Voltammetry of [Re(DMPE)₃]⁺ at Ionomer-Entrapped Composite-Modified Electrodes

Abstract

Nafion or sodium poly(styrenesulfonate) (NaPSS) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) (PVA) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [Re I (DMPE) 3 ] + , where DMPE ) 1,2-bis-(dimethylphosphino)ethane. Among these composite coatings, Nafion-entrapped sol-gel-derived silica (Nafionsilica) exhibited a sensitivity for [Re I (DMPE) 3 ] + ∼4 times higher than that of NaPSS-entrapped sol-gel-derived silica or NaPSS-entrapped PVA. When Nafion was entrapped in cross-linked PVA matrix, however, the voltammetric response was found to be only ∼14% of that of Nafion and Nafion-silica composite coatings. Dispersing Nafion in sol-gel-derived silica matrix improves the slow diffusion of [Re I (DMPE) 3 ] + in Nafion, thus leading to a higher sensitivity than Nafion in a shorter preconcentration time. Such a Nafion-silica composite is promising for both electrochemical and spectroelectrochemical sensing of [Re I (DMPE) 3 ] + . It was also found that increasing the high potential of a cyclic voltammetric scan greatly reduces the amount of [Re II (DMPE) 3 ] 2+ available for reduction in the reverse potential scan, suggesting that the electrochemically generated [Re II (DMPE) 3 ] 2+ was consumed in the more positive potential region.[Re I (DMPE) 3 ] + , where DMPE ) 1,2-bis(dimethylphosphino)-ethane, is a nonradioactive analogue of [ 99m Tc I (DMPE) 3 ] + , which is radioactive and shows potential as a myocardial perfusion imaging agent. 1 Radiopharmaceuticals are routinely used for organ imaging and for radiotherapy in nuclear medicine. One of the fundamental problems associated with the use of radiopharmaceuticals is that, in many circumstances, the composition of an injected radiopharmaceutical is known, but the chemical form of the agent that is actually responsible for the imaging or therapy may be an altered form due to in vivo reactions. 2 This is evidenced by biological studies which show that in vivo redox reactions can markedly affect the biodistributions of technetium-99m and rhenium-186 radiopharmaceuticals. 3,4 Therefore, gaining the information regarding the chemical form that is responsible for imaging or therapy is crucial for developing more efficacious radiopharmaceuticals. By investigating the nonradioactive species, [Re I (DMPE) 3 ] + , information directly applicable to its radioactive analogue can be acquired and information related to other radiopharmaceuticals may also be extracted.We have recently shown the preferential uptake of [Re I -(DMPE) 3 ] + by Nafion, a perfluorosulfonated ionomer, and the potential utility of Nafion as an electrode modifier to enhance electrochemical detection of [Re I (DMPE) 3 ] + . 5,6 [Re I (DMPE) 3 ] + ion strongly partitions into Nafion films, 5 due to the electrostatic interaction and, to some extent, hydrophobic interaction of Nafion ionomer with the hydrophobic cation. However, we have found the partitioning process for [Re I (DMPE) 3 ] + into Nafion films to be slow. 5,6 A slow...

Absorbance‐Based Spectroelectrochemical Sensor for [Re(dmpe)3]+ (dmpe=dimethylphosphinoethane)

“…Although there was very slow uptake into neat Nafion films (a), the peak cathodic current after 1 h was still only about one-fourth of the peak current observed for bare ITO electrodes. Slow diffusion of [Re(dmpe) 3 ] þ in neat Nafion films can be improved by incorporating Nafion into a PVA matrix, [5,26,28] however, the two matrix films, Nafion/ PVA and PAA/PVA (c and d), did not perform as expected based on earlier results with spectroscopic graphite electrodes. On ITO, [Re(dmpe) 3 ] þ apparently penetrated Nafion/ Sensor for [Re(dmpe) 3 …”

“…This is consistent with reported electrochemical properties for this compound. [5,7,26] The reversible Re I/II couple is centered around 50 mV, but further oxidation to Re III at 950 mV decreases the peak current for reduction of Re II back to Re I . Scanning for a second cycle shifted the oxidation peak at 950 mV to 980 mV and the reversible oxidation/reduction peaks for Re I/II were almost completely gone.…”

Electroanalysis with Pure, Chemically Modified and Sol-Gel-Derived Silica-Based Materials

“…They ®rst observed substantial partitioning of methylviologen into the Na®on-silica composite matrix to the electrode surface, which was quicker compared to pure Na®on ®lms [131]. They then exploited the dispersion of Na®on in the sol-gel-derived silica matrix to speed up the extraction of the hydrophobic organometallic cation [Re I (DMPE) 3 ] (DMPE 1,2-bis-(dimethylphosphino)ethane) by Na®on [144]. They then exploited the dispersion of Na®on in the sol-gel-derived silica matrix to speed up the extraction of the hydrophobic organometallic cation [Re I (DMPE) 3 ] (DMPE 1,2-bis-(dimethylphosphino)ethane) by Na®on [144].…”

Sol-Gel Derived Composite Ceramic Carbon Electrodes

“…Several useful ways to prepare such materials include the entrapment of polymer dopants that induce phase separation [16,17], compounds or polymers which can be leached out after ®lm formation [18] or by introducing surfactants at concentrations that approach or exceed the CMC [19,20]. Another possible route to enhance mass transport is to introduce heterogeneity by the incorporation of another polymer or inorganic phase in the silicate [21,22]. Mass transport in CCEs bene®t from both attributes, macroporosity as well as heterogeneity.…”