The vibrational spectrum of TpRhH2(H2): a computational and inelastic neutron scattering study

We report extensive density functional theory studies of the structures and vibrational frequencies of Tp^3,5-MeRhH₂(H₂) in its ground and various transition states as well as the first direct comparison of observed and calculated inelastic neutron scattering (INS) vibrational spectra on this type of compound. Geometry optimizations produced canted η²-dihydrogen dihydride local minima of C₁ symmetry; with HH distances for the C₁ minimum energy structure of 0.842 and 0.898 Å and barriers to rotation of 0.34 and 0.50 kcal mol⁻¹, respectively for B3LYP/BS1 and BP86/BS1 calculations of Tp^3,5-MeRhH₂(H₂). The latter results from one transition state rotated approximately 60° away (a second lower energy transition state which is a few hundreds of a kcal mol⁻¹ above the C₁ MIN is rotated approximately 30° away). With these calculated d(HH) values for the C₁ MIN the previously reported experimental data on the rotation of the dihydrogen ligand yields an experimental barrier to rotation of 1 kcal mol⁻¹ and places the torsional transition at 200 cm⁻¹ in the INS spectrum. Optimization of the Rh structure, that is analogous to the related Ir(V) C_s minimum found for TpIrH₄, generates a high-energy (>4 cal mol⁻¹) C_s transition state TpRh^IIIH₄ structure with an η³-H₃ ⁻ ligand. This transition state (C_s TSE) exchanges the hydrogen in the mirror plane between two chiral C₁ MIN structures. Comparisons between observed and computed INS spectra suggests that the experimental INS spectrum be viewed as resulting from a quantum-averaged ground state encompassing at least two of the low energy structures found in our calculations.     

Rhodium(I) complexes of the type [TpRh(LL)] (LL = 2 CO, NBD, COD) with trifluoromethyl substituted tris (pyrazolyl) borate ligands and their dynamic behaviour in solution. The X-ray crystal structure of TpRh(CO)2

Three seriesof Rh(I) complexes of the type Tp^3R,5RRh(LL), with LL = 2 CO (1), norbornadiene (NBD) (2) and 1,5-cyclooctadiene (COD) (3) and the tris (pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF₃5R=Me (b); and 3R=5R=CF₃ (c) were synthesized and fully characterized by IR and multinuclear NMR spectroscopy. Three isomeric forms were identified in solutions of these complexes: two square-planar isomers with a κ²-Tp³R,5R ligand, the uncoordinated pyrazolyl ring occupying either an equatorial position (type A), or an axial position (type B), and a five-coordinate species with a κ³, Tp³R,5R ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex 1c contained all three isomers simultaneously. ¹⁰³Rh and ¹³C NMR spectral studies indicate that the NBD compounds, 2, preferentially form square-planar complexes when Tp^CF₃,Me and Tp^CF₃,CF₃ are present, while for the COD complexes, 3, square-planar complexes are preferred for all three Tp-type ligands. The X-ray structure of Tp^CF₃,MeRh(CO)₂ (1b) was determined (spacce group C2/ c,a = 21.271(9), B = 11.004(3), C = 21.563(9) Å, β = 114.93(3)°, V=4577(3) ų, Z = 8, R = 3.41, R_w = 4.70). Its structure is of type B, with the third pyrazolyl ring axially placed, the N(4) being almost directly above the Rh atom but exerting only a weak Rh-N interaction.     

Modelling transition state analogues and enzyme-inhibitor complexes of zinc-containing class II aldolases and metalloproteases

The zinc complex Tp^*Zn---OH (1:Tp^* = hydrotris-(3-cumyl,5-methyl-pyrazolyl)borate) which is a model of hydrolytic zinc enzymes was reacted with hydroxamic acids and hydroxyketones. Two hydroxamates Tp^*Zn-Hya (2: Hya = acetohydroxamate, 3: Hya = 2-hydroxamato-4-methylpentanoyl-alanyl-glycylamide) and two ketoalcoholates Tp^*Zn-Kea (4: Kea = hydroxyacetonate, 5: Kea = cumoylacetonate) were obtained. Crystal structure determinations of 2, 3 and 5 have revealed distorted ZnN₃O₂ coordinations in each case. The immediate environment of the zinc ion in the hydroxamates closely resembles that in enzyme-(hydroxamate)inhibitor complexes of zinc-containing metalloproteases like collagenases and thermolysin or of class II aldolases like fuculose-1-phoshate aldolase. Like in the enzymes the hydroxamates and the ketoalcoholates can serve as transition state analogues of the enzyme-catalysed reactions.     

Model compounds for polymeric redox-switchable hemilabile ligands

The syntheses and characterization of two new tetradentate hemilabile ligands 1,2-bis(2-diphenylphosphinoethoxy)benzene (5) and 2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene (10) are reported. Ligands 5 and 10 were synthesized as models to test the suitability of specific phosphinoether coordination environments for complexing Rh(I) in high surface area thiophene-based, redox-active polymeric systems. Ligands 5 and 10 react with the product formed from the reaction between (bicyclo[2.2.1]hepta-2,5-diene)rhodium(I) chloride dimer and AgBF₄ to form [η²-(1,2-bis(2-diphenylphosphinoethoxy)benzene) η⁴-norbornadiene rhodium(I)] tetrafluoroborate (6) and [η²-(2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene) η4-norbornadiene rhodium(I)] tetrafluoroborate (11), respectively. Complexes 6 and 11 react with H₂ in CD₂Cl₂ to form the two new square-planar cis-phosphine, cis-ether Rh(I) complexes 7 and 12, respectively. Compound 7, which could be characterized on the basis of its ³¹P NMR spectrum, is extremely reactive and decomposes in CD₂Cl₂. In THF compounds 6 and 11 react with H₂ to form the dihydride, bis-THF adducts 8 and 16, respectively, which upon removal of solvent form 7 and 12, respectively. Compound 12 is a stable, isolable complex that reacts with acetonitrile to form a cis-phosphine, cis-acetonitrile adduct 15. Removal of solvent from 15 leads to the quantitative reformation of 12. Compound 12 does not react to a detectable extent with gross excesses of benzene or even thiophene, demonstrating the suitability of this ligand environment for implementation into a thiophene-based polymeric system. Compound 12 does catalyze the hydrogenation of cyclohexene to form cyclohexane, and mechanistic implications of such a transformation are discussed.     

Photochemical reactions of transition metal organyl complexes with olefins Part 10. Light-induced formal [5+2] cycloadditions at manganese

Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (1) forms upon UV irradiation in THF at 208 K solvent stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (2). With butynedioic acid dimethyl ester (3) and diphenylacetylene (5) complex 2 yields tricarbonyl-η⁵-1,2-dimethoxycarbonyl-4,6-dimethyl- cyclohepta-2,4-dien-1-yl-manganese (4) and tricarbonyl-η-4,6-dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl- manganese (6) in a formal [5+2] cycloaddition. Addition of carbon monoxide and a 1,4-H shift completes the reaction. Propynoic acid methyl ester (7) forms the 2:1 adduct dicarbonyl-η^5:2-1,3-dimethyl-6-methoxycarbonyl-6- (E-2′-methoxycarbonylvinyl)-cyclohepta-2,4-dien-1-yl-manganese (8). The crystal and molecular structure of 8 was determined by X-ray structure analysis. The molecular structures of the complexes 4 and 6 were established by IR and NMR spectroscopy. Formation mechanisms of 4, 6 and 8 are discussed. Crystal data for 8: monoclinic space group P2₁/c, a=802.6(3), b=1136.6(1), c=8872.3(3) pm, β=93.14(2)°, V=1.705 nm³, Z=4.     

Ricochet inter-ring haptotropic rearrangement of σ-methyl-(η-indenyl) chromium tricarbonyls. Experimental kinetic and theoretical DFT study

σ-Methyl-(η⁵-indenyl) chromium tricarbonyl (III) rearranges quantitatively into η⁶-1-endo-methylindene) chromium tricarbonyl (IV) in C₆D₆ solution at 30–60°C. Methyl group attachment to the positions 2 or 3 of indenyl ligand in (III) has no influence on the activation parameters of this ricochet inter-ring haptotropic rearrangement (ΔG^#=23.6 kcal mol⁻¹; ΔH^#=18.9±0.2 kcal mol⁻¹; ΔS^#=−18.6±0.2 cal K⁻¹ mol⁻¹). (IV) undergoes further irreversible isomerization at 60–120° into (ν⁶-3-methylindene) chromium tricarbonyl (V) with a higher activation barrier (ΔG^#=28.5±0.1 kcal mol⁻¹) via two consecutive [1,5]-sigmatropic hydrogen shifts. The mechanisms of both rearrangements have been studied in detail using density functional theory (DFT) calculations with extended basis sets. Calculations show that the rearrangement (III) → (IV) proceeds in two steps. Methyl group migration from chromium into position 1 of the indenyl ligand is the rate-determining step leading to the formation of the 16-electron intermediate (VII). The calculated activation barrier (E_a=19.6 kcal mol⁻¹) is in good agreement with the experimental one. Further rearrangement (VII) → (V) proceeds via a trimethylenemethane-type transition state (XVIII) with an activation barrier 11.8 kcal mol⁻¹. The coordination of the chromium tricarbonyl group at the six-membered ring has only minor influence on the kinetic parameters of the hydrogen [1,5]-sigmatropic shift in indene.     

Excitation and deexcitation processes of Eu(III) benzo-15-crown-5 complex studied on comparing with its first coordination sphere

The coordination sphere and the deexcitation mechanism of the Eu(III) benzo-15-crown-5 complex, Eu(B15C5), were studied with references of the Eu(III) complexes with a similar coordination sphere; the dibenzo-18-crown-6 complex, Eu₃(B₂18C6)₂, and the cryptand[2.2.1] complex, Eu([2.2.1]). NMR spectroscopy reveals that the Eu(B15C5) complex is quite stable in acetonitrile solution whereas only 40% of the Eu(III) ion forms the complex in the equimolar Eu(NO₃)₃ and B₂18C6 acetonitrile solution. The coordination sphere of the Eu(III) complexes in acetonitrile solutions were also discussed by the degenerate ⁷F₀→⁵D₀ transition energy levels. The Eu(B15C5) have a negative shift compared with the europium(III) nitrate in acetonitrile and it is explained by the coordination of both nitrate ions and the crown ether ligand. Energy transfer from the n–π* excited state located in the catechol structure to the central europium ion was first observed as the sensitized luminescence of ⁵D₀→⁷F_J. The excited state lifetime of the Eu(B15C5) complex was first determined as 201 μs in the present study.     

Synthesis, characterization, and reactivity of organometallic Zr(IV) carboxylate complexes

A series of zirconium(IV) complexes, [ZrX₂(XDK)], where XDK is the constrained carboxylate ligand m-xylylenediamine bis(Kemp's triacid imide), were prepared and structurally characterized. The solid state structure of the mononuclear carboxylate alkyl complex [Zr(CH₂Ph)₂(XDK)] reveals that one benzyl group is bonded in an η²-fashion to the metal center. The reactivity of [Zr(CH₂Ph)₂(XDK)] displays its electrophilic character toward nucleophiles strong enough to displace the η²-benzyl group. Thus, weak sigma donor ligands such as CO, alkynes and anilines do not react, whereas strong sigma donors, such as pyridines and isocyanides, rapidly form the monoadduct [Zr(CH₂Ph)₂(4-tert-butylpyridine)(XDK)] and [Zr{η²-2,6-Me₂PhNCCH₂Ph}₂(XDK)], an η²-iminoacyl derivative, respectively. Attempts to prepare zirconium amido complexes with H₂XDK generally afforded the eight-coordinate [Zr(XDK)₂] complex but use of the small amido ligand precursorZr(NMe₂)₄ allowed [Zr(NMe₂)₂(4-tert-butylpyridine)(XDK)] to be isolated in good yield.     

Palladium complexes with PCP ligands.: Preparation and structural studies of two forms of [(PCP)Pd(OH2)]BF4

Abstraction of chloride from the Pd complex {[η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]PdCl with AgBF₄ in THF gives {[η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]Pd(THF)}⁺BF₄ ⁻. Attemped crystallization of this THF complex produced the aqua complex {[η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]Pd(OH₂)}⁺BF₄ ⁻. Crystal structures of two crystalline forms of this compound are reported. In {[η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]Pd(OH₂)}⁺BF₄ ⁻·THF, one hydrogen of the water is hydrogen bonded to the oxygen of the THF, and the other hydrogen is hydrogen bonded to an F of the BF₄ ⁻ anion. Another crystalline form has no THF, but has both of the hydrogens of water hydrogen bonded to different BF₄ ⁻ anions, such that two different BF₄ ⁻ anions bridge two {[η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]Pd(OH₂)}⁺ cations. A crystal structure is also reported for the palladium chloride complex [η³-2,6-(^tBu₂PCH₂)₂C₆H₃)]PdCl.     

Reactions of benzocyclobutene chromium complexes with carbon, nitrogen and oxygen nucleophiles: nucleophilic addition and unexpected proximal ring opening reactions

Tricarbonyl(η⁶-1-oxobenzocyclobutene)chromium(0) (1) can be transformed to tricarbonyl(η⁶-1-endo-hydroxybenzocyclobutene) chromium(0) derivatives with substituents R (R=CH₃, CH=CH₂, (CH₂)₄CH=CH₂, (CH₂)₄OSi(Me)₂tBu) at Cl on the exo face of the complex. The relative configuration is proven by an X-ray crystal structure analysis of the trimethylsilyl ether 8 (C₁₆H₁₈CrO₄Si: a=8.693(1), b=9.490(1), c=11.063(1) Å, =97.51(1), β=110.32(1), γ=95.38(1)°, triclinic, space group P (No.2), R=0.037, R_w=0.052 for 4609 observed reflections. Attempts directed at an intramolecular cycloaddition of the ortho-quinodimethane complex derived from 17 by anion promoted ring opening unexpectedly resulted in the formation of 12 as the product of an opening of the proximal bond of the anellated ring located between the hydroxy group and the coordinated aromatic ring in 16. The fact that the intermolecular cycloaddition reaction for 16 is possible in the presence of a dienophile is taken as evidence for an equilibrium between the alcoholate 17 and the two ring opened products 16 and 18. The proximal ring opening of 6 is not observed when the free organic ligand 21 is used as the educt. Ketone complexes 1 and 25 undergo proximal ring opening reaction when treated with alcoholate or primary amines.     

Interaction of mono- and triphosphate anions with a protonated polyaza macrocycle and its Cu(II) complexes

The reactions of monophosphate (Mp) and triphosphate (Tp) with the protonated hexaaza macrocyclic ligand 3,6,9,16,19,22-hexaaza-27,28-dioxatricyclo[22.2.1.1^11,14]octacosa-1 (26),11,13,24-tetraene (BFBD) and its mono- and dinuclear copper(II) complexes, have been investigated. Potentiometric studies show that Tp is bound to protonated BFBD and Cu(II) complexes of this ligand more strongly than is MP. The crystal structures of two new binary complexes of Mp and Tp with this ligand are reported. Both of them crystallize in the triclinic system with space group P1. The binary complex 1 has lattice parameters a = 12.630, b = 13.152, c = 12.561 Å, = 96.359(1), β = 98.02(2), γ = 117.85(1)° and Z = 2. It contains the BFBD-Mp binary cation. The binary complex 2 has lattice parameters a = 12.717(4), b = 14.331(7), c = 19.687(7) Å, = 96.66(3), β = 107.68(2), γ = 93.11(3)° and Z = 2. It consists of the BFBD-Tp cation and the BFBD-2Tp anion. Electrostatic attractive forces and hydrogen bonds play major roles in the formation of these binary complexes.     

Molecular structures and some properties of tris(2-aminoethyl) amine cobalt(III) complexes with thiocarboxylato-O,S such as 3-mercaptopropionato, 2-mercaptoacetato and their derivatives

Cobalt(III) complexes with a thiolate or thioether ligand, t-[Co(mp)(tren)]⁺ (2), t-[Co(mtp)(tren)]²⁺ (1Me) and t-[Co(mta)(tren)]²⁺ (2Me), (mp = 3-mercaptopropionate, MA = 3-(methylthio)propionate and MTA = 2-(methylthio)acetate) have been prepared in aqueous solutions. The crystal structures of 1, 2, 1Me and 2Me were determined by X-ray diffraction methods. The crystal data are as follows, t-[Co(mp)(tren)]ClO₄ (1CIO₄): monoclinic, P2₁/n, A = 10.877(8), B = 11.570(4), c = 12.173(7) Å, β = 92.20(5)°, V = 1531(1) ų, Z = 4 and R = 0.060; t-[Co(ma)(tren)]Cl·3H₂O (2Cl·3H₂O): monoclinic, P2₁/n, a = 7.7688(8), B = 27.128(2), C = 7.858(1) Å, β = 100.63(1)°, V = 1627.7(3) ų, Z = 4 and R = 0.066; (+)₄₆₅^CD-t-[Co(mtp)(tren)](ClO₄)₂ ((+)₄₆₅^CD-1Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, A = 10.6610(7), B = 11.746(1), C = 15.555(1) Å, V = 1947.9(3) ų, Z = 4 and R = 0.068; (+)₄₆₅^CD-t-[Co(mta)(tren)](ClO₄)₂ ((+)₄₆₅^CD-2Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, a = 10.564(1), B = 11.375(1), C = 15.434(2) Å, V = 1854.7(4) ų, Z = 4 and R = 0.047. All central Co(III) atoms have approximately octahedral geometry, coordinated by four N, one O, and one S atoms. All of the complexes are only isomer, of which the sulfur atom in the didentate-O,S ligands are located at the trans position to the tertiary amine nitrogen atom of tren. 1 and 1Me contain six-membered chelate ring, and 2 and 2Me do five-membered chelate ring in the didentate ligand. The chirality of the asymmetric sulfur donor atom in (+)₄₆₅^CD-1Me is the S configuration and that in (+)₄₆₅^CD-2Me is the R one. The ¹H NMR, ¹³C NMR and electronic absorption spectral behaviors and electrochemical properties of the present complexes are discussed in relation to their stereochemistries.     

Borane and monoiodoborane derivatives of some bis(diphenylphosphino)alkanes

A series of borane and monoiodoborane derivatives of bis(diphenylphosphino)alkanes. (C₆H₅)₂P--- (CH₂)_n---P(C₆H₅)₂ in which n has values of 2 through 4 has been synthesized. Only compounds with the formulae [(C₆H₅)₂P]₂(CH₂)_n · (BH₃)₂ and (C₆H₅)₂P]₂CH₂)_n · BH₂I were isolable, the latter being boronium iodides. The compounds were characterized by their melting points, elemental analyses, molar conductivities, infrared spectroscopy, and ¹H and ¹¹B nuclear magnetic resonance spectroscopy. The relationship between the length of the carbon chain and the ¹¹B NMR chemical shift is discussed.     

Biological aromatization of delta4,6- and delta1,4,6-androgens and their 6-alkyl analogs, potent inhibitors of aromatase

Enzymic aromatization of Δ⁶- and Δ^1,6-derivatives of the natural substrate androstenedione with human placental aromatase was first studied using gas-chromatography-mass spectrometry. The two steroids were aromatized with apparent K_m and V_max values of 62 nM and 32 pmol/min/mg protein for the Δ⁶-steroid and 167 nM and 10 pmol/min/mg protein for the Δ^1,6-steroid, respectively. We next explored the aromatization of a series of 6-alkyl (methyl, ethyl, n-propyl, and n-pentyl)-substituted Δ⁶-androstenediones and their Δ^1,6-analogs, potent competitive inhibitors of aromatase, to gain insight into the relationships between the inhibitory activity of the 6-alkyl-C₁₉ steroids and their ability to serve as a substrate of aromatase. In a series of the Δ^1,6-androstenediones, all the 6-alkyl steroids were more efficient substrates than the parent Δ^1,6-steroid in which the aromatization rates of the alkyl steroids were about 2-fold that of the parent steroid, in contrast, all of the 6-alkyl-substituted Δ⁶-androstenediones were converted into the corresponding 6-alkyl-Δ⁶-estrogens with the rates of less than about a half that of the parent steroid. These results indicate that the 6-alkyl function decreases the aromatization rate of the Δ⁶-steroid but enhances that of the Δ^1,6-steroid. The relative apparent K_m values for the C₁₉ steroids obtained in this study are different from the relative K_i values obtained previously, indicating that a good inhibitor is not essentially a good substrate in the 6-alkyl-substituted Δ⁶- and Δ^1,6-androstenedione series.     

基于TaqMan探针多重实时荧光PCR的肠道特殊菌群绝对定量方法的建立

本研究旨在建立对肠道主要共生菌的快速定量方法。根据细菌16S rRNA基因的保守序列并参考相关研究,设计针对总肠道菌群的通用引物和探针,以及针对双歧杆菌属、肠球菌属和肠杆菌科的特异性引物和探针,采用引物设计工具(Primer-BLAST) 以及聚合酶链式反应(polymerase chain reaction, PCR)扩增以验证引物和探针的特异性。通过分子克隆技术,构建各目标菌属目的基因的重组质粒作为qPCR检测的标准模板,选择标准模板进行重复性实验,并计算组内和组间重复变异系数。用所建立的方法对不同年龄段的临床粪便标本进行3类细菌的检测,并初步分析这些菌群与增龄的关系。结果显示,引物和探针具有较高的特异性;各目的细菌标准曲线在一定范围内线性关系良好,总菌群或各目标菌属的线性范围分别为：总菌群2.9×10³～2.9×10¹²copies/μL、双歧杆菌3.1×10²～3.1×10⁹ copies/μL、肠球菌5.9×10²～5.9×10⁹ copies/μL、肠杆菌6.3×10²～6.3×10⁹ copies/μL,决定系数R²≥ 0.995;检测的最低拷贝数为总菌群7.5×10² copies/μL、双歧杆菌 46 copies/μL、肠球菌 37 copies/μL、肠杆菌 51 copies/μL;重复性实验变异系数在1.32%以下,具有良好的可重复性。对不同年龄段临床粪便标本检测的结果显示,肠球菌和肠杆菌含量随增龄呈增长趋势,且老年组含量显著高于青年组,但在高龄老年人中未发现肠球菌数量增加。双歧杆菌含量随增龄减少,且各组间差异显著,在高龄老年人中也未观察到双歧杆菌显著减少。结果提示,本研究建立了一种可供临床推广的菌群绝对定量方法,能够同时检测3类细菌和菌群总量,对于菌群定量研究具有实际意义。     

Conformational states of the corticotropin releasing factor 1 (CRF1) receptor: detection, and pharmacological evaluation by peptide ligands

Previous corticotropin releasing factor 1 (CRF₁) receptor characterization has been performed using radiolabeled agonists, which bind predominantly the receptor-G-protein complex. The pharmacological profile of other receptor states, and their abundance, remain poorly characterized. Here we investigated the affinity states of the CRF₁ receptor heterologously expressed in Ltk⁻ cells and endogenously expressed in rat cerebellum. In L-CRF₁ cell membranes, three agonist affinity states were detected: a very-high affinity receptor-G-protein complex state (eliminated by GTPγS) bound by [¹²⁵I]sauvagine (43 pM, RG); a high affinity state insensitive to GTPγS bound by [¹²⁵I]sauvagine (1.4 nM, termed R_O); and a low affinity G-protein-uncoupled state detected by sauvagine displacement of [¹²⁵I]astressin, a labeled antagonist (120 nM, R). The relative abundance of RG:R_O:R was 18%:16%:66%. All three states were demonstrated in rat cerebellum with similar relative abundance (15%:16%:69%). The R state bound CRF with low affinity (270–330 nM), displayed a novel rank order of ligand affinity, and represented the majority of the receptor population in both receptor preparations. This study provides a framework to identify CRF₁ receptor conformational states in various receptor preparations.     

Comparing the spectroscopic and electrochemical properties of ruthenium and osmium complexes of the tridentate polyazine ligands 2,2′:6′,2″-terpyridine and 2,3,5,6-tetrakis(2-pyridyl)pyrazine

A number of osmium and ruthenium complexes of the tridentate ligands 2,2′:6′,2″-terpyridine (tpy) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tpp) have been prepared and characterized by our laboratory. All these complexes possess metal based oxidations and ligand based reductions localized on each polyazine ligand. Polymetallic complexes bridged by the tpp ligand exhibit two sequential tpp based reductions prior to the reduction of other polyazine ligands in these complexes. The spectroscopy of these complexes is dominated by ligand based π-π^* transitions in the ultraviolet and MLCT (metal-to-ligand charge transfer) bands terminating on each polyzine ligand in the visible. For the complexes reported herein the lowest lying optical transitionis a M → BL CT band. For most of the complexes reported, occupation of this excited state gives rise to an observable emission at room temperature. For ruthenium complexes of these tridentate ligands, the presence of a low-lying LF state shortens the excited state lifetimes of these chromophores. This gives rise to ruthenium complexes that display shorter excited state lifetimes than the analogous osmium based systems. Incorporation of tpp based chromophores into polymetallic frameworks leads to the production of bimetallic species with long-lived excited states, 100 ns at room temperature. This makes these chromophores good candidates for the development of stereochemically defined supramolecular complexes. It is possible to measure an electrochemical HOMO-LUMO energy gap and a correlation between this electrochemically measured energy gap and the spectroscopic energy associated with this HOMO→LUMO transition are reported herein (HOMO== highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital).     

Second sphere coordination behavior of aquo and amine ligands bound to a η-benzeneruthenium(II) cation

The bis(oxazoline) ligand, 2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane (bpop), was introduced to the η⁶-benzenemthenium(II) moiety on treatment with [Ru(η⁶-C₆H₆)Cl₂]₂ to give [Ru(η⁶-C₆H₆)(bpop)Cl]⁺. Aquo and amine complexes [Ru(η⁶-C₆H₆)(bpop)(L)]²⁺ (L = H₂O (1), NH₂R; R = H (2) , Me (3) , and n-Bu (4) ) were prepared by treating the chloride complex with AgBF₄ in the presence of L. X-ray structure determinations of 1 and 3 were carried out. Both complexes possessed a three-leg piano stool structure with the N or O donors located at the three comers of a pseudo octahedron. The aquo complex 1 exhibited a dynamic NMR feature in which two magnetically nonequivalent oxazoline parts observed at lower temperatures were interchanged with each other at higher temperatures. This observation was ascribed to the formation of a C₂-symmetric 16-electron intermediate via Ru-OH₂ cleavage, which is slower in acetone than in dichloromethane owing to more effective solvation by acetone around hydrogens of the coordinated water molecule. The two diastereotopic N-hydrogens of 4 underwent deuterium exchange with CD₃OD with greatly different rates from each other owing to different energy of NHO (D) (CD₃) interaction. Carboxylate and sulfonate ions (A⁻) formed second sphere complexes with 4 by means of NHA⁻ hydrogen bonding, as evidenced by continuous shift of NH₂ resonances with increasing amounts of the anions added.     

红灵山亚热带常绿阔叶林维管植物组成与群落结构特征

为了弄清四川天全县红灵山亚热带常绿阔叶林的群落类型及结构特征,在红灵山中山地段（海拔1700~2000 m）设置6个20 m×30 m的代表性样地,采用典型群落调查法,对其物种组成、群落结构、生物量和自然更新能力等进行研究。结果显示：（1）样地内调查到182个物种,属72科117属,显示出典型亚热带常绿阔叶林的植物区系组成特征;（2）以扁刺栲群系为主,可分为3个群丛组、5个群丛;（3）乔木层密度为2583~5383株/hm²,生物量为2.42×10⁵~4.26×10⁵ kg/hm²,冠层藤本植物地上生物量为1.01×10³ kg/hm²,死木质残体生物量为1.65×10⁵ kg/hm²,次生性特征明显;（4）幼苗丰富,其种类组成与乔木层的相似度为88.89%,说明其自然更新良好,群落结构正渐趋稳定。综合分析表明,红灵山的常绿阔叶林以扁刺栲群系为主,虽次生性明显,但目前保存较为完好,值得进一步强化生态保育。     

In vitro steroid metabolic studies in human testes II: Metabolism of cholesterol, pregnenolone, progesterone, androstenedione and testosterone by testes of an estrogen-treated man

The effect of long-term in vivo estrogen treatment on in vitro steroidogenesis by the testes of a young man was investigated. In vitro incubation of testicular tissue of this man with ³H-pregnenolone, ³H-progesterone, ³H-androstenedione and ³H-testosterone demonstrated suppression of 17-hydroxylase activity, with little or no effect of the treatment on Δ⁵-3β-hydroxysteroid oxidoreductase, 5a-reductase and aromatase. Increased 20-hydroxysteroid oxidoreductase activity was observed. Determination of intratesticular steroid concentrations led to similar conclusions.