Reporter molecule, cross-polarization

Figure 19. Topological structure of 2D antiparallel DX arrays. The four arrays are built from DAO or DAE molecules crossings are separated by an even (E) or odd (O) number of double helical half-turns. Strand polarities are shown by the arrowheads on their 3 ends. Strands are drawn with different thicknesses for clarity. Both DAO lattices contain vertical zigzag strands, only. DAE-E consists of molecular chain mail, and DAE-O produces reporter strands in both the horizontal direction (straight) and the vertical direction (zigzag).

Fig. 11. The structure of a-actinin and the two vertebrate Z-band lattices. (A) The ubiquitous protein a-actinin is an anti-parallel homodimer. Each 100 KDa monomer comprises four central spectrin repeats (SI to S4) an EF-hand domain and two calponin homology domains (CH) at the N-terminus. The EF-hand domains bind calcium in non-muscle cells. One a-actinin molecule binds two actin filaments via the calponin homology domains. a-Actinin binds titin via EF-hand domains. (B, C) The Z-band is the site where actin filaments from adjacent sarcomeres overlap in a tetragonal lattice and are crosslinked by a-actinin molecules. The polarity and origin of the actin filaments is indicated by U (up) and D (down). The appearance of the Z-band in cross-section is typically basketweave-like (B) or small square-like (G). The appearance is reported to transform between the two appearances depending on the state of the muscle.

The properties of the microenvironment of soluble synthetic polymers such as polymethacrylamide (PMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(2-vinylpyridine) (P-2VP), poly(4-vinylpyridine) (P-4VP), poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA), polystyrene (PS), poly(4[5]-vinylimidazole) (PVIm), and poly(N-2-hydroxypropyl methacrylamide) (PHPMA) and cross-lined polymers were studied by the shift and shape of the band in electronic spectra of a solvatochromic "reporter" molecule embedded in polymer chains. Preferential interaction of parts of the polymer molecule with a reporter and the shielding of interactions between solvent molecules and a reporter molecule of a polymer causes a shift and broadening of its solvatochromic band. This shift is mechanistically interpreted as a change in the polarity of the microenvironment of a polymer in solution in comparison with polarity of the solvent used. 4-(4-Hydroxystyryl)-N-alkylpyridinium-betaine, spiropyran-merocyanine, and l-dimethylamino-5-sulfonamidonaphthalene (Dansyl) reporters were used. In almost all cases the polarity of the polymer microenvironment was lower than that of the solvent. At the same time, the dependence of the nature of the environment on the distance of the reporters from the polymer chain was studied. 

Properties of the microenvironment of soluble and cross-linked polymers were studied by the shift of bands in the electron spectra of solvatochromic reporter molecules embedded in polymer chains. Generally, the charge-transfer (CT) absorption spectra and emission spectra of a number of compounds were used to correlate solute-solvent interactions with physical and chemical properties of interest. The energy of the band maxima of these chromophores is quite solvent sensitive and is linearly correlated with empirical solvent polarity parameters. The observed shift of the maximum of the solvatochromic reporter embedded in the polymer chains, compared with a low-molecular weight analog in the same solvent, was interpreted in terms of a change in the polarity of the microenvironment of the polymer in solution. 

To determine the polarity of the microenvironment of polymers, polymer labelled with solvatochromic reporters were prepared, either by (1) copolymerization with solvatochromic monomers 2 >3 or (2) polymer analogous reactions (e.g., the reaction of copolymer acUve esters with primary amino groups of the solvatochromic molecule or alkylation reaction of PVIm and cross-linked polymers with solvatochromic mole-cule.34i37 The properties of the microenvironment of polymers were studied by the shift and shape of band in electronic spectra of a solvatochromic reporter molecule embedded in polymers. 

The Carbowax column is very sensitive to oxidation when the stationary phase is exposed to traces of water or air especially at temperatures above about 160°C. A new type of cross-linking has been reported to impart resistance to oxidative degradation of the stationary phase [5-7]. Two other phases which show promise are an oligo-(ethylene oxide)-substituted polysiloxane (glyme) and an 18-crown-6-substituted polysilox-ane [8]. The glyme column offers a polar phase with good operational conditions to a low of a least 20°C with the same selectivity of Carbowax. The crown polysiloxane selectivity is based on the interaction of the solute molecule with the cavity of the crown ether. 

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