HPLC determination of methylphenidate and its metabolite,ritalinic acid,by high-performance liquid chromatography with peroxyoxalate chemiluminescence detection

An HPLC–peroxyoxalate chemiluminescence (PO-CL) method for simultaneous determination of methylphenidate (MPH) and ritalinic acid (RA) was developed. The method was used to monitor MPH and RA after administration of MPH to rats. Deproteinized plasma spiked with 1-(3-trifluoromethylphenyl)piperazine (IS) was dried and labeled with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F). The labeled sample was cleaned with two kinds of solid-phase extraction cartridge, and the DBD-labels were separated on an ODS column with gradient elution using a mixture of CH₃CN and imidazole–HNO₃ buffer. Separation of MPH and RA can be achieved within 33 min. The LODs of MPH and RA at a signal-to-noise ratio of 3 were 2.2 and 0.4 ng mL⁻¹, respectively. Moreover, monitoring of MPH and RA after MPH administration (10 mg kg⁻¹) to rat could be performed. The concentration of RA 480 min after administration was eight times higher than that of MPH. The proposed HPLC–PO-CL method was useful for determination of MPH and RA in rat plasma and was successfully used to monitor these substances after MPH administration.     

Spin-crossover behavior and electrical conduction property in iron(II) complexes with tetrathiafulvalene moieties

Iron(II) complexes with neutral and oxidized tetrathiafulvalene (TTF) moieties were prepared and X-ray crystallographic analyses, magnetic and electrical resistivity measurements suggested an interaction of spin transition and electrical conductivity.     

Conversion of oxido-bridged dinuclear ruthenium complex to dicationic dinitrosyl ruthenium complex using proton and nitric oxide: completion of NO reduction cycle

The hydroxido-bridged dinuclear ruthenium complex 4, which is supported by Tp ligands, has been prepared from protonation of the oxido-bridged dinuclear ruthenium complex 3. Additional protonation of 4, affording the aqua-bridged dinuclear ruthenium complex 5 in situ, and subsequent treatment with NO gave rise to the dicationic dinitrosyl complex 2. These indicate completion of the NO reduction cycle on the dinuclear ruthenium complex.     

One-pot synthesis of cyclophane-type macrocycles using manganese(III)-mediated oxidative radical cyclization

Cyclophane-type macrocyclic compounds from 21 to 56 members having two fused dihydrofuran rings were synthesized by the manganese(III)-mediated oxidation of terminal dienes with bis(3-oxobutanoate)s containing aromatics. The reaction detail, characterization and reaction pathways are described.     

Multinuclear Pd/Zn complex-catalyzed asymmetric alkylative ring-opening reaction of oxabicyclic alkenes

A multinuclear palladium catalyst can be used to realize the efficient catalytic asymmetric alkylative ring-opening reaction of oxabicyclic alkenes using dimethylzinc. The use of (R)-BINOL-PHOS bearing bisphosphine and diol moieties is essential for achieving excellent catalytic performance; the corresponding monophosphine and hydroxy-protected derivatives showed lower catalytic activities and/or enantioselectivities. The generation of Pd/Zn-multinuclear complexes is a key feature of the present catalysis.     

Effects of methylation at position 2 of cation ring on rotational dynamics of imidazolium-based ionic liquids investigated by NMR spectroscopy: [C4mim]Br vs [C4C1mim]Br

We investigated the rotational dynamics of two imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br) and 1-butyl-2,3-dimethylimidazolium bromide ([C(4)C(1)mim]Br), to reveal the effects of methylation at position 2 of the imidazolium ring (C(2) methylation). The rotational correlation time (τ(local)) for each carbon in the cations is derived from the spin-lattice relaxation time of (13)C nuclear magnetic resonance. The τ(local) results obtained here provide three principle insights into the rotational dynamics of ionic liquids. First, all τ(local) values for [C(4)C(1)mim]Br are greater than those for [C(4)mim]Br owing to a viscosity increase due to C(2) methylation. Second, the rate of change in τ(local) on C(2) methylation differs among the carbons in the cation, which indicates that each carbon has a different microviscosity. Third, the τ(local) increase in the (13)C at the root of the butyl group on C(2) methylation is very small compared to both intuitive prediction and the results from quantum chemical calculations. This indicates that the motion of the butyl group root in [C(4)C(1)mim]Br is not significantly inhibited by the methyl group at the position 2 of the imidazolium ring. The finding provides conclusive information on the origin of the increases in the melting point on C(2) methylation. Hunt previously found through calculation that decreases in entropy are caused by two factors, namely, reductions in the rotational mobility of the butyl group and in the number of stable anion interaction sites with C(2) methylation, resulting in an increase in melting point and viscosity. Our finding experimentally illustrates that the origin of the increases in melting point is not the inhibition of butyl group motion and that the reduction in stable anion interaction sites plays a major role in the increases. Additionally, it is suggested that the viscosity increase on C(2) methylation can be interpreted in the same manner.     

Analysis of the unbinding force between telomestatin derivatives and human telomeric G-quadruplex by atomic force microscopy

The force analysis between a macrocyclic hexazole (6OTD) monomer/dimer and telomeric DNA using atomic force microscopy revealed the difference in their binding modes. The 6OTD dimer bound to the G-quadruplex more strongly than the monomer by sandwiching the G-quadruplex.