Cooperative Coefficient Research Articles

Analysis of the dynamic structure factor for semi-dilute solutions of polyisobutylene

The equation for polymer concentration fluctuation derived from Onuki's equations of motion is coupled with Onuki's postulate for the partial stresses generated by concentration fluctuation to formulate the dynamic structure factor S( q, t) [ t is time and q the magnitude of the scattering vector]. The actual calculation is made for systems in which the elastic relaxation modulus L( t) is given by a linear combination of n exponential functions. It is shown that the corresponding S( q, t) consists of n + 1 exponential functions of time, and that the relative strengths and decay rates of these functions are related by a set of algebraic equations to the diffusion coefficient and cooperative diffusion coefficient, as well as the parameters characterizing L( t). These equations for n = 2 are used to analyze dynamic light scattering data on semi-dilute solutions of a polyisobutylene fraction in isoamyl isovalerate (Θ solvent) and n-heptane (good solvent). The results give the instantaneous moduli of the solutions which are well compared with the rubbery plateau moduli from viscoelastic measurements, and the friction coefficients which are identical for both solvents when compared at comparable polymer concentrations.

Three distinct F-actin binding sites in the Dictyostelium discoideum 34,000 dalton actin bundling protein.

The Dictyostelium 34 kDa protein is an actin bundling protein composed of 295 amino acids. However, the region(s) of the molecule that bind actin filaments is (are) unknown. Studies of the cosedimentation of 125I-34 kDa protein and F-actin show that the 34 kDa protein binds to F-actin with positive cooperativity and Hill coefficients of 1.9 and 3.0, for filaments 4.9 microm and 0.6 microm, respectively. The Hill coefficient is larger for short filaments that are more efficiently bundled than long filaments, suggesting that one of the binding sites is used in interfilament contacts or contributes to filament orientation within the bundle. Three distinct actin binding sites were identified using a synthetic peptide, protein truncations, and a novel epitope library screening method. The ability to bind actin was assessed by 125I-F-actin overlays under denaturing and nondenaturing conditions, cosedimentation, viscometry, and pyrene-labeled actin disassembly. The three actin binding domains were identified as amino acids 1-123, 193-254, and 279-295. The 62 amino acid domain (193-254) can cosediment with F-actin. The estimated Kapp obtained by the disassembly of pyrene-labeled actin was 0.11 microM and 2.7 microM for the amino acids 1-123 and 279-295, respectively. These results identify three distinct regions of the 34 kDa protein that may contribute to the positive cooperative formation of F-actin bundles.

Diffusion Dynamics of Hairy-Rod Polymers in Concentrated Solutions

Photon correlation spectroscopy was employed in the polarized geometry in order to investigate the dynamics of solutions of substituted poly(p-phenylenes) at high concentrations. The total concentration fluctuations were found to exhibit a two-step decay. The fast dominant relaxation was the classical cooperative diffusion, controlled by the osmotic pressure of the system, exhibiting a stronger concentration dependence compared to flexible polymers, and discussed in the framework of the wormlike model. On the other hand, the second diffusive process was not related to self-diffusion (as confirmed by independent pulsed field gradient NMR measurements) and could not be accounted for by the existing theories. The self-friction coefficient was found to exhibit a stronger concentration dependence than the cooperative friction coefficient. At high concentrations, a diffusive cluster process was detected, despite the high solubility of these polymers in different solvents. The characteristics of this mode depend...

Oxygen-binding properties of haemolymph from the benthic amphipod Monoporeia affinis from the Baltic

The Baltic benthic amphipod Monoporeia affinis (Lindstrom) has haemocyanin as a respiratory pigment. Haemocyanin constitutes ca. 90% of the total protein in the haemolymph. Oxygen affinity of the pigment is low, a P50 of 4 kPa at pH 7.5 (6 °C). The Bohr factor (Δlog P50/ΔpH) is also low, −0.51, and the cooperativity coefficient, n50, at P50 is 1.5 to 2.5. The pigment characteristics point to a modest role of the haemocyanin, contrary to what could be expected for this sediment-living amphipod. It is suggested that physically dissolved oxygen is most important as oxygen supplier to the tissues.

In situ fluorescence study of slow release and swelling processes in gels formed by solution free radical copolymerization

A novel method based on steady state fluorescence (SSF) measurements is introduced for studying slow release and swelling processes in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in toluene. Gels were prepared at 75°C with various toluene contents with pyrene (P y ) as a fluorescence probe. After drying these gels, slow release and swelling experiments were performed in toluene at 50°C by real-time monitoring of the pyrene fluorescence intensity. Li-Tanaka and Fickian type equations were used to obtain swelling and slow release parameters. It was observed that slow release takes place after the gel is swollen. Cooperative and desorption (slow release) diffusion coefficients (D c and D) were measured and found to be 10 -6 cm 2 s -1 in both cases.

Studies on Polyelectrolyte Solutions VII. Fast, Heterogeneous, and Slow Diffusion Modes of Poly(diallyl-N,N-dimethylammonium chloride) in Aqueous Alcoholic Salt Solvents

Dynamic light scattering measurements were performed on aqueous alcoholic salt solutions of poly(diallyl-N,N-dimethylammonium chloride) (PDADMAC, Mw=2.5×105 g mol−1) in the semidilute regime, where the salts used were NaCl and Na2SO4. The results indicate the existence of three diffusive processes, a fast, heterogeneous, and a slow mode. The fast diffusion mode, Dfast, is interpreted as the coupled motion of a polyion blob with its surrounding small ions. Such a blob contains in average g segments which are connected to give a linear coil where the coil behaves as if it were isolated in a dilute solution. Experimentally, it is found that g increases with increasing salt concentration and increasing alcoholic content. This indicates that the electrostatic segment-segment interactions become more and more screened the poorer the solvent quality is. The slow diffusion mode, Dslow, refers to the motion of large polyion clusters, having an internal ordered structure. These clusters can be as large as 300 nm or more. They are stabilized by intermolecular electrostatic interactions and become destroyed by strong hydrophobic interactions, that is when the degree of polyion dissociation converges versus zero, so that the polyions become neutral. At this limit Dslow disappears and may become equal to Dcop, the cooperative diffusion coefficient of a semidilute solution of neutral polymers. The heterogeneous diffusion mode, Dhetero, is caused by the motion of parts of polyion chains that are not incorporated into the polyion cluster domains. Their total concentration is usually rather small so that an observation is often difficult. At one extreme, such a polyion part can be as small as a blob. Then there is no heterogeneous diffusion mode, that is we have Dhetero=Dfast. At the other extreme, Dhetero may describe the motion of a complete single polyion chain whose dimensions may be as large as a cluster domain so that Dhetero becomes equal Dslow. As a consequence, while Dfast and Dslow are nearly always present, Dhetero may lie too near by Dfast or Dslow, respectively, so that a separation becomes impossible. The simultaneous detection of all three modes is possible only by using the multiple tau technique. With the old correlators and the old conventional analysis methods a decomposition of the diffusion modes is very difficult if not impossible. Mostly one finds only one or two modes, which has lead to the erroneous idea, that there is an extraordinary-ordinary diffusion phase splitting. In reality, however, there is no splitting or phase transition. All three modes are present simultaneously where the only technical problem is their resolution.

Free energy of the binding of uridylic acid oligomers with double stranded poly(A) · poly(U)

The binding parameters ( K, ω) and the free energy ( ΔG 0) of triple helix formation have been estimated for complexes of oligo(U) n ( n = 5, 7–10) with poly(A) · poly(U) on the basis of hypochromicity measurements. The data were treated according to the formula of McGhee and von Hippel [J. Mol. Biol. 86 (1974) 469] by a computer program ALAU [H. Schütz et al., Stud. Biophys. 104 (1984) 23] which takes absorbancies and total concentrations as input. In 1 mM cacodylate buffer pH 7.0 with 10 mM NaCl and 10 mM MgCl 2 at 5°C the free energy of contiguous binding was found to be a linear function of the oligomer length with a slope of ΔG c,U 0 = −0.72 (±0.03) kcal · mol −1 per nucleotide. The mean cooperativity coefficient (ω) was 24.5 (± 5.6), and the corresponding free energy of interaction between the neighbouring oligonucleotides in the third strand was ΔG 0 ω = −1.74 (±0.13) kcal · mol −1.

The “fast” and “slow” mode theories of interdiffusion in polymer mixtures: Resolution of a controversy

AbstractThe theory of interdiffusion of a pair of components in multicomponent polymer mixtures is reviewed from a statistical point of view, and the foundation of the “fast” and “slow” mode theories, as well as the more recent “ANK” theory of interdiffusion is critically examined. The ANK theory reproduces the results of the slow and fast mode theories as the two limits when the vacancy concentration is varied from zero to a large value, and shows that the interdiffusion coefficient in a binary compressible mixture at finite vacancy concentrations can not in general be expressed only in terms of the tracer diffusion coefficients of the components, but it involves in addition the cooperative diffusion coefficient which characterizes the relaxation of total density fluctuations. The predictions of the ANK expression for the molecular dependence of the kinetic factor is compared with recent scattering experiments.

Cooperative upconversion effects on the performance of Er^3+-doped phosphate glass waveguide amplifiers

The cooperative upconversion processes of erbium ions in silver film ion-exchanged waveguides in a phosphate glass were studied from the pump intensity dependence of luminescence decay curves. Cooperative upconversion coefficients of the 4I13/2 level, 7.7±0.7×10-19 and 9.3±0.7×10-19 cm3/s, were obtained for an Er3+ concentration of 1×1020 cm-3 in bulk and waveguide samples, respectively. These values are 1 order of magnitude smaller than the ones reported for silica glass. The increase in the cooperative upconversion coefficient with the increase in Er3+ concentration was found to be small. The effects of cooperative upconversion on the gain performance were analyzed for different Er3+ concentrations by a theoretical model based on experimentally measured gain with a 1.48-µm pump wavelength. Given the small cooperative upconversion coefficients in this glass, Er3+ concentrations potentially as high as 3.7×1020 cm-3 were shown to be feasible. Such high concentrations would result in a 12-dB gain at 150-mW pump power with a 4-cm-long waveguide.

DNA Bending Is Essential for the Site-specific Recognition of DNA Response Elements by the DNA Binding Domain of the Tumor Suppressor Protein p53

We have used circular permutation assays to determine the extent and location of the DNA bend induced by the DNA binding domain of human wild type p53 (p53DBD) upon binding to several naturally occurring DNA response elements. We have found that p53DBD binding induces axial bending in all of the response elements investigated. In particular, response elements having a d(CATG) sequence at the junction of two consensus pentamers in each half-site favor highly bent complexes (bending angle is approximately 50 degrees ), whereas response elements having d(CTTG) bases at this position are less bent (bending angles from approximately 37 to approximately 25 degrees ). Quantitative electrophoretic mobility shift assays of different complexes show a direct correlation between the DNA bending angle and the binding affinity of the p53DBD with the response elements, i.e. the greater the stability of the complex, the more the DNA is bent by p53DBD binding. The study provides evidence that the energetics of DNA bending, as determined by the presence or absence of flexible sites in the response elements, may contribute significantly to the overall binding affinity of the p53DBD for different sequences. The results therefore suggest that both the structure and the stability of the p53-DNA complex may vary with different response elements. This variability may be correlated with variability in p53 function.

Kinetic study of swelling of rubbery poly(ethyl methacrylate) networks in 2-hexanone

Abstract The kinetics of the swelling of cross-linked poly(ethyl methacrylate) gels in 2-hexanone was studied at temperatures varying from 70.0 to 85.0 °C. The sorption curves exhibit the characteristic features of transport processes, apparently the Fickian diffusion of fast rates. The data were analyzed successfully by the contemporary model of Li and Tanaka, resulting in the cooperative diffusion coefficient, Dc, and the ratio of the shear modulus to the longitudinal osmotic modulus. It has been established empirically that the Dc is a composite function consisting of an Arrhenius expression and two simple power laws of the number-average molecular weight between cross-links and the equilibrium volume fraction of the gel. On the basis of the present findings, the quality of the swelling agent is discussed.

Positive allosteric action of eburnamonine on cardiac muscarinic acetylcholine receptors

It was discovered recently that alcuronium and strychnine (which is a precursor of alcuronium) allosterically increase the affinity of cardiac muscarinic receptors for the antagonist, N-methylscopolamine. We have now investigated the effects of l-eburnamonine and vincamine, which are both closely related to strychnine. In experiments on rat heart atria, l-eburnamonine was found to increase the binding of [ 3H] N-methylscopolamine with Ehlert's cooperativity coefficient α = 0.35, which indicates that the strength of its allosteric action is close to that of alcuronium and strychnine (α = 0.31 and 0.44, respectively). However, the affinity of l-eburnamonine for the cardiac muscarinic receptors is lower than the affinities of alcuronium and strychnine ( K AR = 22.6 μM, 0.15 μM, and 3.4 μM, respectively). In spite of its extremely close similarity to l-eburnamonine, vincamine has a negative allosteric effect on the binding of [ 3H] N-methylscopolamine (α = 4.1; K AR = 22.8 μM). It is likely that a systematic investigation of the allosteric effects of the analogues of strychnine will not only yield new allosteric effectors on muscarinic receptors, but also clarify the structural features responsible for the direction (positive or negative) of their allosteric effect.

The concentration dependent cooperative friction coefficient of dilute polymer solutions at the theta point

We combine multiple scattering and renormalization group methods to calculate the leading order dimensionless virial coefficient ks for the friction coefficient of dilute polymer solutions under conditions where the osmotic second virial coefficient vanishes (i.e., at the theta point Tθ). Our calculations are formulated in terms of coupled kinetic equations for the polymer and solvent, in which the polymers are modeled as continuous chains whose configurations evolve under the action of random forces in the velocity field of the solvent. To lowest order in ε=4−d, we find that ks=1.06. This result compares satisfactorily with existing experimental estimates of ks, which are in the range 0.7–0.8. It is also in good agreement with other theoretical results on chains and suspensions at Tθ. Our calculated ks is also found to be identical to the leading order virial coefficient of the tracer friction coefficient at the theta point. We discuss possible reasons for the difficulties encountered when attempting to evaluate ks by extrapolating prior renormalization group calculations from semidilute concentrations to the infinitely dilute limit.

Oxygen binding properties of Eudistylia vancouverii chlorocruorin and its dodecamer subunit

The oxygen equilibrium curves of the extracellular chlorocruorin of the polychaete Eudistylia vancouverii and its dodecamer subunit were determined over the pH range from 7.1 to 8.1 and in the presence and absence of 100 mM Mg 2+. Although the chlorocruorin has a very low oxygen affinity, high cooperativity and a moderate alkaline Bohr effect ( P 50 = 145 mmHg, n max = 6.9, φ = -0.44 at pH 7.1 and 25° C), the dodecamer subunit has higher affinity and lower cooperativity and Bohr coefficient ( P 50 = 58 mmHg, n max = 1.7, φ = -0.22). The presence of 100 mM Mg 2+ increased the oxygen affinity and cooperativity of the chlorocruorin but had no significant effect on the dodecamer subunit. The oxygen binding properties of the chlorocruorin reassociated subsequent to complete dissociation in 4 M urea at neutral pH were similar to the properties of the dodecamer and not to those of the native chlorocruorin. Fitting to the Monod-Wyman-Changeux allosteric model gave K T of 0.0013 mmHg −1, K R of 0.22 mmHg −1 and L o of 2.5 x 10 13 together with a size of the allosteric unit, N = 9.

Cooperative Diffusion of Concentrated Polymer Solutions: A Static and Dynamic Light Scattering Study of Polystyrene in DOP

Solutions of polystyrene in DOP were studied as a function of the concentration (0.2−0.9 g/mL) and temperature (−10 to +130 °C) using static and dynamic light scattering. The concentration and temperature dependence of the cooperative diffusion coefficient and the osmotic modulus were determined. The concentration and temperature dependences of the cooperative diffusion coefficient are explained in terms of the concentration and temperature dependence of the osmotic modulus and the solvent mobility. At the concentrations studied, the effect of hydrodynamic interactions is small. Close to the glass transition temperature the solvent mobility is the dominant factor and can be treated in terms of the free volume theory.

Testing the Correlation between ΔA and ΔV of Protein Unfolding Using m Value Mutants of Staphylococcal Nuclease

The application of hydrostatic pressure to aqueous protein solutions results in the unfolding of the protein structure because the protein-solvent system volume is smaller for the unfolded state. Contributions to this decrease in volume upon unfolding (delta Vu) derive from altered interactions of the protein with solvent and are presumed to include electrostriction of charged residues, elimination of packing defects, and hydration of hydrophobic surfaces upon unfolding. If the contribution of hydrophobic surface area solvation to the observed volume change of unfolding were large and negative, as is generally assumed, then one would expect to find a correlation between the amount of surface area exposed on unfolding, delta A(u), and the volume change, delta Vu. In order to test this correlation, we have determined delta Vu for two mutants of staphylococcal nuclease, A69T + A90S and H121P, whose unfolding by denaturant is, respectively, either significantly more (28%) or significantly less (28%) cooperative than that observed for wild-type (WT). This cooperativity coefficient or m value has been shown to correlate with delta A(u). If, in turn, delta Vu is correlated with delta A(u), we would expect the m+ mutant, A69T + A90S, to exhibit a delta Vu that is more negative than WT nuclease, while the delta Vu for the m- mutant, H121P, should be smaller in absolute value. To verify the correlation between m value and delta A(u) for these mutants, we determined the xylose concentration dependence of the stability of each mutant at atmospheric pressure and as a function of pressure. The efficiency of xylose stabilization was found to be much greater for the m+ mutant than for WT, consistent with an increase in delta A(u), while that of the m- mutant was found to be only slightly greater than for WT, indicating that other factors may contribute to the denaturant m value in this case. Regardless of the denaturant m value or the effect of xylose on stability, the volume changes upon unfolding for both mutants were found to be within error of that observed for WT. Thus, there does not appear to be a correlation between the volume change and the change in exposed surface area upon unfolding. We have previously shown a lack of pH dependence of the volume change, ruling out electrostriction as a dominant contribution to delta Vu of nuclease. These studies implicate either compensation between polar and nonpolar hydration or excluded volume effects as the major determinant for the value of delta Vu.

Analysis of the pH-Sensitive Swelling Rate of a Polyelectrolyte Complex Gel Prepared from Xanthan and Chitosan by the Collective Diffusion Model

The pH-sensitive swelling of a xanthan/chitosan complex gel, which swelled in NaOH solutions of pH 9–12, was analyzed by the collective diffusion model developed by Tanaka and Fillmore, which is based on the diffusion of a polymer network. The time–course for swelling of the gel beads under a change in pH from 11 to 10 fitted well with the equation derived by Tanaka and Fillmore. The collective diffusion coefficient characteristic of the gel was also obtained, although the value of this coefficient was higher than that of the cooperative diffusion coefficient determined from dynamic light scattering experiments by about 4 orders of magnitude. This result indicates that the swelling rate of the gel due to pH change was not controlled by cooperative diffusion of the polymer networks.

Dynamic Light Scattering of Poly(vinyl alcohol) Solutions and Their Dynamical Behavior during the Chemical Gelation Process

Dynamic light scattering experiments have been carried out on semidilute aqueous solutions of poly(vinyl alcohol) (PVA) and on gelling PVA solutions in the presence of a constant amount of cross-linker agent. The time correlation data revealed, for all the solutions and the systems in the pregel domain, the existence of two relaxation modes. The “fast” mode (exhibits an almost exponential profile) was always diffusive. In the solutions, the “slow” mode (described by a stretched exponential) was diffusive at high concentrations and a somewhat stronger wave vector (q) dependence was observed at lower concentrations. The concentration dependence of the slow relaxation time (τs) could be described by a power law (τs ∼ c4). In the pregel domain, the slow mode was diffusive for systems of high polymer concentration, while for systems of low concentration, a much stronger q dependence was detected when the gelation threshold was approached. The cooperative diffusion coefficient (Dc), evaluated from the “fast” mo...

In-Situ Interferometry Studies of the Drying and Swelling Kinetics of an Ultrathin Poly(N-isopropylacrylamide) Gel Film below and above Its Volume Phase Transition Temperature

The temperature influence on the drying and swelling kinetics of ultrathin poly(N-isopropylacrylamide) gel film were studied by in-situ interferometry. The drying rate is greatly dependent on temperature. When T ≲ 31 °C, the original gel film was swollen and contained more than 99% of water before drying. Our results showed that the initial drying rate was a constant. However, it became faster and faster toward the end of the drying. On the other hand, when T ≳ 32 °C, the gel film was in the collapsed state, but still contained ∼70% of water, before drying. Three distinct drying processes were observed, namely, a very fast initial shrinking, a slow transition period, and a normal drying process similar to that of the gel film when T ≲ 31 °C. As for the swelling process, it can be better described by the first-order kinetics developed by Li and Tanaka. The cooperative diffusion coefficient and the ratio of the shear modulus to the longitudinal modulus were determined from a least-squares fitting of the swe...

Spectroscopic and Kinetic Studies on Volume Expansion Processes of Photoresponsive Polyacrylamide Microgels in Water

Abstract Photostimulated volume expansion of polyacrylamide microgels (initial radius = 11—235 μm) bearing triphenylmethyl cyanide moieties (AAm-TPMCN) in water was studied on the basis of simultaneous measurements of the degree of ionic dissociation (α) of TPMCN to TPM+ (triphenylmethyl cation) and the gel radius. The time profile of the radius change, r(t), was analyzed by a convolution relation between r(t) and the time course of α (α(t)). The characteristic time constants of the volume change, related to the cooperative diffusion coefficient of the gel network, were determined for AAm-TPMCN gels with various radii. The faster photoresponse time of the volume change for the smaller AAm-TPMCN gel was explained in terms of the diffusion theory of gel networks in water.