Some Comments on Fulminic Acid (Knallsäure) and a Praise to Heinrich Wieland and his Work on Organic Derivatives of Nitrogen

The structure, vibrational spectrum, the polymerization and [3+2] cycoaddition reactions of fulminic acid are discussed. In the mass spectra of the solid deposit from gaseous fulminic acid (prepared from sodium fulminate and sulfuric acid) the mass of the adduct of HCNO with hydrogen cyanide was detected, which may be formed by Huisgen 1,3‐dipolar cycloaddition. As examples for Heinrich Wieland's experimental mastership the polymerization and his syntheses of fulminic acid and of explosive dinitrosomethanide [HC(NO)₂]^– are emphasized; the structure of the latter has recently been disclosed by X‐ray structure determination.     

Controllable Growth of Perovskite Films by Room‐Temperature Air Exposure for Efficient Planar Heterojunction Photovoltaic Cells

A two‐step solution processing approach has been established to grow void‐free perovskite films for low‐cost high‐performance planar heterojunction photovoltaic devices. A high‐temperature thermal annealing treatment was applied to drive the diffusion of CH₃NH₃I precursor molecules into a compact PbI₂ layer to form perovskite films. However, thermal annealing for extended periods led to degraded device performance owing to the defects generated by decomposition of perovskite into PbI₂. A controllable layer‐by‐layer spin‐coating method was used to grow “bilayer” CH₃NH₃I/PbI₂ films, and then drive the interdiffusion between PbI₂ and CH₃NH₃I layers by a simple air exposure at room temperature for making well‐oriented, highly crystalline perovskite films without thermal annealing. This high degree of crystallinity resulted in a carrier diffusion length of ca. 800 nm and a high device efficiency of 15.6 %, which is comparable to values reported for thermally annealed perovskite films.     

Lamellar versus Micellar Structures—Aggregation Behavior of a Three‐Chain Cationic Lipid Designed for Nonviral Polynucleotide Transfer

The aggregation behavior of a cationic lipid, N‐[6‐amino‐1‐oxo‐1‐(N‐tetradecylamino)hexan‐(2S)‐2‐yl]‐N′‐{2‐[N,N‐bis(2‐aminoethyl)amino]ethyl}‐2,2‐ditetradecylpropandiamide (DiTT4), is investigated in aqueous dispersions at different pH values (5, 7.3, and 10). An unusual aggregation behavior is observed whereby DiTT4 forms bilayer structures at pH 10 and 7.3. At pH 5, rod‐like micelles are the dominant aggregate form. The thermotropic and lyotropic behavior is studied using differential scanning calorimetry, small‐angle X‐ray scattering, and FTIR spectroscopy. In addition, investigations at the air–water interface are performed by recording area–pressure‐isotherms and infrared reflection–absorption (IRRA) spectra. Complementary dynamic light scattering experiments and transmission electron microscopy (TEM and cryoTEM) are also used. The ability of DiTT4 to complex plasmid DNA is investigated using fluorescence techniques and zeta potential measurements. Cell culture experiments demonstrate the ability of DiTT4 to enhance plasmid transfer in A549 cells.     

Synthesis and crystal structures of dialkyl[1,1-bis(alkylchloroalanyl)organylmethyl]phosphine•dialkylchloroalane(1/1) complexes

Dialkyl[1,1-bis(alkylchloroalanyl)organylmethyl]phosphine?dialkylchloroalane(1/1) complexes (1a–1d) were synthesized and fully characterized. In 1a–1d, dative bonding between phosphorus or chlorine as a donor atom and aluminum as an acceptor atom results in a bicyclic system. The ³¹P{¹H} NMR spectra of all compounds dissolved in d₆-benzene indicate the presence of several isomers in solution. The ²⁷Al{¹H} NMR spectra of 1a–1d dissolved in d₆-benzene as well show very broad singlets between 177 and 140 ppm. For all compounds, crystal structures consist of two fused four- and five-membered rings. The 1λ³-phosphaalkyne reacts at the Al–C bond of the starting material, whereas the Al–Cl moiety remains intact. The heterocycle isolated is a molecular complex of the underlying insertion compound and a third equivalent of dialkylaluminum chloride. The four- and five-membered rings both contain two chlorine-bridged aluminum atoms, Al3 and Al1, slightly more symmetrical than that between Al1 and Al6. In the four-membered ring the two aluminum atoms Al1 and Al6 approach each other at an average distance of 289.1 pm which tallies with the element–element distance (286.3 pm) in aluminum metal.     

Synthesis of C2-symmetric bisamidines: a new type of chiral metal-free Lewis acid analogue interacting with carbonyl groups

The chiral bisamidine 5 has been prepared in just two steps from malonodinitrile. In the monocationic form this compound adopts a planar conformation with an almost convergent orientation of two N-H groups. Ketones, aldehydes, and nitro compounds are assumed to bind to this strongly polar cleft via hydrogen bonds, resulting in a Lewis-acid-like activation of the carbonyl groups. A broad scope of reactions (Diels-Alder, hetero-Diels-Alder, Friedel-Crafts) can be catalyzed. The observed accelerations surpass the rate effects of neutral hydrogen-bond donors such as thioureas or TADDOLs.     

A chemical approach to the pharmaceutical optimization of an anti-HIV protein

Chemical protein synthesis is important for dissecting the molecular basis of protein function. Here we advance its scope by demonstrating the significant improvement of the multifaceted pharmaceutical profile of small proteins exclusively via a chemical-based approach. The focus of this work centered on CCL-5 (RANTES) derivatives with potent anti-HIV activity. The overall chemical strategy involved a combination of coded and noncoded amino acid mutagenesis, peptide backbone engineering, and site-specific polymer attachment. The ability to alter specific protein residues, as well as precise control of the position and type of polymer attachment, allows for the exploration of specific molecular designs and resulted in novel CCL-5 analogues with significant differences in their respective biochemical and pharmaceutical properties. Using this approach, the complex-interplay of variables contributing to the noncovalent self-association (aggregation) state, CCR-5 specificity, in vivo elimination half-life, and anti-HIV activity of CCL-5-based protein analogues could be empirically evaluated via total chemical synthesis. This work has led to the identification of potent (sub-nanomolar) anti-HIV proteins with significantly improved pharmaceutical profiles, and illustrates the increasing value of protein chemical synthesis in contemporary therapeutic discovery. These antiviral molecules provide a novel mechanism of action for the development of a new generation of anti-HIV therapeutics which are still desperately needed.     

NMR studies of double proton transfer in hydrogen bonded cyclic N,N'-diarylformamidine dimers: conformational control, kinetic HH/HD/DD isotope effects and tunneling

Using dynamic NMR spectroscopy, the kinetics of the degenerate double proton transfer in cyclic dimers of polycrystalline (15)N,(15)N'-di-(4-bromophenyl)-formamidine (DBrFA) have been studied including the kinetic HH/HD/DD isotope effects in a wide temperature range. This transfer is controlled by intermolecular interactions, which in turn are controlled by the molecular conformation and hence the molecular structure. At low temperatures, rate constants were determined by line shape analysis of (15)N NMR spectra obtained using cross-polarization (CP) and magic angle spinning (MAS). At higher temperatures, in the microsecond time scale, rate constants and kinetic isotope effects were obtained by a combination of longitudinal (15)N and (2)H relaxation measurements. (15)N CPMAS line shape analysis was also employed to study the non-degenerate double proton transfer of polycrystalline (15)N,(15)N'-diphenyl-formamidine (DPFA). The kinetic results are in excellent agreement with the kinetics of DPFA and (15)N,(15)N'-di-(4-fluorophenyl)-formamidine (DFFA) studied previously for solutions in tetrahydrofuran. Two large HH/HD and HD/DD isotope effects are observed in the whole temperature range which indicates a concerted double proton transfer mechanism in the domain of the reaction energy surface. The Arrhenius curves are non-linear indicating a tunneling mechanism. Arrhenius curve simulations were performed using the Bell-Limbach tunneling model. The role of the phenyl group conformation and hydrogen bond compression on the barrier of the proton transfer is discussed.     

Determination of tuaminoheptane in doping control urine samples

Since January 2007, the list of prohibited substances established by the World Anti-Doping Agency includes the sympathomimetic compound tuaminoheptane (1-methyl-hexylamine, 2-heptylamine). Primarily used as nasal decongestant drug it has been considered relevant for sports drug testing due to its stimulating properties. A confirmatory gas chromatographic-mass spectrometric procedure was developed including liquidliquid extraction and imine formation of tuaminoheptane employing various aldehydes and ketones such as formaldehyde, acetaldehyde, benzaldehyde and acetone. Extraction and derivatisation conditions were optimised for utmost efficiency, and characteristic fragment ions obtained after electron ionisation allowed for a sensitive and selective analytical assay, which was validated with regard to recovery (50%), lower limit of detection (20 ng mL(1)) as well as interday- and intraday precision (<15%). The applicability to authentic urine samples was demonstrated using administration study specimens obtained from two male persons using Rhinofluimucil (tuaminoheptane hemisulfate) for intranasal application. The administered drug was detected up to 46 h after repeated topical instillation of a total of approximately 3 mg.     

NMR provides checklist of generic properties for atomic-scale models of periodic mesoporous silicas

MCM-41 and SBA-15 silicas were studied by (29)Si solid-state NMR and (15)N NMR in the presence of (15)N-pyridine with the aim to formulate generic structural parameters that may be used as a checklist for atomic-scale structural models of this class of ordered mesoporous materials. High-quality MCM-41 silica constitutes quasi-ideal arrays of uniform-size pores with thin pore walls, while SBA-15 silica has thicker pore walls with framework and surface defects. The numbers of silanol (Q(3)) and silicate (Q(4)) groups were found to be in the ratio of about 1:3 for MCM-41 and about 1:4 for our SBA-15 materials. Combined with the earlier finding that the density of surface silanol groups is about three per nm(2) in MCM-41 (Shenderovich, et al. J. Phys. Chem. B 2003, 107, 11924) this allows us to discriminate between different atomic-scale models of these materials. Neither tridymite nor edingtonite meet both of these requirements. On the basis of the hexagonal pore shape model, the experimental Q(3):Q(4) ratio yields a wall thickness of about 0.95 nm for MCM-41 silica, corresponding to the width of ca. four silica tetrahedra. The arrangement of Q(3) groups at the silica surfaces was analyzed using postsynthesis surface functionalization. It was found that the number of covalent bonds to the surface formed by the functional reagents is affected by the surface morphology. It is concluded that for high-quality MCM-41 silicas the distance between neighboring surface silanol groups is greater than 0.5 nm. As a result, di- and tripodical reagents like (CH(3))(2)Si(OH)(2) and CH(3)Si(OH)(3) can form only one covalent bond to the surface. The residual hydroxyl groups of surface-bonded functional reagents either remain free or interact with other reagent molecules. Accordingly, the number of surface silanol groups at a given MCM-41 or SBA-15 silica may not decrease but increase after treatment with CH(3)Si(OH)(3) reagent. On the other hand, nearly all surface silanol groups could be functionalized when HN(Si(CH(3))(3))(2) was used.     

Molecularly imprinted sol–gel nanoparticles for mass-sensitive engine oil degradation sensing

Titanate sol–gel layers imprinted with midchain carbonic acids have proven highly useful for detecting engine oil degradation processes owing to selective incorporation of oxidised base oil components. Synthesising the material from TiCl₄ in CCl₄ and precipitating with water leads to imprinted TiO₂ nanoparticles with a diameter of 200–300 nm. Replacing the water by a 1 M ammonium hydroxide solution reduces the average particle size to 50–100 nm with retention of the interaction capabilities. Experiments with the latter solution revealed that the 100-nm particles take up substantially more analyte, indicating a size-dependent phenomenon. As the number of interaction sites within each material is the same, this cannot be a consequence of thermodynamics but must be one of accessibility. The sensor characteristic of water-precipitated particles towards engine oil degradation products shows substantially increased sensitivity and dynamic range compared with the corresponding thin films. Coating quartz crystal microbalances with such nanoparticle materials leads to engine oil degradation sensors owing to incorporation of acidic base oil oxidation products. Interaction studies over a large range of layer thicknesses revealed that both the absolute signal and the steepness of the correlation between the sensor signal and the layer height is 2 times higher for the particles. Figure Generation of molecularly imprinted sol–gel nanoparticles