Time-resolved Resonance Raman Study Research Articles

Time-resolved resonance Raman study of the primary photoprocesses of nickel(II) octaethylporphyrin in solution

Two-color pump-probe time-resolved resonance Raman studies with 3 ps time resolution were carried out for nickel(II) octaethylporphyrin in toluene and tetrahydrofuran solutions. Reliable proofs have been obtained for the existence of both conformational changes and vibrational heating/cooling in the primary photoprocess. Conformational changes from ruffled to planar structures, which were monitored by time evolution of the v 10 ∗ bands at 1616–1629 cm −1, took place in the excited (d,d) state within 15 ps following photoexcitation, while the core expansion of the macrocycle occurs immediately after the excitation energy transfer from the ( π,π ∗ ) to (d,d) states. Intensity changes of the v 4 ∗ and v 7 ∗ bands in the anti-Stokes Raman spectra revealed that the conversion of the electronic excess energy into vibrational heating/cooling occurs with time constants of 5–8 ps and is dependent on pump wavelength.

One-electron photoreduction of flavin mononucleotide: time-resolved resonance Raman and absorption study

Resonance Raman and absorption spectra of the lowest excited triplet state T 1, and semiquinone neutral and anion radicals of flavin mononucleotide (FMN) have been obtained by time-resolved Raman spectroscopy and laser flash photolysis. Both spectra have revealed that photoreduction of FMN is initiated by the process in which the T 1 state of FMN abstracts an electron from substrates such as EDTA to generate the semiquinone anion radical FMN −· both in acidic and basic solutions over the pH range 5–9, and when the pH is smaller than 8.4, FMN −· is further converted into the semiquinone neutral radical FMNH · by combining with H +. The electron transformation is much faster in basic solutions than in acidic solutions. In more strongly acidic solutions pH <4.4, protonation of the T 1 state 3FMN∗ occurs in less than 80 ns and the protonated T 1 state 3[FMNH +]∗ abstracts an electron from the substrate to generate FMNH ·. No indication of the abstraction of a hydrogen atom by 3FMN∗ to generate FMNH · was obtained.

Allosteric intermediates in hemoglobin. 1. Nanosecond time-resolved circular dichroism spectroscopy.

Time-resolved circular dichroism (TRCD) studies performed on photolyzed hemoglobin-CO complex (HbCO) probe room temperature protein relaxations in Hb, including the R --> T allosteric transition. TRCD spectroscopy of photolysis intermediates in the near-UV (250-400 nm) spectral region provides a diagnostic for T-like structure at the alpha 1 beta 2 interface via the effect of quaternary structure on the UV CD of aromatic residues. The TRCD of porphyrin-based transitions in the UV and Soret regions, reflecting transition-dipole couplings between hemes and aromatic residues over a radius wide enough to permit heme-interface and inter-dimer interactions, is modulated by the tertiary and quaternary structure of photolysis intermediates. In the allosteric core model of Hb cooperativity, Fe-CO bond breakage initiates a heme structural change, thought to be heme doming, that is transmitted to the alpha 1 beta 2 interface via the F helix. The TRCD results, analyzed in light of kinetic information from time-resolved absorption studies, suggest specific features for the mechanism by which the ensuing tertiary and quaternary conformational changes propagate through the protein. In particular, the UV-TRCD indicates that the alpha 1 beta 2 interface responds within several hundred nanoseconds to initial events at the heme by shifting from an R toward a T-like interface. The appearance of T-like character at the alpha 1 beta 2 interface tens of microseconds before the appearance of equilibrated T state deoxyHb indicates that the R --> T transition in photolyzed HbCO is a stepwise process, as previously suggested by time-resolved resonance Raman studies.

Time-Resolved Resonance Raman Spectroscopic Studies on the Radical Anions of Menaquinone and Naphthoquinone

Quinones and their radical ion intermediates have been much studied by vibrational spectroscopy to understand their structure−function relationships in various biological processes. In this paper, we present a comprehensive analysis of vibrational spectra in the structure-sensitive region of both the naphthoquinone (NQ) and 2-methyl-1,4-naphthoquinone (MQ, menaquinone) radical anions using time-resolved resonance Raman and ab initio studies. Specific vibrational mode assignments have been made to all the vibrational frequencies recorded in the experiment. It is observed that the carbonyl and CC stretching frequencies show considerable coupling in NQ and MQ radical anions. Further, the asymmetric substitution present in MQ with respect to NQ shows important signatures in the radical anion spectrum. It is concluded that assignments of vibrational frequencies of asymmetrically substituted quinones must take into consideration the influence of asymmetry on structure and reactivity.

Excited States of Water-Soluble Metal Porphyrins as Microenvironmental Probes for DNA and DNA-Model Compounds: Time-Resolved Transient Absorption and Resonance Raman Studies of Ni(TMpy-P4) in [Poly(dG-dC)]2 and [Poly(dA-dT)]2

The dynamics and mechanisms of photoexcitation relaxation of the water-soluble cationic metalloporphyrin nickel(II) 5,10,15,20-tetrakis[4-(N-methylpyridyl)]porphyrin (Ni(TMpy-P4)) bound to DNA-model polynucleotides, i.e. poly(dG-dC)2 and poly(dA-dT)2, and free in a mere phosphate buffer, have been studied in detail by using time-resolved picosecond transient absorption (TA) and nanosecond resonance Raman (RR) spectroscopies. For the Ni(TMpy-P4)−poly(dG-dC)2 complex, double-exponential kinetics of relaxation has been found, with time constants of ≤10 and 350 ± 20 ps, and absolute absorption spectra have been reconstructed from experimentally measured difference spectra. The long-lived transient species has been assigned to the excited intramolecular metal-centered (d,d) state 3B1g of the 4-coordinate Ni porphyrin intercalated between G-C base pairs. Transient RR spectra originating from this state have also been obtained and discussed. A much more complicated process of excitation relaxation has been found for the Ni(TMpy-P4)−poly(dA-dT)2 complex, where at least four relaxation components can be separated with time constants of ≤10, ∼100, ∼450 ps, and ≫1 ns. Our studies support the existence of at least two types of Ni(TMpy-P4) interaction with poly(dA-dT)2, each having its own kinetics of TA decay and transient RR spectra. Both TA and RR sets of data show that a major part of Ni porphyrin molecules yields a photophysical behavior typical for a 4-coordinate species, the excited (d,d) state 3B1g playing the key role in relaxation processes, while a minor part of Ni(TMpy-P4) also participates in axial ligand binding/release photoprocesses. Comparative analysis of transient RR spectra of Ni(TMpy-P4) bound to the A-T sequence and free in a phosphate buffer shows that no 6-coordinate 3B1g(L)2 transient species is photogenerated in the complex with poly(dA-dT)2, and therefore, axial coordination of only one extra-ligand molecule (most probably from the surrounding water solution) to the porphyrin central Ni ion is proposed to explain the experimental results. Possible processes of Ni(TMpy-P4) binding to poly(dA-dT)2 are discussed on the basis of the current photophysical data.

Charge Transfer Switching in Photoexcited Ru(II) Porphyrins: A Time-Resolved Resonance Raman and Spectroelectrochemical Study

The charge transfer (CT) excited states of Ru(II)OEP(Py)2 and Ru(II)TPP(Py)2 (TPP = tetraphenylporphyrin, OEP = octaethylporphyrin, and Py = pyridine) have been investigated by nanosecond time-resolved resonance Raman (TR3) spectroscopy. The spectra reveal unexpected differences between the two species. The TR3 spectrum of [Ru(II)TPP(Py)2]* resembles the resonance Raman (RR) spectrum of the RuTPP(Py)2 radical anion. Both spectra show strong enhancement of nontotally symmetric modes, resulting from a Jahn−Teller distortion due to the eg* orbital degeneracy. The band frequencies are slightly higher in the CT state than in the radical anion, reflecting the effect of the Ru(II) oxidation. Thus, the TR3 spectral features support a 3(dπ,π*) excited state assignment, with an electron transferred from Ru(II) to the porphyrin. In contrast, the TR3 spectrum [Ru(II)OEP(Py)2]* does not resemble the RR spectra of the Ru(II)OEP radical anion. Rather, it contains totally symmetric modes, at frequencies close to those of...

Investigation of Carotenoid Radical Cations and Triplet States by Laser Flash Photolysis and Time-Resolved Resonance Raman Spectroscopy: Observation of Competitive Energy and Electron Transfer

The first nanosecond time-resolved resonance Raman study of carotenoid radical cations is reported for the polyenes septapreno-β-carotene and 7,7‘-dihydro-β-carotene. In addition, previously unreported resonance Raman spectra of the ground and triplet states of these molecules are reported. The radical cations were generated following electron transfer quenching of triplet 1-nitronaphthalene in methanol and Triton X-100 micelles. The quenching of triplet 1-nitronaphthalene by these carotenoids involves solvent-dependent competition between energy transfer and electron transfer, and for both carotenoids, estimates are given for the efficiencies of these two processes in methanol and hexane. The resonance Raman spectra of septapreno-β-carotene ground and triplet states are consistent with spectra reported previously for other carotenoids. However, the resonance Raman spectrum of the triplet state of 7,7‘-dihydro-β-carotene displays an intensity profile not found in the triplet spectra of other carotenoids. In addition, the resonance Raman spectrum of the radical cation of 7,7‘-dihydro-β-carotene is quite distinct from that of septapreno-β-carotene. These observations are attributed to differences in electronic structure arising from septapreno-β-carotene having an odd number of conjugated double bonds while 7,7‘-dihydro-β-carotene, unusually, has an even number.

Time-resolved resonance raman study of the recombination dynamics photodissociated carbon monoxide to sperm whale myoglobin and its mutants

Time-resolved resonance Raman (TR 3) spectroscopy was applied to study the recombination process of photodissociated carbon monoxide with recombinant sperm whale myoglobin (Mb) and its several mutants. The measurements were carried out, with various delay times (Δt=−20 ns − 1 ms) following photolysis for several mutants in which dital or E-7His (His64) was replaced with a aliphatic or aromatic residue. The FeCO stretching bands (v FeCO) showed that the environments around CO in the steady state as well as the kinetics of the CO rebinding process are very different among mutants and these differences seemed to be correlated with the hydrophobicity of the replaced residues. In spite of these differences for each mutant, a common intermediate species was observed at almost the same time region. In this intermediate CO was not bound to the iron ion yet, but the heme state was different from the initial deoxy form. Since this intermediate is common to all the mutants, the difference of the distal residues did not play an important role. The intermediate may it reflect the global dynamics of the protein, but correspond to so-called “open form” of Mb in which the His-64 swings out and a pathway for the ligand to enter the active site in general.

Mechanism of dioxygen reduction at the iron-copper binuclear center of cytochrome [formula omitted] oxidase; time-resolved resonance raman study

Mechanism of dioxygen reduction at the iron-copper binuclear center of cytochrome [formula omitted] oxidase; time-resolved resonance raman study

Photochromic reaction of 6-nitro-1′,3′,3′-trimethylspiro[2 H-1-benzopyran-2,2′-indoline]: time-resolved resonance Raman and absorption study

Time-resolved resonance Raman spectra and time-resolved absorption spectra of transient species of photochromic 6-nitro-1′,3′,3′-trimethylspiro[2 H-1-benzopyran-2,2′-indoline] (6-nitroBIPS) generated by irradiation with UV light in cyclohexane have been measured. Three transients were observed to appear sequentially in the nanosecond-microsecond time region. The first transient (transient I) with the shortest lifetime is identified as the T 1 state of photomerocyanine having an open structure (spiro CO bond-cleaved). The second transient (transient II) is attributed to photomerocyanine produced from transient I, and the last transient to appear (transient III) having the longest lifetime is assigned to a dimeric species of photomerocyanine because of the quadratic dependence of its quantum yield on both the pump UV laser power and the concentration of the solution. It is concluded that the cleavage of the spiro CO bond occurs in the S 1 state of the parent species.

Time-Resolved Resonance Raman Study of Free-Base Octaethylporphyrins in the S0, S1, and T1 States

Time-Resolved Resonance Raman Study of Free-Base Octaethylporphyrins in the S0, S1, and T1 States

Time-Resolved Resonance Raman Study of the Rate of Separation of a Geminate Ion Pair into Free Ions in a Medium Polarity Solvent

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTime-Resolved Resonance Raman Study of the Rate of Separation of a Geminate Ion Pair into Free Ions in a Medium Polarity SolventEric Vauthey, Anthony W. Parker, Bohdana Nohova, and David PhillipsCite this: J. Am. Chem. Soc. 1994, 116, 20, 9182–9186Publication Date (Print):October 1, 1994Publication History Published online1 May 2002Published inissue 1 October 1994https://doi.org/10.1021/ja00099a037RIGHTS & PERMISSIONSArticle Views144Altmetric-Citations26LEARN 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

Structures of transient species in the photochromic reaction of 1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indoline]: Time-resolved resonance Raman study of isotopically substituted analogues

Abstract Time-resolved resonance Raman spectra of seven kinds of isotopically substituted analogues of 1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indoline] in the photomerocyanine form have disclosed that only the vibrations of the cleaved benzopyran part are resonance enhanced significantly in cyclohexane and in acetonitrile solutions with 460-390 nm probe light. Dramatic changes in the resonance Raman spectra of the photomerocyanine on going from non-hydrogen-bond donor solvents to hydrogen-bond donor solvents can be interpreted as being due to changes in the relative contribution of ortho -quinoidal and zwitterionic forms in the resonance hybrid structure of the photomerocyanine: in cyclohexane and in acetonitrile the contribution of the ortho -quinoidal form is substantial, while in methanol the zwitterionic form is stabilized by hydrogen bonding with the solvent and the photomerocyanine takes an almost zwitterionic structure.

Structures and dynamics of the lowest excited triplet state, radical cation and radical anion of 1,4-diphenylbutadiyne: time-resolved resonance Raman study

Time-resolved resonance Raman spectra of the lowest excited triplet state T 1, the radical cation R + and the radical anion R − of 1,4-diphenylbutadiyne (DPB) have been measured. It has been shown that the CC symmetric stretch exhibits low-frequency shifts in the order, S o (2219 cm −1), R + (2156 cm −1), R − (2108 cm −1), and T 1 (1999 cm −1), indicating that the CC triple bond weakens in this sequence. However, the frequency shifts are not as large as those observed for diphenylacetylene (DPA), suggesting that in the case of DPB the unpaired electron (spin density) is distributed over the two CC triple bonds of the conjugated system, which makes the weakening of the CC bonds of DPB much less than that of DPA. It has also been shown that like DPA, the ionization of DPB to generate R + can occur biphotonically through the T 1 state.

A time-resolved resonance Raman study of the T1 excited state of zinc(II) octaalkylporphyrins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA time-resolved resonance Raman study of the T1 excited state of zinc(II) octaalkylporphyrinsRanjit Kumble, Songzhou Hu, Glen R. Loppnow, S. E. Vitols, and Thomas G. SpiroCite this: J. Phys. Chem. 1993, 97, 41, 10521–10523Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://doi.org/10.1021/j100143a004RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations19LEARN 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 (302 KB) Get e-Alerts

Resonance Raman and time-resolved resonance Raman studies of tris(4-methyl-2,2'-bipyridine)ruthenium(II). Polarization of the radical fragment of the 3MLCT states

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTResonance Raman and time-resolved resonance Raman studies of tris(4-methyl-2,2'-bipyridine)ruthenium(II). Polarization of the radical fragment of the 3MLCT statesShelly M. Treffert-Ziemelis, Janusz Golus, Dennis P. Strommen, and James R. KincaidCite this: Inorg. Chem. 1993, 32, 18, 3890–3894Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/ic00070a020RIGHTS & PERMISSIONSArticle Views324Altmetric-Citations38LEARN 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 (556 KB) Get e-Alerts Get e-Alerts

Time-resolved resonance Raman studies of recom bination intermediates of CO-photodissociated myoglobin, hemoglobin and their E7 mutants.

Time-resolved resonance Raman studies of recom bination intermediates of CO-photodissociated myoglobin, hemoglobin and their E7 mutants.

Time-resolved resonance Raman study on the binding of carbon monoxide to recombinant human myoglobin and its distal histidine mutants.

Time-resolved resonance Raman (RR) spectra of the recombined species of photodissociated CO with recombinant human myoglobin (Mb) and several E7 mutants, in which distal His was replaced by Gly (H64G), Gln (H64Q), Ala (H64A), Ile (H64I), Val (H64V), and Leu (H64L) through site-directed mutagenesis, were observed in the time range -20 ns to 1 ms following photolysis. The Fe-CO stretching (VFe-CO) RR band was observed successfully with pulse excitation when the laser power was greatly reduced. H64H, H64G, and H64Q gave the VFe-CO band at 505-510 cm-1 in their stationary states. In their recovery processes 1-100 microseconds after photodissociation, a broad transient band was observed at slightly lower frequencies than those of their equilibrium structures for H64G and H64Q, but a transient VFe-CO band corresponding to the so-called "open" form was not identified around 490 cm-1 for any of the three species. A second group, H64A, H64I, H64V, and H64L, gave the main VFe-CO band at 490-495 cm-1 with a shoulder around 510 cm-1 (except for H64L) in the stationary state and exhibited a much faster recovery than the first group. These latter four species gave a broad transient band around 492-500 cm-1 in the time range of 100-1000 ns, while the approximately 510 cm-1 shoulder appeared much later. The equilibrium relative intensity of the two bands was attained at 500 microseconds, suggesting that the interconversion between the two forms is slower than 100 microseconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Photochemical ring-opening reactions are complete in picoseconds: a time-resolved UV resonance Raman study of 1,3-cyclohexadiene

Photoproduct formation, vibrational, and conformational relaxation kinetics in the photochemical ring-openings of 1,3-cyclohexadiene (CHD) and α-phellandrene (α-PHE) are determined by picosecond, time-resolved UV Stokes and anti-Stokes resonance Raman spectroscopy. The frequency-doubled output from an amplified, synchronously pumped dye laser system was used to perform transient, two-color resonance Raman Stokes experiments on the photoconversion of CHD to cis-hexatriene (c-HT) and of α-PHE to 3,7-dimethyl-1,3,5-octatriene (OT). The appearance time of the Stokes scattering from ground-state c-HT is 6±1 ps, while that of OT is 11±2 ps. In both reactions, the photoproduct anti-Stokes ethylenic intensity appears with a time constant of 8±2 ps and decays in 9±2 ps

Laser photochemistry and transient Raman spectroscopy of silyl-substituted Fischer-type carbene complexes

Pulsed laser irradiation of the silyl-substituted carbene complexes (CO)5W=C(XR)SiPh3 (XR = NC4H8 (1); = OEt (2)) in various solvents has been investigated using transient absorbance and time-resolved resonance Raman scattering as monitoring techniques. Irradiation of (1) in noncoordinating or weakly-coordinating solvents at 355 nm within the ligand field absorption band results in the rapid formation, within the laser pulse duration, of a permanent photoproduct. Saturation of the irradiated solution with CO results in regeneration of the starting complex 1. IR and Raman spectral data suggest that the photoproduct is the internally stabilized 16- electron species (CO)4W=C(NC,iH8)SiPh3. The observations are discussed in relation to the previously reported formation of the same 16-electron species by thermolysis of 1. When the irradiation is carried out in CH3CN as solvent, UV-visible evidence suggests formation of the photosubstituted species (CO)4(CH3CN) W=C(NC4Hg)SiPh3. No photoactivity, either transient or permanent, is seen in any solvent when the irradiation is carried out at 416 nm, a wavelength which falls within the MLCT absorption region of 1. When the ethoxy-substituted carbene complex 2 is irradiated in either the LF or MLCT absorption regions a transient species forms rapidly, within the laser pulse duration, and decays on a time scale of several μs, with a lifetime dependent on solvent polarity but independent of CO concentration in solution. Time-resolved resonance Raman studies in which the sample is photolyzed at 355 nm and probed by means of a delayed pulse at 406 nm show the formation and decay of a transient consistent with the flash photolysis results. The data are interpreted in terms of photoinduced anti-syn isomerization of 2 about the Ccarbene~0 bond.