Room temperature, low-field 13C-n.m.r. spectra of degraded carrageenans: Part III. Autohydrolysis of a lambda carrageenan and of its alkali-treated derivative

Autohydrolysis of lambda and theta carrageenans produces degraded products which are useful for 13C-n.m.r. spectroscopy, with low-field equipment and at room temperature. Data obtained from these spectra are doubly valuable as they are used for the structural study of parent carrageenans and to investigate the reactions carried out during autohydrolysis.

"Flip-flop" orientation of agarose gel fibers in pulsed alternating electric fields

The orientation of the agarose gel matrix in pulsed electric fields has been studied by transient electric birefringence. Two types of agarose with different degrees of charge were studied, in addition to agarose solutions and gels containing beta-carrageenan, a stereoisomer of agarose, and polyacrylamide. Agarose gels exhibit normal orientation behavior when short, high voltage pulses are applied to the gel. The sign of the birefringence is positive and the relaxation times are consistent with the orientation of dangling fiber ends parallel to the electric field. When long, low voltage pulses, of the amplitude and duration used for pulsed field gel electrophoresis, are applied to the gel, completely different orientation effects are observed. The amplitude of the birefringence (i.e., extent of orientation) is much larger than expected from the high field results, and the birefringence decay curves contain multiple components of opposite sign. The relaxation times are consistent with the orientation of long agarose chain bundles or fibers, as well as large three-dimensional domains. Chain bundles or fibers of the lengths observed in the agarose gels are also observed in agarose solutions, suggesting that the fibers that are free to orient in the gels had previously formed in the sol phase and are only weakly integrated into the matrix structure. In rapidly reversing low voltage electric fields, the sign of the birefringence of the agarose gels reverses from positive to negative in phase with the reversing electric field. This alternating change in the sign of the birefringence suggests that the agarose fibers "flip-flop" in orientation from parallel to perpendicular every time the electric field reverses its direction. Similar effects are observed for agarose gels with different charge densities. The flip-flop orientation and reorientation of agarose fibers within the matrix in reversing electric fields may decrease the microscopic viscosity of the gel, increasing the mobility of large DNA molecules migrating through the gel during electrophoresis. Polyacrylamide gels do not exhibit an anomalous reversal of the sign of the birefringence in reversing electric fields. Hence, the orienting fibers in these gels do not change their direction of orientation in reversing electric fields. Extensive orientation is observed in beta-carrageenan gels, similar to that observed in agarose gels. However, little orientation occurs in polyacrylamide gels, which are chemically crosslinked.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for double helical kappa-carrageenan in aqueous LiI-solution and model for iodide binding

NMR experiments with a 21412 Redfield observation pulse were carried out on a kappa-carrageenan aqueous solution containing 0.5M LiI. A detected hydrogen-bonded proton resonance at approximately 17.6 ppm, is in accordance with an ordered carrageenan structure in the solution similar to the double, parallel-stranded helix with interstrand hydrogen-bonds found in the condensed state by R.P. Millane, R. Chandrasekaran, S. Arnott, and I.C.M. Dea (Carbohydr. Res. 198, 1 1988). Starting with the published iota-carrageenan coordinates obtained from the Brookhaven Databank, we modelled this kappa-carrageenan structure by the molecular modelling software INSIGHTH-II. The kappa-carrageenan double-helix has a wide interior that can accommodate iodide. Conversely, the iota-carrageenan double-helix has a narrow interior not suited for a large ion like iodide. We propose that the detected selective iodide binding sites in the ordered kappa-carrageenan structure (H. Grasdalen, and O. Smidsrød, Macromolecules 14, 1842 1981) could very well be in the interior of the double-helix.

Macrocyclization of polysaccharides visualized by electron microscopy

Topological features of the polysaccharides schizophyllan, l-carrageenan and gellan gum were studied using electron microscopy. Electron micrographs of schizophyllan not subjected to any thermal or solvent composition history destabilizing the triple helix, show stiff, linear chains consistent with the structure being triple helical and with contour length proportional to the molecular weight in solution. A blend of linear, cyclic and hairpin topologies and higher molecular weight clusters were observed after renaturation, i.e. return to conditions favouring the triple helical structure, from solvent conditions dissociating the triple helix. Electron micrographs of l-carrageenan in salt-free solution reveal linear extended structures. Addition of 0.15 M LiI to the solution before preparation for electron microscopy, i.e. salt conditions that favour ordering but not gelation, yields a large fraction of cyclic structures with circumference of different lengths. Likewise, adding KCl to aqueous gellan gum changes their appearance from dispersed polymers to suprastrands with several associated chains. Macrocyclic species can also be observed in gellan gum after the addition of a gel-promoting salt. The tendency to form macrocyclic structures in competition with intermolecular aggregates is determined by the three factors: (1) chain stiffness relative to overall length; (2) parallel or antiparallel alignment of interacting chain segments; and (3) polymer concentration. The present study indicates that electron microscopy provides information about the topology adopted by polysaccharides.

Conformational features of carrabiose polymers: I. Configurational statistics of kappa-carrageenan

Potential energy functions evaluating both repulsive-attractive van der Waals non-bonding interactions and electrostatic interactions have been used to evaluate the conformational energies of the repeating units of the kappa-carrageenan polymers. Structural parameters have been obtained by minimization MNDO procedures (MOPAC). Energy maps have been calculated for the (1-3) alpha-D-galactose-4-sulphate (GS) and the (1-4)-3,6-anhydro-alpha-D-galactose (A) residues, taking into account the conformational freedom of the sulphate group. The configurational statistics of the random coiled kappa-carrageenan chain have been explored, disclosing a highly flexible character, which can mainly be ascribed to the random occurrence of two different conformers of the GS-A dimeric unit.

Determination of the structures of cystocarpic carrageenans from Gigartina skottsbergii by methylation analysis and NMR spectroscopy

The combined use of methylation analysis and high-field 1H and 13C NMR spectroscopy allows the determination of the fine structure of the carrageenans produced by the cystocarpic stage of Gigartina skottsbergii.

The effect of gel structure on matrix orientation

Four polymeric gels of different structure, low electroendosmosis (LE) agarose, highest electroendosmosis (HEEO) agarose, beta-carrageenan, and polyacrylamide, were studied by transient electric birefringence to determine the importance of various structural features on the orientation of the gels in an electric field. The two types of agarose, but not the polyacrylamide or beta-carrageenan, exhibited anomalous orientation effects. Both agarose and beta-carrageenan exhibited large birefringence signals, suggesting that the noncovalent hydrogen bonds joining the agarose fibers within the matrix allow the high degree of orientation of the gel. The spatial arrangement of the sugars of the agarose backbone is necessary for the anomalous orientation effects in reversing electric fields.

Mechanical properties of hydrocolloid gels filled with internally produced carbon dioxide gas bubbles

Agar (2%), alginate (1% algin), and kappa-carrageenan (1.5%) gel specimens were prepared from mother solutions that contained 0-2.5% sodium bicarbonate (agar and carrageenan) or calcium carbonate (alginate). Upon immersion in a citric acid bath (0-2%), the carbonate reacted with the diffusing acid to produce numerous carbon dioxide bubbles. The compressive strength and deformability of the gas-filled gels so produced were determined using a Universal testing machine and compared with those of pure gels and gels containing the carbonate but not subjected to the process after various immersion times. While the agar and alginate gels retained considerable mechanical integrity even after several hours, the carrageenan gels disintegrated after about 2-5 h. Under similar conditions, the number of bubbles produced in the agar gels was about twice that in the alginate gels, an observation that cannot be explained solely by stoichiometric considerations.

Screening of whole-cell immobilization procedures for the Δ1-dehydrogenation of steroids in organic medium

Different whole-cell immobilization methods and conditions were tested for the delta 1-dehydrogenation of 6-alpha-methyl-hydrocortisone-21-acetate with Arthrobacter simplex cells, in n-decane-1-ol and chloroform. Among the entrapment methods, polyurethane foams gave the best productivity of n-decane-1-ol, but could not be used in chloroform. Partition and diffusional barriers appeared to be the factors limiting productivity in entrapped-cell systems. The coentrapment of enzyme-stabilizing (glycerol, sucrose, sodium sulfate, monosodium glutamate) or hydrophobic additives did not significantly improve dehydrogenation rates in chloroform, although in some cases higher activities resulted in n-decane-1-ol. Dehydration of kappa-carrageenan-immobilized cells lowered the productivity in both solvents. The use of cell adsorption methods on silica-based carriers produced biocatalysts that in some cases were more active in chloroform than the entrapped cells. However, the surface-attached cells appeared to be more sensitive to solvent toxicity, more hydrophilic supports generally giving higher dehydrogenation rates. The estimated partition coefficients for the substrate between several of the tested supports and the two solvents are also presented. High partition ratios followed high measured activities in entrapment matrices but not in Celite (cell adsorption matrix). Activities in chloroform were always very low (less than 1 mumol product per hour and gram of cell dry weight). Polyurethane entrapment with n-decane-1-ol as a reaction medium was the most promising system, with measured dehydrogenation rates up to 40 times higher.

The use of neocarrabiose oligosaccharides with different length and sulphate substitution as model compounds for 1H-NMR spectroscopy

The high-field 1H-NMR spectra of various carrageenan oligosaccharides at room temperature are given. The assignments were faciliated by the use of proton double-quantum coherence (DQCOSY) and 1H-13C chemical shift correlation 2D NMR spectroscopy, and by comparing high-field 1H-NMR spectra of various 4-sulphated oligosaccharides of the neocarrabiose type. The effects of anomeric configuration on the 1H resonances on the same or neighbouring units are discussed. The 13C-NMR shift data are given for the tetrasaccharide of kappa-carrageenan.

Computer modeling of polysaccharide-polysaccharide interactions: an approach to the kappa-carrageenan-mannan case

A computer program SAINT has been developed for the investigation of the structure and for the prediction of minimum-energy structure of polysaccharide-polysaccharide complexes. The energy minimization is carried out on internal geometrical parameters--namely bond angles, torsional angles, and five parameters describing the mutual orientations of polysaccharide chains. For this purpose, the nonderivative method of conjugated directions is used. This procedure was applied to computer modeling of an idealized model of the binary gelling kappa-carrageenan and galactomannan system. It is shown that the interaction between two chains influences the structure of the individual polysaccharide molecule and that in the minimum-energy structures of the complex, the conformation of the chains does not correspond to the lowest energy.

Room temperature, low-field 13C-n.m.r. spectra of degraded carrageenans. Part II. On the specificity of the autohydrolysis reaction in kappa/iota and mu/nu structures

A kappa/iota carrageenan from Gigartina skottsbergii and a partially cyclized mu/nu carrageenan from Iridaea undulosa were submitted to autohydrolysis. The 13C-n.m.r. spectra of the degraded products give structural information on the polysaccharides and show clearly that besides the known splitting of 3,6-anhydrogalactosidic linkages, the linkage between alpha-D-galactose 2,6-disulphate and beta-D-galactose 4-sulphate is cleaved with similar specific reaction rate.

Molecular characterisation of kappa- and lambda-carrageenan by gel permeation chromatography, light scattering, sedimentation analysis and osmometry

Gel permeation chromatography, in conjunction with a double detection system involving a low angle laser light scattering apparatus (LALLS) and a refractive index monitoring device (RI), has been used to obtain both the molecular weight and the molecular weight distribution of sodium salts of kappa-carrageenan and lambda-carrageenan in saline solutions. The results, Mw and Mn, are in excellent agreement with independent determinations of molar mass based on static light scattering experiments, sedimentation-diffusion analysis and osmometry. The relevance of the data is discussed with respect to current problems in carrageenan research.

Room temperature, low-field 13C-n.m.r. spectra of degraded kappa/iota carrageenans

Using samples previously degraded by autohydrolysis, it is possible to obtain valuable low-field 13C-n.m.r. spectra of samples of kappa/iota carrageenans at room temperature. Spectroscopy of samples extracted at different stages of autohydrolysis helps to determine the mechanism of the reaction and the presence of low proportion kinks and other irregularities in the molecules.

Molecular transforms of kappa carrageenan and furcellaran from mixed gel systems

X-ray fibre diffraction studies of furcellaran-carob, furcellaran-tara, and furcellaran-konjac mannan mixed gels have failed to reveal any evidence for the predicted intermolecular binding between the algal polysaccharide helix and the galactomannan or glucomannan (konjac) mannan). In the absence of such interactions, mixed gels of kappa carrageenan-konjac mannan and furcellaran-konjac mannan, have been used to obtain good quality molecular transforms of the kappa carrageenan and furcellaran molecules in an oriented nematic liquid crystalline form. Analyses of the pattern support double helix structures with threefold symmetry with helix pitch of 2.5 nm. The absence of a 0.83 nm meridional in kappa carrageenan necessitates zero axial translation from the exact half-stagger position, contrary to the model building prediction. An axial translation from half-stagger is necessary for furcellaran.

Dynamic light scattering by kappa- and lambda-carrageenan solutions

The intensity correlation functions of kappa- and lambda-carrageenan in various salt solutions and at different concentrations have been determined with the help of dynamic light scattering. From the first cumulant of these correlation functions the values of the translational diffusion coefficients D have been derived. They increase with macromolecular concentration. The extrapolated values to infinite dilution of the diffusion coefficients increase with increasing salt concentration as expected from the salt concentration dependence of the r.m.s. radii of gyration determined previously by static light scattering. The translational diffusion coefficient of lambda-carrageenan in 0.1 M NaCl is smaller than the corresponding value for the kappa species. This is consistent with the difference in contour length and linear charge density of the two samples used. No satisfactory interpretation for the concentration dependence of the diffusion coefficient seems to be possible at present. Although current theories for the macromolecular and salt concentration dependence of D, taking into account charge effects, seem to be applicable, they do not allow for a consistent interpretation of the data. No specific difference between the solution behaviour of kappa- and lambda-carrageenan has been detected.

Synthesis and conformational studies of carrabiose and its 4'-sulphate and 2,4'-disulphate

Methyl alpha-carrabioside (13), and its 4-sulphate (19) and 2,4-disulphate (20) have been synthesised via glycosylation of methyl 3,6-anhydro-2-O-benzyl-alpha-D-galactopyranoside with 2,3,6-tri-O-acetyl-4-O-benzyl-beta-D-galactopyranosyl bromide and subsequent partial or complete debenzylation, sulphation, and deprotection of the resulting disaccharide derivatives. Conformational studies have been carried out on 13, 19, and 20 on the basis of 1D and 2D 1H-n.m.r. spectroscopy and molecular mechanics calculations.

Molecular structure of 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (neocarrabiose) in the solid state and in solution: an investigation by X-ray crystallography, n.m.r. spectroscopy, and molecular mechanics calculations

The crystal structure of neocarrabiose monohydrate, 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (C12H20O10.H2O) belongs to the monoclinic space group P2(1), and has a unit cell of dimensions a = 6.351(1), b = 7.675(2), c = 15.096(8) A, and beta = 91.11(1) degree. The reducing unit is in the 4C1 conformation, the non-reducing residue is 1C4, with the 3,6-anhydro bridge in an E conformation, and HO-6 is in a gauche-trans conformation. The orientation about the (1----3) linkage is defined by phi = 94.5 degrees and psi = 141.9 degrees. There is an intramolecular hydrogen bond (O-5'...O-2 = 2.777A). The conformation of the pyranose rings in solution, derived from 3JH.H values, were not significantly different from those in the crystal, but the 3,6-anhydro bridge assumed a half-chair conformation. All these features have been rationalised through molecular modelling and computation of potential energy surfaces.

87Rb+ spin relaxation in enzymically purified and in untreated iota-carrageenan

The temperature dependences of the transverse (R2) and longitudinal (R1) n.m.r. relaxation rates of 87Rb+ in aqueous 5% iota-carrageenan have been compared with similar data for a sample purified by treatment with kappa-carrageenase. In each sample, the relaxation rates were sensitive to the conformation (helix or random coil). In the intact sample, the small (less than or equal to 5%) fraction of kappa-carrageenan (which, in its helical state, specifically binds rubidium ions) was solely responsible for the pronounced line-broadening that has been observed hitherto for 87Rb in iota-carrageenan gels. In the purified sample, the effects on the relaxation of 87Rb induced by iota-carrageenan are similar to those found in comparable systems in the absence of site-binding of the ions. Thus, there was a modest enhancement of the relaxation with R1 approximately R2 for the flexible coil conformation and a comparably larger effect, with significant contributions from dynamic processes on the time-scale of the inverse resonance frequency or longer, for the thicker, more highly charged and rigid helix conformation of iota-carrageenan.

N.m.r. studies of synergistic kappa carrageenan-carob galactomannan gels

C-n.m.r. spectroscopy has been used to investigate the carob galactomannan-kappa carrageenan binary gels. Starting from partially depolymerized carob samples, evidence for interaction and intermolecular binding was found by analysis of the spectra obtained in quantitative conditions and in the absolute intensity mode. From these, a reconstitution of the signals corresponding to C-1, C-4, C-5 and C-6 showed the existence of three kinds of galactomannan chains; the first ones with a low galactose content were strongly connected and as such had completely lost their mobility; but the chains with a high galactose content were still detected and could be divided in two groups according to their mobility.

Molecular structure of carrageenans and kappa oligomers: a Raman spectroscopic study

The Raman spectra of kappa and iota carrageenan, a desulphated furcellaran and a series of oligomers have been compared in the region 700-1500 cm-1. Spectral differences depending on the amount and the location of the sulphate group on the ring, the chain length, the nature of the counterion and the conformation are discussed. Indications that the ionic interactions in the Na+ salts of the oligomers are different from those in K+ and Rb+ salts are given. On the macromolecular level it is found that the vibrational movements of the skeleton are related to the chain flexibility and the conformation. In gels of K+ and Rb+ kappa carrageenan spectral evidence is given for the existence of structural order.