Characterization of surfactant and phospholipid vesicles for use as pseudostationary phases in electrokinetic chromatography

The physical, electrophoretic and chromatographic properties (mean diameter, electroosmotic flow, electrophoretic mobility, elution range, efficiency, retention, and hydrophobic, shape, and chemical selectivity) of three surfactant vesicles and one phospholipid vesicle were investigated and compared to a conventional micellar pseudostationary phase comprised of sodium dodecyl sulfate (SDS). Chemical selectivity (solute-pseudostationary phase interactions) was discussed from the perspective of linear solvation energy relationship (LSER) analysis. Two of the surfactant vesicles were formulated from nonstoichiometric aqueous mixtures of oppositely charged, single-tailed surfactants, either cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) in a 3:7 mole ratio or octyltrimethylammonium bromide (OTAB) and SDS in a 7:3 mole ratio. The remaining surfactant vesicle was comprised solely of bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in 10% v/v methanol, and the phospholipid vesicle consisted of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and phosphatidyl serine (PS) in 8:2 mole ratio. The mean diameters of the vesicles were 76.3 nm (AOT), 86.9 nm (CTAB/SOS), 90.1 nm (OTAB/SDS), and 108 nm (POPC/PS). Whereas the coefficient of electroosmotic flow (10(-4) cm2 V(-1) s(-1)) varied considerably (1.72 (OTAB/SDS), 3.77 (CTAB/SOS), 4.05 (AOT), 5.26 (POPC/PS), 5.31 (SDS)), the electrophoretic mobility was fairly consistent (-3.33 to -3.87 x 10(-4) cm2 V(-1) s(-1)), except for the OTAB/SDS vesicles (-1.68). This resulted in elution ranges that were slightly to significantly larger than that observed for SDS (3.12): 3.85 (POPC/PS), 8.6 (CTAB/SOS), 10.1 (AOT), 15.2 (OTAB/SDS). Significant differences were also noted in the efficiency (using propiophenone) and hydrophobic selectivity; the plate counts were lower with the OTAB/SDS and POPC/PS vesicles than the other pseudostationary phases (< or = 75,000/m vs. > 105,000/m), and the methylene selectivity was considerably higher with the CTAB/SOS and OTAB/SDS vesicles compared to the others (ca. 3.10 vs. < or = 2.6). In terms of shape selectivity, only the CTAB/SOS vesicles were able to separate all three positional isomers of nitrotoluene with near-baseline resolution. Finally, through LSER analysis, it was determined that the cohesiveness and hydrogen bond acidity of these pseudostationary phases have the greatest effect on solute retention and selectivity.     

Effect of surfactant concentration and buffer selection on chromatographic figures of merit in chiral microemulsion electrokinetic chromatography

The enantiomeric resolution of 15 different pharmaceutical compounds was explored using chiral microemulsion electrokinetic chromatography (MEEKC). The microemulsion employed was comprised of the chiral surfactant dodecoxycarbonylvaline (DDCV), 1-butanol, and ethyl acetate, at an initial composition of 1% w/v:1.2% v/v:0.5% v/v, respectively. The effect of varying the background buffer composition, voltage, and ultimately the surfactant concentration and/or aggregate phase ratio were examined. Changing from a zwitterionic buffer ((2-[2-amino-2-oxoethyl)amino]ethanesulfonic acid, ACES) to the same concentration of phosphate buffer improved the efficiency and decreased overall analysis time, but also resulted in a decrease in chiral resolution. Furthermore, using phosphate buffer while simultaneously increasing the percent DDCV from 1 to 4% increased the efficiencies from a range of 34,000 to 59,000 N/m to a range of 160,000 to 400,000 N/m. While the enantioselectivities did not change significantly, the improvement in efficiencies, elution range, and retention factors provided an increase in both resolution and the number of enantiomers that were separated. Using an optimized microemulsion comprised of phosphate buffer and 4% DDCV, chiral separation was achieved for all 11 pairs of enantiomers, with a resolution ranging from 0.90 to 4.71. Moreover, the average resolution doubled in going from nonoptimized to optimized conditions for five of the eleven compounds. Finally, a comparison was made of the effect of increasing only the surfactant concentration by a factor of 4 versus increasing the overall composition (or phase ratio) by a factor of 4. Ultimately, the microemulsion containing 4% DDCV provided a larger elution range, greater resolution, and more optimal retention than that provided by the 4x phase increase.     

An Overview of Modified Chitosan Adsorbents for the Removal of Precious Metals Species from Aqueous Media

This mini-review provides coverage of chitosan-based adsorbents and their modified forms as sustainable solid-phase extraction (SPE) materials for precious metal ions, such as gold species, and their complexes in aqueous media. Modified forms of chitosan-based adsorbents range from surface-functionalized systems to biomaterial composites that contain inorganic or other nanomaterial components. An overview of the SPE conditions such as pH, temperature, contact time, and adsorbent dosage was carried out to outline how these factors affect the efficiency of the sorption process, with an emphasis on gold species. This review provides insight into the structure-property relationships for chitinaceous adsorbents and their metal-ion removal mechanism in aqueous media. Cross-linked chitosan sorbents showed a maximum for Au(III) uptake capacity (600 mg/g), while S-containing cross-linked chitosan display favourable selectivity and uptake capacity with Au(III) species. Compared to industrial adsorbents such as activated carbon, modified chitosan sorbents display favourable uptake of Au(III) species, especially in aqueous media at low pH. In turn, this contribution is intended to catalyze further research directed at the rational design of tailored SPE materials that employ biopolymer scaffolds to yield improved uptake properties of precious metal species in aqueous systems. The controlled removal of gold and precious metal species from aqueous media is highly relevant to sustainable industrial processes and environmental remediation.     

A one-bead, one-stock solution approach to chemical genetics: part 2

BACKGROUND: Chemical genetics provides a systematic means to study biology using small molecules to effect spatial and temporal control over protein function. As complementary approaches, phenotypic and proteomic screens of structurally diverse and complex small molecules may yield not only interesting individual probes of biological function, but also global information about small molecule collections and the interactions of their members with biological systems. RESULTS: We report a general high-throughput method for converting high-capacity beads into arrayed stock solutions amenable to both phenotypic and proteomic assays. Polystyrene beads from diversity-oriented syntheses were arrayed individually into wells. Bound compounds were cleaved, eluted, and resuspended to generate 'mother plates' of stock solutions. The second phase of development of our technology platform includes optimized cleavage and elution conditions, a novel bead arraying method, and robotic distribution of stock solutions of small molecules into 'daughter plates' for direct use in chemical genetic assays. This library formatting strategy enables what we refer to as annotation screening, in which every member of a library is annotated with biological assay data. This phase was validated by arraying and screening 708 members of an encoded 4320-member library of structurally diverse and complex dihydropyrancarboxamides. CONCLUSIONS: Our 'one-bead, multiple-stock solution' library formatting strategy is a central element of a technology platform aimed at advancing chemical genetics. Annotation screening provides a means for biology to inform chemistry, complementary to the way that chemistry can inform biology in conventional ('investigator-initiated') small molecule screens.     

A matrix isolation study of the photochemically induced reactions of nitrogen dioxide with 1,2-dibromoethene and 1,2-dichloroethene using Fourier transform infrared spectroscopy

Photolyses of matrices of either BrCHCHBr/NO2/Ar or ClCHCHCl/NO2/Ar using quartz-filtered radiation (lambda>240 nm) led to the appearance of infrared bands attributable to carbonyl, carbon monoxide, and ketene species; no bands belonging to a precursor complex NO2cdots, three dots, centeredXCHCHX (where X=Br or Cl) were observed upon matrix deposition. The possible reaction pathway is discussed.     

Primary ion beam energy effects on secondary ion emission from Ni(001)c(2 × 2)-CO: Classical dynamics calculations and sims

The variation of the SIMS spectra of Ni(001)c(2 × 2)-CO induced by bombardment of Ar⁺ primary ions with kinetic energy between 300 and 1200 eV has been examined in detail. The purpose of the study is to examine the influence of primary ion energy on a number of experimental observables and to test the accuracy of classical dynamics calculations for neutral particles in predicting the experimental results for ejected ions. The calculations were performed using two extreme forms of the Ar⁺ -substrate interaction potential to examine the sensitivity of the results to the parameters that need to be included in the model. We find excellent agreement between the NiCO⁺/Ni⁺ ion yield ratio measured between 300–1200 eV Ar⁺ ion energy and the computational results if the Molière form of the ion-substrate potential is used and if the calculated results are corrected by including an image force. The calculated angular distributions of the ejected particles also agree well with those observed experimentally. From the calculations we see that the extent of CO fragmentation relative to the amount of molecular CO ejection is roughly constant in the 300–1200 eV beam energy range with a slight increase seen at lower (~ 300 eV) energies. The implications of these results are discussed in terms of our ability to study the chemistry and structure of surfaces with SIMS.     

Room temperature electrical conductivity of a highly two dimensional synthetic metal: AsF5-graphite

We report here studies at room temperature of the electrical conductivity of AsF₅-graphite, a lamellar intercalation compound. Compounds with composition C_8nAsF₅ have been synthesized where n is the stage. Preliminary measurements of basal plane electrical conductivities indicating values comparable with OFHC copper have been confirmed. Associated anisotropy ratios $\text{α ≡}\text{σ}{}_{\mathrm{<mtext>a</mtext>}}\text{σ}{}_{\mathrm{<mtext>c</mtext>}}\text{> 10}{}^6$ are observed for n ≤ 3. Data for both the a-axis and c-axis conductivities as a function of stage for low stage compounds is reported.     

Synthesis of Ln(III) chloride tetraphenylporphyrin complexes

The isolation and identification of the first examples of anhydrous lanthanide chloride tetraphenylporphyrin complexes have been described. The purple complexes were generated by the reaction of dilithiotetraphenylporphyrin bis(dimethoxyethane) with lanthanide trichloride tris(tetrahydrofuran) salts to yield the products in up to 85% yield. The crystal structures for the holmium and ytterbium complexes are also presented.     

Phenotyping Reveals Targets of a Pseudo-Natural-Product Autophagy Inhibitor

Pseudo-natural-product (NP) design combines natural product fragments to provide unprecedented NP-inspired compounds not accessible by biosynthesis, but endowed with biological relevance. Since the bioactivity of pseudo-NPs may be unprecedented or unexpected, they are best evaluated in target agnostic cell-based assays monitoring entire cellular programs or complex phenotypes. Here, the Cinchona alkaloid scaffold was merged with the indole ring system to synthesize indocinchona alkaloids by Pd-catalyzed annulation. Exploration of indocinchona alkaloid bioactivities in phenotypic assays revealed a novel class of azaindole-containing autophagy inhibitors, the azaquindoles. Subsequent characterization of the most potent compound, azaquindole-1, in the morphological cell painting assay, guided target identification efforts. In contrast to the parent Cinchona alkaloids, azaquindoles selectively inhibit starvation- and rapamycin-induced autophagy by targeting the lipid kinase VPS34.