Twisted amides: X-ray crystallographic and theoretical study of two acylated glycolurils with aromatic substituents

X-ray crystallography and theoretical analysis were applied to explore the molecular basis for the efficient and selective Claisen-like condensations of diacylglycolurils. The crystal structures of 1-acetyl-6-benzoyl-3,4,7,8-tetramethylglycoluril (4b), and of 1-(3′-oxo-3′-phenylpropionyl)-3,4,7,8-tetramethylglycoluril (5b), the product of base-promoted intramolecular condensation of 4b, were obtained by X-ray diffraction. The acetyl (Ac) group in 4b is essentially coplanar with the attached tetrahydroimidazolone ring of the glycoluril core (τ=7°), while the benzoyl (Bz) group is twisted by τ=45° relative to a plane through the ring to which it is bonded. Product 5b contains a flat amide (τ=7°). Ab initio energy optimizations of the experimental structures for 4b and 5b give optimized geometries which are not dramatically altered, suggesting that crystal packing effects are small. An atoms-in-molecules study of the delocalization of the Fermi hole reveals that electrons in the Bz C=O group of 4b are delocalized into the phenyl ring as well as into the urea moiety of the glycoluril core. This effect stabilizes the Bz over the Ac carbonyl group, and accounts for selective twisting of the Bz group. The Laplacian of the electron density reveals a non-bonded valence shell charge concentration at O of the Ac group, corresponding to a lone-pair region, aligned with a charge depletion in the valence shell of the Bz C=O carbon [(C15–O16C18)=113°]. The angle of approach [(O16C18=O19)] is 100°, equal to the angle for ideal nucleophilic attack on a carbonyl group. Oxygen atom O16 is thus poised to attack C18; only the O16C18 distance (3.248 Å) seems to prevent reaction. These results suggest that the same distance restraint may prevent O-acylation in the enolate intermediate 6b derived from4b. By contrast, the transition state for C-acylation, leading from 6b towards product 5b requires a different geometry, which may explain the observed selectivity for C-acylation in this enolate. The results show that, as 4b is converted to 5b, amide torsional strain is relieved, which may account for the high reactivity of 4b and the efficiency and irreversibility of this condensation process. This study provides a starting point for quantitative correlation of substrate structure in diacylglycolurils with kinetic data for the rearrangement reaction.     

Plasma-Chemical Conversion of Lower Alkanes with Stimulated Condensation of Incomplete Oxidation Products

Oxidative conversion of a mixture of natural gas and oxygen in a barrier-discharge plasma-chemical reaction was investigated experimentally. The process was conducted at atmospheric pressure and room temperature. The discharge was initiated by high-voltage pulses of 50–100 s duration at a repetition frequency of up to 2 kHz. The principal feature of the process was that in the plasma-chemical reactor conditions were created which stimulated the condensation of the products of incomplete oxidation of methane that resulted in the formation of aerosol even from nonsaturated vapor. The removal of intermediate reagents from the gaseous phases into the aerosol prevented them from further oxidation. Depending on the experimental conditions, the mass percentage of the components of the condensate formed varied within the following limits: formic acid from 20 to 40%, methanol from 8 to 15%, methylformate from 4 to 8%, and water from 40 to 60%. The conversion process has been realized on a laboratory setup of average power up to 1 kW. In the single-pass mode, a 57% degree of conversion of the mixture has been achieved. The energy value of the condensate is 15–20 kWh/kg.     

Synthesis and thermal transformations of polyphosphosiloxane based on trimethyl phosphate and (3-aminopropyl)triethoxysilane

A method for the synthesis of polyphosphosiloxane by the thermal condensation of an equimolar mixture of trimethyl phosphate and (3-aminopropyl)triethoxysilane at 200 °C was developed. The reaction affords ethanol and polyphosphosiloxane-{Si(OEt)[(CH₂)₃NR¹R²]-O-P(O)(OMe)-O}_n-(R¹ = H, Me; R² = Me), whose composition and structure were confirmed by ¹H, ¹³C, and ³¹P NMR spectroscopy, IR spectroscopy, and elemental analysis. The scheme of polymerization involving the intermediate formation of methyl-and dimethylphosphoric acids and their condensation with ethoxysilanes was proposed. The calcination of the obtained polyphosphosiloxane in vacuo at 350 °C results in the elimination of the amino groups and alkoxide substituents, and a spatially cross-linked polymer is formed as an amorphous powder. Its further thermolysis at 600 and 1000 °C gives crystalline phosphosilicates Si₅O(PO₄)₆ or SiP₂O₇. Their amorphous and crystalline samples were characterized by IR spectroscopy, X-ray diffraction analysis, and solid-state ¹³C and ³¹P spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2138–2148, November, 2007.     

Condensation of 1-Substituted 1,2,3,9a-Tetrahydro-9H-imidazo[1,2-a]indol-2-one Derivatives with Aromatic Aldehydes

Condensation of 1-alkyl-, 1-allyl-, and 1-benzyl-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones with benzaldehydes in acetic acid and subsequent treatment of the reaction mixture with potassium hydroxide afforded 1-substituted 9a-(2-phenylethenyl)-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one derivatives. 1-Methyl- and 1-ethyl-9a-[2-(4-dimethylaminophenyl)ethenyl]-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones were synthesized by alkylation of 9a-[2-(4-dimethylaminophenyl)ethenyl]-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one with methyl- and ethyl iodides in DMF in the presence of a strong base.     

Tunneling of trapped-atom Bose condensates

We obtain the dynamics in number and phase difference, for Bose condensates that tunnel between two wells of a double-well atomic trap, using the (nonlinear) Gross-Pitaevskii equation. The dynamical equations are of the canonical form for the two conjugate variables, and the Hamiltonian corresponds to that of a momentum-shortened pendulum, supporting a richer set of tunneling oscillation modes than for a superconductor Josephson junction, that has a fixed-length pendulum as a mechanical model. Novel modes include ‘inverted pendulum’ oscillations with an average angle of π; and oscillations about a self-maintained population imbalance that we term ‘macroscopic quantum self-trapping’. Other systems with this phase-number nonlinear dynamics include two-component (interconverting) condensates in a single harmonic trap, and He³B superfluids in two containers connected by micropores.     

缩合法合成磁性荧光高分子CdTe@Fe_3O_4/P(NIPAM-co-AA)复合微球及其表征

具有超顺磁性和荧光特性的CdTe@Fe_3O_4/P(NIPAM-co-AA)多功能复合微球是以P(NIPAMco-AA)为模板制备而成.首先,采用溶胀法使模板微球带有磁性;其次,辅助TEOS和APTES两种化学试剂实现对Fe_3O_4/P(NIPAM-co-AA)微球表面的氨基功能化;最后,携带氨基的磁性微球与巯基乙酸修饰的CdTe量子点通过酰胺缩合反应,将量子点键合到磁性微球表面上,最终获得单分散的磁性荧光高分子复合微球.分别采用扫描电子显微镜、透射电子显微镜、倒置荧光显微成像系统、荧光分光光度计以及振动样品磁强计等方法对所获复合材料的结构与性能进行了表征.结果表明:复合微球单分散性良好,平均粒径约为30μm,饱和磁化强度可达5.4emu/g,具有良好的超顺磁性和较高的荧光发光效率.该材料将磁性、荧光结合到微米级高分子共聚物上,不仅解决了纳米粒子分离和处理的困难,而且奠定了多功能材料在生物标记、荧光成像等诸多领域潜在的应用基础.     

Recent study of nanomaterials prepared by inert gas condensation using ultra high vacuum chamber

The ultra high vacuum chamber was developed in the Department of Nuclear Physics, University of Madras with the funding from DST, India. This UHV chamber is used to prepare nanocrystalline materials by inert gas condensation technique (IGCT). Nanocrystalline materials such as PbF₂, Mn²⁺-doped PbF₂, Sn-doped In₂O₃ (ITO), ZnO, Al₂O₃, Ag₂O, CdO, CuO, ZnSe:ZnO etc., were prepared by this technique and characterized. Results of some of these materials will be presented in this paper. In solid-state²⁰⁷Pb NMR on PbF₂ a separate signal due to the presence of grain boundary has been observed. The structural phase transition pressure during the phase transformation from the cubic phase to orthorhombic phase under high pressure shows an increase with the decrease in grain size. Presence of electronic centres in nanocrystalline PbF₂ is observed from Raman studies and the same has been confirmed by photoluminescence studies. Al₂O₃ was prepared and⁵⁶Fe ions were implanted. After implantation segregation of⁵⁶Fe ions was examined by SEM. The oxidation properties of ITO were studied by HRTEM. As against the expectation of oxide coating on individual nanograins of In-Sn alloy, ITO nanograins grew into faceted nanograins on heat treatment in air and O₂ atmosphere. The growth of ITO under O₂ atmosphere showed pentagon symmetry. The PMN was initially prepared by solid-state reaction. Further, this PMN relaxor material will be used to convert into nanocrystalline PMN by IGCT with sputtering and will be studied     

双模SU(1,1)相干态光场与V型三能级原子玻色-爱因斯坦凝聚体相互作用系统的量子性质

研究了双模SU(1,1)相干态光场与V型三能级原子玻色-爱因斯坦凝聚(BEC)相互作用系统中光场的量子相关性质、振幅平方压缩效应和原子激光压缩效应。结果表明,双模SU(1,1)相干态光场各模的二阶相干度不随时间变化,光场各模光子是反聚束的,呈现非经典效应,光场两模相关性是非经典相关。光场具有周期性的振幅平方压缩效应,讨论了光场相关参数和原子相关参数对压缩深度、压缩频率的影响。双模原子激光不易压缩,压缩深度取决于光场初态。     

Synthesis and biological evaluation of novel phane-structured diazacrowns containing γ-piperidone and pyridine rings

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