The proposed research is based on the hypothesis that the principles of structure-reactivity correlations of molecular chemistry (which is based on the paradigm of intramolecular bonds between the atoms that make up a molecule) can be successfully extended to supramolecular chemistry (which is based on the paradigm of intermolecular bonds between molecules) through the integration of the fundamental concepts of the fields and collaborations involving the PI's laboratory and a national and international group of collaborators. In addition to the electrical interactions between which are the basis for both molecular and supramolecular chemistry, molecules also possess magnetic properties that are related to electron spins and nuclear spins. The rate of change of orientation of electrons spins can control the reactions of electronically excited states and of radical species. The change of the orientation of nuclear spins is the basis of nuclear magnetic resonance spectroscopy. The proposed research will investigate the ability of pairs of electron spins to control chemical processes that are relevant to chemical synthesis and of pairs of nuclear spins to control features of nuclear magnetic resonance spectroscopy that are relevant to magnetic resonance imaging (MRI). Specific examples include (1) the study of the change in nuclear spin orientation of hydrogen molecules (H2) that are contained inside a fullerene, C60 molecule; and (2) the study of the change of electron spin orientation in determining the rate of energy transfer in systems involving luminescent molecular probes of mRNA targets in living cells. In addition to these studies, the proposed research will investigate (3) the synthesis of novel polymer networks by selective polymerization and coupling reactions combined with photochemical cleavage of the polymer networks; and (4) the synthesis of nanoparticles possessing ligands that allow a general and universal modification depending on the desire application of the nanoparticle.
In terms of broader impact and outreach, the PI will (1) continue to identify and establish a interdisciplinary and global network of senior collaborators and their students, from academic institutions and industry; (2) provide collaborators with a multi-user-friendly laboratory at Columbia consisting of state of the art steady state and time resolved laser flash photolysis with luminescence, ESR, IR and UV-VIS absorption detection; (3) present a series of public lectures on the way science operates through paradigms; (4) develop human resources and encouragement of the participation of underrepresented groups through his mentoring of undergraduates, graduate students, postdoctoral associates, visiting scholars and New York City high school teachers.
Understanding the interaction of light and matter is of fundamental interest and important for many current and future technologies. Our research has helped to advance several of these technologies. For example, the ability to rapidly sequence entire human genomes would enable personalized medical treatment with higher success rates. Therefore, DNA sequencing methods need to be developed which are faster and significantly less expensive than current technologies. Sequencing by synthesis is one of the most promising approaches. We have developed photocleavable fluorescence markers (see Image 1) in collaboration with the Columbia University Genome Center for rapid DNA sequencing by synthesis. This new technology is now in the process of being commercialized. Photolithography is a key technology for microelectronic chip manufacturing. The continuous demand for faster computers requires continuous improvements in photolithography. We have explored potential photochemical systems that will meet the challenge of increasing the resolution of photolithographic methods. Polymers have become an irreplaceable part of our daily life. We have explored a wide range of issues and challenges in polymer science: new photoinitiator systems were developed, photopatterning of metal surfaces, synthesis of photodegradable star polymers to generate model polymer networks, and photocrosslinking and cleavage of synthetic polymers and biopolymers. A range of supramolecular host-guest systems were studied to investigate their structure and dynamics. For example, the electron spin communication of molecules inside of a water soluble molecular capsule with molecules outside in the aqueous phase was investigated (see Image 2). The simplest molecule, H2, has two nuclear spin isomers which interconvert rapidly in normal environment. However, if H2 is incapsulated inside a fullerene, C60, interconvertion is slow (several days). Using spin catalysts, such as nitroxides, the rate of H2 spin interconversion can be increased to seconds (see Image 3). To achieve our diverse research we built a interdisciplinary network of over 50 national and international senior collaborators, from academic institutions and industry, who have participated in the accomplished research. The results of our research are documented in 102 publications in scientific journals.
