SPIN-PROBE ANALYSIS

Dendrimers have precise compositional and constitutional aspects, but they can exhibit many possible conformations. Thus, they lack long-range order in the condensed phase, which makes it inappropriate to characterize the molecular-level structure of dendrimers by X-ray diffraction analysis. However, there have been many studies performed using indirect spectroscopic methods to characterize dendrimer structures, such as studies using photophysical and photochemical probes by UV-Vis and fluorescence spectroscopy, as well as studies using spin probes by EPR spectroscopy. 

Numerous studies have indicated that pro-inflammatory mediators (cytokines) are involved in the destruction of the insulin-producing p-cells of the pancreas in the development of type I diabetes. Tabatabaie et al. introduced cytokines and PBN into the pancreas of rats. The analysis of pancreatic extracts revealed that the cytokines stimulate the formation of lipid radicals. Radical generation did not occur in rats treated with streptozotocin, which destroys the P-cells.33 Evidence for the role of radicals in diabetes has also been provided by spin trapping studies in pancreatic homogenates, showing that streptozotocin, which is often used to induce the condition in laboratory animals, stimulates OH production.332 Other workers, using EPR to observe the decay of a spin probe in the abdomen of mice (at 1.2 GHz), have demonstrated that strep-... 

A variety of spin probe methods have also been used to study the morphological features of the nano-channels present within MCM 41, as well as dynamical aspects connected to molecular diffusion in the inner pores,186-188 EPR has been used to investigate the adsorption and interactions of nitroxide-labelled de-ndrimers within porous silica.181 This method allows one to investigate the effective porosity of a solid surface (as a host) which is determined by the accessibility of the host surface to an adsorbed guest molecule. Information on the adsorption and interaction of dendrimers with the porous surface arises from computer-aided analysis of the EPR spectra based on of the well-established procedure proposed by Schneider and Freed.189... 

In conclusion, our analysis is directly concerned with relatively fast and local solvent motions and the results highlight the importance of careful computational modelling for the interpretation of experimental data on the behaviour of nitroxide spin probes in water and other protic solvents. 

Teo, B. K. (1986). EXAFS Basic Principles and Data Analysis, Springer-Verlag, Berlin. Templeton, G. D., and Chasteen, N. D. (1980). Vanadium-fulvic acid chemistry conformational and binding studies by electron spin probe techniques. Geochim. Cosmochim. 

The interaction of probe molecules with acidic OH groups is also studied, " even though the detail is not described in this report. Moreover, the spinning sidebands analysis in H MAS NMR offers the information on the distance between the bridging OH groups and aluminium ions in the zeolite framework. - ... 

Analysis of ESR parameters for bound to transferrin suggests that the inplane donor atoms are comprised of a water ligand, two (or three) phenolate groups from tyrosine and a carboxylate [250]. A spin probe study of apoferritin... 

The spin label technique appeared to be very fruitful recently in research ofmembrane-carotenoids interaction. The shape of a spin probe ESR spectrum is sensitive to the rate of its molecular motion being directly dependent on the membrane fluidity determined by the rate of lipid molecular motion. Thus, the analysis of ESR spectra of spin labels doped into pigmented membranes would provide information on the carotenoid effect on particular regions of lipid bilayers, dependent on the type of probes applied, penetrating different membrane portions. Tfiis technique was applied to study an effect of xanthophylls and j8-carotene on fluidity of lipid membranes formed with several synthetic and nonsaturated phosphatidylcholines (Subczynski et al, 1991,1992,1993 StrzalkaandGruszecki, 1991, Yin and Subczynski, 1996, Wisniewska and... 

The molecular motion of redox couples within polymer-coated electrodes has recently been investigated by making use of both nitroxide spin probes and various cationic spin probes [94-97]. Spin probes, such as the nitroxide probe TEMPO (see Sect. 2.1.2) and its derivatives, have well-defined electrochemistry and their ESR spectra in viscous media exhibit effects due to incomplete rotational averaging of the g and hyperfine coupling constant tensors. Analysis of the spectra [98] allows deductions to be made concerning the molecular rotation. Such analysis has been performed for spin probes incorporated into various polymer films. 

In this section, the EPR spectroscopic characterization of thermoresponsive polymeric systems is presented. The polymeric systems are water-swollen at lower temperatures and upon temperature increase the incorporated water is driven out and the system undergoes a reversible phase separation. Simple CW EPR spectroscopy (see above), carried out on a low-cost, easy-to-use benchtop spectrometer, is used here to reveal and characterize inhomogeneities on a scale of several nanometers during the thermal collapse. Further, neither any physical model of analysis nor chemical synthesis to introduce radicals had to be utilized. Adding amphiphilic TEMPO spin probes as guest molecules to the polymeric systems leads to self-assembly of these tracer molecules in hydrophilic and hydrophobic regions of the systems. These probes in different environments can be discerned and one... 

S. Weber and E. Schleicher on the example of flavoproteins which play a role in both chemically and light-activated electron transfer processes. Chapter 3 on synthetic polymers by D. Hinderberger argues that careful analysis of mundane nitroxide spin label or spin probe CW EPR spectra can reveal a lot of information which is hard to obtain by any other characterization technique. 

The spin probe method was one of the first methods used to evaluate the free volume in polymers [1,7]. It is based on the principle that the rotational frequency of spin probes, usually stable nitroxyl radicals such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is sensitive to the free volume. The relatively complex correlation between spectral data and FV makes this method more suitable for qualitative comparison of different polymers than for quantitative analysis of the FV [1,8]. 

ESR spectra of the rigid spin probe cholestane embedded in model membranes yield information about the molecular order (order parameters and and about the rate of motion of the probe molecules in the membranes (rotational diffusion constants D and Dj ). For a correct analysis of the ESR lineshapes in the slow motion regime (10 stochastic Liouville Equation (SLE) formalism. 

Valic applied TEMPOL spin probe ESR technique to nano-sihca and nanoclay particles filled NR nanocomposites. Figure 25.34 shows the ESR spectra of 10 phr nano-silica filled NR nanocomposites doped with spin probe obtained at the temperature range of —100 to 80 °C. The shape and width of the spectral lines significantly changed with test temperatures. The spectra obtained at temperature below glass transition temperature (TgX — 57 °C from dilferential scanning calorimetry (DSC) analysis) of NR are composed of three... 

Since the result of the saponification of the methyl ester of immobilized 4-iso-cyanatomethyl butanoate was not proven directly by XPS the free acid group was reacted with 4-amino-TEMPO using the carbodiimide method. The immobilized 4-amino-TEMPO leads to an ESR signal characterized by reduced molecular motion in comparison with an uncoupled spin probe as a control sample [133], Consequently, the modified PCU/PVA surface is suitable for the immobilization of the fibronectin fragment GRGDS via the M-terminus [147]. A pepide content of 8 to 15 nmol cm on the PVC/PVA surface immobilized with GRGDS was verified by means of amino acid analysis. 

Line Shape Analysis for Nitroxide Spin Probes. Nitroxide radicals as spin probes and labels are useful for the determination of the motional mechanism, rotational correlation time, to, and local polarity. Figure 2a demonstrates that the relative line widths and line heights depend on the rotational correlation time to, which is inversely proportional to the diffusion constant of rotational diffusion. 

Information on the spatial distribution of paramagnetic molecules deduced from ESRI experiments has been used successfiilly for measurement of the translational diffusion. Diffusion coefficients of paramagnetic diffusants can be deduced from an analysis of the time dependence of the concentration profiles along a selected axis of the sample. The determination of diffusion coefficients for spin probes in liquid crystals and model membranes, and the effect of polymer and probe poly-dispersity, have been described in a series of papers by Freed and co-workers (44). These papers represent an effort to move beyond phantoms, and to extract quantitative information from ESRI experiments. 

Matrix ENDOR of spin probes that reside in an internal interface has the potential to provide detailed information on the microscopic structure of this interface, but measurement techniques and data analysis are still in their infancy, so that only semiquantitative information can be obtained to date. Development of more precise and sensitivity-optimized measurement techniques and better quantification of the spectra are now in progress. 

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