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We characterise a reversible bacterial zinc-containing benzyl alcohol dehydrogenase (BaDH) accepting either NAD+ or NADP+ as a redox cofactor. Remarkably, its redox cofactor specificity is pH-dependent with the phosphorylated cofactors favored at lower and the dephospho-forms at higher pH. BaDH also shows different steady-state kinetic behavior with the two cofactor forms. From a structural model, the pH-dependent shift may affect the charge of a histidine in the 2′-phosphate-binding pocket of the redox cofactor binding site. The enzyme is phylogenetically affiliated to a new subbranch of the Zn-containing alcohol dehydrogenases, which share this conserved residue. BaDH appears to have some specificity for its substrate, but also turns over many substituted benzyl alcohol and benzaldehyde variants, as well as compounds containing a conjugated C=C double bond with the aldehyde carbonyl group. However, compounds with an sp3-hybridised C next to the alcohol/aldehyde group are not or only weakly turned over. The enzyme appears to contain a Zn in its catalytic site and a mixture of Zn and Fe in its structural metal-binding site. Moreover, we demonstrate the use of BaDH in an enzyme cascade reaction with an acid-reducing tungsten enzyme to reduce benzoate to benzyl alcohol. Key points: •Zn-containing BaDH has activity with either NAD+or NADP+at different pH optima. •BaDH converts a broad range of substrates. •BaDH is used in a cascade reaction for the reduction of benzoate to benzyl alcohol. [ABSTRACT FROM AUTHOR]

As a reliable redox mediator, potassium nitrate was employed in homogeneous electrolysis with CH3CN at room temperature to electrochemically oxidize aryl compounds. The oxidation reactions carried out in an undivided cell that was provided with a carbon anode and a stainless steel cathode, along with the minimum amount of H2SO4 at a current density of 50 mA/cm2. A variety of substituted toluenes and aromatic alcohols were effectively oxidized to the corresponding aldehydes with the maximum degree of selectivity. [ABSTRACT FROM AUTHOR]

A set of metals modified TiO2 photocatalysts were prepared starting from titanium tetraisopropoxyde and different metal precursors to study the influence of the addition of the various foreign agents on the physico-chemical and photocatalytic properties of the catalysts. The powders were characterized by X-ray diffraction, Raman spectroscopy, specific surface area measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence, temperature programmed desorption after CO2 adsorption. The photocatalytic activity was evaluated using as probe reactions the partial oxidation of three aromatic alcohols: benzyl alcohol (BA), 4-methoxy benzyl alcohol (4-MBA), and 4-hydroxy benzyl alcohol (4-HBA) under simulated solar light irradiation. Different oxidation and selectivity values were obtained for the three substrates depending not only on the type of metals but also on the nature and position of the substituent in the phenyl ring of benzyl alcohol. As a general behaviour, the doped samples allowed the achievement of a greater selectivity especially for 4-MBA even if sometimes with minor conversions. The presence of W or Nb was beneficial for both conversion and selectivity for all the substrates with respect to bare TiO2. [ABSTRACT FROM AUTHOR]

The fungal secretome comprises various oxidative enzymes participating in the degradation of lignocellulosic biomass as a central step in carbon recycling. Among the secreted enzymes, aryl-alcohol oxidases (AAOs) are of interest for biotechnological applications including production of bio-based precursors for plastics, bioactive compounds, and flavors and fragrances. Aryl-alcohol oxidase 2 (PeAAO2) from the fungus Pleurotus eryngii was heterologously expressed and secreted at one of the highest yields reported so far of 315 mg/l using the methylotrophic yeast Pichia pastoris (recently reclassified as Komagataella phaffii). The glycosylated PeAAO2 exhibited a high stability in a broad pH range between pH 3.0 and 9.0 and high thermal stability up to 55 °C. Substrate screening with 41 compounds revealed that PeAAO2 oxidized typical AAO substrates like p-anisyl alcohol, veratryl alcohol, and trans,trans-2,4-hexadienol with up to 8-fold higher activity than benzyl alcohol. Several compounds not yet reported as substrates for AAOs were oxidized by PeAAO2 as well. Among them, cumic alcohol and piperonyl alcohol were oxidized to cuminaldehyde and piperonal with high catalytic efficiencies of 84.1 and 600.2 mM−1 s−1, respectively. While the fragrance and flavor compound piperonal also serves as starting material for agrochemical and pharmaceutical building blocks, various positive health effects have been attributed to cuminaldehyde including anticancer, antidiabetic, and neuroprotective effects. PeAAO2 is thus a promising biocatalyst for biotechnological applications. Key points: • Aryl-alcohol oxidase PeAAO2 from P. eryngii was produced in P. pastoris at 315 mg/l. • Purified enzyme exhibited stability over a broad pH and temperature range. • Oxidation products cuminaldehyde and piperonal are of biotechnological interest. Graphical abstract [ABSTRACT FROM AUTHOR]

The hydrogenolysis reaction of aromatic alcohols (benzyl alcohol, 1-phenylethanol and diphenylmethanol), promoted by supported palladium catalysts, such as Pd/TiO, Pd/SiO and Pd/CoO, has been investigated at 0.1 MPa H and 323 K. The catalysts have been characterized by BET, TPR, XRD, TEM and XPS. A different kinetic behaviour was observed: in presence of Pd/TiO and Pd/SiO catalysts, prepared by impregnation, the hydrogenolysis activity follows the order benzyl alcohol > 1-phenylethanol ≥ diphenylmethanol, whereas it is totally reversed on Pd/CoO, prepared by co-precipitation. All results indicate that the reactivity of supported Pd catalysts, in the hydrogenolysis reaction, depends on the support nature, the preparation method of catalysts and the aromatic alcohols structure. Kinetic experiments carried out at different partial hydrogen pressure allow to elucidate the pathway of the C-OH bond scission, involving a radical substitution of the carbon bonded OH group by a hydrogen atom coming from the metal surface 'via' associative and dissociative paths. [ABSTRACT FROM AUTHOR]

In the present study, heterogeneous copper(II)-cysteine/SiO-AlO catalyst was successfully prepared by a simple adsorption method. The physical and chemical properties of Cu(II)-cysteine/SiO-AlO were investigated by X-ray diffraction, thermal gravimetric analyzer, FT-IR spectroscopy, Brunauer-Emmett-Teller, UV-Vis spectroscopy, scanning electron microscopy and atomic absorption spectrometer. The obtained composite was effectively employed as catalyst for selective oxidation of various aromatic alcohols to corresponding aldehydes in high yields using hydrogen peroxide as an oxidant under mild condition. The catalyst can be recycled over five times without significant loss of activity. [ABSTRACT FROM AUTHOR]

We have measured the parameters of the bands of the stretching vibrations νOH (frequency width, peak and integral intensities) in the IR spectra of a large number of H‐complexes of 1,1‐diphenylethanol [(C6H5)2C(CH3)OH] with solvents of different protophilic forces, for which systematic data are not available. The enthalpies of formation of the H‐complexes and the protogenic properties of the alcohol indicated were estimated, and also correlations between spectral characteristics were established. [ABSTRACT FROM AUTHOR]