Affinity-based process-related

R = H, X = S, A = Et3N and Py). In solution the former is mainly in an ionic form the latter exists as a complex. The basicity of the amine is assumed to be important. Triethylamine is a stronger base than pyridine and the ionic form is stabilized. When the proton affinity is weak, the basicity in relation to the B(III) atom, a Lewis acid, plays an important role. This involves an equilibrium shift toward the complex. This assumption is confirmed by an easy displacement of pyridine by triethylamine. The reverse process demands more severe conditions. In the NMR spectra of the triethylamine complex the signal is shifted from 22 to 42 ppm as pyridine is added. The absence of signals of two separate forms is evidence in favor of their fast interconversion. The chemical shift of the signal in 3IP spectra is 22 ppm (EtOH), 26 ppm (Py, DMFA), and 42 ppm (EtOH, Py) for complexes with triethylamine and pyridine. 

Recently, Whitesides et al. [88, 164, 165] have replaced Hg with an In/Ga eutectic alloy (E-Gain) (Fig. 5c). In/Ga alloy-based electrodes present few advantages related to (1) the lower affinity for the bottom Au or Ag electrode, so that the junction can be assembled in air, (2) low toxicity and (3) good processability and mouldability. These characteristics indicate E-Gain electrodes as possible candidates for incorporation into functional devices. Some disadvantages are related to the surface of the In/Ga alloy (1) unlike Hg, it is not atomically flat and (2) it forms in few minutes a discontinuous layer of oxide [81]. 

The usual emphasis on equilibrium thermodynamics is somewhat inappropriate in view of the fact that all chemical and biological processes are rate-dependent and far from equilibrium. The theory of non-equilibrium or irreversible processes is based on Onsager s reciprocity theorem. Formulation of the theory requires the introduction of concepts and parameters related to dynamically variable systems. In particular, parameters that describe a mechanism that drives the process and another parameter that follows the response of the systems. The driving parameter will be referred to as an affinity and the response as a flux. Such quantities may be defined on the premise that all action ceases once equilibrium is established. 

In 1984 (2), the thermodynamic cycle-perturbation method was introduced to help compare the binding affinity of a group of similar inhibitors. This method is based on constructing a thermodynamic cycle relating two binding processes ... 

One approach that can overcome immobilization-related problems involves the use of antigen (or ligand) covalently bound to biotin (Ag-B). The Ag-B is added to the solution at the desired concentration to allow solution-phase binding, so that the selection process is based mainly on the differential affinity of each antibody or other binding molecule. The mixture is then added to strepavidin-coated beads or wells, where the formation of the biotin-strepavidin noncovalent complex allows the selection of high affinity antigen-binding molecules. 

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