Electrochemical One‐Electron Oxidation of Low‐Generation Polyamidoamine‐Type Dendrimers with a 1,4‐Phenylenediamine Core

Abstract

A series of polyamidoamine (PAMAM)-type dendrimers with a 1,4-phenylenediamine (PD) core is prepared from PD by procedures including Michael addition of methyl acrylate followed by aminolysis with 1,2-ethanediamine. Their one-electron oxidation potentials are determined by differential pulse voltammetry (DPV) in methanol, acetonitrile, dichloromethane, and dimethyl sulfoxide. The dendrimers are more difficult to oxidize than N,N,N',N'-tetramethyl-p-phenylenediamine (TMePD). The oxidation potentials decrease with increasing dendrimer generation up to G0.5, after which the potential is essentially constant up to G2.0. The structures of both the neutral species and the radical cations are studied by DFT calculations at the B3LYP/6-31G(d,p) level of theory, which include a series of simple PDs for comparison. The data show that the structural arrangement close to the PD core is similar to that of N,N,N',N'-tetra-n-alkyl-p-phenylenediamines, including a planar arrangement of the atoms linked to the two PD nitrogen atoms. Thus, the effect of chain size on the oxidation potential appears to be caused primarily by a simple electronic effect. The calculations indicate considerable reorientation of the dendrimer side chains on oxidation, presumably caused by interactions between the positive charge centered at the core and the neighboring ester or amide dipoles. The relative ease of oxidation of TMePD and the lowest members of the series of the dendrimers can be reproduced theoretically only when solvation was included in the calculations. The DPV peak heights vary approximately as predicted from the Stokes-Einstein-Sutherland equation, but the variation of the relative effective radii with the size of the dendrimer is much larger than predicted from the radii obtained by the DFT calculations, that is, the dendrimers exist in solution mainly as aggregates.

Ortho-substituted aryl monoboronic acids have improved selectivity for d-glucose relative to d-fructose and l-lactate

“…Pyrrolidine is more electron-donating than dimethylamine, thus decreasing the acidity of 1 and 3 compared to 2 and 4. 33 Our results suggest that the binding strength towards D-fructose depend less on the acidity of the boronic acid than the binding strength towards D-glucose. The proposed steric clash with an ortho-substituent, which disfavors tridentate binding of D-fructose is shown in Fig.…”

Computational electrochemistry: prediction of liquid-phase reduction potentials

“…A study of the electrochemical one-electron oxidation of low-generation polyamidoamine-type dendrimers with a 1,4phenylene-diamine core was conducted by using cyclic voltammetry and density functional theory. 416 Combined QM/MM studies of the electron-transfer reactions involving carbon tetrachloride in aqueous solution were carried out by Valiev et al 417 In particular, they studied the reductive dechlorination of CCl 4 by a concerted electron transfer-bond breaking mechanism using either density functional theory or coupled cluster theory [CCSD(T)] for the QM part. Their predicted activation barriers and reduction potentials were found to be consistent with available experimental data.…”

Dendron growth from vertically aligned single-walled carbon nanotube thin layer arrays for photovoltaic devices

“…This is due to the increased dendron size leading to an increased active surface area available to electrons, thus facilitating oxidation. 39 In DPV, the magnitude of the peak current is proportional to the concentration and can therefore be used to determine the amount of PDA and thus be used to monitor the propagating dendron growth. With increasing dendron generation, an increasing DPV signal could be detected, indicating the successful modification of the nanotube array.…”

“…It consists of successive alternating generations of ethylenediamine and methyl acrylate, which are coupled by Michael addition. [34][35][36][37][38][39] p-Phenylenediamine (PDA) has been previously shown to have excellent conductivity superior to ethylenediamine for use as a molecular wire. 40 Thus, in this study we present a system where the ethylenediamine is replaced with p-phenylenediamine.…”