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PubMed1998

The role of osmolality in the absorption of a nutrient solution.

BACKGROUND: Loss of water during enteral nutrition following massive intestinal resection may be severe. Low osmolality of oral rehydration solutions has recently been shown to mediate an increase in water absorption. AIM: To evaluate the effect of osmolality of a nutrient solution on the intraluminal duodenojejunal water flow, and the net absorption rates of total nitrogen and carbohydrate. METHODS: Eight healthy volunteers with a mean age of 27 (range 25-29) years participated in the study. Enteral nutrition (17% protein, 59% carbohydrate, 24% lipid plus 5 g/L PEG 4000) was infused (5 mL/min 2.64 kcal/min) into the descending duodenum either as a hypotonic (160 mOsmol/kg) or as an isotonic solution in a random order. Intestinal samples were aspirated 20 and 45 cm distally to the infusion point. RESULTS: Intraluminal water flow rates were significantly lower with the hypotonic solution than with the isotonic solution, both in the duodenum (4.9 +/- 0.3 vs. 6.7 +/- 0.5 mL/min; P < 0.02) and the upper jejunum (3.0 +/- 0.1 vs. 3.9 +/- 0.2 mL/min; P < 0.005). The net absorption rates of total nitrogen and carbohydrate were similar with both solutions. CONCLUSION: Low osmolality of a nutrient solution decreases intraluminal water flow rates in the upper intestine without affecting the absorption rates of total nitrogen and carbohydrate. Compared with an isotonic solution, the use of a hypotonic solution might lower the water loss in patients with extensive short bowel intestinal resection.

Adult↗

PubMed1990

Rat liver preservation. I. The components of UW solution that are essential to its success.

A total of 278 orthotopic rat liver grafts, without arterialization, were performed, in an attempt to determine which of the individual components of UW solution are essential. Livers were preserved by in situ flushing and cold storage with the following results: 56% of rats survived for 1 week after 9 hr of preservation with UW solution as compared with 44% using Marshall solution, and 10% using Collins solution. Having established LD 50 for UW solution, we then omitted its components one at a time and found that omission of HES, raffinose, allopurinol, adenosine, phosphate buffer, or MgSO4 did not change survival after 9 hr of preservation. Omission of lactobionate, glutathione, and dexamethasone, respectively, resulted in decreased survival, whereas elimination of insulin surprisingly increased survival. In ensuing dose-response studies, the concentrations of lactobionate, glutahione, dexamethasone in UW solution proved to be optimal. Finally, livers were preserved with a solution containing only lactobionate, glutathione, dexamethasone, raffinose, and phosphate buffer, resulting in 53% animal survival, as compared with 56% for the unchanged UW solution. We conclude that UW solution can be simplified without loss of effectiveness in this model.

Adenosine↗

PubMed1994

Cardiac myocyte functional and biochemical changes after hypothermic preservation in vitro. Protective effects of storage solutions.

In this study, we evaluated cardiac myocyte viability and function under hypothermic conditions with four types of storage solutions, saline solution, Euro-Collins solution, University of Wisconsin solution, and MCDB 107 medium. Cardiac myocytes were isolated from neonatal rat ventricles by collagenase dispersion and cultured for 4 days with MCDB 107 medium. A total of 12.5 x 10(5) myocytes per culture dish was used and the myocytes were incubated at 4 degrees C for 6, 12, 18, and 24 hours in the various storage solutions. After each incubation time, creatine kinase and lactate dehydrogenase were measured in the storage solutions. The myocytes were then incubated for 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. In the MCDB 107 group (n = 7), the recovery ratio of myocyte beating rate was complete by 12 hours, then decreased to 44.8% of control (beating rate before hypothermic incubation) at 24 hours. The saline, Euro-Collins, and University of Wisconsin groups (n = 7 each) had significantly lower recovery ratios than the MCDB 107 group (at 12 hours: 61.0%, 32.2%, and 48.9%; at 18 hours: 0.0%, 5.5%, and 15.1% of control, respectively). Release of creatine kinase and lactate dehydrogenase in the MCDB 107 group gradually increased and at 24 hours was 143.2 mIU/flask and 486.2 mIU/flask, respectively. However, the saline and University of Wisconsin groups had significantly increased creatine kinase and lactate dehydrogenase values at 24 hours (creatine kinase: 334.6 and 319.6 mIU/flask; lactate dehydrogenase: 821.6 and 654.4 mIU/flask, respectively). The Euro-Collins group showed the greatest increase in both markers (creatine kinase: 1587.5, lactate dehydrogenase: 2106.9 mIU/flask). In summary, saline and University of Wisconsin solutions showed a beneficial effect on recovery of myocyte viability at 12 hours compared with Euro-Collins solution, however MCDB 107 medium had the best overall protective effect on cultured myocytes. Accordingly, alternate hypothermic storage solutions, such as cell-culture medium, may have protective characteristics that are suitable for cardiac preservation.

Adenosine↗

PubMed2004

Fracture associated with hydrogen absorption of sustained tensile-loaded titanium in acid and neutral fluoride solutions.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600 degrees C. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties.

Biocompatible Materials↗

PubMed1992

Subcutaneous injection of oral cyclosporin A solution.

Cyclosporin A (CyA) is the agent of choice for immunosuppression in the majority of rodent organ and tissue allotransplantation experiments. Subcutaneous injection of suitably dissolved pure CyA powder preparation is the acceptable standard of drug administration. We investigated the possibility of using oral CyA solution in an injectable form and compared its availability with that of the standard solution in a rat model. Oral CyA solution diluted in placebo (olive oil) and standard solution prepared from pure compound were injected subcutaneously at a dose of 5 mg/kg/day to two groups of rats. Trough whole blood CyA concentrations were measured on day 10 following initiation of treatment. Blood CyA levels of the standard solution group (1,167 +/- 246 micrograms/liter, mean +/- SD) were virtually identical to those of the oral solution group (1,105 +/- 179 micrograms/liter; P greater than 0.05). In addition, the oral solution was easier to prepare and caused less injection site morbidity than the standard solution. We conclude that placebo-diluted oral CyA solution may be safely injected subcutaneously to rats and results in consistent blood levels, comparable to those achieved with standard solution prepared from pure compound.

Administration, Oral↗

PubMed2000

A Cryo-TEM Study of Protein-Surfactant Gels and Solutions.

Oppositely charged globular protein and surfactant systems, such as lysozyme-sodium dodecyl sulfate (SDS) and ovalbumin-dodecyltrimethylammonium chloride (DOTAC) form precipitate, gel, and colorless solution in water over a wide concentration range. Bluish solutions are also recognized in connection with the redissolution of precipitate as well as prior to the gel formation. For the lysozyme-SDS system the bluish solution has been suggested to consist of finely dispersed gel particles in solution. The oppositely charged bovine serum albumin (BSA)-DOTAC-water system forms only a large, clear solution phase and a narrow, bluish solution region within a very limited surfactant concentration range. In the lysozyme-SDS system the formation of protein-surfactant aggregates and their growth and breakdown are studied in detail by cryogenic-transmission electron microscopy (cryo-TEM) method. In particular a series of samples with an increased surfactant concentration at fixed 4 wt% of lysozyme is studied. Imaging of the bluish solution at different protein concentrations exhibits large aggregates in the form of rod-like, sheet-like, and star-like objects which are attributed to the gel. At excess amounts of SDS, in the colorless solution, only small objects are detected. In the ovalbumin-DOTAC-water and BSA-DOTAC-water systems large aggregates are also observed in the bluish solutions. Colorless solutions for these two systems show the presence of small objects in the cryo-TEM micrographs. Ultrathin sections of the lysozyme and ovalbumin gels fixed with OsO(4) also show the presence of aggregated structures as judged from the transmission electron microscopy observations. Copyright 2000 Academic Press.

Journal Article↗

PubMed2001

The Effect of Solute Concentration on Equilibrium Partitioning in Polymeric Gels.

The effect of solute concentration on the equilibrium partitioning of sphere-like, colloidal solutes in stiff polymer hydrogels is examined theoretically and experimentally. The theoretical development is a statistical mechanics approach, and allows quantitative calculations to be performed to determine the concentration-dependent partition coefficient correct to first order in solute concentration at specific surface charge densities. The theory predicts that repulsive steric and/or electrostatic solute-fiber interactions exclude solute from the gel phase, but that repulsive solute-solute interactions cause partitioning into the gel to increase with increasing solute concentration. These trends are enhanced for larger solutes, increased fiber volume fractions, or stronger electrostatic repulsion. Partition coefficients have also been measured for two proteins, bovine serum albumin (BSA) and alpha-lactalbumin (ALA), in a system consisting of a salt solution and cubes of agarose hydrogel. To investigate the effect of electrostatic interactions, the experiments were performed at 0.15 M KCl and 0.01 M KCl. The theory underpredicts the strong electrostatic repulsion between BSA macromolecules at the lower ionic strength. The experimental results for ALA show the influence of an attractive interaction between the protein macromolecules, in addition to hard-sphere repulsive and electrostatic interactions. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Curvature Effects in the Analysis of Pendant Bubble Data: Comparison of Numerical Solutions, Asymptotic Arguments, and Data.

The pendant bubble method is commonly used to measure the evolution of the surface tension of surfactant solutions. Initially, the bubble interface is free of adsorbed surfactant. As time progresses, surfactant diffuses to the interface, adsorbs, and reduces the surface tension. The surface tension is assumed to be in equilibrium with the instantaneous surface concentration. Therefore, surface tension data are analyzed in terms of interfacial thermodynamics and mass transfer models in order to infer the mechanisms which determine the surfactant transport. Diffusion from the bulk solution to the bubble can be approximated as diffusion to a spherical interface. Approximating this process as diffusion to a plane introduces significant errors into the data analysis. Mass transfer to a sphere differs from that to a plane; the equilibration of the spherical interface is more rapid simply because of geometry. The failure to account for this effect in the interpretation of pendant bubble data can lead to serious errors in the transport coefficients for the surfactants. In the diffusion-controlled limit, surfactant diffuses to the sublayer immediately adjacent to the interface and adsorbs in local equilibrium according to the adsorption isotherm. There is a closed-form solution for Fick's law describing adsorption to a sphere in an infinite solution which reduces to the Ward and Tordai solution when the bubble radius is large. This equation, along with the adsorption isotherm relating the surface concentration and the sublayer concentration, must be solved numerically in order to solve for the time evolution of the surface concentration. At early times, the adsorption isotherm can be expanded about the clean interface state. At long times, small departures from the equilibrium state can be assumed. In these limits, asymptotic expansions can be obtained. The short- and long-time expansions are found in this study for adsorption to a sphere and compared to those obtained previously for adsorption to a planar interface. In particular, the long-time asymptote for adsorption to a sphere is proportional to t(-3/2); this asymptote differs significantly from that for adsorption to a plane, which goes as t(-1/2). The full solution for adsorption to a sphere is compared to the Ward and Tordai solution for adsorption to a planar interface. From a comparison of the full solutions, it is established that curvature cannot be neglected unless the ratio of the adsorption depth to the bubble radius is negligible. This ratio can be calculated a priori from equilibrium isotherm parameters. Using constants which describe the surfactant C(12)E(8), for which curvature plays a strong role in the surfactant adsorption dynamics, the short- and long-time solutions for adsorption to the interface are compared to the full solutions and to dynamic surface tension data to infer the range of validity of the approximations. Copyright 2001 Academic Press.

Journal Article↗

PubMed1996

An analysis of dimethylsulfoxide-induced action potential block: a comparative study of DMSO and other aliphatic water soluble solutes.

A series of water soluble aliphatic solutes were chosen for study. Fifty percent effective doses (ED50) to block propagated compound action potentials (AP's) were obtained by examining dose-response relations for each solute. All solutes used were liquids at room temperature and are typically used as solvents. The solutes studied were dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide, acetone, and hexamethylphosphoramide (HMPA); the octanol/water partition coefficients for these test substances form an ordered sequence that increased 40-fold from DMSO to HMPA. AP's were recorded from desheathed frog sciatic nerves using the sucrose-gap technique; test solutes were added to Ringer's solution and applied externally to the nerve. ED50's for the solutes could be predicted as a function of the molar volume (dV/dn), polarity (P), and the hydrogen bond acceptor basicity (beta). Voltage-clamp experiments employing the vaseline-gap technique on single muscle fibers showed that each solute reduced Na+ current with little change in their kinetics at all voltages studied. Experiments using DMSO or DMF showed that Na+ channel block alone is insufficient to explain the respective ED50 values of AP block. Experiments conducted using a chloride transport-sensitive membrane fluidity assay, using rat pancreas secretory granules, suggested that each of the solutes act to increase membrane fluidity at doses below and above ED50 values. Light microscopic observations of fixed thick sections of whole nerves previously exposed to DMSO or DMF show structural changes; however, ED50 values cannot be simply explained by osmotic alterations of nerve structure. ED50's are likely to be produced by a combination of effects including osmotically induced nerve structural changes, ion channel block, and fluidity changes. The toxicity (lethal doses or toxic concentrations) of each of these five solutes correlates well with the ED50 and could be predicted as a function of dV/dn, P, and beta.

Acetamides↗

PubMed2005

Linear inverse solutions: simulations from a realistic head model in MEG.

Distributed linear solutions are widely used in source localization to solve the ill-posed EEG/MEG inverse problem. In the classical approach based on dipole sources, these methods estimate the current densities at a great number of brain sites, typically at the nodes of a 3-D grid which discretizes the chosen solution space. The estimated current density distributions are displayed as brain electromagnetic tomography (BET) images. We have tested well known minimum norm solutions (MN, WMN, LORETA) and other linear inverse solutions [WROP, sLORETA, interference uniform, gain uniform, weight vector normalized (WVN), and a new solution named SLF (Standardized Lead Field)], using a MEG configuration (BTi Magnes 2500 WH with 148 axial magnetometers) and a realistic head model using BEM (Boundary Element Method). The solutions were compared in a noise-free condition and in the presence of noise using the classical dipole localization errors (DLE) together with a new figure of merit that we called max gain uniformity, which measures the capability of an inverse linear solution to show spots of activity with similar amplitudes on the brain electromagnetic tomographies when multiple dipole sources with similar moments are simultaneously active. Whereas some solutions (sLORETA, interference uniform and SLF) were capable of zero dipole localization errors in the noise-free case, none of them reached 100% of correct dipole localizations in the presence of a high level of Gaussian noise. The SLF solution, which has the advantage to be independent from any regularization parameter, presented the best results with the lowest max gain uniformities, with almost 100% of correct dipole localizations with 10% of noise and more than 90% of correct localizations with 30% of noise added to the data. Nevertheless, no solution was able to combine at the same time a correct localization of single sources and the capability to visualize multiple sources with comparable amplitudes on the brain electromagnetic tomographies.

Algorithms↗

PubMed2006

Solute crystallization in frozen systems-use of synchrotron radiation to improve sensitivity.

PURPOSE: To demonstrate the sensitivity of low temperature synchrotron X-ray diffractometry (SXRD) for detecting solute crystallization in frozen sodium phosphate buffer solutions. To determine the effect of annealing on solute crystallization in frozen solutions. MATERIALS AND METHODS: Sodium phosphate buffer solutions, at initial buffer concentrations ranging from 1 to 100 mM (pH 7.4) were cooled to -50 degrees C. The crystallization of disodium hydrogen phosphate dodecahydrate (Na(2)HPO(4) *12H(2)O) was monitored using a laboratory as well as a synchrotron source. At selected concentrations, the effect of annealing (at -20 degrees C) was investigated. RESULTS: With the laboratory source, solute crystallization, based on the appearance of one diagnostic peak with a d-spacing of 5.4 A, was evident only when the initial buffer concentration was at least 50 mM. In contrast, using SXRD, crystallization was detected at initial buffer concentrations down to 1 mM. In addition, the use of a high-resolution 2D detector enabled the visualization of numerous diffraction rings of the crystalline solute. At both 10 and 100 mM buffer concentration, there was no increase in solute crystallization due to annealing. CONCLUSION: By using synchrotron radiation, solute crystallization was detected with substantially increased sensitivity, making the technique useful for freeze-drying cycles of practical and commercial importance. Since numerous peaks of the crystalline solute appeared, the technique has potential utility in complex, multi-component systems.

Buffers↗

PubMed1986

Cryoprotection of phosphofructokinase with organic solutes: characterization of enhanced protection in the presence of divalent cations.

Phosphofructokinase (PFK) purified from rabbit skeletal muscle is fully inactivated after being frozen in liquid nitrogen for 30 s and thawed. The addition of 500 mM trehalose, sucrose, or proline to the enzyme solution prior to freezing results in a recovery of over 70% of the original activity after thawing. Slightly less stabilization is imparted by maltose and 4-hydroxyproline whereas glucose, glycine, inositol, and glycerol at concentrations up to 500 mM are relatively ineffective at protecting PFK. With 50 mM trimethylamine-N-oxide, almost 50% of the prefreeze activity is recovered, and this same level of cryoprotection is noted at concentrations up to 500 mM. The addition of ionic zinc to enzyme-organic solute mixtures prior to freezing greatly enhances the cryoprotection imparted by all of the solutes tested. This effect is not simply due to the summation of the individual cryoprotective capacities of zinc and the organic solute because in many instances a great degree of cryoprotection is noted when each component is present at a concentration at which, by itself, it is totally ineffective. In the presence of a constant 50 mM organic solute concentration, freeze-thaw stabilization of PFK is increased as the concentration of zinc is increased. When the zinc concentration is held constant (0.6 mM) and organic solute concentration varied, the maximum cryoprotection, in most cases, is noted with less than 50 mM organic solute. At higher solute concentrations the degree of enhancement decreases such that with 500 mM organic solute the addition of zinc results in only a slight increase in protection. The addition of ionic copper, cadmium, nickel, and cobalt to trehalose-PFK solutions prior to freezing also increases the percentage of activity recovered after thawing. Magnesium, manganese, and calcium are ineffective in this respect.

Amino Acids↗

PubMed1988

Pollen grain column chromatography: quantitation and biochemical analysis of ragweed-pollen solutes.

The kinetics, quantitative yield, and sequence of solute release during the extraction of allergenic substances from short ragweed (Ambrosia artemisiifolia) pollen were compared with a conventional batch-type method and the novel technique of pollen grain column chromatography. With the batch method, 14.6 +/- 1.7 mg of pollen solutes were eluted per 100 mg of dried defatted pollen in 1 minute; the 24-hour solute yield was 27.4 +/- 2.7 mg. With the column method, 3.7 +/- 1.3 mg of pollen solutes were eluted in 1 minute; the 24-hour solute yield was 29.3 +/- 2.1 mg. The kinetics of solute release with the column method were modeled as the simultaneous first-order elution of ragweed-pollen solutes into three hypothetical compartments. The theoretical initial solute concentration was 50 gm/L. The isoelectric focusing patterns, optical properties, distributions of enzymes, Ra5, and antigen E activities were consistent with the sequential separation of ragweed-pollen solutes and the three compartment model. Enzyme activities were eluted either maximally in the first minute (phosphatases and N-acetyl-beta-glucaminidase) or delayed until 10 minutes (leucine aminopeptidase). Ra5 was eluted rapidly, whereas antigen E was eluted during a more prolonged period. Pollen grain chromatography provides a simple, reproducible method for studying pollen solute release.

Acid Phosphatase↗

PubMed1989

Dissolution of metallic mercury in artificial saliva and eleven other solutions.

Dissolution of metallic mercury immersed in various solutions for one, three, seven, and 14 days was investigated by flameless atomic absorption spectrophotometry. Solutions used in this study were artificial saliva, compounds of the four groups forming the artificial saliva (inorganic salts, amino acids, vitamins, other organic compounds) wholly or in part, 0.9% NaCl solution (saline solution), Ringer's solution, and distilled water. Artificial saliva showed a level of mercury dissolution seven times higher than that of saline or Ringer's solution. A large amount of dissolution, similar to that in artificial saliva, was found in the solution of the other organic compounds (containing glutathione) and in a solution containing only glutathione. Mercury dissolution in the solution of vitamins was small. There was a similarity in dissolution amounts between the solution of inorganic salts and that of amino acids. Glutathione played a major role in the dissolution of mercury.

Mercury↗

PubMed2005

Correlations of nonlinear sorption of organic solutes with soil/sediment physicochemical properties.

The estimation of solute sorptive behaviors is essential when direct sorption data are unavailable and will provide a convenient way to assess the fate and the biological activity of organic solutes in soil/sediment environments. In this study, the sorption of 2,4-dichlorophenol (2,4-DCP) on 19 soil/sediment samples and the sorption of 13 organic solutes on one sediment were investigated. All sorption isotherms are nonlinear and can be described satisfactorily by a simple dual-mode model (DMM): q(e)=KpCe+Q0 . bCe/(1+bCe), where Kp (mlg(-1)) is the partition coefficient; Ce (microgml(-1)) is the equilibrium concentration; Q0 (microgg(-1)) is the maximum adsorption capacity; Q0 . b (mlg(-1)) is the Langmuir-type isotherm slope in the low concentration (Henry's law) range and b (mlmicrog(-1)) is a constant related to the affinity of the surface for the solute. Based on these nonlinear sorption isotherms and similar other nonlinear isotherms, it is observed that, for both polar 2,4-DCP and nonpolar phenanthrene, Kp, Q0 and Q0 . b are linearly correlated with soil/sediment organic carbon content (f(oc) in the range of 0.118-53.7%). The results indicate that the nonlinear sorption of organic solutes results primarily from interactions with soil/sediment organic matter. The K*oc K*oc=Kp/f(oc)), Qoc (Qoc=Q0/f(oc)), Loc (Loc=Q0 . b/f(oc)) and b for a given organic solute with different soils/sediments are largely invariant. Furthermore, logK*oc, logb and logLoc for various organic solutes are correlated significantly with the solute logKow or logSw (logKow in the range of 0.9 to 5.13 and logSw in the range of -6.176 to -0.070). A fundamental empirical equation was then established to calculate approximately the nonlinear sorption from soil/sediment f(oc) and solute Sw for a given solute equilibrium concentration.

Adsorption↗

PubMed2006

Application of extraction chromatography to the separation of thorium and uranium dissolved in a solution of high salt concentration.

Extraction chromatography with commercially available UTEVA resin (for uranium and tetravalent actinide) was applied for the separation of Th and U from control solutions prepared from a multi-element control solution and from sample solutions of solidified simulated waste. Thorium and U in control solutions with 1-5mol/dm(3) HNO(3) were extracted with UTEVA resin and recovered with a solution containing 0.1mol/dm(3) HNO(3) and 0.05mol/dm(3) oxalic acid to be separated from the other metallic elements. Extraction behavior of U in the sample solutions was similar to that in the control solutions, but extraction of Th was dependent on the concentration of HNO(3). Thorium was extracted from 5mol/dm(3) HNO(3) sample solutions but not from 1mol/dm(3) HNO(3) sample solutions. We conjecture that thorium fluoride formation interferes with extraction of Th. Addition of Al(NO(3))(3) and Fe(NO(3))(3), which have higher stability constant with fluoride ion than Th, does improve extractability of Th from 1mol/dm(3) HNO(3) sample solution.

Aluminum Compounds↗

PubMed2005

The wettability of polytetrafluoroethylene by aqueous solutions of sodium dodecyl sulfate and propanol mixtures.

Advancing contact-angle (theta) measurements were carried out with aqueous solutions of propanol and four series of aqueous solutions of dodecyl sulfate (SDDS) and propanol mixtures at constant dodecyl sulfate concentrations equal to 1 x 10(-5), 6 x 10(-4), 1 x 10(-3), and 1 x 10(-2)M, respectively. The obtained results indicate that in the range of propanol concentrations studied there were considerable contact-angle changes, with exception of the solution series at a constant concentration value of SDDS higher than its critical micelle concentration. From the results of contact-angle measurements and application of the Gibbs and Young equations the ratio of the excess concentration of surfactant and propanol at the solid-aqueous solution interface to the excess of their concentration at the aqueous solution-air interface was calculated. From the calculations it appears that there is a straight linear dependence between the adhesion tension and surface tension of aqueous solutions of SDDS and propanol mixtures, and the slope of the line is equal to -1, which suggests that the surface excess of the SDDS and propanol mixture at the polytetrafluoroethylene-solution interface is the same as the at the solution-air interface. The extrapolation of the straight line to the point corresponding to the surface tension of the aqueous solution, which completely spreads over the polytetrafluoroethylene surface, gives a critical surface tension of wetting equal to 23.7 mN/m. On the basis of the critical surface tension and the Young and modified Szyszkowski equations it was found that in a polytetrafluoroethylene-aqueous solution of the SDDS and propanol mixture, the interface tension can be predicted by the modified Szyszkowski equation.

Journal Article↗

PubMed1996

Cytoplasmic viscosity near the cell plasma membrane: translational diffusion of a small fluorescent solute measured by total internal reflection-fluorescence photobleaching recovery.

Total internal reflection-fluorescence recovery after photobleaching (TIR-FRAP) was applied to measure solute translational diffusion in the aqueous phase of membrane-adjacent cytoplasm. TIR fluorescence excitation in aqueous solutions and fluorescently labeled cells was produced by laser illumination at a subcritical angle utilizing a quartz prism; microsecond-resolution FRAP was accomplished by acousto-optic modulators and electronic photomultiplier gating. A mathematical model was developed to determine solute diffusion coefficient from the time course of photobleaching recovery, bleach time, bleach intensity, and evanescent field penetration depth; the model included irreversible and reversible photobleaching processes, with triplet state diffusion. The validity and accuracy of TIR-FRAP measurements were first examined in aqueous fluorophore solutions. Diffusion coefficients for fluorescein isothiocyanate-dextrans (10-2000 kDa) determined by TIR-FRAP (recovery t1/2 0.5-2.2 ms) agreed with values measured by conventional spot photobleaching. Model predictions for the dependence of recovery curve shape on solution viscosity, bleach time, and bleach depth were validated experimentally using aqueous fluorescein solutions. To study solute diffusion in cytosol, MDCK epithelial cells were fluorescently labeled with the small solute 2',7'-bis-2-carboxyethyl-5-carboxyfluorescein-acetoxymethyl-ester (BCECF). A reversible photobleaching process (t1/2 approximately 0.5 ms) was identified that involved triplet-state relaxation and could be eliminated by triplet-state quenching with 100% oxygen. TIR-FRAP t1/2 values for irreversible BCECF bleaching, representing BCECF translational diffusion in the evanescent field, were in the range 2.2-4.8 ms (0.2-1 ms bleach times), yielding a BCECF diffusion coefficient 6-10-fold less than that in water. These results establish the theory and the first experimental application of TIR-FRAP to measure aqueous-phase solute diffusion, and indicate slowed translational diffusion of a small solute in membrane-adjacent cytosol.

Animals↗