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Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals.

ABSTRACT: Native plant cellulose has an intrinsic supramolecular structure. Consequently, it can be isolated as nanocellulose species, which can be utilized as building blocks for renewable nanomaterials. The structure of cellulose also permits its end-wise modification, i.e., chemical reactions exclusively on one end of a cellulose chain or a nanocellulose particle. The premises for end-wise modification have been known for decades. Nevertheless, different approaches for the reactions have emerged only recently, because of formidable synthetic and analytical challenges associated with the issue, including the adverse reactivity of the cellulose reducing end and the low abundance of newly introduced functionalities. This Review gives a full account of the scientific underpinnings and challenges related to end-wise modification of cellulose nanocrystals. Furthermore, we present how the chemical modification of cellulose nanocrystal ends may be applied to directed assembly, resulting in numerous possibilities for the construction of new materials, such as responsive liquid crystal templates and composites with tailored interactions.

SUBMITTER: Heise K

PROVIDER: S-EPMC7821002 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals.

Heise Katja K Delepierre Gwendoline G King Alistair W T AWT Kostiainen Mauri A MA Zoppe Justin J Weder Christoph C Kontturi Eero E

Angewandte Chemie (International ed. in English) 20200909 1

Native plant cellulose has an intrinsic supramolecular structure. Consequently, it can be isolated as nanocellulose species, which can be utilized as building blocks for renewable nanomaterials. The structure of cellulose also permits its end-wise modification, i.e., chemical reactions exclusively on one end of a cellulose chain or a nanocellulose particle. The premises for end-wise modification have been known for decades. Nevertheless, different approaches for the reactions have emerged only r ...[more]

PMID: 32329947

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Project description:Bacterial cellulose is a bacterially derived polymer with great potential for application in wound healing due to its innate properties such as high biocompatibility and biodegradability. In addition to this, it is naturally biosynthesized by bacteria as a hydrogel, which makes it an optimal substrate for the treatment of dry wounds, where additional moisture is required to facilitate the healing process. However, this polymer lacks antibacterial properties. As bacterial infections are becoming increasingly common and difficult to treat due to antimicrobial resistance, it is of crucial importance to develop strategies for the modification of cellulose to ensure protection against bacterial contamination. In this study, a green-chemistry approach was proposed for the functionalization of cellulose to introduce antibacterial functional groups. Two different active agents, namely glycidyl trimethylammonium chloride and glycidyl hexadecyl ether, were used for the covalent derivatization of the hydroxyl groups of glucose through a heterogeneous reaction in basic aqueous conditions. The modified material was chemically and mechanically characterized by solid-state techniques and rheological measurements. A biological assessment was then carried out both using bacterial cells and human keratinocytes. It was observed that the functionalization performed induced a reduction of approximately half of the bacterial population within 24 h of direct contact with Staphylococcus aureus subsp. aureus Rosenbach 6538PTM and Escherichia coli (Migula) Castellani and Chalmers ATCC® 8739TM (respectively, a reduction of 53% and 43% in the cell number was registered for the two strains). In parallel, cytotoxicity studies performed on keratinocytes (HaCaT cell line) showed cell viability in the range of 90 to 100% for up to 6 days of direct contact with both unmodified and modified samples. The morphology of the cells was also visually evaluated, and no significant difference was noted as compared to the control. Finally, the in vitro scratch assay evidenced good wound closure rates in the presence of the samples, with complete coverage of the scratched area after 5 days for both the modified cellulose and the positive control (i.e., keratinocytes growth medium). Overall, the modified hydrogel showed promising features, confirming its potential as an alternative substrate to develop a sustainable, antibacterial and biocompatible wound dressing.

Project description:1. Isoionic chemical modification of amino groups of trypsin (EC 3.4.21.4) was studied for the purpose of obtaining a well-defined modified trypsin with minimum changes in physicochemical properties and with sufficient stability at neutral pH. Acetamidination with methyl acetimidate hydrochloride proceeded very rapidly at pH9.8 and 5degrees C and all 14 epsilon-amino groups were modified in 2h. The reaction was limited to epsilon-amino groups. The alpha-amino group of N-terminal isoleucine was modified only by repeated reactions in the presence of 5.5 M-guanidine or 8 M-urea. 2. The epsilon-acetamidinated derivative of beta-trypsin retained enzymic activity at values comparable with those of native enzyme tested with alpha-N-benzoyl-L-arginine ethyl ester and alpha-N-benzoyl-L-arginine p-nitroanilide as substrates; it also showed substrate activation comparable with that of native enzyme. The acetamidination of alpha-trypsin resulted in approx. 50% decrease in its esterolytic activity. 3. The epsilon-acetamidinated beta-trypsin was very stable at pH8 and 25degrees C in the absence of Ca2+. The activity of 0.04% (W/V) enzyme solution remained practically unchanged for 10h, and after 24h 90% of the activity was still retained. Possible autolytic cleavage of peptide bonds of acetamidinated enzymes was followed by N-terminal analysis by using automated Edman degradation. Only the Arg(105)-Val(106) bond was found to be cleaved to an appreciable extent. Thus beta-trypsin can be stabilized simply by complete acetamidination of epsilon-amino groups without modifying guanidino groups of arginine residues. Acetamidinated alpha-trypsin was unstable, but its inactivation at a neutral pH could not be attributed to the cleavage of a single specific peptide bond. 4. The acetamidination of the alpha-amino group of the N-terminal isoleucine results in the inactivation of esterolytic activity. However, this enzyme retained the ability to react with p-nitrophenyl p'-guanidinobenzoate. 5. It was concluded that acetamidination of beta-trypsin is a convenient method for preparing a well-defined stable and soluble trypsin derivative without appreciable change in its physical properties.

Dataset Information

Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals.

Publications

Chemical Modification of Reducing End-Groups in Cellulose Nanocrystals.

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