Porphyrin electron microscopy

Although several metal-containing heterocyclic compounds (such as porphyrins, phthalocyanines, naphthenates) are present in oil fractions most of the bench-scale research has been based on relatively rapid Ni, V, or Ni/V deposition procedures in which experimental FCC formulations have been artificially metal contaminated with solutions of Ni and/or V naphthenate dissolved in benzene (or toluene) (24). Metal levels in these novel FCC are usually above 0.5% that is well above the concentration that today exist on equilibrium FCC, see Figure 1. High metal concentration facilitate the study and characterization of Ni and V effects by modern characterization techniques such as X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (LRS), X-ray diffraction (XRD), electron microscopy, secondary ion mass spectrometry (SIMS), and 51V nuclear magnetic resonance (NMR). 

Kimura, Shirai and coworkers used two chiral dimeric porphyrins 95 and 96 to investigate their self-assembling behavior [162,163]. While incorporation into fibers made of the alkylamide derivatives of (fl,fl)-DACH, 95 formed stable well-resolved fibrous assemblies as visualized by transmission electron microscopy, the fluorescence of which was not quenched by external electron acceptors [162]. However, the induced CD was not detected indicating an inability of 95 to form chirally orientated aggregates under the applied conditions. In contrast, 96 was able to produce optically active inter molecular self-assemblies with an enhanced chiroptical response through the //-oxo bridging in an alkali solution, while intramolecular //-oxo dimer formation was excluded on the basis of steric reasons [163]. 

A sensor for nitric oxide was constructed utilizing multiwaUed carbon nanotubes that were previously modified with ethylenediamine and sonicated in a solution containing Co -TSPP. Drop cast electrodes were prepared and characterized by field-emission transmission electron microscopy, X-ray photoelectron spectroscopy and by electrochemical techniques [220]. Cyclic voltammetry, electrochemical impedance, and chronoamperometry were utilized to evaluate the electrocatalytic activity of the hybrid sensor that exhibited linear response in the 6.6 x 10 to 1.3 X 10 mol L range, with a detection limit of 6.6 x 10 mol L. Electrodes composed of porphyrins, platinum nanowires, and Nafion were proposed for photocatalytic reduction of water [221]. After an extensive search for optimization of each component and under the best conditions (—350 mV and visible light irradiation) a detectable amount of hydrogen was produced, but Nafion can diminish the diffusion of ions to the porphyrin active sites. 

The large size of CPOs allows their direct observation. For this purpose, scanning tunneling microscopy (STM) is the best method [32,34]. Electron microscopic analysis is used for phthalocyanine 3 and its derivatives however, most of the porphyrin derivatives are decomposed by electron beam irradiation. Presently, although only a limited number of researchers are able to perform atomic-scale resolution measurement, this powerful analytical method is expected to be used widely in the future. The author reported a summary of STM studies on porphyrins elsewhere [34]. 

A fluid micelle which dissolves apolar porphyrins but can nevertheless be isolated as a material and characterized by transmission electron (TEM) and atomic force microscopy (AFM) has kanamycin as a head group. This is a trisaccharidelike cyclohexane derivative containing several OH- and four amino groups. One of them was amidated with stearic acid, and upon sonication spherical micelles with a diameter of about 6 nm were formed. TEM shows a large assembly of spheres which look similar to covalent fullerene spheres, but are ten times larger. ... 

---