Laser Light-scattering Measurements Research Articles

Aggregation properties of semisynthetic GD1a ganglioside (IV 3Neu5ACII 3Neu5AcGgOse 4Cer) containing an acetyl group as acyl moiety

GD1a ganglioside containing an acetyl group as aryl moiety, GD1a(acetyl), was synthesized from natural GD1a. The aggregative properties in aqueous solution of GD1a(acetyl) have been studied by static and dynamic laser light-scattering measurements. GD1a(acetyl) spontaneously aggregates as small micelles showing a hydrodynamic radius and molecular mass of 33 Å and 96 kDa, respectively. Vibrio cholerae sialidase showed a very high activity on the micelles of GD1a(acetyl), compared to GDla. This has been explained as a consequence of the high surface curvature of the the small micelles. High resolution proton NMR spectra were recorded from micelles of GD1a(acetyl) in deuterated water. The low overall correlation time of the GDla(acetyl) micelles was calculated to be about 2 × 10 −8s, a value one order of magnitude lower than that determined for natural GD1a.

Inversion of light-scattering measurements for particle size and optical constants: experimental study

Measurements of the light scattered by a sample contain information regarding the physical properties of the sample. Laser light-scattering measurements can be made unobtrusively in environments that are inaccessible to other types of measurements, so laser light-scattering techniques have become an important tool in aerosol research. The primary difficulty associated with using light-scattering techniques to determine aerosol particle properties is inverting the measurements or extracting the desired information from the measurements. In this study we use a 15-channel polar nephelometer to measure the light-scattering patterns of monodisperse polystyrene spheres. The light-scattering measurements are inverted, and the particle size distribution function and optical properties of the particles are retrieved. The results of these inversions are presented after a brief description of the calibration and operation of the nephelometer.

Volume regulation during recovery from chronic hypertonicity in brain glial cells.

Rat C6 glial cells undergo rapid regulatory volume increase (5-10 min) via electrolyte uptake when exposed to a hypertonic medium. With chronic exposure to hypertonicity (greater than 8 h), accumulated electrolyte is replaced partly by inositol. Inositol accumulation is brought about by upregulation of Na(+)-dependent inositol transport. When C6 cells acclimated chronically to hypertonic NaCl medium were returned to isotonic conditions, inositol levels dropped slowly from 478 nmol/mg protein towards control values (117 nmol/mg protein) in 18-24 h. Inositol loss occurred in part by efflux to the external medium via a pathway distinct from the uptake mechanism. Laser light-scattering measurements demonstrated that regulatory volume decrease (RVD) is slow under these experimental conditions. In contrast, cells exposed acutely to hypertonicity swell and then undergo a rapid and nearly complete RVD when returned to isotonic medium. These results suggest that slow inositol loss is rate limiting for RVD during recovery from chronic hypertonic stress. The slow inositol loss and RVD may be due to slow turnover of the efflux mechanism and/or slow downregulation of the hypertonically stimulated inositol uptake pathway.

The treatment of aqueous gum arabic solutions with ultraviolet radiation

Aqueous solutions of gum arabic have been photolysed with UV light from a low-pressure mercury lamp (maximum emission at 254 nm). The survival of the bacteria present was monitored as a function of fluence and it was found that a fluence of ~450 J/m 2 reduced the bacterial concentration in a 200 g/dm 3 gum arabic solution which has a 254 nm absorbance of 0.8 by 90%. The size of the fluence required for 90% bacterial reduction is much larger than that needed for transparent (at 254 nm) solutions, where a fluence of 250 J/m 2 typically reduces the bacterial load by four orders of magnitude. Low-angle laser light-scattering measurements indicate that photolytic degradation of the gum arabic occurs, although with an extremely low efficiency, a fluence of 8 × 105 J/m 2 being required to produce an average of one ‘degradative’ chain break per molecule. Gel permeation chromatography confirmed the low sensitivity of gum arabic to UV-induced degradation, there being no significant increase in the fraction of low-molecular-weight material after an essentially ‘sterilizing’ fluence of 3.9 × 10 3 J/m 2. On photolysis, the absorbance (220–350 nm) of gum arabic solutions increases; for a given fluence the increase is larger when oxygen is present. The emulsifying ability of photolysed gum arabic was tested using orange oil; no difference was detectable between photolysed (3.9 × 10 3 J/m 2) and untreated controls.

Calculation of surface area of sacculi from low-angle light-scattering measurements

Light-scattering provides a non-destructive way to measure the size and shape of bacteria. It is particularly appropriate for the study of isolated sacculi, i.e., the peptidoglycan, bag-shaped, supermacromolecules that are the stress-bearing component of the cell wall. We have developed an apparatus for low-angle laser light-scattering measurements to study gram-negative sacculi in the hydrated state. Here we present the theory based on the approximation that the sacculi are a population of ellipsoidal thin shells of revolution. The program assumes that the semi-minor axis remains constant, but the semi-major axis varies over two-fold during the growth cycle. The calculation approximates the size distribution of bacteria undergoing balanced exponential growth. The computation also averages over all angles of orientation of the sacculi in the suspension with respect to the light beam. The program calculates by a least squares method the best fitting semiminor axis of the newborn cell and from this calculates the mean surface area.

Viscoelasticity of monomolecular films: A laser light-scattering study

Accurate laser light-scattering measurements of the capillary wavemotion of monolayer-covered aqueous substrates are reported. The studied film-forming compounds were octanoic acid, myristic acid, stearic acid, tetradecanol, poly(methyl methacrylate) and poly(dimethyl siloxane). We convincingly found by measuring at two relatively high wavenumbers (83,356 and 139,359 m −1) that the wavemotion is determined, apart from static surface tension, only by a horizontal interfacial elasticity, ϵ, and a horizontal interfacial viscosity, κ. This result is in contrast with D. Langevin ( J. Colloid Interface Sci. 80, 412 (1981)) who found it necessary to propose that transverse viscoelastic properties are significant for myristic acid, stearic acid, and poly(methyl methacrylate) monolayers in a similar, but less accurate, light-scattering study. As one would expect, the measured ϵ is equal to or larger than the static elasticity which is in agreement with our earlier study ( J. Colloid Interface Sci. 83, 315 (1981)). Our κ values are consistently smaller than interfacial viscosities found in other studies, most pronounced for octanoic acid, where κ differed at least by four orders of magnitude when compared with the interfacial viscosities obtained using a mechanical wave-generating rheometer. This demonstrates particularly well one fundamental advantage of the light-scattering technique, i.e., its virtually nondisturbing nature. Furthermore, fluctuating capillary wave properties were observed in the gaseous/liquid-condensed two-phase region for the first time.

Accurate laser light-scattering measurements of capillary waves

Absolute, accurate, and high-resolution laser light-scattering measurements of capillary waves of water and n-dodecane were successfully performed at three wavenumbers. The wavenumbers were directly measured using a new reference grating technique to within ±0.2%. Our results show that the capillary wavemotion follows hydrodynamic theory using standard bulk property values within the experimental inaccuracies which are ±0.3 and ±3% in frequency and damping, respectively. Specifically, clean water exhibits no measurable anomalous surface properties which contradicts the previously unchallenged findings of D. Byrne and J. C. Earnshaw ( J. Colloid Interface Sci. 74, 467 (1980)).

Number- and Weight-Average Molecular Weights for Some Proanthocyanidin Polymers (Condensed Tannins)

The number-average molecular weights (Mn) and weight-average molecular weights (Mw) for proanthocyanidin polymers (condensed tannins) have been measured by vapour pressure osmometry and low-angle laser light-scattering measurements in methanol. These confirm earlier findings (based on gel permeation chromatography of the peracetate derivatives of these polymers) that they are polydisperse. The results also indicate that the incidence of branching in the polymer chains increases as the average chain length increases.

Optical studies of critical phenomena in macrofluid-like three-component microemulsions

Kerr-effect, low-angle laser light-scattering, dielectric time-domain-spectroscopy, and conductivity measurements (stationary and time-dependent both under low and high electrical fields) were carried out in a broad temperature region up to the phase separation temperature of water/Aerosol OT/ isooctane mixtures. From the new data it can be concluded that two independent critical phenomena are occurring. These are related to percolation and phase separation, respectively. The results strongly support the proposed formation of an infinite cluster and a particular percolative electric conduction mechanism.

Time-resolved photoredox reactions of colloidal CdS

Microsecond flash photolysis leads to a hypsochromic shift in the band edge of colloidal CdS. The recovery of the absorption spectrum does not obey simple first- or second-order kinetic but results from a distribution of first-order rate constants, which in turn arise from a distribution of particle sizes. Good agreement is obtained between the kinetic data and the distribution of particle radii calculated from dynamic laser light-scattering measurements. The transient is assigned to electrons trapped on the particles and it can be used to follow directly the rate of interfacial electron transfer from CdS to methyl viologen and O2 when cysteine is present.

Laser light-scattering measurements of interfacial tension using optical heterodyne mixing spectroscopy

The interfacial tension between n-decane and water was determined by laser light scattering. The experimentally measured autocorrelation functions were in good agreement with those derived from the hydrodynamical theory of capillary waves. For comparison, the interfacial tension was measured with the Wilhelmy plate, the du Nou¨y ring, and the spinning drop methods. The laser light-scattering technique showed the same absolute accuracy as the other methods and, within a common uncertainty of 1.5%, the same value for the interfacial tension was found. The important advantages of the laser technique in being nonperturbative and only relying on bulk phase parameters for the analysis are strong arguments for its use in measuring liquid/liquid interfacial tension.

Laser light-scattering measurements of interfacial tension using optical heterodyne mixing spectroscopy

Laser light-scattering measurements of interfacial tension using optical heterodyne mixing spectroscopy

Glass microstructure characterization by lazer light scattering, small angle X-ray scattering and electron microscopy

Transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and laser light scattering (LLS) have been used to characterize the microstructures of mixed alkali-lithia-potassia-silica glasses and soda lime silica glasses. In most cases the three methods complement one another very well. In the mixed alkali silicate glasses LLS measurements of particle size correlate very well with TEM measurements. In addition, there is a direct correlation between particle size measurements by both methods and flaw sizes calculated from strength measurements using the Griffith equation. In the soda lime silica system LLS measurements of the glasses prior to heat treatment in the temperature region of metastable liquid immiscibility correlate very well with SAXS measurements of the heat treated glasses. The merits of each method in studies involving these glass systems will be discussed.

Laser light-scattering measurements of viscoelastic monomolecular films

Laser light-scattering measurements of the capillary wave motion of aqueous surfaces covered with fatty acid and lecithin monomolecular films are reported. An improved measuring technique allowed quantitative determination of both film dilational elasticity and film dilational viscosity. Fluctuating capillary wave properties were observed with surface films in the gaseous—liquid two-phase region. For monolayers in the liquid-expanded state, the elasticity determined by light-scattering measurements is the same as that obtained by film-balance measurements at higher surface concentrations but not at lower concentrations. The well-known transition between liquid-expanded and liquid-condensed films does not show up in the measured elasticity. This result can be expected from reported observations of finite speed, stepwise barrier-compressed pentadecanoic acid films. The viscosities measured by the light-scattering technique are smaller than one surface millipoise and are comparable in magnitude to surface viscosity values obtained with mechanical surface (shear) viscometers.

Virial coefficients in determination of molecular weights on solutions of coal derivatives

A calculation procedure is proposed which allows low-angle laser light-scattering measurements to be used as a practicable method for calibration-free molecular weight determinations of soluble coal derivatives. Application of this method to coal solutions allows thermodynamic parameters for the solvent-coal interaction to be derived.

Physical studies on assimilatory nitrate reductase from Chlorella vulgaris.

Assimilatory nitrate reductase (EC 1.6.6.1 NADH:nitrate oxidoreductase) from Chlorella vulgaris purified by affinity chromatography was found to be homogeneous as judged by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel and by analytical ultracentrifugal techniques. The molecular weight of the intact enzyme and that of the enzyme dissociated in 6 M GuHCl, determined by sedimentation equilibrium studies, were 280,000 +/- 10,000 and 90,000 +/- 5,000, respectively. Comparable values were obtained using the S20,w value and the D20,w values in Svedberg's equation. The D20,w values were determined by laser light-scattering measurements. Active enzyme centrifugation showed that the monomer is an active species. A quantitative re-evaluation of the prosthetic groups present (FAD, heme, and molybdenum) was also made and was consistent with the conclusion that the active monomer contains three subunits as previously deduced by Solomonson et al. ((1975) J. Biol. Chem. 250, 4120). Electron micrographs showed images which corresponded to three subunits, supporting the data obtained by hydrodynamic studies. The enzyme is not cigar-shaped, as previously surmised, but has a roughly globular structure.

The determination of the mean and standard deviation of the size distribution of a colloidal suspension of submicron particles using the Fiber Optic Doppler Anemometer, FODA

Laser light-scattering measurements of the Brownian motion of a colloidal suspension of silica particles, Syton, by means of the Fiber Optic Doppler Anemometer (FODA) were used to determine the mean and standard deviation of the particle size distribution. Measurements over a wide range of concentrations from undiluted Syton to 0.049% Syton solution showed a consistent power spectrum of scattered light amplitude fluctuations. Using a modified Lorentzian model for the power spectrum, a computer least-squares curve fit and a graphical method were used to calculate the mean and standard deviation of particle radius. The results were consistent for all concentrations of Syton, verifying the versatility of the FODA and the accuracy of the modified Lorentzian model. The mean and standard deviation of particle radius in Syton were found to be 46.5 and 20.8 nm, respectively. It was found that clumping in undiluted Syton caused an apparent increase in the mean and standard deviation of the particle size distribution, as compared with all of the other dilutions where clumping did not occur.

Laser light-scattering measurements of particle concentration in a turbulent jet

A laser light-scattering technique has been used to study the relative particle concentration field in a round turbulent air jet. Measurements were made in the far field of a smoke-marked turbulent jet exhausting into a secondary air stream. Radial distributions of mean particle concentration, concentration fluctuation intensity and intermittency were measured at several streamwise locations. Concentration fluctuation power spectra and the micro- and integral scales of the concentration fluctuations were measured on the jet axis. The effects of ambiguity noise and noise due to optical path attenuation on the performance of the laser light-scattering system are discussed.

Current Sheet Structure in an Inductive-Impulsive Plasma Accelerator

Probe and laser light-scattering measurements of electron density have been made in the current sheet of a pulsed inductive accelerator. The discharge consists of a thin flat disk of pure je current. The only current carriers are electrons. The gas is ionized and swept up into a 4 mm thick current sheet. Ions are accelerated by an axial E field, ahead of the mass layer, produced both by electron current and negative electron pressure gradient. This field nearly vanishes at the rear of the mass layer where j x B force balances the positive electron pressure gradient.