Paramagnetic emulsions

The tetrapyrrole nucleus frequently holds a co-coordinated metal atom, but it has been found that only diamagnetic metals such as Zn, Pd, In, Sn, and Lu allow the tetrapyrrole to retain its photosensitizing ability, while paramagnetic metals such as Fe, Cu, and Gd do not (Rosenthal et al., 1986). Many of these compounds are lipophilic and some are even insoluble in water. These compounds must either be delivered in an emulsion or else incorporated in liposomes. 

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]. 

Contrast MRI requires incorporation of paramagnetic material onto the PFC-based targeted particles [48,49]. Incorporation of a gadolinium(lll) complex into the lipid monolayer that coats targeted emulsion droplets provides contrast agents useful for both US and MRI modalities. Paramagnetic fibrin-specific PFC emulsion droplets allowed sensitive detection and localization of thrombi by MRI and may allow early identification of fibrin deposits in vulnerable atherosclerotic plaques. The emulsion droplets had both an antifibrin... 

Another useful method for investigations of water/C02 emulsions and microemulsions is electron paramagnetic resonance (EPR) spectroscopy, because no transparent samples are necessary [9,13]. Furthermore, data from EPR experiments can provide information about the polarity of the local environment of the EPR-active compound. The diagnostic unpaired electron(s) can be introduced either through stable free radicals or by using transition metal ions such as Mn. The active moieties may be incorporated directly in the surfactant [17,18] or added as a soluble probe molecule such as TEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidin-Toxyl) [9]. 

Rao and co-workers [82] used an inverted emulsion process for the synthesis of the emeraldine salt of PAM using a novel oxidising agent, benzoyl peroxide. The polymerisation was carried out in a non-polar solvent in the presence of four different protonic acids as dopants and an emulsifier (sodium lauryl sulfate). The polymer salts were characterised spectroscopically by ultraviolet-visible, Fourier-transform infrared, Fourier-transform Raman and electron paramagnetic resonance spectroscopy. Thermogravimetric analysis, was used to determine the stability of the salts and the activation energy for the degradation. The conductivity of the salts was found to be in the order of 10 S/cm. 

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