Diacetonalkohol‐Komplexe von Lanthanoid‐Trichloriden. Die Kristallstrukturen von [LnCl3(DAA)2] mit Ln = Sm und Eu

Diacetone Alcohol Complexes of Lanthanide Trichlorides. Crystal Structures of [LnCl₃(DAA)₂] with Ln = Sm and Eu The diacetone alcohol complexes [LnCl₃(DAA)₂] with Ln = samarium ( 1 ) and europium ( 2 ) are obtained from the waterfree metal trichlorides with excess diacetone alcohol (4‐hydroxy‐4‐methyl‐2‐pentanone = DAA) forming colourless ( 1 ) and pale yellow crystals ( 2 ), respectively, which are characterized by crystal structure determinations. The europium compound 2 is additionally described by its vibrational spectra (IR, Raman). 1 and 2 crystallize isotypically with one another. The metal atoms of the molecular complex units are unusually coordinated in a distorted pentagonal‐bipyramdial fashion by the three chlorine atoms and by the two alcoholic oxygen atoms of the DAA molecules in the equatorial plane. The apical positions are occupied by the carbonyl oxygen atoms of the chelating DAA molecules. The complex units [LnCl₃(DAA)₂] are associated along [100] by bifurcated —OH···Cl···HO— bridges to form chains. 1 : Space group P2₁, Z = 2, lattice dimensions at —80 °C: : a = 710.2(1), b = 1617.6(2), c = 827.3(1) pm; β = 106.36(1)°; R₁ = 0.026. 2 : Space group P2₁, Z = 2, lattice dimensions at —80 °C: a = 709.7(1), b = 1614.5(2), c = 825.7(1) pm; β = 106.40(1)°; R₁ = 0.0303.     

Selenium speciation in paired serum and cerebrospinal fluid samples

Se speciation was performed in 24 individual paired serum and cerebrospinal fluid (CSF) samples from neurologically healthy persons. Strong anion exchange (SAX) separation, coupled to inductively coupled plasma–dynamic reaction cell–mass spectrometry (ICP-DRC-MS), was employed. Species identification was done by standard matched retention time, standard addition and by size exclusion chromatography followed from SAX (2-D SEC-SAX-ICP-DRC-MS) and by SAX followed from CE-ICP-DRC-MS (2-D SAX-CE-ICP-DRC-MS). Limit of detection (LoD, 3?×?standard deviation (SD) of noise) was in the range of 0.026–0.031 μg/L for all investigated species and thus was set uniformly to 0.032 μg/L. Quality control for total Se determination was performed by analysing control materials “human serum” and “urine”, where determined values met target values. Several Se species were found in both sample types having following median values (sequence: serum/CSF, each in μg Se/L): total Se, 58.39/0.86; selenoprotein P (SePP), 5.19/0.47; Se-methionine (SeM), 0.23/<LoD; glutathione peroxidase (GPx), 4.2/0.036; thioredoxinreductase (TrxR), 1.64/0.035; Se IV, 12.25/0.046; Se-human serum albumin (Se-HSA), 18.03/0.068. Other Se species, such as Se-cystine (SeC), Se VI and up to four non-identified compounds were monitored (if ever) only in very few samples usually close to LoD. Therefore, their median values were <LoD. Linear relationships based on median values provide information about Se-species passage across neural barriers (NB): SePP_-serum is significantly correlated to total Se_-serum when the latter was >?65 μg/L; however, SePP_-CSF appeared independent of SePP_-serum. For Se-HSA_-serum versus (vs.) Se-HSA_-CSF, a weak linear relationship was found (r ²?=?0.1722). On the contrary, for anti-oxidative Se-enzymes, higher r ² values were calculated: GPx_-serum vs. GPx_-CSF, r ²?=?0.3837; TrxR_-serum vs. TrxR_-CSF, r ²?=?0.6293. Q _-Se-species values (= ratios of CSF_-Se-species/serum_-Se-species) were compared with the Q _-Alb value (HSA_-CSF/HSA_-serum?=?clinical index of NB integrity) for deeper information about NB passage of Se species. The Q _-Se-HSA value (3.8?×?10^?3) was in accordance to the molecular mass dependent restriction at NB (Q _-Alb at 5.25?×?10^?3). Increased Q values were seen for TrxR (21.3?×?10^?3) and GPx (8.3?×?10^?3) which are not (completely) explained by molecular size. For these two anti-oxidative Se-enzymes (GPx, TrxR), we hypothesize that there might be either a facilitated diffusion across NB or they might be additionally synthesized in the brain.     

Complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid and related compounds

Summary The complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid as well as with benzoic acid and 4-hydroxybenzoic acid was studied. In aqueous solution weak carboxylic 1 : 1 complexes, are formed in which the carboxyl group is bidentately coordinated to the metal atom. The logarithmic stability constants of these complexes regarding the reaction of the uranyl ion with the single charged anion of the respective ligands are 2.78±0.02, 2.68±0.04, and 2.71±0.04 at an ionic strength of 0.1 mol/l (NaClO₄) and at 25 °C. Bis(4-hydroxy-3-methoxybenzoato)dioxouranium(VI) was obtained as a crystalline compound if the concentrations of the starting components for the synthesis are increased. The monoclinic compound has a reflections-rich X-ray powder diffraction pattern. The lattice constants are a = 13.662(9) ?, b = 21.293(7) ?, c = 11.213(3) ?, b = 107.49(4), and V = 3111(2) ?.³     

Improving the Stability of Maleimide–Thiol Conjugation for Drug Targeting

Maleimides are essential compounds for drug conjugation reactions via thiols to antibodies, peptides and other targeting units. However, one main drawback is the occurrence of thiol exchange reactions with, for example, glutathione resulting in loss of the targeting ability. A new strategy to overcome such retro-Michael exchange processes of maleimide–thiol conjugates by stabilization of the thiosuccinimide via a transcyclization reaction is presented. This reaction enables the straightforward synthesis of stable maleimide–thiol adducts essential in drug-conjugation applications.     

Long-Lived Triplet Excited State Accessed with Spin–Orbit Charge Transfer Intersystem Crossing in Red Light-Absorbing Phenoxazine-Styryl BODIPY Electron Donor/Acceptor Dyads

Orthogonal phenoxazine-styryl BODIPY compact electron donor/acceptor dyads were prepared as heavy atom-free triplet photosensitizers (PSs) with strong red light absorption (ϵ=1.33×10⁵ M⁻¹ cm⁻¹ at 630 nm), whereas the previously reported triplet photosensitizers based on the spin-orbit charge transfer intersystem crossing (SOCT-ISC) mechanism show absorption in a shorter wavelength range (<500 nm). More importantly, a long-lived triplet state (τ_T=333 μs) was observed for the new dyads. In comparison, the triplet state lifetime of the same chromophore accessed with the conventional heavy atom effect (HAE) is much shorter (τ_T=1.8 μs). Long triplet state lifetime is beneficial to enhance electron or energy transfer, the primary photophysical processes in the application of triplet PSs. Our approach is based on SOCT-ISC, without invoking of the HAE, which may shorten the triplet state lifetime. We used bisstyrylBodipy both as the electron acceptor and the visible light-harvesting chromophore, which shows red-light absorption. Femtosecond transient absorption spectra indicated the charge separation (109 ps) and SOCT-ISC (charge recombination, CR; 2.3 ns) for BDP-1 . ISC efficiency of BDP-1 was determined as Φ_T=25 % (in toluene). The dyad BDP-3 was used as triplet PS for triplet-triplet annihilation upconversion (upconversion quantum yield Φ_UC=1.5 %; anti-Stokes shift is 5900 cm⁻¹).     

NMR relaxometry of oil paint binders

Mobile nuclear magnetic resonance (NMR) is a flexible technique for nondestructive characterization of water in plants, the physical properties of polymers, moisture in porous walls, or the binder in paintings by relaxation measurements. NMR relaxation data report material properties and therefore can also help to characterize the state of tangible cultural heritage. In this work, we discuss the relaxation behavior in two series of naturally aged paint mock-up samples. First, paints with different pigment concentrations were prepared and investigated in terms of the longitudinal and transverse relaxation-time distributions. We document the evolution of both relaxation-time distributions during the initial drying stage and demonstrate the heightened importance of transverse over longitudinal relaxation measurements. Second, we observe nonlinear dependences of the relaxation times on the pigment concentration in a typical oil binder. Third, in a study of naturally aged paint samples prepared in the years between 1914 and 1951 and subsequently aged under controlled conditions, we explore the possibility of determining the age of paintings using partial least square regression (PLS) by fitting T₁–T₂ data with the sample age. Our results suggest some correlation, albeit with significant scatter. Estimating the age of a painting stored under unknown conditions from NMR relaxation data is therefore not feasible, as the cumulative effects of light irradiation, humidity, and biological degradation further obfuscate the chemical and physical impact of aging on the relaxation times in addition to the impact of pigment concentration.