Peptidyl Fluorescent Chemosensors for the Detection of Divalent Copper

Abstract

Fluorescent organic chemosensors for the detection of divalent copper with high selectivity and sensitivity are the subject of intense research in the recent years. Structurally, ionophore and fluorophore are two essential parts determining the resultant performance of the chemosensor. While much work has been focused on designing highly selective ligands, little attention has been paid to the possible influence of ionophore-fluorophore interaction on their properties in metal ion binding. We studied here fluorescent chemosensors based on the Gly-His peptidyl motif and found that the functionality of the chemosensors was greatly influenced by the spatial alignment of the fluorophore in the molecules. In Gly-His-Lys(Dns) (1), the dansyl group is on a side branch and does not interact with copper, while in Dpr(Dns)-His-Lys (2), the dansyl group is also on a side branch but the close placement allows it to directly participate in the binding with copper ions. Therefore, although dansyl can signal the binding event in both molecules, the mechanisms involved are quite different, and this difference resulted in different sensing performance, e.g., the selectivity. Even more strikingly, the dansyl group in Dns-Gly-His-Gly (3) exhibited a profound effect on the molecular complexation. The binding constant decreased, and binding mode was affected since only 1:1 binding was observed while in side-branch-labeled ligands, a 2:1 binding may also be involved. In contrast to those side-chain-labeled ligands, molecule 3 is extremely simple in structure and possesses superior detecting qualities such as selectivity, molecular sensitivity, and applicability in a wide range of pH.

An Optode Sensor for Cu2+ with High Selectivity Based on Porphyrin Derivative Appended with Bipyridine

“…The value of the shift is indicative of the degree of the interaction between the fluorophore and the bound Cu 2+ : the bigger the shift, the stronger the interaction. 12 The porphyrin moiety is very close to the recognition site, so a slight shift (3 nm) was observed. Upon addition of Cu 2+ , the absorption spectrum of H2TPP remains almost unchanged.…”

“…Although fluorescence signaling offers the advantage of high sensitivity over absorption or reflectance signaling, only a few optical sensors based on fluorescence are reported for Cu 2+ determination. [10][11][12] These fluorescence sensors are commonly composed of two structural subunits: a fluorophore (for signal transduction) and an ionophore (for selective recongnition of metal ion). The two subunits are connected through a linking bridge.…”

Fluorescent Detection Principles and Strategies

“…12.2a) enables the selective detection of these ions where the emission is either switched on or off . The PET sensors 15 [44] and 16 [45] were developed for the sensing of Cu(II), where, in the case of 16, the use of the tripeptide binding motive GlyGlyHis (from the HAS protein) was used to complex the Cu(II) in competitive media, while 15 employed a simple diamide moiety to complex to the Cu(II) ion.…”

Highly sensitive and selective ratiometric fluorescent copper sensors: Different binding affinities modulated by three separate side chains of naphthalimide

“…It is well known that Cu 2+ is a paramagnetic ion with an unfilled d shell and can strongly quench fluorescence via electron or energy transfer. So far, most of the copper sensors are fluorescence-quenched [5][6][7][8][9][10][11][12][13] with intrinsic disadvantage: lower sensitivity. Only a few reported sensors cause fluorescence enhancement when binding Cu 2+ ion [14][15][16][17][18] .…”