NANO LETTERS
Formation and Manipulation of Confined Water Wires
2004 Vol. 4, No. 4 619-621
Yongjae Lee,† C. Dave Martin,‡ John B. Parise,‡ Joseph A. Hriljac,§ and Thomas Vogt*,†,| Physics Department, BrookhaVen National Laboratory, Upton, New York 11973, Geosciences Department, State UniVersity of New York, Stony Brook, New York 11794, School of Chemical Sciences, UniVersity of Birmingham, Birmingham, B15 2TT, UK, and Center for Functional Nanomaterials, BrookhaVen National Laboratory, Upton, New York 11973 Received January 9, 2004; Revised Manuscript Received February 25, 2004
ABSTRACT Pressure-induced hydration (PIH) in the zeolite natrolite leads to well-ordered one-dimensional “water wires” and “water tubes”. These structures provide urgently needed points of reference for molecular dynamics simulations and serve as models of transient and disordered biological nanowater. We show here that applying simultaneous pressure and temperature using a hydrothermal diamond anvil cell permits the intermolecular manipulation of water wires due to changes in the geometry of the host scaffolding and the enclosed hydrogen bonded water. During this process the ordered water wires formed under pressure change their direction depending on the temperature. This provides the opportunity to study the dynamics of confined water at the nanoscale by temperature and/or pressure-jump experiments. Our studies indicate that confined water responds differently to pressure and temperature than does bulk water.
The interaction of water and biological matter is of fundamental importance. Protein folding and pressure-induced unfolding is associated with water transport out of and into the protein interior.1 A large fraction of cellular water is distinct from bulk water and in a state often referred to as “nanowater”.2 “Water wires” with lifetimes on the order of 10-100 picoseconds are being discussed as the basis of selective proton conductivity in pure lipid bilayers,3 the ATP synthase complex,4 and bacteriothodopsin.5 Yet, despite the great importance, little is known about the structures of these water networks due to their complex nature and difficulties in studying them. One approach to enhance our understanding is to model systems where water resides in a well-defined environment of appropriate dimensionality, such as within carbon nanotubes.6 Other potential model systems with spatially confined water can be found within the tunnels of aluminosilicate zeolites and other molecular sieves. The experimental observation of reversible7 and irreversible pressure-induced hydration (PIH)8 in zeolites with the natrolite topology demonstrates how hydrostatic pressure can be used to control water content and assemble unique water structures within the confinement of nanometer sized channels created by an aluminosilicate framework. The PIH phase * Corresponding author. † Physics Department, Brookhaven National Laboratory. ‡ State University of New York. § University of Birmingham. | Center for Functional Nanomaterials, Brookhaven National Laboratory. 10.1021/nl049946n CCC: $27.50 Published on Web 03/17/2004
© 2004 American Chemical Society
of natrolite at 1.7 GPa, depicted in Figures 1 and 3, contains a unique cation nanowater structure, a 41 spiral along the c-axis with alternating O-O distances of 2.84(2) Å and 3.16(2) Å enclosing sodium cations. Of more significance is that an additional oxygen-oxygen distance of 3.06(2) Å indicates the presence of nonintersecting 1-dimensional water wires that zigzag along the 〈101〉 directions (see Figure 3). To explore the effect of temperature on PIH, a hydrothermal diamond-anvil cell9 was used in conjunction with monochromatic synchrotron X-ray powder diffraction setup at beamline X7A at the National Synchrotron Light Source (NSLS) (see figures in Supporting Information). The primary white beam from the bending magnet is focused in the horizontal plane by a triangular, asymmetrically cut Si (111) monochromator bent to a cylindrical curvature by applying a load to the crystal tip, resulting in microfocused (∼200 µm) monochromatic X-ray radiation with a wavelength of ∼0.7 Å. A tungsten wire crosshair was positioned at the center of the goniometer circle, and subsequently the position of the incident beam was adjusted to the crosshair. A gasproportional position-sensitive detector10 was stepped in 0.25° intervals over the angular range of 5-30° with counting times of 90-150 s per step. The wavelength of the incident beam (0.6642(1) Å), PSD zero channel, and PSD degrees/ channel were determined from a CeO2 standard (SRM 674). A powdered sample of the mineral natrolite (from Dutoitspan, South Africa, EPMA: Na16Al16Si24O80‚16H2O) was loaded
Figure 1. Pressure- and temperature-dependent evolution of the unit cell edge lengths (Å) (upper) and normalized unit cell volume (lower) in natrolite (Na16Al16Si24O80‚xH2O). Unfilled symbols represent data taken at room temperature and filled symbols at 200 °C. Data from Lee et al. (J. Am. Chem. Soc. 2002, 124, 5466-5475) were used to represent the room-temperature evolution. A polyhedral representation of natrolite in the pressure-induced hydration (PIH) state is shown to the right viewed down the spiral natrolite channel. Al tetrahedra are shown unshaded to indicate the ordering of Al/Si over the framework tetrahedral sites. Continuous and dotted open circles represent the original and water molecules inserted under pressure, respectively. The distribution of sodium cations (grey circles) remains intact upon PIH. Arrows illustrate the relationship between ψ angle and the channel opening (see Figure 2).
into the HDAC at ambient pressure and room temperature along with a few small ruby chips. The HDAC was obtained from the Mineral Physics Lab of Cornell University and employs two diamonds with 1.0 mm diameter culets on tungsten-carbide resistive heating supports.9 The temperature calibration was done using the well-determined thermal expansion of MgO at 1 bar prior to the experiment. The sample chamber is provided by a 200 µm hole formed in the center of a 250 µm thick stainless steel gasket. A mixture of 16:3:1 by volume of methanol/ethanol/water was used as a pressure transmission fluid. The pressure at the sample was measured by detecting the shift in the R1 emission line of the included ruby chips. The X-rays are admitted by a 0.5 mm diameter circular aperture, and the exit beam leaves via ∼50° conical slit. The PIH state of natrolite was obtained at 1.7 GPa and then the sample was heated to 200 °C. The structural evolution of Na-AlSi-NAT was determined using the variable-pressure-temperature powder diffraction data and Rietveld structure refinements (see table and figures in Supporting Information).11,12 The observed changes in unit cell lengths and volume are shown in Figure 1. Upon heating under pressure, the zeolitic scaffolding undergoes expansions perpendicular to the spiral channels (a,b-axes) and a marginal contraction along the channels (c-axis). This results in an increase of the unit cell volume at 1.7 GPa by ca. 1.9% compared to the volume at room temperature and an overall increase by ca. 4.3% with respect to the volume extrapolated without PIH. It is interesting to note that while the a- and b-axes expand by about the same amount when applying pressure (∼1.8 and ∼2.1%, respectively), there is a distinct anisotropy of the thermal expansion under pressure: the a-axis expands by 620
Figure 2. Pressure and temperature dependence of the overall rotation angle of the fibrous chains ψ (upper) and the ellipticity of the channel opening (lower). ψ is the mean of the angles between the sides of the quadrilateral around the T5O10 (T ) Al, Si...) tetrahedral building unit projected on the ab-plane (see Figure 1). It is often used to measure the distortion of the natrolite framework from the ideal geometry. The ellipticity of the channel opening is measured by the ratio of the longest and shortest framework oxygen distances across the spiral natrolite channel. The anisotropic thermal expansion at 1.7 GPa results in a decrease in ψ and ellipticity, relieving the framework strain and accommodating the PIH water with a more compatible circular opening (see Figure 1). Data from Lee et al. (J. Am. Chem. Soc. 2002, 124, 5466-5475) were used to represent the room-temperature evolution.
ca. 1.5%, whereas the b-axis expands only by ca. 0.9% when heating to 200 °C at 1.7 GPa. We argue that this anisotropic Nano Lett., Vol. 4, No. 4, 2004
∼104 under pressures of 0.7-0.8 GPa.20 We conjecture that the reversible change in the direction of the shortest oxygenoxygen distances will lead to a concomitant switch in the direction of the protonic current. This could provide an intriguing gating mechanism and proof of principle for a proposed switchable nanoscale semiconductor.21 Finally, the possibility of performing temperature- and/or pressure-jump experiments will provide novel insights into the dynamics of confined waters at the nanoscale. Investigations along these lines are interesting challenges and are now being pursued.
Figure 3. Polyhedral representation of natrolite in the PIH state (Na16Al16Si24O80‚32H2O) at 1.7 GPa and room temperature (left). It contains twice as many water molecules as at ambient conditions. Tetrahedra are shown in two colors to illustrate the ordering of Al/Si over the framework tetrahedral sites. Red and yellow balls represent water molecules and sodium cations, respectively. Ball and stick representations of the channel contents are shown to the right to illustrate the temperature-induced changes in the water nanostructures. At room temperature and 1.7 GPa, the onedimensional water wires run along the 〈101〉 directions. When heated to 200 °C at 1.7 GPa, the hydrogen bonding changes and the one-dimensional water wires now run along the 〈011〉 directions. The measurements were performed using a hydrothermal diamond anvil cell at beamline X7A of NSLS at BNL.
thermal expansion at 1.7 GPa relieves the strain created within the framework due to PIH and leads to a rotation of the chains of tetrahedra resulting in more circular openings to accommodate the ordered arrangements of water molecules and sodium cations inside the channels (Figures 1 and 2). Concomitant with the anisotropic thermal expansion of the host scaffolding, heating under pressure also changes the orientation and symmetry of the above-mentioned ordered water wires. At 200 °C and 1.7 GPa the water wires are now aligned along the 〈011〉 directions and have, within the estimated standard deviations, equidistant oxygen-oxygen separations (2.99(2) Å and 3.02(2) Å) along the wire. This value is very close to the one determined for a water dimer.13,14 In contrast, the closest oxygen-oxygen distance in bulk water is about 2.85 Å and does not change with pressure.15 The hydrogen bonding in our water wires is also weaker than in ice, where O-O distances of 2.75 Å are observed at 15 K.16 It has been put forward that the effect of the aluminosilicate framework on the structure and vibrational frequencies of water in natrolite is negligible.17 This is not always the case when one-dimensional water wires are present in aluminosilicate frameworks.18 We therefore advocate that the experimentally observed wellordered structures of confined one-dimensional water chains in natrolite are models of transient and disordered biological water wires.19 It has been shown by Belitsky et al. that the rate of water diffusion in natrolite increases by a factor of Nano Lett., Vol. 4, No. 4, 2004
Acknowledgment. This work was supported by an LDRD from BNL (Pressure in Nanopores). Y.L. thanks the Edward H. Kraus Crystallographic Research Grant from the Mineralogical Society of America. J.P. acknowledges support from the National Science Foundation (DMR-0095633), and J.H. acknowledges support from the Royal Society. Research carried out in part at the NSLS at BNL is supported by the U.S. DOE (DE-Ac02-98CH10886 for beamline X7A). We gratefully acknowledge Dr. J. Hu and the Geophysical Laboratory of the Carnegie Institute for access to their ruby laser system at beamline X17C. Supporting Information Available: Table of final refined atomic coordinates for natrolite, results of Rietveld refinements, and high-pressure experimental setup details. This material is available free of charge via the Internet at http://pubs.acs.org. References (1) Hummer, G.; Garde, S.; Garcia, A. E.; Paulaitis, M. E.; Pratt, L. R. P. Natl. Acad. Sci. U.S.A. 1998, 95, 1552-1555. (2) Ruffle, S. V.; Michalarias, I.; Li, J. C.; Ford, R. C. J. Am. Chem. Soc. 2002, 124, 565-569. (3) Nagle, J. F. J. Bioenerg. Biomembr. 1987, 19, 413-426. (4) Saraste, M. Science 1999, 283, 1488-1493. (5) Lanyi, J. K. J. Phys. Chem. B 2000, 104, 11441-11448. (6) Hummer, G.; Rasaiah, J. C.; Noworyta, J. P. Nature 2001, 414, 188190. (7) Lee, Y.; Vogt, T.; Hriljac, J. A.; Parise, J. B.; Artioli, G. J. Am. Chem. Soc. 2002, 124, 5466-5475. (8) Lee, Y.; Vogt, T.; Hriljac, J. A.; Parise, J. B.; Hanson, J. C.; Kim, S. J. Nature 2002, 420, 485-489. (9) Bassett, W. A.; Shen, A. H.; Bucknum, M.; Chou, I.-M. ReV. Sci. Instrum. 1993, 64, 2340-2345. (10) Smith, G. C. Synch. Rad. News 1991, 4, 24-30. (11) Larson, A. C.; VonDreele, R. B. GSAS; General Structure Analysis System, Report LAUR 86-748, Los Alamos National Laboratory, New Mexico, 1986. (12) Toby, B. H. J. Appl. Crystallogr. 2001, 34, 210-213. (13) Odutola, J. A.; Dyke, T. R. J. Chem. Phys. 1980, 72, 5062-5070. (14) Dyke, T. R.; Mack, K. M.; Muenter, J. S. J. Chem. Phys. 1977, 66, 498-510. (15) Soper, A. K. Physica B 2000, 276, 12-16. (16) Petrenko, V. F.; Whitworth, R. W. Physics of Ice; Oxford University Press: New York, 1999. (17) Cicu, P.; Demontis, P.; Spanu, S.; Suffritti, G. B.; Tilocca, A. J. Chem. Phys. 2000, 112, 8267-8278. (18) Ferro, O.; Quartieri, S.; Vezzalini, G.; Fois, E.; Gamba, A.; Tabacchi, G. Am. Mineral. 2002, 87, 1415-1425. (19) Venable, R. M.; Pastor, R. W. J. Chem. Phys. 2002, 116, 26632664. (20) Belitsky, I. A.; Fursenko, B. A.; Gubada, S. P.; Kholdeev, O. V.; Seryotkin, Y. V. Phys. Chem. Minerals 1992, 18, 497-505. (21) Mashl, R. J.; Joseph, S.; Aluru, N. R.; Jakobsson, E. Nano Lett. 2003, 3, 589-592.
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