Ultrasonic wave spectroscopy study of sugar oligomers and polysaccharides in aqueous solutions: The hydration length concept

Structural Behavior of Amphiphilic Triblock Copolymer P104/Water System

A detailed study of the different structural transitions of the triblock copolymer PEO₂₇-PPO₆₁-PEO₂₇ (P104) in water, in the dilute and semi-dilute regions, is addressed here as a function of temperature and P104 concentration (C_P104) by mean of complimentary methods: viscosimetry, densimetry, dynamic light scattering, turbidimetry, polarized microscopy, and rheometry. The hydration profile was calculated through density and sound velocity measurements. It was possible to identify the regions where monomers exist, spherical micelle formation, elongated cylindrical micelles formation, clouding points, and liquid crystalline behavior. We report a partial phase diagram including information for P104 concentrations from 1 × 10^-4 to 90 wt.% and temperatures from 20 to 75 °C that will be helpful for further interaction studies with hydrophobic molecules or active principles for drug delivery.

Relationships between Molecular Structure of Carbohydrates and Their Dynamic Hydration Shells Revealed by Terahertz Time-Domain Spectroscopy

Despite more than a century of research on the hydration of biomolecules, the hydration of carbohydrates is insufficiently studied. An approach to studying dynamic hydration shells of carbohydrates in aqueous solutions based on terahertz time-domain spectroscopy assay is developed in the current work. Monosaccharides (glucose, galactose, galacturonic acid) and polysaccharides (dextran, amylopectin, polygalacturonic acid) solutions were studied. The contribution of the dissolved carbohydrates was subtracted from the measured dielectric permittivities of aqueous solutions based on the corresponding effective medium models. The obtained dielectric permittivities of the water phase were used to calculate the parameters describing intermolecular relaxation and oscillatory processes in water. It is established that all of the analyzed carbohydrates lead to the increase of the binding degree of water. Hydration shells of monosaccharides are characterized by elevated numbers of hydrogen bonds and their mean energies compared to undisturbed water, as well as by elevated numbers and the lifetime of free water molecules. The axial orientation of the OH(4) group of sugar facilitates a wider distribution of hydrogen bond energies in hydration shells compared to equatorial orientation. The presence of the carboxylic group affects water structure significantly. The hydration of polysaccharides is less apparent than that of monosaccharides, and it depends on the type of glycosidic bonds.

Hydrophobicity of carbohydrates and related hydroxy compounds

The hydrophobic interaction of carbohydrates and other hydroxy compounds with a C18-modified silica gel column was measured with pure water as eluent, thereby expanding the range of measurements already published. The interaction is augmented by structure strengthening salts and decreasing temperature. Although the interaction of the solute with the hydrophobic interface is expected to only imperfectly reflect its state in aqueous bulk solution, the retention can be correlated to hydration numbers calculated from molecular mechanics studies given in the literature. No correlation can be established towards published hydration numbers obtained by physical methods (isentropic compressibility, O-17 NMR relaxation, terahertz spectroscopy, and viscosity). The hydrophobicity is discussed with respect to the chemical structure. It increases with the fraction and size of hydrophobic molecular surface regions.

Water mobility within arabinoxylan and β-glucan films studied by NMR and dynamic vapour sorption

BACKGROUND

The main purpose of this research was to determine the impact of the structure and organisation of polysaccharides on the hydration properties of the cell walls of cereal grains. In order to remodel the lamellar assembly of arabinoxylan (AX) and (1 → 3)(1 → 4)-β-D-glucan (BG) within the endosperm cell walls, films were prepared and analysed using dynamic vapour sorption and time domain nuclear magnetic resonance spectroscopy.

RESULTS

The water diffusivities within the AX and BG films were measured at 20 °C by observing the water sorption kinetics within a mathematical model based on Fick's second law. The evolution of spin-spin relaxation times of water protons measured by increasing the temperature is explained by the additional contributions of motion of the protons of polysaccharides and/or rapid chemical exchanges of protons between water and hydroxyl groups of polysaccharides.

CONCLUSION

The difference between patterns of water behaviour within the AX and BG films can be related to the difference in their nanostructures. The smaller nanopores of the BG films cause their nanostructure to be more compact.

Evaluation of polymer mucoadhesiveness by the use of acoustic spectroscopy

An innovative and simple methodology has been developed and used for the evaluation of mucoadhesive properties of several polymers by means of sound speed measurements using high-resolution acoustic spectroscopy. In systems made of polymers in water, variations in hydration shell of polymeric chains determine changes of dispersions compressibility, and this phenomenon can be monitored by sound speed measurements. Four different polymers have been selected, namely PEG 6000, Carbopol 974, HPMC K4M, and Pectin 200/USP, all characterised by very different mucoadhesive properties. Samples made of each polymer alone (0.3-1.0% w/w) or in mixture with mucin (mucin fixed at 1.0% w/w) in water were investigated while using high-resolution ultrasonic spectrometer at two different frequencies (5.2 and 8.2 MHz). Polymer-mucin interaction was evaluated comparing experimental sound speed values of polymer-mucin samples with their theoretical values derived from the addition of sound speeds obtained while analysing each component alone. Results demonstrated the ability of the acoustic method to discriminate between mucoadhesive and no mucoadhesive polymer-mucin dispersions and allowed also the comparison between their mucoadhesive strengths. The study has therefore demonstrated the potential of using high-resolution ultrasonic spectroscopy to evaluate the polymers' mucoadhesiveness, with the great advantage of testing small amount of samples even if opaque.

Monitoring the aggregation behaviour of self-assembling polymers through high-resolution ultrasonic spectroscopy

Poloxamer 407 is a well-known self-assembling polymer with a wide range of temperature- and concentration-dependent phase behaviour, such as micellization and gelation. This work was carried out to demonstrate the potential of high-resolution ultrasonic spectroscopy in evaluating aggregation-deaggregation behaviour of self-assembling polymers. In order to achieve this objective, six different concentrations of Poloxamer 407 water dispersion were prepared and analysed between 5 and 35 degrees C using ultrasonic spectroscopy. For comparison, the same samples were also analysed by the DSC technique. The results showed that polymer aggregation process can be successfully monitored using both ultrasonic parameters of sound speed and attenuation. Furthermore, good agreement with DSC data was observed in terms of characteristic transition temperatures and also in terms of micellization kinetics and related parameters.

Using Low-Field NMR To Infer the Physical Properties of Glassy Oligosaccharide/Water Mixtures

Low-field NMR (LF-NMR) is usually used as an analytical technique, for instance, to determine water and oil contents. For this application, no attempt is made to understand the physical origin of the data. Here we build a physical model to explain the five fit parameters of the conventional free induction decay (FID) for glassy oligosaccharide/water mixtures. The amplitudes of the signals from low-mobility and high-mobility protons correspond to the density of oligosaccharide protons and water protons, respectively. The relaxation time of the high-mobility protons is described using a statistical model for the probability that oligosaccharide hydroxyl groups form multiple hydrogen bonds. The variation of energy of the hydrogen bond is calculated from the average bond distance and the average angle contribution. Applying the model to experimental data shows that hydrogen atoms screen the water oxygen atoms when two water molecules solvate a single hydroxyl group. Furthermore, the relaxation time of the oligosaccharide protons is independent of its molecular weight and the water content. Finally, inversion of the FID using the inverse Laplace transform gives the continuous spectrum of relaxation times, which is a fingerprint of the oligosaccharide.

Conformational changes and aggregation of alginic acid as determined by fluorescence correlation spectroscopy

Insight into the conformations and aggregation of alginic acid was gained by measuring its diffusion coefficient at very dilute concentrations using fluorescence correlation spectroscopy. Both the pH and ionic strength (I) had an important influence on the diffusion coefficient of the polysaccharide. For pH, three effects were isolated: (i) below pH 4, the charge density decreased causing increased aggregation; (ii) between pH 4 and 8, a molecular expansion was observed with increasing pH, whereas (iii) above pH 8 some dissociation of the polymer was observed. Increasing I from 0.001 to 0.1 M resulted in a ca. 20% increase in the diffusion coefficient. By coupling these measurements to molar mass determinations obtained by size exclusion chromatography and monomer size estimations determined from ab initio calculations, it was possible to determine the radii of gyration via de Gennes renormalization theory. From diffusion coefficients and radii of gyration obtained as a function of ionic strength, persistence lengths (total, electrostatic, and intrinsic) were calculated from the Benoit-Doty relationship.