24273-80-1Relevant academic research and scientific papers
"Snap-shooting" the interface of AOT reverse micelles: Use of chemical trapping
Srilakshmi, Gollapudi Venkata,Chaudhuri, Arabinda
, p. 2847 - 2853 (2000)
The first use of the phenyl cation trapping technique in "snap-shooting" the local molar concentrations of water and sulfosuccinate head-groups in the interfacial region of AOT-2,2,4-trimethylpentane-water reverse micelles has been accomplished. Our results demonstrate that the interfacial concentrations of the sulfosuccinate head-groups in AOT (0.1M)-2,2,4-trimethylpentane-water reverse micelles are remarkably high (2.75-2.34M) across the W0 (the molar ratio of water to surfactant) range 12 to 44. However, the interfacial concentrations of water in AOT-2,2,4-trimethylpentane-water reverse micelles across the same range of solution compositions are significantly lower (27.9-32.0M) than the molar concentration of bulk water (55.5M). The present results provide new insight on the microenvironments of interfacially located enzymes such as lipases entrapped in AOT-2,2,4-trimethylpentane-water reverse micelles, the most extensively exploited reverse-micellar system in micellar biotechnology.
Kinetic method for determining antioxidant distributions in model food emulsions: Distribution constants of t-butylhydroquinone in mixtures of octane, water, and a nonionic emulsifier
Romsted, Laurence S.,Zhang, Jianbing
, p. 3328 - 3336 (2002)
The absence of reliable estimates of distributions of antioxidants in food emulsions hinders the development of a useful method for comparing the efficiencies of antioxidants. Here we describe the application of a pseudophase kinetic model, originally developed for homogeneous microemulsions, to the determination of distribution constants of tert-butylhydroquinone, TBHQ, in a fluid, opaque, model food emulsion composed of the nonionic emulsifier C12E6, octane, and water. This kinetic method should be applicable to a wide variety of charged and uncharged antioxidants in emulsions composed of charged and uncharged emulsifiers. The distribution constants for partitioning of TBHQ between the oil and surfactant film regions, Kol, and the aqueous and surfactant film regions, Kwl, were obtained by fitting changes in first-order rate constants, kobs, with emulsifier volume fraction for the reaction of 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, with TBHQ. The rate of formation of the reduced arene product hexadecyl-2,6-dimethylbenzene, 16-ArH, was followed by HPLC. About 90% of the TBHQ is in the surfactant film at about 2% volume fraction of C12E6, which suggests that this region may be the primary site of antioxidant activity for neutral phenolic antioxidants.
Molecular Dynamics Simulations of the Initial-State Predict Product Distributions of Dediazoniation of Aryldiazonium in Binary Solvents
Cruz, Gustavo N.,Lima, Filipe S.,Dias, Luís G.,El Seoud, Omar A.,Horinek, Dominik,Chaimovich, Hernan,Cuccovia, Iolanda M.
, p. 8637 - 8642 (2015)
The dediazoniation of aryldiazonium salts in mixed solvents proceeds by a borderline SN1 and SN2 pathway, and product distribution should be proportional to the composition of the solvation shell of the carbon attached to the -N2 group (ipso carbon). The rates of dediazoniation of 2,4,6-trimethylbenzenediazonium in water, methanol, ethanol, propanol, and acetonitrile were similar, but measured product distributions were noticeably dependent on the nature of the water/cosolvent mixture. Here we demonstrated that solvent distribution in the first solvation shell of the ipso carbon, calculated from classical molecular dynamics simulations, is equal to the measured product distribution. Furthermore, we showed that regardless of the charge distribution of the initial state, i.e., whether the positive charge is smeared over the molecule or localized on phenyl moiety, the solvent distribution around the reaction center is nearly the same.
Specific ion pairing and interfacial hydration as controlling factors in gemini micelle morphology. Chemical trapping studies
Geng, Yan,Romsted, Laurence S.,Menger, Fred
, p. 492 - 501 (2007/10/03)
Results from chemical trapping experiments in micellar solutions containing 1.5-5 mM aqueous solutions of three didodecyl dicationic dibromide gemini surfactants with different methylene spacer lengths (12-n-12 2Br where n = 2-4 CH2 groups) gav
Revisiting the reactions of nucleophiles with arenediazonium ions: Dediazoniation of arenediazonium salts in aqueous and micellar solutions containing alkyl sulfates and alkanesulfonates and an ab initio analysis of the reaction pathway
Cuccovia, Iolanda M.,Da Silva, Marcia A.,Ferraz, Helena M.C.,Pliego Jr., Josefredo R.,Riveros, Jose M.,Chaimovich, Hernan
, p. 1896 - 1907 (2007/10/03)
Dediazoniation of 2,4,6-trimethylbenzenediazonium tetrafluoroborate, 1-ArN2BF4 (for the z-Ar compounds described in this paper, z refers to the length of the carbon chain of the substituent at C4 of the benzene ring), in aqueous solutions containing sodium methyl sulfate, NaMeSO4, or sodium methanesulfonate, NaMeSO3, yields 2,4,6-trimethylphenol, 1-ArOH, 2,4,6-trimethylphenyl methyl sulfate, 1-ArOSO3Me and 2,4,6-trimethyl-phenyl methanesulfonate, 1-ArO3SMe, respectively. The relative yields of 1-ArO3SMe or 1-ArOSO3Me and 1-ArOH depend on the NaMeSO4 or NaMeSO3 concentrations. 4-n-Hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate, 16-ArN2BF4, was used to determine the local head group concentration in sodium dodecyl sulfate and sodium dodecanesulfonate micelles by chemical trapping comparing the relative product yields with those obtained in water using the short chain analogs. Ab initio calculations of the spontaneous dediazoniation of phenyldiazonium ion in the gas phase, as well as in aqueous solution with, or without, added MeSO3-, yield potential energy surfaces for the reaction. For this model the calculated and experimental values of the spontaneous dediazoniation rate constants in aqueous solution, as well as the product composition, were similar to those obtained with 1-ArN2+. These results suggest that in aqueous solution nucleophiles can only compete with water if a diazonium ion·nucleophile complex is formed prior to N2 loss. Calculations show that the addition of nucleophiles to the arenediazonium ion occurs without a saddle point in the potential energy surface, suggesting that the free phenyl cation is not an obligatory intermediate in aqueous solutions.
Arenediazonium salts: New probes of the interfacial compositions of association colloids. 3.1,2 distributions of butanol, hexanol, and water in four-component cationic microemulsions
Yao, Jihu,Romsted, Laurence S.
, p. 11779 - 11786 (2007/10/02)
Product yields from dediazoniation of 4-hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate, 16-ArN2BP4, bound to aggregates of four-component microemulsions composed of cetyltrimethylammonium bromide, (CTA)Br, H2O, hexadecane, and an alcohol, R'OH, either 1-butanol, BuOH, or 1-hexanol, HexOH, were used to estimate changes in H2O and R'OH compositions at the microemulsion interface over a range of microemulsion compositions. Analysis of % 16-ArOR'/% 16-ArOH product percent yield ratios obtained in the water-in-oil microemulsion region of the phase diagram at low water content show that mass action binding constants for the distributions of BuOH and HexOH between the interfacial and oil regions in these microemulsions are independent of [R'OH]. These results indicate that (CTA)Br mixes ideally with both alcohols and that alcohol binding is driven primarily by the hydrophobic effect with minimal contributions from specific interactions between R'OH and (CTA)-Br. We also show that our approach provides estimates of molar concentrations of BuOH and H2O in the oil. interfacial, and water regions at any composition of these 4-component microemulsions. Changes in the molar concentrations of H2O and BuOH mark the oil-in-water droplets to bicontinuous to water-in-oil droplets transitions. Potential applications of the dediazoniation method are discussed.
Arenediazonium salts: New probes of the interfacial compositions of association colloids. 1. Basic approach, methods, and illustrative applications
Chaudhuri, Arabinda,Loughlin, John A.,Romsted, Laurence S.,Yao, Jihu
, p. 8351 - 8361 (2007/10/02)
Product yields from the reactions of two different arenediazonium salts, z-ArN2+BF4-, bound to cetyltri-methylammonium halide ((CTA)X; X = Cl, Br) micelles and to aqueous three-component (CTA)X microemulsions containing an alcohol (R'′OH), either 1-butanol (BuOH) or 1 -hexanol (HexOH), are "snapshots" of the relative quantities of halide ion, water, and alcohol nucleophiles at the aggregates' interfaces. Yields of aryl ether, aryl halide, and phenol products measured simultaneously by HPLC are consistent with high concentrations of these nucleophiles in the immediate vicinity of the aggregates' interfaces. The interfacial concentration of each nucleophile is estimated from the yield of its respective product over wide ranges of (CTA)X and ROH concentrations by assuming that the selectivities of the long-chain (hexadecyl), water-insoluble, aggregate-bound arenediazonium ions, 16-ArN2+, toward anionic or neutral nucleophiles compared to water are the same as the selectivities of the short-chain (methyl), water-soluble analogues, 1-ArN2+, toward the same nucleophiles in aqueous solutions. The suitability of dediazoniation reactions as interfacial probes and the basic assumptions used in our approach are described. The observed rate constants for dediazoniation of the arenediazonium salts are almost completely independent of the salt, (CTA)X, and R′OH concentrations, consistent with rate-determining loss of N2 to give an aryl cation which reacts at diffusion-controlled rates with available nucleophiles. Salt-induced spectral shifts indicate formation of ion pairs in the ground state, and all our data are consistent with a heterolytic dediazoniation mechanism in which product distributions are determined by the equilibrium distribution of the ensemble of ground-state arenediazonium cation-anion and arenediazonium cation-molecule intimate pairs. Comparisons with previous results and potential applications are briefly discussed. The companion paper shows that ether product yields can also be used to estimate R′OH binding constants over a wide range of alcohol and surfactant concentrations.
Arenediazonium salts: New probes of the interfacial compositions of association colloids. 2. Binding constants of butanol and hexanol in aqueous three-component cetyltrimethylammonium bromide microemulsions
Chaudhuri, Arabinda,Romsted, Laurence S.,Yao, Jihu
, p. 8362 - 8367 (2007/10/02)
Yields of aryl ether products, 16-ArOR′, were determined by HPLC with excellent reproducibility from dediazoniation of 4-hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate (16-ArN2BF4) bound to surfactant aggregates in three-component microemulsions of cetyltrimethylammonium bromide ((CTA)Br), H2O, and an alcohol (R′OH), either 1-butanol (BuOH) or 1-hexanol (HexOH). The results were used to estimate the mole fractions (XA) of R′OH bound to the microemulsions, their mole fraction partition constants (KA), and mass action binding constants (KA′). Values of KA decrease with added R′OH consistent with literature results. Unexpectedly, values of AA′ are constant at all values of XA, indicating that (CTA)Br mixes ideally with both BuOH and HexOH in aqueous microemulsions and that binding of R′OH to (CTA)Br microemulsions is driven by a hydrophobic effect with minimal contributions from specific interactions between R′OH and (CTA)Br.
