Metal Fluorocarbon Pyrolants,XVI : Theoretical and Experimental Investigation of Poly[bis(2,2,2‐trifluoroethoxy)phosphazene] (PTFEP) as Oxidizer in Magnesium Based Pyrolants

Consolidated magnesium/poly[bis(2,2,2‐trifluoroethoxy)phosphazene] (MPZ) pyrolants display a stable combustion regime between ξ(Mg) 30–83 wt‐%. The combustion rate increases with increasing magnesium content. Mixtures containing between 15–29 wt‐% Mg do ignite with a butane torch but extinguish rapidly thereafter. The combustion flames for each stoichiometric range exhibit particular features such as luminous carbon particles, after burn luminescence of Mg and burning Mg‐rich ejecta. UV/Vis spectra of the combustion flames show a distinct continuum superimposed from signals for transient CF₂, Mg, MgF, MgO, P₂⁺, PH, PN, and PO. The thermochemical calculation using NASA‐CEA indicate the highest adiabatic temperatures 1889 K at ξ(Mg)=35 wt‐%. The aerobic combustion of MPZ yields similar temperatures as common magnesium/polytetrafluoroethylene pyrolants.     

Efficient aerobic oxidation of hydrocarbons with O2 catalyzed by DDQ/NHPI

BACKGROUND: Organocatalysis, a promising strategy for the oxidation of organic compounds, does not involve the use of a catalytic metal. In this work, an efficient organocatalyst system consisting of 2,3‐dichloro‐5,6‐dicyano‐benzoquinone (DDQ) and N‐hydroxyphthalimide (NHPI) was studied. RESULTS: 72.2% conversion with 92.3% selectivity for acetophenone was obtained in ethylbenzene oxygenation catalyzed by DDQ/NHPI under 0.3 MPa of molecular oxygen at 80 °C for 10 h. In addition, other hydrocarbons were also oxidized with high efficiency using this catalyst system. UV/Vis spectroscopy of the catalytic system indicated that DDQ accelerated the generation of free radical phthalimido‐N‐oxyl (PINO) by abstracting a hydrogen atom from NHPI. CONCLUSION: An efficient organocatalyst system consisting of DDQ and NHPI for selective oxidation of hydrocarbons to corresponding ketones with molecular oxygen as oxidant is reported. DDQ promoted the generation of PINO from NHPI, and the oxidation reaction was accelerated via PINO. This organocatalyst system should be useful for the design of highly selective catalysts for hydrocarbon oxidation. Copyright © 2010 Society of Chemical Industry     

Phosphatidylethanolamine‐Binding Proteins,Including RKIP,Exhibit Affinity for Phosphodiesterase‐5 Inhibitors

Identifying protein “interactors” of drugs is of great importance to understand their mode of action and possible cross‐reactivity to off‐target protein binders. In this study, we profile proteins that bind to PF‐3717842, a high‐affinity phosphodiesterase‐5 (PDE5) inhibitor, by using a refined affinity pulldown approach with PF‐3717842 immobilized beads. By performing these pulldowns in rat testis tissue lysate, we strongly and specifically enriched for PDE5 and a few other PDEs. In addition to these expected affinity‐enriched proteins we also detect rodent‐specific phosphatidylethanolamine‐binding protein 2 (PEBP2), as a putative binder to the PDE5 inhibitor. By using recombinant forms of the related murine mPEBP2, mPEBP1 and human hPEBP1 (also known as Raf kinase inhibitor protein or RKIP) we confirm that they all can bind strongly to immobilized as well as soluble PF‐3717842. As the phosphatidylethanolamine‐binding proteins are involved in various important signal transduction pathways, the synthetic PDE5 inhibitor used here might form a platform to synthesize enhanced binders/inhibitors of the family of PEBP proteins. Our approach shows how chemical proteomics might be used to profile the biochemical space (interactome) of small molecule inhibitors.     

Synthesis and Electronic Spectra of Substituted p‐Distyrylbenzenes for the Use in Light‐Emitting Diodes

The influence of substitution on the absorption and Luminescence spectra of oligo(phenylenevinylene)s has been studied using distyrylbenzene (DSB) as a model compound. The degree, character, and pattern of substitution was varied systematically, altering the electronic properties of the DSB, the wavelength of the emitted light could be tuned over a range of 100 nm. The syntheses of 6b—h were performed by twofold Wittig Horner‐olefinations of bisphoshonates 1a, b with substituted benzaldehydes 2a—i, 6i via Heck‐reaction of the dibromosulfonylbenzene 3, 6k by Siegrist‐reaction of 4 with N‐phenylbenzaldimine and the Knoevenagel‐reaction of benzyl cyanide with 5 led to 6l .     

Synthesis of Reactive Condensation Products of Acetylacetone and Their Transformation into Deeply Coloured Methine Dyes

Starting from acetylacetone 1 , boric acid and a diol, or a 2‐aminothiazole 16 and perchloric acid several dimethyl‐substituted 1,3,2‐dioxaborines 5 and thiazolo[3,2‐a]pyrimidinium salts 17 , resp., have been prepared and transformed by raction with 4‐N,N‐dimethylamino‐benzaldehyde 3a or 3‐methyl‐2‐methylmercapto‐benzthiazolium perchlorate 13 into deeply colored polymethine dyes 11, 12, 14, 15, and 18—21 , and 23—24 their spectroscopic data were recorded.     

Effect of Methyl Group on Acyclic Serinol Scaffold for Tethering Dyes on the DNA Duplex Stability

Acyclic serinol derivatives are useful scaffolds for tethering dyes within DNA duplexes. Here we synthesised an inverse l ‐threoninol (il ‐threoninol) scaffold and compared its effect on DNA duplex stability to other acyclic artificial nucleic acid scaffolds that are based on d ‐threoninol, l ‐threoninol, and serinol. When planar trans‐azobenzene was incorporated into the DNA duplex through a single bulge‐like motif (the wedge), the il ‐threoninol scaffold stabilised the duplex most efficiently. When scaffolds were incorporated in complementary positions (dimer motif) or in three adjacent positions (cluster motif), d ‐threoninol was the most stabilising. CD spectra indicated that the effect of scaffold on the duplex stability was closely related to the winding induced by each scaffold. When trans‐azobenzene was photo‐isomerised to non‐planar cis‐azobenzene, il ‐threoninol destabilised the duplex most strongly, irrespective of the number of artificial residues incorporated. The properties of the il ‐threoninol scaffold make it a useful tether for dyes or other functionalities.     

Preparation and UV/Vis Spectroscopic Characterization of N,N‐Disubstituted 2‐Amino‐5‐arylazoselenazoles and Some of Their Carbocyclic and Heterocyclic Analogues

By coupling of aryldiazonium salts 5 with N,N‐disubstituted 2‐amino‐5H‐selenazoles 4 deeply coloured 5‐arylazo‐substituted 2‐amino‐selenazoles 6a—6l have been prepared and their solvatochromic properties determined by means of UV/Vis spectroscopy, and compared with the ones of several other arylazosubstituted N,N‐dialkylanilines 7a—7d , 2‐(N,N‐dialkylamino)‐thiophenes 8a—8e , and 2‐(N,N‐dialkylamino)‐thiazoles 9a—9c .     

Exploring the Protein Folding Dynamics of Beta3s with Two-Dimensional Ultraviolet (2DUV) Spectroscopy

Ultraviolet (UV) spectra of proteins originate from electronic excitations of their backbone chromophore and aromatic side chains and provide a sensitive probe of the secondary structure. Recently developed femtosecond lasers allow multidimensional spectroscopy to be extended into the UV regime. Two-dimensional UV (2DUV) techniques, with short pulses, provide a promising tool to study the structures and dynamics of proteins. We combined 2DUV spectroscopy and molecular dynamics generated free energy profiles to simulate the protein electronic transitions and UV photon echo signals to monitor the protein folding process of the small protein Beta3s. Near-ultraviolet (NUV) and far-ultraviolet (FUV) signals illustrate the variation of the 2D correlation plots when the protein evolves along the underlying free energy landscape. Chiral polarization configurations of the NUV and FUV pulses are sensitive to protein structural evolution. This work provides a protocol for applying multidimensional UV spectroscopy to study protein folding.     

Study of Photoluminescence Excitation Spectra of Tris(8-hydroxyquinoline)aluminum(III) (Alq3) in Solutions and Films

Absorption, photoluminescence, and photoluminescence excitation (PLE) spectra have been investigated for tris(8-hydroxyquinoline)aluminum(III) (Alq₃) in solution at various Alq₃ concentrations and in doped and neat films. The redshifted PLE spectra, with respect to the absorption spectra, are obtained, together with a dip located near the absorption band peak. The dip becomes deeper with increasing concentration. It is found that the unusual PLE spectra are caused by the penetration depth effect, not by previously suggested microcrystallites of Alq₃.     

Spectral Unmixing-Based Reaction Monitoring of Transformations between Nucleosides and Nucleobases

The increased interest in (enzymatic) transformations between nucleosides and nucleobases has demanded the development of efficient analytical tools. In this report, we present an update and extension of our recently described method for monitoring these reactions by spectral unmixing. The presented method uses differences in the UV absorption spectra of nucleosides and nucleobases after alkaline quenching to derive their ratio based on spectral shape by fitting normalized reference spectra. It is applicable to a broad compound spectrum comprising more than 35 examples, offers HPLC-like accuracy, ease of handling and significant reductions in both cost and data acquisition time compared to other methods. This contribution details the principle of monitoring reactions by spectral unmixing, gives recommendations regarding solutions to common problems and applications that necessitate special sample treatment. We provide software, workflows and reference spectra that facilitate the straightforward and versatile application of the method.     

金属/AP颗粒混合物燃烧特性的光谱分析

为了使Al/AP双组元粉末火箭发动机密度比冲最大化,将燃烧室特征长度由2.31 m增至 12.62 m进行了Al/AP粉末火箭发动机点火测试.采用光谱仪、CCD 相机、CO2 激光点火器等对 Al/AP 混合物在 1.0132 5 × 105 Pa的氮气环境中的点火延迟、燃烧时间、燃烧平稳性等燃烧性能进行了研究.测量了Al颗粒的表观堆积密度.作为一种替代燃料,对镁颗粒也进行了研究.结果表明,增加燃烧室特征长度至 12.62 m 时,可以得到最大燃烧室压强振荡幅度±2 .43%的平稳燃烧性能.含粒径 1μm 铝粉的 Al/AP 混合物其燃烧过程的光强远大于含粒径10μm铝粉的样品,并且其在波长 568 nm 发射光谱的光子数强度超过了光谱仪检测上限(65 000 数).而含粒径10μm铝粉样品燃烧过程的568 nm发射光谱信号出现间断且其全程强度低于 19 036 数.粒径 10μm 铝粉点火延迟时间为粒径1μm铝粉点火延迟时间的3.65 倍,燃烧时间为3.03 倍以上,最大RAlO却比 1μm铝粉少 14.3%,密度低21 .3%,说明粒度小的铝粉具有更好的燃烧性能,但是其堆积密度也更低.虽然Mg/AP的理论比冲为Al/AP的95.6%,但是其堆积密度比粒径1μm铝粉高8%,其点火延迟时间比粒径10μm铝粉短 90.3%.火焰照片也表明镁粉可在很大程度上减少凝相沉积.     

Combustion Synthesis of Metal Chromite Powders

Fine-particle metal chromites (MCr₂O₄, where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn) have been prepared by the combustion of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and urea in stoichiometric amounts. The mixtures, when rapidly heated to 350°C, ignite and yield voluminous chromites with surface areas ranging from 5 to 25 m²/g. MgCr₂O₄, sintered in air at 1500°C for 5 h, has a density of 4.0 g/cm³.     

New Halogenated Water‐Soluble Chlorin and Bacteriochlorin as Photostable PDT Sensitizers: Synthesis,Spectroscopy, Photophysics,and in vitro Photosensitizing Efficacy

Chlorin and bacteriochlorin derivatives of 5,10,15,20‐tetrakis(2‐chloro‐5‐sulfophenyl)porphyrin have intense absorptions in the phototherapeutic window, high water solubility, high photostability, low fluorescence quantum yield, long triplet lifetimes, and high singlet oxygen quantum yields. Biological studies revealed their negligible dark cytotoxicity, yet significant photodynamic effect against A549 (human lung adenocarcinoma), MCF7 (human breast carcinoma) and SK‐MEL‐188 (human melanoma) cell lines upon red light irradiation (cutoff λ<600 nm) at low light doses. Time‐dependent cellular accumulation of the chlorinated sulfonated chlorin reached a plateau at 2 h, as previously observed for the related porphyrin. However, the optimal incubation time for the bacteriochlorin derivative was significantly longer (12 h). The spectroscopic, photophysical, and biological properties of the compounds are discussed in relevance to their PDT activity, leading to the conclusion that the bacteriochlorin derivative is a promising candidate for future in vivo experiments.     

Colorimetric Detection of Small Molecules by a Frustrated Lewis Pair Containing a Phosphorus-Functionalized Cycloheptatrienyl?Cyclopentadienyl Titanium Sandwich Complex

The phosphorus-functionalized cycloheptatrienyl cyclopentadienyl (Cht Cp) titanium sandwich complex [(η⁷-C₇H₇)Ti(η⁵-C₅H₄PtBu₂)] ( 7 ) forms a frustrated Lewis pair (FLP) in combination with the borane B(C₆F₅)₃, and this FLP undergoes heterolytic cleavage of dihydrogen and fixation of carbon dioxide and nitrous oxide with a noticeable colorimetric response, which is visible to the naked eye. In their UV/Vis spectra, the H₂, CO₂ and N₂O fixation products exhibit a bathochromic shift of the absorption band that can be assigned to a HOMO LUMO excitation of the Cht Cp titanium (troticene) moiety.     

Biocatalysis with Thermostable Enzymes: Structure and Properties of a Thermophilic ‘ene’‐Reductase related to Old Yellow Enzyme

We report the crystal structure of a thermophilic “ene” reductase (TOYE) isolated from Thermoanaerobacter pseudethanolicus E39. The crystal structure reveals a tetrameric enzyme and an active site that is relatively large compared to most other structurally determined and related Old Yellow Enzymes. The enzyme adopts higher order oligomeric states (octamers and dodecamers) in solution, as revealed by sedimentation velocity and multiangle laser light scattering. Bead modelling indicates that the solution structure is consistent with the basic tetrameric structure observed in crystallographic studies and electron microscopy. TOYE is stable at high temperatures (T_m>70 °C) and shows increased resistance to denaturation in water‐miscible organic solvents compared to the mesophilic Old Yellow Enzyme family member, pentaerythritol tetranitrate reductase. TOYE has typical ene‐reductase properties of the Old Yellow Enzyme family. There is currently major interest in using Old Yellow Enzyme family members in the preparative biocatalysis of a number of activated alkenes. The increased stability of TOYE in organic solvents is advantageous for biotransformations in which water‐miscible organic solvents and biphasic reaction conditions are required to both deliver novel substrates and minimize product racemisation.