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With the support from ACS-PRF we have investigated the ability of various ionic liquids to affect the gelation of molecular organic solvents. Two graduate students, two undergraduate students and one high school student have been involved in various projects, which have been or in the process of being submitted for publications. Details are outlined below.

1. Ionic liquid assisted gelation of an organic molecular solvent
Tetrafluoroborate-containing ionic liquids allow for a room temperature gelation of dimethylsulfoxide, which contains an organogelator at below the minimum gelation concentration. The gel formation has no effect on the mobility of ions as the conductivity values of ionic liquid-DMSO gels are virtually identical to those of ionic liquid-DMSO solutions (Figure 1). The results are published: N. W. Smith, J. Knowles, J. G. Albright, S. V. Dzyuba; Ionic liquid-assisted gelation of an organic solvent. Journal of Molecular Liquids, In Press, doi:10.1016/j.molliq.2010.08.011

In order to understand the mechanistic rationale of the ionic liquid-assested gelation, in collaboration with the group of Professor G. Verbeck at the University of North Texas, we have probed the solvation of ionic liquids by molecular organic solvents using mass spectrometry. It appeared that the nature of the molecular solvent, and the concentration of the ionic liquid in the molecular solvent prior to injection into MS instrument have a significant impact on the aggregation of the ionic liquids. We are exploring various parameters, such as polarity of ionic liquids, intrinsic fluorescence of ionic liquids and the strength of anion-cation interactions (using NMR) in order to identify structural and functional features of ionic liquids that are responsible for the gelation ability of ionic liquids.

2. Silver-free synthesis of nitrate-containing ionic liquids
Nitrate-containing 1-alkyl-3-methylimidazolium ionic liquids, [Cn-mim]NO3, where n = 4, 6, 8, 12, are synthesized in one step by reacting 1-methylimidazole with alkyl nitrates under various conditions without using AgNO3 and 1-alkyl-3-methylimidazolium halides (Scheme 1). The facile nature of this one-step synthesis of [Cn-mim]NO3 should broaden the range of applications of the nitrate-containing ionic liquids.
    The results have been submitted for publication: N. W. Smith, S. P. Gourisankar, J.-L. Montchamp, S. V. Dzyuba, Silver nitrate-free synthesis of nitrate-containing room-temperature ionic liquids. Green Chem. 2010, submitted

3. Sol-gel transitions in molecular-ionic biphasic systems
We continued our studies on evaluating the scope of the gelation of molecular solvents using a two-phase gel system composed of a molecular solvent and an ionic liquid (Figure 2). In addition to imidazolium-based ionic liquids, we have found that similar biphasic gel systems can also be formed by a combination of a specific organogelator, polyethylene glycols and several molecular ionic liquids. The polyethylene glycol-based gel system appears to complement the imidazolium-based gel system: molecular solvents that tend to form biphasic systems with gelled ionic liquids are distinct from those that form a biphasic system with the gelled glycols.
    We are investigating the diffusion process of the fluorescent BODIPY dyes as well as porphyrins and metal porphyrins as a function of the ionic liquids structure, concentration of the organogelator and the nature of the molecular solvent.
    In order to take the full advantage of the ionic liquid-molecular solvent gel systems, we have developed synthetic approaches towards various BODIPY dyes and porphyrin derivatives. The results of this work have been published: ARKIVOC, 2010, 7, 10-18 and Biochem. Biophys. Res. Commun. 2010, 391, 1455-1458.
    Studies on the interphase and within the gel transport of the dyes are ongoing, and they will be submitted for a publication in a due course.

4. Synthesis of novel gel-specific ionic liquids
We have synthesized new chiral, dicationic urea-containing ionic liquid motifs that should be of interest for modulating various supramolecular assemblies, including gel formation (Scheme 2). Although, some urea-containing ionic liquids are known, their applications are limited exclusively to catalysis in the synthetic transformations.
    We also explored the ability of the triazole moiety to serve as a linker that connects two distinct ionic liquid/gelating motifs. In addition, efficient approaches towards the synthesis of modified triazoles were developed and published: Tetrahedron Lett. 2010, 51, 550-553.
Gelating ability of these ionic liquids is currently under investigation.
    Furthermore, we have explored the effect of ionic liquids on quadruple hydrogen bonding motifs, which are are known as viable platforms for directing interactions leading to various assemblies, including organogels and supramolecular polymers. We have prepared a novel chiral ureidopyrimidone 1 (Figure 3) and examined its self-association in molecular and ionic liquids. It appeared that even small variations within the ionic liquids' anionic and cationic counterparts could have a profound effect on the self-assembly of 1. The results of this work are now in preparation for publication.