Professor Garcia-Garibay's Current Research Interests

(b. 1960) B.Sc., 1982, Universidad Michoacana, Mexico; Ph.D., 1988, University of British Columbia; Postdoctoral Fellow, 1989-1991, Columbia University.

Most of us have experienced the fascination of growing crystals. However, it is not commonly recognized that organic crystals may offer some of the most efficient methodologies for controlling chemical reactivity and a unique opportunity to explore the most intimate structural details of selected organic reaction mechanisms. Our group is dedicated to uncover the factors that control the chemical reactivity and physicochemical properties of organic crystalline compounds.
The study of chemical reactivity in organic crystals offers a wealth of structural information. The structures of a reactant and its environment before reaction can be obtained from X-ray diffraction data.
Crystal Chemistry. We design suitable reaction models to test structural and mechanistic aspects of organic reactivity, prepare crystalline compounds to carry out our reactions, and carry out spectroscopic analyses and computer modeling to round up our investigations. Our studies include both thermal and photochemical reactions with emphasis in reactions that involve highly reactive and preferably irreversibly formed intermediates (e.g. carbenes, biradicals, etc.). We select reactions that may occur through common intermediates originating from different precursors to address the role of structural and energetic differences. Carbenes, for instance, may be generated from diazo compounds, from diazirines, from aromatic epoxides, from small ring ketones and from organometallic compounds. By preparing sets of reactants with substituents that are too remote to cause any change in reactivity in solution, but that are able to modify the crystal structure, we address the role of crystal forces in determining the reactivity observed.


 


Stereoselectivity, Stereospecificity and Chemical Dynamics in Organic Crystals. We address challenging aspects of stereochemical control such as the generation of optically active products from achiral (or even racemic!) starting materials without using optically active reagents! Possible mechanisms for the generation and amplification of optical activity using chiral crystals are relevant to the prebiotic origin of optical activity on earth which we explore with crystalline model systems. We follow the course of our solid state reactions by X-ray crystallographic analysis and rationalize aspects such as stereoselectivity and stereospecificity using computer modeling to aid our analysis. Time-resolved spectroscopic techniques are used in our group for measuring reaction rates that allow us to carry out deeper structure-reactivity correlations based on absolute reaction dynamics. Recent structure-reactivity correlations studies in solids have led us to uncover several interesting aspects of quantum mechanical tunneling reactions.

Organic Crystals in Material Sciences. Non-linear optics, organic ferromagnets, organic conductors, and piezoelectric materials are some of the newer technological applications of organic crystals. Our group brings a physical organic point of view to aspects relevant to material science. We focus on problems related to the formation, chemical stability, phase changes, and spectroscopic properties of crystals. Two of the main challenges in the field relate to the rational design of crystals with desirable properties and to the manipulation and design of multicomponent solid systems. We investigate the connection between molecular structure and crystal structure by studying the effect of substituents on the crystal structure of a parent compound. Mixed crystals or solid solutions are useful both in addressing mechanistic questions and in learning the properties of multicomponent materials. This research contributes to the challenging area of crystal engineering and is an important aspect of our work.


 


Chemical Reactivity in Organized Media. In the process of studying chemical reactivity in the crystalline solid state we also analyze our compounds in solution and in other organized and rigid environments such as zeolites, clathrates and inclusion complexes. Complexation through hydrogen bonding and its effect on reactivity are also of interest within the framework of our research. We analyze some of the most general aspects behind the efficient control of organic reactivity and demonstrate their efficiency in selected reaction media.

Representative Publications.

 M. A. Garcia-Garibay, Z. Zhang and N. J. Turro, "Diffusion and Percolation of Radical Pairs in Zeolite Media", J. Am. Chem. Soc. 1991, 113, 6212.

M. A. Garcia-Garibay, J. R. Scheffer and D. Watson, "Hydrogen Bonding Effects on the Di-[[pi]]-methane Photorearrangement", J. Org. Chem., 1992, 57, 241.

M. A. Garcia-Garibay, X. Lei and N. J. Turro, "Radical Scavenging in Zeolite Media" J. Am. Chem. Soc. 1992, 114, 2749.

Garces, F. O.; Rao, V. P.; Garcia-Garibay, M. A.; Turro, N. J. "Comparison of the [1]H-[13]C CP-MAS Dynamics of Inclusion Complexes of Benzaldehyde in [[alpha]]-, [[beta]]-, and [[gamma]]-Cyclodextrin" J. Supramol. Chem., 1992, 1, 65.

Winnik, F. M.; Ottaviani, M. F.; Bossmann, S. H.; Pang, W.; Garcia-Garibay, M. A.; Turro, N. J. "Phase Separation of Poly-(N-Isopropylacrylamide) in Water: Study of a Polymer Tagged with a Fluorescent Dye and a Spin Label" J. Phys. Chem. 1993, 97, 12998.

L. Casswell, M. A. Garcia-Garibay, J. R. Scheffer, J. Trotter, "Optical Activity Can Be Generated from Nothing" J. Chem. Ed., 1993, 70, 785.

M. A. Garcia-Garibay, "Reactivity of Arylcarbenes with Methanol. Triplet State Reactivity or Spin-State Equilibrium as a Moving Target?" J. Am. Chem. Soc., 1993, 115, 7011.

M. A. Garcia-Garibay, C. Theroff, S. Shin, J. Jernelius, "Solvent Effects on the Singlet-Triplet Equilibrium and Reactivity of A Ground Triplet State Arylalkyl Carbene" Tetrahedron Lett., 1993, 52, 8415.

M. A. Garcia-Garibay, S. Shin, I. Chao, K. N. Houk, S. I. Khan, "A Solid State [13]C CPMAS NMR and Molecular Mechanics Study of Conformational Recognition in Mixed Crystals of two Phenylalkyl Ketones" Chem. Mater. 1994, 6, 1297.

M. A. Garcia-Garibay, A. Gamarnik, L. Pang, W. S. Jenks. "Excited State Intra-molecular Hydrogen Atom Transfer at Ultra-Low Temperatures. Evidence for Tunneling and Activated Mechanisms in oMethylanthrone", J. Am. Chem. Soc. 1994, 116, 12095-6

V. Ramamurthy, M. A. Garcia-Garibay, "Zeolites as Supramolecular Hosts for Photochemical Transformations" in Comprehensive Suramolecular Chemistry, Bein, T. Ed., Pergamon Press, Oxford, in press.

M. A. Garcia-Garibay, A. Gamarnik, R. Bise and L. Pang. Jenks, W. S. "Primary Isotope Effects on Excited State Hydrogen Atom Transfer Reactions" J. Am. Chem. Soc., 1995, in press.

Choi, T.; Cizmeciyan, D.; Kahn, S.; Garcia-Garibay, M. A. "An Efficient Solid-to-Solid Reaction via a Steady-State Phase-Separation Mechanism" 1995, submitted to J. Am. Chem. Soc.
 
 


Garcia-Garibay Research Group


 



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Last Revision: 01/20/99 //