Extraordinary transition

The materials and methods used in this work have been described in detail in the original publications (1 3). Briefly, the DNA used in the gelation work was prepared by extensive sonication of calf thymus DNA it had a degree of polymerization of 200 30 base pairs (bp). The DNA used in the ordinary-extraordinary transition studies was prepared by nuclease digestion of chromatin from chicken erythrocytes it was an equimolar mixture of two sizes, 140 bp and 160 bp, averaged to 150 bp. 

Mechanistic Ideas. The ordinary-extraordinary transition has also been observed in solutions of dinucleosomal DNA fragments (350 bp) by Schmitz and Lu (12.). Fast and slow relaxation times have been observed as functions of polymer concentration in solutions of single-stranded poly(adenylic acid) (13 14), but these experiments were conducted at relatively high salt and are interpreted as a transition between dilute and semidilute regimes. The ordinary-extraordinary transition has also been observed in low-salt solutions of poly(L-lysine) (15). and poly(styrene sulfonate) (16,17). In poly(L-lysine), which is the best-studied case, the transition is detected only by QLS, which measures the mutual diffusion coefficient. The tracer diffusion coefficient (12), electrical conductivity (12.) / electrophoretic mobility (18.20.21) and intrinsic viscosity (22) do not show the same profound change. It appears that the transition is a manifestation of collective particle dynamics mediated by long-range forces but the mechanistic details of the phenomenon are quite obscure. 

Figure 5. Regions of stability of isotropic and anisotropic solutions of 150 bp DNA, calculated according to Stigter 22L) The light band corresponds to the coexistence region for fully charged DNA, the dark band to DNA with 76% of charge neutralized by counterion condensation. The salt/DNA concentration regions where the gelation and ordinary-extraordinary transitions were studied are indicated by brackets.

Fig. 46. Schematic order parameter (magnetization) profiles m(z) near a free surface, according to mean field theory. Various cases arc shown (a) Extrapolation length X positive. The transition of the surface from the disordered state to the ordered state is driven by the transition in the bulk ( ordinary transition ). The shaded area indicates the definition of the surface magnetization ms. (b) Extrapolation length X = oo. The transition of the surface is called "special transition ( surfacc-bulk-multicritical point ), (c), (d) Extrapolation length X < 0, temperature above the bulk critical temperature (c) or below it (d). The transition between states (c) and (d) is called the extraordinary transition , (c) Surface magnetic field Hi competes with bulk order (mi, > 0, 0 < H such that mi < -mb). In this case a domain of oppositely oriented magnetization with macroscopic thickness ( welting layer ) separated by an interface from the bulk would form at the surface, ir the system is at the coexistence curve (T < Tv, H = 0). From Binder (1983).

The presence of a slow diffusion seems to be characteristic for most polyelectrolyte solutions. The slow mode was first detected by Schurr et al. [218] for poly(L-lysine) upon variation of salt concentration. A sudden drop of the diffusion coefficient was observed as the salt concentration was decreased below some critical value. Since then, this transition is called ordinary-extraordinary transition , the fast diffusion being referred to as ordinary and the slow diffusion as extraordinary . Drifford and Dalbiez [219] later gave an empirical expression which describes the relation between this critical salt concentration... 

The existence of the cluster has also been proposed from dynamic light scattering experiments the time corrdation function obtained for solutions of some ionic polymers at low salt concentrations showed two or three dynamic modes, fast and slow. The very slow mode was first reported by Lin, Lee, and Schurr, who coined the term ordinary-extraordinary transition for its appearance at low salt concentrations [11]. Several authors have also observed essentially the same phenomena by DLS [bb-TO]. The slow mode has been attributed to the translational diffusion of (temporal) cluster by Schmitz [66], or of multi-chain domains (dusto s) by Sedlak [68,70]. We also observed two modes for polystyrenesulfonate solutions we attributed the slow mode to the translational diffusion of the localized ordered structures [71]. 

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