The modification of the triple helical structure of gelatin in aqueous solution I. The influence of anionic surfactants,pH-value,and temperature

The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations <10^–4 M/dm³. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10^–4 M/dm³. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrations-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c. of SDS. At sufficiently high SDS concentrations,-turns appear.     

Conformations of different gelatins in solutions and in films an analysis of circular dichroism (CD) measurements

The structural behaviour of gelatins from different raw materials and manufacturing processes at thermal denaturation and isothermal dehydration and rehydration is investigated by CD. At both thermal denaturation and isothermal dehydration with all gelatins examined, the triple helix content decreases. Simultaneously, the appearance of cis peptide bonds is observed. At rehydration, a structural hysteresis occurs, the reconstitution of the triple helix structure being correlated with a decrease in the content of cis peptide bonds. The possibility of the formation of chain reversals upon destruction of the triple helix is discussed.     

The influence of surfactants on the structure of transparent gelatin films

The interference image of cold-dried transparent gelatin films containing different surfactants was determined in the conoscopic ray of monochromatic light. From the results obtained the order of the structure of gelatin in the film was characterized. Unlike the ionic surfactants (sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide), which lead to a reduction of the ordered structure, the addition of nonionic and amphoteric surfactants [ethoxylized octylphenole and a technical C₁₂/C₁₄-dipoly(oxyethylene)ammoniopropane sulfonate] causes an increase of the ordered structure of gelatin. The results quantitatively agree with those found for the influence of surfactants on the secondary structure of gelatin in diluted gelatin solutions. The influence is independent of the gelatin/surfactant ratio and has been explained by gelatin/gelatin interaction competing with the gelatin/surfactant interaction if the gelatin concentration becomes sufficiently high.     

Dependence of the activity of a rhizopus lipase on microemulsion composition

Enzymatic hydrolysis of a model triglyceride, palm oil, was carried out with lipase fromRhizopus sp. in microemulsions with varying water content. The microemulsions were based on a nonionic surfactant, pentaethylene glycol monododecyl ether (C12 EO5), buffered water solution and an oil component consisting of isooctane and palm oil at a weight ratio of 20:1. The structure of the microemulsions was characterized using Fourier transform pulsed-gradient spin-echo¹H NMR. The rate of reaction decreased as the water content of the reaction medium was increased. The self-diffusion coefficient of water, D_w was found to be constant within the interval 1–20% water. The difference in reactivity is believed to be due to a difference in structure of the palisade layer between water and hydrocarbon microdomains. The nonionic surfactant was demonstrated to be unsuitable for enzymatic reactions since only partial hydrolysis was obtained in all experiments. The surfactant, however, did not cause enzyme deactivation, even at very high concentrations.     

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

The interaction between cationic surfactants (hexadecyl and dodecyl trimethyl ammonium bromide) and gelatin was characterized by measuring the circular dichroism. The interaction between the cationic surfactants and gelatin is weak in comparison to that of anionic surfactants. When the concentration of cationic surfactants is sufficiently low, refolding of the gelatin-strands to the triple helical structure by rechilling the solution from 298 K to 283 K is complete. The triple helical content of the solution is affected more strongly by the cationic surfactants in acidic solution than at pHs 7 or 10. The interaction depends on the apolar group of the surfactant and is found to be stronger for DTAB than for CTAB at 298 K. Coagulation of the hydrophobic gelatin-cationic surfactant complexes does not comprise that pan of gelatin which is able to refold the triple helical structure. Therefore, the gelatin-strands of lower molecular weights are thought to react favorably with the surfactant ions.     

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.     

Swelling pressure equilibrium of physical networks in the field of an analytical ultracentrifuge

Investigations of the swelling pressure equilibria of a physical network are performed with an analytical ultracentrifuge. The advantage of this method is that in contrast to the known swelling pressure instruments, swelling pressures in a range of composition are obtained from only a single equilibrium experiment. The Schlieren optical system of the ultracentrifuge allows the observation of the concentration gradient during the process of deswelling and swelling, and furthermore, the detection of the gel concentration at every point. The system gelatin/water shows a different behavior than that expected from the theory of Flory-Huggins for a swollen random network. The measured curves of concentration vs. the swelling pressure intersect each other in case of low initial concentrations. This shows that these networks are inhomogeneous. A new method to measure and evaluate the Schlieren pattern is described.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17, 1989.     

Interfacial tension of gelatin/sodium dodecylsulphate solutions against air,toluene, and diethylphthalate

The adsorption isotherms between aqueous solutions of sodium dodecylsulphate and gelatin against air, toluene, or diethylphthalate were determined using the spinning drop method. The results qualitatively and quantitatively agreed with those found by surface tension measurements on sodium dodecylsulphate/gelatin solutions using the ring method in the version of Du Noüy. Interaction between gelatin and the surfactant will yield complexes which are more interfacially active than the components by themselves. The saturation of the interfaces occurs at lower concentrations than in solutions of the single components.     

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.     

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.     

Solubilization of oleyl alcohol by pure and mixtures of surfactants

The solubilization behavior of oleyl alcohol by pure and mixtures of surfactants systems have been studied in terms of the maximum additive concentration (MAC), the solubilizing power, and the particle sizes of micelles with or without oleyl alcohol. The surfactants used are amphoteric (N,N-dimethyl-N-lauroyl lysine, DMLL; N,N,N-trimethyl-N-lauroyl lysine, TMLL; N,N-dimethyl-N-(carboxymethyl)-lauryl ammonium, DMCL), anionic (sodium dodecyl sulfate, SDS) and nonionic (alkyl polyoxyethylene ethers).The maximum additive concentration of oleyl alcohol by pure surfactants is larger by nonionic surfactants than by others.For a nonionic surfactant system mixed with DMLL, the mixing effect of surfactant on the increase in the MAC is not recognized. While, for DMLL mixed with SDS, the MAC becomes larger than that by pure surfactants. This may be attributed to the fact that the large micellar size will result in increasing the maximum additive concentration.     

On the theory of adsorption kinetics of ionic surfactants at fluid interfaces 3. Generalization of the model

It was shown that, in the case of adsorbing ions, the Boltzmann equation cannot be applied in its classical form, but has to be modified by considering the flux of adsorbing ions. From the comparison with the adsorption of nonionic surfactants a ratio results which is the measure of deceleration of adsorption kinetics due to the electric double layerr=K(y _s)/(t). At highr-values the electrostatic deceleration controls the adsorption kinetics process.     

Thermogravimetry and differential scanning calorimetry of γ-irradiated i-polypropylene films

Isotactic polypropylene films, Buplen Type, 40m thick, irradiated by a⁶⁰Co source to doses 0.37–37 Mrad, are investigated by means of optical microscopy, WAXS, thermogravimetry, DSC and DTA. The original film exhibits a paracrystal structure. Irradiation does not change the films' structure. The kinetic parameters of the non-isothermal destruction and the thermodynamic parameters of melting are obtained. The samples irradiated to small doses (up to 3 Mrad) are thermally more stable; the activating energy of the destruction is higher than that of the original film. The temperature of melting slightly increases, while the enthalpy of melting decreases. For the range of doses of 3.7–37 Mrad, the films show low thermal stability and the destruction proceeds with low activating energy. From the results of the data obtained, the following assumptions are made: the-irradiation causes simultaneous crosslinking and chain scission at random sites along the chains. Fragments of partially crosslinked molecules and fractions of low molecular linear segments are formed. The destruction caused by radiation prevails above 3 Mrad.     

CPS LG 313 Phenylalkanol — adsorbates on silica as types of immobilized drugs 1. Chemiadsorption on activated silica surfaces

The chemiadsorption of phenylalkanols onto a porous silica support (d _pore 10 nm) viaSi-O-C bonds was studied. The silica support was activated prior to the alcohol adsorption by annealing or by the introduction ofSi-Cl groups. Different reaction conditions were applied, namely time, temperature, solvent and drug-support ratio. The yield of chemiadsorption was dependent on both the reaction conditions and the structure of the alcohols. Long alkyl chains, especially those with an alcohol OH-group positioned in the vicinity of bulky substituents, reduce the yield considerably. Using chlorinated silica, a reasonable yield of chemiadsorption can be obtained even at relatively low reaction temperatures.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occassion of his 60th birthday.     

Effect of sodium poly(styrene sulfonate) on thermoreversible gelation of gelatin

The effect of an added polyanion, sodium poly(styrene sulfonate) (NaPSS), on the thermoreversible gelation and remelting of gelatin gels has been investigated by polarimetry and rheology. The presence of NaPSS can either enhance or reduce collagenlike helix formation, depending on the polymer concentration relative to that of gelatin and the gelation temperature. At temperatures < 20°C, the helical content is reduced by increasing the amount of added NaPSS, demonstrating the disruption of helical structure of gelatin by the polyanion. Synchronous measurements of optical rotation and modulus at 25°C, in both gelation and remelting, indicate that the optical rotation at the gel point for the pure gelatin is lowered on addition of NaPSS. At low frequency, the storage modulus of gelatin is increased by the addition of a small amount of NaPSS relative to that of gelatin, but decreased with excess NaPSS. The mechanical properties of gelatin with and without NaPSS will be discussed in light of the competition between network junction formation by strands of triple helices among gelatin chains and temporary ionic crosslinking between gelatin and the polyanion. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2287–2295, 1999     

X-ray scattering study of molecular order in a liquid crystal-side group polysiloxane

The molecular structure of a polysiloxane with phenyl benzoate mesogenic side groups was investigated in an x-ray scattering study in the partially crystalline, smectic and nematic phase, and in the melt. In the crystalline phase polymer molecules have the form of straight ribbons with a double-comb-conformation. A bilayer structure is built up by regular stacking. Layers are the dominating structure element not only in the crystalline and smectic phase, but also in the nematic phase, and even in the isotropic melt. Layers are planar in the smectic phase and curved in the nematic phase, with an asymmetric distribution of the normal vectors about the director. In the isotropic melt there is evidence for the occurrence of clusters with layer-like short-range order.     

Effects of urea and a nonionic surfactant on the micellization and counterion binding properties of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate

Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm^–3 and 0.25 mol dm^–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm^–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.     

Formation of monodisperse poly(1-methacryloxybenzotriazole) particles by radiation-induced dispersion polymerization

Radiation-induced dispersion polymerization of 1-methacryloxybenzotriazole (MABt) in ethyl propionate starts as homogeneous mixture and the resulting polymer precipitates as spherical particles. Formation, size, and shape of polymer particles are strongly dependent on the initial monomer concentration. Three regions can be distinguished: formation of deformed particles at concentrations of 15 w/v-% MABt; formation of spherical particles at concentrations from 18 to 35 w/v-% MABt; no precipitation of polymer at concentrations of 40 w/v-% MABt. The spherical particles at 20 w/v-% MABt had a diameter of 0.54 ± 0.31 m for 3 kGy irradiation and 2.93±0.68 m for 30 kGy. The number distribution of the microspheres shows that the spherical particles with small sizes formed at low irradiation dose (low conversion) disappears with increasing irradiation dose because of multi-coating by newly produced polymer.