Porphyrins


In the heaviest fractions such as resins and asphaltenes (see article 1.2), metal atoms such as nickel and vanadium are found. They belong in part to molecules in the porphyrine family where the basic pattern is represented by four pyrrolic rings, the metal being at the center of this complex in the form Wi - or V0+ (< 3)  [c.12]

Lesieur P, Vandevyver M, Ruaudel-Teixier A and Barraud A Orientational studies of Langmuir-Blodgett films of porphyrins with polarized resonant Raman spectroscopy Thin Soiid Fiims 159 315-22  [c.2633]

Heavy oils and especially bitumens contain high concentrations of resins (30-40%) and asphaltenes (<20%). Most heavy oils and bitumens are thought to be derivatives of lighter, conventional crude oils that have lost part or all of their straight-chain alkane contents along with some of their low-molecular-weight cyclic hydrocarbons through processes taking place in the oil reservoirs. Heavy oils are also abundant in heteroatom (N, O, S)-containing molecules, organometallics, and colloidally dispersed clays and clay organics. The prominent metals associated with petroleum are nickel, vanadium [mainly in the form of vanadyl ions (VO )], and iron. Some of these metals are (in part) bound to porphyrins to form metalloporphyrins.  [c.131]

Porphyrins. Chlorophyll a, and Corrins  [c.250]

Porphyrins, Chlorophyll a, and Corrins  [c.250]

Porphyrins, Chlorophyll a, and Corrins  [c.252]

This apparently extremely simple synthesis of symmetrical porphyrins from aldehydes and pyrrole has also been used to produce porphyrins with interesting stereochemical proper-  [c.252]

Porphyrins, Chlorophyll a, and Corrins 253  [c.253]

Porphyrins, Chlorophyll a, and Corrins 255  [c.255]

Porphyrins. Chlorophyll a. and Corrins  [c.256]

With the catalysis of strong Lewis acids, such as tin(IV) chloride, dipyrromethenes may aiso be alkylated. A very successful porphyrin synthesis involves 5-bromo-S -bromomethyl and 5 -unsubstituted 5-methyl-dipyrromethenes. In the first alkylation step a tetrapyrrolic intermediate is formed which cyclizes to produce the porphyrin in DMSO in the presence of pyridine. This reaction sequence is useful for the synthesis of completely unsymmetrical porphyrins (K.M. Smith, 1975).  [c.256]

Porphyrins. Chlorophyll a. and Corrins 257  [c.257]

S 4.2 Porphyrins. Chlorophyll a, and Corrins  [c.258]

Porphyrins, Chlorophyll a, and Corrins  [c.260]

Porphyrins. Chlorophyll a. and Corrins  [c.262]

H2N-CH2C0-CH2CHjC02H. The base unit in the biosynthesis of porphyrins and so furnishing all the carbon and nitrogen atoms in the haem of haemoglobin, myoglobin, cytochromes, catalase and peroxidase as well as the dihydroporphyrin ring of chlorophyll. It is also incorporated into the corrin ring of vitamin Bi2. 5-Aminolaevulinic acid is formed from succinyl coenzyme A and glycine. Condensation of two molecules yields porphobilinogen (a pyrrole derivative) and four molecules of this condense to give the porphyrin skeleton.  [c.29]

The sensitivity is very good for nickel and vanadium but for these metals for which distribution data would be of great value, the chromatographic process is the lirniting factor, heavy molecules are not eluted from the column with the exception of some porphyrins. This detector can be used to supply H/C and S/C profiles for hydrocarbon cuts with the chromatograph operating in the simulated distillation mode.  [c.79]

Levstein P R and van Willigen H 1991 Photoinduced electron transfer from porphyrins to quinones in micellar systems an FT-EPR study Chem. Phys. Lett. 187 415-22  [c.1621]

Jones R, Tredgold R FI and Flodge P 1983 Langmuir-Blodgett films of simple esterified porphyrins Thin Solid Films 99 25-32  [c.2632]

Jones R, Tredgold R FI, Floorfar A and Flodge P 1984 Eleetrioal-eonduetivity in Langmuir-Blodgett films of porphyrins—inplane and through-the-film studies Thin Solid Films 113 115-28  [c.2632]

Jones R, Tredgold R FI and Floorfar A 1985 Effeots of thiokness on surfaoe-potential and surfaoe oonduotivity in non-insulating Langmuir-Blodgett multilayers of porphyrins Thin Solid Films 123 307-14  [c.2632]

Ruaudel-Teixier A, Barraud A, Belbeoch B and Roulliay M 1983 Langmuir-Blodgett films of pure porphyrins Thin Soiid Fiims 99 33-40  [c.2633]

An excess of porphobilinogen in the urine is associated with hepatic disorders and lead poisoning. Porphobilinogen can be separated from other porphyrins by ion exchange chromatography and treated with p-dimethylaminobenzalde-hyde (PDMA) to produce a red compound that absorbs light str ongly at 550 nm. A set of standard solutions was made up with concentrations of 50.0, 75.0, 100.0, 125.0, 150.0, 175.0, 200.0, 225.0, and 250.0 mg/100 niL of porphobilinogen. Their absorbances A after treatment with PDMA were 0.039, 0.061, 0.087, 0.107, 0.119, 0.163, 0.179, 0.194, and 0.213. What is the spectro-photometric calibration curve A = /(concentration) for this method What are the units of slope Three urine specimens treated by this method yielded absorbances A of 0.180, 0.162, and 0.213. What were the porphobilinogen concentrations of these three samples  [c.79]

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975).  [c.129]

Porphyrins and chlorophylls are the most widespread natural pigments. They are associated with the energy-converting processes of respiration and photosynthesis in living organisms, and the synthesis of specific porphyrin derivatives is often motivated by the desire to perform similar processes in the test tube. The structurally and biosynthetically related corrins (e.g. vitamin B,j) catalyze alkylations and rearrangements of carbon skeletons via organocobalt intermediates. The biosyntheses of these chromophores are also of topical interest.  [c.250]

Because of the occurrence of isomers, the synthesis from pyrroles is only useful for porphyrins with eight identical >7-pyrrolic and four identical methine bridge substituents. Famous examples are the syntheses of chloroform-soluble -octaethyl-porphyrin and meso-tetraphenylporphyrin which have been used in innumerable studies on porphyrin reactivity (K.M. Smith, 1975). Porphyrins with four long meso-alkyl side-chains can be obtained by use of analogous reactions. These porphyrins have melting points below 100 °C and are readily soluble in petroleum ether. Sulfonation of olerinic double bonds leads to highly charged, water soluble porphyrins (J.-H. Fuhrhop, 1976).  [c.252]

Naturally occurring porphyrins are usually symmetrically substituted about the 15-methine bridge. These porphyrins can be synthesized by the condensation of two dipyrroiic intermediates. Typical dipyrroiic intermediates in current use arc the dipyrromethanes and the dipyrromethenes. Both methods will shortly be described. This again is a highly specialized  [c.253]

This case history presents only a simple account of one of R.B. Woodward s adventures based on ingenious undentanding of structural features and experimental findings described in the literature. The hydrogenation of porphyrins is still one of the most active subjects in heterocyclic natural products chemistry, and the interested reader may find some modem developments in the publications of A. Eschenmoser (C.Angst, 1980 J.E. Johansen, 1980).  [c.259]

It is conceivable that related ligands, e.g. dehydrocorrins, could be obtained from pyrrolic units using pathways similar to those used for porphyrins and could be hydrogenated to corrins. This has indeed been achieved (I.D. Dicker, 1971), but it is, of course, impossible to introduce the nine chiral centres of cobyrinic acid by such procedures.  [c.259]

A new type of chemical architecture was inspired by the crystal structure determination of bacterial photosynthetic reaction centres (J. Deisenhofer, 1984), where two magnesium porphyrins (the special pair ) and one metal-free porphyrin arc bound in a fixed array. Irradiation of this arrangement with visible light induces an extremely rapid charge separation. Several bis-porphyrins with rigid aromatic spacers in which the components are also fixed, porphyrins and bis-porphyrins with redox-active groups, and other model structures have been synthesized (e.g., XL. Sessler, 1986, 1987, 1988 A, B methods section 4.2.1). Conformationally constrained trimers and pentamers have been synthesized recently and exhibit electronic spectra of fundamental importance. Stacked porphyrin oligomers with 1,8-anthrylene linkages show a blue shift of the maximum absorption of monomeric porphyrins, the Soret band , from 405 nm towards 395 nm. Stretched p-phenylene-linked oligomers give red shifts and splitting of the soret band, and m-phenylene-linked oligomers with tilted porphyrins give a tiny blue shift. Results like this, coupled with other spectral and electrochemical data, permit the assignment of structures to non-covalcnt porphyrin aggregates, help to verify models for energy transfer reactions such as the exciton coupling theory (M. Kasha, 1965), and can lead to systems capable of useful charge separation.  [c.348]

The syntheses given are also useful for connecting porphyrins with other chroihophores and reactive groups, e.g., quinoncs. If the reported yields are reproducible, large electron donor-acceptor supramolecules should become accessible on a large scale.  [c.350]

Porphyrin monomers have a strong tendency to form stacked dimeric aggregates in solutions. If the porphyrins possess side chains with hydrophilic, hydrogen-bonding head groups, they assemble to form long fibers in aqueous suspension (J.-H. Fuhrhop, 1992). The spectroscopic properties of these fibers arc very similar to those of the 1,8-anthrylcnc linked stacked oligomers. The properties of noncovalent oligomers forming by spontaneous self-assembly are often found to be similar to those of certain covalent synthetic oligomers thus providing helpful information on structures and reactivities.  [c.350]


See pages that mention the term Porphyrins : [c.95]    [c.198]    [c.323]    [c.323]    [c.323]    [c.323]    [c.332]    [c.546]    [c.2435]    [c.2616]    [c.215]    [c.251]    [c.128]    [c.251]    [c.251]    [c.254]    [c.255]    [c.349]   
See chapters in:

The molecular modeling workbook for organic chemistry  -> Porphyrins

Advances in heterocyclic chemistry Vol.77  -> Porphyrins


Organic synthesis (0) -- [ c.250 , c.251 , c.252 , c.253 , c.254 , c.255 , c.256 ]

Thin-layer chromatography Reagents and detection methods (1990) -- [ c.99 , c.103 ]