The Zink Group
Home | Research | Publications
Functional Mesostructured Materials for Controlled Release
Mesoporous silica nanoparticles and films prepared by surfactant-templated sol-gel techniques are useful supports for the creation of functional materials. When attached to the silica, molecular machines that undergo large-amplitude motions in response to light, redox, pH, or enzyme activation can be used to control the release of guest molecules trapped within the pores of the supports. Three controlled release systems we have focused on include nanoimpellers, nanovalves, and snap-tops. We are interested in designing new systems, as well as improving the biocompatibility and investigating some of the fundamental physical properties of existing systems.
Biological Applications
Various areas of the Zink lab projects are currently being looked at for their use in biological samples and living systems.
Nanoimpeller-controlled mesostructured silica nanoparticles can be used to deliver and release anticancer drugs into living cells under photocontrol, depending on light intensity, irradiation time, and wavelength of the light to activate the nanoimpeller.
The Zink lab is also interested in using biological molecules as targeting agents for the silica nanoparticles. If a cell line over expresses specific protein receptors or responds to certain key amino acid signals, then the biomolecules that interact with the receptors can be attached to the particle as potential targeting agents. This offers refined selectivity for targeting, as the targeting molecule can be adapted to match the receptors that only one cell line expresses, limiting the potential cells that will uptake the particles.
Compounds for Molecular Motion as a State Variable
Compounds that exhibit large amplitude motion upon electrochemical and/or photochemical control can be synthesized and immobilized onto solid supports. Such systems are attached onto various solid supports by functionalizing the compounds with thiols (for gold immobilization) and alkoxysilanes (for silicon immobilization). When these systems are placed between electrodes, they can serve as an on/off switch, based on conductivity or no conductivity of a series of compounds with respect to each other. This area of research is funded by the Center of Functional Engineered and Nano Architectonics (FENA) and is the Theme 1 of five FENA themes. For more information visit: www.fena.org.
The aim of Theme 1 is to create new self assembled and self organized atomic and molecular functional structures. Theme 1 focuses on new materials with novel properties required for device functionality, interconnects to nanoscale devices and interfaces for monolithic, heterogeneous integration. Of prime importance are new nano-structured materials and functional molecular materials that involve both inorganic and organic materials, which assemble themselves into structures that exhibit spatial control at nanometer length scales. Some of these materials, such as the nanowires and molecular switches, can be integrated with ultimate CMOS systems in a seamless manner; the integration will be achieved through a combination of supra-atomic and supramolecular synthesis and nanosubstructure engineering.
Highly Distorted and Coupled Excited States
Our spectroscopic research focuses on understanding the properties of molecules in excited electronic states. This research relies heavily on absorption, emission and resonance Raman spectroscopies in conjunction with the computational methods of the time-dependent theory of spectroscopy. One important area of investigation is the determination of excited state geometries. Upon excitation, transition metal compounds generally undergo large distortions along many normal modes of vibration. These motions are investigated for large amplitude motions with the potential for use as components in photodriven molecular machines.
A second area of investigation concerns coupled excited states. In particular, we are investigating a category of compounds that have mixed valence excited states. Excited state mixed valence (ESMV) exists when a system possesses two or more interchangeably equivalent sites that have different oxidation states in an excited electronic state but a symmetrical charge distribution in the ground electronic state. Molecules that show ESMV demonstrate interesting spectroscopic effects and present unique interpretive challenges.
Photofragmentation and Photodeposition
By utilizing luminescence and mass spectroscopic techniques to study the photolytic properties of metal organic molecules, we have discovered fragmentation pathways and identified the conditions for producing desired materials in the gas phase. We have obtained action spectra and identified the bound or dissociative excited state origins of these species by monitoring the wavelength dependencies of specific photoproducts. Through these studies activation of specific reaction channels to control the photolytic processes are realized. We can use these results to discover deposition conditions which favor the production of the desired material in the gas phase which may have implications for material deposition. Laser photochemistry of volatile metal-containing molecules is used to deposit films and patterned structures of metals and semiconductors on substrates, also known as Laser-Assisted Chemical Vapor Deposition (LCVD).