Reports: G3
46294-G3 Study the State of Counter-ions in Polyoxometalate Solutions
The project is aiming for understanding the interaction between small counter-ions and giant, porous capsules in solution, as well as the role of counter-ions in the self-assembly of macroions into large blackberry type structures. Our group has obtained important results in the following directions:
1. We used fluorescence, laser light scattering (LLS) and TEM techniques to study the cation transport process across the negatively charged blackberry membrane. The blackberry membrane is a new type of membrane-like, soft, conserved structure formed by the self-assembly of polyoxometalate (POM) macroanions. Blackberry structures have a vesicle-like structure, but they are formed by a single-layer of POMs. Unlike the surfactant bilayer vesicles which are impermeable to small cations, we found that the blackberries allow small cations transport into the cavity inside. The process was monitored by fluorescence spectrometer. Anions are not able to pass the blackberry membrane. The water inside blackberries has different nature from the bulk water. The study can be used as an example of understanding the fundamental interactions between small cations and porous macroanionic systems. Furthermore, this process might be related to some biological processes, such as the cation exchange over the virus capsid shells. (J. Am. Chem. Soc. 2008, 130, 1548-1549)
2. In order to study the radial distribution of small cations around large, porous macroanionic nanocapsules, and how the distribution changes with changing ionic strength, the valent state and/or size of cations, we have applied beam time at the Advanced Photon Source (APS) at Argonne National Laboratory to perform small-angle X-ray scattering (SAXS) experiments. The proposal received very high evaluations and six shifts of beam time was assigned to us at the Beamline 12-ID, one of the best SAXS beamlines at APS. Graduate students Melissa Kistler and Joe Pigga went there and performed SAXS studies with Argonne chemist Dr. Mark Antonio. For the first time, we were able to obtain the radial distribution of small cations around large, porous macroanions. The distribution, and how it changes with increasing salt concentration and/or solvent property, was experimentally determined and then compared with theoretical calculations (done by Professor Chwen-Yang Shew). The results are highly consistent. (Angew. Chem. Int. Ed. 2009, 48, 6538)
3. Studying the interaction between long-chain cationic surfactants and {Mo72V30} macroanions. When the surfactant chains are long enough (over C12), the interaction is stoichiometrical and very strong. Consequently, the effective charge density on the macroions can be successfully decreased, resulting in the formation of larger blackberries. For surfactants with shorter chains, the interaction is weaker as more surfactants exist as single chains in solution. (Langmuir 2009, 25, 7328 7334)
4. For the first time, we studied the self-assembly of POM-organic hybrid materials, a new type of amphiphilic surfactant, in solution. (J. Am. Chem. Soc. 2008, 130, 14408 14409)
Education activities:
Two graduate students (Dong Li and Joseph Pigga) were supported by this grant in the summer of 2008 and 2009, respectively.
The research project supported by the grant has attracted a number of undergraduate students into my lab. Three of them (Yi Lai, Robert DeVito and Williams Yantz) are now working on this project. Robert and Williams get paid hourly for their research work. Yi does not get paid, but earns Lehigh credits instead. They are directly instructed by my graduate students.
The current project will also be part of Lehigh Chemistrys REU (Research for Undergraduate Students) program in the summer. In summer 2008, we accepted an excellent undergraduate student, Ms. Yuriko Takahashi from Augustana College, South Dakota. Yuriko did very well here and later decided to further pursue graduate studies in Chemistry at Syracuse University.
