Catalysis of the alkaline hydrolysis of 4-nitrophenyl diethyl phosphonate by cationic dimeric surfactant micelles

Dimeric (gemini) surfactants containing hydroxyl functional groups have been synthesized and studied. These new surfactants have low critical micelle formation concentrations (<5·10⁻⁵ mol/L) and Krafft temperatures (≤0 °C). Depending on the pH of the medium, the alkaline hydrolysis of 4-nitrophenyl diethyl phosphonate, which is a model of organophosphorus ecotoxicants, proceeds 20–80 times more rapidly in the presence of gemini surfactant micelles than in water.     

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     

Kinetics of the alkaline hydrolysis of isoproturon in CTAB and NaLS micelles

Kinetics of the alkaline hydrolysis of isoproturon has been studied in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (NaLS) micelles. CTAB micelles were found to enhance the rate of reaction, while NaLS micelles inhibited the reaction rate. The reaction obeyed first‐order kinetics in [isoproturon] and was linearly dependent on [NaOH] at lower concentration. The rate of reaction became independent at higher [NaOH]. At lower [NaOH] the reaction proceeded via formation of hydroxide ion addition complex, while at higher [NaOH] the reaction occurred via deprotonation of ? NH? , leading to the formation of isocyanate. The values of k_w, k_m, and K_s were determined by considering the pseudophase ion exchange model. The activation parameters have also been reported. The effect of added salts (NaCl and KNO₃) on the reaction rate has also been studied. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 39–45, 2007     

Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene in a cationic gemini surfactant

Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene (DNCB) in the presence of a conventional cationic surfactant CTAB or a cationic gemini surfactant 1,2-ethane bis(dimethyldodecylammonium bromide) (12-2-12) were studied spectrophotometrically at 25 °C. It was found that both CTAB and 12-2-12 micelles accelerated the alkaline hydrolysis of DNCB, and the binding constant of the substrate to the micelle, K_S, for 12-2-12 (K_S = 310 M⁻¹) was larger than that for CTAB (85 M⁻¹), which suggested that DNCB molecules bound with gemini micelles more easily than with CTAB. However, the second-order rate constant in micellar pseudophase (k_M = 1.22 × 10⁻³ s⁻¹) for 12-2-12 was lower than k_M for CTAB (4.01 × 10⁻³ s⁻¹) because the substrate may enter the interior of the 12-2-12 micelles. It was found also that 12-2-12 had a similar catalysis mechanism to CTAB when the concentration of 12-2-12 was relatively low (ca. <5 mM). However, above this concentration, higher microviscosity and significant increases in aggregation number and micelle size with increased surfactant concentration may remarkably influence the hydrolysis reaction.     

胶束催化对硝基苯酚乙酸酯碱性水解的动力学研究

碱性溶液中羧酸酯的催化水解反应有些报道[1~4],OH-对乙酸酯的亲核进攻,形成了一个阴离子四面体中间物,该四面体中间物的C为sp3杂化,反应裂解成为CH3COO-和对硝基苯酚。然而,目前对胶束溶液中对硝基苯酚乙酸酯的碱性水解方面的系统研究还未见报到,因此,本文在30℃、1·62×10-3     

Inhibiton effect of cationic micelles on the basic hydrolysis of aromatic esters

The basic hydrolysis of 4-acetoxybenzoic acid and 2-naphtyl-acetate have been studied in cationic micelles of N-cetyl-N,N,N-tri-methylaamonium bromide and hydroxide and the results compared with the ones obtained for the basic hydrolysis of acetylsalicylic acid and 3-acetoxy-2-naphtoic acid. The results can be explained with the pseudo-phase kinetic Model and the determined second order rate constants in micelles are also smaller than the second order rate constants in water.     

The effects of cetylpyridinium bromide micelles on the kinetics of alkaline hydrolysis of alkylp-nitrophenyl chloromethylphosphonate

Study of the kinetics of alkaline hydrolysis of alkylp-nitrophenyl chloromethylphosphonates in micellar solutions of cetylpyridinium bromide showed that the observed rate constant depends on the hydrophobicity of the substrates. A minor increase in the length of the alkyl chain in the substituent increases the catalytic effect in the series Et<Bu<C₆H₁₃. Further increase in the substrate hydrophobicity results in a decrease in the bimolecular rate constant in the micellar phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 279–282, February, 1999.     

Ultrafast dynamics of water in cationic micelles

The effect of confinement on the dynamical properties of liquid water is investigated for water enclosed in cationic reverse micelles. The authors performed mid-infrared ultrafast pump-probe spectroscopy on the OH-stretch vibration of isotopically diluted HDO in D(2)O in cetyltrimethylammonium bromide (CTAB) reverse micelles of various sizes. The authors observe that the surfactant counterions are inhomogeneously distributed throughout the reverse micelle, and that regions of extreme salinity occur near the interfacial Stern layer. The authors find that the water molecules in the core of the micelles show similar orientational dynamics as bulk water, and that water molecules in the counterion-rich interfacial region are much less mobile. An explicit comparison is made with the dynamics of water confined in anionic sodium bis(2-ethythexyl) sulfosuccinate (AOT) reverse micelles. The authors find that interfacial water in cationic CTAB reverse micelles has a higher orientational mobility than water in anionic AOT reverse micelles.     

Comparative study of the cationic surfactants and their influence on the alkaline hydrolysis of acetylsalicylic acid

A kinetic study of the reaction of acetylsalicylic acid (aspirin) with sodium hydroxide has been studied in the presence of some conventional and novel cationic surfactants. The pseudo‐first‐order rate constant increases with the surfactant concentration initially and then decreases. In comparison to conventional cationic surfactants, i.e., cetyltrimethylammonium bromide and cetylpyridinium bromide, novel alkyldiethylethanolammonium bromide (R = C₁₆) surfactant accelerated the alkaline hydrolysis significantly. The pseudophase ion‐exchange model has been applied to fit the experimental results. Activation parameters have also been evaluated. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 1–8, 2011     

Encapsulation of DNA by cationic diblock copolymer vesicles

Encapsulation of dsDNA fragments (contour length 54 nm) by the cationic diblock copolymer poly(butadiene-b-N-methyl-4-vinyl pyridinium) [PBd-b-P4VPQ] has been studied with phase contrast, polarized light, and fluorescence microscopies, as well as scanning electron microscopy. Encapsulation was achieved with a single emulsion technique. For this purpose, an aqueous DNA solution is emulsified in an organic solvent (toluene) and stabilized by the amphiphilic diblock copolymer. The PBd block forms an interfacial brush, whereas the cationic P4VPQ block complexes with DNA. A subsequent change of the quality of the organic solvent results in a collapse of the PBd brush and the formation of a capsule. Inside the capsules, the DNA is compacted as shown by the appearance of birefringent textures under crossed polarizers and the increase in fluorescence intensity of labeled DNA. The capsules can also be dispersed in an aqueous medium to form vesicles, provided they are stabilized with an osmotic agent [poly(ethylene glycol)] in the external phase. It is shown that the DNA is released from the vesicles once the osmotic pressure drops below 10(5) N/m(2) or if the ionic strength of the supporting medium exceeds 0.1 M. The method has also proven to be efficient to encapsulate pUC18 plasmid in submicrometer-sized vesicles, and the general applicability of the method has been demonstrated by the preparation of the charge inverse system: cationic poly(ethylene imine) encapsulated by the anionic diblock poly(styrene-b-acrylic acid).     

Effect of counterion geometry on cationic micelles

The critical micelle concentration, aggregation number, and binding properties of decyltrimethylammonium ion micelles are determined as a function of counterion geometry using the dianions of phthalic, isophthalic, and terephthalic acids. Light-scattering methods were used to secure the CMC and AN data whereas binding data were obtained with a specific ion electrode. It is shown that the differences among the micellar parameters are quite small relative to counterion effects induced by variations in polarizability and hydrophobicity. The data are used as evidence for a disorganized micelle surface containing water-filled grooves and fatty patches which do not discriminate among various geometric dispositions of the carboxylates about the aromatic ring.     

Hydration structures of bromides on cationic micelles

The peripheral structures of bromides on dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (HTAB) micelles have been studied by X-ray absorption fine structure (XAFS) at the Br-K edge. The XAFS spectra indicate that water is a dominant scattering group for Br- even in these micellar solutions. However, the oscillation intensity decreases with increasing micellar concentration, suggesting that the bromides are dehydrated to some extent when they are bound to the micelles. A XAFS analysis routine gives unusually short Br-O (water) distances and is inapplicable to the present systems. This comes from the structure of the first coordination shell, in which two or more scattering paths are involved. The second scattering group is obviously the head group of the surfactants forming the micelles. The detailed analysis has allowed us to estimate the hydration number of the bromides bound on the DTAB and HTAB micelles (N = ca. 4.2). The assumption that all of the bromides form direct ion-associates with the head groups causes the contradiction to the results of the XAFS analyses. This strongly implies that some of the bromides partitioned into the micelle are completely hydrated as far as their first coordination shell is concerned. Assuming that the maximum hydration number of the bromides bound to the head groups of the micelle is three, 40% of the bromides partitioned into the micelle are completely hydrated.     

Catalysis by cationic polyelectrolytes and micelles in bisulfite oxidation

The oxidation of sodium bisulfite in the presence of cationic polyelectrolytes or micelles has been studied. The formation of cationic-bisulfite complexes is indicated, and a kinetic analysis suggests the validity of the enzyme kinetics applied to determine the kinetic parameters. Distinct differences in the activity of cationics depend on the configuration of the cationics in solution; micelle-forming cationics are more effective than nonmicellar polycationics, except in the case of poly(diallyldimethylammonium chloride), (PDADM). The oxidation rate is strongly affected by the presence of monomer in the system, especially where nonmicellar polycationics are involved.     

The alkaline hydrolysis of flavonoid glycosides

Conclusions 1. The alkaline hydrolysis of flavonoid glycosides has been studied.2. In an alkaline medium 3-glycosides, C-glycosides, and biosides having 1, 2 bonds between the sugars are stable.3. The difference in the stabilities of the glycosides to alkalis can be used in studying flavonoid O-diglycosides, O-biosides with different positions of the bond, O,C-diglycosides, and O,C-biosides.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 366–369, 1969     

The alkaline hydrolysis of 4-methoxycoumarin

The aqueous alkaline hydrolysis of 4-methoxycoumarin occurs in two stages. In the first, the lactone ring is opened at a rate directly proportional to the concentration of base. In the second, the methoxy group is replaced by an unusual route that depends upon the presence of an $\text{un}$ionised phenolic hydroxy group and is therefore inversely proportional to the concentration of base. Methanolysis by methoxide ion in methanol occurs primarily at position 4 and replaces the methoxy group before the ring is opened; the difference from the aqueous hydrolysis is ascribed to solvent effects.     

Counterion binding on mixed anionic/cationic micelles

Measurements of counterion binding in mixtures of surfactant aqueous solutions have been performed to study the structure of the anionic/cationic mixed micelle/solution interface. The mixtures studied were SDS/DDAC and STS/TDPC. The binding of chloride and sodium ions to mixed anionic/cationic micelles was measured using ion-specific electrodes. Counterion binding was found to be strongly dependent on the molar ratio of surfactants present. The mixed micelle/solution interface includes the headgroups of both surfactants and counterions of surfactant in excess. The addition of oppositely charged surfactant caused an increasing dissociation of counterions.     

Cross-linking of cationic block copolymer micelles by silica deposition

Diblock copolymer micelles comprising cationic poly(2-(dimethylamino)ethyl methacrylate) (PDMA) coronas and hydrophobic poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) cores are used as nanosized templates for the deposition of silica from aqueous solution at pH 7.2 and 20 degrees C. Both noncross-linked and shell cross-linked (SCL) micelles can be coated with silica without loss of colloid stability. Under optimized conditions, the silica deposition is confined to the partially quaternized cationic PDMA chains, leading to hybrid copolymer-silica particles of around 35 nm diameter with well-defined core-shell morphologies. 1H NMR studies confirmed that the PDPA cores of these copolymer-silica particles became protonated at low pH and deprotonated at high pH, which suggests possible encapsulation and controlled release applications. Moreover, in situ silica deposition effectively stabilizes the PDPA-PDMA micelles, which remain intact on lowering the solution pH (whereas the original noncross-linked PDPA-PDMA micelles dissociate in acidic solution). This suggests a convenient route to silica-stabilized SCL micelles under mild conditions.