Recrystallization inhibition

The first generation C-linked analogs were assayed using two conventional techniques. These techniques are recrystallization-inhibition (RI) assay (29, 30) and nanoliter osmometry (31). The RI assay offers a distinct advantage in that it is effective at detecting antifreeze protein-specific activity at concentrations typically too low to cause a thermal hysteretic effect (29). 

Kelvin effect, 153 mattress model of adsorption inhibition, 153-154 medical applications, 155 recrystallization- inhibition applications, 155 repeating tripeptide unit, 152 step pinning model of adsorption inhibition, 153-154 structure, 152 subtypes, 152... 

A major reason why Zr (rather than Cr, Mn, V or Ti) has become the preferred choice as the recrystallization inhibiting element relates to its relatively low effect on quench sensitivity in commercial aluminum alloys [6],... 

Extrusion Resins. Extmsion of VDC—VC copolymers is the main fabrication technique for filaments, films, rods, and tubing or pipe, and involves the same concerns for thermal degradation, streamlined flow, and noncatalytic materials of constmction as described for injection-molding resins (84,122). The plastic leaves the extmsion die in a completely amorphous condition and is maintained in this state by quenching in a water bath to about 10°C, thereby inhibiting recrystallization. In this state, the plastic is soft, weak, and pHable. If it is allowed to remain at room temperature, it hardens gradually and recrystallizes partially at a slow rate with a random crystal arrangement. Heat treatment can be used to recrystallize at controlled rates. 

Just above the melting point the polymer is visually quite viscous and numerous observations have been made that the polymer exhibits a memory effect, that is to say, on recooling the melt crystallites will appear in the same sites where they had been before melting the polymer. Hartley, Lord and Morgan (1954) state It is reasonable to suppose that there will be a few localities in the crystalline polymer which have a very high degree of crystalline order, and therefore the melt can contain, even at considerable temperatures above the observed melting or collapse point, thermodynamically stable minute crystals of the polymer . Especially if the polymer has been irradiated so as to contain a few crosslinks as in irradiated polyethylene, then flow is inhibited and spherulites can be made to appear on recrystallization in the same sites that they had before the polymer was melted, Hammer, Brandt and Peticolas (1957). However, as mentioned above, the specific heat of irradiated polyethylene in the liquid state is identical with that of the unirradiated material, within the limits of experimental error. Dole and Howard (1957). 

FIGURE 17.9 Inhibition of dissolution and recrystallization of sulfathiazone by PVP. Temperature cycling of 2% sulfathiazole suspensions demonstrating the effect of PVP on dissolution and recrystallization. (Publication by Ziller, K. H. and Rupprecht, H. H. (199 )harm. Ind., 52 1017-1022. With permission.)... 

Even more interesting is the addition of the (.S )-cnantiomcr of 2-amino-1-butanol, which itself forms a salt with (R)-mandelic acid. This salt has almost inhnite solubility. With this additive, the resolution of alaninol with (W)-mandelic acid results in the crystallization of an almost diastereoiso-merically pure salt, without incorporation of 2-amino-l-butanol. On use of this method enantiopure (R)-alaninol can be obtained after an additional recrystallization, without the need to separate the alaninol from the 2-amino-l-butanol. We call this procedure reverse Dutch Resolution, to indicate that the family mix remains in solution. Most likely in this case stereoselective nucleation inhibition plays a role by suppressing the nucleation of the (.S )-alaninol-(A )-mandclic acid diastereoisomer. 

Another laboratory invoked the role of water in bread staling involving a zipper mechanism that results in the formation of interchain crosslinks 492 Moisture redistribution from crumb to crust played a significant role in crumb firming and amylopectin recrystallization for breads stored for more than seven days 493 According to Piazza and Masi494 to inhibit staling it is more important to slow the dehydration phenomena than it is to increase the initial moisture content in the bread. 

Freeze-tolerant insects and plants have been found to contain substantial concentrations of AFP s, a phenomenon that may appear paradoxical. However, THPs present in the extracellular fluids may contribute importantly to freeze-tolerance by inhibiting recrystallization, thus keeping the ice crystals that do form in the extracellular space small enough to prevent... 

It was originally thought that lead azide existed in two allotropic forms a and 0 (VoL 111, p. 169). Now it is accepted that tlie substance is polymorphic and exists in four forms o, 0, y and 6. The a-orthorhombic is the only one acceptable for technical application. It is the main product of precipitation with traces of the other forms present [89]. The monoclinic jS-fomi is stable when dr>. but recrystallizes as the a-form. Tlie presence of some organic dyes (e.g. eosin) enhances the fomiation of form and hydrophile colloids inhibit its formation. Breaking a needle of Torm may produce an explosion (contrary to the views of some authors Vol. Ill, p. 173). The monoclinic y-form is less stable than a and jS [90]. It can be obtained from pure reagents at pll 3.5—7.0 or in the presence of vinyl alcohol. The triclinic 6-form precipitates from pure reagents at pH values of between 3.5 and 5.5 [90]. Both forms yand 6 are usually precipitated simultaneously and can be separated (with care ) by hand. 

The major efforts to increase Tg include two noteworthy innovative approaches (i) Synthesis of starburst molecules, suitable for HTLs, whose patently nonplanar structure inhibits recrystallization,71 and (ii) synthesis of novel molecules in which familiar luminescent molecules are synthesized around a spiro-bifluorene core.70 As shown by Spreitzer et al.,70 Tg of these spiro derivatives, such as spiro-DPVBi, is considerably higher than that of the parent molecules, yet their PL and EL spectra are essentially identical. As expected, the lifetime of the OLEDs fabricated from the spiro derivatives is considerably higher than that of the parent-compound-based devices, both at room and at elevated temperatures. 

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