Vol.:(0123456789) 1 3 J Incl Phenom Macrocycl Chem DOI 10.1007/s10847-017-0742-4 ORIGINAL ARTICLE New DTPA-derived bis-naphthalenophanes: fuorescence, protonation, and complexation with aromatic amines Blanca A. Durazo-Bustamante 1  · Reina Vianey Quevedo-Robles 1  · Motomichi Inoue 1  · Jose-Zeferino Ramirez 1  · Hisila Santacruz 1  · Rosa Elena Navarro 1  · Lorena Machi 1   Received: 21 March 2017 / Accepted: 26 July 2017 © Springer Science+Business Media B.V. 2017 and are responsible for the pH‒emission profles and the complexation. Keywords Fluorescent chemosensors · Protonation · Inclusion complexes · Macrocycles · Aromatic amines Introduction Fluorescent cyclophanes, consisting of fuorophore units linked together through suitable bridging chains or spacer groups, have been proven to be a good choice for molecu- lar recognition and ion-sensing [1–16]. Especially, water- soluble fuorescent cyclophanes attract a great deal of interest because of their potential application as sensors in biological media. In the molecular design of fuores- cent cyclophanes, the cavity size, as well as the fuoro- genic properties exhibited by these systems, can be tuned by varying the fuorophore moieties, the bridging units or the spacer groups. The aromatic moieties confer to cyclo- phanes a hydrophobic cavity capable of encapsulating specifc guests, but the hydrophobicity reduces the water solubility of the molecule to limit the use in physiological conditions. A series of chelating, water-soluble, fuores- cent aza-cyclophanes have been synthesized by reactions between aromatic diamines and EDTA (ethylenediami- netetraacetic) or DTPA (diethylenetriaminepentaacetic) dianhydride in our research group; aromatic units linked by amino and amide chains construct a macrocyclic frame, and pendant carboxylate arms enhance water-solubility [8–12]. One of the features of this type of fuorescent macrocycles is that potential binding sites for protona- tion and complexation are integrated within the macrocy- clic frame so that direct infuences on geometrical relation between the fuorogenic groups result in sensitive and novel Abstract Two fuorescent, water-soluble bis-naphthale- nophane isomers with six carboxylate arms, abbreviated as (bis-dtpa14nap)H 6 and (bis-dtpa15nap)H 6 , were synthe- sized, which consist of two 1,4- or 1,5-substituted naphtha- lene rings interlinked by two diethylenetriaminepentaacetic (DTPA) chains through amide-linkages. Both DTPA-based macrocycles exhibit intense excimer and monomer emis- sion bands, which sensitively respond to pH in three proto- nation steps; more sensitive is the 1,4-naphthyl isomer. The full pH-emission profles have confrmed that the mono- protonated anion (bis-dtpanap)H 5 − is the major protonation species at the physiological pH. Fluorometric titrations at pH 7.2 have proven that the 1,4-naphthalenophane anion forms 1:1-complexes with cationic phenethylamine (for- mation constant, 5700 M −1 ) and histamine (3000 M −1 ), excluding tryptamine cation, whereas the 1,5-isomer does not react with any of the three amines. The primary binding forces are electrostatic interactions between the CH 2 CO 2 − arms of 1,4-naphthalenophane and the CH 2 CH 2 NH 3 + chain of an aromatic amine. The resulting ion-pair is stabilized by encapsulation of the guest molecule in 1,4-napthalenophane cavity, while the 1,5-isomer cannot encapsulate. NMR studies have demonstrated that 1,4-napthalenophane has a higher freedom in reorientation of naphthalene rings. Such geometrical properties controlled by selection of naphtha- lene units are the feature of the new naphthalenophanes, Electronic supplementary material The online version of this article (doi:10.1007/s10847-017-0742-4) contains supplementary material, which is available to authorized users. * Lorena Machi lmachi@polimeros.uson.mx 1 Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, 83000 Hermosillo, SON, Mexico