CO2 absorption and desorption in an aqueous solution of heavily hindered alkanolamine: structural elucidation of CO2-containing species.

The pathways for the CO2 absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(t-butylamino)ethanol (TBAE) were elucidated by X-ray crystallographic and (13)C NMR spectroscopic analysis. In the early stage of the CO2 absorption, the formation of carbonate species ([TBAEH]2CO3) was predominant, along with the generation of small amounts of zwitterionic species. With the progress of the absorption, the carbonate species was rapidly transformed into bicarbonate species ([TBAEH]HCO3), and the amounts of the zwitterionic species increased gradually. During desorption at elevated temperature in the absence of CO2, [TBAEH]HCO3 was found to transform into [TBAEH]2CO3, where CO3(2-) strongly interacts with two [TBAEH](+) via hydrogen bondings.

Bredigite-structure orthosilicate phosphor as a green component for white LED: the structural and optical properties.

A green-emitting phosphor, Ca14-xEuxMg2[SiO4]8 (CMS:Eu²âº), has been synthesized as a component of white light emitting diodes (WLEDs). The emission spectrum is broad, with a maximum at about 505 nm under 400 nm excitation due to the transition from the 4f65d excited state to the 4f7-ground state of a Eu²âº ion. The dipole-dipole interaction was a dominant energy transfer mechanism of the electric multipolar character of CMS:Eu²âº. The critical distance was calculated as 12.9 Å and 14.9 Å using a critical concentration of Eu²âº and Dexter's theory for energy transfer. When CMS:Eu²âº and red phosphor are incorporated with an encapsulant on an ultraviolet (λmax = 395 nm) light emitting diodes (LEDs), white light with a color rendering index of 91 under a forward bias current of 20 mA was obtained. The structural and optical characterization of the phosphor is described.

Morphological effect of lipid carriers on permeation of lidocaine hydrochloride through lipid membranes.

We have studied how the transdermal delivery of lidocaine hydrochloride (LHC) is affected by the morphology of lipid carriers, liposomes and micelles, having the same lipid composition of 1-stearoyl-sn-glycero-3-phosphocholine (LPC) and cholesteryl hemisuccinate (CHEMS). In vitro drug permeation study, carried out on guinea pig skin, has revealed that the liposomes made of LPC and CHEMS significantly enhance the permeation rate of entrapped LHC; by contrast, the mixed micelles with the same composition decrease the degree of delivering co-existing LHC. Basically, we have also investigated the release kinetics of LHC through the cellulose membrane and found that both liposomes and micelles have a similar releasing profile. To experimentally demonstrate this unique behavior, we have observed the fluidity of stratum corneum liposomal membranes in the presence of either our liposomes or micelles. From this study, we have found that LPC/CHEMS liposomes fluidize the lipid membrane of stratum corneum lipids; however, lipid micelles rather make the membrane rigid. These findings highlight that controlling the morphology of drug carriers provides us with a means to modulate the permeability of encapsulated drug molecules.

New mechanistic insight into the coupling reactions of CO2 and epoxides in the presence of zinc complexes.

Coupling reactions of CO(2) and epoxide to produce cyclic carbonates were performed in the presence of a catalyst [L(2)ZnX(2)] (L=pyridine or substituted pyridine; X=Cl, Br, I), and the effects of pyridine and halide ligands on the catalytic activity were investigated. The catalysts with electron-donating substituents on pyridine ligands exhibit higher activity than those with unsubstituted pyridine ligands. On the other hand, the catalysts with electron-withdrawing substituents at the 2-position of the pyridine ligands show no activity; this demonstrates the importance of the basicity of the pyridine ligands. The catalytic activity of [L(2)ZnX(2)] was found to decrease with increasing electronegativity of the halide ligands. A series of highly active zinc complexes bridged by pyridinium alkoxy ions of the general formula [((mu-OCHRCH(2)L)ZnBr(2))(n)] (n=2 for R=CH(3); n=3 for R=H; L=pyridine or substituted pyridine) were synthesized and characterized by X-ray crystallography. The dinuclear zinc complexes obtained from propylene oxide adopt a square-planar geometry for the Zn(2)O(2) core with two bridging pyridinium propoxy ion ligands. Trinuclear zinc complexes prepared from ethylene oxide adopt a boat geometry for the Zn(3)O(3) core, in which three zinc and three oxygen atoms are arranged in an alternate fashion. These zinc complexes bridged by pyridinium alkoxy ions were also isolated from the coupling reactions of CO(2) and epoxides performed in the presence of [L(2)ZnBr(2)]. Rapid CO(2) insertion into the zincbond;oxygen bond of the zinc complexes bridged by pyridinium alkoxy ions leads to the formation of zinc carbonate species; these which yield cyclic carbonates and zinc complexes bridged by pyridinium alkoxy ions upon interaction with epoxides. The mechanistic pathways for the formation of active species and cyclic carbonates are discussed on the basis of results from structural and spectroscopic analyses.

Solvate Molecule Effects and Unusual (57)Fe Mössbauer Line Broadening in the Valence Detrapping of Mixed-Valence [Fe(3)O(O(2)CCH(3))(6)(3-Et-py)(3)].S.

A new series of mixed-valence &mgr;(3)-oxo-bridged Fe(3)O complexes with the composition [Fe(3)O(O(2)CCH(3))(6)(3-Et-py)(3)].S, where 3-Et-py is 3-ethylpyridine and the solvate molecule S is either 0.5C(6)H(5)CH(3) (1), 0.5C(6)H(6) (2), CH(3)CN (3), or CH(3)CCl(3) (4), is reported. The complex [Fe(3)O(O(2)CCH(3))(6)(3-Et-py)(3)].0.5C(6)H(5)CH(3) (1) crystallizes in the orthorhombic space group Fdd2 which at 298 K has a unit cell with a = 22.726(8) Å, b = 35.643(14) Å, c = 20.816(6) Å, and Z = 16. Refinement with 5720 observed [F > 5sigma(F(o))] reflections gave R = 0.0337 and R(w) = 0.0390. An analysis of the bond lengths in complex 1 shows that it is the most valence-trapped Fe(3)O complex reported at room temperature. The complex [Fe(3)O(O(2)CCH(3))(6)(3-Et-py)(3)].CH(3)CCl(3) (4) crystallizes in the triclinic space group P&onemacr; which at 238 K has a unit cell with a = 12.764(2) Å, b = 13.1472(2) Å, c = 15.896(3) Å, alpha = 78.01(2) degrees, beta = 89.38(2) degrees, gamma = 61.38(1) degrees, and Z = 2. Refinement with 6264 observed [F > 5sigma(F(o))] reflections gave R = 0.0435 and R(w) = 0.0583. In this &mgr;(3)-oxo-bridged complex all three iron ions are inequivalent. Powder X-ray diffraction patterns taken at room temperature show that complexes 1 and 2 are isostructural and that complexes 3 and 4 are isostructural. Variable-temperature (57)Fe Mössbauer spectra were collected for all four complexes. The data for complexes 1 and 2 clearly indicate that these two complexes are totally valence trapped. On the other hand, Mössbauer spectra (43-293 K) for complexes 3 and 4 show that these two complexes become valence detrapped at temperatures near room temperature. Two doublets are seen at low temperature and they move together to become a single doublet at approximately 293 K. Examination of the line width versus temperature for each of the two components of the two doublets points to a curiosity. The two components of the "Fe(III)" doublet and the lower-velocity component of the "Fe(II)" doublet do not exhibit any line broadening, whereas the higher velocity "Fe(II)" component shows a surge in line width in the approximately 70-150 K range. Possible explanations for these unusual line width responses are discussed.