Conformational change of poly(L-lysine) and poly(L-ornithine) and cooperative binding of sodium alkanesulfonate surfactants with different chain length

Conformations of poly(L-lysine) (PLL) and poly(L-ornithine) (PLO) were examined in aqueous solutions of sodium alkanesulfontates (C_nSO₃Na, n=9, 10, 11, 12) in the presence of 0.02 M NaCl by circular dichroism (CD) spectroscopy. These surfactants induce the-structure for PLL and the-helix for PLO. The binding of surfactants on the polypeptides was measured potentiometrically with a surfactant ion electrode and was found to be highly cooperative. The cooperativity increases with increasing chain length of surfactant. The behavior accompanying the surfactant binding and the conformational change indicated that the conformational change requires a certain amount of bound surfactants in the case of C₉SO₃Na and starts immediately on binding of surfactant in the case of C_{1 2}SO₃Na. The clustering of bound surfactants due to the cooperative binding as well as neutralization of polypeptides contributes to their conformational change. A slow conformational change of PLO was found in the time scale of hours, sometimes days, for C₉- and C₁₀SO₃Na at low concentrations, but the binding process reached the equilibrium quickly. This slow mode might occur due to the slow interaction between surfactant/polypeptide complexes.     

The aggregation behavior of poly-(oxyethylene)-poly-(oxypropylene)-poly-(oxyethylene)-block-copolymers in aqueous solution

Aqueous solutions of blockcopolymers, consisting of a polyoxypropyleneblock (POP) with a polyoxyethylene-block (POE) at each side, were studied using surface and interfacial tension measurements, static and dynamic light scattering and smallangle neutron scattering techniques, electric birefringence, rheological and DSC-measurements. The compounds were commercial samples and had an approximate average composition EO₂₀PO₇₀EO₂₀, EO₁₈PO₅₈EO₁₈, and EO₁₀₆PO₆₉EO₁₀₆. All three compounds formed micelles above a critical concentration. The size of the micellar core is determined by the length of the hydrophobic poly-propyleneoxide block. The transfer energy of a propyleneoxide unit from the aqueous to the micellar phase is about 0.3 kT at room temperature and hence a quarter of the corresponding value for a CH₂-group.The aggregation number of the micelles increases strongly with increasing temperature while the hydrodynamic radius remains constant in first approximation. The smallangle neutron scattering (SANS) data show at higher concentrations a strong correlation peak. Both the SANS- and the light-scattering data can be interpreted on the basis of the theory of hard sphere particles.Solutions with a volume fraction beyond about 0.2 gellifie when the temperature is raised above a characteristic value that is at the lowest concentrations slightly above room temperature, shift to lower values with increasing concentrations. Below this gelation temperature DSC-measurements show a phase transition with enthalpies between 40J/g and 80J/g, which is probably due to the dehydration of the PO-groups; this transition can also be observed at low concentrations where no gelation takes place. The position of the correlation peak of the SANS-data is not affected by the gel formation. Some samples, however, show clear evidence of long-range order and seem therefore to consist of cubic liquid crystalline phases. The shear moduli of the gels can qualitatively be understood on the basis of hard sphere models.     

An estimation of the surface ionization constant of oleic acid in aqueous sodium chloride solution

The zeta potential () measurements and the site binding theory were utilized for calculations of the parameters of the electrical double layer (edl), ionization, and complexation constants for oleic acid-aqueous sodium chloride solution interface. Assuming that is equal to the diffuse layer potential ( _d ) of the edl, the charge of the diffuse part of the edl was calculated from the Gouy-Chapman equation. The intrinsic ionizaiton constant was then determined by an extrapolation method to be . Subsequently, the surface potential ( ₀) was calculated, and it was found that ₀ changes by 50 mV per pH unit (50 mV/pH) or 42.5 mV/pH for 10^–3 and 10^–2 M NaCl, respectively. For further calculations, the integral capacity of the outer zone of the compact part of the edl was assumed to be for both ionic strengths. It was established that the intrinsic complexation constant for the binding of Na⁺ ions with the surface of oleic acid ispK _Na ^int = 2.9±0.5 if the integral capacity of the inner zone of the compact edl (K ₁) is 80 for 10^–3 M NaCl, but 280 for 10^–2 M NaCl. The use of the sameK ₁ value for both ionic strengths gives a differentpK _Na ^int for different NaCl concentrations, and also provides unrealistic surface charge ( _o ) values greaterfor 10^–3 M NaCl than for 10^–2 M NaCl, at the same pH of the solution.     

Thermochemistry of dissolution of sodium alkylsulfonates

The effect of temperature on the solubility of ionic surfactants was interpreted in terms of standard enthalpy and entropy of dissolution at reference temperature by considering the change in the heat capacity. The significant value of the latter quantity causes the curvature of the function logarithm of equilibrium constant (or solubility) vs. the reciprocal thermodynamic temperature. The solubility data for several sodium n-alkylsulfonates, published by Saito, Moroi, and Matuura, were interpreted by nonlinear regression analysis. It was found that both the enthalpy and entropy of dissolution decrease with the chain length. The heat capacity increases in the course of the dissolution process.     

Micelle structure in isotropic aqueous colloids of a poly(oxyethylene) amphiphile C12E8

Micelle structure in aqueous colloids in the isotropic liquid phase (L₁) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C₁₂E₈) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L₁ phase is discussed.     

Thermally stimulated currents in poly(bis(p-fluorophenoxy)phosphazene)

Thermally stimulated currents (TSC) were examined for poly(bis(p-fluorophenoxy)phosphazene) (PBFPP) film. TSC showed peaks at the glass transition temperature (Tg=–4 °C) and atT(1) (160 °C – 170 °C), where-form crystal phase transformed to mesophase of-form structure. Another peak was found atT _cc betweenTg andT(1). Linear relationship between polarization field and peak current ofT _cc -peak was found, which shows thatT _cc -peak was caused by motion of dipolar groups in crystalline phase. When heating (up to 200 °C) and cooling (down to 20 °C) thermal process was repeated,T _cc -peak shifted to higher temperature region approachingT(1) and simultaneously, the peak current ofT(1)-peak became smaller. Activation energy, time constant of dipolar relaxation and charge mobility were evaluated forT _cc -peak. From these results, it was concluded that-form and more ordered- form crystalline phases coexisted in PBFPP once heated aboveT(1) and the content of- form phase increased by repeated thermal hysteresis.     

The properties and behavior of supermolecular formations in aging aqueous poly (vinyl alcohol) solutions

The structure of supermolecular formations and the interparticle interaction in aqueous poly(vinyl alcohol) solutions aging at different concentrations were investigated. Integral light scattering was used to determine the single particle scattering functionP(K), the structure functionS(K), and hence the radial distribution functiong(r). Nonrandom arrangement of the supermolecular formations in solutions under study is much less intensive than that of particles in polymer latices.     

XPS analysis (ESCA) of the surface composition of poly(styrene/2-hydroxyethyl methacrylate) microspheres produced by emulsifier-free emulsion polymerization

Polymer microspheres composed of various compositions of styrene and 2-hydroxyethyl methacrylate (HEMA) were produced by batch emulsifier-free emulsion polymerization. The HEMA content at the surface, [HEMA] _s , of the microspheres powdered by freeze-drying was determined by both quantitativeC ^1s /O ^1s analysis andC ^1s peak shape analysis of the x-ray photoelectron spectroscopic spectra. When the HEMA content in the microsphere, [HEMA] _p , was less than about 5 mole%, the [HEMA] _s values determined by the two different methods showed good agreement. At [HEMA]_p above 5 mole %, [HEMA]_s values determined by the first method were about 15 mole % greater than those determined by the second. They both showed a similar tendency with the [HEMA] _s being higher than the [HEMA] _p , e.g., when [HEMA] _p was 1 mole %, [HEMA] _s was 11 mole %. The intensity of the satellite peak due to the ^* transition of the benzene ring of the styrene component decreased with an increase in [HEMA] _p , to zero at 5 mole % of [HEMA] _p . These results indicate that the HEMA component is localized at the surface.Part CVIII of the series Studies on Suspension and Emulsion.     

Some structural and mechanical properties of bacterially produced poly-β-hydroxybutyrate-co-β-hydroxyvalerate

Some structural and mechanical properties of PHB homopolymer and copolymers containing 17 and 25–30% PHV have been investigated. X-ray scattering, optical microscopy, density measurements and differential scanning calorimetry were used to interpret the results of load-elongation curves and thermomechanical softening measurements.     

Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

Effects of thermal history on the rigid amorphous phase in poly(phenylene sulfide)

The rigid amorphous phase of semicrystalline poly(phenylene sulfide) (PPS) has been studied as a function of thermal history using scanning calorimetry, dielectric relaxation, density, and small-angle x-ray scattering (SAXS). Based on the new heat of fusion of perfect crystalline PPS, which is 26.7±0.8 cal/gram, the weight fraction of rigid amorphous phase is shown to be nearly twice as large as previously reported [1]. The mass fraction of the rigid amorphous phase ranges from 0.24 to 0.42 and is dependent upon thermal treatment. We have taken the approach of assuming a three-phase model for the morphology of semicrystalline PPS consisting of crystalline lamellae, mobile amorphous, and rigid amorphous components. Using this three-phase model, we determine that the average density of the rigid amorphous fraction is 1.325 g/cc, which is slightly larger than the density of the mobile amorphous phase fraction and was insensitive to thermal history. From the SAXS long period, the layer thicknesses of the mobile amorphous phase, rigid amorphous phase, and crystal lamellae were estimated. Only the lamellar thickness shows a systematic variation with thermal history, increasing with melt or cold crystallization temperature, or with decreasing cooling rate.     

An atom-based explanation for the absence of excimer emission in the fluorescence of dilute solutions of poly(pentafluorostyrene)

The steady-state fluorescence emission spectrum of poly(pentafluorostyrene) in dilute fluid solution shows no excimer emission. An atomic level modeling study explains why this polymer cannot form an excimer. Repulsive Coulombic interactions prohibit the attainment of the extensive overlap of the two rings in the classic face-to-face sandwich conformation of a singlet excimer.     

Molecular mechanism for elongation: poly(vinylidene fluoride) form II

Elongation of an unoriented sample of poly(vinylidene fluoride) form II at high temperature (above 140 °C) results in a uniaxially oriented sample of form II during so-called necking. The short-range and long-range order parameters of poly(vinylidene fluoride) form II and measures of the structural order on thec-projection are characterized by the intensity and half-width of the 120 reflection. The elongation under the same condition gives almost the same order parameters, independent of the order parameters before the elongation. Furthermore, the dependence of the order parameters on the elongation temperature behaves in the same way as the dependence of the quenched unoriented sample on the annealing temperature. This suggests that the elongation of the sample during necking corresponds to the crystallization or recrystallization after a much disordered state, approximately molten state; this supports the mechanism proposed by Yoon and Flory.     

Molecular motions in poly(diethyl siloxane) studied by solid-state29Si NMR

Molecular motions in poly(diethyl siloxane) were studied by solid-state²⁹Si-NMR in the temperature range 180–350 K. In this temperature range two solid phases ₁ and ₂, a mesophase _m, and an amorphous isotropic phase exist. The nature of the chain mobility in the different phases was deduced from the resulting changes in the NMR line-shape governed by anisotropic chemical shift. In the intermediate solid phase ₂ its anisotropy is reduced by 25% compared with the low temperature phase ₁ due to the onset of oscillations around the chain axis and conformational transitions. In the mesophase _m the polymer chain rotates about its long axis yielding an axially symmetric chemical shift tensor opposite in sign to that in the ₁, ₂ phases. The broad transition of the mesophase into the isotropic phase is accompanied by an increase in a narrow Lorentzian line arising from the amorphous phase. The results are compared with previous¹H NMR, Raman-spectroscopy and x-ray measurements.After completion of this work we learnt that PDES has recently also been studied through¹³C-MAS and²⁹Si-NMR by Möller et al. [13].     

Electrically conducting,thermally stable,and mechanically strong CuS-poly(parabanic acid) composite films and their shielding effect of electromagnetic wave

Poly(parabanic acid)-CuS composite film (wt-% of CuS=20–50) prepared by using organosol of CuS (=1500 Å) showed electrical conductivity of 0.1–70 S cm^–1, high thermal stability up to 250°C, high mechanical strength (breaking stress=7.0–12 × 10⁷ Pa), and good shielding effect of electromagnetic wave.     

Secondary structural changes of chymotrypsinogen A,alpha-chymotrypsin,and the isolated polypeptides Cys1-Leu13, Ile16-Tyr146, and Ala149-Asn245 in sodium dodecyl sulfate,urea and guanidine hydrochloride

Secondary structural changes of chymotrypsinogen A,-chymotrypsin, and their isolated polypeptides Cys¹-Leu¹³, Ile¹⁶-Tyr¹⁴⁶, and Ala¹⁴⁹-Asn²⁴⁵were examined in aqueous solutions of sodium dodecyl sulfate (SDS), urea, and guanidine hydrochloride (residue numbers from chymotrypsinogen). After the fragmentation by the cleavage of disulfide bridges in-chymotrypsin, the helical structure was formed in the isolated polypeptide 16–146 where the helical segments do not exist in the protein state. The polypeptide 149–245, where the helical segments of the parent protein are originally located, contained no helices. The polypeptide 1–13 was almost disordered. The three polypeptides, chymotrypsinogen,-chymotrypsin and the polypeptide 16–146, clearly showed differences in the stabilities of helical structures in solutions of urea and guanidine hydrochloride. The addition of SDS accelerated the formation of helical structures in each polypeptide except for 1–13.     

Swelling of sodium acrylate gels

The swelling process of sodium acrylate gel is experimentally investigated. It is found that sodium acrylate gels weakly crosslinked with N,N-methylene-bis-acrylamide may undergo volume phase transition and that different kinds of mechanical instabilities occur in sequence at the transition. Peculiar wrinkle patterns appear on the free surface of an unstable gel and are changed in geometry as swelling proceeds. Cellular patterns seen at various instances in the late period of swelling are ascertained to be geometrically similar to each other and different only in size. The radii of spherical acrylate gels allowed to swell in water are measured as functions of time. The results are discussed and compared with the kinetic theories of swelling. As a result, these theories are proved to be unsatisfactory to fully describe the experimental facts.     

Swelling of poly(methacrylic acid) gels and adsorption of L-lysine and its polymer on the gels

Poly (methacrylic acid) gels (PMAA gels) of various degrees of crosslinking were prepared and the dissociation behavior of these gels was examined; the swelling behavior was investigated as a function of the solution pH values. A reentrant phenomenon of swelling was observed and interpreted based on the Flory-Huggins equation and the Donnan equilibrium formula. Moreover, adsorption of L-lysine, oligo(L-lysine)s (Lys-n,n=3, 9, and 19) and poly(L-lysine) onto PMAA gels from aqueous solutions was investigated under different conditions of pH and concentration of adsorbate. The adsorption ratio of L-lysine onto PMAA gel is dependent on both the pH of solution and the degree of crosslinking. In a pH range between 8 and 9, the protonated form of L-lysine is strongly adsorbed on the PMAA gel by electrostatic interactions. Oligomers and polymer of L-lysine are adsorbed in a somewhat different way from the monomeric L-lysine. In addition, the desorption behavior of L-lysine from PMAA gels by a change in pH was also investigated.     

Surfactant association structures in the system water,sorbitol, sodium dodecyl sulfate,and hexanol

The phase regions in the system hexanol, sodium dodecyl sulfate, and concentrated aqueous solutions of sorbitol were similar to the corresponding system with glycerol.In addition to the expected phase regions of a water/sugar micellar solution, a lamellar liquid crystalline phase, and the alcohol solution with solubilized sugar and water, a small region was found with an extremely stable emulsion, which could be separated by ultracentrifugation at 108,000 g. This emulsion consisted of micron sized droplets separated by layers of a lamellar liquid crystal.     

Small angle X-ray scattering study of an extremely elongated micelle system of CTAB-p-toluidine solution

Whenp-toluidine is added to an aqueous solution of CTAB, a remarkable increase of viscosity is accompanied by a spectacular elasticity. We detected the existence of extremely elongated rod-like micelles in electron micrographs. SAXS measurements indicate a closely packed array of cylindrical rod-like micelles, brought about when solutions flow through a thin capillary. A scattering maximum ofd=160 Å almost corresponds to the distance between the nearest neighbours of the cylindrical rod-like micelles. This value agrees with the diameter measured on electron micrographs. The second broad peak (d=75 Å) is assigned to a subsidiary maximum of the shape function of the cylinder with infinite length.