Molecular accordion

While these initial experiments provided good evidence in support of this "molecular accordion" mechanism, many issues remained to be clarified. Here we examine the mechanism of the adsorption and docking of the polymers as they are added, below the LCST, to aqueous liposome suspensions. Special attention was paid to the role of the alkyl pendent groups during the adsorption process and to the importance of the physical state of tne lipid bilayer. These questions were addressed primarily through the use of fluorescence measurements with labeled polymers. Supportive evidence was provided by microcalorimetric studies. 

Ringsdorf H, Venzmer J, Winnik EM. Interaction of hydrophobically modified poly(N-isopropylacrylamide) with model membranes—Or playing a molecular accordion. An w Chem... 

In one extreme, termed the regularly folded-adjacent-re-entry stmcture, the molecular chains appear to be accordion-like, making precise hairpin turns in order to yield the optimum level of possible crystallinity. However, equally consistent with the gross morphological features is the other model illustrated. Here, there is a distinct, disordered, amorphous overlayer. This schematic representation has popularly been termed the switchboard model. Both of these interfacial stmctures, and those in between, are consistent with the electron micrographs. The reason for introducing these concepts here is that a lamellar-type crystallite is also the universal mode of crystallization of a homopolymer from the pure melt. 

The Raman spectra of the spacer-related compounds TMB, HMB, OMB, and DMB have also been examined. The crystal structures of hexa- and decamethonimn bromides [7] were elucidated by a single-crystal X-ray diffraction analysis, which showed that the molecular chain, which included the two nitrogen atoms and one CH3 carbon atom of the terminal N(CH2>3 groups, was in a fully extended form. Thus, the methonium bromide chains should provide evidence for the accordion vibrational bands. 

Because the plots of the band frequencies of the methonium bromides against the reciprocal number of carbon atoms are linear, these bands for TMB, HMB, OMB, and DMB are assigned to the accordion modes of the extended molecular chains [4,5]. 

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