Paramagnetic micelles

Proton Relaxivity of Various Paramagnetic Micelles and Liposomes... 

Table 1). The r value of Gd-DOTA(GACi2)2 (Scheme 2) (34.8 mM s at 298 K and 20 MHz) is the highest reported to date for monohydrated Gd-based paramagnetic micelles. Analogously, the incorporation of the two-chain complex into liposomal structures also brings an important relaxivity gain with respect to the mono-chain derivative (-1-135% at 0.47 T and - -99% at 1.41 T). 

Closs G L, Forbes M D E and Norris J R 1987 Spin-polarized electron paramagnetic resonance spectra of radical pairs in micelles. Observation of electron spin-spin interactions J. Phys. Chem. 91 3592-9... 

This approach was followed by Yushmanov for the localization of papaverine in ionic micelles.42 Another interesting application was reported by Chien43 who measured 19F NMR relaxation times of trifluor-omethyl labelled atrazine induced by paramagnetic probes gadolinium ethylenediamine tetraacetic acid and 2,2,6,6-tertramethyl-piperidine-N-oxyl. The results showed that atrazine solubilized by humic micelles occupied a hydrophobic domain accessible only to neutral hydrophobic molecules. 

It is important to note that in addition to microporous solids, other chemical systems have been used to template the growth of nanomaterials. For example, emulsions have been used to pattern both the pores in titania [14] and the packing of latex particles [46]. Reversed micelles have also been used as patterning agents. Examples include the syntheses of super-paramagnetic ferrite nanoparticles [15] and BaC03 nanowires [47]. Finally, carbon nanotubules have also been used as templates [16,48,49]. A variety of nanomaterials including metal oxides [16,48,49] and GaN have been synthesized inside such tubules [50]. 

Paramagnetic amphiphilic complexes embedded in micelles have their hydrophilic head and thus the paramagnetic ion in contact with the surrounding water. If the complex has only one hydrophobic chain, the access of water to the ion should be easy but when two hydrophobic chains are involved like in DTPA bisamides complexes, the incorporation of both chains in the micellar structure could reduce either the accessibility of water to the ion or the water exchange rate. It has been reported that micellar Gd-DOTA complexes substituted by one hydrophobic chain are characterized by a water residence time similar to that of Gd-DOTA 200 ns) and that their enhanced relax-... 

Various techniques are suitable for the study of binding locations of organic solubi-lizates in micelles and vesicles. Typically, these methods have included changes in NMR chemical shifts as a result of aromatic ring current effects, paramagnetic relaxation... 

Fig. 6a, b. Temperature variation of the paramagnetic shift of ring methyl proton resonances of (a) diaqua hemin, and (b) aqua hydroxo hemin complexes, in 5% aqueous SDS micelles. (Taken from Ref. 20)... 

The effect of the micelles on the paramagnetic shifts of the heme was very clearly demonstrated [22] in NMR of labelled cyanide in [Fe(PP)(Ci"N)2]- and [Fe(PP)(py)(Ci N)] in different micelles as well as in the absence of micelles (Fig. 9). A pronounced systematic downfield shift of the bound cyanide signals is observed on going from a solution without micelles to SDS, to TX-lOO and to CTAB micellar solutions which is also the trend in increasing hydrophobicity. The signal is known to be extremely sensitive... 

The broadening of the heme proton-resonances is mainly due to the increase in the rotational correlation time of the heme inside micelle. The increase in linewidth, Aoobs of a paramagnetic complex inside micelles compared to that in simple aqueous or non-aqueous solution is given as [20-22] ... 

The sensitivity of EPR to multiple coordination environments has been demonstrated in studies of Mn2+-doped CdS nanocrystals (63). In Mn2+ CdS nanocrystalline powders prepared by inverted micelle synthesis, four distinct resonances were observed and deconvoluted by varying experimental parameters including microwave power, microwave frequency, and temperature. The deconvoluted signals are shown in Fig. 18. Four distinct manganese species were detected through this experiment. A six line spectrum characteristic of isolated paramagnetic Mn2+ was observed at 300 K and below [multiline... 

---