The interaction mechanism between the novel rhodamine 6G derivative probe LXY and Fe³⁺ was systematically investigated using multiple analytical techniques to elucidate the structural transformation underlying its fluorescence response. Job’s plot analysis revealed a 1:1 stoichiometry between LXY and Fe³⁺, indicating a direct and specific binding event. This was further corroborated by mass spectrometry, which detected a peak at m/z 698.66 corresponding to the [LXY + NO₃⁻ + H₂O]⁺ ion, confirming the formation of a stable complex without significant fragmentation. Notably, despite strong evidence for Fe³⁺ involvement, the metal ion was absent in the X-ray single-crystal structure of the open-ring form of LXY, suggesting that Fe³⁺ may act as a transient catalyst or induce conformational change without being permanently incorporated into the crystal lattice.
X-ray crystallographic analysis provided definitive structural proof that Fe³⁺ triggers the ring-opening process. The closed lactam form of LXY, which is non-fluorescent, transforms into an open-ring configuration upon Fe³⁺ coordination. This structural transition exposes the chromophore, enabling conjugation and resulting in intense fluorescence at 550 nm.14221-01-3 custom synthesis The spatial arrangement of the molecule in the crystal showed significant changes in bond angles and electron density distribution compared to the closed form, particularly around the rhodamine core and the hippuric acid linker. Density functional theory (DFT) calculations supported these observations, revealing that the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) decreased from 3.6843 eV in the closed form to 2.4394 eV in the open form, consistent with enhanced electronic delocalization and increased fluorescence efficiency.
Scanning electron microscopy (SEM) analysis revealed a dramatic morphological shift: the dendritic nanostructure of free LXY evolved into a porous, planar aggregation pattern after Fe³⁺ addition, indicating structural reorganization driven by metal binding. This aggregation behavior likely contributes to signal amplification and stability in biological environments. The pH-dependent studies confirmed that the probe remains selective within the physiological range (pH 6.8–8.0), with optimal performance at pH 7.4, making it suitable for live-cell and in vivo applications. The absence of interference from other cations, including those with similar charge and size such as Al³⁺ and Ce³⁺, underscores the high specificity of the coordination site formed by the amide-functionalized rhodamine scaffold.CHRNA7 Antibody Epigenetic Reader Domain
These combined results provide a comprehensive understanding of the sensing mechanism: Fe³⁺ induces a reversible ring-opening of the rhodamine moiety through coordination with nitrogen and oxygen atoms in the amide and lactam groups, leading to fluorescence turn-on.PMID:34145996 The integration of crystallographic, spectroscopic, computational, and microscopic data not only validates the design principle but also establishes a robust framework for developing next-generation metal-ion probes based on rhodamine chemistry. This work exemplifies how advanced structural characterization can unlock mechanistic insights critical for rational probe design and real-world application.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
