Bands Of Porphyrins Research Articles

Energy versus electron transfer in pyridylporphyrin osmium(II) dyads

The complex cis-[Os(bpy) 2CO(pyPorH 2)][PF 6] 2 (bpy=2,2′-bipyridine, pyPorH 2=5-pyridyl-10,15,20-triphenylporphyrin), Os–pyPorH 2, was easily synthesized in high yield by a metathesis reaction. Subsequent zinc insertion into Os–pyPorH 2 gave cis-[Os(bpy) 2CO(pyPorZn)][PF 6] 2 (pyPorZn=zinc 5-pyridyl-10,15,20-triphenylporphyrin), Os–pyPorZn. The known compound, cis-[Os(bpy) 2CO(py)][PF 6] 2 (py=pyridine), Os–py, was completely characterized as a model compound for the dyads. These complexes represent the first examples of an osmium attached through coordination directly to the porphyrin periphery. The electronic absorption spectra for the osmium porphyrin dyads show red shifting and broadening of the all the porphyrin bands relative to the model porphyrins, pyPorH 2 and zinc tetraphenylporphyrin. Electrochemical studies show that the porphyrin and bipyridine potentials are essentially unchanged relative to the parent compounds indicating little change in ground state energetics. Upon excitation of the osmium unit, Os–pyPorH 2 exhibits energy transfer from the osmium subunit to the pyridyl porphyrin. Insertion of zinc into the free base dyad in Os–pyPorZn changes the excited state dynamics and energetics such that electron transfer is now favorable upon exclusive excitation of the osmium part of the dyad.

Nonlinear absorption of light: two-photon absorption and optical saturation in metalloporphyrin-doped boric acid glass

Abstract The nonlinear absorption of five metal TMPPs (TMPP: tetrakis-(3,4,5-trimethoxyphenyl)porphyrin) doped in boric acid glass are measured with the linear polarized nanosecond laser pulses at different wavelengths by Z-scan; the two-photon absorption (TPA) is dominant in the near infrared, while the characteristic of saturation absorption (SA) is observed close to the Q(0,0) band of porphyrin. The symmetry allowed two-photon π*←π transitions are suggested to be 1 B 1 g * ← S 0 and 1 B 2 g * ← S 0 , with the cross-sections δ ranging from 25×10−50 to 114×10 −50 cm 4 s / photon . We analyze the property of SA with a four-level system, and find that the magnitudes of excited-state absorptivity and saturation intensity are not affected by changing the central metal ion in these experiments.

Synthesis and photochemistry of free base and zinc tetraaryl porphyrins mono-substituted with tungsten pentacarbonyl via a pyridine linker

A series of free base and zinc porphyrins, mono meso-substituted with a pyridyl group via an amide link, have been prepared by stepwise functionalisation of free base tetraphenylporphyrin, H2tpp. Four [W(CO)5L] (L = pyridyl-porphyrin) complexes have been synthesised; [M{tpp-NHCO-py-W(CO)5}], where M = 2H or Zn, one phenyl group is substituted at the 4-position and the pyridine is substituted at the 3- or 4-position. The spectroscopic data of the [W(CO)5L] complexes have been compared with those of the porphyrin ligands alone and with those of the model compounds, [W(CO)5(3-H2NCO-py)] and [W(CO)5(4-H2NCO-py)]. The UV-Vis spectra of the model compounds show that the MLCT and LF absorption bands overlap and no emission is observed at room temperature in solution. The UV-Vis absorption and emission spectra of the porphyrins with peripheral W(CO)5 are dominated by porphyrin bands. Time-resolved emission was observed from the porphyrin moiety in the [W(CO)5L] complexes and fitted to mono-exponential kinetics to give lifetimes of ≤10 ns for the zinc porphyrins and of ca. 22 ns for the free base porphyrins. Transients characteristic of the porphyrin 3(π–π*) excited state have been observed by time-resolved absorption and their decay kinetics have been fitted to an appropriate rate law. Long wavelength photolysis of [W(CO)5(3-H2NCO-py)] and [W(CO)5(4-H2NCO-py)] in THF resulted in conversion to [W(CO)5(THF)]. The [W(CO)5L] complexes behaved similarly with photolysis at λ > 395 nm but were photostable with λ > 495 nm.

Observation of an isotope-sensitive low-frequency Raman band specific to metmyoglobin.

A resonance Raman band involving significantly the iron(III)-histidine stretching (upsilonFe-His) character is identified for metmyoglobin (metMb) through isotope sensitivity of its low-frequency resonance Raman bands, but the identification was not successful for methemoglobin (metHb) and its isolated alpha and beta subunits. A band at 218 cm-1 of natural abundance metMb exhibited a low-frequency shift for 15N-His-labeled metMb (-1.4 cm-1 shift), while the strong porphyrin bands at 248 and 271 cm-1 did not shift significantly. The frequency of the 218-cm-1 band of metMb decreased by 1.6 cm-1 in D2O, probably due to Ndelta-deuteration of the proximal His, in a similar manner to that of the upsilonFe-His band of deoxyMb in D2O. This 218-cm-1 band shifted slightly to a lower frequency in H2(18)O, whereas it did little upon 54Fe isotopic substitution (<0.3 cm-1), presumably because of the six-coordinate structure. The lack of the 54Fe-isotope shift shows that the 218-cm-1 band is specific to metMb and not due to the deoxy species. The intensity of this band decreased for hydroxymetMb and was indiscernible for cyanometMb. For metHb and its alpha and beta subunits, however, the frequencies of the band around 220 cm-1 were not D2O sensitive. These results suggest an assignment of the band around 220 cm-1 to a pyrrole tilting mode, which significantly contains the Fe-His stretching character for metMb but scarcely for metHb and its subunits. The differences in the isotope sensitivity of this band in different proteins are considered to reflect the heme distortion from the planarity and the Fe-His geometry specific to individual proteins.

Photoluminescence and Transient Spectroscopy of Free Base Porphyrin Aggregates

Solutions of free base meso-tetraphenylporphyrin (H2TPP), meso-tetra(4-carboxyphenyl)porphyrin (H2TPPC), and meso-tetra(4-pyridyl)porphyrin (H2TPyP) under various conditions generate aggregates whose absorption spectra are characterized by invariant Soret bands with bandwidths that are independent of the preparative method. One of the Soret bands is blue-shifted (H-aggregate) relative to the monomeric porphyrin band; other Soret bands are red-shifted (J-aggregates). The aggregates are characterized by different nonradiative rate constants for excited singlet-state decay and by different efficiencies of singlet−singlet annihilation at the high energies of laser excitation. The quantum yields of fluorescence vary between 10-5 and 10-2, and the corresponding fluorescence lifetimes vary in the range from 10-12 to 10-9 s; they are more than 1 order of magnitude smaller than those of the corresponding monomeric porphyrins. Lifetimes (τ) correlate with the characteristic ground-state absorption recovery times of the aggregates. The sizes of the H-aggregate and aggregates that are characterized by a minimal blue shift of the Soret band range from 15 to 27 Å.

Time-resolved resonance Raman study of intermediates generated after photodissociation of wild-type and mutant co-myoglobins

Time-resolved resonance Raman (TR 3) spectroscopy was applied to elucidate transient structures of myoglobin (Mb) involved in its ligand binding. Pump/probe Raman measurements of the Fe–CO stretching bands ( ν Fe–CO) were carried out for various delay times (Δ t=−20 ns–1 ms with a time resolution of 7 ns) after laser photolysis of native and mutant COMb complexes. His64(E7) and Leu29(B10) were replaced with an aliphatic and aromatic residues. The static ν Fe–CO frequencies of the mutants depended strongly on the environments around the bound CO and correlated more with the hydropathy indices of the replaced residues than with their sizes. The kinetics of bimolecular CO recombination correlate with the static ν Fe–CO frequencies; a lower frequency generally results in faster rebinding. Despite these differences, all the proteins exhibited the shift of a porphyrin band from 370 to 379 cm −1 upon binding of CO and also a transient Raman band at ∼497 cm −1, which occurred before recovery of the original ν Fe–CO band. The latter frequency was unaffected by isotopically labeling the ligand with 13C 18O. The 497 cm −1 band was absent in the spectrum at Δ t=0 ns for all of the myoglobins examined except for the His64→Leu (H64L) mutant which shows the band immediately after photolysis. The 370 and 497 cm −1 bands are associated with the C β–C c–C d in-plane bending of the propionic side chains and the out-of-plane γ 12 containing pyrrole swiveling and propionic bending motions, respectively. The 497 cm −1 transient band appears to reflect a deoxyheme intermediate in which the hydrogen bonding lattice between Arg45(CD3), His64(E7), the heme-6-propionate, and an external distal pocket water molecule is temporarily disrupted. This disruption allows larger movements of the propionate side chain, explaining intensity enhancement of the 497 cm −1 band. Recovery of the hydrogen bonding lattice dampens the movements of the propionate C β–C c–C d bond system and finally fixes it in the heme plane in the CO-bound form, causing the frequency shift of the bending mode from 370 cm −1 back to 379 cm −1. In the Leu64 mutant, the external water molecule is already absent, facilitating rapid movement of the heme-6-propionate after photolysis. Larger-scale movements of all three side chains could create an open conformation with a channel from the heme iron to the solvent, allowing ligand escape and/or rebinding.

A chemometric analysis of the resonance Raman spectra of mutant carbonmonoxy-myoglobins reveals the effects of polarity

Resonance Raman spectra of 10 carbonmonoxy-myoglobins have been obtained, including sperm whale native, pig wild-type, and the mutants H64L, H64A, V68T, V68N, H64V/V68T, F43W, F46V, and L29F. This series was chosen in order to study the effect of ligand binding pocket polarity on the positions of the ν(Fe–CO) and δ(Fe–C–O) bands. Spectra of both 12CO and 13CO isotopic forms have been obtained and a detailed analysis has facilitated the identification of both the ligand-specific bands and six underlying porphyrin bands which are insensitive to this isotopic substitution. Along with a band-fitting analysis of infrared spectra, these resonance Raman data provide a comprehensive evaluation of the vibrations of the FeCO unit. The band positions of the ligand-specific modes are found to depend on the structure of the ligand binding pocket, arising from the strength of back-bonding within the FeCO unit, and clear correlations exist between the ν(Fe–CO), δ(Fe–C–O), and ν(C–O) band positions which characterize this synergic bonding. The results are consistent with the proposal that the vibrational band positions are determined primarily by the electrostatic potential at the ligand. Five discrete band sets are observed for this set of mutants, suggesting that 5 discrete conformations occur.

The origin of infrared marker bands of porphyrin .pi.-cation radicals: infrared assignments for cations of copper(II) complexes of octaethylporphine and tetraphenylporphine

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe origin of infrared marker bands of porphyrin .pi.-cation radicals: infrared assignments for cations of copper(II) complexes of octaethylporphine and tetraphenylporphineSongzhou Hu and Thomas G. SpiroCite this: J. Am. Chem. Soc. 1993, 115, 25, 12029–12034Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://doi.org/10.1021/ja00078a047RIGHTS & PERMISSIONSArticle Views416Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Influence of temperature on the electronic spectra of tetrabenzoporphin in n-octane

In the presence of substantial structural changes in the porphyrin ring, such as hydrogenation, azaand benzosubstitution, and others, extremely characteristic changes occur in the electronic absorption and fluorescence spectra. In particular, the incorporation of four benzene rings into the coupled porphine system by their addition to the pyrrole rings of the macrocycle [formation of a tetrabenzoporphine (TBP) molecule] leads to the appearance of a band possessing three maxima in the region of 580-620 nm of the absorption spectrum (see Fig. i). Such an unusual structure for the absorption bands of porphyrins is characteristic only of the absorption spectra of TBP and its close analogs. To reveal the nature of the complex contour of this band, methods of polarization [I] and quasi-line spectra were enlisted [2]. An analysis of the data of quasi-line spectra showed that the contour is formed by two types of transitions: high-frequency electronic-vibrational into the $I state and purely electronic S 2 § So (low-frequency electronic-vibrational repetitions of it are also possible). In this case the nature of the disruption of mirror symmetry of the frequencies and activity of individual normal vibrations of the S I and S o states of TBP made it possible to conclude that the band of the purely electronic S 2 § S o transition corresponds to the central maximum of the complex contour. However, the application of the method of burning spectral holes to TBP (monotosyl-substituted TBP was investigated), using the property of selectivity of the hole burning with respect to different electronic transitions, led in [3] to a somewhat different conclusion on the position of the S 2 level of the TBP molecule. It was shown that not the central maximum of the complex contour in the region of 580-620 nm but the region of the long-wave decay of this maximum corresponds to the purely electronic transition into the S 2 state. Under these conditions, in [3] on the basis of the substantial transformation of the contour of the band in the region of 580-620 nm in the absorption spectrum of TBP in a mixture of THF with ether during the transition from helium to room temperature (a sharp increase in the intensity of one of the three maxima, namely, the short-wave maximum), as well as the change in its position relative to the contour of the band of the S I § So transition, it was suggested that the band of the S 2 § So transition, in contrast to the long-wave shift of the S I + S o band, undergoes a substantial shortwave shift with increasing temperature. We should mention that such a transformation of the contour of the absorption band of TBP at different temperatures is not observed for all solvents; for example, in chloroform [3], pyridine [i, 4, 5], benzene [4], and others, the shape of the band at 300 K is very close to the shape of the band of TBP in a mixture of THF with ether at 77 K [3].

Oxidation of chromium(III) porphyrins to their π-radical cations or to oxochromium(IV) porphyrins

One-electron oxidation of several chromium(III) porphyrins has been studied by steady-state and pulse radiolysis techniques under different conditions. Two types of products are observed: those exhibiting intense broad absorptions at λ 600 nm, ascribed to the π-radical cations, and others exhibiting minor shifts of the porphyrin bands, ascribed to chromium(IV) porphyrins. CrIIIOEP (octaethylporphyrin), CrIIITPP (tetraphenylporphyrin), and CrIIITMP (tetramesitylporphyrin) in CH2Cl2 undergo one-electron oxidation on the ligand to give π-radical cations, which are stable after ligation, and further oxidation gives the dications. In the presence of KOH, however, they form CrIV-porphyrins and further radiolysis gives Crv-porphyrins. CrIIITSPP [tetrakis (4-sulfonatophenyl)porphyrin], CrIIIT3PyP [tetrakis(3-pyridyl)porphyrin], and CrIIIMSP (mesoporphyrin-IX), oxidized in 1 mol dm–3 aqueous HCl, form unstable π-radical cations which decay by disproportionation. The pulse radiolysis results indicate that the initial step in the oxidation of all CrIIIP and OCrIVP species occurs at the porphyrin π-system and that, under certain conditions, the initial π-radical cation may undergo intramolecular electron transfer from the metal centre to the ligand to form the higher oxidation state Cr-porphyrin.

Vibrational spectra of dioxygen adducts and oxo complexes of ruthenium tetraphenylporphine (RuTPP)

Infrared (IR) and resonance Raman (RR) spectra of dioxygen adducts and oxo complexes of ruthenium tetraphenylporphine (RuTPP) are reported. When a thin film of RuTPP reacts with O 2 two dioxygen adducts are observed in the IR spectra. One is formed at ∼ 25 K and exhibits ν(OO) at 1124 cm −1 which shifts to 1114 cm −1 at 45 K. The second one is observed at slightly higher temperature (45 K) and its ν(OO) is located at ∼1167 cm −1. Both ν(OO) are down-shifted when a thin film is warmed up. The former dioxygen adduct is stable up to 270 K while the latter disappears at ∼ 100 K. On the other hand, the ν(OO) of these two dioxygen adducts are not observed in the RR spectra obtained in low temperature solution. Instead, the oxidation of RuTPP in toluene at ∼ 185 K yields the RuO 2Ru peroxo bridged dimer which exhibits the ν s(RuO 2) at 552 cm −1. When the temperature of the solution is gradually raised, the peroxo bridged dimer is transformed to TPPRu(IV)O which, in turn, is converted into TPPRu(VI)(O) 2. The ν(RuO) of the monooxo complex is expected to be at ∼820 cm −1 based on the ∼40 cm −1 up-shift upon 18O/ 16O isotopic substitution [ν(Ru 18O) is located at 780 cm −1] but is oscured by the strong porphyrin band at 826 cm −1. The ν s(ORuO) of the dioxo complex is observed at 811 cm −1 and is shifted to 767 cm −1 by 16O/ 18O isotopic substitution.

Thin-layer chromatography of free porphyrins for diagnosis of porphyria.

In this simple thin-layer chromatographic (TLC) technique for evaluating porphyrin excretion, porphyrins are extracted from urine or feces, then separated on silica-gel TLC plates. The distinct porphyrin bands are observed by viewing the plates under long-wave fluorescent light. Positive screening tests can readily be confirmed or rejected, and a more comprehensive investigation confidently undertaken.

Temperature dependent spectral changes of iron and nickel hemoglobins and their derivatives

Temperature dependent absolute and difference spectra for deoxy and oxy human hemoglobin, α and β subunits, NiHbA, carboxypeptidase A treated deoxy HbA and NiHbA have been investigated. It is shown for the first time that the α subunits are mainly responsible for the temperature dependent spectral changes in the absorption spectra of Hb in the range from 0°C to 40°C. It has also been found that in the R state the spectral alterations caused by temperature variation are about 85% of those found for the T state of Hb. The value of following the temperature dependence of the porphyrin bands of hemoproteins, as a sensitive probe for subtle changes in the region of the heme, is demonstrated.

Resonance raman studies of hemoglobins M: evidence for iron-tyrosine charge-transfer interactions in the abnormal subunits of Hb M Boston and Hb M Iwate.

Resonance Raman spectra have been obtained for Hb M Boston [His-E7(58) alpha leads to Tyr], Hb M Iwate [His-F8-(87) alpha leads to Tyr], and Hb M Milwaukee [Val-E11(67) beta leads to Glu]. The abnormal alpha subunits of Hb M Boston and Hb M Iwate exhibited the porphyrin nu10 band at 1628 and 1627 cm-1, respectively, which indicates that the ferric alpha hemes are five-coordinated in both Hb M Boston and Hb M Iwate. In addition to the porphyrin bands, four extra polarized lines were observed at 1607, 1506, 1278, and 603 cm-1 for the alpha abnormal subunit of Hb M Boston and at 1605, 1506, 1310, and 589 cm-1 for that of Hb M Iwate. By comparison with the vibrational spectra of Fe-tyrosine proteins and Fe-phenolate complexes, the 1605-1607- and 1506-cm-1 lines are assigned to the phenolate ring vibrations of the heme-coordinated tyrosine, and the 1278-cm-1 line of Hb M Boston and the 1310-cm-1 line of Hb M Iwate are assigned to the phenolate CO stretching mode. We propose that the 603-cm-1 line of Hb M Boston and the 589-cm-1 line of Hb M Iwate arise from the Fe-O(tyrosine) stretching mode. These four Raman lines are intensity enhanced upon the excitation around 475-520 nm, probably due to the presence of a charge-transfer interaction between Fe and Tyr. The dissimilarity of the Fe-O and phenolate CO stretching frequencies between Hb M Boston and Hb M Iwate, despite the similarity of frequencies of their porphyrin and phenolate ring modes, suggests that the heme-phenolate bonding angles differ between Hb M Boston and Hb M Iwate although both adopt the five-coordinate form with Tyr as the only axial ligand. The resonance Raman spectra of oxy- and deoxy-Hb M Milwaukee showed no anomaly and can be accounted for by those of the equimolar mixtures of aquomet- and oxy- or deoxy-Hb A.

Single-crystal spectra of ferrimyoglobin complexes in polarized light.

The polarized absorption spectra of ferrimyoglobin cyanide, ammonia, azide, fluoride, formate, and water (acid ferrimyoglobin) complexes in single crystals are described. Special emphasis is placed on the polarization-ratio (PR) spectrum—the spectrum of the intensity ratio for light absorbed along and perpendicular to the crystal symmetry axis. It is shown that the PR spectrum magnifies spectral effects that are otherwise obscured by wide absorption bands, and it is shown to be a most useful parameter for studying the spectra of those systems that are intrinsically broad and whose spectra do not show any sharpening at low temperature. The results confirm many general features of porphyrin spectra such as the polarization of the B and Q states, the vibronic nature of the Qv state, and the intensity imbalance in the Q0 state. The substances studied span a variety of spectral types, from low-spin, through mixed-spin, to high-spin iron complexes. The high-spin spectra show, in addition to porphyrin bands, charge-transfer bands that are associated with iron dxz and dyz orbitals. The spectra manifest the splitting of these iron dπ orbitals, and some reasons for this are discussed. The Soret (B) bands are also shown to be split. The PR spectrum of the low-spin azide complex uncovered a new excited state, transitions to which were shown to be polarized out of plane. Possible mechanisms for this transition are discussed. The absolute intensity of myoglobin crystal absorption spectra are shown to be unchanged from the solution values, indicating that the heme environment is comparable in the two media. The heme orientation is shown to be identical, within the precision of the subtle variations of the PR spectrum, for all the derivatives studied, with the possible exception of the azide.