Synthesis and fluorescence properties of Tb(III) complex with a novel β-diketone ligand as well as spectroscopic studies on the interaction between Tb(III) complex and bovine serum albumin

Study of Judd-Ofelt, Urbach energy and photosensitization process in luminescent Sm(III) complexes with heterocyclic ligands

Six samarium (III) complexes were synthesised by employing the β-ketocarboxylic acid as main ligand and five N-donor systems as ancillary ligands through the environmentally safe liquid-assisted grinding method. Various characterisation techniques were employed to determine the structure of the complexes i.e. NMR, IR, XRD and SEM. Photoluminescent studies were carried out in solid as well as in solution form. In solid and solution form emission spectra show maximum intensity peak at 604 and 602 nm, respectively, assigned to ⁴G_5/2 → ⁶H_7/2 transition which explains orange emission on UV excitation in complexes. CCT, CP, colorimetric parameters and quantum yield (relative and intrinsic) of the synthesized complexes were calculated. With the help of reflectance spectra, band gap and Urbach energy were determined. Lasing parameters were also calculated by employing FWHM values obtained from Gaussian fitting. Energy transfer study revealed the efficacious energy transfer from ligand to metal's emissive level. Further antimicrobial studies revealed higher activity in case of complexes in comparison to ligand.

Applicability of Reddish-Orange Light Emitting Samarium (III) Complexes for Biomedical and Multifunctional Optoelectronic Devices

Six crimson samarium (III) complexes based on β-ketone carboxylic acid and ancillary ligands were synthesized by adopting the grinding technique. All synthesized complexes were investigated via elemental analysis, infrared, UV-Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to ⁴G_5/2 → ⁶H_7/2 electronic transition at 606 nm of samarium (III) ions. Further, energy bandgap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched these complexes (S2-S6) with decay time, quantum yield, luminescence, energy bandgap and biological properties than parent complex (S1). Interestingly, these efficient properties of complexes may find their applications in optoelectronics and lighting systems. In addition to these, the antioxidant and antimicrobial assays were also investigated to explore the applications in biological assays.

Designing of emerald terbium (III) ions with β-ketocarboxylic acid and heterocyclic ancillary ligands for biological and optoelectronic applications

A green and highly efficient grinding method was adopted to synthesize emerald terbium complexes with 1-cyclopropyl-6-fluro-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid as the main organic ligand and 2,2'-bipyridyl, 1,10-phenanthroline, neocuproine, 5,6-dimethyl-1,10-phenanthroline and bathophenanthroline as ancillary ligands. Structural analysis of these complexes was executed via elemental, infrared and ¹ H-nuclear magnetic resonance analysis, which confirmed that the ligand coordinated to the metal ion through β-ketone and hydroxyl groups of carboxylic acid. Thermal stability of these complexes was investigated by study of thermogravimetric/derivative thermogravimetric analysis. Photoluminescence properties were investigated by observing emission spectra (400-700 nm), excitation spectra (250-500 nm) and decay time curves for display devices. The emission spectra revealed that an intense peak at 545 nm was observed due to ⁵ D₄ →⁷ F₅ electronic transition, which is responsible for the emerald colour in synthesized complexes, under 353 nm ultraviolet light excitation. The energy band gap and refractive index were determined, which proclaimed the dormant applications of these complexes in semiconductors. Commission Internationale de l'éclairage colour coordinates confirmed that the emerald emission of these complexes lies in the green region. Furthermore, antioxidant, antimicrobial and antimalarial assays of these complexes were also investigated, which confirmed that these complexes are potent for antioxidant, antimicrobial and antimalarial activities.

Effect of the Heteroaromatic Antenna on the Binding of Chiral Eu(III) Complexes to Bovine Serum Albumin

The cationic enantiopure (R,R) and luminescent Eu(III) complex [Eu(bisoQcd)(H₂O)₂] OTf (with bisoQcd = N,N′-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate and OTf = triflate) was synthesized and characterized. At physiological pH, the 1:1 [Eu(bisoQcd)(H₂O)₂]⁺ species, possessing two water molecules in the inner coordination sphere, is largely dominant. The interaction with bovine serum albumin (BSA) was studied by means of several experimental techniques, such as luminescence spectroscopy, isothermal titration calorimetry (ITC), molecular docking (MD), and molecular dynamics simulations (MDS). In this direction, a ligand competition study was also performed by using three clinically established drugs (i.e., ibuprofen, warfarin, and digitoxin). The nature of this interaction is strongly affected by the type of the involved heteroaromatic antenna in the Eu(III) complexes. In fact, the presence of isoquinoline rings drives the corresponding complex toward the protein superficial area containing the tryptophan residue 134 (Trp134). As the main consequence, the metal center undergoes the loss of one water molecule upon interaction with the side chain of a glutamic acid residue. On the other hand, the similar complex containing pyridine rings ([Eu(bpcd)(H₂O)₂]Cl with bpcd = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate) interacts more weakly with the protein in a different superficial cavity, without losing the coordinated water molecules.

The effect of the antenna moiety on the interaction of two new luminescent Eu(III) complexes with BSA was studied. Results show that the complexes can be conveniently exploited as optical probes for albumin serum proteins by means of opposite mechanisms (switch-on−off of the luminescent signal).

Human plasma protein corona decreases the toxicity of pillar-layer metal organic framework

This scenario was designed to investigate the protein corona pattern on the pillar-layer surface of a Cu-based metal–organic framework (MOF) in human plasma. The [Cu(L)(L^/)].1.3DMA (MOF-1) {L = 4, 4^/-bipyridine and L^/ = 5-aminoisophthalic acid}, was synthesized through the sonochemical irradiation approach as well as characterized by various techniques like scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction and single-crystal X-ray diffraction. The space group was determined to be an orthorhombic space group (Pbam) by single-crystal X-ray diffraction. Single-crystal X-ray analyses on MOF-1 showed that Cu⁺² ion was 6-coordinated. Besides, to study and clarify interactions between MOFs and biological milieu, human whole blood plasma was selected as a model. Fluorescence spectroscopy and SDS-PAGE techniques were employed to explore quantitative and qualitative in situ characterization of protein corona as well. Furthermore, cell viability in a cancerous cell lines was evaluated by MTT assay in the presence and absence of the corona. The results from SDS-PAGE illustrated that the most adsorbed quantity among plasma proteins belongs to fibrinogen (α, β and γ chains), and this protein showed the maximum frequency on the MOF-1s surface, so the possible interactions of MOF-1s with fibrinogen also studied using fluorescence spectroscopy and corresponding data were plotted. According to the obtained data from MTT assay, these structures have concentration-dependent toxicity. In brief, based on the obtained data in the current study, the designed MOF can be introduced as a new desirable carrier for drug/gen delivery after further prerequisite assessments.

Investigations into the bovine serum albumin binding and fluorescence properties of Tb (III) complex of a novel 8-hydroxyquinoline ligand

A novel ligand, 2-methyl-6-(8-quinolinyl)-dicarboxylate pyridine (L), and its corresponding Tb (III) complex, Na4Tb(L)2Cl4·3H2O, were successfully prepared and characterized. The luminescence spectra showed that the ligand L was an efficient sensitizer for Tb (III) luminescence. The interaction of the complex with bovine serum albumin (BSA) was investigated through fluorescence spectroscopy under physiological conditions. The Stern-Volmer analysis indicated that the fluorescence quenching was resulted from static mechanism. The binding sites (n) approximated 1.0 and this meant that interaction of Na4Tb(L)2Cl4·3H2O with BSA had single binding site. The results showed van der Waals interactions and hydrogen bonds played major roles in the binding reaction. Furthermore, circular dichroism (CD) spectra indicated that the conformation of BSA was changed.

Investigation of the interaction of pepsin with ionic liquids by using fluorescence spectroscopy

The molecular mechanism of the interaction between pepsin and two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-octyl-3-methylimidazolium chloride ([C8mim]Cl), was investigated with fluorescence spectroscopy, ultraviolet absorption, and circular dichroism spectroscopy at a pH value of 1.6. The results suggest that ILs could quench the intrinsic fluorescence of pepsin, probably via a dynamic quenching mechanism. The fluorescence quenching constants were determined by employing the classic Stern-Volmer equation. The constant values are very small, indicating that only a very weak interaction between ILs and pepsin exists. The Gibbs free-energy change, enthalpy change (ΔH), and entropy change (ΔS) during the interaction of pepsin and ILs were estimated. Positive values of ΔH and ΔS indicate that the interaction between ILs and pepsin is mainly driven by hydrophobic interaction. Synchronous and three-dimensional fluorescence spectra demonstrate that the addition of ILs (0-0.20 mol L(-1) for each IL) does not bring apparent changes to the microenvironments of tyrosine and tryptophan residues. Activity experiments show that the activity of pepsin is concentration dependent; higher concentrations of ILs (>0.22 mol L(-1) for [C8mim]Cl and >0.30 mol L(-1) for [C4mim]Cl) cause the remarkable reduction of enzyme activity. The presence of ILs also does not improve the thermal stability of pepsin.

Interaction of an amino-functionalized ionic liquid with enzymes: a fluorescence spectroscopy study

The interaction of an amino-functionalized ionic liquid, 1-(2-aminoethyl)-3-butylimidazolium bromide ([NH(2)C(2)C(4)im]Br) with two enzymes, pepsin and papain was investigated using fluorescence spectroscopic technique. It is found that [NH(2)C(2)C(4)im]Br has strong ability to quench the intrinsic fluorescence of pepsin and papain. Quenching mechanisms are considered as static quenching for papain and dynamic quenching for pepsin, respectively. The binding constants and the number of binding sites (n) of [NH(2)C(2)C(4)im]Br to papain were calculated at different temperatures. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The values of ΔG, ΔH and ΔS suggest that interaction of [NH(2)C(2)C(4)im]Br with the two enzymes is spontaneous. Hydrogen bonding and van der Waals interactions play important roles in the binding process of [NH(2)C(2)C(4)im]Br to papain. However, hydrophobic interaction is the main driving force for the interaction of [NH(2)C(2)C(4)im]Br with pepsin. The results of three-dimensional fluorescence spectra show that [NH(2)C(2)C(4)im]Br has no obvious effects on the polypeptide structures of the two enzymes. Additionally, the [NH(2)C(2)C(4)im]Br-containing system can slightly increase the activities of the two enzymes.