Collaborating Authors

Boosted molecular mobility during common chemical reactions


During a chemical reaction, the reorganization of solvent molecules not directly in contact with reactants and products is normally viewed as a simple diffusion response. Wang et al. studied molecular diffusion in six common reactions—including the copper-catalyzed click reaction and the Diels-Alder reaction—with pulsed-field gradient nuclear magnetic resonance. They observed a boost in mobility relative to Brownian diffusion that was stronger for the catalyzed reactions that were studied. The mobilities for the click reaction were verified with a microfluidic gradient method. They argue that energy release produces transient translational motion of reacting centers that mechanically perturbs solvent molecules. Science , this issue p. [537][1] Mobility of reactants and nearby solvent is more rapid than Brownian diffusion during several common chemical reactions when the energy release rate exceeds a threshold. Screening a family of 15 organic chemical reactions, we demonstrate the largest boost for catalyzed bimolecular reactions, click chemistry, ring-opening metathesis polymerization, and Sonogashira coupling. Boosted diffusion is also observed but to lesser extent for the uncatalyzed Diels-Alder reaction, but not for substitution reactions SN1 and SN2 within instrumental resolution. Diffusion coefficient increases as measured by pulsed-field gradient nuclear magnetic resonance, whereas in microfluidics experiments, molecules in reaction gradients migrate “uphill” in the direction of lesser diffusivity. This microscopic consumption of energy by chemical reactions transduced into mechanical motion presents a form of active matter. [1]: /lookup/doi/10.1126/science.aba8425

An enantioconvergent halogenophilic nucleophilic substitution (SN2X) reaction


Biomolecular substitution reactions are widely applied to compounds with carbon-halogen bonds. Typically, an incoming reactive group will attack the carbon from behind its bond with the halogen, causing the halogen to depart in the opposite direction. Zhang et al. now present an asymmetric catalytic substitution reaction that flips the script with an attack on the halogen from the front. Specifically, nitrogen and sulfur nucleophiles stripped bromine from a variety of carbon centers activated by electron-withdrawing groups. A chiral cationic catalyst then directed the carbon fragment back to form a carbon-sulfur or carbon-nitrogen bond enantioselectively.

Google adds emoji reactions to Messages on Android


Messages' long trek to feature parity with other chat apps continues got a boost this week with the addition of emoji reactions. Google has been testing the feature since at least the start of March, but the company is now rolling it out to the broader Messages userbase on Android. You can react to a message someone sends you by long pressing on it. Currently, there are seven animated emoji to choose from: like, love, laughter, surprise, sadness, anger and dislike. You'll need to have Messages' Chat functionality enabled to add reactions, so you won't be able to send them to your friends with iPhones or other Android users who don't have an RCS-compatible device.

[Perspective] Rethinking the SN2 reaction


The SN2 nucleophilic substitution reaction, X RY XR Y, is a paradigm reaction in organic chemistry (1). The modern understanding of the SN2 reaction mechanism is based on work of Hughes and Ingold (2), who proposed that the nucleophile (X) approaches the carbon atom that bears the leaving group (Y). As a result, the bond between the carbon atom and the leaving group becomes weakened. As this bond breaks and a new bond forms between the nucleophile and the carbon atom, the configuration of the carbon atom is inverted. Analyses of gas-phase reaction rates led to the suggestion of a potential energy surface (PES) with two wells connected by a central barrier transition state (3).

On Facebook, love reactions triumph over hate


Ever since Facebook introduced reactions a year ago, there's been a lingering question: which reactions rule? At last, we know... although you can probably guess the answer. Facebook tells Select All that "love" dominated the 300 billion reactions from the past year -- more than half of them were hearts. That's not completely surprising (how many people do you know who use it for just about everything positive?), Also, you might be surprised at where reactions ruled.