Stereocontrolled chemical glycosylation remains a major challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error. Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors. Mechanistic studies show that the reaction is dominated by two distinct intermediates: glycosyl triflates and glycosyl halides from N‐halosuccinimide (NXS)/TfOH. The formation of glycosyl halide is highly correlated with the production of α‐glycoside. These findings enable glycosylation reactions to be foreseen by using RRVs as an α/β‐selectivity indicator and guidelines and rules to be developed for stereocontrolled glycosylation.

7-Hydroxyquinoline-8-carboxylic acid (1), which possesses dual intramolecular hydrogen bonds, undergoes excited-state intramolecular double proton transfer, (ESIDPT) resulting in a quinolinone-like tautomer emission (λ max ∼ 470 nm). ESIDPT of 1 is cooperative, as evidenced by chemically blocking either proton donating site. While the overall rate of ESIDPT is higher than the system response limit, (220 fs) −1 , the theoretical approach favors a concerted, asynchronous ESIDPT with a rather small or negligible barrier, demonstrating an intrinsic proton relay system that undergoes intramolecular double proton transfer in the electronic excited state.

Reactions with post-transition-state bifurcations (PTSBs) involve initial ambimodal transition-state structures followed by an unstable region leading to two possible products. PTSBs are seen in many organic, organometallic, and biosynthetic reactions, but analyzing the origins of selectivity for these reactions is challenging, in large part due to the complex nature of the potential energy surfaces involved, which precludes analyses based on single intrinsic reaction coordinate (IRC; steepest-descent path in mass-weighted coordinate). While selectivity can be predicted using molecular dynamics simulation, connecting results from such calculations to the topography of potential energy surfaces is difficult. In the present work, a method for generating two-dimensional potential energy surfaces for PTSBs is described. The first dimension starts with the IRC for the first transition-state structure, followed by a modified reaction coordinate that reaches the second transition-state structure, which interconverts the two products of a bifurcating reaction path. The IRC for the second transition-state structure constitutes the second dimension. In addition, a method for mapping trajectories from Born–Oppenheimer molecular dynamics simulations onto these surfaces is described. Both approaches are illustrated with representative examples from the field of organic chemistry. The 2D-PESs for five asymmetric cases tested have clear tilted topography after the first transition-state structure, and the tilted direction correlates well with the selectivity observed from previous dynamic simulation. Instead of selecting reaction coordinates by chemical intuition, our method provides a general means to construct two-dimensional potential energy surfaces for reactions with post-transition-state bifurcations.

Stereocontrolled chemical glycosylation remains am ajor challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error.Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors.Mechanistic studies show that the reaction is dominated by two distinct intermediates:glycosyl triflates and glycosyl halides from N-halosuccinimide (NXS)/TfOH. The formation of glycosyl halide is highly correlated with the production of a-glycoside.These findings enable glycosylation reactions to be foreseen by using RRVs as an a/b-selectivity indicator and guidelines and rules to be developed for stereocontrolled glycosylation.

We report the incorporation of salicylaldehyde derivatives onto the hydrazine-tagged amyloidogenic peptides by forming photoisomerizable hydrazones. These hydrazones with positive photochromism are photostable under physiological conditions and enable photoswitching without the addition of external reductants or high-power irradiation. By applying superresolution microscopy, we were able to distinguish polymorphic nanoscopic structures of the hydrazone-incorporated peptides in vitro under different buffer conditions. Moreover, the additive-free condition in our platform allows the exploration of detailed amyloid aggregate morphologies in live cells.

Epithelium of amphibian embryos (Cynops orientalis, Xenopus laevis) was found in preceding experiments to generate and conduct impulses during a limited stage (26-37) of development . In order to elucidate the structural basis of impulse propagation, epithelial cells of four stages were examined by the freeze-etching method: (I) before and (II) during acquisition of conductivity; (III) when propagation was fully established, and (IV) when it was no longer present. Only few gap junctions (GJ) of small size were found in groups I and IV. GJ in epithelia of group III were increased in number and size, and appeared morphologically "coupled", i.e., with more loosely arranged connexons. the size of gap-junctional particles did not differ significantly between coupled and uncoupled stages. Zonulae occludentes seemed "leaky" in stage *, and "tight" in stages II-IV. Thus, the morphological characteristics of specialized junctions between "non excitable cells" correlated with the opening and closing of low resistance intercellular current pathways during embryonic development. Gap junctions in particular seem to form an essential link in the non-neural stimulus-response system, which may facilitate the mobility of the embryo during early phases of aquatic life before the reflex pathways have been established. Coupling and uncoupling of gap junctions may also play an important role in the regulation of cell differentiation and morphogenetic movement. The experimental model used in this study provides a useful tool for further investigations of structural correlates of gap junctional permeability under physiological conditions.

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