Porphyrins optical detection

TTie porphyrin ZnP in a crystalline n-octane matrix at 1.2 K was investigated by optically detected magnetic resonance (ODM) and microwave induced delayed phosphorescence (MIDP) . ... 

Thus, no one peroxidase system is exactly like another, at least on the basis of the evidence accumulated to date. One may suppose that in each case the primary radical formed is located on the porphyrin and that the presence of oxidizable groups in the vicinity of the heme leads to transfer of the oxidizing equivalent out onto an amino acid in the peptide. Transfers of this kind may be quite common in proteins pulse radiolysis studies using optical detection of transients have demonstrated the migration of oxidation from one amino acid site to another [119]. 

The rate constants for radiationless decay of the triplet state of mesoporphyrin IX dimethyl ester at 77 are 26 s-1 in EtOD and 57 s-1 in EtOH.352 The most probable cause is a decrease in the rate of tautomerism in the porphyrin due to deuteriation of the N—H hydrogen. However, for TPPH2 triplet state in n-octane matrices 363 such tautomerism does not appear to be an important mechanism for radiationless deactivation. Several recent reports deal with the low-temperature e.s.r. spectra of triplet states of porphyrins.364-368 The zero field splittings and depopulation rates of the various spin sub-levels of the triplet state of Zn-chlorophyll-a have been determined by an optically detected magnetic resonance method.359... 

Beswick, R. B., and C. W. Pitt. 1988. Optical detection of toxic gases using fluorescent porphyrin Langmuir-Blodgett films. 7. Colloid Interface Sci. 124(f) 146-55. 

The optical detection of vapors was based on the changes in optical properties of thin films, such as dielectric constant, refractive index, and so forth, when they were exposed to the VOCs. In the solid thin films, there are n-n interactions between the analytes and phthalocyanines/porphyrins. Interactions with VOCs can induce a change of these interactions, leading to broad, splitting, and shift of absorbance bands in their UV-vis spectra. UV-vis spectra of phthalocyanines are typically represented... 

Today, UV-visible spectroelectrochemistry has become an essential tool in the study of redox processes, particularly when the processes are reversible and the reagents or products of electrolysis are colored. For example, the technique is of enormous value in the study of the electrochemistry of porphyrins and ph-thalocyanines, though it took some time to catch on. A review of porphyrin electrochemistry from 1986 barely mentions the technique, now an essential, even routine, tool in this field [4]. Another area of chemistry in which spectroelectrochemistry has been extremely important is conducting polymers, a field that had barely started 20 years ago. Spectroelectrochemistry has also been developing rapidly as the technology of electronic and optical detection has advanced. For example, we shall see later how time-resolved spectroelectrochemistry is now able to provide a wealth of information about electrochemical processes. 

Porphyrins are a class of aromatic molecules whose intense absorbance and fluorescence characteristics are influenced by their immediate surroundings (7-9) and, thus, readily reflect their interaction with other molecules. The large extinction coefficient (500,000 A/cm pathlength/M) of porphyrins allows for measuring small absorbance changes ideal for optical detection applications. 

Xu Y, Zhao L, Bai H, Hong W, li C, Shi G. Chemically converted graphene induced molecular flattening of 5,10,15,20-tetrakis(l-methyl-4-pyridinio)porphyrin and its application for optical detection of cadmium(ll) ions. J Am Chem Soc 2009 131 13490-7. 

Porphyrine derivatives are a promising class of chelating agents, being well established as highly sensitive indicators for the spectrophotometric determination of metal ions. The high complexation constants of porphyrins allow very sensitive detection. Furthermore, this class of dyes has extremely high extinction coefficients which can be used for a very sensitive optical detection. In addition, the different metal complexes of porphyrins show very specific absorption bands. This class of dyes makes a multicomponent analysis feasible, with sensors which can detect several metal ions by their specific... 

Determine the cause of the broadening of line in optical detection of magnetic resonance for the triplet excited states of porphyrins ... 

Fig. 37.11. Use of an NO microsensor for detection of the NO release from cultured endothelial cells. The sensor is a dual probe microsensor. The small sensor is a bare Pt UME used to position the sensor in the feedback mode. Onto the larger Pt electrode a polymer was deposited from an acrylic resin containing Ni(4-lV-tetramethyl) pyridyl porphyrin and served as amperometric NO sensor, (a) Schematic of the sensor, (b) optical microphotograph of the sensor surface, (c) Response of the NO sensor to the stimulation of the cells with bradykinin at different distances of the sensor to the surface of the cells. Reprinted with permission from Ref. [104], Copyright 2004, American Chemical Society.

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]. 

Photochromic dithienylethenes have been considered as extremely promising systems to store information. The success of optical information processing requires the facile detection method which can read the stored information in a non-invasive manner. It is to say that the non-destructive readout capability is indispensable. On the basis of the ability to fine-tune the excitation wavelengths of porphyrins and the fact that they exhibit strong luminescence and attractive coordination properties, Branda covalently attached two porphyrins to the dithienylethene backbone, and synthesized a hybrid for non-destructive information processing [29], as shown in Scheme 1. It was the first example of photochromic porphyrinic dithienylethene. 

Amao Y, Miyashita T, Okura I. Platinum tetrakis(pentafluorophenyl)porphyrin immobilized in polytrifluoroethylmetacrylate film as a photostable optical oxygen detection material. / Fluorine Chem 2001 107 101-6. 

T. Balaji, M. Sasidharan, and H. Matsunaga, Optical sensor for the visual detection of mercury using mesoporous silica anchoring porphyrin moiety, Analyst 130, 1162-1167 (2005). 

Second, in addition to the above, the fact that many expanded porphyrins are highly colored makes their use as dyes an obvious possibihty. Here their planar nature makes them particularly attractive as chromophores for use in liquid crystals and optical data storage applications. Also, these properties could make them of interest as photo-sensors in various clinical or pseudo-clinical situations. For instance, the high affinity by certain sapphyrins for enveloped viruses and cholesterol rich liposomes suggests that expanded porphyrins could be used to detect and/or destroy a variety of unwanted biological targets, including arterial sclerotic plaque. 

Oxoiron(IV) tefraphenylchlorin complexes have been prepared as the first models of a reaction intermediate in the catalytic cycle of cytochrome d Optical absorption spectra show a characteristic red-shified band at 630 nm as observed in the oxoferryl intermediate of cytochrome d, and the proton NMR spectra of the N-Melm complex exhibit very small hyperfine shifts of the pyrrole protons, as is true for oxoferryl porphyrin complexes. The pyrroline protons of the saturated pyrrole ring show unusual splitting into upheld and downfield resonances. The N-Melm complex also shows normal Fe =0 stretching frequencies as compared to the corresponding oxoferryl porphyrin complexes. And finally, for iron porphycenes, both peroxo and ferryl intermediates have been detected by H NMR spectroscopy during the oxygenation of the Fe complexes. ... 

The presence of this and other materials presents potential problems in industrial processing, and there is great interest in characterization of the chemical nature of the vanadium species present. EPR is most widely used in these studies since the metal is in the oxo-vanadium(IV) state. Optical spectroscopy in the visible region can also be used on extracts since oxo-vanadium(IV) porphyrins, which absorb at around 572 nm and 534 nm 116,119), can readily be detected. However, it has been shown (120-122) that the total amount of vanadium present in crude oils and tar sand bitumen is higher than can be accounted for by the presence of oxo-vanadium(IV) porphyrins. It has therefore been suggested that the vanadyl may be bound to a range of different tetra-dentate ligands in crude oils (120-123). 

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