Pore formation in unilamellar lipid vesicles is believed to occur when the concentration of membrane-bound drug molecules exceeds a certain value. We treat this phenomenon in analogy with that of the micellization of surfactant in bulk aqueous solutions, thereby relating the threshold concentration of drug molecules to the free energy associated with transferring a molecule to a pore from its uniformly-dispersed state in the membrane. Incorporating the effect of lateral tension induced by osmotic pressure, we calculate the lowering of the pore-formation threshold with increasing tension. These predictions are tested by direct measurements on liposomal dispersions involving the antifungal drug amphotericin B.
A detailed study of the Cd(II)/Cd(Hg) system in 2-mercaptoacetic acid, H2MA, solns. was carried out in 1 M NaClO4 at pH 4.8-12.0. The electrochem. behavior of 2-mercaptoacetic acid at a dropping mercury electrode was studied as well. Since all complexes that are formed in the soln. undergo a reversible two-electron redn., math. anal. of the data, provided the compn. of the various complexes. The stability consts. of the following complexes: Cd(SCH2CO2)34-, Cd(SCH2CO2)22-, Cd(SCH2CO2), CdH(SCH2CO2)33-, CdH2(SCH2CO2)32-, CdH(SCH2CO2)2-, CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ were detd. and their degree of formation as a function of pH were estd. The protonation consts. of the ligand were calcd. The H2MA forms extremely stable bidentate complexes with cadmium ions. The formation of the various complexes as a function of pH reveals that at pH 10.7-12.0 the complex Cd(SCH2CO2)34- predominates, whereas at pH 4.8-6.0 the complexes CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ are dominant. At pH 6.1-10.6 different protonated and unprotonated complexes, composed of one to three ligands, coexist. [on SciFinder(R)]
The association of esterase (EST) activity with resistance to the organophosphorus (OF) insecticide methidathion was investigated in field-collected populations of whitefly (Bemisia tabaci (Gennadius)) in Israel. The inheritance of EST activity was studied by controlled crosses in the laboratory. Among-family variance of EST activity was highly significant although all families were maintained in the same rearing room. This indicates that genetic or common environmental effects due to rearing each family on a different caged plant must have been important. Heritability estimated from son-mother regression was h(2)=0.98, but this estimate seems to be unrealistically high. Daughter-mother and daughter-mid-parent regressions produced lower heritability estimates (as expected). None of the regression coefficients of daughters on mother, however, were significantly different from zero and the regression on parent explained only very small amounts of the activity variation in the offspring. Estimates obtained from intraclass correlations among offspring were higher and outside the acceptable range, reflecting the variance component due to the common environment. The predictive value of the heritability estimates appears to be very low. The frequency distribution of activity among individuals sampled from one insecticide treated site (AM) was skewed to the right, as previously reported. But samples from another site (TZ) showed a symmetrical distribution, unlike the previous pattern. When field collected individuals from AM were released on clean plants in the laboratory, samples taken from the plants one or more days later showed symmetrical EST distribution. Electrophoretic paterns of field and laboratory samples were the same, but band intensity was stronger in samples from laboratory populations. Differences in mean EST activity between populations and sampling years were unrelated to methidathion resistance.
We have isolated the novel murine Sax-1 gene, a member of the NK-1 class of homeobox genes, and report its expression pattern in the developing central nervous system (CNS) in comparison to two other homeobox genes, Evx-1 and Pax-6. Sax-1 was found to be transiently expressed in the developing posterior CNS. First seen in the ectoderm lateral to the primitive streak, the signal later encompassed the neural plate. Posteriorly, the expression domain overlapped with the Evx-1 expression in the streak, while anteriorly it was delimited by the Pax-6 signal in the neural tube. This early phase starting at day 9.5 pc, Sax-1 was expressed in distinct areas of spinal cord, hindbrain and forebrain. Particularly strong signals were detected in rhombomere 1 and in the pretectum. In these areas, subsets of neurons may be marked and specified. In addition to the normal pattern of Sax-1 during development, the expression in different mouse mutants was analysed. In Brachyury curtailed homozygotes, the expression of Sax-1 was found to be reduced during neurulation and even lost at day 9.0 pc. Ventral shift and finally loss of the signal in the ventral spinal cord was observed in Danforth's short tail homozygotes.
Papers delivered at a symposium held in Jerusalem on "Fifty Years after the Racial Laws in Italy." Contents: Wistrich, Robert Solomon : Fascism and the Jews of Italy (13-18); Sznajder, Mario : The Fascist Regime, Antisemitism and the Racial Laws in Italy (19-36); Della Seta, Simonetta : Italian Zionism Confronts Fascism and the Racial Laws (37-48); Michaelis, Meir : The Current Debate over Fascist Racial Policy (49-96). SSC
Cationic guar gums of varying molar mass and charge d. were synthesized and tested as flocculants for bentonite suspensions. The gums were fragmented using ammonium persulfate as a degrading agent, followed by pptn. of the products with ethanol. Cationic charge was added to the guar mol. by reacting it with 2,3-epoxypropyltrimethylammonium chloride. Flocculant performance was assessed by detg. the extent of polymer adsorption, by measuring both residual turbidities of the resulting supernatants and the changes in the particles' electrophoretic mobility (EM). Increasing the flocculant charge d. causes the optimal flocculation concn. (OFC), as well as the efficient flocculant concn. range, to be reduced. Above this range restabilization occurs. The OFC (for highly modified guar) is also the concn. at which the particles' EM is zero. It was found that decreasing the mol. wt. of the guar (at the same charge d.) increases the OFC and decreases the electrophoretic mobility of the clay particles in the overdose range. [on SciFinder(R)]
Surface active antibodies were formed by covalent attachment of hydrophobic groups to the IgG mol. The modified antibodies reduced surface tension and adsorbed onto emulsion droplets at surface concns. higher than the native antibody. The chem. modification led to a decrease in the biol. activity; however, at specific conditions, surface-active antibodies, which retained their recognition ability, could be formed. By using these antibodies, a new emulsion, which has a specific recognition ability for HSV-1 infected cells, was formed. [on SciFinder(R)]
Surface active antibodies were formed by covalent attachment of hydrophobic groups to IgG mols. The modification was carried out at various degrees of attachment and various chain lengths. These modified antibodies spontaneously formed new colloidal micelle-like particles, immunoclusters, which were viewed with a transmission electron microscope and evaluated by light scattering. The size of the immunoclusters increased while either degree of attachment or chain-length were increased, and the biol. activity decreased with an increase of degree of modification. [on SciFinder(R)]
The angular intensity distribution of He beams scattered from compact clusters and from diffusion limited aggregates, epitaxially grown on metal surfaces, is investigated theoretically. The purpose is two-fold: to distinguish compact cluster structures from diffusion limited aggregates, and to find observable signatures that can characterize the compact clusters at the atomic level of detail. To simplify the collision dynamics, the study is carried out in the framework of the sudden approximation, which assumes that momentum changes perpendicular to the surface are targe compared with momentum transfer due to surface corrugation. The diffusion limited aggregates on which the scattering calculations were done, were generated by kinetic Monte Carlo simulations, It is demonstrated, by focusing on the example of compact Pt heptamers, that signatures of structure of compact clusters may indeed be extracted from the scattering distribution. These signatures enable both an experimental distinction between diffusion limited aggregates and compact clusters, and a determination of the cluster structure, The characteristics comprising the signatures are, to varying degrees, the rainbow, Fraunhofer, specular and constructive interference peaks, all seen in the intensity distribution, It is also shown, how the distribution of adsorbate heights above the metal surface can be obtained by an analysis of the specuIar peak attenuation. The results contribute to establishing He scattering as a powerful tool in the investigation of surface disorder and epitaxial growth on surfaces, alongside with STM.
The angular intensity distribution of He beams scattered from compact clusters and from diffusion limited aggregates, epitaxially grown on metal surfaces, is investigated theoretically. The purpose is two-fold: to distinguish compact cluster structures from diffusion limited aggregates, and to find observable signatures that can characterize the compact clusters at the atomic level of detail. To simplify the collision dynamics, the study is carried out in the framework of the sudden approximation, which assumes that momentum changes perpendicular to the surface are targe compared with momentum transfer due to surface corrugation. The diffusion limited aggregates on which the scattering calculations were done, were generated by kinetic Monte Carlo simulations, It is demonstrated, by focusing on the example of compact Pt heptamers, that signatures of structure of compact clusters may indeed be extracted from the scattering distribution. These signatures enable both an experimental distinction between diffusion limited aggregates and compact clusters, and a determination of the cluster structure, The characteristics comprising the signatures are, to varying degrees, the rainbow, Fraunhofer, specular and constructive interference peaks, all seen in the intensity distribution, It is also shown, how the distribution of adsorbate heights above the metal surface can be obtained by an analysis of the specuIar peak attenuation. The results contribute to establishing He scattering as a powerful tool in the investigation of surface disorder and epitaxial growth on surfaces, alongside with STM.
