Synthesis of Spin Labels

Spin labels are almost invariably di-t-alkyl-substituted nitroxide (nitroxyl or aminoxyl) free radicals. These are used because they are quite stable to heat and light, and nitroxides with a wide variety of structures and functional groups can be readily synthesised, so facilitating the labelling of a range of polymers [4]. Many labels are functionalised piperidine and pyrroline derivatives (Table 9.1), although other types are also sometimes used. 

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Heterocyclic iminoxyl radicals, applications for synthesis of spin-labeled... 

Piton N, Schiemann O, Mu YG, Stock G, Prisner T, Engels JW (2005) Synthesis of spin-labeled RNAs for long range distance measurements by PELDOR. Nucleosides Nucleotides Nucleic Acids 24(5-7) 771-775... 

Fig. 31. Scheme of the synthesis of spin-labeled silk fibroin. 

Synthesis of spin-labelled polystyrene has been carried out by the reaction of the polymer containing chlormethyl groups with radical IV (R=OH) [88, 89] ... 

Synthesis via scheme (2.53) has several drawbacks. The mercurated polystyrene is inclined to cross-link, and the polymer containing nitroso groups is unstable. A more suitable method of synthesis of spin-labelled polystyrene is given below [109] ... 

Synthesis of Spin-Labelled Fluorinated Polymers by Free-Radical Reaction in the Presence of NO... 

Thus, widely used aromatic polyamides with high mechanical characteristics and thermal stability [45] are rather reactive relative to NO. This is because of the specific ion-radical initiation. In this process, chemically inert aromatic rings are transformed into active cyclohexadiene structures, and in this way simple synthesis of spin-labeled... 

The reactions of NO2 with double bonds provide a very simple and rapid method for the synthesis of spin-labelled macromolecules of rubbers. The temperature variation of the rotational mobility of macromolecules in block PI has been studied using spin-labelled samples [14]. The temperature dependence of the rotational correlation time r is described by Tc = To exp(J/RT). The Tc values within the fast motion region (Tc < 10 s) are well described by the parameters E = 34.7 kj/mol and log Tq = -14.2. 

We thank Marilena Manea and Marcel Leist for expert help with the synthesis of spin-labeled AP-peptide derivatives, and for critical discussion of the manuscript. This work was supported by the International Research Center Proteostasis at the University of Konstanz, and by the Deutsche Forschungsgemeinschaft, Bonn, Germany. 

Ferroelectric liquid crystals with very fast switching times have been prepared for evenmal use in various sensing and switching devices. Other areas of materials research include the synthesis of spin-labeled polymers for sensing composite interface properties, the structure and function of polymer-stabilized synthetic membranes, and polymers for various sensor applications. 

It has been demonstrated that it is possible to insert paramagnetic probes into nucleic acids in a site- and type-specific manner. To this end, the 2,2,6,6-tet-ramethyl-l-piperidinyloxy free radical-labelled phosphoramidites of 2-amino-2 -deoxyadenosine, 2 -deoxyadenosine, 2 -deoxycytosine and 5-methyl-2 -deoxycytosine have been prepared and used for the automatic synthesis of mono-labeled oligodeoxynucleotides which proved active by EPR. The phosphoramidites carry a nitroxide spin-label directly linked to the exocyclic amino group. Starting from appropriately protected 2 -deoxyguanosine or 2 -deoxyinosine, the precursors to (66a) and (66b) were obtained by nucleophilic... 

An alternative strategy for the introduction of spin labels can be used in protein and peptide chemistry by spin label building blocks, e.g., 4-amino-l-oxyl-2,2,6,6-tetramethyl-piperidine-4-carboxylic acid (TOAC, Fig. 1, right) which are directly incorporated into the peptide during chemical synthesis [20-25]. 

The rate constants of reactions of ARs with solvated electrons, H atoms, OH, and CHj amount to 10 -10 1/mol/s, and 10 -l/mol/s with the radical C HOH [19]. This property of ARs serves as the basis for their use as counters of radicals. The unique property of ARs is their ability to react without participation of unpaired electrons with retention of paramagnetism. Such reactions are widely used for synthesis of new ARs with various substituents [3], for synthesis of metalorganic radicals containing Tl, Hg, and Fe. [20]. In this way, polyradicals were obtained in which paramagnetic fragments were interconnected in a uniform molecular system [21]. These reactions represent a method of spin labels used in chemistry, biochemistry and molecular biology [22]. 

Synthesis and Purification of Spin-Labeled AP-Peptide Derivatives... 

The simplest method of spin labelling is to utilise a functional group on the polymer to attach the label, usually via a condensation reaction (Scheme 1). Labels can also be introduced by less rect methods. For example, the Keana synthesis [6] (Scheme 2) has been used to label polyethylene that had been copolymerised with a small amount of carbon monoxide [7]. Polystyrene has been labelled by reacting the lightly lithiated polymer with either 2-methyl-2-nitrosopropane or nitrosobenzene (Scheme 3) [8]. 

The stereoisomers of l,2,3,4-tetramethyl-l,2,3,4-tetraphenyl-cyclotetrasilane were identified using a combination of spin labeling and chemical derivatization. The dominating isomer obtained in the synthesis possesses an all-trans configuration of the methyl and phenyl substituents. Polymerization of this isomer using silyl cuprates proceeds with two inversions of configuration and results in poly(methylphenylsilylene) with 25% isotactic, no syndiotactic, and 75% heterotactic triads as determined by Si NMR studies. 

The above historical outline refers mainly to the EPR of transition ions. Key events in the development of radical bioEPR were the synthesis and binding to biomolecules of stable spin labels in 1965 in Stanford (e.g., Griffith and McConnell 1966) and the discovery of spin traps in the second half of the 1960s by the groups of M. Iwamura and N. Inamoto in Tokyo A. Mackor et al. in Amsterdam and E. G. Janzen and B. J. Blackburn in Athens, Georgia (e.g., Janzen 1971), and their subsequent application in biological systems by J. R. Harbour and J. R. Bolton in London, Ontario (Harbour and Bolton 1975). 

Gaffney, B.J., Willingham, G.L., and Schopp, R.S. (1983) Synthesis and membrane interactions of a spin-label bifunctional reagent. Biochemistry 22, 881. 

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