Electrochemically Controlled H‐Bonding

Employment of Electrodonating Capacity as an Index of Reactive Modulation by Substituent Effects: Application for Electron-Transfer-Controlled Hydrogen Bonding

“…Hydrogen bonding is a fundamental interaction for stabilizing structures in many systems of biological importance, such as DNA and the secondary structures of proteins and peptide systems . Because of its directional character, this interaction has been used extensively for building molecular aggregates, , which have found many applications. − It is well-known that changing the charge of the molecules involved in the ensemble can enhance the degree of affinity by hydrogen bonding. , An interesting effect provoked by this process occurs in electron transfer reactions, where a change in the oxidation or reduction potentials of the latter molecules to more negative or positive values, respectively, is observed when the amount of the hydrogen-bond donor is increased; this phenomenon is known as Electrochemically Controlled Hydrogen Bonding, or, in a more specific way, as electron-transfer-controlled hydrogen bonding (ETCHB), as electron uptake or withdrawal determines the strength of the hydrogen bond . Because of its strength and directionality, ETCHB has been used for designing electronics devices, molecular machines, ,, sensors, − and systems for anion recognition. − …”

“…This simple reactive system can be represented with the well-known case of the interaction between substituted radical anions electrogenerated from aromatic nitro compounds (R–ϕ–NO 2 •– ) and urea as the hydrogen-bond donor (DH): R−ϕ−NO 2 + normale − ⇄ E 1 / 2 R−ϕ−NO 2 • − R−ϕ−NO 2 • − + DH ⇄ K normalb R−ϕ−NO 2 • − ··· DH ] The magnitude of the affinity constant ( K b , eq ) is the key parameter for describing reactivity in these systems; also, K b determines the extent of the above-mentioned shift in potential values. Concerning substituent effects, Smith and co-workers found that using substituents with different electron-donor/acceptor abilities produced changes in both half-wave potential values of the corresponding nitrobenzene ( E 1/2 ) and a shift in the half-wave potential (Δ E 1/2 ) with concentration: the results showed that substituents with higher electron-donor capacity (characterized by more negative E 1/2 values) lead to an enhancement in the complex stability (Δ E 1/2 increases).…”

“…7,8 An interesting effect provoked by this process occurs in electron transfer reactions, where a change in the oxidation or reduction potentials of the latter molecules to more negative or positive values, respectively, is observed when the amount of the hydrogen-bond donor is increased; this phenomenon is known as Electrochemically Controlled Hydrogen Bonding, or, in a more specific way, as electron-transfer-controlled hydrogen bonding (ETCHB), as electron uptake or withdrawal determines the strength of the hydrogen bond. 7 Because of its strength and directionality, ETCHB has been used for designing electronics devices, 9 molecular machines, 6,9,10 sensors, 11−13 and systems for anion recognition. 14−18 This simple reactive system can be represented with the wellknown case of the interaction between substituted radical anions electrogenerated from aromatic nitro compounds (R− ϕ−NO 2…”