Zink Group: Home

The Zink Group

Click on a person to see his/her research interest.

From left to right, top to bottom: Ryan Hoekstra, Monty Liong, Eunshil Choi, Dr. Zink, Sanaz Kabehie, Travis Pecorelli, Rachel Stephenson, Paul Sierocki, Yuen Lau, Daniel Ferris, Yaroslav Klichko, Sarah Angelos, Courtney Thomas, Bryana Henderson, Philip Rutkowski, Zongxi Li

Camera shy: Marcelle Dibrell

Last Updated: May, 2008

Sarah Angelos
angelos@chem.ucla.edu

The research I am currently working on in the Zink group involves the synthesis and study of functional silicate materials. We use the sol-gel method to synthesize mesostructured silicates including MCM-41 type particles and 2D hexagonal thin films. These materials are derivatized with functional molecules to produce useful materials with a variety of interesting applications.

Rotaxanes and pseudorotaxanes are switchable molecules which can act as nanovalves when tethered to the surface of mesoporous silica nanospheres. The molecular machines can be made to work under a variety of stimuli, and we are currently trying to design these controlled-release systems so that they are bio-friendly for use in drug delivery applications. Another system of interest involves a photoswitchable molecule, azobenzene. When azobenzene derivatives are tethered to the pore walls of sol-gel materials, the large-amplitude motion that accompanies the photoisomerization can be used to impel other molecules through the nanopores.

Eunshil Choi
echoi@chem.ucla.edu

Mesoporous organic-inorganic hybrid materials are attractive because of their symbiotic properties that result from the organic functionalities and the thermal stablilties of the silica frameworks. Based on such advantages of hybrid materials, my research is focused on the syntheses and applications of molecular machines attached to the pore walls of the mesoporous silica materials. Specifically, I am interested in the light-induced molecular impellers which respond to specific wavelengths so as to control the trap and the release of guest molecules. Especially to apply such photo-responsive machines as a nano-valve in the living cells, my research is paid attention to the syntheses of smaller particles with the molecular machines.

Marcelle Dibrell
mdibrell@chem.ucla.edu

My research is concerned with Excited State Mixed Valence molecules, that is, molecules that have two or more equivalent sites that have different oxidation numbers in the excited state, but symmetrical charge distribution in the ground state. To study this phenomenon, the charge transfer region of the absorption spectrum is examined, showing the characteristic multiple bands due to the coupling that can exist between the excited states. It is the goal of the project to calculate this region of the absorption spectrum by using the relationship between the absorption spectrum and the molecular vibrations that are enhanced in a resonance raman spectrum, that is the vibrations that also play a role in electronic transitions.

Daniel Ferris
dferris@chem.ucla.edu

Currently working on the Zink group's nano-machine's project. Work to date includes production of co-condensed G0 and G1 Azo "wagers" within a pour produced via micelles. Utilization of laser light to induce the cis to trans conformational change may allow for a photon induced mixing motion which has may micro fluidic applications. Utilization of spectroscopic techniques for identification of functionality is up coming. Major interest in the nano-project deals with porous microspheres and the ability to selectively target their uptake into cells. This area has potential applications for a drug delivery system that is capable of acting upon specific cell types rather affecting the biochemistry of the entire organism.

Bryana Henderson
bryana@chem.ucla.edu

I am currently involved in studies concerning photofragmentation of organometallic compounds in the gas phase. Visible and ultraviolet laser pulses intersect with jets of gas containing sublimed precursors, producing fragments that are analyzed with time-of-flight (TOF) and resonance-enhanced multi-photon ionization (REMPI) spectroscopy.

Fragmentation often depends on laser wavelength and fluence, and varying experimental parameters can give interesting insights into the processes involved during fragmentation. Although high mass peaks are common, metal and metal diatomic ions are usually among the most intense peaks in the spectra. Since thin films of metals and select metal diatomics are potentially useful for a wide range of applications (especially electronics), this research lays the foundation for development of new and improved thin films.

Ryan Hoekstra
hoekstry@chem.ucla.edu

I study the the spectroscopic consequences of intramolecular charge transfer using a Marcus-Hush type model and time dependent quantum mechanics. Work on this project involves not only the development of theoretical methods but also spectral characterization of specific examples to confirm/develop theory. Further information available upon request.

Sanaz Kabehie
sanaz@chem.ucla.edu

Copper coordination compounds that exhibit redox induced rotational motion have been synthesized and immobilized onto solid supports. The design of these systems includes three components, a bifunctional stator, a copper (I) or copper (II) metal axle, and a rigid rotator. The bifunctional chelating stators bind to the metal center and are grafted to either silicon or gold supports. The copper compounds contain rotators such as 2,9-dimethyl-1,10-phenanthroline, which is about 1 nm in length. In a typical synthesis a modular approach is used where a stator is chemically bound to a silicon or gold substrate. The stator is next bound to a copper (I) or copper (II) metal center through nitrogen or phosphine bidentate ligands. The last step is the addition of a rigid rotator which also binds to the metal center through bidentate nitrogen ligands.

Solution NMR, SSNMR, EPR, Fluorescence and Absorption Spectroscopies, MALDI TOF-MS, Cyclic Voltammetry and XRD, are characterization techniques used in my project. In addition, I collaborate heavily with Mei Xue from Professor Kang Wang's Lab in the Electrical Engineering department at UCLA, which is part of the FENA collaborative goal.

Yaroslav Klichko
yaroslav@chem.ucla.edu

My research involves design and synthesis of functional materials, which are based on mesoporous thin films. These films serve as a substrate or a framework for attachment of molecular machines such as rotaxanes or azobenzenes. Through careful positioning of the molecules inside mesoporous materials we are able to make molecular devices or novel materials with unique properties.

Yuen Lau
ylau@chem.ucla.edu

I am interested in studying the properties and exploring the various applications of functional organosilica materials.

In particular, the type of mesoporous nanoparticles (MSN) that I am currently studying, synthesized by Inagaki et al, exhibits a crystal-like periodic pore wall structure. The composition of the pore wall consists of a continuum of sets of silicate molecules sandwiching between a biphenylene functional group. The periodicity in conjunction with a large network of resonance along the pore wall has distinguished these MSN from the rest of its family. Upon derivatizing this special type of MSN with functional molecules like rotaxanes and pseudorotaxanes, this new class of material can act as a cargo carrier and release guest molecules that were loaded inside the nanopores, in a controllable fashion via light or chemical stimuli. Another unique feature manifests by these MSN is its capability of being photoactive without any incorporation of photosensitizers. Hopefully, more experiments with various functionalized molecules will be performed to further understand the full chemical properties of this new class of MSN.

Secondly, I am also interested in the biological application of some functionalized organosilica particles that have been studying in our group. More specifically, I am testing their applicabilities in delivering drugs inside cancer cells in a more target-oriented manner.

Zongxi Li
zongxili@chem.ucla.edu

Mesoporous silica nanoparticles functionalized by rotaxanes and pseudorotaxanes as nanovalves and by azobenzene as nanoimpellers have shown interesting control release properties. The purpose of my research is to combine the two kinds of machines to obtain the dual controlled mesoporous silica nanoparticles. I am also interested in visualizing the control release process of nanomachines in living cells using fluorescent microscope.

Monty Liong
mshliong@ucla.edu

Fluorescent mesoporous silica particles

Travis Pecorelli
tpecorel@chem.ucla.edu

My research investigates organic/inorganic hybrid mesoporous frameworks for attaching molecular machines. Highly ordered conjugated spacers, i.e. biphenyl or benzene, within the mesoporous silica allow for experiments involving photochemistry and electron transfer.

Another aspect of the reserach is to break out from exclusively silica frameworks to other transition metal oxide nanoparticles to support molecular machines. The most promising example would be titanium dioxide and possibly other transitional metal oxides.

Philip Rutkowski
prutkow@chem.ucla.edu

Gas phase photofragmentation of organometallic precursors used in laser assisted chemical vapor deposition

Paul Sierocki
psierock@chem.ucla.edu

The research I am conducting in the Zink lab involves the synthesis and characterization of novel functional materials. This lab focuses a lot if it's attention on how light interacts with matter. I make functional materials that respond to light.

Functional Materials

We have devised a method for attaching molecular machines to the pore wall of mesoporous materials. This method is adaptable to a variety of machines. The machine I am working on is azobenzene derivatized with a large dendrimer.

Figure 1: Geometric isomers of Azobenzene

Azobenzene has two geometric isomers (see fig.1), Z (cis) and E (trans), with the E form being more stable by about 50kJ/mol. Irradiating the trans isomer with 351 nm light from our krypton laser produces the cis isomer. Irradiation of the cis isomer with 457 nm light from our argon laser yields the trans isomer. Linking one end of the azobenzene molecule to the silica framework and derivatizing the other end with a large dendrimer produces a molecule that displaces a large volume when forced to go from trans to cis. Applications of such systems include molecular valves and moving molecules through pores via light induced molecular motion.

Rachel Stephenson
rachels@chem.ucla.edu

The research I do in the Zink lab looks to answer questions about what is happening when a molecule is in its excited state. The majority of my work uses resonance Raman spectroscopy to look at the vibrational components of electronic transitions. Knowing what vibrations are active and by how much can help to characterize a charge transfer process, for example. Modeling the systems using the time-dependant theory of spectroscopy can help to pull out from the experimental data parameters of the system such as geometry changes, damping and coupling to other excited states. One part of my research looks to expand our current work on Excited State Mixed Valence (ESMV) by looking at compounds involving one or more transition metals. Example compounds have copper, ruthenium and platinum metal components. A second area of my research looks specifically at the involvement of a solvent in the charge transfer processes. The solvent-solute interaction can be very important and can dramatically change the observed spectroscopic features but separating the solvent contributions from the solute contributions can be difficult. The effect of other coupled states is also investigated in addition to the solvent effects.

Courtney Thomas
courtney.thomas@chem.ucla.edu

Mesoporous silica nanoparticles are of particular interest due to their highly ordered and uniform pores. The hydrophobic nature of the interior of the pores, as well as the ability to functionalize the silica surface with hydrophilic functionalities, makes these particles attractive for anti-cancer drug delivery. I am currently working on a few variations of the basic silica nanoparticles. Adding a magnetic core to the particles is of interest for its potential applications in magnetic resonance imaging, as addition of the magnetic core may make it useful as a contrast agent. Additionally, functionalizing the surface of the particles is important so that particular cells are targeted. Since current cancer therapeutics involve targeting a region of cells, being able to deliver anti-cancer drugs only to the cancer cells without affecting healthy cells would be very beneficial.