scholarly journals Contact-mediated triggering of lamella formation by Dictyostelium amoebae on solid surfaces

1988 ◽  
Vol 91 (3) ◽  
pp. 367-377 ◽  
Author(s):  
N.F. Owens ◽  
D. Gingell ◽  
J. Bailey
Keyword(s):  
Ionic Strength ◽  
Charge Density ◽  
Dictyostelium Discoideum ◽  
Electrostatic Potential ◽  
Streaming Potential ◽  
Potential Method ◽  
Solid Surfaces ◽  
Specific Chemical ◽  
Amine Groups ◽  
Chemical Groups

Amoebae of the slime mould Dictyostelium discoideum form broad ultrathin cytoplasmic lamellae by a centripetal contractile process soon after they have spread on certain solid surfaces. We have investigated the surface requirements for initial triggering of this contact-mediated signalling system. The lamellar response is not normally evoked by glass, but is seen on glass covalently derivatized with paraffinic chains, as well as on glass covalently derivatized with amine groups and on glass bearing adsorbed polylysine. We have recorded the frequency of the lamellar response on these surfaces as a function of ionic strength and pH, and have measured the electrostatic potentials of the surfaces by the streaming potential method. Using these data we have concluded that the general trigger for the lamellar response is not a ‘simple’ physical or chemical property of the substrata: it is not dependent on specific chemical groups, degree of hydrophobicity, electrostatic potential, or charge density, taken as isolated factors. It seems likely that triggering is dependent on the overall energetics of cell-substratum interaction.

Charge Characteristics of Nanofiltration Membrane by Streaming Potential Method

2011 ◽  
Vol 396-398 ◽  
pp. 547-551 ◽  
Author(s):  
Bao Wei Su ◽  
Xiao Jie Duan ◽  
Mao Wei Dou ◽  
Xue Li Gao ◽  
Cong Jie Gao
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Charge Density ◽  
Electrostatic Interactions ◽  
Membrane Surface ◽  
Streaming Potential ◽  
Freundlich Isotherm ◽  
Potential Method ◽  
Nanofiltration Membrane ◽  
Membrane Surface Charge

Surface charge properties of DL nanofiltration membrane were studied using streaming potential method. The results indicate that in the experimental concentration range, the relationship between NF membrane surface charge density and electrolyte solution concentration is in good agreement with Freundlich-isotherm adsorption, which indicates that the membrane surface charge comes from the adsorption of ions of the solution. In addition, the analysis of anion and cation adsorption on nanofiltration membrane surface showed that adsorption of common ions to the Inner Helmholtz Plane through specific adsorption increases the charge density, while adsorption of counter ions to the Outer Helmholtz Plane through electrostatic interactions leads to electric double-layer contracting inward, decreasing the membrane surface charge density.

scholarly journals Variation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration

Resources ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 108 ◽  
Author(s):  
Alberto Mannu ◽  
Gina Vlahopoulou ◽  
Paolo Urgeghe ◽  
Monica Ferro ◽  
Alessandra Del Caro ◽  
...  
Keyword(s):  
Particle Size ◽  
Chemical Composition ◽  
Solid Phase ◽  
Volatile Fraction ◽  
X Ray Diffraction ◽  
Specific Chemical ◽  
Waste Cooking Oils ◽  
Main Components ◽  
Cooking Oils ◽  
Chemical Groups

The chemical composition and the color of samples of waste cooking oils (WCOs) were determined prior to and after filtration on two different pads of bentonite differing in particle size. The volatile fraction was monitored by headspace solid-phase microextraction (HS-SPME) coupled with gas-chromatography, while the variation of the composition of the main components was analyzed by 1H NMR. Both techniques allowed the detection of some decomposition products, such as polymers, terpenes, and derivatives of the Maillard process. The analysis of the chemical composition prior to and after bentonite treatment revealed a tendency for the clays to retain specific chemical groups (such as carboxylic acids or double bonds), independent of their particle size. A pair comparison test was conducted in order to detect the sensory differences of the intensity of aroma between the WCO treated with the two different bentonites. In addition, characterization of the bentonite by means of powder X-ray diffraction (XRD) and thermogravimetric measurements (TG) was performed.

The Determination of Electrokinetic Coupling-Coefficient and Zeta Potential of Rock Samples by Electrokinetic Measurements

2012 ◽  
Vol 516-517 ◽  
pp. 1870-1873 ◽  
Author(s):  
Jun Wang ◽  
Heng Shan Hu
Keyword(s):  
Zeta Potential ◽  
Coupling Coefficient ◽  
Streaming Potential ◽  
Potential Method ◽  
Surface Conductivity ◽  
Reliable Estimate ◽  
Surface Conductance ◽  
Streaming Current ◽  
Low Concentrations

The electrokinetic effects are important in the understanding of electric properties in porous medium. In this study, the streaming potential and streaming current of saturated samples are measured at different concentrations, then three methods are applied to obtain the zeta-potential and electrokinetic coupling coefficient. The study shows that the results obtained from streaming potential and streaming current methods agree well with each other, but the results obtained from simplified streaming potential method become seriously inaccurate at low concentrations due to the influence of surface conductance. This experimental study also provides a reliable estimate of the surface conductivity and its contribution to zeta-potential at given concentrations.

Thermal Decomposition of Vulcanized Structures of Deformed Vulcanizates Containing Various Accelerators

1953 ◽  
Vol 26 (4) ◽  
pp. 759-763 ◽  
Author(s):  
B. Dogadkin ◽  
Z. Tarasova
Keyword(s):  
Stress Relaxation ◽  
Physical And Mechanical Properties ◽  
Heat Stability ◽  
Chemical Bonds ◽  
Structural Elements ◽  
Specific Chemical ◽  
Vulcanized Rubber ◽  
Different Temperatures ◽  
Chemical Groups ◽  
The Given

Abstract According to the hypotheses developed by the authors, vulcanized rubber is a system in which the molecular chains are united by local molecular and chemical bonds of varying intensity. The concentration, distribution, and strength of these bonds determine the principal physical and mechanical properties of the vulcanizates. Consequently the study of the structure of the vulcanizate is of primary practical value. The explanation of the nature of the bonds in a vulcanizate by chemical methods is very difficult, mainly because of the impossibility of distinguishing the specific chemical groups which enter into the composition of the different molecular chains from those bonds between the chains which are responsible for the development of spatial structures. From this view point, the thermo-mechanical method described below, which is based on the study of stress relaxation at different temperatures, is of great significance. As was shown by Dogadkin and Reznikovskii˘, the delayed stress relaxation in a vulcanizate at temperatures up to 70° C is caused by rupture of the local intermolecular bonds and the regrouping of the structural elements of the polymeric chains without destruction of the chemical bonds between them. Accordingly, after some time at these temperatures, a practically balanced stress is established, which depends on the number of the stronger bonds remaining. At temperatures above 70° C, rupture of the chemical bonds between the chains takes place; its speed increases with decrease of the energy activating the rupture of the given type of bond. Particularly in the case of sulfur vulcanizates, we can assume that the following types of bonds exist between the chains of the rubber: (1) —C—C—, which develop as a result of the polymerizationprocesses; (2) —C—S—C— monosulfide; (3) —C—S—S—C— disulfide, and (4) —C—Sn—C— polysulfide, formed as a result of the direct participation of the vulcanizing agent, sulfur, in the process of joining of the molecular chains. The energy of these chains can be estimated as 62.7 kcal, per mole for C—C, 54.5 kcal. per mole for C—S, and 27.5 kcal. per mole for the —S—S bond. Naturally, the heat stability of a vulcanizate will depend on which of the indicated types of bonds predominates.

Enhancement of renal concentrating ability in the dog by urea and related compounds

1963 ◽  
Vol 205 (1) ◽  
pp. 112-116 ◽  
Author(s):  
Lawrence Rabinowitz ◽  
Ralph H. Kellogg
Keyword(s):  
Collecting Duct ◽  
Molecular Size ◽  
Urine Osmolality ◽  
Acute Administration ◽  
Membrane Permeation ◽  
Specific Chemical ◽  
Solute Excretion ◽  
Chemical Groups ◽  
Related Compounds ◽  
Unique Ability

Experiments were performed on vasopressin-infused dogs to test the effect on renal concentrating ability of acute administration of urea and seven other organic nonelectrolytes. In each experiment a control assessment of concentrating ability was obtained during administration of mannitol. This was followed by administration of a test compound in an amount designed to maintain the previous rate of solute excretion. When compared to control values, urine osmolality was significantly higher during administration of urea, methylurea, acetamide, 1,2-propanediol and 1,3-dimethylurea, but not during administration of thiourea, glycerol, or hexamethylenetetramine. Others have suggested that the enhancement of concentrating ability by urea is related to the unique ability of urea to diffuse through the collecting-duct membranes. In the present study, there appeared to be no simple correspondence between the degree to which urine osmolality increased and the physical properties generally recognized to affect membrane permeation: oil:water partition coefficient, molecular size, or specific chemical groups.

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