Small-angle X-ray scattering reveals hollow nanostructures in ι- and κ-carrageenan/surfactant complexes

Abstract

Complexes of polyelectrolyte gels with oppositely charged surfactants form ordered polymer matrices with unique structure properties, which can be used in a wide range of medical, chemical and physical applications. Ordered matrices made of natural components are of special interest for medical and biological purposes. In the present study, self‐organised complexes of native ι‐ and κ‐carrageenans formed with oppositely charged cetylpyridinium chloride (CPC) are prepared and structurally characterised using small‐angle X‐ray scattering (SAXS). Starting from the molar ratio CPC/(charge of carrrageenan) of 0.2, the carrageenan gel shrinks and ordered motifs in its internal structure are formed. The internal order in the sample is reflected by the Bragg peaks in the scattering patterns which permit to compute periodicity and characteristic sizes of the ordered regions. Moreover, strong central scattering appears and the calculated fractal dimensions indicate that these regions are organised in well defined clusters. The periodicity of the ordered motifs computed from the Bragg peaks in the scattering patterns corresponds to the width of the surfactant bilayer (about 4.0 nm) for all the complexes. The crystallite size ranges from 25 nm to 40 nm depending on the type of carrageenan and on the amount of CPC. A model of the ordered fragments is proposed whereby the carrageenan/surfactant bilayers are regularly packed at the walls of hollow cylindric clusters with the outer radius of about 8 nm and height 40 nm. More detailed ab initio models indicate that these particles are formed by bent worm‐like substructures with the cross‐section coinciding to the thickness of the carrageenan/CPC bilayer. Thanks to a higher charge density per monomer, ι‐carrageenans form more regular structures than κ‐carrageenans.

Structural and thermal study of mesomorphic dodecylammonium carrageenates

“…WAXD patterns of all (DDA) n CAR with the 1:2 relationship of the reciprocal interplanar spacing of two small-angle maxima indicated their lamellar ordering. Similar second order diffraction maximum, suggesting lamellar type of ordering, has been also observed in the small-angle X-ray scattering (SAXS) patterns of κC and ιC complexes with cationic surfactants [23][24][25][26][27].…”

“…Formation of giant vesicles even at low carrageenan concentrations [7,8] and structural properties of collapsed gels [23] revealed lamellar ordering as an important feature of the dodecylammonium and carrageenan systems. In several papers Reynaers et al [24][25][26][27] have shown that interaction of carrageenan gels with a cationic surfactant cetylpyridinium chloride (CPC) leads to the formation of a lamellar arrangement. Structural investigations of the carageenan and CPC at gelling conditions during reversible heating and cooling cycles have shown that no structural transition are seen in the temperature range between the room temperature and 70 o C [25].…”

Testing Classical Approach to Polymer Solutions on SAXS Data of λ-Carrageenan, κ-Carrageenan and Methylcellulose Systems

“…1,2 Although KC and MC are very similar in structure, their gelling mechanisms differ significantly and have been extensively studied in the case of both polymers. [3][4][5][6][7] It is namely generally accepted that the gelation of KC is a two-step process, where initially the transition from coils to double helices occurs with cooling and with further reduction of the temperature the double helices start to crosslink and form a three dimensional network. This results in the formation of an elastic gel.…”

“…Their presence reduces repulsion between helices therefore a denser network and consequently a much stronger gel is formed. 6 On the other hand, the mechanism of gelation of MC is explained by the three types of interactions: (i) the intramolecular hydrogen bonds between unmodified hydroxyl groups on the polymer chain, (ii) the hydrogen bonds between the hydroxyl groups on polymer chain and the solvent and (iii) the hydrophobic effect, due to the nonpolar nature of MC chains. Gel starts to form at higher temperatures when the hydration cage around MC chains starts to collapse and enables cross-linking between polymer chains and the formation of network due to the hydrophobic association.…”

Structure and Properties of Iron Oxide Nanoparticles Encapsulated by Phospholipids with Poly(ethylene glycol) Tails

“…[40][41][42] In particular, ab initio methods for low-resolution model using SAXS data (e.g., program DAMMIN) 43 were successfully employed for metal-containing polymers. 41,44,45 In the present article, this and other novel methods for SAXS data analysis originally developed for biological systems are for the first time used to build structural models of iron oxide nanoparticles coated with PEGylated phospholipids. Magnetic properties of the samples were also measured and support the conclusions from the SAXS modeling.…”