Effect of microemulsion component purity on the chromatographic figures of merit in chiral microemulsion electrokinetic chromatography

Numerous combinations of one-, two-, and three-chiral-component microemulsions have been previously prepared in our group, using N-dodecoxycarbonylvaline (DDCV), 2-hexanol, and ethyl acetate, dibutyl tartrate, or diethyl tartrate. A few results of the various formulations investigated suggested the possible presence of minor impurities in one or more components of the microemulsion. In this study, the purity of the current lots of R- and S-surfactant were measured, as was the subsequent effect of minor impurities on the relevant chromatographic figures of merit (CFOMs) that describe a chiral separation, i.e., efficiency, enantioselectivity, retention, migration window (elution range), and resolution. Two related methods are proposed for correcting enantioselectivities measured in the presence of chiral impurities in the chiral microemulsion.     

The development and inter-laboratory verification of LC-MS libraries for organic chemicals of environmental concern

The development, verification, and comparison study between LC-MS libraries for two manufacturers’ instruments and a verified protocol are discussed. Compounds in the libraries are among those considered by the U.S. EPA Office of Water as threats to drinking water including pesticides, drugs of abuse, and pharmaceuticals. The LC-MS library protocol was verified through an inter-laboratory study that involved Federal, State, and private laboratories. The results demonstrated that the libraries are transferable between the same manufacturer's product line, and have applicability between manufacturers. Although ion abundance ratios within mass spectra were shown to be different between the manufacturers’ instruments, the NIST search engine match probability was at 96% or greater for 64 out of 67 compounds evaluated.     

Dynamic adsorption properties of n-alkyl glucopyranosides determine their ability to inhibit cytolysis mediated by acoustic cavitation

Suspensions of human leukemia (HL-60) cells readily undergo cytolysis when exposed to ultrasound above the acoustic cavitation threshold. However, n-alkyl glucopyranosides (hexyl, heptyl, and octyl) completely inhibit ultrasound-induced (1057 kHz) cytolysis (Sostaric, et al. Free Radical Biol. Med. 2005, 39, 1539-1548). The efficacy of protection from ultrasound-induced cytolysis was determined by the n-alkyl chain length of the glucopyranosides, indicating that protection efficacy depended on adsorption of n-alkyl glucopyranosides to the gas/solution interface of cavitation bubbles and/or the lipid membrane of cells. The current study tests the hypothesis that "sonoprotection" (i.e., protection of cells from ultrasound-induced cytolysis) in vitro depends on the adsorption of glucopyranosides at the gas/solution interface of cavitation bubbles. To test this hypothesis, the effect of ultrasound frequency (from 42 kHz to 1 MHz) on the ability of a homologous series of n-alkyl glucopyranosides to protect cells from ultrasound-induced cytolysis was investigated. It is expected that ultrasound frequency will affect sonoprotection ability since the nature of the cavitation bubble field will change. This will affect the relative importance of the possible mechanisms for ultrasound-induced cytolysis. Additionally, ultrasound frequency will affect the lifetime and rate of change of the surface area of cavitation bubbles, hence the dynamically controlled adsorption of glucopyranosides to their surface. The data support the hypothesis that sonoprotection efficiency depends on the ability of glucopyranosides to adsorb at the gas/solution interface of cavitation bubbles.     

Analysis of urinary aromatic acids by liquid chromatography tandem mass spectrometry

The separation and detection of 11 urinary aromatic acids was developed using HPLC-MS/MS. The method features a simple sample preparation involving a single-step dilution with internal standard and a rapid 8 min chromatographic separation. The accuracy was evaluated by the recovery of known spikes between 87 and 110%. Inter- and intra-assay precision (CV) was below 11% in all cases and the analytes were observed to be stable for up to 8 weeks when stored at -20 degrees C. The method was validated based upon linearity, accuracy, precision and stability and was used to establish reference intervals for children and adults.     

A facile route for the preparation of nanoparticles of the spin-crossover complex [Fe(Htrz)2(trz)](BF4) in xerogel transparent composite films

Films and monoliths containing the spin crossover complex [Fe(Htrz)(2)(trz)](BF(4)) (trz = 1,2,4-triazole) as nanoparticles have been obtained. The dispersion and consecutive inclusion of the Fe complex in a silica matrix prepared from tetramethoxysilane or tetraethoxysilane afford monoliths or films with a violet colour at room temperature, which turns white above 380 K. This change of colour is reversible. This thermochromic behaviour has been characterized by measuring the magnetic properties together with thermogravimetric studies and Raman spectroscopy, the result of which all demonstrate that both films and monoliths undergo a spin crossover. Microscopy studies confirm the occurrence of the Fe complex as nanoparticles, in both the monoliths and the films. The facile synthesis of these materials as nanoparticles in transparent films should open the possibility of the synthesis of high quality films.     

2,2-Difunctionalization of alkenes via Pd(II)-catalyzed aza-Wacker reactions

N-Ts and N-Boc derivatives of 1,2-diamines and 1,2-amino alcohols are shown to undergo efficient Pd(II)-catalyzed aza-Wacker reactions with a large range of electron-deficient alkenes. The resulting enamine intermediate generally undergoes cyclization with the second heteroatom to form 1,3-heterocycles. The sequence facilitates the rapid synthesis of saturated oxazolidines, imidazolidines, and their derivatives. Use of N-L-valinol derivatives results in highly diastereoselective reactions, where the net stereochemical outcome diverges between N-Ts and N-Boc.     

Vibrational contributions to the second-order nonlinear optical properties of π-conjugated structure acetoacetanilide

FT-Raman and IR spectra of the nonlinear optic (NLO) crystal, acetoacetanilide have been recorded and analyzed. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The various intramolecular interactions that is responsible for the stabilization of the molecule was revealed by natural bond orbital analysis. The Kurtz and Perry powder reflection technique appeared to be very effective in studies of second-order nonlinear optical properties of the molecule.     

The solution phase characterization of poly(ferrocenyldimethylsilane)s by small‐angle neutron scattering

A series of monodisperse (M_w/M_n < 1.1) poly(ferrocenyldimethylsilane)s was prepared with number‐averaged degrees of polymerization, 〈z〉_n, of 9, 33, 206, and 506 ( 2 – 5 , respectively), as determined by gel permeation chromatography (GPC). The polymers were studied by small‐angle neutron scattering (SANS) in solution with the aim of obtaining the radius of gyration, R_g, the weight‐averaged molecular weight, M_w, and the polydispersity index, M_w/M_n. Data were collected over the range 0.008 < Q/Å^?1 < 0.5 and for a series of concentrations (weight fraction, w = 0.0063, 0.0125, 0.025, and 0.05). The scattered intensity, I(Q), was fitted to a model based on a Schultz–Zimm distribution of isolated chains with excluded volume. A comparison of the molecular weight and size data determined by GPC and SANS indicated an acceptable agreement between the values for R_g, M_w and M_w/M_n. The results of this study demonstrate the potential utility of SANS to fully characterize metallopolymers, and other polymer systems where traditional methods cannot be applied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4011–4020     

Structural and Electronic Effects of Carbon‐Supported PtxPd1−x Nanoparticles on the Electrocatalytic Activity of the Oxygen‐Reduction Reaction and on Methanol Tolerance

We report a systematic investigation on the structural and electronic effects of carbon‐supported Pt_xPd_1?x bimetallic nanoparticles on the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acid electrolyte. Pt_xPd_1?x/C nanocatalysts with various Pt/Pd atomic ratios (x=0.25, 0.5, and 0.75) were synthesized by using a borohydride‐reduction method. Rotating‐disk electrode measurements revealed that the Pt₃Pd₁/C nanocatalyst has a synergistic effect on the ORR, showing 50 % enhancement, and an antagonistic effect on the MOR, showing 90 % reduction, relative to JM 20 Pt/C on a mass basis. The extent of alloying and Pt d‐band vacancies of the Pt_xPd_1?x/C nanocatalysts were explored by extended X‐ray absorption fine‐structure spectroscopy (EXAFS) and X‐ray absorption near‐edge structure spectroscopy (XANES). The structure–activity relationship indicates that ORR activity and methanol tolerance of the nanocatalysts strongly depend on their extent of alloying and d‐band vacancies. The optimal composition for enhanced ORR activity is Pt₃Pd₁/C, with high extent of alloying and low Pt d‐band vacancies, owing to favorable O? O scission and inhibited formation of oxygenated intermediates. MOR activity also shows structure dependence. For example, Pt₁Pd₃/C with Pt_rich?corePd_rich?shell structure possesses lower MOR activity than the Pt₃Pd₁/C nanocatalyst with random alloy structure. Herein, extent of alloying and d‐band vacancies reveal new insights into the synergistic and antagonistic effects of the Pt_xPd_1?x/C nanocatalysts on surface reactivity.     

Chiral cyclodextrin-modified microemulsion electrokinetic chromatography

Cyclodextrin (CD)-modified microemulsion electrokinetic chromatography (MEEKC) or CD-MEEKC has not previously been applied to the area of chiral separations. Herein, the results of investigations of various microemulsions with CD additives are presented. Two different microemulsions are explored: an ethyl acetate sodium dodecyl sulfate microemulsion, and a chiral dodecoxycarbonylvaline (DDCV) microemulsion. Each microemulsion is paired separately with a neutral CD (hydroxypropyl-beta-CD) and an anionic CD (sulfated-beta-CD). In addition, the chiral DDCV microemulsion is investigated in both the R- and S- form. By varying simple parameters such as buffer system, applied voltage, surfactant enantiomer, and type of cyclodextrin, dramatic improvements in the chiral separations were noted. Resolution was found to be highly dependent on buffer identity and concentration, and somewhat dependent on whether the CDs used were randomly or highly sulfated. Under optimized conditions, the resolution ranged from 0.8 to 4.8, with plate counts ranging from 4000 to 26 000. Additionally, S- and R-levetiracetam, which had never before been enantioseparated via capillary electrophoresis (CE) methodologies, were separated in less than 8 min, with a resolution of 1.1.