Quasi-elastic Laser Light Scattering Research Articles

A novel method for surface modification of nanoparticles based on control of charge environment

A novel procedure for surface modification of SiO2 nanoparticles is described. Tetraoctylammonium bromide was introduced to modification system for the purpose of controlling the surface charge environment of SiO2 nanoparticles. Then, the SiO2 nanoparticles were treated with the coupling agents firstly, followed by radical grafting polymerization in non-aqueous system to graft Poly (methyl methacrylate) chains onto the surface of modified SiO2 nanoparticles. Fourier transform infrared spectroscopy, thermogravimetric analysis, high-resolution X-ray photoelectron spectra, and 13C nuclear magnetic resonance were used to characterize the modification effect of SiO2 nanoparticles. The results indicated that the method we described is an effective way to modify the surface of nanoparticles. And the morphology and characteristic of SiO2 nanoparticles were characterized by transmission electron microscopy (TEM), quasielastic laser light scattering (QELS), dynamic contact angle. The results of TEM and QELS demonstrated that nanosilica with an average size of 85.8 nm was prepared. The reduction of the contact angle indicated the increase in hydrophobicity of nanosilica. The result of controlling the surface charge environment of SiO2 nanoparticles was characterized by zeta potential. By using this modification method, nanoparticles are of great potential to synthesize versatile organic/inorganic nanocomposite.

Quasi-elastic laser light scattering study of polyacrylamide hydrogel immersed in water and salt solutions

Polyacrylamide (PAAm) hydrogels immersed in water and aqueous NaCl solutions were investigated for their structure and dynamics using static and quasi-elastic laser light scattering (QELS) techniques. Ensemble-averaged electric field correlation function f(q, t) obtained from the non-ergodic analysis of intensity-autocorrelation function for PAAm gel immersed in water and in 5 M NaCl showed an exponential decay to a plateau with an initial decay followed by saturation at long times. The value of the plateau was found to depend on NaCl concentration and was higher than that of water. Collective diffusion coefficient, D, of the polymer network of the hydrogel immersed in water and in different concentrations of NaCl was determined by analysing f(q, t). The measured diffusion coefficient showed linear decrease with increase in concentration of NaCl. The characteristic network parameters were obtained by analyzing f(q, t) with harmonically bound Brownian particle model and from static light scattering studies.

Dynamics of phospholipid monolayers on polarised liquid–liquid interfaces

Quasi-elastic laser light scattering (QELS) is used to investigate dynamics of the polarised water/1,2-dichloroethane (DCE) interface in the presence of adsorbed DL-alpha-dipalmitoylphosphatidylcholine (DPPC) over a range of the interfacial potential differences (+/-0.3 V) and DPPC concentrations (0-20 microM). An analysis of the frequency of thermally excited capillary waves reveals some novel features in the adsorption of DPPC. The effect of the capillary wavenumber on the capillary wave frequency and the damping factor suggest that the dynamic behaviour of ITIES is consistent with the theoretical predictions for a sharp liquid-liquid interface.

Micro-thermal field-flow fractionation: new high-performance method for particle size distribution analysis

Micro-thermal field-flow fractionation (μ-TFFF) was applied to the separation of polystyrene latices. This new high-resolution technique allows determination of the particle size distribution (PSD) if carried out under optimized experimental conditions. The optimum temperature of the accumulation wall, which influences the relaxation processes and, consequently, the zone broadening, was chosen on the basis of our prior work. The flow rate was chosen as a compromise between the theoretical optimum value, which is very low because the diffusion coefficients of the colloidal particles are very small, and a value allowing performance of the PSD analysis in a reasonable time. These experimental conditions can be manipulated easily due to the high versatility of μ-TFFF, which follows from a large decrease of the heat energy flux across the channel with its reduced dimensions in comparison with standard TFFF. The PSDs obtained from μ-TFFF data are compared with results from quasi-elastic laser light scattering (QELS) and transmission electron microscopy (TEM). It has been found that a baseline resolution of a model mixture of two samples of close average particle diameters can be achieved by an appropriate choice of the temperature drop in μ-TFFF, whereas only a broad, unresolved PSD of the mixed sample was obtained from the QELS measurement. The TEM of the mixed sample revealed the presence of two particle size populations. However, the number of particles which are practically counted on a TEM picture is several orders of magnitude lower than the number of particles taken into account in μ-TFFF or QELS. Consequently, the PSD obtained from the TEM did not represent the whole sample. Comparison of μ-TFFF with modern hydrodynamic chromatography (HC) has shown that the methods exhibit roughly the same resolution and time of analysis. Nevertheless, μ-TFFF is a more universal technique because the separation of the colloidal particles or of the macromolecules within a broad range of molar masses is carried out on the same channel, as demonstrated previously.

Quasi-elastic laser light scattering from thermally excited capillary waves on the polarised water/1,2-dichloroethane interface

Quasi-elastic laser light scattering (QELS) from thermally excited capillary waves on the polarised water/1,2-dichloroethane interface was measured using optical heterodyne mixing technique. Interfacial potential difference was controlled by equilibrium partition of tetraethylammonium, tetrapropylammonium, tetrabutylammonium or tetrapentylammonium bromide. Frequency of the capillary wave of a selected wavelength was shown to decrease with the increasing electrolyte concentration. Frequency decrease was related to the decreasing interfacial tension being caused by the increasing relative surface excess of the electrolyte. No significant effect of the electrolyte concentration on the capillary wave damping was observed. Adsorption data obtained from these measurements are consistent with the results of the double layer capacity studies.

Self-organization in complexes of polyacids with oppositely charged surfactants

Formation and structure of water-soluble complexes of alkyltrimethylammonium bromide homologues (AlkTAB) with poly(acrylic acid) (PA) of different polymerization degrees at pH 5.7 have been examined by elastic and quasi-elastic laser light-scattering and high-speed sedimentation technique. It was experimentally shown that generation of intramolecular micellar phase is the necessary condition for formation of PA-AlkTAB complexes. Minimum aggregation number of the surfactant ions in the complex micelle was found to be close to that of the surfactant micelles in polymer-free solution. The structure of the polyelectrolyte-surfactant complexes (i.e. a phase state of the complex, conformation of the polyion coil and the surfactant ion aggregation number) was shown to be largely determined by PA polymerization degree.

Purification of active synaptic vesicles from the electric organ of Torpedo californica and comparison to reserve vesicles

At least two distinguishable forms of synaptic vesicles exist, the active and reserve, but the reserve form is studied most because it has been difficult to purify the active vesicles. In the work reported here the active vesicles (termed VP 2) were highly enriched from the electric organ of Torpedo californica by an improved method developed for the reserve vesicles (termed VP 1) with the addition of density gradient centrifugation based on Percoll. No significant differences between the vesicular types were found in the amounts of SV1, SV2, and SV4 epitopes and P-type and V-type ATPase activities. The buoyant densities (g/ml) of VP 1 and VP 2 vesicles were determined by centrifugation in isosmotic sucrose (1.051, 1.069), Percoll (1.034, 1.040), and glycerol (1.087, 1.090) gradients. The radii were determined by dynamic quasi-elastic laser light-scattering to be (56.6 ± 10.8) nm and (55.0 ± 12.7) nm. For both vesicular types the volume of excluded sucrose is only about 37% of the volume of excluded Percoll, indicating that the surfaces are rough. Approx. 51% of the VP 1 and 32% of the VP 2 vesicular volumes are ‘osmotically active’ water that is exchangeable with glycerol. The different buoyant densities and amounts of osmotically active water in VP 1 and VP 2 vesicles probably are due to the different internal solutes. Previously observed differences in acetylcholine active transport and vesamicol binding by VP 1 and VP 2 synaptic vesicles cannot be explained by major alterations in the protein composition or conformation of the membranes in the two types of vesicles.

Human neutrophil motility: time-dependent three-dimensional shape and granule diffusion.

The locomotion of human polymorphonuclear leukocytes (PMNs) was studied with two complementary methods: Three-dimensional shapes were reconstructed from time series of optical sectioning microscopy using differential interference contrast (DIC) optics, and the diffusion of cytoplasm granules within individual cells was measured using quasielastic laser light scattering (QELS). The three-dimensional cell edges outlined in the optical sections were analyzed qualitatively in time-lapse film strips and quantitatively from morphometry. The fastest locomotion occurred in chemotactic gradient with cell velocity that oscillated between 10 and 30 microns/min with a period of 50-55 seconds. Within the periodic bursts of speed, a fibroblast-like locomotory cycle was observed, with leading lamella extended and contacts formed with the substrate surface, followed by rapid motion of the cell body and nucleus over the immobile contacts. Consistent with this apparent staged motion, correlation analysis revealed a phase lag of 2-3 seconds in velocities between the bottom (ventral) and the top layers of the cell. In addition there was a tendency to a lower cell profile at times of higher velocity. The diffusion of natural cytoplasmic granules within resting PMNs was not affected by cytoskeleton disrupting drugs. During the stage of most rapid motion, when cytoplasmic streaming could be seen, diffusion of the granules decreased two- to 2.5-fold, and then returned to resting levels. These observations suggest that PMN locomotion consists of extensions near the surface to form forward contacts and then stiffening or possibly contraction of the cytoskeleton when the body of the cell is moved forward. Three-dimensional movies of PMN cells are included in the video supplement.

Structural study of fractionated hydroxyethyl‐amylopectin in aqueous solution

AbstractFractionated hydroxyethyl starch was well characterized by coupled LALLS‐SEC (lowangle laser light scattering and steric exclusion chromatography), QELLS (quasi‐elastic laser light scattering), MALLS (multiangle laser light scattering), and viscosimetry. The scaling laws of the molecular weight dependences of the following dimensions are found to exhibit low exponents consistent with a highly grafted structure: Additional X‐ray synchrotonic scattering (SAXS) studies permit us to give a preliminary description of the internal structure of the macromolecules.

Quasi-elastic laser light-scattering studies of size and dispersity of secretory vesicles and neurosecretosomes isolated from vertebrate neurohypophyses

Quasi-elastic laser light-scattering studies of size and dispersity of secretory vesicles and neurosecretosomes isolated from vertebrate neurohypophyses

Changes of some physical properties of isolated and purified plasma and thylakoid membrane vesicles from the freshwater cyanobacterium Synechococcus 6301 ( Anacystis nidulans) during adaptation to salinity

Photoautotrophically growing cultures of the fresh-water cyanobacterium Anacystis nidulans (Synechococcus sp.) became adapted to the presence of 0.4–0.5 m NaCl in the growth medium (about seawater level) with a lag phase of 2 days after which time the growth rate resumed at 80–90% of the control. Major changes in structure and function of the plasma membranes (and, to a much lesser extent, of the thylakoid membranes) were found to accompany the adaptation process. Plasma and thylakoid membranes were separated from crude cell-free extracts of French pressure cell-treated Anacystis by discontinuous sucrose density gradient centrifugation and purified by repeated recentrifugation on fresh gradients. Concentrations of copper, iron, calcium, and magnesium ions were determined by inductively coupled plasma atomic emission spectrometry with EDTA-washed and dialyzed membrane preparations; salt adaptation was found to increase (decrease) the concentration of membrane-bound calcium in plasma (thylakoid) membranes, qualitatively reciprocal results being obtained for magnesium. Levels of plasma membrane-bound copper and iron roughly tripled during the adaptation process; by contrast, corresponding effects on thylakoid membranes were negligible. The size of the membrane vesicles was measured by quasi-elastic laser light-scattering and the electric surface charge of the membranes was measured by laser Doppler velocimetry. Salt adaptation decreased the mean diameter of plasma membrane vesicles to a much higher extent than that of thylakoid membrane vesicles. Overall surface charge densities of resting vesicles were only slightly affected by the salt treatment as was also seen from titration of the electrophoretic mobility of the vesicles with electrolytes. Yet, induction of (photosynthetic or respiratory) electron transport provoked a charge separation across the membrane which was easily measurable in terms of electrophoretic mobility. The results will be discussed with particular emphasis on the stimulated cytochrome c oxidase activity of plasma (but not thylakoid) membranes from salt-adapted cells compared to control cells and also with respect to the decreased ion permeability of the plasma membrane of salt grown cells.

Quasielastic Laser Light Scattering and Laser Doppler Electrophoresis as Probes of Synaptic and Secretory Terminal Function

The intensity fluctuations of scattered laser light provide a rapid, nondestructive probe of hydrodynamic size and polydispersity of nerve-ending subcellular particles. This method yields information on diffusive and directed motion of secretory granules and synaptic vesicles. It also enables accurate measurements of surface charge properties of isolated granules and plasma membranes. Recently, a fast, total intensity light-scattering change, sensitive to many of the factors that influence secretion, has been detected in neurosecretory terminals. Here a slower, but equally reversible, light-scattering change is detected using an intact invertebrate neurosecretory organ. Scattering at rest is dominated by particles of diameter similar to that of secretory vesicles detected in electron micrographs of the same tissue. Simultaneous release and light-scattering observations demonstrate an increase in the proportion of total scatter derived from mobile as opposed to fixed components, with no change in mean particle diameter. Since the major changes in intensity fluctuations are detected during the declining phase of the release of secretory product, they may represent longer term reorganization of terminals following intense secretory activity. As a prelude to dissecting the origin of the fast light-scattering changes, the hydrodynamic properties of secretosomes and purified secretory granules from mouse neurohypophysis have been characterized. In this way, size, dispersity and aggregation can be followed, and subpopulations can be characterized. Application of an electric field to various subcellular fractions enables measurement of electrophoretic mobility, and hence calculation of surface-charge properties of granules and plasma membranes. The effects of divalent cations on granule surface charge in vitro indicate that surface-charge neutralization is not a calcium-specific event in exocytosis. The possibility that some of the light-scattering signal reflects dynamic changes in cytoskeletal components of the secretory terminal is examined.

Thermal and solvent stability of proteoglycan aggregates by quasielastic laser light-scattering

The dissociation behavior of several species of proteoglycan aggregates (PGA) has been studied quantitatively by monitoring the changes in particle size by dynamic laser light-scattering. Firstly, studies of the thermal dissociation of reconstituted PGA from bovine nasal septum and bovine fetal epiphysus are described. The effect of link protein in stabilizing reconstituted PGA against changes in temperature has been demonstrated. It was also confirmed that, upon prolonged heating at 70°, the dissociation of link-containing, reconstituted PGA is effectively irreversible. Secondly, the dissociation characteristics of native PGA isolated from chick chondrocyte and rat chondrosarcoma cell-cultures were investigated in aqueous solvents containing increasing concentrations of guanidine hydrochloride. It was found that the more densely packed, native, aggregate structure has a higher susceptibility to thermal disruption than the reconstituted, link-containing material. Considerable loss of subunits from the native aggregates occurs at temperature where the link protein retains its activity. The dissociation of native PGA is irreversible, in the sense that reconstituted PGA always exhibits smaller sizes than the native PGA, reflecting a smaller degree of aggregation of the subunits.

Quasielastic laser light scattering and electron microscopy studies of the conformational transitions and condensation of poly(dA‐dT) · poly(dA‐dT)

AbstractPoly(dA‐dT) · poly(dA‐dT) undergoes a reversible conformational transition in the presence of Co(NH3) or spermidine in low salt (10 mM NaCl + 1 mM Na cacodylate). This transition is similar, as judged by changes in the CD spectrum, to the B‐to‐X transition of the polymer provoked by alcohol and Cs+ [Vorlickova et al. (1983) J. Mol. Biol. 166, 85–92; (1982) Nucleic Acids Res. 10, 6969–6979] and by meso‐substituted porphyrin ligands [Carvlin et al. (1983) Nucleic Acids Res. 11, 6141–6154]. Under the salt conditions indicated, the CD transition begins with Co(NH3) at about 70 μM and is complete by 150 μM; with spermidine, it begins at about 300 μM and is complete by 600 μM. Total intensity light scattering shows a marked increase at trivalent cation concentrations somewhat below those at which the CD transition begins. Quasielastic laser light scattering (QLS) measurement of the translational diffusion coefficient, DT, shows that, in the presence of Co(NH3), the hydrodynamic radius, Rh, increases from 260 to 1450 Å over the concentration range of 25 to 200 μM. With spermidine, Rh is 550±50 Å up to 200 μM, then increases rapidly. Values of Rh in this range are generally found for toroidal or other compact condensed forms of DNA. Such forms—toroidal, spheroidal, and rodlike structures—are observed in electron micrographs of poly(dA‐dT) · poly(dA‐dT) when the trivalent cation concentration is in the transition range. Above that range, extensive aggregation of the polymer chains is seen. Taken together, these results suggest a sequenc of related secondary and tertiary structure changes as trivalent cations are added to a low‐salt solution of poly(dA‐dT) · poly(dA‐dT). At very low Co(NH3) or spermidine, condensation of the polymer takes place while it is still in the B‐form. Further additions of trivalent cation provoke a transition from B‐ to X‐form, finally resulting in extensively aggregated polymer. These results are different from those generally observed with native DNA, where condensation with polyamines or Co(NH3) in aqueous solution is not accompanied by secondary structural change. They are also different from those we have seen with poly(dG‐me5dC) · poly(dG‐me5dC), where condensation and the B–Z transition occur at the same ionic conditions. These distinctions are another entry in the growing catalog of sequence‐dependent structural effects that may be important in the regulation of the biological activity of DNA.

Toroidal condensation of Z DNA and identification of an intermediate in the B to Z transition of poly(dG-m5dC) X poly(dG-m5dC).

Using a combination of spectroscopic techniques, quasi-elastic laser light scattering (QLS), and electron microscopy (EM), we have been able to show that the B to Z transition of poly(dG-m5dC) X poly(dG-m5dC) is accompanied by extensive condensation of the DNA in both low and high ionic strength buffers. At low concentrations of NaCl (2 mM Na+), an intermediate rodlike form, which exhibits a circular dichroism (CD) spectrum characteristic of an equimolar mixture of B and Z forms, is observed. This is produced by the orderly self-association of about four molecules of the polymer after prolonged incubation of a concentrated solution at 4 degrees C. On addition of 5 microM Co(NH3)63+, the CD spectrum of the intermediate changes to that of the Z form, which is visualized as a dense population of discrete toroids on an EM grid stained with uranyl acetate. On the other hand, addition of NaCl to a solution of poly(dG-m5dC) X poly(dG-m5dC) in the absence of any multivalent ion condenses the polymer to toroidal structures at the midpoint (0.75 M NaCl) of the B to Z transition. Further addition of NaCl unfolds these toroids to rodlike structures, which show characteristic Z-form CD spectra. These results show that Z DNA can take up a variety of tertiary structural forms and indicate that its inverted CD spectrum is due to its left-handed helical sense rather than to differential scattering artifacts.

Studies of rheologically active biological macromolecules by quasielastic light scattering.

Variables which describe the structure and rheological behavior of macromolecules in both dilute solutions and gels may be determined using methods of quasielastic laser light scattering (QELS). Such parameters include diffusion coefficients, molecular size such as hydrodynamic radius, and viscoelastic moduli. If the polymer is polydisperse, the distribution of radii may be estimated. Application of the methods is illustrated with data on the size distribution of a tracheal mucin glycoprotein solution as an example of a polydisperse polymer solution of biorheological interest. A scheme for measuring shear moduli of polymer gels using dynamic laser light scattering is illustrated with data on reconstituted fibrin clots.

Physical properties of the E. coli 4.5S RNA: first results suggest a hairpin helix of unusual thermal stability.

Hyperchromicity measurements and quasi-elastic laser light scattering (QELS) have been used to assess the solution structure of the metabolically stable E. coli 4.5S RNA. Results from thermal denaturation measurements revealed the 4.5S species to be markedly more stable than most other RNAs characterized thus far. Optical Tm's range from 79 degrees to 88 degrees with transitions approximately 25 degrees C wide. The Tm values show little dependence on ionic strength, but stability is enhanced considerably by Mg+2. In the QELS experiments the diffusion coefficient does not decrease until T greater than 70 degrees C. Neither the diffusive melting nor the diffusion coefficient at infinite dilution (D0(20,w)) show dependencies on ionic strength but both are influenced by Mg+2. The diffusion behavior is in agreement with that predicted for a rigid cylindrical molecule 125 to 160 A long and 37 to 26 A in diameter. Taken together these results are consistent with the more stable hypothetical secondary structures that can be formed, in which 70-75% of the 114 bases are paired to form a single extended hairpin helix.

Treatment of mobile phase particulate matter in low-angle quasi-elastic light scattering

The method of quasi-elastic laser light scattering (QLS), particularly at low forward scattering angles, has been complicated by the transient presence of Mie or large Rayleigh scattering particles which contaminate the scattering volume. These large contaminating particles have substantial effects on photon correlation spectroscopy because the presence of these larger scatterers tends to decrease the value of the apparent diffusion coefficient of the particle of interest. A method is presented which yields more accurate diffusion constants by autocorrelation of selected photon count periods representative of minimal Mie or large Rayleigh particle contamination. This method was applied to the determination of the apparent diffusion constant for four proteins—ovalbumin, chymotrypsinogen-A, bovine serum albumin, and ribonuclease-A.

Hydrodynamics, size, and shape of bacteriophage T4D tails and baseplates.

AbstractWe have used translational diffusion coefficient measurements and subunit hydrodynamic theory to determine the dimensions and shape of bacterioophage T4D baseplates and tails. The diffusion coefficient of the baseplate, measured by quasielastic laser light scattering (QLS), was determined previously by Wagenknecht and Bloomfield to be D = 8.56 × 10−8 cm2/s. For the tail, we found D = 5.88 × 10−8 cm2/s by QLS, and D = 6.02 × 10−8 cm2/s by combining sedimentation coefficient and molecular weight in the Svedberg equation. These values, which have an uncertainty of ±2.7%, when combined with subunit hydrodynamic theory, enabled us to refine estimates of dimensions obtained by electron microscopy. For the hexagonal baseplate, the vertex‐to‐vertex distance is about 480 Å, the thickness is 160 Å, and there are six extended short fibers 320‐Å long and 40 Å in diameter. When a baseplate of these dimensions is attached to a tail tube‐sheath‐connector complex 1050‐Å long and 240 Å in diameter, the calculated D is 5.93 × 10−8 cm2/s, within 1% of experiment. This combined use of electron microscopy and hydrodynamics, using the former to ascertain shape, and the latter to obtain solution dimensions, is a powerful approach to the structure of biomolecular complexes.

The structure of an aminosilane coupling agent in aqueous solutions and partially cured solids

The molecular structures of partially cured polyaminopropylsilsesquioxane and aminopropyltriethoxysilane in water have been studied using Fourier-transform infrared, laser Raman, and quasielastic laser light-scattering spectroscopy. A multiply hydrogen-bonded structure is proposed for the intramolecularly interacting amine and silanol groups on the basis of isotope exchange experiment and conformational energy calculations. Conformational restrictions are rather low for the proposed structure, which is thus suitable for the partially cured solid where there are slight perturbations by the surrounding amine and silanol groups. The O.…N distance was experimentally determined to be in the range 2.70–2.67 A and estimated theoretically as 2.49–2.45 A. The aminosilane in very dilute solution is found to be mostly monomeric. The isolated monomer-oligomer transition lies around 0.15% by weight and this transition influences the amount of silane uptake by glass fibers. It is also proposed that this phenomenon may be general for surface treatments by silane coupling agents. Hydrolyzed aminosilane oligomers exist in part as submicron aggregates which can be broken up by the addition of an alcohol. The neutralized aminosilane hydrolyzes very slowly although it dissolves in water instantaneously. Micelle formation is also proposed.