Monolayer-functionalized protonated

Bloembergen et al. (S) have presented a relationship between the correlation time for molecular rotation in liquids and the relaxation times assuming that relaxation takes place via mechanism (i) of Section II,A,3. Although the theory can be at best semiquantitative when applied to the protons of water molecules adsorbed on silica gel, values of the nuclear correlation time have been calculated 18) from the T data. These correlation times as a function of x/m show a definite change of slope near a monolayer coverage. This result, if corroborated by data on other solids, may provide a rather unique method for the determination of monolayer coverage. 

There have been some impressive, relatively recent examples of molecular rectification. Compound 11.52 has proved to be an extremely efficient molecular rectifier, able to actually function as a rectification device by intramolecular tunnelling either as a monolayers or multilayer macroscopic film or on a nanoscopic level.51 Switchable rectification has been demonstrated for a related dye shown in Figure 11.36. The electrical asymmetry can be chemically switched, off and then back on, by treatment with acid and base, respectively. Protonation disrupts the intramolecular charge-transfer axis, destroying the rectification effect.52 Recent calculations, however, suggest that there may be relatively unpromising theoretical limits on the rectification possible by a single molecule.53... 

A further approach to controlling electrical communication between redox proteins and their electrode support through a photo-command interface includes photo stimulated electrostatic control over the electrical contact between the redox enzyme and the electrode in the presence of a diffusional electron mediator (Scheme 12).[58] A mixed monolayer, consisting of the photoisomerizable thiolated nitrospiropyran units 30 and the semi-synthetic FAD cofactor 25, was assembled on an Au electrode. Apo-glucose oxidase was reconstituted onto the surface FAD sites to yield an aligned enzyme-layered electrode. The surface-reconstituted enzyme (2 x 10-12 mole cm-2) by itself lacked electrical communication with the electrode. In the presence of the positively charged, protonated diffusional electron mediator l-[l-(dimethylamino)ethyl]ferrocene 29, however, the bioelectrocatalytic functions of the enzyme-layered electrode could be activated and controlled by the photoisomerizable component co-immobilized in the monolayer assembly (Figure 12). In the... 

Frequency of the crystal after addition of the DNP-Ab to the dinitrospiropyran (31a)-functionalized crystal. (O) Frequency of the crystal after photoisomerization of the (31a)/DNP-Ab monolayer to the protonated dinitromerocyanine (31b), washing offof the DNP-Ab, and back isomerization to (31a) monolayer state. 

Interfacial monolayer, multilayer and polymer species which exhibit interesting examples of light and electrically stimulated functions such as isomerization and proton transfer in ISAs are also presented in this chapter. Such materials may represent the precursors for electrooptic switches and addressable molecular-based machines. 

Figure 5.16 Formal potential of 2,7-AQDS as a function of pH in buffered 0.1 M LiC104 , solution-phase data , monolayer data. The formal potentials are typically reproducible to within +5 mV, which is comparable to the size of the symbols. Reprinted from. Electroanal. Chem., 498, R. J. Forster and J. P. O Kelly, Protonation reactions of anthroquinone-2,7-disulfonic acid in solution and within monolayers, 127-135, Copyright (2001), with permission of Elsevier Science...

A m or challenge to completing a practical model and description of mobile-phase effects in LSC is the further elucidation of hydrogenbonding effects. This will involve a more fundamental classification of solutes and solvents in terms of their proton-donor and proton-acceptor properties, so that values of can be estimated as a function of the molecular structures of solute X and solvent C. It will also require a more precise description of the adsorbate-surface bonding that occurs in the adsorbed monolayer, so that values of can likewise be rationalized and predicted. 

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