The modification of the triple helical structure of gelatin in aqueous solution 3. The influence of nonionic surfactants

Using CD-measurements the influence of nonionic surfactants (dodecyl polyoxyethylene, ethoxylated para tert. octyl phenol, commercial nonionic WON 100 and octyl diethyl phosphinoxid) on the secondary structure of gelatin in aqueous solutions was investigated. At surfactant concentrations smaller than the c.m.c. the triple helical content of the gelatin is increased. At concentrations exceeding the c.m.c. the triple helical content decreases. Chain reversals of the peptide chains after the destruction of the triple helical structure were shown to appear in acidic environment at 298 K. This destruction is reversible by rechilling the solution.     

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.     

Effect of pH on the binding of alkyl sulfates to gelatin

A surfactant-selective eletrode in which the membrane is an o-nitrotoluene phase containing a dissolved complex of cetyltrimethylammonium-dodecyl sulfate has been applied to investigations of the interaction between gelatin and alkyl sulfates as well as gelatin and alkyltrimethylammoniumions in dilute aqueous solutions.The binding isotherms were obtained by comparing emf-values obtained for surfactant in water to the electrode potentials in gelatin solutions plotted in terms of surfactant concentration.The binding of alkyl sulfates was measured as a function of pH at constant free surfactant concentration. At pH values 7 the degree of binding is indpendent of the pH of the solution. The level of binding of alkyl sulfates to gelatin increases strongly with increasing chain length of the alkyl sulfate. At pH values 6 the extent of binding increases steeply with decreasing pH. Octyl sulfate shows a very low level of binding even at low pH. Cationics show much weaker interactions with gelatin than anionic surfactants of comparable alkyl chain length.     

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.     

The interaction of anionic surfactants with gelatin

The binding of sodium dodecyl sulfate and a hydrophilic color coupler anion to gelatin was investigated using a surfactant-selective electrode. The binding isotherms of the surfactants to an alkali-processed bone gelatin, as well as an acid-processed bone gelatin were determined and compared with viscosity data.The comparison shows that viscosity measurements can only be regarded as circumstantial evidence for binding. At nearly identical binding isotherms the viscosity curves were found to be very different.     

Interaction of Na+, K+, Li+ and Ca2+ ions in Tris-HCl buffer substrate with monolayers of phosphatidic acid and homologous phosphatidic acid alkyl esters

The interaction of ions (Na⁺, K⁺, Li⁺, Ca²⁺) with monolayers of phosphatidic acid alkyl esters (alkyl = methyl, ethyl,n-propyl,n-pentyl) were investigated at the air/water interface on Tris-HCl buffer, as well as on the electrolytes containing subphases.Qualitatively it can be stated that there are no considerable interactions between Na⁺ ions in the substrate and the head groups of phosphatidic acid esters in the monolayers. On the whole, the modification of the shape in the /a and v/a isotherms ( ^s = film pressure, v ^s = film potential) of the homologous phosphatidic acid esters as a function of the length of the ester group on the subphase containing NaCl, KCl, and LiCl corresponds to that on Tris-HCl buffer without admixture of electrolytes.On the other hand the strength of interaction between Ca²⁺ ions and the homologous phosphatidic acid esters depends on the length of the ester group. The film-condensing effect of Ca²⁺ ions becomes smaller with increasing length of the ester group.     

Binding of hexadecylammonium surfactants to water-soluble neutral polymers

The binding of hexadecyltrimethylammonium bromide and hexadecyldimethyl-2-hydroxyethylammonium bromide to neutral polymers was measured by a potentiometric titration method using surfactant selective electrodes. Binding to poly(vinyl alcohol) was slightly cooperative, while that to poly(ethylene oxide) lacked the co-operativity. Poly(vinyl pyrrolidone) did not bind them at all. Binding affinity as estimated by a distribution coefficient of the cationic surfactants between the bulk and polymer phases is about 2 orders of magnitude smaller than that of anionic sodium dodecyl sulfate. The heat of binding was estimated from the temperature dependence of the distribution coefficient and found to be endothermic. It is imagined that the cationic surfactants are simply partitioned between the aqueous bulk phase and the polymer coil phase which is regarded as aqueous organic mixed solvent.     

Association of poly-(L-lysine) homologues in sodium carbonate solution

The molecular weights of isopoly(L-Iysine), poly(L-ornithine), and poly(L-, -diaminobutylic acid), the homologues of poly (L-lysine), were determined by the sedimentation equilibrium method in aqueous solutions of 1.0 M NaCl or 0.1 M Na₂CO₃. In every sample the molecular weights in the presence of carbonate ions was twice that in NaCl solution. In a previous paper we reported that poly(L-lysine) behaved as a dimer at concentrations higher than 0.4 g/dl in the presence of carbonate ions and as a monomer in dilute solution, and these two forms were related by a monomer-dimer equilibrium. The homologues did not have a monomer-dimer equilibrium relationship under the conditions of the measurements that we carried out. The CD spectrum of isopoly(L-lysine) in water showed a uniform increase with a decrease in the wave length in the presence of carbonate ions. However, in the alkaline region in NaOH solution, the spectrum changed and a small minimum at 212 nm was found. When additional carbonate ions were added a large minimum at 205 nm was observed. This result can be explained by a change in the conformation from a random coil to a regular structure. We could not compare isopoly(L-lysine) with other polypeptides, because it does not have peptide bonds. The CD spectra of poly(L-ornithine) and poly(L-, -diaminobutylic acid) in NaOH or Na₂CO₃ solutions showed only slightly regular structures. It was also confirmed that the dimer-structures of the poly (L-lysine) homologues do not have regular structures.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17,1989.     

Charge-transfer interaction of some pyridinium salts with hen egg-white lysozyme

The charge-transfer interaction of pyridinium salts with lysozyme and L-tryptophan has been investigated by visible absorption, circular dichroism and fluorescence spectroscopy. Four quaternized and substituted pyridinium salts were used as electron acceptors. L-tryptophan was used as a model compound of electron donor for the purpose of the comparison with lysozyme. The binding constants obtained from absorption and circular dichroism spectra were 2.0–13 M^–1 and the sequence of the magnitude was found as EPCl(1-ethylpyridinium chloride) < MPCl(1-methylpyridinium chloride) < MNCl(1-methylnicotinamide chloride) < MNMCl(1-methyl-3-carbomethoxypyridinium chloride), which could be explained by the electron affinity of the pyridinium salt. The fluorescence spectra of lysozyme and L-tryptophan in the absence and presence of pyridinium salts were interpreted by Stern-Volmer plot. The static constants thus determined were in agreement with the binding constants obtained by other methods.     

The influence of surfactants on latex flocculation with poly(diallyldimethyl ammonium chloride)

Aqueous latex was flocculated by mixtures of poly(diallyldimethyl ammonium chloride), PDADMAC, and anionic surfactants. Sodium dodecyl sulfate, (SDS), and Aerosol OT influenced flocculation whereas nonionic Tergitol NP-10 did not. The flocculation domains were correlated with properties of the polymer-surfactant complexFlocculation was never observed above the CMC of the corresponding surfactant solution without polymer or latex. At SDS concentrations greater than 10^–3.6 M the flocculation boundary corresponded to the first appearance of insoluble polymer-surfactant complex which was characterized by dynamic light scattering and microelectrophoresis. Under these conditions latex (diameter 570 nm) and dispersed polymer-surfactant complex particles (diameters between 30 and 2 000 nm) displayed simultaneous homo and heteroflocculation. The boundaries of the flocculation domains at low surfactant concentration were determined by the ratio of polymer to latex and by the net electrostatic charge of the soluble polymer-surfactant complex. On the other hand, the mechanisms controlling flocculation boundaries in the dispersed polymer-surfactant domain require further clarification.     

Binding of naproxen and 1-anilino-8-naphtalenesulphonic acid to albumin: Characterization of their binding sites in bovine serum albumin

The binding of naproxen (NP) and 1-anilino-8-naphtalenesulphonic acid (ANS) to bovine serum albumin (BSA) has been studied by equilibrium dialysis and spectrophotofluorometry, respectively. The drug protein (D/P) ratio is found to determine the nature of binding sites for NP but not for ANS. At low D/P ratio, NP possesses a specific site in BSA and one of the tryptophan residues is part of it. Fluorometric investigation reveals non-displacement of ANS from its sites by the binding of NP to its specific site. At high D/P ratio, NP instead causes localized conformational changes in BSA. Furthermore, it is possible to infer the location of NP's specific site as loop 4 of BSA. NP and ANS binding sites have also been examined by employing Bromocresol Green (BCG) as a spectrophotometric probe. Competition studies are also able to establish distinct binding pattern for the two ligands in BSA. The displacement pattern points out the presence of independent sites for NP (specific site) and ANS (initially occupied site) in BSA in spite of their amphipathically similar nature.     

Fabrication and characterization of orientation in skew stretched polyethylene terephthalate films

Skew stretched films were prepared by first unaxial stretching and subsequently skew stretching at 30 and 60 angles to various stretch ratios. The films were characterized by refractive index (birefringence), infrared absorption (dichroism) and wide-angle x-ray diffraction measurements. The data are represented in terms of ellipsoids and symmetry axes were determined. The results from the different methods are compared. Biaxial orientation factors are computed based on the experimentally determined axes.     

Spectral studies on the structure and monovalent cation binding to poly(1,3-propylene phosphate) — a synthetic analogue of natural teichoic acids

A poly(1,3-propylene phosphate), (PPP), which can be considered as a synthetic analogue of naturally occurring teichoic acids, has been studied with infrared spectroscopy. Infrared spectra of PPP in acidic and alkali metal forms have been analyzed in detail and the conclusions concerning intermolecular interactions between phosphate diester groups and the monovalent cation binding to PPP of a different degree of polymerization (n) have been drawn out. It has been shown that in anhydrous PPP, acidic groups are extensively hydrogen bonded. The process of association of phosphate diester groups is rather complex, especially in the samples of lowern. The role of H-bonds in some solution properties of high-molecular PPP samples has been discussed.     

Morphological studies of deformed polybutylene terephthalate (PBT)

PBT is a semi-crystalline thermoplastic polymer whose deformation behavior highly depends on processing parameters. This makes it a model polymer for investigating morphological changes caused by deformation on the spherulitic and lamellar level. In the neck region all states of deformation of the spherulites are observed. Even in the fibrillar phase the borders of the spherulites remain visible. The spherulitic structure is not totally destructed in the neck. The lamellar structure of the fibrillar phase significantly differs from that of the spherulitic region. The lamellae are orientated with respect to the direction of deformation and the lamellae heights are reduced distinctly. Scanning electron microscopy of fracture surfaces reveals for some samples a sharp frontier between spherulitic and fibrillar region. This leads to the conclusion that the necking process may be a phase transition between an isotropic and a highly orientated phase, as predicted for a Van der Waals network.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

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 first liquid crystalline diol compound which exhibits nematic,smecticA +, and smecticC + mesophases in the presence of water

A new amphiphilic ethane-1,2-diol derivative with a rodlike 2-phenylpyrimidine rigid core has been synthesized. From the combined results of differential scanning calorimetry and optical polarization microscopy a phase diagram amphiphile/water was constructed. The system exhibits a nematic phase at a very low water content, a smecticA ⁺ and a smecticC ⁺ phase at higher water concentrations. Such a phase sequence has been found for a lyotrophic system for the first time.     

Spectrophotometric behavior of polyvinylpyrrolidone in aqueous and nonaqueous media (I)

Electronic spectral behavior of polyvinylpyrrolidone solutions in various media has been determined by UV-VIS spectrophotometry. A theoretical approach has been developed to explain the experimentally observed concentration dependent spectral behavior of polyvinyl pyrrolidone in aqueous and nonaqueous solvents. Increase in the concentration of the polymer or the addition of guanidine salts caused bathochromic shift. A similar concentration effect has been observed in nonaqueous media in the absence of guanidine salts.     

On the observation of micellar structures by dielectric spectroscopy

Many cationic surfactants form, in the presence of certain organic acids, large supramolecular micellar structures in water. The dielectric response of one such system (cetyl trimethyl ammonium bromide-salicylic acid, CTMAS) has been studied as a function of frequency, concentration and temperature. The results are compared with dynamic mechanical data on the same system, which has been published in the literature.The dielectric response shows that the micelles form a rigid, open network structure, which does not impede ionic transport in the bulk liquid. However, the response also shows the presence of a frequency dispersive barrier capacitance. From the variation of the properties of this capacitance with CTMAS concentration and applied voltage over a range of frequencies, it is deduced that the barrier originates in an ordered micelle structure at each electrode.