Alpha -values

As with the molecular connectivity indices, higher-order shape indices have also been defined. The kappa indices themselves do not include any information about the identity of the atoms. This is the role of the kappa-alpha indices. Tlie alpha value for each atom is a measure of its size relative to some standard (chosen to be the sp -hybridised carbon) ... 

By clicking the appropriate buttons on the form, the user can combine molecular structure queries of sample, CSP and solvent, using operators AND, OR, NOT with data queries in one search. A query for the search of chiral separations of alpha-aromatic acids on any polysaccharide phases coated on silica gel providing an alpha value superior to 1.2 is shown in Eig. 4-4. 

The same effect was also observed for tertiary butyl alcohol (TBA), a substance which is frequently used as a radical scavenger in kinetic experiments (see Section B 4.4). Depending on its concentration (c(TBA) = 0-0.6 mM) alpha values up to afO = 2.5 were measured (Gurol and Nekouinaini, 1985). Since TBA is hard to oxidize by molecular ozone in contrast to phenols (kD(TBA) 3 10 3 L moF1 s pH = 7, Hoigne and Bader, 1985), the effect of TBA on kLa can also be studied in mass transfer experiments with ozone. 

An alpha plot for a buffer (or an amino acid) shows the percentage of each component in a buffer system as a function of pH. Alpha for a given species is the percent of all the material that is present in that form. So, when alpha for the conjugate acid form is 75%, the ratio of conjugate acid to conjugate base is 75 25. Naturally, the sum of the alpha values for the conjugate acid and the conjugate base add up to 100%. 

As we continue to increase pH, the zwitterion concentration reaches a maximum value at pH 6.0. Above this pH, the zwitterion is gradually converted into the anionic form (A"). Once again, we have a buffer system comprised of a weak acid (HA) and its conjugate base (A-). The point where the alpha values for these two species equal 50% corresponds to a pH of 9.6, which is the pRa for the zwitterion. 

The Isoelectric Point The isoelectric point (pi) or isoelectric pH is the pH where the net charge on the amino acid is zero. At pi, the zwitterion is the dominant species, with an alpha value very close to 100%. The tiny equilibrium amounts of the cationic form and the anionic form are equal, so their opposite charges cancel each other out. The net charge on a collection of amino acid molecules at a pH less than pi is positive. The net charge on a collection of amino acid molecules at a pH greater than pi is negative. 

Calculate the average alpha values (K of each component divided by HKK value). The average tower alpha A of each component = (Ai A2 A3)L 3. These A s are the tower top, the tower average temperature, and the tower bottom temperature AjS, all of which are used here to calculate the tower average A S. 

Because we made a good first Step 2 estimate, little if any difference will occur due to running a new set of average alpha values (Step 2 through Step... 

Enter an alpha value if you have chosen F or T for the method. Enter a K value for a light key component if you chose A. Input the factor alpha or K. Alpha is defined as simply the light key K divided by the heavy key K component. The K factor is simply the particular component s vapor phase mole fraction divided by its liquid mole fraction. The alpha value is therefore a ratio of the chosen two key components. These key components should be those that readily point to how well the fractionator is doing its job of separation. For example, for a depropanizer tower, choose propane as the light key component and butane as the heavy key, since you wish to separate the propane from the butane to make a propane product specification. For a multicomponent system, you may try several components to determine a controlling alpha and/or to factor an average tray efficiency. 

Unlike the retentivity measure, k, relatively minor changes in alpha can have very major effects on resolution as shown in Table III. The variances in alpha that can be tolerated from column-to-column to maintain a given separation (R >1.25) is dependent on the alpha value involved. Table IV sfiows these allowable variances for several values of alpha. This table... 

An impressive application of the chelated metal technique was recently reported by LePage et al (26). Optical isomers of dansyl amino acids were resolved using an optically active metal chelate. High alpha values and high efficiency conditions were achieved, as shown in figure 5. 

The alpha value was included in the previous discussion, simply for the sake of completeness, but from this point on, we will ignore the question of standards of proof and simply assume that the normal standard is used (i.e. a = 0.05 a 95 per cent Cl is used or significance accepted if P < 0.05). Figure 8.3 shows the inputs into a formal calculation of the power of an experiment and the effects they would have. 

The effluent gases were sampled after the catalyst was on stream for 3.0 min. First order rate constants and alpha values were calculated as previously described (5). 

We found the acidity of chemically dealuminated mordenites shows a large variation with aluminum content (Figure 9). The alpha values decrease over five orders of magnitude as the aluminum content decreases from four aluminum atoms per unit cell down to 0.8 Al/unit cell. If the Bronsted acid sites associated with boron are of equal strength as those associated with... 

The alpha values of synthetically prepared mordenltes are within the range of 10 -10°. There Ls only a small variation In a values of siliceous mordenlte as the aluminum content of the material varies. This Ls In contrast to dealumlnated mordenltes, which exhibit a much larger variation Ln alpha values as the aluminum content varies. These catalytic results on synthetic and acid dealumlnated mordenltes Indicate that factors other than the total aluminum content must contribute to the variation In activity of the catalysts. The linear correlation of alpha versus aluminum content reported for some zeolites (26) does not apply to the acid dealumlnated samples. Evidence has been presented for the presence of both Bronsted sites and Lewis sites enhancing the strong acidity of zeolite catalysts (27). The presence of extra-lattice aluminum Ln acid dealumlnated mordenlte samples was confirmed by 2 A1 NMR spectroscopy. The presence of both framework aluminum and extra-lattice aluminum Ln the acid treated materials may account for the wide variation Ln alpha values as a function of aluminum content. 

The synthetic boron substituted mordenltes have alpha values similar to the aluminosilicate analogues. This Ls not surprising since boron replaces only 10% of the aluminum In these materials. For boron to affect the alpha values of these samples, the acid strength of a B-OH proton would have to be much greater than for a A1-0H proton, inihlch Ls clearly not the case. 

Figure IS. a trajectory for 8 = 0.11 radians for the quasiparticle diagonal Zpk-TDA 2ph-TDA) dec0Uplxfig, The distances narrow as a = 0.85 is approached and then increase again. The quasi-stable value of the pole at this alpha value is therefore taken to be the best estimate of the energy and width of the Auger resonance from this decoupling.

The alpha values (o) are then plotted on the graph (Figure II. 1) and are used to draw an alpha line from which the y-intercept (AO and o.n/2 are obtained. Criteria that can be used to assess data quality at this... 

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