Bioactive Properties of a Novel Antibacterial Dye Obtained from Laccase-Mediated Oxidation of 8-Anilino-1-naphthalenesulfonic Acid

Fungal laccase obtained from a Cerrena unicolor strain was used as an effective biocatalyst for the transformation of 8-anilino-1-naphthalenesulfonic acid into a green-coloured antibacterial compound, which can be considered as both an antimicrobial agent and a textile dye, simultaneously. The process of biosynthesis was performed in buffered solutions containing methanol as a co-solvent, allowing better solubilisation of substrate. The transformation process was optimised in terms of the buffer pH value, laccase activity, and concentrations of the substrate and co-solvent. The crude product obtained exhibited low cytotoxicity, antibacterial properties against Staphylococcus aureus and Staphylococcus epidermidis, and antioxidant properties. Moreover, the synthesised green-coloured compound proved non-allergenic and demonstrated a high efficiency of dyeing wool fibres.

From Imines to Amides via NHC-mediated Oxidation

The unprecedented NHC mediated oxidation of imines to amides is described. This protocol features broad substrate scope and allows rapid assembly of amides in good to high yields. Notably, this...

Porphyrin in prebiotic catalysis: Ascertaining a route for the emergence of early metalloporphyrins

Metal ions are known to catalyze certain prebiotic reactions. However, the transition from metal ions to extant metalloenzymes remains unclear. Porphyrins are found ubiquitously in the catalytic core of many ancient metalloenzymes. In this study, we evaluated the influence of porphyrin-based organic scaffold, on the catalysis, emergence and putative molecular evolution of prebiotic metalloporphyrins. We studied the effect of porphyrins on the transition metal ion-mediated oxidation of hydroquinone (HQ). We report a change in the catalytic activity of the metal ions in the presence of porphyrin. This was observed to be facilitated by the coordination between metal ions and porphyrins or by formation of non-coordinated complexes. The metal-porphyrin complexes also oxidized NADH, underscoring its versatility at oxidizing more than one substrate. Our study highlights the selective advantage that some of the metal ions would have had in the presence of porphyrin, underscoring their role in shaping the evolution of protometalloenzymes.

Characterization of cellulose and TEMPO-oxidized celluloses prepared from Eucalyptus globulus

Eucalyptus (Eucalyptus globulus) cellulose was isolated from wood powder by dewaxing, delignification, and subsequent 4% NaOH extraction. 2,2,6,6-Tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized eucalyptus celluloses were prepared from never-dried eucalyptus cellulose (EC) in yields of 96% and 72% (based on the dry weight of EC) when oxidized with NaOCl of 5 and 10 mmol/g-EC, respectively. Their carboxy contents were 1.4 and 1.8 mmol/g, respectively, when determined by conductivity titration. The crystallinity of cellulose I for EC decreased by TEMPO-mediated oxidation, showing that the originally crystalline region in EC was partly converted to disordered regions by TEMPO-mediated oxidation. Correspondingly, the relative signal area of C6‒OH/C1 with the trans-gauche (tg) conformation attributed to crystalline cellulose I in the solid-state 13C NMR spectrum of EC decreased from 0.42 to 0.34 by TEMPO-mediated oxidation with NaOCl of 10 mmol/g-EC. TEMPO-oxidized EC prepared with NaOCl of 10 mmol/g-EC was almost completely converted into individual TEMPO-oxidized EC nanofibrils (TEMPO-ECNFs) of homogeneous widths of ∼3 nm widths and lengths of >1 μm by mechanical disintegration in water. However, the TEMPO-ECNFs contained many kinks and had uneven surfaces, probably owing to significant damage occurring on the surface cellulose molecules of crystalline cellulose microfibrils during TEMPO-mediated oxidation.

Chemoenzymatic Stereodivergent Synthesis of All the Possible Stereoisomers of the 2,3-Dimethylglyceric Acid Ethyl Ester

2,3-dihydroxy-2-methylbutyric acid, also known as 2,3-dimethylglyceric acid, constitutes the acyl and/or the alcoholic moiety of many bioactive natural esters. Herein, we describe a chemoenzymatic methodology which gives access to all the four possible stereoisomers of the 2,3-dimethylglyceric acid ethyl ester. The racemic ethyl α-acetolactate, produced by the N-heterocycle carbene (NHC)-catalyzed coupling of ethyl pyruvate and methylacetoin was employed as the starting material. The racemic mixture was resolved through (S)-selective reductions, promoted by the acetylacetoin reductase (AAR) affording the resulting ethyl (2R,3S)-2,3-dimethylglycerate; the isolated remaining (S)-ethyl α-acetolactate was successively treated with baker’s yeast to obtain the corresponding (2S,3S) stereoisomer. syn-2,3-Dimethylgliceric acid ethyl ester afforded by reducing the rac-α-acetolactate with NaBH4 in the presence of ZnCl2 was kinetically resolved through selective acetylation with lipase B from Candida antarctica (CAL-B) and vinyl acetate to access to (2S,3R) stereoisomer. Finally, the (2R,3R) stereoisomer, was prepared by C3 epimerization of the (2R,3S) stereoisomer recovered from the above kinetic resolution, achieved through the TEMPO-mediated oxidation, followed by the reduction of the produced ketone with NaBH4. The resulting 2,3-dimethylglycertate enriched in the (2R,3R) stereoisomer was submitted to stereospecicific acetylation with vinyl acetate and CAL-B in order to separate the major stereoisomer. The entire procedure enabled conversion of the racemic α-acetolactate into the four enantiopure stereoisomers of the ethyl 2,3-dihydroxy-2-methylbutyrate with the following overall yields: 42% for the (2R,3S), 40% for the (2S,3S), 42% for the (2S,3R) and 20% for the (2R,3R).

Intrareticular charge transfer regulated electrochemiluminescence of donor–acceptor covalent organic frameworks

The control of charge transfer between radical anions and cations is a promising way for decoding the emission mechanism in electrochemiluminescence (ECL) systems. Herein, a type of donor-acceptor (D-A) covalent organic framework (COF) with triphenylamine and triazine units is designed as a highly efficient ECL emitter with tunable intrareticular charge transfer (IRCT). The D-A COF demonstrates 123 folds enhancement in ECL intensity compared with its benzene-based COF with small D-A contrast. Further, the COF’s crystallinity- and protonation-modulated ECL behaviors confirm ECL dependence on intrareticular charge transfer between donor and acceptor units, which is rationalized by density functional theory. Significantly, dual-peaked ECL patterns of COFs are achieved through an IRCT mediated competitive oxidation mechanism: the coreactant-mediated oxidation at lower potential and the direct oxidation at higher potential. This work provides a new fundamental and approach to improve the ECL efficiency for designing next-generation ECL devices.