Spontaneous Emergence of Self-Replicating Molecules Containing Nucleobases and Amino Acids.

The conditions that led to the formation of the first organisms and the ways that life originates from a lifeless chemical soup are poorly understood. The recent hypothesis of "RNA-peptide coevolution" suggests that the current close relationship between amino acids and nucleobases may well have extended to the origin of life. We now show how the interplay between these compound classes can give rise to new self-replicating molecules using a dynamic combinatorial approach. We report two strategies for the fabrication of chimeric amino acid/nucleobase self-replicating macrocycles capable of exponential growth. The first one relies on mixing nucleobase- and peptide-based building blocks, where the ligation of these two gives rise to highly specific chimeric ring structures. The second one starts from peptide nucleic acid (PNA) building blocks in which nucleobases are already linked to amino acids from the start. While previously reported nucleic acid-based self-replicating systems rely on presynthesis of (short) oligonucleotide sequences, self-replication in the present systems start from units containing only a single nucleobase. Self-replication is accompanied by self-assembly, spontaneously giving rise to an ordered one-dimensional arrangement of nucleobase nanostructures.

External Reversal of Chirality Transfer in Photoswitches.

The transfer of stereoinformation is at the heart of asymmetric reactions. By incorporating the natural monoterpene l-menthone into the backbone of a diarylethene, we achieved efficient chirality transfer upon photocyclization, resulting in the preferred formation of one major closed isomer in a diastereomeric ratio (d.r.) of 85:15. More significantly, we were able to completely reverse the diastereomeric outcome of the ring closure simply by altering the chemical environment or the irradiation conditions. As a result, we could selectively accumulate the less favored minor closed isomer, with remarkable d.r. values of >99:1 and 74:26, respectively. Computations revealed that a stability inversion after photocyclization is the basis for the observed unprecedented control over diastereoselectivity.

Light-driven molecular trap enables bidirectional manipulation of dynamic covalent systems.

Bond formation between two molecular entities in a closed system strictly obeys the principle of microscopic reversibility and occurs in favour of the thermodynamically more stable product. Here, we demonstrate how light can bypass this fundamental limitation by driving and controlling the reversible bimolecular reaction between an N-nucleophile and a photoswitchable carbonyl electrophile. Light-driven tautomerization cycles reverse the reactivity of the C=O/C=N-electrophiles ('umpolung') to activate substrates and remove products, respectively, solely depending on the illumination wavelength. By applying either red or blue light, selective and nearly quantitative intermolecular bond formation/scission can be achieved, even if the underlying condensation/hydrolysis equilibrium is thermodynamically disfavoured. Exploiting light-driven in situ C=N exchange, our approach can be used to externally regulate a closed dynamic covalent system by actively and reversibly removing specific components, resembling a molecular and bidirectional version of a macroscopic Dean-Stark trap.

Control of Imine Exchange Kinetics with Photoswitches to Modulate Self-Healing in Polysiloxane Networks by Light Illumination.

Various aldehyde-containing photoswitches have been developed whose reactivity toward amines can be controlled externally. A thermally stable bifunctional diarylethene, which in its ring-closed form exhibits imine formation accelerated by one order of magnitude, was used as a photoswitchable crosslinker and mixed with a commercially available amino-functionalized polysiloxane to yield a rubbery material with viscoelastic and self-healing properties that can be reversibly tuned by irradiation.