Exploitation of a Half-Conjugate Polydentate Salamo-Salen Hybrid Ligand and Its Two Phenoxide-Bridged Heterohexanuclear 3d-s Double-Helical Cluster Complexes

A highly selective and recyclable fluorescent sensor based on a Salamo-Salen-Salamo type ligand for continuous detection of Al3+ and phosphates in drug

In this work, a fluorescence chemical sensor continuous detection Al3+ and phosphates by a Salamo-Salen-Salamo type compound (SL) was employed. The sensor continuously recognized Al3+ and phosphates with good selectivity and fast response time, and a low limit of detection of 0.25 μΜ and 0.96 μM, at the same time accompanied by a naked-eye identification specificity. The detection mechanism of SL towards Al3+ is due to the chelating fluorescence enhancement effect and ICT effect, and continuously towards phosphates is due to the collapse of the SL-Al3+ and coordination interaction between Al3+ and phosphates, by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, other spectral characterization and DFT calculation as evidence. In addition, the sensor had good recyclability and reusability. The distribution of Al3+ and phosphates in zebrafish cells was effectively monitored by confocal microscopy based on the good biocompatibility and tissue permeability of SL. Furthermore, the feasibility of using sensor SL to detect the content of Al3+ and phosphate ions in certain drugs was quantitatively analyzed through experiments. It was found SL had a good result in practical application.

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

A unique N-heterocyclic oligo(N,O-donor) salamo-Ni(II)-based probe for highly selective fluorescence detection of Cr2O72

A unique fluorescent probe Ni-DAS was developed by a nitrogenous heterocyclic oligo(N,O-donor) salamo-based compound DAS. DAS exhibits AIE and ESIPT effects which are extremely infrequent in salamo-based multi-oxime compounds. In addition, Ni-DAS can be used as a fluorescent probe with high selectivity and sensitivity to recognize Cr2O72- in DMF with 80 % water content, which enhances the value of the probe for application in real environments, and outperforms most similar molecular fluorescence probes. The probe Ni-DAS can recognize Cr2O72- by oxidative hydrolysis of C = N bonds, which promotes further research on theory of C = N bond hydrolysis, and the binding ratio and recognition mechanism were verified and supported by relevant theoretical calculations (DFT & MESP). The experiments showed that the probe Ni-DAS can be used for ion detection in real environments. It provides a new strategy for the oxidative hydrolysis of C = N bond and the structure of salamo-based compounds with AIE nature, and offers new ideas for study ion recognition and acidity detection.

Spectroscopic and theoretical studies on a novel bis(salamo)-like probe for highly effective fluorimetric-colorimetric identification of Fe3+ and Cu2+ in aquo-organic medium

A novel bis(salamo)-type sensor FT for fluorescence-colorimetric recognition of Fe3+/Cu2+ has been created, which revealed significant fluorescent performance and colorimetric sensing ability for Cu2+ and Fe3+ ions, superior to other related competitive metal ions. Interestingly, the binding of the FT probe with Cu2+ ions manifested an instant color change from colorless to red in sunlight, which is detectable by the naked-eye, and a fluorescence turn-off response under UV light for Fe3+ and Cu2+. The results demonstrated that the probe exhibits better sensitivity, greater affinity and lower limit of detection leading to quick response time in an aquo-organic medium. The excited state property of the FT probe and in the presence of Cu2+/Fe3+ was evaluated on the basis of DFT & TD-DFT results. Furthermore, test strips have been provided for convenient monitoring of Cu2+ and Fe3+ ions by naked eye and fluorescence method.

A nonsymmetrical salamo-like fluorescence chemical sensor for selective identification of Cu2+ and B4O72- ions and practical applications

An innovative salamo-like fluorescent chemical sensor H2L, has been prepared that can be utilized to selectively detect Cu2+ and B4O72- ions. Cu2+ ions can bind to oxime state nitrogen and phenol state oxygen atoms in the chemosensor H2L, triggering the LMCT effect leading to fluorescence enhancement. The crystal structure of the copper(II) complex, named as [Cu(L)], has been achieved via X-ray crystallography, and the sensing mechanism has been confirmed by further theoretical calculations with DFT. Besides, the sensor H2L recognizes B4O72- ions causing an ICT effect resulting in bright blue fluorescence. Moreover, the sensor has relatively high selectivity and sensitivity for Cu2+ and B4O72- ions, and the detection limits are 1.02 × 10-7 and 2.06 × 10-7 M, respectively. In addition, the good biocompatibility and excellent water solubility of the sensor H2L make it very advantageous in practical applications, using H2L powder for fingerprint visualization, using H2L to identify the phenomenon of B4O72- ions emitting bright blue fluorescence, making it an ink that can print encrypted messages on A4 paper, in addition to this, based on H2L, the real water sample was tested for Cu2+ ion recognition, and finally the test strip experiment was carried out.

A fluorescent Salamo-Salen-Salamo-Zn(II) sensor for bioimaging and biosensing H2PO4- in Zebrafish and plants

A newly designed and synthesized Salamo-Salen-Salamo-Zn(II) complex sensor (sensor ZT) was extensively explored for anion sensing studies. The selectivity and sensitivity of the sensor ZT towards H2PO4- ions were based on ICT and CHEF effects, and via displacement pathways in DMSO/H2O (9:1, v/v) medium in the presence of other anions like, PO43-, HPO42- and P2O74- in a short time, separately. The prepared ZT sensor has excellent association constant and low detection lines. The sensing mechanism and binding mode of the sensor were studied by UV-Vis spectroscopy, HR-MS, 1H NMR titration and theory calculations (DFT & TD-DFT) for analytes. The time response and stability of the sensor are also given. Meanwhile, the sensor ZT can be widely used as a simple and effective solid-state optical sensor to detect H2PO4- by intuitive fluorescence changes. In addition, besides the environment can be used as a powerful instrument for detecting H2PO4-, based on the good biocompatibility and tissue permeability of ZT, effectively monitoring H2PO4- in cellular distribution by confocal microscopy using Zebrafish and bean sprout.

Coordination-Driven Salamo-Salen-Salamo-Type Multinuclear Transition Metal(II) Complexes: Synthesis, Structure, Luminescence, Transformation of Configuration, and Nuclearity Induced by the Acetylacetone Anion

A flexible polydentate Salamo-Salen-Salamo hybrid ligand H₄L was designed and synthesized, which has rich pockets (salamo and salen pockets) so that it may have fascinating coordination patterns with transition metal(II) ions. Four multinuclear transition metal(II) complexes, novel butterfly-shaped homotetranuclear [Ni₄(L)(μ₁-OAc)₂(μ_1,3-OAc)₂(H₂O)_0.5(CH₃CH₂OH)_3.5]·4CH₃CH₂OH (1), helical homotrinuclear [Zn₃(L)(μ₁-OAc)₂]·2CH₃CH₂OH (2), double-helical homotrinuclear [Cu₂(H₂L)₂]·2CH₃CN (3), and mononuclear [Ni(H₂L)]·1.5CH₃COCH₃ (4), have been synthesized and characterized by single-crystal X-ray diffraction. The effects of different anions [OAc^- and (O₂C₅H₇)^2-] on the complexation behavior of H₄L with transition metal(II) ions were studied by UV-vis spectrophotometry. The fluorescent properties of the four complexes were studied with zebrafish, which are expected to be a potential light-emitting material. Ultimately, interaction region indicator (IRI) valuations, Hirshfeld surface analyses, density functional theory (DFT & TD-DFT), electrostatic potential analyses (ESP), and simulations were carried out to further demonstrate the weak interactions and electronic properties of the free ligand and its four complexes.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects

The first-row transition-metal ions Mn²⁺-Cu²⁺ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn²⁺-Cu²⁺ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co²⁺ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H₂pdd precursor and the [1 + 1] Cu²⁺ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H₂hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

A highly selective and sensitive salamo-salen-salamo hybrid fluorometic chemosensor for identification of Zn2+ and the continuous recognition of phosphate anions

A salamo-salen-salamo hybrid fluorescent chemical sensor (H₄L) was synthesized and characterized. It exhibits high selectivity and sensitivity to Zn²⁺ in physiological pH range. Meanwhile, its zinc(II) complex (L-Zn²⁺) continuously responses phosphate anions in DMF/H₂O (v/v, 9:1) solution. Moreover, the identification processes are explored using characterization methods such as UV-absorption spectra, IR spectra and ESI-MS spectrum. In addition, the coordination mechanism of H₂PO₄^- and Zn²⁺ were successfully exploited to make the chemical sensor reproducible. In short, the sensors H₄L and L-Zn²⁺ will be promising detection devices for Zn²⁺ and phosphate anions.