Autocatalyses

Autocatalysis is a fundamental concept, used in a wide range of domains. From the most general definition of autocatalysis, that is, a process in which a chemical compound is able to catalyze its own formation, several different systems can be described. We detail the different categories of autocatalyses and compare them on the basis of their mechanistic, kinetic, and dynamic properties. It is shown how autocatalytic patterns can be generated by different systems of chemical reactions. With the notion of autocatalysis covering a large variety of mechanistic realizations with very similar behaviors, it is proposed that the key signature of autocatalysis is its kinetic pattern expressed in a mathematical form.     

Energy Propagation Through a Protometabolism Leading to the Local Emergence of Singular Stationary Concentration Profiles

Living systems rely on chains of energy transfer from an energy source to maintain their metabolism. This task requires functionally identified components and organizations. However, propagation of a sustained energy flux through a cascade of reaction cycles has never been reproduced at a steady state in a simple chemical system. By using energy patterning and a diffusing hub reactant, we achieved the transfer of energy through an abiotic protometabolism. Patterned illumination was applied to a liquid solution of a reversible photoacid. It resulted in the local onset of a proton pump, which subsequently drove an extended reaction–diffusion cycle that involved pH‐sensitive reactants. Thus, light has been used for locally setting out of chemical equilibrium a reaction involving “blind” reactants. The spontaneous onset of an energy‐transfer chain notably drives the local generation of singular dissipative chemical structures; continuous matter fluxes are dynamically maintained at boundaries between spatially and chemically segregated zones, in the absence of any membrane or predetermined material structure.     

Light Activation for the Versatile and Accurate Kinetic Analysis of Disassembly of Self‐Immolative Spacers

Three procedures that rely on photoactivation are introduced to accurately analyze the disassembly kinetics of a collection of self‐immolative spacer groups within the window 10^?2–10³ s. Our results are relevant for deriving quantitative structure–property relationships. In particular, we have been able to access 20 ms temporal resolution, which made possible the measurement of the shortest ever reported disassembly time for an activated self‐immolative spacer.     

High resolution NMR in solids; A simple and improved ‘magic angle’ probe design for conventional small gap 13C FT spectrometers

The mechanical and electronic design of a ‘magic angle’ NMR probe is described. This probe can be incorporated in a conventional small gap ¹³C FT spectrometer, without any hardware or software change, to obtain high resolution ¹³C NMR spectra on organic solids. A simple way of tuning the homogeneity and adjusting the angle is also proposed. Illustrative experimental results on various types of molecular crystals with different molecular mobilities, a clathrate compound and a polymer are discussed.     

o-nitrobenzyl photolabile protecting groups with red-shifted absorption: syntheses and uncaging cross-sections for one- and two-photon excitation

We evaluated the o-nitrobenzyl platform for designing photolabile protecting groups with red-shifted absorption that could be photolyzed upon one- and two-photon excitation. Several synthetic pathways to build different conjugated o-nitrobenzyl backbones, as well as to vary the benzylic position, are reported. Relative to the reference 4,5-dimethoxy-2-nitrobenzyl group, several o-nitrobenzyl derivatives exhibit a large and red-shifted one-photon absorption within the near-UV range. Uncaging after one-photon excitation was studied by measuring UV-visible absorption and steady-state fluorescence emission on model caged ethers and esters. In the whole series investigated, the caged substrates were released cleanly upon photolysis. Quantum yields of uncaging after one-photon absorption lie within the 0.1-1 % range. We observed that these drop as the maximum wavelength absorption of the o-nitrobenzyl protecting group is increased. A new method based on fluorescence correlation spectroscopy (FCS) after two-photon excitation was used to measure the action uncaging cross section for two-photon excitation. The series of o-nitrobenzyl caged fluorescent coumarins investigated exhibit values within the 0.1-0.01 Goeppert-Mayer (GM) range. Such results are in line with the low quantum yields of uncaging associated with cross-sections of 1-50 GM for two-photon absorption. Although the cross-sections for one- and two-photon absorption of o-nitrobenzyl photolabile protecting groups can be readily improved, we emphasize the difficulty in enlarging the corresponding action uncaging cross-sections in view of the observed trend of their quantum yield of uncaging.