A novel calixsalen macrocycle: metal sensing behavior for Zn2+ and intracellular imaging application

Aggregation-Induced Modulation of Ground and Excited State Photophysics of 5-(tert-Butyl)-2-Hydroxy-1,3-Isophthalaldehyde (5-tBHI)

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) is a photochromic material susceptible to either excited state proton transfer or excited state intramolecular proton transfer, depending upon the solvent. However, it has also been found to aggregate in the presence of sodium dodecyl sulfate. In this current study, based on the steady-state and time-resolved spectroscopy, supported by crystallography, quantum chemical density functional theory calculation, and molecular dynamics (MD) simulation, we report on the aggregation of this potential single benzene-based emitter (SBBE) in neat solvents as well as solid phase to modulate its photophysics. It has been found that 5-tBHI forms mixed aggregates of different orders, owing to the presence of both enolic and tautomeric forms, to yield tunable emission, although the emission intensity is quenched. These findings suggest that the intramolecular hydrogen bonding of 5-tBHI not only limits intermolecular interactions but also promotes nonradiative deactivation pathways. Hence, designing and structural engineering, with a focus to suppressing intramolecular hydrogen bonding as well as increasing through space conjugation by replacing the aldehydic moieties with bulky aliphatic or aromatic ketonic groups, can be a plausible approach to yielding improved probes with tunable emission and higher fluorescence quantum yields.

Non-trivial ground and excited state photophysics of a substituted phenol

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) shows solvent dependent single or dual emission. The photophysics of 5-tBHI has been studied in a variety of solvents and the results were compared with that of the methyl derivative of the probe as well as the 5-tBHI anion. It has been found that the intramolecular H-bonded conformer of 5-tBHI predominantly exists in non-polar solvents, and undergoes facile excited state intramolecular proton transfer (ESIPT). On the other hand, a dynamic equilibrium can be found in polar, protic solvents, even in the ground state, except in water. NMR analyses confirm the loss of aromaticity of the probe in the ground state via anion formation, in equilibrium with the solvent mediated intermolecularly H-bonded state, in neat polar protic solvents like methanol. The proton transfer process, either intramolecularly or intermolecularly, was found to be of the order of 1 ps, and even faster than the instrumental resolution in the case of water. The current finding provides important insights on the photophysics of this small, substituted phenol.

Turn on fluorescence strip based sensor for recognition of Sr2+ and CN- via lowerrim substituted calix[4]arene and its computational investigation

Fluorescence sensor L designed around a calix[4]arene scaffold, bearing two fluorogenic aminoquinoline moities, has been synthesized. It is found to be selective and sensitive towards Sr²⁺ and CN^- over a wide range of cations and anions in a spectrofluorometric study in acetonitrile. The ion-binding property of L was monitored by fluorescence spectroscopy, UV-vis spectroscopy, ESI-MS, ¹H NMR, FT-IR investigation and PXRD study. The host L shows a minimum detection limit which is 1.36 nM for Sr²⁺ and 1.23 nM for CN^- having concentration range 5-120 nM and 5-115 nM respectively. The calculated binding constants for L:Sr²⁺ and L: CN^- are respectively 8.859 × 10⁸ M^-1 and 8.574 × 10⁸ M^-1. Our host L has been utilised in formation of a user-friendly, affordable, and disposable paper-based analytical device (PAD) for rapid chemical screening of Sr²⁺ and CN^- ion via single strip. Moreover, the optimization of probe L has also been done by the MOPAC-2016 software package using NM7 popular method resulting -21.71 kcals/mol heat of formation and also determined the HOMO-LUMO energy band gap for L, L:Sr²⁺ and L: CN^-. Further, molecular docking score has been calculated using HEX software. The applicability of our probe in real samples containing Sr²⁺ and CN^- has also been checked by emission study with 94-99% recovery.

Trinuclear Lanthanide Coordination Clusters: Single-Molecule-Magnet Behavior and Catalytic Activity in the Friedel-Crafts Alkylation Reaction

A new multidentate ligand (H₃ L) was synthesized by the condensation reaction of 4-tert-butyl-2,6-diformylphenol and 2-amino-4-nitrophenol. The reaction of the ligand with hydrated lanthanide nitrate produced two isostructural trinuclear coordination clusters: [DyLn₃ L₃ (DMF)₃ (H₂ O)₂ ] ⋅ 3.8DMFLn=Dy (1) and Nd (2) (DMF=N, N-dimethylformamide). Single-crystal X-ray diffraction analysis revealed that there are three lanthanide ions arranged in an almost perfect linear fashion in both complexes. Magnetic studies show single-molecule-magnet (SMM) behavior in the Dy derivative with τ₀ =1.7×10^-6  s and a thermal energy barrier of 7.0 cm^-1 . Both complexes were used as catalysts towards the Friedel-Crafts alkylation reaction of indole with different aldehydes with yields varying from 59-98 %. Complex 1 showed better catalytic efficiency than complex 2. This is the first report of using trinuclear lanthanide coordination clusters as catalysts for the Friedel-Crafts alkylation reaction.

Luminescent behavior of pyrene-allied calix[4]arene for the highly pH-selective recognition and determination of Zn2+, Hg2+ and I−via the CHEF-PET mechanism: computational experiment and paper-based device

In this article, for the first time, we have reported a novel CHEF-PET fluorescence sensor L based on calix[4]arene containing four pyrene groups as binding sites, which is highly selective and sensitive towards Zn²⁺, Hg²⁺ and I⁻.

Single-step fluorescence recognition of As3+, Nd3+ and Br− using pyrene-linked calix[4]arene: application to real samples, computational modelling and paper-based device

A new fluorescence sensor has been synthesized for its selective recognition of As³⁺ (11.53 nM), Nd³⁺ (0.65 nM) and Br⁻ (11.25 nM).

New polyaminocarboxylate macrocycles containing phenolate binding units: synthesis, luminescent and relaxometric properties of their lanthanide complexes

The synthesis of two new polyaminocarboxylate macrocycles incorporating one or two intracyclic phenol units (H₄L¹ and H₈L², respectively) is described. The 12-membered H₄L¹ macrocycle leads to soluble and stable mononuclear Ln^III complexes of [(L¹)Ln(H₂O)₂]^- composition (Ln = Eu, Tb and Gd) in aqueous solutions. In Tris buffer (pH 7.4), the [(L¹)Tb(H₂O)₂]^- complex displays a suitable efficiency for sensitized emission (η_sens = 48%) and a high luminescence quantum yield (Φ = 22%), which is worthy of note for a bis-hydrated terbium complex. Besides, luminescence experiments show that bidentate endogenous anions (citrate, carbonate, and phosphate) do not displace the two inner-sphere water molecules of this complex. In contrast, the possible presence of LMCT states causes the europium complex to be weakly luminescent. The [(L¹)Gd(H₂O)₂]^- complex is characterized by high relaxivity (r = 7.2 s^-1 mM^-1 at 20 MHz) and a very short water residence time of the coordinated water molecules (τ = 9 ns), promising values for the realisation of macromolecular systems with high relaxivities. Thus, the Tb and Gd complexes of the H₄L¹ macrocycle exhibit several improvements in terms of luminescent (lower excitation energy, higher brightness) and relaxometric (shorter τ_M) properties compared to the corresponding LnPCTA complexes, where a phenol moiety substitutes a pyridine ring. On the other hand, the 24-membered H₈L² macrocycle including two phenol units in its structure leads to dinuclear complexes of [(L²)Ln₂]^2- composition. Its terbium complex shows a long luminescence lifetime (2 ms) and a high quantum yield (43%) in aqueous solutions, making this compound a new promising candidate for time-resolved applications.

Unexpected formation of a tubular architecture by optically active pure organic calixsalen

Herein, an unusual tubular formation of a supramolecular organic framework by optically active macrocyclic calixsalen is shown via single crystal X-ray diffraction.

Synthesis, characterization and Cu(2+) triggered selective fluorescence quenching of Bis-calix[4]arene tetra-triazole macrocycle

A novel fluorescent bis-calix[4]arene macrocycle 9 incorporating metal-binding pockets was successfully prepared. The structure of macrocycle 9 and its precursors were characterized via EI-MS, MALDI-TOF-MS, ESI-MS, (1)H NMR, (13)CNMR, 2D NMR, and X-ray crystallography. The macrocycle 9 displayed selective fluorescence quenching after interacting with Cu(2+) in the presence competing metal cations including Mg(2+), Ca(2+), Ba(2+), Ag(+), Zn(2+), Ti(4+),Cd(2+), Hg(2+), Pb(2+), In(3+), La(3+), Cr(3+), Ni(2+), Sb(3+), V(5+), Fe(3+), Co(2+), Sn(2+), Sn(2+), and Tl(+). The Cu(2+) limit of detection was found to be 40 nM much lower than its threshold level (∼ 20 μM) in drinking water permitted by the U.S Environmental Protection Agency (EPA). Furthermore, drinking water samples from Karachi University (Pakistan) spiked with Cu(2+) were analysed with the sensing system and the results showed an excellent agreement with the fluorescence quenching phenomenon of macrocycle 9 examined in deionized water. Importantly, the chemosensor 9 could be used to detect Cu(2+) in living cells.

A Simple and Selective Fluorescent Sensor for Zn(2+) and H(+) Ions in Aqueous Solution with OR Logic Gate Function

The synthesis and properties of a new compound, viz., (N,N'-[1,10-phenanthroline-4,7-diyldi((E)methylylidene)]bis(1,10-phenanthrolin-5-amine) (1), is described. Compound 1 can be used as a selective fluorescent Zn(2+) sensor in buffered solution. Furthermore, 1 induces turn on fluorogenic response to H(+) ions. Finally, it is shown that an OR logic gate can be constructed with 1 by using Zn(2+) and H(+) as two-inputs. Graphical Abstract In this paper, the design, synthesis and physicochemical properties of a new compound 1 based on 1,10-phenanthroline scaffold, is reported. It is noted that 1 can be used as a selective fluorescent Zn(2+) sensor in 0.01 M HEPES buffer containing DMF (2 % v/v, pH = 7.4) at room temperature. Furthermore, the spectrophotometric results suggest that compound 1 can be used as a pH reporter in highly acidic conditions (pH < 5). Finally, it was also shown that an OR logic gate can be constructed with 1 by using Zn(2+) and H(+) as two-inputs.

Readily prepared inclusion forming chiral calixsalens

Chiral, rigid vase-like calixsalens show unprecedented substituent-driven self-association and provide supermolecules of contrasting character.

Dynamic Formation of Noncovalent Calixsalen Aggregates

A procedure for studying "dynamic structural behavior" of large chiral macrocycles is presented. Ion mobility MS, diffusion-ordered NMR spectroscopy (DOSY NMR), and optical rotation (OR) measurements, supported by calculations, are used together as effective complementary methods to study dynamic formation of noncovalent aggregates. It is shown that the monomer-dimer equilibrium is driven by π-π or CH-π interactions and controlled largely by the substitution pattern of the calixsalen skeleton.

An imidazo-phenanthroline scaffold enables both chromogenic Fe(ii) and fluorogenic Zn(ii) detection

A promising dual channel responsive probe, which can simultaneously induce chromogenic and fluorogenic responses to Fe(ii) and Zn(ii) ions, respectively, is described.

Multifarenes: new modular cavitands

Multifarenes, a new class of macrocycles, which are constructed of alternating building blocks, are conveniently accessible by three complementary syntheses that provide modularity and scalability. In addition to metal-ion coordination, these cavitands show increased flexibility with increasing ring size, offering opportunities for induced fit to guest molecules.

The high sensitive and selective "off-on" fluorescent Zn2+ sensor based on the Bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)methane

A fluorescent chemosensor based on the 3,3'-bis(dipyrrin) bearing two chromophoric dipyrrin units was synthesized, which showed a strongly enhanced fluorescent intensity in the presence of Zn(2+) ions and a high selectivity toward Zn(2+) ions over a wide range of tested metal ions in organic solvents.

A highly sensitive fluorescent probe based on simple pyrazoline for Zn2+ in living neuron cells

We develop a pyrazoline-based fluorescent sensor for biological Zn(2+) detection. The sensor shows good binding selectivity for Zn(2+) over competing metal with 40-fold fluorescence enhancement in response to Zn(2+). The new probe is cell-permeable and can be used to detect intracellular zinc ions in living neuron cells.