Deuteron NMR on single crystals. EFGs, signs of quadrupole coupling constants, and assignment of σ tensors in malonic acid

The high-field NMR of two dipolar-coupled deuterons experiencing different EFGs is investigated theoretically and shown to be solvable analytically. The determination of the signs of quadrupole coupling constants from the spectral appearance is discussed. Room-temperature FT deuteron spectra of deuterated crystals of malonic acid were recorded at 54.7 MHz. The dipolar fine structure resulting from the coupling of the deuterons of the CD2 group could be resolved. From the rotation patterns of the line splittings, the EFGs at the sites of the four inequivalent deuterons are determined and compared with the previous work of Derbyshire et al.. The results confirm the conclusion, drawn in a previous paper on the proton NMR of malonic acid, that the methylene deuteron internuclear vector and the normal of the CCC backbone of the molecule subtend an angle of about 6°. The signs of the quadrupole coupling constants of the methylene deuterons are shown to be positive. The correlation of chemical shifts with quadrupole splittings allowed to assign directly the chemical shift tensors measured previously by multiple-pulse proton NMR to the methylene hydrogen sites

Hydration of Hydroxypropylmethyl Cellulose: Effects of pH and Molecular Mass

Magnetic resonance imaging was used to study the diffusion of a water solution of hydrochloric acid (HCl) and sodium hydrochloride (NaOH) into hydroxypropylmethyl cellulose matrices. Polymer in the form of a cylinder was hydrated in a water solvent of pH = 2, 7, and 12 at 37ºC and monitored at equal intervals with a 300 MHz Bruker AVANCE. The spatially resolved spin-spin relaxations times and spin densities, along with a change in the dimension of the glass core of the polymer were determined for hydroxypropylmethyl cellulose tablets as a function of hydration times. The data showed the effects of the pH solvent and of the molecular mass of the polymer on the swelling process, spin-spin relaxation time, and diffusion of solvent molecules into hydroxypropylmethyl cellulose matrices. The time dependence of the diffusion front, effective T$\text{}_{2}$, and proton-density ρ analysis clearly indicate a case II diffusion mechanism in the system composed of a water solution of hydrochloric acid (pH = 2) and hydroxypropylmethyl cellulose, whereas in the case of water solutions with pH = 7 and 12 the anomalous and case I diffusion are observed, respectively