Surface modification of cellulose nanomaterials with amine functionalized fluorinated ionic liquids for hydrophobicity and high thermal stability

A highly hydrophobic fluorinated ionic liquid (IL), 3-aminopropyl-tributylphosphonium bis(trifluoromethylsolfonyl)imide ([aP4443][NTf2]), was synthesized, and applied for the surface modification of cellulose nanomaterials (CNMs) by reductive amination. The modified CNMs were fully characterized for their chemical structure, morphology, thermal stability, and surface hydrophobicity. Results obtained from Nuclear Magnetic Resonance spectroscopy (1H, 13C, 19F and 31P), Fourier Transform Infrared spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray diffraction confirmed the successful grafting of [aP4443][NTf2] onto the surface of CNMs up to a degree of surface functionalization of 2.5 %. Transmission Electron Microscopy analysis confirmed the dimensions of the CNMs were retained after modification but with significant aggregation for modified cellulose nanocrystals (CNCs). Thermal Gravimetric Analysis demonstrated significant increases in the degradation temperatures of modified CNCs from ∼252 °C to ∼310 °C. Modified cellulose nanofibers (CNFs) did not show any increase in thermal stability. The modified CNM suspensions showed reduced affinity for water and the formation of aggregates in aqueous media. Furthermore, a water contact angle test demonstrated enhanced hydrophobicity for modified CNMs. This modification approach holds potential for the use of the [aP4443][NTf2] IL for functional materials to achieve novel hydrophobic CNMs suitable for aqueous processing with thermoplastics, for fabrication of thermally stable composite materials, and for polymer gel electrolytes for batteries.

Hierarchical coassembly of DNA-triptycene hybrid molecular building blocks and zinc protoporphyrin IX

Herein, we describe the successful construction of composite DNA nanostructures by the self-assembly of complementary symmetrical 2,6,14-triptycenetripropiolic acid (TPA)-DNA building blocks and zinc protoporphyrin IX (Zn PpIX). DNA-organic molecule scaffolds for the composite DNA nanostructure were constructed through covalent conjugation of TPA with 5'-C12-amine-terminated modified single strand DNA (ssDNA) and its complementary strand. The repeated covalent conjugation of TPA with DNA was confirmed by using denaturing polyacrylamide gel electrophoresis (PAGE), reverse-phase high-performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). The biologically relevant photosensitizer Zn PpIX was used to direct the hybridization-mediated self-assembly of DNA-TPA molecular building blocks as well as a model guest molecule within the DNA-TPA supramolecular self-assembly. The formation of fiber-like composite DNA nanostructures was observed. Native PAGE, circular dichroism (CD) and atomic force microscopy (AFM) have been utilized for analyzing the formation of DNA nanofibers after the coassembly. Computational methods were applied to discern the theoretical dimension of the DNA-TPA molecular building block of the nanofibers. A notable change in photocatalytic efficiency of Zn PpIX was observed when it was inside the TPA-DNA scaffold. The significant increase in ROS generation by Zn PpIX when trapped in this biocompatible DNA-TPA hybrid nanofiber may be an effective tool to explore photodynamic therapy (PDT) applications as well as photocatalytic reactions.

Directed evolution of a formate dehydrogenase for increased tolerance to ionic liquids reveals a new site for increasing the stability

The formate dehydrogenase (FDH) from Candida boidinii is a well-known enzyme in biocatalysis for NADH regeneration. Nevertheless, it has low activity in a water-miscible ionic liquid (1,3-dimethylimidazolium dimethyl phosphate, [MMIm][Me2 PO4 ]). In this work, this enzyme was subjected to directed evolution by using error-prone PCR, and a mutant (N187S/T321S) displaying higher activity was obtained following selection based on the formazan-based colorimetric assay. The mutation N187S is responsible for improved activity both in aqueous solution and in [MMIm][Me2 PO4 ], through an enhancement of the kcat value by a factor of 5.8. Fluorescence experiments performed in the presence of a quenching agent revealed that the mutant does not unfold in the presence of 50 % (v/v) [MMIm][Me2 PO4 ] whereas the wild-type enzyme does. Molecular modelling revealed that the mutation is located at the monomer-monomer interface and causes an increase in the pKa of residue E163 from 4.8 to 5.5. Calculation of the pKa of this residue in other microbial FDHs showed that thermostable FDHs have a highly basic glutamate at this position (pKa up to 6.2). We have identified a new site for improving FDH thermostability and tolerance to ionic liquids, and it is linked to the local charge of the enzymes in this class.

Chlorine-free alternatives to the synthesis of ionic liquids for biomass processing

Ionic liquids (ILs) are desirable for use in a large number of applications because of their unique properties; however, compositions comprising only a single IL are expensive to synthesize and difficult to purify, and the widely used chloride-based ILs can be toxic and corrosive. Therefore, there is a need for new IL compositions that minimize common disadvantages encountered with single IL composition and synthetic methods which avoid halide intermediates. In this study, IL mixtures, which are chloride-free, were synthesized by a one-pot process, and the mixtures were used to dissolve biopolymers. The synthesized IL mixtures show high capability to dissolve the two exemplary biopolymers, cellulose and chitin.