ECD spectroelectrochemistry: A review

Surface-Enhanced Raman Spectroscopy and Electrochemistry: The Ultimate Chemical Sensing and Manipulation Combination

One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors' sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields-energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.

Hirsutinolide-type sesquiterpenoids with anti-prostate cancer activity from Cyanthillium cinereum

Four previously undescribed hirsutinolide-type sesquiterpenoids, cyanolides A-D (1-4), along with twelve known analogues (5-16), were isolated from the aerial parts of Cyanthillium cinereum. Their structures were determined by comprehensive analysis of NMR, HRESIMS, and ECD spectra. Compound 1 is a rarely occurring hirsutinolide-type sesquiterpenoid with 1,4-ether ring ruptured and containing a chlorine atom, and compounds 13-16 were reported from this plant for the first time. All compounds were tested for their inhibiting effects on prostate cancer cells. As a result, compounds 1, 3, and 8-14 exhibited significant anti-prostate cancer activity against PC-3 and LNCaP cells with IC50 values ranging from 2.2 ± 0.4 to 8.5 ± 0.7 μM and 3.0 ± 0.7 to 10.5 ± 1.1 μM, respectively. The preliminary structure-activity relationship was discussed. Further investigation showed that compound 1 induced apoptosis in PC-3 cells.

Cytotoxic Indole Diterpenoids from a Sphagneticola trilobata-Derived Fungus Aspergillus sp. PQJ-1

Two new indole diterpene derivatives, 5S-hydroxy-β-aflatrem (1) and 14R-hydroxy-β-aflatrem (2), along with one known analogue, 14-(N,N-dimethl-L-valyloxy)paspalinine (3), were isolated from the fermentation broth of the fungus Aspergillus sp. PQJ-1 derived from Sphagneticola trilobata. The structures of the new compounds were elucidated from spectroscopic data and ECD spectroscopic analyses. All the compounds (1-3) were evaluated for their cytotoxicity against A549, Hela, Hep G2, and MCF-7 cell lines. Compounds 1 and 2 exhibited selective inhibition against Hela cells. Further studies showed that 1 significantly induced apoptosis and suppressed migration and invasion in Hela cells. Moreover, 1 could up-regulate pro-apoptotic genes BAX and Caspase-3 and down-regulate anti-apoptotic genes Bcl-xL and XIXP.

UV-vis and ECD spectroelectrochemistry of atropisomeric naphthalenediimide derivative

The UV-vis and ECD spectroelectrochemistry (SEC) of a chiral binaphthalenylamine derivative of the N-butyl naphthalenediimide (NDIB-NH₂) enantiomers were applied to measure UV-vis and ECD spectra of NDIB-NH₂ radicals and dianion formed in the reduction and oxidation processes observed in cyclic voltammetry (CV). The CV curves and EPR spectroelectrochemistry enabled us to establish conditions at which a radical-anion [NDIB-NH₂]̇^.-, a dianion [NDIB-NH₂]^2-, and a radical-cation [NDIB-NH₂]̇^.+ are formed. The DFT restricted open-shell CAM-B3LYP-D3/def2TZVP/PCM calculations demonstrated that in the radical-anion [NDIB-NH₂]̇^.-, spin is spread over the NDI system while in the radical-cation [NDIB-NH₂]̇⁺ it is spread over the aminonaphthalene moiety. The UV-vis spectra of radical-anion and dianion show the most significant changes in the 400-800 nm range. In that range, the ECD spectra varied with the change of electrode potential more than the UV-vis did and enabled the identification of a new ECD band of [NDIB-NH₂]̇^.- at ca. 400 nm hidden in the background in the UV spectra at -1000 mV. A broad structured ECD pattern with a maximum at ca. 530 nm was observed for [NDIB-NH₂]̇^.- (-1000 mV), while a single smooth ECD band of [NDIB-NH₂]^2- was located at 520 nm (-1750 mV). For the first time, an isosbestic point (455 nm) was found in ECD spectroelectrochemical measurements for the radical-cation [NDIB-NH₂]̇^.+ in equilibrium with the NDIB-NH₂ neutral form. The TD-DFT CAM-B3LYP-D3/6-31G** calculations combined with the hybrid (explicit combined with implicit) solvation model fairly well reproduced the UV-vis and ECD SEC of neutral and redox forms of NDIB-NH₂ but the ECD spectrum of [NDIB-NH₂]̇^.+ above 390 nm.

Chemical redox-induced chiroptical switching of supramolecular assemblies of viologens

A chiral supramolecular assembly exhibiting redox-induced changes in its chiroptical properties was prepared using viologen-modified glutamide (G-V²⁺) derivatives. Achiral viologen moieties in the G-V²⁺ assembly were chirally orientated by glutamide groups, affording a unique orange-colored solution, with a visible absorption band at around 470 nm, having electronic circular dichroism (CD) signals (molar ellipticity [θ] = 0.58 × 10⁵ deg cm² dmol⁻¹: absorption dissymmetry factors (g) = 5.2 × 10⁻³ at 512 nm). The G-V²⁺ could be reduced to its cation radical (G-V⁺˙) but retains its chiral assembly. After chemical reduction, the color change from orange to blueish violet, indicating an absorption band at approximately 560 nm, and the sign change of the CD signal from positive to negative ([θ] = −0.36 × 10⁵ deg cm² dmol⁻¹; g = −2.9 × 10⁻³ at 580 nm) were observed in water. Subsequent oxidation re-introduces the G-V²⁺ chiroptical behavior before reduction.

Chiral assemblies of viologen-modified glutamide derivatives exhibit a unique orange-color and CD signals by CT complexes of viologen groups and electro-responsive chiroptical switching behaviors in the visible region in water.