Highly selective and discriminative detection of small alcohols based on a dual-emission macrocyclic samarium complex

Lower alcohols (C1-C7) have a close relationship with our lives and some of them are harmful to our body's health. For example, liquor mixed with a tiny amount of methanol is harmful to our health. Much of this study is about identifying one or two low-level alcohols. How to detect low-level alcohol and high-throughput and distinguish between analogues of alcohol remains a tremendous challenge. In this study, a new large ring Schiff base Sm(III) complex (Sm-2r) is synthesized with a double emission matrix using the template method. Its dynamic imine bond (CN) and organic ligands (H₂L2_r) with molecular rotor properties can respond to changes in viscosity and polarity in external environments. The PCA method is used to turn the data matrix into a fingerprint spectrum to distinguish different alcohols (C1-C7). Sm-2r enables the quantization of cyclopropyl and glycerol. Linear ranges of cyclopropanol and glycerol are 0-9.0% and 0-3.0% (v/v), respectively. In addition, Sm-2r has an excellent ability to distinguish the mixtures of n-PrOH and i-PrOH, C₅H₉OH and C₆H₁₁OH, n-PeOH and n-HeOH, 1,3-PDO and 1,2-PDO, MeOH and EtOH, 1,2-EG and 1,2-PDO at different volume ratios. We have provided a way to distinguish alcohol species based on their molecular polarity and viscosity.

Monitoring Local pH of Membranous Aggregates via Ratiometric Color Changing Response

A series of oxidized di(indolyl)arylmethanes (DIAM) with polyaromatic signaling moieties have been designed for monitoring local pH at interfacial region of surfactant aggregates, such as micelles and vesicles etc. The oxidized DIAMs show changes in solution color from red to yellow when incorporated in cationic surfactants (at pH 7.4) and yellow to reddish pink when exposed to negatively-charged surfactants (at pH 5.0). The changes in surface charge can influence the interfacial pH (distinct from bulk pH of the medium) of the surfactant aggregates. The mechanistic studies indicate the red-shifted absorption maxima observed in the presence of anionic amphiphiles (acidic local pH) was originated from the protonated species. On the contrary, maxima in the blue region, triggered by positively charged amphiphiles (basic local pH), can be attributed to the zwitterionic species. Such prototropic equilibrium affects charge transfer states of the molecules along with their self-assembly properties. Thus, it is evident that probes can predict as well as quantify the local pH change using the pseudophase ion exchange formalism. Also, the probes can detect the presence of anionic amphiphiles even when bound to phospholipid membranes.

Rapid enrichment and separation of two novel minor phenols from Malus hupehensis utilizing liquid-liquid extraction with three-phase solvent system and high-speed counter-current chromatography based on the polarity parameter

For a rapid enrichment and separation of minor components from Malus hupehensis, the selection of suitable solvent system is the great challenge for liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography. According to the concept of "like dissolves like," the similarity of the average polarity between solvent system and target compounds was the significant characteristic of liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography separation. The polarity parameter model provides a way to calculate the polarity of unknown compounds. Under the guidance of the polarity, an efficient enrichment and separation approach was established through liquid-liquid extraction and high-speed counter-current chromatography with solvent systems composed of n-hexane-ethyl acetate-acetonitrile-water (5:3:5:7, v/v), n-hexane-ethyl acetate-methanol-water (1:2:1:2, v/v), respectively. Thus, the total content of minor compounds was increased from 2.6% to 17.2%, and two novel compounds (6´´-O-coumaroyl-2´-O-glucopyranosylphloretin and 3´´´-methoxy-6´´-O-feruloy-2´-glucopyranosylphloretin) were obtained. The discovery of the new dihydrochalcones expanded the structural diversity of compounds produced by the genus Malus. The experimental results demonstrated that compound polarity can be described by the polarity parameter model and is an important reference for investigating optimum solvent systems for liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography.

Protonation-induced pH increase at the triblock copolymer micelle interface for transient membrane permeability at neutral pH

Achieving controlled membrane permeability using pH-responsive block copolymers is crucial for selective intercellular uptake. We have shown that the pH at the triblock-copolymer micelle interface as compared to its bulk pH can help regulate membrane permeability. The pH-dependent acid/base equilibriums of two different interface-interacting pH probes were determined in order to measure the interfacial pH for a pH-responsive triblock copolymer (TBP) micelle under a wide range of bulk pH (4.5-9.0). According to 1H NMR studies, both pH probes provided interfacial pH at a similar interfacial depth. We revealed that the protonation of the amine moiety at the micelle interface and the subsequent formation of a positive charge caused the interface to become relatively less acidic than that of the bulk as well as an increase in the bulk-to-interfacial pH deviation (ΔpH) from ∼0.9 to 1.9 with bulk pH reducing from 8.0 to 4.5. From the ΔpH vs. interface and bulk pH plots, the apparent and intrinsic protonations or positive charge formation pKa values for the micelle were estimated to be ∼7.3 and 6.0, respectively. When the TBP micelle interacted with an anionic large unilamellar vesicle (LUV) of a binary lipid (neutral and anionic) system at the bulk pH of 7.0, fluorescence leakage studies revealed that the pH increase at the micelle interface from that of the LUV interface (pH ∼ 5.5) made the micelle interface partially protonated/cationic, thereby exhibiting transient membrane permeability. Although the increasing interface protonation causes the interface to become relatively less acidic than the bulk at any bulk pH below 6.5, the pH increase at the micelle interface may not be sufficiently large to maintain the threshold for the amine-protonated condition for effecting transient leakage and therefore, a continuous leakage was observed due to the slow disruption of the lipid bilayer.

Determination of proton concentration at cardiolipin-containing membrane interfaces and its relation with the peroxidase activity of cytochrome c

The activities of biomolecules are affected by the proton concentrations at biological membranes. Here, we succeeded in evaluating the interface proton concentration (-log[H+] defined as pH') of cardiolipin (CL)-enriched membrane models of the inner mitochondrial membrane (IMM) using a spiro-rhodamine-glucose molecule (RHG). According to fluorescence microscopy and 1H-NMR studies, RHG interacted with the Stern layer of the membrane. The acid/base equilibrium of RHG between its protonated open form (o-RHG) and deprotonated closed spiro-form (c-RHG) at the membrane interface was monitored with UV-vis absorption and fluorescence spectra. The interface pH' of 25% cardiolipin (CL)-containing large unilamellar vesicles (LUVs), which possess similar lipid properties to those of the IMM, was estimated to be ∼3.9, when the bulk pH was similar to the mitochondrial intermembrane space pH (6.8). However, for the membranes containing mono-anionic lipids, the interface pH' was estimated to be ∼5.3 at bulk pH 6.8, indicating that the local negative charges of the lipid headgroups in the lipid membranes are responsible for the deviation of the interface pH' from the bulk pH. The peroxidase activity of cyt c increased 5-7 fold upon lowering the pH to 3.9-4.3 or adding CL-containing (10-25% of total lipids) LUVs compared to that at bulk pH 6.8, indicating that the pH' decrease at the IMM interface from the bulk pH enhances the peroxidase activity of cyt c. The peroxidase activity of cyt c at the membrane interface of tetraoleoyl CL (TOCL)-enriched (50% of total lipids) LUVs was higher than that estimated from the interface pH', while the peroxidase activity was similar to that estimated from the interface pH' for tetramyristoyl CL (TMCL)-enriched LUVs, supporting the hypothesis that when interacting with TOCL (not TMCL), cyt c opens the heme crevice to substrates. The present simple methodology allows us to estimate the interface proton concentrations of complex biological membranes.

Turn-On Fluorescent Sensors for the Selective Detection of Al3+ (and Ga3+) and PPi Ions

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of L1-L4 in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between L4 and Al³⁺/Ga³⁺ ions. The solution-generated [L-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.

Biomimetic systems trigger a benzothiazole based molecular switch to 'turn on' fluorescence

Molecular switches are valuable tools for the detection of many chemical and biological processes. On the other hand, Schiff bases are known for their simplicity in synthesis and their enormous biochemical applications. In this scenario, when a strategically designed Schiff base acts as a molecular switch in biomimetic environments drags inevitable attention. In this article, we hereby demonstrate an interesting behavior of a strategically designed bioactive benzothiazole based Schiff base (E)-2-(((6-chlorobenzo[d]thiazol-2-ylimino)methyl)-5-diethylamino) phenol (CBMDP) whose fluorescence characteristics dramatically modulate as consequence of its structural modification in aqueous and biomimetic environments individually. Electronic absorption, steady state and time resolved fluorescence spectroscopic techniques along with DFT based quantum chemical calculation evidence that in pure organic solvents CBMDP exists in highly fluorescent enol-imine (N) form which transform into feebly fluorescent hydrated species (H) in bulk aqueous media. Contrariwise, on interaction with the ionic and non-ionic micellar media or with liposome, a structural restoration occurs from less fluorescent hydrated (H) species into a highly fluorescent normal (N) one. This molecular flipping of the title compound upon micellar compartmentalization is possibly caused by the micropolarity of the local environment and further supported by its spectral behavior in different polarity gradient solvent mixture of water-dioxane (protic-aprotic) and water-methanol (protic -protic). Usually, Schiff bases are prone to hydrolysis in aqueous media, interestingly, the structural framework of this strategically designed molecule only allow the first step of hydrolysis, which is hydration of azomethine linkage whereas it withstand the second step, and that possibly helps the structural restoration process. Hence the article described herein may emphasize how a systematically designed Schiff base framework can be used as 'turn off- turn on' fluorescent molecular switch which may be extremely useful for its applications in the area of biochemical sensors.

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature

It is possible that a defined curvature at the membrane interface controls its pH/polarity to exhibit specific bioactivity. By utilizing an interface-interacting spiro-rhodamine pH probe and the Schiff base polarity probe, we have shown that the pH deviation from the bulk phase to the interface (ΔpH)/interfacial dielectric constant (κ(i)) for amphiphilic self-assemblies can be regulated by the curvature geometry (positive/negative) and its radius. According to ¹H NMR and fluorescence anisotropy investigations, the probes selectively interact with an anionic interfacial Stern layer. The ΔpH/κ(i) values for the Stern layer are estimated by UV-vis absorption and fluorescence studies. For the anionic sodium bis-2-ethylhexyl-sulfosuccinate (AOT) inverted micellar (IM) negative interface, the highly restricted water and proton penetration into the Stern layer owing to tight surfactant packing or a reduced water-exposed headgroup area may be responsible for the much lower ΔpH ≈ -0.45 and κ(i) ≈ 28 in comparison to ∼-2.35 and ∼44, respectively, for the anionic sodium dodecyl sulfate (SDS) micellar positive interface with a close similar Stern layer. With increasing AOT IM water-pool radius (1.7-9.5 nm) or [water]/[AOT] ratio ( w₀) (8.0-43.0), the ΔpH and κ(i) increase maximally up to ∼-1.22 and ∼45, respectively, due to a greater water-exposed headgroup area. However, the unchanged ΔpH ≈ -0.65 and κ(i) ≈ 53.0 within radii ∼3.5-8.0 nm for the positive interface of a mixed Triton X-100 (TX-100)/SDS (4:1) micelle justify its packing flexibility. Interestingly, the continuously increasing ΔpH trend for IM up to its largest possible water-pool radius of ∼9.5 nm may rationalize the increase in ΔpH (∼-1.4 to -1.6) with the change in the curvature radii (∼15 to 50 nm) for sodium 1,2-dimyristoyl- sn-glycero-3-phosphorylglycerol (DMPG)/1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) (2:1) large unilamellar vesicles (LUV) owing to its negative interface. Whereas, similar to the micellar positive interface, the unchanged ΔpH at the positive LUV interface was confirmed by fluorescence microscopic studies with giant unilamellar vesicles of identical lipids composition. The present study offers a unique and simple method of monitoring the curvature-radius-dependent interfacial pH/polarity for biologically related membranes.

A unique cysteine selective water soluble fluorescent probe operable in multiple sensing cycles for the detection of biogenic cysteine in multicellular living species

A Cys selective water soluble Cu(ii)-Schiff-base fluorescent probe isolated in the solid state exhibits in vitro and in vivo cyclic fluorescence ‘on–off’ response.

Interfacial pH and polarity detection of amphiphilic self-assemblies using a single Schiff-base molecule

The interfacial pH and polarity for different amphiphilic self-assemblies are estimated at a similar interfacial depth utilizing a unique Schiff-base molecule containing two identical phenol-conjugated-imine moieties.