α,β,γ,δ,ε,η-Bi2O3电子结构和光学性质的第一性原理研究

基于密度泛函理论的CASTEP模块研究了α, β, γ, δ, ε和η-Bi₂O₃晶型, 计算分析了其几何结构、 能带结构、 电子态密度和光学性质. 结果表明, α, ε和η相均为层状结构, 其中, α和ε相为单层—Bi—O—结构, 而η相为双层—Bi—O—结构; β, γ和δ相为—Bi_m—O_n—交错结构, 其中δ相交错尤为密集, 呈现导体特性. 各晶相的导带均由Bi 6p态构成, 价带由O_2p态起主导作用. 电势电位分析结果表明, 6种晶相价带电位均在H₂O/O₂之下, 具有强氧化能力, 与实验报道的光催化氧化能力大小顺序γ-Bi₂O₃>β-Bi₂O₃>α-Bi₂O₃>δ-Bi₂O₃一致, 而导带还原电位低于H₂/H₂O, 预测纯Bi₂O₃很难具备催化产氢能力. 光学性质分析发现, γ和δ相的起始响应波长较大, 说明其应具备红外激发的性质. 这些结果可为获得偏红外激发和较宽光谱响应的Bi₂O₃材料研究提供理论基础, 为研发和应用Bi₂O₃及其复合物提供重要的指导.     

镍催化α,β-不饱和醛的选择性α,β-双芳基化反应

三组分双官能化反应是一种高效、简便构建C―C键、C―X键的方式. 双键广泛存在于众多有机化合物中, 对双键的双官能化反应研究有巨大的应用潜力. 本工作以Ni(COD)₂为催化剂, 以芳基溴化镁、芳基溴化物为芳基化试剂, 实现了3-芳基-2-丙烯醛亚胺中碳碳双键的双芳基化反应. 该反应建立了一个新的镍催化α,β-不饱和醛的α,β-双芳基化方法, 可以高度区域选择性地向底物分子中引入两个不同取代的芳环, 得到多种2,3,3-三芳基丙醛骨架的产物. 利用这一反应作为核心步骤实现了天然产物Quebecol的简便合成. 机理研究表明, 该反应可能经历了亲核加成、金属交换、还原消除的历程.     

Orthoamides and Iminium Salts LXXII: N,N,N′,N′,N′′,N′′,N′′′,N′′′‐Octamethyl‐(but‐2‐yne)‐bis(amidinium) Tetrafluoroborate: The First Bis‐amidinium Salt of Acetylenedicarboxyclic Acid. A New Superelectrophile?

A method for the preparation of the first acetylenedicarboxamidinium salt from a bis‐orthoamide derivative of acetylenedicarboxyclic acid has been established. The salt reacted with cyclopentadiene and furan at room temperature to give bicyclic [4+2]‐cycloaddition products. The solid compounds were characterized by solution NMR spectroscopy and by single‐crystal X‐ray diffraction. Quantum‐chemical calculations of the isolated N,N,N′,N′,N′′,N′′,N′′′,N′′′‐octamethyl‐acetylene‐bis(carboxamidinium) ion showed very good agreement with the spectroscopic and diffraction data.     

An Interplay of Cooperativity between Cation⋅⋅⋅π, Anion⋅⋅⋅π and C?H⋅⋅⋅Anion Interactions

Mixed cation (Li⁺, Na⁺ and K⁺) and anion (F^?, Cl^?, Br^?) complexes of the aromatic π‐surfaces (top and bottom) are studied by using dispersion‐corrected density functional theory. The selectivity of the aromatic surface to interact with a cation or an anion can be tuned and even reversed by the electron‐donating/electron‐accepting nature of the side groups. The presence of a methyl group in the ? OCH₃, ? SCH₃, ? OC₂H₅ in the side groups of the aromatic ring leads to further cooperative stabilization of the otherwise unstable/weakly stable anion???π complexes by bending of the side groups towards the anion to facilitate C? H???anion interactions. The cooperativity among the interactions is found to be as large as 100 kcal mol^?1 quantified by dissection of the three individual forces from the total interaction energy. The crystal structures of the fluoride binding tripodal and hexapodal ligands provide experimental evidence for such cooperative interactions.     

Warum pentose-und nicht hexose-nucleinsäuren? Teil III. Oligo(2′,3′-dideoxy-β-D-glucopyranosyl) nucleotide (‘homo-DNS’): Paarungesigenschaften

Why Pentose-And Not Hexose-Nucleic Acids? Part III. Oligo(2′,3′-dideoxy-β-D -glucopyranosyl)nucleotides. (‘Homo-DNA’): Base-Pairing Properties

1 Summary in collaboration with Prof. Dr. C. E. Wintner, Haverford College, Haverford, PA 19041-1392.

The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part II of this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and – in selected cases – ¹H – and³¹P-NMR spectroscopy. The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H²O, 0.15M NaCl, 0.01M Tris-HCl buffer, pH 7, oligonucleotide concentrations in the μM range, 1:1 ratio of single strands in the case of non-selfcompementary sequences.     

Redox‐Triggered C?C Coupling of Diols and Alkynes: Synthesis of β,γ‐Unsaturated α‐Hydroxyketones and Furans by Ruthenium‐Catalyzed Hydrohydroxyalkylation

Direct ruthenium‐catalyzed C C coupling of alkynes and vicinal diols to form β,γ‐unsaturated ketones occurs with complete levels of regioselectivity and good to complete control over the alkene geometry. Exposure of the reaction products to substoichiometric quantities of p‐toluenesulfonic acid induces cyclodehydration to form tetrasubstituted furans. These alkyne‐diol hydrohydroxyalkylations contribute to a growing body of merged redox‐construction events that bypass the use of premetalated reagents and, hence, stoichiometric quantities of metallic by‐products.     

Synthesis and properties of siRNAs containing 5′-amino-2′,5′-dideoxy-2′α-fluororibonucleosides

Short interfering RNAs (siRNAs) containing P3′→N5′ phosphoramidate linkages were successfully synthesized by introducing 2′-deoxy-2′-fluororibonucleoside and 5′-amino-2′,5′-dideoxy-2′α-fluororibonucleoside in succession. It was found that the introduction of 5′-amino-2′,5′-dideoxy-2′α-fluororibonucleosides into siRNAs improved the nuclease-resistant properties of the siRNAs without loss of their silencing efficacy.     

Rhodium‐catalyzed coupling reactions of β‐ or α,β‐substituted vinylpyridines with alkenes via C?H bond activation

β‐ or α,β‐Substituted vinylpyridines react with 3,3‐dimethylbut‐1‐ene in the presence of Wilkinson catalyst [RhCl(PPh₃)₃] to give the corresponding alkylated products along with unusually isomerized products. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:346–350, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10045     

Partial Hydrolysis of Poly(2‐ethyl‐2‐oxazoline) and Potential Implications for Biomedical Applications?

The hydrolysis of PEtOx is studied to evaluate the potential toxicity of partially hydrolyzed polymers that might interfere with its increasing popularity for biomedical applications. The hydrolysis of PEtOx is studied in the presence of digestive enzymes (gastric and intestinal) and at 5.8 M hydrochloric acid as a function of temperature (57, 73, 90, and 100 °C). It is found that PEtOx undergoes negligible hydrolysis at 37 °C and that thermal and solution properties are not altered when up to 10% of the polymer backbone is hydrolyzed. Mucosal irritation and cytotoxicity is also absent up to 10% hydrolysis levels. In conclusion, PEtOx will not decompose at physiological conditions, and partial hydrolysis will not limit its biomedical applications.

     

Why are reactions of 2‐ and 8‐thioquinoline derivatives with iodine different?

The crystal structures of 1,2‐dihydro‐1,1′‐bi[thiazolo[3,2‐a]quinoline]‐10a,10a′‐diium diiodide hemihydrate, C₂₂H₁₆N₂S₂²⁺·2I⁻·0.5H₂O, and 1,2‐dihydro‐1,1′‐bi[thiazolo[3,2‐a]quinoline]‐10a,10a′‐diium iodide triiodide, C₂₂H₁₆N₂S₂²⁺·I⁻·I₃⁻, obtained during the reaction of 1,4‐bis(quinolin‐2‐ylsulfanyl)but‐2‐yne (2TQB) with iodine, have been determined at 120 K. The crystalline products contain the dication as a result of the reaction proceeding along the iodocyclization pathway. This is fundamentally different from the previously observed reaction of 1,4‐bis(quinolin‐8‐ylsulfanyl)but‐2‐yne (8TQB) with iodine under similar conditions. A comparative analysis of the possible conformational states indicates differences in the relative stabilities and free rotation for the 2‐ and 8‐thioquinoline derivatives which lead to a disparity in the convergence of the potential reaction centres for 2TQB and 8TQB.     

Note: Helix or No Helix of β‐Peptides Containing β3hAla(αF) Residues?

A remote ⁴J(F,H) coupling (F? C(α)? C(O)? N? H) of up to 4.2 Hz in α‐fluoro amides with antiperiplanar arrangement of the C? F and the C?O bonds (dihedral angle F? C? C?O ca. 180°) confirms that previous NMR determinations, using the XPLOR‐NIH procedure, of the secondary structures of β‐peptides containing β³hAla(αF) and β³hAla(αF₂) residues were correct. In contrast, molecular‐dynamics (MD) simulations, using the GROMOS program with the 45A3 force field, led to an incorrect conclusion about the relative stability of secondary structures of these β‐peptides. The problems encountered in NMR analyses and computations of the structures of backbone‐F‐substituted peptides are briefly discussed.     

Stereodefined dinucleoside (3′,5′)-propionamidophosphonates and β-cyanoethylphosphonates and their incorporation into modified oligonucleotides

Base-catalyzed stereospecific anti-Markovnikov addition of dinucleoside (3′,5′)-H-phosphonates to the activated alkenes acrylamide and acrylonitrile resulting in the synthesis of P-chiral diastereomerically pure dinucleoside (3′,5′)-alkylphosphonates is reported.     

α,β‐Unsaturated and Saturated Derivatives of Be,Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

The gas-phase acidity of R--XH (R=H, CH(3), CH(2)CH(3), CH==CH(2), C[triple chemical bond]CH; X=Be, Mg, Ca) alkaline-earth-metal derivatives has been investigated through the use of high-level CCSD(T) calculations by using a 6-311+G(3df,2p) basis set. BeH(2) is a stronger acid than BH(3) and CH(4) for two concomitant reasons: 1) the dissociation energy of the Be--H bond is smaller than the dissociation energies of the B--H and C--H bonds, and 2) the electron affinity of BeH(.) is larger in absolute value than those of BH(2) (.) and CH(3) (.). The acidity also increases on going from BeH(2) to MgH(2) due to these two same factors. Quite importantly, despite the fact that the X--H bonds in the R--XH (X=Mg, Ca) derivatives exhibit the expected X(delta+)--H(delta-) polarity, they behave as metal acids in the gas phase and only Be derivatives behave as carbon acids in the gas phase. The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deprotonation of the system is accompanied by a cyclization that stabilizes the anion. Similarly to that found for derivatives that contain heteroatoms from groups 14, 15, and 16, the unsaturated compounds are stronger acids than the saturated counterparts, with the only exception of the Ca-vinyl derivative. Most importantly, among ethyl, vinyl, and ethynyl derivatives containing a heteroatom of the main group of the Periodic Table, those containing Be, Mg, and Ca are among the strongest gas-phase acids.