Biomedical subjects

H Reynaers

Publications and source records attributed to H Reynaers.

10 recordsLinked to original sources

PubMed1998

Complex melting of semi-crystalline chicory (Cichorium intybus L.) root inulin.

When concentrated solutions (30-45% by weight) of inulin (degree of polymerization 2-66, number average degree of polymerization 12) are cooled at 1 degree C/min or 0.25 degree C/min from 96 degrees C to 20 degrees C, suspensions of semi-crystalline material in water are formed. A thermal nucleation process was detected by optical microscopy: the 8-like shaped crystallites resulting from primary nucleation at higher temperature are larger than those resulting from secondary nucleation at lower temperature. Differential scanning calorimetry (DSC) thermograms display melting profiles with three to four partly overlapping endotherms that vary as a function of concentration, cooling rate during crystallization and storage time at 25 degrees C of the crystallite suspension. Recrystallization during melting was observed. The wide-angle X-ray scattering patterns of the samples at 25 degrees C correspond to those of the hydrated crystal polymorph. The structural changes during melting indicated the existence of a single crystal polymorph throughout melting. A periodicity of 95 A, arising from alternating regions of different electron density, is detected in the small angle X-ray scattering patterns at 25 degrees C. The stepwise increase of the long period upon heating is related to the existence of two types of lamellar stacks: one with a higher long period, resulting from the primary nucleation and thus crystallized at high temperature, and a second one with a smaller long period, formed by crystallization at lower temperature. The lamellae formed at low temperature melt at a lower temperature than those formed at high temperature, explaining the existence of the two DSC-endotherms.

Calorimetry, Differential Scanning↗

PubMed1996

Small-angle X-ray scattering of kappa- and iota-carrageenan in aqueous and in salt solutions.

Aqueous and saline (0.03-0.08 M NaCl) solutions of the Na(+)-salt of kappa- and iota-carrageenan (3-17 mg/ml) have been investigated using small-angle X-ray scattering (SAXS). Investigation of the SAXS curves normalized for concentration allows to detect the transition from the dilute to the semidilute regime. Some of the experimental curves exhibit a clear maximum. In the case of kappa-carrageenan, the position of this maximum is proportional to the cube root of polysaccharide concentration. The fluctuation theory of Borue and Erukhimovich (BE theory), which predicts a maximum in the scattering curves for low ionic strength, gives a good fit for all our experiments. An increase of the polymer concentration or the ionic strength causes the appearance of two subsystems in solution exhibiting a different characteristic screening scale of Coulombic interaction for ideal Gaussian chains (and two different segment lengths). The condition for an increase of the relative contribution of the subsystem with the larger segment length correlates with the one for the disorder-order transition of carrageenan. In the most concentrated (17.1 mg/ml) solution of Na(+)-iota-carrageenan, the increase of NaCl molarity above 0.06 M gives rise to additional scattered intensity at the smallest angles, indicating molecular association.

Carrageenan↗

PubMed1996

Influence of ionic effects on the ordering and association phenomena in dilute and semidilute carrageenan solutions.

A small angle X-ray scattering (SAXS) study was made on Na(+)-kappa- and Na(+)- or Li(+)-iota-carrageenan in aqueous solutions with and without added salt in the dilute (approximately 6 mg/ml) and semidilute (approximately 16 mg/ml) regime close to the critical concentration (approximately 9-11 mg/ml). This concentration should be understood to be determined by contacts between blobs rather than between isolated molecules. The SAXS data of carrageenan solutions are described in terms of the fluctuation model of Borue-Erukhimovich rather than by a particle-type model, although the latter form of scattering appears when aggregates of ordered fragments are formed. According to current models of carrageenan the ordered fragments are single or double chain helices. In conditions favorable for the appearance of the ordered conformation, two polymer subsystems with a different characteristic screening scale of Coulombic interaction for the ideal Gaussian chain are detected. The system with the larger characteristic screening scale corresponds to molecular fragments with an ordered conformation. The contribution of both systems to the scattering can be separated which allows for discussion of their behaviour in the framework of the fluctuation theory. The SAXS results suggest that in all dilute and in the semidilute solutions with added NaCl or LiCl for both kappa- and iota-carrageenans there is a transformation from short-length correlated (disordered) to longer-length correlated (ordered) molecular fragments followed by the association of the ordered fragments, whereas a transformation from an association of disordered fragments to a structure with ordered fragments is detected in semidilute solutions of Li(+)-iota-carrageenan in Li(+)-iota-carrageenan in LiI and Na(+)-kappa-carrageenan in NaI. In the semidilute solutions of Na(+)-iota-carrageenan in NaI the formation of ordered fragments seems to follow an intermediate sequence.

Carbohydrate Conformation↗

PubMed1991

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.

Carrageenan↗

PubMed1991

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.

Carrageenan↗

PubMed1973