Calorimetric measurement of enthalpy change in the isothermal helix-coil transition of poly(L-ornithine) in aqueous solution.

The enthalpy change associated with the isothermal pH-induced uncharged coil-to-helix transition ΔH_h° in poly(L -ornithine) in 0.1 N KCl has been determnined calorimetrically to be ?1530 ± 210 and ?1270 ± 530 cal/mol at 10° and 25°C, respectively. Titration data provided information about the state of charge of the polymer in the calorimetric experiments, and optical rotatory dispersion data about its conformation. In order to compute ΔH_h°, the observed calorimetric heat was corrected for the heat of breaking the sample cell, the heat of dilution of HCl, the heat of neutralization of the OH^? ion, and the heat of ionization of the δ-amino group in the random coil. The latter was obtained from similar calorimetric measurements on poly(D ,L -ornithine). Since it was discovered that poly(L -ornithine) undergoes chain cleavage at high pH, the calorimetric measurements were carried out under conditions where no degradation occurred. From the thermally induced uncharged helix–coil transition curve for poly(L -ornithine) at pH 11.68 in 0.1 N KCl in the 0°–40°C region, the transition temperature T_tr and the quantity (?θ_h/?T)_Ttr have been obtained. From these values, together with the measured values of ΔH_h°, the changes in the standard free energy ΔG_h° and entropy ΔG_h°, associated with the uncharged coil-to-helix transition at 10°C have been calculated to be ?33 cal/mol and ?5.3 cal/mol deg, respectively. The value of the Zimm–Bragg helix–coil stability constant σ has been calculated to be 1.4 × 10^?2 and the value of s calculated to be 1.06 at 10°C, and between 0.60 and 0.92 at 25°C.     

Volume and sound velocity changes associated with coil- transition of poly(S-carboxymethyl L-cysteine) in aqueous solution

The measurements were made for the volume and the sound velocity changes (ΔV and ΔU) on titrating the sodium salt of poly (S-carboxymethyl L -cysteine) with dilute HCl. For the reaction, ? COO^? + H⁺ → ? COOH, ΔV per mole of H⁺ bound was + 12. 7 ml and +11. 4 ml in salt-free and 0. 2 M NaCl solutions, respectively. Corresponding ΔU was about ?13 cm/sec in salt-free polymer solution where 11.5 mM carboxylate ion reacts with equimolar hydrogen ion. ΔV associated with the coil-to-β transition was found to be +2. 35 ml in H₂O and +1. 90 ml in 0. 2 M NaCl per mole of amino acid residue, respectively. These values are larger than those obtained for the coil-to-helix transition of poly (L -glutamic acid). ΔU for the transition was about ?30 cm/sec in salt-free solution of polymer concentration 0.0115 mole/liter. Possible sources of ΔV and ΔU for reaction; coil → β, are (1) the formation of void volume and (2) the changes in the extent of solvation in amide linkage and in side chain.     

Thermodynamic stability of the ordered conformations of carrageenan polyelectrolytes

Manning's counterion condensation theory has been applied to the temperature-induced conformational transition of κ- and ι-carrageenan in the solution and gel states. The formalism of the theory has been extended to transitions between conformations with charge densities below or across the counterion condensation threshold. Measurements of the dependence of the melting temperature on ionic strength, and of the enthalpy of melting, are interpreted with the theory as indicating that the conformational transition is intramolecular and that side-by-side dimerization of chains gives rise to the gel structure.     

Calorimetric studies of the interactions of guanidinium hydrochloride and potassium iodide with model amides in aqueous solution.

The enthalpies of transfer, ΔH_tr, of a series of amides from water to aqueous solutions of either guanidinium hydrochloride (GuHCl) or potassium iodide were obtained from calorimetric measurements at 25°C. The amides were studied at molalities around 10^?2 m while salt molalities ranged from 0–10 m. The amides investigated were Ac-Gly-NHMe, Ac-Gly-Gly-NHMe, Ac-Ala-NHMe, and Ac-Leu-NHMe. Use of an additivity assumption allowed the calculation of group contributions to ΔH_tr in these two salt systems for the methyl group, leucyl side chain, and the peptide backbone unit. Values of the entropy of transfer were also obtained. The great ability of GuHCl to randomize protein structures appears to arise from effects on polar and nonpolar groups, which are characterized by enthalpies and entropies of transfer not substantially different from those with KI, a salt comprised of ions of comparable size and polarizability. The difference in the sign of the free energies of transfer of nonpolar groups from water to MX solutions, negative for GuHCl and positive for KI, is the result of these small differences in enthalpies and entropies of transfer. Variations in water structure produced by differences in ionic properties rather than a mode of action for GuHCl very different from that of other salts characterizes its superior denaturing ability.     

Thermodynamics of the partition of chondroitin sulfate–hexadecylpyridinium complexes in butanol/aqueous salt biphasic solutions

The thermodynamics of the partition of chondroitin sulfate–hexadecylpyridinium complexes wee studied in order to gain further insight into the mechanisms responsible for the sensitivity of the relative solubility of these complexes in aqueous slat and butanol phases to small changes in slat concentration. The dependence of the partition coefficient was measured as a function of temperature at three different salt concentrations. Increasing the temperature was found to favor the form of the complex which was soluble n the aqueous phase. Although the transition could be induced by temperature changes, he transition occurred over a 20°C range in temperature. The transition from the aqueous phase to the butanol phase was strongly exothermic, with ΔH = ?22.3 kcal/mol polymer. The value of ΔS was found to be dependent on the salt concentration, ranging from ?72.7 e.u./mol polymer in 0.05125M NaCl to ?77.1 e.u./mol polymer in 0.05375M MaCl. When placed on a disaccharide basis, the corresponding values are ΔH = ?402 cal/mol and ΔS = ?1.31 to ?1.3 e.u./mol. The sharpness of he transition was found to be due t the similarity in magnitude of ΔH and TΔS, and on the dependence of the later upon the salt concentration.     

Enthalpy and entropy changes for the intercalation of small molecules to DNA. II. Ethidium and propidium fluoride

Enthalpy changes (ΔH_B) for the binding of ethidium (a monocation) and propidium (a dication) to calf thymus DNA have been determined calorimetrically in piperazine-N, N′-bis(2-ethanesulfonic acid) buffer with the fluoride ion as the counterion. Heats of dilution for the fluoride salts of ethidium and propidium were substantially less than the corresponding values found for other halide salts of these cations. At a Na⁺ ion concentrations of 0.019, ΔH_B = ?8.3 and ?7.9 ± 0.3 kcal mol^?1 for ethidium and propidium, respectively. For these two cations, just as was observed for the naphthalene monoimide (monocation) and diimide (dication) [H. P. Hopkins, K. A. Stevenson, and W. D. Wilson, (1986) J. Sol. Chem. 15 , 563–579], ΔH_B is within the same experimental error for both cations. Apparently, charge–charge interactions in DNA–cation complexes produce only small changes in the enthalpy for the system. In the concentration range 0.019–0.207, the ΔH_B values for propidium did not depend appreciably on the Na⁺ ion concentration, and a similar pattern was shown to exist for ethidium. When these results were combined with ΔG_B values for the binding of these cations to DNA, we found the variation of ΔS_B with Na⁺ ion concentration to be remarkably close to the predictions of modern polyelectrolyte theory, i.e., propidium binding to DNA causes approximately twice as many Na⁺ ions to be released into the bulk solution as does the binding of ethidium. The much stronger binding of propidium, relative to ethidium, at low ionic strengths is thus seen to be primarily due to entropic effects.     

Transition temperature and enthalpy change dependence on stabilizing and destabilizing ions in the helix–coil transition in native tendon collagen

The transition temperatures t_t and enthalpy changes ΔH in the helix–coil transition of solid tendon collagen soaked in a solution containing one of the following stabilizing or destabilizing agents, HCHO, NaF, NaCl, NaI, NaBr, NaOH, NH₂CONH₂, CaCl₂, MgCl₂, were measured as a function of molar concentration by a calorimetric method. The temperature and the enthalpy changes accompanying the transition behaved in a similar manner: when the t_t was depressed by the presence of ions, similar behaviour was observed in ΔH. Both parameters (t_t and ΔH) increased for HCHO, and decreased for NaF and NaCl at concentrations lower than 0.2 M. Above 0.2 M they increased for NaF and NaCl, and decreased in the presence of the other reagents listed above. The average t_t and the ΔH observed in collagen soaked in water were 63.5°C and 12.3 cal/g, respectively. In addition to the parameters mentioned above, the molar effectiveness of the various reagents was obtained for the cases where there was a linear relationship between the t_t and molar concentration of the reagent in the solution. Since both the t_t and the ΔH were observed to vary, the entropy change (ΔS) accompanying the transition was calculated using thermodynamic relations. In order to explain the ΔS observed as a function of ionic concentration, the thermodynamic relationships have been obtained from a partition function under suitable assumptions. Since the partition function is dependent on the number of hydrogen bonds responsible for collagen stability, the result obtained has been compared with the values predicted by the two most quoted models for collagen. The present study is in accordance with the Ramachandran model for collagen structure, which predicts more than one hydrogen bond per three residues.     

Determination of stability of the DNA double helix in an aqueous medium

The possibility of determining the free energy of stabilization ΔG₀ of native DNA structure with the help of calorimetric data on heats ΔH of transition from the native to denaturated state is considered. Results of microcalorimetric measurements of heats of denaturation of T₂ phage DNA at, different values of pH and ionic strength of solution are given. Values of free energy of stabilization of the DNA native structure ΔG₀ under various conditions have been obtained. It is shown that under conditions close to physiological ΔG₀ approaches 1200 cal/mole per base pair.     

Calorimetric and spectroscopic investigation of the helix-to-coil transition of the self-complementary deoxyribonucleotide ATGCAT

Differential scanning calorimetry and temperature-dependent uv spectroscopy are used to thermodynamically characterize the double-strand to single-strand transition of the self-complementary deoxyribo-oligonucleotide ATGCAT. The calorimetric experiments provide a value of 33.6 kcal (mol of double strand)^?1 for the transition between 10 and 90° C. In conjunction with available temperature-dependent nmr data (which reveals terminal base pair fraying), we attempt to define specifically those interactions to which the calorimetrically measured enthalpy change refers.Values of ΔH_V.H. (van 't Hoff enthalpy change) are derived from the spectroscopic and calorimetric data and compared with the ΔH obtained directly from the calorimetric experiment. This comparison reveals that the part of the thermally-induced transition that occurs between 10 and 90°C is well represented by a two-state process. It is noted that in assessing the applicability of the two-state model it is best to compare the ΔH_cal. with ΔH_V.H. obtained from the calorimetric rather than the spectroscopic data.     

Effects of salts on the nonequivalent stability of the α-helices of isomeric block copolypeptides

The stability of the α-helices of isomeric block copolypeptides is nonequivalent, as reported previously. In order to explore the origin of the nonequivalence, the stability of α-helix of two block copolypeptides, (L -Ala)₂₀-(L -Glu)₂₀-(L -Phe) (designated as AEF) and (L -Glu)₂₀-(L -Ala)₂₀-(L -Phe) (EAF), in aqueous solution was investigated as a function of pH, temperature, and salt concentration by the measurement of the α-helical content using CD at 223 nm. The transition temperature, T_m, as a measure of the stability of the α-helix, decreased with increasing the salt concentration for EAF, while T_m increased for AEF. The results indicate that electrostatic interactions affect the nonequivalence of such helical stability. Thermodynamic quantities, ΔG, ΔH, and ΔS, of the thermal transition from random coil to α-helix were obtained by applying the curve-fitting method to the data. The major contribution to the effects of salts seems to be the entropic term, not the enthalpy term. This is unexpected, since the salt ions would weaken electrostatic interactions between ionized groups and the dipole along the helical axis, which affect the enthalpy term. In addition, the dependence of the electrostatic effect on the salt concentration is different for EAF and AEF. There fore, the nonequivalence cannot be accounted for by only the electrostatic effect, suggesting that it originates from some intrinsic property of the α-helix.     

Influencing factors of dsDNA dye (high-resolution) melting curves and improved genotype call based on thermodynamic considerations

High-resolution melting of dsDNA using suitable dyes is a simple and cost-effective alternative for mutation scanning. Analytical variation can result from salt and template concentration (C_T). To overcome this problem the van’t Hoff transition enthalpy ΔH_vH from dsDNA melting curves was estimated and used for robust genotype calling or mutation scanning. Model calculations show the effect of salt, C_T, and temperature resolution on (1) T_m, (2) difference plots, (3) melting peaks, and (4) calculated ΔH_vH. Using the LightCycler480, the influence of dye (ResoLight) and scanning speed was assessed. The model calculations show that only ΔH_vH is not influenced by salt and C_T. Higher amplicon enthalpy ameliorates the ability to discriminate mutations. Temperature resolution is important for peak- but not for curve-based genotyping. ResoLight increases T_m by 3.4 °C, while lowering ΔH_vH. Using a 4-bp deletion in a 200-bp amplicon as a model, the miscalling rate improved substantially, when using ΔH_vH instead of difference plots. Melting curves of duplex DNA are influenced by dye and salt and less so by duplex concentrations. As predicted from theory, ΔH_vH is a robust measure for mutation detection in two-state melting. The influence of dyes on enthalpy is of general impact for PCR assays.     

Chain length and oligonucleotide stability at high pressure

The effect of hydrostatic pressure on the helix-coil transition temperature (T_m) was measured for the DNA oligomers (dA)_n(dT)_n, where n = 11, 15, and 19, in 50 mM NaCl. The data were analyzed in light of previously published data for the polymer, poly(dA)·poly(dT) under the same conditions. As has been observed for DNA polymers, increasing the hydrostatic pressure led to an increase in the T_m of the oligomers; however, the effect of pressure diminished with decreasing chain length. The value of dT_m/dP decreased linearly with the inverse of the chain length varying from 3.15 × 10⁻²°C MPa⁻¹ for the polymer to 0.7 × 10⁻²°C MPa⁻¹ for the 11-mer. The two-state or van't Hoff enthalpy (ΔH_vH) of the helix-coil transition was obtained by analysis of the half-width of the thermal transition. As expected, ΔH_vH decreases with decreasing chain length. In contrast to the behavior of the polymer, poly(dA)·poly(dT), and (dA)₁₉(dT)₁₉, the ΔH_vH of the two shorter duplex oligonucleotides displayed a small pressure dependence dΔH_vH/dP≃−0.4 kJ MPa⁻¹ in both cases. The changes observed in the T_m and ΔH_vH were not sufficient to explain the magnitude of the chain-length dependence of the pressure effect. To interpret the large chain-length dependence of dT_m/dP, we propose that the terminal base pairs contribute a negative volume change to the helix-coil transition. Base pairs distant from the ends exhibit behavior characterized by the polymer where end effects are assumed to be negligible, i.e., a positive volume change for the helix-coil transition. The negative volume change of separating terminal bases may originate from the imperfect interactions these base pairs form with water due to the existence of several energetically equivalent conformations. This is reminiscent of one of the mechanisms proposed to be important in the pressure-induced dissociation of multimeric proteins into their constituent subunits. © 1996 John Wiley & Sons, Inc.     

Effects of sugars and polyols on the sol-gel transition of k-carrageenan: calorimetric study

The effects of sugars and polyols on the sol-gel transition of k-carrageenan were studied in 0.025 m KCl by means of differential scanning calorimetry. Addition of these compounds invariably raised the gelling temperature T_g, with an increase in their concentration, accompanying a decreased (less negative) enthalpy of gelation, ΔH_g. This indicates that it is not ΔH_g but the entropy of gelatin, ΔS_g, which plays an essential role in the gel stabilizatiion by them, thus differing from the enthalpy-driven stabilization by addition by KCl, ethanol or carrageenan. It seemed that such a large change in ΔS_g relative to ΔH_g predominantly occurs in the process of replacing polymer solvent hydrogen bonds by polymer—polymer hydrogen bonds with minor contribution of the conformational entropy of polymer chains. The gel-stabilizing ability of different sugars and polyols is discussed in terms of their different influences on the structure of water.     

Experimental thermodynamics of the helix--random coil transition. 3. Determination of the transition enthalpies of the helical complexes poly(I+C) and poly I in solution

The enthalpies of the helix-coil transitions of the ordered polynucleotide systems of poly(inosinic acid)–poly(cytidylic acid) [poly(I + C)], (helical duplex), and of poly (inosinic acid) [poly(I + I + I)], (proposed secondary structure: a triple-stranded helical complex), were determined by using an adiabatic twin-vessel differential calorimeter. Measuring the temperature course of the heat capacity of the aqueous polymer solutions, the enthalpy values for the dissociation of the helical duplex poly (I + C) and the three-stranded helical complex poly(I + 1 + 1), respectively, were obtained by evaluating the additional heat capacity involved in the conformational change of the polynucleotide system in the transition range. The ΔH values of the helix-coil transition of poly (I + C) resulting from the analysis of the calorimetric measurements vary between the limits 6.5 ± 0.4 kcal/mole (I + C) and 8.4 ± 0.4 kcal/mole (I + C). depending on the variation of the cation concentration ranging from 0.063 mole cations kg H₂O to 1.003 mole cations/kg H₂O. The calorimetric investigation of an aqueous poly I solution (cation concentration 1.0 mole/kg H₂O) yielded the enthalpy value ΔH = 1.9 ± 0.4 kcal/mole (I), a result which has been interpreted qualitatively following current models of inter- and intramolecular forces of biologically significant macromolecules. Additional information on the transition behavior of poly(I+ C)Was obtained by ultraviolet and infrared absorption measurements.     

Interaction of calcium ions with α-elastin: An equilibrium dialysis,circular dichroism,and microcalorimetric study

The interaction of calcium ions with α-elastin has been investigated by equilibrium dialysis, CD, and microcalorimetric techniques. Consistent with literature data, it was found that the interaction in water is very poor. In trifluoroethanol (TFE), equilibrium dialysis experiments showed that calcium ions bind to ～-elastin with an association constant of ～250 L × mol^?1. Such a figure is not consistent with highly specific, highly selective binding. It was also found that the CD response is not directly proportional to the amount of bound calcium but depends on the protein concentration. From microcalorimetric experiments it was found that the heat effect relative to the binding process is of the order of 1.9 kcal/g ion. From this figure and from the binding constant, a positive ΔS value of about 17 e.u. was evaluated, leading to the conclusion that the binding process is entropy driven. From microcalorimetric measurements a ΔH of 1.5 kcal/residue was found for the calcium-induced conformational transition of the protein.     

Calorimetric,density and circular dichroism studies of the reversible structural transition in Pf1 filamentous bacterial virus

The macromolecular structural transition of Pf1 filamentous bacterial virus detected by X-ray diffraction analysis has been studied in virus solutions by density, circular dichroism, and microcalorimetric measurements. The reversible structural change occurring between 5 °C and 25 °C has a calorimetrically determined transition enthalpy ΔH_t,cal of 14·5 ± 1.5 kJ (mol protein)^?1. The transition curves resulting from the density, circular dichroism, and calorimetric measurements have been analysed in terms of a two-state process to extract the van't Hoff enthalpy. Comparison of the effective transition enthalpy and the calorimetric ΔH_t,cal values gives about 26 protein subunits as the size of the co-operative unit. Parallel heat capacity and density measurements on fd virus show no such transition, in agreement with X-ray diffraction studies.     

Studies on κ-carrageenan/locust bean gum mixtures in the presence of sodium chloride and sodium iodide

The solution properties of κ-carrageenan and κ-carrageenan/locust bean gum mixtures have been studied by small deformation oscillation measurements and differential scanning calorimetry (DSC) in the presence of sodium chloride and sodium iodide. Both salts induced the κ-carrageenan to undergo a coil-helix conformational change as noted by an increase in the storage and loss moduli (G′, G′) and by an exothermic peak in the DSC cooling curves. The enthalpy ΔH_c-h and temperature of the conformational transition T_c-h were higher in Nal compared to NaCl and T_c-h increased with increasing the concentration of both electrolytes. Gelation was not observed for carrageenan or carrageenan/locust bean gum mixtures in the presence of up to 200 mM Nal. Although carrageenan alone did not gel in the presence of 100 mM NaCl, a weak gel was obtained for a mixture containing 0.9%/0.1% carrageenan/locust bean gum. Furthermore, the mixture showed hysteresis in both the rheological and DSC cooling and heating curves. A strong gel was produced for carrageenan alone in the presence of 200 mM NaCl and the gel strength increased on adding a small proportion of locust bean gum (0.9%/0.1%). © 1997 John Wiley & Sons, Inc. Biopoly 41: 657–671, 1997     

Thermodynamic analysis of nonelectrolyte sorption in plant cuticles: The effects of concentration and temperature on sorption of 4-nitrophenol

The sorption of 4-nitrophenol (4-NP) in enzymatically isolated cuticles ofLycopersicon esculentum fruits andFicus elastica leaves was studied as a function of temperature and solute concentration. Plots of the concentrations of 4-NP sorbed in the cuticle versus the equilibrium concentrations in the aqueous phase gave linear isotherms at low concentrations that tended to approach plateaus at higher sorbate concentrations ( 10 mmol·kg^-1). At low concentrations of sorbed 4-NP, cuticles have sorptive properties similar to those of organic solvents which are able to form intermolecular hydrogen bonds, while at higher concentrations their solid nature becomes apparent. During sorption of 4-NP the cutin matrix swells and new sorption sites are successively formed. The partition coefficients of 4-NP in the system cuticle/buffer are functions of temperature and concentration. At high sorbate concentrations (approx. 1 mol·kg^-1) they approach a value of 1. Different sorptive properties were observed for the cutin regions normally encrusted with soluble cuticular lipids (SCL) and those without SCL. Increasing temperature augmented the number of sorption sites in the cutin ofLycopersicon while no effect was observed withFicus. The changes of partial molar free energy (G ^o _tr), enthalpy (H ^o _tr), and entropy (S ^o _tr) for the phase transfer of 4-NP also depended on sorbate concentration: H ^o _tr and S ^o _tr were negative and steeply decreased at high sorbate concentrations. This is due to solute-solute interactions replacing solute-cutin interactions at high concentrations resulting in solid precipitates of solute within the cutin matrix. This formation of ordered solid domaines starting from a small number of nonelectrolyte molecules interacting with the cutin is proposed as a model for the intracuticular deposition of SCL.Abbreviations CM cuticular membrane - MX polymer matrix membrane - 4-NP 4-nitrophenol - SCL soluble cuticular lipids     

Solution properties of synthetic polypeptides. XII. Enthalpy changes accompanying helix-coil transition of polypeptide

For helix-coil transitions of polypeptide in binary mixtures consisting of helix-forming solvent and coil solvent, the transition enthalpy ΔH(T,x) has been found to depend significantly on temperature (T) and solvent composition (x). For such systems, calorimetric measurements may yield some averages of ΔH(T,x) which are no longer amenable to direct comparison with ΔH itself. Theoretical equations relating calorimetric data to ΔH(T,x) are derived and tested favorably with experimental data. It is demonstrated that the transition enthaply from heat capacity measurements is approximately equal to ΔH_cfm, while those from heat of dilution and heat of solution measurements are equal to ΔH_c. Here ΔH_c denotes the value of ΔH at the transition point and f_m represents the maximum helical content attained in a thermally induced transition. The discrepancies among calorimetric data are also discussed.     

Salt dependence and ion specificity of the coil–helix transition of furcellaran

The conformational transition and the cation-binding properties of aqueous furcellaran (a gel-forming, low-sulfated polysaccharide of the carrageenan family) in various salts and salt mixtures was studied by optical rotation and by ¹³³Cs-nmr. The results were compared with theoretical predictions based on the Poisson–Boltzmann cell model (PBCM). The conformational transition of furcellaran occurs in a single step, which implies a nonblocklike distribution of sulfate groups along the polymer chain. The chloride salts of sodium, lithium, and tetramethylammonium are equally potent in inducing helix formation of furcellaran, indicating that these ions act by nonspecific electrostatic interactions. In contrast, the potassium and cesium ions specifically promote helix formation and aggregation (gelation) of furcellaran. The divalent calcium and magnesium ions are nonspecific, but more potent than the nonspecific monovalent ions in inducing helices. Anions differ in their capacity to stabilize the furcellaran helix in the sequence Cl^? < NO < Br^? < SCN^? < I^?. The iodide and thiocyanate anions impede aggregation and gel formation. ¹³³Cs-nmr chemical shifts indicate specific binding of cesium ions to the furcellaran helix. Thus, with respect to its ion specificity and ion-binding properties, furcellaran, with 0.6 sulfate group per repeating disaccharide, resembles κ-carrageenan (1 sulfate/disaccharide) but differs from ι-carrageenan (2 sulfates/disaccharide). The conformational transition temperatures of furcellaran are, however, generally higher than those of κ-carrageenan under comparable conditions, and in mixtures of the two polysaccharides, separate transitions still occur, indicating that no mixed helices are formed. The observed ion sensitivity and cation-binding properties of furcellaran agree with predictions, by the PBCM, for a K-carrageenan with a reduced charge density.