The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Rienk Van Grondelle - One of the best experts on this subject based on the ideXlab platform.
-
mixed exciton charge transfer states in photosystem ii Stark Spectroscopy on site directed mutants
Biophysical Journal, 2012Co-Authors: Elisabet Romero, Bruce A Diner, Peter J Nixon, Wiliam J Coleman, Jan P Dekker, Rienk Van GrondelleAbstract:We investigated the electronic structure of the photosystem II reaction center (PSII RC) in relation to the light- induced charge separation process using Stark Spectroscopy on a series of site-directed PSII RC mutants from the cyanobacte- rium Synechocystis sp. PCC 6803. The site-directed mutations modify the protein environment of the cofactors involved in charge separation (PD1 ,P D2, ChlD1, and PheD1). The results demonstrate that at least two different exciton states are mixed with charge- transfer (CT) states, yielding exciton states with CT character: (PD2 dþ PD1 dChlD1)*673nm and (ChlD1 dþ PheD1 d� )*681nm (where the subscript indicates thewavelength of theelectronic transition). Moreover, the CT state PD2 þ PD1 � acquires excited-state character due to its mixing with an exciton state, producing (PD2 þ PD1 � ) d *684nm. We conclude that the states that initiate charge separation are mixed exciton-CT states, and that the degree of mixing between exciton and CT states determines the efficiency of charge separation. In addition, the results reveal that the pigment-protein interactions fine-tune the energy of the exciton and CT states, and hence the mixing between these states. This mixing ultimately controls the selection and efficiency of a specific charge sepa- ration pathway, and highlights the capacity of the protein environment to control the functionality of the PSII RC complex.
-
Mixed exciton–charge-transfer states in photosystem II: Stark Spectroscopy on site–directed mutants
Biophysical Journal, 2012Co-Authors: Elisabet Romero, Bruce A Diner, Peter J Nixon, Wiliam J Coleman, Jan P Dekker, Rienk Van GrondelleAbstract:We investigated the electronic structure of the photosystem II reaction center (PSII RC) in relation to the light- induced charge separation process using Stark Spectroscopy on a series of site-directed PSII RC mutants from the cyanobacte- rium Synechocystis sp. PCC 6803. The site-directed mutations modify the protein environment of the cofactors involved in charge separation (PD1 ,P D2, ChlD1, and PheD1). The results demonstrate that at least two different exciton states are mixed with charge- transfer (CT) states, yielding exciton states with CT character: (PD2 dþ PD1 dChlD1)*673nm and (ChlD1 dþ PheD1 d� )*681nm (where the subscript indicates thewavelength of theelectronic transition). Moreover, the CT state PD2 þ PD1 � acquires excited-state character due to its mixing with an exciton state, producing (PD2 þ PD1 � ) d *684nm. We conclude that the states that initiate charge separation are mixed exciton-CT states, and that the degree of mixing between exciton and CT states determines the efficiency of charge separation. In addition, the results reveal that the pigment-protein interactions fine-tune the energy of the exciton and CT states, and hence the mixing between these states. This mixing ultimately controls the selection and efficiency of a specific charge sepa- ration pathway, and highlights the capacity of the protein environment to control the functionality of the PSII RC complex.
-
the charge transfer properties of the s2 state of fucoxanthin in solution and in fucoxanthin chlorophyll a c2 protein fcp based on Stark Spectroscopy and molecular orbital theory
Journal of Physical Chemistry B, 2008Co-Authors: Lavanya Premvardhan, Daniel J Sandberg, Robert R Birge, Claudia Buchel, Rienk Van GrondelleAbstract:Fucoxanthin chlorophyll-a/c2 protein (FCP), the membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, is characterized by Stark Spectroscopy to obtain a quantitative measure of the excited-state dipolar properties of the constituent pigments. The electro-optical properties of the carotenoid fucoxanthin (Fx), the primary light harvester in FCP, were determined from the Stark spectrum measured in a MeTHF glass (77 K) and compared to the results from electronic-structure calculations. On photon absorption by Fx, a 17 D change in the static dipole moment (|Δμ|exp), and a somewhat larger |Δμ|exp at the red edge, are measured for the S0 → S2 (11Ag−-like →11Bu*+-like) transition. The large change in dipole moment indicates that Fx undergoes photoinduced charge transfer (CT), and underscores the influence of the S2 state on the polarity-dependent excited-state dynamics of Fx that has so far been attributed to, and discussed in terms of, the S0 and the S1/ICT states. MNDO-PSDCI and...
Gary E Douberly - One of the best experts on this subject based on the ideXlab platform.
-
two center three electron bonding in clnh3 revealed via helium droplet infrared laser Stark Spectroscopy entrance channel complex along the cl nh3 clnh2 h reaction
Journal of Chemical Physics, 2016Co-Authors: Christopher P Moradi, Matin Kaufmann, Gary E DouberlyAbstract:Pyrolytic dissociation of Cl2 is employed to dope helium droplets with single Cl atoms. Sequential addition of NH3 to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction Cl + NH3 → ClNH2 + H. Infrared Stark Spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C3v symmetric top. Frequency shifts from NH3 and dipole moment measurements are consistent with a ClNH3 complex containing a relatively strong two-center three-electron (2c–3e) bond. The nature of the 2c–3e bonding in ClNH3 is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence in experimental spectra of two other complexes, NH3Cl and Cl–HNH2, which are predicted in the entry valley to the hydrogen abstraction reaction Cl + NH3 → HCl + NH2.
-
Infrared laser Stark Spectroscopy of hydroxymethoxycarbene in 4He nanodroplets
Chemical Physics Letters, 2015Co-Authors: Bernadette M Broderick, Christopher P Moradi, Gary E DouberlyAbstract:Abstract Hydroxymethoxycarbene, CH 3 O C ¨ OH , was produced via pyrolysis of monomethyl oxalate and subsequently isolated in 4He nanodroplets. Infrared laser Spectroscopy reveals two rotationally resolved a,b-hybrid bands in the OH-stretch region, which are assigned to trans,trans- and cis,trans-rotamers. Stark Spectroscopy of the trans,trans-OH stretch band provides the a-axis inertial component of the dipole moment, namely μa = 0.62(7) D. The computed equilibrium dipole moment agrees well with the expectation value determined from experiment, consistent with a semi-rigid CH 3 O C ¨ OH backbone computed via a potential energy scan at the B3LYP/cc-pVTZ level of theory, which reveals substantial conformer interconversion barriers of ≈17 kcal/mol.
-
reactive intermediates in 4he nanodroplets infrared laser Stark Spectroscopy of dihydroxycarbene
Journal of Chemical Physics, 2015Co-Authors: Bernadette M Broderick, Laura Mccaslin, Christopher P Moradi, John F Stanton, Gary E DouberlyAbstract:Singlet dihydroxycarbene (HOCOH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark Spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark Spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μa, μb) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOCOH torsional interconversion and tautomerization barriers.
Jennifer P Ogilvie - One of the best experts on this subject based on the ideXlab platform.
-
two dimensional electronic Stark Spectroscopy
Journal of Physical Chemistry Letters, 2017Co-Authors: Anton Loukianov, Andrew Niedringhaus, Brandon Berg, Seckin S Senlik, Jennifer P OgilvieAbstract:Characterizing ultrafast energy and charge transfer is important for understanding a wide range of systems, from natural photosynthetic complexes to organic photovoltaics. Distinguishing the kinetic processes of energy transfer and charge separation in such systems is challenging due to the lack of clear spectral signatures of charge transfer states, which are typically nonradiative. Stark Spectroscopy has proven to be a valuable method for uncovering charge transfer states. Here we extend the dimensionality of Stark Spectroscopy to perform two-dimensional electronic Stark Spectroscopy. We demonstrate the method on TIPS-pentacene in 3-methylpentane at 77 K. The additional frequency dimension of two-dimensional Stark Spectroscopy promises to enable the identification of charge transfer states, their coupling to other charge transfer and exciton states, and their involvement in charge separation processes.
-
2d electronic Stark Spectroscopy
Conference on Lasers and Electro-Optics, 2016Co-Authors: Anton Loukianov, Andrew Niedringhaus, Jennifer P OgilvieAbstract:We describe a novel nonlinear Spectroscopy method that combines the high sensitivity of background-free heterodyne-detected 2D electronic Spectroscopy with Stark Spectroscopy for observation of ultrafast charge-transfer kinetics. We demonstrate the method on the photosystem II reaction center.
-
2d electronic Stark Spectroscopy
International Conference on Ultrafast Phenomena (2016) paper UM3A.6, 2016Co-Authors: Anton Loukianov, Andrew Niedringhaus, Jennifer P OgilvieAbstract:We developed a novel nonlinear Spectroscopy method for observation of ultrafast charge-transfer kinetics combining a background-free heterodyne-detected 2D electronic Spectroscopy setup with Stark Spectroscopy. We demonstrate the method on the photosystem II reaction center.
-
transient grating Stark Spectroscopy
19th International Conference on Ultrafast Phenomena (2014) paper 09.Wed.P3.48, 2014Co-Authors: Anton Loukianov, Daniel E Wilcox, Jennifer P OgilvieAbstract:We describe a novel nonlinear Spectroscopy that combines the high signal-to-noise of heterodyne-detected transient-grating Spectroscopy with Stark Spectroscopy, enabling sensitive detection of charge transfer kinetics. We demonstrate the method on the carotenoid fucoxanthin.
Hideki Hashimoto - One of the best experts on this subject based on the ideXlab platform.
-
Probing the Effect of the Binding Site on the Electrostatic Behavior of a Series of Carotenoids Reconstituted into the Light-Harvesting 1 Complex from Purple Photosynthetic Bacterium Rhodospirillum rubrum Detected by Stark Spectroscopy
Journal of Physical Chemistry B, 2008Co-Authors: Katsunori Nakagawa, Satoru Suzuki, Ritsuko Fujii, Alastair T Gardiner, Richard J Cogdell, Mamoru Nango, Hideki HashimotoAbstract:Reconstitutions of the LH1 complexes from the purple photosynthetic bacterium Rhodospirillum rubrum S1 were performed with a range of carotenoid molecules having different numbers of C=C conjugated double bonds. Since, as we showed previously, some of the added carotenoids tended to aggregate and then to remain with the reconstituted LH1 complexes (Nakagawa, K.; Suzuki, S.; Fujii, R.; Gardiner, A. T.; Cogdell, R. J.; Nango, M.; Hashimoto, H. Photosynth. Res. 2008, 95, 339-344), a further purification step using a sucrose density gradient centrifugation was introduced to improve purity of the final reconstituted sample. The measured absorption, fluorescence-excitation, and Stark spectra of the LH1 complex reconstituted with spirilloxanthin were identical with those obtained with the native, spirilloxanthin-containing, LH1 complex of Rs. rubrum S 1. This shows that the electrostatic environments surrounding the carotenoid and bacteriochlorophyll a (BChl a) molecules in both of these LH1 complexes were essentially the same. In the LH1 complexes reconstituted with either rhodopin or spheroidene, however, the wavelength maximum at the BChl a Qy absorption band was slightly different to that of the native LH1 complexes. These differences in the transition energy of the BChl a Qy absorption band can be explained using the values of the nonlinear optical parameters of this absorption band, i.e., the polarizability change Tr(Δα) and the static dipole-moment change lΔμl upon photoexcitation, as determined using Stark Spectroscopy. The local electric field around the BChl a in the native LH1 complex (Es) was determined to be ∼3.0 x 10 6 V/cm. Furthermore, on the basis of the values of the nonlinear optical parameters of the carotenoids in the reconstituted LH1 complexes, it is possible to suggest that the conformations of carotenoids, anhydrorhodovibrin and spheroidene, in the LH1 complex were similar to that of rhodopin glucoside in crystal structure of the LH2 complex from Rhodopseudomonas acidophila 10050.
-
probing binding site of bacteriochlorophyll a and carotenoid in the reconstituted lh1 complex from rhodospirillum rubrum s1 by Stark Spectroscopy
Photosynthesis Research, 2008Co-Authors: Katsunori Nakagawa, Satoru Suzuki, Ritsuko Fujii, Alastair T Gardiner, Richard J Cogdell, Mamoru Nango, Hideki HashimotoAbstract:Stark Spectroscopy is a powerful technique to investigate the electrostatic interactions between pigments as well as between the pigments and the proteins in photosynthetic pigment–protein complexes. In this study, Stark Spectroscopy has been used to determine two nonlinear optical parameters (polarizability change Tr(Δα) and static dipole-moment change |Δμ| upon photoexcitation) of isolated and of reconstituted LH1 complexes from the purple photosynthetic bacterium, Rhodospirillum (Rs.) rubrum. The integral LH1 complex was prepared from Rs. rubrum S1, while the reconstituted complex was assembled by addition of purified carotenoid (all-trans-spirilloxanthin) to the monomeric subunit of LH1 from Rs. rubrum S1. The reconstituted LH1 complex has its Qy absorption maximum at 878 nm. This is shifted to the blue by 3 nm in comparison to the isolated LH1 complex. The energy transfer efficiency from carotenoid to bacteriochlorophyll a (BChl a), which was determined by fluorescence excitation Spectroscopy of the reconstituted LH1 complex, is increased to 40%, while the efficiency in the isolated LH1 complex is only 28%. Based on the differences in the values of Tr(Δα) and |Δμ|, between these two preparations, we can calculate the change in the electric field around the BChl a molecules in the two situations to be EΔ ≈ 3.4 × 105 [V/cm]. This change can explain the 3 nm wavelength shift of the Qy absorption band in the reconstituted LH1 complex.
-
Electrostatic effect of surfactant molecules on bacteriochlorophyll a and carotenoid binding sites in the LH1 complex isolated from Rhodospirillum rubrum S1 probed by Stark Spectroscopy
Photosynthesis Research, 2008Co-Authors: Katsunori Nakagawa, Satoru Suzuki, Ritsuko Fujii, Alastair T Gardiner, Richard J Cogdell, Mamoru Nango, Hideki HashimotoAbstract:The LH1 complexes were isolated from the purple photosynthetic bacterium Rhodospirillum rubrum strain S1. They were initially solubilized using LDAO and then purified in the presence of Triton X-100. The purified complexes were then either used directly or following an exchange into LDAO. Stark Spectroscopy was applied to probe the electrostatic field around the bacteriochlorophyll a (BChl a) and carotenoid binding sites in the LH1 complexes surrounded by these two different surfactant molecules. Polarizabilty change (\(\Updelta\varvec{\upalpha}\)) and dipole moment change (\(\Updelta\varvec{\upmu}\)) upon photoexcitation were determined for the BChl a Qy band. Both of these parameters show smaller values in the presence of LDAO than in Triton X-100. This indicates that polar detergent molecules, like LDAO, affect the electrostatic environment around BChl a, and modify the nonlinear optical parameters (\(\Updelta\varvec{\upalpha}\) and \(\Updelta\varvec{\upmu}\) values). The electrostatic field around the BChl a binding site, which is generated by the presence of LDAO, was determined to be |EL| = ∼3.9 × 105 [V/cm]. Interestingly, this kind of electrostatic effect was not observed for the carotenoid-binding site. The present study demonstrates a unique electrostatic interaction between the polar detergent molecules surrounding the LH1 complex and the Qy absorption band of BChl a that is bound to the LH1 complex.
-
Electrostatic effect of surfactant molecules on bacteriochlorophyll a and carotenoid binding sites in the LH1 complex isolated from Rhodospirillum rubrum S1 probed by Stark Spectroscopy.
Photosynthesis research, 2007Co-Authors: Katsunori Nakagawa, Satoru Suzuki, Ritsuko Fujii, Alastair T Gardiner, Richard J Cogdell, Mamoru Nango, Hideki HashimotoAbstract:The LH1 complexes were isolated from the purple photosynthetic bacterium Rhodospirillum rubrum strain S1. They were initially solubilized using LDAO and then purified in the presence of Triton X-100. The purified complexes were then either used directly or following an exchange into LDAO. Stark Spectroscopy was applied to probe the electrostatic field around the bacteriochlorophyll a (BChl a) and carotenoid binding sites in the LH1 complexes surrounded by these two different surfactant molecules. Polarizabilty change (deltaalpha)) and dipole moment change (deltamicrom) upon photoexcitation were determined for the BChl a Q(y) band. Both of these parameters show smaller values in the presence of LDAO than in Triton X-100. This indicates that polar detergent molecules, like LDAO, affect the electrostatic environment around BChl a, and modify the nonlinear optical parameters (deltaalpha and deltamicrom values). The electrostatic field around the BChl a binding site, which is generated by the presence of LDAO, was determined to be |E ( L )| = approximately 3.9 x 10(5) [V/cm]. Interestingly, this kind of electrostatic effect was not observed for the carotenoid-binding site. The present study demonstrates a unique electrostatic interaction between the polar detergent molecules surrounding the LH1 complex and the Q(y) absorption band of BChl a that is bound to the LH1 complex.
-
Probing binding site of bacteriochlorophyll a and carotenoid in the reconstituted LH1 complex from Rhodospirillum rubrum S1 by Stark Spectroscopy.
Photosynthesis research, 2007Co-Authors: Katsunori Nakagawa, Satoru Suzuki, Ritsuko Fujii, Alastair T Gardiner, Richard J Cogdell, Mamoru Nango, Hideki HashimotoAbstract:Stark Spectroscopy is a powerful technique to investigate the electrostatic interactions between pigments as well as between the pigments and the proteins in photosynthetic pigment-protein complexes. In this study, Stark Spectroscopy has been used to determine two nonlinear optical parameters (polarizability change Tr(Deltaalpha) and static dipole-moment change |Deltamu| upon photoexcitation) of isolated and of reconstituted LH1 complexes from the purple photosynthetic bacterium, Rhodospirillum (Rs.) rubrum. The integral LH1 complex was prepared from Rs. rubrum S1, while the reconstituted complex was assembled by addition of purified carotenoid (all-trans-spirilloxanthin) to the monomeric subunit of LH1 from Rs. rubrum S1. The reconstituted LH1 complex has its Q(y) absorption maximum at 878 nm. This is shifted to the blue by 3 nm in comparison to the isolated LH1 complex. The energy transfer efficiency from carotenoid to bacteriochlorophyll a (BChl a), which was determined by fluorescence excitation Spectroscopy of the reconstituted LH1 complex, is increased to 40%, while the efficiency in the isolated LH1 complex is only 28%. Based on the differences in the values of Tr(Deltaalpha) and |Deltamu|, between these two preparations, we can calculate the change in the electric field around the BChl a molecules in the two situations to be E (Delta) approximately 3.4 x 10(5) [V/cm]. This change can explain the 3 nm wavelength shift of the Q(y) absorption band in the reconstituted LH1 complex.
Christopher P Moradi - One of the best experts on this subject based on the ideXlab platform.
-
two center three electron bonding in clnh3 revealed via helium droplet infrared laser Stark Spectroscopy entrance channel complex along the cl nh3 clnh2 h reaction
Journal of Chemical Physics, 2016Co-Authors: Christopher P Moradi, Matin Kaufmann, Gary E DouberlyAbstract:Pyrolytic dissociation of Cl2 is employed to dope helium droplets with single Cl atoms. Sequential addition of NH3 to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction Cl + NH3 → ClNH2 + H. Infrared Stark Spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C3v symmetric top. Frequency shifts from NH3 and dipole moment measurements are consistent with a ClNH3 complex containing a relatively strong two-center three-electron (2c–3e) bond. The nature of the 2c–3e bonding in ClNH3 is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence in experimental spectra of two other complexes, NH3Cl and Cl–HNH2, which are predicted in the entry valley to the hydrogen abstraction reaction Cl + NH3 → HCl + NH2.
-
Infrared laser Stark Spectroscopy of hydroxymethoxycarbene in 4He nanodroplets
Chemical Physics Letters, 2015Co-Authors: Bernadette M Broderick, Christopher P Moradi, Gary E DouberlyAbstract:Abstract Hydroxymethoxycarbene, CH 3 O C ¨ OH , was produced via pyrolysis of monomethyl oxalate and subsequently isolated in 4He nanodroplets. Infrared laser Spectroscopy reveals two rotationally resolved a,b-hybrid bands in the OH-stretch region, which are assigned to trans,trans- and cis,trans-rotamers. Stark Spectroscopy of the trans,trans-OH stretch band provides the a-axis inertial component of the dipole moment, namely μa = 0.62(7) D. The computed equilibrium dipole moment agrees well with the expectation value determined from experiment, consistent with a semi-rigid CH 3 O C ¨ OH backbone computed via a potential energy scan at the B3LYP/cc-pVTZ level of theory, which reveals substantial conformer interconversion barriers of ≈17 kcal/mol.
-
reactive intermediates in 4he nanodroplets infrared laser Stark Spectroscopy of dihydroxycarbene
Journal of Chemical Physics, 2015Co-Authors: Bernadette M Broderick, Laura Mccaslin, Christopher P Moradi, John F Stanton, Gary E DouberlyAbstract:Singlet dihydroxycarbene (HOCOH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark Spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark Spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μa, μb) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOCOH torsional interconversion and tautomerization barriers.
