Purification of the precursor for the automated radiosynthesis of [18F]FCWAY by counter-current chromatography

Radiolabeled FCWAY (N-(2-[4-(2-methoxyphenyl)piperazino])-N-(2-pyridinyl) trans-4-fluorocyclohexanecarboxamide) was prepared for human positron emission tomography (PET) studies by a simple one-step radiosynthesis. The LC-MS analysis of the products indicated that it contained impurities which may interfere with FCWAY uptake of 5-HT1A receptors and that these impurities were derived from an impurity originally present in the precursor preparation. Since preparative HPLC failed to resolve one of the impurities from the precursor, preparative-scale high-speed counter-current chromatography (HSCCC) was used for purification of this FCWAY precursor. A suitable two-phase solvent system composed of cyclohexane-ethyl acetate-methanol-water at a volume ratio of 1:1:1:1 or 4:5:4:5 was selected based on the partition coefficients of the precursor and impurity as determined by a LC-MS method. Using the second solvent ratio of 4:5:4:5 with the organic phase as a mobile phase, a 2.57 g amount of precursor preparation was successfully purified yielding 2.2 g of the pure precursor by a single run.     

Enhancement of polarographic reduction currents by a static magnetic field

The effect of a magnetic field on d.c. polarographic reduction currents was studied with a static magnetic field applied perpendicularly to the dropping mercury electrode. In the presence of the magnetic field, diffusion or migration currents show a slight but distinct increase. The factors which can influence this effect have been examined experimentally. The effect is interpreted in terms of suppression of transfer of concentration polarization from one drop to the next. It is shown that certain types of maxima are enhanced by application of a magnetic field.     

Novel Bis-Fused pi-Electron Donors for Organic Metals: 2-(1,3-Dithiol-2-ylidene)-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene

Bis-fused pi-electron donors composed of tetrathiafulvalene (TTF) and 2-(thiopyran-4-ylidene)-1,3-dithiole (TPDT), 2-(1,3-dithiol-2-ylidene)-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene (1a, TPDT-TTP), and its derivatives (1b-d, 2a-d) have been synthesized as donor components for organic conductors. An X-ray structure analysis of bis(methylthio)-1 (1c) revealed that the TPDT-TTP skeleton is almost planar except for the outer 1,3-dithiole ring, and that the crystal has a two-dimensional "theta-type" arrangement of molecules. The cyclic voltammograms of TPDT-TTPs exhibit four pairs of single-electron redox waves. The first oxidation potential (E(1)) of 1a (+0.37 V vs SCE, in PhCN) is comparable to that of TTF (+0.35 V) and is higher by 0.1 V than that of TPDT (+0.27 V). The observed substituent effect on E(1) values suggests that the first one-electron oxidation mainly occurs in the 2-(thiopyran-4-ylidene)-1,3-dithiole (TPDT) moiety. On the other hand, on-site coulombic repulsion estimated from the E(2) - E(1) value is lower than in TTF and TPDT. MNDO MO calculations reveal that all the sulfur atoms in the 1,3-dithiole rings have the same phase in the HOMO, a condition necessary for realization of effective transverse intermolecular interaction. The present donors have produced many charge-transfer complexes and cation radical salts showing relatively high conductivity (sigma(rt) = 10(-)(1)-10(1) S cm(-)(1)), several of which display metallic temperature dependence.     

Convenient laboratory synthesis of vinylic silicon compounds via the reactions of acetylene with hydrosilanes catalyzed by group-VIII metal phosphine complexes

The hydrosilylation of acetylene (HCCH) with trichlorosilane, triethoxysilane, methyldichlorosilane, methyldiethoxysilane and $\text{n}$-hexyldichlorosilane in an inert solvent in the presence of various phosphine complexes of Group-VIII metals such as Ru, Rh, Pd and Pt, as well as chloroplatinic acid, was investigated. Among the complexes studied, RuCL₂ (PPh₃)₃, PtCl₂ (PPh₃)₂, RhCl (PPh₃)₃, RhH(PPh₃)₄ and Pt(PPh₃)₄ were found to be the catalysts of choice for the selective syntheses of vinyltrichlorosilane, vinyltriethoxysilane, methylvinyldichlorosilane, methylvinyldiethoxysilane and $\text{n}$-hexylvinyldichlorosilane, respectively.     

Dynamics of excited and ionic states of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) under ablation condition

The nanosecond transient dynamics of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) has been investigated under ablation condition. Time-resolved spectroscopic data can be interpreted in terms of the dynamics of the lowest excited singlet and triplet states and the cation of TMPD. The decay processes of all the detected transients became rapid with an increase in the laser fluence. It is shown directly that TMPD absorbs about eight 248 nm photons during a nanosecond laser pulse at the ablation threshold of 220 mJ/cm². These results are well explained by cyclic multiphotonic absorption mechanism where dopant transients work as repetitive absorbers of laser photons.     

Highly conducting crystals based on single-component gold complexes with extended-TTF dithiolate ligands

Highly conducting crystals based on single-component gold complexes with extended-TTF dithiolate ligands [Au(dmdt)(2)](0+) (1) and [Au(tmdt)(2)](0+) (2) were prepared (dmdt = dimethyltetrathiafulvalenedithiolate and tmdt = trimethylenetetrathiafulvalenedithiolate). On the basis of the synchrotron radiation powder diffraction data, the MEM electron density of 2 was successfully obtained. The conductivities of compacted powder samples of 1 and 2 at room temperature were 12 and 15 S cm(-1), respectively. Pauli-like susceptibility of 1 suggested the system to be essentially metallic at least above 50 K, while 2 showed a magnetic transition around 100 K without loss of its high conductivity.     

The solution chemistry of organotin compounds V. Proton relaxation and dynamic NMR studies of solute-solvent interactions in solutions of dimethyltin dichloride plus 2,2′-bipyridine complex

¹H T₁ and dynamic NMR measurements (T₁ = relaxation time) were made with Me₂SnCl₂ and its bpy complex in mixed solvents of CH₂Cl₂ and weak bases to elucidate the role of the solvent in the dynamic behaviour of organotin compounds. In the line shape analysis of the exchange reaction between Me₂SnCl₂ and its bpy complex, the dissociation rate constant k_d of the Me₂SnCl₂ · bpy complex supported an exchange mechanism of the dissociation followed by a rapid recombination step. Weak bases in the mixed solvents decreased the Eyring activation parameters ΔH^‡ and ΔS^‡ for the dissociation reaction of the complex, indicating more extensive solvation in the activated state than in the ground state of the complex. In the ¹H T₁ measurements, the reorientational correlation time τ_c was shorter and its activation energy E_a was larger in Me₂SnCl₂ than in Me₂SnCl₂ · bpy, in conformity with their molecular sizes. E_a and τ_c increased on addition of weak bases, such as nitromethane, nitrobenzene and acetonitrile, even for the Me₂SnCl₂ · bpy complex, whose acidity is reduced considerably from that of the free tin compound. The major cause of this result is suggested to be the interaction of the weak bases with CH₂Cl₂, resulting in a change of the physical properties of the mixed solvent.     

A computer program system — new chemics — for structure elucidation of organic compounds by spectral and other structural information

Computer-assisted structure elucidation is improved by the introduction of substructures selected by the user, in addition to analyses of the spectral data of an unknown organic compound. The substructure is called a 'macrocomponent' in the system. The macrocomponent which is input at will is authenticated by comparison with the set of components assembled by the automated analyses of the spectra before it is used for structure construction. It is shown that the introduction of the macrocomponent enhances the correctness and practicality of structure elucidation by computer.     

A comparison of the photochemical reactivity of N@C60 and C60: photolysis with disilirane

N@C60 has a lower photochemical reactivity toward disilirane than C60, although N@C60 does not differ from C60 in its thermal reactivity; theoretical calculations reveal that N@C60 and C60 have the same orbital levels and that N@3C60* has a shorter lifetime than 3C60*.     

Accurate mass measurement in nano-electrospray ionization mass spectrometry by alternate switching of high voltage between sample and reference sprayers

An electrospray dual sprayer, which generates separate sample and reference sprays by alternately switching the high voltage between the two sprayers, is described. The technique permits accurate mass measurements in nano-electrospray ionization mass spectrometry (ESI-MS) to be obtained using a quadrupole/orthogonal acceleration time-of-flight mass spectrometer (Q-TOF). Similar to the method employed with a dual ESI source (Wolff JC et al., Anal. Chem. 2001; 73: 2605), the two sprays are orthogonal with respect to each other, but can be independently sampled without any baffle between these sprays. The reference sprayer is used in the original configuration of the ESI source and was optimized for a 1-2 muL/min flow, whereas the sample sprayer can be either a conventional glass capillary or a borosilicate tip of the type used for nano-ESI. Both sprayers can be positioned close to the cone so as to give maximum ion currents. The sample and reference sprays are independently generated by raising the potentials on the sample and reference sprayers to 1.4 and 3.0 kV, respectively; the high voltages can be rapidly turned on and off in ca. 1 ms. A nano-ESI-MS or nano-flow LC/ESI-MS experiment using a Q-TOF coupled with the above system gave mass accuracies within 3 ppm for measurements of ions up to m/z 1000 using subpicomole samples.