Progress 09/01/01 to 02/29/04
Outputs
The objective of this project is to explore biocatalysis for the preparation of sugar-containing biodegradable polymers -- an effort in developing value-added chemicals from agricultural products. Specifically this research is to demonstrate the feasibility of an enzymatic approach to the preparation and manipulation of a model copolymer, glucose-lactide copolymer. The project was originally approved for the period of Sept. 1, 2001 through Aug. 31, 2002. Since this award was made after the fall semester started in 2001, student recruitment was delayed. As a result, no-cost extension was applied to have the project officially terminated on February 29, 2004. Exciting success has been made in conducting the proposed research tasks; in addition, extra efforts were made in developing a new enzyme modification method to improve the efficiency of enzyme for the proposed application. The following provides further details of these achievements. In one direction, the synthesis
of the proposed unique sugar-lactic copolymer was proven successful. The synthesis was composed of two enzymatic reaction steps, namely glycoside lactate monomer preparation and non-aqueous polymerization reaction. The developed process uses ethyl lactate and lactose as the starting materials without complicated protection and deprotection steps as usually required for chemical processes. A high molecular weight sugar-lactate alternative copolymer was prepared. The Mw of the polymer was measured up to 71 KDa by GPC, with its chemical structure confirmed with 13C NMR spectrum. The polymer is highly water-soluble and is expected to be highly biocompatible. The multiple hydroxyl groups of the sugar moiety can afford easy further manipulation such as attachment of functional groups or crosslinking to form materials for different applications. In another exploration, we explored the possibility of increasing the stability and activity of enzymes in non-aqueous environment. A new enzyme
modification method was developed and shown effective through this research. Specifically, proleather from Bacillus sp. was chemically modified with decanoyl chloride for enhanced activity and was tested for the preparation of poly(lactic acid) in organic solvents. The modified enzyme was highly soluble (up to 44 mg-protein/ml, in comparison to the <1mg/ml solubility of pegylated enzymes) and active in various organic solvents including chloroform, tetrahydrofuran (THF), pyridine and acetone. The organic-soluble proleather efficiently catalyzed the polymerization of ethyl lactate. The reaction rate was 4 to 22 times that of native proleather, depending upon the solvent applied.
Impacts
An enzymatic route to prepare sugar-lactate copolymers was developed; in addition, a new method to improve the efficiencies of enzymes for such an application was demonstrated. The strategy evolved from this research opens a new avenue for the synthesis of sugar-based polymers for use as biodegradable materials. Since the sugar moiety is chemically incorporated into the backbone molecular chains of the polymers, the product represents a new class of biomaterials that offer tunable physicochemical properties in a wide range for applications such as drug formulation, tissue engineering, water absorbents, disposable plastics, etc.
Publications
- Kelley A. Distel, Guangyu Zhu, Ping Wang*, Biocatalysis Using an Organic-Soluble Enzyme for the Preparation of Poly(lactic acid) in Organic Solvents, Bioresource Technology. 2004. In press.
- Hongfei Jia and Ping Wang*, Enzymatic Synthesis of a Unique Sugar-Lactate Alternative Copolymer for Use as Biomaterials. Biomacromolecules. 2004(In preparation)
- Ping Wang, Enzymatic biotransformation for production of chemicals and polymers. Chapter in Shang-Tian Yang (Ed.), Bioprocessing for Value-Added Products from Renewable Resources: New Technologies and Applications (in preparation, Book proposal was accepted by Elsevier). 2004.
- P. Wang and H. Jia, Sugar-lactate copolymers via enzymatic synthesis, Patent application (in preparation). 2004
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Progress 10/01/01 to 09/30/02
Outputs
The project was extended (no-cost) to August 31, 2003, due to the initiating date of the project (9/1/01) was at the beginning of an academic school year, and no graduate student was available immediately to join the project. Starting spring 02, two graduate students have been working on this project as their thesis research subjects (one is supported through this grant, while the other is supported through teaching assistantship at University of Akron). This objective of this research is focused on the exploration of enzymatic reactions for the formation and manipulation of sugar containing biodegradable polymers. Toward that, several findings have been achieved: 1. By using enzymatic tranglycosylation reaction, glucosyl-3'-ethyl lactate was synthesized. The use of enzymes secured that the lactate was attached to the sugar moiety specifically at the 3'-hydroxyl position, and left the primary 6' hydroxyl group open for further esterification reaction to eventually for
a sugar-lactate linear polymer. 2. The selective esterification between octyl glucose and ethyl lactate was conducted. Novozyme 435 and Lipases were found effective in catalyzing this reaction. The model reaction provide the mechanism for the polymerization of the sugar-lactate monomer as prepared in the first step. The conversion rate was over 80%. 3. To test the potential of using enzymes for the esterification reactions involving lactate, lipase catalyzed polymerization of ethyl lactate was conducted. The structure of the polymer was confirmed through both MALDI-TOF mass spectrometry and GPC molecular weight analysis. The polymer Mw achieved so far was around 2000 Da. Further study is underway to optimize the reaction to improve the molecular weight of the polymer. 4. To improve the active of lactate, synthesis of trifluorol ethyl-lactate ester was performed. While the product was formed with a conversion yield of 20% of lactic acid, difficulties have been experienced in the
purification of the product. 5. With the above findings, several activities are currently underway: a) enzymatic polymerization of sugar-lactate ester; b) enzymatic polymerization of ethyl lactate; c) potential reactions to expand the current technologies to include other organic acid such as amino acid to form a variety of sugar-containing biolpolymers.
Impacts
Enzymes are protein catalysts that manipulate the construction of various polymers and chemicals in biological world. To learn and use the enzymatic processes occurring in nature for the development of novel biomaterials has therefore been a vigorous research effort for many scientists and engineers. Nevertheless, we are still at the beginning to explore and demonstrate the potentials and merits of enzymes for polymer synthesis. The results obtained through this research are helpful to develop highly effective enzymatic processes for the production of a new class of sugar-containing polymers that are biodegradable and biocompatible. The products incorporate extremely hydrophilic sugars and relatively hydrophobic lactide, thus afford desirable physiochemical properties in terms of mechanical behaviors, hydrophilicity, and rate of decomposition. These properties are tunable within a wide range by controlling the sugar content; make it possible to satisfy the
requirements for a variety of applications including biomedical materials, absorbents, adhesives, cosmetic products, and general disposable polymers. The proposed work is aimed to promote the production of non-fuel chemicals and materials from agricultural resources. In addition to the raw materials including sugars and lactide, the protein enzymes applied for the polymer synthesis are also produced from agricultural commodities. The use of enzymes will provide simple reactions, clean products, and environmentally friendly processes. The success of this work will ultimately lead to the development of industrial processes and products that are both biobased, and will considerably enhance the value of agricultural raw materials.
Publications
- Distel, K., Jia, H. F., and Wang, P. "Enzymatic Synthesis of Sugar-Containing Biomaterials", AIChE Annual Meeting, Indianapolis, Nov. 3-8, 2002.
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