Fluids in nanoscopic confinements possess a variety of unusual properties, and in particular, remarkable dynamical heterogeneities which vary on length scales as short as a fraction of a nanometer. While the surface forces apparatus provides an experimental probe of macroscopic properties of fluids in contact with atomically smooth solid surfaces, few experimental probes are available which test the microscopic origins of these heterogeneities. In this article we describe our recent efforts to apply nuclear magnetic resonance spectroscopy to nanoscopically confined poly͑styrene͒ ͑PS͒ created by intercalation into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin-echo experiments which probe the entire organic layer suggests that PS in the center of the nanopores is more mobile than the bulk at comparable temperatures, while chain segments which interact with the surface are dynamically inhibited.

Solid-state 13C NMR spectroscopy of a series of crystalline nucleosides and nucleotides allows direct measurement of the effect of the deoxyribose ring conformation on the carbon chemical shift. It is found that 3'-endo conformers have 3' and 5' chemical shifts significantly (5-10 ppm) upfield of comparable 3'-exo and 2'-endo conformers. The latter two conformers may be distinguished by smaller but still significant differences in the carbon chemical shifts at the C-2' and C-4' positions. High-resolution solid-state NMR of three modifications of fibrous calf thymus DNA shows that these trends are maintained in high-molecular-weight DNA and confirms that the major ring pucker in A-DNA is 3'-endo, while both B-DNA and C-DNA are largely 2'-endo. The data show that 13C NMR spectroscopy is a straightforward and useful probe of DNA ring pucker in both solution and the solid state.

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I4N single-crystal nuclear magnetic resonance studies of the nitrates of lead, silver, and barium have shown that, in all three cases, the unit cell has a center of symmetry, thus resolving a controversial issue in the crystallographic literature. The quadrupolar coupling constants of the nitrates are relatively small and show a wide variation, attributed to near-cancellation of opposing contributions from the intramolecular and intermolecular parts of the electric field gradient tensor. The chemical shielding tensors are very similar to each other and to those of previously reported nitrates. The orientations of the nitrate quadrupolar and chemical shielding tensors are as predicted from the local symmetry, with the unique axes perpendicular to the plane of the anion in both cases. No evidence for significant static or dynamical disorder is observed.Despite the simplicity of their chemical formulas, the crystal structures of many of the anhydrous metal nitrates are still controversial. The controversy hinges on the existence or absence of a center of symmetry in the unit cell, an age-old problem of crystallography. In the past 30 years, two sets of X-ray structures have appeared for the room-temperature modification of silver nitrate: a noncentric structure in the orthorhombic space group P2,2,2', with two independent sets of silver and nitrate ions in the asymmetric unit,' and a centric structure of space group Pbca in which there exists an additional center of symmetry and only single chemically distinct silver and nitrate ions in the unit ce11.2,3 Early morphologic4 and X-ray studiesS favored the noncentric structure; more recent infrared and Raman studies6 show no detectable deviation from central symmetry. Diffraction studies have never detected reflections that would be unique to the lower symmetry space group P212121 and would tend to rule out Pbcu.A more extensive literature still has accumulated around the anhydrous divalent metal nitrates of lead, calcium, strontium, and barium,' which along with the high-temperature phase of cadmium nitrate* form an isomorphous set of crystals which give a continuous set of solid s o l~t i o n s .~ The dispute in this case involves the centric cubic space group Pa3 and the corresponding noncentric group P2,3. Again, early morphological studies gave a noncentric structure,I0 while both centric"-Is and n~n c e n t r i c l~* '~ diffraction structures have been published. Neutron diffraction studies initially favored the centric s t r~c t u r e ;~~J~ however, more recent neutron work on the barium saltIS detected very weak reflections that are formally forbidden in Pa3 and thus favored P213. A recent X-ray paper has also claimed weak Pu3-forbidden re-flection~'~ in the barium and lead salts and therefore deduced RI13.Piezoelectric and optical activity measurements on this group of nitrates have generally yielded negative results18 and thus favor the centric structure. Raman and infrared measurements show several anomalous bands which have variously been interpreted as evi...