Multinuclear NMR study of aluminosilicate sol-gel synthesis using the prehydrolysis method

Tetraethoxysilane (TEOS), water and aluminum sec-butoxide (Al(OBu^s)₃) are combined in several stages of prehydrolysis technique, and reaction intermediates at each stage were examined by means of both liquid and solid nuclear magnetic resonance of ¹³C, ²⁹Si, ¹⁷O, and ²⁷Al nuclei. The spectra indicate that when Al(OBu^s)₃ is added to a prehydrolyzed TEOS solution an aluminosilicate precursor is formed in which the aluminum is tetrahedrally coordinated by four silicate ligands. When further water is added, gelation is accompanied by the expansion of aluminum coordination; the spectra indicate that this occurs by the nucleophilic attack of silanol groups. At water contents for which gels of low transparency result, this coordination expansion is accompanied by the formation of new siloxane linkages, but at water contents so high that opaque gels result, the coordination expansion proceeds much more quickly and no new siloxane linkages are observed.     

Molecular deformation and free-solution electrophoresis of DNA-uncharged polymer conjugates at high field strengths: theoretical predictions. Part 1: hydrodynamic segregation

Recent advancements in DNA sequencing by end-labeled free-solution electrophoresis (ELFSE) show the promise of this novel technique which overcomes the need for a gel by using a label (or drag-tag) to render the free solution mobility of the DNA size-dependent. It is the attachment of an uncharged drag-tag molecule of a set size to various lengths of DNA in the sample that selectively slows down smaller DNA chains which have less force to pull the drag-tag than larger DNA. So far, only globally random coil conformations have been associated with ELFSE, i.e., the DNA and the label together form a single, undeformed hydrodynamic unit. This paper investigates the conditions under which the DNA and label will segregate into two hydrodynamically distinct units, based on a theoretical approach developed for the electrophoresis of polyampholytes. Optimal experimental conditions tailored to the available label sizes and voltages are predicted along with insight into ideal label architecture.     

Water-Soluble Random and Graft Copolymers for Utilization in Enhanced Oil Recovery

Copolymer structure has a marked effect on solution properties and thus behavioral characteristics of water-soluble copolymers utilized in enhanced oil recovery. The ability of random and graft copolymers to maintain large hydrodynamic volumes in dilute solutions in the presence of mono- and divalent electrolytes is critical for mobility control. The differences in viscosity behavior are described for a series of random and graft copolymers of acryl-amide with sodium-2-acrylamido-2-methylpropane sulfonate (NaAMPS), diacetone acrylamide (DAAM), and sodium acrylate (NaA) as a function of polymer microstructure, temperature, concentration, and added electrolytes. Copolymers of AM-NaAMPS show enhanced salt tolerance and phase stability over their AM-NaA counterparts with similar compositions and molecular weights. The AM-DAAM copolymers show unusual solution behavior with increases in viscosity in the presence of added salt.     

Water-Soluble Copolymers. XX. Copolymers of Acrylamide with Sodium 3-(N-Propyl)Acrylamido-3-Methylbutanoate: Solution Properties

Dilute solution properties of copolymers of acrylamide (AM) with sodium 3-(N-propyl)acrylamido-3-methylbutanoate (NaPAMB) of known molecular weight have been studied as a function of composition, temperature, time, pH, and added electrolytes. Phase separation and potentiometric studies have also been performed. The AM-NaPAMB copolymers possess lower molecular weights and solution viscosities than the AM-NaAMB copolymers. In addition, the AM-NaPAMB polymers exhibit moderate viscosity-temperature coefficients and poor salt tolerance. These polymers undergo phase separation in the presence of divalent cations as a function of temperature. The observed properties can be related to the steric and hydrophobic effects caused by the presence of the n-propyl substituent at the amide nitrogen.