Monitoring the Discontinuous Dodecamer–Icosamer Transition of a Calix[4]arene-Derived Surfactant by Time-Resolved Small-Angle X-ray Scattering

Calix[4]arene-derived surfactants form monodisperse micelles with a well-defined aggregation number (N_agg) of 4, 6, 8, 12, or 20, corresponding to the Platonic solids. This feature is in strong contrast to conventional micelles. In this study, a transition from a dodecamer (N_agg=12) to an icosamer (N_agg=20) was induced by a rapid increase in the NaCl concentration (C_NaCl) using a stopped-flow device and directly observed by time-resolved small-angle X-ray scattering. The N_agg remained unchanged during the first 60 s after the increase in C_NaCl , and then abruptly increased to 20. This feature resembles phase transitions in supersaturated or supercooled states, or highly cooperative phenomena. We surmise that this finding may be due to the fact that only a few N_agg values are thermodynamically allowed when N_agg is sufficiently small. This is the first observation of such an induction time in micellar aggregation.     

Synthesis of maltopentaose‐conjugated surface‐active styrenic monomers and their micellar homopolymerization in water

Maltopentaose (Mal₅)‐conjugated surface‐active styrenic monomers 1a , 1b , and 1c are described, which contain hydrophobic spacers, such as C1, C5, and C7 alkylene chains, respectively. The glycomonomers 1a‐c were synthesized by the direct β‐N‐glycosyl reaction of styrene derivatives with aminoalkyl groups 4a‐c onto Mal₅ in dry methanol, followed by the N‐acetylation with acetic anhydride. The self‐assembling properties for the aqueous solutions of 1a‐c were characterized by surface tension measurements and light scattering experiments, providing the physicochemical parameters for the formed 1a‐c micelles including the critical micelle concentration, apparent hydrodynamic radius (R_h,app), and weight average aggregation number (N_agg). The transmission electron microscope observations revealed the most important result in this study that 1a produced loose spherical micelles with the number average diameter (d_n) of 26 nm, while both 1b and 1c formed worm‐like micelles with the polymerizable core and the Mal₅ shell, whose number average contour lengths (l_ns) were 130 nm and 68 nm, respectively. The radical homopolymerizations of 1a‐c in water provided a substantial result in this study that 1b and 1c , that is, the glycomonomers forming the worm‐like micelles, showed a very high homopolymerizability in water. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1671–1679     

Reversible Morphological Evolution of Responsive Giant Vesicles to Nanospheres by the Self‐Assembly of Crystalline‐b‐Coil Polyphosphazene Block Copolymers

The preparation of long‐term‐stable giant unilamellar vesicles (GUVs, diameter ≥1000 nm) and large vesicles (diameter ≥500 nm) by self‐assembly in THF of the crystalline‐b‐coil polyphosphazene block copolymers [N=P(OCH₂CF₃)₂]_n‐b‐[N=PMePh]_m ( 4 a : n=30, m=20; 4 b : n=90, m=20; 4 c : n=200, m=85), which combine crystalline [N=P(OCH₂CF₃)₂] and amorphous [N=PMePh] blocks, both of which are flexible, is reported. SEM, TEM, and wide‐angle X‐ray scattering experiments demonstrated that the stability of these GUVs is induced by crystallization of the [N=P(OCH₂CF₃)₂] blocks at the capsule wall of the GUVS, with the [N=PMePh] blocks at the corona. Higher degrees of crystallinity of the capsule wall are found in the bigger vesicles, which suggests that the crystallinity of the [N=P(OCH₂CF₃)₂] block facilitates the formation of large vesicles. The GUVs are responsive to strong acids (HOTf) and, after selective protonation of the [N=PMePh] block, they undergo a morphological evolution to smaller spherical micelles in which the core and corona roles have been inverted. This morphological evolution is totally reversible by neutralization with a base (NEt₃), which regenerates the original GUVs. The monitoring of this process by dynamic light scattering allowed a mechanism to to be proposed for this reversible morphological evolution in which the block copolymer 4 a and its protonated form 4 a⁺ are intermediates. This opens a route to the design of reversibly responsive polymeric systems in organic solvents. This is the first reversibly responsive vesicle system to operate in organic media.     

Studying Effect of Typical Nonplanar Cyclic Alcohols (n = 5‐7) on Micellization of Sodium Dodecyl Sulfate (SDS) in Aqueous Solution and Locating Their Solubilization Site in SDS Micelles

Cyclic alcohols (n = 5‐7) are compounds of distinctive nonplanar structure. Effect of the alcohols on micellization of sodium dodecyl sulfate (SDS) in aqueous solution are examined by determining the critical micelle concentration (CMC) by conductometry and the micelle aggregation numbers (N_agg) by fluorometry, respectively. In general, the CMC of SDS decreases with increase in volume of a cyclic alcohol in water and increases further after attaining a minimum value. The N_agg of SDS varies little with small addition of a cyclic alcohol, but decreases when added in sufficient volume. Both the changes of the CMC and N_agg with carbon number in the ring of the alcohols occur irregularly due to their steric reasons and nonplanar nature. The irregularity makes a difference between the cyclic alcohols and their chain counterparts. Based on ¹H NMR chemical shift measurements, the cyclic alcohols are found to be solubilized in the palisade layer in SDS micelles.     

Syntheses and micellar properties of well‐defined amphiphilic AB2 and A2B Y‐shaped miktoarm star copolymers of ε‐caprolactone and 2‐(dimethylamino)ethyl methacrylate

Well‐defined amphiphilic PCL‐b‐(PDMA)₂ and (PCL)₂‐b‐PDMA Y‐shaped miktoarm star copolymers and PCL‐b‐PDMA linear diblock copolymer were synthesized via a combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP), where PCL is poly (ε‐caprolactone) and PDMA is poly(2‐(dimethylamino)ethyl methacrylate). All of these three types of copolymers have comparable PCL contents and overall molecular weights. The PCL block is hydrophobic while the PDMA block is hydrophilic, and they behave like polymeric surfactants and self‐assemble into PCL‐core micelles in aqueous media. The chain architectural effects on the micellization properties, including the aggregation number, size, polydispersity, and micelle densities of (PCL₂₉)₂‐b‐PDMA₄₅, PCL₆₁‐b‐(PDMA₂₄)₂, and PCL₅₆‐b‐PDMA₄₉ in dilute aqueous solution, were then explored by dynamic and static laser light scattering (LLS). The intensity–average hydrodynamic radius, 〈R_h〉, the aggregation number per micelle, N_agg, and the core radius, R_core, of the PCL‐core micelles all increased in the order PCL₆₁‐b‐(PDMA₂₄)₂ < (PCL₂₉)₂‐b‐PDMA₄₅ < PCL₅₆‐b‐PDMA₄₉. The surface area occupied per soluble PDMA block at the core/corona interface increased in the order PCL₆₁‐b‐(PDMA₂₄)₂ < PCL₅₆‐b‐PDMA₄₉ < (PCL₂₉)₂‐b‐PDMA₄₅. PCL₆₁‐b‐(PDMA₂₄)₂ micelles had the largest overall micelle density, possibly because of that the presence of two soluble PDMA arms at the junction point favors the bending of the core–corona interface and thus the formation of densely‐packed core‐shell nanostructures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1446–1462, 2007     

Bending Energetics of Tablet‐Shaped Micelles: A Novel Approach to Rationalize Micellar Systems

A novel approach to rationalize micellar systems is expounded in which the structural behavior of tablet‐shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H₀), bending rigidity (k_c), and saddle‐splay constant (k?_c). As a result, experimentally accessible micellar properties, such as aggregation number, length‐to‐width ratio, and polydispersity, may be related to the different bending elasticity constants. It is demonstrated that discrete micelles or connected cylinders form when H₀>1/4ξ, where ξ is the thickness of a surfactant monolayer, whereas various bilayer structures are expected to predominate when H₀<1/4ξ. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet‐shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critical surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydisperse elongated micelles (large length‐to‐width ratio) form as the bending rigidity is lowered, approaching the critical point at k_c=0, whereas monodisperse globular micelles (small length‐to‐width ratio) are expected to be present at large k_c values. The spontaneous curvature mainly determines the width of tablet‐shaped or ribbonlike micelles, or the radius of disklike micelles, whereas the saddle‐splay constant primarily influences the size but not the shape of the micelles.     

Hydrogen‐bonded ribbons in ethyl (E)‐3‐[2‐amino‐4,6‐bis(dimethylamino)pyrimidin‐5‐yl]‐2‐cyanoacrylate and 2‐[(2‐amino‐4,6‐di‐1‐piperidylpyrimidin‐5‐yl)methylene]malononitrile

The pyrimidine rings in ethyl (E)‐3‐[2‐amino‐4,6‐bis(dimethylamino)pyrimidin‐5‐yl]‐2‐cyanoacrylate, C₁₄H₂₀N₆O₂, (I), and 2‐[(2‐amino‐4,6‐di‐1‐piperidylpyrimidin‐5‐yl)methylene]malononitrile, C₁₈H₂₃N₇, (II), which crystallizes with Z′ = 2 in the space group, are both nonplanar with boat conformations. The molecules of (I) are linked by a combination of N—H...N and N—H...O hydrogen bonds into chains of edge‐fused R₂²(8) and R₄⁴(20) rings, while the two independent molecules in (II) are linked by four N—H...N hydrogen bonds into chains of edge‐fused R₂²(8) and R₂²(20) rings. This study illustrates both the readiness with which highly‐substituted pyrimidine rings can be distorted from planarity and the significant differences between the supramolecular aggregation in two rather similar compounds.     

Effects of stereocomplexation on the physicochemical behavior of PLA/PEG block copolymers in aqueous solution

A series of polylactide/poly(ethylene glycol) (PLA/PEG) block copolymers were synthesized by ring‐opening polymerization of L ‐ or D ‐lactide in the presence of mono‐ or di‐hydroxyl PEG. The effects of stereocomplexation on the physicochemical behavior of PLA/PEG copolymers in aqueous solution were investigated by varying the degree of stereocomplexation or PLLA/PEG to PDLA/PEG ratio. In mixture solutions of insoluble and soluble copolymers, stereocomplexation strongly affects the solubility of the copolymers. In mixture solutions of soluble copolymers, both the size and aggregation number (N_agg) of the aggregates vary as a function of the degree of stereocomplexation. It is suggested that the size variation of the aggregates with increasing the degree of stereocomplexation is dependent on N_agg changes which are determined by two effects: the self‐adjusting of the aggregates so as to minimize the free energy and thus to increase the N_agg, and the kinetics of aggregation which tend to form more aggregates and thus to decrease the N_agg. Combination of the two opposite effects well explains the diverse variations of N_agg and size of the aggregates as a function of the degree of stereocomplexation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Structural and Relaxometric Characterization of Peptide Aggregates Containing Gadolinium Complexes as Potential Selective Contrast Agents in MRI

The structural and relaxometric characterization of a novel class of supramolecular aggregates, as potential tumor‐specific contrast agents in magnetic resonance imaging (MRI), is reported. The aggregates are based on a new monomer with an upsilon shape (MonY) that contains, in the same molecule, all three fundamental tasks that are required: 1) a hydrophobic moiety that allows the formation of supramolecular aggregates; 2) the bioactive CCK8 peptide for target recognition; and 3) a chelating agent able to give stable gadolinium complexes. As indicated by dynamic light scattering and small‐angle neutron scattering (SANS) measurements, MonY and its gadolinium complex MonY(Gd) aggregate in aqueous solution to give ellipsoidal micelles with a ratio between the micellar axes of ≈1.7 and an aggregation number N_agg of ≈30. There are no differences in the aggregation behavior of MonY and MonY(Gd), which indicates that the presence of metal ions, and therefore the reduction of the net charge, does not influence the aggregation behavior. When MonY or MonY(Gd) are blended with dioleoyl phosphatidylcholine (DOPC), the aggregation behavior is dictated by the tendency of DOPC to give liposomes. Only when the amount of MonY or MonY(Gd) is higher than 20 % is the coexistence of liposomes and micelles observed. The thickness d of the bilayer is estimated by SANS to be ≈35–40 Å, whereas cryogenic transmission electron microscopy images show that the diameter of the liposomes ranges from ≈50 to 150 nm. Self‐assembling micelles of MonY(Gd) present high relaxivity values (r_1p=15.03 mM ^?1 s^?1) for each gadolinium complex in the aggregate. Liposomes containing MonY(Gd) inserted in the DOPC bilayer at a molar ratio of 20:80 present slightly lower relaxivity values (r_1p=12.7 mM ^?1 s^?1), independently of their internal or external position in the liposome.     

CO2‐Activated Reversible Transition between Polymersomes and Micelles with AIE Fluorescence

Fluorescent polymersomes with both aggregation‐induced emission (AIE) and CO₂‐responsive properties were developed from amphiphilic block copolymer PEG‐b‐P(DEAEMA‐co‐TPEMA) in which the hydrophobic block was a copolymer made of tetraphenylethene functionalized methacrylate (TPEMA) and 2‐(diethylamino)ethyl methacrylate (DEAEMA) with unspecified sequence arrangement. Four block copolymers with different DEAEMA/TPEMA and hydrophilic/hydrophobic ratios were synthesized, and bright AIE polymersomes were prepared by nanoprecipitation in THF/water and dioxane/water systems. Polymersomes of PEG₄₅‐b‐P(DEAEMA₃₆‐co‐TPEMA₆) were chosen to study the CO₂‐responsive property. Upon CO₂ bubbling vesicles transformed to small spherical micelles, and upon Ar bubbling micelles returned to vesicles with the presence of a few intermediate morphologies. These polymersomes might have promising applications as sensors, nanoreactors, or controlled release systems.     

End‐functionalization of polystyrene by malto‐oligosaccharide generating aggregation‐tunable polymeric reverse micelle

This article describes that glucose, maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose ( a , b , c , d , e , and f , respectively) were introduced into the initiating chain‐end of polystyrene (PSt) through the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated radical polymerization. A series of glycoconjuaged TEMPO‐adducts, 1a–f , was synthesized and used as the initiators for the polymerization of styrene (St) for 6 h at 120 °C to afford the end‐functionalized PSt's with the acetyl saccharides, 2a–f , in the yields of 37–43%. For 2a–f obtained by the polymerizations using the [St]/[ 1 ] of 125, 250, and 500, the number‐average molecular weights determined by size exclusion chromatography (SEC), M_n,SEC's, were 4800–6300, 8800–10,600, and 18,400–25,200, respectively, which fairly agreed with the predicted values. The end‐functionalized PSt's with saccharides, 3a–f , which were obtained from the deacetylation of 2a–f using sodium methoxide in dry THF, formed the polymeric reverse micelles consisting of a saccharide‐core and a PSt‐shell in chloroform and toluene. The static laser light scattering (SLS) measurements provided the average molar mass of the aggregates in toluene, M_w,SLS's, which ranged from 7.50 × 10⁴ to 1.77 × 10⁵ for 3a , from 1.90 × 10⁵ to 4.93 × 10⁵ for 3b , from 4.41 × 10⁵ to 7.21 × 10⁵ for 3c , from 5.85 × 10⁵ to 8.51 × 10⁵ for 3d , from 7.55 × 10⁵ to 8.53 × 10⁵ for 3e , and from 8.54 × 10⁵ to 9.26 × 10⁵ for 3f . The aggregation numbers, N_agg's, which were calculated from the M_w,SLS's, were from 7 to 24 for 3a , from 20 to 37 for 3b , from 34 to 89 for 3c , from 39 to 116 for 3d , from 41 to 145 for 3e , and from 31 to 146 for 3f . It was confirmed that the aggregation property, such as the M_w,SLS or N_agg values, was strongly related to the polymerization degrees of St (DP's) or the number of the glucose residues (n's) for 3a–f . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4864–4879, 2006     

Synthesis and Self‐Assembly of pH‐Responsive Amphiphilic Poly(dimethylaminoethyl methacrylate)‐block‐Poly(pentafluorostyrene) Block Copolymer in Aqueous Solution

We report the synthesis of a novel pH‐responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)‐block‐poly(pentafluorostyrene) (PDMAEMA‐b‐PPFS) using RAFT‐mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, N_agg ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, R_h of these micelles is large, at pH 2–5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the R_h. However, the radius of gyration, R_g remains independent of pH as the dense PPFS cores predominate.

     

Mesoscopic simulation of alkylimidazoline self-aggregation in aqueous solution

A dissipative particle-dynamics method was used to simulate the self-aggregation behavior of 15 alkylimidazoline surfactants of different structures. The effects of concentration and structure of hydrophilic and lipophilic groups of the alkylimidazolines on the configuration and aggregation number (N_agg) of the micelles were also explored. Results show that the concentration of the alkylimidazoline has a significant influence on the configuration of the micelles generated. More specifically, alkylimidazolines of different concentrations are found to generate different structures (spherical, rod-shaped, layered, and interlaced) in aqueous solution. At low (1–10?wt%) and medium (40?wt%) concentrations, the micelles generated in aqueous solution are spherical and rod-shaped, respectively. At higher concentrations (80?wt%), the micelles generated present interlaced shapes with rod-shaped and layered micelles when the length of the lipophilic chain is greater than C₁₃ or the hydrophilic group is H_c. N_agg is strongly dependent on alkylimidazoline concentration and increases as concentration increases. N_agg is also greatly dependent on the structure of the hydrophilic and lipophilic groups present: it increases as the chain length of the lipophilic group increases but decreases as that of the hydrophilic group increases.     

Metallo‐supramolecular block copolymer micelles: Improved preparation and characterization

Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS₂₀‐[Ru]‐PEO₇₀ and PS₂₀‐[Ru]‐PEO₃₇₅. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS₂₀‐[Ru]‐PEO₇₀ micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (d_h) of 18 nm. For PS₂₀‐[Ru]‐PEO₃₇₅ micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and d_h = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004     

Influence of Surfactant and Charged Monomer Concentrations on Micro-Block Length of Associative Polymers by Micellar Polymerization

In the micellar polymerization to prepare associative polyelectrolyte, the influence of solution environment on hydrophobical micro-block length has been investigated. The results revealed that the aggregation number (N_agg) of surfactant micelles and micro-block length (N_H) of polymers closely related to electrolyte concentration in polymerization solution, and all of the surfactant and charged monomer concentration can change the free counterion concentration (C_aq) to affect N_agg and N_H. Therefore, the N_H with traditional calculation method which N_agg is looked as constant value was not accurate enough. Subsequently, we studied the attribution of N_H to rheological properties. The results indicated that the micro-block length can increase obviously the reversible network strength in solution to make a few contribution of thickening properties of associative polymer.     

Synthesis,micelle formation,and bulk properties of poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐polyhedral oligomeric silsesquioxane amphiphilic hybrid copolymers

The synthesis, micelle formation, and bulk properties of semifluorinated amphiphilic poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐cubic polyhedral oligomeric silsesquioxane (PEG‐b‐PPFS‐g‐POSS) hybrid copolymers is reported. The synthesis of amphiphilic PEG‐b‐PPFS block copolymers are achieved using atom transfer radical polymerization (ATRP) at 100 °C in trifluorotoluene using modified poly(ethylene glycol) as a macroinitiator. Subsequently, a proportion of the reactive para‐F functionality on the pentafluorostyrene units was replaced with aminopropylisobutyl POSS through aromatic nucleophilic substitution reactions. The products were fully characterized by ¹H‐NMR and GPC. The products, PEG‐b‐PPFS and PEG‐b‐PPFS‐g‐POSS, were subsequently self‐assembled in aqueous solutions to form micellar structures. The critical micelle concentrations (cmc) were estimated using two different techniques: fluorescence spectroscopy and dynamic light scattering (DLS). The cmc was found to decrease concomitantly with the number of POSS particles grafted per copolymer chain. The hydrodynamic particle sizes (R_h) of the micelles, calculated from DLS data, increase as the number of POSS molecules grafted per copolymer chain increases. For example, R_h increased from ～60 nm for PEG‐b‐PPFS to ～80 nm for PEG‐b‐PPFS‐g‐POSS25 (25 is the average number of POSS particles grafted copolymer chain). Static light scattering (SLS) data confirm that the formation of larger micelles by higher POSS containing copolymers results from higher aggregation numbers (N_agg), caused by increased hydrophobicity. The R_g/R_h values, where R_g is the radius of gyration calculated from SLS data, are consistent with a spherical particle model having a core‐shell structure. Thermal characterization by differential scanning calorimetry (DSC) reveals that the grafted POSS acts as a plasticizer; the glass transition temperature (T_g) of the PPFS block in the copolymer decreases significantly with increasing POSS content. Finally, the rhombohedral crystal structure of POSS in PEG‐b‐PPFS‐g‐POSS was verified by wide angle X‐ray diffraction measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 152–163, 2010     

Interactions Between the Cationic Surfactants Bearing Different Polar Head Groups: Interfacial,Conductivity, NMR,and Fluorescence Studies

Interfacial tension (γ), conductivity (κ), nuclear magnetic resonance (NMR), and fluorescence measurements have been carried out to study the mixed interfacial and micellar behavior of cationic surfactants cetyltributylphosphonium bromide (CTBB) and the cetyltrimethylammonium bromide (CTAB). From the γ versus log C _s plots, the values of critical micellar concentration (cmc) and various interfacial parameters were computed. From κ measurements, the equivalent conductivities of the monomers (Λ _mon), the micelles (Λ _mic) states and the degree of counterion dissociation (δ) have been evaluated. The cmc values have been analyzed in the context of the pseudophase separation model and regular solution theory. The interaction parameters, β^m and β^σ, in the mixed micelle as well as in the mixed monolayer, respectively, also have been computed. The self‐diffusion coefficients for the micelles have been evaluated by using NMR spectroscopy. From the fluorescence quenching method, the mean micellar aggregation number (N _agg) of the pure and mixed micelles has been obtained from the slope of the ratio of fluorescence intensities in the absence and in the presence of quencher (ln (I _1,0/I ₁) versus [Q] plots. It was found that the incorporation of CTBB into the mixed micelle decreases the N _agg. The microviscosity of the fluorescence probe Rhodamine (RB) was monitored by using fluorescence polarization measurements. The values of fluorescence anisotropies (r) indicate that the penetration of CTBB monomer into CTAB micelles produced less rigid mixed micelles.     

Formulation of Aluminum Chloride Phthalocyanine in Pluronic™ P‐123 and F‐127 Block Copolymer Micelles: Photophysical properties and Photodynamic Inactivation of Microorganisms

Aluminum Chloride Phthalocyanine (AlPcCl) can be used as a photosensitizer (PS) for Photodynamic Inactivation of Microorganisms (PDI). The AlPcCl showed favorable characteristics for PDI due to high quantum yield of singlet oxygen (Φ_Δ) and photostability. Physicochemical properties and photodynamic inactivation of AlPcCl incorporated in polymeric micelles of tri‐block copolymer (P‐123 and F‐127) against microorganisms Staphylococcus aureus, Escherichia coli and Candida albicans were investigated in this work. Previously, it was observed that the AlPcCl undergoes self‐aggregation in F‐127, while in P‐123 the PS is in a monomeric form suitable for PDI. Due to the self‐aggregation of AlPcCl in F‐127, this formulation did not show any effect on these microorganisms. On the other hand, AlPcCl formulated in P‐123 was effective against S. aureus and C. albicans and the death of microorganisms was dependent on the PS concentration and illumination time. Additionally, it was found that the values of PS concentration and illumination time to eradicate 90% of the initial population of microorganisms (IC₉₀ and D₉₀, respectively) were small for the AlPcCl in P‐123, showing the effectiveness of this formulation for PDI.     

Two polymorphic forms of N‐(4‐chloro­phenyl)‐5‐[(4‐chlorophenyl)aminomethyl]‐6‐methyl‐2‐phenyl­pyrimidin‐4‐amine

Two polymorphic forms of the title compound, C₂₄H₂₀Cl₂N₄, were obtained and characterized using X‐ray crystal structure analysis. Colourless crystals of polymorph (Ia) were obtained from the oily mother residue. Recrystallization of polymorph (Ia) from an acetone–methanol mixture resulted in pale‐yellow crystals of polymorph (Ib). The major feature distinguishing the two polymorphic forms is their inter­action modes, and hence their packing arrangements. In the crystal structure of polymorph (Ia), there are N—H⋯N hydrogen bonds and also aromatic π–π stacking inter­actions between mol­ecules. The mol­ecules of polymorph (Ib) are linked by N—H⋯Cl hydrogen bonds only.     

Anion‐Dependent Tendency of Di‐Long‐Chain Quaternary Ammonium Salts to Form Ion Quadruples and Higher Aggregates in Benzene

The self‐aggregation tendency of [N(CH₃)₂(C₁₈H₃₇)₂]X [ 1 X; X^?=BF₄^?, PF₆^?, OTf^?, NTf₂^?, BPh₄^?, BTol₄^?, BAr^F?, and B(C₆F₅)₄^?] salts to form ion quadruples (IQs) and higher aggregates (HAggs) in [D₆]benzene is investigated by means of diffusion NMR spectroscopy. The experimental results indicate that salts containing small anions ( 1 BF₄, 1 PF₆, and 1 OTf) are present in solution as IQs even at the lowest investigated concentration of C=5×10^?5 M and show a limited tendency to further self‐aggregate, reaching a maximum average aggregation number (N=V_H/${V_{\rm{H}}^{{\rm{0IP}}} }$ , where V_H=measured hydrodynamic volume and ${V_{\rm{H}}^{{\rm{0IP}}} }$ =hydrodynamic volume of the ion pair) of about 6–8 (C=0.050–0.100 M ). Salts with larger counterions [ 1 BPh₄, 1 BTol₄, 1 BAr^F, and 1 B(C₆F₅)₄] form instead ion pairs at low concentration but steadily self‐aggregate (especially the non‐fluorinated ones) on increasing their concentration up to N values exceeding 50 (C=0.030–0.050 M ). 1 NTf₂ behaves in an intermediate fashion. The self‐aggregation tendency of salts is quantified by formulating the dependence of V_H on C by means of the equations of indefinitive aggregation models. The following rankings for the formation of IQs and HAggs are obtained: IQs: 1 BF₄≈ 1 PF₆≈ 1 OTf> 1 NTf₂> 1 B(C₆F₅)₄≥ 1 BPh₄≥ 1 BTol₄≥ 1 BAr^F; HAggs: 1 BTol₄> 1 BPh₄> 1 NTf₂> 1 B(C₆F₅)₄> 1 BAr^F> 1 BF₄≈ 1 PF₆≈ 1 OTf. Interionic NOE NMR studies and DFT calculations were conducted in order to determine the relative anion–cation orientation in the self‐aggregating units.