A new surfactant-fluorescence probe for detecting shape transitions in self-assembled systems

A study of [2 + 2] cycloaddition-retroelectrocyclization in water: observation of substrate-driven transient-nanoreactor-induced new reactivity

Organic solvents limit [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) in biological fields. We examined the formation of 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) through CA-RE reactions and their unusual reactivity to produce N-heterocyclic compounds when the nature of the surfactant and the concentrations were varied in the aqueous phase. An environment in which transient self-assemblies (vesicles) were induced by the substrate and surfactant molecules initiated new reactivity through H₂O addition on the TCBD, generating the enol form of the intermediate, which results in the formation of the 6,6-dicyano-heteropentafulvene (amidofulvene) compound, while lamellar sheets at higher concentrations favored TCBD generation. Interestingly, the amidofulvene underwent a clean transformation to 6-membered heterocycles that resemble cardiotonic drugs (milrinone, amrinone) via keto-enol tautomerism mediated by a polar aprotic solvent, opening up a new avenue for drug discovery. Unlike organic-solvent-mediated CA-RE reactions, the present nanoreactor-mediated approach enabled the selective production of TCBDs as well as new heterocycles using H₂O as a green solvent. In addition to the widely explored organic electronics/materials, we believe that this study will help to overcome the long-standing limitation of CA-RE reaction applicability in biological fields.

Determination of the critical micelle concentration of surfactants using fluorescence strategies

The increasing importance of surfactants in various fields has led to growing interest in the comprehensive characterization of surfactants. The critical micelle concentration (CMC), the most fundamental property of surfactants, is a parameter that must be measured. In particular, with the continuous expansion of the molecular structure of surfactants, numerous novel amphiphilic molecules have been developed that are capable of forming ordered aggregates in various solvent systems. Fluorescence spectroscopy, based on the differences in fluorescence intensity and wavelength of the fluorescent probe in the solvent phase and micellar phase, can sensitively detect the CMC of surfactants. This review aims to summarize the various fluorescence methods used to determine the CMC, including aggregation-induced emission (AIE), excimer formation, intramolecular charge transfer (ICT), and other miscellaneous strategies. The difficulties and limitations in the CMC determination process are also described. Further suggestions are provided to guide the existing fluorescence probes and the corresponding fluorescence methods to detect critical aggregation concentrations of amphiphilic molecules.

PH Responsive Polyurethane for the Advancement of Biomedical and Drug Delivery

Due to the specific physiological pH throughout the human body, pH-responsive polymers have been considered for aiding drug delivery systems. Depending on the surrounding pH conditions, the polymers can undergo swelling or contraction behaviors, and a degradation mechanism can release incorporated substances. Additionally, polyurethane, a highly versatile polymer, has been reported for its biocompatibility properties, in which it demonstrates good biological response and sustainability in biomedical applications. In this review, we focus on summarizing the applications of pH-responsive polyurethane in the biomedical and drug delivery fields in recent years. In recent studies, there have been great developments in pH-responsive polyurethanes used as controlled drug delivery systems for oral administration, intravaginal administration, and targeted drug delivery systems for chemotherapy treatment. Other applications such as surface biomaterials, sensors, and optical imaging probes are also discussed in this review.

Construction of a pH-sensitive self-assembly in aqueous solutions based on a dansyl-modified β-cyclodextrin

Here we present a pH-responsive self-assembly based on a β-cyclodextrin (β-CD) derivative bearing a dansyl terminus (βCD-C₆-Dns). Vesicular structures were formed over the entire studied pH range (8.5-0.7); however, the molecular configuration and packing within the vesicles were different at different pH values. Intramolecular host-guest complexation occurred mainly between the dansyl group and β-CD at pH values where the dansyl group was not protonated. The alkyl chain also acted as a competitive guest to form host-guest inclusions as confirmed by 2D ¹H NMR measurements. The pH-responsive βCD-C₆-Dns vesicles have potential application prospects in pH-controlled drug release based on the low cytotoxicity of βCD-C₆-Dns.

A dansyl fluorescent pH probe with wide responsive range in aqueous solution

A fluorescent pH probe based on diphenylalanine-modified dansyl (FF-Dns) was designed and synthesized. The probe showed sensitive fluorescence emission to pH change over a wide range of 1-13 in aqueous solution. At pH 4-10, FF-Dns displayed the characteristic fluorescent emission of dansyl group (yellow); while protonation of the dimethylamino group caused a very weak fluorescence emission at pH 1-4, and deprotonation of the sulfonamide group caused an emission blue-shift to the green region at pH 11-13. These properties endow FF-Dns with the potential to detect pH variation in physiological environments.

Dual pH-/temperature-responsive and fluorescent hydrogel for controlled drug delivery

The purpose of this investigation is to develop a dual pH-/temperature-responsive and fluorescent hydrogel based on piperazine and Pluronic F127 (PF127). Firstly, polyurethane was synthesized using 1,6-hexamethylene diisocyanate, 1,4-bis(hydroxyethyl) piperazine, and PF127 by a step polymerization process. Erythrosine B (EB) is then incorporated into copolymers to offer a fluorescence property. The polyurethane-PF127-EB copolymer can spontaneously self-assemble into hydrogels with a great number of closely packed micelles, and the hydrogels also have the ability to undergo thermo-sensitive sol-gel phase transition above the critical gelation concentration. The gelation temperature can be adjusted near the physiological condition by modulating the concentration of the copolymer in an aqueous medium. The acid-titration curves indicate a good pH-responsive property, and the UV-vis and fluorescence spectra exhibit strong self-fluorescence signals for hydrogels. As a result, the hydrogels not only can serve as drug carriers but can also be utilized as fluorescence imaging probes in biomedical applications.

Naphthalimide-Based Fluorophore for Soft Anionic Interface Monitoring

A naphthalimide-based low-molecular-mass fluorophore (NA) was designed and synthesized by introducing an azetidine unit onto the aromatic ring of the compound as an electron-donating structure, and a hydrophilic (2-(2-aminoethyl-amino)ethanol) moiety into the "N-imide site" of the core structure. UV-vis absorption and fluorescence measurements revealed that the fluorophore is soluble in water and shows a fluorescent quantum yield of ∼20% and lifetime of ∼3.7 ns in the solvent within a wide pH range. Moreover, the fluorescence emission and anisotropy of the fluorophore as produced are both dependent upon the viscosity and polarity of the medium. Further studies demonstrated that NA can be used as a selective probe to monitor the aggregation of anionic surfactants owing to its accumulation onto the anionic surfaces of the aggregates as formed. Inspired by the discovery, NA was successfully applied for detection of cell membranes and E. coli via monitoring of their negatively charged surfaces, which is important for fast checking of biological contamination of water. Importantly, all the tests could be performed in a visualized manner. We believe that the new, low-molecular-mass fluorophore as created may find applications in chemical and biochemical sensing and imaging.

Determination of Shape Transition Concentrations in Self-Assembled Surfactant Micelles by UV-Visible Spectrophotometry

In this study, the first and second critical micelle concentration (FCMC and SCMC) were determined by recording the absorbance at various surfactant concentrations using a dye probe and ultra violet (UV)-visible spectrophotometer. This method could predict the concentrations of hexagonally packed rods and palisade layer structure of ionic surfactants. The UV-visible absorbance graphs were plotted at specific concentrations. Sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) were used as the model surfactants, and methylene blue was used as the dye probe. The FCMC and SCMC were obtained from the concentration vs. absorbance graphs. The results are in good agreement with those obtained from the fluorescence, scattering, conductivity, and surface tension measurements.

Dansyl-labeled anionic amphiphile with a hexadecanoic carbon chain: synthesis and detection for shape transitions in organized molecular assemblies

The probing properties of a new fluorophore-labeled anionic surfactant, sodium 16-(N-dansyl)aminocetylate (16-DAN-ACA) were investigated systematically in molecular assemblies, especially in the transitions between micelles and vesicles. 16-DAN-ACA can efficiently differentiate the two different aggregate types in mixed cationic and anionic surfactant systems. The fluorescence anisotropy of 16-DAN-ACA was found to be sensitive for directly detecting the micellar growth in micelles containing oppositely charged surfactants; both cationic cetyltrimethylammonium bromide (CTAB) systems and anionic sodium dodecyl sulfate (SDS) systems were studied. The results indicated that the 16-DAN-ACA is a good fluorescent probe for differentiating the different aggregates, and even more can be used to detect the micellar growth.

Synthesis of dye/fluorescent functionalized dendrons based on cyclotriphosphazene

Functionalized phenols based on tyramine were synthesized in order to be selectively grafted on to hexachlorocyclotriphosphazene, affording a variety of functionalized dendrons of type AB(5). The B functions comprised fluorescent groups (dansyl) or dyes (dabsyl), whereas the A function was provided by either an aldehyde or an amine. The characterization of these dendrons is reported. An unexpected behaviour of a fluorescent and water-soluble dendron based on dansyl groups in mixtures of dioxane/water was observed.