A new rhodamine-based fluorescent chemosensor for transition metal cations synthesized by one-step facile condensation

Three compounds of rhodamine-triazine aminopyridine derivatives (sensor RC2P-RC4P) had been synthesized. Spectroscopic analyses revealed that differing structural substitution patterns of RC2P-RC4P resulted in different sensitivity for Fe3+ ions. Sensor RC2P due to having a suitable space coordination structure was more selective for Fe3+ over other metal ions and amino acids in water when compared with RC3P and RC4P. Density functional theory (DFT) calculations of RC2P-RC4P were carried out to rationalize the design. The detection limit of RC2P for Fe3+ was 4.1 × 10−8 M, which presented a pronounced sensitivity toward Fe3+. In addition, a simple paper test strip for the rapid monitoring of Fe3+ was developed, and sensor RC2P was successfully applied to the imaging of Fe3+ in living HL-7702 cells.

Rhodamine-aminopyridine based fluorescent sensors for Fe3+ in water: Synthesis, quantum chemical interpretation and living cell application

A coumarin–amide–dipicolylamine linkage (L) was synthesized and used as a fluorescent receptor for metal cations in water. The receptor dissolved in water with neutral pH shows almost no fluorescence due to the photoinduced electron transfer (PET) from the amide and amine nitrogens to the excited state coumarin moiety. Coordination of Zn2+ or Cd2+ with L creates strong fluorescence at 437 or 386 nm, respectively, due to the suppression of PET. In contrast, other metal cations scarcely show fluorescence enhancement. IR, NMR, and potentiometric analysis revealed that both Zn2+ and Cd2+ are coordinated with two pyridine N, amine N, and amide O; however, the Zn2+ center is also coordinated with a hydroxide anion (OH–). The structure difference for Zn and Cd complexes results in longer- and shorter-wavelength fluorescence. Ab initio calculations revealed that π electrons on the excited state Cd complex are delocalized over the molecules and the Cd complex shows shorter-wavelength emission. In contrast, π elect...

Mechanism for different fluorescence response of a coumarin-amide-dipicolylamine linkage to Zn(II) and Cd(II) in water.

Oxidative addition of donor-functionalised 4-iodoimidazolium salts to palladium(0) provides a selective route for the preparation of abnormal chelating N-heterocyclic carbene complexes and enables the introduction of a variety of donor groups. The activation of the C4 position does not necessitate protection of the imidazolium C2 position, thereby leaving this site available for further modification. While metallation of the unsubstituted C2 position of the N-heterocyclic carbene ligand was unsuccessful when palladium was bound to the C4 carbon atom, sequential metallation of first the C2 position, by means of transmetallation, followed by C4–I oxidative addition, afforded a dimetallic complex comprised of two palladium centres bridged by a single NHC ligand.

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Chelating C4-bound imidazolylidene complexes through oxidative addition of imidazolium salts to palladium(0)

Complexation of 1,4-phenylenebis(methylene) diisonicotinate, L1, with cis-protected Pd(II) components, [Pd(L')(NO3 )2 ], in an equimolar ratio yielded binuclear complexes, 1 a-d of [Pd2 (L')2 (L1)2 ](NO3 )4 formulation where L' stands for ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), and phenanthroline (phen). The combination of 4,4'-bipyridine, L2, with the cis-protected Pd(II) units is known to yield molecular squares, 2 a-d. However, 2 b-d coexist with the corresponding molecular triangles, 3 b-d. Combination of an equivalent each of the ligands L1 and L2 with two equivalents of cis-protected Pd(II) components in DMSO resulted in the D-shaped heteroligated complexes [Pd2 (L')2 (L1)(L2)](NO3 )4 , 4 a-d. Two units of the D-shaped complexes interlock, in a concentration dependent fashion, to form the corresponding [2]catenanes [Pd2 (L')2 (L1)(L2)]2 (NO3 )8 , 5 a-d under aqueous conditions. Crystal structures of the macrocycle [Pd2 (tmeda)2 (L1)(L2)](PF6 )4 , 4 b'', and the catenane [Pd2 (bpy)2 (L1)(L2)]2 (NO3 )8 , 5 c, provide unequivocal support for the proposed molecular architectures.

R. Raghunathan

Papers

Manifestation of diamagnetic chemical shifts of proton NMR signals by an anisotropic shielding effect of nitrate anions