Catalytic and bioelectrocatalytic properties of four white rot fungal laccases (Trametes hirsuta, ThL; Coriolopsis caperata, CcL; Steccherinum murashkinskyi, SmL; and Antrodiella faginea, AfL) from different orthologous groups were comparatively studied in homogeneous reactions of electron donor substrate oxidation and in a heterogeneous reaction of dioxygen electroreduction. The ThL and CcL laccases belong to high-redox-potential enzymes (E0T1 = 780 mV), while the AfL and SmL laccases are medium-redox-potential enzymes (E0T1 = 620 and 650 mV). We evaluated the efficiency of laccases in mediatorless bioelectrocatalytic dioxygen reduction by the steady-state potential (Ess), onset potential (Eonset), half-wave potential (E1/2), and the slope of the linear segment of the polarization curve. A good correlation was observed between the T1 center potential of the laccases and their electrocatalytic characteristics; however, no correlation with the homogeneous reactions of electron donor substrates’ oxidation was detected. The results obtained are discussed in the light of the known data on the three-dimensional structures of the laccases studied.

Methods of the pretreatment of reeds (grinding, hydrothermal treatment, treatment with acid or alkali solutions, organosolv, deep eutectic solvents) and their effect on the subsequent enzymatic hydrolysis by cellulase and hemicellulase complexes have been studied. Substrates with the highest reactivity were obtained by exposing the reeds to a weakly alkaline deep eutectic solvent (DES) and an alkali solution. The depth of enzymatic hydrolysis of these pretreated substrates was 63 and 59

Lignin, the second most abundant natural polymer, is a by-product of the biorefinery and pulp and paper industries. This study was undertaken to evaluate the properties and estimate the prospects of using lignin as a by-product of the pretreatment of common reed straw (Phragmites australis) with deep eutectic solvents (DESs) of various compositions: choline chloride/oxalic acid (ChCl/OA), choline chloride/lactic acid (ChCl/LA), and choline chloride/monoethanol amine (ChCl/EA). The lignin samples, hereinafter referred to as Lig-OA, Lig-LA, and Lig-EA, were obtained as by-products after optimizing the conditions of reed straw pretreatment with DESs in order to improve the efficiency of subsequent enzymatic hydrolysis. The lignin was studied using gel penetration chromatography, UV-vis, ATR-FTIR, and 1H and 13C NMR spectroscopy; its antioxidant activity was assessed, and the UV-shielding properties of lignin/polyvinyl alcohol composite films were estimated. The DES composition had a significant impact on the structure and properties of the extracted lignin. The lignin’s ability to scavenge ABTS+• and DPPH• radicals, as well as the efficiency of UV radiation shielding, decreased as follows: Lig-OA > Lig-LA > Lig-EA. The PVA/Lig-OA and PVA/Lig-LA films with a lignin content of 4% of the weight of PVA block UV radiation in the UVA range by 96% and 87%, respectively, and completely block UV radiation in the UVB range.

The conventional chemical polymerization of aniline has been described in multiple publications, while enzymatic polymerization has been poorly explored. A comparative study of the template-assisted enzymatic and chemical polymerization of aniline in a buffer solution of sodium dodecylbenzenesulfonate micelles was performed for the first time. The high-redox potential laccase from the fungus Trametes hirsuta was used as a catalyst and air oxygen served as an oxidant. Potentiometric and spectral methods have shown that oligomeric/polymeric products of the enzymatic polymerization of aniline are synthesized in the conducting emeraldine salt form immediately after the reaction is initiated by the enzyme. The use of the laccase–mediator system enabled a higher rate of enzymatic polymerization and a higher yield of final products. Potassium octocyanomolybdate (IV) served as a redox mediator. The products of the enzymatic polymerization of aniline were studied by the ATR-FTIR, MALDI-TOF and atomic force microscopy methods. The chemical oxidative polymerization of aniline under the same conditions resulted in forming a non-conducting dark brown product.

The methods of cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy were used to study the effect of electrolyte redox on the electrochemical characteristics of a composite based on a poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer and multiwalled carbon nanotubes (MWCNTs). To form a uniform thin layer of PEDOT on the surface of nanotubes, an enzymatic polymerization of the monomer was used. The electrochemically active compound sodium 1,2‑naphthoquinone-4-sulfonate (NQS) was a dopant in the main PEDOT chain and, at the same time, a component of the electrolyte. The addition of 12.5 mM NQS to the electrolyte increased the specific capacitance of the PEDOT–NQS/MWCNT composite electrode from 390 to 800 F/g at a potential sweep rate of 10 mV/s. In a 1 M H2SO4 + 12.5 mM NQS redox electrolyte, the composite electrode exhibited higher cyclic stability and lower charge transfer resistance compared to 1 M H2SO4. After 1000 cycles of potential scanning in the range from –0.1 to 0.8 V at a rate of 100 mV/s, the specific capacitance of the composite electrode in a solution of 1 M H2SO4 decreased by 8

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.

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.

1. Abbott AP, Capper G, Davies DL, Rasheed RK, Tambyrajah V. Novel solvent properties of choline chloride/urea mixtures. Chem Commun (Camb). 2003;(1):70-71. doi:10.1039/b210714g CrossRef Pubmed Google Scholar

Deep eutectic solvents (DESs) are an alternative to conventional organic solvents in various biocatalytic reactions. Meanwhile, there have been few studies reporting on synthetic reactions in DESs or DES-containing mixtures involving oxidoreductases. In this work, we have studied the effects of several DESs based on betaine as the acceptor of hydrogen bonds on the catalytic activity and stability of laccase from the basidial fungus Trametes hirsuta and performed enzymatic polymerization of the flavonoid dihydroquercetin (DHQ, taxifolin) in a DES–buffer mixture containing 60 vol.% of betaine-glycerol DES (molar ratio 1:2). The use of the laccase redox mediator TEMPO enabled an increased yield of DHQ oligomers (oligoDHQ), with a number average molecular weight of 1800 g mol−1 and a polydispersity index of 1.09. The structure of the synthesized product was studied using different physicochemical methods. NMR spectroscopy showed that oligoDHQ had a linear structure with an average chain length of 6 monomers. A scheme for enzymatic polymerization of DHQ in a DES–buffer mixture was also proposed.

Deep eutectic solvents (DESs) are an alternative to traditional organic solvents for enzymatic reactions between compounds with poor solubility. Biocatalytic polymerization of the flavonoid (+)-catechin (CC) was carried out with laccase from the fungus Trametes hirsuta in a DES–buffer mixture (betaine/glycerol 60 vol %–buffer 40 vol %). The conditions for the synthesis of catechin oligomers (oligoCCs) soluble in organic solvents have been selected. According to the data from high-performance liquid chromatography, the oligoCCs had average molecular weights of 10 620 and 2540 g/mol with polydispersity indices of 1.1 and 1.09, respectively. The physicochemical properties of the obtained oligomers were studied via UV-visible, FTIR, 1H and 13C NMR spectroscopy. The resulting oligoCCs inhibited the α-glucosidase activity (IC50 ~ 8 μg/mL).

Photo-chemically induced dynamic nuclear polarization (photo-CIDNP) is a promising solution to the inherent lack of sensitivity in NMR spectroscopy. It is particularly interesting in biological systems since it operates in water, at room temperature, and it can be repeated if the bleaching of the system can be controlled. However, the photo-CIDNP signal enhancement is well below those of other hyperpolarization techniques. While DNP, PHIP, and SABRE reach polarization enhancements of 103 to 104-fold, photo-CIDNP enhancement is typically only one order of magnitude for 1H and two orders of magnitude for 13C in the amino-acids tryptophan and tyrosine. Here we report on a photo-oxidation product of tryptophan that is strongly photo-CIDNP active under continuous wave light irradiation. In conjunction with the dye Atto Thio 12, a 1H signal enhancement of 120-fold was observed on a 600 MHz spectrometer, while at 200 MHz the enhancement was 380-fold. These enhancements in signal to noise correspond to a reduction in measurement time of 14 400-fold and 144 400-fold, respectively. The enhancement for 13C is estimated to be over 1200-fold at 600 MHz which corresponds to an impressive measurement time reduction of 1 440 000-fold. This photo-CIDNP active oxidation product of tryptophan has been identified to be 3α-hydroxypyrroloindole. The reasons for its improved signal enhancement compared to tryptophan have been further investigated.

Enzymatic synthesis of polyaniline (PANI) doped with bivalent copper ions was carried out on a sodium polystyrene sulfonate (PSS) template. The synthesized interpolymer complex PANI-Cu2+/PSS had an inhibitory effect on the growth of Staphylococcus aureus and Escherichia coli cells.

The oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) using ammonium peroxydisulfate and the high redox potential laccase from Trametes hirsuta is studied in order to clarify the significant differences in the chemical and enzymatic polymerization reactions of aniline. As opposed to the laccase-catalyzed reaction, the chemical oxidation of TMPD proceeds in two stages. The radical cation formed at the first stage is oxidized by the peroxydisulfate ion to quinoiddiimine that can interact with the initial TMPD. The kinetics of the formation of the radical cation $${\text{TMP}}{{{\text{D}}}^{{\centerdot + }}}$$ is studied by ultraviolet–visible (UV–Vis) and electron paramagnetic resonance spectroscopy. The obtained data allow making an assumption about the difference in the mechanisms of chemical and enzymatic polymerization of aniline.

The copolymers of aniline (ANI) and 2-aminophenethyl alcohol (APA) were synthesized on a poly (2-acrylamido-2-methyl-1-propanesulfonic) acid (PAMPS) template with the fungal laccase Trametes hirsuta, which has a high redox potential, as the catalyst. Atmospheric oxygen was the oxidizing agent. The copolymer/PAMPS complexes were pseudo-soluble and were characterized by various physicochemical methods. The electrical conductivity of the copolymers depended on the initial molar ratio of the monomers. The copolymer synthesized at an APA : ANI ratio of 2 : 8 possessed the best characteristics. It is shown that the laccase/mediator system can be to oxidize the primary alcohol groups of the copolymer to reactive aldehyde groups.

Template polymerization of aniline was performed using a laccase-mediator system. The high redox-potential laccase from the basidiomycete fungus Trametes hirsuta was a catalyst for polymerization. The aniline dimer served as the redox mediator; atmospheric oxygen served as the oxidant. Sodium dodecylbenzenesulfonate micelles were used as a “soft” template. The biocatalytic polymerization of aniline resulted in conducting polyaniline/sodium dodecylbenzene sulfonate complex that was tested as a protective coating. The efficiency of the inhibition of copper corrosion by the complex was 86–87%, and the dissipation rate of positive and negative charges from cotton fabrics increased by 56 and 27 times, respectively.

Laccase-mediator systems (LMS) are extensively used both for degradation of various xenobiotics and synthesis of new compounds. In this work a laccase-mediator system was applied to copolymerization of aniline and 2-aminophenythyl alcohol on a 'soft' poly(2-acrylamido-2-methyl-1-propansulfonic acid) (PAMPS) template. The one-pot biocatalytic reaction resulted in obtaining a conducting copolymer/PAMPS complex with reactive aldehyde groups which enabled grafting the physiologically active compound 3,4-dihydroxy-L-phenylalanine (DOPA) to it.