Chiral discrimination of aliphatic amines and amino alcohols using NMR spectroscopy.

Two methods are compared for analyzing the enantiomeric purity of aliphatic amines and amino alcohols using NMR spectroscopy. The first employs (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as a chiral NMR solvating agent in methanol-d(4) . The second involves a derivatization scheme in which the amine is reacted with naphtho[2,3-c]furan-1,3-dione to form the corresponding amide. The naphthyl amide is then mixed with a chiral calix[4]resorcinarene in deuterium oxide. The crown ether only produces sufficient enantiomeric discrimination to determine enantiomeric purity for three of the nine substrates studied. The system with the naphthyl amide and a calix[4]resorcinarene produces enantiomeric discrimination of sufficient magnitude to determine enantiomeric purity for all nine substrates. The H1 and H4 resonances of the naphthyl ring are especially suitable to monitor for enantiomeric discrimination. The order of the (R)- and (S)-enantiomers of the H1 and H4 resonances exhibit specific trends for aliphatic amines and amino alcohols that correlate with the absolute configuration.

Social and economic aspects of immigration.

The absolute size of the foreign-born U.S. population is at a historical high, but neither the share of the population that is foreign born nor the share of children in immigrant families is high compared with the beginning of the 20th century. While poverty rates for immigrants and children in immigrant families are substantial, poverty is concentrated among certain groups, particularly Hispanics and blacks, non-citizens, and recent arrivals. The general economic well-being of immigrants improves with the move to the United States and as time in the United States increases. However, immigrants remain disadvantaged in terms of health insurance coverage. The economic situation of children in immigrant families has declined since the late 1960s, despite the high labor force participation of immigrant men and the lower prevalence of single-parent households among immigrant families. Still, children in immigrant families are at least as healthy as children in native families and are less likely to engage in risky behaviors. With socioeconomic factors taken into account, children in immigrant families do as well as other children in school. Analyses of the socioeconomic well-being of immigrants have been hampered by lack of information in major data sets about legal status and about the visa status of legally present immigrants, as well as by limited availability of longitudinal data.

Chiral quantification of D-, L-, and meso-tartaric acid mixtures using a mass spectrometric kinetic method.

Accurate quantification of the optical isomers in a ternary mixture of D-, L-, and meso-tartaric acids is achieved using electrospray ionization tandem mass spectrometry for in-situ metal complex formation and a three-point calibration method to quantify the dissociation kinetics.

Quotient ratio method for quantitative enantiomeric determination by mass spectrometry.

The quotient ratio (QR) method, a new quantitative method for enantiomeric determination by mass spectrometry, is presented. The method is illustrated by the case in which a chiral analyte (A) and a chiral reference compound (ref*) are simultaneously coordinated to a transition metal ion (e.g., Cu2+ or Zn2 ) to form a singly charged deprotonated cluster ion in the course of electrospray ionization. The trimeric complex ion (three chiral ligands-2 mol of the analyte and 1 mol of the reference compound) is collisionally activated and undergoes dissociation by competitive loss of either a neutral reference or a neutral analyte. The ratio of the product ion branching ratios measured when pure chiral reference compounds (ref*D and ref*L) are employed in separate experiments is related via the kinetic method to the enantiomeric composition of the chiral mixture. This quotient ratio is logarithmically related to enantiomeric purity. In contrast to the previous single ratio method (Tao, W. A.; Zhang, D.; Wang, F.; Thomas, P. D.; Cooks, R. G. Anal. Chem. 1999, 71, 4427), the QR method reported here requires only one sample of the analyte with known optical purity to allow construction of a calibration curve. Accurate determinations of enantiomeric excess for amino acids and the chiral drug DOPA are demonstrated.