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Concentration dependence of the sol-gel phase behavior of agarose-water system observed by the optical bubble pressure tensiometry.

ABSTRACT: We have studied an expansion behavior of pressurized bubbles at the orifice of a capillary inserted in gelator-solvent (agarose-water) mixtures as a function of the gelator concentration in which the phase transition points are included. The pressure (P) -dependence of the radius of the curvature (R) of the bubbles monitored by laser beam has shown a discontinuous decrease in the exponent (m) of the experimental power law R?=?K?P^-m (K: constant) from 1 to 1/2 and a discontinuous increase in the average surface tension (?_ave) obtained from the work-area plots of the mixtures exceeding that of pure water (72.6 mN/m) at 0.02?app?=??P/2?R) of the system in the concentration range of 0.03-0.20?wt% has been analyzed by a modified Shuttleworth equation ?_app?=??₀?+??ln(A/A₀), where ?₀ is an isotropic constant component and the second term is a surface area (A) -dependent elastic component, in which ? is the coefficient and A₀ is the area of the orifice. The analysis has indicated that ?₀ coincides with the ?_app value of the mixture of 0.02?wt% and the second term at >0.02?wt% is the dominant component. From the appearance of the elastic component and concentration dependence of ?, the plateau of ? for the agarose-water mixtures at 0.03-0.10?wt% (Region II) has been explained to the phase separation giving two-phase mixtures of 0.02?wt% sol and 0.10?wt% gel and the upward inflection of ? at 0.10?wt% has been assigned to an increase in the elasticity of the gel with the increase of the agarose concentration in the range of >0.10?wt% (Region III). On considering the concentration dependence of the surface tension of agarose-water mixtures, the discontinuous and inflection points were assigned to the 1st- and 2nd-order phase transition concentrations of the agarose gel, respectively. Given the results with our tensiometry based on the optical bubble pressure method, distinct gelation points for other systems could be determined both mechanically and thermodynamically which will provide a diagnostic criterion of sol-gel transitions.

SUBMITTER: Ichinose N

PROVIDER: S-EPMC7021719 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Concentration dependence of the sol-gel phase behavior of agarose-water system observed by the optical bubble pressure tensiometry.

Ichinose Nobuyuki N Ura Hodaka H

Scientific reports 20200214 1

We have studied an expansion behavior of pressurized bubbles at the orifice of a capillary inserted in gelator-solvent (agarose-water) mixtures as a function of the gelator concentration in which the phase transition points are included. The pressure (P) -dependence of the radius of the curvature (R) of the bubbles monitored by laser beam has shown a discontinuous decrease in the exponent (m) of the experimental power law R = KΔP<sup>-m</sup> (K: constant) from 1 to 1/2 and a discontinuous incre ...[more]

PMID: 32060370

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Project description:Advances in supramolecular assembly have enabled the design and synthesis of functional materials with well-defined structures across multiple length scales. Biopolymer-synthetic hybrid materials can assemble into supramolecular structures with a broad range of structural and functional diversity through precisely controlled noncovalent interactions between subunits. Despite recent progress, there is a need to understand the mechanisms underlying the assembly of biohybrid/synthetic molecular building blocks, which ultimately control the emergent properties of hierarchical assemblies. In this work, we study the concentration-driven self-assembly and gelation of π-conjugated synthetic oligopeptides containing different π-conjugated cores (quaterthiophene and perylene diimide) using a combination of particle tracking microrheology, confocal fluorescence microscopy, optical spectroscopy, and electron microscopy. Our results show that π-conjugated oligopeptides self-assemble into β-sheet-rich fiber-like structures at neutral pH, even in the absence of electrostatic screening of charged residues. A critical fiber formation concentration cfiber and a critical gel concentration cgel are determined for fiber-forming π-conjugated oligopeptides, and the linear viscoelastic moduli (storage modulus G' and loss modulus G″) are determined across a wide range of peptide concentrations. These results suggest that the underlying chemical structure of the synthetic π-conjugated cores greatly influences the self-assembly process, such that oligopeptides appended to π-conjugated cores with greater torsional flexibility tend to form more robust fibers upon increasing peptide concentration compared to oligopeptides with sterically constrained cores. Overall, our work focuses on the molecular assembly of π-conjugated oligopeptides driven by concentration, which is controlled by a combination of enthalpic and entropic interactions between oligopeptide subunits.

Dataset Information

Concentration dependence of the sol-gel phase behavior of agarose-water system observed by the optical bubble pressure tensiometry.

Publications

Concentration dependence of the sol-gel phase behavior of agarose-water system observed by the optical bubble pressure tensiometry.

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