Stochastic relaxed inertial forward-backward-forward splitting for monotone inclusions in Hilbert spaces

Computational Optimization and Applications - We develop a globalized Proximal Newton method for composite and possibly non-convex minimization problems in Hilbert spaces. Additionally, we impose...     

Protic Anions [H(B12X12)]− (X=F,Cl, Br,I) That Act as Brønsted Acids in the Gas Phase

The acidity of protic cations and neutral molecules has been studied extensively in the gas phase, and the gas‐phase acidity has been established previously as a very useful measure of the intrinsic acidity of neutral and cationic compounds. However, no data for any anionic acids were available prior to this study. The protic anions [H(B₁₂X₁₂)]^? (X=F, Cl, Br, I) are expected to be the most acidic anions known to date. Therefore, they were investigated in this study with respect to their ability to protonate neutral molecules in the gas phase by using a combination of mass spectrometry and quantum‐chemical calculations. For the first time it was shown that in the gas phase protic anions are also able to protonate neutral molecules and thus act as Brønsted acids. According to theoretical calculations, [H(B₁₂I₁₂)]^? is the most acidic gas‐phase anion, whereas in actual protonation experiments [H(B₁₂Cl₁₂)]^? is the most potent gas‐phase acidic anion for the protonation of neutral molecules. This discrepancy is explained by ion pairing and kinetic effects.     

Gapmer Antisense Oligonucleotides Containing 2′,3′-Dideoxy-2′-fluoro-3′-C-hydroxymethyl-β-d-lyxofuranosyl Nucleotides Display Site-Specific RNase H Cleavage and Induce Gene Silencing

Off-target effects remain a significant challenge in the therapeutic use of gapmer antisense oligonucleotides (AONs). Over the years various modifications have been synthesized and incorporated into AONs, however, precise control of RNase H-induced cleavage and target sequence selectivity has yet to be realized. Herein, the synthesis of the uracil and cytosine derivatives of a novel class of 2′-deoxy-2′-fluoro-3′-C-hydroxymethyl-β-d -lyxo-configured nucleotides has been accomplished and the target molecules have been incorporated into AONs. Experiments on exonuclease degradation showed improved nucleolytic stability relative to the unmodified control. Upon the introduction of one or two of the novel 2′-fluoro-3′-C-hydroxymethyl nucleotides as modifications in the gap region of a gapmer AON was associated with efficient RNase H-mediated cleavage of the RNA strand of the corresponding AON:RNA duplex. Notably, a tailored single cleavage event could be engineered depending on the positioning of a single modification. The effect of single mismatched base pairs was scanned along the full gap region demonstrating that the modification enables a remarkable specificity of RNase H cleavage. A cell-based model system was used to demonstrate the potential of gapmer AONs containing the novel modification to mediate gene silencing.     

Crystalline Nitridophosphates by Ammonothermal Synthesis

Nitridophosphates are a well-studied class of compounds with high structural diversity. However, their synthesis is quite challenging, particularly due to the limited thermal stability of starting materials like P₃N₅. Typically, it requires even high-pressure techniques (e.g. multianvil) in most cases. Herein, we establish the ammonothermal method as a versatile synthetic tool to access nitridophosphates with different degrees of condensation. α-Li₁₀P₄N₁₀, β-Li₁₀P₄N₁₀, Li₁₈P₆N₁₆, Ca₂PN₃, SrP₈N₁₄, and LiPN₂ were synthesized in supercritical NH₃ at temperatures and pressures up to 1070 K and 200 MPa employing ammonobasic conditions. The products were analyzed by powder X-ray diffraction, energy dispersive X-ray spectroscopy, and FTIR spectroscopy. Moreover, we established red phosphorus as a starting material for nitridophosphate synthesis instead of commonly used and not readily available precursors, such as P₃N₅. This opens a promising preparative access to the emerging compound class of nitridophosphates.     

Sr3P3N7: Complementary Approach by Ammonothermal and High-Pressure Syntheses

Nitridophosphates exhibit an intriguing structural diversity with different structural motifs, for example, chains, layers or frameworks. In this contribution the novel nitridophosphate Sr₃P₃N₇ with unprecedented dreier double chains is presented. Crystalline powders were synthesized using the ammonothermal method, while single crystals were obtained by a high-pressure multianvil technique. The crystal structure of Sr₃P₃N₇ was solved and refined from single-crystal X-ray diffraction and confirmed by powder X-ray methods. Sr₃P₃N₇ crystallizes in monoclinic space group P2/c. Energy-dispersive X-ray and Fourier-transformed infrared spectroscopy were conducted to confirm the chemical composition, as well as the absence of NH_x functionality. The optical band gap was estimated to be 4.4 eV using diffuse reflectance UV/Vis spectroscopy. Upon doping with Eu²⁺, Sr₃P₃N₇ shows a broad deep-red to infrared emission (λ_em=681 nm, fwhm≈3402 cm⁻¹) with an internal quantum efficiency of 42 %.     

Intermediates of N-Heterocyclic Carbene (NHC) Dimerization Probed in the Gas Phase by Ion Mobility Mass Spectrometry: C−H⋅⋅⋅:C Hydrogen Bonding Versus Covalent Dimer Formation

N-Heterocyclic carbenes (NHCs, :C ) can interact with azolium salts ( C−H⁺ ) by either forming a hydrogen-bonded aggregate ( CHC⁺ ) or a covalent C−C bond ( CCH⁺ ). In this study, the intramolecular NHC–azolium salt interactions of aromatic imidazolin-2-ylidenes and saturated imidazolidin-2-ylidenes have been investigated in the gas phase by traveling wave ion mobility mass spectrometry (TW IMS) and DFT calculations. The TW IMS experiments provided evidence for the formation of these important intermediates in the gas phase, and they identified the predominant aggregation mode (hydrogen bond vs. covalent C−C) as a function of the nature of the interacting carbene–azolium pairs.     

Oxoanionic Noble Metal Compounds from Fuming Nitric Acid: The Palladium Examples Pd(NO3)2 and Pd(CH3SO3)2

The oxidation of elemental palladium at 100 °C in a mixture of fuming nitric acid and a pyridine‐SO₃ complex leads to the anhydrous nitrate Pd(NO₃)₂ (monoclinic, P2₁/n, Z=2, a=469.12(3) pm, b=593.89(3) pm, c=805.72(4) pm, β=105.989(3)°, V=215.79(2) ų). The Pd²⁺ ions are in square‐planar coordination with four monodentate nitrate groups which are connected to further palladium atoms, leading to a layer structure. The reaction of elemental palladium with a mixture of fuming nitric acid and methanesulfonic acid at 120 °C leads to single crystals of Pd(CH₃SO₃)₂ (monoclinic, P2₁/n, Z=2, a=480.44(1) pm, b=1085.53(3) pm, c=739.78(2) pm, β=102.785(1)°, V=376.254(17) ų). Also in this structure the Pd²⁺ ions are in square‐planar coordination with four monodentate anions; however, the connection to adjacent palladium atoms leads to a chain‐type structure. The thermal decomposition of the compounds has been investigated by means of DSC/TG measurements. Furthermore, IR and Raman spectra have been recorded, and an assignment of the observed vibrational frequencies has been carried out based on theoretical investigations.     

Towards Polysulfuric Acids: The Hydrogentrisulfate Anion [HS3O10]− in A[HS3O10] (A=Na,K, Rb)

The reaction of Na₂SO₄ and K₂SO₄ with fuming sulfuric acid (65 % SO₃) yielded colorless extremely sensitive crystals of Na[HS₃O₁₀] (monoclinic; P2₁/n (No. 14); Z=4; a=707.36(2), b=1378.56(4), c=848.10(3) pm; β=94.817(1)°; V=824.09(4) ? 10⁶ pm³) and K[HS₃O₁₀] (orthorhombic; Pccn (No. 56); Z=4; a=1057.16(3), b=807.81(2), c=897.57(2) pm; V=766.51(3) ? 10⁶ pm³). The analogous rubidium compound Rb[HS₃O₁₀] (orthorhombic; Pnma (No. 62); Z=4; a=891.43(3), b=1095.34(4), c=839.37(3) pm; V=819.58(5) ? 10⁶ pm³) originates from the reaction of Rb₂CO₃ and SO₃. All of the different structures contain the hitherto unknown anion [HS₃O₁₀]^? and are stamped by strong hydrogen bonds linking the anions either to dimers or chains. Theoretical investigations by DFT methods give further insight in the structural characteristics of [HS₃O₁₀]^?. The preparation of the [HS₃O₁₀]^? anion can be seen as an important milestone on our way to the still elusive polysulfuric acids.