Microheterogeneity and microviscosity of F127 micelle: the counter effects of urea and temperature

Effect of salt addition on a triblock copolymer-zwitterionic surfactant assembly: insight from excited-state proton transfer

Copolymer-surfactant assemblies are frequently utilized across various fields, from medicine to nanotechnology. Understanding the organization of the mixed assemblies in a saline environment will further expand their application horizons, especially under physiological conditions. Excited-state proton transfer (ESPT) can provide insight into the hydration nature and organization of the non-toxic assembly of a triblock copolymer F127 (poly-(ethylene oxide)101 (PEO101)-poly(propylene oxide)56 (PPO56)-PEO101)) and a zwitterionic sulfobetaine surfactant N-dodecyl-N,N-dimethyl-3-ammoniopropane sulfonate (SB12). Here, we present a comprehensive investigation of the compactness and hydration nature of the F127-SB12 mixed assemblies at different salt concentrations using the ESPT of 8-hydroxy pyrene-1,3,6-trisulfonate (HPTS). In the absence of salts, gradual SB12 addition to a premicellar (0.4 mM) or a post-micellar (4 mM) F127 solution leads to an anomalous modulation of the protonated and deprotonated emission bands. The emission intensity ratio (protonated/deprotonated) first increases to a maximum at a particular SB12 concentration (6 mM and 35 mM for the premicellar and post-micellar F127 assemblies, respectively), and then the ratio decreases with a further increase in the surfactant concentration. Since the intensity ratio is an indicator of the retardation of the ESPT process, the mixed micellar configuration displaying a maximum intensity ratio represents the most compact and least hydrated state. Salt addition to this configuration lowers the intensity ratio, signifying an enhanced ESPT process. Dynamic light scattering (DLS) results indicate that the size of the mixed assembly remains almost unaltered with the addition of salts. Thus, salinity enhances the ESPT process inside the F127-SB12 mixed assemblies without significantly altering the hydrodynamic radius.

Fluorescent intracellular imaging of reactive oxygen species and pH levels moderated by a hydrogenase mimic in living cells

The catalytic generation of H₂ in living cells provides a method for antioxidant therapy. In this study, an [FeFe]-hydrogenase mimic [Ru + Fe₂S₂@F127(80)] was synthesized by self-assembling polymeric pluronic F-127, catalytic [Fe₂S₂] sites, and photosensitizer Ru(bpy)₃²⁺. Under blue light irradiation, hydrated protons were photochemically reduced to H₂, which increased the local pH in living cells (HeLa cells). The generated H₂ was subsequently used as an antioxidant to decrease reactive oxygen species (ROS) levels in living cells (HEK 293T, HepG2, MCF-7, and HeLa cells). Our findings revealed that the proliferation of HEK 293T cells increased by a factor of about six times, relative to that of other cells (HepG2, MCF-7, and HeLa cells). Intracellular ROS and pH levels were then monitored using fluorescent cell imaging. Our study showed that cell imaging can be used to evaluate the ability of Ru + Fe₂S₂@F127 to eliminate oxidative stress and prevent ROS-related diseases.

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An [FeFe]-hydrogenase mimic was synthesized for H₂ photogeneration.

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The catalytic generation of H₂ was evaluated in HEK 293T cells.

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The H₂ generated by Ru + Fe₂S₂@F127(80) was able to decrease ROS levels.

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Light irradiation of Ru + Fe₂S₂@F127(80) led to an increase in intracellular pH.

Dynamics of small molecules within the F127 PEO-PPO-PEO triblock copolymer gel and sol phases studied at the molecular scale

Triplet excited states of guest molecules with different hydrophobicities were used to probe the association and dissociation dynamics of these guests with F127 micelles in the gel and sol phases. The dynamics probed was on a longer length scale than amenable with fluorescence techniques, but at a shorter length scale than probed in translational diffusion studies. The mobility of the guests at the molecular scale showed that subtle changes in the guest's structure affect the guest's release time from the micelles, where the structural features of the guest are more important than the phase, gel vs. sol, of the system.

Nature of Saccharide-Induced F127 Micellar Dehydration: An Insight with FDAPT (2-Formyl-5-(4'-N,N-dimethylaminophenyl)thiophene), a Multiparametric Fluorescent Probe

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) is an efficient environment-sensitive fluorescent probe, which senses the alteration of its microenvironment with six different fluorescent parameters, namely, emission intensity, wavelength, fluorescence anisotropy, and corresponding three time-dependent parameters fluorescence lifetime, time-resolved emission spectrum, and anisotropy decay. In the present work, the nature of saccharide-induced dehydration of a F127 polymeric micelle is investigated in detail with FDAPT emission. Using a multiparametric fluorescence approach, it is observed that the saccharide molecules not only decrease the critical micellization temperature of the F127 solution but also strongly alter the physical properties inside the micellar structures. The local polarity and fluidity significantly decrease in the saccharide-induced micelle as compared to the normal F127 micelle. The probe solvation dynamics study reveals that the water content in the core as well as corona domain diminishes significantly in the saccharide-induced micelle as compared to the normal micelle. More precisely, dehydration occurs more in the core region than in the corona region. Also, the saccharide-induced dehydration alters the relative size of the core and corona regions. The extent of dehydration varies with different saccharide molecules. It is also found that the dehydration efficiency order is trisaccharide (raffinose) > disaccharide (sucrose) > monosaccharide (glucose and fructose).

Aqueous Systems with Tunable Fluorescence Including White-Light Emission for Anti-Counterfeiting Fluorescent Inks and Hydrogels

White-light-emitting materials have attracted wide interest for potential applications in information displays and lighting. To date, the majority of reported white-light-emitting materials have been multicomponent systems that are typically processed with organic solvents. These features are associated with complex processing, poor white-light quality, and environmental pollution. Herein, a white-light-emitting aqueous system is realized by encapsulating a fluorophore, which has a vibration-induced emission effect, in Pluronic F127 micelles. Tunable multicolor fluorescence is achieved by changing the temperature, and the use of organic solvents is effectively avoided. Through this process, white-light emission with Commission Internationale de l'Eclairage coordinates of (0.3351, 0.3326) is obtained, which is very close to pure white light, and its color rendering index is as high as 89. The fluorescence color tunability of this system could be performed in a wide temperature range, rendering it a potential material in optical thermometry. Besides, the aqueous system also allows for the application of the material as a fluorescent ink and white-light-emitting hydrogels. Information could be embedded in paper-based materials and hydrogels through the fluorescence quenching effect of iron ions (Fe³⁺) on the fluorophore. Fluorescence could then be recovered upon removal of Fe³⁺ by adenosine 5'-triphosphate. Thus, fluorescent patterning and triple-mode anti-counterfeiting could be expected due to the temperature-sensitive emission, fluorescence quenching, and recovering properties.

Morphological Evolution of Strongly Fluorescent Water Soluble AIEEgen-Triblock Copolymer Mixed Aggregates with Shape-Dependent Cell Permeability

Dimethyl-2,5-bis(4-methoxyphenylamino)terephthalate (DBMPT) is a water-insoluble fluorogenic molecule, which has been rendered water-soluble in physiological conditions, by the addition of triblock copolymers (TBPs), P123 (PEO₁₉PPO₆₉PEO₁₉), and F127 (PEO₁₀₀PPO₆₅PEO₁₀₀). DBMPT-TBP mixed aggregates, formed in the process, exhibit significant aggregation-induced enhancement of emission, with nanosecond fluorescence lifetimes. Dynamics involved in suppression of nonradiative pathways and consequent enhancement of fluorescence are followed by femtosecond transient absorption and time-resolved fluorescence spectroscopic techniques. Interestingly, shapes of the aggregates formed with the two TBPs are found to be very different, even though they differ only in the length of hydrophilic blocks. DBMPT-P123 aggregates are micrometer-sized and spherical, while DBMPT-F127 aggregates form nanorods. Evolution of their morphologies, as a function of TBP concentration, is monitored using cryo-TEM, FESEM, and fluorescence lifetime imaging microscopy. Fluorescence lifetime distribution provides useful insight into microheterogeneity in these mixed aggregates. Excellent cell permeability is observed for DBMPT-F127 nanorods, in contrast to DBMPT-P123 microspheres. These fluorescent nanorods exhibit the ability to mark lipid droplets within the cell and hence bear the promise for application in intracellular imaging.

Micelle Heterogeneity from the 2D Kinetics of Solute Rotation

The chemical and physical properties of microstructured materials vary with position. The photophysics of solute molecules can measure these local properties, but they often show multiple rates (rate dispersion), which complicates the interpretation. In the case of micelles, rate dispersion in a solute's anisotropy decay has been assigned to either local anisotropy or heterogeneity in the local viscosity. To resolve this conflict, the rotation of PM597 molecules in SDS micelles has been measured by polarized MUPPETS (multiple population-period transient spectroscopy). This 2D technique shows that heterogeneity is strong and that local anisotropy is minimal. The results suggest that on a subnanosecond time scale, the solute sees only one strong fluctuation of the micelle structure. The anisotropic, average structure emerges on longer time scales.

Triblock-Copolymer-Assisted Mixed-Micelle Formation Results in the Refolding of Unfolded Protein

The present work reports a new strategy for triblock-copolymer-assisted refolding of sodium dodecyl sulfate (SDS)-induced unfolded serum protein human serum albumin (HSA) by mixed-micelle formation of SDS with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO₂₀PO₆₈EO₂₀ (P123) under physiological conditions. The steady-state and time-resolve fluorescence results show that the unfolding of HSA induced by SDS occurs in a stepwise manner through three different phases of binding of SDS, which is followed by a saturation of interaction. Interestingly, the addition of polymeric surfactant P123 to the unfolded protein results in the recovery of ∼87% of its α-helical structure, which was lost during SDS-induced unfolding. This is further corroborated by the return of the steady-state and time-resolved fluorescence decay parameters of the intrinsic tryptophan (Trp214) residue of HSA to the initial nativelike condition. The isothermal titration calorimetry (ITC) data also substantiates that there is almost no interaction between P123 and the native state of the protein. However, the mixed-micelle formation, accompanied by substantial binding affinities, removes the bound SDS molecules from the scaffolds of the unfolded state of the protein. On the basis of our experiments, we conclude that the formation of mixed micelles between SDS and P123 plays a pivotal role in refolding the protein back to its nativelike state.

Characterization of chlorophyll derivatives in micelles of polymeric surfactants aiming photodynamic applications

The spectrophotometric properties of chlorophylls' derivatives (Chls) formulated in the Pluronics® F-127 and P-123 were evaluated and the results have shown that the Chls were efficiently solubilized in these drug delivery systems as monomers. The relative location of the Chls in the Pluronics® was estimated from the Stokes shift and micropolarity of the micellar environment. Chls with phytyl chain were located in the micellar core, where the micropolarity is similar to ethanol, while phorbides' derivatives (without phytyl chain) were located in the outer shell of the micelle, i.e., more polar environment. In addition, the thermal stability of the micellar formulations was evaluated through electronic absorption, fluorescence emission and resonance light scattering with lowering the temperature. The Chls promote the stability of the micelles at temperatures below the Critical Micellar Temperature (CMT) of these surfactants. For F-127 formulations, the water molecules drive through inside the nano-structure at temperatures below the CMT, which increased the polarity of this microenvironment and directly affected the spectrophotometric properties of the Chls with phytyl chain. The properties of the micellar microenvironment of P-123, with more hydrophobic core due to the small PEO/PPO fraction, were less affected by lowering the temperature than for F-127. These results enable us to better understand the Chls behavior in micellar copolymers and allowed us to design new drug delivery system that maintains the photosensitizer's properties for photodynamic applications.

Facile and Scalable Preparation of Solid Silver Nanoparticles (<10 nm) for Flexible Electronics

Metal conductive ink for flexible electroncs has exhibited a promising future recently. Here, an innovative strategy was reported to synthesize silver nanocolloid (2.5±0.5 nm) and separate solid silver nanoparticles (<10 nm) effectively. Specifically, silver nitrate (AgNO3) was used as a silver precursor, sodium borohydride (NaBH4) as a reducing agent, fatty acid (CnH2n+1COOH) as a dispersant agent, and ammonia (NH3·H2O) and hydrochloride (HCl) as a pH regulator and complexing agent in aqueous solution. The main mechanism is the solubility changes of fatty acid salts (CnH2n+1COO-NH4+) and fatty acid (CnH2n+1COOH) coated on the synthesized silver nanoparticles (NPs) in aqueous solution. This change determines the suspension and precipitation of silver NPs directly. The results show that when n in dispersant is 12 and molar ratio (C12H24O2/AgNO3) is 1.0, the separation yield of silver NPs is up to 94.8%. After sintering at 125 °C for 20 min, the as-prepared conductive silver nanoink (20 wt %) presents a satisfactory resistivity (as low as 6.6 μΩ·cm on the polyester-PET substrate), about 4 times the bulk silver. In addition, the efficacy of the as-prepared conductive ink was verified with the construction of a radio frequency antenna by inkjet printing and conductive character pattern (Fudan-Fudan) by direct wiring, showing excellent electrical performance.

Role of textile substrate hydrophobicity on the adsorption of hydrosoluble nonionic block copolymers

The adsorption of polyalkylene glycols and co-polymers of ethylene oxide and propylene oxide on substrates relevant to textiles with varying surface energies (cellulose, polypropylene, nylon and polyester) was studied by using quartz crystal microgravimetry. Langmuirian-type isotherms were observed for the adsorption profiles of nonionic block polymers of different architectures. The affinity with the surfaces is discussed based on experimental observations, which highlights the role of hydrophobic effects. For a given type of block polymer, micellar and monomeric adsorption is governed by the balance of polymer structure (mainly, chain length of hydrophobic segments) and substrate's surface energy.

How does bile salt penetration affect the self-assembled architecture of pluronic P123 micelles? – light scattering and spectroscopic investigations

The triblock copolymer of the type (PEO)₂₀–(PPO)₇₀–(PEO)₂₀ (P123) forms a mixed supramolecular aggregate with different bile salts, sodium deoxycholate (NaDC) and sodium taurocholate (NaTC), having different hydrophobicity.

1-Naphthol as an ESPT fluorescent molecular probe for sensing thermotropic microenvironmental changes of pluronic F127 in aqueous media

Thermotropic microenvironmental changes and the level of hydration in different microenvironments of pluronic F127 (PF127), (PEO₁₀₆ PPO₇₀ PEO₁₀₆, average molar mass 13 000) in aqueous media have been studied using 1-naphthol, which is an ESPT fluorescent molecular probe.