First Observed by Isidor Rabi in 1938, later refined by Felix Bloch and Edward Purcell in 1946.
NMR allows one to “tune in to” the desired nucleus by choosing the correct frequency (1-1000 MHz), because each nucleus has a specific Larmor frequency at a given magnetic field.
NMR is not a sensitive technique. NMR requires a minimum concentration of ~1mM and a minimum sample volume of ~1 ml. Because of this, we need large surface area samples to study molecules at interfaces.
Despite the above limitation, NMR is the one of the most powerful technique known for characterization of molecular structure and dynamics.
1. Molecular dynamics simulations, scanning polarization force microscopy (SPFM), and sum frequency generation spectroscopy have shown the formation of room temperature “ice-like bilayers” on the surface of muscovite mica 1 , a hydrophilic aluminosilicate that can be used to “seed” clouds.
Room temperature solid state water is also commonly found in crystalline hydrates. 2
At elevated pressure and temperatures slightly above the freezing point of pure water, solid state water is found as well in clathrate hydrates. 3
Previous evidence for solid state water at room temperature:
1. (a) Hu, J; Xiao, X.-d.; Ogletree, D. F.; Salmeron, M. Surf. Sci. 1995 , 344 , 221-236. (b) Hu, J; Xiao, X.-d.; Ogletree, D. F.; Salmeron, M. Science 1995 , 268 , 267-269. (c) Odelius, M.; Bernasconi, M.; Parrinello, M. Phys. Rev. Lett. 1997 , 78 , 2855-2858. (d) Salmeron, M.; Bluhm, H. Surf. Rev. and Lett. 1999 , 6 , 1275-1281 .
(a) Weiss, A.; Weiden, N. In Advances in Nuclear Quadrupole Resonance, Smith, J. A. S., Ed. Heyden: 1980, Vol. 4, pp. 149-248. (b) Reeves, L. W. In Progress in NMR Spectroscopy, Emsley, J. W.; Feeney, J.; Sutcliffe, L. H. Eds. Pergamon:1969, Vol. 4, pp. 193-234.
(a) Bach-Verges, M.; Kitchin, S. J.; Harris, K. D. M.; Zugic, M.; Koh, C. A. J. Phys. Chem. B 2001 , 105 , 2699-2706. (b) Kirschgen, T. M.; Zeidler, M. D.; Geil, B.; Fujara, F. Phys. Chem. Chem. Phys. 2003 , 5 , 5247-5252.
We have used 2 H NMR techniques, isothermal calorimetry, and FT-IR to investigate water ( 2 H 2 O and 1 H 2 O) in a variety of hydrated materials: Kanemite, Zeolite A, Silicalite, Montmorillonite, Silica Gel, Porous Glass, Hydrated Tricalcium Silicate (cement), Hydroxyapatite, Cellulose, Nafion, and Sulfonimide substituted polyphosphazenes We have found room temperature solid state water in all of these samples! We have published some of the work in the papers below: A. J. Benesi, M. W. Grutzeck, B. O’Hare, and J. W. Phair, “Room Temperature Solid Surface Water with Tetrahedral Jumps of 2 H Nuclei Detected in 2 H 2 O-Hydrated Porous Silicates”, J. Phys. Chem. B , 108, 17783-17790, 2004. A. J. Benesi, M. W. Grutzeck, B. O’Hare, and J. W. Phair, “Room Temperature Ice-Like Water in Kanemite Detected by 2 H NMR T 1 Relaxation”, Langmuir , 21 , 527-529, 2005. B. O’Hare, M.W. Grutzeck, D.B. Asay, S.H. Kim, and Alan J. Benesi “Solid State Water Motions Revealed by Deuterium Relaxation in 2 H 2 O –Synthesized Kanemite and 2 H 2 O Hydrated Na + -Zeolite A”, Journal of Magnetic Resonance, 195, 85-102, 2008.
Why we use 2 H NMR? Because: We use 2 H 2 O to hydrate our samples…
2 H NMR well suited for studying molecular motion because: Quadrupolar interaction dominates, so other interactions can be ignored. “ Rigid” qcc = e 2 qQ/h = 160-300 kHz gives rise to characteristic powder pattern in spectrum (shown below for : 3/2 qcc ¾ qcc
There is a direct link between the observed 2 H spectral frequency and the orientation of the (quadrupolar PAS) covalent bond relative to the 2 H nucleus and the applied magnetic field. Because all possible angles are found in a powdered sample, this gives rise to the powder pattern. O 2 H B 0 Because of this sensitivity to motion, 2 H NMR can be used to characterize motions with frequencies ranging from ~1 x10 -2 s -1 < < 10 15 s -1 .
d5- Benzoic Acid -At 22 deg C the phenyl ring flips are not apparent. -All that is observed is a static powder pattern. -Motion << Qcc
Phenyl Ring Flips (Calculated) -The deuterons undergo 180 o rotations as the phenyl ring rotates -This is a common occurrence in proteins and other large molecules with phenyl groups
d18- HMB Methyl groups experience fast 3 site jumps and produce a “mini” powder pattern as do other low symmetry fast motions. Motion >> Qcc
d4-L-Alanine (Slow Pulse) 2 types of motion 2 types of deuterons - fast 3 site jumps - slow 1 site motion Motion >> Qcc Motion << Qcc
Vertical Expansion of L-Alanine This expansions shows the static pattern more clearly Motion << Qcc
Frozen D2O The deuterons in ice slightly below its melting point exhibit highly symmetric, fast tetrahedral jumps which produce isotropic like lineshapes. Motion >~ Qcc
D 2 O ice, -120 C D 2 O ice, 0 C freezing pt. = 3.84 C, qcc D 2 O liquid, 21 C >> qcc qcc 2 H quadrupole echo spectra of 2 H 2 O (D 2 O): This is why everyone missed room temp solid state water
Brief Comparison of the Arrhenius versus the Eyring Plot
They are essentially equivalent
The Eyring plots Δ H ‡ is the Arrhenius E a.
The Δ S ‡ is entropic data not available from the Arrhenius equation
Arrhenius Equation Eyring Equation
Eyring Plots of Zeolite-A Activation parameters are determined from the dynamic lineshape simulation data Activation parameters are determined by high temperature T 1 experimental data The plot of ln k/T versus 1/T gives a straight line with slope of from which the enthalpy of activation can be derived and with intercept from which the entropy of activation is derived.