Macromolecular structures chemical shifts

The specific correlations of functional groups with the chemical shifts of carbon and associated protons are always important tools for structure elucidation of simple sugars as well as complex oligosaccharides. The conformational behavior [65,66] of a particular disaccharide and oligosaccharide in solution is determined not only by intramolecular interactions but also by potential interactions that exist between the oligosaccharide and its environment. In particular, the nature of the solvent or more generally the environment in which the compound finds itself, can profoundly affect its geometry. Two such important factors, namely the fully solvated state (i. e. the molecule free in solution) and the molecule solvated by a macromolecular receptor (i. e. the molecule bound to the active site of the protein) contribute to the preferred conformation. 

Thus, in addition to the well-received applications of NMR for structure characterization, there are additional physicochemical aspects of complex macromolecular architectures, biohybrid structures, and aggregates and complexes, which can be investigated using NMR. In particular the measurement of displacements based on PEG NMR for either measuring diffusion or the electrophoretic mobility offers additional information on the size and charge of these various macromolecular architectures and compositions. The inherently available chemical shift information allows the identification of the moving species, which is important in multicomponent systems or when the formation of complexes is studied. 

The reaction dipole moment zfM of a dipolar equilibrium may be obtained from the measurement of continuum properties such as the dielectric permittivity as well as from direct monitoring of concentration shifts produced by an externally applied electric field. In both approaches to reaction properties it is primarily the chemical part of the total polarization that is aimed at. However, the chemical processes are intimately connected with the physical processes of polarization and dipole rotation. In the case of small molecules the orientational relaxations are usually rapid compared to the diffusion limited chemical reactions. When, however, macromolecular structures are involved, the rotational processes of the macromolecular dipoles may control a major part of the chemical relaxations. Two types of processes may be involved if a vectorial perturbation like an external electric field is applied a chemical concentration change and a change in the orientation of the reaction partners. 

Molecular dynamics of a macromolecular chain involves both cOTiformational and rotational motions. Along these lines, the backbone dynamics of poly(n-alkyl methacrylates) has been elucidated by advanced solid state NMR, which enables conformational and rotational dynamics to be probed separately [41], The former is encoded in the isotropic chemical shift. The latter is probed via the anisotropic chemical shift [14] of the carboxyl group with unique axis along the local chain direction. Randomization of conformations and isotropization of backbone orientation occur on the same time scale, yet they are both much slower than the slowest relaxation process of the polymer identified previously by other methods [40]. This effect is attributed to extended backbone conformations, which retain conformational memory over many steps of restricted locally axial chain motion (Fig. lb, c). These findings were rationalized in terms of a locally structured polymer melt, in... 

Conformational Sampling Distance Geometry Theory, Algorithms, and Chemical Applications Macromolecular Structure Calculation and Refinement by Simulated Annealing Methods and Applications NMR Chemical Shift Computation Structural Applications NMR Refinement. 

In such a way, IPNs have a much broader set of relaxation times than the pure constituent networks. The relaxation spectra of IPNs cannot be obtained by simple superposition of the spectra of the constituent networks. The broader spectra of the IPNs may be explained by the existence of a two-phase structure where each phase is enriched in one of the components. Simultaneously, the existence of two phases is reflected in the relaxation spectra by their broadening and shift along the time axis. It is evident that in spite of the incompatibility of the two networks, there exists a strong physical interaction between macromolecular chains of dissimilar chemical nature, which may be described in terms of entanglements, and strong polar interactions. The latter may be the reason why 50 50 IPN has its relaxation spectrum shifted to higher relaxation times than that for 65 35 IPN. 

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