Thermally reversible organogels, comprised of a variety of organic liquids and low concentrations of relatively low molecular mass aza analogues of previously investigated ALS (i.e., aromatic linker steroid) molecules have been investigated. The aza-ALS gelators are derivatives of 3β-cholesteryl 4-(2-anthrylamino)butanoate (CAAB) and 5R-cholestan-3β-yl aryl-or alkylcarbamates. The relationship between gelator structure and efficiency of gelation is explored. The molecular packing arrangements of the gelators in the gel (strands) and other phases are investigated by several physical methods. The results provide insights into the factors that do and do not lead to efficient gelators of this type. For instance, UV-vis absorption and fluorescence spectra of the gel and crystalline phases of 5R-cholestan-3β-yl N-(2-anthryl)-N-methylcarbamate (CAMC) exhibit red-shifted bands that can be associated with J-type aggregates. From comparative infrared spectral investigations, it is concluded that there are no hydrogen-bonding interactions of 5R-cholestan-3β-yl N-(2-anthryl)carbamate (CAC) or 5R-cholestan-3β-yl N-(2-naphthyl)carbamate (CNC) molecules in the gels; the larger interactions of CAC molecules than of CAMC molecules in the gels appear to be a consequence of the smaller size of the N-substituent of CAC that allows closer molecular packing in strands. The small transition dipoles of naphthyl rings of CNC molecules are apparently too weak to promote detectable exciton coupling of aggregates (if present) in their gel and solution phases. Strong extrinsic circular dichroism of the gel phases of CAC indicate that its aggregates are in macrochiral arrangements. More than one strand morph can be formed by changing the cooling protocol associated with sol w gel transitions of CAC/1-pentanol samples. Dichroism of the gel phases of CAMC and CNC is large but significantly weaker and less well defined than that of CAC. Although CAAB, the amino analogue of the excellent "oxa" gelator, 3β-cholesteryl 4-(2-anthryloxy)butanoate, gelled none of several liquids examined, its amide derivatives did. As with CAC, IR spectra of CAAB and single-crystal X-ray diffraction and IR data for 5R-cholestan-3β-yl N-(4-n-butylphenyl)carbamate (CBPC, a nongelator) provide no clear evidence for H-bonding to oxygen atoms in their crystalline phases. Thus, hydrogen bonding, a critical factor in many other aggregate geometries, including those of various gelator strands, is subordinated to other van der Waals forces.

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Spherical polyacrylamide/magnetite (PAM) composite beads, suitable for use in a magnetically stabilized fluidized bed (MSFB), were manufactured by a suspension polymerization method. Yield of beads depended on the type and concentration of buffer used during polymerization as well as the pH. More stabilizer was needed to prevent bead agglomeration as magnetite concentration increased. Bead diameter ranged from less than 60 to 600 μm, depending on reaction conditions, and the bead mean diameter and size distribution decreased with increasing impeller speed. The density and roundness factor of the beads were 1.19 ± 0.02 g cm‐3 and 1.08 ± 0.03, respectively. The beads had high magnetization at a low applied magnetic field strength (60 mT at 75 kA m‐1) and retained little residual magnetization (<2 mT) after the field was removed. Incorporation of magnetite did not significantly affect the physical strength of the beads: the beads' average elastic modulus was 14 ± 4 kPa, similar to reported values for polyacrylamide gels (15.8 kPa). The beads were stable in a range of buffers from pH 1 to 10 and were resistant to microbial degradation. The fluidization and stabilization behavior of the beads was examined in a bench‐scale MSFB. The minimum fluidization velocity (Umf) of the beads (0.035 mm s‐1) allowed the MSFB to be operated at superficial velocities close to those used in HPLC systems. Against expectations, at high superficial velocities, the stabilized bed of the MSFB had a greater expansion than the unstabilized bed. The PAM beads could be derivatized and activated for soybean trypsin inhibitor immobilization by a standard carbodiimide method, and the affinity separation of trypsin from chymotrypsin was demonstrated. The PAM beads show excellent potential for use in MSFB chromatography. © 1997 John Wiley & Sons, Inc.

The condensation of bis(o-formylphenyl) selenide with 1,2-diaminoethane or 1,3-diaminopropane yielded the new macrocyclic ligands 1 and 2 in very good yields. Crystals of 1 are monoclinic, space group P2 1 /c with a = 10.0648 (10)

The reaction of equimolar quantities of 1,8bistrimethylstannylnaphthalene (1) and GaCl 3 in toluene yields a stannagallacycle, namely, bis(µ-1,8-naphthalenediyl)(µ-chloride)methyltin(IV)chlorogallium(III) (2). Compound 2 is insoluble in solvents of low polarity and has been characterized by EA, MSCI, and X-ray analysis. The latter revealed the existence of a folded eightmembered dimetallacycle as well as the presence of a chloride ligand bridging the two metals. When treated with pyridine, formation of a soluble bis(pyridine) adduct (3) occurs. Compound 3 has been characterized by EA and 1 H, 13 C, and 119 Sn NMR spectroscopy. As shown by X-ray single-crystal analysis of 3, the central eightmembered dimetallacycle of the molecule has remained intact on going from 2 to 3. Compound 3 does not feature a bridging chloride, and its structure is that of a Lewis acid-Lewis base adduct in which two independent pyridine molecules coordinate the metal centers.