Unusual species of methane hydrate detected in nanoporous media using solid state 13C NMR.

Methane is considered to be a cubic structure I (CS-I) clathrate hydrate former, although in a number of instances, small amounts of structure II (CS-II) clathrate hydrate have been transiently observed as well. In this work, solid-state magic angle spinning 13C NMR spectra of methane hydrate formed at low temperatures inside silica-based nanoporous materials with pores in the range of 3.8-20.

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective.

In light of the intense recent interest in the methylammonium lead halides, CHNHPbX (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H, N, and Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ, for the C-N axis of the iodide salt is 0.

Managing Hydrogen Bonding in Clathrate Hydrates by Crystal Engineering.

Methanol is one of the most common inhibitors for clathrate hydrate formation. Crystalline clathrate hydrates containing methanol were synthesized and analyzed by powder X-ray diffraction and C NMR spectroscopy. The data obtained demonstrate that methanol can be a helper guest for forming structure I, structure II, and structure H clathrate hydrates, as long as the lattice framework contains NH F.

Facilitating guest transport in clathrate hydrates by tuning guest-host interactions.

The understanding and eventual control of guest molecule transport in gas hydrates is of central importance for the efficient synthesis and processing of these materials for applications in the storage, separation, and sequestration of gases and natural gas production. Previously, some links have been established between dynamics of the host water molecules and guest-host hydrogen bonding interactions, but direct observation of transport in the form of cage-to-cage guest diffusion is still lacking. Recent calculations have suggested that pairs of different guest molecules in neighboring cages can affect guest-host hydrogen bonding and, therefore, defect injection and water lattice motions.

Inter-cage dynamics in structure I, II, and H fluoromethane hydrates as studied by NMR and molecular dynamics simulations.

Prospective industrial applications of clathrate hydrates as materials for gas separation require further knowledge of cavity distortion, cavity selectivity, and defects induction by guest-host interactions. The results presented in this contribution show that under certain temperature conditions the guest combination of CH3F and a large polar molecule induces defects on the clathrate hydrate framework that allow intercage guest dynamics. (13)C NMR chemical shifts of a CH3F/CH4/TBME sH hydrate and a temperature analysis of the (2)H NMR powder lineshapes of a CD3F/THF sII and CD3F/TBME sH hydrate, displayed evidence that the populations of CH4 and CH3F in the D and D' cages were in a state of rapid exchange.

Methanol incorporation in clathrate hydrates and the implications for oil and gas pipeline flow assurance and icy planetary bodies.

One of the best-known uses of methanol is as antifreeze. Methanol is used in large quantities in industrial applications to prevent methane clathrate hydrate blockages from forming in oil and gas pipelines. Methanol is also assigned a major role as antifreeze in giving icy planetary bodies (e.

Multiple H2 occupancy of cages of clathrate hydrate under mild conditions.

Experiments were carried out by reacting H(2) gas with N(2) hydrate at a temperature of 243 K and a pressure of 15 MPa. The characterizations of the reaction products indicated that multiple H(2) molecules can be loaded into both large and small cages of structure II clathrate hydrates. The realization of multiple H(2) occupancy of hydrate cages under moderate conditions not only brings new insights into hydrogen clathrates but also refreshes the perspective of clathrate hydrates as hydrogen storage media.

Structural phase transitions induced by pressure in ammonium borohydride.

A combined experimental and theoretical study of hydrogen-rich ammonium borohydride (NH4BH4) subjected to pressures up to 10 GPa indicates two phase transitions, detected by synchrotron radiation powder X-ray diffraction, Raman spectroscopy and Car-Parrinello molecular dynamics calculations, at 1.5 and 3.4 GPa.

Size reduction of CdSe/ZnS quantum dots by a peptidic amyloid supergelator.

Anchoring of a self-assembling dipeptide on the surface of core/shell CdSe/ZnS quantum dots resulted in a competition between coordination of the surface atoms of the QDs and the strong tendency for the dipeptide to self-assemble in toluene. This resulted in a mild QD etching and in a corresponding increase in the band gap of the nanocrystals whose photoluminescent emission gradually turns blue with time. The FmocLeuLeuOH dipeptide supergelator self-assembles in fibrils in which the Fmoc groups are surrounded by the pendant isobutyl side chains of the leucine residues with vibrational circular dichroism (VCD) and liquid- and solid-state NMR attributes of twist anti-parallel β-sheets.

Multinuclear solid-state nuclear magnetic resonance and density functional theory characterization of interaction tensors in taurine.

A variety of experimental solid-state nuclear magnetic resonance (NMR) techniques has been used to characterize each of the elements in 2-aminoethane sulfonic acid (taurine). A combination of (15)N cross-polarization magic angle spinning (CPMAS), (14)N ultrawideline, and (14)N overtone experiments enabled a determination of the relative orientation of the nitrogen electric field gradient and chemical shift tensors. (17)O spectra recorded from an isotopically enriched taurine sample at multiple magnetic fields allowed the three nonequivalent oxygen sites to be distinguished, and NMR parameters calculated from a neutron diffraction structure using density functional theory allowed the assignment of the (17)O parameters to the correct crystallographic sites.

13C NMR studies of hydrocarbon guests in synthetic structure H gas hydrates: experiment and computation.

(13)C NMR chemical shifts were measured for pure (neat) liquids and synthetic binary hydrate samples (with methane help gas) for 2-methylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, methylcyclopentane, and methylcyclohexane and ternary structure H (sH) clathrate hydrates of n-pentane and n-hexane with methane and 2,2-dimethylbutane, all of which form sH hydrates. The (13)C chemical shifts of the guest atoms in the hydrate are different from those in the free form, with some carbon atoms shifting specifically upfield. Such changes can be attributed to conformational changes upon fitting the large guest molecules in hydrate cages and/or interactions between the guests and the water molecules of the hydrate cages.

Interaction tensors and local dynamics in common structural motifs of nitrogen: a solid-state 14N NMR and DFT study.

(14)N solid-state NMR powder patterns have been obtained at high field (21.1 T) using broadband, frequency-swept pulses and a piecewise acquisition method. This approach allowed the electric field gradient (EFG) tensor parameters to be obtained from model organic and inorganic systems featuring spherically asymmetric nitrogen environments (C(Q) values of up to ca.

Crystal structure based design of signal enhancement schemes for solid-state NMR of insensitive half-integer quadrupolar nuclei.

A combination of density functional and optimal control theory has been used to generate amplitude- and phase-modulated excitation pulses tailored specifically for the (33)S nuclei in taurine, based on one of several reported crystal structures. The pulses resulted in significant signal enhancement (stemming from population transfer from the satellite transitions) without the need for any experimental optimization. This allowed an accurate determination of the (33)S NMR interaction parameters at natural abundance and at a moderate magnetic field strength (11.

Anhydrous proton conduction at 150 °C in a crystalline metal-organic framework.

Metal organic frameworks (MOFs) are particularly exciting materials that couple porosity, diversity and crystallinity. But although they have been investigated for a wide range of applications, MOF chemistry focuses almost exclusively on properties intrinsic to the empty frameworks; the use of guest molecules to control functions has been essentially unexamined. Here we report Na(3)(2,4,6-trihydroxy-1,3,5-benzenetrisulfonate) (named β-PCMOF2), a MOF that conducts protons in regular one-dimensional pores lined with sulfonate groups.

Structure and dynamics of ammonium borohydride.

Synchrotron powder X-ray diffraction, ab initio molecular dynamics calculations and solid state (1)H and (2)H NMR are used to refine the structure of crystalline NH(4)BH(4) including H atoms. Rapid reorientations of both ions mean that on average half-hydrogens occupy the corners of a cube around B or N.

Thermodynamic and molecular-scale analysis of new systems of water-soluble hydrate formers + CH4.

Among a variety of cyclic ether, cyclic ester, and cyclic ketone compounds, six new formers were found to form binary sII or sH hydrates with CH(4) gas. Hydrate-phase equilibria for all the hydrate formers were measured. The results obtained showed distinct relationships between the hydrate-phase equilibrium curve and the molecular size of the guests.

Facile proton conduction via ordered water molecules in a phosphonate metal-organic framework.

A new phosphonate metal-organic framework (MOF) with a layered motif but not that of the classical hybrid inorganic-organic solid is presented. Zn(3)(L)(H(2)O)(2)·2H(2)O (L = [1,3,5-benzenetriphosphonate](6-)), henceforth denoted as PCMOF-3, contains a polar interlayer lined with Zn-ligated water molecules and phosphonate oxygen atoms. These groups serve to anchor free water molecules into ordered chains, as observed by X-ray crystallography.

Ultra-wideline 14N NMR spectroscopy as a probe of molecular dynamics.

We show that ultra-wideline solid-state (14)N NMR can be used as a quantitative probe of molecular dynamics. Jump rates for the molecular flipping mechanism in crystalline urea are determined at various temperatures and are shown to be in good agreement with other NMR techniques.

CdS magic-sized nanocrystals exhibiting bright band gap photoemission via thermodynamically driven formation.

CdS magic-sized nanocrystals (MSNs) exhibiting both band gap absorption and emission at 378 nm with a narrow bandwidth of approximately 9 nm and quantum yield (QY) of approximately 10% (total QY approximately 28%, in hexane) were synthesized via a one-pot noninjection approach. This CdS MSN ensemble is termed as Family 378. It has been acknowledged that magic-sized quantum dots (MSQDs) are single-sized, and only homogeneous broadening contributes to their bandwidth.

Photoluminescent quantum dot?cucurbituril nanocomposites.

The preparation of entrapped CdSe?ZnS fluorescent quantum dots (QDs) in cucurbituril (CB) polymer capsules is reported.

Inclusion complexes of coumarin in cucurbiturils.

Coumarin was found to form stable inclusion complexes with cucurbiturils. In the presence of cucurbit[7]uril (CB[7]), 1 : 1 inclusion complexes were observed in aqueous solution, as monitored by (1)H NMR and UV-visible absorption spectroscopies, and further supported by ab initio calculations, whereas with cucurbit[8]uril (CB[8]) a solid phase 1 : 2 host : guest complex was found in a single crystal X-ray diffraction structure determination.

Probing cucurbituril assemblies in water with TEMPO-like nitroxides: a trinitroxide supraradical with spin-spin interactions.

Nitroxide free radicals are demonstrated to be useful guests for probing cucurbit[n]uril (CB[n]) assemblies in water by EPR spectroscopy. CB[7] and CB[8] significantly aggregate either in solution or in the solid state (as evidenced by a single-crystal X-ray structure in which CB[8] forms supramolecular triangles with 4-methoxy-TEMPO). The included nitroxides show a striking resistance to biologically relevant reduction, benefiting from the carcerand effect of CB[7] and CB[8] solutions.

Single-sized colloidal CdTe nanocrystals with strong bandgap photoluminescence.

One brand-new colloidal ensemble of single-sized CdTe nanocrystals, exhibiting a sharp first excitonic absorption peak at 427 nm and bright bandgap photoluminescence at 427 nm with narrow full width at half maximum (FWHM) of only ca. 10 nm, was synthesized in 1-octadecene (ODE) via a non-injection one-pot approach which features high synthetic reproducibility with potential for industrial scale production.