Phenolic spheres

Microballons, BJOA-0840 Hollow phenolic spheres 10% 40-100 mesh 74% 40-200 mesh 18% through 200 mesh 0.3-0.4... 

The foam elements in syntactic foams may be glass microspheres, with diameters ranging from 20 to 200 microns, or other spheres with diameters ranging from 0.05 mm to 2 cm, which are classed as macro-spheres. The materials used to form the spherical particles are glass, phenolic resins, silica, and naturally occurring materials such as perlite and coal dust. The most commonly used materials are glass and phenolic spheres. The syntactic foams are made by simply mixing the micro- or macrospheres into the catalyzed resin until the desired consistency is... 

Spheres. HoUow spherical fillers have become extremely useflil for the plastics industry and others. A wide range of hoUow spherical fillers are currently available, including inorganic hoUow spheres made from glass, carbon, fly ash, alumina, and 2h conia and organic hoUow spheres made from epoxy, polystyrene, urea—formaldehyde, and phenol—formaldehyde. Although phenol—formaldehyde hoUow spheres are not the largest-volume product, they serve in some important appHcations and show potential for future use. 

Section 18.2). The latest generation of such catalysts (1 in Fig. 18.17) reproduces the key features of the site (i) the proximal imidazole ligation of the heme (ii) the trisi-midazole ligation of distal Cu (iii) the Fe-Cu separation and (iv) the distal phenol covalently attached to one of the imidazoles. As a result, binding of O2 to compound 1 in its reduced (Fe Cu ) state appears to result in rapid reduction of O2 to the level of oxides (—2 oxidation state) without the need for outer-sphere electron transfer steps [Collman et ah, 2007b]. This reactivity is analogous to that of the heme/Cu site of cytochrome c oxidase (see Section 18.2). 

Figure 7 Mixld for iron (Fe) deficiency induced changes in root physiology and rhizo-sphere chemistry associated with Fc acquisition in strategy I plants. (Modified froin Ref. 1.) A. Stimulation of proton extru.sion by enhanced activity of the plasnialemma ATPase —> Felll solubilization in the rhizospherc. B. Enhanced exudation of reductanls and chela-tors (carhoxylates. phenolics) mediated by diffusion or anion channels Pe solubilization by Fein complexation and Felll reduction. C. Enhanced activity of plasma membrane (PM)-bound Felll reductase further stimulated by rhizosphere acidificalion (A). Reduction of FolII chelates, liberation of Fell. D. Uptake of Fell by a PM-bound Fell transporter.

Figure 22 Positioning of the Tyr8 phenol ring (colored stick structures) relative to the Ni11 (purple sphere) and its chelate ring (ball-and-stick structure). The lowest-energy representatives of conformational families 1-3 are shown in blue, green, and yellow, respectively. The phenol oxygen is a red sphere.1747...

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

Sphere, flow across, 15 72 It Sphere-of-influence (SOI), 19 355-356, 358 Spherical bubbles, in foams, 12 7-8 Spherical fillers, phenolic resin,... 

Rates of ligand exchange depend quite strongly on the coordina-tive environment of the metal center. The water exchange rate of Fe(H2O)5(OH)is almost three orders of magnitude higher than that of Fe(H20)g+, and follows a dissociative, rather than an associative exchange mechanism (20). Fe(1120)5(OH)has also been shown to form inner-sphere complexes with phenols (27), catechols (28), and a-hydroxycarboxylic acids (29) much more quickly than Fe(H20) +. The mechanism for complex formation with phenolate anion (A-) is shown below (27) ... 

Finally, metal- and resin-bonded composites are also classified as particulate composites. Metal-bonded composites included structural parts, electrical contact materials, metal-cutting tools, and magnet materials and are formed by incorporating metallic or ceramic particulates such as WC, TiC, W, or Mo in metal matrixes through traditional powder metallurgical or casting techniques. Resin-bonded composites are composed of particulate fillers such as silica flour, wood flour, mica, or glass spheres in phenol-formaldehyde (Bakelite), epoxy, polyester, or thermoplastic matrixes. 

Figure 7-18 Stereoscopic MolScript ribbon drawings of the B chains (A chains omitted) of (A) hexameric 2-zinc pig insulin. (B) A phenol complex of the same protein. Within each dimer the B chains are shaded differently. The Zn2+ ions are represented by white spheres and the coordinating histidine side chains are shown. Six noncovalently bound phenol molecules can be seen, as can several conformational differences. From Whittingham et al.B7 Courtesy of Peter C. E. Moody.

The Philadelphia Quartz Company in USA produces Q-Cel quartz micro-spheres 20,21. These have an apparent density of 300 kg/m3, a bulk density of 100 kg/m3, and an average diameter of 75 pm. They are mechanically very strong and are very cheap (half the price of glass and one third of the price of phenolic microspheres). 

---