senior thesis presentation
TRANSCRIPT
Quantum Mechanical Modeling of Organic-Oxide Surface Complexation ReactionsUNDERGRADUATE SENIOR THESISDEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERINGUNIVERSITY OF CONNECTICUT
BRIANNA DATTI
Organic pollutants in the environment are a growing concern.
Agriculture
Industry
Pharmaceutical
We can expand on current models to increase the understanding of adsorption of contaminants in the environment.
(Kung & McBride, 1989)
The model utilizes quantum mechanics to predict binding energies of adsorption.
(Ebinding, Enonbinding)
Schrödinger equation:
The adsorption of organic acids to iron oxide was investigated.
Figure 1. Adsorption of organic acids to iron oxide. The following are the organic acids: (A) meta-hydroxybenzoic acid; (B) ortho-hydroxybenzoic acid; (C) Carboxybenzoic acid; (D) Methylbenzoic acid; (E) Methoxybenzoic acid; (F) Malonic acid;
(G) Lactic acid; (H) Phthalic acid; (I) Aminobenzoic acid; (J) Nitrobenzoic acid; (K) Bisulfide benzoic acid.
Results: Thermodynamic favorability of adsorptionCompound ΔrG°(298K) (KJ/mol) ΔrH°(298K) (KJ/mol)Para-hydroxybenzoic acid -40.7038 -40.0609Carboxybenzoic acid -47.5986 -47.5227Methylbenzoic acid -42.3473 -41.9869Meta- hydroxybenzoic acid -41.6365 -41.391Ortho- hydroxybenzoic acid -40.9961 -40.7976Nitrobenzoic acid -53.2728 -53.3361Aminobenzoic acid -39.8923 -39.3759Methoxybenzoic acid -40.281 -39.9421Bisulfide-benzoic acid -45.8215 -45.6282Malonic acid -413.5957 -413.2736Lactic acid -42.0809 -42.2158Phthalic acid -57.5008 -57.1641Para-hydroxybenzoic acid with bidentate binuclear iron oxide
-48.0664 -45.0541
Para-hydroxybenzoic acid with bidentate mononuclear iron oxide
125.2468 127.0777
The existence of para-hydroxybenzoic acid adsorbed to bidentate mononuclear iron oxide has been debated.Bidentate mononuclear
VS
Bidentate binuclear
Adsorption strength is correlated to Hammet constants, but has little correlation to pKa values.
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10
10
20
30
40
50
60
R² = 0.852964182382582
Hammet Constant
|ΔG|
2 4 6 8 10 12 14 160
10
20
30
40
50
60
70
R² = 0.125127195869873
pKa
|ΔG
|
05001000150020002500300035004000
Wavenumber (cm-1)
Inte
nsity
Meta-hydroxybenzoic acid
Ortho-hydroxybenzoic acid
Para-hydroxybenzoic acid
Theoretical spectra indicate bonding geometries and allow comparisons to experimental data.
05001000150020002500300035004000 Wavenumber (cm-1)In
tens
ity
Bisulfide-benzoic acid
Nitrobenzoic acid
Aminobenzoic acid
Methylbenzoic acid
Methoxybenzoic acid
Carboxybenzoic acid
05001000150020002500300035004000
Wavenumber (cm-1)
Inte
nsity
Bidentate mononuclear iron oxide Bidentate binuclear iron oxide
Theoretical spectra indicate bonding geometries and allow comparisons to experimental data.
05001000150020002500300035004000Wavenumber (cm-1)
Inte
nsity
Phthalic acid
Lactic acid
Malonic acid
Shift in spectra peaks from aqueous to adsorbed structures represent inner-sphere complexes.
05001000150020002500300035004000 Wavenumber (cm-1)
Inte
nsity
Ortho-hydroxybenzoic acid
Meta-hydroxybenzoic acid
Para-hydroxybenzoic acid
Aqueous Structures
05001000150020002500300035004000Wavenumber (cm-1)
Inte
nsity
Meta-hydroxybenzoic acid
Ortho-hydroxybenzoic acid
Para-hydroxybenzoic acid
Adsorbed Structures
Combining quantum mechanical modeling, as presented, with molecular dynamics simulations will provide a greater scope of knowledge concerning contaminant fate.
Molecular Dynamics Simulation: para-hydroxybenzoic acid
Inner-Sphere complexation:
Conclusions• Thermodynamic favorability of the investigated organic acids sorption to iron oxides
o Except para-hydroxybenzoic acid adsorbed to bidentate mononuclear iron oxide• Adsorption increases with increasing Hammet constants; electron withdrawing group
substituents having the greatest sorption• Quantum mechanical modeling results validated by comparison of theoretical spectra
to experimental IR spectrao Theoretical spectra indicate presence of inner-sphere and outer-sphere complexes,
with inner-sphere complexes being dominant for para substituted benzoic acids• Combining quantum mechanical modeling and molecular dynamics simulations can
expand the study of adsorption to a whole new class of chemicals
Acknowledgments
Major Advisor: Dr. Chad Johnston
Fellow Thesis Students:• Grant Bedard• Luke McNaboe• Stefanie Shea
Questions?
ReferencesKung, K. H., McBride, M. B. (1989). Adsorption of Para-substituted Benzoates on Iron Oxides. Soil Science Society of
America Journal, (53), 1673-1678.
Ochterski, J. W. (2000). Thermochemistry in gaussian. Gaussian Inc, Pittsburgh, PA, 1-17.
Gaussian 09, Frisch M. J., G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
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Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D.
Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
Chad Johnston, personal communication, April 29, 2015