Water and polymer dynamics in a model polysaccharide hydrogel: the role of hydrophobic/hydrophilic balance

Abstract

The molecular dynamics of water and a polymer matrix is here explored in a paradigmatic model of a polysaccharide hydrogel, by the combined use of UV Raman scattering and infrared measurements. The case example of cyclodextrin nanosponges (CDNS)/hydrogel is chosen since the simultaneous presence in the structure of the polymer matrix of both hydrophilic and hydrophobic sites mimics the complexity of polysaccharide hydrogels. In this way, the contributions provided by the balance between the hydrophilicity/hydrophobicity and the grade of entanglement of the polymer hydrogel to lead to the formation of the gel phase are separately accounted and evaluated. As main results, we found that the hydrophobic CH groups inserted on the aromatic ring of CDNS experience a more pronounced dynamic perturbation with respect to the carbonyl groups due to the collision between the solvent and vibrating atoms of the polymer. The overall results provide a detailed molecular picture of the swelling phenomena occurring when a chemically cross-linked polymer contacts with water or biological fluids and exploits the potentiality of UV Raman spectroscopy to retrieve dynamic information besides their structural counterpart obtained by the classical analysis of the basic features of vibrational spectra.

Guest–matrix interactions affect the solvation of cyclodextrin-based polymeric hydrogels: a UV Raman scattering study

“…As was previously reported 14,29 , the Raman spectra of NS hydrogels in this spectral region mainly display the vibrational signatures of the molecular moieties belonging to the PMA residues that compose the polymeric network of NS. 14,38 A comparison between the Raman spectra of NS hydrogels with and without the addition of Caf (inset of Fig.…”

“…[10][11][12] Besides these practical aspects, hydrogels are interesting model systems for studying the role of hydrophobic and hydrophilic interactions in determining the gelling behaviour of biomacromolecules. This has been recently shown in the case of polysaccharidebased hydrogels, which are characterized by the presence in their polymeric backbone of both hydrogen bond donor and acceptor groups, [13][14][15] around which water can be rearranged in different ways. It is well known that important chemical and physical properties of hydrogels are determined, at the molecular level, by both structural features of the hydrogel matrix (e.g., the density of cross-links) and intermolecular interactions such as hydrophobic associations and hydrogen bonds.…”

“…The study was performed on two types of NS, which were obtained by varying during the synthesis the molar ratio of cyclodextrin to the cross-linker. This choice was made on the basis of structural knowledge of the polymeric network of NS 14,15,30 and by considering previous results for the diffusivity of guest molecules inside NS gels. 31 Finally, the analysis of the thermal dependence of dynamical Raman parameters such as the dephasing time can be correlated with the mechanism of the release of Caf from NS hydrogels in response to external stimuli such as variations in temperature.…”

“…[23][24][25][26] Additional uses of NS in agriculture 27 and environmental control 28 are also reported in the literature. A description of the gelling behaviour of NS hydrogels in terms of their structural and dynamical properties has been provided in some recent works, [13][14][15]29 mainly via the analysis of vibrational spectra. These studies suggest that the hydration of NS and the viscosity of the gel phase can be tuned by controlling specific factors during the synthesis of NS 15,30 and by regulating the hydration level 14 and the pH of the system.…”

“…The isotropic Raman spectra were fitted using a combination of Kubo-Anderson functions, following the steps described in detail by Rossi et al 14,29 For Raman peaks that were found to be approximated by a Lorentzian function, the corresponding dephasing time t deph was computed using the relation:…”