Effective molarity , supramolecular

Since the dinuclear catalysts transform the intermolecular reaction of ethoxide with substrate into an intramolecular reaction within a supramolecular complex (Scheme 5.3), the effective molarity (EM) parameter, defined as kintra/fcinten strictly applies to the catalytic process at hand and, more in general, to processes in which molecular receptors promote the reaction of two simultaneously complexed reactants [35]. 

The basis of the rate acceleration by this host is an increased effective molarity within the assembly cavity. This principle has been demonstrated with other supramolecular compounds that possess a defined inner space [27, 28]. This is a powerful but narrow capability of these assemblies, employing size- and shape-complementarity to bring molecules together in the promotion of bimolecular reactions. Importantly, this phenomenon does not depend on perturbation of the potential energy surface to effect the rate accelerations. 

Both rigid and flexible porphyrin sandwiches were studied by Hunter et aL [28,34]. A rigid bis-porphyrin, connected via naphthalene diimide (Fig. 12), theoreticaUy forms a number of complexes with DABCO, depending on the porphyrin to hgand ratio. To characterize the supramolecular system, and to find the optimum conditions for cyclization to form the sandwich complex, the effective molarity (EM) was determined by NMR and UV-vis titration experiments. The EM may represent a composite of the real effective molarity and cooperative effects (a), but it is nevertheless a useful parameter for predicting the stabihty of the sandwich complex. Here, the EM was determined to be 2 mM, which means that the macrocychc complex 14 is... 

For an alternative analysis of supramolecular effects in bimolecular reactions using the effective molarity approach, see S. Di Stefano, L. Mandolini, Effective molarities in supramolecular catalysis of two-substrate reactions, Acc. Chem. Res., 2004, 37, 113. 

Di Stefano S, Cacciapaglia R, Mandolini L. Supramolecular control of reactivity and catalysis — effective molarities of recognition-mediated bimolecular reactions. Eur J Org Chem. 2014 7304-7315. 

Adams H, Chekmeneva E, Hunter CA, Misuraca MC, Navarro C, Tmega SM. Quantification of the effect of conformational restriction on supramolecular effective molarities. /Hm Chem Sac. 2013 135 1853-1863. 

Sun H, Navarro C, Hunter CA. Inflnence of non-covalent preorganization on supramolecular effective molarities. Org Biomol Chem. 2015 13 4981-4992. 

Jinks MA, Sun H, Hunter CA. Measurement of supramolecular effective molarities for intramolecular H-bonds in zinc porphyrin—imidazole complexes. Org Biomol Chem. 2014 12 1440-1447. 

Sun H, Hunter CA, Navarro C, Turega S. Relationship between chemical structure and supramolecular effective molarity for formation of intramolecular H-bonds. J Am Chem Soc. 2013 135 13129-13141. 

Supramolecular Complexes With Very Large Values of Effective Molarity 90... 

Supramolecular Complexes With Very Small Values of Effective Molarity 93... 

Appendix Collection of Thermodynamic Effective Molarity Values for Supramolecular 99... 

Kinetic effective molarities (EM) that quantify the increase in reaction rate for intramolecular formation of covalent bonds compared with the corresponding intermolecular process often have physically impossible values (up to 10 M). It is therefore widely assumed that multivalent supramolecular systems could attain similarly large values of thermodynamic EM for formation of cooperative intramolecular noncovalent... 

The constant C has units of concentration and denotes the concentration at which intramolecular and intermolecular reactions have the same rate. In the 1970s, the term effective molarity (EM) was widely adopted to describe this parameter and characterize the rate enhancements observed for intramolecular reactions. The EM defined by Eq. (1) is a kinetic EM, because it is based on the ratio of two reaction rates, but it is possible to define a thermodynamic EM in the same way, if equibbrium constants are substituted for rate constants (Eq. (2)). In this review, we will use thermodynamic EM to quantify the chelate cooperativity associated with multivalent noncovalent interactions in supramolecular systems. 

Figure 8 Distribution of (A) thermodynamic effective molarity (EM) values for noncova-lent bond formation in supramolecular complexes (data for intramolecular H-bond formation in zinc porphyrin—pyridine complexes plotted separately as DMC) and (B) kinetic and (C) thermodynamic EM values for covalent bond formation.

Figure 9 Distribution of effective molarity values for different types of supramolecular complex (A) H-bonding, (B) metal coordination, (C) biomolecular complexes, (D) hydro-phobic effects and (E) complexes with multiple binding interactions.

APPENDIX COLLECTION OF THERMODYNAMIC EFFECTIVE MOLARITY VALUES FOR SUPRAMOLECULAR COMPLEXES... 

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