Abstract
A simplified procedure to synthesize zwitterionic cellulose by means of N-protected aspartic anhydride under mild conditions was developed. The preparation of modified cellulose samples was carried out under heterogeneous, aqueous conditions by reacting NH4OH-activated cellulose with aspartic anhydrides N-protected with trifluoroacetyl (TFAc) and carbobenzyloxy (Cbz). Modified cellulose samples Cel-Asp-N-TFAc and Cel-Asp-N-Cbz were characterized by Fourier Transform Infrared (FTIR) and 13C solid state Nuclear Magnetic Resonance (NMR) spectroscopy. The functionalization degree of each cellulose sample was determined by the 13C NMR signal integration values corresponding to the cellulose C1 vs. the Cα of the aspartate residue and corroborated by elemental analysis. In agreement, both analytical methods averaged a grafting degree of 20% for Cel-Asp-N-TFAc and 16% for Cel-Asp-N-Cbz. Conveniently, Cel-Asp-N-TFAc was concomitantly partially N-deprotected (65%) as determined by the ninhydrin method. The zwitterion character of this sample was confirmed by a potentiometric titration curve and the availability of these amino acid residues on the cellulose was inspected by adsorption kinetics method with a 100 mg L−1 cotton blue dye solution. In addition, the synthesis reported in the present work involves environmentally related advantages over previous methodologies developed in our group concerning to zwitterionic cellulose preparation.
Highlights
Cellulose is the most abundant structural component in plants, i.e., 10% to 20% of leaf dry weight, almost 50% in wood and bark and 90% in cotton linters
Typical signals corresponding to the cellulose chemical groups are observed at 3334 and 3276, 2900 and 1053 and 1023 cm−1 which are due to O-H, C-H and C-O stretching vibrations, respectively [29,30]
In the sample cellulose aspartate (Cel-Asp)-N-TFAc, there are some spectral differences compared to untreated cellulose which are shown in the highlighted inset between 1800 and 1500 cm−1
Summary
Cellulose is the most abundant structural component in plants, i.e., 10% to 20% of leaf dry weight, almost 50% in wood and bark and 90% in cotton linters It is one of the most abundant natural polymers in the world, easy to get, economically profitable, biodegradable, renewable and has attractive mechanical, biological and chemical properties [1]. Hydroxyls (-OH) are the main functional group, which are suitable for chemical modification by means of substitution, addition and oxidation reactions [2,3,4] Many of these chemical modifications take place in homogenous reactions where cellulose is solubilized under different chemical conditions in order to increase the degree of substitution and improve the distribution of the chemical groups along the polymer [5,6].
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