Chain basic transformations

Two chain variants of opposite phase exist, as represented in Fig. 7.14, called L- and R-type. An L-chain is transformed into an R-chain by a mirror operation perpendicular to the chain direction or by a rotation of 180° about the c-axis. In [7.57, 7.58], the average stmcture was determined on the basis of X-ray data for the 1212-Ga compound. In the basic undistorted unit cell all chains are parallel, and of the same type. The rectangular quasi-square (OOl)p mesh is... 

Fig. 1.12. Four basic transformations of pairs of linear chain segments. Excess volume of pairs refers to PE, with Vq being the volume of a CH2-group [381.

The ability to stack genes in transgenic plants by successive crosses between individually transformed parental plants is a considerable advantage in attempting to construct multimeric protein complexes, such as secretory antibodies. As described earher, slgA consists of two basic Ig monomeric units (heavy and tight chains) that are dimerized by a joining (J) chain and then associated with a fourth polypeptide, the secretory component (SC) [36]. 

An Indian team carried out the transformation of mercaptotriazole 320 using an oxazolone reagent <2001IJB252> and found that a series of triazolothiazines with the substitution pattern 321 can be obtained in high yields. Treatment of the mercaptotriazole with an unsaturated ketone side chain 322 under basic conditions gave rise to ring closure to 323 <1998JRM2056>. 

Chojnowski and co-workers have studied the polymerization of octamethyltetrasila-l,4-dioxane, a monomer more basic than cyclosiloxanes, which is capable of forming more stable oxonium ions, and thus being a useful model to study the role of silyloxonium ions.150-152 In recent work, these authors used Olah s initiating system and observed the formation of oxonium ion and its transformation to the corresponding tertiary silyloxonium ion at the chain ends.153 The 29Si NMR spectroscopic data and theoretical calculations were consistent with the postulated mechanism. Stannett and co-workers studied an unconventional process of radiation-initiated polymerization of cyclic siloxanes and proposed a mechanism involving the intermediate formation of silicenium ions solvated by the siloxane... 

The solution is transformed to an oil-in-oil emulsion in which a polystyrene solution forms the disperse phase and the elastomer polyester component solution the continuous phase. The point of phase separation is observed experimentally by the onset of turbidity, due to the Tyndall effect. The conversion required for phase separation to occur depends basically on the solubility of the polystyrene chains in the elastomer solution, which in turn is governed by the elastomer concentration and compatibility of the two polymers. 

---