What is the direction of learning in on-line and in-class institutions? What are the real-world applications of advanced knowledge? Can in-depth study reveal information that can be broadly applicable to everyday technologies?
Recent examples of in-depth study revealing new technology is in photocatalysis. Materials discovered by group heads such as, Nate Lewis at Caltech, Peidong Yang, Mike Crommie, Jefferey Long, Chris Chang, and T. Don Tilley at UC Berkeley, Daniel Nocera at MIT and Heinz Frei at Berkeley Lab are breaking ground in the artificial photosynthesis field. They are all using metal ions stabilized by carbon, oxygen, nitrogen, and/or silicon-based molecules. These molecules are able to absorb an amount of visible light which is directly related to the excitability of the electrons within these atoms. Not unlike freshman chemistry models of electrons being shared between atoms in molecules to make bonds, these metal-organic (organometallic) systems share their electrons with all of the atoms in the molecule (although not equally). The organic terminology refers to the presence of carbon. Therefore, these molecules are energized by light of a longer wavelength and lower energy than is typical for these atoms on their own; save carbon because it is very versatile when in nano-sized formations. The lower energy (longer wavelength and lower frequency) light absorbed is in the visible spectrum which resonates with the dispersed electron wavefunctions that model the molecule's surface in modern quantum mechanics allowing the molecule's electron to absorb light and become more energetic.
The outstanding properties of some metal complexes comes from the difference between the resting energy (ground state) of the valence (outermost) electron and the next highest allowed energy (excited state) of that electron. The allowed and resting state energy levels are dependent on factors directly related to the unique structure of the molecule. For example, the level of symmetry the molecule has largely affects the allowed electron energies. Almost all octahedral arrangements of atoms around a metal ion (in the center of the octahedron) will have characteristic allowed energies (eg* and t2g). Furthermore, an increase in the effective nuclear charge the valence electron feels reduces it's resting energy making it less excitable by lower energy longer wavelength visible light. For example, the molecules that Frei and Nocera are studying absorb visible light and so are brightly colored, thus they have relatively unstable resting state electrons. Moreover, the metal ions being largely affected by their new electronic environment are able to oxidize water H2O molecules into oxygen gas O2, protons H+, and electrons e-. The enhanced reactivity of metal ions bound to other molecules (glutamate, aspartate, lysine, tyrosine, and other amino acids present in our enzymes)) is how plants achieve photosynthesis; plants use Manganese oxide cube shaped clusters that are buried and bound inside enzymes to do a water oxidation process, then the protons and electrons are transferred through and to several other proteins and small molecules to ultimately be used in converting Carbon Dioxide CO2 into sugar CxH2xOx which is their form of sunlight energy storage and our own body's energy source. Interestingly enough, we do the opposite process in our bodies by converting sugars CxH2xOx and oxygen O2 into carbon dioxide CO2 and water H20.
A prime example of light absorbing metal complexes that transfer energy through excited electrons is chlorophyll a which is a Magnesium ion surrounded by 4 Nitrogen atoms. The nitrogen atoms along with 20 carbon atoms come to form planar cyclic ring molecule that acts as a light antennae for increasing the surface area and energy range of photons that can be absorbed. This forms what is called a square planar metal complex. This complex absorbs light strongly and broadly in the red region of the visible spectrum thereby appearing bright green to our light sensing retinas. Many plants are green due to chlorophyll a and b which absorb light energy and transfer it to other chromophores that shuttle electrons to an enzyme that oxidizes 2 water molecules H20 into oxygen gas O2 and 4 electrons e- and 4 protons H+. The enzyme which does water oxidation has a Magnanese and oxygen MnO cubic cluster that accepts excited electrons from molecules that previously accepted electron energy (chromophores) from chlorophyll that previously accepted energy from photons (light quanta or bundles of energy). The Manganese oxide clusters then react with water to convert it or split it into oxygen gas O2. The resulting electrons and protons H+ from the reaction are then combined with CO2 to produce sugar and water by other enzymes that contain metal ions at their centers, collectively termed metalloenzymes, they use Iron, Nickel, and Copper, among other metals. It turns out our bodies need many of these metal ions to perform these crucial catalytic reactions. Light or electron energy is transported molecule to molecule by a process called charge transfer. Charge transfer occurs when the donor molecule's excited electron energy closely matches the energy of a potential allowed electron configuration in the acceptor molecule (LUMO = Lowest Occupied Molecular Orbital).
My proposal involves using synthetic molecules that absorb the maximum amount of sunlight and coupling them to metal ions which are active for converting 2 protons H+ and 2 electrons to generate hydrogen gas H2. To do this will require a knowledge of inherent allowed excited and resting states of the valence electrons in the proposed molecules. These energies can be probed using ultraviolet and visible light spectroscopy, x-ray photoelectron spectroscopy, and edge x-ray absorption fine structure spectroscopy. The structure of the complexes also play a crucial role in the rate at which electrons are transported across and between molecules. The structure will be probed using x-ray diffraction, nuclear magnetic resonance spectroscopy, diffuse reflectance and infrared spectroscopy. Finally, the catalytic rate of production of hydrogen gas and lifetime of the catalyst will be monitored using gas chromatography and pre and post-test assays. Nature performs proton reduction elegantly using a very complex system, but nature has a lot of other things to worry about, our goal is simply to isolate and amplify a particular chemical transformations to facilitate our energy independence and promote environmental reform. This technology will allow energy to be directly stored in the form of hydrogen gas using only water and sunlight. The trick will be to create a catalyst which is long-lasting, created from abundant metals, and is active enough to produce industrial amounts of hydrogen. This green process will usurp the current coal and natural gas-based cracking processes that generate hydrogen gas and carbon dioxide CO2 using wasting electricity and fossil fuels.
I find myself pensive lately, I have been told I am a doppleganger of a professor of chemistry that will likely be my thesis advisor.
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