Makoto Takemasa

Rheology of schizophyllan solutions in isotropic and anisotropic phase regions

In this paper, we discuss the rheological properties of aqueous solutions of a rigid triple-helical polysaccharide, schizophyllan (SPG), in isotropic, biphasic, and fully anisotropic phases. Both steady shear and dynamic rheological behaviors reveal remarkable changes when SPG solutions pass through the three phases. The steady shear flow exhibits shear thickening at low shear rates for anisotropic SPG liquid crystalline samples, which is attributed to the shear-induced cholesteric to nematic transformation. The first normal stress difference and transient rheological experiments demonstrate that director tumbling is absent or negligible in SPG liquid crystals in the range of examined shear rates. Additionally, the stress relaxation of SPG liquid crystals after flow cessation shows an inverse relation between the relaxation time and preshear rate, as expected by Larson and Mead’s theory [Larson and Mead (1989)]. Small amplitude oscillation measurements following flow cessation show decreasing complex modulus with time for SPG liquid crystals, which is probably related to an increase of molecular orientation after flow cessation. The evolutions of complex modulus after flow cessation are discussed in terms of chain persistence length.

Single molecular pair interactions between hydrophobically modified hydroxyethyl cellulose and amylose determined by dynamic force spectroscopy.

Interactions among HMHEC (hydrophobically modified hydroxyethyl cellulose) and between HMHEC and amylose were investigated by means of dynamic force spectroscopy of single molecular pairs. The technique was realized using a scanning probe based platform, and the molecular pair interactions were investigated in aqueous solutions over a range of force loading rates. Both hydrophobic interactions among hydrophobe C(16) alkyl side chains in HMHEC and association between these hydrophobes in HMHEC and amylose showed a stretching type peak. The distribution analysis of rupture force based on Bell-Evanss model revealed that the peaks had a most probable rupture force ranging from 27 pN at a force loading rate r(f) = 0.43 nN/s to 125 pN at r(f) = 170 nN/s for HMHEC-HMHEC, and from 13 pN at r(f) = 0.20 nN/s to 34 pN at r(f) = 33.7 nN/s for HMHEC-amylose interactions. The distance of the energy barrier relative to the minimum, x(beta), and the apparent lifetime in the absence of external force, tau, were found to depend on the force loading rate, and the average values are estimated to be 0.99 nm and 0.89s for HMHEC-HMHEC and 0.31 nm and 0.075s for HMHEC-amylose interactions. The obtained data for these pairwise molecular interactions are underpinning the associative behavior of the macroscopic properties of aqueous solutions of these polysaccharides.

Solution Structure of Molecular Associations Investigated Using NMR for Polysaccharides: Xanthan/Galactomannan Mixtures

Although the intermolecular nuclear Overhauser effect (NOE) signal was valuable to elucidate molecular association structure, it could not always be observed for associated molecules due to the short spin-spin relaxation time T2 in NMR measurements, especially for high molar mass systems. While almost no study has been reported for high molar mass polymers (>1 × 10(6)), especially for polysaccharide-polysaccharide interactions, NOE signals were observed for the first time between two different types of polysaccharides, xanthan and galactomannan (locust bean gum), forming a synergistic gel, as a direct evidence of intermolecular binding of polysaccharides. The NOE peak was found between pyruvic acid in xanthan and anomeric proton of mannose of galactomannan. This NOE signal was observed only when mixing time >0.5 s, indicating indirect NOEs caused by spin diffusion. Therefore, this NOE could not be used to construct the molecular models. However, it is a direct evidence for the binding between two different types of polysaccharide to elucidate the synergistic gelation. This NOE signal was observed only for low molar mass galactomannans (1.4 × 10(4)). T2 of pyruvate methyl drastically decreased at low temperatures in the presence of synergistic interaction, suggesting that pyruvate group at terminal end of side chain in xanthan plays an essential role in synergistic interaction.

Glycan Analysis Using a Solid State Nanopore

Single molecular translocation events were observed for polysaccharides using a solid state nanopore, and multi-level pulses were observed due to the local folded structure when using larger pore size compared with the diameter of the polysaccharides. These phenomena are essentially the same as those reported for DNA. This analysis technique, cross-sectional area scanning based on nanopore, is promising not only for glycans but also for branched polymer in more general.

Bridging the Gap Between Single-Molecule Unbinding Properties and Macromolecular Rheology

Conformation and interactions between biological macromolecules are crucial for the mechanical properties of biological soft matter. In this chapter, the method and applications of the mechanical characteristics at the single-molecule level, from a fundamental point of view, are described as basis for understanding aspects of rheology. Atomic force microscope (AFM) and optical tweezers can be applied to investigate mechanical properties and interactions of molecules in the single molecular level. The force between two molecules as a result of specific and/or non-specific interactions can be determined as a function of distance between two molecules. Selected examples for interactions in macromolecules were highlighted based on observations by AFM-based force spectroscopy. This includes polysaccharide pairs such as interactions among hydrophobically modified hydroxyethyl cellulose (HMHEC), between protein polysaccharides and mucin–alginate. The mechanism of physically cross-linked hydrogel formation, HMHEC–amylose gel and alginate gels was also discussed based on single molecular pair interactions. For slower bond formation systems, which may not be capable with normal dynamic force spectroscopy, slide contact force spectroscopy can be applied. For slower dissociation rate, Dudko–Hummer–Szabo model and Friddle–Noy–De Yoreo model can be used for the analysis as an extension of the Bell–Evans model. The relation between characteristic timescale of interaction estimated in the single molecular study and relaxation spectra in the mechanical properties obtained at the macroscopic scale is presented as a possible way forward in understanding the gap between the mechanical properties in macroscopic and microscopic scale.