Journal of the American Chemical Society最新文献

We report the synthesis of amphiphilic poly(l-methionine sulfoxide)_x-b-poly(dehydroalanine)_y, diblock copolypeptides, M^O_xA^DH_y, and their self-assembly into submicrometer-diameter unilamellar vesicles in aqueous media. The formation of vesicles was observed over an unprecedented range of copolypeptide compositions due to the unique properties and chain conformations of A^DH hydrophobic segments. These copolypeptides incorporate two distinct thiol reactive components where each segment can respond differently to a single thiol stimulus. Incubation of M^O₃₅A^DH₃₀ vesicles with glutathione under intracellular mimetic conditions resulted in vesicle disruption and release of cargo. Further, incubation of M^O₃₅A^DH₃₀ vesicles with thiolglycolic acid resulted in a reversal of amphipilicity and successful in situ inversion of the vesicle assemblies. This conversion of biomimetic polymer vesicles into stable inverted vesicles using a biologically relevant stimulus at physiological pH and temperature is unprecedented. These results provide insights toward the development of advanced functional synthetic assemblies with potential uses in biology and medicine.

The hexagonal perovskites Cs₃NaFe₂Cl₉ and Cs₃NaMnFeCl₉ have been synthesized and investigated. Both compounds adopt the 6H perovskite structure with P6₃/mmc symmetry. This structure consists of dimers of face-sharing octahedra arranged on the vertices of a triangular network. The transition metal ions occupy sites in these octahedra, leading to Fe₂Cl₉^4- and FeMnCl₉^4- bioctahedra, respectively. The bioctahedral clusters are sandwiched by layers of corner-sharing octahedra occupied by Na⁺ cations. Diffuse reflectance spectroscopy reveals optical transitions that arise from metal-to-metal charge transfer (Cs₃NaMnFeCl₉) and intervalence charge transfer (Cs₃NaFe₂Cl₉) excitations. In Cs₃NaFe₂Cl₉, magnetic susceptibility measurements reveal local ferromagnetic coupling (θ_CW = 16.7 K), mediated by the rapid exchange of an electron between the iron sites within each dimer. In contrast, the magnetic coupling between Fe³⁺ and Mn²⁺ in Cs₃NaMnFeCl₉ is antiferromagnetic (θ_CW = -41.4 K). At 100 K, the Mössbauer spectrum is dominated by a single type of iron that corresponds to Fe^2.5+, signaling electron exchange between iron sites that is faster than the Mössbauer time scale (∼100 ns). Upon further cooling, the Fe^2.5+ signal gives way to a 1:1 ratio of Fe²⁺ and Fe³⁺, as the thermally activated hopping slows down.

Triplet-triplet annihilation (TTA) enables photon upconversion by combining two lower-energy triplet excitons to produce a higher-energy singlet exciton. This mechanism enhances light-harvesting efficiency for solar energy conversion and enables the use of lower-energy photons in bioimaging and photoredox catalysis applications. The magnetic modulation of such high-energy excitons presents an exciting opportunity to develop molecular quantum information technologies. While the spin dynamics of triplet exciton pairs are sensitive to external magnetic fields, the magnetic field effects (MFEs) associated with these pairs are generally limited by spin statistics to at most 10% at low fields (<1 T), making them challenging to apply in technological advancements. In contrast, MFEs on spin-correlated radical pairs (SCRPs) can be significantly greater, surpassing those on triplet pairs. By using SCRPs-based molecular qubits as triplet sensitizers in the sensitized TTA scheme, we can magnetically modulate TTA and consequently, the delayed fluorescence of annihilators. In our current system, we have achieved more than 70% magnetic modulation of delayed fluorescence, effectively harnessing and even amplifying magnetic modulation within SCRPs to influence high-energy excitons. This work opens new opportunities for advancing spin-controlled chemical reactions and molecular quantum information technologies.