Coordination of Co²⁺ Ions in the Interior of Poly(propylene amine) Dendrimers Containing Fluorescent Dansyl Units in the Periphery

Abstract

We have investigated the interaction of Co 2+ ions (as nitrate salt) with dendrimers of the poly-(propylene amine) family functionalized in the periphery with fluorescent dansyl units. Each dendrimer nD, where the generation number n goes from 1 to 5, comprises 2 (n+1) dansyl functions in the periphery and 2 (n+1) -2 tertiary amine units in the interior. For comparison purposes, the behavior of a monodansyl reference compound (I) has also been investigated. The results obtained have shown that: (i) the absorption and fluorescence spectra of the reference compound I are not affected by addition of Co 2+ ions; (ii) in the case of the dendrimers, the absorption spectra are unaffected, but a strong quenching of the fluorescence of the peripheral dansyl units is observed; (iii) the fluorescence quenching takes place by a static mechanism involving coordination of metal ions in the interior of the dendrimers; (iv) metal ion coordination by the dendrimers is a fully reversible process; (v) a strong amplification of the fluorescence quenching signal is observed with increasing dendrimer generation. For the larger dendrimers (n ) 3, 4, and 5), at very low metal ion concentration 1:1 metal/dendrimer species are formed, in which the Co 2+ ion guest quenches each one of the dansyl units that becomes excited after light absorption.

Synthetic regimes due to packing constraints in dendritic molecules confirmed by labelling experiments

“…There is no universal label and the choice of the reagent should be customized to the synthetic chemistry used. When NH 2 groups are involved one may use the Sanger reagent 51,52 or Dansyl [54][55][56] . The Sanger reagent is less prone to aggregation and its smaller size is advantageous at high g. (iv) The labelling method can quantify all free ends for 1rgtg max , that is,…”

Design of fluorescent materials for chemical sensing

“…In the field of chemical sensing, it has been demonstrated that luminescent dendrimers could be used for chiral amino alcohols, [96][97][98] and metal ion sensing. 95,[99][100][101] 3.1.1 Molecular imprinted polymers. A special case of fluorescent polymers are fluorescent molecular imprinted polymers.…”

“…They estimated that a single metal ion produced the quenching of 44 dye molecules. 63,99,234 Tonellato and co-workers modified silica nanoparticles via the reaction of commercially available silica nanoparticles with average size of 18 nm with a trimethoxysilane derivatized dansylamide as reporter and a picolinamide as Cu 2+ binding subunit. 77 In this case receptor and fluorophores are not bound together but the spatial proximity is ensured by selfassembly of the sensing elements.…”

Synthesis and characterization of new optically active poly(acrylamide/methacrylurea-co-vinyl acetate) copolymers with dansyl units

“…In all cases, the mechanism of switching off the fluorescence signal could be interpreted in terms of energy or intermolecular photo-induced electron transfer between transition metal ions and the excited state of the dansyl molecule from copolymers. [37] On the other hand, the selectivity studies have clearly demonstrated the higher selectivity of such photopolymers toward Fe 2+ ions in comparison with the others foreign ions under identical conditions. These results suggest that dansyl moiety in the side chain of the above copolymers could act as the special recognition site of a fluorescent chemosensor utilized for sensitive and selective detection of transition metal ions.…”