Synthesis and Characterization of Polyrotaxane−Amino Acid Conjugates: A New Synthetic Pathway for Amino-Functionalized Polyrotaxanes

Post-synthesis modification of slide-ring gels for thermal and mechanical reconfiguration

Ring-sliding behavior in polyrotaxanes imbues gels, elastomers, and glasses with remarkable stress-dissipation and actuation properties. Since these properties can be modulated and tuned by structural parameters, many efforts have been devoted to developing synthetic protocols that define the structures and properties of slide-ring materials. We introduce post-synthetic modifications of slide-ring gels derived from unmodified α-cyclodextrin and poly(ethylene glycol) polyrotaxanes that enable (i) actuation and control of the thermo-responsive lower critical solution temperature (LCST) behavior of ring-modified slide-ring hydrogels, and (ii) chemically bonding separate gels into hybrid or shape-reconfigured macro-structures with a slide-ring adhesive solution. The mechanical properties of the post-modified gels have been characterized by shear rheology and uniaxial tensile tests, while the corresponding xerogels were characterized by wide-angle X-ray scattering. These demonstrations show that post-synthetic modification offers a practical solution for re-configuring the properties and shapes of slide-ring gels.

High-performance cationic polyrotaxanes terminated with polypeptides as promising nucleic acid delivery systems

A novel cationic polyrotaxane consisting of hydroxyl-rich polycationic units and degradable end-capping polypeptides was prepared for promising nucleic acid delivery.

Steric stabilization of "charge-free" cellulose nanowhiskers by grafting of poly(ethylene glycol)

A sterically stabilized aqueous suspension of "charge-free" cellulose nanowhiskers was prepared by hydrochloric acid hydrolysis of cotton powders and subsequent surface grafting of monomethoxy poly(ethylene glycol) (mPEG). The preparation scheme included carboxylation of the terminal hydroxyl groups in mPEG via oxidation with silica gel particles carrying 2,2,6,6-tetramethyl-1-pyperidinyloxyl (TEMPO) moieties and subsequent esterification between terminal carboxyls in mPEG and surface hydroxyl groups of cellulose nanowhiskers, mediated by 1,1'-carbonyldiimidazole (CDI) in dimethyl sulfoxide or dimethylacetamide. Some of the prepared PEG-grafted samples showed remarkable flow birefringence and enhanced stability after 24 h, even in 0.1 M NaCl, suggesting successful steric stabilization by efficient mPEG grafting. Actual PEG grafting via ester linkages was confirmed by attenuated total reflectance-Fourier transform infrared spectrometry. In a typical example, the amount of grafted mPEG was estimated as ca. 0.3 g/g cellulose by two measurements, i.e., weight increase after grafting and weight loss after alkali cleavage of ester linkages. Transmission electron microscopy indicated unchanged nanowhisker morphology after mPEG grafting.

Synthesis of peptide-cellulose conjugate mediated by a soluble cellulose derivative having β-Ala esters

A derivatization of cellulose was investigated for gaining up the solubility for subsequent conjugation reaction. N(β)-Boc-β-Ala, was introduced to the parent cellulose using carbonyl diimidazole. Degree of substitution towards the cellulose hydroxyls was 49%. Subsequent removal of Boc in trifluoroacetic acid (TFA) yielded β-Ala-cellulose·TFA salt. A protected hexapeptide, Boc-Ser(Bzl)-Gly-Tyr(Bzl)-Ser(Bzl)-Gly-Lys(Z) was synthesized via 9 steps of peptide elongation, and the C-end carboxyl groups of the peptide was coupled with the β-Ala-cellulose in a homogenous dimethyl sulfoxide solution, using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide monohydrochloride to ensure the N(β)-selective acylation. The degree of substitution of the protected peptide towards the β-amino groups of β-Ala-cellulose (DS%(/NH(2))) was 52% for 1.0 eq.mol of the protected peptide feed, and in the presence of N-hydroxysuccinimide, DS%(/NH(2)) was increased to 61%. At 4.0 eq.mol feed, almost quantitative conjugation was observed as DS%(/NH(2))=98-99%. Deprotection of the conjugate using thioanisole-TFA resulted in complete removal of Boc, Bzl on Tyr, and Z on Lys, while a very trace amount of Bzl on Ser seemed to be left uncleaved.