A highly potential acyclic Schiff base fluorescent turn on sensor for Zn2+ ions and colorimetric chemosensor for Zn2+, Cu2+ and Co2+ ions and its applicability in live cell imaging

A novel one-stepped synthesized Schiff-base fluorescence probe for specific recognition of zinc ions with highly sensitive and its application in living cells

Fluorescent turn-on receptors are extensively employed for the detection of Zn ions contamination in the environment due to its simplicity, convenience and portability. However, developing highly sensitive and cell-imageable fluorescent turn-on probe for the recognition of Zn ions in living organisms remains a significant challenge. Herein, we have successfully synthesized a novel Schiff base probe (H2L) with a significant fluorescence turn-on response (Zn ions) by one-step synthetic method. In this work, H2L exhibited high sensitivity to Zn2+ ions upon interaction with various common metal ions in HEPES buffer solution. Its detection limit is 1.87 × 10-7 M, which is lower than the requirement of Environmental Protection Agency (EPA) and World Health Organization (WHO) guidelines. The fluorescence titration and Job's plot analysis suggested a 1:1 binding ratio between the probe and Zn ion, and the single-crystal structures obtained further confirmed this inference. In addition, the fluorescent sensor demonstrated recyclability, maintaining its fluorescence intensity for up to 6 cycles without significant decrease, which holds promise for future investigations on reversible fluorescent chemosensors. Notably, fluorescence imaging experiments demonstrated that H2L could be successfully used for the detection of Zn2+ in live cells.

The comparative study of two new Schiff bases derived from 5-(thiophene-2-yl)isoxazole as "Off-On-Off" fluorescence sensors for the sequential detection of Ga3+ and Fe3+ ions

Two new Schiff bases, TIC ((E)-N'-(2-hydroxybenzylidene)-5-(thiophene-2-yl)isoxazole-3-carbohydrazide) and TIE ((E)-N'-(3-ethoxy-2-hydroxybenzylidene)-5-(thiophene-2-yl)isoxazole-3-carbohydrazide), have been designed and synthesized as chemosensors for distinct recognition of Ga3+ and Fe3+ ions. TIE demonstrated a prominent "turn on" response characterized by clear distinguished fluorescence when coordination with Ga3+ ions in the DMSO/H2O buffer solution. In comparison, TIC also showed "turn on" response of blue fluorescence which was more selective and sensitive than that of TIE due to the steric hindrance of ethoxy group of TIE. The newly formed complexes TIC-Ga3+ and TIE-Ga3+ may act as selective "turn-off" fluorescent probes towards Fe3+ ions. Limits of detection of TIC and TIE towards Ga3+ ions were 7.8809 × 10-9 M and 2.6277 × 10-8 M, respectively. Limits of detection of TIC-Ga3+ and TIE-Ga3+ towards Fe3+ ions were 8.6562 × 10-9 M and 3.3764 × 10-7 M, respectively. The molar ratio of the complex between the sensor and Ga3+ or Fe3+ ions were all 1:2 determined through Job's Plot, mass spectrometry, and theoretical calculations. Both sensors were utilized for the determination of target ions in environment water samples, and the portable paper sensors for detecting Ga3+ ions have been successfully developed.

Air-Stable Iron(III) Salen Complexes for Selective Hydroboration of Ketones and Unactivated Imines without Base Activation

Herein, we designed and synthesized a series of air-stable, cost-effective, and readily synthesizable iron(III) salen complexes (Fe-1 and Fe-2) for facilitating the selective hydroboration of ketones and unactivated imines with pinacolborane in the absence of any additive. These catalyst systems exhibited good yields, chemoselectivity, high atom economy, and a broad substrate scope under mild reaction conditions with a minimal catalyst loading of 0.2 mol %. The catalytic efficiency of Fe-1 has been demonstrated through the hydroboration of diverse aromatic, aliphatic, and heterocyclic ketones and imines with a turnover number of up to 1000, highlighting its broad substrate scope. Ketones are chemoselectively hydroborated over other functional groups such as imines, alkenes, esters, nitriles, acids, and alcohols. Besides, the synthetic utility of this strategy has also been showcased by the construction of a natural chiral monoterpenoid carveol. This protocol can be readily scaled up for gram-scale synthesis of alcohols, which underscores the potential industrial applicability of our catalyst system in the synthesis of secondary alcohols on a larger scale.

Development of a water-soluble fluorescent Al3+ probe based on phenylsulfonyl-2-pyrone in biological systems

BACKGROUND

Al exists naturally in the environment and is an important component in acidic soils, which harm almost all plants. Furthermore, Al is widely used in food additives, cosmetics, and medicines, resulting in living organisms ingesting traces of Al orally or dermally every day. Accordingly, Al accumulates in the body, which can cause negative bioeffects and diseases, and this concern is gaining increasing attention. Therefore, to detect and track Al in the environment and in living organisms, the development of novel Al-selective probes that are water-soluble and exhibit fluorescence at long wavelengths is necessary.

RESULTS

In this study, an Al3+-selective fluorescent probe PSP based on a novel pyrone molecule was synthesized and characterized to detect and track Al in biological systems. PSP exhibited fluorescence enhancement at 580 nm in the presence of Al3+ in aqueous media. Binding analysis using Job's plot and structural analysis using 1H NMR showed that PSP formed a 1:1 complex with Al3+ at the two carbonyl groups of the dimethyl malonate of the pyrone ring. Upon testing in biological systems, PSP showed good cell membrane permeability, detected intracellular Al3+ in human breast cancer cells (MDA-MB-231), and successfully imaged accumulated Al3+ in Microcystis aeruginosa and the larvae of Rheocricotopus species.

SIGNIFICANCE

The novel Al3+-selective fluorescent probe PSP is highly effective and is expected to aid in elucidating the role of Al3+ in the environment and living organisms.

Synthesis, Sensing Performance and DFT Studies of a Novel Coumarin-based Schiff Base As a Turn-on Fluorescence Probe for Zinc Ion Detection

The design and development of novel efficient fluorescent chemical sensors for the selective detection of ions is currently of significant importance in supramolecular chemistry. Since zinc is a ubiquitous, indispensable and the second most abundant metal ion in the human body, developing chemosensors that can accurately discriminate between Zn2+ and Cd2+ ions has been a challenge due to their similar properties as they are in the same group of the periodic table. Therefore, a technique to trace and visualize free zinc ions is demanded. In this study, an innovative coumarin-based Schiff base (L) was synthesized and characterized by 1H NMR, 13C NMR and mass spectroscopy. A novel "Turn On" fluorescence chemosensor platform was developed for trace amounts of Zn2+ ions. The fluorescence Job's plot measurement was used to determine the complexation ratio between the probe and Zn2+ ion, which showed a maximum point indicating the formation of a ML2 adduct. Additionally, the geometrical parameters calculated using DFT and TD-DFT calculations were in close agreement with the experimentally observed values.

A new Schiff base derived from 5-(thiophene-2-yl)oxazole as "off-on-off" fluorescence sensor for monitoring indium and ferric ions sequentially and its application

A new Schiff base sensor (E)-N'-((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)-5-(thiophen-2-yl)oxazole-4-carbohydrazide (TOQ) was synthesized and found to emit yellowish green fluorescence upon introduction of In³⁺. Furthermore, the resulting complex TOQ-In³⁺ was quenched selectively by Fe³⁺. The detection limits of TOQ for In³⁺ and Fe³⁺ were 1.75 × 10^-10 M and 8.45 × 10^-9 M, respectively. The complex stoichiometry of TOQ with target ions was determined to be 1:2 via Job's plot analysis, which further was verified by ESI-MS titration and theoretical calculations. Moreover, TOQ can be used for the determination of target ions in environmental water samples. A portable paper sensor of TOQ was successfully developed for detecting In³⁺ to assess its applicability.

Dual-mode colorimetric/fluorescent chemosensor for Cu2+/Zn2+ and fingerprint imaging based on rhodamine ethylenediamine bis(triazolyl silsesquioxane)

A novel dual functional and visual rhodamine ethylenediamine bis(triazolyl silsesquioxane) (RBS) chemosensor was successfully synthesized using "click" chemistry. The results have unambiguously demonstrated that RBS can act in fluorescent and colorimetric sensing of Cu²⁺ and Zn²⁺ by their respective coordination with triazole structures and, more importantly, it has also been found that triazole-amide of RBS could turn on chelation-enhanced fluorescence (CHEF) of Cu²⁺. Remarkably, the addition of Cu²⁺ triggered an enhanced fluorescent emission by 63.3-fold (ϕ_F = 0.41), while Zn²⁺ enhanced it 48.3-fold (ϕ_F = 0.29) relative to the original RBS (ϕ_F = 0.006) in acetonitrile (MeCN) solvent. The fluorescent limit of detection for Cu²⁺ and Zn²⁺ is similar and fall within 3.0 nM, while under colorimetric sensing the responses were 2.14 × 10^-8 and 4.0 × 10^-8 mol L^-1, respectively. Moreover, the effective sensing profile of RBS and extended applications of RBS-Cu²⁺ and RBS-Zn²⁺ for fingerprinting detection and imaging were observed with adequate sensitivity, stability and legibility under the dual visual responses.

A Bifunctional Fluorescence Probe Based on AIE-ICT Strategy for Visual Detection of Cu2+/Co2+ in Complex Matrix

A novel fluorescence chemical sensor-based probe 1-{[(E)-(2-aminophenyl)azanylidene]methyl}naphthalen-2-ol (AMN) was designed and synthesized, which performed a "naked eye" detection ability toward Cu²⁺ and Co²⁺ based on aggregation-induced emission (AIE) fluorescence strategy. It has sensitive detection ability for Cu²⁺ and Co²⁺. In addition, the color changed from yellow-green to orange under the sunlight, realizing the rapid identification of Cu²⁺/Co²⁺, which has the potential of on-site visual detection under the "naked eye". Moreover, different "on" and "off" fluorescence expressions were exhibited under excessive glutathione (GSH) in AMN-Cu²⁺ and AMN-Co²⁺ systems, which could be employed to distinguish Cu²⁺ from Co²⁺. The detection limits for Cu²⁺ and Co²⁺ were measured to be 8.29 × 10^-8 M and 9.13 × 10^-8 M, respectively. The binding mode of AMN was calculated to be 2:1 by Jobs' plot method analysis. Ultimately, the new fluorescence sensor was applied to detect Cu²⁺ and Co²⁺ in real samples (tap water, river water, and yellow croaker), and the results were satisfying. Therefore, this high-efficiency bifunctional chemical sensor platform based on "on-off" fluorescence detection will provide significant guidance for the advance development of single-molecule sensors for multi-ion detection.

Two near-infrared fluorescent probes based on dicyanoisfluorone for rapid monitoring of Zn2+and Pb2

Zinc (Zn2+) and lead (Pb2+) ions in the environment have important effects on human health and environmental safety. Therefore, it is of great significance to realize convenient and reliable detection of these two metal ions. In this study, two near-infrared fluorescent probes for the fast detection of Zn2+ and Pb2+ were synthesized by a simple Schiff base reaction between the dicyanoisophorone skeleton and carbohydrazide derivatives. Among them, the probe with the thiophene-2-carbohydrazide group showed a selective fluorescence response to Zn2+ and Pb2+ with a maximum emission wavelength of 670 nm. And the detection limits of the probe for Zn2+ and Pb2+ were 1.59 nM and 1.65 nM, respectively. In contrast the probe modified by the furan-2-carbohydrazide group achieved quantitative detection of Zn2+, with a detection limit of 2.7 nM. These results were attributed to the fact that the probes bind to Zn2+ and Pb2+ in stoichiometric ratios of 1:1, blocking the intramolecular PET effect. Furthermore, these two probes can be recycled through the action of EDTA and have been successfully used to detect Zn2+ and Pb2+ in real water samples.