Conformational instability

The release of energy to the dye molecule or fluorescer is driven by the conformational instability of the C2O4 intermediate (the flat highly strained C2O4 prefers to be two linear CO2 molecules). The sensitized fluorescer, denoted fluorescer, returns to the ground state via the emission of light ... 

Such an attraction would overcome, at least in part, the conformational instability imposed by the erected oxygen atom. For pyranosides which are not deoxygenated at C-6, the added electron-withdrawing power of the hydroxymethyl (or acyloxymethyl) group at C-5 should increase the charge on C-5, thus favoring a-D-glycoside formation even more.M(b)... 

Miller, J. A. Leong, W. Zweifel, G. Conformational instability of a-alkenyl and a-alkynyl vinyllithiums. Synthesis of stereodefined... 

Fig. 2.—The Arrangement of Carbon-Oxygen Valences about Carbon Atoms 1 and 2 Resulting in Increased Conformational Instability (the A2 Condition).

It is simplest to think of sharkskin as a result of a quasi-periodic perturbation on the overall extrudate swell. This small amplitude fluctuation of extrudate swell arises from the oscillation of the boundary condition at the exit wall that produces an oscillation of the local stress level as the interfacial chains suffer a conformational instability. The local boundary condition oscillates between noslip and slip, resulting in the fluctuation of the stress level at the die exit. To determine whether some sort of melt fracture occurs, we need to know not only the... 

Scheme 8 Conformational instability of chains from sp carbon atoms and strategies to avoid it. Some basic combinations of the stilbene and polyarene type.

Ring conformations are believed to be important in drug activity. For example, experimental evidence suggests that the analgesic fentanyl binds to opiate receptors preferentially in the conformation shown in Fig. 21, where the bulky substituents are positioned equatorially to minimize conformational instability. 

These data extend to the pyranoside series the relationship between steric strain and reactivity, and indicate that the conformational instability and non-bonded interaction of the axial substituents in the favored chair conformation result in a higher rate of hydrolysis. Another aspect of these theoretical considerations is that the methyl /3-d and fi-L aldopyranosides are only hydrolyzed faster than their corresponding a anomer when the normal chair conformation is favored, and thus, when the glycosidic group of the (3 anomer assumes an exposed, equatorial position (see page... 

The greater reactivity of 91 as compared with 90 (at low pH) is reminiscent of the difference between the idoses and the glucoses in regard to the ease of 1,6-anhydride formation, and is probably a reflection of the conformational instability inherent in D- or L-idopyra-nose structures. 

The conformational instability of DPM is partially transmitted to derivatives that are important in supramo-lecular chemistry, such as cavitands. " " Resorcarenes are conformationally mobile, with a AG for the rotation... 

The reversed-phase HPLC method is a traditional method for the analysis of peptides and proteins. A good choice for the stationary phase could be a short-alkyl reversed-phase (e.g., C4) with wide pores (30 nm). It has been shown that large pore supports give distorted peaks with small collagens and triple helical peptides, resulting in poor resolution. The formation of broad peaks has been ascribed to conformational instability of the separated solutes and slow cis-trans isomerization of the peptide bonds. The best sorbents of those examined were diphenyl or non-porous Cig reversed-phases standard water-acetonitrile gradients were recommended as mobile phases. 

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