Effect of Acute Exposure to Hydrogen Peroxide on the Production of Phytoplankton and Bacterioplankton in a Mesohumic Lake

Abstract— Active oxygen species such as hydrogen peroxide are produced as a result of UV radiation interaction with natural organic matter and can build up to high concentrations in many aquatic environments. Although the resulting oxidizing potential may affect biological materials and processes, the ecological effects have not yet been studied in any detail. We examined the influence of hydrogen peroxide exposure on phytoplankton and bacterioplankton production in Lac Cromwell, a small humic lake in the Laurentian Hills (Quebec, Canada). A range of hydrogen peroxide concentrations were added to natural samples that were incubated in situ; results indicate that even small amounts of added hydrogen peroxide (50 n M inhibited bacterial production in this lake. A 100 n M addition inhibited bacteria by as much as 40%. On the other hand, low concentrations of added hydrogen peroxide usually stimulated photosynthesis. Catalase addition to eliminate hydrogen peroxide from water usually stimulated bacterial production but had no effect on algal carbon fixation. If these results represent true changes in growth rate, they indicate very different sensitivities of phytoplankton and bacteria to oxidative stress.     

Leveraging the Knorr Pyrazole Synthesis for the Facile Generation of Thioester Surrogates for use in Native Chemical Ligation

Facile synthesis of C‐terminal thioesters is integral to native chemical ligation (NCL) strategies for chemical protein synthesis. We introduce a new method of mild peptide activation, which leverages solid‐phase peptide synthesis (SPPS) on an established resin linker and classical heterocyclic chemistry to convert C‐terminal peptide hydrazides into their corresponding thioesters via an acyl pyrazole intermediate. Peptide hydrazides, synthesized on established trityl chloride resins, can be activated in solution with stoichiometric acetyl acetone (acac), readily proceed to the peptide acyl pyrazoles. Acyl pyrazoles are mild acylating agents and are efficiently exchanged with an aryl thiol, which can then be directly utilized in NCL. The mild, chemoselective, and stoichiometric activating conditions allow this method to be utilized through multiple sequential ligations without intermediate purification steps.     

Fluorinated pyridine derivatives: Part 1. The synthesis of some mono- and bis-quaternary pyridine salts of potential use in the treatment of nerve agent poisoning

Experiments were performed to determine whether F- and CF₃-substituted pyridines undergo quaternization with iodomethane (1:1 molar ratio in THF) and 1,3-diiodopropane (2:1 molar ratio in MeCN). 2-Fluoropyridine and 2-(trifluoromethyl)pyridine did not react with MeI even under prolonged reflux, while 3-fluoropyridine, 3,5-difluoropyridine, 3-(trifluoromethyl)pyridine and 4-(trifluoromethyl)pyridine gave methiodide salts in 28-72% yield. 2-Fluoropyridine did not react with I(CH₂)₃I, 3-fluoropyridine gave the bis-quaternary salt and 3,5-difluoropyridine yielded a mono-quaternary derivative. Both 3- and 4-(trifluoromethyl)pyridine furnished the bis-quaternary products in 53 and 55% yield, respectively. The bis-quaternary salts are potentially useful in the treatment of organophosphorus nerve agent poisoning.     

Synthesis of new stable analogues of prostacyclin: (±)-6a-oxo-6,9-metrano-15-hydroxyprosta-5,13-dienoic acids

The synthesis is described of (±)-6a-oxo-6,9-methano-15-hydroxyprosta-5,13-dienoic acids as stable analogues of prostacyclin with blood platelet aggregation inhibiting activity.