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The dynamics of the α-relaxtion in three glass-forming polymeric systems has been studied by means of quasielastic neutron scattering as well as by relaxation techniques. By using these techniques, we have covered a wide time-scale ranging from mesoscopic to macroscopic times (10−10-101 s). All relaxation data have been interpreted in terms of a Havriliak-Nagami relaxation function, ΦHN. Neutron scattering data were described in terms of a scattering law S(Q, ω) which was also built starting from ΦHN. The results obtained indicate that the dynamics of the α-relaxation in a wide timescale can be well described by means of the same spectral shape, i.e. the same Havriliak-Negami parameter values. Moreover, the Havriliak-Negami characteristic times deduced from the fitting of the experimental data can also be described using only one Vogel-Fulcher functional form. Then, this implies a self-consistent description of the dynamics of the α-relaxation obtained by very different probes. [ABSTRACT FROM AUTHOR]

Local dynamics of a chain in the bulk state is strongly controlled by the immediate environment of the chain. The excessive friction exerted by the environment precludes large scale kinetic displacements of the chain atoms. In the presence of strong constraining effects of the environment, a transition from one configuration to the other is expected to take place by strongly correlated and relatively small range rearrangements of torsional motions. In the present study, local dynamics of the chain is analyzed as a succession of configurational rearrangements such that the change in the chain radius of gyration at each step is minimum. The degree of cooperativity among neighboring bonds along the chain resulting from the constraint of the environment is found to be highly localized. A 120° rotation of an internal bond is observed to be possible by cooperative adjustments of a few bonds in its immediate neighborhood along the chain. Changes in the mean-square anisotropic polarizability tensor when the ends of a relatively short chain (n≤50) are subject to a prescribed deformation, are also calculated. Calculations show that changes in the mean-square anisotropic polarizability depend strongly on chain length. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and some studies of the dynamics of a new rod/sphere composite liquid are discussed here. The composite liquid consists of silica spheres (39.4 and 60.4 nm radius) and poly(γ-benzyl-α,L-glutamate) rods (102 000 and 249 700 g/mol molecular weight) dispersed without aggregation in dimethylformamide (DMF) or a mixture of DMF and pyridine. The solvent mixture was used to refractive-index-match dilute solutions of spheres. Dynamic light scattering (DLS) was used to measure the diffusion constants of both the rods and the spheres simultaneously in the solution. Two dynamical regimes were observed for the diffusion of the rods with or without the spheres. The transition point between these two regimes was attributed to the change from dilute to semidilute dynamics. Sphere diffusion constants up to a value two times larger than expected from the Stokes-Einstein equation were measured for the composite liquid containing the large rod (249 700 g/mol) and the small sphere (39.4 nm) in accordance with the argument of Langevin and Rondelez [17]. The sphere diffusion constants measured for the liquid containing the large sphere (60.4 nm) and the small rod (102 000 g/mol) followed a stretched exponential decay with increasing polymer concentration: D/D0=exp (−0.16 c0.81). The c0.81 dependence compares well to experimental results using coil polymers but not to the theories for rod solutions which predict a c0.5 dependence. The similar concentration dependence found for rod and coil solutions suggests that polymer flexibility alone does not account for the deviation from the theoretical c0.5 predictions. Instead, rod-rod hydrodynamic interactions may play an important role in this deviation. [ABSTRACT FROM AUTHOR]

The relation between main- and normal-mode relaxation is studied on poly(propyleneoxide) of different molecular weights by dielectric measurements in a very large frequency range. The evaluation by a special technique shows a merging of α-relaxation and of normal-mode relaxation at an essential higher temperature than the Vogel temperature of the α-relaxation. This means the Rouse model is not applicable to the normal-mode relaxation near the glass transition temperature. [ABSTRACT FROM AUTHOR]

The basic notions of dynamic light scattering (DLS) on non-ergodic media are presented and discussed. We present the results, obtained by DLS, for the intermediate scattering function of polystyrene latex particles that are dispersed in aqueous polyacrylamide gels. It is shown that these systems display non-ergodic features, implying that the time-averaged intensity correlation function (ICF) is not equal to the ensemble-averaged ICF. [ABSTRACT FROM AUTHOR]

Static and dynamic laser light scattering and viscometry have been used to study the dynamics and structure of coil-to-globule transition. With the prism-cell laser light scattering spectrometer, very small scattering angles of the order of 3o could be reached which enabled us to determine the pure translational motion of large polymer chains. The contraction size of a polymer chain during the collapse process has been measured in terms of the radius of gyration, the hydrodynamic radius and the intrinsic viscosity. In the thermodynamically stable region, the coil size obeyed the scaling theory. However, a kinetic study of the collapse has demonstrated a two-stage collapse process in agreement with the theoretical prediction of Grosberg et al. Experimental results of the coil-to-globule transition from polystyrene in cyclohexane and from a polyelectrolyte (sodium polystyrene solfonate) in aqueous solution are presented. [ABSTRACT FROM AUTHOR]

The dynamic light-scattering spectrum from a polymer solution is shown to be related to the cooperative diffusion and longitudinal stress relaxation modes. Experimental results are presented to corroborate the theoretical analysis. [ABSTRACT FROM AUTHOR]

We discuss experimental results on molecular motion in polymer melts, obtained by neutron spin-echo spectroscopy (NSE). For longer times we observe systematic deviations from the Rouse model, revealing the presence of a well-defined intermediate dynamical length scale beyond which density fluctuations within a given chain are strongly reduced. Its value is found to be in excellent agreement with the entanglement distance obtained from rheological measurements. Measurements of the temperature dependence and polymer volume fraction dependence of the entanglement distance give an insight into the molecular origin of entanglement constraints. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of two polystyrene-polymethylmethacrylate (PS-PMMA) diblock copolymers has been studied in toluene by quasielastic light scattering in the vicinity and above the overlap concentration C* of the copolymer chains. At the macromolecular scale two relaxation modes have been found near C*. The slow mode has been ascribed to the classical cooperative motion of the transient physical network formed by the copolymer molecules. It is identical to the motion that is observed in the equivalent binary PS/toluene solution where PS has the same molecular weight as the molecular weight of the whole copolymer and where the PS and the PS-PMMA concentrations are equal. The fast mode is a structural mode that reflects the fluctuations of concentration of one species with respect to the other. Above C* a third motion appears that is not anticipated by the theories. The frequency of this mode is very low and decreases when the copolymer concentration increases. This mode is attributed to the formation of aggregates that can occur even at relatively low concentrations (4C*) for the systems under investigation. [ABSTRACT FROM AUTHOR]

Concentrated solutions (volume fraction 0.1-0.9) of polystyrene (PS) in toluene and of polybutylacrylate (PBA) in dioxane have been examined using dynamic light scattering (DLS) as a function of angle and temperature. With PS there is a pronounced maximum in the cooperative diffusion coefficient (Dc) at about Φ=0.5 as the glassy state is approached. By contrast, with PBA, which has a very low Tg, there is a crossover to a stronger concentration dependence for Dc, which is attributed to an increase in solvent mobility. In the PS/toulene system at Φ=0.78 a transition is noted between the diffusion mode and the main relaxational mode. At 17°C q-independence is observed and at 50 °C q2-dependence. At Φ=0.89, both relaxations are observed simultaneously in the DLS time window, the slower process being a structural relaxation. [ABSTRACT FROM AUTHOR]

The dynamic scattering properties of ternary mixtures made up of two polymer components and a solvent are considered. Examples of symmetrical and nonsymmetrical mixtures are examined. Particular attention is focused on the interpretation of the eigenmodes. It was recently shown that the eigenmodes for ternary mixtures could be rigorously identified with the cooperative and interdiffusive modes only if the two polymer components are identical, except for their optical properties. Here, we consider several mixtures made up of different polymer constituents and compare the variations of the relaxation frequencies with the scattering wave vector q. In all the examples considered, the behavior of (Γ, ΓT) and (Γ′, Γ1) are found to be qualitatively the same. This leads to the conclusion that, although the eigenmodes can be identified rigorously as the cooperative and interdiffusive dynamical processes only for symmetrical mixtures with a finite χ-parameter, they can still be so-identified approximately even in the case of different polymers and nonsymmetrical mixtures under certain experimental conditions. [ABSTRACT FROM AUTHOR]

Neutron-scattering experiments have been performed on elongated polystyrene melts consisting of relatively short labelled chains (M<100 000) dispersed in a matrix of very long ones (M>106), which were not labelled. Important anomalies with respect to the theoretical predications have been observed. In particular, the iso-intensity lines exhibit, in a large range of relaxation times, striking butterfly shapes and an unexpected orientation: the long axis of these patterns is oriented parallel to the stretching direction. As a working assumption, we propose to relate this phenomenon to a non-homogeneous arrangement of chain entanglements in the melts. As a matter of facts, it has been proposed that elongated gels should exhibit butterfly patterns (The whole solvent being labelled) as a result of a sort of anisotropic unscreening of cross-linking heterogeneities. Experiments were performed on samples synthesized specially in order to match the assumptions of the model and butterfly patterns have effectively been observed. The same type of mechanism can be driven by an heterogeneity of chain entanglement in the case of assymetrical melts: the short labelled chains may behave as a kind of polymeric solvent and accumulate, during the relaxation, in the less entangled regions (which should be also regions of lower constraint). [ABSTRACT FROM AUTHOR]

A diblock copolymer of poly(styrene-block-para-emthylstyrene) (PS-b-PMS) is investigated near its microphase separation temperature with respect to the formation of organized structures in thin films. A contract between components is achieved by deuteration of the PS-block, and the surface-induced order is detected by neutron reflectometry and 15N nuclear reaction analysis. While the PMS component is always enriched at the surface, an exponentially decaying lamellar order of alternating layers of PS and PMS parallel to the surface is observed depending on annealing time. Those observations are discussed with respect to the influence of surface and substrate on the development of organized structures in a block copolymer melt. [ABSTRACT FROM AUTHOR]

The ordering of thin films of symmetric diblock copolymers of polystyrene and polymethylmethacrylate has been investigated by neutron reflectivity. It is shown that the order-disorder transition temperature depends strongly on the film thickness, increasing as the film thickness decreases. The transition is shown to lose all its first-order characteristics in the thin films. For films thinner than ∼2000 Å it is not possible to obtain the copolymer flms in the disordered state at temperatures below the decomposition temperature. A transition is observed where the copolymer goes from a partially to a fully ordered state. For thick specimens, this transition corresponds to the bulk order-disorder transition temperature. However, for thinner specimens this transition temperature depends on the film thickness in a power law manner. [ABSTRACT FROM AUTHOR]

We investigated diffusion between deuterated and protonated polystyrene films at short times using neutron reflectometry (NR) and nuclear reaction analysis (NRA). We covered six orders of magnitude in time and identified two time regimes of diffusion with a crossover at the reptation time τrep. Below τrep the interfacial profile can be described by two superposed error functions attributed to the Rouse-type mobility and reptation. The contribution due to reptation shows a discontinuity at the position of the interface. There are some strong indications for an enhanced concentration of chain ends at the interface. The reliability of the results is supported by the agreement of the three values of τrep obtained by the use of the two complementary techniques. [ABSTRACT FROM AUTHOR]

The morphology of thin films of symmetric diblock copolymers has been investigated by neutron and X-ray reflectivity and X-ray photoelectron spectroscopy, for thicknesses less than 3L/2, where L is the long period of the lamellar morphology in the bulk. The constrains placed on a copolymer film by the presence of the two surfaces can produce severe perturbations on the morphology, due to the interactions of the copolymer blocks with the air and the substrate interfaces. It is possible to induce variations in the chain extension and in the interfacial mixing, and to force a normally microphase separated copolymer into a homogenecous state. [ABSTRACT FROM AUTHOR]

We report results on adsorbed layers of polystyrene (PS)-polyethylene oxide (PEO) diblock and PEO-PS-PEO triblock copolymers at the solid/liquid interface. The volume fraction profiles of the adsorbed PS-PEO diblock copolymers at the the quartz/toluene interface determined by neutron reflectometry are consistent with a parabolic profile as predicted by theory. Ellipsometry was used to investigate the adsorption kinetics of PS-PEO diblock copolymer chains on SiO2 from toluene. The results show a rapid diffusion-controlled process, characterized by a linear increase in the adsorbed amount with the square-root of time, at the early stages of adsorption, while at late times adsorption is slow and appears to be governed by an exponential time behavior. Studies of the PEO-PS-PEO copolymer, using the surface-force apparatus, reveal conformational rearrangements for the adsorbed triblock chains between mica surfaces. When two such surfaces are in close proximity to each other, triblock chains originally adsorbed in a "loop" conformation may open into a "bridge" conformation with both PEO blocks of a given chain adsorbing onto opposing mice surfaces. This is indicated by the appearance of clearly detectable attractive forces and their evolution with compression-decompression cycles. The time evolution of these forces reflects the dynamics of the rearrangement of chains between the two surfaces. [ABSTRACT FROM AUTHOR]

Mechanical measurements in the glass transition zone were carried out on a series of polydienes to study the effect of chemical structure on the segmental relaxation. The breadth of the glass transition dispersion in the mechanical spectrum increased with increasing concentration of pendant vinyl groups on the main chain. The broader relaxations exhibited stronger temperature dependences. Both observations are consistent with the compling model of relaxation. Enhanced intermolecular coupling arises due to steric interferences among the vinyl moieties, and the coupling model predicts that more cooperative relaxations will be both broader and more temperature sensitive. In miscible blends the glass transition dispersion is further broadened due the distribution of local environments engendered by concentration fluctuations. The coupling model is extended to consider the effect of concentration fluctuations on the local variation in the degree of intermolecular cooperativity. The shape of the relaxation spectra of miscible blends in the glass transition zone, as well as both composition and temperature dependencies of the dispersion, are markedly influenced by the concentration fluctuations specific to miscible blends. Application of the model to two blends is demonstrated to successfully describe the prominent features of the measurements. [ABSTRACT FROM AUTHOR]

A series of polystyrene/(cis 1-4)polyisoprene diblock copolymers is studied using small-angle x-ray scattering (SAXS), real-time SAXS, photon correlation spectroscopy (PCS) and dielectric spectroscopy (DS). The static structure of concentration fluctuations is found to deviate from the Gaussian coil assumption in a temperature regime above the microphase separation transition (MST). The dynamic experiments in this temperature regime test concentration fluctuations (real-time SAXS) as well as single-block dynamics (PCS and DS) making use of the intrinsic labelling properties of this specific diblock copolymer. They provide evidence for the existence of partially ordered domains above the MST. The assumption of a weakly segregated state is, therefore, questionable. [ABSTRACT FROM AUTHOR]

It has been reported by us, for the first time, that segmented polyurethanes (SPUs) based on 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment could form spherulite structures upon melt-quenching to an annealing temperature (TA) above 120°C. Synchrotron small-angle x-ray scattering (SAXS) experiments were performed to investigate the microphase separated structures corresponding to the spherulite formation. With increasing hard-segment content, both the integrated scattered intensity (Q) and the interdomain spacing (d) increased first and then decreased when the hard segment was above 50%, possibly due to phase inversion. With increasing TA, the Q values increased first, reached a maximum at ∼107°C, and then decreased with further increase in TA; the d values showed a monotonic increase. The kinetics of phase separation was investigated after the samples were quenched from the melt to 140°C. Interdomain spacing remained unchanged throughout the whole process. The results indicated that the hard-segment mobility and the system viscosity were the two key factors controlling the phase structure. [ABSTRACT FROM AUTHOR]

We examine the relevance of the strong-fragile classification scheme for glass-forming polymeric systems using results from Brillouin and photon correlation spectroscopy. The dynamics of salt doped polypropylene oxide (PPO) have been investigated in relation to induced local structural ordering. It is accomplished by forming complexes of NaCF3SO3-PPO in which the cations act as transient cross-links between chains. The amount of cross-links depends on salt concentration and temperature. This allows for a test of the suggested relation between structural properties and some characteristics of the relaxation function such as its non-exponential time decay and non-Arrhenius temperature dependence. [ABSTRACT FROM AUTHOR]

By measuring the complex dielectric susceptibility over 15 decades, we compare the scaling behavior of the α-relaxation for low-molecular-weight glass-forming liquids and polymers. The characteristic differences found for these both classes of substances are discussed in terms of segmental dynamics. [ABSTRACT FROM AUTHOR]

The cluster growth dynamics and the equilibrium cluster correlation length were studied in 1,1-di(4′-methoxy-5′-methyl-phenyl)-cyclohexane (BMMPC also called BKDE in previous papers) in the temperature range from 40°C to 70°C by means of static light scattering (SLS) and photon correlation spectroscopy (PCS). The equilibrium cluster correlation length obtained from PCS and SLS using the Ornstein Zernike formula are in a good agreement with each other. The analysis of the SLS data based on the Debye formula results in much lower values of the cluster correlation length. The relaxation processes in BMMPC were studied using depolarized Rayleigh spectroscopy (DRS). The relaxation times obtained from DRS exhibit an Arrhenius behaviour and with decreasing temperature diverge from the relaxation times of the primary α process measured by means of dielectric spectroscopy which follow the usual Williams-Landel-Ferry temperature dependence. [ABSTRACT FROM AUTHOR]

Translational diffusion coefficients D of photochronic dye molecules have been measured by forced Rayleigh scattering in polymer diluent systems at compositions from pure polymer to pure diluent. D could be measured down to below the glass transition temperature Tg. In the pure diluent, D(Tg) was found typically about two decades below that in the pure polymer but still far above the Stokes-Einstein prediction extrapolated from high temperatures. Some experimental results are in contrast with predictions from free-volume theory. [ABSTRACT FROM AUTHOR]

The relaxation processes in the glass-transition temperature range of bulk PIMA and PIMA-PMMA copolymer have been studied by means of Photon Correlation Spectroscopy (PCS) and dielectric spectroscopy (DR). The experimental results were treated in a conistent way employing an inverse Laplace transform analysis of the density Cϱ(t) and dipole moment ϕμ(t) autocorrelation functions. The latter was obtained from the ɛ″ (ω) data utilizing a recently developed algorithm. For bulk PIMA, Cϱ(t) clearly shows two distinct relaxation processes, whereas ϕμ(t) is dominated by the slower (α-) relaxation mode. The fast process in Cϱ(t) is probably related to the rotation of the rigid isobornyl group about the C-O bond. The copolymer displays a β-relaxation process and a slower α-relaxation dielectric process in agreement with the PCS results. The molecular origin of these processes is outlined. [ABSTRACT FROM AUTHOR]

In this paper it is shown, on the basis of a simple mean field approach to the dynamics of concentration and density fluctuations, that the interdiffusion coefficient Dint(ϕ) in a blend (A/B) of composition ϕ can be related to the self-diffusion coefficients D*A/B of the pure melts. However, the relation is predicted to be a linear combination of the so-called fast and slow modes: Dint−1=(1−U){Dslow*}−1+ U{Dfast*}−1. The parameter U=U(T) is given and is shown to be a measure of the nearness of the glass transition to the experimental temperature T. Far above the glass transition (U→0) the interdiffusion coefficient reduces to D*slow and should show the simple linear dependence on concentration according to {Dslow*}−1={ϕDA*}−1+{(1−ϕ) DB*}−. [ABSTRACT FROM AUTHOR]

Dynamic rotational isomeric state formalism is used to compute dipolar correlation functions for cis-polyisoprene in the bulk state. Transitions between rotational isomeric states take place through coupled motion of triplets of neighboring bonds in a given repeat unit, as follows from the study of intramolecular conformational energetics in the polymer. The intermolecular effect on local chain dynamics is included in two stages. First the relaxation in a homogeneous environment is treated through adoption of a local effective frictional resistance increasing with the size of the kinetic segment. Secondly, free-volume or density fluctuations of the medium are approximated by a bistate environment. The frequency distribution of relaxational modes is found to broaden with increasing number of bonds cooperatively participating in the segmental mode process. From a comparison with recent dielectric measurements of bulk cis-polyisoprene, the experimentally observed Kohlrausch-Williams-Watts (KWW) exponent of 0.39 is attributed to the cooperative relaxation of a kinetic segment of about three repeat units in a fluctuating environment. [ABSTRACT FROM AUTHOR]

Hydrodynamic radius, rh, may be determined from the limiting diffusion coefficient, D0, from the limiting sedimentation coefficient, s0, or, using simple models for the concentration dependence, from the sedimentation coefficient, s, at a finite concentration. For water/AOT/heptane water-in-oil microemulsions, values of rh determined from s are shown to agree well with those obtained from s0 or D0 determined using an analytical ultracentrifuge, and with literature values from dynamic light scattering. For several aqueous polyurethane dispersions, sedimentation velocity demonstrated the presence of small species with rh<5 nm and medium-sized species with rh in the range 10-17 nm, as well as much larger aggregates. For these complex dispersions, dynamic light scattering behavior was dominated by the large aggregates and analysis by the CONTIN method was not able to detect all the species present. [ABSTRACT FROM AUTHOR]

The particle size distribution of dispersions is an important parameter for viscosity, gloss and opacity and can be determined with great precision by analytical ultracentrifugation. A method using this technique has been developed at Bayer [1] and is now in widespread use. It was recently found to be the most satisfactory method in a recent ringtest of techniques for the submicron range. The high performance of this method is seen from the fact that a sample containing nine components can be analysed exactly. Its high resolving power is proved by a baseline separation of monodisperse components, differing by 10% of diameter only. To detect low quantities of small particles, measurements are performed at different concentrations and then coupled, yielding a high degree of precision. This method has been successfully applied to competitive growth experiments in emulsion polymerization and other areas. [ABSTRACT FROM AUTHOR]

In a centrifugal field a gel is a continuous system with a radial concentration gradient due to the volume force of the field and diffusion. In contrary to the known definition of the sedimentation coefficient of a gel where the movement of the gel meniscus is related to the driving force, the velocity of the center of mass of the polymer with respect to its acceleration has been introduced using irreversible thermodynamics. It is shown that there will be no induction period of this velocity although the meniscus does not move. From extrapolation to times where the selected rotor speed had just been reached, the sedimentation coefficient of the polymer of a κ-carrageenan/water gel could be determined. In addition to the sedimentation coefficient, the phenomenological and the diffusion coefficients were also calculated from the data. Differences between the sedimentation of a sol and a gel are pointed out and discussed. [ABSTRACT FROM AUTHOR]

Self-assembling systems composed of organic molecules and metal ions represent one of the topics in modern supramolecular chemistry. Up to now, their physical characterization was essentially limited to crystals or to surface layers. Studies on solubilized systems, e.g., on their molecular mass distribution or association behavior, are rare. We have explored whether sedimentation equilibrium analysis in the Beckman Optima XL-A analytical ultra-centrifuge can be successfully applied. A grid-like cobalt coordination array ("[2×2]-Co(II)-grid") was used as a model compound. The technical problem involved, concerning the chemical resistance of the cell components against organic solvents, was solved by using titanium centerpieces and polyethylene gaskets. Another potential problem, the high UV absorbance of the solvents, could be circumvented by measuring the absorbance versus radius profiles in the visible wavelength range, where "grids" and most other related compounds show absorption bands. Special efforts were made to solve the remaining problems: (1) the suppression of nonidealities in sedimentation behavior, which could prevent or greatly complicate a successful analysis of self-associating systems, and (2) the determination of the partial specific volume $$\bar v$$ of the complexes, in particular considering compounds either not available in sufficient quantities for density measurements or exhibiting low solubility. With respect to problem (1), solvent/salt systems were found in which the model compound apparently shows ideal sedimentation behavior. Procedures are suggested to overcome problem (2). [ABSTRACT FROM AUTHOR]

In our lab we have transformed all the application of the analytical ultracentrifuge (AUC) in colloid and polymer science from the Schlieren optical system of the Beckman model-E to the interference optics of the Beckman XL-I. Two basic experiments, the sedimentation velocity run and the density gradient run are described in this paper. The advantages of the interference optics together with the sedimentation velocity run are a much higher data density that gives together with the "dc/dt"-analysis method of W. Stafford very accurate results. In the field of colloid science this means that very precise particle size distributions are available, with an especially high resolution for small particles. Density gradient experiments were carried out and gave very good interference pictures. These pictures were analyzed after the formation of the density gradient was complete and also during its formation ("dynamic density gradient"). The method of analysis described in the paper is the same for both cases resulting in very good values for the particle density of the sample. The method is based on the determination of the absolute refractive index of the gradient forming medium and the transformation of the refractive index into a radial density distribution within the measuring cell. [ABSTRACT FROM AUTHOR]

A method for the direct refractometric determination of the density gradient in an analytical ultracentrifuge has been described. It is based on two assumptions: 1) the Schlieren optics measure the refractive index gradient, the interference optics the refractive index, and the absorption optics the absorption of the density gradient solution (consisting of a light and a heavy solvent component) and 2) there is a relationship between the refractive index or the absorption, on the one hand and the density of the density gradient solution, on the other. The method has been demonstrated on water/metrizamide/polystyrene latex solutions with different concentrations of metrizamide (a heavy sugar). Advantages of this method are: first, the pressure and the composition effect are included in this method and must not be corrected as usual and second, it is not necessary to measure at sedimentation equilibrium; it would be possible to measure at times before the equilibrium is achieved. That means the method represents a quasi-dynamic density gradient method. [ABSTRACT FROM AUTHOR]

An extended Hermans-Ende equation for real solutions has been derived in order to calculate the density as a function of the radial distance in a density gradient mixture (light/heavy medium) inside an ultracentrifugal cell. The equation has been tested with equilibrium density gradient measurements of the system H2O/methanol/metrizamide/polystyrene latex where metrizamide is the heavy medium. Additionally, density measurements of the systems with a vibrating tube densitometer at normal pressures and at pressures up to 400 bar have been performed in order to complete the measurements. The solvent compositions were 8-25% metrizamide, 20-100% water and 0-80% methanol. The latex concentration was 0.03%. It is demonstrated that the density gradient is highly influenced by nonideality effects with respect to the solvent composition and by the pressure gradient in the ultracentrifuge. [ABSTRACT FROM AUTHOR]

Quantum size colloids attract a steadily growing scientific and economical interest because of their size-dependent optical and electrical properties. It is shown that the fractionation in the analytical ultracentrifuge enables the characterization of individual species even in complicated mixtures. If an ultracentrifuge with combined UV-absorption and Rayleigh interference optics is used, dependence of the spectra as well as of extinction coefficients on the particle size can be examined. As it is also possible to monitor particle growth from its initial stages, the combined spectral and particle size information can lead to an understanding of the particle growth mechanism. This is demonstrated for model systems of aggregates of small individual particles and grown particles of the same size. Furthermore, sedimentation velocity experiments prove to be very useful for determining the effectiveness of reactions performed in "micellar nanoreactors" and for determining the extinction coefficient of one component in a complicated mixture. [ABSTRACT FROM AUTHOR]

Synthetic quaternary ammonium polyelectrolytes have been investigated in aqueous 0.5 M NaCl solution by analytical ultracentrifugation using the "low speed" sedimentation equilibrium technique with interference detection. Lower molecular mass poly(diallyldimethylammonium chloride) (poly-DADMAC)-samples (MW<105 g/mol) and poly(methacryloyloxyethylbenzyl-dimethylammonium chloride) (poly-MADAMBQ) exhibit "ideal" sedimentation equilibrium behavior. Linear log [η] vs. log MW — and log sO vs. log MW relations could be derived for poly-MADAMBQ. For higher molecular mass poly-DADMAC (MW>105 g/mol) and DADMAC-acrylamide copolymers a "non-ideal" solution behavior was observed resulting in deviations between molecular masses Mw obtained by sedimentation equilibrium and by elastic light scattering. The experimental conditions desired for the molecular characterization of synthetic polyelectrolytes by sedimentation equilibrium are discussed. [ABSTRACT FROM AUTHOR]

The DNA of the marine sponge Geodia cydonium (G.c.), a member of the phylogenetically old phylum Porifera, was characterized by density gradient centrifugation and by determining its genetic complexity by reassociation kinetics. At least five subcomponents were identified by curve-fit analyses of analytical density gradient centrifugation profiles of total G.c.-DNA. Four of these subcomponents were isolated from total G.c.-DNA by preparative density gradient centrifugation. The GC-contents of the subcomponents were determined to be 36.4%, 44.0%, 58.7%, and 66.1%, respectively. To our knowledge, such an extreme heterogeneity of DNA composition has never before been observed for any organism. The genetic complexities within the subcomponents were determined by reassociation kinetics to 2.1×108, 2.8×108, 9.2×108, and 1.4×109 bp, respectively. The orders of magnitude of the genetic complexities clearly indicate that the DNA subcomponents mainly contain eukaryotic single copy DNA, since DNA of symbiotic prokaryotes should show significantly lower complexities. [ABSTRACT FROM AUTHOR]

As part of a study into the homo- and hetero-oligomerization properties of muscle-specific transcriptional factors, and their interation with DNA, sedimentation equilibrium studies, accompanied by circular dichroism measurements, have been made on peptides derived from the helix-loop-helix regions of MyoD and E47. In addition, a chimeric peptide, in which residues from the loop region of E47 were substituted into that of MyoD, a fluorescently labelled derivative of the MyoD-bHLH peptide and a disulphide crosslinked version of MyoD-bHLH have also been investigated. MyoD-bHLH has been found to form a monomer tetramer equilibrium in the µM concentration range, while E47-bHLH exists as a highly associated dimer. The MyoD-bHLH derivatives appear to exhibit the same oligomerization behavior as their MyoD-bHLH parent. CD studies of the disulphide-crosslinked peptide show that a level of organization higher than that of the dimer is required for structural stability in the MyoD-bHLH system. The rôle of self-association in the context of the biological function of these peoteins is discussed. [ABSTRACT FROM AUTHOR]

Knowledge of the structure of protein-SDS complexes and the constituent free proteins and SDS micelles is important for our understanding of protein-detergent interactions and for the application and improvement of physicochemical techniques connected with the purification and characterization of proteins. Several reasons are responsible for present controversies regarding the size and structure of macrosolutes, e.g. presence of a variety of low- and high-molecular solutes, the fact that macrosolutes show heterogeneity and may exhibit equilibria that are strongly influenced by the environmental conditions, and the point that techniques available for their structural investigation refer to different global or local properties. Sedimentation velocity and equilibrium experiments of the detergent-protein complexes and their constituents were performed under a variety of experimental conditions, such as rotor speed, scanning wavelength, choice of the baseline, the solvent or additives, and the concentrations of the components. Monitoring the sedimentation profiles of micellar SDS is facilitated by labeling the detergent micelles using a fluorescent dye, and discriminating the species under analysis by scanning at specific wavelengths. Interpretation of the results is facilitated by monitoring absorption spectra at discrete radial distances in the centrifuge cells, in addition to spectra recording of mixtures and components outside the centrifuge. In order to estimate the amount of bound detergent, sedimentation data (sedimentation coefficients, particle weights and mass distributions) were complemented by size-exclusion chromatographic studies. In the case of nonreduced proteins about 0.4 g SDS/g protein are bound at low detergent concentrations, and about 0.8 to 1.2 g/g at elevated concentrations. [ABSTRACT FROM AUTHOR]

Crystallins, the major eye lens proteins, were investigated after preceding irradiation with X-rays or UV light by using analytical ultracentrifugation and other physicochemical and analytical techniques. Sedimentation velocity and sedimentation equilibrium runs of unirradiated and irradiated samples of the crude extract and individual fractions of calf-lens crystallins (α, βH, βL, γ) were performed under varying experimental conditions. While by the impact of radiation sedimentation coefficients remain essentially unchanged, high-speed sedimentation equilibrium experiments revealed significant changes of the molar masses of the respective crystallin species, depending on the crystallin class and the nature of the radiation used. The γ-crystallins turned out to be the most stable species against radiation-induced damages. UV absorption and fluorescence spectroscopy, size-exclusion chromatography, SDS electrophoresis, viscometry, and the analysis of SH and SS contents provided useful complementary information. In conclusion, several radiation damages could be registered: aggregation, crosslinking, dissociation, fragmentation, destruction of aromatic amino acids, cysteines and cystines. The OH scavenger formate and the chaperone α-crystallin turned out to protect the crystallin crude extract to some extent against X-ray-induced aggregation phenomena. [ABSTRACT FROM AUTHOR]

The tertiary and quaternary structure of α-crystallin is still a matter of controversy. We have examined α-crystallins isolated at different temperature (4°C, 20°C and 33°C), using equilibrium sedimentation and light scattering. Both techniques give the same structural and interaction parameters (molar mass, second virial coefficient) and complementary information (hydrodynamic radius, hydrodynamic volume). The quaternary structure changes as a function of the temperature of isolation and processing. On cooling the cytoplasma below 30 °C, the quaternary structure of α-crystallin slowly changes to a larger particle which is unstable at 20 °C. On cooling further to lower temperatures (4 °C), the α-crystallin apparently recovers its stability, so it can be stored for longer times. The structural transition between 33 °C and 4 °C is reversible as we can conclude from our data of α-crystallin isolated and measured at 33 °C and α-crystallin isolated at 4 °C, stored at 33 °C for 24 h and measured at 33 °C. The high hydrodynamic volume of α-crystallin suggests a very loose structure for this particle: a string of beads or a random coil. This loose structure suggests a rather limited interaction between the peptides and dramatically reduces the light scattering. This structure can also explain the chaperone activity of the α-crystallin. The loose interaction between the crystallin peptides allows the interaction of the latter with the hydrophobic surfaces of the stressed proteins. So both functions of α-crystallin, its chaperone activity and its low scattering capacity even at high concentration, are enhanced by its expanded quaternary structure. [ABSTRACT FROM AUTHOR]

Difference sedimentation velocity has provided an extremely convenient procedure for detecting and quantifying ligand-mediated conformational changes in enzymes by virture of differences in hydrodynamic volume. However, the replacement of the Beckman model E instrument by the XL-A has necessitated reexamination of the existing method of analysis, which relied upon the comparison of simultaneously recorded distributions of solute in the two cells. After demonstration of the validity of the revised procedure by its application to simulated sedimentation velocity data, differential sedimentation velocity has been used to confirm the effect of phenylalanine on the sedimentation coefficient of rabbit muscle pyruvate kinase. Corresponding studies of the effect of glucose on the sedimentation coefficient of yeast hexokinase have demonstrated the substrate-mediated decrease in enzyme size that is evident from X-ray crystallographic studies, and identified this effect as the consequence of substrate perturbation of a preexisting enzyme isomerization rather than of substrate-induced isomerization of yeast hexokinase. [ABSTRACT FROM AUTHOR]

Demonstration of the formation of ternary complexes of proteins, in the presence of all constituents and binary complexes, and analysis of their stoichiometries is a difficult task. For the band 3/ankyrin/aldolase complex from erythrocyte membranes in detergent solutions, we have solved this problem by sedimentation equilibrium analysis in the analytical ultracentrifuge. Labelling of the ankyrin with a dye (fluorescein isothiocyanate) and measuring the absorbance versus radius profiles at a wavelength where only the dye absorbs allowed us to focus on the ankyrin-containing complexes. So, the different oligomers of uncomplexed band 3, the uncomplexed aldolase and the various binary complexes of band 3 and aldolase could be disregarded in the analysis. The ternary band 3/ankyrin/aldolase complex could be unambiguously detected. Its stoichiometry (band 3/ankyrin/aldolase tetramer) was found to vary between 4:1:1 and 4:1:4, depending on the abundancy of the enzyme. [ABSTRACT FROM AUTHOR]

In order to utilize the high sensitivity of the fluorescence detection system for sedimentation equilibrium in analytical ultracentrifugation, a new evaluation method was developed. In comparison to absorption recording the sensitivity could be raised 100-1000 fold as shown for a series of proteins (bovine serum albumin, immunoglobulin G and chymotrypsin). Sedimentation equilibrium runs can be analysed down to sample concentrations of 0.25 ng/µl with a minimal sample volume of 40 µl. The accuracy of the molecular weights is comparable to that recorded by the absorption optics. Analysis of infectious prions in the analytical ultracentrifuge requires strict safety conditions. A biohazard safety containment with a vacuum system is constructed to prevent contamination of the laboratory. Decontamination of the cells is ensured by the use of self-manufactured titanium cells, which could be autoclaved at 134 °C in 1 N NaOH. Analysis of SDS-solubilized PrP(27-30) which is a N-terminal truncated fragment of the whole prion protein, showed by anlytical ultracentrifugation relatively homogeneous fractions with molecular masses between 20.000 Da and 120.000 Da, depending on the conditions of solubilization. [ABSTRACT FROM AUTHOR]

Bead models, composed of overlapping spheres of different or identical radii, were generated from the crystal structures of selected proteins (citrate synthase, lactate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase). Starting from the atomic coordinates taken from the Brookhaven Protein Data Bank, different methods ("running mean" or "cubic grid") were used for reducing the initially large number of coordinates to a practicable size. The structure of the multibody models was checked by comparing the pair distance distribution function and the radius of gyration of the reduced models with the corresponding quantities of an initial model. For models consisting of beads of unequal size both reduction methods may be used. The concept of equal beads was found to be compatible with the "running mean" method, whereas the use of the "cubic grid" method for generating models composed of equal spheres led to quite distorted structures. The program HYDRO (by García de la Torre et al. (1994) Biophys J 67:530-531) was applied for predictions of the sedimentation coefficient s, diffusion coefficient D, and intrinsic viscosity [η]. Reliable and numerically stable results were only obtained after the program had been modified in order to improve the treatment of overlapping unequal spheres. The hydrodynamic parameters thus predicted were compared with experimental values as well as with the results from whole-body approaches. In general, a good conformity of predicted and observed values for s and D, including the extent of changes due to conformational alterations, was obtained by multibody approaches if appropriate refinements of the models with respect to radius of gyration and volume were applied. By contrast, the values predicted for [η] usually exceeded the experimental results considerably. [ABSTRACT FROM AUTHOR]

A calculation procedure is presented which relates solution scattering and hydrodynamic parameters. Biopolymers are modeled by whole-body approaches, approximating their overall shape by spheres or prolate/oblate ellipsoids of revolution. Molar masses, partial specific volumes, radii of gyration, volumes and surface-to-volume ratios are used for predicting sedimentation and diffusion coefficients and intrinsic viscosities of a variety of biopolymers, in addition to the derivation of several further parameters such as frictional coefficients, Simha factors, Stokes and viscosity radii. The establishment of a comprehensive set of structural and hydrodynamic data including several correlations allows the examination of observed and predicted parameters. In this context also the validity of some empirical relations was tested. A variety of roughly globular biopolymers (simple and conjugated proteins, ribonucleic acids) of different molar mass and shape have been examined. The comparisons comprise both the native states of the biopolymers under analysis and structural alterations in response to changes in environment or state of ligation. Far-reaching conformity between experimental values and anticipated parameters was achieved. Detailed error propagation calculations allow a close scrutiny of the accuracy of the parameters to be predicted. [ABSTRACT FROM AUTHOR]

A computer program, written in BASIC, has been developed for the characterization of either solute self-association or the interaction between macromolecular acceptor and ligand. Simplicity and model independence of the procedure to evaluate the free concentration of smallest macromolecular species are features which are illustrated by analysis of simulated Rayleigh distributions based on α-chymotrypsin dimerization, and of simulated absorbance records of the distribution based on 1:1 interaction between trimethylamine dehydrogenase (acceptor) and electron transferring flavoprotein (ligand). [ABSTRACT FROM AUTHOR]

We present a method for the direct molecular mass determination from sedimentation velocity experiments. It is based on a non-linear least-squares fitting procedure of the radial concentration profiles and simultaneous estimation of the sedimentation coefficient and the ratio of sedimentation/diffusion coefficients considering approximate solutions of the Lamm equation. Different model functions from Faxén as well as Archibald type derived by Fujita [4] were used to describe the sedimentation behavior of macro-molecules during the centrifugation. By means of a computer program, LAMM sedimentation and diffusion constants of some proteins were determined. The method presented here appears to be useful for the rapid molecular mass determination of proteins large than 10 kDa. One of the equations of the Archibald type is also suitable for substances of low molecular mass of about 1 kDa. The model function neither requires the existence of a plateau region nor a meniscus region free of solute. [ABSTRACT FROM AUTHOR]

In equilibrium or velocity sedimentation experiments with the XL-A analytical ultracentrifuge it is customary to acquire absorbance data. The least-squares method is most widely used for fitting non-linear models to such collected data. It is here shown that due to the non-Gaussian characteristics of the noise in the absorbance data, the least-squares method is not optimal and introduces a systematic bias to the estimated parameters. This bias can be eliminated by either using the maximum-likelihood method on the absorbance data or otherwise by fitting the intensity data directly. The probability distribution of the noise in the latter is Gaussian and the least-squares estimation is equivalent to maximum likelihood. The methodology for using the intensity data is developed and simulations for a variety of systems are performed. [ABSTRACT FROM AUTHOR]

Four strategies for the analysis of sedimentation equilibrium of solutions containing two solute components in the context of models for equilibrium association are described:(1)Direct modeling of the equilibrium gradients of a single experimentally measurable signal measured in each of several samples of differing composition;(2)Direct modeling of the equilibrium gradients of two (or more) signals measured in each of several samples of differing composition;(3)Calculation of the independent component concentration gradients in individual samples via analysis of the gradients of two or more signals in the sample, followed by modeling of the component concentration gradients from several samples of differing composition; and(4)Calculation of the signal-average buoyant molar mass as a function of solution composition, followed by modeling of the composition dependence of the signal-average buoyant molar mass in the context of an association model. Examples of the application of each strategy are presented and compared, and conclusions are drawn regarding the relative utility of each method for different types of experiments and systems studied. [ABSTRACT FROM AUTHOR]