Template-free enzymatic synthesis of electrically conducting polyaniline using soybean peroxidase

Degradable π-Conjugated Polymers

The integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.

Enzymatically Synthesized Polyaniline Doped with Copper Ions: Physico-Chemical and Antimicrobial Properties of the Product

Enzymatic synthesis of the polyaniline (PANI)/sodium polystyrenesulfonate (PSS) interpolyelectrolyte complex, in which PANI is doped with Cu(II) ions, has been developed. The biocatalyst for aniline (ANI) polymerization was the fungal laccase Trametes hirsuta and the oxidizing agent was atmospheric oxygen. The resulting PANI-Cu/PSS complex was studied by UV–visible and FTIR-ATR spectroscopy, and X-ray fluorescence analysis. The copper content in PANI‑Cu/PSS was ~8 wt %. The minimum inhibitory concentration (MIC) of the PANI-Cu/PSS complex against gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria was 2.65 and 0.66 mg/mL, respectively.

Betaine-Based Deep Eutectic Solvent as a New Media for Laccase-Catalyzed Template-Guided Polymerization/Copolymerization of Aniline and 3-Aminobenzoic Acid

Deep eutectic solvents (DESs) can compensate for some of the major drawbacks of traditional organic solvents and ionic liquids and meet all requirements of green chemistry. However, the potential of their use as a medium for biocatalytic reactions has not been adequately studied. In this work we used the DES betaine-glycerol with a molar ratio of 1:2 as co-solvent for enzymatic template-guided polymerization/copolymerization of aniline (ANI) and 3-aminobenzoic acid (3ABA). The laccase from the basidial fungus Trametes hirsuta and air oxygen served as catalyst and oxidant, respectively. Sodium polystyrene sulfonate (PSS) was used as template. Interpolyelectrolyte complexes of homopolymers polyaniline (PANI) and poly(3-aminobenzoic acid) (P3ABA) and copolymer poly(aniline-co-3-aminobenzoic acid) (P(ANI-3ABA)) were prepared and their physico-chemical properties were studied by UV-Vis and FTIR spectroscopy and cyclic voltammetry. According to the results obtained by atomic force microscopy, PANI/PSS had a granular shape, P(ANI-3ABA)/PSS had a spherical shape and P3ABA/PSS had a spindle-like shape. The copolymer showed a greater antimicrobial activity against Escherichia coli and Staphylcocus aureus as compared with the homopolymers. The minimal inhibitory concentration of the P(ANI-3ABA)/PSS against the gram-positive bacterium S. aureus was 0.125 mg mL⁻¹.

Biomimetic Synthesis of PANI/Graphitic Oxidized Carbon Nitride for Supercapacitor Applications

Polyaniline (PANI) composites have gained momentum as supercapacitive materials due to their high energy density and power density. However, some drawbacks in their performance remain, such as the low stability after hundreds of charge-discharge cycles and limitations in the synthesis scalability. Herein, we report for the first time PANI-Graphitic oxidized carbon nitride composites as potential supercapacitor material. The biomimetic polymerization of aniline assisted by hematin, supported by phosphorous and oxygen-modified carbon nitrides (g-POCN and g-OCN, respectively), achieved up to 89% yield. The obtained PAI/g-POCN and PANI/g-OCN show enhanced electrochemical properties, such as conductivity of up to 0.0375 S/cm, specific capacitances (C_s) of up to 294 F/g (at high current densities, 5 A/g) and a stable operation after 500 charge-discharge cycles (at 3 A/g). In contrast, the biomimetic synthesis of Free PANI, assisted by stabilized hematin in cosolvents, exhibited lower performance properties (65%). Due to their structural differences, the electrochemical properties of Free PANI (conductivity of 0.0045 S/cm and C_s of up to 82 F/g at 5 A/g) were lower than those of nanostructured PANI/g-POCN and g-OCN supports, which provide stability and improve the properties of biomimetically synthesized PANI. This work reveals the biomimetic synthesis of PANI, assisted by hematin supported by modified carbon nitrides, as a promising strategy to produce nanostructured supercapacitors with high performance.

Enzyme-Catalyzed Polymerization Process: A Novel Approach to the Preparation of Polyaniline Colloidal Dispersions with an Immunomodulatory Effect

A green, nature-friendly synthesis of polyaniline colloidal particles based on enzyme-assisted oxidation of aniline with horseradish peroxidase and chitosan or poly(vinyl alcohol) as steric stabilizers was successfully employed. Physicochemical characterization revealed formation of particles containing the polyaniline emeraldine salt and demonstrated only a minor effect of polymer stabilizers on particle morphology. All tested colloidal particles showed in vitro antioxidation activity determined via scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. In vitro, they were able to reduce oxidative stress and inhibit the production of reactive oxygen species by neutrophils and inflammatory cytokines by macrophages. The anti-inflammatory effect observed was related to their antioxidant activity, especially in the case of neutrophils. The particles can thus be especially advantageous as active components of biomaterials modulating the early stages of inflammation. In addition to the immunomodulatory effect, the presence of intrinsically conducting polyaniline can impart cell-instructive properties to the particles. The approach to particle synthesis that we employed─an original one using environmentally friendly and biocompatible horseradish peroxidase─represents a smart way of preparing conducting particles with unique properties, which can be further modified by the stabilizers used.

Genetically targeted chemical assembly of functional materials in living cells, tissues, and animals

The structural and functional complexity of multicellular biological systems, such as the brain, are beyond the reach of human design or assembly capabilities. Cells in living organisms may be recruited to construct synthetic materials or structures if treated as anatomically defined compartments for specific chemistry, harnessing biology for the assembly of complex functional structures. By integrating engineered-enzyme targeting and polymer chemistry, we genetically instructed specific living neurons to guide chemical synthesis of electrically functional (conductive or insulating) polymers at the plasma membrane. Electrophysiological and behavioral analyses confirmed that rationally designed, genetically targeted assembly of functional polymers not only preserved neuronal viability but also achieved remodeling of membrane properties and modulated cell type-specific behaviors in freely moving animals. This approach may enable the creation of diverse, complex, and functional structures and materials within living systems.

Radical addition polymerization: Enzymatic template-free synthesis of conjugated polymers and their nanostructure fabrication

Conjugated polymers are attractive for many applications due to their unique properties. Their molecular structure can easily be tuned, making them suitable for an enormous number of specific applications. Conjugated polymers have the potential to achieve electrical properties similar to those of noncrystalline inorganic semiconductors; however, their chemical structure is much more complex and somewhat resembles that of biomacromolecules. The molecular conformation and interactions of conjugated polymers play an important role in their functionality. The use of enzymes has emerged as a highly valuable alternative method to synthesize these polymers and is very useful in the fabrication of their nanostructures. Here, we present established strategies for the synthesis of conjugated polymers in template-free systems that do not interfere with the preparation of their nanostructures. These strategies are based on the use of peroxidases (class III; EC 1.11.1.7, donor: hydrogen peroxide oxidoreductase), which are enzymes that have the ability to catalyze the oxidation of a number of compounds (including aromatics such as aniline, pyrrole, thiophene and some of their derivatives), in the presence of hydrogen peroxide, to obtain conjugated polymers.

Cell-assisted synthesis of conducting polymer - polypyrrole - for the improvement of electric charge transfer through fungal cell wall

In this research we report the biological synthesis of electrically conducting polymer - Polypyrrole (Ppy). Cell-assisted enzymatic polymerization/oligomerization of Ppy was achieved using whole cell culture and cell-free crude enzyme extract from two white-rot fungal cultures. The selected fungal strains belong to Trametes spp., known laccase producers, commonly applied in bioremediation and bioelectrochemical fields. The biocatalytic reaction was initiated in situ through the copper-containing enzymes biosynthesized within the cell cultures under submerged aerobe cultivation conditions. The procedure was inspired by successful reports of laccase-catalyzed pyrrole polymerization. The usage of whole culture and/or crude enzyme extract has the advantage of overcoming enzyme purification and minimizing the liability of enzyme inactivation through improved stability of enzymes in their natural environment. Spectral and electrochemical techniques (UV-vis spectroscopy, infrared spectroscopy; cyclic voltammetry (CV)) and pH measurements provided insight into the evolution of pyrrole polymerization/oligomerization and the electrochemical features of the final product. Microscopy techniques (optical microscopy and scanning electron microscopy (SEM)) were primary tools for visualization of the formed Ppy particles. The relevance of our research is twofold: Ppy prepared in crude enzyme extract results in enzyme encapsulated within Ppy and/or Ppy-modified fungal cells can be formed when polymerization occurs in whole cell culture. The route of biocatalysis can be chosen according to the desired bioelectrochemical application. The reported study focuses on the improvement of charge transfer through the fungal cell membrane and/or cell wall by modification of the fungal cells with conducting polymer - polypyrrole.

Modification of Aspergillus niger by conducting polymer, Polypyrrole, and the evaluation of electrochemical properties of modified cells

The enhancement of bioelectrochemical properties of microorganism by in situ formation of conducting polymer within the cell structures (e.g. cell wall) was performed. The synthesis of polypyrrole (Ppy) within fungi (Aspergillus niger) cells was achieved. Two different Aspergillus niger strains were selected due to their ability to produce glucose oxidase, which initiated the Ppy formation through products of enzymatic reaction. The evolution of Ppy structural features was investigated by absorption spectroscopy, cyclic voltammetry and Fourier transform infrared spectroscopy.

Tyramine-modified pectins via periodate oxidation for soybean hull peroxidase induced hydrogel formation and immobilization

Pectin was modified by oxidation with sodium periodate at molar ratios of 2.5, 5, 10, 15 and 20 mol% and reductive amination with tyramine and sodium cyanoborohydride afterwards. Concentration of tyramine groups within modified pectin ranged from 54.5 to 538 μmol/g of dry pectin while concentration of ionizable groups ranged from 3.0 to 4.0 mmol/g of dry polymer compared to 1.5 mmol/g before modification due to the introduction of amino group. All tyramine-pectins showed exceptional gelling properties and could form hydrogel both by cross-linking of carboxyl groups with calcium or by cross-linking phenol groups with peroxidase in the presence of hydrogen peroxide. These hydrogels were tested as carriers for soybean hull peroxidase (SHP) immobilization within microbeads formed in an emulsion based enzymatic polymerization reaction. SHP immobilized within tyramine-pectin microbeads had an increased thermal and organic solvent stability compared to the soluble enzyme. Immobilized SHP was more active in acidic pH region and had slightly decreased K m value of 2.61 mM compared to the soluble enzyme. After 7 cycles of repeated use in batch reactor for pyrogallol oxidation microbeads, immobilized SHP retained half of the initial activity.

Enzymatic oligomerization and polymerization of arylamines: state of the art and perspectives

The literature concerning the oxidative oligomerization and polymerization of various arylamines, e.g., aniline, substituted anilines, aminonaphthalene and its derivatives, catalyzed by oxidoreductases, such as laccases and peroxidases, in aqueous, organic, and mixed aqueous organic monophasic or biphasic media, is reviewed. An overview of template-free as well as template-assisted enzymatic syntheses of oligomers and polymers of arylamines is given. Special attention is paid to mechanistic aspects of these biocatalytic processes. Because of the nontoxicity of oxidoreductases and their high catalytic efficiency, as well as high selectivity of enzymatic oligomerizations/polymerizations under mild conditions-using mainly water as a solvent and often resulting in minimal byproduct formation-enzymatic oligomerizations and polymerizations of arylamines are environmentally friendly and significantly contribute to a "green" chemistry of conducting and redox-active oligomers and polymers. Current and potential future applications of enzymatic polymerization processes and enzymatically synthesized oligo/polyarylamines are discussed.

Advanced Synthesis of Conductive Polyaniline Using Laccase as Biocatalyst

Polyaniline is a conductive polymer with distinctive optical and electrical properties. Its enzymatic synthesis is an environmentally friendly alternative to the use of harsh oxidants and extremely acidic conditions. 7D5L, a high-redox potential laccase developed in our lab, is the biocatalyst of choice for the synthesis of green polyaniline (emeraldine salt) due to its superior ability to oxidize aniline and kinetic stability at the required polymerization conditions (pH 3 and presence of anionic surfactants) as compared with other fungal laccases. Doses as low as 7.6 nM of 7D5L catalyze the polymerization of 15 mM aniline (in 24 h, room temperature, 7% yield) in the presence of different anionic surfactants used as doping templates to provide linear and water-soluble polymers. Aniline polymerization was monitored by the increase of the polaron absorption band at 800 nm (typical for emeraldine salt). Best polymerization results were obtained with 5 mM sodium dodecylbenzenesulfonate (SDBS) as template. At fixed conditions (15 mM aniline and 5mM SDBS), polymerization rates obtained with 7D5L were 2.5-fold the rates obtained with commercial Trametes villosa laccase. Moreover, polyaniline yield was notably boosted to 75% by rising 7D5L amount to 0.15 μM, obtaining 1g of green polyaniline in 1L-reaction volume. The green polymer obtained with the selected system (7D5L/SDBS) holds excellent electrochemical and electro-conductive properties displayed in water-dispersible nanofibers, which is advantageous for the nanomaterial to be readily cast into uniform films for different applications.

Conducting Polymer Based Nanobiosensors

In recent years, conducting polymer (CP) nanomaterials have been used in a variety of fields, such as in energy, environmental, and biomedical applications, owing to their outstanding chemical and physical properties compared to conventional metal materials. In particular, nanobiosensors based on CP nanomaterials exhibit excellent performance sensing target molecules. The performance of CP nanobiosensors varies based on their size, shape, conductivity, and morphology, among other characteristics. Therefore, in this review, we provide an overview of the techniques commonly used to fabricate novel CP nanomaterials and their biosensor applications, including aptasensors, field-effect transistor (FET) biosensors, human sense mimicking biosensors, and immunoassays. We also discuss prospects for state-of-the-art nanobiosensors using CP nanomaterials by focusing on strategies to overcome the current limitations.

Enzyme mediated synthesis of polypyrrole in the presence of chondroitin sulfate and redox mediators of natural origin

Polypyrrole (PPy) was synthesized by enzyme mediated oxidation of pyrrole using naturally occurring compounds as redox mediators. The catalytic mechanism is an enzymatic cascade reaction in which hydrogen peroxide is the oxidizer and soybean peroxidase, in the presence of acetosyringone, syringaldehyde or vanillin, acts as a natural catalysts. The effect of the initial reaction composition on the polymerization yield and electrical conductivity of PPy was analyzed. Morphology of the PPy particles was studied by scanning electron microscopy and transmission electron microscopy whereas the chemical structure was studied by X-ray photoelectron and Fourier transformed infrared spectroscopic techniques. The redox mediators increased the polymerization yield without a significant modification of the electronic structure of PPy. The highest conductivity of PPy was reached when chondroitin sulfate was used simultaneously as dopant and template during pyrrole polymerization. Electroactive properties of PPy obtained from natural precursors were successfully used in the amperometric quantification of uric acid concentrations. PPy increases the amperometric sensitivity of carbon nanotube screen-printed electrodes toward uric acid detection.

Evaluation of poly(pyrrole-2-carboxylic acid) particles synthesized by enzymatic catalysis

In this study an environmentally friendly synthesis of poly(pyrrole-2-carboxylic acid) (PCPy) particles dispersed in water–ethanol medium using enzymatic catalysis is proposed.

Soybean hull peroxidase immobilization on macroporous glycidyl methacrylates with different surface characteristics

Soybean hull peroxidase (SHP, E.C. 1.11.1.7) was immobilized by a glutaraldehyde and periodate method onto series of macroporous copolymers of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA), poly(GMA-co-EGDMA) with various surface characteristics and pore size diameters ranging from 44 to 200 nm. Glutaraldehyde immobilization method and poly(GMA-co-EGDMA) named SGE 20/12 with pore sizes of 120 nm gave immobilized enzyme with highest specific activity of 25 U/g. Deactivation studies showed that immobilization increased stability of SHP and that surface characteristics of the used copolymer had a major influence on a stability of immobilized enzyme at high temperatures and in an organic solvent. The highest thermostability was obtained using the copolymer SGE 20/12 with pore size of 120 nm, while the highest stability in dioxane had SHP immobilized onto copolymer SGE 10/4 with pore size of 44 nm. Immobilized SHP showed a wider pH optimum as compared to the native enzyme especially at alkaline pH values and 3.2 times increased K m value for pyrogallol. After 6 cycles of repeated use in batch reactor, immobilized SHP retained 25 % of its original activity. Macroporous copolymers with different surface characteristics can be used for fine tuning of activity and stability of immobilized SHP to obtain a biocatalyst suitable for phenol oxidation or polymer synthesis in organic solvents.

Protein-Induced Synthesis of Chiral Conducting Polyaniline Nanospheres

A green and novel method for the synthesis of chiral conducting polyaniline was developed. Chiral polyaniline induced by protein was obtained by using the template-assisted polymerization route. The experimental results demonstrated that proteins such as bovine hemoglobin and bovine serum albumin had the capacity to direct enantio specificity of PANI which may be ascribed to the α-helix structure within the proteins. The achieved chiral conducting polyaniline exhibited nanometered, spherical shape according to scanning electron microscopy and transmission electron microscopy images. Moreover, the high degree of crystallinity and conductivity of chiral polyaniline induced by protein was acquired.

Synergistic effect of microwave irradiation and conjugated polymeric catalyst in the facile degradation of dyes

Degradation of Orange G under controlled conditions using microwave irradiation.

Synthesis of polyaniline via DNAzyme-catalyzed polymerization of aniline

Under simple and mild conditions, G-quadruplex DNAzyme-catalyzed oxidation and polymerization of aniline by hydrogen peroxide is achieved in aqueous medium.

Laccase-catalyzed synthesis of aniline oligomers and their application for the protection of copper against corrosion

A new method for the enzymatic synthesis of oligoaniline soluble in organic solutions is developed. Aniline oligomers showed a high inhibition of copper corrosion in aqueous HCl and NaCl solutions.

Vesicles as soft templates for the enzymatic polymerization of aniline

The feasibility of using surfactant vesicles as soft templates for the peroxidase-triggered polymerization of aniline was investigated. It was found that mixed anionic vesicles (diameter approximately 80 nm) composed of sodium dodecylbenzenesulfonate (SDBS) and decanoic acid (1:1, molar ratio) are promising templates. In the presence of the vesicles and horseradish peroxidase/hydrogen peroxide (H2O2) as initiator system, aniline polymerizes under optimized conditions at pH=4.3 to the desired conductive emeraldine form of polyaniline (PANI). The optimal polymerization conditions were elaborated, and some of the chemical and physicochemical aspects of the reaction system were investigated. After addition of aniline and peroxidase to the vesicles, aniline is only loosely associated with the vesicles, as shown by NOESY-NMR and zeta potential measurements. In contrast, the peroxidase strongly binds to the vesicle surface, as shown by fluorescence measurements using TNS (2-(p-toluidino)naphthalene-6-sulfonate) as vesicle membrane probe. This binding of the enzyme to the vesicle surface indicates that the polymerization reaction is initiated predominantly on the surface of the vesicles. Cryo-transmission electron microscopy indicates that the polymerization product remains associated with the vesicles on their surface. For short reaction times (30 s<t<60 s), it is shown that oligoanilines containing an excess of oxidized units are obtained, as shown by VIS/NIR spectroscopy and MALDI-TOF mass spectrometry. For longer reaction times (1 min<t<30 min), the relative amount of over oxidized units in PANI decreases until polymers are obtained which have a VIS/NIR spectrum that is typical for the emeraldine salt form of PANI (lambdamax approximately 1000 nm). The appearance of stable unpaired electrons during the reaction was demonstrated by EPR measurements, in full support of the in situ formation of the conductive emeraldine salt form of PANI. At the end of the reaction (after 1 h), the PANI formed remains homogenously dispersed in the aqueous solution thanks to the presence of the vesicles. No precipitation occurs on a time scale of at least several weeks. FTIR and 13C NMR measurements of the product isolated from the reaction mixture confirm the formation of the emeraldine form of PANI. If the polymerization reaction is carried out in the absence of vesicles but under otherwise identical reaction conditions, the outcome of the reaction is very different, i.e., no indication at all for the formation of the conductive form of PANI.