Hydrogen sulfide production during early yeast fermentation correlates with volatile sulfur compound biogenesis but not thiol release.

Yeasts undergo intensive metabolic changes during the early stages of fermentation. Previous reports suggest the early production of hydrogen sulfide (H2S) is associated with the release of a range of volatile sulfur compounds (VSCs), as well as the production of varietal thiol compounds 3-sulfanylhexan-1-ol (3SH) and 3-sulfanylhexyl acetate (3SHA) from six-carbon precursors, including (E)-hex-2-enal. In this study, we investigated the early H2S potential, VSCs/thiol output, and precursor metabolism of 11 commonly used laboratory and commercial Saccharomyces cerevisiae strains in chemically defined synthetic grape medium (SGM) within 12 h after inoculation. Considerable variability in early H2S potential was observed among the strains surveyed. Chemical profiling suggested that early H2S production correlates with the production of dimethyl disulfide, 2-mercaptoethanol, and diethyl sulfide, but not with 3SH or 3SHA. All strains were capable of metabolizing (E)-hex-2-enal, while the F15 strain showed significantly higher residue at 12 h. Early production of 3SH, but not 3SHA, can be detected in the presence of exogenous (E)-hex-2-enal and H2S. Therefore, the natural variability of early yeast H2S production contributes to the early output of selected VSCs, but the threshold of which is likely not high enough to contribute substantially to free varietal thiols in SGM.

Enantioselective Total Synthesis of (R,R)-Blumenol B and d9-(R,R)-Blumenol B.

C13-norisoprenoids are of particular importance to grapes and wines, as these molecules influence wine aroma and have been shown to significantly contribute to the distinct character of various wine varieties. Blumenol B is a putative precursor to a number of important wine aroma compounds, including the well-known compounds theaspirone and vitispirane. The enantioselective synthesis of (R,R)-blumenol B from commercially available 4-oxoisophorone was achieved using a short and easily scaleable route, which was then successfully applied to the synthesis of poly-deuterated d9-blumenol B.

Metabolite characterization of fifteen by-products of the coffee production chain: From farm to factory.

Approximately 11.4 million tonnes of solid by-products and an increased amount of waste water will be generated during the 2020/21 coffee harvest. There are currently no truly value-adding uses for these potentially environmentally threatening species. This work presents the most wide-ranging chemical investigation of coffee by-products collected from farms to factories, including eight never previously investigated. Twenty compounds were found for the first time in coffee by-products including the bioactive neomangiferin, kaempferol-3-O-rutinoside, lup-20(29)-en-3-one and 3,4-dimethoxy cinnamic acid. Five by-products generated inside a factory showed caffeine (53.0-17.0 mg.g-1) and/or chlorogenic acid (72.9-10.1 mg.g-1) content comparable to coffee beans, while mature leaf from plant pruning presented not only high contents of both compounds (16.4 and 38.9 mg.g-1, respectively), but also of mangiferin (19.4 mg.g-1) besides a variety of flavonoids. Such by-products are a source of a range of bioactive compounds and could be explored with potential economic and certainly environmental benefits.

First use of grape waste-derived building blocks to yield antimicrobial materials.

Grape marc is an underutilised waste material that poses significant environmental issues. This study offers the first proof-of-concept investigation into the polymerisation of both crude and purified Sauvignon blanc grape marc extracts using the diacyl chlorides terephthaloyl chloride, succinyl chloride, adipoyl chloride, sebacoyl chloride, and the tartaric acid derivative (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbonyl dichloride to obtain new materials, in what to the best of our knowledge is the first reported example of a direct polymerisation of an agricultural waste extract. A total of 26 novel materials were prepared. It has also shown that quercetin, a phenolic monomer found in grape marc extracts, can be polymerised with (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbonyl dichloride to give a polymer that shows activity towards S. aureus.

A single run liquid chromatography-tandem mass spectrometry method for the analysis of varietal thiols and their precursors in wine.

This research details the development of a novel LC-MS/MS method involving a QuEChERS-based extraction that, for the first time, achieves the fast and concurrent analysis of both free varietal thiols (3-sulfanylhexan-1-ol, 3-sulfanylhexyl acetate, and 4-methyl-4-sulfanylpentan-2-one) and their S-glutathionylated/S-cysteinylated precursors in wine samples. Limits of detections for the free thiols were comparable to or lower than those obtained with previously reported more laborious methods. Repeatability for the free thiols ranged between 3-19% and from 0.1-7.7% for the thiol precursors. The method was subsequently applied to the analysis of a selection of 22 wines from a range of different grape varieties. The rapidity of this method combined with its sensitivity makes it suitable for both research and industry applications.

Does H3O+ Really Act as a Ligand in the Solid State?

The evidence for the existence of metal complexes containing H3O+ as a ligand in the solid state is examined. Each of the 68 examples in the Cambridge Structural Database in which H3O+ is bound to a transition metal, lanthanoid, actinoid, or main group metal ion is detailed and critically appraised. It is concluded that none of the reported examples of complexes containing coordinated H3O+ have been unequivocally characterized and that they result from either curation errors or misinterpretations of the crystallographic data. These conclusions are supported by computational techniques, which show that three purported H3O+ complexes based on the 1,4,7,10,13,16,21,24-octa-azabicyclo(8.8.8)hexacosane azacryptand skeleton are better described as aqua complexes, with protonation occurring at the amine ligand.

Five-coordinate transition metal complexes and the value of τ5: observations and caveats.

The τ5 parameter, first proposed by Addison and coworkers, is the principal measure of the geometry of five-coordinate transition metal complexes, with τ5 = 0 said to describe a perfect square pyramidal geometry and τ5 = 1 a perfect trigonal pyramidal geometry. Therefore, the geometries of all five-coordinate complexes are assumed to lie on a continuum between these two extremes. Herein we show that there are a significant number of examples of transition metal complexes having τ5 > 1, leading to an equatorially distorted trigonal bipyramidal geometry with the transition metal ion lying out of the plane of the equatorial donor atoms. We also show that complexes having τ5 = 0 and displaying perfect square pyramidal geometry are very much the exception, and that the majority of complexes for which τ5 = 0 have the metal ion sitting above the mean plane of the donor atoms in the square plane, in a basally distorted square pyramidal geometry. Density functional theory computations on a number of these complexes show that the structural distortions are inherent features of the complexes, and not merely the result of intermolecular interactions.