Soret Band Region Research Articles

Porphyrins with exocyclic rings. 16. Synthesis and spectroscopic characterization of fluoranthoporphyrins, a new class of highly conjugated porphyrin chromophores.

Porphyrins with fused aromatic rings are under detailed investigation due to their unique spectroscopic properties. To gain more insights into the effects due to ring annealation on the porphyrin chromophore, a series of fluoranthoporphyrins have been synthesized. Reaction of 3-nitrofluoranthene with isocyanoacetate esters in the presence of a phosphazene base afforded good yields of the fluorantho[2,3-c]pyrrole esters 8. Cleavage of the ester moiety with KOH in ethylene glycol afforded the parent heterocycle 9, and this condensed with 2 equiv of acetoxymethylpyrroles 10 in refluxing acetic acid-2-propanol to afford tripyrranes 11. Following cleavage of the tert-butyl ester protective groups with TFA, "3 + 1" condensation with pyrrole dialdehyde 12 gave the fluoranthoporphyrins 13 in good overall yields. In addition, reaction of tripyrrane 11 with acenaphthopyrrole dialdehyde 16 gave the mixed acenaphthofluoranthoporphyrin 17 in excellent yields. A difluoranthoporphyrin 18 was also prepared via a "2 + 2" MacDonald condensation. Reaction of fluoranthopyrrole 8a with dimethoxymethane in the presence of p-toluenesulfonic acid gave the symmetrical dipyrrylmethane 19, and following ester saponification, this was condensed with a dipyrrylmethane dialdehyde to afford the adj-difluoranthoporphyrin 18. The UV--vis spectra for these fluoranthoporphyrins gave a series of three broadened absorptions in the Soret band region, although the Q-bands were little effected by ring fusion. The nickel(II), copper(II), and zinc chelates were more unusual, showing strong absorptions near 600 nm. Difluoranthoporphyrin 18 showed many of the same spectroscopic features, although the presence of two ring fusions gave rise to an increase in the spectroscopic shifts. The mixed system 17 gave spectra that showed larger red shifts due to the acenaphthylene unit combined with the features due to the fluoranthene rings. This work further demonstrates the utility of aromatic ring fusion in altering the properties of porphyrinoid systems.

Identification of H-aggregate in a monolayer amphiphilic porphyrin–TiO 2 nanoparticle heterostructure assembly and its influence on the photoinduced charge transfer

The spectral properties of the monolayer 5,10,15-tri(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl) porphyrin molecule (TriHHP)–TiO 2 nanoparticle heterostructure assembly were investigated with absorption, fluorescence emission and excitation spectra, in comparison with those of CHCl 3 solution and monolayer films deposited from pH 3 and pH 10 water subphases. A new fluorescence emission band, arising from a blue-shifted Q-absorption band, was observed in the assembly or the monolayer film deposited from pH 3 water subphase. An H-aggregate type species from the protonated TriHHP molecules was assigned to cause this new emission band. According to the Frontier orbital theory, this H-aggregate is suggested in the configuration of face-to-face π–π stacking interaction among the protonated TriHHP molecules. In the heterostructure assembly, the efficient fluorescence emission quenching of TriHHP by the photoinduced charge transfer occurs under excitation in Soret band region of the unprotonated TriHHP molecules. No contribution to the photoinduced charge transfer.

Synthesis, Optical Properties, Structures and Molecular Orbital Calculations of Subazaporphyrins, Subphthalocyanines, Subnaphthalocyanines and Related Compounds

The synthesis of and spectroscopic data on subazaporphyrins, subphthalocyanines, subnaphthalocyanines and their related compounds reported to date are summarized, together with the results of molecular orbital (MO) calculations from our laboratory. Thus the problems and key points in the synthesis of these subazamacrocycles and their electronic absorption and magnetic circular dichroism (MCD) spectra are discussed, together with those of the monosubstituted-type low-symmetrical phthalocyanines obtained by their ring expansion reaction. The Q bands of these subazamacrocycles are orbitally doubly degenerate, and in the Soret band region, three transitions to the orbitally degenerate state are found. The MO calculations suggest that the HOMO levels destabilize considerably while the LUMO levels change slightly with increasing size of the π system. In addition, the electronic adsorption data are reproduced by the calculation only when the two pyrrole hydrogens in the monosubstituted-type phthalocyanines are assumed to be linked to the two pyrrole nitrogens along the short axis.

A One-pot, One-step, High-yield Reaction Leading to Metal–Metal Dimacrocycles: the Phthalocyanine Dimer with a Direct Si—Si Linkage

A new concept widely applicable in organometallic chemistry has been introduced for the preparation of cofacial macrocyclic dimers or oligomers. The most notable feature is the use of dimetal or oligometal salts/compounds as templates. In order to exemplify the advantage of this method, a cofacial diphthalocyanine linked by an Si—Si bond has been synthesized in 30% yield in a one-step reaction using hexachlorodisilane as a template and characterized. The cofacial dimer structures are supported by various spectroscopic techniques, including electronic absorption, magnetic circular dichroism, nuclear magnetic resonance and differential pulse voltammetry. However, the unusual phenomenon of a red shift of the main band in the Soret band region was observed.

Density functional theory calculations of the visible spectrum of chlorophyll a

The molecular structure of chlorophyll a including the phytyl chain has been fully optimized at density-functional level. The excitation energies and oscillator strengths obtained at density-functional time-dependent perturbation theory level are in good agreement with experiment. The present calculations show that Gouterman's generally accepted four-orbital model does not correctly describe the excitation spectrum of chlorophyll a. Thirteen excited states are found in the visible region: four are found in the long-wavelength region, two weak transitions are obtained at about 490 nm, while seven transitions are in the Soret band region.

Resonance Raman spectroscopic study of the caa3 oxidase from Thermus thermophilus.

The terminal caa3 oxidase of Thermus thermophilus has been studied by resonance Raman spectroscopy. Using different excitation wavelengths in the Soret band region, it was possible to disentangle the resonance Raman spectra of the fully oxidized and fully reduced state in terms of the component spectra of the individual hemes a, a3, and c. For the heme a and a3 groups, the spectra reveal only minor differences compared to those of beef heart cytochrome c oxidase attributable to subtle modifications of the heme environment. These differences are not more pronounced than those between the oxidases from beef heart and Paracoccus denitrificans confirming the view that this oxidase of Th. thermophilus is a typical member of the aa3 oxidase superfamily. The heme c component spectra display far-reaching similarities with those of c-type cytochromes which serve as mobile electron carriers in the respiratory chain. These results imply that caa3 oxidase represents an integrated version of the noncovalent redox complex between cytochrome c and cytochrome c oxidase in higher organisms. On the other hand, the structural changes of cytochrome c in the noncovalent complex have no counterpart in the heme c component of the caa3 oxidase indicating a specific cytochrome c binding site for the mitochondrial enzyme.

B-DNA Binding with Cobalt(III) and Vanadyl(2+) Derivatives of Tetracationic 5,10,15,20-Tetrakis(4-N-methylpyridyl)porphine: Combined CD, Optical, and Electronic MCD Spectra.

Electronic MCD is used for the first time to obtain electronic and geometric structural insight into the free and DNA-bound states of the six-coordinate CoIII and VO2+ derivatives of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine. Correlations between MCD, CD, and optical spectra measured in the porphyrin Soret band (or B0) region, and FLDr literature data, are consistent with each metalloporphyrin having a face-on orientation in the major groove of CT DNA, sites 5‘AT3‘ and 5‘CG3‘ being preferred, and with porphyrin electric dipole transition moments (edtms) μexD (most perturbed direction in the bound porphyrin) and μexD (least perturbed) having orientation angles of α/β/β‘ = ∼45°/180°/90° and ∼45°/180°/270°, respectively.

Porphyrins with Exocyclic Rings. 13.1 Synthesis and Spectroscopic Characterization of Highly Modified Porphyrin Chromophores with Fused Acenaphthylene and Benzothiadiazole Rings

As part of a survey on the influence of fused aromatic rings on the porphyrin chromophore, a series of novel structures with fused acenaphthylene or benzothiadiazole rings have been synthesized. Base-catalyzed condensation of 1-nitroacenaphthylene or 4-nitrobenzothiadiazole with esters of isocyanoacetic acid afforded good yields of the annelated pyrroles 5 and 28. Cleavage of the ester moieties with KOH in refluxing ethylene glycol gave the unsubstituted heterocycles, and subsequent condensation with 2 equiv of acetoxymethylpyrroles 9 in acetic acid/ethanol produced the modified tripyrranes 12 and 31. Tripyrranes with terminal tert-butyl ester units were treated with TFA and condensed with 3,4-diethyl-2,5-pyrroledicarboxaldehyde 13 in dichloromethane to give, following oxidation with DDQ, the corresponding π-extended porphyrins 14 and 32. Acenaphthoporphyrins 14 showed unique UV−vis spectra with a triply split Soret band region and a relatively strong band near 660 nm. Strongly red-shifted absorptions wer...

Porphyrin–TiO 2 nanoparticle heterostructure assembly by Langmuir–Blodgett method

Surface pressure–area ( π–A) isotherm characteristics of 5,10,15-(4-hydroxyphenyl)-20-(4-hexadecyloxyphenyl) porphyrin monolayers on both the water and TiO 2 hydrosol subphases, the UV–vis absorption and fluorescence spectra of the monolayers deposited onto CaF 2 substrates are investigated. π–A isotherms find that the porphyrin ring extends to lie more flat on a TiO 2 hydrosol surface than on a water surface. The UV–vis absorption spectra of the deposited monolayers prove that the porphyrin TiO 2 nanoparticle heterostructure assembly is formed, in which the J-aggregated effect of porphyrin is weakened, comparing with that in the monolayer deposited from water subphase. The fluorescence spectra show that the fluorescent emission quenching by the photoinduced electron transfer from the excited porphyrin molecule to TiO 2 nanoparticle, occurs under excitation in the Soret band region of porphyrin.

Resonance Raman spectroscopic study of the caa3 oxidase from Thermus thermophilus

The terminal caa3 oxidase of Thermus thermophilus has been studied by resonance Raman spectroscopy. Using different excitation wavelengths in the Soret band region, it was possible to disentangle the resonance Raman spectra of the fully oxidized and fully reduced state in terms of the component spectra of the individual hemes a, a3, and c. For the heme a and a3 groups, the spectra reveal only minor differences compared to those of beef heart cytochrome c oxidase attributable to subtle modifications of the heme environment. These differences are not more pronounced than those between the oxidases from beef heart and Paracoccus denitrificans confirming the view that this oxidase of Th. thermophilus is a typical member of the aa3 oxidase superfamily. The heme c component spectra display far-reaching similarities with those of c-type cytochromes which serve as mobile electron carriers in the respiratory chain. These results imply that caa3 oxidase represents an integrated version of the noncovalent redox complex between cytochrome c and cytochrome c oxidase in higher organisms. On the other hand, the structural changes of cytochrome c in the noncovalent complex have no counterpart in the heme c component of the caa3 oxidase indicating a specific cytochrome c binding site for the mitochondrial enzyme. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 365–377, 1998

Resonance Raman spectroscopic study of thecaa3 oxidase fromThermus thermophilus

The terminal caa3 oxidase of Thermus thermophilus has been studied by resonance Raman spectroscopy. Using different excitation wavelengths in the Soret band region, it was possible to disentangle the resonance Raman spectra of the fully oxidized and fully reduced state in terms of the component spectra of the individual hemes a, a3, and c. For the heme a and a3 groups, the spectra reveal only minor differences compared to those of beef heart cytochrome c oxidase attributable to subtle modifications of the heme environment. These differences are not more pronounced than those between the oxidases from beef heart and Paracoccus denitrificans confirming the view that this oxidase of Th. thermophilus is a typical member of the aa3 oxidase superfamily. The heme c component spectra display far-reaching similarities with those of c-type cytochromes which serve as mobile electron carriers in the respiratory chain. These results imply that caa3 oxidase represents an integrated version of the noncovalent redox complex between cytochrome c and cytochrome c oxidase in higher organisms. On the other hand, the structural changes of cytochrome c in the noncovalent complex have no counterpart in the heme c component of the caa3 oxidase indicating a specific cytochrome c binding site for the mitochondrial enzyme. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 365–377, 1998

Changes in Absorbance at 413 nm in Plasma from Three Rodent Species Exposed to Phosgene

Mice, rats and guinea pigs were exposed to phosgene (COCl2), a highly irritating and oxidizing gas. Animals were exposed to 87 mg/m3phosgene for 20 min in a whole-body exposure chamber. Within 55-65 minutes after the start of exposure, plasma was scanned spectrophotometrically from 200-600 nm. A distinct and significant increase in area under the curve in the Soret band region at 413 nm was observed in plasma from phosgene-exposed animals when compared with air-exposed controls in all three species. These peaks were consistent with hemoglobin, an indication that the integrity of the erythrocyte membrane had been compromised by exposure. An erythrocyte osmotic fragility assay on blood from mice exposed to phosgene indicated that 30% less NaCl was needed to cause 50% hemolysis compared to air-exposed mice. These results suggest a new mechanism of phosgene-induced acute lung injury that may be linked, in part, to a direct attack on the erythrocyte membrane.

Resonance Raman spectroscopy of the integral quinol oxidase complex of Sulfolobus acidocaldarius.

The integral quinol oxidase complex of Sulfolobus acidocaldarius (DSM 639) was investigated by resonance Raman spectroscopy. The complex includes four heme a groups which constitute two functional entities, a587 and aa3, containing two low-spin hemes and a low-spin as well as a high-spin heme, respectively. RR spectra were obtained from the fully oxidized and fully reduced states of the complex using different excitation wavelengths in the Soret band region in order to disentangle the contributions from the four heme groups. For the oxidized state, this approach allowed for the identification of two spectrally different types of heme a which were assigned to the bishistidine ligated hemes a of aa3 and a587 (type II) and to the additional heme a of a587 which is ligated by a histidine and methionine (type I). The spectra of both heme a types differ substantially from that of beef heart cytochrome c oxidase. In particular, the formyl stretching modes of types II and I are upshifted by 8 and 15 cm-1, respectively, implying a largely hydrophobic environment of the formyl groups in the quinol oxidase of Sulfolobus. Furthermore, the RR spectra of the oxidized state reveal the characteristic marker bands of a five-coordinated and a six-coordinated high-spin state, indicating that heme a3 exists in a coordination equilibrium, which is in sharp contrast to the purely six-coordinated high-spin configuration of heme a3 in any (quinol or cytochrome) oxidases studied so far. Also the formyl stretching mode of heme a3 appears to be unusual as its frequency is substantially lower than in beef heart oxidase. In the fully reduced state, no heterogeneity of heme a3 is observed and also the spectra of the various hemes a are nearly indistinguishable. Moreover, the formyl stretching vibrations of all hemes a and a3 apparently coincide to one prominent peak at 1658 cm-1 characteristic for a non-hydrogen-bonded carbonyl group. This finding is unique compared to other aa3 oxidases in which the formyl stretchings give rise to widely separated bands at approximately 1610 and approximately 1665 cm-1 for heme a and a3, respectively. In both the oxidized and the reduced states, the spectra of the aa3 entity in the integral complex differ significantly from those of the isolated aa3 entity studied previously [Heibel, G., Anzenbacher, P., Hildebrandt, P., & Schäfer, G. (1993a) Biochemistry 32, 10878-10884], indicating substantial interactions between the various subunits of the integral complex.

Reduction of a water-soluble iron(III) porphyrin and an iron(II) nitrosyl porphyrin by benzophenone ketyl radical

Reactions of benzophenone ketyl radicals with the water-soluble iron(III)porphyrin, [FeIII(tpps)]3–[tpps =meso-tetrakis(p-sulfonatophenyl)porphyrinate], and a nitric oxide adduct of the iron(II) form of the porphyrin, [FeII(tpps)(NO)]4–, have been studied by laser photolysis in aqueous solutions. Reactions of ferricytochrome c and metmyoglobin with the ketyl radicals were also studied for comparison with the iron(III) porphyrin. Benzophenone ketyl radicals were produced from the reaction of the triplet state of benzophenone with the glucose used as a suitable hydrogen atom donor. The transient absorption spectrum observed after 266 nm laser pulse excitation for the [FeIII(tpps)]3– solution containing benzophenone and glucose shows that the iron(III) porphyrin is reduced by the ketyl radical to the iron(II) form. Ferricytochrome c and metmyoglobin were found also to be reduced to the iron(II) form by the ketyl radical. The rate constants for the reductions of [FeIII(tpps)]3–, ferricytochrome c and metmyoglobin were determined to be 3.0 × 109, 4.5 × 108 and 2.2 × 108 dm3 mol–1 s–1 respectively. Nitric oxide irreversibly reacts with [FeII(tpps)]4– to yield [FeII(tpps)(NO)]4– in an aqueous solution. The transient absorption spectrum observed 500 µs after laser pulsing for the [FeII(tpps)(NO)]4– solution containing benzophenone and glucose indicates that the ketyl radical reacts with [FeII(tpps)(NO)]4– to form a new transient species which displays the spectrum with a peak at 418 nm in the Soret band region. The transient species has been identified as a one-electron adduct of [FeII(tpps)(NO)]4– where the added electron possibly exists on the coordinated NO moiety.

Resonance Raman spectroscopy of a chlorophyll-porphyrin heterodimer: excitation profile in the 400-450-nm region

Photophysical studies carried out previously on a chlorophyll-porphyrin heterodimer consisting of a zinc methyl pyrochlorophyllide a that is directly bonded at its 3-position to the 5-position of a zinc 2,8,12,18-tetraethyl-3,7,13,17-tetramethyl-15-(p-tolyl)porphyrin have shown that the chlorophyll and porphyrin interact within the excited singlet manifold. Steric hindrance between adjacent substituents rigidly positions the π systems of both macrocycles perpendicular to one another. A similar orientation occurs between the primary donor and accessory bacteriochlorophyll in the photosynthetic reaction center. To better understand the relationship between the structure and the electronic states of the chlorophyll-porphyrin heterodimer, we have carried out a series of resonance Raman measurements in the Soret band region of the chlorophyll-porphyrin heterodimer

Catalytic antibodies. Circular dichroism and UV-vis studies of antibody-metalloporphyrin interactions

Circular dichroism and UV-vis measurements were used to study the interaction between several water-soluble metalloporphyrins and monoclonal antibodies (MABs) that were elicited against a structurally related dihydroxytin(IV) porphyrin, la. Some of the MAB-metalloporphyrin complexes studied were previously shown to mimic hemoprotein-like activity, such as catalytic epoxidation of styrene by iodosobenzene. MAB-metalloporphyrin complex formation is usually accompanied by significant bathochromic shift and hypo-/hyperchromicity changes of the absorption maxima in the porphyrin Soret band region. Induced CD spectra in the same region (350-450 nm) are detected upon complex formation. They follow Beer’s law, exhibit isosbestic behavior, and show no significant change in the general shape of the Cotton effect as a function of the antibody:porphyrin ratio. Signal intensity (ellipticity) increases with increasing antibody:metalloporphyrin ratio, reaching an upper limit that represents saturation complexation, all indicating a specific 1:l binding phenomenon. Strong dependence of both signal shape and signal intensity upon the specific metal and antibody were observed, suggesting that induced CD may serve as a powerful tool for the unequivocal differentiation of two seemingly identical MAB clones. In cases of intense induced CD signals, it is possible to obtain MAB-metalloporphyrin dissociation constants using a titration curve where ellipticity is measured as a function of the antibody:porphyrin ratio and presented as a Scatchard plot. Both the UV-vis absorbance and induced CD spectrum of the metalloporphyrin-MAB complex remain unchanged over a broad pH range between 6 and 11, indicating remarkable stability of these complexes and reflecting the dominant role of electrostatic interactions between the hapten carboxylate groups and the antibody combining site.

Single site spectra of free base isobacteriochlorin in an n-octane matrix at 10 K

Single site spectroscopy is reported for the cis and trans tautomers of unsubstituted free base isobacterioclorin in an n-octane matrix at 10 K. Both the Q and Soret band regions were investigated. The vibrational frequencies of the ground state and several ππ * excited states of both isomers were determined from the fluorescence and the excitation spectra, respectively. An abrupt change of bandwidth in the cis tautomer's excitation spectrum suggests the presence of a relatively low-energy nπ * transition

Effect of KCl on the interactions between NADPH:cytochrome P-450 reductase and either cytochrome c, cytochrome b5 or cytochrome P-450 in octyl glucoside micelles.

Significant dissociation of FMN from NADPH:cytochrome P-450 reductase resulted in loss of the activity for reduction of cytochrome b5 as well as cytochrome c and cytochrome P-450. However, the ability to reduce these electron acceptors was greatly restored upon incubation of FMN-depleted enzyme with added FMN. The reductions of cytochrome c and detergent-solubilized cytochrome b5 by NADPH:cytochrome P-450 reductase were greatly increased in the presence of high concentrations of KCl, although the stimulatory effect of the salt on cytochrome P-450 reduction was less significant. No apparent effect of superoxide dismutase could be seen on the rate or extent of cytochrome reduction in solutions containing high-salt concentrations. Complex formation of the flavoprotein with cytochrome c, which is known to be involved in the mechanism of non-physiological electron transfer, caused a perturbation in the absorption spectrum in the Soret-band region of cytochrome c, and its magnitude was enhanced by addition of KCl. Similarly, an appreciable increase in ellipticity in the Soret band of cytochrome c was observed upon binding with the flavoprotein. However, only small changes were found in absorption and circular dichroism spectra for the complex of NADPH:cytochrome P-450 reductase with either cytochrome b5 or cytochrome P-450. It is suggested that the high-salt concentration allows closer contact between the heme and flavin prosthetic groups through hydrophobic-hydrophobic interactions rather than electrostatic-charge pairing between the flavoprotein and the cytochrome which causes a faster rate of electron transfer. Neither alterations in the chemical shift nor in the line width of the bound FMN and FAD phosphate resonances were observed upon complex formation of NADPH:cytochrome P-450 reductase with the cytochrome.

Structure and mercaptan oxidation activity of cobalt(II) phthalocyanines covalently bonded to silica of low surface area

Cobalt(II) 2,9,16,23-tetracarboxyphthalocyanine and cobalt(II) 2,9,16,23-tetraamino-phthalocyanine were covalently bonded to two different species of modified silica with low surface area. The immobilized phthalocyanines exhibit high catalytic activity in the oxidation of 2-mercaptoethanol, being comparable to that of the dissolved low molecular weight tetracarboxy- or tetrasulfo-phthalocyanine cobalt complexes. The diffuse reflectance spectra of the complexes bonded to nonporous silica exhibit a vibrational fine structure which clearly appears in the Soret band region, indicating a coupling between the electronic 1A 1g → 1E u transition and a vibrational transition of the aromatic ring system around 1600 cm −1.

The 'Q-band' absorption spectra of hematoporphyrin monomer and aggregate in aqueous solution.

Abstract The resolution of the absorption spectra in the Q band (480 nm‐620 nm) spectral region of monomeric and dimeric hematoporphyrin species present in aqueous solutions has been achieved using absorption, fluorescence and computer analysis methods. The absorption maxima of the dimer in this spectral region are red shifted about 12 nm with respect to those of the monomer. The significance of this finding in relationship to the well documented blue shift of hematoporphyrin aggregate observed in the Soret band region (λmalx∼400 nm) of the absorption spectrum is discussed.