Extent of cooperativity

Cu(II) Complexes with Diethylethylenediamine. The complexes [Cu(dieten)2]X2, where X is an anion and dieten is the bivalent ligand N, V-diethylethylendiamine, well illustrate the effect of the medium on the extent of cooperativity of the transformation. These systems present interesting properties, and they have been investigated extensively [498-503]. When X is BF4, CIO4, or NO3 the complexes have thermochromic behavior and the color changes from red, at low temperature, to blue in the high-temperature form [499, 504]. 

When this model is applied to the interpretation of spin relaxation of polymers in solution the extent of cooperation motion can he measured hy a parameter R = (W /Wb) / which is found to take on values from 1 to 50. If a bond is the smallest moving unit, then R, called the "range", corresponds approximately to the number of bonds Involved in cooperative or coupled motion ( ). Both Wg and are strongly temperature dependent and vary non-monoton-Ically with temperature which appears to complicate this simple identification of R. 

In order to analyse the extent of cooperativity of the motions involved in the j transition of BPA-PC, quite a large series of copolymers has been synthesised. The (BPA-C)n blocks (denoted Bn) and (TMBPA-C) blocks (denoted Tn) have been studied by dynamic mechanical measurements. 

In the absence of pending groups or antiplasticisers, the motions of the hydroxypropyl ether units in the high-temperature part of the transition force motions of the crosslink points that are spatial neighbours of the moving HPE sequence. A crude estimate leads to an extent of cooperativity at high temperatures reaching more than six crosslink points in densely crosslinked networks. 

The investigations of PMMA at two temperatures (- 40 and 60 °C) by multidimensional solid-state 13C and 2H NMR (Sect. 8.1.4) have led to quite a precise description of the ester group motions and the associated main-chain motions. However, it has not been possible to get information on the origin of the observed distribution of activation energies, nor on the extent of cooperativity along the main chain required by the 7r-flip of the asymmetric ester group. 

The quaternary stractures of He s are strongly dependent on pH and the presence or absence of divalent cations such as Ca + or Mg +. Thus, most arthropodan He s can be dissociated to functional units by simply raising the pH above 9 with the concomitant removal of divalent cations by chelating agents (e.g. EDTA). This dissociation can be reversed by dropping the pH and/or addition of divalent cations (> 10 mM). A very similar behavior is also observed for He s from molluscs. He s from both phyla typically exhibit cooperative oxygen binding. The extent of cooperativity is dependent upon several parameters such as pH, temperature, and the presence of divalent cations such as Ca + and... 

Although this picture was found to be in a satisfying agreement with SR-SW calculations, further extension of these studies appears quite pointless now because more accurate DV-Xa modelling of this topic has been carried out in the mean time (e.g., see [29]). The application of the latter method could lead to a ftnal decision as to the extent of cooperation between polarization (pvai) and core reorganisation (3p) in shifting the ratio R, and as to whether the interpretation of these variations as pure valency effects [27] is on safe groimds. 

Sen, T.Z., Feng, Y, Garcia, J.V, Kloczkowski, A., Jernigan, V.L. The extent of cooperativity of protein motions observed with elastic network models is similar for atomic and coarser-grained models, J. Chem. Theory Comput. 2006, 2, 696. 

The catalytic efficiencies of regioisomeric complexes 14-Ba2 and IS-Baa in the basic ethanolysis of esters 18-21 are compared in Table 8.1 with that of the dinuclear barium complex of the closely related ligand 16, as well as with that of the mononuclear control 17-Ba. Rate measurements refer to conditions where no less than 90% of the ester is bound to the catalyst in the productive (Michaelis) complex n (Scheme 8.4), while the concentration of the unproductive 2 1 complex HI is negligibly low. The superiority of dinuclear catalysts over the mononuclear counterpart demonstrates that the two metal ions work in a cooperative fashion, in accordance with the bifunctional catalytic mechanism in Scheme 8.4, but the extent of cooperation is strongly dependent on the catalyst-substrate combination. This is not really surprising, as the catalytic mechanism implies that the substrate and the catalyst must form a well matched pair in terms of size and geometrical features. A convenient comparison of catalytic performances of regioisomeric... 

Zn2, the extent of cooperation of the two metal centres is quite high for esters 22 and 19, significantly lower for ester 20 and even lower for ester 21. Clearly, catalyst 24-Zn2 experiences an increasing difficulty to fit the altered substrate in the transition state when the ester size exceeds that of 19. A similar trend of reactivity is seen in the reactions carried out in the presence of the less effective catalyst 25-Zn2. In this case, however, there is no sign of cooperation between metal centres in the reactions of 20 and 21. 

Hence equilibrium measurements of the ratio of active to inactive enzymes versus ApH permit determination of the reaction order (= number of protons translocated for activation of one enzyme molecule). Equilibria between enzymes with loosely bound ADP (E ADP) to those with tightly bound ADP (E=ADP) may be treated correspondingly. The results of measurements of enz3nne activities and levels of tightly bound ADP as function of ApH in the presence of 10 pM ADP are plotted as Hill diagrams in Fig. 1. The results allow two important conclusions (i) both, activation and nucleotide release exhibit positive cooperativity with regard to the protons translocated (ii) the extent of cooperativity is different for the two reactions (n = 2.2 and 1.4, respectively). As the Hill coefficients give minimum numbers, extrapolation to 3 H /ATPase for activation and 2 H /ATPase for ADP release may be justified. 

Artificial phosphodiesterases that combine a guanidinium unit with a general base connected by a m-xylylene linker catalyse the transesterification of the RNA model compound 2-hydroxypropyl /t-nitrophenyl phosphate (Scheme 20 e.g., B = imidazole). The bifunctional catalysts showed varying extents of cooperation between catalytic units, and a rate enhancement of 4 x 10" was seen in the most favourable case. ... 

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