Tumbling measurement

TROSY spectra. Relative domain orientation could then be modelled in MODULE, prior to refinement of the entire structure in XPLOR-NIH under RDC, ambiguous NOE and radius of gyration restraints. In the model, domains 2, 4 and 6 pack together into a core flanked by propeller blades of 1,3 and 5, explaining the increased rotational tumbling measured from amide backbone dynamics in these domains. Mitogen-activated... 

The dynamic absorption test measures the resistance of fabrics to wetting by water, not the repeUency of the total fabric surface. A weighed portion of fiber, yam, or fabric is tumbled ia water for 20 minutes it is then removed and reweighed to determine the percentage of water absorbed (AATCC Test Method 70). 

Measuring Uniformity Except for cases in which a coating of one ingredient with another takes place, the theoretical end result of mixing will not be an arrangement in which one type of particle is directly next to a different type. Rather, the theoretical end result when random tumbling takes place will be a random mixture along the lines shown in Fig. 19-8. 

There are two important safety measures that can be taken at very low cost. The first is to equip shelves with guard rails to keep reagent bottles from falling. The height of such rails should be adapted to the size of the containers. This is a requirement in California. The second is to fasten tall objects to the wall, a simple and inexpensive procedure. With bookcases, for example, the books may fall out but the case will stay in position and not tumble down with the whole load. 

This simple relaxation theory becomes invalid, however, if motional anisotropy, or internal motions, or both, are involved. Then, the rotational correlation-time in Eq. 30 is an effective correlation-time, containing contributions from reorientation about the principal axes of the rotational-diffusion tensor. In order to separate these contributions, a physical model to describe the manner by which a molecule tumbles is required. Complete expressions for intramolecular, dipolar relaxation-rates for the three classes of spherical, axially symmetric, and asymmetric top molecules have been evaluated by Werbelow and Grant, in order to incorporate into the relaxation theory the appropriate rotational-diffusion model developed by Woess-ner. Methyl internal motion has been treated in a few instances, by using the equations of Woessner and coworkers to describe internal rotation superimposed on the overall, molecular tumbling. Nevertheless, if motional anisotropy is present, it is wiser not to attempt a quantitative determination of interproton distances from measured, proton relaxation-rates, although semiquantitative conclusions are probably justified by neglecting motional anisotropy, as will be seen in the following Section. 

R,1S isomer. However, this proposal is tentative, because X-ray diffraction has shown that another specimen of asperlin, possessing a different crystalline form, has structure 49b. It should be noted that 1 tumbles somewhat anisotropically, with D /D = 1.3, as deduced from C relaxation measurements. If, however, the anisotropic motion of 1 were not properly corrected for, the largest error in the measurement of its interproton distances would not exceed 4%. 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

In microphase-separated systems, ESR spectra may consist of a superposition of two contributions, from nitroxides in both fast and slow-tumbling regimes. Such spectra provide evidence for the presence of two types of domains with different dynamics and transition temperatures. This case was detected for a HAS-derived nitroxide radical in heterophasic polyfacrylonitrile-butadiene-styrene) (ABS) as shown in Figure 5, the fast and slow components in the ESR spectrum measured represent nitroxide radicals located in butadiene-rich (B-rich) and styrene/acrylonitrile-rich (SAN-rich) domains, respectively [40]. These two components were determined by deconvoluting the ESR spectrum of HAS-NO measured at 300 K. 

The -factor also depends on the orientation of the molecule in the field. Fortunately, in solution, rapid tumbling gives rise to an average g factor and therefore to sharp epr signals. It also depends on the electronic structure of the molecule and the measurement of g can give some such information. However, it is more commonly employed as an aid to the identification of the radical species. 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

Tumble dryers use pressure sensors for filter measurements by measuring the differential pressure across the lint filter signalling the user when to clean the filter. 

CD spectra are usually measured in solution, and these spectra result from the interaction of the individual chromophores of a single molecule with the electromagnetic field of light. The interaction with neighboring molecules is often negligible. Moreover, because molecules in solution are tumbling and randomly oriented, the mutual interaction between two molecules, which is approximated by a dipole-dipole interaction, is negligible. 

Fig. 12.1 Illustration of the temperature sensitivity of 15N relaxation parameters, Rlf R2t and NOE, as indicated. Shown are the relative deviations in these relaxation parameters from their values at 25 °C as a function of temperature in the range of + 3 °C. The expected variations in / ] and R2 due to temperature deviations of as little as +1 °C are already greater than the typical level of experimental precision ( % ) of these measurements (indicated by the dashed horizontal lines). For simplicity, only temperature variation of the overall tumbling time of the molecule (due to temperature dependence of the viscosity of water) is taken into account the effect of temperature variations on local dynamics is not considered here.

Up to this point only overall motion of the molecule has been considered, but often there is internal motion, in addition to overall molecular tumbling, which needs to be considered to obtain a correct expression for the spectral density function. Here we apply the model-free approach to treat internal motion where the unique information is specified by a generalized order parameter S, which is a measure of the spatial restriction of internal motion, and the effective correlation time re, which is a measure of the rate of internal motion [7, 8], The model-free approach only holds if internal motion is an order of magnitude (<0.3 ns) faster than overall reorientation and can therefore be separated from overall molecular tumbling. The spectral density has the following simple expression in the model-free formalism ... 

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