Research Interests

My research interests are centered on the theoretical investigation of a wide variety of chemical processes that include organic and biological systems, catalytic and electrochemical phenomena.  An integral part of my research involves the development of methods and techniques that facilitate these studies.  My research makes use of available molecular modeling codes and locally developed or modified ones. A number of both undergraduate and graduate students have been involved in research in my lab.

A.  Chemical reaction dynamics in gas phase and in solutions

The main project currently ongoing in my lab focuses on studying the chemical dynamics of hydrogen abstraction from fluorocarbons by hydroxyl radical.  These reactions are important atmospheric and environmental reactions.  The chemical dynamics of some of these hydrogen abstraction reactions have been successfully investigated using variational transition state theory (VTST) with multidimensional tunneling contributions.  The main advantage of the VTST is that it allows calculations of the dynamical quantities based on the local information on the potential energy surface (PES).  The accuracy of the dynamics results is however limited by the level of electronic structure theory underlying the dynamics so part of the study involves generating accurate PES using hybrid density functional theory (HDFT) with specific reaction parameters (SRP).  The use of HDFT methods is preferred because they are easily parameterized and affordable electronic structure methods.  HDFT-SPR studies have been completed for the HO + CH₃F [A1,A2], HO + CH₂F₂ [A3], and HO + CHF₃ [A4] reactions, are being finalized for the hydrogen abstraction from fluoroethanes, and are currently ongoing for the hydrogen abstraction from fluoropropanes.

Another continuous research interest concerns the chemical transformations of carbenes.  Most of these studies are collaborations with Dr. Weston Borden from University of North Texas and Dr. Donald Truhlar from University of Minnesota.  Two such studies focusing on the rearrangements involving both hydrogen and carbon migrations are already published [A5,A6], one of them in prestigious Science magazine.  In this particular study dealing with theoretical investigation of the rearrangements in methylcyclobutylhalocarbenes, an extraordinary example of a reaction involving exclusively through tunneling involving large carbon motions was reported.  Another study [A7], close to being finalized, involves a more detailed analysis of these carbene rearrangements involving carbon migration that also includes the temperature dependence of the rate constants and of the activation energies, the determination of ¹³C kinetic isotope effect, and the relative distribution of the product for these isotopic reactions.

I am also currently working on a collaborative project (with Dr. Piotr Paneth from University of Lodz) in which we are carrying out theoretical determination of isotopic effects and comparison with experimentally determined ones to predict the mechanism of the base-promoted elimination of hydrogen fluoride from 4-fluoro-4-(4’-nithophenyl)butane-2-one in 75% methanol solution.  Preliminary results show that calculated isotope effects are consistent with a stepwise mechanism in which the first step is entirely rate determining.

Another research interest is dealing with the mechanism and the electronic effects that govern the oxidation of amines by quinones.  It is known that quinones act as cofactor in amine oxidases.  Free quinones (not covalently bound to the enzyme) have also been identified in the cell.  The role of these free quinones is not completely understood, however it is believed that some of them oxidize primary amines to aldehydes.  An ongoing investigation looks into the reactions of quinones and hydroxyquinones with a number of amines with a special focus on the reactivity of the quinone toward amine oxidation, the position of amine attack and its dependence of amine reactivity, the structures of the intermediates and of the final products.  This project is carried out in collaboration with Dr. Jisook Kim from Tennessee Tech University.

[A1] "Hybrid Density Functional Theory Investigation of the Hydrogen Abstraction Reaction of Fluoromethane by the Hydroxyl Radical," S. E. Mikel, T. V. Albu, Journal of Undergraduate Chemistry Research 2006, 5, 75-81.

[A2] "Hybrid Density Functional Theory with Specific Reaction Parameter: Hydrogen Abstraction Reaction of Fluoromethane by the Hydroxyl Radical," T. V. Albu, S. Swaminathan, Journal of Physical Chemistry A 2006, 110, 7663-7671.

[A3] "Hybrid Density Functional Theory with a Specific Reaction Parameter: Hydrogen Abstraction Reaction of Difluoromethane by the Hydroxyl Radical," T. V. Albu, S. Swaminathan, in preparation.

[A4] "Hybrid Density Functional Theory with a Specific Reaction Parameter: Hydrogen Abstraction Reaction of Trifluoromethane by the Hydroxyl Radical," T. V. Albu, S. Swaminathan, Theoretical Chemistry Accounts 2006, in press.

[A5] "Dynamics of 1,2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes," T. V. Albu, B. J. Lynch, D. G. Truhlar, A. C. Goren, D. A. Hrovat, W. T. Borden, R. A. Moss, Journal of Physical Chemistry A 2002, 106, 5323-5338.

[A6] "Carbon Tunneling from a Single Quantum State," P. S. Zuev, R. S. Sheridan, T. V. Albu, D. G. Truhlar, D. A. Hrovat, W. T. Borden, Science 2003, 299, 867-870.

[A7] "Kinetic Isotope Effects Calculated for a Carbene Rearrangement that Proceeds by Carbon Tunneling at 8 K," D. A. Hrovat, T. V. Albu, D. G. Truhlar, C. L. Perrin, W. T. Borden, in preparation.

B.  Algorithms for efficient chemical dynamics calculations

This research focuses in the development and the application of methodologies to create semiglobal and global PES to be used in dynamics calculations in conjunction with VTST calculations.  The technique developed, called multi-configuration molecular mechanics (MCMM) algorithm, has been used to create semiglobal PES for reactive systems [B1].  MCMM combines electronic structure theory information (energy, gradient, Hessian) at a small number of points on the surface with molecular mechanics potential functions in a form of a nonadiabatic (i.e., diabatic) Hamiltonian matrix:

whose lowest eigenvalue is the Born–Oppenheimer potential function.  V₁₁ and V₂₂ are classical molecular mechanics potential functions describing reactant and product valence bond configuration, and V₁₂ is the resonance energy function or the resonance integral and is obtained from the electronic structure information.  Recent advancements of the method involve the use of only few Hessian elements calculated using electronic structure theory while the other elements are calculated using molecular mechanics [B2].  The future development involves establishing a similar methodology where the molecular mechanics potentials will be replaced by electronic structure theory potentials describing different electronic states.  One application of this new method is on creating reactive PES for electron transfer processes, particularly electrochemical processes.

[B1] "Molecular Mechanics for Chemical Reactions: A Standard Strategy for Using Multiconfiguration Molecular Mechanics for Variational Transition State Theory with Optimized Multidimensional Tunneling," T. V. Albu, J. C. Corchado, D. G. Truhlar, Journal of Physical Chemistry A 2001, 105, 8465-8487.

[B2] "Efficient Molecular Mechanics for Chemical Reactions: Multiconfiguration Molecular Mechanics Using Partial Electronic Structure Hessians," H. Lin, J. Pu, T. V. Albu, D. G. Truhlar, Journal of Physical Chemistry A 2004, 108, 4112-4124.

C.  Computational investigation of electrocatalytic and surface processes

The need for an environmentally clean and a highly efficient source of energy has generated a special interest in fuel cell development over the past years.  The biggest problem in the fuel cell industry is the cathodic process of oxygen reduction because of its very slow kinetics that leads to a high overpotential and high current flow only at potentials with lower technological interest.  For acid-electrolyte fuel cells, the best electrocatalysts for the oxygen reduction reaction (ORR) are platinum and its alloys.  Some platinum alloys with transition metals have shown enhanced electrocatalytic activity for ORR with respect to Pt alone.  The reason for the improvement is however still disputable, and theoretical studies could bring a better understanding of the energetics of chemisorbed species on the surfaces of these alloys as well the factors responsible for the enhanced activity of platinum alloys.  The number of theoretical studies on ORR is still limited due to their enhanced difficulty considering that the methodology should include the electrode and its electrochemical potential, the reaction center, and the solvent.  The original studies on uncatalyzed and Pt-catalyzed ORR date back to my graduate work [C1-C3].  A more recent study on the performance of HDFT methods for ORR was finalized and is being published [C4].  In this study it was found that HDFT methods with half Hartree-Fock exchange contribution give more accurate results that the generic HDFT methods and should be more appropriate for applications to bigger reaction systems.  Current work focuses on the dependence of the electrode model (for with we use clusters containing 4, 6, 7, or 10 platinum atoms) on the adsorption energies of intermediate species, especially hydroperoxyl radical.

[C1] "Ab Initio Approach to Calculating Activation Energies as Functions of Electrode Potential. Trial Application to Four-Electron Reduction of Oxygen," A. B. Anderson, T. V. Albu, Journal of the American Chemical Society 1999, 121, 11855-11863.

[C2] "Catalytic Effect of Platinum on Oxygen Reduction. An Ab Initio Model Including Electrode Potential Dependence," A. B. Anderson, T. V. Albu, Journal of The Electrochemical Society 2000, 147, 4229-4238.

[C3] "Studies of Model Dependence in an Ab Initio Approach to Uncatalyzed Oxygen Reduction and the Calculation of Transfer Coefficients," T. V. Albu, A. B. Anderson, Electrochimica Acta 2001, 46, 3001-3013.

[C4] "Performance of Hybrid Density Functional Theory Methods toward Oxygen Electroreduction over Platinum," T. V. Albu, S. E. Mikel, Electrochimica Acta 2006, in press.

D.  Modeling properties of molecules, ions and materials

Synthetic diamond obtained by chemical vapor deposition has been shown great potential for use in a number of areas.  Pure diamond is an isolator but doped diamond can act as either p-type or n-type semiconductor.  The nature and the properties of the dopants is, in some cases, not completely understood.  In an initial investigation carried out during my graduate studies, using cluster models and HDFT methods, a large number of dopants were explored to determine the method limitations and to search among various potential n-type dopants [D1].  A more recent study (in collaboration with Dr. Alfred B. Anderson from Case Western Reserve University), currently in press, focuses on possible interpretations for the n-type conductivity observed for boron-doped diamond with hydrogen and sulfur co-doping [D2].  A possible explanation for the n-type behavior, created by co-doping diamond films with boron and sulfur, is given in terms of thermally activated electron donation from an SVS (V is vacancy) donor to a BB acceptor band.  Both lie deep in the band gap.  It is proposed that electrons in the BB acceptor band are mobile charge carriers.  It is also proposed that the conversion of boron-doped diamond from p-type conductivity, with hole charge carriers in the top of the valence band, to n-type conductivity, following treatment in a deuterium plasma, may arise from formation of interstitial hydrogen donor levels and acceptor levels based on both boron and hydrogen that create an acceptor band in which electrons are mobile.  Another study that looks to the influence of cluster size and cluster surface to calculated results is currently ongoing in my lab.

Electron ionization mass spectrometry is a useful tool in structural investigation of organic compounds.  The method has however some limitations due to its lack of discrimination between stereoisomers, which typically show very similar mass spectra.  Recently, it was reported important differences in the abundances of fragment ions obtained in mass spectrometry of the cis,cis and trans,trans diastereoisomers of four 2(r)-R-2,4(R),6(S)-trimethyl-1,3-dioxane derivatives.  To explain the high differences observed between the electron ionization mass spectra of these diastereoisomers, the authors propose, as one possibility, the formation of two pairs of isomeric ions by the loss of the substituent located in the equatorial or axial position at C(2), respectively.  These isomeric ions were postulated to exhibit large differences in their stabilities.  The conformational preference of three ions involved in the mass spectrometry of these 1,3-dioxane derivatives using HDFT calculations was investigated [D3].  It was found that there are indeed more than one stable ion conformations for each of the investigated ions, but due to relatively small rotation barrier height, the different conformers are unlikely to be involved in distinct fragmentation pathways leading to different electron-ionization mass spectra.  Energy profiles along the torsional coordinates connecting the conformers were presented, and factors influencing the relative stability of ion conformations were discussed.

Thiosemicarbazones and their complexes with transition metals have gained considerable interest due to their antitumor effects, antiviral activities, and their anticancer activity.  Recently, the synthesis and the NMR characterization of a series of eight alloxan-based thiosemicarbazones and semicarbazones were reported.  These compounds exhibit a strongly hydrogen-bonded hydrazinic proton that is a part of a characteristic six-membered ring.  This proton is highly deshielded and resonates far downfield in the proton NMR spectra.  In a theoretical study in press [D4], electronic structure theory calculations have been used to investigate the structure and other molecular properties of these eight compounds.  The relationship between the ¹H and ¹³C NMR chemical shifts and various geometric parameters was investigated, and linear relationships for proton peaks that are involved in hydrogen-bond interactions were found.  Another study is investigating similar relationships for other series of thiosemicarbazones.

An investigation (in collaboration with Dr. Donald Visco from Tennessee Tech University, Chemical Engineering Department) into the association patterns of hydrogen fluoride and water has been started recently and is currently ongoing.  The focus is on determining the average strength of hydrogen bond interactions between various types of hydrogen/protons and oxygen or fluorine, their dependence with respect to the size of the model (i.e., the number of H₂O and HF molecules).  Preferred association patterns are investigated.  The results will be used in statistical modeling of water-hydrogen fluoride mixtures.

[D1]     "Dopants in Diamond Nanoparticles and Bulk Diamond. Density Functional Study of Substitutional B, N, P, SB, S, PN, O, NN, and Interstitial H," T. V. Albu, A. B. Anderson, J. C. Angus, Journal of The Electrochemical Society 2002, 149, E143-E147.

[D2]     "The Origin of Shallow n-type Conductivity in Boron-Doped Diamond with H or S Co-Doping: Density Functional Theory Study," Y. Cai, T. Zhang, A. B. Anderson, J. C. Angus, L. N. Kostadinov, T. V. Albu, Diamond and Related Materials 2006, accepted.

[D3]     "Hybrid Density Functional Theory Study of Fragment Ions Generated during Mass Spectrometry of 1,3-Dioxane Derivatives," T. V. Albu, Rapid Communications in Mass Spectrometry 2006, 20, 1871-1876.

[D4]     "Hybrid Density Functional Theory Investigation of a Series of Alloxan-Based Thiosemicarbazones and Semicarbazones," N. W. S. V. N. De Silva, E. C. Lisic, T. V. Albu, Central European Journal of Chemistry 2006, 4, 646-665.

Current and Former Group Members

E-mail your comments and questions to: albu@tntech.edu