Research

Journal of Physical Chemistry B, in press 2008  jp-2008-04047x

Workman Reynolds Freezing Potential Measurements Between Ice and Dilute Salt Solutions for Single Ice Crystal Faces

P.W. Wilson and A.D.J. Haymet, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, USA

ABSTRACT:

Workman Reynolds freezing potentials have been measured for the first time across the interface between single crystals of ice 1h and dilute electrolyte solutions. The measured electric potential is a strictly non-equilibrium phenomenon, and is a function of concentration of salt, freezing rate, orientation of the ice crystal and time. When all these factors are controlled, the voltage is reproducible to the extent expected with ice growth experiments. Zero voltage is obtained with no growth or melting. For rapidly grown ice 1h basal plane in contact with a solution of 10-4 M NaCl the maximum voltage exceeds 30 Volts, and decreases to zero at both high and low salt concentrations. These single crystal experiments explain much of the data captured on this remarkable phenomenon since the year 1948.  

Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008) 
Vancouver, British Columbia, Canada, July 6-10, 2008

Heterogeneous Nucleation of Clathrates from Supercooled THF/Water Mixtures and the Effect of an Added Catalyst

P.W. Wilson and A.D.J. Haymet, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, USA

ABSTRACT:

The statistics of liquid-to-crystal nucleation are measured for clathrate-forming mixtures of tetrahydrofuran and water using an automatic lag time apparatus (ALTA). We measure the nucleatio temperature where a single sample is repeatedly cooled, nucleated and thawed. This is done for a series of tetrahydrofuran concentrations and in several different sample tubes since the nucleation is heterogeneous and occurring on the tube wall. The measurements are also done at the same concentrations and tubes but with an added catalyst, a single crystal of silver iodide. We discuss the need for this type of measurement if the true nucleation temperature of the clathrate is to be found.  Comparisons are also made with our high pressure data on real-world clathrate formers.

Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008)

Vancouver, British Columbia, CANADA, July 6-10, 2008

A New Method for the Statistical Evaluation of Natural Gas Hydrate Nucleation at Elevated Pressure

K. A. Kozielskski∗, N. C. Becker & P. G. Hartley, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Molecular and Health Technologies, Bayview Avenue, Clayton, VIC 3169, Australia
P. W. Wilson & A. D. J. Haymet, Scripps Institution of Oceanography, 8602 La Jolla Shores Drive, CA 92037, USA
R. Gudimetla & A. L. Ballard, BP America Production Company, 501 West Lake Park Boulevard, Houston, TX 77079, USA
R. Kini, Chevron Energy Technology Company,1600 Smith St. Houston, Texas 77002,  USA

ABSTRACT: 

Nucleation is a stochastic process, most accurately represented by a probability distribution. Obtaining sufficient data to define this probability distribution is a laborious process. Here, we describe a novel instrument capable of the automated determination of hydrate nucleation probability under non-equilibrium conditions for a range of natural gas mixtures at pressures up to 10MPa. The instrument is based on the automated lag time apparatus (ALTA) which was developed to study the stochastic nature of nucleation in ambient pressure systems [1].We demonstrate that the probability distribution represents a robust and reproducible tool for the quantitative evaluation of hydrate formation risk under pseudo-realistic pressure conditions. We also describe use of the instrument to evaluate factors affecting nucleation, including pressure, cooling rate, impurities and chemical additives and conclude that it is an effective method for evaluating even subtle changes to the environment in which the hydrates are formed.

Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008)

Vancouver, British Columbia, CANADA, July 6-10, 2008

Nucleation of Clathrates from Supercooled THF/Water Mixtures Shows that No Memory Effect Exists

P.W. Wilson and A.D.J. Haymet, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, USA
K.A. Kozielski, P. Hartley & N.C. Becker, CSIRO Molecular & Health Technologies,Ian Wark Laboratory, Clayton, Victoria 3150, Australia.

ABSTRACT:

The liquid-to-crystal nucleation temperature is measured for clathrate-forming mixtures of tetrahydrofuran and water using both an automatic lag time apparatus (ALTA) and a ball screening apparatus. Our results are conclusive evidence that no so-called “memory effect” exists. Either the solid form melts fully or it does not. If it does not, then no supercooling is possible on the next cooling down of that sample, and if it does then the second cooling run and freezing on a sample is just as likely to have a colder nucleation temperature as a hotter one.    

American Chemical Society Meeting,
Park City, Utah, June 15-18, 2008

New Measurements of the Workman-Reynolds Freezing Potential Between Ice and Dilute Salt Solutions, for Both Polycrystalline Ice and Single Ice Crystal Faces

P.W. Wilson and A.D.J. Haymet, Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, USA

ABSTRACT:

We have measured the so-called Workman-Reynolds or Freezing Potential between polycrystalline ice and dilute salt solutions.  We have also used single ice crystals with various faces as the ice / salt water boundary. These measurements are done as a function of concentration, freezing rate and salt species in order to fully understand the preferential exclusion of ions from ice. This concept is claimed to play a crucial role in many diverse phenomena including thunderstorms and the biology of cold tolerance and avoidance.  

Biophysical Journal 2007; 93:1442-1451

Antifreeze Proteins at the Ice/Water Interface: Three Calculated Discriminating Properties for Orientation of Type I Proteins

ABSTRACT:

The number of hydrogen bond count, for example; and the sidechain Antifreeze proteins (AFPs protect many plants and organisms from freezing in low temperatures. Of the different AFPs, the most studied AFP Type I from winter flounder is used in the current computational studies to gain molecular insight into its adsorption at the ice/water interface. Employing molecular dynamics simulations, we calculate the free energy difference between the hydrophilic and hydrophobic faces of the protein interacting with ice. Furthermore, we identify three properties of Type I "antifreeze" proteins that discriminate among these two orientations of the protein at the ice/water interface. The three properties are: the "surface area" of the protein; a measure of the interaction of the protein with neighboring water molecules as determined by orientation angles of the threonine residues. All three discriminants are consistent with our free energy results which clearly show that the hydrophilic protein face orientations towards the ice/water interface, as hypothesized from experimental and ice/vacuum simulations, is incorrect, while supporting the hydrophobic protein face orienting towards the interface. The adsorption free energy is calculated to be 2-3 kJ/mol. Read full abstract

234th ACS National Meeting,
Boston, MA, August 19-23, 2007

Division of Computers in Chemistry
Ions at Water Interfaces

A.D.J. Haymet, Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0210, Fax: 858-453-0167, haymet@ucsd.edu, and Taras Bryk, Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine

ABSTRACT:

The behavior of ions and molecules at the ice/gas and ice/water interfaces is a fundamental process encountered in a range of physical and biological systems and has relevance to unsolved problems in atmospheric chemistry, for example charge separation at the ice/water interfaces known as Workman-Reynolds effect. Recent studies on the behavior of Na+ and Cl- ions at the ice/water interface question the inherent (or induced) electrostatic potential at ice/water interfaces. Others have reported very thorough calculations on the electrostatic potential for water/vapor interfaces. Our results on free energy profiles for Na+ and Cl- ions across the basal ice/water interface indicate that the ice/water interface can function as a capacitor. Similar profiles have been calculated for Na+ and Cl- at the basal ice surface / vacuum interface. For each solute ion at the ice surface, the minimum in the free energy profiles is located in the top surface liquid-like layers.

234th ACS National Meeting,
Boston, MA, August 19-23, 2007

Division of Computers in Chemistry
Molecular Dynamics Simulations of Antifreeze Proteins at a Lipid/Water Interface

E. J. Smith, Math, Science and Healthcare, Kingwood College, 20000 Kingwood Dr, Kingwood, TX 77339, erica.j.smith@nhmccd.edu, Pranav Dalal, Schrodinger, Inc, Jeffry D. Madura, Department of Chemistry and Biochemistry, Center for Computational Sciences, Duquesne University, and ADJ Haymet, Scripps Institution of Oceanography, UC San Diego

ABSTRACT:

Antifreeze proteins (AFP's), found in certain fish, insects and plants, allow the host organism to survive in lower than the equilibrium freezing point of their blood and/or internal fluids via suppression of ice crystal growth and the protection of cell membranes from cold-induced damage. Using molecular dynamics simulation techniques, a solvated dimyristolyphosphatidylcholine (DMPC) lipid bilayer containing an AFP type I at the lipid/water interface was constructed, simulated and characterized at several temperatures (310, 295, 288 and 260 K). Lipid structural characteristics were monitored and all results agreed well with other lipid bilayer simulation and experimental data. The simulations performed at 260 K showed (i) a distinct broadening of the lipid headgroup distribution in the pure system that was not observed in the system containing the AFP and (ii) that the phosphate-nitrogen (P-N) tilt angle decreased for the pure solvated system but remained the same for the system containing the AFP.