase separation kinetics. Capillary invasion studies of porous Vycor glass by the critical isobutyric acid-water mixture, close to the consolute solution temperature, corroborate our analysis.

Journal Article↗

PubMed1996

Precataractous changes affect lens transparency in the selenite cataract.

Selenite treatment of the preweanling rat stabilized the transparency of the lens nucleus to decreasing temperature. Hence, we compared properties of the cortex and nucleus from lenses of selenite-treated and age-matched control rats. A subcutaneous dose of 30 nmol Na2SeO3/g body weight was administered to 10- to 13-day-old Sprague-Dawley rats. Uninjected, age-matched littermates served as controls. As required, lenses were frozen in liquid N2 and separated into nuclear and cortical-epithelial fractions. Transparency of solutions of lens proteins (90-100 mg per ml) was monitored from 30 to 2 degrees C as percent transmittance (%T) at 490 nm. The critical phase separation temperature, Tc, was the temperature at 80%T. Protein associations were monitored with gel filtration chromatography. The nuclear 'cold cataract', in intact lenses, formed at similar temperatures at 14 and 15 days of age, but at a significantly lower temperature when the lenses were from a selenite-treated rat. The Tc, however, was greater by 1.5-2 degrees C for solutions of proteins isolated from whole lenses or lens nuclei from rats 24 and 48 h after treatment with selenite. Further, less gamma-crystallin was associated with the alpha-crystallin fraction in extracts from the nucleus of lenses from treated rats. Altered phase separation properties occurred as an early event in the etiology of selenite cataract. The different in vivo and in vitro responses to temperature indicated that properties of lens crystallins do not solely establish transparency in the intact lens.

Animals↗

PubMed1999

Two-dimensional model of phase segregation in liquid binary mixtures.

The hydrodynamic effects on the late stage kinetics of phase separation in liquid mixtures is studied using the model H. Mass and momentum transport are coupled via a nonequilibrium body force, which is proportional to the Peclet number alpha, i.e., the ratio between convective and diffusive molar fluxes. Numerical simulations based on this theoretical model show that phase separation in low viscosity, liquid binary mixtures is mostly driven by convection, thereby explaining the experimental findings that the process is fast, with the typical size of single-phase domains increasing linearly with time. However, as soon as sharp interfaces form, the linear growth regime reaches an end, and the process appears to be driven by diffusion, although the condition of local equilibrium is not reached. During this stage, the typical size of the nucleating drops increases like t(n), where 1/3< n <1/2, depending on the value of the Peclet number. As the Peclet number increases, the transition between convection- and diffusion-driven regimes occurs at larger times, and therefore for larger sizes of the nucleating drops.

Journal Article↗

PubMed1986

Thermotropic characterization of phosphatidylcholine vesicles containing ganglioside GM1 with homogeneous ceramide chain length.

The thermotropic behavior of dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine large unilamellar vesicles containing ganglioside GM1 of homogeneous long chain base composition has been studied by high-sensitivity differential scanning calorimetry and fluorescence spectroscopy. At neutral pH and in the absence of Ca2+, the thermotropic behavior of these systems is independent of the ganglioside chain length composition. The presence of Ca2+ at concentrations higher than 5 mM induces ganglioside phase separation in a manner dependent upon the length difference between the ganglioside long chain base and the phosphatidylcholine acyl chains. The analysis of the chain length dependence of the thermotropic behavior suggests that the driving force for ganglioside phase separation is not a Ca2+-induced cross-bridging of the ganglioside head group but a passive ganglioside exclusion from Ca2+-perturbed phosphatidylcholine-rich regions within the bilayer. Experiments with native ganglioside GM1, primarily a mixture of C18:1 and C20:1 long chain bases, indicate that the individual components of the mixture maintain their characteristic behavior within the lipid bilayer matrix. These results, together with the presence of a phase transition in native GM1 micellar dispersions, absent in purified C18:1 or C20:1 ganglioside micelles, strengthen the idea of a possible role of chain length composition in the modulation of ganglioside function.

Animals↗

PubMed2005

The nonequilibrium phase and glass transition behavior of beta-lactoglobulin.

Concentrated solutions of bovine beta-lactoglobulin were studied using osmotic stress and rheological techniques. At pH 6.0 and 8.0, the osmotic pressure was largely independent of NaCl concentration and could be described by a hard sphere equation of state. At pH 5.1, close to the isoelectric point, the osmotic pressure was lower at the lower NaCl concentrations (0 mM, 100 mM) and was fitted by an adhesive hard sphere model. Liquid-liquid phase separation was observed at pH 5.1 at ionic strengths of 13 mM and below. Comparison of the liquid-liquid and literature solid-liquid coexistence curves showed these solutions to be supersaturated and the phase separation to be nonequilibrium in nature. In steady shear, the zero shear viscosity of concentrated solutions at pH 5.1 was observed at shear rates above 50 s(-1). With increasing concentration, the solution viscosity showed a progressive increase, a behavior interpreted as the approach to a colloidlike glass transition at approximately 60% w/w. In oscillatory shear experiments, the storage modulus crossed the loss modulus at concentrations of 54% w/w, an indication of the approaching glass transition. Comparison of the viscous behavior with predictions from the Krieger-Dougherty equation indicates the hydrodynamic size of the protein decreases with increasing concentration, resulting in a slower approach to the glass transition than a hard sphere system.

Computer Simulation↗

PubMed2004

Structure and properties of nano-hydroxyapatite/polymer composite scaffolds for bone tissue engineering.

To better mimic the mineral component and the microstructure of natural bone, novel nano-hydroxyapatite (NHAP)/polymer composite scaffolds with high porosity and well-controlled pore architectures were prepared using thermally induced phase separation (TIPS) techniques. The morphologies, mechanical properties and protein adsorption capacities of the composite scaffolds were investigated. The high porosity (90% and above) was easily achieved and the pore size was adjusted by varying phase separation parameters. The NHAP particles were dispersed in the pore walls of the scaffolds and bound to the polymer very well. NHAP/polymer scaffolds prepared using pure solvent system had a regular anisotropic but open 3D pore structure similar to plain polymer scaffolds while micro-hydroxyapatite (MHAP)/polymer scaffolds had a random irregular pore structure. The introduction of HAP greatly increased the mechanical properties and improved the protein adsorption capacity. In a dioxane/water mixture solvent system, NHAP-incorporated poly(L-lactic acid) (PLLA) scaffolds developed a fibrous morphology which in turn increased the protein adsorption three fold over non fibrous scaffolds. The results suggest that the newly developed NHAP/polymer composite scaffolds may serve as an excellent 3D substrate for cell attachment and migration in bone tissue engineering.

Adsorption↗

PubMed2004

Emulsifying properties of acylated rapeseed (Brassica napus L.) peptides.

A peptide fraction having an average size of 5.6 amino acids has been purified from a rapeseed hydrolyzate, acylated using C(10)-C(14) acyl chlorides, and the surface tension values at the air-water interface and emulsifying properties studied. As compared with standard surface-active proteins, such as bovine serum albumin (BSA), and with detergents such as sodium dodecyl sulfate (SDS), acylated peptides exhibited particular surface characteristics. The surface tension at air-water interface of acylated peptides ranged from 29.1 to 37.8 mN/m at equilibrium; these values were considerably lower than those for BSA and closer those for SDS, suggesting that acylated peptides pack at the air-water interface more like detergents than like proteins. The adsorption of acylated peptides to the oil-water interface was slower than for SDS or BSA, as deduced from the rather large size of oil droplets in emulsions (31-17 microm). Consequently, these emulsions creamed extensively during aging. Nevertheless, emulsions generated from acylated peptides were in general more stable to phase separation than those prepared from SDS. The C(14) acylated peptides were more effective for generating emulsions than the C(10) and C(12) derivatives, especially concerning the stability of emulsions against coalescence and phase separation, which was better than SDS and close to BSA.

Acylation↗

PubMed1980

Guanosine 5'-triphosphate and guanosine 5'-[beta gamma-imido]triphosphate effect a collision coupling mechanism between the glucagon receptor and catalytic unit of adenylate cyclase.

1. GTP, but not p[NH]ppG (guanosine 5'-[betagamma-imido]triphosphate), abolishes the sensitivity of glucagon-stimulated adenylate cyclase to the lipid-phase separations occurring in the outer half of the bilayer in liver plasma membranes from rat. 2. When either GTP or p[NH]ppG alone stimulate adenylate cyclase, the enzyme senses only those lipid-phase separations occurring in the inner half of the bilayer. 3. Trypsin treatment of intact hepatocytes has no effect on the basal, fluoride-, GTP- or p[NH]ppG-stimulated adenylate cyclase activity. However, (125)I-labelled-glucagon specific binding decays with a half-life matching that of the decay of glucagon-stimulated adenylate cyclase activity. 4. When GTP or p[NH]ppG are added to assays of glucagon-stimulated activity, the half-life of the trypsin-mediated decay of activity is substantially increased and the decay plots are no longer first-order. 5. Trypsin treatment of purified rat liver plasma membranes abolishes basal and all ligand-stimulated adenylate cyclase activity, and (125)I-labelled-glucagon specific binding. 6. Benzyl alcohol activates the GTP- and p[NH]ppG-stimulated activities in an identical fashion, whereas these activities are affected differently when glucagon is present in the assays. 7. We suggest that guanine nucleotides alter the mode of coupling between the receptor and catalytic unit. In the presence of glucagon and GTP, a complex of receptor, catalytic unit and nucleotide regulatory protein occurs as a transient intermediate, releasing a free unstable active catalytic unit. In the presence of p[NH]ppG and glucagon, the transient complex yields a relatively stable complex of the catalytic unit associated with a p[NH]ppG-bound nucleotide-regulatory protein.

Adenylyl Cyclases↗

PubMed2006

Tuning of heteronuclear interactions in a degenerate Fermi-Bose mixture.

We demonstrate tuning of interactions between fermionic 40K and bosonic 87Rb atoms by Feshbach resonances and access the complete phase diagram of the harmonically trapped mixture from phase separation to collapse. On the attractive side of the resonance, we observe a strongly enhanced mean-field energy of the condensate due to the mutual mean-field confinement, predicted by a Thomas-Fermi model. As we increase heteronuclear interactions beyond a threshold, we observe an induced collapse of the mixture. On the repulsive side of the resonance, we observe vertical phase separation of the mixture in the presence of the gravitational force, thus entering a completely unexplored part of the phase diagram of the mixture. In addition, we identify the 515 G resonance as p wave by its characteristic doublet structure.

Journal Article↗

PubMed1989

Effect of Mg2+ concentration on Ca2+ uptake kinetics and structure of the sarcoplasmic reticulum membrane.

Direct measurements of phosphorylation of the Ca2+ ATPase of the sarcoplasmic reticulum (SR) have shown that the lifetime of the first phosphorylated intermediate in the Ca2+ transport cycle, E1 approximately P, increases with decreasing [Mg2+] (Dupont, Y. 1980. Eur. J. Biochem. 109:231-238). Previous x-ray diffraction work (Pascolini, D., and J.K. Blasie. 1988. Biophys. J. 54:669-678) under high [Mg2+] conditions (25 mM) indicated that changes in the profile structure of the SR membrane could be responsible for the low-temperature transient trapping of E1 approximately P that occurs at temperatures below 2-3 degrees C, the upper characteristic temperature th for lipid lateral phase separation in the membrane. We now present results of our study of the Ca2+ uptake kinetics and of the structure of the SR membrane at low [Mg2+] (less than or equal to 100 microM). Our results show a slowing in the kinetics of both phases of the Ca2+ uptake process and an increase in the duration of the plateau of the fast phase before the onset of the slow phase, indicating an increase in the lifetime (transient trapping) of E1 approximately P. Calcium uptake kinetics at low [Mg2+] and moderately low temperature (approximately 0 degree C) are similar to those observed at much lower temperatures (approximately -10 degrees C) at high [Mg2+]. The temperature-induced structural changes that we observed at low [Mg2+] are much more pronounced than those found to occur at higher [Mg2+]. Also, at the lower [Mg2+] the upper characteristic temperature th for lipid lateral phase separation was found to be higher, at approximately 8-10 degrees C. Our studies indicate that both temperature and [Mg2+] affect the structure and the functionality (as measured by changes in the kinetics of Ca2+ uptake) of the SR membrane. Membrane lipid phase behavior and changes in the Ca2+ ATPase profile structure seem to be related, and we have found that structural changes are responsible for the slowing of the kinetics of the fast phase of Ca2+ uptake, and could also mediate the effect that [Mg2+] has on E1 approximately P lifetime.

Animals↗

PubMed1989

Effect of the mitogenic lectin concanavalin A on the thermotropic behavior of glycosyl-free cationic lipids and their mixtures with zwitterionic lipids.

The effect of concanavalin A (Con A) on the thermotropic behavior of positively charged, glycosyl-free lipids and their mixtures with zwitterionic lipids was investigated by differential scanning calorimetry. The gel to liquid-crystal phase transition enthalpy of pure dipalmitoylcholine (DPC) was found to be significantly increased in the presence of Con A (delta H = 31.2 and 42.5 KJ mol-1 lipid in the presence and in absence of Con A, respectively). Addition of the lectin to DPC liposomes, furthermore, induces the appearance of a new phase transition centered at 320 K. These results are interpretable by a partial hydrophobic interdigitation of the lectin molecule into the liposomal bilayer. The effect of Con A on the phase behavior of three 2:1 mixtures of zwitterionic and of positively charged lipids was also investigated. Phase diagrams of the systems dipalmitoyl-phosphatidylcholine-dihydrosphingosine (DPPC-DHS), sphingomyelin-dipalmitoylcholine (SPM-DPC), and dimyristoylphosphatidylcholine-dipalmitoylcholine (DMPC-DPC) are presented. In lipid mixtures of limited miscibility (DPPC-DHS and SPM-DPC), Con A induces pronounced phase-separation effects. These effects are attributable to a direct hydrophobic interaction of the lectin with the liposomal bilayer and do not require the presence of specific receptor groups. The possible relationship between lectin-induced phase separations in the lipid matrix of biomembranes, and the observed changes in membrane permeability, membranal enzymatic activities, etc., is briefly discussed.

Calorimetry, Differential Scanning↗

PubMed2004

Sugar-based microemulsion glass templates.

Complex fluids comprising of surfactants with water and/or oil form a rich variety of dynamic self-assembled structures, ranging from spherical swollen micelles, viscous rod-like micelles, and bicontinuous microemulsions to ordered liquid crystalline phases. The wide range of practical and specialized applications of complex fluids has made them the subject of intense research for many decades. Here, we demonstrate for the first time how bicontinuous microemulsions containing equal masses of oil and sugar can be driven to the glassy state without phase separation at ambient temperatures by controlled desiccation of sugar-rich microemulsions. The robust nanostructure of these microemulsion glasses allows polymerization of hydrophobic liquid monomers within the interstices of the glassy microemulsion template without macroscopic phase separation. Yet after polymerization, the sugar and surfactant template can be easily removed by dissolution in water.

Carbohydrates↗

PubMed2004

Spontaneous assembly of subnanometre-ordered domains in the ligand shell of monolayer-protected nanoparticles.

The properties of materials can be created and improved either by confining their dimensions in the nanoscale or by controlling their nanostructure. We have combined these two concepts, and here we describe a new class of nanostructured nanosized materials that show ordered phase-separated domains at an unprecedented molecular length scale. Scanning tunnelling and transmission electron microscope images of monolayer-protected metal nanoparticles, with ligand shells composed of a mixture of molecules, show that the ligands phase-separate into ordered domains as small as 5 A. Importantly, the domain shape and dimensions can be controlled by varying the ligand composition or the metallic core size. We demonstrate that the formation of ordered domains depends on the curvature of the underlying substrate, and that novel properties result from this nanostructuring. For example, because the size of the domains is much smaller than the typical dimensions of a protein, these materials are extremely effective in avoiding non-specific adsorption of a variety of proteins.

Adsorption↗