Nature chemistry最新文献

Extending the chain lengths of conductive polymers, such as unsubstituted poly(para-phenylene) (PPP), is crucial for their application in high-performance organic devices and processing into high-quality functional materials. While surface-assisted Ullmann coupling has increased PPP chain lengths to ~100 nm, from ~32 nm achieved by solution-based reactions, its step-growth reaction mechanism limits further elongation. Here we report the synthesis of PPP via radical ring-opening polymerization of [6]cyclo(para-phenylene) on a Cu(111) surface. This process has been identified as a chain-growth polymerization, substantially enhancing the PPP chain length to the micrometre range (~0.9 μm). The obtained ultralong PPP chains on an otherwise clean surface undergo selective C-H bond scission, forming an upright-standing poly(para-benzyne) intermediate, which further couples into the unsubstituted biphenylene ribbon with length up to ~40 nm. The ring-opening polymerization provides a versatile route to high-quality polymers and non-benzenoid carbon nanoribbons with precise structural control.

Expanding the genetic code has revolutionized our ability to study and manipulate biological systems through site-specific incorporation of noncanonical amino acids (ncAAs). However, current methods are primarily limited to single-type ncAA incorporation in mammalian cells owing to translation inefficiency. Here we introduce a multi-type rare codon recoding strategy that addresses this limitation. By systematically evaluating and repurposing rare codons, alongside engineering mutually orthogonal aminoacyl-tRNA synthetase/tRNA pairs, we achieve the expression of proteins containing two or three distinct ncAAs at site-specific positions with recoding rates of up to 90% at wild-type protein expression levels in mammalian cells. This approach facilitates a broad range of applications, including dual bioorthogonal labelling and sequential protein activation. We further demonstrate the utility of this strategy by incorporating up to five distinct ncAAs into a single protein, revealing a redefinable nature of the genetic code and opening unprecedented avenues for future applications in biomedicine and synthetic biology.

Fluorochemicals improve our quality of life; however, there is increasing concern over how they are produced and their negative effects on health and the environment. Here we report an approach to the recycling of fluorochemicals. Treatment of hydrofluorocarbons with a potassium base (KHMDS or KO^tBu) results in rapid defluorination to produce anhydrous potassium fluoride. This potassium fluoride can then be used to prepare a wide range of fluorinated organic and inorganic molecules, including sulfonyl fluorides, aryl fluorides, alkyl fluorides and a range of p-block fluorides, in an overall one-pot transfer fluorination process. The scope of fluorochemicals that can be recycled by transfer fluorination includes industrially relevant refrigerants (hydrofluorocarbons), hydrofluoroolefins, fluoroethers-including anaesthetics and battery additives-perfluorooctanoic acid and poly(vinylidene) difluoride. Aspects of the transfer fluorination mechanism have been investigated using density functional theory calculations, and approaches to scale up using batch (50 g) and flow (1.5 g h^-1) chemistry are presented.

Sulfur-sulfur bonds are ubiquitous across broad classes of natural products, peptides and proteins, drug molecules, and synthetic polymers and materials. The ability to make and break these bonds in a controlled manner is critical for their many scientific and technological applications. Here we report the discovery of an unusual S-S metathesis reaction of organic trisulfides. When exposed to certain polar aprotic solvents, trisulfides were found to undergo spontaneous metathesis, with the reaction equilibrium established in seconds in some cases. No exogenous reagents, heat, light or other stimuli were required to provoke this reaction. Furthermore, the trisulfide metathesis process can occur both inter- and intramolecularly. Understanding the scope and mechanism of this reaction enabled diverse applications of this chemistry in dynamic combinatorial library synthesis, the covalent modification of complex natural products, and S-S metathesis polymerization and depolymerization as a platform for chemically recyclable plastics.

Direct carbonyl desaturation to prepare α,β-unsaturated carbonyl compounds is an important area of research in organic synthesis owing to the significance of these molecules in medicinal chemistry and chemical biology. Despite numerous methods developed for this transformation, approaches that enable precise control over the site selectivity of the reaction on substrates containing multiple potential reactive sites remain rare, limiting their applications in late-stage functionalization of complex molecules. Here we report the engineering of 'ene'-reductases for the direct carbonyl desaturation of diverse cyclic ketones to their corresponding enones with excellent site divergence. This study leverages the distinctive ability of 'ene'-reductases to differentiate the stereochemical environments of hydrogens at the carbonyl β-positions. The synthetic utility of this biocatalytic platform is further demonstrated through the successful late-stage dehydrogenation on terpenoids with complementary site selectivity to existing methods. In addition, the method could efficiently prepare chiral enones with a β-all carbon quaternary stereogenic centre via biocatalytic desaturative kinetic resolution. Mechanistic studies elucidate key enzyme-substrate interactions responsible for the enzyme-controlled site divergence.