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Trimethylphosphine reacts with protons in acidic zeolites to form [(CH3)3P−H]+ complexes within the cavities and channels. The mobility of the protonated adduct strongly depends on the available space, which is a function of the amount of (CH3)3P in the zeolite and the size of the guest molecule relative to the cavity or channel dimensions. In an H-Y zeolite containing one molecule per large cavity, the motion is sufficiently rapid to average out a large P−H dipolar interaction, such that even in a static NMR experiment the lines due to J P - H coupling are well resolved. The motional rate is greater than 100 kHz. By contrast, the geometric constraints imposed by the smaller channels in ZSM-5, which are comparable in size to trimethylphosphine, severely restrict the motion. The chemical shift and J coupling values were determined for H-ZSM-5 and dealuminated H-Y zeolites, which are known to be strongly acidic, and for a normal H-Y zeolite, which is less acidic. The 31P chemical shift values were the same within experimental error, but a smaller J coupling in H-ZSM-5 is opposite from what one might expect on the basis of the extent of proton donation. The latter observation suggests that other factors, such as the radius of curvature of the cavities and channels, may play a role in acid−base interactions.

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In 1991, A. Salam proposed that the electroweak interaction might promote tunneling through the potential barrier existing between chiral molecules (i.e., a phase transition at a critical temperature, T c ), which could change the structure of D-amino acids into the reputedly more stable L-form of the enantiomer. A recent report by Wang et al. has presented experimental evidence for such a transition at T c ≈ 270 ( 1 K in enantiomorphs of L-and D-alanine and -valine crystals using differential scanning calorimetry (DSC), magnetic susceptibility, and Raman spectroscopy. Experimental verification of the Salam prediction has great implications for the origins of specific homochirality in biomolecules, that is, the exclusive use of L-amino acids in proteins. In this contribution, we reexamine these measurements, as well as present measurements of the temperature dependence of X-ray diffraction and C-13 solid-state NMR for alanine. While the DSC measurements show interesting features similar to those reported by Wang et al. at ∼270 K, there are significant differences, including the observation that the small feature observed in the DSC experiments becomes even smaller upon recrystallization (i.e., purification). Also, the small change in specific heat at ∼270 K is found to be absent in (natural) L-valine. We find no unusual behavior in our additional X-ray diffraction or NMR experiments in this temperature range. We also present arguments against the Salam hypothesis for the molecules under study.