Excited state intramolecular proton transfer (ESIPT) in a dioxotetraamine derived schiff base and its complexation with Fe(III) and Cr(III)

Pyrogallol-based dipodal optical probe as new smart analytical tool for sustainable detection of cobalt in biosystem

The present research focuses on the micro-level detection of cobalt ions in biological and environmental samples using a new probe. The probe is a multifunctional symmetrical dipodal molecule with two pyrogallol binding units attached to the malonate scaffold through a propylene spacer. It was synthesized and characterized by 1H NMR, 13C NMR, IR, electronic spectroscopy, and mass spectrometry. The molecule's binding, thermodynamic, and photophysical properties are also described. The designed probe demonstrates an excellent sensing ability for Co(II) based on the ESIPT "OFF-ON" fluorescence mechanism. The experiments explore the high selectivity of the ligand for cobalt sensing over a wide range of metal ions of biological and environmental importance. The fluorescence intensity shows a linear response to Co(II) in 5-100 μM concentration with a detection limit of 8.75 x 10-5 and a 2.65-fold enhancement in the intensity. These results establish its potential application as a fluorescence sensor. The probe is also employed as a colorimetric sensor for the qualitative determination of cobalt ions in DMSO solution. The interesting behavior of the probe motivated us further to study its coordination properties with divalent cobalt in solution. The pre-organized assembly with an appropriate cavity size favors the ligand for an efficient Co(II) encapsulation by coordinating through imine-Ns and aromatic ring-Os donors, giving high formation constants.

Novel schiff base as Fe3+ sensor as well as an antioxidant and its theoretical studies

A novel Schiff base derivative L (N1-(thiophene-2-ylmethylene)benzene-1,2-diamine) was synthesized via condensation reaction of 3-thiophene carboxaldehyde and 1,2-diamino benzene. The synthesized compound was authenticated using 1 H NMR, 13 C NMR, HRMS, and IR spectroscopy. The compound L was found to be a Fe3+ sensor with the complexation ratio of 1 : 3 as revealed by Job’s plot with maximum absorption at 318 nm. The photophysical properties were studied using absorption and emission spectra. DFT and TD-DFT studies were carried out in order to support the photophysical outcomes of compound L. An antioxidant behaviour of compound L was studied using TAC, FRAP, and DPPH assays and it was found to be showing better TAC activity than the used standard i.e. gallic acid.

A chemosensing approach for the colorimetric and spectroscopic detection of Cr3+, Cu2+, Fe3+, and Gd3+ metal ions

Metal cations are present in domestic and industrial wastewater and have adverse effects on human and aqueous life. The present study describes the development of the molecular probe 9-anthracen-9-ylmethylene)hydrazineylidene)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (AMHMPQ) to detect Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions by using UV-visible, fluorescence, colorimetric and excitation-emission matrix (EEM) spectroscopy techniques. The interaction of Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ can be observed by the absorption maxima shift, turn-off, colour changes, and EEM shifts. In addition, fluorescence limits of detection 17.66 × 10^-6 M, 6.44 × 10^-9 M, 28.87 × 10^-8 M, and 12.49 × 10^-6 M in wide linear ranges, low limits of quantifications, high values of Stern-Volmer constant, Job's plot and Benesi-Hildebrand plot justify the 1:1 association affinity with association constants of 1.46 × 10⁴ M^-1, 1.86 × 10⁷ M^-1, 2.69 × 10⁵ M^-1, 2.13 × 10⁴ M^-1 for AMHMPQ-metal ions (Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions), respectively. Paper- and mask-based kits are developed to explore the utility of the designed chemosensor. Additionally, AMHMPQ acts as a reusable sensor for two, seven, two, and zero cycles for Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions, respectively, when checked with EDTA.

Probing biothiols using a red-emitting pyridoxal derivative by adopting copper(II) displacement approach and cell imaging

An aggregation-induced emission (AIE) active Schiff base L was synthesized by condensing pyridoxal and 2-hydroxy-1-naphthaldehyde with p -phenylenediamine in two simple steps in ethanol. The colorimetric, UV-Vis and fluorescence studies of L revealed that the weak yellow emissive L (λ em =540 nm, λ ex = 450 nm) in pure DMSO turned to a red-emissive L upon increasing the poor solvent fraction (HEPES buffer, 10 mM, pH 7.4) above 50% in DMSO. The DLS and SEM analysis supported the formation of self-aggregates of L that restricted the intramolecular motion and activated the ESIPT. The cations sensing ability of the AIEgen L was explored in HEPES buffer (5% DMSO, 10 mM, pH 7.4), where Cu 2+ selectively quenched the fluorescence at 608 nm due to the chelation-enhanced fluorescence quenching (CHEQ) effect with an estimated sensitivity limit of 0.9 µM. Subsequently, the in situ formed AIEgen L-Cu 2+ complex was applied for the cascade detection of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). The decomplexation of Cu 2+ from the AIEgen L-Cu 2+ upon addition of Cys, Hcy and GSH restored the quenched fluorescence emission of AIEgen L at 608 nm. With this Cu 2+ displacement approach, the concentration of Cys, Hcy and GSH can be detected down to 2.8 µM, 3.12 µM and 2.0 µM, respectively. The practical utility of AIEgen L and AIEgen L-Cu 2+ was validated by quantifying the selective analytes in various environmental and biological samples, and also applied successfully for the cell imaging applications.

An aggregation-induced emissive pyridoxal derived tetradentate Schiff base for the fluorescence turn-off sensing of copper(ii) in an aqueous medium

An aggregation-induced emissive pyridoxal derived tetradentate Schiff base was developed for the fluorescence sensing of copper(ii) and sulphide ions.

An aggregation-induced emission active vitamin B6 cofactor derivative: application in pH sensing and detection of latent fingerprints

Aggregation-induced emission (AIE) properties of an easy-to-prepare and structurally planar Schiff base derivative of the vitamin B₆ cofactor pyridoxal (L) were investigated in DMSO–H₂O mixed solvents.

An o-hydroxyl aldehyde structure based naphthalimide derivative: Reversible photochromic properties and its application in ClO- detection in living cells

A bifunctional organic compound 2-butyl-6-hydroxy-1,3-dioxo-2,3-dihydro-1H-benzo[de] isoquinoline-5-carbaldehyde (BHC) with photochromic properties in solid state and probe detection for ClO^- in complete water solution was synthesized and fully characterized. A 'white-yellow-white' reversible photochromic behavior could be observed when alternating UV/vis light irradiation on the solid BHC powder. Good fatigue resistance and adjustable bleaching rate were shown when heating conditions changes. In addition, BHC displayed a high selectivity and low detection limit (1.16 × 10^-8 M) for ClO^-. The photoluminescent fluorescence "on-off" recognition result can be easily identified and BHC has been tested for safely imaging living cells and detecting hypochlorite anion in vitro and vivo. A better water solubility of BHC effectively reduces damage caused by organic solvent in cell imaging progress.

Low-Lying Excited States of hqxcH and Zn-hqxc Complex: Toward Understanding Intramolecular Proton Transfer Emission

Excited state intramolecular proton transfer (ESIPT) has been a topic of interest due to its potential to lead to multiple emissions. Although many organic molecules showing ESIPT emission are already known, studies on metal complexes showing ESIPT and their related theoretical understandings are very limited. In this study, we focus on [Zn(hqxc)₂(DMSO)₂] (Zn-hqxc: hqxc = 3-hydroxy-2-quinoxalinecarboxylate, DMSO = dimethyl sulfoxide), which shows ESIPT emission in the solid state, even though the hqxcH ligand does not show ESIPT emission. To gain insights into the role of the zinc atom and the emission mechanisms, we examined excited states of free hqxcH and the Zn-hqxc complex using time-dependent density functional theory calculations. From the results, it was shown that the zinc atom triggers a structural change of the hqxcH ligand from the lactam form (3,4-dihydro-3-oxo-2-quinoxalinecarboxylic acid) to the enol form (3-hydroxy-2-quinoxalinecarboxylic acid), where the latter form has several stable excited states. Several stable geometries were found for singlet and triplet excited states, suggesting that emissions for the Zn-hqxc complex can be both phosphorescence and fluorescence caused by the enol-enol, keto-keto, and keto-enol forms of the two hqcx ligands in the complex. We found that the photophysical properties of the Zn-hqxc complex are dominated by the ligand due to the filled d¹⁰ of Zn(II). The presented results suggest that, to design new ESIPT metal complexes, one possible approach is to combine a metal atom showing ligand centered emission and a ligand that has separate ESIPT and coordination sites.

Development of a C₃-symmetric benzohydroxamate tripod: Trimetallic complexation with Fe(III), Cr(III) and Al(III)

The design, synthesis and physicochemical characterization of a C3-symmetry Benzene-1,3,5-tricarbonylhydroxamate tripod, noted here as BTHA, are described. The chelator was built from a benzene as an anchor, symmetrically extended by three hydroxamate as ligating moieties, each bearing O, O donor sites. A combination of absorption spectrophotometry, potentiometry and theoretical investigations are used to explore the complexation behavior of the ligand with some trivalent metal ions: Fe(III), Cr(III), and Al(III). Three protonation constants were calculated for the ligand in a pH range of 2-11 in a highly aqueous medium (9:1 H2O: DMSO). A high rigidity in the molecular structure restricts the formation of 1:1 (M/L) metal encapsulation but shows a high binding efficiency for a 3:1 metal ligand stoichiometry giving formation constant (in β unit) 28.73, 26.13 and 19.69 for [M3L]; M=Fe(III), Al(III) and Cr(III) respectively, and may be considered as an efficient Fe-carrier. The spectrophotometric study reveals of interesting electronic transitions occurred during the complexation. BTHA exhibits a peak at 238 nm in acidic pH and with the increase of pH, a new peak appeared at 270 nm. A substantial shifting in both of the peaks in presence of the metal ions implicates a s coordination between ligand and metal ions. Moreover, complexation of BTHA with iron shows three distinct colors, violet, reddish orange and yellow in different pH, enables the ligand to be considered for the use as colorimetric sensor.

Fluorescent organic nanoparticles (FONs) for selective recognition of Al3+: application to bio-imaging for bacterial sample

(a) Changes in fluorescence upon successive addition of Al³⁺ ions to salpn-ONPs; (b) titration profile of fluorescence; (c) recognition of Al³⁺ through bio-fluorescence Staphylococcus aureus bacterial cells.

The Synthesis and Anion Recognition Property of Symmetrical Chemosensors Involving Thiourea Groups: Theory and Experiments

The synthesis of four symmetrical compounds containing urea/thiourea and anthracene/nitrobenzene groups was optimized. N,N’-Di((anthracen-9-yl)-methylene)thio-carbonohydrazide showed sensitive and selective binding ability for acetate ion among the studied anions. The presence of other competitive anions including F⁻, H₂PO₄⁻, Cl⁻, Br⁻ and I⁻ did not interfere with the strong binding ability. The mechanism of the host-guest interaction was through multiple hydrogen bonds due to the conformational complementarity and higher basicity. A theoretical investigation explained that intra-molecular hydrogen bonds existed in the compound which could strengthen the anion binding ability. In addition, molecular frontier orbitals in molecular interplay were introduced in order to explain the red-shift phenomenon in the host-guest interaction process. Compounds based on thiourea and anthracene derivatives can thus be used as a chemosensor for detecting acetate ion in environmental and pharmaceutical samples.

Spectroscopic, potentiometric and theoretical studies of novel imino-phenolate chelators for Fe(III)

The present study was targeted to explore the binding properties of two strong chelators for Fe(III) based on tripodal-iminophenolate moiety. Complexation behavior of the tripodal systems cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({2-[(2-hydroxy-benzylidene)-amino]-ethyl}-amide (CYCOENSAL, L(1)) and cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({3-[(2-hydroxy-benzylidene)-amino]-propyl}-amide (CYCOPNSAL, L(2)) is described. Three protonation constants obtained are assigned for three hydroxyl groups of aromatic ring were employed for the evaluation of the formation constants of the metal complexes. Both ligands liberate three protons each forming monomeric complexes of type FeLH3, FeLH2, FeLH and FeL (L=L(1) and L(2)). The first species FeLH3 depicted at low pH, where the ligands were coordinated through three imine nitrogen and other species form subsequently from FeLH3 in steps upon deprotonation and coordination of the phenolic oxygen giving encapsulated tris(phenolate) complexes. The probable structures of the metal complexes formed in solution were proposed through molecular modeling calculations. L(2) was observed to be highly selective towards Fe(III) as compared to L(1).

Iron(III) selective molecular and supramolecular fluorescent probes

Iron is one of the most important elements in metabolic processes, being indispensable for all living systems and therefore it is extensively distributed in environmental and biological materials. However, both its deficiency and excess from the normal permissible limit can induce serious disorders. Therefore, several analytical techniques have been adopted for the detection of iron. Among the various techniques used for its detection, the method based on fluorescent sensors has received considerable interest in recent years because of its ability to provide online monitoring of very low concentrations without any pre-treatment of the sample together with the advantages of spatial and temporal resolution. In this article, efforts have been made to review the various molecular and supramolecular fluorescent sensors that have been developed for the selective detection of iron(III).

A new Schiff base system bearing two naphthalene groups as fluorescent chemodosimeter for Zn2+ ion and its logic gate behavior

1-((E)-(2-((2-nitrobenzyl)(2-((E)-(2-hydroxynaphthalen-1-yl)methyleneamino)ethyl)amino)ethylimino)methyl)naphthalen-2-ol (H(2)L), The new compound featuring two naphthalene units was synthesized and characterized. We find that H(2)L has high selectivity and sensitivity to detect Zn(2+) ion over other metal ions such as Na(+), Ag(+), Cd(2+), Co(2+), Cr(3+), Cu(2+), Hg(2+), Mn(2+), Ni(2+), Fe(3+), and the sensitivity is about 10(-7)M. The fluorescent changes of H(2)L upon the addition of cations Zn(2+) and triethylamine is utilized as an AND logic gate at the molecular level, using Zn(2+) and triethylamine as chemical inputs and the fluorescence intensity signal as output.

Photoisomerization of a maleonitrile-type salen Schiff base and its application in fine-tuning infinite coordination polymers

Strategically designed salen ligand 2,3-bis[4-(di-p-tolylamino)-2-hydroxybenzylideneamino]maleonitrile (1), which has pronounced excited-state charge-transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z*-->1E isomerization takes place by rotation about the C2--C3 bond, which takes on single-bond character due to the charge-transfer reaction. The isomerization takes place nonadiabatically from the excited-state (1Z) to the ground-state (1E) potential-energy surface in the singlet manifold; 1Z and 1E are neither thermally inconvertible at ambient temperature (25-30 degrees C), nor does photoinduced reverse 1E*-->1Z (or 1Z*) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a Zn(II) precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N'-dicyanoethenebis(salicylideneimine)dicarboxylic acid (2). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere- and needlelike nanostructure, respectively) of their infinite coordination polymers with Zn(II).