Effect of micellization on acid dissociation and headgroup conformation of hexadecyl(2-hydroxyethyl)dimethylammonium bromide

Yunes, Santiago Francisco; Foroudian, Houshang J.; Gillitt, Nicholas D.; Bunton, Clifford A.

doi:10.1016/j.colsurfa.2005.05.011

Cited by 5 publications

(6 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The alkyl side chains of all the surfactants were simplified to ethyl groups as the effect of added methylene groups on electronic structure becomes negligible. 27 In light of low aggregation number of 15 reported earlier 15 for C 16 TPB and the low value of 25 for C 16 TBuB determined by our group using steady state fluorescence quenching, 48 the examination at molecular level is relevant. Simple modeling of a micelle of C 16 TPB using GaussView03 visualization program 49 (structure is not reported due to complexity) depicted a significant distance (over 14 Å ) between surfactant head groups.…”

Section: Molecular Modelingmentioning

confidence: 85%

See 1 more Smart Citation

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

Mohareb

Ghosh

Orlova

et al. 2006

J of Physical Organic Chem

View full text Add to dashboard Cite

The effects of alkyltriphenylphosphonium bromides (C n TPB, n ¼ 10, 12, 14, 16) on the rates of S N 2 reactions of methyl 4-nitrobenzenesulfonate and bromide ion have been studied. Observed first-order rate constants are significantly higher than those found for other cationic surfactants for the same reaction. The results have been analyzed by the pseudophase model of micellar kinetics and show true micellar catalysis in the sense that second-order micellar rate constants are higher than the second-order rate constants in water. An attempt has also been made to investigate mixed cationic-cationic surfactant systems with respect to observed rates and pseudophase regression parameters. In addition, modeling of some cationic head groups has illustrated possible differences in head group charges and counterion interactions that may prove kinetically relevant.

show abstract

Section: Molecular Modelingmentioning

confidence: 85%

“…Molecular modeling technique of selective head groups interacting with bromide ion was carried out in the present study, to evaluate structures and charge distribution that may be kinetically relevant. 27,28…”

Section: Introductionmentioning

confidence: 99%

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

Mohareb

Ghosh

Orlova

et al. 2006

J of Physical Organic Chem

View full text Add to dashboard Cite

show abstract

“…The p K a shift in micellar solutions is attributed to the fact that the microenvironment of the solute, particularly the dielectric constant, is different in the micelle and in the bulk aqueous solvent. − , To quantify this effect, the notion of a micellar K a , denoted as K a,m , can be used. K a,m is the value of K a,app in the presence of surfactant only.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, we decided to take advantage of the acid−base properties of the solutes (presence of a carboxylic group) to determine the partition coefficients by the quantitative evaluation of p K a . Indeed, the effect of the micellar systems on the acid−base properties of a large variety of molecules is well- known. − A p K a shift is usually observed in the presence of micelles and can be explained in terms of differences between the properties of the solvent in the bulk and in the micellar pseudophase (modification of the dielectric constant and electrostatic effects) . Pramauro and Pelizzetti first introduced a relation between these p K a shifts and the partition coefficients. , In the present work, this relation is modified by taking into account the micellar pseudophase and bulk volumes.…”

Section: Introductionmentioning

confidence: 88%

Solubilization of Amphiphilic Carboxylic Acids in Nonionic Micelles: Determination of Partition Coefficients from pK_a Measurements and NMR Experiments

et al. 2007

View full text Add to dashboard Cite

The solubilization of octylamidotartaric acid (C8T) and octanoic acid (C8C) in Triton X-100 and Brij 58 nonionic micelles has been studied by pHmetric and 1H NMR self-diffusion experiments. As both C8C and C8T exhibit acid-base properties, a distinction between the partition of the neutral acidic form, in terms of the partition coefficient KPH, and the partition of the charged basic form, in terms of the partition coefficient KP-, has been made. The acidity constants, Ka, of C8T and C8C in the presence of micelles have been evaluated from pHmetric experiments. For both solutes, an increase in the pKa is observed in micellar media due to the difference in the partition of acidic and basic forms of the solutes. A model has been developed to determine KPH and KP- from the pKa shifts observed. The values obtained by this pKa shift modeling method and those from self-diffusion coefficient measurements are in good agreement. The acidic form of C8C is incorporated to a larger extent into the Brij 58 micelles than the acidic form of C8T, whereas the opposite trend is observed for the basic forms. Both the acidic and basic forms of C8T are more easily incorporated into Brij 58 micelles than into Triton X-100 micelles. The influence of the structure of the polar head on the solubilization properties is demonstrated. Moreover, evidence for the localization of the solutes in the micelles is obtained from the comparison of the partition coefficients and from 1H NMR data.

show abstract

“…However, under experimental conditions with pH < 11, the contribution of these pathways to the observed reaction rate is extremely small since, firstly, the values of pK a1 and pK a2 , in all likelihood, are ³12.0 (for choline-like monomeric surfactants IV-VI, the pK a values were found to be~12.9 (IV),~12.4 (V), and~12.7 (VI) [8]) and, secondly, the reactivity of the highly-basic alcoholate ions in water is comparable to or even less than for the hydroxide ion [9]. Thus, taking account of the pK a1 and pK a2 values, the fraction of the reactive anionic form of detergents I and II cannot exceed 5·10 -2 , i.e., the contribution of alcoholysis to the observed reaction rate constant is negligible.…”

mentioning

confidence: 96%

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

et al. 2011

View full text Add to dashboard Cite

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.The enormous interest in recent decades concerning the preparation and study of dimeric (gemini) surfactants and derived organized molecular systems has been due to the unique physicochemical characteristics of these compounds [1, 2], primarily, their anomalously low critical micelle concentrations (CMC » 10 -5 -10 -6 mol/L), which are one or two orders of magnitude less than for the corresponding monomeric surfactants, more efficient lowering of the surface tension of aqueous solutions, better solubilization of compounds with low solubility in water, and micelle polymorphism [2].Gemini surfactants may be seen as a promising basis for organized molecular systems corresponding to the requirements of "green chemistry" for the detoxification and utilization of toxic phosphorus acid esters [3]. The decomposition of ecotoxicants should be carried out under mild conditions using inexpensive and nontoxic solvents. Water is the preferred solvent from this viewpoint but most organophosphorus compounds have low aqueous solubility. This problem may be solved using surfactant additives providing for the solubilization of hydrophobic substrates and an increased rate of nucleophilic substitution reactions, including alkaline hydrolysis. While the effect of monomeric surfactants on the rate of acyl group transfer reactions has been studied in considerable detail [3][4][5], the reactivity of nucleophilic reagents in the presence of gemini surfactant micelles has been studied much less extensively [2,6,7].In the present work, we studied the effect of new gemini surfactants I and II on the rate of alkaline hydrolysis of 4-nitrophenyl diethyl phosphonate (NPDEPS), which is a model analog of highly toxic organophosphorus pesticides and chemical warfare agents. The micellar effects of I and II are comparable to those for cetyltrimethylammonium bromide (CTAB), which is a monomeric surfactant.New gemini surfactants I and II feature a bridging unit (spacer) functionalized by hydroxyl groups. Modification of the spacer by the introduction of hydroxyl groups improves the solubility of these compounds in water since gemini surfactants with the general formula m-s-m [2] have relatively high Krafft temperatures and low solubility in water, which hinders both the 108 0040-5760/11/4702-0108

show abstract

Effect of micellization on acid dissociation and headgroup conformation of hexadecyl(2-hydroxyethyl)dimethylammonium bromide

Cited by 5 publications

References 28 publications

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

Solubilization of Amphiphilic Carboxylic Acids in Nonionic Micelles: Determination of Partition Coefficients from pK_a Measurements and NMR Experiments

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

Contact Info

Product

Resources

About

Effect of micellization on acid dissociation and headgroup conformation of hexadecyl(2-hydroxyethyl)dimethylammonium bromide

Cited by 5 publications

References 28 publications

SN2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

SN2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

Solubilization of Amphiphilic Carboxylic Acids in Nonionic Micelles: Determination of Partition Coefficients from pKa Measurements and NMR Experiments

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

Contact Info

Product

Resources

About

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

S_N2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic‐cationic systems

Solubilization of Amphiphilic Carboxylic Acids in Nonionic Micelles: Determination of Partition Coefficients from pK_a Measurements and NMR Experiments