43871-AC2
Clay-Gas-Hydrate Intercalates
Na-rich swelling clays (smectite), montmorillonite and nontronite, form intercalate complexes
with methane hydrate. The upper stability of Na-rich montmorillonite – methane-hydrate
complexes is nearly identical to that of methane hydrate, whereas that of Na-rich
nontronite – methane-hydrate complex is approx. 1 oC lower. The low-temperature stability of
these complexes is controlled by dehydration reactions of the montmorillonite and nontronite.
At temperatures of < 2 oC, the d(001) value of the montmorillonite complex decreases step-wise
with decreasing temperature from approx. 2.2 nm at < 2 oC to 1.6 nm at < -5 oC, indicating that
H2O is progressively expelled from the interlayer. All methane is probably expelled at approx. 0
oC. The d(001) value of the nontronite complex did not show a similar step-wise reduction and,
consequently, the lower stability of this complex is not well established. At conditions of
reduced salinity, smectite may sufficiently swell and intercalate with methane hydrate at the
conditions of the intermediate to deep-ocean floor environment. The significance of these results
is that smectite – methane-hydrate complexes in the sub-ocean-floor surface may store
substantial quantities of carbon, and this carbon, if present, may be a significant contributor to
the global carbon cycle. A manuscript on this research is in press.
The existence of methane complexes in clay suggests a potential use of other complexes in clays.
Membrane proteins, which are very poorly understood, regulate the cell’s energy level and
transport of materials across the cell boundary. These proteins are difficult to crystallize for
single-crystal X-ray studies because they do not readily dissolve in water and must be solubilized
by detergents. Clay surfaces interact with both organic molecules and detergent micelles,
thereby suggesting that intercalate complexes may promote membrane protein crystallization.
Non-swelling (kaolinite, halloysite) and complexed swelling-clay minerals [inorganic: Na- and
Ca-exchanged hectorite; organic: TMA(tetramethylammonium)-exchanged and
TMPA(trimethylphenylammonium)-exchanged hectorite] were used as nucleants in the
crystallization process to produce enhanced protein-crystal growth and single crystals. The
hanging-drop vapor-diffusion crystallization technique was used with lysozyme as a model
protein. TMPA-exchanged hectorite was used also as the nucleant for crystallization of AP2-β3+
PIP3-kinase peptide, and a single crystal X-ray refinement of its atomic structure was performed.
The clay-mineral type structure, the nature of the exchange, and particle size are important
parameters to enhance protein crystallization. A paper on this subject is in review.
Aluminum substitutions in micas are being examined as an approximate analogue system to the
smectite minerals. Thirty-five Al-rich, natural phlogopite-1M samples that are of high
metamorphic grade and that are apparently Al saturated, along with a newly determined Al-saturated phlogopite structure, exhibited crystal chemical trends related to increasing Al content.
Computer models were used also to simulate electrostatic interactions in phlogopite with variable
Al concentrations utilizing Pauling’s electrostatic valency principle. The model results were
compared to the maximum Al concentrations in natural and synthetic phlogopite samples. There
were no indications that charge saturation/undersaturation of the apical oxygen atoms at Al
contents equal to the maximum in natural and/or synthetic samples causes instability that could
not be balanced by bond-length variation. This suggests that any charge instability imposed by
Al-substitution does not appear to limit Al-saturation and that cation size is the more important
variable. In addition, a Fe-rich mica, anandite-2M, has been structurally determined. Both
projects are being developed by Graduate Student Thomas Bujnowski for a Master’s degree; one
paper (on phlogopite) is in press and one paper (on anandite) is in preparation.
The impact of this research effort on the career of the Principal Investigator is that these studies
represent a continuing effort to understand the behavior of phyllosilicate minerals. Because
methane is a greenhouse gas, smectite behavior may have an impact on global climate change.
In addition, smectite minerals are encountered in petroleum wells, and these minerals affect
petroleum production. Thus, smectite is important in energy resource development (in addition
to the possible exploitation of methane on the ocean floor). The mica structural studies relate to
a better theoretical understanding of how chemical composition can affect the smectite structure.
The latter studies support a student (T. Bujnowski) working toward a Master’s degree, with an
anticipated graduation date of December, 2008. In addition, two undergraduate students, Stacy
Niemiec and James Olech, have been introduced to laboratory work with clay-mineral techniques
as preparation for possible continuation in studies at the graduate level in the earth sciences.
Candice Morrison, who was supported last year as an undergraduate student under this grant, is
now a graduate student here at UIC in earth sciences.
