Kinetics of H →P NMR cross-polarization and dynamics in a layered crystalline α-Sn(IV) phosphate.

The proton-phosphorus (H-P) cross-polarization (CP) is effective in Sn(HPO)·HO despite of the presence of paramagnetic ion impurities. Polarization constants T and H T times are measured in static Sn(HPO)·HO by the kinetic variable-temperature H-P CP experiments. The temperature dependence of the H T times is interpreted in terms of proton movements in the interlayer space occurring between the phosphate groups without participation of the water molecules.

Spin diffusion in the Phosphorus-31 NMR relaxation in a layered crystalline α-Sn(IV) phosphate contaminated by paramagnetic impurities.

The study of a layered crystalline Sn(IV) phosphate by solid-state NMR has demonstrated that the P T relaxation of phosphate groups, dependent on spinning rate is completely controlled by the limited spin diffusion to paramagnetic ions found by EPR. The spin-diffusion constant, D(SD), was estimated as 2.04 10 cms.

Acidic Centers on the Surface of a Crystalline α-Sn(IV) Phosphate Characterized by the Solid-State H, H, P, and Sn MAS NMR Techniques.

A layered crystalline phosphate α-Sn(HPO)·HO (), prepared and characterized in the present study by the multinuclear solid-state nuclear magnetic resonance (NMR), powder X-ray diffraction, and thermogravimetric analysis techniques, was treated with DO and HOD imitating the reaction conditions in a water medium. The H solid-echo magic angle spinning NMR spectra of the products have revealed on their surface low mobile water molecules and hydronium ions, forming a structure close to the Zundel cation, [DO···D-OD]. All the deuterons in the hydronium ions are tangled by hydrogen bonds with the water and the surface phosphate groups and stabilized by ionic interactions.

On Librational and Rotational Motions of Aromatic Rings in Layered Sn(IV) and Zr(IV) Phosphonate Materials: A Variable-Temperature C, P Solid-State NMR Study.

According to the solid-state C, P NMR study and C chemical shift anisotropy (CSA) measurements, aromatic rings in the layered metal(IV) phosphonate materials behave as low-energy rotors at rotation activation energy, , of 1.4-3.0 kcal/mol.

Pyridine-d as a H NMR probe for investigation of macrostructure and pore shapes in a layered Sn(iv) phosphonate-phosphate material.

Isotropic and anisotropic motions and molecular states of pyridine-d, adsorbed on the surface within the pores of a layered Sn(iv) phosphonate-phosphate material (1) have been characterized thermodynamically and kinetically by solid-state NMR. The data obtained provide formulation of macrostructure and shapes of pores in 1.

Guest Molecules in a Layered Microporous Tin(IV) Phosphonate-Phosphate Material: Solid State NMR Studies.

There is little systematic understanding of pore surfaces in layered microporous metal(IV) phosphate-phosphonate materials and their interactions with guest molecules. In this paper, we show how to probe the mobility of guest molecules in such poorly crystalline systems using multinuclear solid-state NMR and relaxation time measurements. Anisotropic motions of benzene- d molecules absorbed on the pore walls of material Sn(OPCHPO)(OPOH) (1) have been recognized as the fast in-plane C rotation due to metal-π interactions with pore walls.

Benzene-d and toluene-d as guest molecules in micropores of a layered zirconium phosphonate: H, C{ H}, and P{ H} solid-state NMR, deuterium NMR relaxation, and molecular motions.

For the first time, pore spaces in the Zr (IV) phosphonate (1) as a representative of layered metal (IV) phosphonate materials have been investigated by studying mobility of guest molecules, benzene-d , and toluene-d . Guest molecules located in micropores of 1 have been characterized by solid-state C{ H} and H NMR spectra in static samples with varying temperatures. At moderately low temperatures, the benzene and toluene molecules experience fast isotropic reorientations and show the motionally averaged liquid-like carbon and deuterium line shapes in the NMR spectra.

Backbone motion in elastin's hydrophobic domains as detected by (2) H NMR spectroscopy.

The elasticity of vertebrate tissue originates from the insoluble, cross-linked protein elastin. Here, the results of variable-temperature (2) H NMR spectra are reported for hydrated elastin that has been enriched at the Hα position in its abundant glycines. Typical powder patterns reflecting averaged quadrupolar parameters are observed for the frozen protein, as opposed to the two, inequivalent deuterons that are detected in a powder sample of enriched glycine.

X-ray and NMR crystallography in an enzyme active site: the indoline quinonoid intermediate in tryptophan synthase.

Chemical-level details such as protonation and hybridization state are critical for understanding enzyme mechanism and function. Even at high resolution, these details are difficult to determine by X-ray crystallography alone. The chemical shift in NMR spectroscopy, however, is an extremely sensitive probe of the chemical environment, making solid-state NMR spectroscopy and X-ray crystallography a powerful combination for defining chemically detailed three-dimensional structures.

De-Pake-ing transform analysis of fully deuterated malonic acid.

The analysis of deuterium wideline NMR spectra has been an essential step in characterizing the dynamics of molecules in the solid-state. Although clearly important, the identification of quadrupolar coupling constants (QCCs) from the powder patterns is often complicated by poor sensitivity and/or spectral overlap. Previously, others have demonstrated the utility of "de-Pake-ing", a mathematical transform that yields the QCCs in a straightforward manner for symmetric (eta=0) sites.

Penetration depth of surfactant peptide KL4 into membranes is determined by fatty acid saturation.

KL(4) is a 21-residue functional peptide mimic of lung surfactant protein B, an essential protein for lowering surface tension in the alveoli. Its ability to modify lipid properties and restore lung compliance was investigated with circular dichroism, differential scanning calorimetry, and solid-state NMR spectroscopy. KL(4) binds fluid lamellar phase PC/PG lipid membranes and forms an amphipathic helix that alters lipid organization and acyl chain dynamics.

Sensitive absorptive refocused scalar correlation NMR spectroscopy in solids.

A new two-dimensional NMR experiment is described which is suitable for obtaining magic angle spinning (MAS) scalar correlation spectra in solids. The new experiment has several advantages, including increased cross peak intensities, coupled with good suppression of the diagonal. Its utility is demonstrated via assignments of the carbon-13 MAS spectra of progesterone at natural abundance and of the polymer phase of 50%-U-13C-CsC60.

Interactions of the C-terminus of lung surfactant protein B with lipid bilayers are modulated by acyl chain saturation.

Lung surfactant protein B (SP-B) is critical to minimizing surface tension in the alveoli. The C-terminus of SP-B, residues 59-80, has much of the surface activity of the full protein and serves as a template for the development of synthetic surfactant replacements. The molecular mechanisms responsible for its ability to restore lung compliance were investigated with circular dichroism, differential scanning calorimetry, and (31)P and (2)H solid-state NMR spectroscopy.

Constant-time through-bond 13C correlation spectroscopy for assigning protein resonances with solid-state NMR spectroscopy.

Even as available magnetic fields for NMR continue to increase, resolution remains one of the most critical limitations in assigning and solving structures of larger biomolecules. Here we present a novel constant-time through-bond correlation spectroscopy for solids that offers superior resolution for 13C chemical shift assignments in proteins. In this experiment, the indirect evolution and transfer periods are combined into a single constant time interval, offering increased resolution while not sacrificing sensitivity.

Uniform-sign cross-peak double-quantum-filtered correlation spectroscopy.

We detail the uniform-sign cross-peak double-quantum-filtered correlation spectroscopy (UC2QF COSY) experiment, a new through-bond correlation method for disordered solids. This experiment is a refocused version of the popular double-quantum-filtered correlation spectroscopy experiment in liquids. Its key feature is that it provides in-phase and doubly absorptive line shapes, which renders it robust for chemical shift correlation in solids.

Through-bond 13C-13C correlation at the natural abundance level: refining dynamic regions in the crystal structure of vitamin-D3 with solid-state NMR.

Recently, we presented a novel nuclear magnetic resonance experiment for establishing through-bond connectivity in disordered solids using scalar coupling-driven correlation. This method, a variant of the popular double-quantum-filtered correlation spectroscopy experiment in liquids, is robust under fast magic-angle-spinning conditions and in the presence of dynamics. Here, we show that this new experiment, the UC2QF COSY, can be extended to 13C natural abundance correlation in moderately sized molecules, allowing the assignment of the 54 peaks of the solid-state NMR spectrum of microcrystalline vitamin-D3.

Establishing through-bond connectivity in solids with NMR: structure and dynamics in HC(60)(+).

We present a novel nuclear magnetic resonance experiment for establishing through-bond connectivity in solids using scalar coupling-driven correlation. This method, a variant of the popular double-quantum-filtered correlation spectroscopy experiment in liquids, is robust under fast magic-angle-spinning conditions and in the presence of dynamics. In HC(60)(+), where anisotropic molecular motion renders through-space dipolar-driven correlation ineffective, this through-bond correlation method answers a significant structural question by accurately identifying the direct bond between the protonated sp(3) hybridized carbon site and the sp(2) hybridized cationic site.

Crystallographic evidence for a free silylium ion.

Evidence for a three-coordinate silyl cation is provided by the crystal structure of [(Mes)3Si][H-CB11Me5Br6].C6H6 (where Mes is 2,4,6-trimethylphenyl). Free (Mes)3Si+ cations are well separated from the carborane anions and benzene solvate molecules.