Effects of Nonionic and Mixed Cationic-Nonionic Micelles on the Rate of Alkaline Hydrolysis of 4-Nitrophthalimide

Pseudo-first-order rate constants (k_obs) for alkaline hydrolysis of 4-nitrophthalimide show a monotonic decrease with increase in [C₁₂E₂₃]_T (total concentration of Brij 35) at constant [CH₃CN] and [NaOH]. This micellar effect is explained in terms of a pseudophase micelle model. The rate of hydrolysis becomes too slow to monitor at [C₁₂E₂₃]_T≥0.03 M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C₁₂E₂₃]_T≥0.04 M in the presence of 0.006–0.02 M CTABr at 0.01 M NaOH. The plots of k_obs versus [C₁₂E₂₃]_T show minima at 0.006 and 0.01 M CTABr, while such a minimum is not visible at 0.02 M CTABr.     

Effects of Cationic Micelles on the Rate of Intramolecular General Base-Catalyzed Reaction of Ionized Phenyl Salicylate with DL-Proline

Pseudo-first order rate constants (k_obs) obtained for the reaction of ionized phenyl salicylate (PS^-) with anionic DL-proline (Prl^-) at a constant [NaOH] and [CTABr] (where CTABr represents cetyltrimethylammonium bromide) and 35°C, show a linear increase with increasing total concentration of Prl^-; Nucleophilic second-order rate constants (k_n ^obs) for the reactions of Prl^- with PS^- reveal a nearly 5-fold decrease with the increase in [CTABr] from 0.0 to 0.01 M.     

Solubilization of Aliphatic Carboxylic Acids (C3-C6) by Sodium Dodecyl Sulfate and Brij 35 Micellar Pseudophases

The apparent dissociation constants of 1-propanoic, 1-butanoic, 1-pentanoic and 1-hexanoic acids were obtained for the first time in Brij 35 micellar solutions with concentration from 0.03 to 0.20 mol⋅L⁻¹ and sodium dodecyl sulfate (SDS) micellar solutions with concentrations from 0.01 to 0.30 mol⋅L⁻¹. A pronounced effect of Brij 35 micelles on the acid-base properties of aliphatic acids was observed. The binding constants, K _b, of carboxylic acids to micellar pseudophases of SDS and Brij 35 were estimated within the framework of the pseudophase model. The dependences of Gibbs energies of transfer from water to the micellar pseudophases were constructed, and Gibbs energies were evaluated for methylene and carboxylic group transfers into Brij 35 and SDS micelles. Comparison of the Gibbs energies of methylene group transfer from water to Brij 35 and SDS suggests that the mechanisms of hydrocarbon group transfer into the core of nonionic and anionic micelles involving the same monomer hydrophobic tail length are similar.     

Unusual Effects of Pure Nonionic and Mixed Nonionic–Cationic Micelles on the Rate of Alkaline Hydrolysis of N-Hydroxyphthalimide

Pseudo-first-order rate constants, k_obs, for the alkaline hydrolysis of N-hydroxyphthalimide, 1, at 0.02 M NaOH and 30°C remain essentially independent of the total concentration of C₁₂E₂₃, [C₁₂E₂₃]_T, at ≤0.005 M C₁₂E₂₃. The increase in [C₁₂ E₂₃]_T from 0.005 to 0.015 M causes a nonlinear decrease in k_obs. The rate of hydrolysis becomes either too slow or the change in absorbance values becomes significantly small to allow a reliable observed data fit to a first-order kinetic equation at ≥0.020 M C₁₂E₂₃ in the absence and presence of total concentration of cetyltrimethylammonium bromide, [CTABr]_T ranging from 0.003 to 0.020 M. The values of fraction of nonionized 1, F_SH, obtained at reaction time t = 0 and 0.02 M NaOH, remain ～0 at ≤0.010 M C₁₂E₂₃ while they increase from 0.39 to 0.89 with the increase of [C₁₂E₂₃]_T from 0.015 to 0.10 M. The values of k_obs show a nonlinear decrease of ～5-fold with the increase of [C₁₂E₂₃]_T from 0.0 to 0.010 M in the presence of 0.02 M NaOH and [CTABr]_T range of 0.003 to 0.020 M. The values of F_SH remain ≤～0.10 at ≤0.015 M C₁₂E₂₃ while they vary between 0.40 and 0.90 within a [C₁₂E₂₃]_T range 0.02 to 0.05 M in the presence of 0.02 M NaOH and [CTABr]_T ranging from 0.003 to 0.020 M. The values of F_SH represent the fraction of nonionized 1 trapped almost irreversibly by pure C₁₂E₂₃, and mixed C₁₂E₂₃–CTABr micelles.     

Effects of Organic Salts on the Rate of Alkaline Hydrolysis of Phthalimide in the Presence Ofcationic Micelles

Pseudo-first order rate constants (k_obs) for alkaline hydrolysis of phthalimide (PTH), obtained at constant concentration of cetyltrimethylammonium bromide (CTABr) and 35°C, vary with the concentration of organic salts ([MX]) according to the relationship: k_obs = (k₀ + K [MX])/(1 + K [MX]) where and K are empirical parameters. The values of K at 0.01 M CTABr are nearly 2 times larger than the corresponding K values at 0.02 M CTABr for sodium benzoate, disodium phthalate and disodium isophthalate.     

Surface charge modulation of poly(ethylene glycol)–poly( , -lactide) block copolymer micelles: conjugation of charged peptides

Block copolymer micelles with aldehyde functionality were prepared in aqueous medium by dialyzing the N,N-dimethylacetamide solution of α-acetoxy-poly(ethylene glycol)-poly( , -lactide) block copolymer (acetal-PEG–PDLLA) against water, followed by mild acid treatment to convert the acetal moiety of the micelle to the aldehyde group. Peptidyl ligands (phenylalanine (Phe) and tyrosyl–glutamic acid (Tyr–Glu)) were then chemically conjugated to the micelle through Schiff base formation and successive reductive amination using NaBH₃CN. Micelles with peptidyl ligands thus prepared have a size of approximately 40 nm with extremely narrow distribution (μ₂/ ²<0.1) based on cumulant analysis of dynamic light scattering. A maximum 53% of the PEG-chain end of the micelle could be converted into peptidyl groups. Zeta potential values of Tyr–Glu derivatized micelles were well correlated with the amount of conjugated ligands, controllable over the range of 0 to−9 mV in sodium phosphate buffer (pH 7.4, 10 mM). These micelles with peptidyl ligands may have a utility for exploring the effect of the surface charge on the pharmacokinetic behavior of particulate systems as well as for modulated drug delivery where cellular peptidyl receptors play a substantial role.     

Lactic acid‐ and carbonate‐based crosslinked polymeric micelles for drug delivery

Our objective was to synthesize and evaluate lactic acid‐ and carbonate‐based biodegradable core‐ and core‐corona crosslinkable copolymers for anticancer drug delivery. Methoxy poly(ethylene glycol)‐b‐poly(carbonate‐co‐lactide‐co‐5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxane‐2‐one) [mPEG‐b‐P(CB‐co‐LA‐co‐MAC)] and methoxy poly(ethylene glycol)‐b‐poly(acryloyl carbonate)‐b‐poly(carbonate‐co‐lactide) [mPEG‐b‐PMAC‐b‐P(CB‐co‐LA)] copolymers were synthesized by ring‐opening polymerization of LA, CB, and MAC using mPEG as an macroinitiator and 1,8‐diazabicycloundec‐7‐ene as a catalyst. These amphiphilic copolymers which exhibited low polydispersity and critical micelle concentration values (0.8–1 mg/L) were used to prepare micelles with or without drug and stabilized by crosslinking via radical polymerization of double bonds introduced in the core and interface to improve stability. mPEG₁₁₄‐b‐P(CB₈‐co‐LA₃₅‐co‐MAC_2.5) had a higher drug encapsulation efficiency (78.72% ± 0.15%) compared to mPEG₁₁₄‐b‐PMAC_2.5‐b‐P(CB₉‐co‐LA₃₉) (20.29% ± 0.11%).¹H NMR and IR spectroscopy confirmed successful crosslinking (～70%) while light scattering and transmission electron microscopy were used to determine micelle size and morphology. Crosslinked micelles demonstrated enhanced stability against extensive dilution with aqueous solvents and in the presence of physiological simulating serum concentration. Furthermore, bicalutamide‐loaded crosslinked micelles were more potent compared to non‐crosslinked micelles in inhibiting LNCaP cell proliferation irrespective of polymer type. Finally, these results suggest crosslinked micelles to be promising drug delivery vehicles for chemotherapy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Physicochemical investigation of cobalt–iron cyanide nanoparticles synthesized by a novel solid–solid reaction in confined space

Cobalt–iron cyanide (Co_x[Fe(CN)₆]) nanoparticles have been synthesized by a novel solid–solid reaction in the confined space of dry sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles dispersed in n-heptane. The reaction has been carried out by mixing two dry AOT/n-heptane solutions containing CoCl₂ and K₄Fe(CN)₆ or K₃Fe(CN)₆ nanoparticles in the micellar core, respectively. By UV-Vis spectroscopy it was ascertained that, after the mixing process, the formation of stable nanoparticles is fast and complete. Microcalorimetric measurements of the thermal effect due to the Co_x[Fe(CN)₆] nanoparticle formation allowed the determination of the stoichiometric ratio (x) and of the molar enthalpy of reaction in the core of AOT reversed micelles. The observed behavior suggests the occurrence of confinement effects and surfactant adsorption on the nanoparticle surface. Further structural information was achieved by small-angle X-ray scattering (SAXS) measurements. From all liquid samples, interesting salt/AOT composites were prepared by simple evaporation of the apolar solvent. Size, crystal structure, and electronic properties of Co_x[Fe(CN)₆] nanoparticles containing composites were obtained by wide-angle X-ray scattering (WAXS) and X-ray photoelectron spectroscopy (XPS).     

Spectrophotometric study of thiocyanato complexation of cobalt(II) and nickel(II) ions in micellar solutions of a nonionic surfactant triton X-100

Complexation of cobalt(II) and nickel(II) with thiocyanate ions has been studied by precise spectrophotometry in aqueous and micellar solutions of a nonionic surfactant Triton X-100 of varying concentrations (20–100 mmol-dm^–3). With regard to cobalt(II), the formation of [Co(NCS)]⁺, [Co(NCS)₂], and [Co(NCS)₄]^2– was established. The formation constant of [Co(NCS)₄]^2–, is increased with increasing concentration of the surfactant, suggesting that the [Co(NCS)₄]^2– complex is formed in micelles. In contrast, the formation constants of [Co(NCS)]⁺ and [Co(NCS)₂] are remained practically unchanged. On the other hand, with nickel(II), the formation of sole [Ni(NCS)]⁺ and [Ni(NCS)₂] was established in both aqueous and micellar solutions examined, their formation constants being also remained unchanged. Interestingly, no higher complex was confirmed in the nickel(II) system, unlike cobalt(II). The unusual affinity of the [Co(NCS)₄]^2– complex with micelles will be discussed from thermodynamic and structural points of view.     

A new semiempirical kinetic method for the determination of ion exchange constants for counterions of cationic micelles: Study of the rate of pH‐independent hydrolysis of phthalimide as the kinetic probe

Pseudo‐first‐order rate constants (k_obs) for pH‐independent hydrolysis of phthalimide ( 1 ), obtained at a constant total concentration of cetyltrimethylammonium bromide and hydroxide ([CTABr]_T), 2.0 × 10^?4 M 1 , 0.02 M MOH (M⁺ = Li⁺, Na⁺ and K⁺) and various concentrations of inert salt MX (= LiCl, LiBr, NaCl, NaBr, KCl and KBr), follow a relationship derived from the pseudophase micellar (PM) model coupled with an empirical equation. This relationship gives empirical constants, F_X/S and K_{X /S}, with S representing anionic 1 . The magnitude of F_X/S is the measure of the fraction of micellized anionic 1 (S^?_M) transferred to the aqueous phase by the limiting concentration of X^?. The value of K_X/S is the measure of the ability of the counterions (X^?) to expel the reactive counterions (S^?) from the cationic micellar surface to the aqueous phase. The values of F_{X/ S} are ～ 1 for MBr (M⁺ = Li⁺, Na⁺ and K⁺) and in the range ? 0.7 to ? 0.5 for MCl (M⁺ = Na⁺ and K⁺) at 0.006, 0.010 and 0.016 M CTABr. For LiCl, the values of F_X/S become ～1 at 0.006 and 0.010 M CTABr and 0.8 at 0.016 M CTABr. The values of the empirical constants, F_X/S and K_X/S, have been used to determine the usual ion exchange constant (K^Cl_Br). The mean values of K^Cl_Br are 3.9 ± 0.5, 2.7 ± 0.1, and 2.6 ± 0.3 for LiX, NaX, and KX, respectively. These values of K^Cl_Br are comparable with those obtained directly by other physicochemical techniques. Thus, this new method for the determination of ion exchange constants for various counterions of cationic micelles may be considered as a reliable one. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 9–20, 2011     

Kinetics and mechanism of alkaline hydrolysis of 4‐nitrophthalimide in the absence and presence of cationic micelles

Pseudo‐first‐order rate constants (k_obs) for alkaline hydrolysis of 4‐nitrophthalimide (NPTH) decreased by nearly 8‐ and 6‐fold with the increase in the total concentration of cetyltrimethyl‐ammonium bromide ([CTABr]_T) from 0 to 0.02 M at 0.01 and 0.05 M NaOH, respectively. These observations are explained in terms of the pseudophase model and pseudophase ion‐exchange model of micelle. The increase in the contents of CH₃CN from 1 to 70% v/v and CH₃OH from 0 to 80% v/v in mixed aqueous solvents decreases k_obs by nearly 12‐ and 11‐fold, respectively. The values of k_obs increase by nearly 27% with the increase in the ionic strength from 0.03 to 3.0 M. The mechanism of alkaline hydrolysis of NPTH involves the reactions between HO^? and nonionized NPTH as well as between HO^? and ionized NPTH. The micellar inhibition of the rate of alkaline hydrolysis of NPTH is attributed to medium polarity effect. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 407–414, 2001     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Interaction between Nickel(II) and Anions of Short-Chain Dialkyl Dithiphosphoric Acids in Aqueous Surfactant Solutions

Spectrophotometry was used to study the complexation of nickel(II) with anions L^– of diisopropyl and dibutyl dithiophosphoric acids in water and aqueous solutions of nonionic surfactant, Triton X-100 (T). Weak bis-complexes [NiL₂], whose formation are stimulated by the addition of nonionic surfactant, were found in water. Within the framework of simple model including equilibria of the formation of micelle-bound complexes {[NiL₂]T} and ligand associates {LT₂ ^-}, the values of logK = 3.87 ± 0.01 and 1.3 ± 0.3 for diisopropyl dithiophosphoric acid anions and logK = 5.47 ± 0.03 and 2.8 ± 0.2 for dibutyl dithiophosphoric acid anions, respectively, were calculated. The obtained results showed that the stability of associates of hydrophobic anions of dialkyl dithiophosphates and their nickel bis-complexes with nonionic micelles increases with the length of ligand chain.     

The effect of complexing agents on the DMF–chromium(VI) reaction. A kinetic study

The kinetics of the reduction of chromium(VI) by dimethylformamide (DMF) in the presence of ethylenediaminetetraacetic acid (EDTA) and 2,2-bipyridyl (bpy) was investigated in aqueous HClO₄ acid solutions spectrophotometrically. The experimental findings, that the reaction has an induction period followed by autoacceleration, is explained. After the reduction, chromium(III) is present as the EDTA- and bpy-complexes, although such complexes form very slowly under the same experimental conditions from chromium(III) and the EDTA and bpy, respectively. Increases in the reaction rate with increasing [EDTA] were observed, while added bpy had negligible effect on the reaction rate. The reaction is first-order each in [Cr^VI] and [H⁺]. The first-order kinetics with respect to EDTA at low concentrations shift to zero-order at higher concentrations. The reaction is considered to proceed through the formation of a very stable chromium(VI)–DMF–EDTA complex. The suggested mechanism refers only to the induction period of the reaction. The net rate of oxidation of DMF, as measured by the consumption of chromium (VI), is given by: –d[Cr^VI]/dt = kK ₁ K _b[H⁺][DMF]_T[EDTA][Cr^VI]_T/(1 + K ₁[EDTA])(1 + K _b[H⁺])     

Amphiphilic diblock copolymers based on poly(2‐ethyl‐2‐oxazoline) and poly(4‐substituted‐ε‐caprolactone): Synthesis,characterization, and cellular uptake

Amphiphilic diblock copolymers with various block compositions were synthesized on poly(2‐ethyl‐2‐oxazoline) (PEtOz) as a hydrophilic block and poly(4‐methyl‐ε‐caprolactone) (PMCL) or poly(4‐phenyl‐ε‐caprolactone) (PBCL) as a hydrophobic block. These PEtOz‐b‐PMCL and PEtOz‐b‐PBCL copolymers consisting of soft domains of amorphous PEtOz and PM(B)CL had no melting endothermal peaks but displayed T_g. The lower critical solution temperature (LCST) values for the PEtOz‐b‐PMCL, and the PEtOz‐b‐PBCL aqueous solution were observed to shift to lower temperature than PEtOz homopolymers. Their aqueous solutions were characterized using fluorescence techniques and dynamic light scattering (DLS). The block copolymers formed micelles with critical micelle concentrations (CMCs) in the range 0.6–11.1 mg L^?1 in an aqueous phase. As the length of the hydrophobic PMCL or PBCL blocks elongated, lower CMC values were generated. The mean diameters of the micelles were between 127 and 318 nm, with PDI in the range of 0.06–0.21, suggesting nearly monodisperse size distributions. The drug entrapment efficiency and drug‐loading content of micelles depend on block polymer compositions. In vitro cell viability assay showed that PEtOz‐b‐PMCL has low cytotoxicity. Doxorubicin hydrochloride (DOX)‐loaded micelles facilitated human cervical cancer (HeLa) cell uptake of DOX; uptake was completed within 2 h, and DOX was able to reach intracellular compartments and enter the nuclei by endocytosis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2769–2781     

Electrocatalytic response of carbohydrates at copper-alloy electrodes

The voltammetric responses observed for carbohydrates and polyalcohols at 0.60 V in 0.10 M NaOH are significantly larger at preanodized CuMn (95:5) electrodes as compared to preanodized pure Cu electrodes. Apparent values for the number of electrons transferred (n_app) and the corresponding values of heterogeneous rate constants (k_app) are estimated for selected reactants from the slopes and intercepts, respectively, of Koutecký–Levich plots of background-corrected voltammetric currents obtained at CuMn and Cu rotated disk electrodes (RDEs). Values of n_app (and k_app) for sorbitol and glucose are 11.8 (9.2×10⁻³ cm s⁻¹) and 11.7 (8.0×10⁻³ cm s⁻¹), respectively, at a CuMn RDE. These are compared to the values 10.4 (1.8×10⁻³ cm s⁻¹) and 9.6 (2.0×10⁻³ cm s⁻¹) for sorbitol and glucose, respectively, at a Cu RDE. The larger sensitivities observed at the CuMn RDE in comparison to the Cu RDE are concluded to be the beneficial result of larger k_app values at the alloy electrode. Furthermore, the larger k_app values are speculated to result from enhanced preadsorption of the reactant species at Mn(IV) sites in the preanodized CuMn surface. In flow-injection measurements, the peak signals obtained for successive injections of glucose using a CuMn electrode (0.60 V vs. SCE) were quite stable with a standard deviation of 1.5%. However, large day-to-day variations (±15%) observed in the average peak signals are attributed to the temperature sensitivities of the k_app value and the diffusion coefficient for glucose.     

Self aggregation of binary mixtures of sodium dodecyl sulfate and polyoxyethylene alkyl ethers in aqueous solution

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter ₁₂ and the chain–chain contribution parameter (B₁) are extracted from the analysis of the results. This parameter B₁ is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.     

Protolytic equilibria of 2-hydroxytropolone (4,5-d) thiophene in homogeneous and micellar solutions

The present study comprises an investigation of the optical absorption and fluorescence spectra of the title compound (HT) in homogeneous solutions of ethanol, cyclohexane, and sulphuric acid, and in aqueous micellar systems of anionic (NaLS), cationic (CTABr) and non-ionic (Triton X-100) surfactants.This compound behaves as monoprotic acid in buffer solutions of pH = 1–13 containing 3% v/v ethanol. It has pK = 8.2, but in the first excited singlet state the p_K* drops to 3.9. However, another protolytic equilibrium is established with pK₂ = 0.45 and pK*₂ = 2.15 in concentrated H₂SO₄ solutions.Contrary to all other media studied, the dissociated form of HT was observed in CTABr micellar solution with an apparent red shift indicating that the HT molecules are incorporated into the detergent layer of the micelles and at the interface of the aggregates.The influence of micellar solutions on the acid—base equilibrium of HT reveals that the effect of the charge distribution of the counter ions in the double layer is much larger than the effective dielectric constant at the site of solubilization.     

Catalytic effects of cationic nanoparticle (CTABr/NaX/H<Subscript>2</Subscript>O,X = Cl,Br) for the piperidinolysis of phenyl salicylate ions

The expression of pseudo-second-order rate constants (k _X) for cationic nanoparticle (CN) [CTABr/NaX/H₂O, X = Br, Cl, CTABr = cetyltrimethylammonium bromide] catalyzed piperidinolysis-ionized phenyl salicylate (PSa^–), at constant [CTABr]_T, 0.1 M piperidine (Pip), and 35°C, were calculated from the relationship: k _obs = (k ₀ + k _X[NaX])/(1 + K ^X/S[NaX]), in which k ₀, k _X, and K ^X/S are constant kinetic parameters and k _obs represents the pseudo-first-order rate constant for Pip reaction with phenyl salicylate ion in the presence of CN. The source of the large catalytic effect of CN catalyst was shown to be due to the transfer of PSa^– from pseudo-phase of the CNs to the bulk aqueous phase through X^–/PSa^– ion exchange at the surface of the CNs.