Optically active (aR)- and (aS)-linear and vaulted biaryl ligands: deracemization versus oxidative dimerization.

The copper-mediated deracemization of the C2-symmetric vaulted biaryl ligands VANOL and VAPOL has been investigated. In the course of the studies that have led to a more reliable procedure for this process, an unprecedented oxidative dimerization of these ligands has been uncovered. The structures of these oxidative dimerization products were elucidated by a series of NMR experiments, and these assignments were supported by other spectroscopic techniques as well as their chemical reactivity. This oxidative dimerization process was not observed for the linear biaryl ligands BANOL and BINOL, although the new deracemization procedure was effective for the generation of BINOL with high optical purity. The (aS)-enantiomers of BINOL, VANOL and VAPOL were accessible with a copper complex of (-)-sparteine, and the (aR)-enantiomeric series were accessible with a copper complex of O'Brien's diamine. Both (-)-sparteine and O'Brien's diamine give higher optical purities with VANOL and VAPOL than with BINOL, and this is consistent with the steric congestion present in the matched and mismatched copper complexes of these diamines with the biaryl ligands.

Electroosmotic pumps for microflow analysis.

With rapid development in microflow analysis, electroosmotic pumps are receiving increasing attention. Compared to other micropumps, electroosmotic pumps have several unique features. For example, they are bi-directional, can generate constant and pulse-free flows with flow rates well suited to microanalytical systems, and can be readily integrated with lab-on-chip devices. The magnitude and the direction of flow of an electroosmotic pump can be changed instantly. In addition, electroosmotic pumps have no moving parts. In this article, we discuss common features, introduce fabrication technologies and highlight applications of electroosmotic pumps.

Bare nanocapillary for DNA separation and genotyping analysis in gel-free solutions without application of external electric field.

In this work, we demonstrate DNA separation and genotyping analysis in gel-free solutions using a nanocapillary under pressure-driven conditions without application of an external electric field. The nanocapillary is a approximately 50-cm-long and 500-nm-radius bare fused-silica capillary. After a DNA sample is injected, the analytes are eluted out in a chromatographic separation format. The elution order of DNA molecules follows strictly with their sizes, with the longer DNA being eluted out faster than the shorter ones. High resolutions are obtained for both short (a few bases) and long (tens of thousands of base pairs) DNA fragments. Effects of key experimental parameters, such as eluent composition and elution pressure, on separation efficiency and resolution are investigated. We also apply this technique for DNA separations of real-world genotyping samples to demonstrate its feasibility in biological applications. PCR products (without any purification) amplified from Arabidopsis plant genomic DNA crude preparations are directly injected into the nanocapillary, and PCR-amplified DNA fragments are well resolved, allowing for unambiguous identification of samples from heterozygous and homozygous individuals. Since the capillaries used to conduct the separations are uncoated, column lifetime is virtually unlimited. The only material that is consumed in these assays is the eluent, and hence, the operation cost is low.