RESUMO
The dynamic nature of calamitic liquid crystals is exploited to perform isothermal phase transitions driven by dynamic covalent chemistry. For this purpose, nematic (N) arrays based on aldehyde 1 were treated with different amines (A-E) in an on-surface process, which resulted in different isothermal phase transitions. These phase transformations were caused by in-situ imination reactions and are dependent on the nature of the added amine. Transitions from the N to crystal (1A, 1E), isotropic (1B), and smectic (Sm) (1C, 1D) phases were achieved, while the resulting materials feature thermotropic liquid crystal behavior. A sequential transformation from the N 1 to the Sm 1C and then to the N 1B was achieved by coupling an imination to a transimination processes and adjusting the temperature. All of these processes were well characterized by microscopic, spectroscopic, and X-ray techniques, unlocking not only the constitutional but also the structural aspects of the phase transitions. This work provides new insights into designing constitutionally and structurally adaptable liquid crystal systems, paving the way toward the conception of programable evolutive pathways and adaptive materials.
RESUMO
Water-soluble multinuclear complexes based on ruthenium 2,2'-bipyridine-6,6'-dicarboxylate (bda) and ditopic bipyridine linker units are investigated in three-component visible light-driven water oxidation catalysis. Systematic studies revealed a strong enhancement of the catalytic efficiency in the absence of organic co-solvents and with increasing oligomer length. In-depth kinetic and morphological investigations suggest that the enhanced performance is induced by the self-assembly of linear Ru(bda) oligomers into aggregated superstructures. The obtained turnover frequencies (up to 14.9â s-1 ) and turnover numbers (more than 1000) per ruthenium center are the highest reported so far for Ru(bda)-based photocatalytic water oxidation systems.
RESUMO
A novel core-shell structured columnar liquid crystal composed of a donor-acceptor dyad of tetraphenoxy perylene bisimide (PBI), decorated with four bithiophene units on the periphery, was synthesized. This molecule self-assembles in solution into helical J-aggregates guided by π-π interactions and hydrogen bonds which organize into a liquid-crystalline (LC) columnar hexagonal domain in the solid state. Donor and acceptor moieties exhibit contrasting exciton coupling behavior with the PBIs' (J-type) transition dipole moment parallel and the bithiophene side arms' (H-type) perpendicular to the columnar axis. The dyad shows efficient energy and electron transfer in solution as well as in the solid state. The synergy of photoinduced electron transfer (PET) and charge transport along the narcissistically self-assembled core-shell structure enables the implementation of the dye in two-contact photoconductivity devices giving rise to a 20-fold increased photoresponse compared to a reference dye without bithiophene donor moieties.
RESUMO
Cauliflower Orange (Or) mutant is characterized by high level of ß-carotene in its curd. Or mutation affects the OR protein that was shown to be involved in the posttranslational control of phytoene synthase (PSY), a major rate-limiting enzyme of carotenoid biosynthesis, and in maintaining PSY proteostasis with the plastid Clp protease system. A transposon integration into the cauliflower wild-type Or gene (BoOR-wt) results in the formation of three differently spliced transcripts. One of them is characterized by insertion (BoOR-Ins), while the other two have exon-skipping deletions (BoOR-Del and BoOR-LD). We investigated the properties of individual BoOR variants and examined their effects on carotenoid accumulation. Using the yeast split-ubiquitin system, we showed that all variants were able to form OR dimers except BoOR-LD. The deletion in BoOR-LD eliminated the first of two adjacent transmembrane domains and was predicted to result in a misplacement of the C-terminal zinc finger domain to the opposite side of membrane, thus preventing OR dimerization. As interaction with PSY is mediated by the N-terminus of BoOR, which remains unaffected after splicing, all BoOR variants including BoOR-LD maintained interactions with PSY. Expression of individual BoOR mutant variants in Arabidopsis revealed that their protein stability varied greatly. While expression of BoOR-Del and BoOR-Ins resulted in increased BoOR protein levels as BoOR-wt, minimal amounts of BoOR-LD protein accumulated. Carotenoid accumulation showed correlated changes in calli of Arabidopsis expressing these variants. Furthermore, we found that OR also functions in E. coli to increase the proportion of native, enzymatically active PSY from plants upon co-expression, but not of bacterial phytoene synthase CrtB. Taken together, these results suggest that OR dimerization is required for OR stability in planta and that the simultaneous presence of PSY interaction-domains in both OR and PSY proteins is required for the holdase function of OR. The more pronounced effect of simultaneous expression of all BoOR variants in cauliflower Or mutant compared with individual overexpression on carotenoid accumulation suggests an enhanced activity with possible formation of various BoOR heterodimers.
