Photosynthetic Model Research Articles

Quantum Beats of the Radical Pair State in Photosynthetic Models Observed by Transient Electron Paramagnetic Resonance

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuantum Beats of the Radical Pair State in Photosynthetic Models Observed by Transient Electron Paramagnetic ResonanceKarl Laukenmann, Stefan Weber, Gerd Kothe, Claudia Oesterle, Alexander Angerhofer, Michael R. Wasielewski, Walter A. Svec, and James R. NorrisCite this: J. Phys. Chem. 1995, 99, 12, 4324–4329Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://doi.org/10.1021/j100012a064RIGHTS & PERMISSIONSArticle Views145Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (688 KB) Get e-Alerts

Novel biomimetic models for photosynthesis: Porphyrins covalently linked to redox-active crown ether quinones

The synthesis of biomimetic photosynthetic model compounds, composed of 5,10,15-triphenylporphyrins covalently linked to redox active crown ether quinones via different bridges, is described. Using the zinc complex with the flexible butylene spacer in non polar solvents backfolding of the crown ether quinone over the porphyrin plane is observed by 1H NMR chemical shift studies. This conformational effect is supported by molecular modelling calculations. The backfolding is induced by complexation of the acceptor with the central atom since it is not observed in the metal free-base porphyrin derivative. Due to steric constraints the zinc porphyrin cyclohexylene crown ether quinones lack this backfolding. Cyclic voltammetry measurements show a significant shift of the reduction potential of the quinone crown ether moiety in the presence of alkali metal cations.

One-dimensional numerical simulation of primary production: Lagrangian and Eulerian formulations

It has been argued (Wolf and Woods, in Toward a Theory On Biological-Physical Interactions in the World Ocean, Rothschild, (ed.), 1988) (WW88) that phytoplankton growth models are sensitive to Lagrangian effects because populations at a given depth and time contain a wide distribution of photoadaptive properties. On the other hand, Lande and Lewis (Deep-Sea Research. 36. 1161–1175. 1989) (LL89) have claimed that for a different photosynthetic model, this distribution of properties can be adequately represented by a mean value in a much simpler and more efficient Eulerian formulation. This study compares Lagrangian and Eulerian integrations of these two different models of photosynthesis under two mixing regimes. For relatively weak mixing, the growth rate predicted by the different formulations of the two models is small (≤5%). In vigorously mixed conditions, Lagrangian effects cause a significant (˜20%) reduction in the mean growth rate of the WW88 model, while the differences in the two integrations of the LL89 model differ only slightly (˜3%) The apparent discrepancy in the comparisons betwen Lagrangian and Eulerian integrations of the two different photosynthesis models is a result of different parameterizations of photoadaptive reaction kinetics.

Photoinduced energy transfer in associated, but noncovalently-linked photosynthetic model systems.

The synthesis and photophysical characterization of nucleobase-substituted porphyrins designed to form rigid hydrogen-bonded ensembles, and to allow for energy transfer within the resulting complexes, is reported Watson-Crick nucleobase-pairing interactions between guanosine- and cytidine-bearing porphyrins are used to assemble the hydrogen-bonded ensembles. Likewise, zinc(II) and free-base porphyrins are used respectively as the donors and acceptors within these ensembles that, depending on design, contain either two or three total porphyrin subunits within the supramolecular assembly. The association constant for guanosine-to-cytidine association representing the primary interaction in each donor-acceptor assembly, is ca, 22 000 [+-] 200 M[sup [minus]1] in CD[sub 2]Cl[sub 2] as determined from [sup 1]H NMR titration analyses. Both singlet and triplet energy transfer was observed within the various donor-acceptor assemblies. Whereas the singlet-state energy-transfer dynamics are consistent with a Foerster-type process, triplet energy transfer within the same complex is believed to occur through the hydrogen-bonded interface. The presently-described noncovalent approach to donor-acceptor ensemble generation is thus considered to provide a novel and useful approach to modeling aspects of the photon antennae that are part of the natural photosynthetic process. 31 refs., 8 figs., 2 tabs.

Mn(salphen)(EtOH)2](BPh4) [salphenH2 = N,N'-bis(salicylidene)-1,2-diaminobenzene], a further example of a photosynthetic model compound forming dimers linked by hydrogen and π bonds

The title molecule, bis(ethanol-O){2,2'-[o-phenylenebis(nitrilomethylidyne)diphenolato]-N,N',O,O'}manganese(III) tetraphenylborate, [Mn(C 20 H 14 N 2 O 2 )(C 2 H 6 O) 2 ](C 24 H 20 B), comprises a planar tetradentate Schiff base tightly bound to Mn III via Mn-N bonds of 1.97 (1) and 1.99 (2) A, and two Mn-O bonds of 1.85 (1) A, with capping ethanol groups at the longer Mn-O distances of 2.27 (1) and 2.28 (1) A completing a distorted octahedral arrangement. Pairs of molecules are linked across inversion centres by hydrogen bonds from the ethanol to the phenoxy O atoms [O...O 2.90 (2) A], which are augmented by π-bonds between overlapping phenyl rings, resulting in an Mn...Mn separation of 4.995 (6) cf. 5.21 (1) A for the salpn analogue [salpn = N,N'-bis(salicylidene)-1,3-diaminopropane] [Ashmawy, Beagley, McAuliffe, Parish & Pritchard (1990). J. Chem. Soc. Chem. Commun. pp. 936-937]

Effects of leaf nutrient status on photosynthetic capacity in loblolly pine (Pinus taeda L.) seedlings grown in elevated atmospheric CO(2).

We measured needle photosynthesis of loblolly pine seedlings grown in a factorial experiment with two CO(2) partial pressures (35 and 65 Pa) and three nutrient treatments (7 mM NH(4)NO(3) + 1 mM PO(4); 7 mM NH(4)NO(3) + 0.2 mM PO(4); 1 mM NH(4)NO(3) + 1 mM PO(4)). The data were used to parameterize a physiologically based photosynthetic model that included limitations imposed by ribulose-1,5-bisphosphate carboxylase/oxygenase activity, electron transport capacity and inorganic phosphate availability. With nonlimiting nutrients, seedlings grown at 65 Pa CO(2) had significantly higher net photosynthesis and lower stomatal conductance than seedlings grown at 35 Pa CO(2). Nutrient limitations by either N or P significantly reduced photosynthetic capacity. When either N or P was limiting, there was no effect of growth CO(2) partial pressure on photosynthesis, but stomatal conductance was significantly lower for seedlings grown at 65 Pa CO(2). Modeled biochemical parameters suggest that, in all cases, photosynthesis was co-limited by carboxylation, electron transport and phosphate regeneration. Acclimation to growth in elevated CO(2) involved a reduction in leaf N content. In the low-N and low-P treatments, modeled parameters indicated that the biochemical processes of photosynthesis were down regulated to the point that there was no effect of increasing CO(2) partial pressure. The capacity to regenerate phosphate was reduced in both low nutrient treatments, but was only reduced by elevated CO(2) when seedlings were grown under low soil P conditions. Increased photosynthetic water use efficiency and nutrient use efficiency in response to CO(2) enrichment occurred in all three nutrient treatments and have important implications for whole-plant water and nutrient balance. These data support the contention that soil nutrient status in forest ecosystems will be a critical influence on tree seedling response to increasing atmospheric CO(2) partial pressures.

Long-range photoinduced electron transfer in an associated but non-covalently linked photosynthetic model system

Long-range photoinduced electron transfer in an associated but non-covalently linked photosynthetic model system

Influence of Shoot Structure on the Photosynthesis of Sitka Spruce (Picea sitchensis)

All parameters for a biochemical photosynthetic model of Sitka spruce shoots were obtained from responses of CO 2 assimilation to quantum flux density and CO 2 concentration. Comparable parameters for needles on a shoot were derived using a shoot structure model. Photosynthetic response of a shoot to absorbed quantum flux density was not satisfactorily predicted using the biochemical model unless co-limitation by potential electron transport and Rubisco was taken into account. Co-limitation of a shoot is affected by the absorbed quantum flux density and ambient CO 2 concentration, as well as by the structure of the shoot (...)

RESPONSE OF CROP PHOTOSYNTHESIS TO CO2, TEMPERATURE, AND LIGHT: EXPERIMENTATION AND MODELING

Increasing atmospheric carbon dioxide concentration [CO2] is expected to result in a CO2 level of 600 μL L-1 sometime during the 21st century, which will likely affect global climate primarily by increasing air temperature 3-6°C. Several studies were conducted on the interactive effects of [CO2] and temperature in various combinations on cotton photosynthesis, respiration, transpiration, water use efficiency, and dry matter accumulation. The data were used to develop and test various types of photosynthesis models. The dependence of canopy light utilization efficiency and canopy conductivity for CO2 transfer on temperature and CO2 concentration was determined. The complete model of CO2, exchange for cotton as a function of environmental factors contains 7 parameters. Methods of validation, parameterization, and comparison of photosynthetic models are described.

Synthesis of 1,2-Phenylene-Bridged Diporphyrin Linked with Porphyrin Monomer and Its Intramolecular Singlet-Singlet Excitation Energy Transfer

Abstract A new photosynthetic model, in which 1,2-phenylene-bridged diporphyrin is connected with monomeric porphyrin through strapped chain, was synthesized by acid-catalyzed intramolecular cyclization reaction. Picosecond time-resolved fluorescence spectroscopy has revealed the efficient unidirectional singlet-singlet energy transfer from the monomeric porphyrin to the diporphyrin.

Synthesis and Characterization of Doubly-Strapped Porphyrins

Abstract Synthesis of a “doubly-strapped” porphyrin is described, which has two –O(CH2)10O– straps on both sides of the porphyrin ring. This porphyrin did not form the zinc complex when treated with zinc acetate, even under forcing conditions. Such inertness toward zinc insertion can be attributed to the steric hindrance of the –O(CH2)10O– straps. Oligoporphyrins with one strapped ring were also synthesized. Reaction of these porphyrins with zinc acetate resulted in insertion of zinc into all non-strapped rings, while the strapped ring remained unchanged. These doubly-strapped porphyrins will be useful in constructing oligoporphyrins as photosynthetic model compounds, in which photochemical and electrochemical properties are controlled by selective metal insertion.

Picosecond studies of quinone-substituted monometalated porphyrin dimers: evidence for superexchange-mediated electron transfer in a photosynthetic model system

Time-resolved studies are reported for a series of quinone-substituted porphyrin monomers and monometalated phenyl-linked dimers. Irradiation of the simple porphyrin monomer systems Ph-Zn-Q, Ph-H 2 -Q, and H 2 -Q in toluene at 295 K elicits charge separation to produce the oxidized free-base (H 2 ) or zinc (Zn) porphyrin and the reduced quinone (Q) within the 350-fs excitation flash

Spin-Polarized Radical Ion Pair Formation Resulting from Two-step Electron Transfer from the Lowest Excited Singlet State of a Fixed-Distance Photosynthetic Model System at 5 K

Abstract A photosynthetic reaction center model consisting of a zinc porphyrin primary electron donor, ZP, positioned between a naphthoquinone electron acceptor, NQ, and an N,N,N,N–tetraalkyl–p–phenylenediamine secondary electron donor, TAPD, was synthesized. The resulting rigid structure places the TAPD donor at a fixed 23 A center–to–center distance from the NQ acceptor. Excitation of ZP with 540 nm light in butyronitrile glass at 5 K results in two–step sequential electron transfer: TAPD–1*ZP–NQ > TAPD–ZP+−NQ− −> TAPD+−ZP–NQ−. The final TAPD+−ZP–NQ− radical pair lives for 4 ms and exhibits a spin–polarized EPR spectrum characteristic of a spin–correlated radical pair. The EPR spectrum of this long–lived, spin–polarized radical ion pair closely mimics the bacteriochlorophyll cation – quinone anion radical pair produced in photosynthetic reaction centers.

Photoinduced spin-polarized radical ion pair formation in a fixed-distance photosynthetic model system at 5 K

Photoinduced, multistep charge separation in bacterial reaction centers proceeds from the lowest excited singlet state of the dimeric bacteriochlorophyll electron donor in two steps, to yield a weakly interacting dimer cation-quinone anion radical pair, P{sup +}-Q{sup {minus}}, separated by 28 {angstrom}. Recently, we developed criteria for achieving high quantum yield charge separation in porphyrin-based-donor-acceptor systems at cryogenic temperatures. Using this information as a predictive model, we synthesized compound 1, TAPD-ZP-NQ, which consists of a zinc porphyrin primary electron donor, ZP, positioned between a naphthoquinone electron acceptor, NQ, and an N,N,N,N-tetraalkyl-p-phenylenediamine secondary electron donor, TADP.

ChemInform Abstract: Synthesis of a Photosynthetic Model Compound with a Long Alkyl Chain and Its Incorporation into Bovine Serum Albumin.

AbstractWith a view to investigating the effect of protein on the photosynthetic electron transfer, the title compound (XIb) is synthesized and its water‐soluble complex with bovine serum albumin (BSA) is formed.

Quinone substituted monometallated porphyrin dimers: Evidence for “superexchange” mediated electron transfer in multicomponent photosynthetic model systems

Quinone substituted monometallated porphyrin dimers: Evidence for “superexchange” mediated electron transfer in multicomponent photosynthetic model systems

Time-resolved (dynamical) Mössbauer study of light-induced valence state changes in iron (II) model complexes of photosensitive bacterial reaction centres

Abstract A Mossbauer spectrometer, modified to carry out time-resolved (dynamical) Mossbauer studies, has been utilised to study the light-induced chemical changes in the photosynthetic model complexes of iron-quinones, in a time-domain of milliseconds. It is found that the high-spin ferrous ions present in some of these complexes get partly converted into high-spin ferric ions on illumination with near infrared radiation. It has also been found further that the photo-induced chemical changes are reversible in nature. It is possible to set an upper limit of 6 ms duration for the illumination to be “on” for affecting the photo-induced chemical changes observed.

Absorption and static emission properties of monometalated quinone-substituted porphyrin dimers: evidence for “superexchange” mediated electron transfer in multicomponent photosynthetic model systems

The absorption and static emission properties of several selectively metalated quinone-substituted porphyrin dimers and control compounds are described. Whereas the unsubstituted metal-free and bis-zinc dimers 16, 19, 17, and 20 give rise to fluorescence emission spectra characteristic of typical monomeric free-base and zinc-containing porphyrins (e.g. 13 and 14), the corresponding monometalated dimers ( 15 and 18) display emission spectra characteristic only of free-base porphyrins, indicating that rapid exothermic energy transfer takes place between the metalated and free-base subunits in these latter systems. In the case of the control monomers, direct covalent attachment of a quinone subunit (to give 9–12) serves to quench all detectable fluorescence emission. Similar results are obtained in the case of the metal-free ( 3), bis-zinc ( 4), and “distal” monometalated materials ( 2) in either 2-methyl THF or toluene at room temperature. This suggests that in these systems net electron transfer from the porphyrin dimer ensemble to the quinone is fast compared to the rate of fluorescence emission. In the case of the “proximal” monometalated complex, 1, however, a weak but detectable fluorescence signal is observed when the sample is irradiated in toluene at room temperature, indicating that the built-in energy barrier provided by the “proximal” zinc porphyrin subunit is slowing the rate of net electron transfer. Nonetheless, even in the case of this system, the rate of net electron transfer remains exceedingly high, suggesting that the central or “proximal” metalated porphyrin serves to mediate the electron transfer process. The quantum yield for fluorescence for this material in 2-methyl THF is essentially temperature independent, increasingly by only a factor of 3 upon cooling from room temperature to 77 K. This suggests that that net electron transfer from the “distal” free-base subunit to the quinone is not thermally activated but takes place by a direct superexchange mediated process. A similar conclusion is derived from analogous studies of the “flat” compounds 5–8. Here, however, the quantum yields for fluorescence are higher through-out the series suggesting that net electron transfer is slower for these more open photosynthetic models.

Synthesis of a photosynthetic model compound with a long alkyl chainand its incorporation into bovine serum albumin

Synthesis of a photosynthetic model compound with a long alkyl chainand its incorporation into bovine serum albumin

Picosecond charge separation and triplet formation in a closely spaced photosynthetic model system

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 recombination (CR) between porphyrin and anthraquinone ( k CS > 3 × 10 11 s −1 and k CR = 5.9 × 10 10 s −1 in CH 2Cl 2). The less-folded meta- and para-linked porphyrins have smaller electron transfer rate constants. For the ortho-linked compound in toluene a biphasic charge separation is observed. The triplet state is formed in high yield via fast intersystem crossing in the charge-separated state.