The Soret absorption band of isolated chlorophyll a and b tagged with quaternary ammonium ions

The true colors of chlorophyll a and b, isolated in vacuo, are revealed from a combination of gas-phase ion spectroscopy and TD-DFT calculations.

Synthesis and Solution Self-Assembly Behavior of Porphyrin Tethered by Fullerene C60

This paper focuses on the synthesis, spectroscopic studies and self-assembly behavior of porphyrin phenyl linked fullerene C60 dyad, which included COOH groups in its fullerene unit so as to promote its adsorption onto TiO2. UV-Vis spectrum and steady-state fluorescence spectrum measurement, showed that the self-assembly of this compound in different solvents with different polarities. The results show that the soret absorption peak slightly blue shifted by 5 nm in acetonitrile and 2 nm in tetrahydrofuran, while the soret peaks in toluene solution was the same as in chloroform. Increasing concentration from 1x10-6 mol/L to 2x10-5 mol/L in chloroform resulted into aggregation, also the slight red shifting on cooling from 900C to 100C was observed from a temperature dependant UV-Vis absorption spectra, thus indicates aggregation. All these features may indicate presence of J-type aggregation happening in 4-methylphenyl-H2porhyrin-fullerene C60-COOH. In addition, the fluorescence of 4-methylphenyl-H2Porhyrin-fullerene C60-COOH has been quenched compared to that of pure 4-methylphenyl-H2porhyrin-OH under the same concentration. Therefore, this novel material design may find good application in photoelectric devices.

Synthesis and spectral property study of porphyrin-anthraquinone dyads bonded through azo

To determine if the dihedral angle between the phenyl group and the porphyrin ring in the meso-phenyl porphyrin (H2TPP) could be adjusted by selective substitution of the naphthyl group for phenyl groups, novel dyads with a free-base porphyrin donor and anthraquinone acceptor linked by a rigid azo bond were synthesized and their spectral properties were investigated in detail. The Soret absorption band of dyads with meso-naphthyl groups in porphyrin shows 5–7 nm red shift as compared to the corresponding raw materials due to the introduction of the anthraquinone moiety. Fluorescence from the porphyrin moiety was found to be intensely quenched with the addition of anthraquinone moiety in the dyads; the highest quenching rate was observed to be 95% in the dyad prepared by meso-tetranaphthyl porphyrin. This indicates that the efficiency of the intramolecular photoinduced electron transfer in porphyrin-anthraquinone dyads could be changed by substituting the meso-phenyl group in porphyrin for the meso-naphthyl group.

Solvent effects on the electronic and vibrational properties of high-valent oxomolybdenum(V) 5,10,15-triphenylcorrole probed by UV-visible and resonance Raman spectroscopy

Solution UV-visible electronic absorption and resonance Raman (RR) scattering spectra in 25 aprotic organic solvents have been measured and analyzed for a high-valent molybdenum( V ) oxo complex of 5,10,15-triphenylcorrole, (MoVO)CorPh3 . Optical absorption data in the visible region show a significant positive solvatochromism upon increasing solvent polarizability (ca. 660 cm-1 for the violet Soret band on going from acetonitrile to carbon disulfide), described by an excellent linear correlation between the bathochromic shifts of corrole π → π* electronic transitions and the solvent refractive index [Formula: see text]. Isotope labeling of the terminal oxo group with 18 O revealed the oxo-Mo(V) stretch of (MoVO)CorPh3 to vibrate at frequency ν(MoVO) ≈ 970 cm-1 [Δ(16O-18O) = 46 cm-1] , consistent with a MoV≡O triple bond. This vibration is greatly enhanced in the RR spectra with excitations within the Soret absorption band and its frequency is sensitive to solute-solvent interactions that weaken the MoV≡O triple bond by inhibiting O2- → Mo5+ electron donation. The ν(MoVO) frequency decreases in direct proportion to the Swain's solvent polarity parameter (A + B), from 969.4 cm-1 in n-hexane solution down to 955.6 cm-1 in dimethyl sulfoxide solution. However, only weak linear correlation was found when the ν(MoVO) frequencies were plotted as a function of the Gutmann's solvent acceptor numbers (ANs). A molecular association occurs between chloroform and (MoVO)CorPh3 through MoV≡O⋯H-CCl3 hydrogen-bonding interactions, manifested as an upshift of the ν(MoVO) RR band in deuteriochloroform solution. The ν(MoVO) stretching frequencies of (MoVO)CorPh3 and its fluorinated derivative (MoVO)Cor(Ph(CF3)2)3 {Cor(Ph(CF3)2)3 = 5,10,15-tris-[3,5-bis(trifluoromethyl)phenyl]corrole} are compared, and the increased strength of the MoV≡O bond in the latter oxo-Mo(V) species is attributed to the cis effect of the electron-withdrawing -C6H3(CF3)2 groups, as judged by a 6 cm-1 elevation of the ν(MoVO) frequency. Raman excitation profiles of ν(MoVO) and corrole skeletal vibrations show the presence of charge-transfer and π → π* electronic transitions within the Soret absorption band of oxomolybdenum( V ) corroles.

Equilibrium, photophysical, photochemical and quantum chemical examination of anionic mercury(I) porphyrins

Hg22+ ion and 5,10,15,20-tetrakis(parasulphonato-phenyl)porphyrin anion can form 2:1 (2 clusters:1 porphyrin) and 2:2 complexes, while the formation of the 1:1 species is not observable: it is only an intermediate, similarly to the cases of other large metal ions of small charge-density. The differences between mercury(I) and mercury(II) porphyrins in the composition of monoporphyrins (2:1 vs. 1:1), in the stability and the Soret absorption based on the arrangement of 2:2 complexes (asymmetric vs. probably symmetric sandwich-structure), in the kinetic behavior (molecularities and the special dimerization of HgIIP4-), in the product of the photoinduced dissociations of 2:2 bisporphyrins (free-base ligand vs. 1:1 complex) can prove that no mercury(II) porphyrins can form due to the possible disproportion of dimercury(I) ions. However, the similarities in the absorption, photophysical and photochemical features (also to other out-of-plane metalloporphyrins) suggest that the out-of-plane position of metal center and the distorted structure of complexes may be responsible for these common properties, the so-called sitting-atop characteristics. Moreover, the calculated structural data of the theoretically studied 1:1 mercury(I) porphyrin are very similar to those of Hg II P as a consequence of the charge separation in the cluster based on the strength of metal-nitrogen bonds. In the case of the 2:2 species, neither the increased distance (because of the Hg-Hg bond), nor the absence of 45° rotation of the two ligands can significantly modify the π-π interaction because its both measured and calculated absorption spectra are similar to those of Hg II2 P 2.

Photooxidation of cobalt(II) meso-tetraphenylporphyrin by p-benzoquinone and its mechanism studied by optical absorption and resonance Raman spectroscopies

Laser excitation of Co II TPP within the Soret absorption band in the presence of p-benzoquinone (p-BQ) results in oxidation of the complex. Oxidation occurs both at the metal center and the porphyrin ring depending upon the experimental conditions. Under anaerobic conditions, oxidation takes place at the metal center to produce the cobaltic species Co III( TPP )+, while in the presence of molecular oxygen oxidation also occurs at the porphyrin ring giving Co III( TPP )2+• cation radical as oxidation product. From the inhibiting effect of peroxy radical trapping agent on the photooxidation of Co II TPP under aerobic conditions, the two-electron oxidation is suggested to involve solvent radicals and we discuss the mechanistic details of the process in this work.

Modification of the porphyrin chromophore by ring fusion: identifying trends due to annelation of the porphyrin nucleus

The effects exerted by fused aromatic rings on the UV-vis spectra of porphyrins are surveyed. Modified porphyrin chromophores with fused benzene, 1,2-naphthalene, 9,10-phenanthrene or phenanthroline rings are surprisingly little affected even when a maximum number of ring fusions are incorporated. Linearly annealed naphtho- or anthraporphyrins show large red shifts to the Q bands but the Soret absorptions are weakened and undergo only minor bathochromic shifts. Fluoranthoporphyrins give multiple bands in the Soret region, but the Q band region is virtually unaffected by this tetracyclic ring system. On the other hand, metal chelates of fluoranthoporphyrins show surprisingly strong bands near 600 nm. Benzothiadiazole rings split and weaken the Soret band, but the Q bands region is unexceptional. However, metal coordination again produces relatively intense bands near 600 nm. The most significant results were obtained for porphyrins with fused acenaphthylene rings. Monoacenaphthoporphyrins (41) have three Soret bands at 387, 431 and 454 nm, and the longest wavelength Q band is shifted to 658 nm. opp-Diacenaphthoporphyrin (43) further shifts these bands with two Soret absorbances at 443 and 470 nm, and an additional strong peak is observed at 692 nm. The metal complexes of these systems also show strong bands between 602 and 656 nm. Still larger effects are produced by tetraacenaphthoporphyrin (47), the dication for which in trifluoroacetic acid (TFA)–chloroform has a Soret absorption at 528 nm. Tetraaryltetraacenaphthoporphyrins (48) are even more red shifted, showing Soret bands between 556 and 570 nm for the free bases and 565 to 588 nm for the related dications. The lead(II) chelate for tetraphenylporphyrin (48a) shows an additional 'hyper' spectral shift that brings the Soret band to 604 nm, and this effect can also be achieved by introducing four meso-phenylethynyl substituents onto the tetraacenaphthoporphyrin nucleus (49). In addition, by combining these two factors for the lead(II) chelate of 49, a record-breaking value for the Soret band of 642 nm can be achieved. Spectral shifts due to ring annelation in porphyrin analogues are also discussed, including those for oxybenziporphyrins, oxypyriporphyrins, carbaporphyrins and sapphyrins.

Mechanism of Fluconazole Resistance inCandida krusei

ABSTRACT The mechanisms of fluconazole resistance in three clinical isolates of Candida krusei were investigated. Analysis of sterols of organisms grown in the absence and presence of fluconazole demonstrated that the predominant sterol of C. krusei is ergosterol and that fluconazole inhibits 14α-demethylase in this organism. The 14α-demethylase activity in cell extracts of C. kruseiwas 16- to 46-fold more resistant to inhibition by fluconazole than was 14α-demethylase activity in cell extracts of two fluconazole-susceptible strains of Candida albicans. Comparing the carbon monoxide difference spectra of microsomes fromC. krusei with those of microsomes from C. albicans indicated that the total cytochrome P-450 content ofC. krusei is similar to that of C. albicans. The Soret absorption maximum in these spectra was located at 448 nm forC. krusei and at 450 nm for C. albicans. Finally, the fluconazole accumulation of two of the C. krusei isolates was similar to if not greater than that ofC. albicans. Thus, there are significant qualitative differences between the 14α-demethylase of C. albicansand C. krusei. In addition, fluconazole resistance in these strains of C. krusei appears to be mediated predominantly by a reduced susceptibility of 14α-demethylase to inhibition by this drug.