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Human serum albumin (HSA) is regarded as a useful biomarker for rapid medical diagnosis of various disorders mainly related to the kidneys and liver. Hence, it is crucial to identify and monitor the HSA level in complex biofluids (urine and blood samples) using a simple approach. Herein, we have designed and synthesized an intramolecular charge transfer (ICT) based environment-sensitive fluorescent molecular probe, (E)-2-(3-(2-(5-methoxy-1H-indol-3-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCI-MIN), that can selectively interact with HSA in PBS buffer solution and exhibit a ~78-fold enhancement in fluorescence intensity with a significant Stokes shift (~126 nm), which is important to avoid interference from the excitation light. The significant red fluorescence response can be attributed to the suppression of free intramolecular rotation of the DCI-MIN probe inside the hydrophobic binding cavity of HSA and the low polar microenvironment present within HSA. According to the 3σ/slope method, the detection limit was found to be 1.01 nM (0.0671 mg L-1) in aqueous solutions, which is significantly lower than the normal level of HSA in healthy urine and blood serum, indicating its high sensitivity. DCI-MIN has the ability to exhibit useful applications, including the detection and quantification of HSA concentration in complex biofluids (human urine and blood samples) as well as the imaging of serum albumin in living cells. [ABSTRACT FROM AUTHOR]

Here, we report the design and synthesis of a Schiff base probe, DBNHC ((E)-2-(2,4-dihydroxybenzylidene)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide), and its interaction with bovine serum albumin (BSA). In ∼100% PBS buffer, the probe DBNHC can self-assemble into nonfluorescent nanoaggregates due to the aggregation caused quenching (ACQ) effect. However, it becomes highly fluorescent (∼14 fold) in the presence of BSA which facilitates the disassembly of nanoaggregates into its monomer. The site-selective fluorescence displacement assay and molecular docking simulations reveal that mainly hydrogen bonding, π⋯sulphur and π⋯alkyl interactions are responsible for the disassembly of nanoaggregates leading to encapsulation of DBNHC monomer at site II in BSA, resulting in a cyan green emission. The detection limit determined by the 3σ/slope method was found to be 58 nM, and the lower dissociation constant [Kd = (1.506 ± 0.196) μM] value suggests strong binding between the probe and BSA. Further, DBNHC was used for cell incubation and in vitro fluorescence imaging of BSA. [ABSTRACT FROM AUTHOR]

A fluorescein hydrazone based conjugate (H2L3) was synthesized by coupling fluorescein hydrazide (L1) with 2-(pyridin-2-ylmethoxy)-naphthalene-1-carbaldehyde (L2). H2L3 was well characterized by several spectroscopic methods such as IR, 1H, 13C-NMR and ESI-MS. The probe H2L3 exhibited high selectivity and high sensitivity towards toxic Hg2+ ions in semi-aqueous medium (pH 7.2, 10 mM HEPES) over other metal ions. The significant enhancement in fluorescence emission centered at 520 nm was attributed to the Hg2+-induced ring opening of the spirolactam moiety in the fluorescein structure. The 1 : 1 binding of H2L3 to Hg2+ was established by Job's method and confirmed by ESI-MS+ (m/z) studies and the binding constant was calculated as (0.43 ± 0.04) × 104 M−1 with a detection limit of 1.24 μM. Then again, the [Hg(HL3)]+ ensemble could be utilized as a reversible fluorescent sensor for S2−. On addition of S2− to the [Hg(HL3)]+ complex, the fluorescence intensity was totally quenched because Hg2+ in the complex was grabbed by S2− because of the stronger binding force between Hg2+ and S2−. The tentative coordination environment in the [Hg(HL3)]+ complex was established by DFT studies. The fluorescence “OFF–ON–OFF” mode of H2L3 was examined in the presence of Hg2+ and S2− and finds applications in devices with logic gate functions. H2L3 also exhibits bio-compatibility and negligible cytotoxicity and is suitable for fluorescence cell imaging of Hg2+ ions in live HepG2 cells. [ABSTRACT FROM AUTHOR]

We introduce herein, a novel copper complex-based fluorescent probe [CuII(DQ468)Cl]+ that exhibits a significant fluorescence turn-on response towards nitroxyl (HNO) with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide (NO). A smart strategy, involving HNO-induced reduction of paramagnetic [CuII(DQ468)Cl]+ to diamagnetic [CuI(DQ468)]+ with concomitant fluorescence enhancement via a PET mechanism is focused here. This reduction-based strategy was also supported by X-band EPR response and mass spectroscopy. The metal free probe (DQ468) showed high affinity towards Cu2+ to form [CuII(DQ468)Cl]+ with a 0.091 μM detection limit, which subsequently enabled the detection of HNO in an organo-aqueous medium at biological pH (7.4) in the green wavelength region (λem = 543 nm) with a LOD of 0.41 μM. The ground-state geometries of DQ468, [CuII(DQ468)Cl]+ and [CuI(DQ468)]+ were optimized by DFT calculations, which revealed that the central metal ion in [CuII(DQ468)Cl]+ is in a distorted tetrahedral geometry with the C1 point group. Additionally, the negligible cytotoxicity and good biocompatibility make the developed probe useful for the in vitro detection of HNO. [ABSTRACT FROM AUTHOR]

A Cu(ii) based sensor (1) prepared by the complexation between (quinolin-8-ylamino)-acetic acid hydrazide (L2) and Cu2+ ions has been developed for a highly sensitive and selective recognition of HNO and S2− over other biologically abundant anions with prominent enhancement in absorption and emission intensities. The sensor (1) shows weak fluorescence due to ET (electron transfer) but upon addition of HNO and S2− a large enhancement in the fluorescence intensity (F.I.) was observed over other possible competitive anions on the basis of reduction of Cu(ii) to Cu(i) and formation of CuS, respectively. The 1 : 1 complexation was characterized by mass spectrometry (MS), elemental analysis and Job's plot. The corresponding Kf value was evaluated to be (4.934 ± 0.05) × 104 M−1 for Cu2+ from UV-Vis absorption titration. Quantum yields of L2 and [Cu-L2 + S2−] and [Cu-L2 + HNO] complexes in acetonitrile (CH3CN) are found to be 0.107, 0.09 and 0.07, respectively, using quinine sulphate as the standard. [ABSTRACT FROM AUTHOR]

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques. In 3 : 7 water : MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, μ = 0.05 M LiCl), it selectively recognizes Fe3+ through 1 : 1 complexation resulting in a 106-fold fluorescence enhancement and a binding constant of 8.10 × 104 M−1. The otherwise non-fluorescent spirolactam form of the probe results a dual-channel (absorbance and fluorescence) recognition of Fe3+via CHEF (chelation enhanced fluorescence) through the opening of the spirolactam ring. We have also carried out fluorescence titration and anisotropy (r) studies in pure water in the presence of SDS (sodium dodecyl sulphate). Based on the dependence of FI (fluorescence intensity) and r on [SDS] it was proposed that the probe is trapped between two SDS monolayers which again interact among themselves by π…π stacking. As a result, there is an increase in FI up to [SDS] ∼ 7 mM – a phenomenon reminiscent of aggregation-induced enhancement of emission (AIEE). Beyond this concentration of SDS (7 mM), micelle formation takes place and the π…π stacked polymer now becomes a monomer and is trapped inside the micellar cavity. As a result, there is a decrease in FI at [SDS] ＞ 7 mM. But for anisotropy, it increases with [SDS] beyond 7 mM. Ligand, metal, and SDS interactions are well established through different optical and morphological studies. [L–Fe(NO3)]2+ thin films on FTO (Fluorine-doped Tin Oxide) glass substrates have been designed with the help of the spin-coating deposition technique. The deposited film of thickness 1.6 × 10−5 cm is well characterized by optical band gap calculation with a direct band gap, εg∼ 1.6 eV. FESEM was also performed for the [L–Fe(NO3)]2+/FTO film. The current–voltage characteristics were measured by the two-probe technique. Light-dependent exciton generation was carried out by taking the top and bottom contacts with graphite paste on FTO and on the [L–Fe(NO3)]2+ films for the measurement of switching behavior. The response ratio curve for the light-induced frequency-switching phenomena has been obtained. The frequency taped here is the oscillation frequency of the photo-generated electron and the hole in an exiton. Thus, the light-induced frequency-switching behavior and Schottky barrier diode characteristics of the material were established. [ABSTRACT FROM AUTHOR]

A novel di-coordinating rhodamine-based chemosensor, HL with NO donor atoms, selectively and rapidly recognizes Fe3+ in the presence of all biologically relevant as well as toxic metal ions and numerous anions and also with other reactive oxygen and nitrogen species. It exhibits a lower detection limit (0.17 μM) and comparatively higher formation constant (Kf = 1.72 × 104 M−1). The DNA-binding properties of [LFe(NO3)2]+ complex have been comprehensively studied by using UV-Vis, fluorescence, and optical melting studies and circular dichroism, which clearly indicate that [LFe(NO3)2]+ interacts with DNA via a groove binding mode. In particular, competition experiments with Hoechst and DAPI constitute firm evidence for this binding mode, and clearly rule out intercalation. The negative ΔG0 and positive ΔS0 values obtained from a calorimetric technique confirm the spontaneity of the binding of [LFe(NO3)2]+ with DNA. The resulting [LFe(NO3)2]+/DNA composite material could be a valuable candidate for future photonics and/or biological applications. [ABSTRACT FROM AUTHOR]

A novel hexa-coordinating rhodamine-based chemosensor, HL6, with N4O2 donor atoms, selectively and rapidly recognizes Fe3+ in the presence of all biologically relevant as well as toxic metal ions, numerous anions (except for F− and I−, which quench FI) and amino acids. The lower detection limit (110 nM) along with cytoplasmic cell imaging applications with negligible cytotoxicity provides a good opportunity towards in vitro/in vivo cell imaging of Fe3+ ions. Scanning electron microscopy (SEM) studies reveal a spherical microstructure for the free ligand, HL6, which melts upon increasing the applied voltage (≥2 kV); however, this is reduced in size in the presence of SDS, morphology remaining the same. [L6-Fe]2+ gives hexagonal rod-like microstructures due to π…π stacking extended in a one dimensional fashion, which, in the presence of SDS, turn into cubic microstructures. However, in the presence of HSA both HL6 and [L6-Fe]2+ agglomerated severely. A plot of FI (or r) vs. [SDS] at constant [L6-Fe2+] (20 μM) shows a rapid decrease in FI (or r); FI or r reaches a minimum at ∼2 mM SDS and then increases and becomes saturated at ≥8 mM SDS. The initial rapid decrease in FI or r with the increase in [SDS] arises due to the breakdown of the self-assembled microstructures of [L6-Fe]2+ formed probably through π…π stacking in pure aqueous solution in the presence of SDS (≤2 mM). The increase in FI or r with [SDS] beyond 2 mM may arise due to trapping of the [L6-Fe]2+ moiety inside the micellar cavity thereby giving it a thermodynamically rigid structure. Again, fluorescence anisotropy measured as a function of HSA concentration (0–70 μM) at a fixed concentration of HL6 and Fe3+ (20 μM each) at 555 nm showed a gradual increase in r with the increase in [HSA]. Site selective binding and molecular modeling studies revealed that [L6-Fe]2+ predominantly binds in the subdomain IIA of HSA by both hydrophobic and electrostatic forces. A circular dichroism (CD) study clearly points towards the reduction in α-helical organization of the protein and subsequent increase in the coiled structure upon binding with [L6-Fe]2+ indicating a small but definitive partial unfolding of the protein. [ABSTRACT FROM AUTHOR]

A sensor (HL5) based on rhodamine 6G–en and 3-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-hydroxy-5-methyl-benzaldehyde (HL4) has been developed for a highly sensitive and selective CHEF based recognition of trivalent metal ions M3+ (M = Al, Fe and Cr) over mono- and di-valent and other biologically abundant trivalent metal ions with prominent enhancement in absorption and emission intensities. A large enhancement of fluorescence intensities for Fe3+ (21 fold), Al3+ (14 fold) and Cr3+ (10 fold) was observed upon addition of 1.8 equivalents of these metals into the probe in methanol/H2O (1 : 1, v/v, pH 7.2) with the possibility of naked eye detection. The corresponding Kf values were evaluated to be 6.7 × 104 M−1 (Fe3+); 8.2 × 104 M−1 (Al3+) and 6.0 × 104 M−1 (Cr3+). The quantum yields of HL5 and [HL5–Fe3+] and [HL5–Cr3+] and [HL5–Al3+] complexes in methanol/H2O (1 : 1, v/v, pH 7.2) are found to be 0.013, 0.290, 0.120, and 0.158, respectively, using rhodamine-6G as the standard. The LOD for Fe3+, Al3+ and Cr3+ were determined by 3σ methods with values 0.29, 0.34 and 0.31 μM, respectively. An arsenate ion snatches Al from the Al–HL5 complex and quenches its fluorescence via its ring closed spirolactam form. Advanced level molecular logic devices using the inputs 2 and 4 and memory devices, have been constructed. The low cytotoxicity and large enhancement in fluorescence intensity of HL5 upon complexation with M3+ metal ions make the probe suitable for bio-imaging of M3+ (M = Al, Fe and Cr) in living cells and native cellular iron pools. [ABSTRACT FROM AUTHOR]

A covalently bonded hexanuclear neutral complex, [Mn 6 (μ 3 -O) 2 (3-MeO-salox) 6 (OAc) 2 (H 2 O) 4 ] (1), has been synthesized and characterized by single crystal X-ray diffraction analysis along with IR and HRMS studies. Complex 1 has been found to selectively interact with human serum albumin (HSA), a model transport protein. The interaction of 1 with HSA was investigated by monitoring the change in the absorbance value of HSA at λ = 280 nm with increasing concentration of 1. Likewise, fluorescence titrations were carried out under two conditions: (i) titration of a 5 μM solution of complex 1 with the gradual addition of HSA, showing a ∼9-fold fluorescence intensity enhancement at 424 nm, upon excitation at 300 nm; and (ii) upon excitation at 295 nm, titration of 5 μM HSA solution with the incremental addition of complex 1, showing a quenching of fluorescence intensity at 334 nm, with simultaneous development of a new emission band at 424 nm. A linear form of the Stern-Volmer equation gives K SV = 9.77 × 10 4 M -1 and the Benesi-Hildebrand plot yields the binding constant as K BH = 1.98 × 10 5 M -1 at 298 K. The thermodynamic parameters, Δ S °, Δ H °, and Δ G °, were estimated by using the van't Hoff relationship which infer the major contribution of hydrophobic interactions between HSA and 1. It was observed that quenching of HSA emission arises mainly through a dynamic quenching mechanism as indicated by the dependence of average lifetime 〈 τ 〉 on the concentration of 1. The changes in the CD (circular dichroism) spectral pattern of HSA in the presence of 1 clearly establish the variation of HSA secondary structure on interaction with 1. The most probable interaction region in HSA for 1 was determined from molecular docking studies which establish the preferential trapping of 1 in the subdomain IIA of site I in HSA and substantiated by the results of site-specific marker studies. Complex 1 was further evaluated for its antiproliferative effects in lung cancer A549 cells, which strictly inhibits the growth of the cells in both 2D and 3D mammospheres, indicating its potential application as an anticancer drug.

Multipurpose applications of a newly developed homobimetallic Ru(II) complex, Ru-NDI[PF6]4, which incorporates 1,10-phenanthroline and triazole-pyridine ligands and linked via a (-CH2-)3 spacer to the reputed anion-π interacting NDI system, are described. Solution-state studies of the bimetallic complex, including EPR, PL, UV-vis, and NMR experiments, reveal two sequential one-electron transfers to the NDI unit, generating NDI·- and NDI2- in the presence of F- selectively. This process inhibits the primary electron transfer from Ru(II) to the NDI unit, thereby allowing the 3MLCT-based emission of the complex to be recovered, resulting in a corresponding ten-fold increase in luminescence intensity. DFT and TD-DFT computational studies further elucidate the experimentally observed absorption spectra of the complex. Secondly, CT-DNA binding studies with the complex are performed using various spectroscopic analyses such as UV-vis, PL, and CD. Comparative DNA binding studies employing EB and molecular docking reveal that the binding with CT-DNA occurs through both intercalative and groove binding modalities. Thirdly, the photocatalytic activities of the complex towards C-C, C-N, and C-O bond formation in organic cross-coupling reactions, including the amidation of α-keto acids to amines and the oxidation of alcohol to aldehydes, are also demonstrated., (© 2024 Wiley‐VCH GmbH.)

We introduce herein, a novel copper complex-based fluorescent probe [CuII(DQ468)Cl]+ that exhibits a significant fluorescence turn-on response towards nitroxyl (HNO) with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide (NO). A smart strategy, involving HNO-induced reduction of paramagnetic [CuII(DQ468)Cl]+ to diamagnetic [CuI(DQ468)]+ with concomitant fluorescence enhancement via a PET mechanism is focused here. This reduction-based strategy was also supported by X-band EPR response and mass spectroscopy. The metal free probe (DQ468) showed high affinity towards Cu2+ to form [CuII(DQ468)Cl]+ with a 0.091 μM detection limit, which subsequently enabled the detection of HNO in an organo-aqueous medium at biological pH (7.4) in the green wavelength region (λem = 543 nm) with a LOD of 0.41 μM. The ground-state geometries of DQ468, [CuII(DQ468)Cl]+ and [CuI(DQ468)]+ were optimized by DFT calculations, which revealed that the central metal ion in [CuII(DQ468)Cl]+ is in a distorted tetrahedral geometry with the C1 point group. Additionally, the negligible cytotoxicity and good biocompatibility make the developed probe useful for the in vitro detection of HNO.

A Cu(ii) based sensor (1) prepared by the complexation between (quinolin-8-ylamino)-acetic acid hydrazide (L2) and Cu2+ ions has been developed for a highly sensitive and selective recognition of HNO and S2- over other biologically abundant anions with prominent enhancement in absorption and emission intensities. The sensor (1) shows weak fluorescence due to ET (electron transfer) but upon addition of HNO and S2- a large enhancement in the fluorescence intensity (F.I.) was observed over other possible competitive anions on the basis of reduction of Cu(ii) to Cu(i) and formation of CuS, respectively. The 1 : 1 complexation was characterized by mass spectrometry (MS), elemental analysis and Job's plot. The corresponding Kf value was evaluated to be (4.934 ± 0.05) × 104 M-1 for Cu2+ from UV-Vis absorption titration. Quantum yields of L2 and [Cu-L2 + S2-] and [Cu-L2 + HNO] complexes in acetonitrile (CH3CN) are found to be 0.107, 0.09 and 0.07, respectively, using quinine sulphate as the standard.