Two new beta-orcinol depsidones, 1 and 2, together with 13 known compounds were isolated from the lichen Usnea articulata. The structures of 1 and 2 were elucidated by spectroscopic analyses and those of known compounds by comparison of their spectroscopic data with literature values or by direct comparison with authentic standards. Compounds 1, 2, and 5 exhibited moderate antiradical activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The depsidones 4 and 5 showed better superoxide anion scavenging activity (IC50 = 566 and 580 microM, respectively) than quercetin (IC50 = 754 microM).

Abstract:The photophysical properties of a Keggin-type polyoxometalate (POM) covalently bounded to a benzospiropyran (BSPR) unit have been investigated. These studies reveal that (i) both closed and open forms are emissive with distinct spectral features (λem, (closed form) = 530 nm, λem, (open form) = 670 nm); (ii) the fluorescence of the BSPR unit of the POM-based hybrid is considerably enhanced compared to BSPR reference compounds. While the fluorescence excitation energy of the BSPR reference compounds (370 nm) is close to the intense absorption responsible of the photochromic character (350 nm), the fluorescence excitation of the hybrid is shifted to lower energy (400 nm), facilitating the population of the emissive state. Combined NOESY NMR and theoretical calculations of the closed form of hybrid give an intimate understanding of the structural conformation adopted by the hybrid and show that the nitro-aryl moieties of the BSPR is folded toward the POM, which should affect the electronic properties of the BSPR.Photo-responsive molecules and materials are currently receiving considerable attention regarding their potentiality for the development of advanced photonic devices in various applications such as information storage, optical switches, protection, smart labelling and super-resolution microscopy. [1] Particularly, the elaboration of molecular systems combining photo-switching and fluorescence properties constitute a promising research field because of the high sensitivity, resolution, contrast and fast response times of the fluorescence. Furthermore, the emergence of single-molecule fluorescence spectroscopy opens the route to high memory density nanodevices, in which a single molecule would work as one bit of memory, [2] and thus strongly supports the molecular approach. Until now, the development of molecular systems displaying photo-modulated emissive properties has mostly relied on the association of luminescent and photochromic components in a molecular assembly. [3] In these systems, the transformation of the photochromic component is exploited to modulate the emission intensity of the luminescent component on the basis of electron and/or energy transfer. [4] However, molecular systems displaying tuneable fluorescence features, i.e. having different emission energies, according to the form of the photochromic unit, have been scarcely reported in the literature. [5] The coexistence of photochromic and fluorescence properties, in a single photoactive unit, is rarely achieved since in case of fast internal conversion only one photophysical property (photochromic vs fluorescence) is observed. Furthermore the ns timescale of fluorescence [6] is considerably slower than the fs to ps timescale of the ring opening/closure dynamics occurring in the photochromic events. [7] POMs are nanosized molecular oxo cluster that are currently receiving considerable attention because of their wide range of properties and their potential applications in various fields such as analytical chemistry, medicine and ...

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The reaction between a-hydroxy-(or a-acetoxy) cyclopenten-aziridines (6-azabicyclo[3.1.0]hex-3-en-2ols or acetates) and C-based nucleophiles in the presence of Pd(0)-catalysis was investigated. In all the cases studied, the reaction was totally regio-and diastereo-selective, affording a single adduct in moderate to good yields. Specifically, attack of the nucleophile at position 3 of the cyclopentene moiety, anti to the vicinal oxy group, with vinylogous ring opening of the aziridine ring, was observed. When the carbon acid is a very acidic methylene (pK a (DMSO) 7.3), the resulting adduct is a zwitterion, resulting from an intramolecular proton transfer between the amino group and the carbon acid moiety taking place after the CeC bond formation. A plausible mechanism for this transformation is put forward.

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The design and synthesis of a supramolecular square composed of polyoxometalate-based hybrid donors and ethylenediamine palladium­(II) nodes are reported. The structure of the metallomacrocycle scaffold was inferred by diffusion NMR, small-angle X-ray scattering (SAXS), and molecular modeling. The metallomacrocycle scaffold that contains negatively and positively charged subunits can further self-assemble owing to a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. When the dissociating character of the solvent was lowered or when in the presence of a protic solvent, different types of multiscale organizations (vesicles and pseudo-1D structures) were selectively formed and were characterized by SAXS and transmission electron microscopy.

Online monitoring by flow NMR spectroscopy is a powerful approach to study chemical reactions and processes, which can provide mechanistic understanding, and drive optimisations. However, some of the most useful methods for mixture analysis and reaction monitoring are not directly applicable in flow conditions. This is the case of classic diffusion‐ordered NMR spectroscopy (DOSY) methods, which can be used to separate the spectral information for mixture's components. We describe a fast and flow‐compatible diffusion NMR experiment that makes it possible to collect accurate diffusion data for samples flowing at up to 3 mL/min. We use it to monitor the synthesis of a Schiff base with a flow‐tube with a time resolution of approximately 2 minutes. The one‐shot flow‐compatible diffusion NMR described here open many avenues for reaction monitoring applications.