The partitioning of primary alcohols into the aggregates of gemini amphiphiles determined from diffusion NMR experiments.

The partition constants (p-values) of primary alcohols in solutions containing aggregates of symmetric gemini surfactants of the family N,N'-dimethyl, N-dialkyl-α,ω-alkanediammonium dibromide (m-s-m = symmetric gemini surfactants) have been computed from the measured values of their diffusion coefficients obtained from NMR-diffusion experiments. From the p-values, both mole-fraction and concentration-based partition coefficients and Gibbs energies of transfer for the alcohols from the bulk D2O phase to the gemini aggregate phase have been calculated. As expected, the Gibbs energy of transfer decreased linearly with an increase in the alcohol carbon length for each of the primary alcohol/gemini amphiphile series studied. The Gibbs transfer energy increment per CH2 for the alcohols was consistent for all the alcohol/gemini amphiphile series and was in excellent agreement with the values measured for the same primary alcohol series in conventional single-headed, single-tailed surfactants. Surprisingly, the partition coefficients of the alcohols in the symmetric gemini aggregates exhibited little, if any, dependence on the spacer length of the gemini amphiphiles and were remarkably consistent as the length of the main surfactant chain increased at constant spacer length. When these results are compared to the partition coefficients of the same alcohols in corresponding monomeric surfactants, we observe little difference in the thermodynamic driving forces governing the transfer of alcohols from water to the aggregates of either monomeric or symmetric gemini surfactants.

Improved Green Synthesis and Crystal Structures of Symmetrical Cationic Gemini Surfactants.

Gemini surfactants are composed of two hydrocarbon tails with corresponding polar headgroups, linked via a covalent spacer. The synthesis of these surfactants is a very active area of research due to their application as catalysts and other applied areas of study. The modification of green microwave techniques developed in our research on ionic liquids has resulted in the significant improvement of the synthesis of N,N'-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide (m-s-m type) symmetrical gemini surfactants. This approach utilizes a remarkably more economical, green, and sustainable methodology for the production of symmetrical gemini surfactants that can be utilized in numerous commercial applications. The improved synthetic approach of these gemini surfactants has led to the characterization of their crystalline packing for the first time ever using X-ray crystallographic analysis.

Electrochemical surface-enhanced Raman spectroscopy (E-SERS) of novel biodegradable ionic liquids.

Electrochemical SERS (E-SERS) was used for the first time to study the interfacial behavior of a class of pyridinium-based biodegradable ionic liquids at a silver nanoparticle (AgNP) electrode surface. An isomeric series of ionic liquids (IL) based on 3-butoxycarbonyl-1-methylpyridinium bis(trifluoromethanesulfonyl)imide were prepared, which have demonstrable biodegradability. It was found that all four of the isomeric ionic liquids studied exhibited excellent electrochemical stability as binary mixtures combined with methanol, with the absence of any specific redox processes occurring over nearly 3.0 V of applied potential. Normal Raman measurements of the neat isobutyl IL showed a signal rich in vibrational features, with strong contributions from both the anion and the bulky organic cation. E-SERS of the neat isobutyl IL was shown to exhibit excellent potential stability, with no potential-induced orientational change at the metal surface. When the ionic liquids were prepared as methanolic binary mixtures, dissociation of the IL ions was observed, and only the organic cation was shown to adsorb at the Ag/solution interface. The nature of the substituent on the ester group of the IL series was observed to have a significant effect on the orientation of the cation on the metal surface, based on the application of the metal surface selection rules combined with computational data. Notably, the isobutyl and sec-butyl isomers were observed to have an orientation wherein the pyridinium ring was oriented perpendicular to the surface, while the tert-butyl and n-butyl isomers were observed to have an orientation wherein the pyridinium ring was lying flat on the metal surface.

Two-step iron(0)-mediated N-demethylation of N-methyl alkaloids.

A mild and simple two-step Fe(0)-mediated N-demethylation of a number of tertiary N-methyl alkaloids is described. The tertiary N-methylamine is first oxidized to the corresponding N-oxide, which is isolated as the hydrochloride salt. Subsequent treatment of the N-oxide hydrochloride with iron powder readily provides the N-demethylated amine. Representative substrates include a number of opiate and tropane alkaloids. Key intermediates in the synthesis of semisynthetic 14-hydroxy pharmaceutical opiates such as oxycodone and oxymorphone are also readily N-demethylated using this method.

Spontaneous vesicle formation with an ionic liquid amphiphile.

A simple and effective method for the formation of stable multilamellar vesicles is reported as a potential application of ionic liquid materials (IL's) and as replacements for conventional surfactants used in such applications. The methodology is based on the various approaches for the formation of vesicles from oppositely charged surfactants. Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) have been used to estimate the size of the aggregates; the TEM studies have also revealed morphological differences in the self-assembled systems with changing ionic liquid material. Size measurements from PCS indicate consistent growth of the ionic-liquid containing vesicles with increasing concentration of added anionic surfactant. 2D NOESY NMR spectroscopy have been used to examine the manner in which IL amphiphile self-assembles with the second surfactant in solution. A comparison has been made between the aggregates formed from hexylpyridinium tetrafluoroborate ([HexPy][BF4-])/sodium dodecylsulfate (SDS) and hexylpyridinium bromide ([HexPy][Br])/sodium dodecylsulfate (SDS).

Removal of metal ions from aqueous solutions using chelating task-specific ionic liquids.

A new class of imidazolium salts with appended aminodiacetic acid moieties as di-tert-butyl esters has been synthesized. An improved synthetic route compared to that previously reported is described. These task specific ionic liquids have been used for the formation of metal chelates with Cu(II), Ni(II) and Co(II) in aqueous solutions. The hydrophobicity and solubility of these metal complexes has been fine-tuned by changing the properties of the imidazolium salts from which they are derived through the introduction of alkyl chains onto the imidazolium core.

Salicylaldoxime and salen containing imidazolium ionic liquids for biphasic catalysis and metal extractions.

Imidazolium salts containing salicylaldoxime or salen ligands readily form ionic metal complexes with copper and manganese; hence offering applications in metal extractions and biphasic catalysis.

Metal chelate formation using a task-specific ionic liquid.

An imidazolium-based task-specific ionic liquid containing an ethylaminediacetic acid moiety readily results in the formation of 2:1 octahedral chelate complexes with aqueous Co2+, Ni2+, and Cu2+.

Silylstannations of alpha,beta-unsaturated carbonyl compounds via the generation of Bu3Sn- in ionic liquids.

The tributylstannyl anion, Bu3Sn-, can be generated in imidazolium based ionic liquids from Me3SiSnBu3 and reacted with alpha,beta-unsaturated carbonyl compounds to afford 3-tributylstannylated products in good yields.

A reassessment of the transition-metal free suzuki-type coupling methodology.

We present here a reassessment of our transition-metal free Suzuki-type coupling protocol. We believe that, although the reaction can be run without the need for addition of a metal catalyst, palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate are responsible for the generation of the biaryl rather than, as previously suggested, an alternative non-palladium-mediated pathway. We present a revised methodology for Suzuki couplings using ultralow palladium concentrations for use with aryl and vinyl boronic acids and discuss the effects of the purity of the boronic acid on the reaction.

Efficient N-demethylation of opiate alkaloids using a modified nonclassical Polonovski reaction.

A modified Polonovski reaction has been employed to N-demethylate several opiate alkaloids in moderate to high yield. This method provides an alternative to traditional N-demethylation procedures which utilize toxic reagents such as cyanogen bromide or expensive reagents such as vinyl chloroformate. The current synthesis involves N-oxide formation, isolation of the corresponding N-oxide hydrochloride, and an FeSO(4).7H(2)O mediated Polonovski reaction to afford the desired secondary amine.

Silylstannation of terminal alkynes using a recyclable palladium(0) catalyst immobilised in an ionic liquid.

Silylstannanes can be regioselectively added across terminal alkynes in a quantitative fashion in the presence of a palladium(0) catalyst immobilised in the [bmim]PF6 ionic liquid which can be recycled without loss of activity.