PP model

Van Dam D, De Devn PP. Model organisms drug discovery in dementia the role of rodent models, Nature Reviews Drug Discovery 5 956-970 (2006). 

The Suter-Flory RIS model of PP (A 027 is employed to calculate the 13C NMR chemical shifts expected at the 9-Ca and the CH3 carbons and at the 8- and 10-CHj carbons in the various stereoisomers of the PP model compound 3,5,7,9,11,13,15-heptamethylheptadecane. Differences in the chemical shifts of the same carbon atom in the various stereoisomers are assumed to be attributable solely to stereo-sequence dependent differences in the probability that the given carbon atom is involved in three-bond gauche or y interactions with other carbon atoms. The Suter-Flory model provides an accurate description of the conformational characteristics of PP which permits a detailed understanding of its 3C NMR spectrum. On the other hand, the failure of Provasoti and Ferro s calculations [Macromolecules 1977, 10, 874] is directely attributed to the inadequacies of the Boyd and Breitling three-state RIS model of PP (A 022). 

To begin, we discuss the results of calculations using the GVB-PP model, Le., results based on the use of the SOPP restrictions on the wave function, Eq. (4). GVB-PP calculations for CO2 (1), C2F2 (2) and benzene (5) have given descriptions of the multiple bonds in these molecules as being made up of bent... 

There has been some recent concern (8,9) however, that this bent bond description of multiple bonds derived from the GVB-PP model may be an artifact of the model. The concern takes two forms first, that the SOPP restrictions on the GVB wave function are the source of the bent bonds and the full GVB model will produce the usual <7,7r-bond description and second, if an MCSCF or Cl wave function which is more general than GVB is used, this will give back the c,7r description. 

Thus, there is legitimate cause for concern that our few examples of bent bonds within the GVB-PP model may not reflect the situation for the full GVB model. In order to resolve this issue on the interpretation of multiple bonds within the valence bond framework it is necessary to perform full GVB calculations on a series of molecules to remove the strong orthogonality and perfect pairing restrictions of the GVB-PP model. This is essential in order to assess the validity of the bent bond concept for multiple bonds. Full GVB calculations have in fact been carried out and the details will be presented elsewhere (5). Here we provide a brief summary of the results. 

The general picture which emerges from the large number of calculations performed is the following (1) those cases (e.g, CO2 and C2F2) which were found to prefer bent bonds within the GVB-PP model are found to retain the bent bond description when the SO and PP restrictions are removed from the wave function, ie., full GVB model is used to evaluate the nature of the multiple bonds (2) in those cases (e.g., C2H2 and C2H4) for which the 0,%... 

The PP Model has to be open, extensible, adaptable, and dynamical. Here are some of the reasons. ... 

Vergnes and Berzin (2004), Vergnes et al. (1998) of PP model of polymer flow in co-rotating, selfwiping, twin-screw extruders, coupled with degradation reaction kinetics shear rate, viscosity, residence time... 

Alternatives to the bipolaron have been diseussed earlier and espeeially the two polarons on a single ehain or polaron pair (PP) model [9] (PPs, +2e and 0-ESR silent) was proposed to be preferable eompared with the BP model, sinee the latter eontradiets optieal data whereas the former leads to a eonsistent explanation of optieal data. The eorresponding equation of state has been eonsidered only reeently [24] and led to a new eontradietion. In Seetion... 

A typieal dependeney of the P and BP eoneentrations on the potential is de-pieted in Figure 16.10 for energetically favoured BPs the BP concentration saturates for high potential and the P coneentration shows a maximum at the potential for the two-electron reaction. This dependency is in accordance with the maximum in the spin concentration observed in ESR spectro-eleetroehemieal experiments. In spite of this agreement, the BP model is in disagreement with optical data and has been ruled out therefore by the PP model [9]. 

Figure 2 depicts the FT-IR spectra of C-Al-pp and C-Fe-pp models, contrasted with C. In the C-Al-pp and C-Fe-pp aggregates, the peculiar C reference peak at 3627 cm disappears, and the peak at 3420 cm is left-shifted toward larger wavenumber values. The strong carbonilic group effects at 1708-1715 cm, detected in the pp model, also fade away, whereas the peak at 1520 cm, associated to the aromatic C=C in pp and C-pp, are left-shifted to 1505 cm, with decreasing intensity from C-Al-pp to C-Fe-pp. 

The X-ray diffraction patterns of Al-pp and Fe-pp (not shown) did not give any significant regular reflection, thus suggesting that the presence of polyphenol inhibits the crystallization of A1 or Fe polymers, likely by effective chelation reactions. However, two contiguous, broad diffusion bands, with minimum at 8.72, 23.92 and 40.00 °20, were observed in the Fe-pp model. This could be attributed to the higher charge density of Fe ion, which promotes the... 

Fig. 2. FT-IR spectra of C, C-Al-pp, and C-Fe-pp models. Vertical bars indicate standard reference peaks of montmorillonite clay.

The interaction of polyphenol with Al- and Fe- led to the formation of complexes with very different physical features. The Al-pp model formed small microaggregates, with particle size ranging from 2 to 10 pm, and moderate stability (30% of material with particle size 2-5 pm after sonication). Differently, Fe-pp formed larger aggregates, up to 100 pm, which were easily disrupted by ultra-sound treatment. However, about 49% of particles still keep a dimension of 5-10 pm after sonication. This should confirm the overall tendency of Fe- to form polymers larger than AI-. 

By extending the hot oxidative treatment to 120 minutes, the amount of oxidized C did not exceed 84% for Fe-pp, C-Al-pp, and C-Fe-pp models, but it was still nearly 60% for Al-pp. This clearly proves that /IZ-oxy-hydroxides were more effective than Fe-oxy-hydroxides in stabilizing and protecting the organic matter. 

As reference values, Table 3b also presents the amounts of C oxidized after 30 or 120 min for pure tannic acid pp and for the C-pp model. It is evident that, in the absence of an efficient complexing cation, the whole amount of organic C is definitively oxidized within 120 min. Interestingly, in the C-pp model, the large amount of C already oxidized after 30-min could be ascribed to a possible priming catalytic effect by the clay mineral differently, the flakes of pure pp probably clotted, thus needing more time to be completely oxidized [15]. 

Fig. 1. EUF-P release from C-Al-pp model at different aggregation states.

The desiccation via air-drying definitively stabilized the P pool, especially in the C-Al-pp model for this sample, the P/ and Pm where about 2 or 3% of Pa, respectively, while the P/ of C-Fe-pp represented about the 20% of Pa (please, note that P caimot be estimated for C-Fe-PP)-... 

It is also interesting to note that, in accordance with the observations above, the equation parameters for P desorption from air-dried C-Al-pp model were almost similar to those obtained for the respective re-suspended model (Table 5). An analogous behavior was observed for the C-Fe-pp model (Table 5). Consequently, for whichever C-Al-pp and C-Fe-pp models, the P release isotherms curves from the respective air-dried or re-suspended materials were practically coincident (Figs. 1,2). 

The C-Fe-pp model exhibited Cation Exchange Capacity, Specific Surface Area, Specific Cationic Surface Charge, Titratable Acidity, and P sorption capacity higher than C-Al-pp. For both model, the amounts of P desorbable by EUF were much lower than the amounts of P initially added. However, the C-Fe-pp model was less able than C-Al-pp in retaining the initially added P. Evidently, distinct mechanisms controlled the interactions of P with C-Al-pp or C-Fe-pp in both sorption and desorption phenomena. In particular, the presence of Al- or... 

In the perfect pairing (PP) model, each pair of electrons is described by its own geminal. In contrast, the AGP and Pfaffian functions share the same geminal for all electron pairs. The perfect pairing geminal has a more constrained form than the previously described wave functions. In each geminal, a pair of active occupied orbitals, ifiir i, has a corresponding pair of active virtual orbitals, tA, ... 

The first work which directly measured the interaction strengths for PP blends involved the use of model PPs made by the satiuation of poly dienes [3]. Two PP models can be produced in this way, one with a head-to-tail structure, as in commercial PP (htPP), and the other with a head-to-head conformation (hhPP) these two polymers have strikingly different phase behavior with other pol)uners. Table 1 shows some examples of the values of the interaction strength that have been... 

The PP model has been rdntroduced recendy, ° after it had been first investigated in the context of assodating fluids by Werthdm. While in the original model the surface patches were considered as discrete spot-like interactions, it is more appropriate to consider rather extended (attractive or repulsive) surface regions, which act as branching sites in the self-assembled dusters and characterize chemical or physical patterning of the partide surfaces. 

In this Section we introduce the overall PPS model-driven design process which is the frame where the proposed pattern-based modelling approach is situated. 

In view of assumption 1, each micelle acts as a microreactor of one domain that provides a new reaction medium and alters the distributions of reactants in solution. Thus, the classical PP model may also be called the two-domain pseudophase model of micelles, in which the bulk aqueous region and the entire micellar pseudophase are considered to be two different reaction domains. A refinement of Equation 3.2 consists of including the possibility of different reaction domains within the micelle. A three-domain pseudophase model is one in which, for example, the bulk aqueous region, the Stem region, and the hydro-phobic micellar core are treated as separate reaction regions. ... 

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