Detailed Research Overview
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Department of Chemistry
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In my research group we view a photon both as a reagent (photon
absorption) for initiating photoreactions and as a product (photon
emission) which allows molecules to be imaged in space and time.
Photons as reagents possess some outstanding properties, e.g., they
may be used to selectively excite specific groups of atoms in a
single molecule or a specific molecule in a mixture, because the
light absorption depends on definite and unique electron energy
gaps. This selectivity of photon absorption may be controlled and
varied at will by use of lasers or by a monochrometer. The concentration
of photons may be varied at will by controlling the light intensity.
Photons can even be made optically active by the use of circularly
polarized light. Finally, by use of lasers that can produce short
pulses of light, high concentrations of photons can be injected
into a system to trigger reactions in times as short as a trillionth
of a second (a picosecond). We study the structure and dynamics of a range of reactive intermediates such as carbenes, singlet oxygen, radicals, radical pairs, and biradicals. These species are produced by photochemical excitation. Their chemistry is investigated directly by a range of time-resolved techniques and then characterized in real time by UV-VIS, IR, ESR or NMR analysis. Our group is developing a novel field termed "supramolecular
photochemistry”, or photochemistry beyond the conventional
intellectual and scientific constraints implied by the term "molecular
photochemistry." In supramolecular processes, non-covalent
bonds between molecules play a role analogous to that of covalent
bonds between atoms of a molecule. Many of the supramolecular structures
of interest may be considered as "guest@host" complexes,
where the @ represents a non-covalent bond between guest and host.
Among the host structures investigated are polymers (such as starburst
dendrimers),
porous solids (such as molecular sieve zeolites),
and biological molecules (such as DNA and RNA). Photochemical and photophysical methods are employed
to investigate the structure and dynamics of reactive intermediates
produced by photolysis of guest@host complexes. Current projects
include: the use of photoemission to track mRNA molecules in living
cells with “molecules beacons” which are specifically
designed to “light up” when they hybridize with their
complimentary strand on the mRNA; an investigation of the mechanism
of reversible oxidation of carbon nanotubes; the stereoselective
addition of singlet oxygen to double bonds; the characterization
of the surface of nanocrystals; and the mechanism of paramagnetic
interconversion of electron and spin paired systems. The research of students in my group is strongly interdisciplinary and collaborative. Typically, a student will be working together and actively with other research groups in the Chemistry Department, other departments at Columbia, or even departments in other universities. This approach familiarizes students with the advantages of teamwork in research, and allows students to be exposed to a range of intellectual and scientific methods to solve scientific problems and to be engaged in projects ranging from materials science, to environmental science, to chemical biology. Selected Publications (Recently Published)J. Wu, S. Zhang, Q. Meng, H. Cao, Z. Li, X. Li, S. Shi, D. H. Kim, L. Bi, N.J. Turro, and J. Ju, “3’0-Modified Nucleotides as Reversible Terminators for Pyrosequencing,” Proc. Nat’l. Acad. Soc., 104, 16462-16467 (2007). PDF B. White, S. Banarjee, S. O’Brien, N.J. Turro, and Irving P. Herman, “Zeta-Potential Measurements of Surfactant-Wrapped Individual Single-Walled Carbon Nanotubes,” J. Phys. Chem., C, 111, 13684-13690 (2007). PDF C. Abeywickrama, H. Matsuda, S. Jockusch, J. Zhou, Y. P. Jang, B.-X. Chen, Y. Itagaki, B. F. Erlanger, K. Nakanishi, N. J. Turro and J. R. Sparrow, “Immunochemical Recognition of A2E, a Pigment in the Lipofuscin of Retinal Pigment Epithelial Cells.” Proc. Nat’l Acad. Sci., 104, 14610-14675 (2007). PDF N. Stevens, J. Dyer, A. A. Marti, M. Solomon, and N.J. Turro, “FRETView: A Computer Program to Simplify the Process of Obtaining Fluorescence Resonance Energy Transfer Parameters,” Photochem. Photobiol. Sci., 6, 909-911 (2007). PDF J. Lopez-Gejo, J. T. Kunjappu, J. Zhou, B. W. Smith, P. Zimmerman, W. Conley, and N.J. Turro, “Polycycloalkanes as Potential Third-Generation Immersion Fluids for Photolithography at 193 nm”, Chem Mater., 19, 3641-3647 (2007). PDF A. A. Marti, C. A. Puckett, J. Dyer, N. Stevens, S. Jockusch, J. Ju, J. K. Barton, and N.J. Turro, “Inorganic-Organic Hybrid Luminescent Binary Probe for NDA Based on Spin-Forbidden Resonance Energy Transfer,” J. Am. Chem. Soc., 129, 8680-8681 (2007). PDF I. Washington, J. Zhou, S. Jockusch, N.J. Turro, K. Nakanishi, and J. Sparrow, “Chlorophyll Derivatives as Visual Pigments for Super Vision in the Red,” Photochem. Photobiol. Sci., 6, 775-779 (2007). PDF J. A. Johnson, M. G. Finn, J. T. Koberstein, and N.J. Turro, “Synthesis of Photocleavable Linear Macromonomers by ATRP and Star Macromonomers by a Tandem ATRP-Click Reaction: Precursors to Photodegradable Model Network,” Macromolecules, 40, 3589-3598 (2007). PDF Y. Yagci, S. Jockusch, and N.J. Turro, “Mechanism of Photoinduced Step Polymerization of Thiophene by Onium Salts: Reactions of Phenyliodinium and Diphenylsulfinium Radical Cations with Thiophene,“ Macromolecules, 40, 4481-4485 (2007). PDF S. Jockusch, Q. Zheng, G. S. He, H. E. Pudavar, D. J. Yee, V. Balsanek, M. Halim, D. Sames, P. N. Prasad, and N.J. Turro, “Two-Photon Excitation of Fluorogenic Probes for Redox Metabolism: Dramatic Enhancement of Optical Contrast Ratio by Two-Photon Excitation,” J. Phys. Chem. C, 111, 8872-8877 (2007). PDF M. Halim, M. S. Tremblay, S. Jockusch, N. J. Turro, and D. Sames, “Transposing Molecular Fluorescent Switches into the Near-IR: Development of Luminogenic Reporter Substrates for Redox Metabolism,” J. Am. Chem. Soc., 129, 7704-7705 (2007). PDF E. Sartori, I. V. Khudyakov, X. Lei, and N. J. Turro, “A Time-Resolved Electron Paramagnetic Resonance Investigation of the Spin Exchange and Chemical Interactions of Reactive Free Radicals with Isotopically Symmetric (14N-X-14N) and Isotopically Asymmetric (14N-X-15N) Nitroxyl Biradicals,” J. Am. Chem. Soc., 129, 7785-7792 (2007). PDF A. A. Marti, S. Jockusch, N. Stevens, J. Ju, and N.J. Turro, “Fluorescent Hybridization Probes for Sensitive and Selective DNA and RNA Detection,” Acc. Chem. Res., 40, 402-409 (2007). PDF D. K. Balta, N. Arsu, Y. Yugci, S. Jockusch, and N.J. Turro, “Thioxanthone-Anthracene: A New Photoinitiator for Free Radical Polymerization in the Presence of Oxygen,” Macromolecules, 40, 4138-4141 (2007). PDF S. Funk, U. Burghaus, B. White, S. O’Brien, and N.J. Turro, “Adsorption Dynamics of Alkanes on Single-Wall Carbon Nanotubes: A Molecular Beam Scattering Study,” J. Phys. Chem. C, 111, 8043-8049 (2007). PDF A. Natarajan, L. S. Kaanumalle, S. Jockusch, C. L. D. Gibb, B. C. Gibb, N.J. Turro, and V. Ramamurthy, “Controlling Photoreactions with Restricted Spaces and Weak Intermolecular Forces: Exquisite Selectivity during Oxidation of Olefins by Singlet Oxygen,” J. Am. Chem. Soc., 129, 4132-4133 (2007). PDF P. Deo, N. Deo, P. Somasundaran, A. Moscatelli, S. Jockusch, N.J. Turro, K. P. Ananthapadmanabhan, and M. F. Ottaviani, “Interactions of a Hydrophobically Modified Polymer with Oppositely Charged Surfactants,” Langmuir, 23, 5906-5913 (2007). PDF A.A. Marti, X. Li, S. Jockusch, N. Stevens, Z. Li, B. Raveendra, S. Kalachikov, I. Morozova, J. J. Russo, D. L. Atkins, J. Ju and N.J. Turro, “Design and Characterization of Two-Dye and Three-Dye Binary Fluorescent Probes for mRNA Detection,” Tetrahedron, 63, 3591-3600 (2007). PDF H. Saito, J. Sivaguru, S. Jockusch, J. Dyer, Y. Inoue, W. Adam and N.J. Turro, “Controlled Diastereoselectivity at the Alkene-Geometry through Selective Encapsulation: E-Z Photoisomerization of Oxazolidinone-Functionalized Enecarbamates within Hydrophobic Nano-Cavities,” Chem. Comm., 819-821 (2007). PDF G. E. Khalil, E. K. Thompson, M. Gouterman, J. B. Callis, L. R. Dalton, N. J. Turro, and S. Jockusch, “NIR Luminescence of Gadolinium Porphyrin Complexes,” Chem. Phys. Letts., 435, 45-49 (2007). PDF |
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