Heterogeneous deoxygenation of ketones

Relatively unhindered ketones are converted directly to the corresponding hydrocarbons in the presence of hydrogen at normal pressures and a Ni/Al₂O₃ catalyst in a simple gas-phase reactor.     

Adsorption of DNA and electric fields decrease the rigidity of lipid vesicle membranes

The adsorption of calf-thymus DNA-fragments of 300 +/- 50 base pairs (bp) to the outer membrane monolayer of unilamellar lipid vesicles in the presence of Ca2+ ions has been quantified by the standard method of chemical relaxation spectrometry using polarized light. The vesicles of radius a = 150 +/- 45 nm are prepared from bovine brain extract type III containing 80-85% phosphatidylserine (PS) and palmitoyl-oleoyl-phosphatidylcholine (POPC) in the molar ratio PS : 2POPC; total lipid concentration [L(t)] = 1 mM in 1 mM HEPES buffer, pH 7.4 at T = 293 K (20 degrees C). The turbidity relaxations of vesicle suspensions, at the wavelength lambda = 365 nm at two characteristic electric field strengths are identified as electroelongation of the whole vesicle coupled to smoothing of thermal membrane undulations and membrane stretching, and at higher fields, to membrane electroporation (MEP). The elongation kinetics indicates that the DNA adsorption renders the membrane more flexible and prone to membrane electroporation (MEP). Remarkably, it is found that the Ca-mediated adsorption of DNA (D) decreases both, bending rigidity kappa and stretching modulus K, along an unique Langmuir adsorption isotherm for the fraction of bound DNA at the given Ca concentration [Ca(t)] = 0.25 mM. The characteristic chemo-mechanical parameter of the isotherm is the apparent dissociation equilibrium constant K(D,Ca) = 100 +/- 10 microM (bp) of the ternary complex DCaB of DNA base pairs (bp) and Ca binding to sites B on the outer vesicle surface. Whereas both kappa and K decrease in the presence of high electric fields (E), the key parameter K(D,Ca) is independent of E in the range 0 < or = E/(kV cm(-1)) < or = 40.     

Kinetic and energetic analysis of the free electron transfer

In this paper, the bimolecular free (unhindered) electron transfer (FET) from various trityl-containing compounds to the solvent radical cations of n-BuCl is described. In good agreement with the previously studied cases, the FET involving trityl-derived compounds results in the formation of two different types of the radical cation, which undergo the subsequent fragmentation via two alternative reaction channels. This unusual effect is caused by the intramolecular rotational motion in the ground-state molecules around the arrow-marked bond Ar-//-X-CPh 3 (Ar = aromatic moiety; X = S, O, NH, CH 2), since such oscillations are directly connected with the electron distribution within the molecule. An unhindered electron jump from the donor trityl compound to the solvent radical cation, taking place in the subfemtosecond time range, generates the solute radical cation with the inherited geometry and the electron distribution of its precursor. Among the whole variety of produced radical cations, two extreme conformer states can be distinguished, namely, a planar and a twisted state. The planar type represents the structures with minimum energy, whereas the twisted type is destabilized by the increased value of the rotational barrier in the ionized state. The difference in the energetic profiles between planar and twisted radical cations plays a crucial role in their subsequent fragmentation. The planar radical cation follows the thermodynamically favored pathway generating ArX (*) and Ph 3C (+). A distinct part of the twisted radical cation dissociates faster than it relaxes into the more preferable planar conformation and, therefore, produces a thermodynamically unfavorable couple of products: ArX (+) and Ph 3C (*). This fragmentation channel is exclusively caused by FET. The undertaken quantum chemical calculations enable the judgment of the energetics of the different dissociation channels of the radical cations of the trityl derivatives.     

Synthesis and Photophysical Properties of Monometallic C^C* Platinum(II) Formamidinate Complexes using Sterically Demanding Ligands

A novel class of cyclometalated platinum(II) complexes—previously considered to be inaccessible—was synthesized by an improved synthetic route utilizing ligands predicted by density functional theory calculations. Based on a concise quantum chemical screening three model ligands with varying steric demand were chosen and a series of six photoluminescent C^C* cyclometalated platinum(II) formamidinate complexes was obtained. The least sterically demanding ligand led to a bimetallic complex in two isomeric forms, which could be separated and confirmed by the corresponding solid-state structures. Sterically more hindered amidinate ligands gave the monometallic complexes supporting the theoretical predictions. The monometallic complexes show a significant hypsochromic shift of the emission wavelength, explained by the loss of the metal-metal interactions. Depending on the cyclometalating ligand quantum yields up to 87 % with short decay times were found for this new class of phosphorescent green-blue to pure blue platinum(II) emitters.     

Isoprenoid Biosynthesis in Pathogenic Bacteria: Nuclear Resonance Vibrational Spectroscopy Provides Insight into the Unusual [4Fe‐4S] Cluster of the E. coli LytB/IspH Protein

The LytB/IspH protein catalyzes the last step of the methylerythritol phosphate (MEP) pathway which is used for the biosynthesis of essential terpenoids in most pathogenic bacteria. Therefore, the MEP pathway is a target for the development of new antimicrobial agents as it is essential for microorganisms, yet absent in humans. Substrate‐free LytB has a special [4Fe‐4S]²⁺ cluster with a yet unsolved structure. This motivated us to use synchrotron‐based nuclear resonance vibrational spectroscopy (NRVS) in combination with quantum chemical‐molecular mechanical (QM/MM) calculations to gain more insight into the structure of substrate‐free LytB. The apical iron atom of the [4Fe‐4S]²⁺ is clearly linked to three water molecules. We additionally present NRVS data of LytB bound to its natural substrate, (E)‐4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl diphosphate (HMBPP) and to the inhibitors (E)‐4‐amino‐3‐methylbut‐2‐en‐1‐yl diphosphate and (E)‐4‐mercapto‐3‐methylbut‐2‐en‐1‐yl diphosphate.     

Polythiolactone-Decorated Silica Particles: A Versatile Approach for Surface Functionalization,Catalysis and Encapsulation

The surface chemistry of colloidal silica has tremendous effects on its properties and applications. Commonly the design of silica particles is based on their de novo synthesis followed by surface functionalization leading to tailormade properties for a specific purpose. Here, the design of robust “precursor” polymer-decorated silica nano- and microparticles is demonstrated, which allows for easy post-modification by polymer embedded thiolactone chemistry. To obtain this organic-inorganic hybrid material, silica particles (SiO₂P) were functionalized via surface-initiated atom transfer radical polymerization (SI-ATRP) with poly(2-hydroxyethyl acrylate) (PHEA)-poly(thiolactone acrylamide (PThlAm) co-polymer brushes. Exploiting the versatility of thiolactone post-modification, a system was developed that could be used in three exemplary applications: 1) the straightforward molecular post-functionalization to tune the surface polarity, and therefore the dispersibility in various solvents; 2) the immobilization of metal nanoparticles into the polymer brushes via the in situ formation of free thiols that preserved catalytic activity in a model reaction; 3) the formation of redox-responsive, permeable polymer capsules by crosslinking the thiolactone moieties with cystamine dihydrochloride (CDH) followed by dissolution of the silica core.     

Fourier-transform infrared study of the switching process in a ferroelectric liquid crystalline polymer

The implementation of the step-scan technique on our FT-IR spectrometer enabled us to follow the electric-field induced reorientation dynamics of different molecular segments of a ferroelectric liquid crystalline polymer on a sub-millisecond time scale. It was detected that not only the mesogen but also the spacer and at least part of the backbone take part in the reorientation process.     

VII Zwei Oxidationsstufen und vier verschiedene Koordinationen von Eisen in einer Verbindung. Synthese,Kristallstruktur und spektroskopische Charakterisierung von 1,4‐Dimethylpiperazinium‐Chloroferrat(II,III), (dmpipzH2)6[FeIICl4]2[FeIIICl4]2[FeIICl5] [FeIIICl6]

Halogeno Metallates of Transition Elements with Cations of Nitrogen‐containing Heterocyclic Bases. VII Two Oxidation States and Four Different Iron Coordinations in one Compound. Synthesis, Crystal Structure, and Spectroscopic Characterization of 1,4‐Dimethylpiperazinium Chloroferrate(II, III), (dmpipzH₂)₆[Fe^IICl₄]₂[Fe^IIICl₄]₂[Fe^IICl₅] [Fe^IIICl₆] The title compound being stable on air crystallizes from aqueous hydrochloric acid solutions in the trigonal space group R3 with a = 13,197(1), c = 38,405(6) Å. Besides the cations in chair form, the structure contains six discrete, mononuclear chloroferrate anions arranged on a threefold axis. Tetrahedral, octahedral, and, for the first time with iron(II), trigonal bipyramidal metal coordinations occur. Four sub‐spectra contributing to the ⁵⁷Fe Mössbauer spectrum can be distinguished and have been attributed to all four types of chloroferrate anions in the structure. The Raman spectroscopic investigation of orientated single crystals allows to recognize polarized and non‐polarized vibrations as well as to attribute all observed frequencies.     

An Imidazolium-Based Lipid Analogue as a Gene Transfer Agent

A dicationic imidazolium salt is described and investigated towards its application for gene transfer. The polar head group and the long alkyl chains in the backbone contribute to a lipid-like behavior, while an alkyl ammonium group provides the ability for crucial electrostatic interaction for the transfection process. Detailed biophysical studies regarding its impact on biological membrane models and the propensity of vesicle fusion are presented. Fluorescence spectroscopy, atomic force microscopy and confocal fluorescence microscopy show that the imidazolium salt leads to negligible changes in lipid packing, while displaying distinct vesicle fusion properties. Cell culture experiments reveal that mixed liposomes containing the novel imidazolium salt can serve as plasmid DNA delivery vehicles. In contrast, a structurally similar imidazolium salt without a second positive charge showed no ability to support DNA transfection into cultured cells. Thus, we introduce a novel and variable structural motif for cationic lipids, expanding the field of lipofection agents.