Molecular ordering of ethanol at the calcite surface

TY - JOUR

T1 - Molecular ordering of ethanol at the calcite surface

AU - Sanchez Pasarin, Ivan Jesus

AU - Yang, Mingjun

AU - Bovet, Nicolas Emile

AU - Glyvradal, Magni

AU - Nielsen, Martin Meedom

AU - Bohr, Jakob

AU - Feidenhans'l, Robert Krarup

AU - Stipp, Susan Louise Svane

PY - 2012/2/7

Y1 - 2012/2/7

N2 - To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [ Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S.Palentology 2004, 43 (Part 3), 725-743 ] and molecular dynamics (MD) modeling [ Yang, M., Stipp, S. L. S., and Harding, J. H.Cryst. Growth Des. 2008, 8 (11), 4066-4074 ], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH 3-CH 2-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH 3 ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems.

AB - To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [ Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S.Palentology 2004, 43 (Part 3), 725-743 ] and molecular dynamics (MD) modeling [ Yang, M., Stipp, S. L. S., and Harding, J. H.Cryst. Growth Des. 2008, 8 (11), 4066-4074 ], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH 3-CH 2-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH 3 ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems.

U2 - 10.1021/la2021758

DO - 10.1021/la2021758

M3 - Journal article

C2 - 22060260

SN - 0743-7463

VL - 28

SP - 2545

EP - 2550

JO - Langmuir

JF - Langmuir

IS - 5

ER -