Aggregation behavior of Brij-35/perfluorononanoic acid mixtures

The mixed system of a nonionic hydrocarbon surfactant, polyoxyethylene (23) lauryl ether (Brij-35), and a perfluorinated surfactant, perfluorononanoic acid, was investigated by a combination of methods. The critical micelle concentrations (cmc's) have been determined over a wide range of sample compositions by fluorescence and UV-visible spectrophotometry using pyrene and N-(4-nitrophenyl) perfluorononanamide, respectively, as molecular probes. The values of the cmc's obtained were considerably different with the two techniques employed. Measurements of the (19)F nuclear magnetic resonance chemical shift of the same mixtures showed two breaks in the plots of Δδ(f) versus molar fraction of the perfluorinated surfactant. Conductivity and surface tension measurements also showed two breaks. The behavior is attributed to the formation of mixed micelles that change their composition when the fraction of the fluorinated compound increases and some segregation of the fluorinated compound takes place at a high total surfactant concentration.     

Electrophoretic mobility and molecular distribution studies of poly(amidoamine) dendrimers of defined charges

Generation 5 ethylenediamine (EDA)-cored poly(amidoamine) (PAMAM) dendrimers (E5, E denotes the EDA core and 5 the generation number) with different degrees of acetylation and carboxylation were synthesized and used as a model system to investigate the effect of charge and the influence of dendrimer surface modifications on electrophoretic mobility (EM) and molecular distribution. The surface-modified dendrimers were characterized by size-exclusion chromatography, 1H NMR, MALDI-TOF-MS, PAGE, and CE. The focus of our study was to determine how EM changes as a function of particle charge and molecular mass, and how the molecular distribution changes due to surface modifications. We demonstrate that partially modified dendrimers have much broader migration peaks than those of fully surface functionalized or unmodified E5 dendrimers due to variations in the substitution of individual dendrimer surfaces. EM decreased nonlinearly with increases in surface acetylation for both PAMAM acetamides and PAMAM succinamic acids, indicating a complex migration activity in CE separations that is not solely due to charge/mass ratio changes. These studies provide new insights into dendrimer properties under an electric field, as well as into the characterization of dendrimer-based materials being developed for medical applications.     

Electrophoretic field gradient focusing: an investigation of the experimental parameters

Electrophoretic field gradient focusing has been used to separate the two oxidation states of myoglobin (Mb), and to separate Mb from bromophenol blue (BPB). Polyacrylamide and Sephadex were shown to be suitable packing materials whilst silica led to band broadening with Mb. BPB and Mb could be simultaneously focused apart using either a fixed 21-electrode setup or a dynamic 6-electrode setup. Using a dynamic three-electrode setup either analyte could be focused but not both simultaneously. It was shown that a higher ionic strength buffer in the separation channel compared to the coolant channel enhanced focusing between electrodes due to a conductivity gradient. Different running buffers were investigated and it was found that using a pH 8.6 buffer containing N,N,N-tris(hydroxymethyl)aminomethane (Tris) and phosphate ions the oxidation states of Mb could be separated but the separation of Mb from BPB was not as good as would be hoped for. Using a pH 8.6 buffer containing Tris, N-2-hydroxyethylpiperazine-N'-3-propanesulphonate and chloride ions as running buffer, BPB and Mb could be well separated but the two oxidation states of Mb merged.     

Removal of envelope protein-free retroviral vectors by anion-exchange chromatography to improve product quality

We have investigated the role of the retroviral lipid bilayer and envelope proteins in the adsorption of retroviral vectors (RVs) to a Fractogel DEAE matrix. Intact RVs and their degradation components (envelope protein-free vectors and solubilized vector components) were adsorbed to this matrix and eluted using a linear gradient. Envelope protein-free RVs (Env(-)) and soluble envelope proteins (gp70) eluted in a significantly lower range of conductivities than intact RVs (Env(+)) (13.7-30 mS/cm for Env(-) and gp70 proteins vs. 47-80 mS/cm for Env(+)). The zeta (zeta)-potential of Env(+) and Env(-) vectors was evaluated showing that envelope proteins define the pI of the viral particles (pI (Env(+)) < 2 versus 3 < pI (Env(-)) < 4) and that Env(+) and Env(-) vectors have similar zeta-potentials within pH 5 and 8. The results presented herein indicate that the adsorption of retroviral particles occurs through multi-point interaction of the envelope proteins with the cationic groups on the chromatographic matrix. The strength of this adsorption is thus dependent on the amount of envelope protein present in the viral lipid bilayer. In conclusion, AEXc enables the separation of gp70 proteins as well as envelope protein-free vectors constituting a significant improvement to the quality of retroviral preparations for gene therapy applications.     

Electronic interactions in a new pi-extended tetrathiafulvalene dimer

The first pi-extended tetrathiafulvalene (exTTF) dimer in which the two exTTF units are covalently connected by 1,3-dithiole rings has been obtained in a multistep synthetic procedure involving the Ullmann cross-coupling reaction by using copper(I) thiophene-2-carboxylate (CuTC). The electronic spectrum reveals a significant electronic interaction between the exTTF units. The electrochemical study carried out by cyclic voltammetry in solution and in thin-layer conditions, and the electrochemical simulation and spectroelectrochemical (SEC) measurements confirm the electronic communication and show that the oxidation of dimer 14 occurs as two consecutive 2 e(-) processes D(0)-D(0)-->D(2+)-D(0)-->D(2+)-D(2+). Theoretical calculations, performed at the B3P86/6-31G* level, confirm the experimental findings and predict that 14(2+) exists as a delocalized D(.+)-D(.+) species in the gas phase and as a localized D(2+)-D(0) species in solution (CH(3)CN or CH(2)Cl(2)). Oxidation of 14(2+) forms the tetracation 14(4+) which is constituted by two aromatic anthracene units bearing four aromatic, almost orthogonal 1,3-dithiolium cations.     

Acyclic Schiff base salts derived from 1,3‐diaminopropane and 1,3‐diamino‐2‐hydroxypropane

Two salts of acyclic Schiff base cationic ligands, namely N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride monohydrate, C₁₇H₂₂N₄O₄²⁺·2Cl⁻·H₂O, (I), and 2‐hydroxy‐N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride, C₁₇H₂₂N₄O₅²⁺·2Cl⁻, (II), were synthesized as precursors in order to obtain new acyclic and macrocyclic multidentate ligands and complexes. The cation conformations in compounds (I) and (II) are different in the solid state, although the cations are closely related chemically. Similarly, the hydrogen‐bonding networks involving ammonium cations, hydroxyl groups and chloride anions are also different. In the cation of compound (II), the hydroxyl group is disordered over two sets of sites, with occupancies of 0.785 (8) and 0.215 (8).     

Sc(OTf)3-catalyzed efficient synthesis of beta,beta-bis(indolyl) ketones by the double indolylation of acetic acid 2-methylene-3-oxobutyl ester

In the presence of 5 mol% Sc(OTf)3, double indolylation of acetic acid 2-methylene-3-oxo-butyl ester with differently substituted indoles readily afforded beta,beta-bis(indolyl) ketones. The reaction may proceed via a Sc(OTf)3-catalyzed SN2'-type substitution and subsequent conjugate addition.     

Control of the mutual arrangement of cyclometalated ligands in cationic iridium(III) complexes. Synthesis, spectroscopy, and electroluminescence of the different isomers

Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)(2)(L^L)](+) (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 °C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.     

Mercury speciation in sea food by flow injection cold vapor atomic absorption spectrometry using selective solid phase extraction

An on-line inorganic and organomercury species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS or CV-ETAAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (i.d., 3 mm; length 3 cm) packed to a height of 0.7 cm with a chelating resin aminopropyl-controlled pore glass (550 A) functionalized with [1,5-bis (2 pyridyl)-3-sulphophenyl methylene thiocarbonohydrazyde] placed in the injection valve of a simple flow manifold. Methylmercury is not directly determined. Previous oxidation of the organomercurial species permitted the determination of total mercury. The separation of mercury species was obtained by the selective retention of inorganic mercury on the chelating resin. The difference between total and inorganic mercury determined the organomercury content in the sample. The inorganic mercury was removed on-line from the microcolumn with 6% (m/v) thiourea. The mercury cold vapor generation was performed on-line with 0.2% (m/v) sodium tethrahydroborate and 0.05% (m/v) sodium hydroxide as reducing solution. The determination was performed using CV-AAS and CV-ETAAS, both approaches have been used and compared for the speciation of mercury in sea food. A detection limit of 10 and 6 ng l(-1) was achieved for CV-AAS and CV-ETAAS, respectively. The precision for 10 replicate determinations at the 1 microg l(-1) Hg level was 3.5% relative standard deviation (R.S.D.), calculated from the peak heights obtained. Both approaches were validated with the use of two certified reference materials and by spiking experiments. By analyzing the two biological certified materials, it was evident that the difference between the total mercury and inorganic mercury corresponds to methylmercury. The concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total Hg(2+) and CH(3)Hg(+), according to the t-test for a 95% confidence level. It is amazing how this very simple method is able to provide very important information on mercury speciation.     

Methoxycarbonylation of olefins catalyzed by palladium complexes bearing P,N-donor ligands

The methoxycarbonylation of alkenes catalyzed by palladium(II) complexes with P,N-donor ligands, 2-(diphenylphosphinoamino)pyridine (Ph2PNHpy), 2-[(diphenylphosphino)methyl]pyridine (Ph2PCH2py), and 2-(diphenylphosphino)quinoline (Ph2Pqn) has been investigated. The results show that the complex [PdCl(PPh3)(Ph2PNHpy)]Cl or an equimolar mixture of [PdCl2(Ph2PNHpy)] and PPh3, in the presence of p-toluensulfonic acid (TsOH), is an efficient catalyst for this reaction. This catalytic system promotes the conversion of styrene into methyl 2-phenylpropanoate and methyl 3-phenylpropanoate with nearly complete chemoselectivity, 98% regioselectivity in the branched isomer, and high turnover frequency, even at alkene/Pd molar ratios of 1000. Best results were obtained in toluene-MeOH (3 : 1) solvent. The Pd/Ph2PNHpy catalyst is also efficient in the methoxycarbonylation of cyclohexene and 1-hexene, although with lower rates than with styrene. Related palladium complexes [PdCl(PPh3)L]Cl (L = Ph2PCH2py and Ph2Pqn) show lower activity in the methoxycarbonylation of styrene than that of the 2-(diphenylphosphinoamino)pyridine ligand. Replacement of the last ligand by (diphenylphosphino)phenylamine (Ph2PNHPh) or 2-(diphenylphosphinoaminomethyl)pyridine (Ph2PNMepy) also reduces significantly the activity of the catalyst, indicating that both the presence of the pyridine fragment as well as the NH group, are required to achieve a high performing catalyst. Isotopic labeling experiments using MeOD are consistent with a hydride mechanism for the [PdCl(PPh3)(Ph2PNHpy)]Cl catalyst.