Silvia Völker - Academia.edu (original) (raw)
Papers by Silvia Völker
The Journal of Chemical Physics, 1980
Photochemical hole-burning has been used to study selective and reversible phototautomerism in ch... more Photochemical hole-burning has been used to study selective and reversible phototautomerism in chlorin (dihydroporphin) incorporated in matrices of n-hexane, n-octane, and n-decane at 4.2 K. The energy difference between the S1↔S0 transitions of the two forms, distinguished by the position of the two inner protons, is ∼1500 cm−1; the stable tautomer absorbing near 6350 Å. The back reaction from the less stable form to the stable one is 103 times faster than the forward reaction, and under wide band excitation in the Soret band a dynamic equilibrium exists between the two forms. Very narrow holes (∼40 MHz) can be burnt in the inhomogeneous lines of both tautomers. The width of these holes is consistent with a limit imposed by the fluorescence lifetime of 8 ns.
Chemical Physics Letters, 1987
ABSTRACT Zeeman shifts of the order of 10−4 to 10−3 of the inhomogeneous spectral linewidth have ... more ABSTRACT Zeeman shifts of the order of 10−4 to 10−3 of the inhomogeneous spectral linewidth have been observed in the 0-0 transition of free-base porphin embedded in amorphous polyethylene at 4.2 K by means of optical hole burning. From fits of the experimental results to calculated line shapes as a function of frequency and field strength, the value of the change in the magnetic susceptibility of the molecule in a magnetic field on excitation to the first excited singlet state, χz′,z′ = 60.6 MHz/T2, was determined. This is in good agreement with the value previously found for the same molecule in a crystalline host.
Spectroscopy of Biological Molecules: New Directions, 1999
The green fluorescent protein (GFP) has recently attracted great attention because it is the only... more The green fluorescent protein (GFP) has recently attracted great attention because it is the only cloned protein that exhibits strong fluorescence without any extraneous chromophores [1]. When fused to other proteins, it becomes a marker for gene expression and allows visualization of dynamic events inside living cells [2, 3]. Although the crystal structure of GFP has been solved [4], its photophysical properties remained puzzling. It was known that wild-type GFP in the ground state can exist in two forms, A (neutral) and B (anionic), and it was suggested [5] that a photoconversion from A to B involves an excited-state proton transfer, while an intermediate I-form, not identified in the spectra, was held responsible for the green fluorescence observed at 508 nm.
Chemical Physics Letters, 1981
Abstract Zeeman experiments are reported on the S 1 ← S 0 O-O transitions of chlorin (7,8-dihydro... more Abstract Zeeman experiments are reported on the S 1 ← S 0 O-O transitions of chlorin (7,8-dihydroporphin) and its photoisomer in an n -hexane crystal by photochemical hole burning at 4.2 K. The holes shift with a quadratic field dependence of -39.0 MHz/T 2 (chlorin) and −245.3 MHz/T 2 (photoisomer). For chlorin A = ¦ 1 ¦ L z ¦S 2 > ¦=4.5. Single-site absorption and fluo spectra are reported. PPP calculations were performed.
Chemical Physics Letters, 1982
The homogeneous hncwvrdth rho,,, oi the O-O S,-So IranjlIion oi ircc-baw porphm m saw31 orgamc gl... more The homogeneous hncwvrdth rho,,, oi the O-O S,-So IranjlIion oi ircc-baw porphm m saw31 orgamc glssscs 1135 been mcasurcd by photochcmwal holc-burmnp at 7 = I 1-Xl E. For 7 + 0 rhom cwapolatcs to IIIC hict~me-hrmtcd value. At T = i .2 K rhom = 180 hlHz m plyccrol. \\ tuch ts an order oi msgruludc lxgcr tlon m cryst31> rhom mcrcdscs 3s 7' 3=o ', tndcpcndcnt of the @ISS uud
Chemical Physics Letters, 1985
In the mqonty of the experiments done to determine homogeneous linewidths (Fhorr,) in amorphous o... more In the mqonty of the experiments done to determine homogeneous linewidths (Fhorr,) in amorphous orgamc solids at low temperatures, the hole-burning technique has been used. The holes are permanent (at least for many hours or days), and the burning mechanism mvolved may be erther photochemical [l-3] or non-photochemical (photophysrcal) [4,5] Until recently, however, the holewidths reported m the hterature for many of these systems [ 1,431 were orders of magmtude larger than m organic crystals [6], and theu temperature dependence was found m some cases to be proportronal to T2 [2], and lrnear rn others [s] In addition, residual linewidths for T + 0 of the order of 0 5-l cm-l (= lo4 MHz) were reported [2,5], mstead of the expected lifetime-limited values (~IFT~)-~ of the order of tens of MHz In contrast to these fmclings, we have shown that much narrower holes can be obtamed [3] and that Fhom follows a T 1 3 dependence [3,7,8] for many orgamc glasses Furthermore we observed that Fuo, mvarrably extrapolates to the hfetrme-lmuted value [7,8] and that some systems reach this value at T > 03 K [9] Srrmlar results regardmg the T dependence of Fho, have also been found by other groups with hole-burning [lo] , phosphorescence line-narrow-mg [ 1 l] and photonecho techmques [12] m drfferent amorphous systems Thus, it seems that T1-3 is charactenstic for relaxation m organic glasses at low temperatures and that it might be related to a fundamental property of disordered systems In all organic glasses studied thus far at hquid-hehurn temperature, the absolute value of Fh,, for a given guest molecule varies from tens of MHz to a few GHz The question whrch anses from these results is whether there exrsts a correlation between this large spread in values and the structure of the glasses used To answer this question, we first have to consider the relation between I',.,,,,., and the total holewidth, since the latter may be broadened by laser power, long burning times and/or heating effects [1,8,9,13] This subject wrll be discussed m detail m section 3 1 1. Secondly, only the guest and the host, without additional traces of solvent should be present m the sample. It is very hard m some mstances to get rid of a solvent used to introduce the guest into the polymeric host 1141 A study of the influence of traces of solvent on the value of rhom between 1.2 and 4.2 K wall be presented in section 3.1.2. Recent experiments performed by us on a series of alcohohc glasses have shown that there is a relation between I'l.,o, and the structure of these glasses For instance, r,,,.,, decreases wrth mcreasmg number of hydroxyl groups 496 0 009-2614/85/S 03.30 0 Elsevier Scrence Publishers B V.
Zeitschrift für Physikalische Chemie, 1975
The reaction kinetics of the dissociation equilibrium ROH + Aí± RO+ AH (ROH = 8-hydroxypyrene-l,3... more The reaction kinetics of the dissociation equilibrium ROH + Aí± RO+ AH (ROH = 8-hydroxypyrene-l,3,6-trisulphonic acid trisodium salt) has been studied by absorption spectroscopy following nanosecond laser excitation of ROH in aqueous solution for a series of neutral acids AH (maleic, acetic, phenylacetic, benzoic, formic, chloroacetic and bromoacetic acid). The rate constants for the weaker acids are proportional to their dissociation constants in agreement with the Bronsted theory of acid-base catalyzed reactions with the exponent 1; with increasing acidity a limiting value of 3.6 · 109 M-1 s_1 is reached, which is slightly smaller than the theoretical rate of a diffusion controlled reaction when no Coulomb forces are involved.
Proceedings of the National Academy of Sciences, 2000
We demonstrate by using low-temperature high-resolution spectroscopy that red-shifted mutants of ... more We demonstrate by using low-temperature high-resolution spectroscopy that red-shifted mutants of green fluorescent protein are photo-interconverted among three conformations and are, therefore, not photostable “one-color” systems as previously believed. From our experiments we have further derived the energy-level schemes governing the interconversion among the three forms. These results have significant implications for the molecular and cell biological applications of the green fluorescent protein family; for example, in fluorescence resonant energy transfer experiments, a change in “color” on irradiation may not necessarily be due to energy transfer but can also arise from a photo-induced conversion between conformers of the excited species.
The Journal of Chemical Physics, 1986
Optical dephasing in the S1←S0 0–0 transitions of organic guest molecules in semicrystalline poly... more Optical dephasing in the S1←S0 0–0 transitions of organic guest molecules in semicrystalline polyethylene hosts has been studied via hole burning from 0.3 to 4.2 K and compared to amorphous systems. In contrast to the latter, a temperature dependence of the homogeneous linewidth much steeper than T1.3 was found, which approaches that of crystalline materials and varies with the degree of crystallinity of the polymer. Parameters which fit the equations of specific theoretical models to the experimental data are calculated.
Chemical Physics Letters, 1981
Abstract Site-selection spectroscopy of free-base bacteriochlorin (7,8,17,18-tetrahydroporphin) i... more Abstract Site-selection spectroscopy of free-base bacteriochlorin (7,8,17,18-tetrahydroporphin) in n -hexane, n -octane and n -decane at 4.2 K are reported. The vibrational frequencies of the ground state, and first and second excited singlet states were determined from the fluorescence and excitation spectra. Low-frequency modes were observed, from which the angle of reorientation of the Molecule upon excitation is estimated (
Radiation Effects and Defects in Solids, 1991
Physical Review B, 1994
Persistent and time-resolved transient holes were burnt into the Dg E-H4 transition of Pr + and t... more Persistent and time-resolved transient holes were burnt into the Dg E-H4 transition of Pr + and the Do E-Fo transition of Eu + in silicate glasses. The holewidths were studied as a function of burning-Quence density, wavelength, and temperature between 0.4 and 12 K. Transient holes arising from optical pumping of ground-state nuclear hyperfine levels were found for both ions at T (3 K. Their lifetime decreases with increasing temperature. They are accompanied by symmetrically placed antiholes. For Eu +, two pairs of antiholes were found which are attributed to the two europium isotopes, Eu and Eu. For Pr +, an additional mechanism leading to persistent hole burning dominates above 3 K. The holewidth follows a T + dependence for Pr + and a T + dependence for Eu +. The temperature dependence is the same as that of the contribution of the two-level systems to the specific heat measured on the same samples and in the same temperature range. The quadrupole splittings of the Fo ground state and the crystal-field splittings of the Fq and F2 levels of Eu + as a function of excitation wavelength indicate that the strength of the noncubic component of the crystal field varies monotonically for excitation across the Dp M Fo absorption band, falling to zero at the long wavelength edge. The hole width shows a similar variation with excitation frequency. No inBuence of the experimental time scale on the hole width was detected for either sample between 10 and 10 s.
The Journal of Physical Chemistry B, 1999
Spectroscopic properties of the B820 and B777 subunits of the core light-harvesting complex LH1 o... more Spectroscopic properties of the B820 and B777 subunits of the core light-harvesting complex LH1 of purple bacteria Rhodospirillum rubrum G9 were studied by hole burning (HB) and fluorescence line narrowing (FLN) between 1.2 and 4.2 K. We have found that an equilibrium exists between the three forms B820, B777, and the native LH1-complex in the presence of the detergent n-octyl-D-glucopiranoside (OG). The shift of this equilibrium was followed as a function of OG concentration by means of absorption and fluorescence spectra. Low-frequency modes at 19 cm-1 for B820 and at 25 cm-1 for B777 were identified by FLN. From the spectral position of these modes as a function of excitation wavelength λ exc and from the homogeneous line width Γ′ hom as a function of λ exc , we conclude that "downhill" energy transfer does not take place either among B820 or among B777 subunits. The temperature dependence of Γ′ hom , however, indicates that optical dephasing and/or spectral diffusion does occur in these subunits. The positions of side holes and antiholes, furthermore, suggest that the hole-burning mechanisms in B820 and B777 are similar, although their HB efficiencies differ by a factor of 10.
Chemical Physics Letters, 1991
ABSTRACT
The Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1986
Journal of the Optical Society of America
Optics and Spectroscopy, 2005
Laser spectroscopic techniques at low temperature, such as fluorescence line-narrowing and hole b... more Laser spectroscopic techniques at low temperature, such as fluorescence line-narrowing and hole burning, enable an increase of spectral resolution by a factor of 10 3-10 5 compared to conventional spectroscopy at room temperature. With these methods, it is possible to retrieve a fingerprint of the species involved and to measure the rates of dynamic processes that normally remain hidden in the broad absorption bands. A few applications carried out in our laboratory will be discussed: (1) the determination of energy transfer rates in the peripheral LH2 complex of purple bacteria; (2) the study of spectral diffusion and its implications in three types of systems: (a) the B820 and B777 subunits of the LH1 complex of purple bacteria, (b) the photosystem II reaction center (PSII RC) and CP47 antenna complex of green plants, and (c) an organic glass doped with bacteriochlorophyll a ; (3) the unraveling of 0-0 transitions and the pathways of photoconversion between a number of conformations of the green fluorescent protein mutant S65T; (4) the measuring of electron-phonon coupling strengths in PSII RC and the red fluorescent protein DsRed; and (5) the determination and comparison of the homogeneous linewidths and optical dephasing in photosynthetic chromoprotein complexes and autofluorescent proteins.
Molecular Physics, 1976
It is known that the porphyrin free base (H 2 P) can be incorporated in an n -octane Shpol's... more It is known that the porphyrin free base (H 2 P) can be incorporated in an n -octane Shpol'skii matrix. In slowly grown crystals the solute molecules occur in two orientations, which are co-planar and have their NH HN axes at right angles; in the S 1 ↔ S 0 `quasi-line' absorption and ...
Journal of Luminescence, 1991
Photochemical hole-burning (PHB) experiments have been performed on two types of complex organic ... more Photochemical hole-burning (PHB) experiments have been performed on two types of complex organic systems. Results on the Q 0-0 transition of bacteriochlorophyll-a (BChI-a) in triethylamine (TEA) between 0.4 and 4.2 K, obtained with a diode laser at 780nm, show that the homogeneous line width, Thom, follows a Tls*oL dependence. Such a power law has been found for many organic glassy systems at low temperatures. The absolute value of 'hon~in a solution of water and detergent is almost one order of magnitude larger than in TEA, which suggests that energy transfer takes place between BChI-a molecules within a micelle. Holes burnt in the 800 nm band of the B800-850 antenna pigment-protein complex of purple bacteria Rhodobacter sphaeroides show no variation in hole width between 1.2 and 30 K. The results yield an energy transfer time of 2.3 ±0.4 ps between the aggregated BChl 800 and BChI 850 molecules. The same value is found for intact chromatophores at 1.2 K.
The Journal of Chemical Physics, 1980
Photochemical hole-burning has been used to study selective and reversible phototautomerism in ch... more Photochemical hole-burning has been used to study selective and reversible phototautomerism in chlorin (dihydroporphin) incorporated in matrices of n-hexane, n-octane, and n-decane at 4.2 K. The energy difference between the S1↔S0 transitions of the two forms, distinguished by the position of the two inner protons, is ∼1500 cm−1; the stable tautomer absorbing near 6350 Å. The back reaction from the less stable form to the stable one is 103 times faster than the forward reaction, and under wide band excitation in the Soret band a dynamic equilibrium exists between the two forms. Very narrow holes (∼40 MHz) can be burnt in the inhomogeneous lines of both tautomers. The width of these holes is consistent with a limit imposed by the fluorescence lifetime of 8 ns.
Chemical Physics Letters, 1987
ABSTRACT Zeeman shifts of the order of 10−4 to 10−3 of the inhomogeneous spectral linewidth have ... more ABSTRACT Zeeman shifts of the order of 10−4 to 10−3 of the inhomogeneous spectral linewidth have been observed in the 0-0 transition of free-base porphin embedded in amorphous polyethylene at 4.2 K by means of optical hole burning. From fits of the experimental results to calculated line shapes as a function of frequency and field strength, the value of the change in the magnetic susceptibility of the molecule in a magnetic field on excitation to the first excited singlet state, χz′,z′ = 60.6 MHz/T2, was determined. This is in good agreement with the value previously found for the same molecule in a crystalline host.
Spectroscopy of Biological Molecules: New Directions, 1999
The green fluorescent protein (GFP) has recently attracted great attention because it is the only... more The green fluorescent protein (GFP) has recently attracted great attention because it is the only cloned protein that exhibits strong fluorescence without any extraneous chromophores [1]. When fused to other proteins, it becomes a marker for gene expression and allows visualization of dynamic events inside living cells [2, 3]. Although the crystal structure of GFP has been solved [4], its photophysical properties remained puzzling. It was known that wild-type GFP in the ground state can exist in two forms, A (neutral) and B (anionic), and it was suggested [5] that a photoconversion from A to B involves an excited-state proton transfer, while an intermediate I-form, not identified in the spectra, was held responsible for the green fluorescence observed at 508 nm.
Chemical Physics Letters, 1981
Abstract Zeeman experiments are reported on the S 1 ← S 0 O-O transitions of chlorin (7,8-dihydro... more Abstract Zeeman experiments are reported on the S 1 ← S 0 O-O transitions of chlorin (7,8-dihydroporphin) and its photoisomer in an n -hexane crystal by photochemical hole burning at 4.2 K. The holes shift with a quadratic field dependence of -39.0 MHz/T 2 (chlorin) and −245.3 MHz/T 2 (photoisomer). For chlorin A = ¦ 1 ¦ L z ¦S 2 > ¦=4.5. Single-site absorption and fluo spectra are reported. PPP calculations were performed.
Chemical Physics Letters, 1982
The homogeneous hncwvrdth rho,,, oi the O-O S,-So IranjlIion oi ircc-baw porphm m saw31 orgamc gl... more The homogeneous hncwvrdth rho,,, oi the O-O S,-So IranjlIion oi ircc-baw porphm m saw31 orgamc glssscs 1135 been mcasurcd by photochcmwal holc-burmnp at 7 = I 1-Xl E. For 7 + 0 rhom cwapolatcs to IIIC hict~me-hrmtcd value. At T = i .2 K rhom = 180 hlHz m plyccrol. \\ tuch ts an order oi msgruludc lxgcr tlon m cryst31> rhom mcrcdscs 3s 7' 3=o ', tndcpcndcnt of the @ISS uud
Chemical Physics Letters, 1985
In the mqonty of the experiments done to determine homogeneous linewidths (Fhorr,) in amorphous o... more In the mqonty of the experiments done to determine homogeneous linewidths (Fhorr,) in amorphous orgamc solids at low temperatures, the hole-burning technique has been used. The holes are permanent (at least for many hours or days), and the burning mechanism mvolved may be erther photochemical [l-3] or non-photochemical (photophysrcal) [4,5] Until recently, however, the holewidths reported m the hterature for many of these systems [ 1,431 were orders of magmtude larger than m organic crystals [6], and theu temperature dependence was found m some cases to be proportronal to T2 [2], and lrnear rn others [s] In addition, residual linewidths for T + 0 of the order of 0 5-l cm-l (= lo4 MHz) were reported [2,5], mstead of the expected lifetime-limited values (~IFT~)-~ of the order of tens of MHz In contrast to these fmclings, we have shown that much narrower holes can be obtamed [3] and that Fhom follows a T 1 3 dependence [3,7,8] for many orgamc glasses Furthermore we observed that Fuo, mvarrably extrapolates to the hfetrme-lmuted value [7,8] and that some systems reach this value at T > 03 K [9] Srrmlar results regardmg the T dependence of Fho, have also been found by other groups with hole-burning [lo] , phosphorescence line-narrow-mg [ 1 l] and photonecho techmques [12] m drfferent amorphous systems Thus, it seems that T1-3 is charactenstic for relaxation m organic glasses at low temperatures and that it might be related to a fundamental property of disordered systems In all organic glasses studied thus far at hquid-hehurn temperature, the absolute value of Fh,, for a given guest molecule varies from tens of MHz to a few GHz The question whrch anses from these results is whether there exrsts a correlation between this large spread in values and the structure of the glasses used To answer this question, we first have to consider the relation between I',.,,,,., and the total holewidth, since the latter may be broadened by laser power, long burning times and/or heating effects [1,8,9,13] This subject wrll be discussed m detail m section 3 1 1. Secondly, only the guest and the host, without additional traces of solvent should be present m the sample. It is very hard m some mstances to get rid of a solvent used to introduce the guest into the polymeric host 1141 A study of the influence of traces of solvent on the value of rhom between 1.2 and 4.2 K wall be presented in section 3.1.2. Recent experiments performed by us on a series of alcohohc glasses have shown that there is a relation between I'l.,o, and the structure of these glasses For instance, r,,,.,, decreases wrth mcreasmg number of hydroxyl groups 496 0 009-2614/85/S 03.30 0 Elsevier Scrence Publishers B V.
Zeitschrift für Physikalische Chemie, 1975
The reaction kinetics of the dissociation equilibrium ROH + Aí± RO+ AH (ROH = 8-hydroxypyrene-l,3... more The reaction kinetics of the dissociation equilibrium ROH + Aí± RO+ AH (ROH = 8-hydroxypyrene-l,3,6-trisulphonic acid trisodium salt) has been studied by absorption spectroscopy following nanosecond laser excitation of ROH in aqueous solution for a series of neutral acids AH (maleic, acetic, phenylacetic, benzoic, formic, chloroacetic and bromoacetic acid). The rate constants for the weaker acids are proportional to their dissociation constants in agreement with the Bronsted theory of acid-base catalyzed reactions with the exponent 1; with increasing acidity a limiting value of 3.6 · 109 M-1 s_1 is reached, which is slightly smaller than the theoretical rate of a diffusion controlled reaction when no Coulomb forces are involved.
Proceedings of the National Academy of Sciences, 2000
We demonstrate by using low-temperature high-resolution spectroscopy that red-shifted mutants of ... more We demonstrate by using low-temperature high-resolution spectroscopy that red-shifted mutants of green fluorescent protein are photo-interconverted among three conformations and are, therefore, not photostable “one-color” systems as previously believed. From our experiments we have further derived the energy-level schemes governing the interconversion among the three forms. These results have significant implications for the molecular and cell biological applications of the green fluorescent protein family; for example, in fluorescence resonant energy transfer experiments, a change in “color” on irradiation may not necessarily be due to energy transfer but can also arise from a photo-induced conversion between conformers of the excited species.
The Journal of Chemical Physics, 1986
Optical dephasing in the S1←S0 0–0 transitions of organic guest molecules in semicrystalline poly... more Optical dephasing in the S1←S0 0–0 transitions of organic guest molecules in semicrystalline polyethylene hosts has been studied via hole burning from 0.3 to 4.2 K and compared to amorphous systems. In contrast to the latter, a temperature dependence of the homogeneous linewidth much steeper than T1.3 was found, which approaches that of crystalline materials and varies with the degree of crystallinity of the polymer. Parameters which fit the equations of specific theoretical models to the experimental data are calculated.
Chemical Physics Letters, 1981
Abstract Site-selection spectroscopy of free-base bacteriochlorin (7,8,17,18-tetrahydroporphin) i... more Abstract Site-selection spectroscopy of free-base bacteriochlorin (7,8,17,18-tetrahydroporphin) in n -hexane, n -octane and n -decane at 4.2 K are reported. The vibrational frequencies of the ground state, and first and second excited singlet states were determined from the fluorescence and excitation spectra. Low-frequency modes were observed, from which the angle of reorientation of the Molecule upon excitation is estimated (
Radiation Effects and Defects in Solids, 1991
Physical Review B, 1994
Persistent and time-resolved transient holes were burnt into the Dg E-H4 transition of Pr + and t... more Persistent and time-resolved transient holes were burnt into the Dg E-H4 transition of Pr + and the Do E-Fo transition of Eu + in silicate glasses. The holewidths were studied as a function of burning-Quence density, wavelength, and temperature between 0.4 and 12 K. Transient holes arising from optical pumping of ground-state nuclear hyperfine levels were found for both ions at T (3 K. Their lifetime decreases with increasing temperature. They are accompanied by symmetrically placed antiholes. For Eu +, two pairs of antiholes were found which are attributed to the two europium isotopes, Eu and Eu. For Pr +, an additional mechanism leading to persistent hole burning dominates above 3 K. The holewidth follows a T + dependence for Pr + and a T + dependence for Eu +. The temperature dependence is the same as that of the contribution of the two-level systems to the specific heat measured on the same samples and in the same temperature range. The quadrupole splittings of the Fo ground state and the crystal-field splittings of the Fq and F2 levels of Eu + as a function of excitation wavelength indicate that the strength of the noncubic component of the crystal field varies monotonically for excitation across the Dp M Fo absorption band, falling to zero at the long wavelength edge. The hole width shows a similar variation with excitation frequency. No inBuence of the experimental time scale on the hole width was detected for either sample between 10 and 10 s.
The Journal of Physical Chemistry B, 1999
Spectroscopic properties of the B820 and B777 subunits of the core light-harvesting complex LH1 o... more Spectroscopic properties of the B820 and B777 subunits of the core light-harvesting complex LH1 of purple bacteria Rhodospirillum rubrum G9 were studied by hole burning (HB) and fluorescence line narrowing (FLN) between 1.2 and 4.2 K. We have found that an equilibrium exists between the three forms B820, B777, and the native LH1-complex in the presence of the detergent n-octyl-D-glucopiranoside (OG). The shift of this equilibrium was followed as a function of OG concentration by means of absorption and fluorescence spectra. Low-frequency modes at 19 cm-1 for B820 and at 25 cm-1 for B777 were identified by FLN. From the spectral position of these modes as a function of excitation wavelength λ exc and from the homogeneous line width Γ′ hom as a function of λ exc , we conclude that "downhill" energy transfer does not take place either among B820 or among B777 subunits. The temperature dependence of Γ′ hom , however, indicates that optical dephasing and/or spectral diffusion does occur in these subunits. The positions of side holes and antiholes, furthermore, suggest that the hole-burning mechanisms in B820 and B777 are similar, although their HB efficiencies differ by a factor of 10.
Chemical Physics Letters, 1991
ABSTRACT
The Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1986
Journal of the Optical Society of America
Optics and Spectroscopy, 2005
Laser spectroscopic techniques at low temperature, such as fluorescence line-narrowing and hole b... more Laser spectroscopic techniques at low temperature, such as fluorescence line-narrowing and hole burning, enable an increase of spectral resolution by a factor of 10 3-10 5 compared to conventional spectroscopy at room temperature. With these methods, it is possible to retrieve a fingerprint of the species involved and to measure the rates of dynamic processes that normally remain hidden in the broad absorption bands. A few applications carried out in our laboratory will be discussed: (1) the determination of energy transfer rates in the peripheral LH2 complex of purple bacteria; (2) the study of spectral diffusion and its implications in three types of systems: (a) the B820 and B777 subunits of the LH1 complex of purple bacteria, (b) the photosystem II reaction center (PSII RC) and CP47 antenna complex of green plants, and (c) an organic glass doped with bacteriochlorophyll a ; (3) the unraveling of 0-0 transitions and the pathways of photoconversion between a number of conformations of the green fluorescent protein mutant S65T; (4) the measuring of electron-phonon coupling strengths in PSII RC and the red fluorescent protein DsRed; and (5) the determination and comparison of the homogeneous linewidths and optical dephasing in photosynthetic chromoprotein complexes and autofluorescent proteins.
Molecular Physics, 1976
It is known that the porphyrin free base (H 2 P) can be incorporated in an n -octane Shpol's... more It is known that the porphyrin free base (H 2 P) can be incorporated in an n -octane Shpol'skii matrix. In slowly grown crystals the solute molecules occur in two orientations, which are co-planar and have their NH HN axes at right angles; in the S 1 ↔ S 0 `quasi-line' absorption and ...
Journal of Luminescence, 1991
Photochemical hole-burning (PHB) experiments have been performed on two types of complex organic ... more Photochemical hole-burning (PHB) experiments have been performed on two types of complex organic systems. Results on the Q 0-0 transition of bacteriochlorophyll-a (BChI-a) in triethylamine (TEA) between 0.4 and 4.2 K, obtained with a diode laser at 780nm, show that the homogeneous line width, Thom, follows a Tls*oL dependence. Such a power law has been found for many organic glassy systems at low temperatures. The absolute value of 'hon~in a solution of water and detergent is almost one order of magnitude larger than in TEA, which suggests that energy transfer takes place between BChI-a molecules within a micelle. Holes burnt in the 800 nm band of the B800-850 antenna pigment-protein complex of purple bacteria Rhodobacter sphaeroides show no variation in hole width between 1.2 and 30 K. The results yield an energy transfer time of 2.3 ±0.4 ps between the aggregated BChl 800 and BChI 850 molecules. The same value is found for intact chromatophores at 1.2 K.