Synthesis,Reactions and Applications of Phosphorus Containing Carbon Centered Radicals

A general method for synthesis of C_n-C (n=1, 2...) phosphonate bonds involving a reaction of 1-diethoxy-phosphorylalkan-1-, -2-and -3-yl radicals 1,3,6 with alkenes 4, a new example of functional group interconversion in 1-heterosubstituted phosphonates and synthesis of useful phosphoroorganic compounds and methylenomycin B are described.     

New Type of Prototropic Tautomerism Involving Carbon,Hydrogen, and Oxygen Atoms

A low-molecular weight analog of the vinyl chloride–maleic anhydride copolymer, chloromethylsuccinic anhydride gives rise to a new type of prototropic tautomerism, cyclic anhydride–enol, with formation of quasiaromatic enol and dienol derivatives. The ratio of the anhydride and enol tautomers in solution at room temperature is 7 : 1.     

New Hexazirconium Clusters Containing Hydrogen Atoms

Reduction of ZrBr₄ with HSnBu₃ yielded a blue solid. When this blue solid was treated with PMe₃, a hexanuelear cluster [Zr₆Br₁₄H₄( PMe₃)₄] (2) was isolated. Reaction of the blue solid with [PPh₄]Br in CH₂Cl₂ resulted in the formation of a paramagnetic and unstable cluster anion, [Zr₆Br₁₈H₅]^2– (3), which disproportionated to form a new cluster anion, [Zr₆Br₁₈H₅]^3– (4) and some Zr(IV) species. Compounds containing 4 can also be obtained from reaction of the blue solid with Br^– in MeCN. Reduction of ZrCl₄ with HsnBu₃ gave a red–brown solid, and [Zr₆Cl₁₄H₄(AsMe₃)₄] (9) and [Zr₅Cl₁₂H₄(AsMe₃)₅](8) were obtained by reaction of the red–brown solid with AsMe₃. No cluster compounds containing amine ligands were obtained in the reaction of the red–brown solid with amines; only compounds containing the [Zr₆Cl₁₈ H₅]^3– anion and ammonium cations were isolated. Altogether ten products were characterized by single crystal X-ray diffraction and where possible, by ¹H NMR studies.     

Decarboxylative Borylation of Stabilized and Activated Carbon Radicals

Redox-active esters (RAEs) as active radical precursors have been extensively studied for C−B bond formations. However, the analogous transformations of stabilized radicals from the corresponding acid precursors remain challenging owing to the strong preference towards single-electron oxidation to the stable carbocations. This work describes a general strategy for rapid access to various aliphatic and aromatic boronic esters by mild photoinduced decarboxylative borylation. Both aryl and alkyl radicals could be generated from the leaving group-assisted N-hydroxybenzimidoyl chloride esters, even α-CF₃ substituted substrates could be activated for further elaboration.     

Spectra of Conic Carbon Radicals

Conic carbon radicals with non-trivial automorphism groups are topologically possible when the curvature originates from 1, 3 or 5 pentagons in the otherwise hexagonal graphene sheet. By splitting determinants of quotient graphs, we determine the bonding nature of the last occupied and first unoccupied Hückel orbitals of the radicals constituting the three infinite series with the most plausible topologies. Each member of the series with three pentagons at the tip has one electron in the first anti-bonding orbital, each member of the series with one or five pentagons at the tip has one vacancy in the last bonding orbital, and none of the radicals have any un-bonding orbital. Within the limits of the Hückel model, this implies, respectively, stable conic cations and anions. The quotient graphs also give the collected Hückel energy for each of the one-dimensional irreducible representations of the point groups.     

A Mitochondrion-Localized Two-Photon Photosensitizer Generating Carbon Radicals Against Hypoxic Tumors

The efficacy of photodynamic therapy is typically reliant on the local concentration and diffusion of oxygen. Due to the hypoxic microenvironment found in solid tumors, oxygen-independent photosensitizers are in great demand for cancer therapy. We herein report an iridium(III) anthraquinone complex as a mitochondrion-localized carbon-radical initiator. Its emission is turned on under hypoxic conditions after reduction by reductase. Furthermore, its two-photon excitation properties (λ_ex=730 nm) are highly desirable for imaging. Upon irradiation, the reduced form of the complex generates carbon radicals, leading to a loss of mitochondrial membrane potential and cell death (IC₅₀^light=2.1 μm , IC₅₀^dark=58.2 μm , PI=27.7). The efficacy of the complex as a PDT agent was also demonstrated under hypoxic conditions in vivo. To the best of our knowledge, it is the first metal-complex-based theranostic agent which can generate carbon radicals for oxygen-independent two-photon photodynamic therapy.     

青络锗和青络铜对清除氧自由基的研究

以邻苯三酚（ＰＡ）为氧自由基释放剂,以四氮唑蓝（ＮＢＴ）为显色剂,利用样品对ＰＡ自身氧化释放氧自由基的抑制作用,对样品清除自由基能力进行比色测定,效果满意。     

氢、碳氢燃料对向扩散火焰

A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffu-sion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH₄ to C₁₆H₃₄. The basic diffusion flame struc-tures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The de-tailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory(LLNL) are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H₂ has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.     

金属-氮氧自由基层状配合物磁性体系

介绍了金属与氮氧自由基所形成的层状体系的结构特点、磁耦合特征及其发展前景。     

Metal Complexes of Pentadentate Macrocyclic Ligands Containing Oxygen and Nitrogen as Donor Atoms

Four macrocyclic ligands have been synthesized: 1-oxa-4,7,10,13-tetraazacyclopentadecane ( 1 ), 1,4-dioxa-7,10,13-triazacyclopentadecane ( 2 ), 1,4-dioxa-7,11,14-triazacyclohexadecane ( 3 ), 1,4-dioxa-7,11,15-triazacycloheptadecane ( 4 ), one of them 3 , for the first time. The protonation constants of the ligands and the stability constants of the complexes formed by the four ligands with some divalent first-series transition-metal ions, Cd²⁺ and Pb²⁺, were determined by potentiometric methods, in aqueous solution, at 25° and I = 0.10M (KNO₃). The sequence of protonation of ligand 1 was studied by ¹H-NMR spectroscopy. The Irving-Williams' order of stability is obeyed for the complexes of all the ligands, and the metal complexes of 1 present the higher values of stability. A drop in the stability of all the metal complexes studied is observed when the metal complexes of 1 are compared with the corresponding complexes of 2 . The effect of the increase of the ring size of the macrocycle can be observed for metal complexes of the series of ligands 2 4 , where, in spite of the slight increase of the overall basicity of the ligands (20.28, 22.25, and 24.96 for 2, 3 , and 4 respectively), small differences in stability are found for the corresponding complexes of 2 and 3 , but a significant drop occurs for all the metal complexes formed with the 17-membered ligand, specially for the larger metal ions like Mn²⁺ and Pb²⁺.     

Dynamic Visualization of Free Radicals at Single Oxygen Bubbles using Chemiluminescence

The generation of free radicals is a key process in the formation and the collapse of the bubbles in water, however, the direct and dynamic observation of the radicals in this process at single bubbles has never been achieved. Here, the hydroxyl (OH^.) and oxygen (O₂^.−) radicals at single oxygen bubbles are continuously traced using chemiluminescence (CL), in which these radicals at the bubble react with the surrounding luminol in the solution emitting the light. Varied increase trends of luminescence are observed in the generation of a bubble, floating, short parking at the water/air interface and the final explosion, revealing the complexity in the distribution of radicals at the bubble unprecedentedly. Despite more radicals are observed at the bubble generated at a deep position under the water for the stabilization, almost the same amount of radicals are included in the bubbles that is independent on the water pressure during the production of the bubble. This rich information collected from the dynamic study of bubbles illustrates the complicated generation and distribution process of radicals at the bubbles, and will facilitate the understanding of the function about the bubbles.     

A Spin-Frustrated System Composed of Organic Radicals and Magnetic Metal Ions

Despite antiferromagnetic coupling between any two neighboring spins, parallel alignment of the 3d spins of the Mn^II ions and the 2p spins of the organic ligand is observed for the (degenerate) ground state of [{Mn(hfac)₂}₂(bnn)] (shown on the right). The “butterfly”-shaped arrangement of the spins contributes to this noteworthy spin configuration. hfac=hexafluoroacetylacetonate, bnn=2,2′-bis(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolinyl).     

Synthetic Strategies toward Natural Products Containing Contiguous Stereogenic Quaternary Carbon Atoms

Strategies for the total synthesis of complex natural products that contain two or more contiguous stereogenic quaternary carbon atoms in their intricate structures are reviewed with 12 representative examples. Emphasis has been put on methods to create quaternary carbon stereocenters, including syntheses of the same natural product by different groups, thereby showcasing the diversity of thought and individual creativity. A compendium of selected natural products containing two or more contiguous stereogenic quaternary carbon atoms and key reactions in their total or partial syntheses is provided in the Supporting Information.     

Effect of Oxygen Free Radicals on Myosin in Muscle Fibres. A DSC and EPR study

Differential scanning calorimetry (DSC) and electron paramagnetic resonance spectroscopy (EPR, both conventional and saturation transfer EPR) were used to study the motional dynamics and segmental flexibility of myosin in muscle fibres in the presence of free radical generating system. Muscle fibre bundles isolated from psoas muscle of rabbit were spin-labelled with maleimide- and isothiocyanate-based probe molecules at the reactive sulfhydryl sites (Cys-707) of the motor domain. In the presence of hydroxyl free radicals the spectral intensity of the maleimide probe molecules decreased with time following a single exponential curve. MgADP and MgATP plus orthovanadate that produce flexibility changes in the multisubunit structure of myosin enhanced the reduction of the attached nitroxide molecules in free radical generating system. The analysis of the EPR spectra of spin-labelled and oriented fibres showed that the narrow distribution of spin labels changed in the presence of hydroxyl free radicals. Spectrum analysis by computer subtraction showed that short irradiation by UV light resulted in the enhancement of the ordered population at the expense of the disordered population. This suggests a transition of myosin heads from weak- binding state into strong-binding state. DSC measurements performed on calf cardiac myosin resulted in two main transitions at 49.4 and 54.1°C, respectively. Addition of MgADP produced a decrease of the 49.4°C transition, whereas a shift towards higher temperature was detected at the 54.1°C transition. It shows that there is an inter-site communication between the domains of the myosin. Hydroxyl free radicals induced further shifts of the transition temperatures and affected the width of the heat absorption curves. This revised version was published online in July 2006 with corrections to the Cover Date.     

含氢碳原子团簇的初步研究

介绍直接用激光溅射芳香化合物固态样品产生的含氢磷原子团簇离子（C_nH~＋_m），并用飞行时间质谱仪研究了其组成和结构．实验发现，在低质量区（n＝32－56）得到了具有奇偶碳原子数的含氢磷原子簇，而在高质量区（n＞100）除了得到纯碳原子簇以外，还得到了含氢碳原子簇．根据对实验结果的分析提出了两种结构模型：对低质量区的团簇，其结构为芳香基团与富勒烯笼状框架的复合体；对高质量区的团簇，其结构为蜗牛形与圆柱形的复合体．     

Photoelectrochemical Behavior of Electrodes Containing One-Walled Carbon Nanotubes

Photoelectrochemistry of electrodes containing single-walled carbon nanotubes is studied for the first time ever. Photoemission of electrons from such electrodes illuminated by UV light is discovered. It is established that the photocurrent amplitude as a function of the imposed potential obeys the 5/2 law and that the work function into solution for nanotubes and a mercury electrode coincide to within 0.08 eV. Similarity of electrochemical behavior of intermediates on the nanocarbon and mercury electrodes is shown with the reduction of radicals CH₂Cl as an example.