Spin labeling acid

Sodium dodecyl sulfate micelle 71,72,77,79 Spin label 139 Starch 100, 104 —, crosslinked 106 —, graft polymers 105, 107, 125, 127 Styrene 160—162 Styrene-divinylbenzene resins 167 Styrenesulfonic acid, copolymers 74—76 Surface area 147... 

The spin label in question may as well be in the carboxylic acid fragment as in the alcohol moiety. Photoreactive esters bear azido groups in their carboxylic acid moieties. The esterification of nitroxide- or azide-bearing carboxylic acids with complex alcohols and CDI is illustrated in Table 3-6 by way of some examples. 

The following reaction illustrates conversion of a nitroxide radical-bearing alcohol by CDI and azide ion to a spin-labeled ester of azido formic acid, which is used for the labeling of amino acids, giving carbamates [137]... 

Spin-labeled Esters and Amides of Phosphoric Acid 343... 

Spin-labeled phosphoramidates are synthesized analogously by the reaction of phosphoric imidazolides with primary or secondary amines[189] or amino acid esters.11883... 

Observed collisions between 14N 15N spin-label pairs are indicated. DMPC and POPC molecules are also shown. POPC represents the major component (70%) of the EYPC mixture, (b) Bimolecular collision rate for a nitroxide moiety at the C16 position of the stearic acid alkyl chain with other SASLs in the DMPC alone and the DMPC with 10mol% lutein at 27°C. (From Yin, J.J. and Subczynski, W.K., Biophys../., 71, 832,1996. With permission.)... 

Kusumi, A., W. K. Subczynski, and J. S. Hyde. 1982a. Effects of pH on ESR spectra of stearic acid spin labels in membranes Probing the membrane surface. Fed. Proc. 41 1394. 

Based on our current understanding of ribosomal protein synthesis, several strategies have been developed to incorporate amino acids other than the 20 standard proteinogenic amino acids into a peptide using the ribosomal machinery . This allows for the design of peptides with novel properties. On the one hand, such a system can be used to synthesize nonstandard peptides that are important pharmaceuticals. In nature, such peptides are produced by nonribosomal peptide synthetases, which operate in complex pathways. On the other hand, non-natural residues are a useful tool in biochemistry and biophysics to study proteins. For example, incorporation of non-natural residues by the ribosome allows for site-specific labeling of proteins with spin labels for electron paramagnetic resonance spectroscopy, with... 

The effects of ultrasound upon the permeability of the cell walls of the gram-negative bacteria Pseudomonas aeruginosa toward hydrophobic compounds particularly antibiotics have been examined [8]. The penetration and distribution of 16-dosylstearic acid (16-DS) in the cell membranes of the bacteria was quantified by a spin-labeling electron spin resonance (ESR) method. The results indicated that the intracellular concentration of 16- D S was higher in insonated cells and increased linearly with the sonication power. 

Penetration of the biomembrane is undoubtedly essential for most membrane activity. Araki and Rifkind (13) obtained esr spectra of stearic acid spin labelled erythrocyte membranes in the presence of diverse compounds including Triton XlOO, chlorpromazine and glutaraldehyde. The two surfactants chlorpromazine and Triton XlOO both increase the rate of haemolysis and are shown to increase membrane fluidity. Glutaraldehyde as expected decreases fluidity and decreases the rate of haemolysis. 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

Michel, C., et al.. Penetration of spin-labeled retinoic acid from liposomal preparations into the skin of SKHl hairless mice measurement by EPR tomography. Int. J. Pharm., 98, 131-39, 1993. 

Spin-labelling of free, or cell-surface, sialic acids has been used in order to obtain information about the rate of rotational orientation of the label after attachment to macromolecules this knowledge is important in the investigation of the orientation and mobility of sialogly-coproteins in, for example, cell membranes. In a first approach, the label was introduced into the carboxyl groups by a carbodiimicle-me-diated, amidation procedure.177 This method is, however, not specific... 

Spin trapping has also been applied to the investigation of lipid peroxidation catalysed by myoglobin in linoleate emulsions,204 as well as the oxidation of phospholipids in low-density lipoproteins (18.1) by HOC1.205 Hiramoto et al. have shown that, by quenching the attacking radicals, linoleic acid can protect DNA from oxidation.206 Lipid peroxidation has also been monitored by spin labelling.207... 

Spin-labelled synthetic peptides were used to study coil-coil formation.41 Strong exchange interaction at sites near the N-terminus of a 35-amino acid peptide demonstrate parallel coil formation. In a 30-residue peptide corresponding to residues 468-497 of osmoregulatory transporter ProP, strong spin-spin interaction was observed for label near the centre of the peptide and weak interaction was observed for label near the C-terminus, consistent with antiparallel coil alignment. 

Amyloid fibrils formed from a-synuclein have been found in Lewy bodies of patients with Parkinson s disease.64 Spin labels were introduced at 36 positions between amino acid 5 and 136 of a-synuclein. Distributions of interspin distances between the same labels on neighboring chains were determined by analysis of CW line-shapes in solution. For the fibrils analysis of the percent of molecules with distances <15 A, 15-20 A, and > 20 A revealed a highly ordered and specifically folded core region of 70 amino acids ( residues 34 to 101). In contrast, the N terminus region is structurally heterogeneous and the C terminus appears to be completely unfolded. 

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