Labelled monomer

The proportionality between the concentration of chromophores and the measured absorbance [Eqs. (6.8) and (6.9)] requires calibration. With copolymers this is accomplished by chemical analysis for an element or functional group that characterizes the chromophore, or, better yet, by the use of isotopically labeled monomers. 

MMA polymerization is one of the most studied systems and was thought to be explicable, within experimental error, in terms of Bemoullian statistics. Moad et ai.jb have made precise measurements of the configurational sequence distribution for PMMA prepared from 13C-labeled monomer. It is clear that... 

Of the purine nucleosides, dATP may be derivatized at its N-6 position using a long linker arm terminating in a detectable group without losing the ability to be enzymatically incorporated into DNA probes. By contrast, if modification is done at the C-8 position of purine bases, DNA polymerase cannot by used to add the labeled monomer to an existing strand. C-8 derivatives, however, can be added at the 3 terminal using terminal transferase enzyme. 

Polymers Polyacrylamide and hydrolyzed polyacrylamide were prepared by the American Cyanamid Company specifically for this project, starting with l C labelled monomer. The radioactivity level of the monomer was kept below 0.20 mC /g in order to avoid significant spontaneous polymerization, utilizing a copper inhibitor. The homopolymer was synthesized by free radical solution polymerization in water at 40°C, using monomer recrystallized from chloroform, an ammonium persulfate-sodium metabisulfite catalyst system, and isopropanol as a chain transfer agent. Sodium... 

The PMMA-Phe synthesis, characterization, film preparation, apparatus and experimental scheme are described elsewhere (H) Briefly, the PMMA chains, copolymerized from MMA and Phe-labelled monomers, were characterized via gel permeation chromatography (GPC) M = 411,000, M = 197,000 and M M - 2.08. UV-absoifption measurementsnindicated that ca. I % of all monomer units were Phe-labelled. The sample was dissolved in toluene and was spin-coated onto 1-inch diameter quartz disks. Then, the films (ca. 1 /zm thick) were annealed at 160 C for 60 minutes under vacuum. 

In the case of a symmetric (protein-protein) homodimer, the preparation of molecules with differently labeled monomers is often far from trivial, and special approaches have been described in the literature [8, 9]. However, when successful, differential isotopic labeling of a symmetric homodimer, in combination with isotope editing/filtering techniques, offers a unique access to the NMR investigation of the monomer interfaces. 

POLYELECTROLYTE DYNAMICS The mean-square displacement of a labeled monomer is... 

Turning to propylene, cis addition was found also for syndiotactic polymers (4(X), 401). This result deserves additional comment. It is known that only one disyndiotactic polymer is obtained from a CHA=CHB olefin (see Sect. II-B) but this is no longer true when one considers the syndiotactic copolymers between two differently labeled monomers. The syndiotactic copolyriKr between perdeuteropropylene and propylene-l-d, can have either of the two structures 99 Ot 199. Hew 9ve motvomet mil deti ixv% from Ihe second mononvei (present in small quantity) can be clearly identified as to its stereochemistry. 

Table 5. Copolymer analysis using labelled monomers...

Labelled monomers have been used in co-polymerizations for analysis of the resulting co-polymers and consequent determination of monomer reactivity ratios (15, 16). This technique is of particular value when the compositions of the different monomer units are rather similar or when the co-polymer contains only very small amounts of one of the monomers. These points can be appreciated by considering calculations on co-polymers of methyl methacrylate and methyl acrylate summarized in Table 1. The analyses have been calculated ignoring contributions of end-groups it assumed that the acrylate ester is labelled with carbon-14 and that specific activities are expressed in units such as curies/g of carbon. 

In a specimen of a monomer labelled with carbon-14 or other radioactive isotope, only a small fraction of the molecules actually contain an atom of the isotope if only part of the labelled monomer is polymerized, the specific activity of the part which has reacted may be a little different from that of the residual monomer because of a kinetic isotope effect. The polymerization of a labelled monomer might therefore be regarded as a co-polymerization with a drift in the composition of the feed. This effect has been examined by comparing the polymerizations of unlabelled styrene, a-14C-styrene and /3-14C-styrene in both radical and cationic reactions (18). 

The addition of a new chain at the growth front is not hindered by a barrier, in contradiction with the underlying assumptions of the LH theory. Simultaneous to the addition of new chains at the growth front, chains inside the lamella move cooperatively. The center of mass of the lamella diffuses in space while the lamella thickens by a process of internal rearrangements for details, see [30]. The mean squared displacement of a labeled monomer varies with the elapsed time, t, with an effective power law of t0Ji by shuffling back and forth between the lamellar and amorphous regions. 

The solid-phase synthesis of biopolymers via iterative coupling of monomeric building blocks has found widespread application. It can be adapted easily for the incorporation of non-natural building blocks or labeled monomers, which will be used as probe molecules in chemical biology. 

The potential utility of N-labelcd oligonucleotides to probe unique nucleic acid structure, drug binding, and nucleic acid- protein interactions has led to considerable interest in the development of routes to the requisite N-labeled monomers. In the purine series, chemically synthesized N 1-labeled hypoxanthine was incorporated into a yeast tRNA by fermentation and... 

Water in a never-dried fresh-cut tree, when exchanged with a series of organic solvents, could be replaced with H- (or tritium-) labeled MMA (42). After polymerization and the use of autoradiography the H-labeled MMA was located in the cell wall and compound middle lamella. The polymer (polymethyl methacrylate) labeled with was removed from the capillaries and void spaces in the wood by solvent extraction, but the labeled polymethyl methacrylate in the wood structure remained. The same wood, after oven drying, was treated with the H-labeled monomer by using the full cell method. Again, by autoradiography, the H-labeled polymethyl methacrylate was located in the capillaries and void spaces. After solvent extraction of the poly methyl methacrylate no labeled polymer... 

The two sets of 180-labeled monomers [180] -15 and [180] -17 described above and their unlabeled counterparts allowed for the synthesis of medium size oligonucleotides with any combination of internucleotide bonds with respect to... 

SddC ) labeled monomer pair contribution to scattering,... 

Radiochemical Standards. The most widely used method for obtaining standards for calibrating IR analysis consists of copolymerizing 14C-labelled monomers (generally ethylene1) so that the copolymer composition is determined by radioactive counting, by either a solution or a microcombustion technique (20,26, 29, 57, 59, 73). 

The first hints about how actin mediates bacterial movement were provided by a microinjectlon experiment in which fluorescence-labeled G-actIn was Injected into Listeria infected cells. In the microscope, the labeled monomers could be seen incorporating Into the tall-like meshwork at the end... 

A curve in space, as shown in Fig. 1.10, is described by a position vector r = R(u) where m is a parameter that denotes the points along the curve in a simple, one-dimensional manner — e.g., u might label monomers in a polymer chain. The infinitesimal arc-length, dUj is the distance along the contour of the chain between two points labeled by ui and U2 in the limit that ui U2. The actual distance in space between those points is denoted by s. For discrete points As = — R u2), which in the limit that u -> U2 is... 

This is simple, but we have to explain the notations. First, i and j label monomers along the chain, from 1 to N. Second, sequence is described in terms of A i) (or A j)) chemical name of aminoacid for each position along the chain. Third, and final, Cij is the so-called contact matrix, it is simply 1 if i is in contact with j and it is zero otherwise. Thus, formula (10.1)... 

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