Exchange rate, guest

Finally, when the exchange rate is much faster than the reciprocal frequency difference the line is sharpened and no kinetic information can be obtained. The position of the line in the spectrum is determined by the values of vG and vHG weighted by the fractions of the free and bound guest. 

The 2 2 complex formed between /i-CD and reduced tetracyanoquinodimethane shows separate signals for the free and bound CD.203 2D exchange spectroscopy gave an exchange rate of 0.9 s 1 at 30 °C for the exchange between the free guest and the 2 2 complex. The exchange may occur via numerous steps, but no resolution of the intermediate steps could be achieved from the data treatment. 

Table 7.8 Kinetics and thermodynamics of protonated amine encapsulation in 1. The self-exchange rates ( 277) ofthe protonated guests were measured at 277 K. /< eff(298) is the binding constant of the encapsulated protonated amine and has an estimated uncertainty of 10%.

Given a measurement of guest exchange rate, application of the Eyring equation (3.6) allows the activation free energy AG of the complexation process to be determined. 

Reduction of the exchange rate of the alkyldiammonium guest B compared to the alkylammonium A... 

A cavitand-porphyrin combination (22) has been synthesized O5ACIE3810, 06BCSJ1431, 06OL4275> and reported to have sufficient flexibility to facilitate moderate guest exchange rates for kinetic measurements the encapsulation of methane has been shown to have a half-life of 0.5 s <07JOC9448>. 

Case 1 The host-guest complexation equilibrium, which has a very slow exchange rate compared with the NMR time scale. 

When the host-guest complexation equilibrium has a very slow exchange rate compared with the NMR time scale, the concentration of the complex is expressed as follows (a = 1 in Eq. (2.53)). 

When the host-guest complexation equilibrium has a very fast exchange rate... 

Rudkevich, D. M., Hilmersson, G., Rebek, J., Intramolecular hydrogen bonding controls the exchange rates of guests in a cavitand. J.Am. Chem. Soc. 1997, 119, 9911-9912. 

As we have discussed, FTC does not spectroscopically examine the free and the bound states in a host-guest system but instead determines the overall enthalpy change upon addition of multiple aliquots of guest to a solution of the host. Hence, the aforementioned discussion of experimental timeframes and their relationship to the exchange rates do not apply to ITC. Instead, it is important to determine whether upon addition of each aliquot the mixture has equilibrated before an addition aliquot has been added. In other words, in ITC it is important that the time to equilibration for the system be faster than the pause between each injection. 

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