Characterization of soluble oligomers produced by electrochemical oxidation of o‐phenylenediamine by electrospray ionization sequential mass spectrometry

Abstract

Soluble species generated during the electropolymerization of o-phenylenediamine (o-PD) on platinum electrodes in aqueous buffers at different pH values were investigated by electrospray ionization ion trap sequential mass spectrometry (ESI-ITMS(n)). The main protonated molecules (MH(+)) detected in the full scan ESI-MS spectra of the electrolytic solutions were isolated in the ion trap and sequentially fragmented (MS(n), with n up to 5) to obtain fragmentation patterns. The latter led to hypotheses as to the molecular structures of the soluble products of o-PD electropolymerization; it appeared that all of them are actually oligomeric species in different oxidation states. In particular, o-PD dimers, trimers and tetramers could be identified and three common structural features were found, namely: the presence of phenazine, 1,4-benzoquinonediimine, and secondary amine (acting as bridges between benzene rings) units. These findings are in agreement with those already reported for the surface structure of the polymeric films formed on the platinum electrodes during o-PD polymerization, thus suggesting that a close relationship exists between the soluble oligomers and the polymer itself.

Nanoceria Facilitates the Synthesis of Poly(o-phenylenediamine) with pH-Tunable Morphology, Conductivity, and Photoluminescent Properties

“…Results show that when the 1-D p OPD microcrystals were dissolved in water pH 1.0 or pH 7.0, they displayed similar spectra to those in Figure 1. HPLC-MS of the p OPD microcrystals dissolved at pH 1.0 and 7.0 show a prominent peak corresponding to a mass of 268.7, suggesting the presence of fragmented trimers of OPD as reported previously [21] (Figure 3A–3B). Interestingly, similar results were obtained in aqueous solution of the crystals obtained by electropolymerization (Figure 3C–3D) suggesting that in all these cases the p OPD crystals are composed an assembly in solution of 268.7 sc OPD fragmented trimers as suggested by others.…”

Modelling of the initial stages of the electropolymerization mechanism of o-phenylenediamine

“…On the basis of recently reported results the ''open'' structure appears as the dominant polymer structure [27,7]. Thus, five possible dimers of ''open'' structure have been consider: P1-P5, Scheme 3.…”

Characterization of permselective coatings electrosynthesized on Pt–Ir from the three phenylenediamine isomers for biosensor applications

“…1 that the peak current of mPD was much smaller than that for oPD and pPD. The greater initial charge flow associated with oPD and pPD oxidation may be attributed to the formation of solution oligomers during the polymerization [77], because a dark cloud was visible around the electrode during polymerization of both oPD and pPD, which appeared to disperse gradually. This was not observed during the polymerization of mPD, presumably due to the more unstable (reactive) nature of the meta oxidized radical which causes it to react with solution monomer more completely much closer to the electrode surface, and leads to a faster and more charge-efficient deposition of insulating polymer (see Sections 3.2 and 3.3.3).…”

“…Despite the low yields and poor solubility of the ultra-thin PPD films formed on the Pt-Ir cylinders (Section 3.3.2), the high sensitivity of MS [48,56,77] was exploited to gain insights into the oligomeric species formed on the surface. To minimize contamination of the MS sample with buffer salts, electropolymerization was carried out in the absence of any background electrolyte.…”