Utilization of hypervalent iodine in organic synthesis: A novel and facile two‐step protocol for the synthesis of new derivatives of 1H‐Imidazo[1,2‐b]pyrazole by the cyclocondensation involving α‐Tosyloxyacetophenones

A series of new 2‐aryl‐7‐cyano/ethoxycarbonyl‐6‐methylthio‐1H‐imidazo[1,2‐b]pyrazoles ( 5 ) have been synthesized in moderate to good yields, via a two‐step cyclocondensation procedure of 5‐amino‐4‐cyano/ethoxycarbonyl‐3‐methylthio‐1H‐pyrazole ( 1 ) and α‐bromoacetophenones ( 3 ) or α‐tosyloxyacetophenones ( 2 ), which were prepared by the reactions of acetophenones with [hydroxy(tosyloxy)iodo]benzene (HTIB). The intermediates, 5‐amino‐1‐(aroylmethyl)‐4‐ cyano/ethoxycarbonyl‐3‐methylthio‐1H‐pyrazoles ( 4 ), have been isolated, serving as evidence for the regioselectivity. When utilizing α‐tosyloxy‐acetophenones, the reactions were more eco‐friendly, the reaction time was significantly reduced and the synthetic procedure was more convenient and easier to manipulate. Surprisingly, using potassium carbonate to displace sodium carbonate in the synthesis of 4 , in the case of 1 (R? CN), two novel cyclocondensation products have been isolated and fully characterized, followed by the proposal of a plausible mechanism.     

Thermochemistry of rare earth complexes [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr, Gd)

The two complexes, [Ln(Ala)₂(Im)(H₂O)](ClO₄)₃ (Ln=Pr, Gd), were synthesized and characterized. Using a solution-reaction isoperibol calorimeter, standard enthalpies of reaction of two reactions: LnCl₃⋅6H₂O(s)+2Ala(s)+Im(s)+3NaClO₄(s)=[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)+3NaCl(s)+5H₂O(l) (Ln=Pr, Gd), at T=298.15 K, were determined to be (39.26±0.10) and (5.33±0.12) kJ mol^–1 , respectively. Standard enthalpies of formation of the two complexes at T=298.15 K, Δ_fH^Θ_m {[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)} (Ln=Pr, Gd), were calculated as –(2424.2±3.3) and –(2443.4±3.3) kJ mol^–1 , respectively.     

一些金属氧化物在TiO_2(锐钛矿)载体上的分散 嵌入模型的应用

一些金属氧化物在ＴｉＯ２（锐钛矿）载体上的分散＊嵌入模型的应用徐斌董林陈懿（南京大学化学系亚微观固态化学研究所，南京２１００９３）关键词嵌入模型，金属氧化物，分散容量，锐钛矿我们曾以γ－Ａｌ２Ｏ３，ＣｅＯ２和ＳｉＯ２为载体研究了离子化合物的分散，认为...     

Sn0.5Ti0.5O2催化剂上SO2、NO和CO反应的机理

Sn0.5Ti0.5O2催化剂对NO＋CO反应活性不高， 350 ℃时NO的转化率只有50％,但反应气中含有SO2时， NO的转化率接近100％,说明SO2对Sn0.5Ti0.5O2催化剂上的NO＋CO反应具有促进作用. XPS表征发现,SO2＋CO、SO2＋NO＋CO反应后催化剂表面有微量硫存在，而反应前没有检测到硫的存在.结合反应性能测定、瞬变应答实验、XRD、TPD研究等，发现催化剂上的表面硫参与了NO的催化还原反应，是NO＋CO反应更重要的活性中心.据此，提出了SO2＋NO＋CO反应的氧化还原反应机理.     

分子的模糊对称性

将模糊数学方法引入对分子对称点群的研究,建立描述具有不完整分子对称性的模糊点对称群(集合).建立具有模糊对称性分子轨道的模糊表示及其模糊特征标(模糊广义宇称).通过对典型的线状分子、平面分子以及非平面的立体分子等进行分析,展示了一个新的理论化学园地.初步探讨了具有模糊对称性的动态反应体系.从模糊对称性出发,探讨了分子轨道对称守恒原理的半定量特征.     

Stability of neutral and charged Si50 cage and stacked structure and in comparison with Si60 structures

We have performed calculations on the fullerene cage and stacked structures of neutral and ionic Si₅₀ cluster by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. It is found that the neutral and charged fullerene cages relax into distorted structures resembling puckered balls. Their electronic structures are remarkably similar besides their geometrical structures. However, the relaxed cages are still not so stable as the stacked structure built from tricapped trigonal prism. By comparison, for the fullerene cages and stacked structures of neutral and ionic Si₆₀ cluster, similar characteristics are found.     

The physicochemical properties of aqueous mixtures of cationic-anionic surfactants: I. The effect of chain length symmetry

The solution behaviors of equimolar mixtures of cationic-anionic surfactants have been studied by means of the dynamic light scattering technique and surface tension measurements. The surface activity and the micellization properties are different for systems of different hydrophobic chain length symmetry. For systems of lower symmetry (e.g., C₆H₁₃NC₅H₅Br-C₁₂H₂₅SO₄Na mixture), the surface tension at cmc (γ_cmc) is rather high (above 30 mN m⁻¹) and the mixtures form genuinely homogeneous micellar solutions above the cmc. For the systems of high symmetry (e.g., C₈H₁₇NC₅H₅Br-C₈H₁₇SO₄Na mixture), γ_cmc is very low (about 24 mN m⁻¹, near the value of pure hydrocarbon) and in the apparently homogeneous and clear mixtures slightly above cmc, the aggregates grow slowly and eventually form small droplets; as the concentration is further increased, all these solutions become turbid. We have proposed a new concept of conformation energy of aggregates to account for all these phenomena. Mixtures of octyltriethylammonium bromide and sodium octylsulfate form clear homogeneous micellar solutions in keeping with predictions based upon this concept.     

Photoinduced intramolecular electron transfer and triplet energy transfer in a steroid-linked norbornadiene-carbazole dyad

Bichromophoric compound 3 beta-((2-(methoxycarbonyl)bicyclo[2.2.1]hepta-2,5-diene-3-yl)carboxy)androst-5-en-17 beta-yl-[2-(N-carbazolyl)acetate] (NBD-S-CZ) was synthesized and its photochemistry was examined by fluorescence quenching, flash photolysis, and chemically induced dynamic nuclear polarization (CIDNP) methods. Fluorescence quenching measurements show that intramolecular electron transfer from the singlet excited state of the carbazole to the norbornadiene group in NBD-S-CZ occurs with an efficiency (Phi SET) of about 14 % and rate constant (kSET) of about 1.6 x 10(7) s-1. Phosphorescence and flash photolysis studies reveal that intramolecular triplet energy transfer and electron transfer from the triplet carbazole to the norbornadiene group proceed with an efficiency (TET + TT) of about 52 % and rate constant (kTET + kTT) of about 3.3 x 10(5) s-1. Upon selective excitation of the carbazole chromophore, nuclear polarization is detected for protons of the norbornadiene group (emission) and its quadricyclane isomer (enhanced absorption); this suggests that the isomerization of the norbornadiene group to the quadricyclane proceeds by a radical-ion pair recombination mechanism in addition to intramolecular triplet sensitization. The long-distance intramolecular triplet energy transfer and electron transfers starting both from the singlet and triplet excited states are proposed to proceed by a through-bond mechanism.     

Patterned polyelectrolyte multilayer: surface modification for enhancing selective adsorption

This paper describes the use of surface chemical modification to enhance the difference of the surface charge on a patterned polyelectrolyte multilayer, which can be used for selectively adsorbing functional materials. We fabricated a patterned multilayer by combining the layer-by-layer self-assembly technique and photolithography and taking advantage of the different solubility of polyelectrolyte multilayers of diazo resins (DAR)/poly(acrylic acid) before and after UV irradiation. This patterned surface can be used as a matrix for selective adsorption of small molecular dyes, such as Methylene Blue. However the difference in surface charge on the patterned surface was not enough when we used it to selectively adsorb polystyrene (PS) nanoparticles using electrostatic force as the driving force. Therefore, we modified the patterned surface by interfacial chemistry. After modification, the patterned polyelectrolyte multilayer can be used as a good matrix for selective adsorption of PS nanoparticles with both positive and negative charges.     

New Clerodane Diterpenoids from Casearia membranacea

Bioassay‐guided fractionation of an AcOEt extract of Casearia membranacea resulted in the isolation of six new clerodane diterpenes, caseamembrins G–L ( 1 – 6 ). The structures of the new compounds, including their relative configurations, were established by an extensive study of their spectral data, especially 2D NMR. The cytotoxic activities of the isolated diterpenes against human oral epidermoid (KB), cervical epitheloid (Hela), and liver (Hep59T/VGH) carcinoma cell lines were investigated.