Synthesis of profluorescent isoindoline nitroxides via palladium-catalysed Heck alkenylation

The synthesis of a new structural class of isoindoline nitroxides (aminoxyls), accessible via the palladium-catalysed Heck reaction, is presented. Reaction of the aryl bromoamine, 5-bromo-1,1,3,3-tetramethylisoindoline (4) or dibromoamine, 5,6-dibromo-1,1,3,3-tetramethylisoindoline (5) or the analogous bromonitroxides 6 and 7 with methyl acrylate gives the acrylate substituted tetramethylisoindoline amines 8 and 10 and nitroxides 12 and 14. Similarly, the reaction of the aryl bromides and dibromides 4-7 with methyl 4-vinylbenzoate gives the carboxystyryl substituted tetramethylisoindoline amines 9 and 11 and the analogous nitroxides 13 and 15. The carboxystyryl tetramethylisoindoline nitroxides demonstrate strongly suppressed fluorescence, which is revealed upon removal of the free radical by reduction or radical coupling.     

The role of water in synthesised hydrotalcites of formula Mg(x)Zn(6 - x)Cr2(OH)16(CO3) x 4H2O and Ni(x)Co(6 - x)Cr2(OH)16(CO3) x 4H2O--an infrared spectroscopic study

Infrared spectroscopy has been used to characterise synthesised hydrotalcites of formula Mg(x)Zn(6 - x)Cr2(OH)16(CO3) x 4H2O and Ni(x)Co(6 - x)Cr2(OH)16(CO3) x 4H2O. The infrared spectra are conveniently subdivided into spectral features based (a) upon the carbonate anion (b) the hydroxyl units (c) water units. Three carbonate antisymmetric stretching vibrations are observed at around 1358, 1387 and 1482 cm(-1). The 1482 cm(-1) band is attributed to the CO stretching band of carbonate hydrogen bonded to water. Variation of the intensity ratio of the 1358 and 1387 cm(-1) modes is linear and cation dependent. By using the water bending band profile at 1630 cm(-1) four types of water are identified (a) water hydrogen bonded to the interlayer carbonate ion (b) water hydrogen bonded to the hydrotalcite hydroxyl surface (c) coordinated water and (d) interlamellar water. It is proposed that the water is highly structured in the hydrotalcite interlayer as it is hydrogen bonded to both the carbonate anion, adjacent water molecules and the hydroxyl surface.     

Konstitutionsfragen und Papierchromatographie, 1. Mitt

Zusammenfassung Um kleinste Mengen sekundärer (oder primärer) Amine neben tertiären nachweisen zu können, wird auf dem Startpunkt des Chromatogramms acetyliert. Sekundäre (und primäre) Amine verschwinden aus dem Chromatogramm, dafür treten die Flecke ihrer Acetylierungsprodukte auf, welche in organischen Solventien schneller, in Elektrolytlösungen langsamer laufen.Mit 2 AbbildungenHerrn Prof. Dr.F. Feigl zum 70. Geburtstag gewidmet!     

STRUCTURAL AND FUNCTIONAL INTEGRITY OF THE PHOTOSYSTEM II REACTION CENTER ON SILVER ELECTRODES: FLUORESCENCE AND REDOX PROBES

Two simple and sensitive methods have been developed to assess the structural and functional integrity of isolated photosystem II reaction centers deposited on a roughened Ag electrode. Surface-enhanced resonance Raman scattering (SERRS) spectra useful for ascertaining structural information can be obtained from biological materials with this technique. The first method presented is based on observing differences in the fluorescence emission properties of reaction centers; these depend on the activity of the material. The second is based on the observation of changes in Raman bands that are sensitive to the redox state of cytochrome b₅₅₉ present in the reaction center complex. It is concluded that the conditions used here to obtain SERRS spectra do not affect the structural or functional integrity of the isolated photosystem II reaction center complex. In principle these approaches also could be used with other chromoproteins.     

Stepwise nitrosylation of the nonheme iron site in an engineered azurin and a molecular basis for nitric oxide signaling mediated by nonheme iron proteins

Mononitrosyl and dinitrosyl iron species, such as {FeNO}⁷, {FeNO}⁸ and {Fe(NO)₂}⁹, have been proposed to play pivotal roles in the nitrosylation processes of nonheme iron centers in biological systems. Despite their importance, it has been difficult to capture and characterize them in the same scaffold of either native enzymes or their synthetic analogs due to the distinct structural requirements of the three species, using redox reagents compatible with biomolecules under physiological conditions. Here, we report the realization of stepwise nitrosylation of a mononuclear nonheme iron site in an engineered azurin under such conditions. Through tuning the number of nitric oxide equivalents and reaction time, controlled formation of {FeNO}⁷ and {Fe(NO)₂}⁹ species was achieved, and the elusive {FeNO}⁸ species was inferred by EPR spectroscopy and observed by Mössbauer spectroscopy, with complemental evidence for the conversion of {FeNO}⁷ to {Fe(NO)₂}⁹ species by UV-Vis, resonance Raman and FT-IR spectroscopies. The entire pathway of the nitrosylation process, Fe(ii) → {FeNO}⁷ → {FeNO}⁸ → {Fe(NO)₂}⁹, has been elucidated within the same protein scaffold based on spectroscopic characterization and DFT calculations. These results not only enhance the understanding of the dinitrosyl iron complex formation process, but also shed light on the physiological roles of nitric oxide signaling mediated by nonheme iron proteins.

Stepwise nitrosylation from Fe(ii) to {FeNO}⁷, {FeNO}⁸ and then to {Fe(NO)₂}⁹ is reported for the first time in the same protein scaffold, providing deeper understanding of the detailed mechanism of dinitrosyl iron complex formation.     

Derivate des 5, 9-Methano-6, 7,8, 9-tetrahydro-5 H-benzocycloheptens und Umlagerungen zum 1, 4-Äthano-1,2,3,4-tetrahydronaphtalin-System

Derivatives of 5,9-Methano,7,8,9-tetrahydro-5H-benzocycloheptene and Rearrangements to the 1,4-Ethano-I,2,3,4-tetrahydronaphthalene System Reduction of the oxime 2 with Raney alloy gives the amine 3a , with AlH₃ a mixture of the isomeric amines 3a and 3b , whilst LiAlH₄ yields the aziridines 4a and 4b . The bicyclo[3.2.1]octane 4b rearranges under acidic conditions to the bicyclo[2.2.2]octane 5 . The olefin 7 can be converted to the aminoalcohol 9 via the epoxide 8 and to the amine 13 using iodine isocyanate: the carbon skeleto. remains intact. However, treatment of the olefin 17 with iodine isocyanate leads to the bicyclo[2.2.2]octanes 21 and 24 in which a skeletal rearrangement has taken place. The configuration was determined by NMR. and X-ray analysis.     

Compact embeddings of Sobolev spaces with power weights perturbed by slowly varying functions

We study compact embeddings of weighted Sobolev spaces into Lebesgue spaces on the unit ball in . The weight is of slowly varyingly disturbed polynomial growth with a singularity at the origin. It extends 21 , 27 to a wider class of weights. Special attention is paid to the influence of the growth rate of the weight on the quality of compactness, measured in terms of entropy and approximation numbers. In case of Hilbert spaces, the results are related to the distribution of eigenvalues of some degenerate elliptic operators.     

Nucleation and Growth of Amino Acid and Peptide Supramolecular Polymers through Liquid–Liquid Phase Separation

The transition of peptides and proteins from the solution phase into fibrillar structures is a general phenomenon encountered in functional and aberrant biology and is increasingly exploited in soft materials science. However, the fundamental molecular events underpinning the early stages of their assembly and subsequent growth have remained challenging to elucidate. Here, we show that liquid–liquid phase separation into solute‐rich and solute‐poor phases is a fundamental step leading to the nucleation of supramolecular nanofibrils from molecular building blocks, including peptides and even amphiphilic amino acids. The solute‐rich liquid droplets act as nucleation sites, allowing the formation of thermodynamically favorable nanofibrils following Ostwald's step rule. The transition from solution to liquid droplets is entropy driven while the transition from liquid droplets to nanofibrils is mediated by enthalpic interactions and characterized by structural reorganization. These findings shed light on how the nucleation barrier toward the formation of solid phases can be lowered through a kinetic mechanism which proceeds through a metastable liquid phase.