Determination of fluoxetine enantiomers in rat plasma by pre-column fluorescence derivatization and column-switching high-performance liquid chromatography

A column-switching HPLC method employing both octadecylsilica (ODS) and chiral columns with fluorescence detection was developed for the determination of enantiomer of fluoxetine (FLX), an antidepressant drug, in rat plasma. Racemic FLX was derivatized with a fluorescent reagent, 4-(N-chloroformylmethyl-N-methyl)amino-7-nitro-2,1,3-benzoxadiazole (NBD-COCl) or 4-(N-chloroformylmethyl-N-methyl)amino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole (DBD-COCl) and the enantiomeric separation of the resultant derivatives was examined on an amylose-based chiral column (CHIRALPAK AD-RH) in the reversed-phase mode. The derivative with NBD-COCl (NBD-FLX) showed a sufficient separation factor (a) and resolution (Rs) compared with that with DBD-COCl. Thus, FLX was derivatized with NBD-COCl and the resultant NBD-FLX was first quantified on the ODS column and then introduced to the CHIRALPAK AD-RH column via a six-port switching valve to examine the enantiomeric ratio. The intra- and inter-day accuracy (97.6-112.7%) and precision (1.47-10.60%) were satisfactory in the range 10-1000 nM FLX and the limit of quantification was approximately 10 nM. The absolute recoveries of FLX with hexane from rat plasma were in the range 87.5-92.2% (n = 3). The method was applied to determine FLX enantiomers in the plasma of rats administered FLX orally, and it was shown that the R-isomer was eliminated faster than the S-isomer.     

Photocurrent generation system incorporated with antenna function

Porphyrin accumulation onto a self-assembled monolayer (SAM) of imidazole-substituted porphyrins by a supramolecular method to form a chain structure leads to significant increase of light absorption in the visible light region and therefore photocurrents.     

Hyperfine structure of the electron spin resonance of phosphorus-doped Si nanocrystals

Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si.     

A linear algorithm for the domination number of a series-parallel graph

A vertex u in an undirected graph G = (V, E) is said to dominate all its adjacent vertices and itself. A subset D of V is a dominating set in G if every vertex in G is dominated by a vertex in D, and is a minimum dominating set in G if no other dominating set in G has fewer vertices than D. The domination number of G is the cardinality of a minimum dominating set in G.The problem of determining, for a given positive integer k and an undirected graph G, whether G has a dominating set D in G satisfying ¦D¦ ≤ k, is a well-known NP-complete problem. Cockayne have presented a linear time algorithm for finding a minimum dominating set in a tree. In this paper, we will present a linear time algorithm for finding a minimum dominating set in a series-parallel graph.     

Photocontrol of lactate dehydrogenase-spiropyran collagen membrane

Collagen fibrils were modified with β-l-[3,3-dimethyl-6′-nitrospiro-(indoline-2,2′-2H-benzopyran)] propionic anhydride. The spiropyran collagen membrane showed reverse photochromism. Lactate dehydrogenase (LDH, E.C. 1.1.1.27) was entrapped in the spiropyran collagen membrane. The activity of the LDH-spiropyran collagen membrane decreased under visible-light irradiation, and then increased again after incubation in the dark. The optimum pH of the LDH-spiropyran collagen membrane was displaced toward lower pH values under visible-light irradiation. The activity change of the LDH-spiropyran collagen membrane under visible-light irradiation depended on the LDH content.     

Spontaneous racemization and epimerization behavior in solution of chiral nitroxides

[reaction: see text] Enantiomerically enriched samples of chiral cyclic nitroxides with a 4-hydroxyphenyl group on the stereogenic center bearing the NO radical group undergo unprecedented spontaneous racemization and/or epimerization in aprotic solvents, which can be well accounted for by the multistep equilibrations involving planar quinoid intermediates.     

Possible one-dimensional 3He quantum fluid formed in nanopores

Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D 3He fluid is indicated by a predominantly linear temperature dependence below about 30 mK.     

Nickel-catalyzed arylcyanation of alkynes

A nickel catalyst coordinated by trimethylphosphine is found to effect the addition reaction of Ar-CN bonds in aromatic nitriles across alkynes to give rise to various beta-arylalkenenitriles.