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PubMed1997

Nanoporous Molecular Sandwiches: Pillared Two-Dimensional Hydrogen-Bonded Networks with Adjustable Porosity

Crystal engineering of molecular materials is commonly frustrated by the absence of reliable structural paradigms that are needed for systematic design of crystal lattices with predictable structure and desirable function. This problem can be attributed, at least partially, to the absence of robust supramolecular motifs that serve as synthons for the assembly of crystal lattices. A novel class of molecular crystals based on two-dimensional hydrogen (H)-bonded networks comprising guanidinium ions and the sulfonate groups of alkane- or arenedisulfonate ions is described. The disulfonate ions act as pillars that connect opposing H-bonded sheets and form nanoporous galleries with one-dimensional channels. The flexibility of the H-bonded network allows the galleries to adapt to changes in the steric requirements of guest molecules that occupy the channels. This robustness reduces crystal engineering to the last remaining dimension, enabling rational adjustment of the gallery heights by choice of the disulfonate pillar.

Journal Article↗
PubMed1979

Adherence of bacteria, yeast, blood cells, and latex spheres to large-porosity membrane filters.

Strong adherence of bacteria, yeast, erythrocytes, leukocytes, platelets, spores, and polystyrene spheres to membrane filter materials was noted during filtration through membranes with pore size diameters much larger than the particles themselves. Quantitative recovery on the membrane filters of these particles from low-concentration suspensions was achieved during gravity- or vacuum-assisted filtration through membranes with pore diameters as much as 30 times that of the filtered particles. Mechanical sieving was not responsible. The phenomenon was judged to be electrostatic. It could be partially blocked by pretreating the filter with a nonionic surfactant (Tween 20), and elution of adherent particles was achieved with 0.05% Tween 20. Gram-positive cocci were removed from suspension more efficiently than gram-negative rods. The commonly used cellulose membranes adsorbed more bacteria, blood cells, and other particles than did polycarbonate filters. Of lesser adsorptive capacity were vinyl acetate, nylon, acrylic, and Teflon membranes. Backwashing with saline, serum, 6% NaCl, dextran solutions, or phosphate buffers of varying molality and pH removed only a fraction of adherent particles. Tween 20 (0.05%) eluted up to 45% of adherent particles in a single back-filtration. Selected filters quantitatively removed the particles tested, which then could be washed and subjected to reagents for a variety of purposes. It is important to anticipate the removal of particles during membrane filtration, since it is not a simple mechanical event.

Adsorption↗
PubMed1991

Ultrastructure, inferred porosity, and gram-staining character of Methanospirillum hungatei filament termini describe a unique cell permeability for this archaeobacterium.

By light microscopy, Methanospirillum hungatei GP1 stains gram positive at the terminal ends of each multicellular filament and gram negative at all regions in between. This phenomenon was studied further by electron microscopy and energy-dispersive X-ray spectroscopy of Gram-stained cells, using a platinum compound to replace Gram's iodine (J. A. Davies, G. K. Anderson, T. J. Beveridge, and H. C. Clark, J. Bacteriol. 156:837-845, 1983). Crystal violet-platinum precipitates could be found only in the terminal cells of each filament, which suggested that the multilamellar plugs at the filament ends were involved with stain penetration. When sheaths were isolated by sodium dodecyl sulfate-dithiothreitol treatment, the end plugs could be ejected and their layers could be separated from one another by 0.1 M NaOH treatment. Each plug consisted of at least three individual layers; two were particulate and possessed 14.0-nm particles hexagonally arranged on their surfaces with a spacing of a = b = 18.0 nm, whereas the other was a netting of 12.5-nm holes with spacings and symmetry identical to those of the particulate layers. Optical diffraction and computer image reconstruction were used to clarify the structures of each layer in an intact plug and to provide a high-resolution image of their interdigitated structures. The holes through this composite were three to six times larger than those through the sheath. Accordingly, we propose that the terminal plugs of M. hungatei allow the access of larger solutes than does the sheath and that this is the reason why the end cells of each filament stain gram positive whereas more internal cells are gram negative. Intuitively, since the cell spacers which partition the cells from one another along the filament contain plugs identical in structure to terminal plugs, the diffusion of large solutes for these cells would be unidirectional along the filament-cell axis.

Actin Cytoskeleton↗
PubMed1979

Activity staining for glutamate and alanine dehydrogenases in polyacrylamide gels of varying porosity. A study of bovine placental enzyme forms.

A procedure has been developed for characterizing the various molecular forms of placental and liver glutamate dehydrogenases through a combination of activity staining and varying gel pore size in electrophoresis. At a concentration of 2 mg/ml, the bovine liver GDH remained associated in a very high molecular weight form, while the placental enzyme was substantially dissociated to a molecular species of near 240,000 molecular weight and several charge isomeric species of near 160,000 molecular weight. The general approach outlined here provides a means of definitely correlating the electrophoretic behavior of various dehydrogenase isozymes with both glutamate and alanine dehydrogenase activities and molecular size and should be applicable, even in crude extracts to other dehydrogenase enzymes which exhibit multiple forms or states of association.

Alanine↗