Rethinking Uncaging: A New Antiaromatic Photocage Driven by a Gain of Resonance Energy

Photoactivatable compounds for example photoswitches or photolabile protecting groups (PPGs, photocages) for spatiotemporal light control, play a crucial role in different areas of research. For each application, parameters such as the absorption spectrum, solubility in the respective media and/or photochemical quantum yields for several competing processes need to be optimized. The design of new photochemical tools therefore remains an important task. In this study, we exploited the concept of excited-state-aromaticity, first described by N. Colin Baird in 1971, to investigate a new class of photocages, based on cyclic, ground-state-antiaromatic systems. Several thio- and nitrogen-functionalized compounds were synthesized, photochemically characterized and further optimized, supported by quantum chemical calculations. After choosing the optimal scaffold, which shows an excellent uncaging quantum yield of 28 %, we achieved a bathochromic shift of over 100 nm, resulting in a robust, well accessible, visible light absorbing, compact new photocage with a clean photoreaction and a high quantum product (ϵ⋅Φ) of 893 M⁻¹ cm⁻¹ at 405 nm.     

Selective Modification for Red-Shifted Excitability: A Small Change in Structure,a Huge Change in Photochemistry

We developed three bathochromic, green-light activatable, photolabile protecting groups based on a nitrodibenzofuran (NDBF) core with D-π-A push–pull structures. Variation of donor substituents (D) at the favored ring position enabled us to observe their impact on the photolysis quantum yields. Comparing our new azetidinyl-NDBF (Az-NDBF) photolabile protecting group with our earlier published DMA-NDBF, we obtained insight into its excitation-specific photochemistry. While the “two-photon-only” cage DMA-NDBF was inert against one-photon excitation (1PE) in the visible spectral range, we were able to efficiently release glutamic acid from azetidinyl-NDBF with irradiation at 420 and 530 nm. Thus, a minimal change (a cyclization adding only one carbon atom) resulted in a drastically changed photochemical behavior, which enables photolysis in the green part of the spectrum.     

椭圆齿旋流口平带传热管内自动清洗及其传热强化

介绍了一种特殊结构的旋流口椭圆齿平带的研制。平带上的每个椭圆齿都是使平带自转的流体动力结构元素,平带两侧的旋流口结构能够使管内的部分液体形成螺旋线流,因而具有近似斜齿纽带那样能够在较低流速下自转实现管内污垢在线自动清洗的宝贵性能。由于椭圆齿后的大量涡流、管内部分液体流线转变为螺旋线流股以及螺旋线流股与轴向流股分合交错这样3方面的作用,管内的对流传热强化的幅度由此远远高于光滑纽带。试验结果表明,这种平带不仅容易制造,并且综合性能好,在管内流速0.5m/s左右就可运行;管内侧的传热系数提高170%,流体阻力在一般工程许可的范围内,因此具有较高的工程应用价值。     

A rare nuclear decay process: The internal conversion between bound atomic states

We shall report on the recently observed dependence of the lifetime of the first excited state in ¹²⁵Te on the ionic charge state. Then we shall give an interpretation of the dependence of the half-life in terms of a new type of nuclear internal conversion without emission of the electron into the continuum of electron energies. We have named this process internal conversion between bound atomic states or BIC. The resonant character of the BIC will be established and the main parameters governing the decay process will be discussed [1–3]. Finally the results of a recent experiment performed at the GANIL accelerator attempting to measure directly the value of the internal conversion coefficient associated with BIC in ¹²⁵Te ions with charge states ranging between 44+ and 48+ will be given. In conclusion we shall discuss the relation between the BIC and nuclear excitation by electron transition, NEET, in the excitation of some nuclear isomeric states.     

GoldL-shell ionization probability by 1 MeV proton at large scattering angles

The impact parameter dependence of the ionization of GoldL-subshells has been measured and compared to theoretical values calculated in the SCA framework by Aashamar et al. [17]. Special attention has been paid to large scattering angle measurements and results are obtained for0 _lab=30°, 45°, 65°, 90°, 110°, 130°, 153° and 166°. Taking into account the sum ofL _α ,L _β ,L _γ ,L _α ,L _l lines we conclude firstly that the experimental ionization probabilityP(b) is in good agreement with the theoretical values. Secondly, comparing experimental and theoretical intensity of (L _α +L _l ) and (L _γ +L _β ) X-ray lines, we show that ionization ofL _II andL _III subshells is also fairly well described by the SCA model.     

Homo-/heterotrinuclear mixed-valent oxo-centered iron/nickel clusters-Mössbauer studies on internal electron-exchange processes

In a one-pot reaction of N-(5-methylthiazole-2-yl)-thiazole-2-carboxamide HL2 (3) with iron(II) acetate in air, the homotrinuclear heteroleptic mixed-valent oxo-centered iron cluster [Fe(II)Fe(III)O(L2)3(OAc)3] (4) was formed. Exchange of iron(II) in 4 by nickel(II) afforded the heteronuclear cluster [Ni(II)Fe(III)O(L2)3(OAc)3] (6). To obtain crystals suitable for X-ray structure analyses, in 4 and 6, the OAc- co-ligands were exchanged by OBz- ligands to give [Fe(II)Fe2(III)O(L2)3(OBz)3] (5) and [Ni(II)Fe(III)O(L2)3(OBz)3] (7). The complexes 5 and 7 are isostructural and made up of three ditopic, tridentate ligands (L2)- and three bridging benzoate co-ligands, which fix the three metal ions in the corners of a triangle with an mu3-O2- ion in the center. The mixed-valent character of 4-7, their intramolecular electron-exchange processes, and their redox properties were studied by variable-temperature M?ssbauer spectroscopy and cyclic voltammetry.