Highly 3,4-Selective Polymerization of Isoprene with NPN Ligand Stabilized Rare-Earth Metal Bis(alkyl)s. Structures and Performances

Deprotonation of (ArNHPPh2NAr2)-N-1 (H[NPN](n), n = 1 - 10) by Ln(CH2SiMe3)(3)(THF)(2) (Ln = Lu, Y, Sc, Er) generated a series of rare-earth metal bis(alkyl) complexes [NPN](n)Ln(CH2SiMe3)(2)(THF)(2) (1-10), which under activation with [Ph3C][B(C6F5)(4)] and AliBu(3) were tested for isoprene polymerization. The correlation between catalytic performances and molecular structures of the complexes has been investigated. Complexes 1-5 and 8, where Ar-1 is nonsubstituted or ortho-alkyl-substituted phenyl, adopt trigonal-bipyramidal geometry. The Ar-1 and Ar-2 rings are perpendicular in 1-4 and 8 but parallel in 5. When Ar-1 is pyridyl, the resultant lutetium and yttrium complexes 9a and 9b adopt tetragonal geometry with the ligand coordinating to the metal ions in a N,N,N-tridentate mode, whereas in the scandium analogue 9c, the ligand coordinates to the Sc3+ ion in a N,N-bidentate mode. These structural characteristics endow the complexes with versatile catalytic performances, With increase of the steric bulkiness of the ortho-substituents Ar-1 and Ar-2, the 3,4-selectivity increased stepwise from 81.6% for lutetium complex 1 to 96.8% for lutetium complex 6 and to 97.8% for lutetium complex 7a. However, further increase of the steric bulk of the ligand led to a slight drop of 3,4-selectivity for the attached complex 5 (95.1%).

Fluorescent conjugated polymer-stabilized gold nanoparticles for sensitive and selective detection of cysteine

We report a new fluorescent detection method for cysteine based on one-step prepared fluorescent conjugated polymer-stabilized gold nanoparticles. The as-prepared fluorescent conjugated polymer-stabilized gold nanoparticles fluoresce weakly due to the fluorescence resonance energy transfer between the fluorophore and the gold nanoparticles. Upon the addition of cysteine, a thiol-containing amino acid, the fluorescence of the colloidal solution increases significantly, indicating that cysteine can modulate the energy transfer between fluorophore and gold. This phenomenon then allows for sensitive detection of cysteine with a limit of detection (LOD) of 25 nM. The linear range of determination of cysteine is from 5 x 10(-8) to 4 x 10(-6) M. None of the other amino acids found in proteins interferes with the determination. Moreover, due to the excellent protecting ability of the fluorescent conjugated polymers, the synthesis of metal nanoparticles and modifying with fluorophores can be accomplished within one step, which makes our method much simpler than conventional methods. We also expect that it will be possible to detect other biologically important analytes based on the fluorescent conjugated polymer-stabilized metal nanoparticles.

Selective hydrogenation of citral with transition metal complexes in supercritical carbon dioxide

The activity and selectivity of the transition metal complexes formed from Ru, Rh, Pd and Ni with triphenylphosphine (TPP) have been investigated for hydrogenation of citral in supercritical carbon dioxide (scCO(2)). High activities are obtained with Ru/TPP and Pd/TPP catalysts, and the overall activity is in the order of Pd approximate to Ru > Rh > Ni. The Ru/TPP complex is highly selective to the formation of unsaturated alcohols of geraniol and nerol. In contrast, the Pd/TPP catalyst is more selective to partially saturated aldehydes of citronellal. Furthermore, the influence of several parameters such as CO2 and H-2 pressures, N-2 pressure and reaction time has been discussed. CO2 pressure has a significant impact on the product distribution, and the selectivity for geraniol and nerol can be enhanced from 27% to 75% with increasing CO2 pressure from 6 to 16 MPa, while the selectivity for citronellol decreases from 70% to 20%. Striking changes in the conversion and product distribution in scCO(2) could be interpreted with variations in the phase behavior and the molecular interaction between CO2 and the substrate in the gas phase and in the liquid phase.

Selective synthesis of mesoporous and nanorod CeVO4 without template

A simple and efficient method has been established for the selective synthesis of mesoporous and nanorod CeVO4 with different precursors by sonochemical method. CeVO4 nanorod can be simply synthesized by ultrasound irradiation of Ce(NO3)(3) and NH4VO3 in aqueous solution without any surfactant or template. While mesoporous CeVO4 with high specific surface area can be prepared with Ce(NO3)(3), V2O5 and NaOH in the same way. Mesoporous CeVO4 has a specific surface area of 122 m(2) g(-1) and an average pore size of 5.2 nm; CeVO4 nanorods have a diameter of about 5 nm, and a length of 100-150 nm. The ultrasound irradiation and ammonia in the reactive solution are two key factors in the formation of such rod-like products. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and differential thermal analyses (DTA), UV/vis absorption spectroscopy and Brunauer-Emmett-Teller (BET) were applied for characterization of the as-prepared products.

An ionic liquid based on a cyclic guanidinium cation is an efficient medium for the selective oxidation of benzyl alcohols

A novel room temperature ionic liquid (RTIL) has been prepared containing a cyclic hexaalkylguanidinium cation. The selective oxidation of a series of substituted benzyl alcohols has been carried out in it, with sodium hypochlorite as the oxidant. The RTIL acts as both phase transfer catalyst (PTC) and solvent. The ionic liquid could be recycled after extraction of the benzaldehyde product with ether.

Carbon nanotubes selective destabilization of duplex and triplex DNA and inducing B-A transition in solution

Single-walled carbon nanotubes (SWNTs) have been considered as the leading candidate for nano-device applications ranging from gene therapy and novel drug delivery to membrane separations. The miniaturization of DNA-nanotube devices for biological applications requires fully understanding DNA-nanotube interaction mechanism. We report here, for the first time, that DNA destabilization and conformational transition induced by SWNTs are sequence-dependent. Contrasting changes for SWNTs binding to poly[dGdC]:poly[dGdC] and poly[dAdT]:poly[dAdT] were observed. For GC homopolymer, DNA melting temperature was decreased 40 degrees C by SWNTs but no change for AT-DNA. SWNTs can induce B-A transition for GC-DNA but AT-DNA resisted the transition. Our circular dichroism, competitive binding assay and triplex destabilization studies provide direct evidence that SWNTs induce DNA B-A transition in solution and they bind to the DNA major groove with GC preference.

Selective separation of yttrium by CA-100 in the presence of a complexing agent

The selective separation of Y from yttrium solution containing small heavy rare earth (HRE) impurities (Ho, Er, Tm, Yb, Lu) by liquid-liquid extraction using CA-100 in the presence of a water-soluble complexing agent of ethylenediaminetetraacetic acid (EDTA) was experimentally studied at 298K. Experiments were carried Out in two feeds, Feed-I: [RE](f) = 4.94 x 10(-3) M, Y = 98.5%, HRE (Ho, Er, Tm, Yb, Lu) = 1.5%; Feed-II: [RE](f) = 4.94 x 10(-3) M, Y = 99.9%, HRE (Ho, Er, Tm, Yb, Lu) = 0.1%, as a function of equilibrium pH (pH(eq)), the concentration ratio of [EDTA]:[HRE impurities]. It was shown that the extraction of HRE in the presence of EDTA was suppressed when compared to that of Y because of the masking effect, while the selective extraction of Y was enhanced and the separation factors increased to maximum at appropriate condition for Feed-I: Y/Ho = 1.53, Y/Er = 3.09, Y/Tm = 5.61, Y/Yb = 12.04, Y/Lu = 27.51 at pH 4.37 and [EDTA]:[HRE impurities] = 4: 1, for Feed-II: Y/Ho = 1.32, Y/Er = 1.91, Y/Tm = 2.00, Y/Yb = 3.05, Y/Lu = 3.33 at pH 4.42 and [EDTA]: [HRE impurities] = 8:1. The separation and purification of Y by this method was discussed.

Selective penetration of liquid-phase organic probe molecules into SAM of 2-mercapto-3-n-octylthiophene

An inherently disorganized self-assembled monolayer (SAM) of 2-mercapto-3-n-octylthiophene (MOT) has been formed on a gold bead electrode from its dilute ethanolic solution. The disorganization of the monolayer is attributed to the loose packing of the aliphatic chains of the MOT adsorbates, which results from a large difference in dimension/or cross-sectional area between the head (thiophene thiolate) and the tail (alkane chain) groups. Electrochemical measurements including ac impedance spectroscopy and metal underpotential deposition have shown that the monolayer is almost pinhole free. However, the MOT SAM can be penetrated by an organic probe molecule with affinity for the alkane chain part of the monolayer. Some typical probe molecules with different size and hydrophilicity have been employed to assess the permselectivity of the monolayer. Measurement results demonstrate that the ability of the employed probe molecules to penetrate into the monoalyer is mainly dominated by their hydrophilicity/or hydrophobicity. The results presented here suggest the potential application of MOT monoalyer to effectively modify the electrode surface for several research areas such as electrochemical sensors, electrocatalysis, electroanalysis, and supported hybrid bilayer membranes.

Helix-sense-selective polymerization of N,N-diphenyl (meth)acrylamide by anionic catalysts

In this paper, the helix-sense-selective polymerization of N,N-diphenyl acrylamide (DPAA) and N,N-diplienyl methacrylamide(DPMAA) were studied with living helix prepolymer as anionic initiator, and the chiral optical properties of the obtained polymers were investigated too. It was shown that optically active polymers of DPAA and DPMAA could be obtained under the experimental condition, and exhibited the same screw sense as that of the prepolymer.

Selective crystallization of BaF2 under a compressed Langmuir monolayer of behenic acid

Selective crystallization of BaF2 crystals under a compressed Langmuir monolayer of behenic acid [CH3(CH2)(20)COOH] has been studied by using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. It was found that, in the absence of a monolayer, three kinds of crystals (Ba2ClF3, BaClF, and BaF2) can be obtained by mixing BaCl2 with a NH4F solution. However, in the presence of the monolayer of behenic acid, only BaF2 crystals appear at the monolayer-subphase interface and crystals have a special crystal face (100). During this process of crystallization, the monolayer plays a very important role and acts as a template that can preferentially select a special crystal and a special crystal face. The above results can be explained in terms of a specific molecular interaction between ions and the headgroups of the monolayer and specific electrostatic, geometric, and stereochemical interactions at the organic-inorganic interface.

A simple method for the selective enrichment of endohedral metallofullerenes

The concentration of a polar solvent DMF extract was found to be very effective for the selective enrichment of endohedral metallofullerenes against empty fullerenes. As the solvent evaporated, endohedral metallofullerenes were effectively enriched in the solution, while most of empty fullerenes (especially C-60 and C-70) were precipitated because of their scant solubility in DMF. Matrix-assisted laser-desorption-ionization time-of-fligh mass spectrometry analysis indicated that the purity of endohedral metallofullerenes increased dramatically after concentration of the DMF extract solution. Upon transferring the extract into toluene, a solution containing significantly enriched endohedral metallofullerenes was obtained. The different solubilities of endohedral metallofullerenes versus empty fullerenes are considered to account for this selective enrichment of endohedral metallofullerenes.

INVESTIGATION ON SELECTIVE DOPING OF POLYANILINE ENCAPSULATED IN THE CHANNELS OF ZEOLITE MOLECULAR-SIEVES

The aniline encapsulated in the channels of zeolite molecular sieves was polymerized electrochemically. The doping reaction of polyaniline was studied in 12-Molybdophosphoric acid and sulfuric acid solution. The results indicate the zeolite modified ele

HIGHLY SENSITIVE AND SELECTIVE DETERMINATION OF RIBOFLAVIN BY FLOW-INJECTION ANALYSIS USING PARALLEL DUAL-CYLINDER MICROELECTRODES

A novel wall-jet cell with parallel dual cylinder (PDC) microelectrodes was constructed and used for flow injection analysis (FLA). The detector takes the advantages of ''redox recycling'' between bipotentiostated microcylinder electrodes (- 0.4 V/SCE an

An electrochemical DNA sensor based on electrodepositing aluminum ion films on stearic acid-modified carbon paste electrode and its application for the detection of specific sequences related to bar gene and CP4 Epsps gene

An electrochemical DNA biosensor was fabricated by immobilizing DNA probe on aluminum ion films that were electrodeposited on the surface of the stearic acid-modified carbon paste electrode (CPE). DNA immobilization and hybridization were characterized with cyclic voltammetry (CV) by using methylene blue (MB) as indicator. MB has a couple of well-defined voltammetric redox peaks at the CPE. The currents of redox peaks of MB decreased after depositing aluminum ion films on the CPE (Al(III)/CPE) and increased dramatically after immobilizing DNA probe (ssDNA/Al(III)/CPE). Hybridization of DNA probe led to a marked decrease of the peak currents of MB, which can be used to detect the target single-stranded DNA. The conditions for the preparation of Al(III)/CPE, and DNA immobilization and hybridization were optimized. The specific sequences related to bar transgene in the transgenic corn and the PCR amplification of CP4 epsps gene from the sample of transgenic roundup ready soybean were detected by differential pulse voltammetry (DPV) with this new electrochemical DNA biosensor. The difference between the peak currents of MB at ssDNA/Al(III)/CPE and that at hybridization DNA modified electrode (dsDNA/Al(III)/CPE) was applied to determine the Specific sequence related to the target bar gene with the dynamic range comprised between 1.0 X 10(-7) mol/L to 1.0 x 10(-4) mol/L. A detection limit of 2.25 x.10(-8) mol/L. of oligonucleotides can be estimated.