Reactions
within van der Waals (vdW) clusters, spectroscopy
of small molecules, magnetic field effects, energy
transfer collisions, atmospheric photochemistry.
Molecular recognition, chemical and biological sensors,
immobilization of proteins in sol-gel materials.
Our research group is interested in the photochemistry, chemical dynamics
and structure of vdW clusters, dynamics of elementary reactions and magnetic field studies of non-radiative
transitions. We employ pulsed laser beams to initiate reactions, for excited state preparation, and in
state-resolved detection schemes. Supersonic jet expansions allow the preparation of molecules with "rotational
temperatures" as low as 5 K for spectroscopic studies and the formation of weakly-bound clusters. The laser-initiated processes are probed employing laser fluorescence excitation
(LFE), resonance-enhanced multiphoton ionization time-of-flight (REMPI-TOF) and photoelectron detection techniques.
A project underway examines the photochemistry of (SO2)m(NO)n vdW clusters.
An objective of our work is to advance the photochemistry of sulfur- and nitrogen-containing clusters as this
information is essential to model the photochemistry of the Earth's atmosphere. Students in the group
have obtained numerous unexpected results while investigating these systems. For instance, cationic cluster (e.g.,
SO2-NO+) as well as SO2 fragments (e.g., SO+, S+) are observed upon irradiating the (SO2)m(NO)n clusters
at different laser frequencies. The cluster ion (SO2)2+, which is produced non-resonantly exciting at 266
nm, is not observed in the 222 to 235 nm region, indicating the 2-photon photodissociative ionization
(PDI) of the cluster, (SO2)2 + 2 hn ® SO2+ + SO2 + e-. Another unexpected observation is that the mass-resolved
excitation spectrum (MRES) obtained monitoring the NO-SO+ cluster ion is similar to the 1 + 1 REMPI
spectrum of NO, whereas that of (SO2)2+ resembles the MRES of SO+.
Another project is concerned with the stability of proteins entrapped in sol-gel materials. The interest in immobilizing proteins in porous materials stems from the prospect of enhancing their chemical and thermal stability, to catalyze reactions under non-physiologic conditions and to develop biosensing devices. It is possible to control different physical properties of sol-gels by making changes in the preparation procedures, thereby being able to fine-tune the performance of the biosensors. In a collaborative effort with Professor Morales' group, we are performing spectroscopic and kinetic experiments on phospholipases and azurin (the blue copper protein) immobilized in sol-gel glasses. The activity of these proteins is assessed through chemical and thermal denaturation, reaction kinetics, fluorescence quenching and energy transfer experiments. The next generation of experiments include the immobilization of peptides, antibodies and receptors for clinical applications.
Selected Publications:
A.A. Dixit, Y. Lei,
K.W. Lee, E. Quiñonesand
P.L. Houston, “Dissociation of sulfur dioxide
by ultraviolet multiphoton absorption between 224
and 232 nm” J. Phys. Chem. A, 2005,
109, 1770-1775.
Lymari Fuentes, Jessica
Oyola, Monica Fernandez and Edwin Quinones,
Conformational changes in azurin from Pseudomonas
aeruginosa induced through chemical and physical
protocols, Biophys. J., 87, 1873-1880 (2004).
Yuxiu Lei, Vladimir
I. Makarov, Carlos Conde and Edwin Quinones,
Laser-initiated processes within (SO 2) m(NO) n weakly-bound
clusters, Chem. Phys., 295, 131-136 (2003).
Vladimir I. Makarov
and Edwin Quinones, Magnetic field
quenching of individual rotational levels of the ˜A
1 A u, 2v 3' state of acetylene, J. Chem. Phys.,
118, 87-92 (2003).
Carlos Crespo-Hernandez,
Rafael Arce and Edwin Quinones,
Magnetic field-enhanced photoionization of 6-methylpurine,
Chem. Phys. Lett., 382, 661-664 (2003).
V.I. Makarov, Á.R.
Cruz, and E. Quiñones, "Collisional
Nature of the Magnetic Field Quenching of the Acetylene Ã1Au
State", Chem. Phys. 2001, 264,
101-110.
E. E. Méndez,
C. Crespo-Hernández, R. Figueroa, R. Arce,
and E. Quiñones, "Mechanism
of formation of the MVo+ Radical During the UV Excitation
of Methylviologen" J. Photochem. Photobiol.
A: Chem. 2001, 142, 19-24.
E. Quiñones,
Y. Ishikawa, and J. Leszczynski "Conformational
Properties of Dimethylaminobenzonitrile in the Gas
Phase and Polar Solvents: Ab Initio HF/6-31G(d,p)
and MP2/6-31G(d,p) Investigation" J. Theor.
Chem. 2000, 529, 127-134.
V.I. Makarov, and E. Quiñones, "Photobleaching
of the SO2 C1B2 X1A1 Transition Caused by Optically Pumping the ã3B1 State" J. Photochem. Photobiol. A: Chem. 2000, 135, 1-5.
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