Solid Aggregates Research Articles

Equation of State of Polymeric Materials in the Solid Aggregate State

Equation of State of Polymeric Materials in the Solid Aggregate State

Adsorption of dyes from aqueous solution — the effect of adsorbent pore size distribution and dye aggregation

The removal of acid dyes, Tectilon Blue 4R, Tectilon Red 2B and Tectilon Orange 3G, from single component solution by adsorption on activated carbon and bone char has been investigated in isotherm experiments. Results from these experiments were successfully modelled using Langmuir and Freundlich isotherm analyses. Nitrogen adsorption analysis was also undertaken and indicated that the activated carbon had a much higher specific surface than the bone char. Calculations involving the pore size distribution data indicate that only 14% of the total specific surface of the activated carbon is available for adsorption due to the high molecular area and aggregation of the dye. The equilibrium data indicate that dye aggregation takes place in the solid phase of both adsorbents with higher solid phase aggregation numbers found using the bone char, which is indicative of multilayer adsorption.

CHARACTERIZATION OF OIL-MINERAL AGGREGATES

ABSTRACT Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed on mineral surfaces, but also as a discrete phase to form microscopic oil-mineral aggregates (OMA). On the basis of recent studies, OMA formation now is believed to be instrumental in the natural recovery of oil spill impacted shorelines and in the efficacy of cleanup techniques such as surf washing. A better understanding of the nature and properties of OMA will help predict the fate of oil spilled in the aquatic environment. This work describes the various instruments and methods currently available for the detection and identification of OMA. Three types of OMA have been characterized by microscopy techniques: droplet, solid, and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or aggregated mineral particles. Solid aggregates are a mixture of oil and minerals blended into microscopic bodies of various shapes. Flake aggregates are thin sheets reaching several millimeters across in which mineral and oil are arranged in a regular pattern. Energy from breaking waves facilitates OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate.

Measurements of temperature and melting heat of some pure fatty acids and their binary and ternary mixtures by differential scanning calorimetry

Differential scanning calorimetry (DSC) is used to study the melting process of three pure fatty acids (palmitic, stearic and oleic) and both their binary and ternary mixtures. The results obtained for palmitic ( T=337 K, Δ H=208.2 J g −1) and stearic ( T=344 K, Δ H=210.8 J g −1) acids indicate the existence of a simple process. However, oleic acid presents a reversible solid–solid phase transition ( T=225 K, Δ H=3.6 J g −1) prior to melting ( T=278 K, Δ H=75.5 J g −1). The solidification of this acid is a complex process, since a liquid–liquid transformation ( T=272 K, Δ H=−10.5 J g −1) takes place prior to the change of the liquid–solid aggregation state ( T=260 K, Δ H=−61.0 J g −1). The presence of the oleic acid in the binary and ternary mixtures produces melting points at different levels of temperature. The eutectic temperature is determined for the palmitic/stearic mixture ( T=331 K), its non-ideal behavior being demonstrated. The melting heat in the binary mixtures hardly changes, while in the ternary mixtures a lineal decrease is observed when the oleic composition is increased.

Cutaneous myoepithelioma: an under-recognized cutaneous neoplasm composed of myoepithelial cells.

Benign and malignant neoplasms of myoepithelial cells comprise a rare but well-characterized group of tumors, among which myoepithelioma of the salivary glands is the best known. Extrasalivary examples of myoepithelioma also have been described in the breast, larynx, and retroperitoneum. Recently, myoepithelioma of the soft tissue also has been reported. According to this description, myoepithelioma and mixed tumors arising in the skin and subcutis represent points along a clinicopathologic spectrum of cutaneous and soft-tissue tumors. To the best of our knowledge, there has been only one case report of an entirely cutaneous myoepithelioma in the literature. We report herein five additional examples of purely myoepithelial tumors located exclusively in the dermis. Histopathologically, the neoplasms were well-circumscribed dermal lesions composed of fascicles of spindle cells with eosinophilic cytoplasm and ovoid-to spindle-shaped nuclei. Focally, neoplastic aggregations of more epithelioid cells representing large round cells with abundant pale cytoplasm arranged in solid clusters, cords, or strands were also seen. Ductal differentiation was not identified in either of these solid aggregations of epithelioid cells or in the fascicles of spindle-shaped cells. Nuclear pleomorphism in epithelioid and spindle-cell areas was mild, and mitotic figures were very sparse. In some cases, small, necrotic areas were seen within the solid aggregations of spindle-shaped cells. Neoplastic stroma was scant and composed of fibrillary collagen and abundant mucin. In one case, the stroma consisted of clusters of mature adipocytes intermingled with fascicles of myoepithelial cells. Areas of chondroid or osteoid metaplasia were not seen in any of the cases. Immunohistochemically, neoplastic cells expressed positivity for muscle specific actin (HHF35), alpha smooth muscle actin (IA4), S-100 protein, glial fibrillary acidic protein (GFAP), and epithelial membrane antigen (EMA), whereas stains for pan-cytokeratin (MNF116) were focal and weak. The findings in this report expand the clinical and histopathologic spectrum of cutaneous myoepithelioma, an under-recognized cutaneous neoplasm of myoepithelial cells.

Oxygen adsorption and photoreduction on fractal melanin particles

The main putative functions of melanins in living cells, that is photoprotection and dark or light-dependent oxido-reductive activity, still requires an interpretation which takes into account the micro–mesoscopic structure of native melanin particles. It is indeed well established that a different chemical composition of melanins, even if derived from different biosynthetic pathways, has only a little influence on the biological and physical properties of the solid aggregates, the common form in which the pigment is found [P.R. Crippa et al., Chemistry of melanins, in: A. Brossi (Ed.) The Alkaloids, vol. 36, Academic Press, New York, 1989, pp. 253–323]. In the present work a model for interfacial electron transfer is proposed describing the process of light induced superoxide formation through a monoelectronic reduction of dioxygen adsorbed on melanin solid surface. This process is presumed to be dependent on the surface fractal characteristics, and its kinetics must be interpreted as a heterogeneous interfacial reaction involving light produced carriers and the adsorbed acceptor, like in colloidal inorganic semiconductors such as TiO 2.

Two sets of nuclear magnetic resonances in the CH2Cl2-treated (31R)-type bacteriochlorophyll c solid aggregates under ultra high magnetic field

Chlorosome in green sulfur and filamentous bacteria is a special light harvesting entity with absorption maximum around 740 nm. Bacteriochlorophyll (BChl) c is well-known to form rod-like large aggregates in the chlorosome without influence of protein. BChl c is characterized by the hydroxyl group at 31-position, which brings about a unique self-aggregation of BChl c, and the difference in stereochemistry is considered to influence the behavior of self-aggregation. In this study, we are concerned with the (31R)-type BChl c ((31R)-[E,E]BChl cF) which is the most abundant component in the chlorosome of green bacteria Chlorobium tepidum. (31R)-[E,E]BChl cF forms two small aggregates with absorption maxima at 680 and 703-10 nm in CH2Cl2, and CCl4. For the small aggregates, we have demonstrated that (31R)-[E,E]BChl cF forms an unstable T-shaped dimer with absorption only at ~680 nm and a stable antiparallel dimer with two Qy(0-0) exiton components at ~680 nm and ~710 nm. For the solid aggregates, we could form the solid aggregates with absorption maximum at 734 nm by drying the BChl c-CH2Cl2 solution. The CH2Cl2-treated solid aggregates are formed through the antiparallel dimer, and further, give rise to X-ray diffraction, differently from the aggregates treated with other methods. In this study, we have measured the solid-state 13C- and 15N- NMR spectra for the CH2Cl2-treated solid aggregates of (31R)-[E,E]BChl cF at ultra high magnetic field in order to discuss the structure of solid aggregates in relation with the antiparallel dimer in solution.

Microtubule integrity is essential for apical polarization and epithelial morphogenesis in the thyroid.

In this study, we examined the contribution of microtubules to epithelial morphogenesis in primary thyroid cell cultures. Thyroid follicles consist of a single layer of polarized epithelial cells surrounding a closed compartment, the follicular lumen. Freshly isolated porcine thyroid cells aggregate and reorganize to form follicles when grown in primary cultures. Follicular reorganization is principally a morphogenetic process that entails the assembly of biochemically distinct apical and basolateral membrane domains, delimited by tight junctions. The establishment of cell surface polarity during folliculogenesis coincided with the polarized redistribution of microtubules, predominantly in the developing apical poles of cells. Disruption of microtubule integrity using either colchicine or nocodazole caused loss of defined apical membrane domains, tight junctions and follicular lumina. Apical membrane and tight junction markers became randomly distributed at the outer surfaces of aggregates. In contrast, the basolateral surface markers, E-cadherin and Na(+),K(+)-ATPase, remained correctly localized at sites of cell-cell contact and at the free surfaces of cell aggregates. These findings demonstrate that microtubules play a necessary role in thyroid epithelial morphogenesis. Specifically, microtubules are essential to preserve the correct localization of apical membrane components within enclosed cellular aggregates, a situation that is also likely to pertain where lumina must be formed from solid aggregates of epithelial precursors.

Self-aggregation of synthetic zinc-chlorophylls possessing an interactive w-hydroxyalkyl group

Zinc-chlorins possessing 2-hydroxyethyl (Zn-EtOH-Chl) or 3-hydroxypropyl groups (Zn-PrOH-Chl) at the 3-position were synthesized as model compounds of self-aggregative chlorophylls in light-harvesting antenna complex (chlorosome) of green bacteria. Their self-aggregation behavior was examined in nonpolar solution and compared with that of zinc-chlorin possessing hydroxymethyl group (Zn-MeOH-Chl), which is a good model for chlorosomal chlorophylls. Effect of covalent linkage between the interactive hydroxy group and chlorin moiety on the self-assembly was investigated. In 1%THF-hexane, Zn-EtOH-Chl formed self-aggregates having Qy absorption maxima at 704 nm, of which red-shifted value from the corresponding monomeric band at 644 nm in THF was smaller than that of Zn-MeOH-Chl (644® 740 nm). The aggregated Zn-EtOH-Chl gave specific CD signals characteristic of self-aggregates, which were weaker than those of aggregated Zn-MeOH-Chl. These results indicate that Zn-EtOH-Chl excitonically coupled in the aggregates more weakly than Zn-MeOH-Chl did. IR spectra of the solid aggregates of Zn-EtOH-Chl showed that three interactive sites (32-OH, Zn, 13-C=O) formed intermolecular C=O···H?O···Zn bonding as Zn-MeOH-Chl did. Therefore, change of 3-CH2OH to 3-CH2CH2OH does not disturb C=O···H?O···Zn bonding but disturbs close p-p interaction between chlorin chromophores in their aggregation. On the contrary, Zn-PrOH-Chl possessing 3-CH2CH2CH2OH gave no red-shifted absorption and specific CD signals even in 1%THF-hexane. Moreover, IR spectra of the solid aggregates of Zn-PrOH-Chl showed lack of the C=O···H?O···Zn bonding. Therefore, insertion of a methylene group to the 3-31 bond of Zn-EtOH-Chl disturbs C=O···H?O···Zn bonding as well as tight p-p interaction.

Important parameters affecting efficiency of protein refolding by reversed micelles.

Refolding of denatured RNase A as a model of inclusion bodies was performed by reversed micelles formulated with sodium di-2-ethylhexyl sulfosuccinate (AOT) in isooctane. In the novel refolding process, a solid-liquid extraction was utilized as an alternative to the ordinary protein extraction by reversed micelles based on a liquid-liquid extraction. First, the effects of operational parameters such as concentration of AOT, W(o) (= [H(2)O]/[AOT]), and pH were examined on the solubilization of solid denatured proteins into a reversed micellar solution. The solubilization was facilitated by a high AOT concentration, a high W(o) value, and a high pH in water pools. These conditions are favorable for the dispersion of the solid protein aggregates in an organic solvent. Second, the renaturation of the denatured RNase A solubilized into the reversed micellar solution was conducted by addition of glutathione as a redox reagent. A complete renaturation of RNase A was accomplished by adjusting the composition of the redox reagent even at a high protein concentration in which protein aggregation would usually occur in aqueous media. In addition, the renaturation rates were improved by optimizing water content (W(o)) and the pH of water pools in reversed micelles. Finally, the recovery of renatured RNase A from the reversed micellar solution was performed by adding a polar organic solvent such as acetone into the reversed micellar solution. This precipitation method was effective for recovering proteins from reversed micellar media without any significant reduction in enzymatic activity.

On the Axial Movement of Solids in Gas-Solid Fluidized Beds

Solids movement in a gas-solid fluidized bed was monitored by a Radioactive Particle Tracking (RPT) technique. The gas was air at room temperature and atmospheric pressure and the solid was sand or FCC powder. The experiments were done at superficial gas velocities from 0.5 to 2.8 ms−1 for sand, and 0.44 to 0.9 ms−1 for FCC, covering both bubbling and turbulent regimes. A variety of solids behaviours, including restricted axial movement and unrestricted axial movement of solids, were studied by processing the data in an appropriate manner. The variance test was performed on the Residence Time Distribution (RTD) of solids in the restricted upward and downward movement. The results of the test clearly showed that upward movement of solids could be explained by a diffusive mechanism, while the mechanism of downward movement of solids should be considered as convective. The variance test for unrestricted axial movement of solids showed that this type of movement cannot be explained by either of the two above mentioned mechanisms. In order to model the axial movement of the solids, it was assumed that solids move according to the two diffusive and convective mechanisms. By comparing the RTD of unrestricted movement of solids with the unsteady state formulation of the solid movement, it was found that the solid velocity in the convective term of the model have to be less than the velocity of a single particle moving in a fluidized bed at the same condition. This fact suggests that the solid particles do not move separately in the fluidized bed, butmove as part of a solid aggregate, or cluster, which exercises a drag force greater than that of a single particle and, therefore, moves at a lower velocity.

EFFECT OF ASPHALTENE AND RESINS ON THE STABILITY OF WATER-IN-WAXY OIL EMULSIONS

ABSTRACT Asphaltene, resins and paraffin waxes, their mutual interactions and their influence on the stability of water-in-oil emulsions have been studied. 20 wt % paraffin wax dissolved in decalin was used to model the waxy crude oil. Asphaltene and resins separated from a crude oil were used to stabilize the water-in-oil emulsions. Synthetic formation water was utilized as the aqueous phase of the emulsion. The emulsion stability increased with increasing the concentration of asphaltene with a subsequent decrease in the average particle size distribution of the emulsion. Resins alone are not capable of stabilizing the emulsion, however, in the presence of asphaltene they form very stable emulsions. Dynamic viscosity and pour point measurements provided evidence for resins-paraffin waxes interactions. Asphaltene in the form of solid aggregates form suitable nuclei for the wax crystallites to build over with a mechanism similar to that of paraffin wax crystal-modifiers. As asphaltene are polar in nature they are derived at the oil/water interface which was proved by the ability of asphaltene to reduce oil/water interfacial tension. Consequently, nucleation of the wax crystallites by asphaltene and resins at the interface will add to the thickness of the oil-water interfacial film and hence increase the stability of the emulsion.

ELECTROKINETIC ANALYZERS

Electrokinetic analysis is a family of techniques for estimating the charge on solid surfaces, macroscopic particles, colloidal species, and macromolecular aggregates. Charges on surfaces are critical to the behavior of colloids, coatings, films, fibers, and many other materials in a variety of application areas. In addition to estimating the charge, electrokinetic analysis provides the means for measuring how the surrounding medium and imposed electric fields interact with extended flat surfaces, channels, pores, particles, and molecular aggregates to produce motion. Such motion has found wide use as a means for separating complex mixtures into their components. This section will present how measurements are made, some theoretical underpinnings, and examples of the instrumentation used for making measurements.

Investigation of the dielectric relaxation and the transport propertiesof porous silicates containing humidity

The dielectric relaxation responses of pelite, which is a porous silicatesediment containing a low content of inherent humidity, were identified andcharacterized by employing the experimental scheme of the thermally stimulateddepolarization current (TSDC) spectroscopy. Comparative experiments wereperformed on dry samples. The elementary responses that compose the dielectricspectrum were recorded by applying certain sampling techniques. The dielectricrelaxation spectrum consists of two low-temperature mechanisms, which arerelated to different modes of relaxation of water molecules. A third one isprobably produced by permanent dipoles consisting of point defects in the calciumparticipant. Three relaxation mechanisms were sampled within the intermediatetemperature region and were strongly affected by the outgassing of the porenetwork. They correspond to polarization processes occurring in the multi-layershell of humidity over the surface the solid aggregates. At higher temperatures,two mechanisms were traced: the first is related to the homogeneous polarizationof the specimen as charge carriers migrate within conducting territories untilthey are trapped at internal boundaries and the latter is described as along-distance conduction mechanism which is enhanced by the presence ofhumidity. The activation energy profiles of the above-mentioned relaxationmechanisms were obtained from the analysis of the experimental signals of thethermal sampling and the partial heating schemes.

Cross-Flow Filtration of Synthetic Electroplating Wastewater by Ceramic Membranes Using High Frequency Backpulsing

Cross-flow microfiltration (MF) was investigated as a viable option for separating colloidal particles from electroplating wastewater. Filtration experiments with Cr(OH)3 suspension as synthetic electroplating wastewater were performed on a pilot filter unit equipped with a backpulse device using porous alumina ceramic membranes of various pore sizes (0.2-5.0 µm). The membranes were characterized by nitrogen and clean water permeation. In filtration with Cr(OH)3 suspension, water permeate flux decreases with decreasing membrane pore size and increasing solute concentration in suspension. All membranes are fouled in filtration primarily due to the cake formation. With backpulse in operation, a constant water permeate flux can be maintained using membranes with pore size smaller or larger than the size of solid aggregates in the suspension. The rejection coefficient of suspended solid is about 100% for the smaller pore membranes but drops to only 70% for the larger pore membrane. The backpulse is not effective in maintaining a constant water permeate flux for filtration using membranes of pore size close to the suspension aggregate size due to entrapment of fine aggregates in the membrane pores. The fouled membranes could be completely regenerated by a chemical rinsing method with NaOH and HNO3 solutions.

Nuclear pseudoinclusions in fine-needle aspiration cytology of hepatic angiomyolipoma: Case report

A nodular lesion was found in the fourth segment of the liver in a 51-yr-old Caucasian woman and subjected to aspiration cytology. Smears exhibited solid sheets or small aggregates of epithelioid cells with numerous nuclear pseudoinclusions, scanty mature adipocytes, and red blood cells. With a presumptive diagnosis of angiomyolipoma, the patient underwent laparotomy with resection of the nodule; histologic and immunohistochemical findings confirmed the diagnosis, identifying the trabecular variant. Although the presence of nuclear pseudoinclusions has been previously reported in renal angiomyolipomas, this cytologic feature has not received adequate attention in liver localization, where only cell block samples have been reported. Therefore, when the typical different cellular components of angiomyolipomas are absent in cytologic smears, nuclear pseudoinclusions should not be regarded as a criterion of malignancy, but they may be considered as an additional nonspecific cytological feature in hepatic angiomyolipoma.

Alpha-L-iduronidase forms semi-crystalline spherulites with amyloid-like properties.

While seeking conditions for single crystals of human alpha-L-iduronidase, solutions were discovered (pH 3.0-8.5 containing calcium or zinc salts) that transform soluble alpha-L-iduronidase to a solid aggregate. This aggregate is a spherulite of semi-crystalline protein. The X-ray diffraction pattern and ability to bind Congo red characterize the alpha-L-iduronidase spherulite as 'amyloid-like', in that it displays two of the characteristics of amyloidogenic proteins. In addition, alpha-L-iduronidase also interacts with heparin, as do some amyloid-forming proteins.

Diffusion-limited aggregation: A relationship between surface thermodynamics and crystal morphology

We have combined the original diffusion-limited aggregation model introduced by Witten and Sander with the surface thermodynamics of the growing solid aggregate. The theory is based on the consideration of the surface chemical potential as a thermodynamic function of the temperature and nearest-neighbor configuration. The Monte Carlo simulations on a two-dimensional square lattice produce the broad range of shapes such as fractal dendritic structures, densely branching patterns, and compact aggregates. The morphology diagram illustrating the relationship between the model parameters and cluster geometry is presented and discussed.

Liquid-Crystalline Physical Gels: Self-Aggregation of a Gluconamide Derivative in Mesogenic Molecules for the Formation of Anisotropic Functional Composites

Liquid-crystalline physical gels have been obtained by the self-aggregation of a gluconamide derivative through intermolecular hydrogen bonding in liquid crystals. These liquid-crystalline gels are microphase-separated composites consisting of the solid fibrous aggregates of the gelling agent and the liquid-crystalline phase of mesogenic molecules. Thermoreversible three states, isotropic liquid, normal (isotropic) gel, and liquid-crystalline gel, have been achieved for the mixtures of liquid crystals and the gelling agent. As the concentration of the gelling agent increases, the sol−gel transition temperature and the enthalpy change of the transition from isotropic to anisotropic increase. The increase of the enthalpy change suggests that some mesogenic molecules are anchoring strongly to the surface of the fibrous gelling agents. Variable-temperature infrared spectra show that the association and the dissociation of intermolecular hydrogen bonding of the gelling agent occur in the process of the sol−gel transition. Liquid-crystalline gels are responsive to electric fields in a twisted nematic (TN) cell. These anisotropic gels would be applicable to new dynamically functional materials.

The solid state aggregation of two gold(I) nitrate complexes †

(Trimethylphosphine)gold(I) nitrate was prepared from the reaction of (Me3P)AuCl and AgNO3 in MeOH–CH2Cl2. Single crystals from CH2Cl2–pentane contain trimers [(Me3P)Au(ONO2)]3 as sub-units of polymeric chains. The organization is based on short aurophilic Au–Au contacts. A discussion considering all other known (Me3P)AuX structures leads to the conclusion that small, electronegative anions X favour aurophilic multi-coordination with longer Au⋯Au contacts, while less electronegative, bulky groups X induce dimerization with short Au⋯Au contacts. In all cases neighbouring molecules are arranged with their principal axes roughly perpendicular (staggered). Crystals of (tBuNC)Au(ONO2) grown from CH2Cl2–pentane at −25 °C were shown to be a 2∶1 dichloromethane solvate with a new meander-type structure, which is stable only at low temperature and under the standard pressure of a dichloromethane atmosphere. The structure is based on aurophilic interactions of a similar nature as in the solvent-free phase (obtained at 5 °C) as judged from the bond distance parameters, but the solvent molecules are accommodated in cavities formed through a different puckering of the chains. A comparison with other structures of (RNC)AuX molecules suggests that the parallel (eclipsed) head-to-tail alignment of the molecules is the preferred organization in the absence of other structure-determining effects.