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Anti-cooperativity

For chain-like or cyclic hydrogen bond patterns between three alcohol molecules A, B, and C, Vabc is usually negative (attractive). If molecule B acts as an acceptor for both A and C, Vabc is typically repulsive (positive), because A and C compete for the electron density at B [61]. This anti-cooperativity provides the main explanation why branching of hydrogen-bonded chains is discouraged in alcohols. [Pg.9]

The structures of polyamines are shown here as di-and tri-cations, but it should be realized that there are multiple positions for protonation and therefore various tautomers. Also, polyamines show extreme anti-cooperativity in proton binding, i.e., successive pKa values range from very low to very high for the last proton to leave. Polyamines are thought to have... [Pg.1380]

Annealing mechanism 607 Anti-cooperativity—see negative cooperativity... [Pg.320]

The value A Ef = —35.6 mV has the particular interest of corresponding to a 50 % of character E e-E c and E2c At the average formal potential Ef, the intermediate species reaches half of its maximum value and, hence, at this A Ef species 02 may or may not gain a second electron (and as a direct consequence, for higher AEf it will be considered that the intermediate species is no more stable at the average formal potential). So, this AEf could be considered as the boundary between anti-cooperative and cooperative behavior of both electron transfer reactions [35, 43]. Indeed, it is well known that the voltamogram of an EE mechanism under these conditions is identical to that of an E mechanism multiplied by a factor... [Pg.179]

Czaplewski C, Rodziewicz-Motowidlo S, Liwo A, Ripoli DR, Wawak RJ, Scheraga HA. Comment on anti-cooperativity in hydrophobic interactions A simulation study of spatial dependence of three-body effects and beyond . J. Chem. Phys. 2002 116 2665-2667. [Pg.1923]

In other cases, one of the interactions can be so strong that optimal contact with other binding sites cannot materialize. Examples for this have been discussed above, e.g., with the porphyrin-based host, which cannot differentiate between nucleotides and nucleosides due to fhe dominating stacking effects. Even adverse, anti-cooperative effects between selectivity and affinity sites can be tolerated, in particular if fhe aim is stereoselectivity. In the chiral crown ether (Fig. 2.16), which is the basis of Crarris chiral resolution machine [69], stereoselection is due to interactions between amino acid side groups and the crown ether... [Pg.35]

This system, however, is much more complex than the simple description in Figure 5.45 suggests. The proper analysis of such systems has to involve the Curtin-Hammett analysis of interconversion of reactive and unreactive conformers and the evolution of stereoelectronic effects along the interconnected reaction pathways. The critical examination of APL theory by Perrin also suggested that the role of conformational equilibria of reactive species, the involvement of syn-periplanar lone pairs, and the different stability of products should be included in the analysis. We will continue our discussion of cooperativity and anti-cooperativity between stereoelectronic effects in Chapter 11. [Pg.92]

The studies performed on these model systems indicate that the electrostatic model for pair wise interactions to be inadequate to describe the major component of cooperativity in case of long chains. Thus quite a few studies have focused on cooperativity observed in hydrogen bonded systems. However studies considering rigorous quantitative estimation of cooperativity or anti cooperativity in systems with cation-jt interactions are rather limited. [Pg.541]

The common coexistence of M-jt and jt-jt interactions in biology and chemistry has been explored in order to garner a better understanding of how one kind of noncovalent interaction affects the strength of another [82]. This influence is typically described in terms of cooperativity and anti cooperativity in bonding. The occurrence of M-jr-n (M = Li+, K+, Na+, Mg +, and Ca " ") interactions in... [Pg.541]

Amit R (2012) TetR anti-cooperative and cooperative interactions in synthetic enhancers. J Comp Biol 19 115-125... [Pg.17]

In my view, solvents themselves usually avoid anti-cooperativity situations. However, whenever a solute is involved, if a given group has a solvation number greater than one, anti-cooperativity occurs. This is especially the case for anions such as the halide ions. The charge of the ion is so effective that high solvation numbers are exhibited despite the fact that each bond is, as a consequence, quite weak. Of course, this anti-cooperativity for primary solvent molecules is greatly reduced because of the cooperative effects of secondary solvation. [Pg.45]

Both these processes nicely illustrate our principle of anti-cooperativity ... [Pg.56]

Mej S -O, which is pyramidal and hence has an exposed dipole, produces the largest shift whereas non-dipolar solvents such as hexane or tetra-chloromethane (CCI4) are treated as causing zero shifts for condensed systems such as these. Often, the shifts are to lower frequencies when hydrogen bonds form, as in this case. The shift from zero is proportional to the total H-bond strength, but the individual shifts decrease as the number of bound water molecules increases. This is another example of the anti- cooperativity principle. [Pg.63]

If the anti-cooperative behavior postulated is occurring, then lower molecular weight material might be a better ionophore, because the electrostatic repulsion caused by bound cations would be distributed over a larger number of independent polymer chains, resulting in a smaller incidence of intrapolymeric repulsion. [Pg.314]

When investigating multi-body effects, the question of cooperative and anti-cooperative interactions can become an additional consideration of the utmost importance. [Pg.448]

Figure 9.9 illustrates one of the two near-equivalent /Jc-tt NO interactions of N0" (C0)2 in two-dimensional contour and three-dimensional surface plots for comparison with the analogous interaction I of Fig. 9.8, showing the anti-cooperative weakening of in the trimeric complex. Note that the dihedral fold-angle... [Pg.222]


See other pages where Anti-cooperativity is mentioned: [Pg.262]    [Pg.9]    [Pg.346]    [Pg.497]    [Pg.171]    [Pg.171]    [Pg.45]    [Pg.112]    [Pg.195]    [Pg.836]    [Pg.144]    [Pg.307]    [Pg.497]    [Pg.196]    [Pg.346]    [Pg.287]    [Pg.483]    [Pg.285]    [Pg.537]    [Pg.14]    [Pg.45]    [Pg.63]    [Pg.71]    [Pg.313]    [Pg.288]    [Pg.221]    [Pg.221]    [Pg.223]    [Pg.76]   
See also in sourсe #XX -- [ Pg.171 ]

See also in sourсe #XX -- [ Pg.537 ]

See also in sourсe #XX -- [ Pg.45 , Pg.56 , Pg.63 , Pg.71 ]




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Anti-cooperative process

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