New synthesis of 3′-deoxypurine nucleosides using samarium(III) iodide complex

Regio- and stereoselective iodinative cleavage of 2′,3′-anhydropurine nucleosides was achieved with samarium diiodide and ethyl bromoacetate to produce the corresponding 3′-iodopurine nucleosides, which were then converted to 3′-deoxypurine nucleosides including the natural product cordycepin.     

Lithium isotope separation by chemical exchange with polymer-bound azacrown compounds

The chromatographic separation of lithium isotopes was investigated by chemical exchange with the recently synthesized polymer-bound dibenzo pyridino diamide azacrown (DBPDA) and reduced dibenzo pyridino diamide azacrown (RDBPDA). Column chromatography was employed for the determination of the effect of solvents and ligand conformation on the separation coefficients. The maximum separation coefficients, , for the DBPDA and RDBPDA at 20.0±0.02°C with acetonitrile as eluent, were found to be 0.034±0.002 and 0.035±0.002, respectively. The isotope separation coefficient and adsorption capability of the lithium ion on the DBPDA and RDBPDA were only slightly dependent on ligand structure, but strongly dependent on the solvent. DBPDA and RDBPDA appeared to have almost the same value for the isotope separation coefficient of lithium.     

A convergent approach to huperzine A and analogues

We describe a concise and convergent synthesis of (rac)-5-methoxy-6-azatricyclco[7.3.1.0(2,7)]trideca-2(7),3,5,11-tetraen-13-ol, which has the basic ring system of huperzine A, a potent inhibitor of acetylcholinesterase. We also describe the synthesis of the novel system 5-methoxy-6-azatricyclo[7.2.2.0(2,7)]trideca-2(7),3,5-trien-10-one and a series of related systems.     

Hydrogen peroxide oxidation of di(hydroxo)platinum(II) species in carboxylic acids

A facile procedure for synthesizing the mono(hydroxo)tris(carboxylato)platinum(IV) species has been achieved. The reaction of [Pt^II(OH)₂(dmpda)] (dmpda=2,2-dimethyl-1,3-propanediamine) with a 30% aqueous solution of H₂O₂ in the presence of a carboxylic acid produces a stable [Pt^IV(OOCR)₃(OH)(dmpda)] (R=Me, Et) complex in high yield. The crystal structures of [Pt^IV(OOCMe)₃(OH)(dmpda)] . H₂O (triclinic P1 bar, a=8.761(2) Å, b=9.245(3) Å, c=10.659(2) Å, =106.25(2)°, =93.90(2)°, =98.92(2)°, V=813.1(3) ų, Z=2, R= 0.0474) and [Pt^IV(OOCEt)₃(OH)(dmpda)] (monoclinic P2₁/c, a=12.777(4) Å, b=10.514(2) Å, c=14.971(3) Å, =107.40(2)°, V=1919.2(8) ų, Z=4, R=0.0611) show that the hydroxyl group has been selectively positioned at an axial site. The intramolecular hydrogen bond between the OH and C=O moiety exists (O(H)...=C, 2.83 Å for [Pt^IV(OOCMe)₃(OH)(dmpda)] · H₂O; 2.72 Å for [Pt^IV(OOCEt)₃(OH)(dmpda)]. Formation of the axial-mono(hydroxo)tris(carboxylato)platinum(IV) species may be ascribed to a combination of `reactive-equatorial effects' with `cis-addition' in the carboxylic acid.     

Surface modulation of magnetic nanocrystals in the development of highly efficient magnetic resonance probes for intracellular labeling

High-quality biocompatible magnetic iron oxide (Fe3O4) nanocrystals were developed through a ligand exchange process of hydrophobically capped nanocrystals with hydrophilic molecules. By simple modulation of the nanocrystal surface ligand charge properties, we have been able to prepare magnetic nanocrystals with excellent intracellular labeling capabilities that efficiently label a variety of cell types without the need for additional transport facilitating agents. The excellent intracellular labeling capability of the newly developed cationic WSIO has further led to successful MRI monitoring of the migration of neural stem cells in rat spinal cord. The magnetic nanocrystals developed here have great potential in applications for labeling of various cell types and also the monitoring of cell-based medical treatments and cancer metastasis.     

catena‐Poly[[copper(II)‐μ‐2‐[bis­(2‐pyridylmeth­yl)amino]butyrato‐κ4N,N′,N′′,O:κO′] perchlorate]

The copper(II) ion in the syn–anti carboxyl­ate‐bridged one‐dimensional zigzag chain title complex, {[Cu(C₁₆H₁₈N₃O₂)]ClO₄}_n, exhibits a distorted trigonal–bipyramidal environment. Two N atoms and one carboxyl­ate O atom of the ligand form the basal plane, while the axial positions are filled by an N atom of the ligand and one O atom belonging to the carboxyl­ate group of an adjacent mol­ecule. The crystal packing is enhanced by C—H⋯O(perchlorate) hydrogen bonds.     

Regioselective coupling of pentafluorophenyl substituted alkynes: mechanistic insight into the zirconocene coupling of alkynes and a facile route to conjugated polymers bearing electron-withdrawing pentafluorophenyl substituents

The reaction of Cp(2)ZrCl(2) with 2 equiv of BuLi at -78 degrees C, followed by the addition of an unsymmetrical tetra- or pentafluorophenyl substituted alkyne R(1)C[triple bond]CAr(f) (R(1), Ar(f) = (CH(2))(4)Me, p-C(6)F(4)H; Me, p-C(6)F(4)H; Ph, C(6)F(5)), resulted in regioselective couplings of these alkynes to zirconacyclopentadienes in which the Ar(f) substituents preferentially adopt the 3,4-positions (beta beta) of the zirconacyclopentadiene ring. With Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) as the zirconocene reagent, the couplings could be carried out at room temperature; however, at higher temperatures significant quantities of the 2,4-fluoroaryl substituted (alpha beta) isomers were also formed. None of the conditions employed produced the 2,5-fluoroaryl substituted (alpha alpha) isomers. These fluoroaryl-substituted zirconacyclopentadienes were readily converted to butadienes via reactions with acids. The zirconacyclopentadiene Cp(2)ZrC(4)-2,5-Ph(2)-3,4-(C(6)F(5))(2), which resulted from the coupling of PhC[triple bond]C(C(6)F(5)), was converted to the corresponding thiophene by reaction with S(2)Cl(2), and to an arene by reaction with MeO(2)CC[triple bond]CCO(2)Me/CuCl. Mechanistic studies on zirconocene couplings of (p-CF(3)C(6)H(4))C[triple bond]C(p-MeC(6)H(4)) indicate that the observed regioselectivities are determined by an electronic factor that controls the orientation of at least one of the two alkynes as they are coupled. Additionally, these studies suggest an unsymmetrical transition state for the zirconocene coupling of alkynes, and this is supported by DFT calculations. The reaction of [(C(6)F(5))C[triple bond]CCH(2)](2)CH(2) with Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) resulted in a zirconacyclopentadiene in which the pentafluorophenyl substituents have been forced into the 2,5-positions (alpha alpha). Zirconocene coupling of the diyne (C(6)F(5))C[triple bond]C-1,4-C(6)H(4)-C[triple bond]C(C(6)F(5)) provided a route to conjugated polymers bearing electron-withdrawing pentafluorophenyl groups.     

Xanthine Sensors Based on Anodic and Cathodic Detection of Enzymatically Generated Hydrogen Peroxide

A xanthine biosensor was fabricated by the covalent immobilization of xanthine oxidase (XO) onto a functionalized conducting polymer (Poly‐5, 2′: 5′, 2″‐terthiophine‐3‐carboxylic acid), poly‐TTCA through the formation of amide bond between carboxylic acid groups of poly‐TTCA and amine groups of enzyme. The immobilization of XO onto the conducting polymer (XO/poly‐TTCA) was characterized using cyclic voltammetry, quartz crystal microbalance (QCM), and X‐ray photoelectron spectroscopy (XPS) techniques. The direct electron transfer of the immobilized XO at poly‐TTCA was found to be quasireversible and the electron transfer rate constant was determined to be 0.73 s^?1. The biosensor efficiently detected xanthine through oxidation at +0.35 V and reduction at ?0.25 V (versus Ag/AgCl) of enzymatically generated hydrogen peroxide. Various experimental parameters, such as pH, temperature, and applied potential were optimized. The linear dynamic ranges of anodic and cathodic detections of xanthine were between 5.0×10^?6?1.0×10^?4 M and 5.0×10^?7 to 1.0×10^?4 M, respectively. The detection limits were determined to be of 1.0×10^?6 M and 9.0×10^?8 M with anodic and cathodic processes, respectively. The applicability of the biosensor was tested by detecting xanthine in blood serum and urine real samples.     

End-labeled free-solution electrophoresis of DNA

DNA is a free-draining polymer. This subtle but "unfortunate" property of highly charged polyelectrolytes makes it impossible to separate nucleic acids by free-flow electrophoresis. This is why one must typically use a sieving matrix, such as a gel or an entangled polymer solution, in order to obtain some electrophoretic size separation. An alternative approach consists of breaking the charge to friction balance of free-draining DNA molecules. This can be achieved by labeling the DNA with a large, uncharged molecule (essentially a hydrodynamic parachute, which we also call a drag-tag) prior to electrophoresis; the resulting methodology is called end-labeled free-solution electrophoresis (ELFSE). In this article, we review the development of ELFSE over the last decade. In particular, we examine the theoretical concepts used to predict the ultimate performance of ELFSE for single-stranded (ssDNA) sequencing, the experimental results showing that ELFSE can indeed overcome the free-draining issue raised above, and the technological advances that are needed to speed the development of competitive ELFSE-based sequencing and separation technologies. Finally, we also review the reverse process, called free-solution conjugate electrophoresis (FSCE), wherein uncharged polymers of different sizes can be analyzed using a short DNA molecule as an electrophoretic engine.     

Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.