Micellar Formation Study of Crown Ether Surfactants

Fluorescence probe and nuclear magnetic resonance (NMR) methods were employed to investigate the micellation of prepared crown ether surfactants, e.g. decyl 15‐crown‐5 and decyl 18‐crown‐6. Pyrene was employed as the fluorescence probe to evaluate the critical micellar concentration (CMC) of these surfactants in aqueous solutions while spin lattice relaxation times (T₁) and chemical shifts of H‐1 NMR were applied in non‐aqueous solutions. Decyl 15‐crown‐5 with lower CMC forms micelles much easier than decyl 18‐crown‐6 with higher CMC in aqueous solutions, whereas decyl 18‐crown‐6 forms micelles easier than decyl 15‐crown‐5 in nonaqueous solutions. Comparison of the CMC of crown ether surfactants and other polyoxyethylene surfactants such as decylhexaethylene glycol was made. Effects of salts and solvents on the micellar formation were also investigated. In general, additions of both alkali metal salts and polar organic solvents into the aqueous surfactant solutions increased in the CMC of these surfactants. The formation of micelles in organic solvents such as methanol and acetonitrile was successfully observed by the NMR method while it was difficult to study these surfactants in organic solutions by the pyrene fluorescence probe method. The NMR study revealed that the formation of micelles resulted in the decrease in all H‐1 spin lattice relaxation times (T₁) of hydrophobic groups, e.g. CH₃ and CH₂, and hydrophilic group OCH₂ of these surfactants. However, upon the micellar formation, the H‐1 chemical shifts (δ) of these surfactant hydrophobic groups were found to shift to downfield (increased δ) while the chemical shift of the hydrophilic group OCH₂ moved to up‐field. Comparison of the spin lattice relaxation time and H‐1 chemical shift methods was also made and discussed.     

Abnormal micellar growth in sugar-based and ethoxylated nonionic surfactants and their mixtures in dilute regimes using analytical ultracentrifugation

To develop structure-property relationships for surfactants that control their adsorption, solubilization, and micellization behavior in mixed systems and to develop predictive models based on such relationships, it is necessary to acquire quantitative information on various species present in these complex systems. The analytical ultracentrifugation technique is selected for the first time to characterize the species present in mixed micellar solutions due to its powerful ability to separate particles on the basis of their size and shape. Two nonionic surfactants, n-dodecyl-beta-D-maltoside (DM) and nonyl phenol ethoxylated decyl ether (NP-10), and their 1:1 molar ratio mixture were investigated in this study. Micelles of the nonionic surfactants and their mixture are asymmetrical in shape at the critical micelle concentration (cmc). Interestingly, unlike ionic surfactants, the micellar growths of the nonionic surfactants were found to occur at concentrations immediately above the cmc. The results from both sedimentation velocity and sedimentation equilibrium experiments suggest coexistence of two types of micelles in nonyl phenol ethoxylated decyl ether solutions and in its mixture with n-dodecyl-beta-D-maltoside, while only one micellar species is present in n-dodecyl-beta-D-maltoside solutions. Type 1 micelles were primary micelles at the cmc, while type 2 micelles were elongated micelles. The differences in the micellar shapes of n-dodecyl-beta-D-maltoside and nonyl phenol ethoxylated decyl ether are attributed to packing parameters detected by their molecular structures.     

Thermal gelation or gel melting: (ethylene glycol)113‐(l‐alanine)12 and (ethylene glycol)113‐(l‐lactic acid)12

When PEG (M.W.～5000 Daltons) is conjugated to poly(l ‐alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol‐to‐gel (thermal gelation), whereas it is conjugated to poly(l ‐lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel‐to‐sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)‐poly(l ‐alanine) (PEG‐PA; EG₁₁₃‐A₁₂) and poly(ethylene glycol)‐poly(l ‐lactic acid) (PEG‐PLA; EG₁₁₃‐LA₁₂) are synthesized and their aqueous solution behavior is investigated. PEG‐PAs with an α‐helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG‐PLA aqueous solutions occurs. The core‐rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol‐to‐gel or gel‐to‐sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, , 52, 2434–2441     

Syntheses and self‐assembly of poly(benzyl ether)‐b‐poly(N‐isopropylacrylamide) dendritic–linear diblock copolymers

This article describes the syntheses and solution behavior of model amphiphilic dendritic–linear diblock copolymers that self‐assemble in aqueous solutions into micelles with thermoresponsive shells. The investigated materials are constructed of poly(benzyl ether) monodendrons of the second generation ([G‐2]) or third generation ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM). [G‐2]‐PNIPAM and [G‐3]‐PNIPAM dendritic–linear diblock copolymers have been prepared by reversible addition–fragmentation transfer (RAFT) polymerizations of N‐isopropylacrylamide with a [G‐2]‐ or [G‐3]‐based RAFT agent, respectively. The critical micelle concentration (cmc) of [G‐3]‐PNIPAM₂₂₀, determined by surface tensiometry, is 6.3 × 10^?6 g/mL, whereas [G‐2]‐PNIPAM₂₃₅ has a cmc of 1.0 × 10^?5 g/mL. Transmission electron microscopy results indicate the presence of spherical micelles in aqueous solutions. The thermoresponsive conformational changes of PNIPAM chains located at the shell of the dendritic–linear diblock copolymer micelles have been thoroughly investigated with a combination of dynamic and static laser light scattering and excimer fluorescence. The thermoresponsive collapse of the PNIPAM shell is a two‐stage process; the first one occurs gradually in the temperature range of 20–29 °C, which is much lower than the lower critical solution temperature of linear PNIPAM homopolymer, followed by the second process, in which the main collapse of PNIPAM chains takes place in the narrow temperature range of 29–31 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1357–1371, 2006     

The effect of cationic groups on the stability of 19F MRI contrast agents in nanoparticles

Fluorine‐19 (¹⁹F)‐based contrast agents are increasingly used for magnetic resonance imaging. Conjugated to polymers, they provide an excellent quantitative imaging tool to detect the movement of the polymeric nanoparticles in vivo as there is no background signal in tissue. One of the challenges is the decline in signal intensity when the conjugated hydrophobic fluorinated functionalities aggregate. Therefore, a new fluorinated monomer was prepared from l ‐arginine that carries a 2,2,2‐trifluoroethyl functional group for imaging. The resulting monomer, 2,2,2‐trifluoroethylamide l ‐arginine methacrylamide (3FArgMA), was copolymerized with poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), [2‐(2,3,4,6‐tetra‐O‐acetyl‐α‐d ‐mannopyranosyloxy)ethyl methacrylate or 1‐O‐methacryloyl‐2,3:4,5‐di‐O‐isopropylidene‐β‐d ‐fructopyranose, respectively, using poly(methyl methacrylate) macro‐reversible addition–fragmentation chain transfer polymerization agent. The resulting block copolymers, which varied in 3FArgMA content, were self‐assembled into micelles of hydrodynamic diameters from 25 to 60 nm. The permanently positively charged arginine functionality on the 3FArgMA displayed repulsive forces against aggregation enabling high spin–spin relaxation times (T₂) in acidic as well as alkaline solutions. However, the longer poly(ethylene glycol) side functionality in PEGMEMA enabled better steric stabilization (T₂~30 ms) while the short fructose side chain was not enough to maintain high T₂ values, in particular when a higher 3FArgMA content was used. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1994–2001     

Partitioning of unsaturated hydrophilic monomer in microemulsion media monitored by pyrene fluorescence method

The extent of intra‐ and interchain associations of (un)charged water‐soluble monomers in the homogeneous and micellar solutions was studied with steady‐state fluorescence spectroscopy. Fluorescence spectroscopic experiments were performed on uncharged (acryl amide) and charged hydrophilic monomers [zwitterionic 3‐dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS), etc.] with pyrene as a probe. In both the homogeneous and micellar solutions, linear Stern–Volmer plots were obtained that implied that the quenching process can be considered as totally dynamic. The Stern–Volmer constant (K_SV) for DMAPS decreased with an increasing dielectric constant of solvent and the concentration of simple electrolyte. An abrupt decrease in K_SV was observed in the presence of a small amount of anionic emulsifier [below the critical micelle concentration (cmc)]. The dependence of K_SV on pH for DMAPS was described by a curve with a maximum at about pH = 7. This was interpreted in terms of segregation of DMAPS and the variation of a optimal microenvironment for the probe and quencher with pH. The quenching rate in the micellar solutions strongly increased above the cmc but was lower than that in the homogeneous solutions. In the micellar solutions (above the cmc), the microenvironment for an interaction between the probe and quencher was suggested to be the whole microdroplet. The dependence of K_SV on pH for DMAPS is described by a curve with a maximum at about pH = 9.3. The synergistic effect arises from the segregation of charged quencher molecules within the microdroplets. The complex (or strong interaction) between quencher and additive(s) is supposed to increase the dynamic nature of microdroplets that provides an optimal microenvironment for probe and quencher. A good coemulsifier, however, removes quencher from the interface and creates a barrier for entering monomer (quencher) into the core of micelles; therefore, quenching is depressed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 571–581, 2003     

Effects of alcohols on micellization and on the reaction methyl 4‐nitrobenzenesulfonate + Br− in cetyltrimethylammonium bromide aqueous micellar solutions

The effects of n‐hexanol, n‐pentanol, and n‐butanol on the critical micelle concentration (cmc), on the micellar ionization degree (α), and on the rate of the reaction methyl 4‐nitrobenzenesulfonate + Br^? have been investigated in cetyltrimethylammonium bromide (CTAB) aqueous solutions. An increase in the alcohol concentration present in the solution produces a decrease in the cmc and an increase in the micellar ionization degree. Kinetic data show that the observed rate constant decreases as alcohol concentration increases. This result was rationalized by considering variations in the equilibrium binding constant of the methyl 4‐nitrobenzenesulfonate molecules to the micelles, variations in the interfacial bromide ion concentration, and variations in the characteristics of the water–alcohol bulk phase provoked by the presence of alcohols. When these operative factors are considered, kinetic data in this and other works show that the second‐order rate constants in the micellar pseudophases of water–alcohol micellar solutions are quite similar to those estimated in the absence of alcohols. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 634–641, 2004     

Synthesis and photophysical characterization of amphiphilic dendritic–linear–dendritic block copolymers

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl‐terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D ‐Si‐1G) and second (PEO–D ‐Si‐2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore‐type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 10⁴ for PEO–D ‐Si‐1G and 9.57 × 10⁴ for PEO–D ‐Si‐2G). The steady‐state fluorescence anisotropy values (r) of 1,6‐diphenyl‐1,3,5‐hexatriene were 0.06 for PEO–D ‐Si‐1G and 0.09 for PEO–D ‐Si‐2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 918–926, 2001     

Monomer Concentrations in Simple Micellar Systems from NMR Relaxation Times and C‐13 Chemical Shifts

The monomer concentrations for some simple micelle forming surfactants, octylammonium bromide (OTAB), sodium decyl sulphate, SDecS, and dodecyltrimethylammonium bromide (DTAB) were determined from the NMR‐paramagnetic relaxation enhancement experiment (the NMR‐PRE) on the H‐1 spin lattice relaxation times for the surfactant protons as a function of the surfactant concentration above and below the critical micelle concentration (cmc region). The NMR relaxation times, determined from the inversion recovery method, decrease steadily as the concentration of the surfactant is increased above the cmc value. A second, simple method is proposed whereby the p‐value of the surfactant in the micelle is determined from the two‐site model via extrapolation of the observed relaxation rate data to high concentrations. The p‐values and the calculated monomer concentrations are compared to each other and to those obtained using the mass‐action and phase separation models. In most cases, the monomer concentrations appear to remain constant at concentrations up to 2–3 times the cmc value, and then begin to decrease thereafter. These results are compared to the trends in monomer concentrations obtained from other NMR experiments in other surfactant systems.     

Scrambled Self‐Assembly of Bacteriochlorophylls c and e in Aqueous Triton X‐100 Micelles

Bacteriochlorophyll (BChl) e was coassembled with BChl c in Triton X‐100 micelles in aqueous solutions. The Q_y absorption bands of the coaggregates were positioned between those of aggregates consisting solely of BChl c or e. The electronic absorption spectra of the coaggregates could not be reproduced by linear combinations of the spectra of the aggregates consisting solely of each pigment, but they were in line with the simulated spectra for the self‐aggregates in which both BChls were randomly distributed. These suggest that BChls c and e are not spatially separated; they are homogenously distributed over the self‐aggregates to give electronic spectra that are different from those of the aggregate consisting solely of each pigment. Deaggregation of the scrambled self‐aggregates by excess Triton X‐100 did not produce any spectral components assigned to an aggregate consisting solely of either BChl c or e. Acid‐induced decomposition of the scrambled aggregates showed different kinetics from those of the aggregates consisting solely of each pigment. These also support the homogeneous distribution of BChls c and e in the scrambled self‐aggregates. These results will be useful to investigate the major light‐harvesting antenna systems of green photosynthetic bacteria that contain two kinds of chlorosomal BChls.     

Viscoelastic properties of dilute polymer solutions: The effect of varying the concentration

Dynamic viscoelastic behavior was investigated for solutions of polystyrene in tricresyl phosphate, a good solvent, at concentrations, c, less than the coil‐overlapping concentration, c*. At the infinite dilution limit, the behavior was in accord with the theory of Doi and Edwards involving the excluded volume potential and hydrodynamic interaction (HDI). Thus, the viscoelastic functions were completely derived from the intrinsic viscosity–molecular weight relation. At finite c, the complex modulus was represented by the sum of two terms. One was a Rouse–Zimm (RZ) term conveniently represented by the Zimm theory with an arbitrarily chosen value of the HDI parameter. The other was a term with a single relaxation time, longer than the longest RZ relaxation time, and with a high‐frequency modulus proportional to the square of c [the long‐time (LT) term]. The behavior of the RZ term indicated the stronger screening of HDI with increasing c. Using the experimental c dependence of the longest RZ relaxation time to get the relevant parameter, we compared the RZ viscoelastic function with the Muthukumar–Freed theory. The agreement was good at low concentrations, c < c*. The contribution of the LT term, which was not included in the theory, was quite significant at low frequencies; about 60% of the Huggins coefficient was attributable to this term. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 211–217, 2001     

Chiroptical aggregates from block copolymer bearing amino acid moieties in aqueous solution

Optically active poly(ethylene glycol) monomethyl ether‐b‐poly(methacryloyl‐L ‐leucine methyl ester) (denoted as MPEG‐b‐PMALM) copolymers were prepared via atom transfer radical polymerization (ATRP), using bromine (Br) end‐capped poly(ethylene glycol) monomethyl ether (denoted as MPEG‐Br) as macroinitiator in the presence of CuBr/tris(2‐dimethylaminoethy1)amine (Me₆TREN) as catalytic system. Broad range of morphologies, such as spherical, cylindrical, and vesicular micelles, which were prepared by initially dissolving prepared polymer in organic solvent at different concentration followed by addition various amount of water before dialysis against water to remove any added solvent, was observed by transmission electron microscope (TEM). More detailed chiroptical properties of the micelles/aggregates in aqueous solution were evaluated by circular dichroism (CD) spectroscopy as a function of micelles morphologies, polymer concentration, solvents employed, temperature, etc. The micellar solutions exhibit almost the same CD spectra regardless of its morphologies. The intensity of the CD spectra of the cylindrical micelles decreased in the molar ellipticities as the micellar concentration in water was increased. The Cotton effect was markedly changed when the solvent hydrophobicity was changed by addition of trifluoromethyl ethanol (TFME) to water. The intensity of the CD spectra decreased not too much within the temperature range from 20 °C to 90 °C, indicating good stability of the micelles upon temperature variation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1345–1355, 2009     

Rheological and microcalorimetric studies of a model alkali‐soluble associative polymer (HASE) in nonionic surfactant solutions

Rheological experiments were carried out on a 1 wt % hydrophobically modified alkali‐soluble emulsion (HASE) solutions at pH ∼ 9 in the presence of nonionic polyoxyethylene ether type surfactant (C₁₂EO₂₃). The low shear viscosity and dynamic moduli increases at c > cmc until they reach a maximum at a critical concentration, c^m of approximately 1 mM (∼17 times the cmc of free surfactant) and then decrease. The dominant mechanism at cmc < c < c^m is an increase in the number of intermolecular hydrophobic junctions and a strengthening of the overall associative network structure. Above c^m, the disruption of the associative network causes a reduction in the number of junctions and strength of the overall network structure. The influence of C₁₂EO₂₃ on HASE before cmc could not be detected macroscopically by the rheological technique. However, isothermal titration calorimetry enables the determination of complex binding of surfactant to the polymer. Isothermal titration of C₁₂EO₂₃ into 0.1 wt % HASE indicates that the C₁₂EO₂₃ aggregation in water and 0.1 wt % HASE polymer solutions is entropically driven. A reduction in the critical aggregation concentration (cac) confirms the existence of polymer–surfactant interactions. The hydrophobic micellar junctions cause a decrease in the ΔH and ΔS of aggregation of the nonionic surfactant. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2019–2032, 2000     

Investigations on a detergent system with rodlike micelles

Conductivity, kinetic, static and dynamic light scattering, electric birefringence and rheological measurements were carried out on aqueous solutions of Tetradecylpyridinium-n-Heptanesulfonate (C₁₄PyC₇SO₃) up to high concentrations. In dilute solutions between the critical micelle concentration (cmc) and another characteristic concentration (c _t) spherical micelles were detected whose radii were independent of detergent concentration and equal to the length of a detergent molecule; the aggregation numbern of these micelles of about 100 monomers per micelle was also in agreement with the existence of normal spherical micelles of aC ₁₄-detergent.Above the concentrationc _t, the spherical micelles were found to grow to rodlike aggregates whose short axis was still independent of concentration and equal to the length of a monomer, while the lengthsL of the rods increased with increasing detergent concentration. When the lengthsL of the rods became comparable with the mean distancea between them, the starting interaction between the rods slowed down their growth. In this concentration range of overlapping rods, the data could be evaluated with a recently developed theory by Doi and Edwards for stiff rods. The rods reached finally a maximum length of about 500 å and decreased again in size upon further increase of concentration when the overlap ratioL/a reached a value of about 1,5.     

Synthesis of poly(L‐lysine)‐graft‐polyesters through Michael addition and their self‐assemblies in aqueous solutions

A series of poly(L ‐lysine)s grafted with aliphatic polyesters, poly(L ‐lysine)‐graft‐poly(L ‐lactide) (PLy‐g‐PLLA) and poly(L ‐lysine)‐graft‐poly(?‐caprolactone) (PLy‐ g‐PCL), were synthesized through the Michael addition of poly(L ‐lysine) and maleimido‐terminated poly(L ‐lactide) or poly(?‐caprolactone). The graft density of the polyesters could be adjusted by the variation of the feed ratio of poly(L ‐lysine) to the maleimido‐terminated polyesters. IR spectra of PLy‐g‐PCL showed that the graft copolymers adopted an α‐helix conformation in the solid state. Differential scanning calorimetry measurements of the two kinds of graft copolymers indicated that the glass transition temperature of PLy‐g‐PLLA and the melting temperature of PLy‐g‐PCL increased with the increasing graft density of the polyesters on the backbone of poly(L ‐lysine). Circular dichroism analysis of PLy‐g‐PCL in water demonstrated that the graft copolymer existed in a random‐coil conformation at pH 6 and as an α‐helix at pH 9. In addition, PLy‐g‐PCL was found to form micelles to vesicles in an aqueous medium with the increasing graft density of poly(?‐caprolactone). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1889–1898, 2007     

A three‐dimensional homochiral metal–organic framework constructed from manganese(II) with S‐carboxymethyl‐N‐(p‐tosyl)‐l‐cysteine and 4,4′‐bipyridine

In the chiral polymeric title compound, poly[aqua(4,4′‐bipyridine)[μ₃‐S‐carboxylatomethyl‐N‐(p‐tosyl)‐l ‐cysteinato]manganese(II)], [Mn(C₁₂H₁₃NO₆S₂)(C₁₀H₈N₂)(H₂O)]_n, the Mn^II ion is coordinated in a distorted octahedral geometry by one water molecule, three carboxylate O atoms from three S‐carboxyatomethyl‐N‐(p‐tosyl)‐l ‐cysteinate (Ts‐cmc) ligands and two N atoms from two 4,4′‐bipyridine molecules. Each Ts‐cmc ligand behaves as a chiral μ₃‐linker connecting three Mn^II ions. The two‐dimensional frameworks thus formed are further connected by 4,4′‐bipyridine ligands into a three‐dimensional homochiral metal–organic framework. This is a rare case of a homochiral metal–organic framework with a flexible chiral ligand as linker, and this result demonstrates the important role of noncovalent interactions in stabilizing such assemblies.     

Synthesis and characterization of biodegradable pH and reduction dual‐sensitive polymeric micelles for doxorubicin delivery

Novel pH and reduction dual‐sensitive biodegradable polymeric micelles for efficient intracellular delivery of anticancer drugs were prepared based on a block copolymer of methyloxy‐poly(ethylene glycol)‐b‐poly[(benzyl‐l ‐aspartate)‐co‐(N‐(3‐aminopropyl) imidazole‐l ‐aspartamide)] [mPEG‐SS‐P(BLA‐co‐APILA), MPBA] synthesized by a combination of ring‐opening polymerization and side‐chain reaction. The pH/reduction‐responsive behavior of MPBA was observed by both dynamic light scattering and UV–vis experiments. The polymeric micelles and DOX‐loaded micelles could be prepared simply by adjusting the pH of the polymer solution without the use of any organic solvents. The drug release study indicated that the DOX‐loaded micelles showed retarded drug release in phosphate‐buffered saline at pH 7.4 and a rapid release after exposure to weakly acidic or reductive environment. The empty micelles were nontoxic and the DOX‐loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. Confocal microscopy observation demonstrated that the DOX‐loaded MPBA micelles can be quickly internalized into the cells, and effectively deliver the drugs into nuclei. Thus, the pH and reduction dual‐responsive MPBA polymeric micelles are an attractive platform to achieve the fast intracellular release of anticancer drugs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1771–1780     

Cancer‐associated pH‐responsive tetracopolymeric micelles composed of poly(ethylene glycol)‐b‐poly(L‐histidine)‐b‐poly(L‐lactic acid)‐b‐poly(ethylene glycol)

To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH‐sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol)‐b‐poly(L ‐histidine)‐b‐poly(L ‐lactic acid)‐b‐poly(ethylene glycol)] consisted of a hydrophobic poly(L ‐histidine) (polyHis) and poly(L ‐lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1–3.5 µg/ml and an average size of 65–80 nm pH 7.4. Importantly, they showed a pH‐dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd.     

Role of manganese(II), micelles,and inorganic salts on the kinetics of the redox reaction of L‐sorbose and chromium(VI)

The kinetics of the reduction of chromium(VI) to chromium(III) by L ‐sorbose in HClO₄ was studied between 30 and 80°C at various concentrations of reactants and acidities in both aqueous and micellar sodium dodecyl sulfate (SDS)/TritonX‐100(TX‐100) solutions. Under pseudo‐first‐order conditions the reaction rate is fractional‐order in [L ‐sorbose] and [H⁺], and first‐order in [Cr^VI] both in the absence and in the presence of surfactant micelles. The reaction is accelerated by addition of manganese(II) and is routed through the same mechanism as shown by the kinetic studies in the absence and presence of surfactants. The rate enhancement in presence of SDS/TX‐100 micelles indicates that essentially all the reactive species are bound to micelles under the experimental conditions. The observed catalyses are explained with the modified Menger and Portnoy model. Inorganic salts (NaBr, LiBr, NH₄Br) inhibit the reaction in presence of SDS micelles, which confirms exclusion of the reactive species of chromium(VI) from the reaction site. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 543–554, 2003     

Self‐Assembly of Poly(γ‐benzyl L‐glutamate)‐graft‐Poly(ethylene glycol) and Its Mixtures with Poly(γ‐benzyl L‐glutamate) Homopolymer

Summary: Self‐association behaviors of poly(γ‐benzyl L ‐glutamate)‐graft‐poly(ethylene glycol) (PBLG‐graft‐PEG) and its mixtures with PBLG homopolymer in aqueous media were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and nuclear magnetic resonance (NMR) spectroscopy. It was revealed that PBLG‐graft‐PEG could self‐assemble to form polymeric micelles with a core‐shell structure in the shape of spindle. The introduction of PBLG homopolymer not only decreases the critical micelle concentration, but also changes the morphology of the micelles.

The excitation fluorescence spectra of pyrene as a function of concentrations for the mixture of PBLG‐graft‐PEG with PBLG and a TEM image of the formed micelles.