Dinuclear iron(II)-cyanocarbonyl complexes linked by two/three bridging ethylthiolates: relevance to the active site of [Fe] hydrogenases

Dinuclear iron(II)-cyanocarbonyl complex [PPN](2)[Fe(CN)(2)(CO)(2)(mu-SEt)](2) (1) was prepared by the reaction of [PPN][FeBr(CN)(2)(CO)(3)] and [Na][SEt] in THF at ambient temperature. Reaction of complex 1 with [PPN][SEt] produced the triply thiolate-bridged dinuclear Fe(II) complex [PPN][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)] (2) with the torsion angle of two CN(-) groups (C(5)N(2) and C(3)N(1)) being 126.9 degrees. The extrusion of two sigma-donor CN(-) ligands from Fe(II)Fe(II) centers of complex 1 as a result of the reaction of complex 1 and [PPN][SEt] reflects the electron-rich character of the dinuclear iron(II) when ligated by the third bridging ethylthiolate. The Fe-S distances (2.338(2) and 2.320(3) A for complexes 1 and 2, respectively) do not change significantly, but the Fe(II)-Fe(II) distance contracts from 3.505 A in complex 1 to 3.073 A in complex 2. The considerably longer Fe(II)-Fe(II) distance of 3.073 A in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 A in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of pi-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition ([Na.(5)/(2)H(2)O][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)])(n)((1)/(2)O(Et)(2))(n) (3), the Na(+) cations and H(2)O molecules combining with dinuclear [(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)](-) anions create a polymeric framework wherein two CN(-) ligands are coordinated via CN(-)-Na(+)/CN(-)-(Na(+))(2) linkages, respectively.     

Preparation of mesoporous aluminophosphate using poly(amido amine) as template

Mesoporous aluminophosphate was prepared by using G4.0 poly(amido amine)dendrimer as a template and characterized by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption/desorption methods. Results show that the title compound exhibits a typical mesoporous structure with the average pore size from 5 to 8 nm. The formation mechanism of the nanoporous structure using dendrimer as a template was also discussed. __________ Translated from Journal of Fujian Normal University (Natural Science Edition), 2007, 23(2): 67–70 [译自: 福建师范大学学报 (自然科学版)]     

Synthetic approaches to 2-substituted 1-oxo- and 3-oxotetrahydroisoquinolines

2-Substituted homophthalimides 2a-c were reduced regioselectively with sodium borobydride to carbinol-lactam intermediates 3a-c , which were dehydrated, followed by hydrogenation, to give 1-oxo-tetrabydroisoquinolines or 3,4-dihydroisoquinolin-1(2H)ones 5a-c . The isomeric 3-oxo-tetrahydro-isoquinolines or 1,4-dihydroisoquinolin-3(2H)-ones 8a-i were obtained in satisfactory yields via heating 3-isochromanone ( 6 ) with the corresponding amines 7a-i in the presence of aluminum chloride.     

Vapor‐Phase Reaction of Citronellal over Mesoporous Molecular Sieves MCM‐41 and Zeolites

The vapor‐phase reaction of citronellal (CTN) at 220 °C and atmospheric pressure has been studied using mesoporous molecular sieves and zeolites in a fixed‐bed reactor. The primary products included isopulegol (IPG), menthone, and pulegol with subsequent reactions to form cyclic hydrocarbons. The CTN conversion and the product selectivity depend on the acidity and the textural property of catalysts. Lewis and/or Brönsted acid sites are essential for catalyzing this reaction. An increase of SiO₂/Al₂O₃ mol ratio diminishes the acid amount of all catalysts and enhances both the surface area and the structural order of MCM‐41. The catalytic activity follows the order of MCM‐41 > HZSM‐5 > Hβ > USY, in accordance with the relative total acid amount except that of MCM‐41. Despite its low acidity, Si‐MCM‐41 exhibits the best catalytic performance due to its uniform mesopores, large surface area and good stability; the CTN conversion and the IPG yield attain 91.9% and 58.6%, respectively, after at least 25 h time‐on‐stream.     

Elucidating Factors Manipulated the Formation of Multiply Charged Protein Homomultimeric Complexes by Electrospray Ionization

Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)_mⁿ⁺ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)_mⁿ⁺ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH₄OH also promotes the formation of (Cyt c)_mⁿ⁺. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)_mⁿ⁺ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS.     

Synthesis,photophysical and electrochemical studies of di-2-pyridyl ketone complexes of rhodium(III)

Complexes of rhodium(III) with di-2-pyridyl ketone (dpk), Rh(dpk)(MeCN)Cl₃ (1) and cis-[Rh(dpk)₂Cl₂]⁺ (2), have been successfully prepared and characterized. At low temperature (77 K), complex (2) in EtOH/MeOH (4:1, v/v) shows a broad, symmetric and structureless red emission with a microsecond lifetime and, hence, is assigned as the dd* phosphorescence. Electrochemical data, including cyclic voltammetry, normal pulse voltammetry, triple pulse voltammetry and controlled potential electrolysis, have been obtained for the two dpk complexes of rhodium(III) in MeCN. On the basis of analysis of the electrochemical (1,2) and luminescence data (2), electron transfer mechanisms are proposed. For complex (1), two reduction processes occur at the metal-localized orbitals with elimination of chlorides during the first reduction step. This is followed by a one-electron reduction at the metal. For complex (2), three electrons are transferred to the metal in two successive reduction steps accompanied by elimination of two chlorides. After these two reduction steps another one-electron reduction occurs at the dpk ligand.     

Carbon-carbon bond cleavage in the photoionization of ethanol and 1-propanol clusters

Tunable VUV laser was used to initiate the ion-molecule reactions in the clusters of ethanol and 1-propanol by photoionization in the region between 10.49 to 10.08 eV. Ionic products were detected by the time-of-flight mass spectrometer. In addition to the protonated clusters from proton transfer reactions, the products corresponding to beta carbon-carbon bond cleavage were found to be one of the major products for small sizes of clusters. A comparison with photoionization of methanol clusters and the results of ab initio calculation has been made.     

Determination of catecholamines in pheochromocytoma cell (PC-12) culture medium by microdialysis-microbore liquid chromatography

An in vitro microdialysis system was constructed for the measurement of catecholamines in pheochromocytoma cell culture medium. The novel microdialysis device is composed of a petri dish, a dialysis membrane and two transmission tubes. The dialysis membrane is located in the space of a petri dish such that it is immersed in the culture medium. Catecholamines contained in the culture medium diffused into a designed dialysis membrane with sufficient recovery (about 60%). Dialysates were collected by a sampling loop and introduced by an on-line injector to a microbore liquid chromatographic system for analysis of catecholamines. This assay yielded a detection limit of 0.2–0.5 pg/injection with acceptable intra- and inter-assay reproducibilities in 5 μl of dialysates. To evaluate the on-line microdialysis system, PC-12 cells were cultured in a petri dish within an incubator. The baseline concentration of dopamine in PC-12 cell culture medium was about 0.29 ng/ml which was elevated to 2.43 ng/ml after treatment with 0.5 mM potassium cyanide. In conclusion, the present microassay provides for the sensitive, direct measurement of catecholamines in culture medium while minimizing pretreatment procedures for sample preparation.     

A Study of Concentration Polarization on Ion Exchange Membrane Electrodialysis

The concentration polarization phenomena in ion exchange membrane electrodialysis have been studied with single exchange membrane cell. The limiting current densities of Asahi ion-permselective membranes CK-1 and CK-2, Selemion ion-exchange membranes CMV, AMV, DMV and ASV have been measured with Ag-AgCl reversible electrode in various electrolyte solutions under 25°C and constant flow rate. In sodium chloride solution, the cation exchange membrane is easier to occur concentration polarization than the anion exchange membrane. The limiting current density increases as the concentration of solution increases for the same kind of ion exchange membrane. The experimental limiting current densities of Selemion CMV and AMV in NaCl, KCl, MgCl₂, CaCl₂, BaCl₂, Na₂SO₄, NaOH and HCl aqueous solutions are measured. The results show that the limiting current density increases as the ion mobility and diffusivity increase, and is affected by the transference number of ion. For the mixture of electrolyte solution, there are linear relationship between limiting current density and equivalent fraction of electrolytes.