Synthesis and characterization of new heterometallic iron sulfur nitrosyl clusters

The reactivity of the (PPN)₂[Fe₈S₆(NO)₈] and (PPN)₂[Fe₆S₆(NO)₆] clusters is explored and new derivative clusters have been synthesized and structurally characterized. The unique (PPN)₂Fe₄S₄(NO)₆ “open-cubane” cluster with a chair like Fe₄S₄ core is obtained along with the mixed metal pentandite-like clusters (PPN)₂[Mo₂Fe₆S₆(NO)₆(CO)₆], (PPr₃)₂Cu₂Fe₆S₆(NO)₆, (PPr₃)₄Cu₄Fe₄S₆(NO)₄, (PPr₃)₂Ni₂Fe₆S₆(NO)₆, (PPr₃)₃Ni₃Fe₄S₆(NO)₄. The rich electrochemistry of the mixed metal clusters is presented as well.     

Synthesis and in vitro biological activity of some 7-[hydrazino], -[hydrazonyl] and -[pyrazolyl]quinolone-3-carboxylic acids

1-Ethyl-6-fluoro-7-hydrazino-1,4-dihydro-4-oxoquinoline-3-carboxylic acid ( 8 ) has been prepared and served as a versatile intermediate from which a number of hydrazone, pyrazole and dihydropyridazine derivatives were synthesized. The in vitro biological activity of some of these derivatives is reported.     

2-cyano Δ3 piperidines III: Total synthesis 0f (±) 20-epiuleine

The total synthesis of the indole alkaloid (±) 20-epiuleine has been achieved starting from indole itself and the appropriate 2-cyano Δ³ piperidine $\text{7}$.     

聚呲咯的研究

本文研究了不同电化学氧化聚合条件下所得聚吡咯的红外光谱,X射线光电子能谱、元素分析、X射线衍射图及扫描电子显微镜图等。对聚吡咯的电导性、电导率的依赖性、化学结构及结晶性等进行了讨论。     

Contrasting linear and quadratic nonlinear optical behavior of dipolar pyridinium chromophores with 4-(dimethylamino)phenyl or ruthenium(II) ammine electron donor groups

In this article, we contrast the optical properties of dipolar chromophores having 4-(dimethylamino)phenyl electron donor (D) and pyridinium acceptor (A) groups with those of closely related cations having pyridyl-coordinated Ru(II) donors. A range of physical data, including that from Stark (electroabsorption) spectroscopy, permits unprecedented quantitative comparisons, most notably regarding the effects of extension of bridging polyene chains. The purely organic compounds display normal optical properties in that their intense, visible pi --> pi intramolecular charge-transfer (ICT) bands red-shift as the number of E-ethylene units (n) increases from 1 to 3 and the associated static first hyperpolarizabilities beta(0) increase steadily with n. The related Ru(II) complexes show intense, visible d --> pi metal-to-ligand charge-transfer (MLCT) bands, which are found to lower energy when compared with the ICT transitions of the corresponding organics. Abnormally, these MLCT bands blue-shift as n increases, and beta(0) maximizes at n = 2. Time-dependent density-functional theory and finite field calculations verify these empirical trends for both types of compound, which can be rationalized as arising from the differing orbital structures of the chromophores and the associated degrees of D-A electronic coupling.     

Separation of ritalin racemate and its by-product racemates by capillary electrophoresis

Ritalin, [(+)-threo]methylphenidate hydrochloride, is a chiral drug substance with two chiral centers. The drug substance may contain three pairs of enantiomers, [(+)-threo], [(-)-threo], [(+)-erythro] and [(-)-erythro] isomers, and its degradation products, threoritalinic acid racemate. Determination of the optical purity of ritalin drug substance and the amount of its by-product isomers is a critical step in the single-isomer drug development. In order to efficiently recognize the three pairs of enantiomers by one method, capillary electrophoresis (CE) was employed for the separation. The three pairs of enantiomers in CE showed different enantioselectivities with eight different types of CDs. Only 2,6-di-o-methyl-beta-cyclodextrin (DM-beta-CD) and carboxymethyl-beta-cyclodextrin (CM-beta-CD) showed enantioselectivity to all these pairs of enantiomers. With respect to separation resolution and efficiency, DM-beta-CD was chosen as the chiral selector. For optimization of the separation conditions, the concentration of DM-beta-CD, pH of the buffer solution, and temperature of the capillary were further studied.     

19-electron intermediates and cage-effects in the photochemical disproportionation of [CpW(CO)3]2 with Lewis bases

The role of 19-electron intermediates in the photochemical disproportionation of [CpW(CO)3]2 (Cp = C5H5) with Lewis bases (PR3; R = OMe, Bu, Ph) is investigated on the ultrafast time scale using femtosecond VIS-pump, IR-probe spectroscopy. Formation of a 19-electron (19e) species CpW(CO)3PR3*by coordination of PR3 with photogenerated 17-electron (17e) radicals CpW(CO)3* is directly observed, and equilibrium is established between the 17e radicals and the 19e intermediates favoring 19e intermediates in the order: Bu > OMe > Ph. Steric effects dominate the 17e/19e equilibrium when the cone-angle of the Lewis base exceeds a certain limiting value (between 132 degrees and 145 degrees ), but below this value electronic properties of the Lewis base control the 17e/19e dynamics. Disproportionation occurs in less than 200 picoseconds by electron transfer between a solvent caged 17e radical and 19e, highly reducing species. The rate and extent of ultrafast disproportionation depends on both the identity and concentration of the Lewis base. In low concentrations of PR3 (typically 1-2 M or less) or with Lewis bases whose equilibrium heavily favors 17e radicals (e.g., PPh3), disproportionation is rate-limited by breakdown of the solvent cage. Density functional theory calculations on vibrational frequencies and charge distributions of the various complexes support the experimental results.     

Kinetic analysis of cyclic CMP-specific and multifunctional phosphodiesterases by quantitative positive-ion fast-atom bombardment mass spectrometry

Two enzymes, cyclic CMP-specific phosphodiesterase and multifunctional phosphodiesterase, are responsible for the hydrolysis of cytidine 3',5'-cyclic monophosphate in living cells. Quantitation of both enzymes has been carried out by positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubates after termination of the reaction. The kinetic data obtained are in close agreement with parallel data obtained by the conventional radiometric assay. The extra facility of the mass spectrometry based assay to monitor several incubation components simultaneously has been exploited to study the concurrent hydrolysis of alternate cyclic nucleotide substrates and provides kinetic parameters of significance in interpreting substrate-enzyme interactions. This is extended by the use of collisionally-induced dissociation of the protonated molecules of the liberated products to identify the mononucleotide isomers resulting from the cyclic nucleotide hydrolysis.     

A finite element based algorithm for determining interfacial tension (gamma) from pendant drop profiles

This paper introduces a robust algorithm to determine the interfacial tension (gamma) from pendant drop profiles using the Galerkin finite element method (gamma-PD-FEM) to solve the axisymmetric form of the Young-Laplace (YL) equation. In this algorithm, the theoretical profiles are generated by solving the spherical coordinate form of the YL equation. gamma-PD-FEM also solves for the parameter estimates by minimizing the difference between the theoretical and experimental surface functions, f(theta). This technique is compared to the widely used method of converting the YL equation to the three arc length-based (ALB) first-order ODEs developed by Bashforth and Adams (BA) in 1883, or as denoted in this paper, the gamma-PD-BA method. The drop apex is the initial condition for the gamma-PD-BA algorithm and the integration is terminated at a specified location along the drop profile. In contrast to techniques based on the BA approach, computation of the theoretical drop profile in gamma-PD-FEM is obtained from a second-order ordinary differential equation and requires boundary conditions at the drop apex and at the contact line of the drop to the nozzle. By incorporating both boundary conditions into the problem formulation, the algorithm can also determine if the drop shape is at static equilibrium. Results to be presented include an outline of the computer algorithm, and comparison of gamma values obtained from the gamma-PD-FEM and the traditional gamma-PD-BA method using simulated and experimental drop profile data sets.     

Proton-transfer dynamics in the activation of cytochrome P450eryF

Molecular dynamics simulations are combined with quantum chemistry calculations of instantaneous proton-transfer energy profiles to investigate proton-transfer events in the transient pathway of cytochrome P450eryF (6-deoxyerythronolide B hydroxylase; CYP107A1), from the oxyferrous species to the catalytically active ferryl oxygen species (compound I). This reaction is one of the most fundamental unresolved aspects in the mechanism of oxidation that is common to all cytochrome P450s. We find that this process involves an ultrafast proton transfer from the crystallographic water molecule W519 to the distal oxygen bound to the heme group, and a subsequent proton-transfer event from W564 to W519. Both proton-transfer events are found to be endothermic in the oxyferrous state, suggesting that the oxyferrous reduction is mechanistically linked to the proton-transfer dynamics. These findings indicate that the hydrogen bond network, proximate to the O(2)-binding cleft, plays a crucial functional role in the enzymatic activation of P450s. Our results are consistent with the effect of mutations on the enzymatic efficacy.