Liquid Crystallinity versus Gelation of κ-Carrageenan in Mixed Salts: Effects of Molecular Weight, Salt Composition, and Ionic Strength (original) (raw)
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Phase transitions of κ-carrageenan gels in various types of salts
Journal of Applied Polymer Science, 2006
Sol-gel and gel-sol phase transitions of k-carrageenan in various types of salts were studied using photon transmission technique. Here, LiCl, NaCl, KCl, MgCl 2 , CaCl 2 , and SrCl 2 were chosen as the proper salts for the k-carrageenan-water system. Photon transmission intensity, I tr was monitored against temperature to determine the sol-gel and gel-sol temperatures (T sg and T gs ) and activation energies (DE sg and DE gs ). It was observed that T gs temperatures were notably higher than T sg due to the hysteresis on the phase transition loops. It was observed that stronger carrageenan gels are formed in the presence of KCl compared to the others.
Biophysical Chemistry, 2003
We have studied, by optical rotation dispersion, light scattering and rheology, the κ-Carrageenan system to elucidate the processes involved in gel formation (on decreasing the temperature) and gel melting (on increasing the temperature). Our results show that, on decreasing the temperature, a conformational transition from coils to double helices first occurs, followed by aggregation of the double helices into domains and gel formation at appropriate polymer concentration. Structural details of this sequence are better revealed by re-heating the system. Melting appears as a two-step process characterized by first a conformational change of helices involved in junction zones between aggregates, followed by the conformational transition of the helices inside the aggregates. These helices can regain the coil conformation only when the aggregates melt at higher temperature, in full agreement with the old ‘domain’ model. The full description of the sol–gel mechanism of this system can be useful in the search for new methods to control the gel texture, a relevant property for many industrial applications.
Cation effects on sol–gel and gel–sol phase transitions of κ-carrageenan–water system
International Journal of Biological Macromolecules, 2003
Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of -carrageenan gels. Transmitted photon intensity, I tr , increased exponentially as swelling time is increased for all gel samples. The behaviour of I tr was interpreted by Monte-Carlo Simulation. The increase in I tr was quantified by employing Li-Tanaka equation, from which time constants τ 1 and collective diffusion coefficients, D o were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in I tr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system.
Monovalent and Divalent Cation Effects on Phase Transitions of -carrageenan
Journal of Bioactive and Compatible Polymers, 2007
Phase transitions of -carrageenan in a variety of monovalent (Li, Na, K) and divalent (Mg, Ca, Sr) cation solutions were studied during heating and cooling by using photon transmission technique. Photon transmission intensity (I tr ) was monitored against temperature to determine the transition temperatures and activation energies during the heating and cooling processes in the monovalent and divalent systems. Three distinct transition regions were observed during the heating and cooling cycles for the carrageenan-divalent salt system. At the first step of the heating process, dimer groups were transformed into dimers that presented (g-d) transitions, then these dimers were directly converted into a double helix by undergoing a (d-h) transition. In the higher temperature region, a double helix-to-coil (h-c) transition took place. During the cooling process, these transitions are arranged in the order of (c-h), (h-d), and (d-g). The carrageenan-monovalent salt system presented only coil-to-rod-like helix (c-r) and rod-like helix-to-coil (r-c) transitions during the cooling and heating processes, respectively. A hysteresis was observed between (r-c)-(c-r) and (g-d)-(d-g) transitions for the monovalent and divalent cations, respectively.
K + and Na + effects on the gelation properties of κ-Carrageenan
Biophysical Chemistry, 2005
The effects of K+, Na+ ions and their mixture on the conformational transition and macroscopic gel properties of κ-Carrageenan system have been studied using different experimental techniques. The macroscopic gelation properties of κ-Carrageenan were found to be dependent upon cosolute type. Indeed, a more ordered and strong gel was obtained in the presence of K+ with respect to Na+ ions. The gel properties obtained using mixtures of two cosolutes are shown to depend on the [K+]/[Na+] ratio.
Molecular recognition during sol–gel and gel–sol transition of kappa–iota carrageenan mixtures
Phase Transitions, 2005
Sol-gel and gel-sol phase transitions of kappa-iota (-) carrageenan mixtures in two types of salts were studied using photon transmission technique. Here, KCl and CaCl 2 were chosen as the proper salts for the carrageenan mixtures. Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of carrageenan mixtures in monovalent and bivalent cation solutions were studied upon heating and cooling by using photon transmission technique. Photon transmission intensity, I tr was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (T ch and T nd ). Two distinct transition regions were observed in both heating and cooling of the carrageenan-bivalent CaCl 2 salt system. At the first step of heating process dimers decompose into double helices by making (d-h) transition. At the high temperature region (h-c) transition takes place. Carrageenan-monovalent KCl salt system presented only (c-h) and (h-c) transitions upon cooling and heating processes. Transition temperatures at the heating and cooling processes were obtained. A hysteresis was observed between (h-c)-(c-h) and (d-h)-(h-d) transitions for the monovalent and bivalent cations respectively.
Critical Exponents of Thermal Phase Transitions of κ -Carrageenan in Various Salt Solutions
Macromolecular Symposia, 2009
The steady state fluorescence (SSF) technique was employed to study the phase transitions of k-carrageenan in NaCl and KCl solutions. Pyranine was used as a fluorescence probe for monitoring these transitions. Scattered light, I sc , and fluorescence intensity, I, was monitored against temperature to determine transition temperatures and exponents. It was observed that transition temperatures are strongly correlated with the NaCl and KCl contents. The weight-average degree of polymerization, DP w and gel fraction G, exponents (g and b) were measured and found to be in accord with the classical Flory-Stockmayer model.
Viscoelastic properties of κ-carrageenan in saline solution
Journal of Thermal Analysis and Calorimetry, 2010
Viscoelastic properties of j-carrageenan in saline solution at various concentrations and pH were investigated by dynamic rheological techniques, viscosity, elasticity measurements, and IR spectrometry. The viscosity and elasticity at low concentrations of j-carrageenan do not depend on pH, confirming that j-carrageenan is in a disordered conformation. At 0.7% j-carrageenan, the disordered confirmation transforms into an ordered helical confirmation with the possibility of weak-type gel formation. The transformation is also confirmed by dynamic measurements of loss and storage moduli. Furthermore, at this concentration, the viscosity and elasticity are highly dependent on pH. At higher concentrations of NaCl (0.5 M) at some pHs, we observed that storage moduli is greater than loss moduli for the entire frequency region. Hence, there is a possibility of structure transformation from weak-type gel to a somewhat intermediate gel. The lowest viscosity and elasticity were obtained at extreme pH, confirming that there are structural changes occurring at these pHs due to hydrolysis. This is confirmed by IR data.