Oleksandr

Dynamic self-correcting nucleophilic aromatic substitution

Dynamic self-correcting nucleophilic aromatic substitution, Published online: 03 September 2018; doi:10.1038/s41557-018-0122-8

Dynamic covalent chemistry offers promise for the formation of elaborate extended network materials in high yields, but the limited number of reactions available confines the scope and functionality of the materials synthesized. Now, nucleophilic aromatic substitution has been shown to be reversible, and thus self-correcting, enabling the easy synthesis of sulfur-rich materials.

Angewandte Chemie International Edition, EarlyView.

Angewandte Chemie International Edition, EarlyView.

All roads lead to life? The search for prebiotic and abiotic origin of biological chemistry continues to be guided largely by reliance on clues from extant life's processes. Here, it is suggested such an approach may be misleading, and that decoupling the emphasis on extant biology may actually be beneficial in finding unscripted solutions leading to the chemical origin(s) of life.

Abstract

Research into understanding the origins—and evolution—of life has long been dominated by the concept of taking clues from extant biology and extrapolating its molecules and pathways backwards in time. This approach has also guided the search for solutions to the problem of how contemporary biomolecules would have arisen directly from prebiotic chemistry on early earth. However, the continuing difficulties in finding universally convincing solutions in connecting prebiotic chemistry to biological chemistry should give us pause, and prompt us to rethink this concept of treating extant life's chemical processes as the sole end goal and, therefore, focusing only, and implicitly, on the respective extant chemical building blocks. Rather, it may be worthwhile “to set aside the goal” and begin with what would have been plausible prebiotic reaction mixtures (which may have no obvious or direct connection to life's chemical building blocks and processes) and allow their chemistries and interactions, under different geochemical constraints, to guide and illuminate as to what processes and systems can emerge. Such a conceptual approach gives rise to the prospect that chemistry of life‐as‐we‐know‐it is not the only result (not a “destiny”), but one that has emerged among many potential possibilities (a “destination”). This postulate, in turn, could impact the way we think about chemical signatures and criteria used in the search for alternative and extraterrestrial “life”. As a bonus, we may discover the chemistries and pathways naturally that led to the emergence of life as we know it.

TORC about: The utilization of tunable orthogonal reversible covalent (TORC) bonds is highlighted in this Minireview. The focus lies in the variety of different applications that are possible, including controlling molecular assembly, operating complex molecular machines, and designing dynamic, self‐healable polymer networks.

Abstract

Dynamic assembly of macromolecules in biological systems is one of the fundamental processes that facilitates life. Although such assembly most commonly uses noncovalent interactions, a set of dynamic reactions involving reversible covalent bonding is actively being exploited for the design of functional materials, bottom‐up assembly, and molecular machines. This Minireview highlights recent implementations and advancements in the area of tunable orthogonal reversible covalent (TORC) bonds for these purposes, and provides an outlook for their expansion, including the development of synthetically encoded polynucleotide mimics.

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

Light-driven molecular trap enables bidirectional manipulation of dynamic covalent systems, Published online: 13 August 2018; doi:10.1038/s41557-018-0106-8

Light can selectively drive and control the reversible reaction between a nitrogen nucleophile and a photoswitchable carbonyl electrophile by inducing wavelength-specific tautomerization cycles. This enables external and bidirectional regulation of closed dynamic covalent systems via C=N exchange, resembling a light-powered bidirectional molecular-scale Dean–Stark trap.

The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.

Given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (UV) light, we identify some general constraints on which stars produce sufficient UV for this photochemistry. We estimate how much light is needed for the UV photochemistry by experimentally measuring the rate constant for the UV chemistry ("light chemistry", needed for prebiotic synthesis) versus the rate constants for the bimolecular reactions that happen in the absence of the UV light ("dark chemistry"). We make these measurements for representative photochemical reactions involving SO32– and HS^–. By balancing the rates for the light and dark chemistry, we delineate the "abiogenesis zones" around stars of different stellar types based on whether their UV fluxes are sufficient for building up this macromolecular prebiotic inventory. We find that the SO32– light chemistry is rapid enough to build up the prebiotic inventory for stars hotter than K5 (4400 K). We show how the abiogenesis zone overlaps with the liquid water habitable zone. Stars cooler than K5 may also drive the formation of these building blocks if they are very active. The HS^– light chemistry is too slow to work even for early Earth.

Chemistry – A European Journal, EarlyView.

Angewandte Chemie International Edition, EarlyView.

Angewandte Chemie International Edition, EarlyView.

Chemistry – A European Journal, EarlyView.

Angewandte Chemie International Edition, EarlyView.

The crystallization problem is an outstanding challenge in the chemistry of porous covalent organic frameworks (COFs). Their structural characterization has been limited to modeling and solutions based on powder x-ray or electron diffraction data. Single crystals of COFs amenable to x-ray diffraction characterization have not been reported. Here, we developed a general procedure to grow large single crystals of three-dimensional imine-based COFs (COF-300, hydrated form of COF-300, COF-303, LZU-79, and LZU-111). The high quality of the crystals allowed collection of single-crystal x-ray diffraction data of up to 0.83-angstrom resolution, leading to unambiguous solution and precise anisotropic refinement. Characteristics such as degree of interpenetration, arrangement of water guests, the reversed imine connectivity, linker disorder, and uncommon topology were deciphered with atomic precision—aspects impossible to determine without single crystals.