Highly enantioselective hydrogenation of aromatic-heteroaromatic ketones

Asymmetric hydrogenation of ketone 1 using trans-RuCl(2)[(R)-xylbinap][(R)-daipen] (3) as a catalyst afforded secondary alcohol 2 quantitatively and in 99.4% ee. Further exploration of the effect of the thiazole ring substitution revealed that the catalyst was highly effective for the enantioselective hydrogenation of 5-benzoyl thiazoles, which afforded corresponding alcohols in 92-99% ee. The same protocol was applicable to a variety of aromatic-heteroaromatic ketones to generate secondary alcohols in excellent enantioselectivities. [reaction: see text]     

High-performance liquid chromatographic assays for protoporphyrinogen oxidase and ferrochelatase in human leucocytes

Rapid, sensitive and specific high-performance liquid chromatographic assays are described for protoporphyrinogen oxidase and ferrochelatase in human leucocytes. The enzyme reaction products were separated and quantitated by reversed-phase high-performance liquid chromatography with fluorescence detection. The optimal pH for the protoporphyrinogen oxidase assay was 8.6 and the Michaelis constant for protoporphyrinogen IX was 9.78 +/- 0.96 microM (mean +/- S.D.). The mean (+/- S.D.) activity of protoporphyrinogen oxidase in fourteen apparently healthy subjects was 0.146 +/- 0.023 nmol protoporphyrin IX per min per mg protein. In one patient with variegate porphyria, the activity was 0.028 nmol protoporphyrin IX per min per mg protein. The optimal pH for ferrochelatase was 7.4 and with protoporphyrin and Zn2+ as substrates, the Michaelis constants were 1.49 and 8.33 microM, respectively. The mean activity of ferrochelatase in ten control subjects was 0.24 nM Zn-protoporphyrin or 2.05 nM Zn-mesoporphyrin formed per h per mg protein.     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Automated system for simultaneous analysis of delta(13)C, delta(18)O and CO(2) concentrations in small air samples

In this paper we present an automated system for simultaneous measurement of CO(2) concentration, delta(13)C and delta(18)O from small (<1 mL) air samples in a short period of time (approximately 1 hour). This system combines continuous-flow isotope ratio mass spectrometry (CF-IRMS) and gas chromatography (GC) with an inlet system similar to conventional dual-inlet methods permitting several measurement cycles of standard and sample air. Analogous to the dual-inlet method, the precision of this system increases with the number of replicate cycles measured. The standard error of the mean for a measurement with this system is 0.7 ppm for the CO(2) concentration and 0.05 per thousand for the delta(13)C and delta(18)O with four replicate cycles and 0.4 ppm and 0.03 per thousand respectively with nine replicate cycles. The mean offset of our measurements from NOAA/CMDL analyzed air samples was 0.08 ppm for the CO(2) concentration, 0.01 per thousand for delta(13)C and 0.00 per thousand for delta(18)O. A specific list of the parts and operation of the system is detailed as well as some of the applications for micrometeorological and ecophysiological applications.     

Mechanistic study of enantiomeric recognition with native gamma-cyclodextrin by capillary electrophoresis,reversed-phase liquid chromatography,nuclear magnetic resonance spectroscopy,electrospray mass spectrometry and circular dichroism techniques

The possible mechanisms for the chiral recognition of 2(S)-(3,5-bis-trifluoromethyl-phenyl)-2-[3(S)-(4-fluorophenyl)-4-(1H-[1,2,4]triazol-3-ylmethyl)-morpholin-2(R)-yloxy]-ethanol (compound A) and its enantiomer with native gamma-cyclodextrin (gamma-CD) were investigated using capillary electrophoresis (CE), reversed-phase liquid chromatography (RPLC), proton (1H), fluorine (19F) and carbon (13C) nuclear magnetic resonance spectroscopy (NMR), electrospray mass spectrometry (ESI-MS) and circular dichroism (CD). All experiments provided clear evidence of the formation of diastereomeric complexes between the enantiomers and gamma-CD. Proton, fluorine and carbon NMR spectra suggested that both aromatic rings, with mono-fluoro and bis-tri-fluoro functional groups, on the guest molecule were partially included into the cavity of the gamma-CD. ESI-MS spectra indicated that the diastereomeric complexes have a 1:1 stoichiometric ratio. The binding constants of the diastereomeric complexes obtained by CE, RPLC and CD were compared. The effects of the gamma-CD concentration, organic modifiers and temperature on the CE-chiral separation were also investigated.     

Fluorescence resonance energy transfer between a quantum dot donor and a dye acceptor attached to DNA

We show that direct coupling of a dye-labelled DNA (acceptor) to a quantum dot (QD) donor significantly reduces the donor-acceptor distance and improves the FRET efficiency: a highly efficient FRET (approximately 88%) at a low acceptor-to-donor ratio of 2 has been achieved at the single-molecule level.     

Rapid deposition of triangular silver nanoplates on planar surfaces: application to metal-enhanced fluorescence

A simple and rapid wet-chemical technique for the deposition of silver triangles on conventional glass substrates, which alleviates the need for lithography, has been developed. The technique is based on the seed-mediated cetyltrimethylammonium-bromide-directed growth of silver triangles on glass surfaces, where smaller spherical silver seeds that were attached to the surface were subsequently converted and grown into silver triangles in the presence of a cationic surfactant and silver ions. The size of the silver triangles was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration time of immersion. Atomic force microscopy studies revealed that the size of the silver triangles ranged between 100 and 500 nm. Interestingly, these new surfaces are a significant improvement over traditional silver island films for applications in metal-enhanced fluorescence. A routine 16-fold enhancement in emission intensity was typically observed, for protein-immobilized indocyanine green, with a relatively very low loading density of silver triangles on the glass surface.