INVESTIGATION OF THE STATE OF WATER ADJACENT TO SOLID SURFACES USING DEUTERIUM NMR SPECTROSCOPY
Open Access
- Author:
- Slipak, Sasha H
- Area of Honors:
- Chemistry
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Alan James Benesi, Thesis Supervisor
Alan James Benesi, Thesis Supervisor
Przemyslaw Maslak, Thesis Honors Advisor
James Bernhard Anderson, Faculty Reader - Keywords:
- Solid-state
Starch
Cellulose
NMR
Deuterium
D2O
Tetrahedral
C2
High symmetry - Abstract:
- The state of water adjacent to solid surfaces in freeze-dried starch and cellulose has been investigated using 2H NMR techniques. Quadrupole echo spectra of all samples at room temperature include a sharp central peak that corresponds to 2H2O. Both compounds also showed additional powder patterns that have been attributed to rigid glucose O-2H groups. At lower temperatures (≤ -50°C), the central peak became irresolvable due to transition into the intermediate and slow exchange regime. T1 values spanning a range of temperatures obtained at two different magnetic fields closely match previous values for theoretical calculations that assumed fast tetrahedral jumps in a solid-state lattice. These low values suggest that the rate of motion is comparable to the Larmore frequency. Movement at this frequency (~10^7 Hz) is typically only seen in solids. The findings are consistent with previous data for a variety of porous silicates, which could not be matched with isotropic rotational diffusion models for liquid state D2O. The sharp central peak at higher temperatures exhibited spin-lattice relaxation times of almost two orders of magnitude shorter than those of bulk D2O, and exhibited magnetic field dependence, with T1 values at room temperature of 5.59 ms at 7.02 T and 9.67 ms at 11.75 T for starch, and 6.31 ms at 7.02 T and 10.6 ms at 11.75 T for cellulose. This data supports a hypothesis for solid-state water within the lattice structures of both starch and cellulose at room temperature and above.