Studies on chelates of selected pyrazylmethyl ketones

Summary Several pyrazylmethyl ketones have been investigated in regard to their potential analytical utility as chelating agents for metal ions. Proton dissociation constants of the ligands and metal chelate formation constants were calculated from potentiometric data using the method of Irving and Rossotti. Chelate formation constants obtained in this study allow comparisons to be made between pyrazylmethyl ketones and other chelating agents possessing similar structures. The potential analytical utility of the title compounds is discussed.

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Zusammenfassung Einige Pyrazylmethylketone wurden auf ihre Fähigkeit zur Chelatbildung mit Metallionen untersucht. Die Protonendissoziationskonstanten der Liganden und die Chelatbildungskonstanten wurden aus potentiometrischen Daten berechnet, die nach Irving und Rossotti ermittelt wurden. Die Chelatbildungs-konstanten der Pyrazylmethylketone wurden mit denen ähnlich strukturierter Chelatbildner verglichen. Die analytische Brauchbarkeit der untersuchten Ketone wurde diskutiert.

     

Synthesis of (+/-)-3H-epivincamine via a Rh(II)-triggered cyclization/cycloaddition cascade

A synthesis of (+/-)-3H-epivincamine is reported. Important steps include (1) a Rh(II)-catalyzed intramolecular [3+2]-cycloaddition of an alpha-diazo indolo amide, (2) a reductive ring opening of the cycloadduct, (3) a decarboethoxylation reaction, and (4) a base-induced keto-amide ring contraction.     

Functional graft poly(N-isopropyl acrylamide)s using reversible addition-fragmentation chain transfer (RAFT) polymerisation

A series of NIPAM/4-vinyl benzyl chloride copolymers were substituted with 4(5)-imidazole dithioic acid or N-pyrrole dithioic acid to form multi-functional linear dithioate-functional polymers, which can be used as macromolecular transfer agents in a controlled radical polymerisation (RAFT) process. The presence of imidazole dithioate or N-pyrrole dithioate units along the NIPAM copolymer was determined by (1)H NMR, which showed broad CH-imidazole or CH-N-pyrrole resonances. Subsequent reaction of these multi-branch point polymers to produce graft polymers was achieved by reaction with NIPAM in the presence of AIBN. The graft polymers are produced as mixtures containing the desired product and linear polymer. The linear polymer is produced following transfer to the pendant dithioate group. Some of the branched polymers formed from the imidazole dithioate polymers were insoluble in water whilst others were found to be water soluble only in the presence of copper(II) ions. The use of N-pyrrole dithioate groups was found to substantially increase the solubility of the branched polymers in conventional solvents.     

Chemical denaturants inhibit the onset of dewetting

The mechanism by which the aqueous cosolvents guanidinium chloride and urea denature proteins is a matter of controversy. Here, we use all-atom molecular dynamics simulations to study the effect of both denaturants on the dewetting of water confined between nanoseparated hydrophobic plates. It is found that the denaturants inhibit the onset of dewetting, so that it occurs at shorter interplate distances than in pure water. Our results support a role for urea and guanidinium in assisting in the solvation of nonpolar surfaces, thereby weakening hydrophobic effects known to be important for protein stability.     

General access to the vinca and tacaman alkaloids using a Rh(II)-catalyzed cyclization/cycloaddition cascade

The total synthesis of several members of the vinca and tacaman classes of indole alkaloids has been accomplished. The central step in the synthesis consists of an intramolecular [3+2]-cycloaddition reaction of an alpha-diazo indoloamide which delivers the pentacyclic skeleton of the natural product in excellent yield. The acid lability of the oxabicyclic structure was exploited to establish the trans-D/E ring fusion of (+/-)-3H-epivincamine (3). Finally, a base induced keto-amide ring contraction was utilized to generate the E-ring of the natural product. A variation of the cascade sequence of reactions used to synthesize (+/-)-3H-epivincamine was also employed for the synthesis of the tacaman alkaloids (+/-)-tacamonine and (+/-)-apotacamine.     

Synthesis and Confinement of Carbon Dots in Lysozyme Single Crystals Produces Ordered Hybrid Materials with Tuneable Luminescence

The synthesis and confinement of graphitic nanoparticles (carbon dots) in the nanoscale solvent channels of cross‐linked lysozyme single crystals is used to prepare novel biohybrid luminescent materials. Co‐sequestration of acridine orange within the biohybrid crystals from acidic or neutral solutions yields FRET‐mediated phosphors emitting white or green light, respectively. The results offer a route to new types of tuneable multicolour luminescent materials based on microcrystalline host–guest energy‐transfer systems.     

The effect of density ratio on the near field of a naturally occurring oscillating jet

The triangular oscillating jet nozzle generates a triangular jet partially confined within an axi-symmetric chamber to produce a large scale flow oscillation that has application in thermal processes. Particle image velocimetry and oscillation frequency measurements were conducted to investigate the influence of the jet fluid to ambient fluid density ratio on the resulting oscillating flow. The investigation was conducted with a jet momentum flux of 0.06 kg m s⁻² (Re = 7.3−47.2 × 10³) and density ratios ranging from 0.2 to 5.0. The initial spread and decay of the emerging jet was found to depend upon the density ratio but in a more complex way than does an unconfined jet. Both the spread and decay are strongly influenced by the instantaneous angle of jet deflection, with greater deflection leading to increased spreading and decay of the jet. Decreasing the density ratio below unity results in a rapid decrease in the deflection angle, while increasing the density ratio above unity results in an increase in the deflection angle, albeit with less sensitivity. The frequency of oscillation was also shown to depend on the density ratio with an increase in the density ratio causing a decrease in the dominant oscillation frequency.