How (77)Se NMR chemical shifts originate from pre-alpha, alpha, beta, and gamma effects: interpretation based on molecular orbital theory

Plain rules founded in a theoretical background are presented that can be used to determine the structure of selenium compounds on the basis of delta(Se) data and to predict delta(Se) data from a given structure with satisfactory accuracy. As a first step to establish such rules, the origin of delta(Se) is elucidated on the basis of MO theory. The Se(2-) ion was chosen as the standard for the analysis. The concept of the pre-alpha effect is proposed, which is defined as the downfield shift due to protonation of a lone-pair orbital of Se. The pre-alpha effect of two protons in H(2)Se is explained by the generation of double sigma(Se--H) and sigma*(Se--H) through protonation of the spherical Se(2-) ion. The orbitals, together with n(p)(Se), result in effective transitions for the pre-alpha effect. The alpha effect is the downfield shift caused by the replacement of Se--H by Se--Me. The extension of HOMO-2 [4p(y)(Se)], HOMO-1 [4p(x)(Se)], and HOMO [4p(z)(Se)] over the whole Me(2)Se molecule is mainly responsible for the alpha effect. The beta effect originates not from the occupied-to-unoccupied (psi(i)-->psi(a)) transitions but from the occupied-to-occupied (psi(i)-->psi(j)) transitions. Although psi(i)-->psi(j) transitions contribute to upfield shifts in Me(2)Se, the magnitudes become smaller as the methyl protons are substituted by Me groups one after another. The gamma effect of upfield shifts is also analyzed, although complex. The effect of p(Se)-pi(C==C) conjugation is analyzed in relation to the orientational effect. Contributions from each MO (psi(i)) and each psi(i)-->psi(a) transition are evaluated separately, by using a utility program derived from the Gaussian 03 program suite (NMRANAL-NH03G). The treatment enables us to visualize and understand the origin of (77)Se NMR chemical shifts.     

Synthesis of trifluoromethyl‐1,2,4‐triazine‐ and trifluoromethylpyrimidine‐fused uracils

A variety of trifluoromethyl‐1,2,4‐triazine‐ and trifluoromethylpyrimidine‐fused uracils ( 9 ), ( 12 ), ( 15 ) and ( 18 ) were synthesized from trifluoroacetaldehyde ethyl hemiacetal or trifluoroacetic anhydride and corresponding uracil derivatives.     

Rhodium-catalyzed substitution reaction of aryl fluorides with disulfides: p-orientation in the polyarylthiolation of polyfluorobenzenes

In the presence of a catalytic amount of RhH(PPh3)4 and 1,2-bis(diphenylphosphino)benzene, an aromatic fluoride, an organic disulfide (0.5 equiv), and triphenylphosphine (0.5 equiv) reacted in refluxing chlorobenzene to give an aryl sulfide in high yield. Since triphenylphosphine trapped fluoride atoms forming phosphine difluoride, both organothio groups of the disulfide reacted effectively, and the fluoride substituent reacted more readily than the chloride and bromide. The reaction of hexafluorobenzene and a diaryl disulfide gave 1,4-diarylthio-2,3,5,6-tetrafluorobenzene, 1,2,4,5-tetraarylthio-3,6-difluorobenzene, and hexaarylthiobenzene in a stepwise manner; pentafluorobenzene gave 1-arylthio-2,3,5,6-tetrafluorobenzene; 1,2,3,4-tetrafluorobenzene gave 1,2-diarylthio-3,6-difluorobenzene; and 1,2,4,5-tetrafluorobenzene gave 1,4-diarylthio-2-5-difluorobenzene. The polyarylthiolation reaction of polyfluorobenzenes exhibited a strong tendency to form 1,4-difluorobenzenes.     

Application and mechanism of inhalation profile improvement of DPI formulations by mechanofusion with magnesium stearate

In our previous paper, we reported the inhalation properties of dry powder inhaler (DPI) formulations containing Compound A and mechanofusion-processed lactose carriers. The mechanofusion process with magnesium stearate (Mg-St) on the lactose carrier enhanced the fine particle fraction (FPF) value of the Andersen cascade impactor (ACI) study. The increase of FPF seemed to be associated with the increase of the dispersibility of drug particles. The objectives of this study were (1) to evaluate the applicability of lactose carrier mechanofusion-processed with Mg-St and (2) to examine the mechanism of FPF alteration by the mechanofusion process applied on the lactose carrier with or without additive. The inhalation profiles of DPI formulations containing four different pharmaceutical compounds were evaluated with an ACI. The dispersibility of the formulations was observed by particle size distribution measurement in the air stream and the adhesive force was measured bydirect separation method. It was found that higher FPF was obtained with lactose mechanofusion-processed with Mg-St as compared to control lactose carriers for all four compounds. This suggested that mechanofusion process with Mg-St is widely applicable in DPI formulations. The homogenization of surface adhesiveness was attributed to the increased FPF of the DPI including lactose mechanofusion-processed with Mg-St, as suggested by the combination of several physicochemical characteristics. Combination of different characterization methods would be of help to clarify the whole mechanism which defines the inhalation properties of DPI formulations.     

Rhodium-catalyzed alkylthio exchange reaction of thioester and disulfide

The Wilkinson complex RhCl(PPh₃)₃ catalyzes equilibrating alkylthio exchange reaction of thioesters with disulfides. The treatment of a thioester and a dialkyl disulfide in refluxing diethyl ketone in the presence of RhCl(PPh₃)₃ (2.5 mol %) for 1.5 h gave an alkylthio exchanged thioester. The reaction of S-methyl ester was conducted shifting the equilibrium by removing volatile dimethyl disulfide.     

Micro- and nanopatterned copper structures using directed self-assembly on templates fabricated from phase-separated mixed Langmuir-Blodgett films

We report a versatile method to confine metal thin films in micro- and nanopatterns using directed self-assembly on the templates fabricated from phase-separated mixed Langmuir-Blodgett (LB) films. The pattern of the mixed LB films can be tuned by adjusting intermolecular interaction between the film-forming molecules in the LB films and by varying the fabrication conditions of the films such as the mixing ratio, subphase temperature, and surface pressure. We use the patterned LB films for templates to confine metal in patterned regions, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayer of the silane coupling agent. Au nanoparticles are confined onto the patterned films as a catalyst for the succeeding Cu electroless deposition. The atomic force microscopic images, Auger electron spectra, and scanning Auger electron maps of a Cu-deposited film show that Cu is selectively deposited on the patterns of phase separation of the original mixed LB films.     

Salt effect on complex formation of neutral/polyelectrolyte block copolymers and oppositely charged surfactants

The salt effect on the complex formation of poly(acrylamide)- block-poly(sodium acrylate) (PAM- b-PAA) as a neutral-anionic block copolymer and dodecyltrimethylammonium bromide (DTAB) as a cationic surfactant at different NaBr concentrations, CNaBr, was investigated by turbidimetric titration, steady-state fluorescence spectroscopy, and dynamic light scattering. At C NaBr < 0.25 M, DTAB molecules may form micelle-like aggregates on PAM- b-PAA chains to form a PAM- b-PAA/DTAB complex above the critical surfactant concentration C critical for the onset of complex formation. In the region of relatively high turbidity, a larger complex is likely to form a core-shell structure, of which the core is a dense and disordered microphase made of surfactant micelles connected by the PAA blocks. The corona was a diffuse shell of PAM chains, and it ensured steric stability. At CNaBr = 0.25 M, a higher electrostatic intermicellar repulsion and intercomplex repulsion induced by a large amount of bound DTAB micelles may lead to a redissolution of large colloidal complexes into intrapolymer complexes. Moreover, a salt-enhancing effect on the complex formation was observed in the PAM- b-PAA/DTAB system; the critical surfactant concentration decreased with increasing salt concentration at CNaBr < 0.10 M. The salt-enhancing effect is due to the larger increase of interaction in comparison to the screening of the interaction.     

Growth of giant two-dimensional crystal of protein molecules from a three-phase contact line

A novel method to fabricate a two-dimensional (2D) crystal of protein molecules has been developed. The method enables us to control both the position of nucleation and the direction of the crystal growth. The crystal obtained using a protein molecule, ferritin, was found to be composed of a number of densely packed single crystal domains with an unprecedentedly large size of approximately 100 microm(2). This method also reveals characteristic behavior of the spatiotemporal evolution of the crystal; for example, "fusion" of the crystal domains, which is never observed in an ordinary crystal composed of atoms or ions, was demonstrated. Our approach could have potential in fabricating extraordinarily large and highly ordered nanoparticle arrays of organic or inorganic materials.     

Characterizing the structural transition of cationic DPPC liposomes from the approach of TEM, SAXS and AFM measurements

The structural transition of L-alpha-dipalmitoylphosphatidylcholine (DPPC) liposomes, caused by the addition of a small amount of stearylamine (SA), has been characterized. It has been reported that the shape of DPPC liposomes changes from multilamellar vesicles to large-unilamellar vesicles at the molar concentration ratio of DPPC/SA=9.5/0.5, however, the possible diving factors for this phenomenon have not so far been presented. Flat lipid membranes consisting of DPPC and SA, prepared by the quasi-Bangham method or the Langmuir-Blodgett (LB) technique, are employed in this study when considering the molecular interaction in and between lipid membranes, which should play a key role for determining the liposome shape. The colloid probe atomic force microscopy reveals that the addition of SA results in an inter-film electrosteric repulsion. This repulsive interaction causes a significant increase in the inter-film distance, which is confirmed with freeze-fracture transmission electron microscopy (FF-TEM) and small-angle X-ray scattering (SAXS), and thereby, the large-unilamellar vesicles are formed for reducing the inter- and intra-firm repulsive forces. Taking the molecular structures into consideration, it seems that the shape transition of DPPC liposomes results from such electrostatic interactions as well as packing geometry of the two components.     

Evaluation of microwave-assisted extraction for the analysis of polychlorinated biphenyls and organochlorine pesticides in fish

The efficiency of microwave-assisted extraction (MAE) was evaluated for the analysis of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in fish. An isotope dilution method was used for quantification via analysis of the samples by gas chromatography and mass spectrometry. MAE solvent, temperature, and time were optimized, and observed concentrations were compared. The MAE results were also compared to those of other extraction techniques (Soxhlet extraction, pressurized liquid extraction, saponification, and homogenization). Concentrations of PCBs and OCPs obtained by MAE at 120 degrees C for 10 min were comparable to those by the other techniques. The results suggest that MAE can be used for the analysis of PCBs and OCPs in fish.