Vibrational spectroscopy investigation of swelling phenomena in cyclodextrin nanosponges (original) (raw)
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Physical chemistry chemical physics : PCCP, 2015
A detailed experimental and theoretical vibrational analysis of hydrogels of β-cyclodextrin nanosponges (β-CDNS), obtained by polymerization of β-cyclodextrin (β-CD) with the cross-linking agent ethylenediaminetetraacetic acid (EDTA), is reported here. Thorough structural characterization is achieved by exploiting the complementary selection rules of FTIR-ATR and Raman spectroscopies and by supporting the spectral assignments by DFT calculations of the spectral profiles. The combined analysis of the FTIR-ATR spectra of the polymers hydrated with H2O and D2O allowed us to isolate the HOH bending of water molecules not involved in symmetrical, tetrahedral environments. The analysis of the HOH bending mode was carried out as a function of temperature, showing the existence of a supercooled state of the water molecules. The highest level of cooperativity of the hydrogen bond scheme was reached at a value of the β-CD/EDTA molar ratio n = 6. Finally, the connectivity pattern of "unco...
Journal of Raman Spectroscopy, 2013
The vibrational dynamics of a new class of cross-linked polymers obtained from both native and modified cyclodextrin, referred to as cyclodextrin nanosponges, is here investigated. The main purpose is to spot the structure of these materials at molecular level unlikely to be characterized by diffraction methods due to the low or null degree of crystallinity. The analysis of the spectral features of the vibrational bands observed between 1650 and 1800 cm À1 in both Raman and infrar Q3 ed spectra, and assigned to the carbonyl stretching modes of the polymeric network, is performed by using band deconvolution procedures. At the same time, a detailed inspection of the low-wavenumber vibrational dynamics of these polymers is carried out, focusing on the modifications occurring on the so-called boson peak.
Hydrogen-bond dynamics of water confined in cyclodextrin nanosponges hydrogel
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2014
Cyclodextrin nanosponges (CDNS) are a very promising class of cross-linked polymers, made up of cyclodextrins. CDNS swollen in aqueous solution give rise to cyclodextrin-based hydrogel in different states-gel or liquid suspension-depending on the hydration level of the system. Here we present a thorough inspection of the vibrational dynamics of these hydrogel by Raman scattering experiments, with the aim of clarifying the role played by the hydrogen-bond dynamics of water molecules confined into the nano-sized pores of nanosponges in determining the rigidity of the hydrogel network and their maximum water-holding capacity. Changes occurring in the spectral shape of the OH stretching band of water were interpreted by accounting the connectivity pattern of water molecules concurring to the gelation process. Spectral deconvolution analysis gives evidence of the existence of a characteristic cross-over hydration level associated to the rearrangement of water molecules in more cooperative, bulk-like networks as a consequence of saturation sites of water confinement of nanosponges. This interpretation is further confirmed by the inspection of the estimated collective intensities. These findings also support the existence of a specific phase diagram of the cyclodextrin nanosponges hydrogel, where the molecular structure of the crosslinking agent used during the synthesis of nanosponge plays a fundamental role in defining the nano-and microscopic properties of the system.
Food Biophysics, 2010
Depolarized low-frequency Raman spectra from several cyclodextrin-water solutions have been investigated as a function of both temperature and macrocycle concentration. The differences between the vibrational spectra of solutions and pure water have been discussed, focusing the attention on the modifications of the vibrational bands assigned to the H-bond bending and stretching intermolecular modes of water. These features are in turn related to the structural changes occurring in the H-bonded water molecules allowing us to evince a destructuring effect on the tetrahedral hydrogen bonding arrangements induced in solution by increasing temperature and solute concentration.
The Journal of Physical Chemistry B, 2012
The vibrational dynamics of cyclodextrin nanosponges (CDNS), a new class of nanostructured soft materials synthesized via cross-linking reaction of natural cyclic oligosaccharide β-cyclodextrin (β-CD) with suitable organic reagents, is investigated by means of the combined use of Raman and infrared spectroscopy, supported by numerical simulations. The vibrational spectra of the polymers show significant changes in the frequency ranges 3000−3700 and 1500−1800 cm −1 correlated to the relative amount of cross-linker with respect to monomeric CD. By using band deconvolution and best-fit procedure of the experimental data and quantum chemical computations, a correlation between such changes and the degree of cross-linking of the polymeric network is proposed. This experimental−numerical approach, here applied to a model class of nanoporous polymeric systems, appears to be of general application for the study of polymeric matrixes of interest for biolife applications.
Soft Matter, 2013
The vibrational dynamics of a new class of cyclodextrin-based hydrogel is explored in depth here with the aim to clarify the intimate relationship between the structural and functional properties of these innovative polymeric materials. The thorough quantitative analysis of the FTIR-ATR and Raman spectra of the hydrogel obtained by swelling of cross-linked polymers of cyclodextrins with heavy water is performed in the wavenumber range between 1600 and 1800 cm À1 by using best-fitting and deconvolution procedures. The use of D 2 O instead of H 2 O allowed us to separately examine in the vibrational spectra of the hydrogel the C]O stretching bands assigned to the polymer network and the bending mode of engaged water molecules, giving the possibility to explore the structural changes occurring in the polymer network during the hydration process. The experimental findings were interpreted in the light of a comprehensive model which attempts to understand how physical and covalent cross-links combine to determine the macroscopic properties of the gel, like its water holding capacity and the whole rigidity of the gel network. These results shed light on the complex interplay between physical and chemical interactions which yield the formation and stabilization of the hydrogel network, opening the possibility of a rational design of these innovative soft materials for specific technological applications.
Vibrational spectrum of water confined in and around cyclodextrins
Chemical Physics Letters, 2011
The effects of a-, band nd c-cyclodextrins (ACD, BCD, and GCD) on the low-frequency vibrational spectrum of water present around them and those confined inside their cavities have been investigated from molecular dynamics simulations. Attempts have been made to understand the effects of variation of the number of glucose rings and the ability of these macromolecules to form hydrogen bonds with water on the distribution of the vibrational density of states of water. It is observed that these bands for water in and around the cyclodextrins suffer blue shifts, the extent of the shifts are sensitive to the degree of confinement within the cavities and their hydrogen bonding status.
Gel-sol evolution of cyclodextrin-based nanosponges: role of the macrocycle size
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2014
The effect of the macrocycle size on the gel-tosol evolution of cyclodextrin-based hydrogel is here investigated by using Fourier transform infrared absorption in attenuated total reflectance geometry (FTIR-ATR). Different types of nanosponges obtained by polymerization of aand b-cyclodextrin (CDNS) with an activated derivative of ethylenediaminetetraacetic acid have been progressively hydrated in order to follow the evolution of these systems from a gel state to a liquid suspension. The in deep analysis of the high-frequency vibrational dynamics of the hydrogel during its gel-sol evolution revealed that the microscopic origin of this phenomenon is strictly connected to different hydrogen bond environments in which water molecules confined in the pores of nanosponges can arrange. By following a well consolidated approach, the OH stretching band of water, clearly observed in the high-frequency range of the vibrational spectra of nanosponges hydrogel, has been decomposed into sub-bands assigned to different arrangements of water molecules at various degrees of cooperativity. A comparison of the diagrams obtained for homologous CDNS prepared from aand b-CD shows how the size of cyclodextrin macrocycle allows to efficiently modulate the gelation points at constant cyclodextrin/crosslinker molar ratio n.
Hydrogen bonding dynamics of cyclodextrin-water solutions by depolarized light scattering
Journal of Raman Spectroscopy, 2011
Depolarized light scattering measurements performed on aqueous solutions of α-cyclodextrin are used for investigating the hydration properties of this natural cyclic oligosaccharide, which is well known for its ability to form inclusion complexes with a large variety of guest hydrophobic molecules. The spectral analysis allows the characterization of the solvent relaxation process assigned to hydration water, which is found to be seven to eight times slower than the bulk. As a structural information, the number of water molecules involved in the hydration process is also estimated at about 46. These results are a key step for understanding the role played by water in determining the properties of different forms of cyclodextrins and their derivatives, in turn related to complexation ability of these macrocycles.