Tjeerd Schaafsma

• Ph.D.
• Professor at Wageningen University & Research

historic novel (in Dutch)

Abstract A system is described for the photo-induced biocatalytic reduction of enoates in reversed micelles composed of detergent, buffer and mixtures of alcohol and octane as cosurfactant and dispersant respectively. The photosystem consisted of the sacrificial electron donor tributylamine, Zn(II) meso-mono(4-N-decyipyridyl)-tri(phenyl)porphyrin a...

The electron spin polarization (ESP) pattern of the donor-triplet state (PR) of reaction centers (RC's) of the purple bacterium Rhodobacter (formerly Rhodopseudomonas) sphaeroides R-26 was investigated. δm =±1 triplet EPR spectra were recorded of unmodified RC's as well as of RC's from which Fe2+ or ubiquinone was removed, or ubiquinone was substit...

In this paper a discussion is given of the effect of molecular rotation on the E.S.R. spectrum of the NO2 radical embedded in a polycrystalline host matrix of N2O4. The phenomenon is only observed if the host matrix containing the radical is properly annealed and slowly cooled to 77°k. Computer simulation of the spectrum shows unambiguously that in...

The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in 5-25-nm-thick films spin-coated onto quartz slides have been investigated by optical spectroscopy. Analysis of the polarized absorption spectra using a dipole-dipole exciton model with two mutually perpendicular transition dipole moments per molecule s...

Exciton diffusion has been studied in 5-25-nm-thick films of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides by intentional doping with quenchers using steady-state as well as time-resolved fluorescence spectroscopy. The fluorescence spectra of the films are very similar to those of solutions, indicating emission from l...

Fluorescence detected magnetic resonance (FDMR) has been applied to approximately 25-nm-thick porphyrin films, containing ordered domains of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides. Illuminating the films at 1.4 K with 457.9-nm light from a continuous wave Ar(+) laser produces at least two different, Jahn-Teller...

Enoate reductase (EC 1.3.1.31) can stereospecificially reduce a variety of α,β‐unsaturated carboxylates. Its use was extended to apolar media by incorporating the enzyme into a reversed micellar medium. The kinetics of the enzyme in such a medium have been investigated using 2‐methylbutenoic acid as substrate and NADH as a cofactor and compared wit...

The photophysical properties of thin films of Zn-monopyridyltriphenylporphyrin (Zn(4-Py)TrPP) obtained by the method of centrifugation on a quartz film substrate have been investigated. The results of the analysis of the measured excitation and luminescence spectra and also of the kinetic curves of fluorescence depolarization, as they decay, of the...

The effect of osmotic stress (−0.35 MPa) on the cell water balance and apical growth was studied non‐invasively for maize (Zea mays L., cv. LG 11) and pearl millet (Pennisetum americanum L., cv. MH 179) by 1H NMR microscopy in combination with water uptake measurements. Single parameter images of the water content and the transverse relaxation time...

First published as an Advance Article on the web 20th September 2001 Host–guest composites with photonic antenna properties are described. The material consists of cylindrical zeolite L crystals the channels of which are filled with chains of joined but electronically non-interacting dye molecules. Light shining on a crystal is first absorbed and t...

Excited-state kinetics of complexes of a functionalized zinc tetraphenylporphyrin (ZnTPP) derivative, zinc mono(4-pyridyl)triphenylporphyrin (ZnPyP) in toluene and polystyrene/toluene mixtures have been investigated by time-resolved fluorescence spectroscopy. In addition to the ~2.0 ns monomer fluorescence lifetime, a 1.5 ns component was found by...

Aggregation of zinc mono-(4-pyridyl)-triphenylporphyrin (ZnPyP) in toluene and polystyrene/toluene mixtures has been investigated by steady-state optical spectroscopy. The Q-band absorption spectra, as well as the fluorescence spectra, show a temperature-dependent red shift as a result of ligation of the porphyrin zinc center. The smallest aggregat...

An improved application is presented of the Monte Carlo method including simultaneous parameter fitting to analyze the experimental time-resolved fluorescence and fluorescence anisotropy decay of two organized molecular systems exhibiting a number of different, nonisotropic energy transfer processes. Using physical models and parameter fitting for...

Energy transfer in thin films of zinc tetra(-octylphenyl)-porphyrin (ZnTOPP) doped with the copper (CuTOPP) or free-base (H2TOPP) analogues were investigated by time-resolved fluorescence and Monte Carlo simulations, applied to a single domain model of parallel porphyrin stacks. Rate constants for intra- and inter-stack energy transfer are (0.8–1.1...

Ground- and excited-state absorption and fluorescence properties of three free base porphyrins with graded degrees of a macrocycle distortion have been studied. The different degrees of nonplanarity were introduced by successive addition of ethyl groups at the β-pyrrole positions of free base 5,10,15,20-tetraphenylporphyrin (H2TPP):  from four ethy...

The effects of increasing concentration (10-7-2.5 x 10-3 mol/g) of Erythrosin B (Ery B) in poly(vinyl alcohol) films on its visible absorption spectrum have been investigated. In a concentration range of 2 x 10-7-10-5 mol/g, no effects on the absorption spectrum are found. By contrast, within this concentration range, time-resolved fluorescence exp...

This paper describes the absorbance properties of pigments in disordered films. The fluorescence quenching of pigment systems at low concentrations are usually attributed to the presence of so-called statistical pairs. We show that, if line broadening mechanisms are taken into account such as homogeneous and inhomogeneous broadening and statistical...

The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by differential scanning calorimetry and Polarized Optical Microscopy. The occurrence of multiple phase transitions indicates several crystalline and several liquid crystalline phases. The liquid crystalline phases display high structural ordering in all three...

The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by differential scanning calorimetry and polarized optical microscopy. The occurrence of multiple phase transitions indicates several crystalline and several liquid crystalline phases. X-ray diffraction measurements show that the liquid crystalline phases displ...

The photophysical properties of the lowest excited singlet states, S1(π,π*), of two porphyrin diacids have been investigated. The diacids are H4TPP2+ and H4OEP2+, the diprotonated forms of free base tetraphenylporphyrin (H2TPP) and octaethylporphyrin (H2OEP), respectively. Both diacids exhibit perturbed static and dynamic characteristics relative t...

The photophysical properties of the lowest excited singlet states, S1(,*), of two porphyrin diacids have been investigated. The diacids are H4TPP2 and H4OEP2 , the diprotonated forms of free base tetraphenylporphyrin (H2TPP) and octaethylporphyrin (H2OEP), respectively. Both diacids exhibit perturbed static and dynamic characteristics relative to t...

Photoelectrochemical cells have been constructed by depositing monolayers of oriented covalently linked zinc/free base porphyrin heterodimers onto ~30 nm nonporous layers of TiO2 on ITO, deposited by metal-organic chemical vapor deposition (MO-CVD), and onto ~100 nm porous, nanostructured TiO2 layers, spin-coated from a suspension of P25 (Degussa)...

Results of investigation of the optical properties of zinc complexes of mesotetraphenylporphyrin and monopyridyltriphenylporphyrin in impurity-free organic solvent are presented. Analyses of absorption and emission spectra and fluoresence decay kinetics in terms of both a sum of exponentials and using simulation of energy-transformation processes i...

Experimental and calculated absorption spectra are compared for four different porphyrin dimers covalently linked by alkyl- or phenyl bridges. The spectra of the corresponding monomers were used as a reference to determine the experimental exciton,ic shift(s) of the absorption spectrum in the Soret region. The excitonic interaction was calculated u...

Experimental and calculated absorption spectra are compared for four different porphyrin dimers covalently linked by alkyl- or phenyl bridges. The spectra of the corresponding monomers were used as a reference to determine the experimental excitonic shift(s) of the absorption spectrum in the Soret region. The excitonic interaction was calculated us...

Free base 5,10,15,20-tetrakis(4-n-octylphenyl) porphyrin (H{sub 2}TOPP) belongs to a class of self-organizing porphyrins. Since its LUMO lies above the conduction band of titanium dioxide (TiO{sub 2}) and its visible light absorption is very strong, sensitization of TiO{sub 2} with H{sub 2}TOPP thin films is possible. After spin-coating this porphy...

In the present work we study the spectral and photophysical properties of a relatively simple porphyrin system with an electron-withdrawing substituent, namely 2-nitro-5, 10, 15, 20-tetraphenylporphyrin (H2TPP-NO2). Similar β-nitro-substituted tetraaryl-porphyrins have been studied recently in [1–4], for which unusual fluorescence properties were r...

The study of optical properties of films of porphyrin-like compounds has gained much interest in the past decade because of their potential application in photovoltaic cells. Since a couple of years the possibilities to construct a completely solid state solar cell by sensitizing semi-conductors with porphyrins have been investigated [1].

The mean free path length for excitons was determined in flat organic dye films. From simulations of the photocurrent response of solar cells, consisting of n-type perylene tetracarboxy diimide and a p-type organic dye, we found an exciton diffusion length of 30±10 nm for zinc phthalocyanine (ZnPc), and 7±3 nm for zinctetra-(octylphenyl)-porphyrin...

2-NO2-5,10,15,20-tetraphenylporphyrin (H2TPP-NO2) is shown to exist in solution as an equilibrium mixture of two NH tautomers with different spectral and photophysical properties. At 77 K in a rigid glass solution the fluorescence spectra of the tautomers contain two well-resolved narrow bands that are slightly (similar to 300 cm(-1)) Stokes-shifte...

Charge carrier photogeneration in solid porphyrin films was investigated using optical and photocurrent action spectroscopy. In electropolymerized DA porphyrin films on ITO, acting as photo diodes, unidirectional charge separation occurs within interfacial heterodimers if Ed,a(S1)-Ect in solution is sufficiently large. In covalent porphyrin dimers...

Fluorescence detected magnetic resonance (FDMR) was used to study the lowest triplet state of bacteriochlorophylls (BChls) c and d in Chlorobium (Chl.) tepidum and Chl. vibrioforme, respectively. These pigments were studied both in the oligomeric form (in whole cells) and in the monomeric form (after conversion using a 1% 1-hexanol treatment). Fluo...

Using impedance spectroscopy, the formation of a depletion layer is demonstrated upon contacting two films of different types of porphyrins. This depletion layer can be described in the same way as in a conventional p/n heterojunction of inorganic semiconductors. From Mott-Schottky plots the doping concentration is found to be ≈1017 cm-3 for electr...

Fluorescence detected magnetic resonance (FDMR) spectra detected at 596 nm of zinc-substituted hemoglobins at 4.2 K show a split D-E transition, which is not observed for zinc protoporphyrins ligated by methylimidazole in glasses. Incorporation of the zinc heme into the globin pocket is also accompanied by a blue shift of the fluorescence of 20 nm...

Hydroxyphenyl-substituted metalloporphyrins have been electropolymerized as films onto ITO substrates. An ether bond between the phenyl rings of two monomers links the porphyrin units, leaving the porphyrin macrocycles undisturbed. During electrochemical oxidation of the films using a 0.0-0.9 V potential window, a single, semireversible reaction is...

Using impedance spectroscopy, the formation of a depletion layer is demonstrated upon contacting two films of different types of porphyrins. This depletion layer can be described in the same way as in a conventional p/n heterojunction of inorganic semiconductors. From Mott-Schottky plots the doping concentration is found to be ≈ 1017 cm-3 for elect...

Electropolymerized porphyrin films on indium–tin–oxide substrates have been characterized using Rutherford backscattering spectrometry, absorption spectroscopy, electrical characterization methods and with step profiling. With these methods the density of the films (ρ=1.35 g/cm³) and the absorption coefficients α(λ) have been determined....

Free base methyl pyridinium porphyrins were adsorbed on microscope glass slides, quartz plates or silicon wafers from a borate buffer solution at pH 10. Adsorption of the porphyrins is strongly enhanced by electrostatic interaction of the positively charged methyl pyridium side groups with the SiO surface groups. Using UV-visible absorption spectro...

Porphyrin organic dye layers on oxidic surfaces may play a key role in the light absorption and charge separation of organic solar cells. We report a study of the adsorption characteristics of positively charged porphyrins from an aqueous solution onto soda lime glass. Advanced surface analytical techniques (RBS, ERD and XPS) have been employed to...

Organic heterojunctions made by deposition of two different types of porphyrins onto an ITO substrate by electro-polymerisation and spin-coating exhibit rectification upon illumination. The redoxpotentials for the various porphyrin D/A combinations can be varied by using different porphyrin metal centers. Different exothermicities for photo-induced...

The deposition of a fourfold positively charged tetrakis(4-methyl pyridinium) porphyrin (H2TMPyP) and its metal derivatives on glass surfaces from basic aqueous solutions has been studied by optical and ion beam techniques. Upon exposure to a buffered porphyrin solution, the glass surface is initially almost completely coated with a monomolecular p...

The factors determining the performance of organic solar cells of the porphyrin sandwich type are investigated, both with flat and structured substrates. The focus is on the construction of and the photo physical processes in the various constituent parts of such cells: the interfaces between the photo-active organic dye layer and an oxidic semicon...

The fluorescent properties of the cationic free base tetrakis (4-N-methylpyridyl)porphyrin (H(2)TMPyP(4)) in aqueous solution have been the subject of considerable discussion. Conclusions by various authors on the presence of home-aggregation of H(2)TMPyP in these solutions are contradictory. The present work reports spectroscopic data for three is...

The fluorescent properties of the cationic free base tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP(4)) in aqueous solution have been the subject of considerable discussion. Conclusions by various authors on the presence of homo-aggregation of H2TMPyP in these solutions are contradictory. The present work reports spectroscopic data for three isomers...

Fluorescence Detected Magnetic Resonance (FDMR) spectra have been measured for whole cells and isolated chlorosomal fractions for the green photosyntheic bacteria Chlorobium phaeobacteroides (containing bacteriochlorophyll e, and isorenieratene as major carotenoid) and Chlorobium limicola (containing bacteriochlorophyll c, and chlorobactene as majo...

A portable 1H NMR spectrometer has been applied to whole plants in situ, i.e. in climate rooms and in a greenhouse, to study plant water relations under these conditions. The spectrometer consists of a 30 kg permanent magnet system of 0.235 T, modified Bruker Minispec electronics, and a standard XT pc for spectrometer control. Unattended, the syste...

Photoinduced charge separation was studied in a variety of microemulsions. The photosystem consisted of a porphyrin equipped with a hexadecyl chain, methylviologen as the electron acceptor and tributylamine as an irreversible electron donor. The cetyltrimethylammonium bromide (CTAB) based microemulsions were varied with respect to the alkyl chain o...

The Photosystem I reaction centre protein CP1, isolated from barley using polyacrylamide gel electrophoresis showed an EPR (Electron Paramgnetic Resonance) spectrum with the polarisation pattern AEEAAE, typical of the primary donor triplet state (3)P700, created via radical pair formation and recombination. (3)P700 could also be detected by Fluores...

The acceptor QA of PS II was doubly reduced by treatment of PS II-enriched membranes (200–300 chlorophylls per PS II-reaction centre) with dithionite and benzyl viologen. After double reduction of QA, two major differences appeared in the fluorescence decay kinetics (at 4′C), as compared to the situation with all QA singly reduced: (1) a dominant f...

NMR and MRI have been applied to transport processes, that is, net flow and diffusion/perfusion, of water in whole plants, cells, and porous materials. By choosing proper time windows and pulse sequences, magnetic resonance imaging can be made selective for each of the two transport processes. For porous media and plant cells the evolution of the s...

Picosecond as well as femtosecond transient absorption measurements have been performed on eight water-soluble heterodimers consisting of combinations of oppositely charged free base and metal porphyrins which have been electrochemically characterized. The ultrafast non-exponential absorption increase, attributed to solvent-controlled, intradimer c...

It is shown that electron spin polarization can be used to probe the anisotropy of singlet-triplet interconversion of radical pairs involved in photosynthetic charge separation. Anisotropic polarization may be observed with non-oriented reaction centres, provided an anisotropic interaction (e.g. zero-field splitting or g-tensor anisotropy) produces...

Förster-type energy transfer (ET) in solutions containing rhodamine 6G and zinc-tetraphenylporphyrin has been studied using zero-field optically detected magnetic resonance (ODMR). Transitions between the porphyrin triplet sublevels monitored via the rhodamine (donor) fluorescence have the opposite sign as compared to those detected via the porphyr...

The photosystem II (PSII) reaction centre (rc) can be isolated in a purified form containing only about 4–5 chlorophyll (chl) a per cyt b559, bound to a D1/D2 polypeptide heterodimer (1). This preparation does not evolve O2, but still has a secondary acceptor, probably D.On the acceptor side there are two pheophytins, but no quinone acceptors, and...

In the literature measurements of kinetic data of enzymes in reversed micelles have been interpreted in two ways. In the first, all enzyme parameters are expressed with respect to the total volume of the reversed micellar solution. In the second, the enzymatic conversion is related only to the fraction of the volume consisting of aqueous solution (...

Enoate reductase (EC 1.3.1.31) can stereospecifically reduce a variety of alpha,beta-unsaturated carboxylates. Its use was extended to apolar media by incorporating the enzyme into a reversed micellar medium. The kinetics of the enzyme in such a medium have been investigated using 2-methylbutenoic acid as substrate and NADH as a cofactor and compar...

High resolution (h.r.) 13C NMR is increasingly applied to studies of carbohydrate metabolism in plant cells and tissues, as an analytical technique allowing non-invasive observation of endogenous intermediates and end products in intact biomass (1). One of the major advantages of h.r. 13C NMR apart from being non-destructive is its high spectral re...

In the literature measurements of kinetic data of enzymes in reversed micelles have been interpreted in two ways. In the first, all enzyme parameters are expressed with respect to the total volume of the reversed micellar solution. In the second, the enzymatic conversion is related only to the fraction of the volume consisting of aqueous solution (...

500 MHz 1H NMR spectra were obtained of solutions containing oligomeric and monomeric forms of Chl a/b-P2, the major light-harvesting chlorophyll a/b-protein complex of photosystem II, isolated from thylakoid membranes of barley (Hordeum vulgare). Oligomers showed only a broad unresolved spectrum, but for monomers several downfield-shifted chloroph...

Primary photochemical processes in photosystem II (PSII) — energy transfer and charge separation — can be best studied free from possible interference from photosystem I (PSI), by separating the photosystems using biochemical techniques or by the use of mutants of plants which specifically lack PSI. The use of surfactants necessary for the preparat...

The uptake and utilization of sucrose by embryogenic suspension cultures of carrot (Daucus carota L.) growing in the presence of 2,4-D and by somatic embryos derived from these cultures was monitored using (13)C nuclear magnetic resonance. The exogeneously supplied sucrose was completely hydrolyzed before cell entry; glucose was taken up preferenti...

An explanation is proposed for the electron spin polarization pattern in the ΔmS = ± 1 EPR spectrum of the donor triplet state in pre-reduced Rhodopseudomonas viridis reaction centres at temperatures above 20 K. Calculations based on a simple model of the reaction centre indicate that rapid spin-lattice relaxation of the iron-semiquinone complex (Q...

The EPR transients in the three canonical transitions of the Δm = ± 1 triplet spectrum of Rhodopseudomonas viridis RC's have been measured following a 10 ns laser-flash. At microsecond time-resolution, the initial amplitude of these transitions at 100 K is inverted for the Y peaks, zero for the Z peaks, and not affected (thus firmly emissively pola...

Dimeso-substituted octaalkylporphyrins, carrying an (arylsulfonyl)oxy group at the ortho position of the two (meso) phenyl groups, were synthesized from dipyrrolylmethanes and aldehydes. On account of a 1H NMR upfield shift in CDCl 3 solution of 2-5 ppm for the aryl protons, a folded conformation is assumed in which the substituted aryl groups lie...

Intramolecular electron transfer has been investigated for three diphenyletioporphyrins covalently linked to an anthraquinone via a sulfonyloxy bridge at the ortho, meta or para substitution position of the phenyl groups of the porphyrin. The ortho-linked porphyrin is strongly folded and exhibits extremely fast charge separation (CS) and recombinat...

Nuclear magnetic resonance (NMR) was used to investigate the effects of changes in root temperature, of changes in the area of root in contact with culture solution and of day/night rhythm on the water balance of a cucumber and a gherkin plant. Results are discussed in terms of water potential, flow rate and resistance using a previously presented...

CPl, the isolated reaction centre (RC) chlorophyll(chl)-protein of plant photosystem I(PSI) containing P700 and ca. 40 antenna Chl has been isolated using sodium dodecyl sulphate and gel electrophoresis. It retained the triplet e.s.r. polarisation pattern characteristic of active charge separation and recombination. Low-temperature and time-resolve...

The aggregation of the water-soluble porphyrins tetra(4-carboxyphenyl)porphyrin free base (H2TPPC), tetra(4-N-methylpyridyl)porphyrin free base (H2TMPyP) and their zinc derivatives (ZnTPPC and ZnTMPyP) was studied by 1H NMR and optical absorption spectroscopy. In the solvent H2OCH3OH (4:1), mixing of the anionic H2TPPC or ZnTPPC with the cationic H...

The triplet state of 5,15-diphenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin was investigated at 4.2 K by fluorescence-detected magnetic resonance (FDMR). Two clearly distinct sites (site I: D=462 × 10−4 cm−1 and E=20 × 10−4 cm−1; site II: D=442 × 10−4 cm−1 and E=16 × 10−4 cm−1) can be distinguished in a solid octane matrix. The triplet-s...

In this paper we demonstrate the study of plant water balance by the non-invasive measurement of tissue water content and water flow using proton nuclear magnetic resonance (NMR). Sap velocity and flux were measured independently in the presence of an excess of stationary tissue water. The instrumentation described allows automated and unattended m...

The solution structures of dimers consisting of negatively charged Zn[tetra(4-carboxyphenyl)porphyrin], ZnTPPC, with positively charged Zn[tetra(4-N-methylpyridyl)porphyrin], ZnTMPyP, and with H2[tetra(4-N-methylpyridyl)porphyrin], H2TMPyP, were determined by 1H NMR ring current shifts. The conformation is not affected by the presence of the metal...

Charge-separation in synthetic donor-pigment-acceptor (DPA) compounds and concentration dimers of porphyrins was investigated by fluorescence quenching, EPR-spectroscopy and picosecond optical absorption spectroscopy.

The excited-state properties of heterodimers oftetra(4-carboxyphenyl)porphyrin (TPPC) and tetra(N-methylpyridyl) porphyrin (TMPyP) are studied by absorption and emission spectroscopy, EPR and zero-field ODMR. The excited singlet and triplet states of dimers formed by pairing H2TPPC with H2TMPyP or ZnTMPyP are localized on H2TPPC. The dimers formed...

The hypothesis [(1986) Photobiochem. Photobiophys. 11, 95-100] that the temperature dependence of the electron spin polarization (ESP) pattern of the Δm = ± 1 EPR spectrum of the triplet state PR of the Rhodopseudomonas viridis reaction center is caused by magnetic interaction between the reduced menaquinone-iron complex Q−Fe2+ and the electron spi...

Fluorescence-detected magnetic resonance of triplets in zero magnetic field (FDMR), fluorescence fading (FF) due to triplet-formation, both at 4.2 K, and prompt fluorescence decay kinetics (FDK) at room temperature have been measured for free pheophorbide-a (f-Pheo) and bound (b-Pheo) to a synthetic polypeptide (L-Lys-L-Ala-L-Ala)n, dissolved in di...