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Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite.

ABSTRACT: Most ice in nature forms because of impurities which boost the exceedingly low nucleation rate of pure supercooled water. However, the microscopic details of ice nucleation on these substances remain largely unknown. Here, we have unraveled the molecular mechanism and the kinetics of ice formation on kaolinite, a clay mineral playing a key role in climate science. We find that the formation of ice at strong supercooling in the presence of this clay is about 20 orders of magnitude faster than homogeneous freezing. The critical nucleus is substantially smaller than that found for homogeneous nucleation and, in contrast to the predictions of classical nucleation theory (CNT), it has a strong two-dimensional character. Nonetheless, we show that CNT describes correctly the formation of ice at this complex interface. Kaolinite also promotes the exclusive nucleation of hexagonal ice, as opposed to homogeneous freezing where a mixture of cubic and hexagonal polytypes is observed.

SUBMITTER: Sosso GC

PROVIDER: S-EPMC4939469 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

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Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite.

Sosso Gabriele C GC Li Tianshu T Donadio Davide D Tribello Gareth A GA Michaelides Angelos A

The journal of physical chemistry letters 20160610 13

Most ice in nature forms because of impurities which boost the exceedingly low nucleation rate of pure supercooled water. However, the microscopic details of ice nucleation on these substances remain largely unknown. Here, we have unraveled the molecular mechanism and the kinetics of ice formation on kaolinite, a clay mineral playing a key role in climate science. We find that the formation of ice at strong supercooling in the presence of this clay is about 20 orders of magnitude faster than hom ...[more]

PMID: 27269363

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Project description:As an important neuropathological hallmark of Alzheimer's disease (AD), the oligomerization of amyloid-? (A?) peptides has been intensively investigated in both theoretical and experimental studies. However, the oligomerization space in terms of the kinetics, molecular mechanism, and oligomer structures remains mysterious to us. An equation that can quantitatively describe the time it takes for A? oligomers to appear in the human brain at a given A? monomer concentration is extremely vital for us to understand the development and disease progression of AD. In this study, we utilized molecular dynamics (MD) simulations to investigate the oligomerization of A?42 peptides at five different monomer concentrations. We have elucidated the formation pathways of A? tetramers, characterized the oligomer structures, estimated the oligomerization time for A? dimers, trimers, and tetramers, and for the first-time derived equations that could quantitatively describe the relationship between the oligomerization time and the monomer concentration. Applying these equations, our prediction of oligomerization time agrees well with the experimental and clinical findings, in spite of the limitations of our oligomerization simulations. We have found that the A? oligomerization time depends on the monomer concentration by a power of -2.4. The newly established equations will enable us to quantitatively estimate the risk score of AD, which is a function of age. Moreover, we have identified the most dominant pathway of forming A? tetramers, probably the most important and toxic A? oligomer. Our results have shown that the structures of A?42 dimer, trimer, and tetramer, which are distinguishable from each other, depend on the monomer concentration at which the oligomers form. Representative oligomer structures, which can serve as potential drug targets, have been identified by clustering analysis. The MD sampling adequacy has been validated by the excellent agreement between the calculated and measured collisional cross section (CCS) parameters (the prediction errors are within 2%). In a conclusion, this study provides the kinetics and structure basis for developing inhibitors to decelerate the A? oligomerization process.

Dataset Information

Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite.

Publications

Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite.

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