H. van der Laan’s research while affiliated with Leiden University and other places

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Publications (13)


Excited-state dynamics of mutated antenna complexes of purple bacteria studied by hole-burning
  • Article

September 1993

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19 Reads

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45 Citations

Chemical Physics Letters

H. van der Laan

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Th. Schmidt

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S. Völker

Absorption and fluorescence excitation spectra of various LH2 antenna complexes of two purple bacteria at low temperature (1.2 and 4.2 K) have been measured, and energy transfer rates within these complexes have been determined by spectra hole-burning. The systems studied were membranes of a wild-type strain of Rhodobacter sphaeroides, membrane samples from four LH2-only strains containing specifically mutated LH2 complexes of the same bacterium, and the isolated B800–820 complex of Rhodopseudomonas acidophila (strain 7050). The mutants exhibit blue-shifted B850 absorption bands with their spectral positions depending on the specific amino acid residues replaced in the α-polypeptide sequence. Energy transfer rates from B800 to B850 (or to their respectively blue-shifted bands) have been obtained by hole-burning experiments in the B800 band. The mutants of Rb. sphaeroides and the LH2 complex of Rps. acidophila yielded transfer times similar to those of the B800–850 complex of Rb. sphaeroides. These values, which for the various complexes vary between 1.7 and 2.5 ps in the wavelength region from 798 to 805 nm, do not decrease monotonically with the spectral distance between the bands. Various models based on Förster's energy transfer mechanism are discussed, of which only one is consistent with the results. In this model the energy is assumed to be transferred not directly from the Qy 0-0 band of B800 to that of the (blue-shifted) B850, but indirectly through the excitation of a vibrational mode.


(a) Experimental setup for permanent hole-burning with a temperature- and current-controlled single-mode diode laser. M’s, mirrors; T-contr., temperature control; I-contr., current control; P, Peltier element; FP, Fabry–Perot interferometer (FSR = 1.5 GHz); HV, high voltage for the photomultiplier (PM); L’s, lenses; F, color filters; BS’s, beam splitters; OD, neutral-density filter; PC, personal computer; ADC, analog-to-digital converter; DAC, digital-to-analog converter. (b) Example of a hole burned with the diode laser at ∼780 nm in BChl a in TEA at 1.2 K.
(a) Wavelength λ of the single-mode diode laser as a function of temperature T measured at constant laser power (P = 1.13 mW). (b) Change in frequency of the single-mode diode laser Δν as a function of injection current I at constant temperature (T = 18.3°C).
Determination of the single-mode diode laser linewidth Γlaser with a Fabry–Perot interferometer FP (FSR = 1.5 GHz). Measured linewidth Γmeas as a function of the inverse of the laser output power P. Γlaser ≈ 45 MHz was obtained as the difference between Γmeas at an average output power used in the experiments and the width ΓFP (see text).
Absorption (solid curve) and fluorescence (dashed curve) spectra of BChl a in TEA at 4.2 K. The maximum of the S1 ← S0 0–0 (Qy) transition lies at ∼775 nm, the wavelength region of the diode laser. Notice that the Qx transition has two peaks (see text). The spectrum of the Soret band at the left was taken at room temperature. Inset: bacteriochlorophyll a and triethylamine.
Site-selected fluorescence spectra of BChl a in various glasses at 4.2 K, excited at 716 nm. Notice the loss of sharpness in the peaks when going from TEA to 0.1% LDAO:water (see text).

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Permanent hole burning with a diode laser: excited-state dynamics of bacteriochlorophyll in glasses and micelles
  • Article
  • Publisher preview available

June 1992

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7 Reads

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29 Citations

A temperature- and current-controlled diode laser at ∼780 nm was used to perform permanent hole-burning experiments on the S1 ← S0 0–0 (Qy) transition of bacteriochlorophyll a (BChl a) in amorphous hosts. Hole widths were obtained for the glass triethylamine (TEA) between 0.4 and 15 K, for micelles of the detergent lauryldimethylamine N-oxide (LDAO) between 1.2 and 4.2 K, and for wet and dry CCl4 at 1.2 K. The homogeneous linewidth, Γhom, of BChl a in TEA follows a T1.3±0.1 dependence at temperatures T < 7 K, whereas at T ≈ 7 K a crossover to an exponential dependence with an activation energy of 33 ± 3 cm⁻¹ is observed. The results, when compared with those obtained for free-base porphin in the same glass, suggest that a low-frequency mode of TEA is responsible for the dephasing. From the experiments on micelles conclusions are drawn about the molecular conformations of BChl a in the detergent.

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Picosecond Energy Transfer in Genetically Modified Photosynthetic Antenna Complexes Studied by Hole-Burning.

January 1992

Information on dynamic guest-host interactions is contained in the homogeneous linewidth Γ hom [1]: where T 1 represents the population decay time of the excited state, and T 2 * the pure dephasing time determined by thermally induced fluctuations of the optical transition frequency. The first term includes all de-excitation steps, i.e. direct de-excitation to the ground state and energy transfer processes from the excited state. If energy transfer does not occur, then T 2 * usually dominates, since T 1 ≫ T 2 * . This is the case for most organic molecules doped in glasses and polymers [1] and some biological model systems at low temperature [2]. By contrast, for many pigment-protein complexes Γ hom is principally given by population decay, thus T 1 ≪ T 2 * [3].


Energy transfer and dynamics of photosynthetic antenna complexes and biological model systems: A study by photochemical hole-burning

February 1991

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3 Reads

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2 Citations

Journal of Luminescence

Photochemical hole-burning (PHB) experiments have been performed on two types of complex organic systems. Results on the Qy O-O transition of bacteriochlorophyll-a (BChl-a) in triethylamine (TEA) between 0.4 and 4.2 K, obtained with a diode laser at 780 nm, show that the homogeneous line width, Γhom, follows a T1.3±0.1 dependence. Such a power law has been found for many organic glassy systems at low temperatures. The absolute value of Γhom 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 BChl-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 BChl 850 molecules. The same value is found for intact chromatophores at 1.2 K.


Energy transfer in the B800–850 antenna complex of purple bacteria Rhodobacter sphaeroides: A study by spectral hole-burning

July 1990

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7 Reads

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136 Citations

Chemical Physics Letters

The energy-transfer process within the isolated B800–850 pigment-protein complex of the purple bacterium Rhodobacter sphaeroides has been studied by means of spectral hole-burning. The band at 800 nm is inhomogeneously broadened because holes could be burnt into it. The widths of these permanent holes are independent of wavelength and temperature between 1.2 and 30 K. The BChl 800→BChl 850 energy-transfer time deduced from these widths is 2.3±0.4 ps for the isolated complex, and also for chromatophores at 1.2 K.


photosynthetic antenna complexes and reaction centers.
Photoreactive Disordered Systems Studied by Permanent and Transient Hole-Burning

January 1990

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51 Reads

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4 Citations

Molecular Crystals and Liquid Crystals

Permanent and transient hole-burning experiments carried out on various types of amorphous systems at temperatures between 0.3 and 20 K are presented. Optical dephasing on organic molecules in glasses and polymers measured on different time scales are discussed in relation to spectral diffusion processes and compared to the literature. The pure dephasing time appears to be proportional to the excited state lifetime of the guest. Organic molecules adsorbed on the surface of porous silica glass show that their homogeneous linewidth is an order of magnitude larger than in polymers and glasses in the bulk, but follows the same temperature dependence. Hole-burning results on bacteriochlorophyll in various disordered hosts are compared to those on a isolated light-harvesting photosynthetic pigment-protein complex (B800–850). From the holewidth in the latter the energy transfer rate between aggregated bacteriochlorophyll pigments is determined and compared to time-resolved spectroscopy results in the literature.


The effects of quaternary ammonium chloride (alpha C12 DME AHCl) on enamel hardness and mineral loss under intra oral cariogenicity test conditions

April 1988

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11 Reads

Journal de Biologie Buccale

The effects of a quaternary ammonium compound; 2-hydroxy-ethyl-2-hydroxydodecyl-dimethyl-ammonium chloride (alpha C12 DMEAHCl) on enamel hardness and mineral loss in enamel slabs were studied under intra-oral cariogenicity test conditions. The quaternary ammonium compound without fluoride reduced enamel softening as well as the mineral loss from enamel significantly up to a depth of 100 microns from the surface. Moreover the Ca/P molar ratio of the treated enamel was comparable to untreated enamel controls. These findings suggest that the quaternary ammonium compound itself inhibits mainly demineralisation rather than remineralization under intra-oral cariogenicity test conditions.


Magnetic field effects in doped amorphous solids studied by optical hole-burning

February 1988

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3 Reads

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1 Citation

Journal of Luminescence

Zeeman shifts of the order of 10-4-10-3 of the inhomogeneous spectral linewidths have been observed in the 0-0 transition of free-base porphin dissolved in amorphous polyethylene at 4.2 K by means of hole-burning. The value of the magnetic susceptibility,, was determined, in good agreement with that found in a crystalline host. Thus quantitative information on magneto-optical properties of excited states of complex molecules can be extracted from disordered materials with a resolution in the MHz-regime.


The Milli-Jansky Radio Galaxies

January 1988

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2 Reads

The study of radio source populations is a long term programme at Leiden Observatory, based primarily on surveys with the Westerbork Synthesis Radio Telescope. The first two references1) 2) and literature cited therein provide the overview of what was achieved since the early seventies. Oort’s thesis4) is the fourth one in this context and it enters new domains in terms of flux density range and angular size limits for statistically large samples.


Zeeman effects in amorphous solids: A hole-burning study of free-base porphin in polyethylene

December 1987

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3 Reads

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11 Citations

Chemical Physics Letters

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.


Citations (3)


... Summarizing, we conclude that an apparent agreement between the data and the weak-coupling limit predictions does not prove a real weak coupling with a single QLM (as has been previously assumed [26,27,60,61]). The evidence based on the agreement between the experimental data and Eq. (16) is illusive, and the generally accepted approach to the ZPL broadening based on perturbative expressions should be reconsidered. ...

Reference:

Key role of chromophore-modified vibrational modes on thermal broadening of single-molecule spectra in disordered solids
Permanent hole burning with a diode laser: excited-state dynamics of bacteriochlorophyll in glasses and micelles

... Since the electronic excitations of the B800 molecules are rather localized on a small part of the structure, these molecules have been exploited as local probes, to monitor the dynamics of the protein in their local environment [22,[38][39][40][41][42]. The character of the delocalized B850 excitations are strongly influenced by the intermolecular interactions between the BChl a molecules and, therefore, provide information about the mutual arrangement of the chromophores. ...

Excited-state dynamics of mutated antenna complexes of purple bacteria studied by hole-burning
  • Citing Article
  • September 1993

Chemical Physics Letters

... The B850 band has a higher lying set of excited states known as B850* that absorb near 800 nm, overlapping with the B800 band. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The overall bandwidth of the B850 excitons has been shown to extend from $760 nm to $865 nm at low temperatures. 7 The absorption spectra of these LH2 bands can be seen in Fig. 1B. ...

Energy transfer in the B800–850 antenna complex of purple bacteria Rhodobacter sphaeroides: A study by spectral hole-burning
  • Citing Article
  • July 1990

Chemical Physics Letters