Skimming behaviour and spreading potential of Stenus species and Dianous coerulescens (Coleoptera: Staphylinidae).

Rove beetles of the genus Stenus Latreille and the genus Dianous Leach possess pygidial glands containing a multifunctional secretion of piperidine and pyridine-derived alkaloids as well as several terpenes. One important character of this secretion is the spreading potential of its different compounds, stenusine, norstenusine, 3-(2-methyl-1-butenyl)pyridine, cicindeloine, α-pinene, 1,8-cineole and 6-methyl-5-heptene-2-one. The individual secretion composition enables the beetles to skim rapidly and far over the water surface, even when just a small amount of secretion is emitted. Ethological investigations of several Stenus species revealed that the skimming ability, skimming velocity and the skimming behaviour differ between the Stenus species. These differences can be linked to varied habitat claims and secretion saving mechanisms. By means of tensiometer measurements using the pendant drop method, the spreading pressure of all secretion constituents as well as some naturally identical beetle secretions on the water surface could be established. The compound 3-(2-methyl-1-butenyl)pyridine excelled stenusine believed to date to be mainly responsible for skimming relating to its surface activity. The naturally identical secretions are not subject to synergistic effects of the single compounds concerning the spreading potential. Furthermore, evolutionary aspects of the Steninae's pygidial gland secretion are discussed.

Catalysts by the meter: rapid screening approach of N-heterocyclic carbene ligand based catalysts.

Here, we demonstrate a versatile screening platform for NHC ligand based catalysts by coating fused-silica micro capillaries with a bonded 1,3-bismesityl-2-imidazolidinylidene ligand. Such micro capillaries can be efficiently converted into (pre)-catalysts from various organometallic precursors by solid-phase chemistry techniques and can be quantitatively screened using on-column reaction chromatography.

The mechanism of the (bispidine)copper(II)-catalyzed aziridination of styrene: a combined experimental and theoretical study.

Experimental and DFT-based computational results on the aziridination mechanism and the catalytic activity of (bispidine)copper(I) and -copper(II) complexes are reported and discussed (bispidine=tetra- or pentadentate 3,7-diazabicyclo[3.1.1]nonane derivative with two or three aromatic N donors in addition to the two tertiary amines). There is a correlation between the redox potential of the copper(II/I) couple and the activity of the catalyst. The most active catalyst studied, which has the most positive redox potential among all (bispidine)copper(II) complexes, performs 180 turnovers in 30 min. A detailed hybrid density functional theory (DFT) study provides insight into the structure, spin state, and stability of reactive intermediates and transition states, the oxidation state of the copper center, and the denticity of the nitrene source. Among the possible pathways for the formation of the aziridine product, the stepwise formation of the two N-C bonds is shown to be preferred, which also follows from experimental results. Although the triplet state of the catalytically active copper nitrene is lowest in energy, the two possible spin states of the radical intermediate are practically degenerate, and there is a spin crossover at this stage because the triplet energy barrier to the singlet product is exceedingly high.

Influence of polymorphic form, morphology, and excipient interactions on the dissolution of carbamazepine compacts.

To gain a deeper understanding of the behavior of carbamazepine (CBZ) and CBZ dihydrate (DH) compacts during in vitro dissolution tests various factors were investigated: hydrate formation of CBZ, crystal morphology, surface area, and excipient influence. Dissolution tests were performed in three different dissolution media: distilled water, hydroxypropyl methylcellulose (HPMC), and polyethylene glycol (PEG) solutions. For the CBZ compacts, the dissolution rate of CBZ in water was fastest (0.338 mg L(-1) min(-1)). With increasing ability of the excipients to inhibit the hydration of CBZ (PEG < HPMC), surprisingly the dissolution rate of CBZ compacts decreased: PEG solution (0.314 mg L(-1) min(-1)) > HPMC solution (0.257 mg L(-1) min(-1)). This implies that DH formation resulted in an apparent increase in the dissolution rate rather than slowing it down. For the DH compacts, the dissolution rate in water (0.055 mg L(-1) min(-1)) was slower than that of PEG and HPMC solutions (0.174 and 0.178 mg L(-1) min(-1), respectively). The contact angle measurements showed a significantly higher value in water (61.0 degrees) than in PEG and HPMC solutions (44.8 degrees and 43.1 degrees, respectively). Although the dissolution of CBZ and DH compacts in various dissolution media are complex processes, the influence and relative importance of these factors were clearly detected providing better understanding of the dissolution behavior of the drug.