Dansyl—Naphthalimide Dyads As Molecular Probes: Effect of Spacer Group on Metal Ion Binding Properties

Abstract

Interaction of a few dansyl-naphthalimide conjugates 1a-e linked through polymethylene spacer groups with various metal ions was investigated through absorption, fluorescence, NMR, isothermal calorimetric (ITC), and laser flash photolysis techniques. The characteristic feature of these dyads is that they exhibit competing singlet-singlet energy transfer (SSET) and photoinduced electron transfer (PET) processes, both of which decrease with the increase in spacer length. Depending on the spacer group, these dyads interact selectively with divalent Cu(2+) and Zn(2+) ions, as compared to other mono- and divalent metal ions. Jobs plot analysis showed that these dyads form 2:3 complexes with Cu(2+) ions, while 1:1 complexes were observed with Zn(2+) ions. The association constants for the Zn(2+) and Cu(2+) complexes were determined and are found to be in the order 10(3)-10(5) M(-1). Irrespective of the length of the spacer group, these dyads interestingly act as fluorescence ratiometric molecular probes for Cu(2+) ions by altering the emission intensity of both dansyl and naphthalimide chromophores. In contrast, only the fluorescence intensity of the naphthalimide chromophore of the lower homologues (n = 1-3) was altered by Zn(2+) ions. (1)H NMR and ITC measurements confirmed the involvement of both sulfonamide and dimethylamine groups in the complexation with Cu(2+) ions, while only the latter group was involved with Zn(2+) ions. Laser excitation of the dyads 1a-e showed formation of a transient absorption which can be attributed to the radical cation of the naphthalimide chromophore, whereas only the triplet excited state of the dyads 1a-e was observed in the presence of Cu(2+) ions. Uniquely, the complexation of 1a-e with Cu(2+) ions affects both PET and SSET processes, while only the PET process was partially inhibited by Zn(2+) ions in the lower homologues (n = 1-3) and the higher homologues exhibited negligible changes in their emission properties. Our results demonstrate that the spacer length dependent variations of the photophysical properties of these novel conjugates not only enable the selective detection of Cu(2+) and Zn(2+) ions but also aid in discriminating these two biologically important metal ions.

Combined photophysical, NMR and theoretical (DFT) study on the interaction of a multi component system in the absence and presence of different biologically and environmentally important ions

“…45 Additionally, the dimethylamino group present in the dansylamide moiety also has the ability to bind cations through coordination of the Natom lone pair. [15][16][17][18][19][20] The uorescence quantum yield of DANSn2 in ACN medium measured from the steady state emission spectra is found to be 0.52 (using anthracene as the standard, f std ¼ 0.36 in cyclohexane). S1, † in order to conrm the purity of the molecule.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Signaling via optical means and uorescence, in particular, have attracted more attention compared to classical techniques due to their ability to monitor in situ analyte concentrations in real time and in real space. 15,16 In the case of metal ions, electron rich ligand centres have been used such that an effective metalligand (receptor) coordinative interaction is responsible for the binding of cations. 27 Signalling systems have been designed by employing organic chromophores/luminophores, inorganic-metal frameworks, coordination frameworks or by a suitable combination of any of these.…”

FRET versus PET: ratiometric chemosensors assembled from naphthalimide dyes and crown ethers

“…23,24 To date some examples of naphthalimide based FRET probes have been reported in literature. 29,30 A few chemosensors for metal cations and protons containing aminonaphthalimide and rhodamine units in which spirolactam to ring-open amide equilibrium of rhodamine dyes is used to switch FRET from the amino-naphthalimide fragment were studied. [25][26][27] A FRET-based ratiometric chemosensor for in vitro cellular fluorescence analyses of pH based on naphthalimide-coumarin system was reported by Zhou et al 28 Selective ratiometric chemosensors for Cu 2+ and Zn 2+ were obtained using dansylamidenaphthalimide conjugates with variable polymethylene linker length between the chromophores.…”

Intra- and Interlayer Energy Transfer in Planar Systems Based on Amphiphilic Naphthalimide Derivatives

“…Наличие у нафталимидного ядра электроно-акцепторных свойств в возбужденном состоянии делает эти соединения удобными моделями для изучения распространенных в живой природе процессов фотоин-дуцированного переноса электрона, [8,9] а также процес-сов безызлучательного резонансного переноса энергии электронного возбуждения по механизму Г. Фёрстера (Forster Resonance Energy Transfer, FRET). [10][11][12][13][14][15][16] В связи с этим большой интерес представляют возможности исследования механизмов FRET-процессов, открываю-щиеся при использовании модельных бисхромофорных систем, состоящих из высокоорганизованных мономоле-кулярных слоев соединений данного типа, с контролиру-емыми условиями сборки. Однако большинство опубли-кованных в этой области работ направлено на изучение процессов переноса энергии между производными нафта-лимида в растворах, [1][2][3][4][5][6][7][8][9][10][11][12][13]15,16] где FRET-эффектреализуется в ковалентно связанных бисхромофорных системах, [11][12][13][14][15][16] что существенно усложняет синтез необходимых соеди-нений.…”