Reversal module

Figure 3.20 Profiles of p( V) (in-phase component) against electrode potential H for anodic and cathodic-going potential sweeps taken to 3 different anodic end potentials A = 0.86 V B =0.95 V and C = 1.12 V vs. RHE. showing progressive diminution of reversibility. Modulation frequency = 32.5Hz. amplitude = lOOmV peak-to-peak. The scan rate was SmVs 1. From...

Investigation on the molecular interfacing of redox enzymes yields the following important findings. The molecular-interfaced redox enzymes showed the potential dependency of enzyme activity. The enzyme was inactive when the electrode potential was set below a certain threshold. In contrast, the enzyme activity increased with an increase in the electrode potential above the threshold. The activity of the molecular-interfaced enzyme is reversibly modulated by changing the electrode potential. 

In the past, changes in RTj were viewed in terms of assembly/disassembly of the tight junctional complex (reviewed in 93). Recent studies in human vaginal-cervical epithelia have shown acute and reversible modulation of Rtj that are the result of conformational changes in assembled tight junctions [13], The examples presented below relate to effects of modulation of extracellular calcium level (Ca0) and treatments with ATR... 

Medintz, I. L., S. A. Trammell, H. Mattoussi, and J. M. Mauro. Reversible modulation of quantum dot photoluminescence using a protein-bound photochromic fluorescence resonance energy transfer acceptor. J. Am. Chem. Soc. 126, 30-31 (2004). 

The TTF-porphyrin dyad 3 was described by the group of Odense.11 The fluorescence of 3 is significantly quenched by the photoinduced electron transfer process. Notably, the fluorescence intensity of dyad 3 increases largely after addition of Fe3 + that oxidizes TTF into TTF" +. Successive reduction of TTF" + is not reported. Nevertheless, it is anticipated that the fluorescence of dyad 3 can be reversibly modulated by redox reactions. In fact, the fluorescence of the supramolecule 4, formed between Zn-tetraphenylporphyrin and a pyridine-substituted TTF (TTF- ), can be reversibly tuned by sequential oxidation and reduction of the TTF moiety in 4.12 It should be noted in this context that the synthetically challenging system associating a porphyrin ring fused to four TTFs (5) was also reported.13... 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

Ferrocene has been widely investigated as an electron donor and its electron donating ability can be tuned by redox reactions. As anticipated, when a ferrocene unit is covalently connected to an electron acceptor moiety that shows intrinsic fluorescence, the fluorescence of the acceptor moiety would be largely quenched because of the photoinduced electron transfer between ferrocene and the fluorescent acceptor. For instance, triad 15 that contains perylene diimide flanked by two ferrocene moieties, shows rather weak fluorescence due to the photoinduced electron transfer between perylene diimide and ferrocene units. Either chemical or electrochemical oxidation of ferrocene unit lead to fluorescence enhancement. This is simply because the electron donating ability of ferrocene is reduced after oxidation and accordingly the photoinduced electron transfer is prohibited. In this way, the fluorescence intensity of 15 can be reversibly modulated by sequential electrochemical oxidation and reduction. Therefore, a new redox fluorescence switch can be established with triad 15.25... 

Similarly, the fluorescence intensity of the 1,4-disubstituted azine with ferrocene and pyrene units (17) can be reversibly modulated by sequential redox reactions of ferrocene moiety. In the neutral state, compound 17 displays weak fluorescence owing to the electron transfer from the ferrocenyl group to the excited pyrene unit or by energy transfer from the excited pyrene unit to the ferrocenyl unit. Oxidation of the ferrocenyl unit, however, leads to remarkable fluorescence enhancement. This is because the ferrocenium cation shows weak electron donating ability and also the corresponding spectral overlap becomes small.27... 

Kessler and coworkers immobilized RGD peptides to a PMMA surface via a spacer incorporating an azobenzene unit [ 187]. The molecules were arranged in such a way that the RGD motifs were accessible to cells approaching the surface when the azo unit was in the E-form, and were hidden from the cells when the azo unit was in the Z-form. This enabled the reversible modulation of mouse osteoblast adhesion by irradiation with visible or UV light. However, the difference between on and off states is not very pronounced. Possibly, the accessibility of the RGD motif is not... 

A switching function that allows for the reversible modulation of electrochemical properties by photoirradiation is of basic importance for the development of... 

The experiments described reveal the potential of perimidinespirocyclohexa-dienones for the design of multiswitchable devices. Such molecular switching processes are considered to be crucial to the reversible modulation of a given physical property by means of a certain external trigger, in particular of light.31"33... 

Hajime K, Yoshizawa S, Hirayama, S. Oxygen triggering reversible modulation of Vibrio fischeri strain Y1 bioluminescence in vivo. Photochem Photobiol 2004 79 120-5. 

Ingebritsen, T.S. Lee, H.-S. Parker, R.A. Gibson, D.M. Reversible modulation of the activities of both liver microsomal hydroxymethylglutaryl coenzyme A reductase and its inactivating enzyme. Evidence for regulation by phosphorylation-dephosphorylation. Biochem. Biophys. Res. Commun., 81, 1268-1277 (1978)... 

A similarly designed surface where the azobenzene SAM was derivatized with an RGD-containing peptide has enabled the reversible modulation of cell adhesion... 

In cells, DAG, along with calcium, reversibly modulates the subceUular distribution of cPKC isoenzymes. A three-step model has been proposed to explain this regulation ... 

Figure 9.13b shows the expected force curves for two successive Gaussian defects with different forces. Depending on the defect strength, either a reversible modulation (as in the left part of the curve in Fig. 9.13b) or a hysteresis cycle (as in the right part of the curve in Fig. 9.13b) is observed. The two defects of Fig. 9.13a therefore correspond to weak and strong defects, respectively. 

In Table 1 is shown the effect of ATP concentration on the reactivation of microsomal ACAT by a partially purified microsomal protein kinase. This data illustrates that cholesterol oleate formation increases with an increase in the amount of ATP added. In Fig. k is shown the reversible modulation of ACAT activity where dephosphorylating conditions bring about a decrease in the enzyme activity, which is reactivated in the presence of ATP and protein kinase. These data, taken together, illustrate (Fig. 5) that ACAT is active when phosphorylated— that is, in the presence of protein kinase and ATP—while it is inactive when it is dephosphorylated or in the presence of protein phosphatase and magnesium. 

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