Resolution molecular mechanism

Each of the three fractions was applied to a combined SEC system of Fractogel/Superose to investigate their molecular characteristics in detail. These high resolution and mechanically stable gels allow the application of eluents with increased ionic strengths (e.g., 0.05 M KCl) at a reasonable resolution of sample components (Fig. 16.15). 

Sakai K, Sakurai R, Hirayama N (2007) Molecular Mechanisms of Dielectrically Controlled Resolution (DCR). 269 233-271... 

It is difficult to evaluate the shape of such dendritic particles experimentally. However, some insight can be gained by atomic force microscopy (AFM) and transmission electron microscopy experiments (TEM). AFM experiments can give information about the overall size of the dendrimers, as shown by De Schryver [43], by spincoating very dilute solutions of dendrimers like 30 on mica, then visualizing single dendrimers. Their height measured in this manner corresponds very well to the diameters calculated by molecular mechanics simulations. First results from TEM measurements also confirm the expected dimensions [44]. Unfortunately, due to resolution limits, up to now direct visual information could not be obtained about the shape of the dendrimers. 

The three isomers of [Co(dien)2]3+/2+ have, as predicted by molecular mechanics calculations (see also Table 7.1 in Chapter 7, Section 7.1 for calculated and observed isomer ratios of [Co(dien)2]3+), measurably different redox potentials1415. However, the strain energy differences between various conformers of each isomer were calculated to be too small for a measurable difference of the redox potentials, and the order of stability in both oxidation states was the same[44]. A similar problem occurred with [Co(sep)]3+/2+t44]. For [Co (S)-pn 3]3+/2+ the four redox potentials between isostructu-ral pairs lie within the predicted range of 20 mV However due to lack of resolution, a quantitative analysis was not possible. An unambiguous proof of the model is, therefore, still lacking. 

High resolution NMR studies, in combination with molecular mechanics, were performed to unequivocally assign the prochiral P-protons for the phenylalanine sidechain and to define the shape of the sweet receptor [49], The previous assignment [48] of the NMR signals for the P-protons of phenylalanine was shown to be in error. 

Investigations of multicentre electrochemical metalloprotein function including metalloenzyme function have also been brought to a level, where both direct and catalytic modes, and elements of molecular mechanisms can be addressed. The latter are, however, entangled by features such as composite electrochemistry, extremely complicated molecular interaction patterns when more than two metallic redox centres are involved, fragile surface enzyme preparations, and lack of structural surface characterization of the adsorbed metalloenzymes. In this respect, two-centre metalloproteins constitute interesting promising intermediates where the coop-erativity between the metallic redox centres can be accurately addressed with molecular resolution within reach. 

This, however, introduces a number of complications, and for information on the molecular mechanics of transport it would be desirable to work with a simpler system, such as membrane vesicles, and such experiments are in progress (84). Many unresolved questions in siderophore transport await resolution. 

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