Routes to metallodendrimers: synthesis of isomeric neutral metallomacromolecules based on bis(2,2':6',2"-terpyridine)ruthenium(II) connectivity

Routes for the syntheses of isomeric, zwitterionic, bisterpyridine-Ru(II)-based macromolecules are described. Access to these novel architectures is facilitated by the construction of terpyridine-modified, 1-->3 C-branched, ester-terminated building blocks. Constitutional isomers result from the interchangable placement of methyl and tert-butyl ester groups on both the branched framework near the Ru(II) centers and the termini of the branched construct. Water solubility is imparted to each isomer through selective transformation of the tert-butyl esters to their corresponding carboxylates. Along with the standard characterization techniques, electrochemical and spectroscopic data also support the structural formation.     

Determination of antiferromagnetic exchange coupling in the tetrahedral thiolate-bridged diferrous complex [Fe2(SEt)6]2-

Protein-bound iron-sulfur clusters and their synthetic analogues are characterized by tetrahedral metal sites, multiple oxidation levels, and exchange coupling. The recent attainment of several all-ferrous protein clusters and the presence of sulfide- and thiolate-bridged sites in the all-ferrous state of the nitrogenase P-cluster provides an imperative for determination of exchange coupling between tetrahedral Fe(II) sites with sulfur bridges. The cluster in the previously reported compound (Et(4)N)(2)[Fe(2)(SEt)(6)] is centrosymmetric with distorted tetrahedral coordination and a planar Fe(2)(mu-SEt)(2) bridge unit. The compound is diamagnetic at 4.2 K, indicating antiferromagnetic coupling. The lower limit J > 80 cm(-)(1) (H = JS(1).S(2)) is obtained by M?ssbauer spectroscopy. Analysis of magnetic susceptibility data affords J = 165 +/- 15 cm(-)(1). It is noteworthy that the J value of the diferrous pair obtained here is comparable to the J values reported for the mixed-valence state of plant-type Fe(2)S(2) ferredoxins. The near temperature independence of the quadrupole splitting (DeltaE(Q) = 3.25 mm/s at 4.2 K and 3.20 mm/s at 180 K) indicates that no excited orbital states are appreciably populated at temperatures less than 300 K. The paramagnetism arises solely from thermal population of the S = 1 state of the spin ladder. This work provides the only measure of antiferromagnetic coupling by Fe(II) pairs in a tetrahedral sulfur environment.     

Practical and robust method for regio- and stereoselective preparation of (E)-ketene tert-butyl TMS acetals and beta-ketoester-derived tert-butyl (1Z,3E)-1,3-bis(TMS)dienol ethers

We developed an efficient, practical, robust method for the regio- and stereoselective preparation of (E)-ketene trimethylsilyl acetals (KSAs) derived from tert-butyl esters 1. The reaction was performed under convenient reaction conditions; LDA-TMSCl, 0-5 degrees C, and cyclopentyl methyl ether (CPME) solvent. Two kinds of (Z)- and (E)-KSAs derived from alpha-oxygen and alpha-nitrogen-substituted tert-butyl esters, respectively, were also obtained in good yield. The present protocol was successfully applied to a stereocontrolled preparation of useful, but highly reactive (less accessible) beta-ketoester-derived tert-butyl (1Z,3E)-1,3-bis(TMS)dienol ethers 2.     

HPLC-electrospray ionization-MS-MS analysis of Cephalotaxus harringtonia leaves and enhancement of the extraction efficiency of alkaloids therein by SFE

A high-performance liquid chromatographic method is developed for use in the electrospray mass spectrometric (MS)-MS analysis of alkaloids contained in Cephalotaxus harringtonia leaves. Nine alkaloids having ester groups can be separated and detected with good sensitivity. The MS and MS-MS spectra obtained provides information on their chemical structures. Supercritical fluid extraction is also applied in order to improve the extraction efficiency of Cephalotaxus alkaloids such as cephalotaxine, harringtonine, homoharringtonine, and isoharringtonine. When carbon dioxide-methanol-water (80:18:2, v/v) is used the extraction yield is found to be higher than that using the other supercritical solvents evaluated and conventional organic solvent extraction.     

Efficient synthesis of a configurationally stable l-serinal derivative

An efficient synthesis of a configurationally stable l-serinal derivative 8 was achieved using an N-hydroxymethyl group in about 50% overall yield in four steps from l-serine. Not more than 1% racemization was observed during the preparation of 8. Its enantiomeric integrity was maintained for at least 15 days at room temperature, and it was stable on silica gel. The orthogonal protective groups of 8 would make it a useful chiral synthon.     

Disposable amperometric glucose sensor electrode with enzyme-immobilized nitrocellulose strip

Electrochemical properties of screen-printed carbon paste electrodes (CPEs) with a glucose oxidase-immobilized and hexamineruthenium (III) chloride ([Ru(NH₃)₆]³⁺) containing nitrocellulose (NC) strip were examined. The NC strip (2×8 mm) placed on the CPEs printed on polyester (PE) film is tightly sealed using another PE film on the top with open edges on both sides. Samples containing macromolecules and particles (e.g. proteins and blood cells) are applied at one edge of the NC strip and reach the detection area, chromatographically separating small molecules (e.g. glucose, ascorbate, acetaminophen, and uric acid) of analytical interests. Since sample volumes and the amount of catalytic reagents (mediator and glucose oxidase) are precisely predefined by the dimension and pore size (8 μm) of the NC strip, the sensor-to-sensor reproducibility and accuracy of analysis are greatly improved. The use of [Ru(NH₃)₆]³⁺ mediator, which exhibits characteristic substantially lowers the applied potential (0.0 V vs Ag/AgCl) for glucose determination and eliminates the interference from other oxidizable species, providing improved analytical results.     

Effect of metal ions on the stability of metallothionein in the degradation by cellular fractions in vitro

Metallothioneins (MT), small molecular weight metal binding proteins are known to play an important protective role against heavy metal toxicity, either as antioxidants or pre-oxidants. However, the mode of metabolic fate of MTs in various metal complexes is not clearly understood. This study was carried out to better understand the mode of selective turnover rate of various form of MT in complexes with different metals. The degradation of in vitro translated mouse 35S-cysteine-MT was examined in lysosomal or cytosolic fractions from mouse liver by gel electrophoresis and autoradiography. Overnight incubations of MT showed extensive proteolysis in the lysosomal fraction but not in cytosolic fractions. However, Cu2+-MT was found to be stable under the same experimental condition. In contrast, Zn did not interfere with MT degradation. These results suggest that lysosomes are chiefly responsible for MT removal and appears to be selective on the metals involved in the MT complex. In vitro, translated, radiolabeled MT provides a suitable substrate for investigating the characteristics of MT degradation.     

Diastereoselectivity control in photosensitized addition of methanol to (R)-(+)-limonene

Highly diastereodifferentiating bimolecular asymmetric photoreaction was achieved in the photosensitized polar addition of methanol to (R)-(+)-limonene. The diastereomeric excess (de) of the photoadduct could be controlled and fine-tuned by changing the internal/external factors such as solvent polarity, reaction temperature, and structure of the sensitizers. The de increased from 23% obtained upon xylene photosensitization in pure methanol at room temperature to >96% upon singlet sensitization with methyl benzoate at -75 degrees C in 0.5 M methanol/diethyl ether solution.     

Counterion-dye staining method for DNA in agarose gels using crystal violet and methyl orange

Sensitive and safe methods for visualization of DNA in agarose gels are described. 0.001% crystal violet dissolved in distilled water was used for DNA staining on agarose gels and it could detect as little as 16 ng of DNA (3 kb, pGem-7Zf/EcoRI) without destaining procedure. The detection limit is four times lower than that of ethidium bromide. To improve the sensitivity, we studied a counterion-dye staining method using methyl orange as a counterion-dye which contributes to reduce excessive background staining by crystal violet. Dye concentration, pH of staining solution, mixing molar ratio of two dyes, and staining times were optimized for the counterion-dye staining. By the staining with a mixed solution of 0.0025% crystal violet and 0.0005% methyl orange in distilled water, 8 ng of the 3 kb DNA in an agarose gel was detected within 30 min.     

Synthesis and structure of ruthenium-silylene complexes: activation of Si-Cl bonds in N-heterocyclic silanes

Ru(0) complexes of bis(imino)pyridine ligands, [eta2-N3]Ru(eta6-Ar) and {[N3]Ru}2(mu-N2), where Ar = C6H6 or C6H5Me and [N3] = 2,6-(MesN=CMe)2C5H3N, react with N-heterocyclic silicon(IV) compounds to yield Ru(II) silylene complexes of the type [N3]Ru(X)(Cl){Si(NN)} (X = H, Cl, and Si(NN) = N,N'-bis(neopentyl)-1,2-phenylenedi(amino)silylene). The activation of two groups on the silane occurs in a stepwise fashion: initial oxidative addition of a Si-X bond, followed by 1,2-migration (alpha-elimination) of the Si-Cl group to the metal. Reversible dissociation from the Ru(II) center leads to free silylene, which can be preferentially trapped with Ru(0) complexes to generate a zero-valent silylene complex, [N3]Ru(N2){Si(NN)}, which also contains a terminal dinitrogen ligand.