Absorption maxima association constant

The ideal substrate for a sensitised reaction should absorb light at a wavelength, which is at least 50 nm shorter than the absorption maximum of the sensitiser. It should coordinate with an association constant, which is significantly higher than its dimerisation constant, and it... 

Relaxation times and dispersion amplitudes" change when ions are added. If ion pairs are formed, a new relaxation region appears on the solvent relaxation spectrum on the low-frequency side. Figure 4.105 shows the dielectric absorption spectrum of LiBr in acetonitrile, and how a maximum is developed in the low-frequency region as the concentration of solute increases and ion pairs are formed. Association constants can be determined from these data and contribute to the identification of the ion pan-present. 

In Table II are collected all the literature data on molecular complexes of small biological molecules which we have been able to locate. It would be superfluous to discuss in detail every case, since the table has been made fairly detailed. In particular, the wavelength at which the association constant was determined, or the maximum of new absorption is given, and compared with the absorption maximum of uncomplexed material. In a very large number of the cases listed in Table II a charge-transfer band is not observed and a donor-acceptor interaction is therefore questionable. 

One of our aims in using ultrasonics was to study the kinetics of the association-dissociation process. Kinetic effects would produce a maximum of absorption when the pH is changed at constant frequency. No information about the kinetics has been obtained so far. However, the difference of absorption in capsides and in the dissociated system turned out to be of interest, because of the unexpected increase of absorption by capsides. 

The spectral changes associated with the protonatiop of p -dimethylamino-derivatives [45] contrast sharply with those described above. There is a hypsochromic shift of the maximum absorption and the absorption spectrum of the conjugate acid of benzylidene-p -dimethylaminoaniline is closely similar to that of benzylideneaniline free base, which leads to the conclusion that the monocation has the ammonium structure. The conjugate acid of benzylidene-p -dimethylaminoaniline shows, however, an additional peak at 455 nm, which was ascribed to the anilium form, but the position of the tautomeric equilibrium could not be determined without the knowledge of the extinction coefficients of the two forms, p/fj-values of only a few of these compounds were estimated from these measurements on flowing solutions. So, for example, p-trimethylammonium-benzylidene-p-toluidine has a p/La-value of 1 85, and for variable p -substituents a p-constant of T5 has been calculated. The p -dimethylamino group may be expected to have p/fa in excess of 5. 

When one of the solvents has a limited and low solubility, C, we find the classic Langmuir absorption isotherm is obtained with a sli t modification to the activity axis as shown in Figure 9.13. Such a solubility limit can be obtained by precipitation cn- micellization in the case of surfactants. Micellization is the association of ionized surfactant molecules into structures where the hydrophobic parts of the surfactant molecules expel water. Micelles have different structures (i.e., spheres, cylinders, and lamellar structures) depending on the surfactant molecule and its concentration of surfactant in solution. Each structure has a different maximum concentration, C , which limits adsorption. In Figure 9.13, the activity is replaced by concentration in the dilute solution case and the ooncentraticm axis C2 becomes dimensionless by division by the solubility limit when the constant b is replaced by 6C in equation 9.40. 

---