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Lignin is a complex polymeric molecule constituting various linkages between aromatic moieties. Typically, the β-O-4 linkage accounts for more than half of the linkage structures present in lignin. The current study focuses on the oxidative transformation of veratryl alcohol (VA)-a compound that can be formed by cleavage of β-O-4 linkages in lignin-to veratraldehyde (VAld) with air using ruthenium supported on γ-alumina or silica as catalyst with water or methanol as solvent in a batch reactor. Ru/AlO, prepared with ruthenium(IV)oxide hydrate showed superior catalytic activity, yielding 89 % VAld in water at 160 °C with 5 bar air pressure after 8 h of reaction. Prolonged reaction time led to significant formation of the decarbonylated product veratrol from VAld. When the reaction was completed under 20 bars of argon in methanol instead of water, the methyl ether of VA (i.e. 1,2-dimethoxy-4-(methoxymethyl)benzene) prevailed, indicating that methanol protected the hydroxyl group in VA from being oxidized to VAld. Catalysts containing alternative transition metals (Mn, Co, Cu and Ag) supported on AlO gave significantly lower activities compared to Ru/AlO under identical reaction conditions. The Ru/AlO catalyst was reused in three consecutive reaction runs in water, but a decrease in VAld yield was obtained after the third cycle possibly due to leaching of Ru from the support. [ABSTRACT FROM AUTHOR]

• CuO/SBA-15 is an active, stable and selective catalyst for the oxidation of alcohols. • Veratryl alcohol was selectively oxidized to veratraldehyde. • Propylene glycol was selectively oxidized to hydroxy acetone. Selective oxidation of veratryl alcohol (VAlc) to veratraldehyde (VAld) under mild conditions using heterogeneous catalysts is advantageous for industrial applications. In the present study, newly developed SBA-15 supported copper oxide catalyst designated as CuO(5,10,15 wt.%)/SBA-15 was examined for the selective oxidation of VAlc to VAld using tert-butyl hydroperoxide (TBHP) as an oxidant between 40 and 100 °C. CuO(10 wt.%)/SBA-15 showed high conversion (82.5%) compared to others by forming VAld with 100% selectivity. We examined its selective oxidising power using a substrate possessing both the primary and secondary alcoholic functions, namely propylene glycol (PG). In this substrate, only the secondary alcoholic group was oxidized to hydroxyacetone (HA). It suggests preferential adsorption of the primary alcoholic group of PG on the catalyst surface close to the adsorbed TBHP, thus leaving only the secondary alcoholic group positionally favourable for oxidation. In addition, the catalyst effectively oxidized 2-butanol to 2-butanone. So, the catalyst is verified active against both primary and secondary alcohols, but when both of them are present on the adjacent carbons of the same compound, only the secondary alcoholic function is oxidized. So, the present catalyst could have tremendous applications for selective oxidation in organic synthesis. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Nano-structured, spinel Co3O4 catalyst was developed for the aqueous phase oxidation of veratryl alcohol, which showed the highest conversion of 85% with 96% selectivity to veratryl aldehyde. The co-existence of Co3+ and Co2+ species in the octahedral and tetrahedral positions respectively, was confirmed by XPS, cyclic voltammogram, TPR and TPO characterization. The rod-like morphology of Co3O4 catalyst was confirmed by HRTEM. The effects of various reaction parameters namely, catalyst concentration, temperature and partial oxygen pressure on conversion and selectivity patterns were also studied for the oxidation of veratryl alcohol. This catalyst also showed an excellent stability as evidenced by successful reusability for three times. [Copyright &y& Elsevier]

Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for the industry. Herein we report the synthesis and characterization of six manganese(III) complexes 1-6, incorporating dianionic hexadentate Schiff base ligands (H2L¹-H2L4) and different anions. Complex 4, 2 Mn2L²2(H2O)2(DCA)2 was crystallographically characterized. Complexes 1-4 behave as more efficient mimics of peroxidase in contrast to 5-6. We have studied the use of these complexes as catalysts for the degradation of the lignin model compound veratryl alcohol. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratryl alcohol conversion to veratraldehyde have been achieved at room temperature in presence of air flow using 0.5% of catalyst. [ABSTRACT FROM AUTHOR]

Ionic ligands derived from a salen ligand containing two proximal 1,3-disubstituted imidazolium ionic liquid cores form cobalt(III) complexes capable of selectively oxidizing veratryl alcohol, a lignin model compound, to veratraldehyde using air as the source of oxygen. These complexes are easy to prepare, inexpensive, water stable, and soluble in ionic liquids, making them viable candidates for use as oxidation catalysts. [ABSTRACT FROM AUTHOR]

Lignin peroxidase has been purified to homogeneity using a process of concentration by ultrafiltration and anion exchange chromatography on diethylaminoethyl (DEAE) cellulose from the liquid culture filtrate of the brown rot fungi Gleophyllum striatum MTCC-1117. The molecular mass of the purified enzyme is 43 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The Km values for the enzyme using veratryl alcohol, hydrogen peroxide and n-propanol were 66 µM, 82 µM and 476 µM, respectively. The pH and temperature optima of the enzyme were 2.8 and 25°C, respectively. The enzyme is completely inhibited by 20% of the water miscible organic solvents acetone dioxane, diethylether, acetonitrile and dimethylformamide. The lignin peroxidase oxidizes polycyclic aromatic hydrocarbons pyrene, acenaphthene, anthracene, dibenothiophene and 9-methyl anthracene. [ABSTRACT FROM AUTHOR]

Sixteen phenolic compounds, 14 of which naturally occurring, were compared to the synthetic 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and violuric acid (VA) in terms of their ability to act as mediators/enhancers in: (1) laccase oxidation of veratryl alcohol as a lignin model compound, and (2) electrochemical oxidation of kraft and flax lignins. HPLC analysis revealed that the syringyl-type phenols methyl syringate and acetosyringone were the most efficient natural enhancers in the laccase oxidation of veratryl alcohol. Both compounds, though far from the performance of ABTS were able to generate veratraldehyde in amount similar to that obtained with VA. By contrast, the best performing phenolic enhancers for the electrochemical oxidation of lignins were sinapinaldehyde, vanillin, acetovanillone, and syringic acid. Catalytic efficiencies close to those achieved with ABTS and VA were calculated for these phenolic compounds. [ABSTRACT FROM AUTHOR]

Veratryl alcohol (VA) is a product from the biodegradation of lignocellulosic biomass. The objective of this study was to explore the possibility whether VA could be used as the fuel of the microbial fuel cell (MFC) to generate power. Two types of MFCs, a two-chamber MFC and a single-chamber air-cathode MFC, were set up for experiments. In the two-chamber MFC, average maximum current outputs higher than 700 μA were obtained using various mixtures of glucose and VA as the fuel. The highest power density of 35.17 W m-3 was achieved using the mixture of 1000 mg L-1 glucose and 50 mg L-1 VA as the fuel. With 500 mg L-1 VA as the fuel in the MFC, we obtained an average maximum current output of 181 μA. In the single-chamber MFC, the maximum current output reached up to 178 μA with 500 mg L-1 VA in the fed-batch mode and the maximum CE reached 23.77% with 100 mg L-1 VA. At the end of all operation cycles of the MFCs, the glucose and VA were undetectable in the solution, and the removal efficiencies of COD were between 75% and 88%. The denaturing gradient gel electrophoresis profiles of 16S rRNA gene indicated that the dominant species on the anode biofilm did not change significantly with the different substrates, but the abundance of some species increased greatly. The scanning electron micrographs showed that the most abundant bacteria on the electrode were bacilli. The dominant species belonged to bacteroidetes and proteobacterium. [ABSTRACT FROM AUTHOR]

Aims: A sterile red fungus (SRF) isolated from cortices of roots of both wheat ( Triticum aestivum cv. Gamenya) and ryegrass ( Lolium rigidum cv. Wimmera) was found to protect the hosts from phytopathogens and promote plant growth. In this work, the major secondary metabolites produced by this SRF were analysed, and their antibiotic and plant-growth-promoting activities investigated. Methods and Results: Two main compounds, veratryl alcohol (VA) and 4-(hydroxymethyl)-quinoline, were isolated from the culture filtrate of the fungus. In antifungal assays, VA inhibited the growth of Sclerotinia sclerotiorum and Pythium irregulare even at low amounts, while high concentrations (>100 μg per plug) of 4-(hydroxymethyl)-quinoline were needed. Both metabolites revealed weak inhibition of Rhizoctonia solani. Furthermore, both compounds showed a growth promotion activity on canola ( Brassica napus) seedlings used as bioassays. Conclusions: Isolation and characterization of the main secondary metabolites from culture filtrates of a root-inhabiting sterile fungus are reported. The biological assays indicate that these secondary metabolites may have a role in both plant growth regulation and antifungal activity. Significance and Impact of the Study: This study provides a better understanding of the metabolism of a cortical fungus that may have a useful role in the biological suppression of root-infecting soil-borne plant pathogens. [ABSTRACT FROM AUTHOR]

Abstract: Heterologous expression of Trametes cervina lignin peroxidase (LiP), the only basidiomycete peroxidase that has a catalytic tyrosine, was investigated. The mature LiP cDNA was cloned into the pET vector and used to transform Escherichia coli. Recombinant LiP protein accumulated in inclusion bodies as an inactive form. Refolding conditions for its in vitro activation—including incorporation of heme and structural Ca2+ ions, and formation of disulfide bridges—were optimized taking as a starting point those reported for other plant and fungal peroxidases. The absorption spectrum of the refolded enzyme was identical to that of wild LiP from T. cervina suggesting that it was properly folded. The enzyme was able to oxidize 1,4-dimethoxybenzene and ferrocytochrome c confirming its high redox potential and ability to oxidize large substrates. However, during oxidation of veratryl alcohol (VA), the physiological LiP substrate, an unexpected initial lag period was observed. Possible modification of the enzyme was investigated by incubating it with H2O2 and VA (for 30min before dialysis). The pretreated enzyme showed normal kinetics traces for VA oxidation, without the initial lag previously observed. Steady-state kinetics of the pretreated LiP were almost the same as the recombinant enzyme before the pretreatment. Moreover, the catalytic constant (k cat) for VA oxidation was comparable to that of wild LiP from T. cervina, although the Michaelis–Menten constant (K m) was 8-fold higher. The present heterologous expression system provides a valuable tool to investigate structure–function relationships, and autocatalytic activation of the unique T. cervina LiP. [Copyright &y& Elsevier]

Abstract: Heterogeneous catalytic oxidation of veratryl alcohol to veratryaldehyde with o-iodoxybenzoic acid (IBX) in the presence of cucurbit[8]uril (Q[8]) has been investigated. The evidence of oxidation kinetics affirmed the supramolecular catalysis of Q[8]. Experimental investigation of addition of catalyst and the initial pH suggested that the optimum proportion of reagents is a 0.1:1:1M ratio (Q[8]:alcohol:IBX) and neutral pH value. The screening of macrocycles, such as cucurbiturils and cyclodextrins, indicated the obvious dependence of catalytic activity on the cavity size and chemical structure of catalysts. The Q[8]-catalytic transformation of benzyl alcohol and 3-methoxybenzyl alcohol exhibited a very satisfying conversion. [Copyright &y& Elsevier]

Lignin peroxidase from the liquid culture filtrate of Gloeophyllum sepiarium MTCC-1170 has been purified to homogeneity. The molecular weight of the purified enzyme was 42 kDa as determined by SDS-PAGE. The Km values were 54 and 76 µM for veratryl alcohol and H2O2, respectively. The pH and temperature optima were 2.5 and 25°C, respectively. Depolymerization of coal by the fungal strain has been demonstrated using humic acid as a model of coal. Depolymerization of humic acid by the purified lignin peroxidase has been shown by the decrease in absorbance at 450 nm and increase in absorbance at 360 nm in presence of H2O2. Depolymerization of humic acid by the purified enzyme has also been demonstrated by the decrease in the viscosity with time of the reaction solution containing humic acid, H2O2, and the purified lignin peroxidase. The influence of NaCl and NaN3 and inhibitory effects of various metal chelating agents on the lignin peroxidase activity were studied. [ABSTRACT FROM AUTHOR]

Abstract: Metals can potentially play a role in the non-enzymatic processes involved in wood biodegradation. Dihydroxybenzenes reduce Cu(II)–Cu(I), which then react with H2O2 driving a Fenton reaction. In this work the degradation of veratryl alcohol (VA), the simplest non-phenolic lignin model compound, via a cuprous Fenton reaction mediated by 1,2-dihydroxybenzene (catechol, CAT) was studied. A factorial experimental design was performed to assess the impact of several experimental variables including, pH, and CAT, CuCl2 and H2O2 concentrations on VA degradation. Optimized conditions were determined using a response surface modeling methodology (RSM). The greatest amount of VA degradation occurred at a CAT:CuCl2:H2O2 ratio of 0.287:0.313:4.062, a pH of 3.6. A time-course measurement for VA degradation was performed under these experimental conditions and after an 8h reaction period, 31% of the VA was degraded. Under the same experimental conditions, VA degradation by an iron CAT-driven Fenton reaction was more effective than the copper CAT-driven Fenton reaction. In a similar experiment, carboxymethyl cellulose (CMC) depolymerization was also determined. Only the iron CAT-driven Fenton reaction was found to depolymerize CMC. We suggest that the greater redox potential of the Fe(III)CAT complex compared to the Cu(II)CAT complex would dictate that under most environmental conditions, degradation of VA would occur by the iron complex only. This research has important implications for the mechanisms of brown rot fungal degradation in wood because it eliminates a pathway that had previously been proposed as a mechanism explaining free radical generation in the oxidative depolymerization of cellulose in the cell wall. [Copyright &y& Elsevier]

Abstract: In this study a new biomimetic lignin-peroxidase-like catalyst was investigated. Such a heterogeneous catalyst could be of potential interest for oxidative degradation of plant effluents, containing soluble lignin derivatives. 5,10,15,20-Tetrakis(4-sulfonato-phenyl)porphine-Mn(III) was coordinated to imidazole-bearing silica to give a stable adduct; by contrast, the metalloporphine did not significantly interact with plain silica gel or aminopropylsilica. The adduct showed a remarkable ability to catalyze veratryl alcohol oxidation at the expenses of H2O2. Kinetic and operational characterisation of the catalyst is also reported. [Copyright &y& Elsevier]

Abstract: Bioelectrocatalytic reduction of H2O2 catalysed by lignin peroxidase from Phanerochaete chrysosporium (LiP) was studied with LiP-modified graphite electrodes to elucidate the ability of LiP to electro-enzymatically oxidise phenols, catechols, as well as veratryl alcohol (VA) and some other high-redox-potential lignin model compounds (LMC). Flow-through amperometric experiments performed at +0.1 V vs. Ag|AgCl demonstrated that LiP displayed significant bioelectrocatalytic activity for the reduction of H2O2 both directly (i.e., in direct electron transfer (ET) reaction between LiP and the electrode) and using most of studied compounds acting as redox mediators in the LiP bioelectrocatalytic cycle, with a pH optimum of 3.0. The bioelectrocatalytic reduction of H2O2 mediated by VA and effects of VA on the efficiency of bioelectrocatalytic oxidation of other co-substrates acting as mediators were investigated. The bioelectrocatalytic oxidation of phenol- and catechol derivatives and 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulphonate) by LiP was independent of the presence of VA, whereas the efficiency of the LiP bioelectrocatalysis with the majority of other LMC acting as mediators increased upon addition of VA. Special cases were phenol and 4-methoxymandelic acid (4-MMA). Both phenol and 4-MMA suppressed the bioelectrocatalytic activity of LiP below the direct ET level, which was, however, restored and increased in the presence of VA mediating the ET between LiP and these two compounds. The obtained results suggest different mechanisms for the bioelectrocatalysis of LiP depending on the chemical nature of the mediators and are of a special interest both for fundamental science and for application of LiP in biotechnological processes as solid-phase bio(electro)catalyst for decomposition/detection of recalcitrant aromatic compounds. [Copyright &y& Elsevier]

Abstract: Dihydroxybenzenes reduce Fe(III) to Fe(II), which react with H2O2 driving a Fenton reaction. This non-enzymic mechanism operates in wood degradation by brown-rot fungi, which mainly degrade wood carbohydrates and, to a lesser extent, lignin. Consequently, less attention has been focussed on lignin transformation by these organisms. In this work, the degradation of veratryl alcohol (VA), the simplest lignin model compound, via a Fenton reaction driven by 1,2-dihydroxybenzene (catechol, CAT) was studied. Multivariate analysis performed in order to determine the relationship between pH and concentrations of CAT, FeCl3 and H2O2 showed that the highest VA degradation, 1mol base, was obtained at the CAT:FeCl3:H2O2 ratio of 0.375:0.375:5.0 at pH 3.4. Under these reaction conditions, VA degradation and mineralisation were, respectively, 3.8 and almost 40 times greater than for a Fe(II)-Fenton reaction. [Copyright &y& Elsevier]