High resolution NMR spectroscopy of heteroaromatic cations. II—pyrylium,thiapyrylium and seleninium cations

The barriers to internal rotation about the C? N bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG^?) increases in the series cinnamoylthiopiperidide<thiobenzoylpiperidide<phenylthioacetylpiperidide. This trend was discussed in terms of the electronic structure, using HMO calculations. For m-and p-substituted cinnamoylthiopiperidides the barriers were shown to increase with the electron withdrawing character of the substituent in the aromatic ring.     

Analysis of class I phosphoinositide 3-kinase autophosphorylation sites by mass spectrometry

This article describes the identification of the autophosphorylation sites of the G protein-sensitive class I phosphoinositide 3-kinase isoforms beta and gamma by mass spectrometry. Since discrimination and suppression effects prevented the immediate detection and sequencing of phosphopeptides in complex mixtures, a strategy was applied that involved (32)P-radiolabeling of the phosphoproteins, cleavage of the phosphoproteins with several proteases and/or cyanogen bromide, separation of the resulting peptide mixtures by micro-reversed-phase liquid chromatography, and mass spectrometric analysis of fractions containing phosphopeptides. As a result the primary autophosphorylation sites of phosphoinositide 3-kinase p110beta and p110gamma subunits could be unambiguously assigned to the C-terminal Ser 1070 and Ser 1101, respectively.     

Orthogonal self-assembly of low molecular weight hydrogelators and surfactants

The concurrent self-assembly of new 1,3,5-trisamide-cyclohexane-based low molecular weight hydrogelators and various surfactants in water leads to the formation of self-assembled fibrillar networks with encapsulated micelles. This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.     

Reaktionen auf der Spur

A new technique, desorption electrospray ionization coupled to mass spectrometry (DESI‐MS), has been used as a tool for reaction analysis. Charged droplets of a reagent are sprayed onto the catalyst, which has previously been deposited on a surface in front of a mass analyzer. The reaction starts as the droplets impact the catalyst on the surface and continues inside secondary microdroplets that are desorbed from the surface. These are directed toward the mass spec inlet. Using this technique, the very first milliseconds of a reaction can be observed. The first example describes the discovery of an extremely short‐lived intermediate in a C‐H amination reaction cycle. Another example describes how DESI‐MS has been used to identify catalyst arrest mechanisms in ruthenium catalyzed C‐H hydroxylation.