Guest exchange reaction

The gas-phase guest-exchange reaction 29 has been employed to probe the enantioselectivity of permethylated /3-CD for pharmacologically important compounds, such as DOPA, amphetamine, ephedrine, and penicillamine (Scheme... 

Mugridge JS, Bergman RG, Raymond KN (2010) The steric isotope effect in a supramolecular host-guest exchange reaction. Angew Chem Int Ed Engl 49(21) 3635-3637... 

Figure 26.17 Dynamical processes for molecular information and expression in the cases of protein (upper) and steroidal molecules (lower), (a) A molecule as an information carrier, (b) a molecular architecture based on folding or assembly, (c) a host-guest complexation, and (d) a guest exchange reaction.

This example nicely demonstrates how different gas-phase experiments provide more than one piece of evidence. The assignment of pseudorotaxane structure for the 1 1 complex can now firmly be based on (i) the qualitative binding strengths, (ii) size compatibility arguments, and (iii) the kinetic behavior observed for guest exchange reactions. 

When the alkylamine is chiral too (e.g., 2-aminobutane is used as reactant), a comparison of the different rates of the guest exchange reaction can yield an authentic picture of the enantioselectivity exhibited by the resorc[4]arene hosts. Furthermore, the support of MM calculations and MD simulations may provide... 

A detailed smdy of the mechanism of guest exchange reactions for 1 1 cage complexes of the tetrahedral MtLe coordination capsules with... 

J. Santamaria, T. Martin, G. Hilmersson, S. L Craig, J. Rebek, Jr, Guest exchange in an encapsulation complex A supramolecular substitution reaction , Proc Natl. Acad. Sci. USA 1999, 96, 8344-8347. 

The molecular asymmetry of 9 is due to the four axial pendants containing the chiral L-vahne group. The efficiency of the gas-phase exchange reaction 30 where A are representative amino acids and B is either (5)-(- -)- or R)- — )-2-butylamine is appreciably affected by the configuration of both A and B. The guest exchange kinetic results are reported in Table 17. The presence of more than one reacting [9-H-A]" structure is observed with A = DOPA. A similar behavior was observed with permethylated /8-CD as the host." " ... 

Table 19 reports multicollisional dissociation thresholds of the selected complexes. A direct correlation exists between them and the proton affinity (PA) of the guest. However, although chiral specificity has been observed in similar systems using ligand-exchange reactions (see previous sections), the results of Table 19 show no such specificity. The differences in binding of the Ala and Phe enantiomers are evidently too small to be measured with this method. 

Scheme 6.20 Reaction of a resorcarene triol with dihaloalkanes to give a hemicarcerand with a portal for guest exchange.

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