Binding constants, measuring techniques

Gale and coworkers have appended the ferrocene moiety onto the 2,5-diamidopyrrole core described previously. Receptor 153 showed a large anodic shift in the redox potential of -130 mV with F in dichloromethane. This compares to only —75 mV for chloride, and this selectivity corresponds well with binding constants measured by NMR techniques (K = 170 M for H2P04 and <20 for Cl in dichloromethane). 

The equilibrium binding constant for this 1 1 association is Xu = ki/lLi. The Xu values were measured spectrophotometrically, and the rate constants were determined by the T-jump method (independently of the X,j values), except for substrate No. 6, which could be studied by a conventional mixing technique. Perhaps the most striking feature of these data is the great variability of the rate constants with structure compared with the relative insensitivity of the equilibrium constants. This can be accounted for if the substrate must undergo desolvation before it enters the ligand cavity and then is largely resolvated in the final inclusion complex. ... 

Using the above techniques we have measured binding constants for a number of compounds to dissolved humic materials. Some of the results will be summarized in the following paragraphs. 

The binding constants of a number of compounds were measured using dialysis, solubility and sorption techniques. The solubility technique was used for compounds which were not radiolabeled. All data was collected at pH = 8.3. The binding constants were then compared to the octanol/water partition coefficients for the compounds and the molar solubilities of the compounds. The data is presented in Table II. The Kow values were taken from the literature.18 22-2 The solubility values were determined in this research with the exception of DDT and Lindane, which were taken from the literature. A plot of log Kc vs. log Kow is presented in Figure 5. The slope of this line is 0.71, the intercept is 0.75 and the value of the correlation coefficient is 0.9258. The regression is highly significant... 

The partial-filling technique is a modification of ACE that has been shown to be very suitable for measuring binding constants. The methodology and interesting examples of application of this technique are summarized in... 

Table 1 lists some of the binding constants and rate constants measured for the reaction of CO2 with redox-active molecules. Various techniques have been used to measure these constants including cyclic voltammetry, pulsed radiolysis, and bulk electrolysis followed by UV-visible spectral measurements. The binding constants span an enormous range from less than 1 to 10 M [13-17]. Co(I) and Ni(I) macrocyclic complexes have been studied in some detail [13-16]. For the cobalt complexes, the CO2 binding constants K) and second-order rate constants for CO2 binding (kf) are largely determined by the Co(II/I) reduction potentials... 

A discussion of the fundamentals of the NMR technique is beyond the scope of this work, but may be found in the key reference. However, there are one or two aspects of NMR that are of particular interest to supramolecular chemists, as well as the obvious general need for a technique for characterising new chemical compounds. We have already seen in Section 1.4 the use of the NMR spectroscopic titration technique for the measurement of host-guest association constants in dilute solutions. However, more information may be gained from NMR spectroscopy than just binding constants. 

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