Development & Application of Theoretical Methods. We
emphasize Cartesian space electron and spin density analysis to
study bonding and most of our developmental efforts are dedicated
to advancements in this area. We focus on ab initio methods achieving
high accuracy with perturbational approaches (MP, G1, G2), density
functional theory (DFT), and CI methods (CASSCF, QCISD). Semi-empirical
formalisms and molecular mechanics are used sporadically as well.
Current developments focuses on density based electrostatic methods
for the study of DNA stacking and intercalation. Our recently
developed density analysis methods for radicals are now being
employed to investigations of radical reaction mechanisms and
novel materials, to atmospheric radical chemistry, and to ESR
spectroscopy. Our interest in fundamental bonding theory concerns
aspects of dative bonding and analyses of energy distributions
in molecules via fragment transfer energy analysis.
Deamination Chemistry: Nucleic Acid Alkylation & Cross-Linking. We have been interested in two types of deaminations and their relation to modifications of DNA bases. The first type relates to the deamination of amines (and derivatives) and their role in the alkylation of DNA. The other relates to the deamination of amino groups in DNA bases. Both of these processes have important biological consequences. In this context, we have been studying decomposition pathways "from the bottom up" beginning with diazonium ions. We proposed a new bonding model and established crucial links between theory and experiment. Current studies of diazonium ions focus on the mechanisms of their SN chemistry and studies of the diazonium ions of DNA bases. To address questions as to the consequences of alkylation on DNA and RNA structure and properties, our initial studies have focused on studies of base pairing.
Non-Synergistic Bonding & Thymine Dimerization. Our
analysis of H-bonded Adenine-Thymine, A=T, suggests that A is
stabilized in A=T while T is significantly destabilized. The notion
of such "non-synergistic bonding", that is, the destabilization
of a molecule by non-covalent association with another molecule
without charge transfer, offers exciting prospects for catalysis.
Current research focuses on detailed analyses of the origins for
non-synergetic bonding. Experimental tests of this theoretical
result focus on physical organic studies of the thymine dimerization,
a process that also is of significance in the context of UV damage
N-Perturbed Extended pi-Systems in
Azines: Crisscross Reactions & Nonlinear Optical Materials.
The stereochemistry and stereoelectronics are studied of push-push,
pull-pull, and push-pull azines X-Ph-(R'C=CR")n-CR=N-N=CR-(R"C=CR')
n-Ph-Y. These azines are important to advancing crisscross
reaction chemistry, that is, the tandem 1,3-dipolar cycloaddition
of azines with dienophiles and they show promise as novel nonlinear
optical materials. In particular, we have found that one of these
azines is highly dipole parallel-aligned in the crystal and indeed
the such a degree of ferroelectric alignment is unprecedented
and was thought to be impossible to achieve. The lattice architecture
of the prototype is now being studied in great detail in collaboration
New Electron-Deficient Materials: Diphosphonium Ions &
Polycharged High-Multiplicity Ions. Our work suggests that
the P analogues of RNN+ might exist. The experimental
approach to diphosphonium ions primarily focuses on the Lewis-acid
assisted ionization of polar diphosphenes. In collaboration with
inorganic chemists, we are studying the oxidation of group VIb
stabilized carbenium ions to polycharged radicals [C(XR)3]y+
(X = S, Se, Te, y = 1-3). State-of-the-art theory (QCISD(T) PES)
indicates novel and unexpected properties which are now being
explored more fully.
(1) "Spin Polarization versus Spin Delocalization."
R. Glaser and G. S.-C. Choy J. Chem. Phys. 1994,
98, 11379-11393, and our publications cited there.
(2) (a) "Benzenediazonium Ion. Generality, Consistency, and
Preferability of the Electron Density Based Dative Bonding Model."
Glaser, R. and Horan C. J. J. Org. Chem. 1995, 60,
7518-7528. (b) "Importance of the Anisotropy of Atoms in
Molecules." R. Glaser & G. S.-C. Choy J. Am. Chem.
Soc. 1993, 115, 2340-2347.
(3) (a) "Crystal Structure of Fe(CO)3(PPh3)2
and ab Initio Study of the Bonding" R. Glaser, Y.-H.Yoo,
G. S. Chen, and C. L. Barnes Organometallics 1994,
13, 2578-2586. (b) "Electron Density Distribution
of beta,beta-Dichlorovinyldiazonium Ion." G. S. Chen, R. Glaser,
and C. L. Barnes J. Chem. Soc., Chem. Commun. 1993,
(4) (a) "Push-Pull Substitution versus Intrinsic or
Packing Related N-N Gauche Preferences in Azines. Synthesis,
Crystal Structures and Packing of Asymmetrical Acetophenone Azines."
G. S. Chen, J. K. Wilbur, C. L. Barnes, and R. Glaser J. Chem.
Soc., Perkin Trans. 2, 1995, 2311-2317. (b) "Polymorphism
and Conformational C=N-N=C Bond Isomers of Azines." G. S.
Chen, M. Anthamatten, C. L. Barnes, and R. Glaser Angew. Chem.
Int. Ed. Engl. 1994, 33, 1081-1083.
(5) (a)"Tris(chalogeno)carbenium-Ionen C(XR)3+
(X = O, S, Se, Te)." D. Ohlmann, C. M. Marchand, H. Grützmacher,
G. S. Chen, D Farmer, R. Glaser, A. Currao, R.
Nesper, and H. Pritzkow Angew. Chem. Int. Ed. Engl. 1996,
35, 300-303. (b) "Phosphorus Analogues of Diazonium
Ions." R. Glaser, C. Horan, and P. Haney J. Phys.
Chem. 1993, 97, 1835-1844.