Macromolecules, labeling

This relation shows that the rotational correlation time is uncoupled from the excited-state lifetime, in contrast to classical steady-state or time-resolved fluorescence polarization measurements (see Chapter 5). The important consequence is the possibility of observing slow rotations with fluorophores of short lifetime. This is the case for biological macromolecules labeled with fluorophores (e.g. rhodamine) whose lifetime is of a few nanoseconds. 

The particular case of macromolecule labelling with fluorine-18 45... 

THE PARTICULAR CASE OF MACROMOLECULE LABELLING WITH FLUORINE-18... 

Figure 4.34 Fluorescence spectroscopy of single biomolecules (A) Localization of a macromolecule labeled with a single fluorophore F with nanometer accuracy. The point-spread-function (PSF) can be...

The primary use of EIA when it was first developed was for histological labeling and localization of specific cell macromolecules. Eor example, enzymes labeled with peroxidase were used to locate specific cellular compartments and stmctures for microscopic examination. The flexibiUty of EIA was recognized quickly and it was adapted for use as a laboratory assay. 

It is clear that, having the same chain length, these macromolecules are in reality experimentally indistinguishable. One could however think of a labelling technique to make Nf different from Nj, for example by using a chromophore-bound radical scavenger which added selectively to the macroradicals issued from the chain scission. Equation (87) can be split into a system of two equations (100) and (101)... 

Johnson et al. [186] measured diffusion of fluorescein-labeled macromolecules in agarose gels. Their data agreed well with Eq. (85), which combined the hydrodynamic effects with the steric hindrance factors. Gibbs and Johnson [131] measured diffusion of proteins and smaller molecules in polyacrylamide gels using pulsed-field gradient NMR methods and found their data to fit the stretched exponential form... 

VoUcel, AR Noolandi, J, Mobilities of Labeled and Unlabeled Single-Stranded DNA in Free Solntion Electrophoresis, Macromolecules 28, 8182, 1995. 

Under current treatment of statistical method a set of the states of the Markovian stochastic process describing the ensemble of macromolecules with labeled units can be not only discrete but also continuous. So, for instance, when the description of the products of living anionic copolymerization is performed within the framework of a terminal model the role of the label characterizing the state of a monomeric unit is played by the moment when this unit forms in the course of a macroradical growth [25]. 

In order to obtain the expression for the components of the vector of instantaneous copolymer composition it is necessary, according to general algorithm, to firstly determine the stationary vector ji of the extended Markov chain with the matrix of transitions (13) which describes the stochastic process of conventional movement along macromolecules with labeled units and then to erase the labels. In this particular case such a procedure reduces to the summation ... 

An exhaustive statistical description of living copolymers is provided in the literature [25]. There, proceeding from kinetic equations of the ideal model, the type of stochastic process which describes the probability measure on the set of macromolecules has been rigorously established. To the state Sa(x) of this process monomeric unit Ma corresponds formed at the instant r by addition of monomer Ma to the macroradical. To the statistical ensemble of macromolecules marked by the label x there corresponds a Markovian stochastic process with discrete time but with the set of transient states Sa(x) constituting continuum. Here the fundamental distinction from the Markov chain (where the number of states is discrete) is quite evident. The role of the probability transition matrix in characterizing this chain is now played by the integral operator kernel ... 

Knowing the functions (26) and(27) it is possible by means of the formalism of the theory of Markovian processes [53] to find any statistical characteristic in an ensemble of macromolecules with labeled units. A subsequent label erasing procedure is carried out by integration of the obtained expressions over time of the formation of monomeric units. Examples of the application of this algorithm are reported elsewhere [25]. 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Some workers have used spin labels attached to a membrane or biological macromolecule to study the motion of these components of living cells (Chapter 5). 

If the g- and hyperfine anisotropies are known from analysis of a solid-state spectrum, the line-width parameters (1, and yt can be used to compute the rotational correlation time, tr, a useful measure of freedom of motion. Line widths in ESR spectra of nitroxide spin labels, for example, have been used to probe the motional freedom of biological macromolecules.14 Since tr is related to the molecular hydrodynamic volume, Ft, and the solution viscosity, r, by a relationship introduced by Debye 15... 

Studies using radioactivity-labeled acrylonitrile indicate that acrylonitrile or its metabolites form covalent adducts with cellular macromolecules in most tissues. Studies to develop chemical or immunological methods for measuring these adducts would be especially valuable in detecting and perhaps even quantifying human exposure to acrylonitrile. Adverse health effects demonstrated following exposure to acrylonitrile, particularly acute exposures, were characteristic of cyanide toxicity. Because these effects are also indicative of exposure to many other toxicants, additional methods are needed for more specific biomarkers of effects of acrylonitrile exposure. 

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