Discrimination of fluorescence light-up effects induced by pH and metal ion chelation on a spirocyclic derivative of rhodamine B

• Type: Article in International Scientific Journal
• Date: 2013

Authors

Andreia Leite (Author) Other; Ana M G Silva (Author) Other; Luis Cunha Silva (Author) Other; Baltazar de Castro (Author) FCUP; Paula Gameiro (Author) FCUP; Maria Rangel (Author) ICBAS

Journal

Title: Dalton Transactions

Vol. 42

Pages: 6110-6118

ISSN: 1477-9226

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 24 Citations

Scopus - 26 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-005-3JQ

DOI: 10.1039/c2dt32198j

Abstract (EN): In the present work we describe the structure and the spectroscopic characterization of a spirocyclic derivative of a rhodamine B ligand whose properties allow discrimination of light-up effects induced by metal ion chelation and variation of pH. Distinction of the two effects is important for the use of this type of ligand to detect and monitor metal ions in aqueous solutions. The synthesis of the ligand was performed in two steps, which involve the reaction of rhodamine B with hydrazine hydrate to form rhodamine B hydrazide followed by condensation with 2-pyridinecarboxaldehyde and was successfully optimized using a solvent free approach under microwave irradiation. The ligand was obtained in the expected spirolactam form and was characterized in the solid state by EA, MS and single-crystal X-ray diffraction. The ligand was characterized in solution by NMR and absorption and fluorescence spectroscopies and its properties were found to be sensitive to pH and concentration of iron(III). The study of the fluorescence properties at variable pH shows that the compound is fluorescent in the range 2 < pH < 4 with maximum intensity at pH 3 and allowed the determination of two pK(a) values (pK(a1) = 2.98, pK(a2) = 2.89) and establishment of the corresponding distribution diagram. The very low pK(a) values guarantee that above pH equal to 4 the ligand is mostly present in the fully non-protonated and non-fluorescent form L. The study of the interaction of the ligand with iron(III) was performed in DMSO and DMSO-H2O to exclude the influence of pH and due to the low solubility of the compound. The results indicate that the presence of iron(III) triggers the opening of the spirolactam form of the ligand and the maximum intensity obtained at a metal : ligand ratio of 1 : 2 is consistent with the formation of an iron(III) complex with the tridentate ligand.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9