Project description:The production of enantiopure materials and molecules is of uttermost relevance in research and industry in numerous contexts, ranging from nonlinear optics to asymmetric synthesis. In the context of the latter, dehalogenation, which is an essential reaction step for a broad class of chemical reactions, is investigated; specifically, dehalogenation of prochiral 5-bromo-7-methylbenz(a)anthracene (BMA) on prototypical, chiral, intermetallic PdGa{111} surfaces under ultrahigh vacuum conditions. Asymmetric halogen elimination is demonstrated by combining temperature-programmed X-ray photoelectron spectroscopy, scanning probe microscopy, and density functional theory. On the PdGa{111} surfaces, the difference in debromination temperatures for the two BMA surface enantiomers amounts up to an unprecedented 46 K. The significant dependence of the dehalogenation temperature of the BMA surface enantiomers on the atomic termination of the PdGa{111} surfaces implies that the ensemble effect is pronounced in this reaction step. These findings evidence enantiospecific control and hence promote intrinsically chiral crystals for asymmetric on-surface synthesis.
Project description:The reactivity of RNA 2'-OH groups with acylating agents has recently been investigated for high-yield conjugation of RNA strands. To date, only achiral molecules have been studied for this reaction, despite the complex chiral structure of RNA. Here we prepare a set of chiral acylimidazoles and study their stereoselectivity in RNA reactions. Reactions performed with unfolded and folded RNAs reveal that positional selectivity and reactivity vary widely with local RNA macro-chirality. We further document remarkable effects of chirality on reagent reactivity, identifying an asymmetric reagent with 1000-fold greater reactivity than prior achiral reagents. In addition, we identify a chiral compound with higher RNA structural selectivity than any previously reported RNA-mapping species. Further, azide-containing homologs of a chiral dimethylalanine reagent were synthesized and applied to local RNA labeling, displaying 92% yield and 16:1 diastereoselectivity. The results establish that reagent stereochemistry and chiral RNA structure are critical elements of small molecule-RNA reactions, and demonstrate new chemical strategies for selective RNA modification and probing.
Project description:We report a method for increasing the rate of target hybridization on DNA-functionalized surfaces using a short internal complement DNA (sicDNA) strand. The sicDNA causes up to a 5-fold increase in association rate by inducing a conformational change that extends the DNA away from the surface, making it more available to bind target nucleic acids. The sicDNA-induced kinetic enhancement is a general phenomenon that occurred with all sequences and surfaces investigated. Additionally, the process is selective and can be used in multicomponent systems to controllably and orthogonally "turn on" specific sequences by the addition of the appropriate sicDNA. Finally, we show that sicDNA is compatible with systems used in gene regulation, intracellular detection, and microarrays, suggesting several potential therapeutic, diagnostic, and bioinformatic applications.
Project description:The oxygen reduction reaction (ORR) in acidic media suffers from sluggish kinetics, primarily due to the spin-dependent electron transfer involved. The direct generation of spin-polarized electrons at catalytic surfaces remains elusive, and the underlying mechanisms are still controversial due to the lack of intrinsically chiral catalysts. To address this challenge, we investigate topological homochiral PdGa (TH PdGa) crystals with intrinsically chiral catalytic surfaces for ORR. Through spin-resolved photoemission spectroscopy and theoretical simulations, we show that both structural chirality and spin-orbit coupling are critical for inducing spin polarization at the surface of TH PdGa. As a result, TH PdGa achieves a kinetic current density over 100 times higher than the achiral PdGa (AC PdGa) at 0.85 V versus the reversible hydrogen electrode. This work underscores the pivotal role of spin polarization in enhancing acidic ORR activity and lays the groundwork for the rational design of chiral catalysts for spin-dependent catalysis.
Project description:Chiral graphene nanoribbons are extremely interesting structures due to their narrow band gaps and potential development of spin-polarized edge states. Here, we study their band structure on low work function silver surfaces. The use of a curved Ag single crystal provides, within the same sample, regions of disparate step structure and step density. Whereas the former leads to distinct azimuthal growth orientations of the graphene nanoribbons atop, the latter modulates the substrate's work function and thereby the interface energy level alignment. In turn, we disclose the associated charge transfer from the substrate to the ribbon and assess its effect on the nanoribbon's properties and the edge state magnetization.
Project description:Detection of chiral molecules in a high-efficiency way is very important to meet the demands for chiral analysis in drug testing, asymmetric synthesis, etc. Herein, we have developed a novel route to realize the rapid determination of concentration and configuration of primary amine-based chiral molecules. An aldehyde functionalized acid & base-sensitive fluorane dye (R-C) was used as the active agent to be reacted with the chiral molecules through an aldimine condensation reaction. After the mixing operation, concentration and configuration of the detected chiral molecule could be facilely read from the UV-vis absorption spectra and CD spectra, respectively.
Project description:Electrolytic hydrogen is identified as a crucial component in the desired decarbonisation of the chemical industry, utilizing renewable energy to split water into hydrogen and oxygen. Water electrolysis still requires important scientific advances to improve its performance and lower its costs. One of the bottlenecks in this direction is related to the sluggish anodic oxygen evolution reaction (OER). Producing anodes with competitive performance remains challenging due to the high energy losses and the harsh working conditions typically required by this complex oxidation process. Recent advancements point to spin polarization as an opportunity to enhance the kinetics of this spin-restricted reaction, yielding the paramagnetic O2 molecule. One powerful strategy deals with the generation of chiral catalytic surfaces, typically by surface functionalisation with chiral organic molecules, to promote the chiral-induced spin selectivity (CISS) effect during electron transfer. However, the relationship between optical activity and enhanced electrocatalysis has been established only from indirect experimental evidence. In this work, we have exploited operando electrochemical and spectroscopic tools to confirm the direct relationship between the faster OER kinetics and the optical activity of enantiopure Fe-Ni metal oxides when compared with that of achiral catalysts in alkaline conditions. Our results show the participation of chiral species as reactive intermediates during the electrocatalytic reaction, supporting the appearance of a mechanistic CISS enhancement. Furthermore, these intrinsically chiral transition-metal oxides maintain their enhanced activity in full cell electrolyser architectures at industrially relevant current densities.
Project description:Electron crystallography has recently gained attentions in multiple fields of research, as it has been demonstrated to determine atomic structures for inorganic, organic, and macromolecular materials from nano-sized crystals that were not amenable to conventional X-ray crystallography. Here, we demonstrate continuous-rotation microcrystal electron diffraction (microED) in a 200 kV transmission electron microscope using a DE-64 camera-a low-noise direct electron detector that can accommodate a linear response up to ∼1200 electrons per pixel per second at 20 fps with 2x-hardware-binning, making it ideal for acquisition of high-quality diffraction patterns. We have used this method and camera to determine a 0.75 Å structure of an organic molecule, biotin, with an exceptional goodness-of-fit, as well as a 0.88 Å structure of a chiral molecule, L-serine.