Thermal stability of porphyrins with chemicaly active NH bond and their associates with electron-donor solvents

The composition and stability of the crystalline H associates of NH active tetrapyrroles with electron-donor solvents were investigated by thermogravimetry. It was found that common porphyrins and their analogs can form 1: 1 and 1: 2 macrocycle solvent H associates whose energy of formation depends on their composition and ranges from 20 to 115 kJ/mol. Based on the results from an analysis of the Stokes shifts, we concluded that the formation of H associates in a solution is accompanied by variations in the degree of macrocycle nonplanarity. The stability of a series of tetrapyrroles with regard to thermal destruction in argon atmosphere and in the presence of atmospheric oxygen was shown to drastically vary.     

Bilitrienones from the chemical oxidation of dodecasubstituted porphyrins

The structure of the ring-opened product from direct oxidation of meso-tetra-arylporphyrins has been controversial for three decades. Herein we show that bilitrienones 2 are obtained from oxidation of metal-free dodecasubstituted porphyrins 1 in the presence of sodium nitrite, trifluoroacetic acid, and air oxygen. The presence of the para-nonyl groups in 1b stabilized the corresponding bilitrienone 2b, which was characterized by X-ray crystallography. In the absence of the para-nonyl groups bilitrienone 2a undergoes a rapid hydration reaction, giving biladienone 3a as the major isolated product. The molecular structures of 2b and 3a, and the photochemical isomerization of 3a are discussed.     

Synthesis of beta-functionalized porphyrins via palladium-catalyzed carbon-heteroatom bond formations: expedient entry into beta-chiral porphyrins

A procedure was developed for the preparation of beta-monobromo-tetraphenylporphyrin (BrTPP) in a greatly improved yield from the selective bromination of tetraphenylporphyrin (TPP) by NBS. BrTPP was successfully employed as a versatile synthon for convenient synthesis of a wide range of beta-monofunctionalized porphyrins with various heteroatom functionalities via palladium-mediated carbon-heteroatom bond formations. Examples include beta-amino, -amido, -oxo, and -mercaptoporphyrins from reactions with amines, amides, alcohols, and thiols, respectively. Applying the synthetic approach to chiral amides, beta-chiral porphyrins were effectively constructed.     

肾上腺素在咖啡酸修饰电极上的电化学研究

研究了咖啡酸(CFA)修饰电极的性质,测定了电极反应的动力学常数.结果表明在pH 7.0的的磷酸盐缓冲溶液中,肾上腺素(Ep)在该修饰电极上产生一灵敏的氧化峰,峰电流与Ep浓度在5.0×10-6～1.0×10-4 mol/L范围内线性关系良好,检出限为7.0×10-7 mol/L.修饰电极制备简单,稳定性好.     

Magnetic resonance spectroscopic investigations of the electronic ground and excited states in strongly nonplanar iron(III) dodecasubstituted porphyrins

A series of axially ligated complexes of iron(III) octamethyltetraphenylporphyrin, (OMTPP)Fe(III), octaethyltetraphenylporphyrin, (OETPP)Fe(III), its perfluorinated phenyl analogue, (F(20)OETPP)Fe(III), and tetra-(beta,beta'-tetramethylene)tetraphenylporphyrin, (TC(6)TPP)Fe(III), have been prepared and characterized by (1)H NMR spectroscopy: chloride, perchlorate, bis-4-(dimethylamino)pyridine, bis-1-methylimidazole, and bis-cyanide. Complete spectral assignments have been made using 1D and 2D techniques. The temperature dependences of the proton resonances of the complexes show significant deviations from simple Curie behavior and evidence of ligand exchange, ligand rotation, and porphyrin ring inversion at ambient temperatures. At temperatures below the point where dynamics effects contribute, the temperature dependences of the proton chemical shifts of the complexes could be fit to an expanded version of the Curie law using a temperature-dependent fitting program developed in our laboratory that includes consideration of a thermally accessible excited state. The results show that, although the ground state differs for various axial ligand complexes and is usually fully consistent with that observed by EPR spectroscopy at 4.2 K, the excited state often has S = (3)/(2) (or S = (5)/(2) in the cases where the ground state has S = (3)/(2)). The EPR spectra (4.2 K) of bis-4-(dimethylamino)pyridine and bis-1-methylimidazole complexes show "large-g(max)" signals with g(max) = 3.20 and 3.12, respectively, and the latter also shows a normal rhombic EPR signal, indicating the presence of low-spin (LS) (d(xy))(2)(d(xz),d(yz))(3) ground states for both. The bis-cyanide complex also yields a large-g(max) EPR spectrum with g = 3.49 and other features that could suggest that some molecules have the (d(xz),d(yz))(4)(d(xy))(1) ground state. The EPR spectra of all five-coordinate chloride complexes have characteristic features of predominantly S = (5)/(2) ground-state systems with admixture of 1-10% of S = (3)/(2) character.     

Preparation,properties and analytical application of silica with chemically grafted hydroxamic acid groups

The synthesis of silica chemically modified with propanohydroxamic acid groups and salicylhydroxamic acid is described. Sorption of 13 metal ions is studied as a function of pH. The composition of the sorbed complexes is determined and the apparent stability constants of the complexes in the sorbent phase are calculated. A correlation between the stabilities of the complexes in the sorbent phase and in aqueous solution is observed in some cases. Some analytical applications of the sorbents are demonstrated: trace amounts of elements can be concentrated from large volumes; molybdenum(VI) and zirconium(IV) can be separated from 10⁴-fold amounts of accompanying elements, and vanadium(V) can be determined in the sorbent phase by using diffuse reflection and photoacoustic spectrometric techniques.     

Photophysical properties of crowned porphyrins

In this study, we evaluated the photophysical properties of 5,10,15,20-tetrakis[4-(1,4,7,10,13-pentaoxacyclopentadecane-2-aminomethyl)2,3,5,6-(tetrafluoro)-phenyl]-porphyrin (H2C4P) and Zn(II)5,10,15,20-tetrakis[4-(1,4,7,10,13-pentaoxacyclopenta-decane-2-aminomethyl)2,3,5,6-(tetrafluoro)-phenyl]-porphyrinate (ZnC4P). We observed that these porphyrins have unique properties when compared with classical porphyrins. The porphyrins H2C4P and ZnC4P showed efficient transfer energy S1 to T1 by intersystem crossing with high and reasonable yields of triplet excited state and singlet oxygen production. These amphiphilic structures of these porphyrins could improve its localization in the tumor cells due to the presence of the crown ether in its framework. We also believed that the crown ether could modulate the change in ion homeostase (Ca(+2), K+, Na+) as already described by some new phthalocyanine dye. This fact makes us believe that it could be reasonably used as a photosensitizer for PDT purposes.     

Sesquiterpene lactones as stimulators of photodynamically active porphyrins

The photosensitizing properties of sesquiterpene lactones have been considered by means of a study of their influence on the pigmentary system of plants. An investigation of the action of germacranolides, eudesmanolides, guaianolides, and pseudoguaianolides on the fluorescence spectra of leaves in the presence of exogenous 5-aminolevulinic acid (5-ALA) has permitted the conclusion that these compounds are capable of inhibiting the transformation of 5-ALA in the chain of the biosynthesis of chlorophyll.     

Sesquiterpene lactones as stimulators of photodynamically active porphyrins

The photosensitizing properties of sesquiterpene lactones have been considered by means of a study of their influence on the pigmentary system of plants. An investigation of the action of germacranolides, eudesmanolides, guaianolides, and pseudoguaianolides on the fluorescence spectra of leaves in the presence of exogenous 5-aminolevulinic acid (5-ALA) has permitted the conclusion that these compounds are capable of inhibiting the transformation of 5-ALA in the chain of the biosynthesis of chlorophyll.Institute of Organic Synthesis and Coal Chemistry, Kazakhstan Academy of Sciences. Institute of Physiologically Active Compounds, Russian Academy of Sciences, Chernogolovka. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 637–640, November–December, 1992.     

NH-acid properties of porphyrins in acetonitrile

The thermodynamics of acid dissociation of synthetic porphyrins (H₂P) in alkaline acetonitrile solution is studied. The low stability of the anionic species is attributed to the previously formulated electronic, steric, and solvation factors. The solvent plays an important role in the stabilization of anionic porphyrin species in acetonitrile. The electronic absorption spectra of anionic species of H₂P are analyzed.     

Basic properties of porphyrins with polyethylenoxide spacers of various length

Basic properties of bis[5-(3-oxyphenyl)-2,8,12,18-tetrabutyl-3,7,13,17-tetramethylporphyrinyl]-3,6,9-trioxyundecane-1,11 and bis[5-(3-oxyphenyl)-2,8,12,18-tetrabutyl-3,7,13,17-tetramethylporphyrinyl]-3,6,9,12-tetraoxytetradecane-1,14 were studied by the spectrophotometric titration in ethanol-sulfuric acid system at 298 K. It was established that protonation of nitrogen atoms in tetrapyrrole fragments of dimeric porphyrins proceeds in two steps. The corresponding ionization constants and the concentration limits of existence of di- and tetracationic forms of the compounds under study were evaluated.     

Synthesis and photophysical properties of porphyrins with fluorenyl pendant arms

Symmetrical-A₄-porphyrins bearing four fluorene donor moieties TOFP (5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin) as well as eight fluorene arms OOFP (5,10,15,20-octa(3,5-(2-methyloxyfluorenyl)phenyl)porphyrin) were synthesized and characterized. Preliminary photophysical properties are reported. In comparison to the reference tetraphenylporphyrin TPP, the luminescence properties are slightly improved. The fluorescence quantum yields of tetrafluorenylporphyrin TOFP (1) and octafluorenylporphyrin OOFP (2) are 0.10 and 0.13, respectively.     

Synthesis of meso-arylsulfanyl- and alkylsulfanyl-substituted porphyrins via palladium-mediated C-S bond formation

A family of new meso-arylsulfanyl- and alkylsulfanyl-substituted porphyrins were efficiently synthesized from direct reactions of meso-brominated porphyrins with thiols via palladium-mediated C-S bond formation. The catalytic method can be performed under mild conditions with both mono- and bis-substituted meso-bromoporphyrins as well as their zinc complexes and is suitable for different types of thiols. With the use of selenols, meso-seleno-substituted porphyrins can also be prepared similarly.     

O-O bond cleavage in dinuclear peroxo complexes of iron porphyrins: a quantum chemical study

To gain insight into the mechanisms of O2 activation and cleavage in metalloenzymes, biomimetic metal complexes have been constructed and experimentally characterized. One such model complex is the dinuclear peroxo complex of iron porphyrins observed at low temperature in a non-coordinating solvent. The present theoretical study examines the O-O bond cleavage in these complexes, experimentally observed to occur either at increased temperature or when a strongly coordinating base is added. Using hybrid density functional theory, it is shown that the O-O bond cleavage always occurs in a state where two low-spin irons (S = +/-1/2) are antiferromagnetically coupled to a diamagnetic state. This state is the ground state when the strong base is present and forms an axial ligand to the free iron positions. In contrast, without the axial ligands, the ground state of the dinuclear peroxo complex has two high-spin irons (S = +/-5/2) coupled antiferromagnetically. Thus, the activation barrier for O-O bond cleavage is higher without the base because it includes also the promotion energy from the ground state to the reacting state. It is further found that this excitation energy, going from 10 unpaired electrons in the high-spin case to 2 in the low-spin case, is unusually difficult to determine accurately from density functional theory because it is extremely sensitive to the amount of exact exchange included in the functional.     

The structuring and properties of hydrogels prepared with a biologically active macromonomer

The copolymerization of a macromonomeric inhibitor of proteolytic enzymes with acrylamide and N,N′-methylenebis(acrylamide) in an aqueous solution in the presence of a redox catalyst has been studied. It has been shown that the addition of mercaptoacetic acid as a chain-transfer agent to the polymerization system results in a change in the structure of the forming hydrogel, i.e., a decrease in the number of large pores. Simultaneously, a substantial increase in the degree of the macromonomer incorporation into the hydrogel is attained and favorable conditions for the development of the biological activity of the macromonomer are created.     

Mass spectrometric identification of a stable catalytic cysteinesulfinic acid residue in an enzymatically active chemically modified glucoamylase mutant.

Mass spectrometric identification of cysteinsulfinic acid resulting in restoration of activity of chemically modified Glu400 Cys catalytic-base glucoamylase (GA) mutants is described. This oxidation unexpectedly occurred during attempts to carboxyalkylate the Cys400 GA mutant using three different alkylation reagents. However, mass spectrometric peptide mapping did not show the presence of carboxyalkylation of the Cys400 residue but suggested an oxidation to cysteinsulfinic acid based on the observed mass increment. The presence of cysteinsulfinic acid was confirmed by employing matrix-assisted laser desorption/ionization mass spectrometry combined with post-source decay analysis. Furthermore, strong enhancement of metastable fragmentation was observed for peptides containing oxidized Cys in comparison with non-oxidized peptide.