Lynmarie Posey
Associate Professor Office: 61 Chemistry
Phone: 517-355-9715 210 /
Websites: Research Group - Area
Awards & Honors
Genealogy/Graduates
Cluster Spectroscopy
(Research Description PDF - 1148 kb)Interactions at the molecular level influence the outcome of chemical reactions in condensed phases and control phenomena such as solvation and protein folding. My research group addresses questions related to the roles played by molecular-scale interactions in condensed phases using laser spectroscopy. One aspect of our program focuses on using gas-phase clusters consisting of an ionic chromophore surrounded by a specific number of neutral solvent molecules as models for condensed-phase systems. Gas-phase clusters permit control over the local environment surrounding an ion to an extent that is unattainable in the condensed phase. In this work, laser photodissociation mass spectrometry serves to probe the electronic structure of chromophores in clusters prepared by electrospray ionization. Recently, we have begun to develop the infrastructure required to employ time-resolved fluorescence and resonance Raman spectroscopies to investigate the nature of molecular-scale interactions and the associated dynamics in condensed-phase systems directly. The gas-phase-cluster and condensed-phase studies provide complementary perspectives on the interactions of molecules with their surroundings.
Environmental Effects in Charge Transfer. We have been engaged in studies of the effects of sequential solvation on the energetics of photoinitiated charge transfer. Our studies of metal-to-ligand charge transfer (MLCT) in Fe(II)-polypyridine coordination complexes clustered with solvent have yielded the first direct measurements of the contributions to the solvent reorganization energy from individual molecules found in the first solvent shell. The results from our gas-phase cluster work and vibrational coherence measurements performed by Prof. Warren Beck's research group have led to a collaborative effort to explore the hypothesis that low frequency, intermolecular vibrations with clustered solvent molecules are coupled to light-driven metal-to-ligand and intervalence charge-transfer transitions and control the lifetime of charge-transfer excited states. My research group will be using time-resolved resonance Raman spectroscopy to detect the high-frequency vibrational modes in the Franck-Condon region of the charge-transfer excited state surface, while the Beck group will probe the low-frequency intermolecular vibrational modes coupled to the charge-transfer coordinate using femtosecond vibrational coherence spectroscopy. Understanding the exact nature of the role played by the surrounding environment in charge transfer is important for optimization of solar energy conversion systems.
Protein Refolding and Misfolding. Formation of misfolded proteins has been associated with numerous diseases (Alzheimer's, Parkinson's, Creutzfeldt-Jakob, and bovine spongiform encephalopathy). We are studying the refolding and misfolding of small proteins on the nanosecond to millisecond timescales using tunable pump-probe fluorescence and resonance Raman spectroscopies. In these experiments, protein unfolding is triggered through electronic excitation of a chromophore within the protein by the pump pulse. A probe pulse follows after a specified time-delay, and the fluorescence Stokes shift or time-resolved resonance Raman spectra are used to monitor protein refolding. These studies will probe the structural origin of the stability of the native state and the mechanisms for the formation of misfolded structures.
Selected Publications
Microsolvation of Coordinated Divalent Transition-Metal Ions: Establishing a Spectroscopic Connection with the Condensed Phase, L. A. Posey in Advances in Metal and Semiconductor Clusters; M. A. Duncan, Ed., Elsevier Science B. V., New York 2001, Vol. 5 p. 145.Influence of Sequential Solvation on Metal-to-Ligand Charge Transfer in Bis(2,2',2''-terpyridyl)iron(II) Clustered with Dimethyl Sulfoxide, T. G. Spence, B. T. Trotter, and L. A. Posey, J. Phys. Chem. A 1998, 102, 7779.
Metal-to-Ligand Charge Transfer in the Gas-Phase Cluster Limit, T. G. Spence, B. T. Trotter, T. D. Burns, and L. A. Posey, J. Phys. Chem. A 1998, 102, 6101.
Ligand-Field Photochemistry of the [CuII(bpy)
(serine?H)]+. Complex in the Gas Phase, T. G. Spence, B. T. Trotter, and L. A. Posey, Int. J. Mass Spectrom. Ion Processes 1998, 177, 187.
Controlled Synthesis of Transition-Metal Ion Complex/Solvent Clusters by Electrospray Ionization, T. G. Spence, T. D. Burns, and L. A. Posey, J. Phys. Chem. A 1997, 101, 139.
