Size-discriminating effect

It has been claimed in the literature [6] that a size discriminating effect can be observed with PdSalen complexes encaged in faujasite-type zeolites In the competitive hydrogenation of an equimolar mixture of hexene-(l) and cyclohexene in the liquid phase, hydrogenation of the slim 1-alkene is strongly prefered, whereas in the homogeneous phase both alkenes are hydrogenated with a comparable rate. In... 

The evolution of the formation constants of the binuclear triple-stranded helicates [1 2(L11)3] (NNN-S-NNN donor sets) and [R2(L13 )3] " " (ONN-S-NNO donor sets) along the lanthanide series mimics the size-discriminating effects previously established with the mononuclear precursors (Figure 31). When NNN donor sites are used in Lll, the stability constants drops for the smaller R , a trend removed when the terminal benzimidazole rings are replaced with carboxamide units in (Table 8). The connection of electron-withdrawing halo-... 

Although SPMDs are simple in design, the mechanisms governing their performance as passive samplers of HOCs can be quite complex (see Chapter 3). The underlying principle of molecular-size discrimination in the uptake and loss of chemicals by SPMDs is shown in Eigure 2.1. The sizes of the molecules shown in the illustration are scaled to the postulated 10 A diameter of the transient pores in the membrane. Temperature and the presence of plasticizers/solvent will affect the effective pore sizes. 

The technique has been evaluated by Langhorst et. al. [44,45] and reviewed by Miller and Lines [46]. HDC suffers from poor resolution and particle size discrimination. In principle, more accurate particle size determinations are possible but require special software with correction for the extensive band dispersion [47,48]. It has also been shown that the molecular weight and concentration of non-ionic surfactants adsorbed on latex particles have a significant effect on their separation factor [49]. 

Several collimator sizes discriminate between radiations reaching the sensor at different incident angles. Inner-polished aluminum collimators of several sizes can be used to determine the effective extinction coefficients and to assess the total radiation transmission through the sluny at the outer reactor wall (Figure 3.7). 

Zeolites of controlled pore sizes of the order of a few angstroms have become popular catalysts and adsoibents because of their abili to discriminate effectively the shape and size differences among molecules. Weisz et al. describe applications of these shape-selective catalysts in oxidation of normal paraffins and olefins in the presence of the branched isomers. Observed diffusion coefficients in these zeolites are often found to be quite small (10 m /s) but precise interpretations of the measurements and mechanisms of transport in zeolites ate not available as yet. 

The simplest molecular cation is the ammonium ion which cannot be discriminated from by size very effectively. However, a clear difference in charge distribution exists, being spherical for and tetrahedral for NH4. Selective binding of a tetrahedral guest requires the construction of a receptor... 

Figure 10 Images of domains of monolayers of the o-enantiomer, L-enantiomo-, and racemic mixture of A-stearoylserine methyl ester clearing showing chiral discrimination effects. The domains of the enantiomers display unique curvature, and the domain of the racemic mixture shows featnres with both senses of curvature and hence evidence for chiral segregation. Reproduced from Ref. 62. American Chemical Society, 2003, and the figure caption reads as follows Chiral discrimination of the condensed-phase domains of N-stearoyl serine methyl ester monolayers spread on pH 3 water, (a) D-enantiomer (b) L-enantiomer (c) and (d) 1 1 dl racemate. Image size 80 x 80 pm.

One strategy that has been employed in our laboratories in an effort to minimize mass discrimination effects has been to couple GPC, either off-line or directly on-line to MS. In GPC, the separation mechanism involves an equilibrium between solutes in the mobile phase and those which can permeate the inner volume of a stationary phase that is porous. Molecules with hydrodynamic volumes (or size in solution) that are smaller than the pore sizes in the stationary... 

The activated areas determined as described above (n, B-3) are indicated as red regions in Fig.3. Most of the activated areas were in the left occipital lobe. These activated areas were considered to include the processing areas for both motion itself and motion-defined pattern perception. We then tried to discriminate the areas for pattern perception by utilizing the correlation analyses between the sizes of effect and the correct rates for pattern discrimination task at 4 velocity levels. The only one voxel significantly correlated in such analyses was the area designated by the black square at BA19 in Fig.3 (t(3) = 5.185, p<0.05). The correlation coefficient ( r = 0.967) revealed very strong correlation. The location of this area is listed in Table. 1. 

The activated areas of 14.4 deg/s condition subtracted by 57.6 deg/s were indicated as red region. The location of significant correlation between the sizes of effect and correct rates for pattern perception is designated as black square. The locations of significant correlations with those for motion discrimination are depicted as white circles. 

In this study, we carried out the correlation analyses between the data obtained by the psychophysical experiments and those acquired in the psychopysiological experiments. As suggested from the results in Fig.3, the close correlation between the data of correct rate for pattern discrimination task and of the size of effect by fMR measurements well contributed to identify the location of the processing area for mo ton-defined pattern perception as BA19. Accordingly, it is suggested that the correlation analyses between the... 

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