Zwitterionic Dye Research Articles

Evidence of electronic influence in the adsorption of cationic and zwitterionic dyes on zeolites

The adsorption of a cationic dye, Methylene blue (MB), and a zwitterionic dye, 8-Hydroxyquinoline (8-HQ), onto zeolites synthesized from different clays has been investigated. The presence of certain metals and the Si/Al ratio of the parent clay has an overall effect on the type of zeolites produced. Zeolites LTA and FAU Y were obtained using the hydrothermal method. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) spectral analysis was used to study the adsorption phenomena of the adsorbates on the adsorbents. The adsorption profile of MB (Topological Polar Surface Area (TPSA) 43.9 Å2 and 8-HQ (TPSA 33.1 Å2) compared favourably with a Freundlich isotherm with R2 > 0.9 for all the zeolitic materials synthesized. Adsorption capacities of zeolite FAU was significantly different from zeolite LTA for MB removal. The higher adsorption capacity of zeolite FAU was attributed to geometric effects resulting in greater shrinkage in the inter lattice spacing of zeolite LTA leading to a reduction in surface area. Adsorption of the relatively smaller 8-HQ however, did not show significant difference in the two zeolite types. Surface and structural characterization showed that adsorbates/adsorbents interactions were driven by both geometric (inter lattice spacing which imparts higher surface area of the adsorbent) and electronic (electrostatic repulsions through electron back donation from metals in the zeolitic structure) considerations.

Near-Infrared Fluorescence Imaging of Pancreatic Cancer Using a Fluorescently Labelled Anti-CEA Nanobody Probe: A Preclinical Study

Molecular fluorescence-guided surgery using near-infrared light has the potential to improve the rate of complete resection of cancer. Typically, monoclonal antibodies are being used as targeting moieties, however smaller fragments, such as single-domain antibodies (i.e., Nanobodies®) improve tumor specificity and enable tracer injection on the same day as surgery. In this study, the feasibility of a carcinoembryonic antigen-targeting Nanobody (NbCEA5) conjugated to two zwitterionic dyes (ZW800-1 Forte [ZW800F] and ZW800-1) for visualization of pancreatic ductal adenocarcinoma (PDAC) was investigated. After site-specific conjugation of NbCEA5 to the zwitterionic dyes, binding specificity was evaluated on human PDAC cell lines with flow cytometry. A dose escalation study was performed for both NbCEA5-ZW800F and NbCEA5-ZW800-1 in mice with subcutaneously implanted pancreatic tumors. Fluorescence imaging was performed up to 24 h after intravenous injection. Furthermore, the optimal dose for NbCEA5-ZW800-1 was injected in mice with orthotopically implanted pancreatic tumors. A dose-escalation study showed superior mean fluorescence intensities for NbCEA5-ZW800-1 compared to NbCEA5-ZW800F. In the orthotopic tumor models, NbCEA5-ZW800-1 accumulated specifically in pancreatic tumors with a mean in vivo tumor-to-background ratio of 2.4 (SD = 0.23). This study demonstrated the feasibility and potential advantages of using a CEA-targeted Nanobody conjugated to ZW800-1 for intraoperative PDAC imaging.

Dye-induced photoluminescence quenching of quantum dots: role of excited state lifetime and confinement of charge carriers.

We investigate the role of quantum confinement and photoluminescence (PL) lifetime of photoexcited charge carriers in semiconductor core/shell quantum dots (QDs) via PL quenching due to surface modification. Surface modification is controlled by varying the number of dye molecules adsorbed onto the QD shell surface forming QD-dye nanoassemblies. We selected CuInS2/ZnS (CIS) and InP/ZnS (InP) core/shell QDs exhibiting relatively weak (664 meV) and strong (1194 meV) confinement potentials for the conduction band electron. Moreover, the difference in the emission mechanism gives rise to a long and short excited state lifetime of CIS (ca. 290 ns) and InP (ca. 37 ns) QDs. Dye molecules of different ionic characters (rhodamine 575: zwitterionic and rhodamine 560: cationic) are used as quenchers. A detailed analysis of Stern-Volmer data shows that (i) quenching is generally more pronounced in CIS-dye assemblies as compared to InP-dye assemblies, (ii) dynamic quenching is dominating in all QD-dye assemblies with only a minor contribution from static quenching and (iii) the cationic dye shows a stronger interaction with the QD shell surface than the zwitterionic dye. Observations (i) and (ii) can be explained by the differences in the amplitude of the electronic component of the exciton wavefunction near the dye binding sites in both QDs, which results in the breaking up of the electron-hole pair and favors charge trapping. Observation (iii) can be attributed to the variations in electrostatic interactions between the negatively charged QD shell surface and the cationic and zwitterionic dyes, with the former exhibiting a stronger interaction. Moreover, the long lifetime of CIS QDs facilitates us to easily probe different time scales of the trapping processes and thus differentiate the origins of static and dynamic quenching components that appear in the Stern-Volmer analysis.

A promising small-sized near-infrared absorbing zwitterionic dye for DSSC and NLO applications: DFT and TD-DFT approaches.

Herein we investigate three quinoid zwitterionic dye sensitizers having donor-donor (4-dimethylaniline; ZIDM), donor-acceptor (4-dimethylaniline and 4-benzoic acid; ZIMCA), and acceptor-acceptor (4-benzoic acid; ZIDCA) that can be used in dye sensitized-solar cells and non-linear optical (NLO) application through density-functional theory (DFT) and time-dependent-DFT computations. ZIDM showed better charge transfer than ZIMCA and ZIDCA, which showed similar trends in chemical potential, electrophilicity index, hardness, and hyperhardness. The higher values of open circuit voltage, light harvesting efficiency, lower binding, and adsorption energy values for the dye to bind with the TiO2 cluster were observed for ZIDM. The results suggest that these dyes can easily hold with the TiO2 cluster through the monodentate binding mode possible between Ti and oxygen of the zwitterionic backbone. The examination of the linear and NLO properties of these dyes revealed that ZIDM has a higher α0 = 80.64 × 10-24 esu, β0 = 448.54 × 10-30 esu, and γ = 2219.23 × 10-36 esu in DCM. Similarly, higher values of molecular hyperpolarizability of 1335.0 × 10-48 esu and 8818.3 × 10-48 esu were observed in gas and DCM for ZIDM than ZIMCA and ZIDCA.

Picosecond to Second Fluorescence Correlation Spectroscopy for Studying Solute Exchange and Quenching Dynamics in Micellar Media.

Numerous studies have been devoted to understand the reaction kinetics in micelles, where the accessible kinetic time window is often limited by the dynamic range of the employed spectroscopic technique. This is usually accompanied by a selection of probes that comfortably explore time scales where slow solute exchange kinetics is negligible, as compared to the fast excited state reactions. This has led to an undervaluation of the role played by dynamic partitioning of hydrophilic solutes in microheterogeneous media. Here, we employ fluorescence correlation spectroscopy (FCS) and the zwitterionic dye Rhodamine 110 to quantitatively explore the impact of solute exchange on the photoinduced electron transfer between this dye and N,N-dimethylaniline in micellar media. Our study elucidates the coupling and interplay between the kinetics of photophysics, quenching, and solute exchange through a quantitative unified molecular-state quenching-kinetic model that describes the steady-state ensemble and FCS data from subnanosecond photon antibunching to millisecond diffusions.

Insight into Organic Pollutant Adsorption Characteristics on a g-C3N4 Surface by Attenuated Total Reflection Spectroscopy and Molecular Dynamics Simulation

Herein the adsorption characteristics of zwitterionic dye pollutant Rhodamine B (Rh+B-) on a g-C3N4 surface were investigated by both an attenuated total reflection spectroscopy (ATRS) experiment and a molecular dynamics simulation (MDS). For experimental investigation, g-C3N4 was coated on a silica optical fiber (SOF) surface to fabricate an adsorption film. According to the ATRS response, adsorption thermodynamics and thermodynamics results were in situ obtained and evaluated. The isothermal Langmuir model was used to calculate the adsorption equilibrium constants (Kads) and adsorption energies (ΔGads) for Rh+B- as 27.25 × 104 M-1 and -31.01 kJ mol-1, respectively, which indicated the spontaneous adsorption behavior of Rh+B- at the g-C3N4 surface. Using dynamic Elovich modeling, the rate constants of Rh+B- were found to be k1 = 0.0063 min-1 and k2 = 0.0004 min-1, which indicated two-stage adsorption at the g-C3N4 surface. For theoretical simulation, adsorption configurations and adsorption energies were systematically calculated by a molecular dynamics simulation (MDS) . Rh+B- molecules were inclined to orient in a parallel position at the g-C3N4 surface during low concentration but a perpendicular position at the g-C3N4 surface during high concentration. Combined with experimental and calculation results, this work revealed the microscopic adsorption performance and elucidated the intermolecular interaction between localized interfaces of g-C3N4 and hazardous dye pollutant. We propose an adsorption model to explain the process of surface interaction, which is based on molecular orientation and a force-driven mechanism. Electrostatic attraction and π-π interaction dominated the adsorption interaction with an adsorption energy of ΔGlow(ads) = -38.96 kJ mol-1 for low Rh+B- concentration, and electrostatic attraction dominated the adsorption interaction with an adsorption energy of ΔGhigh(ads) = -25.76 kJ mol-1 for high Rh+B- concentration. This work can provide a fundamental basis for a dye-pollutants removal application by g-C3N4 in both adsorption and photocatalyzation.

Evolution of Surface Catalytic Sites on Bimetal Silica-Based Fenton-Like Catalysts for Degradation of Dyes with Different Molecular Charges.

We present here important new findings on the direct synthesis of bimetal Cu-Mn containing porous silica catalyst and the effects of structure-directing agent removal from the prepared nanomaterial on the evolution of surface catalytic sites. The extraction-calcination procedure of the structure-directing agent removal led to the formation of Cu and Mn oxo-clusters and Cu and Mn oxide nanoparticles smaller than 5 nm, while the solely calcination procedure led to the mentioned species and in addition to the appearance of CuO nanoparticles 20 nm in size. Catalysts were tested in the Fenton-like catalytic degradation of dyes with different molecular charge (cationic, anionic, and zwitterionic) as model organic pollutants in wastewater at neutral pH. Significantly faster degradation of cationic and anionic dyes in the first 60 min was observed with the catalyst containing larger CuO nanoparticles (>20 nm) due to the less hindered generation of •OH radicals and slower obstructing of the active sites on the catalysts surface by intermediates. However, this was not found beneficial for zwitterionic dye with no adsorption on the catalysts surface, where the catalyst with smaller Cu species performed better.

Zwitterionic dye rhodamine B (RhB) uptake on different types of clay minerals

Increased use of color dyes in textile industries resulted in great needs of treating dye-containing wastewater. As such, researches and developments for effective removal of dyes from wastewater have been conducted extensively and good progresses have already been made. However, there are still needs to understand the mechanisms of interactions between dyes and solids and to evaluate factors controlling such interactions. In this study, the interactions between different types of clay minerals and rhodamine B (RhB), a zwitterionic dye, were examined under different physic-chemical conditions. The solution pH, ionic strengths, and temperature had minimal influence of RhB uptake on these clay minerals. Uptake of RhB was limited to the external surfaces for the non-swelling clay minerals kaolinite and palygorskite. In contrast, both external and interlayer spaces are responsible for the uptake of RhB on swelling clay mineral montmorillonite. The RhB molecules intercalated into the interlayer of montmorillonite may adopt a monolayer or a bilayer configuration under low and high uptake levels. Under neutral pH condition, the RhB molecules exist as zwitterionic species in solution. The extensive uptake of RhB by the clay minerals, up to their cation exchange capacity (CEC) values, was attributed to electrostatic interactions between cationic end of the amine and the negatively charged clay minerals surfaces. The significant RhB uptake suggested that clay minerals are also good sorbents for the removal of zwitterionic dyes.

Hybrid coumarin-difluoroboron dyes for mitochondrial staining

To develop new dyes with mitochondria staining capacity, a series of zwitterionic dyes of hybrid coumarin-difluoroboron have been synthesized. The hybrid dyes are conjugated by 7-diethylaminocoumarin, difluoroboron (BF2) β-diketone and electron-donating group. The dyes show deep-red emission (600–680 nm) and high fluorescence quantum yield in organic solvents. The nature of ICT and zwitterion has been fully researched by TD-DFT and ESP calculations. Co-staining with the Mito–Tracker Green shows staining capability to mitochondria in living cells by confocal cell imaging experiments. This work can provide a new strategy for the design of neutral cellular probes for mitochondria staining.

Alkyl-Group-Wrapped Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells: Branched Alkyl Chains Modulate the Aggregation of Dyes and Charge Recombination Processes.

Electron transfer processes at the interfaces dictate the factors that improve the photovoltaic parameters, such as open-circuit voltage (Voc) and short-circuit current (Jsc), of a dye-sensitized solar cell device, besides selection of a set of suitable anode, dye, electrolyte, and cathode materials. An inefficient charge injection process at the dye-TiO2 interface and charge recombination at the TiO2-dye/electrolyte interface have detrimental effects on improving both Jsc and Voc. Hence, tailoring the factors that govern the improvement of Jsc and Voc will be an ideal approach to get the desired sensitizers with good device efficiencies. Squaraines are far-red-active zwitterionic dyes and have a high molar extinction coefficient along with unique aggregation properties due to the large dipole moment associated with them. Here, we report a series of unsymmetrical squaraine dyes, SQS1 to SQS6, with systematic variation of alkyl groups at the sp3-C and N-atoms of the indoline unit that is away from the anchoring group to control the dye-dye interactions on the TiO2 surface. The branched alkyl groups help in modulating the self-assembly of sensitizers on the TiO2 surface, besides passivating the surface that helps avoid the charge recombination processes. Light harvesting efficiency and cyclic voltammetry studies of dye-sensitized TiO2 electrodes indicate that the aggregation and charge hopping process between the dye molecules can be modulated, respectively, by systematically increasing the number of carbon atoms in the alkyl groups. Such a variation in the branched alkyl group helps enhance Voc from 672 (SQS1) to 718 mV (SQS6) and Jsc from 7.95 (SQS1) to 12.22 mA/cm2 (SQS6), with the device efficiency ranging from 3.82% to 6.23% without any coadsorbent. Dye SQS4 achieves the highest efficiency of 7.1% (Voc = 715 mV, Jsc = 13.05 mA/cm2) with coadsorbent chenodeoxycholic acid (CDCA) using an iodine (I-/I3-) electrolyte compared to its analogues. An analysis of the incident photon-to-current efficiency profiles indicates that the major contribution to photocurrent generation is from the aggregated squaraine dyes on TiO2.

Photodynamic activity of indolenine-based aminosquaraine cyanine dyes: Synthesis and in vitro photobiological evaluation

The synthesis and characterization of several indolenine-based symmetrical squaraine dyes is herein reported. These compounds, possessing different amine groups bound to the squaric ring, display strong absorption within the so-called “phototherapeutic window”, have high singlet oxygen generation ability and high stability in the presence of radiation. Moreover, their potential as photosensitizers was evaluated in vitro by a photodynamic activity test in several tumor (Caco-2, MCF-7 and PC-3) and non-tumor (NHDF and N27) cell lines. Light-emitting diode systems emitting radiation at wavelengths close to those of maximum dye absorption were constructed and used in the in vitro assays. Of these, the dye with the unsubstituted four-membered central ring exhibited the most relevant photodynamic properties, with an interesting selectivity for PC-3 cells when compared to the normal human cell line (NHDF) being observed. Aminosquaraine dyes bearing amino and ethanolamino groups, despite showing marked cytotoxicity compared to the zwitterionic dye, produced some phototherapeutic effect. Flow cytometry, using propidium iodide as a viability staining, demonstrated that this zwitterionic dye induces death within the range of 4–24 h after exposure to light. Our study also showed that this dye does not accumulate preferentially in cell's mitochondria. Although in different extents, the squaraine dyes involved in this work presented promising in vitro results as photosensitizers.

Plasma Membrane Potential of Candida albicans Measured by Di-4-ANEPPS Fluorescence Depends on Growth Phase and Regulatory Factors.

The potential of the plasma membrane (Δψ) regulates the electrochemical potential between the outer and inner sides of cell membranes. The opportunistic fungal pathogen, Candida albicans, regulates the membrane potential in response to environmental conditions, as well as the physiological state of the cell. Here we demonstrate a new method for detection of cell membrane depolarization/permeabilization in C. albicans using the potentiometric zwitterionic dye di-4-ANEPPS. Di-4-ANEPPS measures the changes in the cell Δψ depending on the phases of growth and external factors regulating Δψ, such as potassium or calcium chlorides, amiodarone or DM-11 (inhibitor of H+-ATPase). We also demonstrated that di-4-ANEPPS is a good tool for fast measurement of the influence of amphipathic compounds on Δψ.

Phenylalanine-based low-molecular-weight gelator for the removal of metal ions and dyes from wastewater

ABSTRACTIncreasing water pollution is a major concern for the global community. So, purification and reuse of wastewater are very much urgent. In this work, methyl ester of phenylalanine (Phe-OMe), a non-gelator, has been successfully applied to produce two-component charge transfer–induced organogel and metallohydrogel using picryl chloride and Cu(II) respectively. These gels and their gelation processes were utilized to mop up different toxic metal ions and ionic dyes (especially zwitterionic dye) from wastewater. Phe-OMe can drop down these metal concentrations below the permissible limit of WHO within 10 min. Interestingly, the organogel instantly turns into sol upon the addition of either base or acid. This property makes the gel act as sensors of harmful acidic and basic vapors like HCl, ammonia, and so on in the laboratories and in different industries.

Synthesis and in vitro evaluation of the antitumoral phototherapeutic potential of squaraine cyanine dyes derived from indolenine

In this work several symmetrical indolenine squaraine dyes with different groups positioned on the four-membered central ring, such as sulfur, barbituric acid, amino and methylamino, were synthesized, and their structures were fully characterized. All dyes displayed intense and narrow absorption bands in the visible region. To evaluate their singlet oxygen formation ability, the 1,3-diphenylisobenzofuran assay was used. The degradation of these squaraine dyes upon light exposure was evaluated in order to infer about their photostability. The in vitro potential of these compounds as photosensitizers for photodynamic therapy was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay in several tumor (Caco-2, MCF-7 and PC-3) and non-tumor (NHDF and N27) cell lines, using a custom-built LED based light exposure system emitting radiation with the central wavelength close to the maximum absorption wavelength of the squaraine dyes. The indolenine squaraine dyes showed a high ability to produce singlet oxygen and good photostability. The zwitterionic dyes, namely the unsubstituted dye, the barbituric acid derivative and the monothiosquaraine dye, showed relevant photodynamic activity. It was noteworthy that the unsubstituted squaraine dye exhibited a cytotoxic selectivity for the Caco-2 tumor cell line when compared to the NHDF normal cell line.

Cascade sensing of iodide and fluoride by tryptophan derived low molecular weight gelator

An optical cascade sensor of iodide and fluoride ions based on simple tryptophan derivative containing urea functional group has been designed and synthesized via one-step reaction and characterized by different spectroscopic techniques. The tetrahydrofuran solution of the sensor becomes yellow in the presence of iodide ion and this binary yellow solution shows bright green emission under 366 nm UV irradiation in the presence of fluoride ion. The sensor is one of the very few examples of cascade sensors. The sensor was utilized to detect iodide present in water which can be helpful for monitoring of iodide in real samples. A stable organogel was obtained from the same compound in 1,2-dichlorobenzene which showed acid vapor responsive gel to sol transformation. This can be utilized for sensing acid vapors present in the air. Along with that, the gel shows good selectivity for adsorbing zwitterionic dye compared to cationic, anionic or neutral dye.

Metal-enhanced fluorescence of the trimethine cyanine dyes complexed with amyloid fibrils

In this work, we present the investigation of metal enhancement effect of silver island films (SIF) on the fluorescence intensity and correspondingly reporting properties of amyloid- sensitive trimethine cyanine dyes. The benzothiazole dyes zwitterionic D-51 and multiply positively charged D-151 as well as their complexes with amyloid fibrils of proteins insulin and lysozyme were examined. The obtained data revealed that the presence of SIF causes aggregation of the positively charged dye D-151 and the destruction of the dye-fibril complex. That could be explained by electrostatic interactions between multiply charged molecules and electrically polarized silver islands. For the zwitterionic dye D-51, the presence of SIF caused metal enhancement of fluorescence emission intensity in 5.2, 6 and 3.4 times for the free dye and its complexes with fibrils of insulin and lysozyme respectively. Thus metal enhancement as emission intensity enhancement method offers a potential platform to increase the sensitivity of probes detecting protein amyloid fibrils.

An MD simulation study of Reichardt’s betaines in surfactant micelles: Unlike orientation and solvation of cationic, zwitterionic, and anionic dye species within the pseudophase

Solvatochromic indicators of the pyridinium N-phenolate series, also known as Reichardt’s betaines, or Reichardt’s dyes, are often used for examining not only pure or mixed solvents, but also various colloidal aggregates, such as surfactant micelles, droplets of microemulsions etc. In order to disclose the locus of these molecular probes within the micellar pseudophase, we recently utilized the molecular dynamics (MD) simulations for the standard dye, i.e. 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate, and three other dyes of this family of higher and lower hydrophobicity. Both zwitterionic (colored) and protonated (cationic, colorless) species were involved into the research, as these compounds are also used as acid-base indicators for micellar systems. In the present paper, we extended this investigation further. MD modeling was applied to another three dyes incorporated in sodium n-dodecyl sulfate and cetyltrimethylammonium bromide micelles. The following compounds were examined: (i) the most hydrophobic dye, bearing five tert-butyl groups, 4-[2,4,6-tri(4-tert-butylphenyl)pyridinium-1-yl]-2,6-di(4-tert-butylphenyl)phenolate, (ii) a dye with a hydrocarbon loop around the oxygen atom, 4-(2,4,6-triphenylpyridinium-1-yl)-n-(3,5-nonamethylene)phenolate, and (iii) the dye with additional carboxylate group attached to the phenyl group opposite to the phenol, 4-(4-carboxylatophenyl-2,6-diphenylpyridinium-1-yl)-2,6-diphenylphenol. The orientation and solvation of the cations, zwitterions (both colored and colorless), and the anion of the last-mentioned dye in micelles appeared to be dissimilar, depending on the molecular structure and ionization state. The results were compared with those obtained previously for the standard betaine dye. In some cases, the most probable orientation of the dyes in their colorless form was opposite to that of the standard Reichardt’s dye, i.e., their OH group is directed towards the center of the micelle.

Changes in optical properties of conjugated molecules and polymers upon adsorption onto graphene

ABSTRACTWe compared the changes in optical transmission spectrum induced by self-assembly on CVD graphene of (i) a model squarylium dye, namely n-butyl-squarylium dye (1,3-Bis[4-(dibutylamino)phenyl]-2,4-squaraine) and (ii) a conjugated polymer, poly(3-hexyl thiophene). We analyse the results based on Scanning Tunnelling Microscope images. The self-assembly of the zwitterionic dye is controlled by electrostatic interactions. A strong red-shift is observed and is explained in terms of electrostatic interactions with graphene. The self-assembly of polyalkylthiophenes presents a large red shift due to a strong alignment and planarization of the conjugated π-electron system and the formation of a new molecule-graphene charge-transfer exciton state.

Amplified singlet oxygen generation in metallated-porphyrin doped conjugated polymer nanoparticles

We report on the mechanism and efficiencies of singlet oxygen O2(1Δg) generation of nanoparticles (NP) of the conjugated polymer (CP) poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) doped with platinum octaethylporphyrin (PtOEP) suspended in water. A detailed study of the photophysics of these NP, using stationary and time-resolved absorption and emission techniques, indicates that O2(1Δg) is generated by the triplet excited state of F8BT and not by that of PtOEP, as previously observed for other porphyrin doped CP NP. O2(1Δg) quantum yields (ΦΔ) were measured by quantifying the characteristic phosphorescence of O2(1Δg) in the NIR region (∼1268 nm). It was found that incorporation of relatively small amounts of PtOEP to F8BT NP results in a significant increase of ΦΔ. NP containing 10% PtOEP (w/w) show a ΦΔ ∼ 0.24, which is 3 times larger than that observed for undoped F8BT NP, and larger than the reported for most water-soluble porphyrins. ΦΔ were also calculated from the oxidation rates (v0) of 3-[10-(2-carboxyethyl)anthracen-9-yl]propanoic acid (ADPA), a well-known chemical O2(1Δg) trap. Unexpectedly, this method was found to significantly overestimate the ΦΔ values due to the adsorption of ADPA on the surface of NP. The ADPA/NP adsorption process was characterized using a simple adsorption model yielding an (average) equilibrium constant of ∼8 × 103 M−1 and an (average) number of NP-binding sites of ∼14000. These results necessarily caution about the use of ADPA as a probe to evaluate ΦΔ in these NP systems. In addition, the interaction of F8BT NP with other anionic, cationic and zwitterionic dyes (dissolved in water) was studied. It was found that even at nano-molar concentrations all the dyes efficiently adsorb on the NP surface. This general and simple self-assembly strategy can be used to prepare superficially-dye-doped CP NP with potentially interesting technological applications.

Clouding in fatty acid dispersions for charge-dependent dye extraction

The clouding phenomenon in non-ionic surfactant systems is a common feature that remains rare for ionic detergents. Here, we show that fatty acid (negatively charged) systems cloud upon cooling hot dispersions depending on the concentration or when adding excess guanidine hydrochloride. The clouding of these solutions yields the formation of enriched fatty acid droplets in which they exhibit a polymorphism that depends on the temperature: upon cooling, elongated wormlike micelles transit to rigid stacked bilayers inside droplets. Above this transition temperature, droplets coalesce yielding a phase separation between a fatty acid-rich phase and water, allowing extraction of dyes depending on their charge and lipophilicity. Positively charged and zwitterionic dyes were sequestered within the droplets (and then in the fatty acid-rich upper phase) whereas the negatively charged ones were found in both phases. Our results show an additional case of negatively charged surfactant which exhibit clouding phenomenon and suggest that these systems could be used for extracting solutes depending on their charge and lipophilicity.