Annelated Pyridines as Highly Nucleophilic and Lewis Basic Catalysts for Acylation Reactions

New heterocyclic derivatives of 9‐azajulolidine have been synthesized and characterized with respect to their nucleophilicity and Lewis basicity. The Lewis basicity of these bases as quantified through their theoretically calculated methyl‐cation affinities correlate well with the experimentally measured reaction rates for addition to benzhydryl cations. All newly synthesized pyridines show exceptional catalytic activities in benchmark acylation reactions, which correlate only poorly with Lewis basicity or nucleophilicity parameters. A combination of Lewis basicity with charge and geometric parameters in the framework of a three‐component quantitative structure–activity relationship (QSAR) model is, however, highly predictive.     

Highly Efficient C?H Oxidative Activation by a Porous MnIII–Porphyrin Metal–Organic Framework under Mild Conditions

A simple strategy to rationally immobilize metalloporphyrin sites into porous mixed‐metal–organic framework (M′MOF) materials by a metalloligand approach has been developed to mimic cytochrome P450 monooxygenases in a biological system. The synthesized porous M′MOF of [Zn₂(MnOH–TCPP)(DPNI)] ? 0.5 DMF ? EtOH ? 5.5 H₂O ( CZJ‐1 ; CZJ=Chemistry Department of Zhejiang University; TCPP=tetrakis(4‐carboxyphenyl)porphyrin); DPNI=N,N′‐di(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarboxydiimide) has the type of doubly interpenetrated cubic α‐Po topology in which the basic Zn₂(COO)₄ paddle‐wheel clusters are bridged by metalloporphyrin to form two‐dimensional sheets that are further bridged by the organic pillar linker DPNI to form a three‐dimensional porous structure. The porosity of CZJ‐1 has been established by both crystallographic studies and gas‐sorption isotherms. CZJ‐1 exhibits significantly high catalytic oxidation of cyclohexane with conversion of 94 % to the mixture of cyclohexanone (K) and cyclohexanol (A) (so‐called K–A oil) at room temperature. We also provided solid experimental evidence to verify the catalytic reaction that occurred in the pores of the M′MOF catalyst.     

Intramolecular Participation of Amino Groups in the Cleavage and Isomerization of Ribonucleoside 3′‐Phosphodiesters: The Role in Stabilization of the Phosphorane Intermediate

A dinucleoside‐3′,5′‐phosphodiester model, 5′‐amino‐4′‐aminomethyl‐5′‐deoxyuridylyl‐3′,5′‐thymidine, incorporating two aminomethyl functions in the 4′‐position of the 3′‐linked nucleoside has been prepared and its hydrolytic reactions studied over a wide pH range. The amino functions were found to accelerate the cleavage and isomerization of the phosphodiester linkage in both protonated and neutral form. When present in protonated form, the cleavage of the 3′,5′‐phosphodiester linkage and its isomerization to a 2′,5′‐linkage are pH‐independent and 50–80 times as fast as the corresponding reactions of uridylyl‐3′,5′‐uridine (3′,5′‐UpU). The cleavage of the resulting 2′,5′‐isomer is also accelerated, albeit less than with the 3′,5′‐isomer, whereas isomerization back to the 3′,5′‐diester is not enhanced. When the amino groups are deprotonated, the cleavage reactions of both isomers are again pH‐independent and up to 1000‐fold faster than the pH‐independent cleavage of UpU. Interestingly, the 2′‐ to 3′‐isomerization is now much faster than its reverse reaction. The mechanisms of these reactions are discussed. The rate accelerations are largely accounted for by electrostatic and hydrogen‐bonding interactions of the protonated amino groups with the phosphorane intermediate.     

An Automatic Molecular Dispenser of Chloride

The combined activity of the 1.1.1‐cryptand and of a dicopper(II) bistren cryptate complex including chloride makes the Cl^? ion be continuously and slowly delivered to the solution, without any external intervention. The 1.1.1‐cryptand slowly releases OH^? ions, according to a defined kinetics, and each OH^? ion displaces a Cl^? ion from the cryptate. Chloride displacement induces a sharp colour change from bright yellow to aquamarine and can be conveniently monitored spectrophotometrically, even in diluted solutions. The 1.1.1‐cryptand is the motor of a molecular dispenser (the dicopper(II) cryptate) delivering chloride ion automatically, from the inside of the solution.     

Expanded Organic Building Units for the Construction of Highly Porous Metal–Organic Frameworks

Two new organic building units that contain dicarboxylate sites for their self‐assembly with paddlewheel [Cu₂(CO₂)₄] units have been successfully developed to construct two isoreticular porous metal–organic frameworks (MOFs), ZJU‐35 and ZJU‐36, which have the same tbo topologies (Reticular Chemistry Structure Resource (RCSR) symbol) as HKUST‐1. Because the organic linkers in ZJU‐35 and ZJU‐36 are systematically enlarged, the pores in these two new porous MOFs vary from 10.8 Å in HKUST‐1 to 14.4 Å in ZJU‐35 and 16.5 Å in ZJU‐36, thus leading to their higher porosities with Brunauer–Emmett–Teller (BET) surface areas of 2899 and 4014 m² g^?1 for ZJU‐35 and ZJU‐36, respectively. High‐pressure gas‐sorption isotherms indicate that both ZJU‐35 and ZJU‐36 can take up large amounts of CH₄ and CO₂, and are among the few porous MOFs with the highest volumetric storage of CH₄ under 60 bar and CO₂ under 30 bar at room temperature. Their potential for high‐pressure swing adsorption (PSA) hydrogen purification was also preliminarily examined and compared with several reported MOFs, thus indicating the potential of ZJU‐35 and ZJU‐36 for this important application. Studies show that most of the highly porous MOFs that can volumetrically take up the greatest amount of CH₄ under 60 bar and CO₂ under 30 bar at room temperature are those self‐assembled from organic tetra‐ and hexacarboxylates that contain m‐benzenedicarboxylate units with the [Cu₂(CO₂)₄] units, because this series of MOFs can have balanced porosities, suitable pores, and framework densities to optimize their volumetric gas storage. The realization of the two new organic building units for their construction of highly porous MOFs through their self‐assembly with [Cu₂(CO₂)₄] units has provided great promise for the exploration of a large number of new tetra‐ and hexacarboxylate organic linkers based on these new organic building units in which different aromatic backbones can be readily incorporated into the frameworks to tune their porosities, pore structures, and framework densities, thus targeting some even better performing MOFs for very high gas storage and efficient gas separation under high pressure and at room temperature in the near future.     

Nanoscale Control of Polyoxometalate Assembly: A {Mn8W4} Cluster within a {W36Si4Mn10} Cluster Showing a New Type of Isomerism

Two near isomeric clusters containing a novel {Mn₈W₄} Keggin cluster within a [W₃₆Mn₁₀Si₄O₁₃₆(OH)₄(H₂O)8]^24? cluster are reported: K₁₀Li₁₄ [W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1 ) and K₁₀Li1_3.5Mn_0.25[W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1′ ). Bulk characterization of the clusters has been carried out by single crystal X‐ray structure analysis, ICP‐MS, TGA, ESI‐MS, CV and SQUID‐magnetometer analysis. X‐ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two “intermediate” types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X‐ray analysis and revealed to be novel clusters K₄Li₂₂[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?56 H₂O ( 2 ) and Mn₂K₈Li₁₄[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?45 H₂O ( 3 ). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X‐ray crystallography directly facilitated understanding the means by which a POM assembled.     

Multi‐Pathway Excited State Relaxation of Adenine Oligomers in Aqueous Solution: A Joint Theoretical and Experimental Study

The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time‐dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time‐resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)₂₀ in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9‐methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π–π* or charge‐transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC‐induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) “neutral” excited dimers decaying on the sub‐nanosecond timescale, being the dominant species, and 3) charge‐transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge‐transfer states.     

SnS2纳米材料的水热合成及光催化性质

在不同的表面活性剂和硫源的条件下,采用水热法制备了多种形貌的SnS₂纳米材料,详细讨论了反应条件对其形貌和性质的影响,并采用X射线衍射(XRD)、扫描电镜(SEM)、和BET比表面积法对制备的样品的物相、形貌和组成进行了表征,通过光催化降解罗丹明B研究了所得样品的光催化性能。结果表明：表面活性剂和硫源对产物的结构和形貌起到了重要的作用。当Sn⁴⁺与表面活性剂的物质量的比为1：1时,样品均为纯的六方相SnS₂。采用柠檬酸三钠为表面活性剂、硫脲为硫源时制得的SnS₂纳米片具有最大的比表面积,同时表现出了最优的光催化性能。     

Hochschild and cyclic (co)homology of superadditive categories

We define the Hochschild and cyclic (co)homology groups for superadditive categories and show that these (co)homology groups are graded Morita invariants. We also show that the Hochschild and cyclic homology are compatible with the tensor product of superadditive categories.     

Codimension-4 resonant homoclinic bifurcations with orbit flips and inclination flips

The paper studies a codimension-4 resonant homoclinic bifurcation with one orbit flip and two inclination flips, where the resonance takes place in the tangent direction of homoclinic orbit.Local active coordinate system is introduced to construct the Poincar′e returning map, and also the associated successor functions. We prove the existence of the saddle-node bifurcation, the perioddoubling bifurcation and the homoclinic-doubling bifurcation, and also locate the corresponding 1-periodic orbit, 1-homoclinic orbit, double periodic orbits and some 2n-homoclinic orbits.