Mobility intramolecular

Intramolecular mobility of metal complexes of rotaxanes and catenanes with macroheterocyclic fragments 98ACR611. 

The investigation of structural dynamics of CP is particularly topical in connection with the establishment of correlation between local intramolecular mobility and the reactivity of chain fragments. It has been established that groups located in the most mobile parts of the polymer chain exhibit the greatest reactivity [48], The chemical heterogeneity in relationship to local mobility is particularly... 

This reaction bears a close similarity to the one discovered by J.F. Klebe who found that acid amides with dialkyldichlorosilanes yield disilaoxadiazines (2). The interesting intramolecular mobility of these compounds was studied by 11NMR spectroscopy and the mechanism of internal silyl migrations within their molecules arose some discussion in the literature (3,4). 

Job emphasized the reaction dynamics of inter- and intramolecular mobilities, the presence of unstable intermediary compounds (sometimes visible by a brief change in coloration), and the electronic or ionic character of transitory complexes. We are led to suppose, with the English chemist Lowry, he said,... 

G. I. Likhtenstein and A. I. Kotelnikov, The studies of fluctuational intramolecular mobility in proteins by physical labels, Mol. Biol, (Moscow) 17, 505-519 (1983). 

The intramolecular mobility, which yields many other conformations between these two extremes, is the basis for viscoelasticity in polymers. Pendant groups, such as the methyl group in isobutane, and lower temperatures decrease the mobility of model compounds such as ethane as well as the polymer chains of polyethylene. 

Because of intramolecular mobility (rotations, inversions) and intermolecular interactions, chemicals shifts depend on temperature, solvent, and concentration. Coupling constants, however, for the most part do not depend on these conditions. 

Intramolecular Mobility and the Temperature Dependence of 13C Chemical Shifts and Line Widths... 

Many molecules show intramolecular mobility Rotations of groups about a bonds or inversions of cycloaliphatic rings are representative phenomena. A well-known example is N,N-dimethylformamide, which exists as an equilibrium mixture of ris and tram isomers due to the partial n character of the N — CO bond Rotation of the dimethyl-amino group is restricted at room temperature but occurs upon heating. 

As a generalization, intramolecular mobility may give rise to equilibria of isomerization between two species A and B ... 

Due to the third condition and the fact that the rate constant kr is a function of temperature according to eq. (3.9), the NMR spectra of molecules susceptible to interconversion due to intramolecular mobility are temperature dependent. This behavior, which is discussed in more detail in standard texts (e.g. [5]) and reviews [107, 108], is illustrated in Fig. 3.10. 

Fig. 3. tO. Temperature dependence of chemical shifts and line shapes due to intramolecular mobility. 

Using the temperature dependence of NMR spectra, thermodynamic data of interconversions due to intramolecular mobility can be determined. If the coalescence temperature is known, the rate constant at Tc is calculated according to eq. (3.10). Often, Tc and (vA — vB) are not known exactly. In this case, a rough value for kr can be calculated by measuring the half maximum intensity line widths dv1/2(T, at temperatures near Tc and using eq. (3.11) [107, 108],... 

In a majority of works on LC polymers, the main attention was paid to the synthesis and structural studies of such polymers. Significantly less information is available on physical properties of LC polymers, especially, when compared to low-molecular liquid crystals. In this chapter some rheological and dielectric properties of polymeric liquid crystals, characteristics of their dynamic properties and intramolecular mobility, are considered. 

This was qualitatively shown in investigations of conformational behaviour and intramolecular mobility (IMM) of cholesterol-containing polymers in dilute solutions as of a function of solvent quality 134-136,185-l88) and temperature. Polarization luminescence provides one of the most fruitful methods for the evaluation of IMM l75,176). The method permits to get direct information about rotational mobility of the macromolecule as a whole, as well as about the mobility of the main chains and side branches. This is achieved via the attachment to macromolecules of so called luminescent markers (LM) — anthracylacyloxymethane groups in the case reported. Below are shown the chain fragments with LM which give information on the mobility of main chains (LM-1) and of side groups (LM-2) ... 

Table 17 presents relaxation time values characterizing the intramolecular mobility of various fragments of cholesterol-containing polymers with LM in various solvents9. As is seen, the values of relaxation times measured for the same polymer in various solvents differ significantly, which reflects the specificity of conformational state and intramolecular organization. 

But the question may also be answered differently. It is perhaps legitimate to claim that the fact that so many researchers are attracted and fascinated by the field and find it intellectually challenging, is a good enough justification in itself. For those who want to put their experimental or theoretical method to a critical test, large amplitude motion studies are to be recommended. Like many other fields of science, the study of intramolecular mobility is primarily carried out on its own merits, leaving possible application to future research. 

Kaivarainen, A.I., Rozhkov, S.P., Franek, F., Olshovska, Z. (1983) Intramolecular mobility in antiDNP antibodies and their Fab fragments. ESR spectra of the complexes with a spin-labelled hapten in H20-D20 mixtures at various temperatures, Folia biologica 29, 209-220. 

In the 1960 s and 1970 s, much indirect evidence was obtained in favour of protein intramolecular mobility, i.e. the entropy and energy specificity of enzyme catalysis (Likhtenshtein, 1966, 1976a, b, 1979, 1988 Lumry and Rajender, 1970 Lumry and Gregory, 1986). The first observations made concerned the transglobular conformational transition during substrate-protein interaction (Likhtenshtein, 1976), the reactivity of functional groups inside the protein globule, and proteolysis. 

The composition of the polymer complexes usually is well known. They may therefore be considered as new individual compounds and their properties strongly differ from those of the constituent polymers160. Thus, when entering the complex, the reacting chains of the macromolecular components lose their flexibility and intramolecular mobility. Having reacted, the complementary groups of polymers screen each other from interactions with the surrounding medium and usually the solubility decreases. 

Investigation of the intermolecular mobility of the individual PMAA and PEG macromolecules by means of the polarized luminescence method confirms the assumption that in PMAA-PEG polymer complexes there exist sequences having a ladder structure. The relaxation times of luminescence-labelled PMAA and PAA macromolecules differ almost by two orders of magnitude. The low intramolecule mobility of PMAA macromolecules in water is caused by their specific conformation namely by the presence of the locally structured segments. The high intramolecular mobility of PEG is induced by its high kinetic flexibility. As seen from Table 1, the relaxation times of separate macromolecules disappear and the relaxation time of the complex is much longer. 

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