Synthesis, Spectral Characterization and Potential Fluorescent Properties of Three Lanthanide(III) Ions Complexes with Nalidixic Acid

Three new solid lanthanide complexes with nalidixic acid (HNal) with the stoichiometry [Ln(Nal)₃]·5·.5H₂O (Ln = Tb, Dy and Ho) were synthesized applying the green synthesis method from the aqueous solutions without the organic solvent addition and fully characterized by the elemental analysis, XRF, complexometric titration, gravimetric analysis, molar conductivity and solubility measurements, powder X-Ray diffraction, UV-Vis and infrared (FT-IR) spectroscopies. Moreover, the luminescent properties of the Tb(III), Dy(III), and Ho(III) complexes in the solid state and in the solutions were investigated. On the basis of the detailed spectral analysis, it was concluded that the nalidixate ligands bind to the lanthanide ions by the bidentate carboxylate and carbonyl groups while water molecules belong to the outer coordination sphere. At the excitation of UV light, the complexes exhibited characteristic emission of central lanthanide ions, the intensity of which depends significantly on the excitation wavelength and/or the solvent. Thus, the application of nalidixic acid (apart from biological activity) for the synthesis of luminescent lanthanide complexes was confirmed which can find potential applications in the field of photonic devices and/or bioimaging agents.

Riboflavin based conjugated biomolecule for ultrasensitive detection of nitrophenols

Real time detection of explosive compounds in today's time is of utmost necessity due to security and severe environmental safety issues. Herein, we have synthesized a biobased conjugated molecular system from riboflavin and l-cystine utilized it for detecting picric acid in trace amount using optical sensing technique. The bioconjugate probe showed high quenching efficiency towards picric acid, which is 92.2%. In depth mechanistic study showed that ground state electrostatic interaction and inner filter effect are the factors leading to the diminishing of the probe's fluorescence intensity on addition of trace amount of the nitrophenol, picric acid. The detection limit of the conjugate is 0.37 nM which is extremely low and highly desirable for clinical applications of this system.

Photographs of fluorescent bioconjugate RC which acts as a very simple and highly efficient optical sensor with practical applicability for real-time detection of picric acid.

Synthesis, structural, spectral and antimicrobial activity studies of copper-nalidixic acid complex with 1,10-phenanthroline: DFT and molecular docking

The mix-ligand coordination compound, [Cu(Nal)(Phen)(H₂O)].(Phen).ClO₄.(H₂O)₂ (Nal= Monoanion of nalidixic acid and Phen = 1,10- Phenanthroline), was investigated by focusing on its supramolecular architecture. Structural properties of the complex were characterized by XRD, spectroscopic methods and elemental analysis. The complex has crystallized in the triclinic crystal system and P-1 space group. In the structure where the Cu (II) ion is in the center of symmetry, nalidixate anion and water molecule coordinated to Cu (II) metal through oxygen atoms while phen coordinated through nitrogen atoms. The monomer units are connected by hydrogen bonds to form supramolecular structures. The ground state molecular structure of the complex was optimized using DFT/B3LYP/LANL2DZ method, and compared with experimental X-ray geometry. The FT-IR study of the complex was carried out in the middle IR region focusing on the characteristic vibrations of the free ligands and the complex. Scaled calculated vibrational frequencies are compared with experimental values. The magnetic properties of the complex were investigated by electron paramagnetic resonance (EPR) spectroscopy. Further ultra-violet (UV)-visible spectral analysis was also performed to understand optical properties. The experimental UV-Vis data were associated with the calculated frontier molecular orbitals HOMO/LUMO and, molecular electrostatic potentials (MEP) are also investigated. Biological study of the complex against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Candida albicans showed very strong antibacterial activity with MIC values ranging from 128 μg/ml to 1 μg/ml concentration. The optimized complex is docked to the DNA Gyrase (3LPX) and gyrase tip IIA topoisomerase (3UC1).

Porphyrinic Metal-Organic Framework Nanorod-Based Dual-Modal Nanoprobe for Sensing and Bioimaging of Phosphate

Herein, a dual-modal fluorescent/colorimetric "Signal-On" nanoprobe based on PCN-222 nanorods (NRs) toward phosphate was proposed for the first time. Due to the high affinity of the zirconium node in PCN-222 NRs for phosphate, the structure collapse of PCN-222 NRs was triggered by phosphate, resulting in the release of the tetrakis(4-carboxyphenyl)porphyrin (TCPP) ligand from PCN-222 NRs as well as the enhancement of fluorescence and absorbance signals. The PCN-222 NR-based nanoprobe could be employed for phosphate detection over a wide concentration range with a detection limit down to 23 nM. The practical application of the PCN-222 NR-based nanoprobe in real samples was evaluated. Moreover, benefitting from the good biocompatibility and water dispersibility of PCN-222 NRs, this nanoprobe was successfully employed in the intracellular imaging of phosphate, revealing its promising application in the biological science. The present work would greatly extend the potential of nanostructured MOFs in the sensing and biological fields.

Photostable Anisometric Lanthanide Complexes as Promising Materials for Optical Applications

Uniform luminescent films with high optical quality are promising materials for modern molecular photonics. Such film materials based on β-diketonate complexes of lanthanides have the following application problem: rapid luminescence degradation under UV radiation, low thermostability, poor mechanical properties, and aggregation propensity. An alternative approach to solving these problems is the use of anisometric analogues of β-diketonate compounds of lanthanides (III). The main advantage of such compounds is that they do not crystallize because of long hydrocarbon substituents in the structure of complexes, so they can be used to fabricate thin nano-, micro-, and macroscale uniform film materials by a melt-processing technique at relatively low temperatures, as well as by spin-coating. The method of fabrication of microscale luminescent film materials with controlled optical properties from anisometric analogues of Ln(DBM)3Phen and Ln(bzac)3Phen complexes (Ln = Eu, Tb) is proposed in this paper. Within the framework of this research, we developed original films which are highly uniform and transparent. An important advantage of these films is their high photostability and potential for applications as reusable luminescent sensors and light converters.

A Novel Tb@Sr-MOF as Self-Calibrating Luminescent Sensor for Nutritional Antioxidant

Sesamol, is well-known antioxidant and can reduce the rate of oxidation and prolong expiration date. It is also potentially antimutagenic and antihepatotoxic, the detection of sesamol is important and remains a huge challenge. Herein, a new 3D alkaline earth Sr metal organic framework [Sr(BDC)DMACH₂O]n (BDC = benzene-1,4-dicarboxylate; DMAC = N,N-dimethylacetamide) is synthesized and a probe based on Tb3+ functionalized Sr-MOF. The Tb(3+)@Sr-MOF showed good luminescence and thermal property. Due to the energy competition between sesamol and ligand, the luminescence intensity of sesamol increases meantime luminescence intensity of Tb3+ decreases, the ratio of the emission intensities (I344/I545) linearly increases with sesamol in concentrations ranging from 1 × 10-7 to 8 × 10-4 M. Furthermore, the fluorescence-detected circular test shows that the composite Tb(3+)@Sr-MOF can serve as ratiometric sensor for sensing of sesamol. This is the first example for self-calibrated detecting sesamol based on metal-organic framework (MOF).

A Toolbox of Chromones and Quinolones for Measuring a Wide Range of ATP Concentrations

A series of 26 3-hydroxychromones, three bis-flavonols and four 3-hydroxyquinolones were studied to evaluate their fluorescence response to interaction with ATP in buffer. The dyes differ by the total charge, the size and number of their aromatic units, as well as the position or electron-donating ability of their substituents. All of them were suggested to form complexes with ATP of 1:1 and 1:2 stoichiometry, which can be evidenced by their bright fluorescence and their 3000-6000 cm^-1 red-shifted excitation band. These fluorescent complexes allow detection of ATP concentrations over 3 orders of magnitude, whereas most other known probes cover no more than two orders. In total, the dyes allow ATP detection from 0.001 to 57 mm. In addition, most of the dye-ATP complexes can be excited in the visible and monitored in the red region of the spectrum. The response amplitude of the described dyes to ATP is as high as for the best known probes. Considering that complexation takes place at neutral pH, the studied dyes form a toolbox of fluorescent probes for intensiometric and ratiometric measurements of ATP concentration in a broad concentration range. Finally, the obtained results stimulate the idea that most of natural 3-hydroxyflavones in living cells may form complexes with ATP.