Search

Your search keyword '"Jankowiak, Ryszard"' showing total 395 results
Start Over Author "Jankowiak, Ryszard"
395 results on '"Jankowiak, Ryszard"'

106. Primary charge-separation rate at 5 K in isolated photosystem II reaction centers containing five and six chlorophyll a molecules

Author

Jankowiak, Ryszard J., Rätsep, Margus, Hayes, John M., Zazubovich, Valter, Picorel Castaño, Rafael, Seibert, Michael, Small, Gerald J., Jankowiak, Ryszard J., Rätsep, Margus, Hayes, John M., Zazubovich, Valter, Picorel Castaño, Rafael, Seibert, Michael, and Small, Gerald J.

Abstract

Although the primary charge-separation rate in the photosystem II (PSII) reaction center (RC) has been the subject of many time- and frequency-domain experiments, its value is still an unsettled issue, especially at or near room temperature. As a first step toward understanding its temperature dependence, it is important to have a reliable value for the rate at liquid helium temperatures. Presented are results from triplet bottleneck hole-burning (TBHB) experiments at 5.0 K on RCs isolated from spinach that contain either six or five chlorophyll a (Chl) molecules per two pheophytin (Pheo) molecules (referred to as RC-6 and RC-5). RC-5 possesses only one of the two peripheral Chls of the RC. The triplet state that serves as the population bottleneck is formed by charge recombination of the radical ion pair P680+ Pheo1 -, where P680 is the primary electron donor and Pheo1 is the acceptor on the active (D1) branch. In the TBHB experiments, the laser burn intensity was varied over 2 orders of magnitude to assess the contribution from fluence broadening to the width of the zero-phonon hole (ZPH) burned into the P680 absorption band. The widths of the ZPH were also corrected for interference from a weak and sharp hole contribution from a state(s) that is unlikely to be involved in efficient charge-separation. The corrected ZPH widths for RC-5 and RC-6 were the same (2.3 ± 0.2 cm-1) and correspond to a charge-separation rate of (4.6 ± 0.4 ps)-1, in good agreement with a value recently measured for RC-6 by femtosecond pump-probe spectroscopy at 7 K (Greenfield, S. R.; Seibert, M.; Wasielewski, M. R. J. Phys. Chem. B 1999, 103, 8364). It appears that the removal of a peripheral Chl does not lead to structural changes in the core region of the RC that affect primary charge separation.

Published
2003

118. Supercoiled DNA Promotes Formation of Intercalated cis-N2-Deoxyguanine Adducts and Base-Stacked trans-N2-Deoxyguanine Adducts by (+)-7R,8S-Dihydrodiol-9S,10R-epoxy-7,8,9,10-tetra- hydrobenzo[a]pyrene

Author

Jiang, Guohui, primary, Jankowiak, Ryszard, additional, Grubor, Nenad, additional, Banasiewicz, Marzena, additional, Small, Gerald J., additional, Skorvaga, Milan, additional, Van Houten, Bennett, additional, and States, J. Christopher, additional

Published
2004
Full Text
View/download PDF

120. High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

Author

Reddy, N. R. S., Wu, H. M., Jankowiak, Ryszard J., Picorel Castaño, Rafael, Cogdell, R. J., Small, Gerald J., Reddy, N. R. S., Wu, H. M., Jankowiak, Ryszard J., Picorel Castaño, Rafael, Cogdell, R. J., and Small, Gerald J.

Abstract

High pressure is used with hole burning and absorption spectroscopies at low temperatures to study the pressure dependence of the B800→B850 energy transfer rate in the LH2 complex of Rhodobacter sphaeroides and to assess the extent to which pressure can be used to identify and characterize states associated with strongly coupled chlorophyll molecules. Pressure tuning of the B800-B850 gap from ~ 750 cm-1 at 0.1 MPa to ~ 900 cm-1 at 680 MPa has no measurable effect on the 2 ps energy transfer rate of the B800-B850 complex at 4.2 K. An explanation for this resilience against pressure, which is supported by earlier hole burning studies, is provided. It is based on weak coupling nonadiabatic transfer theory and takes into account the inhomogeneous width of the B800-B850 energy gap, the large homogeneous width of the B850 band from exciton level structure and the Franck-Condon factors of acceptor protein phonons and intramolecular BChl a modes. The model yields reasonable agreement with the 4.2 K energy transfer rate and is consistent with its weak temperature dependence. It is assumed that it is the C9-ring exciton levels which lie within the B850 band that are the key acceptor levels, meaning that BChl a modes are essential to the energy transfer process. These ring exciton levels derive from the strongly allowed lowest energy component of the basic B850 dimer. However, the analysis of B850s linear pressure shift suggests that another Forster pathway may also be important. It is one that involves the ring exciton levels derived from the weakly allowed upper component of the B850 dimer which we estimate to be quasi-degenerate with B800. In the second part of the paper, which is concerned with strong BChl monomer-monomer interactions of dimers, we report that the pressure shifts of B875 (LH2), the primary donor absorption bands of bacterial RC (P870 of Rb. sphaeroides and P960 of Rhodopseudomonas viridis) and B1015 (LH complex of Rps. viridis) are equal and large in value

Published
1996

121. Detection and Quantification of Depurinated Benzo[a]pyrene-Adducted DNA Bases in the Urine of Cigarette Smokers and Women Exposed to Household Coal Smoke

Author

Casale, George P., primary, Singhal, Maria, additional, Bhattacharya, Sumitra, additional, RamaNathan, Regulan, additional, Roberts, Kenneth P., additional, Barbacci, Damon C., additional, Zhao, John, additional, Jankowiak, Ryszard, additional, Gross, Michael L., additional, Cavalieri, Ercole L., additional, Small, Gerald J., additional, Rennard, Stephen I., additional, Mumford, Judy L., additional, and Shen, Meilan, additional

Published
2001
Full Text
View/download PDF

127. Does theSinglet Minus Triplet Spectrum with MajorPhotobleaching Band Near 680–682 nm Represent an Intact ReactionCenter of Photosystem II?

Author

Chauvet, Adrien, Jankowiak, Ryszard, Kell, Adam, Picorel, Rafael, and Savikhin, Sergei

Subjects
*PHOTOSYSTEMS, *BLEACHING (Chemistry), *SPECTRUM analysis, *CHEMICAL reactions, *TIME-domain analysis, *LOW temperatures
Abstract

We use both frequency- and time-domainlow-temperature (5–20K) spectroscopies to further elucidate the shape and spectral positionof singlet minus triplet (triplet-bottleneck) spectra in the reactioncenters (RCs) of Photosystem II (PSII) isolated from wild-type Chlamydomonas reinhardtiiand spinach. It is shownthat the shape of the nonresonant transient hole-burned spectrum indestabilized RCs from C. reinhardtiiis very similar to that typically observed for spinach. This suggeststhat the previously observed difference in transient spectra betweenRCs from C. reinhardtiiand spinachis not due to the sample origin but most likely due to a partial destabilizationof the D1 and D2 polypeptides. This supports our previous assignmentsthat destabilized RCs (referred to as RC680) (Acharya, K. et al. J. Phys. Chem. B2012, 116, 4860–4870), with a major photobleaching band near 680–682nm and the absence of a photobleaching band near 673 nm, do not representthe intact RC residing within the PSII core complex. Time-resolvedabsorption difference spectra obtained for partially destabilizedRCs of C. reinhardtiiand for typicalspinach RCs support the above conclusions. The absence of clear photobleachingbands near 673 and 684 nm (where the PD1chlorophyll andthe active pheophytin (PheoD1) contribute, respectively)in picosecond transient absorption spectra in both RCs studied inthis work indicates that the cation can move from the primary electrondonor (ChlD1) to PD1(i.e., PD1ChlD1+PheoD1–→PD1+ChlD1PheoD1–). Therefore, we suggest that ChlD1is the major electrondonor in usually studied destabilized RCs (with a major photobleachingnear 680–682 nm), although the PD1path (where PD1serves as the primary electron donor) is likely presentin intact RCs, as discussed in Acharya, K. et al. J. Phys.Chem. B2012, 116, 4860–4870. [ABSTRACT FROM AUTHOR]

Published
2015
Full Text
View/download PDF

128. Effect of the LHCII pigment–protein complex aggregation on photovoltaic properties of sensitized TiO2 solar cells.

Author

Yang, Yiqun, Jankowiak, Ryszard, Lin, Chen, Pawlak, Krzysztof, Reus, Michael, Holzwarth, Alfred R., and Li, Jun

Abstract

A modified dye-sensitized solar cell consisting of a thin TiO2 barrier layer sensitized with natural trimeric light-harvesting complex II (LHCII) from spinach was used as a biomimetic model to study the effects of LHCII aggregation on the photovoltaic properties. The aggregation of individual trimers induced molecular reorganization, which dramatically increased the photocurrent. The morphology of small- and large-size LHCII aggregates deposited on a surface was confirmed by atomic force microscopy. Enhanced LHCII immobilization was accomplished via electrostatic interaction with amine-functionalized photoanodes. The photocurrent responses of the assembled solar cells under illumination at three characteristic wavelength bands in the UV-Vis absorption spectra of LHCII solutions confirmed that a significant photocurrent was generated by LHCII photosensitizers. The enhanced photocurrent by large aggregated LHCII is shown to correlate with the quenching in the far-red fluorescence deriving from chlorophyll–chlorophyll charge transfer states that are effectively coupled with the TiO2 surface and thus inject electrons into the TiO2 conduction band. The large aggregated LHCII with more chlorophyll–chlorophyll charge transfer states is a much better sensitizer since it injects electrons more efficiently into the conduction band of TiO2 than the small aggregated LHCII mostly consisting of unquenched chlorophyll excited state. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days. [ABSTRACT FROM AUTHOR]

Published
2014
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results