Twin chain

The effect of mixtures of surfactants and polyelectrolytes on spontaneous, water-catalysed hydrolysis (Fadnavis and Engberts, 1982) was mentioned in Section 4, but mixtures of functionalized polyelectrolytes and cationic surfacants are effective deacylating agents (Visser et al., 1983). Polymerized isocyanides were functionalized with an imidazole group and the deacylation of 2,4-dinitrophenyl acetate in the polyelectrolyte was speeded by addition of single or twin chain quaternary ammonium ion surfactants, up to a plateau value. Anionic surfactants had essentially no effect. It is probable that the cationic surfactants accelerate the reaction by increasing the deprotonation of the imidazole groups. 

Fig. 22 a PVBA forms enantiomorphous twin chains of homochiral composition on Ag(lll) and Au(lll). b,c Depending on the coverage the twin chain distances vary, indicating repulsion between them. Only equally handed chains are observed within one domain. Reprinted with permission from [55]. Copyright (2001) American Physical Society... 

Termination. Two radicals react to form one or two molecules having no unpaired spins. If the radicals are assumed randomly distributed in space, the termination rate is second order in radical concentration. Under conditions where diffusion is restricted, however, the twin chains initiated by radicals from the same initiator molecule may remain close together for a time, so that termination has a higher probability than in the case of random distribution of radicals. This case has been discussed by Allen and Patrick (I, 3). It results in a rate expression formally equivalent to a reaction first order in radical concentration, with half-life t. Termination by initiator radicals is also taken into account here. 

A third class of QAC emerged 30 years later in 1965, when new synthetic techniques were developed to allow the economically feasible formation of twin chain or dialkyldimethylquaternary ammonium chlorides (DDACs) [4], These QACs exhibit even higher biocidal efficacy than their predecessors. 

ID-supramolecular PVBA (6.88) twinned chains on the Ag (111) surface. The spontaneous resolution leads to enantiomorphic domains. The chains run along the [ll-2]-direction of the Ag-lattice. 

The next step of condensation is reached when chains are fused together. There exist a number of different structure types based on the characteristic building unit of the twin chain, e.g. in R6X7C2, R7X10C2, SC7CI10 and GdjIjC. With the exception of SC7Q10 the presence of interstitial atoms is well established in all of these structures. 

Crystallographic data of metal-rich rare earth halides with twin chains. 

Fig. 21. Twin chain of edge-sharing Scg octahedra in the structures of Sc CIjq.

Compounds containing either twin chains or layers of octahedra are metallic, at... 

Figure 5-33. Central projections along the shortest axes of the structures of a) Gd4lsC (chains), b) Gd BrvQ (twin chains), c) Gd2Cl2C2 (discrete layers), d) Gd2lC (layers bridged via I atoms), and e) Gd ClsCs (tilted...

It was mentioned earlier that the interstitial atoms in the octahedral void of a discrete cluster may also be transition metal instead of nonmetal atoms as, for example in [Gd6li2Fe]. [190] Octahedral clusters which are centered by a transition metal atom and condensed into chains (Pr4l5M) [191] and twin chains... 

The height of a flight is normally between 3 and 6 times thef light spacing. Its width will depend on the particle size of the material to be handled. With a twin chain... 

In a first approximation we therefore have one single bond to the equatorial Cl and two half bonds within the chains (chain angle 105.6°). In the real structure each single Cl atom makes weak bonds (Sn—Cl =3.06 A) with two Sn atoms of the neighboring chain, thus linking the chains pairwise. These twin chains are arranged in a layered manner, with distances Sn—Cl = 3.22 A to the next twin chain. The distance between these pseudolayers is Sn—Cl = 3.30 A. The structure thus is intermediate between fibrous and layered. 

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