A low cost route to hexagonal mesostructured carbon molecular sieves.

A mesoporous carbon molecular sieve with a hexagonal framework structure (denoted C-MSU-H) has been prepared using a MSU-H silica template that can be assembled from a low cost soluble silicate precursor at near-neutral pH conditions.

Redirect the assembly of hexagonal MCM-41 into cubic MCM-48 from sodium silicate without the use of an organic structure modifier.

In contrast to earlier methods requiring the presence of organic modifiers for the preparation of cubic MCM-48 mesostructures from low cost sodium silicate, we show that this three dimensional framework structure can be readily assembled in the absence of co-surfactants simply by using the overall SiO2/OH- ratio as means of controlling the surfactant packing parameter.

Templating of mesoporous molecular sieves by nonionic polyethylene oxide surfactants.

Mesoporous silica molecular sieves have been prepared by the hydrolysis of tetraethylorthosilicate in the presence of low-cost, nontoxic, and biodegradable polyethylene oxide (PEO) surfactants, which act as the structure-directing (templating) agents. This nonionic, surfactant-neutral, inorganic-precursor templating pathway to mesostructures uses hydrogen bonding interactions between the hydrophilic surfaces of flexible rod- or worm-like micelles and Si(OC(2)H(5))(4-x)(OH)(x) hydrolysis products to assemble an inorganic oxide framework. Disordered channel structures with uniform diameters ranging from 2.0 to 5.8 nanometers have been obtained by varying the size and structure of the surfactant molecules. Metal-substituted silica and pure alumina mesostructures have also been prepared by the hydrolysis of the corresponding alkoxides in the presence of PEO surfactants. These results suggest that nonionic templating may provide a general pathway for the preparation of mesoporous oxides.

A neutral templating route to mesoporous molecular sieves.

A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S degrees ) and neutral inorganic precursors (l degrees ). The S degrees l degrees templating pathway produces ordered mesoporous materials with thicker framework walls, smaller x-ray scattering domain sizes, and substantially improved textural mesoporosities in comparison with M41S materials templated by quaternary ammonium cations of equivalent chain length. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods. The S degrees 1 degrees templating route provides for the synthesis of other oxide mesostructures (such as aluminas) that may be less readily accessible by electrostatic templating pathways.

Structure sensitivity of amino proton exchange in 2'- and 5' - guanosine monophosphate dianions.

Proton NMR line broadening methods were used to determine the rates of amino proton exchange for disordered 2'- and 5' - GMP dianions in aqueous solutions containing tetramethylammonium (TMA+) cations. Replacing TMA+ with Na+ does not substantially alter the exchange rates, provided that H-bonded, Na(+)-directed tetramer structures are absent. Activation enthalpies (kcal/mol) and entropies (eu) for 2'-GMP are: delta H not equal to = 18.5 +/- 1.3, delta S not equal to = 9.6 +/- 4.2 for TMA+ salt at pH 8.10, and delta H not equal to = 14.7 +/- 2.6, delta S not equal to = -3.7 +/- 8.0 for the Na+ salt at pH 8.11. Extrapolated values of pseudo first-order rate constants at 25 degrees C are in the range of k = 1-10 sec-1. At suitable concentrations and temperatures, the Na+ salts of both 2'- and 5' - GMP formed stacked and unstacked tetramer units. Relative to the exchange kinetics observed for the disordered nucleotide, the exchange process in the tetramer units was catalyzed in half the amino protons and inhibited in the other half. The catalytic process (k > 10(3) sec-1) has been attributed to amino protons not involved in interbase H-bonding, where as the inhibited process (k < 10(-1) sec-1) was assigned to those protons which do form such bonds. The structure-catalyzed process in both the stacked and unstacked tetramers was manifested by a loss of NMR amino proton intensity due to weighted time-averaging with the resonance for bulk water. A bridging water molecule between an amino proton and a phosphate on an adjacent nucleotide in the tetramer unit may provide a mechanistic pathway for the structure-catalyzed process.

Titanium-containing mesoporous molecular sieves for catalytic oxidation of aromatic compounds.

Titanium silicalite is an effective molecular-sieve catalyst for the selective oxidation of alkanes, the hydroxylation of phenol and the epoxidation of alkenes in the presence of H2O2 (refs 1-3). The range of organic compounds that can be oxidized is greatly limited, however, by the relatively small pore size (about 0.6 nm) of the host framework. Large-pore (mesoporous) silica-based molecular sieves have been prepared recently by Kresge et al. and Kuroda et al.; the former used a templating approach in which the formation of an inorganic mesoporous structure is assisted by self-organization of surfactants, and the latter involved topochemical rearrangement of a layered silica precursor. Here we describe the use of the templating approach to synthesize mesoporous silica-based molecular sieves partly substituted with titanium--large-pore analogues of titanium silicalite. We find that these materials show selective catalytic activity towards the oxidation of 2,6-di-tert-butyl phenol to the corresponding quinone and the conversion of benzene to phenol.

Intercalated clay catalysts.

Recent advances in the intercalation of metal complex cations in smectite clay minerals are leading to the development of new classes of selective heterogeneous catalysts. The selectivity of both metal-catalyzed and proton-catalyzed chemical conversions in clay intercalates can often be regulated by controlling surface chemical equilibria, interlamellar swelling, or reactant pair proximity in the interlayer regions. Also, the intercalation of polynuclear hydroxy metal cations and metal cluster cations in smectites affords new pillared clay catalysts with pore sizes that can be made larger than those of conventional zeolite catalysts.

Stability constant of the 1:1 complex of sodium with guanosine 5'-monophosphate.

The stability of the 1:1 complex of sodium ion with the dianion of guanosine 5'-monophosphate has been determined by means of a potentiometric titration employing a specific ion electrode. The stability constant for the reaction Na(+) + 5'-GMP(2-) Na(5'-GMP)(-) was found to be 2.85 +/- 0.36 M(-1) at 5 degrees C and an ionic strength of 1.1 +/- 0.1 M. Although 5'-GMP forms ordered self-structures at high concentration in the presence of sodium ions, in dilute solution and at low sodium ion concentrations the Na(+) binding is weak and typical of that for other nucleotides.

Use of phospholipid-clay complexes for determining vibrational spectra of membrane related systems.

For determining the infrared and Raman spectra of membrane related systems, a method is developed to incorporate phospholipid bilayer assemblies in a clay matrix to form ultra-thin, self-supporting films. These films, containing stabilized bilayers arranged between the silicate layers of hectorite, are in the shape of discs which measure about 2 cm in diameter and 25 microns thick and require approximately 2 mg of phospholipid for preparation. Although several spectral regions below 1100 cm-1 are masked by the host clay, both head group and acyl chain vibrations may be conveniently observed and monitored for phospholipid conformational changes.