AH-b-X model

The above discussions, in conjunction with previous results, support our previous idea that the receptor site for sweet taste is composed of the AH-B-X system and its most likely shape is a "pocket" as shown in Figure 6 (5). In this model, the spatial... 

Sweet taste is produced by a wide variety of compounds. SHAL-LENBERGER and ACREE (6) regard an acid/base system (AH/B-System) as the shared structural element. This system must satisfy certain steric conditions and can interact with a complementary system of a receptor via 2 hydrogen bonds (Fig. 1). KIER (7) expanded this model by assuming an additional interaction witfi an apolar group X in a suitable position (Fig. 1). Both models are applicable to compounds with great variations in structure. There are no similar comprehensive concepts for bitter compounds which can also occur in the most varying chemical classes. 

FIGURE 4 Three of the most popular indirect models of the active site of the sweet taste receptor. (A) Main contour ofthe active site proposed by Temussi and coworkers (Kamphuis et al., 1992 Temussi et al., 1978,1984,1991), hosting a molecular model of aspartame in an extended conformation. (B) A topological model, developed by Goodman et al. (1987). The L -shaped model and an L -shaped conformation of aspartame are superimposed. The hydrophobic side chain of Phe is denoted X, since it corresponds to the Kier s dispersion point. (C) 3D model of an idealized sweetener proposed by Tinti and Nofre (1991). Besides the AH-B entity, the model has six additional interaction points connected by a complex network of distances. 

Recently, an ah m feo-based model of the ultrafast C B X internal-conversion process in the benzene cation (Bz+) has been proposed by Koppel, Domcke, and Cederbaum. The diabatic potential matrix... 

Figure 1 The Goodman L-shape model. AH, B, and X are defined as in the Shallenberger-Acree-Kier model (reproduced by permission of the American Chemical Society)...

Fig. 7. a Cross sectional profile of an ultrathin film of dendrimer 23 on HOPG along x-x as indicated in (b). The height difference between adjacent terraces has the dimension of a monolayer [Ah = 4.3 ( 0.2) nm]. Large scale (2.4 x2.4 pm2) SFM image of monomolecular terraces, c Schematic model of closely packed molecular cylinders in thin films of 23 on HOPG... 

If the sought model, X, has the structure AB then fitting a bilinear model to the scaled data provides the model in the form AH. Thus, the score matrix (or a rotated version of it) is directly provided in A whereas the loadings of the original problem are found by premultiplying the found loadings, H, with W 1, as B W = H => B = H W-1 => B = W-1H. 

To facilitate illustration, we select a Mandat d model ZB and a standard model AH. Both are chosen to he iiiiiiully in contact (x - 0). I-or the standard Z.B. ue choose parameter values that lit data for the (irignard reactions of primary alkyl bromides in Dl. l at —40 C (Section 7.2.St. 

The dynamic surface tension studies of Tritons indicate that the surface tension decrease in the short time range is faster (as compared with the usual diffusion models) [60,61]. This fact supports the conclusion about the existence of a reorientation process for Tritons at the surface. Similarly to the CnEOm, in the homologous series of Tritons the b value also increases with the m (cf Fig. 3.38). This again supports the hydrophilic-hydrophobic character of the EO groups. From the temperature dependence of the adsorption equilibrium constant b (cf. Table 3.15), one can estimate the thermodynamic characteristics of Triton X-100 adsorption at the water/air interface. In particular, the AG values can be calculated at various temperatures using Eq. (3.11), and then estimate the standard enthalpy (AH ) and standard entropy of adsorption (AS ) via Eqs. (2.180) and (2.181). 

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