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A neat non-aqueous universal solvent: Developed using Protein Polymer Surfactant Bio-conjugation

Name: Anasua Mukhopadhyay

Department: Chemistry

Program: Ph D. (5th year)

Name of supervisor: Prof. Kamendra P. Sharma

Importance or applications of the research: 

Extensive use of petrochemical solvents in both chemical and pharmaceutical industries in large scales for product manufacturing is causing severe adverse implication on our environment. Demand for ‘Green/bio-solvents’ particularly becomes apparent after the Montreal Protocol outlined environmental hazards of using toxic, volatile petrochemical based solvents and the need for green solvents for industrial production. According to a recent report (Inkwood 2019)1 projected market share of bio-solvent production is $7 billion in 2018 and is estimated to generate net revenue of approximately $13 billion by 2027. Various methodologies were undertaken to conceptualize a low cost, low volatile green solvent by scientists around the world that includes employing ionic liquids, deep eutectic solvents, liquid polymers and supercritical fluids. However, solubility of different solutes, toxicity of chemicals used and associated cost are the main challenges that still persist on the way of a sustainable green solvent. Through our research we aim to develop a universal solvent which can be effective for dissolving different surface chemistry solutes along with the retention of their functions.

Its novelty and methodologies adopted: 

We have utilized a recently developed protein polymer surfactant bio-conjugation methodology to synthesize Bovine Serum Albumin (BSA) based bioconjugates. Natural structural materials such as cellulose, sugar, proteins are emerging as the key raw materials in sustainable chemical and material production due to overgrowing interest in recent times towards exploitation of biomass as the new environmental resource. Amongst those, protein based materials are particularly growing as the building blocks of engineering materials because of its diverse structural and functional properties. We have surface re-engineered BSA protein using a three step methodology that involves: i) preparation of positively charged BSA (pBSA), ii) electrostatic coupling of the anionic polymer surfactant glycolic acid ethoxylate lauryl ether (PS) to positively charged BSA to form PSpBSA bio-conjugates, and then iii) freeze drying and followed by thermal annealing at 60 °C to produce water-less liquid (WL-PSpBSA) conjugates. Along with the retention of proteins secondary structure one of the interesting property of the water-less bioconjugates is that it is a soft-solid below 25 °C, but transitions to a liquid phase at higher temperatures.

Most significant results:

We have utilized this melting transition as a pathway for dissolution of various dry and powdered species of different sizes, and surface chemistries; molecular (angstrom sized) hydrophobic coumarin 153 dye, nanometeric α-chymotrypsin (digestive enzyme), and micrometer sized hydrophilic 1 μm fluorescent polystyrene beads. Using a combination of bright field optical microscopy, fluorescence spectroscopy and MALDI-ToF analysis we found that dispersion of protease leads limited BSA digestion by α-Chy enzyme. We found a similarity in binding of dye molecule C153 within the BSA, and a retained site specificity, irrespective of its mode of addition. Our experiments performed with dried micron sized hydrophilic polystyrene beads also show dissolution in the water-less bio-conjugates suggesting that the polymer surfactant chains on the surface of the protein interact probably via hydrogen bonding interactions to solubilize the beads.

Conclusions:

We have highlighted the ability of WL-PSpBSA liquid to dissolve different species that may allow it to act as a new non- aqueous reaction media which itself is biologically active to carry out reactions such as proteolytic digestion. Also we have successfully extended our designed  stategy to prepare a low viscous bio-catalytic solvent medium by incorporating enzyme polymer surfactant bio-conjugates in neat ionic liquids.3 We believe that our developed universal solvent matrix is a significant alternative for the current challenges of sustainable solvent research and development.

 

Figure: Schematic showing dissolution of different sizes and surface chemistry solutes in Water-less Protein-Polymer surfactant based non-aqueous universal solvent