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.

Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J.

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