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Hantzsch reaction is one of the typical multicomponent reactions (MCRs), and it is employed herein to endow cellulosic materials with fluorescent properties. For example, acetoacetyl (ACAC)-bearing cotton fabric prepared via transesterification with tert-butyl acetoacetate is subjected to an aqueous Hantzsch reaction with formaldehyde and ammonium acetate at ambient temperature. A strong fluorescent emission around 460 nm is achieved within 10 min. XPS, fluorescent spectroscopy, and elemental analysis are used to confirm the presence of 1,4-dihydropyridine (DHP) rings on the surface of the fabric. TGA, SEM, XRD, and mechanical testing results show that the modification process has minimum impact on intrinsic properties of the fabric. The strategy is also shown to be generally applicable to various forms of cellulosic materials and different aldehydes. This fast and simple approach enriches the application of MCR in modification of cellulose and cellulose derivatives.

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The effect of the degree of substitution (DS) on the aqueous solubility of cellulose acetoacetates (CAA) was investigated by molecular dynamics simulations and density functional theory calculations. Using average non-covalent interaction and the electrostatic potential analyses done on cellobiose as the model, it was showed both polar and non-polar areas of the system increased as the more hydroxyls were replaced by acetoacetate groups. Analyses of the solvation free energies of a celludecose (glucan containing 10 monosaccharide sugar units) at constant pressure and temperature showed the polar solvation free energies and the number of decose-water hydrogen bonds increased as DS was varied from 0.3 to 0.8, which contributes to higher solubility in water. When the DS of CAA increased from 0.8 to 1.5, it became insoluble again because the plateaued increase in solvation free energy could no longer compensate for the decreasing CAA-water hydrogen bonding interactions. The growing van der Waals interactions among CAA molecules as the molecule grows bigger with each attached AA group also contributes to the decreasing water solubility.

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Organo-hydrogels are widely used in various fields, due to functional organic ingredients immobilized by the gel network or stored and protected by the gels. Herein, cellulose acetoacetate (CAA) served as reactive natural polymer emulsifier to stabilize thyme oil-in-water (O/W) emulsions. Hydroxypropyl chitosan (HPCS) was added to the continuous phase in emulsions to achieve the organo-hydrogel via the enamine bonds under mild conditions. The thyme@CAA emulsion with different loadings of the inner phase (up to 50%) displayed uniform droplets distribution (3-5 µm) and favorable stability. The organo-hydrogel was systematically analyzed by Fourier transform infrared spectroscopy, optical microscope, rheology analyses. The emulsion droplets evenly dispersed in the three-dimensional network. The modulus of organo-hydrogels depended on the viscosity of precursor emulsions and the crosslinking density. The resulting organo-hydrogel displayed favorable antibacterial activity against E. coli and S. aureus. CAA, as the reactive emulsifier and crosslinking agent, was a promising alternative candidate to fabricate a series of organo-hydrogel.

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The Biginelli multicomponent reaction has been used as an effective and model method to efficiently prepare a library of cellulose derivatives based on cellulose acetoacetate (CAA). Various cellulose derivatives containing 3, 4-dihydropyrimidin-2(1 H)-ones (DHPMs) with different functional groups (carboxyl, methoxyl, and nitro) are synthesized. The entire reaction process is followed using FT-IR, 1H NMR. The results demonstrate that more than 80% of the acetoacetyl groups are converted within four hours. Additionally, all the cellulose derivatives are confirmed to have favorable thermostability and good solubility in selected solvents. Furthermore, polymers (in this case, poly (ethylene glycol) monomethyl ether (mPEG)) can also be anchored to the cellulose backbone via this facile modular approach. Therefore, the Biginelli multicomponent reaction offers a straightforward method for diverse and large-scale cellulose derivatization. These results are expected to prompt broader study of this multicomponent reaction in interdisciplinary fields.

RESUMEN

In the present work, cellulose acetoacetates (CAA) was used as a precursor for preparing diversely functionalized cellulose derivatives. Four amino-bearing compounds, namely hexylamine (HA), l-glutamic acid (Glu), cysteine (Cys), and tyramine (TA) were reacted with acetoacetyl groups providing alkyl-, carboxyl-, thiol-, or phenolic functionalized cellulose. The reaction was conducted under mild conditions without catalysts and UV light. The products were characterized with FT-IR, NMR and solubility measurement. 1H NMR measurement demonstrated the conversion of acetoacetyl groups were ideal, and all the cellulose derivatives demonstrated good solubility in certain solvent. Besides, CAA held a good stability under room temperature. This approach offers broad possibilities for developing new cellulose based materials. Moreover, this protocol can also be applied to fabricate other polysaccharide derivatives.

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