Sequence-Specific Relay Recognition of Multiple Anions: An Interplay between Proton Donors and Acceptors

Ultrafast conformation-dependent charge transfer in N, N, N', N'-tetramethyl-1,3-propanediamine: Effect of flexible carbon skeleton on electron lone pair interactions

Flexible three-carbon skeleton makes N, N, N', N'-tetramethyl-1,3-propanediamine (TMPDA) an important diamine system to investigate the conformation-dependent electron lone pair interactions and charge delocalization. The charge transfer process linked to structural motions of the three-carbon skeleton has been monitored in real time by the Rydberg electron binding energy (BE) spectra of TMPDA coupled with quantum chemical calculations. Optical excitation to the 3p state with a 200 nm pump pulse initially generated a localized charge on one of the two nitrogen atoms that may partially transfer to the other one. Rapid internal conversion (IC) from the 3p to 3s state occurred within 430 fs, resulting in an initial charge delocalized 3s_h/3s_l population ratio of 23.6 %/76.4 %. A final 3s_h/3s_l (51.9 %/48.1 %) equilibrium proceeded within about 2.64 ps. The 3s_h (TTTT+, GG'TG+ and G'GG'G+) and 3s_l (GG'GG'+ and GG'G'G+) (see text for structure definitions) are identified as the extended and folded conformers, respectively. Two types of electron lone pair interactions, i.e., through-space interaction (TSI) and through-bond interaction (TBI), are found to coexist in TMPDA to drive charge transfer. The GG'GG'+ and GG'G'G+ structures exhibit TSI, while the TTTT+ structure shows TBI. The GG'TG+ and G'GG'G+ structures exhibit both TSI and TBI. Flexible three-carbon skeleton provide more opportunities for the two N-electron lone pairs to overlap in space (i.e., TSI), making TMPDA to be favorable for the most stably folded conformation.

Construction of a novel fluorescent probe for sensitive determination of glyphosate in food and imaging living cells

Glyphosate is a widely used broad-spectrum herbicide in agriculture and horticulture to control a variety of weeds and undesirable plants. However, the excessive use of glyphosate has raised a number of environmental and human health concerns. It is urgent to develop tools to detect glyphosate. Herein, a novel dual-signal probe CCU-Cu2+ was designed and synthesized on the basis of CCU. CCU exhibited excellent selectivity and great sensitivity for Cu2+ which were based on both fluorescence "turn-off" reaction and comparative color visualisation methods. Due to the strong chelating ability of glyphosate on Cu2+, the CCU-Cu2+ complex was applied to glyphosate detection in practical samples. The experimental results in vitro showed that the CCU-Cu2+ complex was highly selective and rapid, with a low detection limit (1.6 μM), and could be recognised by the naked eye in the detection of glyphosate. Based on the excellent properties of the CCU-Cu2+ complex, we also constructed a smartphone-assisted detection sensing system for glyphosate detection, which has the advantages of precision, sensitivity, and high interference immunity. Moreover, the CCU-Cu2+ complex was also successfully employed for exogenous glyphosate imaging in living cells. These characteristics demonstrated that CCU-Cu2+ holds significant potential for detection and imaging of glyphosate in bio-systems.

Comparative Analysis of the Hydrazine Interaction with Arylene Diimide Derivatives: Complementary Approach Using First Principles Calculation and Experimental Confirmation

Suitable functional group-engineered π-conjugated aromatic dimides based on perylene (PDI) and naphthyl scaffolds (NDI) demonstrated excellent sensitivity toward different gaseous analytes. However, to date, no methodical analysis has been performed to rationalize molecular-level interactions in the context of optical transduction, which is essential for systematic performance optimization of NDI/PDI-based molecular sensors. Therefore, in this present work, NDI/PDI scaffolds have been designed with amino acid functional groups (alanine, ALA and glutamic acid, GLU) at the terminal positions, and we subsequently compared the efficacy of four different imide derivatives as model hosts for hydrazine adsorption. Specifically, the adsorption of hydrazine at different interaction sites has been thoroughly investigated using ab initio calculations, where the adsorption energy, charge transfer, and recovery time have been emphasized. Theoretical results exhibit that irrespective of host specification the COOH groups offer a primary interaction site for hydrazine through the hydrogen bonding interaction. The presence of more COOH groups and relatively stronger interaction with secondary edge oxygen ensure that GLU functional moieties are a superior choice over ALU for efficient hydrazine binding. The molecular energy spectrum analysis exhibits more favorable HOMO/LUMO gap variations after hydrazine interaction in the case of PDI derivatives irrespective to the nature of the amino acid residues. Therefore, by a combination of both factors, PDI-GLU has been identified as the most suitable host molecule for hydrazine among four derivatives. Finally, the key theoretical predictions has been later experimentally validated by analyzing UV-visible spectroscopy and NMR studies, wherein the mechanism of interaction has also been experimentally verified by EPR analysis and FT-IR studies.

Selective and Effective Sensing of Cyanide Ion with no Interference in Water by Phenothiazine-indolium Fused Optical Sensor

The sensor with electron donor phenothiazine-2-carbaldehyde and electron acceptor indolium carboxylic acid, is developed with an intramolecular charge transfer transition between them. The synthesized molecule senses cyanide ion in water. The cyanide ion reacts with the molecule via nucleophilic addition in the indolium ring with a noticeable purple to colorless change in the solution observed. Also with the cyanide ion interaction, the sensor exhibits change in UV-visible absorption and fluorescence spectra. While the other ion does not show spectral and visual changes when interacts with the sensor molecule. Also the interference study reveals that the molecule is highly selective towards cyanide ion. Different source of water samples confirms the CN- ion sensing efficiency of the molecule. 1:1 interaction between the molecule PTI and cyanide ion is confirmed from the results of Jobs plot, 1H NMR and HRMS. Paper strips were prepared and this can act as a simple tool to sense cyanide ion in various water samples.

AIE active fluorescent organic nanoparticles based optical detection of Cu2+ ions in pure water: a case of aggregation-disaggregation reversibility

An AIE-active pyrene-terpyridine derivative, (4'-(pyren-1-yl)-2,2':6',2''-terpyridine) (1) was found to form nanoaggregate in an aqueous medium. The probe involved hydrogen bonding with solvent molecules that modulated the charge transfer behavior and consequently resulted in different spectroscopic behavior due to the formation of fluorescent organic nanoparticles (FONs). In the presence of Cu2+ ions, FONs displayed a ratiometric red shift of the absorption band (360 to 420 nm) accompanied by a prominent naked-eye color change from colorless to light yellow. With a gradual increase in water content, 1 displayed a huge red shift of the emission band (430 to 475 nm) denoting its switching from monomer to FONs. In the presence of Cu2+, the 475 nm emission band of FONs gradually diminished, facilitating the micromolar scale detection of Cu2+ (LOD = 8.57 μM) in a 100% aqueous medium with a fluorogenic color change from cyan to dark. The SEM and DLS data indicated the cation-induced disaggregation of FONs, which was further confirmed by mass spectral analysis and electron paramagnetic resonance measurement. In addition, the high selectivity of FONs towards Cu2+ ions over other potential cations and the 2 : 1 (1-Cu2+) binding stoichiometry were also determined. Moreover, the spectroscopic behavior of the monomeric amphiphilic probe was well supported by extensive DFT study. Such detection of Cu2+ ions in pure aqueous medium denoting an aggregation-disaggregation event is very rare in the literature.