Intraband optical activity of semiconductor nanocrystals

Here we review our three recently developed analytical models describing the intraband optical activity of semiconductor nanocrystals, which is induced by screw dislocations, ionic impurities, or irregularities of the nanocrystal surface. The models predict that semiconductor nanocrystals can exhibit strong optical activity upon intraband transitions and have large dissymmetry of magnetic‐dipole absorption. The developed models can be used to interpret experimental circular dichroism spectra of nanocrystals and to advance the existing techniques of enantioseparation, biosensing, and chiral chemistry.     

Bioaccumulation of heavy elements by Armadillidium vulgare (Crustacea,Isopoda) exposed to fallout of a municipal solid waste landfill

This paper reports the response of isopods exposed to fallout of a municipal solid waste landfill located in central Italy. Soil samples and specimens of Armadillidium vulgare were collected at different distances from the landfill and analyzed to determine the concentrations of heavy elements such as As, Cd, Co, Cr, Cu, Ni, Pb, Sb, V and Zn. The isopod analysis was performed on unpurged and purged specimens. Analytical data indicate that the soil contents of heavy elements were quite uniform and within the respective local geochemical background. Slight enrichments of Cu and Pb were found in some soils collected within the solid waste. Purged isopods showed an accumulation of As, Co, Cr, Ni, Sb and V whose body levels decreased as the distance from the landfill increased. Cd, Cu, Pb and Zn concentrations in purged specimens were rather uniform and no significant variation trend occurred. This result probably was due to the fact that the isopods are provided with physiological mechanisms of regulation for these heavy elements. Analytical data also indicate the ability of A. vulgare to adsorb differently the heavy elements according to the following order: As > Co > Ni > Pb > V. The contents of heavy elements in unpurged specimens were higher than in purged ones. This finding suggested that the defecation has marked effects on the tissue levels of heavy elements in isopods. This study indicates that the isopods provide useful information about environmental quality in areas characterized by low and discontinuous emission of heavy elements and their low accumulation in soil.     

Computational Oral Absorption Simulation for Low‐Solubility Compounds

Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed.     

The effect of antibiotics on the photocycle and protoncycle of purple membrane suspensions

The interrelation was studied between the phototransient absorbing maximally at 412 nm (M₄₁₂) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M₄₁₂ was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M₄₁₂ which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M₄₁₂ was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M₄₁₂ without affecting the level of M₄₁₂ which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca²⁺ and their antagonists La³⁺ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed.     

Transdermal enhancement through rat skin of luciferase plasmid DNA loaded in elastic nanovesicles

Transdermal absorption of luciferase plasmid (pLuc) was enhanced by loading in elastic cationic liposomes and niosomes and the application of iontophoresis or the stratum corneum (SC) stripping method. Cationic liposomes (DPPC/Chol/DDAB at a 1:1:1 molar ratio) and niosomes (Tween61/Chol/DDAB at a 1:1:0.5 molar ratio) were prepared by the freeze-dried empty liposomes method. The elastic vesicles were prepared by hydrating the lipid or surfactant film by 25% of ethanol instead of distilled water. Gel electrophoresis of all nanovesicles showed the 100% pLuc entrapment efficiency. All nanovesicles loaded with pLuc showed larger vesicular sizes than the nonloaded vesicles of about 1.4 times for liposomes and 1.7 times for niosomes. The nanovesicles loaded with pLuc demonstrated less positive zeta potential than the nonloaded vesicles. The pLuc loaded in elastic vesicles kept at 4 ± 2 and 27 ± 2°C for 8 weeks gave the remaining pLuc of about 70 and 60% for liposomes and 85 and 73% for niosomes, respectively. For nonelastic vesicles kept at 4 ± 2°C, 56 and 61% of the remaining pLuc were observed for liposomes and niosomes, respectively, while at 27 ± 2°C, all pLuc were degraded. The deformability indices of the elastic liposomes and niosomes loaded with the pLuc were 16.64 ± 2.92 and 20.72 ± 0.82, whereas the nonelastic vesicles gave 9.35 ± 0.09 and 10.08 ± 0.12, respectively. Transdermal absorption through rat skin pretreated with SC stripping or treated with iontophoresis of pLuc loaded in nanovesicles by vertical Franz diffusion cells was investigated at 37°C. The cells were stopped and the skin and the receiving solution were withdrawn at 1, 3, and 6 hours and the pLuc contents in the stripped SC, whole skin (viable epidermis and dermis; VED), and the receiving solution were assayed by the modified gel electrophoresis and gel documentation. Without the SC stripping technique or iontophoresis, the pLuc loaded and nonloaded in nonelastic cationic liposomes or niosomes were not found in SC, VED, and receiving solution. The fluxes in the whole skin of pLuc loaded in nonelastic liposomes and niosomes with SC stripping and iontophoresis at 6 hours gave 2.73 ± 0.46 and 3.83 ± 0.73, and 7.01 ± 1.22 and 9.60 ± 1.31 g/cm²/h, respectively, while pLuc loaded in elastic liposomes and niosomes without the SC stripping and iontophoresis at 6 hours showed 2.79 ± 0.09 and 2.84 ± 0.04 g/cm²/h, respectively. The pLuc loaded in elastic niosomes or in nonelastic niosomes with iontophoresis was found in the receiving solution with a higher amount than that loaded in elastic liposomes or nonelastic liposomes with iontophoresis. The fluxes in the receiving solution of pLuc loaded in nonelastic liposomes and niosomes with iontophoresis at 6 hours were 6.71 ± 0.31 and 8.82 ± 0.28 g/cm²/h, respectively. For elastic liposomes and niosomes, the fluxes of the loaded pLuc in the receiving solution were the same, at about 1.9 g/cm²/h. Although pLuc loaded in nonelastic niosomes with iontophoresis gave the highest delivery of the plasmid in VED and receiving solution, a more promising applicable approach for gene delivery has been suggested to be the elastic niosomal systems, since no equipment is required.     

X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

The relationship between iron status and lead absorption in rats

The absorption of lead from loops of small intestinein situ was investigated in rats in which iron absorption was increased by stimuli varying in type, intensity, or duration. Lead absorption was increased by a short period of severe iron restriction before any change in hematological indices became apparent. A period of hypoxia, which markedly increased iron absorption, did not influence absorption of lead. An extended period of moderate iron restriction resulted in a marked reduction in liver iron stores and increased iron absorption throughout the 17-wk experiment. Under these conditions lead absorption was initially also increased, but after 12 wk, when iron intake had become adequate to meet essential requirements, lead absorption was similar to that in iron-supplemented rats. These results are discussed in the light of evidence for a receptor-mediated absorption process for iron.