Regulating Spin Density using TEMPOL Molecules for Enhanced CO2-to-Ethylene Conversion by HKUST-1 Framework Derived Electrocatalysts.

The selectivity of multicarbon products in the CO2 reduction reaction (CO2RR) depends on the spin alignment of neighboring active sites, which requires a spin catalyst that facilitates electron transfer with antiparallel spins for enhanced C-C coupling. Here, we design a radical-contained spin catalyst (TEMPOL@HKUST-1) to enhance CO2-to-ethylene conversion, in which spin-disordered (SDO) and spin-ordered (SO) phases co-exist to construct an asymmetric spin configuration of neighboring active sites. The replacement of axially coordinated H2O molecules with TEMPOL radicals introduces spin-spin interactions among the Cu(II) centers to form localized SO phases within the original H2O-mediated SDO phases. Therefore, TEMPOL@HKUST-1 derived catalyst exhibited an approximately two-fold enhancement in ethylene selectivity during the CO2RR at -1.8 V versus Ag/AgCl compared to pristine HKUST-1. In situ ATR-SEIRAS spectra indicate that the spin configuration at asymmetric SO/SDO sites significantly reduces the kinetic barrier for *CO intermediate dimerization toward the ethylene product. The performance of the spin catalyst is further improved by spin alignment under a magnetic field, resulting in a maximum ethylene selectivity of more than 50%. The exploration of the spin-polarized kinetics of the CO2RR provides a promising path for the development of novel spin electrocatalysts with superior performance.

Chiral Benzene Triimide (BTI) Radical Anions for Probing the Interplay of Unpaired Electron Spin and Chirality.

Herein a series of chiral BTI radical anions bearing different chiral substituents were efficiently prepared by chemical reduction. X-ray crystallography revealed finely-tuned packing and helix assemblies of the radicals by the size of chiral substituents in crystalline state. In accordance with the crystalline-state packing, the powder ESR spectra indicate that 4 a- ⋅CoCp2 + and 4 c- ⋅CoCp2 + π-dimers exhibit thermally excited triplet states arising from strong spin-spin interactions, while discrete 4 b- ⋅CoCp2 + shows a broad doublet-state signal reflecting weak spin-spin interactions. The interplay between the unpaired electron spin and chiral substituents was studied by UV-Vis-NIR spectra, electronic circular dichroism (ECD) and TD DFT calculations. Different NIR absorptions of the radicals attributing to isolated SOMO→LUMO+1 (~889 nm) transitions were recorded. The emergence of Cotton effects (CEs) at the NIR region for 4 c- ⋅CoCp2 + radical enantiomers suggest the interplay between chirality and unpaired electron spin. The origin of the different circularly polarized light absorptions regarding SOMO derived transitions (around 880 nm) was attributed to chiral substitutes regulated electric and magnetic transition dipole moments of the unpaired electron participated transition.

Benzene Triimide Cage as a Selective Container of Azide.

Benzene triimide (BTI, or mellitic triimide) is a C3-symmetric backbone with a highly electron-deficient, extended π surface and three easy functionalization sites. Here, we report the first BTI-based cage composed of two face-to-face BTIs pillared by three m-xylylene spacers and efficient and selective binding of azide through cooperative anion-π interactions. The cage was easily synthesized in two steps from benzene triimide. Crystal structures showed that the two BTI planes can be separated at about 5-6 Å and form a well-defined electron-deficient cavity. Among a series of anions tested, the cage was found able to bind N3-, SCN-, and I-. In particular, the binding toward N3- is very strong (Ka = 11098 ± 46 M-1) and highly selective, over 150 and 250 times higher than SCN- and I-, respectively. The control single BTI, however, showed only very weak binding (Ka < 5 M-1). The crystal structure showed that N3- is tightly trapped within the cavity through multiple, very short anion-π interactions. The slow enter-release of N3- from the cavity was observed in the NMR. The charge-transfer and electron-transfer character of the interactions was also discussed.

Anion Transporters Based on Noncovalent Balance including Anion-π, Hydrogen, and Halogen Bonding.

Anion transmembrane transport mediated by novel noncovalent interactions is of central interest in supramolecular chemistry. In this work, a series of oxacalix[2]arene[2]triazine-derived transporters 1 and 2 bearing anion-π-, hydrogen-, and halogen-bonding sites in rational proximity were designed and synthesized by a one-pot strategy starting from gallic acid ester derivatives and mono- or di-halogen-substituted triazines. 1H NMR titrations demonstrated efficient binding of 1 and 2 toward Cl- and Br- in solution, giving association constants in the range of 102-104 M-1. Cooperation of anion-π, hydrogen, and halogen bonding was revealed as a driving force for anion binding by single-crystal structures of two complexes and density functional theory calculations. Fluorescence assays indicated that compounds 1 are efficient chloride transporters with effective concentrations (EC50) falling in the range of 3.1-7.4 µM and following an order of 1a > 1b > 1c > 1d. The contribution of halogen bonding and cooperative noncovalent bonds to ion transport was then discussed. Significantly, transporters 1 exhibit high anticancer activity. In the presence of 1 and KCl (60 mM), the cell survival of HCT116 reduces to 11.9-24.9% with IC50 values in the range of 52.3-66.4 µM.

Antitumor Activity of a 5-Hydroxy-1H-Pyrrol-2-(5H)-One-Based Synthetic Small Molecule In Vitro and In Vivo.

Alternative chemo-reagents are in great demand because chemotherapy resistance is one of the major challenges in current cancer treatment. 5-hydoxy-1H-pyrrol-2-(5H)-one is an important N-heterocyclic scaffold that is present in natural products and medicinal chemistry. However, its antitumor activity has not been systematically explored. In this study, we screened a panel of 5-hydoxy-1H-pyrrol-2-(5H)-one derivatives and identified compound 1d as possessing strong anti-proliferative activity in multiple cancer cell lines. Cell cycle analysis revealed that 1d can induce S-phase cell cycle arrest and that HCT116 was sensitive to 1d-induced apoptosis. Further analysis indicated that 1d preferentially induced DNA damage and p53 activation in HCT116 cells and that 1d-induced apoptosis is partly dependent on p53. Furthermore, we showed that 1d significantly suppressed tumor growth in xenograft tumor models in vivo. Taken together, our results suggest that 5-hydoxy-1H-pyrrol-2-(5H)-one derivatives bear potential antitumor activity and that 1d is an effective agent for cancer treatment.

Catalytic asymmetric Passerini-type reaction: chiral aluminum-organophosphate-catalyzed enantioselective alpha-addition of isocyanides to aldehydes.

A chiral Lewis acid catalyst was prepared by mixing 2 equiv of chiral binol-derived organophosphoric acid and 1 equiv of Et(2)AlCl. In the presence of a catalytic amount of [4j](2)Al(III)Cl complex (0.05 equiv), reaction between alpha-isocyanoacetamides (2) and aldehydes (3) afforded the corresponding 5-aminooxazoles (1) in good yields and enantioselectivities. Complex [4j](2)Al(III)Cl isolated as a white solid displayed similar reactivity as that prepared in situ.

Chiral salen-aluminum complex as a catalyst for enantioselective alpha-addition of isocyanides to aldehydes: asymmetric synthesis of 2-(1-hydroxyalkyl)-5-aminooxazoles.

In the presence of a catalytic amount of (salen)Al(III)Cl complex (4e), reaction between alpha-isocyanoacetamides (1) and aldehydes (2) afforded the corresponding 5-aminooxazoles (3) in good yields and enantioselectivity.