Motional characteristics

The inherent sensitivity of NMR signals to the fluid-substrate interactions via a large number of mechanisms provides a direct connection between the NMR measurables, the pore structure and the motional characteristics of the imbibed fluid. While the large number of potential NMR variables makes the experimental design and analysis complex, it also provides the potential for a measurement method capable of measuring and spatially resolving the parameters of interest to functionalized ceramics. 

Exchange of magnetization due to cross-relaxation (NOE, nuclear Overhauser effect) does lead to intensity changes of individual resonances which provide valuable information about spatial and motional characteristics of the spins involved [4, 5]. It is currently mostly measured in two-dimensional NMR, where the NOE is measured as cross-peak intensity. Cross-relaxation is caused by mutual spin flips in dipolar coupled spin pairs. 

Chemists pay much less attention to the NMR relaxation rates than to the coupling constants and chemical shifts. From the point of view of the NMR spectroscopist, however, the relaxation characteristics are far more basic, and may mean the difference between the observation or not of a signal. For the quadrupolar nucleides such as 14N the relaxation characteristics are dominated by the quadrupole relaxation. This is shown by the absence of any nuclear Overhauser effect for the 14N ammonium ion despite its high symmetry, which ensures that the quadrupole relaxation is minimized. Relaxation properties are governed by motional characteristics normally represented by a correlation time, or several translational, overall rotational and internal rotational, and thus are very different for solids, liquids and solutions. 

The motional characteristics of interest are typically those governed by the phospholipid fatty acyl chains and head-group region and the neutral lipid or protein components of membranes. Rotational motion can be subdivided into a structural component, the order or degree of orientational constraint,... 

NMR measurements can distinguish hydrogen In rigid molecular structures of coals, l.e. structures that do not undergo appreciable reorientation and/or translation during time Intervals < 10 s, from hydrogen In mobile structures which possess more rapid molecular motions characteristic of fused or rubbery materials. 

A regularly periodic motion characteristic of a pendulum, spring, or many chemical bonds. See Hooke s Law... 

One of these models the plume itself, attempting to provide a predictive capability for describing the characteristics of the plume in a measured environment. Knowing the motion characteristics of the medium—air or water—the models seek to predict the concentration and dimensions of the plume at distances downstream. Of course, the nature of the problem quickly leads to use of statistical descriptions. This provides a model quite adequate for constructing tracking algorithms. 

Table 1 Motion Characteristics of Floating Production Systems... 

In conclusion, NMR spectroscopy on polyethylene in the melt implies the existence of a variety of segmental motions characteristic of long-chain molecules, but does not support the argument that the structure is not homogeneous. 

Fig. 53 Dynamic mechanical loss spectrum of BPA-PC. The solid line is the result of simulation using the phenyl ring motion characteristics (from [34])...

Thus, what is observed is a decoupling between the motions of the transition and those involved in the a transition. Indeed, in PMMA, along the high-temperature side of the j3 peak, more and more cooperativity between ester flips and chain motions is involved, in such a way that the chain motions in this temperature region could be considered as the beginning of cooperative chain motions characteristic of the a processes. The presence of rigid CMI units within the chain backbone interrupts this cooperativity and, consequently, the motions involved in the j3 transition are confined to small MMA sequences and cannot reach the extent required by the chain motions occurring at the onset of the a transition. 

As gene carriers are internalized by endocytosis, the motion characteristics inside the cell resembles the movement of the endosomal compartments within the cell and the formed vesicles are transported along the microtubule network [38]. Suh et al. [41] quantified the transport of individual internalized polyplexes by multiple-particle tracking and showed that the intracellular transport characteristics of polyplexes depend on spatial location and time posttransfection. Within 30 min, polyplexes accumulated around the nucleus. An average of the transport modes over a 22.5 h period after transfection showed that the largest fraction of polyplexes with active transport was found in the peripheral region of the cells whereas polyplexes close to the nucleus were largely diffusive and subdiffusive. Disruption of the microtubule network by nocodazole completely inhibits active transport and also the perinuclear accumulation of polyplexes [37, 40, 47]. 

Through measurements of 13C spin-lattice relaxation times, a number of noteworthy motional characteristics related to overall molecular tumbling, hydrogen... 

In order to determine the extent of propagation of this correlated motion, the T s of hexadecanediol were obtained (Table VIII). The results indicate that the motional characteristics responsible for field dependent relaxation are present to C-16 at 75°. This behavior disappears between 80° and 95°. Although it is desirable to extend these measurements to longer alkyl chains, even for HDD, resolution of C-5 through Cn 3 is not possible, and only composite relaxation curves are obtained. 

Protein rate processes are strongly affected by hydration. The dry protein shows greatly reduced internal motions, measured by Moss-liauer spectroscopy, neutron scattering, fluorescence spectroscopy, and other methods. Surface motions, monitored by spin probes or spin or Mossbauer labels, are similarly frozen in the dry protein. The following paragraphs comment on the appearance of motion characteristic of the hydrated protein and on the coupling between protein and solvent motions. 

Hence, although the equilibrium rigidity of the main chain of polymer molecules with mesogenic side groups is not h h (A 50 A), their polar groups are oriented in the electric field by large-scale intramolecular motions characteristic of rigid-chain polymers. 

Segmental motions of P(3HB) and P(3HB-co-27%3HV) in chloroform-d solution have been studied by measuring NMR relaxation times and NOE factors as a function of temperature [72, 73]. Analysis of the relaxation data on the basis of the Dejean-Laupretre-Monnerie (DLM) model, which describes the dynamics of polymer chains [74], indicates that the local dynamics of a comonomer unit, e.g., 3HB, are independent of the presence of a nearby 3HV unit and vice versa that segmental motion of the P(3HB-co-27%3HV) copolymer described by cooperative conformational transitions [73] is similar to that for the P(3HB) homopolymer [72]. These motional characteristics of the P(3HB-co-3HV) copolymer chain are consistent with the conformational characteristics derived by the analysis of spin coupling as shown in Section 21.2.2.3 [63] and are consistent with the occurence of cocrystallization in this copolymer system. 

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