Monthly Archives: September 2023

Chiral Ligands for Au(I), Au(III), and Au(I)/Au(III) Redox Catalysis

Posted on by
Chiral Ligands for Au(I), Au(III), and Au(I)/Au(III) Redox Catalysis


Abstract

Gold catalysis has emerged as an efficient tool for the selective functionalisation of C−C multiple bonds. Despite significant progress in this field, the potential of asymmetric gold catalysis has not been fully explored to date. A historical retrospect on the progress in this area reveals that enantioselective gold catalysis is based on three pillars: Au(I) catalysis, Au(III) catalysis, and Au(I)/Au(III) redox catalysis. Irrespective of the mode of catalysis being operative, the design of new ligands is crucial for the development of gold-catalysed organic transformations. This minireview summarizes the progress made in the development of ligand design for enantioselective Au(I) catalysis, Au(III) catalysis, and Au(I)/Au(III) redox catalysis focusing on the ligands which were specially designed for gold catalysis.

Fused Polycyclic NHC Ligands in Gold Catalysis: Recent Advances

Posted on by
Fused Polycyclic NHC Ligands in Gold Catalysis: Recent Advances


Abstract

Thanks to their appealing properties, N-heterocyclic carbene (NHC) ligands gained considerable significance as highly powerful ancillary ligands in gold catalysis. While NHC-gold catalysis is still dominated by the classical imidazole-derived NHC ligands, annelated NHC systems, which feature fused aromatic rings to the carbenic heterocycle, have drawn wider attention over the last few years thanks to their unique structural and electronic properties. Fused polyaromatic NHCs are indeed versatile platforms that offer unique stereoelectronic tuning possibilities to exhibit superior activity and/or selectivity in NHC-gold catalysis. But their polycyclic scaffolds also provide further scope for functionalization and the introduction of chirality, stimuli-responsiveness, or cooperativity within the NHC-gold systems. In this review, the recent advances in this area are discussed and a particular attention is drawn on the unique role of the annelation.

Transition Metal‐Catalyzed Rearrangement and Cycloisomerization Reactions Toward Hedonic Materials

Posted on by
Transition Metal-Catalyzed Rearrangement and Cycloisomerization Reactions Toward Hedonic Materials


Abstract

Over the last century, the fragrance industry had relied on the synthetic chemists for the development of new odors, but also for the replacement of some known materials due to allergy or toxicity. Transition metal-catalyzed transformations have allowed atom economy and synthetic efficiency for several transformations and they caught the attention of fragrance industrials. The metal-catalyzed cyclization reactions have been particularly successful toward the synthesis of key skeletons. This review highlights the developments of selected hedonic materials according to transition metal-catalyzed according to cycloisomerization reactions and related rearrangements.

Cationic Complexes with Au→Ge Bonds – Synthesis and Carbophilic Reactivity

Posted on by
Cationic Complexes with Au→Ge Bonds – Synthesis and Carbophilic Reactivity


Abstract

As part of our efforts to interface late transition metals with Lewis acidic main group fragments, we have decided to investigate gold complexes bearing halogermanes as Z-type ligands. Toward this end, we have synthesized complexes of general formula [(o-(Ph2P)C6H4)2(Ph)(X)GeAuCl] (X = F, Cl). Experimental and computational analyses indicate the presence of an Au→Ge interaction in both cases. Chloride abstraction reactions have also been investigated. In the case of X = Cl, double chloride abstraction with AgSbF6 affords a putative dication that gradually abstracts fluoride from its counterion. This putative dication is also significantly more active as a catalyst than its monocationic analog in alkyne hydroamination reactions.

Enantioselective Synthesis of [5]Helicenes Containing Two Additional Chiral Axes

Posted on by
Enantioselective Synthesis of [5]Helicenes Containing Two Additional Chiral Axes


Abstract

A Au-catalyzed protocol for the enantioselective synthesis of molecular architectures containing an internal [5]helicene and two peripherical axial stereogenic elements is described. While the diasteroselectivity of the double alkyne hydroarylation sequence is not optimal, and mixtures that contain similar amounts of two of the four possible diasteromeric products are obtained (one C2 and one non-symmetric), the assembly of the C2-symmetric isomer often occurs with high enantioselectivity (up to 98 % ee). The absolute configurations of the products obtained were determined by X-ray crystallography. Studies on the thermal racemization of the internal [5]helicene moiety in the C2-symmetric isomers determined the half-life of this element to be approximately 3 h at 50 °C.

Evaluation of Toxicity and Genotoxicity of Concrete Cast with Steel Slags Using Higher Terrestrial Plants

Posted on by

Abstract

The potential impact of concrete mixtures containing steel slag (SS) as a partial replacement of natural aggregates (NA) on the terrestrial ecosystem was assessed using a battery of plant-based bioassays. Leaching tests were conducted on four concrete mixtures and one mixture containing only NA (reference concrete). Leachates were tested for phytotoxicity using seeds of Lepidium sativum, Cucumis sativus, and Allium cepa. Emerging seedlings of L. sativum and A. cepa were used to assess DNA damage (comet test). The genotoxicity of the leachates was also analyzed with bulbs of A. cepa using the comet and chromosome aberration tests. None of the samples caused phytotoxic effects. On the contrary, almost all the samples supported the seedlings; and two leachates, one from the SS-containing concrete and the other from the reference concrete, promoted the growth of C. sativus and A. cepa. The DNA damage of L. sativum and A. cepa seedlings was significantly increased only by the reference concrete sample. In contrast, the DNA damage in A. cepa bulbs was significantly enhanced by the reference concrete but also by that of a concrete sample with SS. Furthermore, all leachates caused an increase in chromosomal aberrations in A. cepa bulbs. Despite some genotoxic effects of the concrete on plant cells, the partial replacement of SS does not seem to make the concrete more hazardous than the reference concrete, suggesting the potential use of SS as a reliable recycled material. Environ Toxicol Chem 2023;42:2193–2200. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

An Assessment of the Toxicity of Pesticide Mixtures in Periphyton from Agricultural Streams to the Mayfly Neocloeon triangulifer

Posted on by

Abstract

Residual concentrations of pesticides are commonly found outside the intended area of application in Ontario's surface waters. Periphyton are a vital dietary component for grazing organisms in aquatic ecosystems but can also accumulate substantial levels of pesticides from the surrounding water. Consequently, grazing aquatic organisms are likely subjected to pesticide exposure through the consumption of pesticide-contaminated periphyton. The objectives of the present study were to determine if pesticides partition into periphyton in riverine environments across southern Ontario and, if so, to determine the toxicity of pesticides in periphyton when fed to the grazing mayfly Neocloeon triangulifer. Sites with low, medium, and high pesticide exposure based on historic water quality monitoring data were selected to incorporate a pesticide exposure gradient into the study design. Artificial substrate samplers were utilized to colonize periphyton in situ, which were then analyzed for the presence of approximately 500 pesticides. The results demonstrate that periphyton are capable of accumulating pesticides in agricultural streams. A novel 7-day toxicity test method was created to investigate the effects of pesticides partitioned into periphyton when fed to N. triangulifer. Periphyton collected from the field sites were fed to N. triangulifer and survival and biomass production recorded. Survival and biomass production significantly decreased when fed periphyton colonized in streams with catchments dominated by agricultural land use (p < 0.05). However, the relationship between pesticide concentration and survival or biomass production was not consistent. Using field-colonized periphyton allowed us to assess the dietary toxicity of environmentally relevant concentrations of pesticide mixtures; however, nutrition and taxonomic composition of the periphyton may vary between sites. Environ Toxicol Chem 2023;42:2143–2157. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Uptake of Pharmaceuticals by Crops: A Systematic Review and Meta‐analysis

Posted on by

Abstract

Studies on the uptake of pharmaceuticals from soils into crops were first conducted in the 2000s. Since then a wealth of such data has been generated, but to the best of our knowledge, these studies have not been systematically reviewed. We present a quantitative, systematic review of empirical data on the uptake of pharmaceuticals into crops. We developed a custom-made relational database on plant uptake of pharmaceuticals that contained details of the experimental design and associated results from 150 articles, spanning 173 pharmaceuticals, 78 study crops, and 8048 unique measurements. Analysis of the data in the database showed clear trends in experimental design, with lettuce being the most studied crop and carbamazepine and sulfamethoxazole being the most studied pharmaceuticals. Pharmaceutical properties were found to create the greatest range in uptake concentrations of any single variable studied. Uptake concentrations were also found to vary between crops, with relatively high uptake concentrations identified in cress, lettuce, rice, and courgette crops. An understanding of the influence of soil properties on pharmaceutical uptake was limited by a lack of information on key soil properties across the published literature. The data comparisons were inhibited by differences in quality of the different studies. Moving forward, a framework for best practice in this field is needed to maximize the value and further applications of the data produced. Environ Toxicol Chem 2023;42:2091–2104. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Addressing Uncertainties in Potential Human Dietary Exposure to Mercury in the Watershed of the South River, Virginia, USA

Posted on by

Abstract

Much has been published about the harmful effects to humans when they are exposed to mercury (Hg) in environmental media including their diet. Numerous health advisories around the world, including for the South River, Virginia, USA, warn against consumption of Hg-contaminated fish species. Fewer studies have focused on other dietary sources of Hg and how to advise humans potentially exposed by this route. In undertaking a human health risk assessment for the former DuPont facility in Waynesboro, Virginia, USA, and the nearby South River and surrounding watershed, the available published information on Hg exposure through dietary consumption of nonfish items proved unsuitable for extrapolation purposes. In response, an evaluation of potential Hg exposure to residents who might consume livestock, poultry, and wildlife raised or collected in the South River watershed was conducted to inform the risk-assessment process. The newly collected data on Hg in these dietary items filled an important data gap, suggesting that there was little concern about limiting dietary consumption for most items. These results were communicated to the public through print and electronic platforms, in the form of “fact sheets.” We describe the studies and actions taken to better explain the potential for human exposures to Hg in nonfish dietary items from a portion of the watershed of the South River. Environ Toxicol Chem 2023;42:2237–2252. © 2023 SETAC