Presence Of Cationic Micelles Research Articles

Dissociation of the DCF-Hb complex in presence of cationic micelles: A spectroscopic and computational approach

Diclofenac sodium (DCF) is a derivative of phenyl acetic acid and a model representative of the family of non-steroidal anti-inflammatory drugs (NSAIDs). It is extensively consumed for treating inflammation and degenerative disorders like rheumatoid arthritis. The micelles or aggregates of surfactants have ability to solubilize poorly soluble drugs thereby increasing bioavailability of the drugs. Thus, in the current study we have shown a systematic approach for the association of diclofenac with haemoglobin and deintercalation of DCF from hemoglobin (Hb) by hexadecyltrimethylammonium bromide (CTAB) micelles by using various spectroscopic techniques. The fluorescence and UV–visible spectral results revealed that DCF interacts with CTAB micelles and resides in its hydrophobic core. Thus, steady fluorescence and UV–visible measurements provides a strong sign for the relocation of DCF molecules from the hemoglobin interior to the micellar interface of CTAB above cmc. The CD results hinted that CTAB micelles do not disturb the structure of hemoglobin, which further supported that CTAB micelles can be applied as a reliable delivery vehicle for DCF. The present study may be significant for the discovery of improved micelle-based vehicles to the delivery of non-steroidal anti-inflammatory drugs in their targeted site.

Kinetic study on the Oxidation of Dibenzyl Sulfide with iron(III) polypyridyl complexes in the presence of Cationic micelle

Kinetic study on the Oxidation of Dibenzyl Sulfide with iron(III) polypyridyl complexes in the presence of Cationic micelle

Photophysical and photochemical properties of manganese complexes with cationic porphyrin ligands: Effects of alkyl substituents and micellar environment

Abstract Although Mn(III) porphyrins were considered earlier to be very weakly emissive, the fluorescence displayed by Mn(III) complexes with the cationic TMPyP 2+ ligand (H 2 TMPyP 4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin) as well as with its other alkyl (such as hexyl and dodecyl) derivatives proved to be strong enough for a comparative study. Elongation of the alkyl substituent increased both the quantum yield and the lifetime of the emission for the Mn(III) porphyrins, while resulted in an opposite effect for the corresponding free bases in homogeneous solutions. The presence of cationic micelles, however, reversed this tendency regarding the emission lifetime of the complexes. These cationic metalloporphyrins were applied in a photocatalytic system involving triethanolamine (TEOA) as a sacrificial electron donor and methylviologen (MV 2+ ) as an acceptor. In the first step of the catalytic process outer-sphere photoinduced reduction of the metal center took place via quenching of the triplet excited state of these metalloporphyrins by TEOA. The corresponding manganese(II) porphyrins formed in this way were also photoactive; they forwarded an electron to MV 2+ upon irradiation, regenerating the starting complex. Elongation of the alkyl substituents increased the quantum yield of the formation of methylviologen radical (MV ●+ ) in this system, but considerably decreased the durability of the photocatalyst. Anionic micelles totally hindered the photoinduced generation of Mn(II) porphyrins, while cationic micellar environment appreciably increased the efficiency of the accumulation of MV ●+ .

Visible light-induced reduction of Cr(VI) in cationic micelle solution

Cr(VI) reduction was successfully achieved in the presence of cationic micelles (CMs) under visible light illumination. Micelle formation of cationic surfactants seems to be critical in Cr(VI) reduction. Cr(VI) was reduced very fast above the critical micelle concentration (cmc) of CTAB solutions, but was not reduced at all either below or around the cmc of CTAB. The reduction rate of Cr(VI) was enhanced in the absence of dissolved oxygen, supporting that the removal of Cr(VI) should be achieved via a reductive pathway. When CTAB was substituted by Brij 35 or SDS, the reduction of Cr(VI) was negligible. This indicates that the electrostatic interaction between Cr(VI) and headgroups of surfactants is important in the visible light-induced Cr(VI) reduction in micellar solutions.

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.

Kinetics of hydrolysis of procaine in aqueous and micellar media

AbstractThe kinetics of alkaline hydrolysis of procaine under the pseudo–first‐order condition ([OH−] ≫ [procaine]) has been carried out. N,N‐Diethylaminoethanol and p‐aminobenzoate anion were obtained as the hydrolysis product. The rate of hydrolysis was found to be linearly dependent upon [NaOH]. The addition of cationic cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DDTAB) and tetradecyltrimethylammonium bromide, and anionic sodium dodecyl sulfate (SDS) micelles inhibited the rate of hydrolysis. The maximum inhibitive effect on the reaction rate was observed for SDS micelles, whereas among the cationic surfactants, CTAB inhibited most. The variation in the rate of hydrolysis of procaine in the micellar media is attributed to the orientation of a reactive molecule to the surfactant and the binding constant of procaine with micelles. The rate of hydrolysis of procaine is negligible in DDTAB micelles. The observed results in the presence of cationic micelles were treated on the basis of the pseudophase ion exchange model. The results obtained in the presence of anionic micelles were treated by the pseudophase model, and the various kinetic parameters were determined. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 1–9, 2013

Comparative studies on reaction of bis(p-nitrophenyl) phosphate and α-nucleophiles in cationic micellar media

We studied the cleave of bis(p-nitrophenyl) phosphate (BNPP) over a pH range of 7.0–12.0 in the presence of cationic micelles of cetyldiethylethanolammonium bromide, cetyldimethylethanolammonium bromide, cetylpyridinium bromide, cetyltrimethylammonium bromide, and cetylpyridinium chloride by using different α-nucleophiles, viz acetohydroxamate, benzohydroxamate, salicylhydroxamate, butane-2,3-dione monooximate, and α-benzoin oximate ions. With the use of α-nucleophiles in cationic micellar media, the hydrolytic cleavage of BNPP was found to be approximately 105-fold faster than its spontaneous hydrolysis. All reactions followed pseudo-first-order kinetics. The effect of various concentrations of cationic micelles for the reaction of BNPP and α-nucleophiles has been studied. The variation of kobs values of the reactions depends on the micellar structure, that is, head groups, hydrophobic tail length, and counter ion. Copyright © 2012 John Wiley & Sons, Ltd.

Micelles-Assisted Oxidation of Isoleucine: A Kinetic Study

The title reaction has been studied spectrophotometrically as a function of [], [isoleucine], [H2SO4], and temperature in absence and presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). Under pseudo-first order conditions, the reaction follows first order kinetics with respect [isoleucine]. At lower values of [CTAB] (≤40.0 × 10−4 mol dm−3), the catalytic effect of cationic micelles of CTAB may be due to the incorporation/solubilization of isoleucine and into the interfacial region of Stern- and palisade layer.In contrast, at higher values of [CTAB] (≥40.0 × 10−4 mol dm−3), the inhibitory effect was observed due to the dilution.Thermodynamic parameters were computed by studying the reactions at different temperatures (303–333 K). Plausible mechanisms are suggested.

Kinetic study of oxidation of galactose by N-bromo phthalimide in the presence of cationic micelle in acidic medium

The kinetics of micellar catalyzed oxidation of galactose by N-bromophthalimide was studied in the presence of acidic medium at 308 K. The oxidation reaction exhibits first-order kinetics with respect to oxidant (N-bromophthalimide), fractional order with respect to substrate (galactose) and positive fractional order with respect to HClO4 on the rate of reaction. The rate of the reaction increased with decreasing the dielectric constant of the medium. With a progressive increase in the concentration of CTAB, the rate of reaction increased and after reaching peak kobs, decreased at higher concentrations of CTAB. There catalytic roles are best explained by Berezin’s model. The influence of salts on the reaction rate was also studied. The various activation parameters have been calculated. The rate constant and binding constant with the surfactant have also been evaluated. A suitable mechanism consistent with the experimental findings has been proposed.

Effects of [NaBr] on the Rate of Intramolecular General Base-Assisted Hydrolysis of N-(2′-Hydroxyphenyl)phthalimide in the Presence of Cationic Micelles: Kinetic Evidence for the Probable Micellar Structural Transition

Pseudofirst-order rate constants for aqueous cleavage of N-(2'-hydroxyphenyl)phthalimide (1), obtained at 0.001 M NaOH, 2 x 10(-4) M 1, 2% v/v CH(3)CN, and 30 degrees C, show a nonmonotonic decrease with the increase in the total concentration of cetyltrimethylammonium bromide ([CTABr](T)) within its range >/=9 x 10(-5)-<or= 0.17 M. Similar observations have been obtained in the presence of the constant concentration of NaBr at <or=0.02 M. The values of k(obs) become independent of [CTABr](T) at >or=0.04 M CTABr and within a [NaBr] range of 0.0-0.005 M. These observations, in view of the pseudophase (PP) model of the micelle, reveal the presence of presumably spherical micelles at <or=3 x 10(-4) M CTABr in the presence of a constant concentration of NaBr within its range of 0.0-0.01 M. The average value of the CTABr micellar binding constant (K(S)) of ionized 1 (i.e., 1(-)), under these conditions, is (1.88 +/- 0.62) x 10(3) M(-1). The increase in [CTABr](T) at >or=4 x 10(-4) M causes a micellar structural transition from most likely spherical to cylindrical, which is evident from the increase in K(S) values from 3.46 x 10(3) to 11.4 x 10(3) M(-1) with the increase in [CTABr](T) from 4 x 10(-4) to approximately 1 x 10(-3) M in the absence of NaBr. The values of k(obs) at different [NaBr] and at a constant [CTABr](T) follow a kinetic relationship derived from an empirical equation coupled with a PP model of micelle. This relationship gives the value of a kinetic parameter, F(X/S), which represents the fraction of micellized S(-) (S(-) = 1(-)) transferred to the aqueous phase by the limiting concentration of X(-) (X(-) = Br(-)) through ion exchange X(-)/S(-). The value of F(Br/1) is 0.65 +/- 0.12.

The influence of the structural characteristics of the substrate and the medium on the stability of triflusal and acetylsalicylic acid in micellar systems

A spectrophotometric study of the alkaline hydrolysis of two salicylic acid (SA) derived drugs, performed on acetylsalicylic acid (ASA) and triflusal, both in the absence and presence of cationic micelles. In the absence of micelles, a catalytic effect is produced by the favoured OH − ion in the molecule of triflusal, due to the presence of the trifluoromethyl group. The surfactants used were: hexadecyltrimethylammonium hydroxide (HDTAOH), hexadecyltrimethylammonium chloride (HDTACl), hexadecyltrimethylammonium bromide (HDTABr), hexadecylethyldimethylammonium bromide (HDEDABr) and tetradecyltrimethylammonium bromide (TDTABr). In micelles with reactive counterions, the pseudo-first-order rate constant ( k obs) increases with the increase in surfactant concentration, while in micelles with non-reactive counterions, the rate constant increased with surfactant concentration at low concentration, reaching a maximum, and decreased at high surfactant concentration, even to below the value found in the absence of micelle. The micellar binding constant of both drugs ( K S), the micellar rate constant ( k M) and the ion-exchange constant ( K X OH) were determined according to variation in k obs in relation to surfactant concentration, through the application of the pseudophase ion-exchange model (PPIE) proposed. The empirical parameters obtained were found to depend on the substrate and the surfactant structure, these parameters were: the counterion of the micelle, the size of the headgroup and the chain length of the hydrophobic tail of the surfactant.

An empirical approach to study the occurrence of ion exchange in the alkaline hydrolysis of phthalimide in the presence of cationic micelles and inert salts

Pseudo first-order rate constants, k obs, for pH-independent hydrolysis of phthalimide, PTH, obtained at constant [CH 3CN], [CTABr] T (total concentration of cetyltrimethylammonium bromide), and varying concentrations of MX (MX = sodium acetate, sodium butanoate, disodium adipate, sodium phenoxyacetate, sodium 4-methoxybenzoate, sodium 3-, 4- and 2-toluate) follow a relationship derived from an empirical equation coupled with a pseudophase model of micelle. This relationship gives an empirical constant ( K X/S) whose magnitude is the measure of the ability of an ion, X −, to expel another counterion, S −, from a cationic micellar to the aqueous pseudophase. The empirical K X/S is used to derive the usual ion-exchange constant ( K X Y). The values of K X Br have been calculated for all X − ions of the present study, and most of the calculated values of K X Br are comparable with the corresponding K X Br values obtained directly by other physical techniques.

Interactions of gemini cationic surfactants with anionic azo dyes and their inhibited effects on dyeability of cotton fabric

The interactions of two anionic azo dyes, Methyl Orange (MO) and Congo Red (CR), with a series of gemini cationic surfactants and dodecyl trimethyl ammonium bromide (DTAB) in aqueous solution have been investigated by means of UV–Vis spectroscopy. It was observed that the aggregation of surfactant and dye takes place at surfactant concentrations far below the critical micelle concentration of the individual surfactants. Aggregations with anionic dyes were reflected by hypsochromic shifts with a decrease in the intensity of absorption band. Further addition of surfactant results in an absorption spectrum of the dye characteristic in the presence of cationic micelles. The results also show bathochromic shifts for MO followed by sharp increase in intensity of the absorption bands at λ max after the CMC points of these surfactants. Such a behavior is observed for CR solutions in higher surfactant concentrations. The inhibiting effect of cationic surfactants on dyeability of cotton fabric with CR has also been studied at three different temperatures (30, 50, 90–92 °C). Results show large differences between DTAB and gemini cationic surfactants.

Tautomerization of 2-acetylcyclohexanone in assemblies of cationic surfactants

The kinetic study of the keto-enol interconversion of 2-acetylcyclohexanone (ACHE) has been performed in organic solvents such as dimethylsulfoxide, 1-propanol, 2-propanol, methanol, dioxane, tetrahydrofuran and acetonitrile, as well as in aqueous micellar solutions of the cationic surfactants tetradecyltrimethylammonium chloride and tetradecyltrimethylammonium bromide at 25 °C. Either the solvent-assisted or H+-catalyzed reaction rates of tautomerization are reduced in both organic solvents and in micellar medium. In 70% v/v solvent–water or at fixed concentration of any cationic surfactant, the observed rate constant moderately increases with [H+]. The nitrosation of the enol has also been studied in micellar solutions of both cationic and anionic surfactants. Under experimental conditions of first-order dependence on [H+], [nitrite], and [X−] (X = Cl or Br), the presence of cationic micelles reduces strongly the rate of nitrosation, whereas in the presence of anionic micelles, the first-order rate constant, ko, goes through a maximum on increasing the surfactant concentration.

Kinetics and Mechanism of the Reaction of Copper(II)-tryptophan Complex with Ninhydrin in Aqueous and Micellar Media

Kinetics of the title reaction has been investigated spectrophotometrically in aqueous solution as well as in the presence of cetyltrimethylammonium bromide (CTAB) cationic micelles. The reaction rate is first- and fractional-order with respect to [substrate] and [ninhydrin], respectively, both in the absence and presence of cationic micelles. Whereas SDS addition shows formation of a different product, the reaction of copper(II)-tryptophan complex with ninhydrin is catalyzed by CTAB: the maximum rate enhancement being ca . 5-fold. The data are interpreted in terms of the pseudo-phase model (assuming the association/incorporation of both the reactants at the micellar surface). The binding constants of copper(II)-tryptophan ( K S ) and ninhydrin ( K N ) with CTAB micelles have been calculated. The presence of inorganic salts (NaCl, NaBr, NaNO 3 and Na 2 SO 4 ) leads to a decrease in the rate followed by an increase and it is found that tightly bound/incorporated anions are most effective.

An empirical approach to study the occurrence of ion-exchange in the alkaline hydrolysis of phenyl benzoate under the presence of cationic micelles

Pseudo-first-order rate constants (k obs), obtained for the alkaline hydrolysis of phenyl benzoate (PB) at constant [NaOH], [MeCN], [CTABr] T (total concentration of cetyltrimethyl-ammonium bromide) and varying concentrations of MX (where MX = Na 2SO 4, NaF and NaOOCCH 3), follow the relationship: (k obs = k 0 + θ K [MX])/(1+ K [MX]) where θ and K are empirical parameters. The values of θ show a decrease with the increase in [CTABr] T while K values are almost independent of [CTABr] T within its range 0.01 – 0.02 M. The values of θ and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: K OH = K OH 0/(1 + K X/OH [MX]) where K OH and K OH 0 are CTABr micellar binding constants of HO − in the presence and absence of MX, respectively. The values of K X/OH for SO 4 2− are nearly 12- and 9-fold larger than those for F − and CH 3COO − anions, respectively. The values of K remain unchanged with the change in the content of CH 3CN from 2 to6 % v/v at [CTABr] T ≥ 0.01 M for Na 2SO 4 and NaF.

Effects of salts and mixed aqueous-acetonitrile solvent on the rate of alkaline hydrolysis of 4-nitrophthalimide in the presence of cationic micelles

Pseudo-first-order rate constants ( k obs) for alkaline hydrolysis of 4-nitrophthalimide decrease with the increase in [CTABr] T (total concentration of cetyltrimethylammonium bromide) at constant [CH 3CN] and [NaOH]. This micellar effect is explained in terms of pseudophase model of micelle. The increase in the content of CH 3CN from 5 to 15% v/v decreases CTABr micellar binding constant ( K S) of ionized 4-nitrophthalimide (NPT −) from 3650 to 370 M −1, increases the critical micelle concentration (cmc) from 2.8×10 −4 to 7.0×10 −4 M and decreases the pseudo-first-order rate constants ( k M h) for hydrolysis of NPT − in the micellar pseudophase from 3.57×10 −4 to 2.24×10 −4 s −1. The rate constants k obs, obtained at constant [NaOH], [CH 3CN], [CTABr] T and varying concentrations of NaX (X −=Br − and Cl −), follow the relationship: k obs=( k 0′+ θK[NaX])/(1+ K[NaX]), where θ and K are empirical parameters. The values of θ and K are explained in terms of pseudophase model of micelle coupled with an empirical relationship: K S= K S 0/(1+ K X/S[NaX]), where K S is the CTABr micellar binding constant of NPT − in the presence of NaX. The value of K Br/S/ K Cl/S(= K Br Cl) is 3.5.

Cationic Micelles Induced Nitrosation of 1,1,1-Trifluoro-3-(2-thenoyl)acetone in Mild Acid Medium: Reactivity of the Enolate

In a previous paper, it was determined from spectroscopic measurements that 1,1,1-trifluoro-3-(2-thenoyl)acetone (TTeA) was less than 2% enolized in water; the presence of cationic micelles did not increase the enol content, but a strong increase of its acid character was observed; e.g., in 0.02 M tetradecyltrimethylammonium bromide (TTABr), the measured pKa was nearly 3 u lower than that determined in water (Iglesias, E. Langmuir 2000, 16, 8438). In the present work, the nitrosation reaction of TTeA in both water and aqueous micellar solutions of the cationic surfactants TTABr and tetradecyltrimethylammonium chloride is studied. The reaction performed in water at low acidities (e.g., pH > 4) is extremely slow; conversely, in aqueous micellar solutions of cationic surfactants, the reaction is too slow at high acidities (e.g., pH < 2). Cationic micelles induce the nitrosation of TTeA at low acidities because of the rapid formation of enolate anions in the positively charged micellar interface. Rate enhance...

Dual fluorescence of naphthylamines in alkaline aqueous solution

Dual fluorescence was observed with N-(1-naphthyl)aminoacetate (1-NAA) in aqueous solution of pH 13.0 in the presence of cationic surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), below and after the critical micelle concentration (CMC). Similar dual fluorescence was also found with 1- and 2-naphthylamine (1-NA, 2-NA), N-(2-naphthyl)aminoacetate (2-NAA) and (1-naphthyl)ethylenediamine (1-NEDA), in the presence and absence of the cationic surfactants, but not with N, N-disubstituted 1- and 2-NAs. We concluded that the dual fluorescence was due to the excited-state deprotonation of the amino group in these NAs. The p K a *s of the dual fluorescent NAs were estimated to be around 14 from the dual fluorescence pH titrations. No clear correlation was found for p K a * with the amino substitution and the presence of cationic micelle.

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

AbstractPseudo‐first‐order rate constants (kobs) 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 kobs by nearly 12‐ and 11‐fold, respectively. The values of kobs 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 &amp; Sons, Inc. Int J Chem Kinet 33: 407–414, 2001