Molecular recognition: Evidence of the redox role of ferrocenyl-imine derivatives in the presence of copper (II) ions Nicol  as Agurto a, b , Carlos P. Silva a, b , Geraldine S. Jara a, b , Tamara Maldonado a , Erick Flores a , Carolina F. Morales a, b , Allen Oliver c , Fernando Godoy a, ** , Jorge Pavez a, b, * a Departamento de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Av. Libertador B. O'Higgins, 3363, Casilla 40, Correo 33, Santiago, Chile b Soft Matter Research and Technology Center, SMAT-C, Santiago, Chile c Department of Chemistry and Biochemistry, University of Notre Dame, IN, 46556, USA article info Article history: Received 15 November 2018 Received in revised form 12 June 2019 Accepted 14 June 2019 Available online 15 June 2019 Keywords: Ferrocenyl-copper reaction Imine-copper reaction Spectroelectrochemistry Molecular sensor Chemosensor abstract The design and development of new selective and sensitive chemosensors for metal ions is an area of intense research activity due to their important roles in medicine, living systems, and the environment. In this work, novel ferrocenyl derivatives functionalized with a crown ether linked via an olefin-imine spacer have been designed as versatile molecular recognizers for a series of metal ions (Na þ , Ca þ2 , Cu 2þ , and Cd 2þ ). By using UV-vis titrations, these systems showed a high affinity for Cu 2þ among other metal ions, nevertheless, with unexpected optical behavior. With Spectroelectrochemical studies and electrochemical titrations we revealed that redox reactions between the ferrocenyl and the imine moieties of the spacer and the copper ions took place. These experimental results prove a redox reaction mechanism between both ferrocenyl and imine moieties in the presence of Cu 2þ . Therefore, this work puts a notice about the redox reaction that takes place between copper (II) and ferrocenyl-imine de- rivatives, and this information should be considered when designing metal ion chemosensors based on ferrocenyl and imine units, because this redox interaction would become a possible competition reaction. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction There is great current research interest in the design and syn- thesis of new selective and sensitive chemical sensors as molecular devices with electrochemical responses, in which a redox-active center is very close to a host binding site and is able to detect charged or neutral substrates [1]. These systems have become the focus of numerous studies due to their several applications in cell biology, medicine, analytical chemistry, and environmental sci- ences [2,3]. A molecular sensor can be designed to electrochemi- cally recognize a host species through electronic communication, by the nature of the linker used, or due to effects of conformational changes [4]. These systems are composed of three major subunits: the receptor (host-guest interaction site); the transducer (signal transduction); and the spacer (modulation and electronic communication). The host-guest interaction between the receptor and the analyte must produce changes in the physicochemical properties of the system such that the transducer converts the detection event into a measurable signal. However, in designing these systems, the search for an appropriate spacer which can effectively communicate the subunits mentioned above should be essential. In particular, numerous research groups [5e8] have included an iminic spacer (-R-CH¼N-Rʹ- or Schiff base) as it is an easily obtainable functional group (via condensation reaction) with good yields [5,6], and a crown-type receptor because they can provide are different cavity sizes. However, some studies have revealed that when the iminic spacer is exposed to different envi- ronments, it will interact with or coordinate specific cations, competing with the crown [7]. Chen et al. proposed the formation of an intermolecular sandwich between the iminic nitrogen and the cavity of the macrocycle 4ʹ-R-benzo-15-crown-5, in a 2:2 ratio. Considering these findings, several studies have reported the for- mation of host-guest complexes (imine-Cu 2þ ) as an explanation for * Corresponding author. Departamento de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Av. Libertador B. O'Higgins, 3363, Casilla 40, Correo 33, Santiago, Chile. ** Corresponding author. E-mail addresses: fernando.godoy@usach.cl (F. Godoy), jorge.pavez@usach.cl (J. Pavez). Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta https://doi.org/10.1016/j.electacta.2019.06.090 0013-4686/© 2019 Elsevier Ltd. All rights reserved. Electrochimica Acta 318 (2019) 479e485