A pH-responsive carboxylic β-1,3-glucan polysaccharide for complexation with polymeric guests

Abstract

The helix-forming nature of β-1,3-glucan polysaccharides is a characteristic that has potential for producing gene carriers, bio-nanomaterials and other chiral nanowires. Herein, carboxylic curdlan (CurCOOH) bearing the β-1,3-polyglucuronic acid structure was successfully prepared from β-1,3-glucan polysaccharide curdlan (Cur) by one-step oxidation using a 4-acetamido-TEMPO/NaClO/NaClO(2) system as the oxidant. The resulting high-molecular-weight CurCOOH was proved to bear the 6-COOH group in 100% purity. The optical rotatory dispersion (ORD) spectra indicated that the obtained CurCOOH behaves as a water-soluble single-strand in various pH aqueous media. This advantage has allowed us to use CurCOOH as a polymeric host to form various macromolecular complexes. For example, complexation of CurCOOH with single-walled carbon nanotubes (SWNTs) resulted in a water-soluble one-dimensional architecture, which formed a dispersion in aqueous solution that was stable for several months, and much more stable than SWNTs complexes of the similar negatively-charged polyacrylic acid (PAA) and polymethacrylic acid (PMAA). It was shown that in the complex, SWNTs are effectively wrapped by a small amount of CurCOOH, enabling them to avoid electrostatic repulsion. This pH-responsive CurCOOH formed a very stable complex with cationic water-soluble polythiophenes (PT-1), which was stabilized not only by the hydrophobic interaction but also by the electrostatic attraction between trimethylammonium cations in PT-1 and dissociated anionic COO(-) groups in CurCOOH. The included PT-1 became CD-active only in the neutral to basic pH region, and the positive Cotton effect suggested that the conjugated main chain is twisted in the right-handed direction. We also found that CurCOOH can interact with polycytidylic acid (poly(C)) only under high NaCl concentrations, the binding and release of which could be controlled by a change in the salt concentration. We believe, therefore, that CurCOOH bearing a dissociable COOH group can act as a new potential polymeric host to construct novel polymeric complexes applicable for gene carriers, biosensors, chiral polymer assemblies, etc.

Supramolecular Assembly of Achiral Alkynylplatinum(II) Complexes and Carboxylic β‐1,3‐Glucan into Different Helical Handedness Stabilized by Pt⋅⋅⋅Pt and/or π–π Interactions

“…Upon addition of CurCOOH to a solution of complex 1 , a significant decrease in the absorption at approximately 275 nm was found, with a concomitant growth of a low‐energy absorption shoulder centered at 550 nm (Figure 1 a). Given that CurCOOH does not absorb in the visible region,27a the absorption spectral changes cannot be accounted for by the intrinsic UV/Vis absorption of the newly added CurCOOH. The p K a value of CurCOOH has been reported to be 3.11,27a therefore the carboxylic acid groups on CurCOOH should undergo deprotonation, and hence CurCOOH would likely exist as a polyanion in the pH 6.8 buffer solution.…”

“…Given that CurCOOH does not absorb in the visible region,27a the absorption spectral changes cannot be accounted for by the intrinsic UV/Vis absorption of the newly added CurCOOH. The p K a value of CurCOOH has been reported to be 3.11,27a therefore the carboxylic acid groups on CurCOOH should undergo deprotonation, and hence CurCOOH would likely exist as a polyanion in the pH 6.8 buffer solution. As a result, the cationic complex 1 molecules would probably form helical assemblies with the anionic CurCOO − in the pH 6.8 buffer solution through electrostatic interactions.…”

“…They are well‐known for their strong helix‐forming features and the highly reversible denaturation/renaturation process of the helical structures 25. 27 An example is carboxylic curdlan (CurCOOH), which has been reported to exist in a single‐stranded random coil and to form two‐component ensembles with guest molecules only in a single‐stranded right‐handed helical structure 27a. This is different from other β‐1,3‐glucans, which can form triple‐stranded helical structures 25.…”

Rheological properties of a β-1,3-polyglucuronic acid derivative from 4-acetamido-TEMPO-mediated oxidation of curdlan

“…Moreover, the material shows potential in the production of gene carriers, bio-nanomaterials, and other chiral nanowires through hydrogen bonding interactions, hydrophobic interactions, and electrostatic attraction. 49 Thus, a possible mechanism underlying the rheological behavior of the carboxylic curdlan is proposed in Fig. 6.…”

The transformation of chiral signals into macroscopic properties of materials using chirality-responsive polymers

“…34 Recently, pH-responsive carboxylic b-1,3-glucan polysaccharide was used to selectively complex single-walled carbon nanotubes and PT1s in aqueous solution. 35 More interestingly, natural polypeptides are also pH-responsive systems with helical structures. In 2010, Cho et al 36 reported the synthesis of a basic oligopeptide, Api 8 , composed of eight non-natural achiral amino acids.…”