Resonance-enhanced Raman Bands Research Articles

O2 Activation and Double C-H Oxidation by a Mononuclear Manganese(II) Complex.

A Mn(II) complex, [Mn(dpeo)2](2+) (dpeo=1,2-di(pyridin-2-yl)ethanone oxime), activates O2, with ensuing stepwise oxidation of the methylene group in the ligands providing an alkoxide and ultimately a ketone group. X-ray crystal-structure analysis of an intermediate homoleptic alkoxide Mn(III) complex shows tridentate binding of the ligand via the two pyridyl groups and the newly installed alkoxide moiety, with the oxime group no longer coordinated. The structure of a Mn(II) complex of the final ketone ligand, cis-[MnBr2(hidpe)2] (hidpe=2-(hydroxyimino)-1,2-di(pyridine-2-yl)ethanone) shows that bidentate oxime/pyridine coordination has been resumed. H2(18)O and (18)O2 labeling experiments suggest that the inserted O atoms originate from two different O2 molecules. The progress of the oxygenation was monitored through changes in the resonance-enhanced Raman bands of the oxime unit.

In Vivo Resonance Raman Detection of Ferrous Cytochrome c from Mitochondria of Single Living Yeast Cells

Abstract Raman spectra of mitochondria in living budding yeast cells (zygote of Saccharomyces cerevisiae and Saccharomyces bayanus) have been recorded with 532 nm excitation. Strong and sharp Raman bands are observed at 1584, 1315, 1129, 749, and 601 cm−1, in addition to known phospholipid bands. These Raman bands are not observed in the corresponding Raman spectrum of mitochondria obtained with 632.8 nm excitation. Their peak positions and relative intensities agree excellently with the reported resonance-enhanced Raman bands of ferrous cytochrome c, which has a Q-band absorption at 520 nm. We have thus succeeded in detecting ferrous cytochrome c, one of the key intermediates in the electron-transport chain in mitochondria, in vivo without any pretreatment. In vivo resonance Raman detection of ferrous cytochrome c opens up new possibilities for real-time and quantitative tracing of respiration dynamics in mitochondria in a single living cell.

Resonance Raman spectroscopy of highly fluorescing lignin containing chemical pulps: Suppression of fluorescence with an optical Kerr gate

Abstract Raman spectroscopy using 400 nm excitation was successfully applied to chemical pulp samples and the fluorescence background that usually limits the application of this method to such samples was effectively suppressed. This enabled the detection of much weaker Raman bands from the pulps. The rejection ratio of the fluorescence background to Raman scattering was estimated to be about 250. The resonance Raman spectra of peroxide bleached chemical pulps had chromophoric lignin bands at 1605 and 1655 cm−1, whereas the chlorine dioxide bleached pulps had only the aromatic band at 1605 cm−1. The square root of the aromatic chromophore band relative to cellulose band correlated linearly with the brightness which is in accordance with the Kubelka-Munk theory. This correlation indicated that the resonance enhanced Raman bands were mainly due to chromophoric lignin structures. Chlorine dioxide and peroxide bleached pulps gave different correlations to brightness, which was an indication of different kinds of chromophores in these pulps. The intensity of the aromatic band relative to the cellulose band was about 20 times higher with the ultraviolet (257 nm) than with the visible (400 nm) excitation. This clearly illustrated the importance of working with different excitation wavelengths. On one hand the UV excitation is more sensitive towards aromatic residual lignin in pulp, and on the other hand the visible excitation enables the selective detection of chromophoric lignin structures.

Electronic excited states of [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm= bis(dimethylphosphine)methane).

We present studies of the resonance Raman and electronic luminescence spectra of the [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm = bis(dimethylphosphine)methane) complex, including excitation into an intense band at 256 nm and into a weaker absorption system centered about approximately 300 nm. The resonance Raman spectra confirm the assignment of the 256 nm absorption band to a (1)(dsigma --> psigma) transition, a metal-metal-localized transition, in that nu(Au-Au) and overtones of it are strongly enhanced. A resonance Raman intensity analysis of the spectra associated with the 256 nm absorption band gives the ground-state and excited-state nu(Au-Au) stretching frequencies to be 79 and 165 cm(-1), respectively, and the excited-state Au-Au distance is calculated to decrease by about 0.1 A from the ground-state value of 3.05 A. The approximately 300 nm absorption displays a different enhancement pattern, in that resonance-enhanced Raman bands are observed at 103 and 183 cm(-1) in addition to nu(Au-Au) at 79 cm(-1) The compound exhibits intense, long-lived luminescence (in room-temperature CH(3)CN, for example, tau = 0.70 micros, phi(emission) = 0.037) with a maximum at 550-600 nm that is not very medium-sensitive. We conclude, in agreement with an earlier proposal of Mason (Inorg. Chem. 1989, 28, 4366-4369), that the lowest-energy, luminescent excited state is not (3)(dsigma --> psigma) but instead derives from (3)(d(x2-y2,xy --> psigma) excitations. We compare the Au(I)-Au(I) interaction shown in the various transitions of the [Au(2)(dmpm)(3)](ClO(4))(2) tribridged compound with previous results for solvent or counterion exciplexes of [Au(2)(dcpm)(2)](2+) salts (J. Am. Chem. Soc. 1999, 121, 4799-4803; Angew. Chem. 1999, 38, 2783-2785; Chem. Eur. J. 2001, 7, 4656-4664) and for planar, mononuclear Au(I) triphosphine complexes. It is proposed that the luminescent state in all of these cases is very similar in electronic nature.

Coordination of semiquinone and superoxide radical anions to the zinc ion in SOD model complexes that act as the key step in disproportionation of the radical anions.

Reactions of imidazolate-bridged CuII-ZnII heterodinuclear and CuII-CuII homodinuclear complexes, [CuIIZnII(bdpi)(CH3CN)2](ClO4)3 x 2CH3CN (1) and [CuII2(bdpi)(CH3CN)2](ClO4)3 x CH3CN x 3H2O (2) (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole), with the p-benzosemiquinone radical anion (Q*-) have been examined to provide mechanistic insight into the role of the ZnII ion in copper-zinc superoxide dismutase (Cu,Zn-SOD). The addition of less than one equivalent of Q*- to a deaerated solution of 1 or 2 in propionitrile at -80 degrees C results in the oxidation of Q*- accompanied by the appearance of a new absorption band at 585 nm due to the CuI-Q complex (3 or 4), the absorbance of which increases linearly with the increase in Q*- concentration. Both the resonance Raman spectra of 3 and 4 exhibit a strong resonance-enhanced Raman band at 1580 cm(-1), which can be assigned to a CO stretching vibration in the CuI-Q complexes. Further addition of Q*- to a deaerated solution of 3 in propionitrile results in the reduction of Q*-, whereas no reduction of Q*- occurs with 4, which does not contain the ZnII ion. Thus, the coordination of Q*- to the ZnII ion is essential for the reduction of Q*- by the CuI ion in 3. The coordination of O2*- and Q*- to the ZnII ion has been confirmed by the electronic and ESR spectra of the O2*- and Q*- complexes with mononuclear ZnII complexes, [ZnII[MeIm(Py)2](CH3CN)](ClO4)2 (5) and [ZnII[MeIm(Me)2](H2O)](ClO4)2 (6) (MeIm(Py)2 = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)2 = (1-methyl-4-imidazolylmethyl)bis(6-methyl-2-pyridylmethyl)amine). The binding energies of O2*- with the ZnII ion in 5 and 6 have been evaluated from the deviation of the g values of the ESR spectra from the free spin value.

Characterization of imidazolate-bridged dinuclear and mononuclear hydroperoxo complexes.

Dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi, HMe(2)bdpi, and HMe(4)bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe(2)bdpi = 4,5-bis((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)aminomethyl)imidazole, HMe(4)bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper-zinc superoxide dismutase (Cu,Zn-SOD). The corresponding mononucleating ligands, MeIm(Py)(2), MeIm(Me)(1), and MeIm(Me)(2) (MeIm(Py)(2) = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)(1) = (1-methyl-4-imidazolylmethyl)(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine, MeIm(Me)(2) = (1-methyl-4-imidazolyl-methyl)bis(6-methyl-2-pyridylmethyl)amine), have also been synthesized for comparison. The imidazolate-bridged Cu(II)-Cu(II) homodinuclear complexes represented as [Cu(2)(bdpi)(CH(3)CN)(2)](ClO(4))(3).CH(3)CN.3H(2)O (1), [Cu(2)(Me(2)bdpi)(CH(3)CN)(2)](ClO(4))(3) (2), [Cu(2)(Me(4)bdpi)(H(2)O)(2)](ClO(4))(3).4H(2)O (3), a Cu(II)-Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH(3)CN)(2)](ClO(4))(3).2CH(3)CN (4), Cu(II) mononuclear complexes of [Cu(MeIm(Py)(2))(CH(3)CN)](ClO(4))(2).CH(3)CN (5), [Cu(MeIm(Me)(1))(CH(3)CN)](ClO(4))(2)( )()(6), and [Cu(MeIm(Me)(2))(CH(3)CN)](ClO(4))(2)( )()(7) have been synthesized and the structures of complexes 5-7 determined by X-ray crystallography. The complexes 1-7 have a pentacoordinate structure at each metal ion with the imidazolate or 1-methylimidazole nitrogen, two pyridine nitrogens, the tertiary amine nitrogen, and a solvent (CH(3)CN or H(2)O) which can be readily replaced by a substrate. The reactions between complexes 1-7 and hydrogen peroxide (H(2)O(2)) in the presence of a base at -80 degrees C yield green solutions which exhibit intense bands at 360-380 nm, consistent with the generation of hydroperoxo Cu(II) species in all cases. The resonance Raman spectra of all hydroperoxo intermediates at -80 degrees C exhibit a strong resonance-enhanced Raman band at 834-851 cm(-1), which shifts to 788-803 cm(-1) (Deltanu = 46 cm(-1)) when (18)O-labeled H(2)O(2) was used, which are assigned to the O-O stretching frequency of a hydroperoxo ion. The resonance Raman spectra of hydroperoxo adducts of complexes 2 and 6 show two Raman bands at 848 (802) and 834 (788), 851 (805), and 835 (789) cm(-1) (in the case of H(2)(18)O(2), Deltanu = 46 cm(-1)), respectively. The ESR spectra of all hydroperoxo complexes are quite close to those of the parent Cu(II) complexes except 6. The spectrum of 6 exhibits a mixture signal of trigonal-bipyramid and square-pyramid which is consistent with the results of resonance Raman spectrum.

Identifying Framework Titanium in TS-1 Zeolite by UV Resonance Raman Spectroscopy

Framework titanium in Ti-silicalite-1 (TS-1) zeolite was selectively identified by its resonance Raman bands using ultraviolet (UV) Raman spectroscopy. Raman spectra of the TS-1 and silicalite-1 zeolites were obtained and compared using continuous wave laser lines at 244, 325, and 488 nm as the excitation sources. It was only with the excitation at 244 nm that resonance enhanced Raman bands at 490, 530, and 1125 cm-1 appeared exclusively for the TS-1 zeolite. Furthermore, these bands increased in intensity with the crystallization time of the TS-1 zeolite. The Raman bands at 490, 530, and 1125 cm-1 are identified as the framework titanium species because they only appeared when the laser excites the charge-transfer transition of the framework titanium species in the TS-1. No resonance Raman enhancement was detected for the bands of silicalite-1 zeolite and for the band at 960 cm-1 of TS-1 with any of the excitation sources ranging from the visible to UV regions. This approach can be applicable for the identification of other transition metal ions substituted in the framework of a zeolite or any other molecular sieve.

The nature of the normal modes of [Mo2(CN)8]4−

The 1(δ → δ*) resonance-Raman and infrared spectra of [NEt4]4[Mo2(13CN)8] have been determined and are compared with those previously reported for the natural-abundance isotopomer. The three totally symmetric resonance-enhanced Raman fundamentals of the 12C compound in the 300–415 cm−1 region shift to lower wavenumbers (as, of course, do the ν(CN) bands at ca. 2100 cm−1) and change in relative intensity upon 13C substitution. Normal-coordinate calculations on the two isotopomers of the [Mo2(CN)8]4− ion reveal that the three modes responsible for the resonance-enhanced Raman bands are strongly mixed and of ν(MoMo), ν(MoC), and λop(MoCN) parentage, and that their intensities roughly scale with the amount of ν(MoMo) character in the modes.

Ground and electronically excited states of Cr(CO) 4(bipyridine): energy factored force field analysis of CO stretching vibrations and resonance Raman study

IR spectra of Cr(CO) 4(bipyridine) and its 13CO-containing isotopomers were used to calculate all the stretching and interaction CO force constants and the normal coordinates of the CO stretching vibrations. Resonance Raman (rR) spectra of Cr(CO) 4(bpy) were measured and compared with the Fourier transform Raman spectra. The most resonance enhanced Raman bands belongs to the ring-deformation vibrations of the bpy ligand and the A 1 ν(CO) vibration at 2004 cm −1. The rR spectral pattern confirms a localized Cr → bpy metal-to-ligand charge transfer (MLCT) character of the electronic transition responsible for the visible absorption band. It is shown that the MLCT excitation also affects the bonding within the Cr(CO) 4 molety. Of the two A 1 ν(CO) vibrations, only the one at higher frequency (A 1 2, 2004 cm −1) gives rise to a resonance enhanced Raman band. Analysis of this effect, based on the energy factored force field (EFFF) calculated normal coordinates of both symmetric ν(CO) vibrations, shows that the MLCT excitation affects the CO bonds in both the axial and equatorial CO ligands, the influence on the axial ligands being larger. The Raman band due to the A 1 1 symmetric ν(CO)_vibration is not resonance enhanced because of an out-of-phase coupling between the symmetric vibrations of the axial and equatorial pairs of CO ligands. Raman bands due to CrC stretching and CrCO bending vibrations, apparently coupled with the vibrations of the Cr(bpy) moiety, were identified by the 13CO isotope effect and found to be resonance enhanced.

Raman spectroscopic studies of metal-metal halide molten mixtures: the mercury-mercury(II) halide systems

Raman spectra of molten HgX 2 -Hg (X=Cl, Br, I) systems have been obtained at compositions up to 30 mol% in Hg from 550 to 818 K. The dissolution of mercury in mercury halides gives rise to resonance-enhanced Raman bands which were interpreted to account for Hg 2 X 2 type molecular species formed in all mercury compositions and Hg 2 X 2 type molecules formed at high mercury mole fractions. Spectra were also obtained from HgX 2 -HgX' 2 -Hg (X=F, Cl, Br, I) mixtures and were attributed to mixed mercury(I) (sub)halide molecules Hg 2 XX'formed in the melt

Assignment of the electronic spectra of tris(.mu.-halo)bis(triammineruthenium)(2+) ions using resonance Raman spectroscopy

In the present work, RR spectra in the region of the metal-ligand vibrations have been recorded for exciting wavelengths that cover most of the visible region. In addition, the depolarization ratios of the resonance-enhanced Raman bands have been recorded with greater accuracy and over a wide range of exciting wavelengths. These measurements indicate that intensity enhancement of the Ru-X bands in the RR spectra is due to a z-polarized transition that has been assigned as σ→σ* (in accord with the previous RR study)

ChemInform Abstract: Triplet (T1) State Resonance Raman Spectroscopy of Some Azanaphthalenes.

The time‐resolved Tn←T1 resonance Raman spectra of quinoline (1‐azanaphthalene), isoquinoline (2‐azanaphthalene), quinoxaline (1,4‐diazanaphthalene), and quinazoline (1,3‐diazanaphthalene) molecules in cyclohexane solution are reported, and vibrational assignments and structural implications are discussed. In each of the four compounds, the most resonance enhanced Raman band lies in the 1340–1270 cm−1 region and corresponds to nuclear displacements involving in‐plane stretching motions of the CC and CN bonds. In diazanaphthalenes, drop in the frequency of this vibration on S0 to T1 excitation (97 cm−1 in quinoxaline, 76 cm−1 in quinazoline) is observed to be higher than in azanaphthalenes (31 cm−1 in quinoline, 58 cm−1 in isoquinoline) implying pronounced elongation of the CN bonds, in comparison to the CC bonds, in the T1 states. The T1 Raman spectra of azanaphthalenes, in contrast to naphthalene, are observed to exhibit significant solvent dependency.

Triplet (T1) state resonance Raman spectroscopy of some azanaphthalenes

The time-resolved Tn←T1 resonance Raman spectra of quinoline (1-azanaphthalene), isoquinoline (2-azanaphthalene), quinoxaline (1,4-diazanaphthalene), and quinazoline (1,3-diazanaphthalene) molecules in cyclohexane solution are reported, and vibrational assignments and structural implications are discussed. In each of the four compounds, the most resonance enhanced Raman band lies in the 1340–1270 cm−1 region and corresponds to nuclear displacements involving in-plane stretching motions of the CC and CN bonds. In diazanaphthalenes, drop in the frequency of this vibration on S0 to T1 excitation (97 cm−1 in quinoxaline, 76 cm−1 in quinazoline) is observed to be higher than in azanaphthalenes (31 cm−1 in quinoline, 58 cm−1 in isoquinoline) implying pronounced elongation of the CN bonds, in comparison to the CC bonds, in the T1 states. The T1 Raman spectra of azanaphthalenes, in contrast to naphthalene, are observed to exhibit significant solvent dependency.

ChemInform Abstract: TIME RESOLVED RESONANCE RAMAN SCATTERING OF TRANSIENT RADICALS: THE P‐AMINOPHENOXYL RADICAL

p‐aminophenoxyl radical exhibits a resonance enhanced Raman band at 1647 cm−1. Radicals were produced in aqueous solutions at concentrations of the order of 10−5 M by pulse radiolysis and observed by time resolved Raman methods.

Time resolved resonance Raman scattering of transient radicals: The p-aminophenoxyl radical

p-aminophenoxyl radical exhibits a resonance enhanced Raman band at 1647 cm−1. Radicals were produced in aqueous solutions at concentrations of the order of 10−5 M by pulse radiolysis and observed by time resolved Raman methods.

Ribonucleotide reductase: A structural study of the dimeric iron site

The iron-containing B2 subunit of ribonucleotide reductase from Escherichia coli has been investigated by Raman spectroscopy. Both the tyrosyl radical-containing native protein and the radical-free protein exhibit a resonance-enhanced Raman band at 500 cm −1. This band is assigned to an Fe-O vibrational mode arising from an oxygen-containing ligand. The failure to observe any tyrosinate ring modes makes it unlikely that ribonucleotide reductase is an iron-tyrosinate protein and rules out tyrosinate oxygen as a ligand. It is proposed that the 500 cm −1 band in ribonucleotide reductase is analogous to the 510 cm −1 Fe-O vibrational mode of methemerythrin and arises from an oxo- or carboxylate-bridge between the antiferromagnetically-coupled Fe(III) ions.

Laser raman investigation of intact single muscle fibers: Protein conformations

Raman spectra, in the frequency region of the protein vibrations, of intact single muscle fibers of the giant barnacle are presented. Strong bands at 1521 and 1156 cm −1 in the spectra are attributed to resonance-enhanced Raman bands of membrane-bound β-carotene. Many bands of the myofibrillar proteins are also observed, and at least three spectral features confirm that these proteins adopt a predominantly α-helical structure: (1) the amide I band at 1648 cm −1, (2) the weak scattering in the amide III region, and (3) a strong skeletal C-C stretching band at 939 cm −1. Deuterated fibers have also been examined in order to find the exact shape of the amide III band. The presence in the fibers of paramyosin, which is only found in catch muscles, is also apparent from the spectra.

Resonance Raman spectra of iron(III)-, copper(II)-, cobalt(III)-, and manganese(III)-transferrins and of bis(2,4,6-trichlorophenolato)diimidazolecopper(II) monohydrate, a possible model for copper(II) binding to transferrins.

Fe(III), Cu(II), Co(III), and Mn(III) complexes of ovo- and human serum transferrins show resonance enhanced Raman bands near 1600, 1500, 1270, and 1170 cm-1 upon excitation with laser frequencies which fall within the visible absorption bands of those metalloproteins. Comparison of the visible absorption and resonance Raman spectra of the Cu(II)-transferrin complexes with those for the Cu(II) model compound, bis(2,4,6-trichlorophenolato)diimidazolecopper(II) monohydrate, indicates that the resonance Raman bands are due to enhancement of phenolic vibrational modes. For the model (Cu(II) compound, a normal coordinate analysis was used to aid our assignment of the observed resonance bands at 1562, 1463, 1311, and 1122 cm-1 to A1 vibrational modes of the 2,4,6-trichlorophenolato moiety. These assignments are consistent with those made for Cu(II)-transferrins. The latter assignments were based upon calculated A1 frequencies for p-methylphenol (Cummings, D.L., and Wood, J.L. (1974), J. Mol. Struct. 20, 1). The wavelength shifts in the resonance bands for the model compound from those for Cu(II)-transferrins are due to the influence of the chloro substituents on the planar vibrations of phenol. These results clearly identify tyrosine as a ligand in copper binding to transferrins.