A unifying perspective of the ultrafast photo-dynamics of Orange Carotenoid Protein from Synechocystis: peril of high-power excitation, existence of different S* states and influence of tagging

A substantial number of Orange Carotenoid Protein (OCP) studies have aimed to describe the evolution of singlet excited states leading to the formation of photo-activated form, OCPR. The most recent one suggests that three picosecond-lived excited states are formed after the sub-100 fs decay of the initial S2 state. The S* state which has the longest reported lifetime of a few to tens of picoseconds is considered to be the precursor of the first red photoproduct P1. Here, we report the ultrafast photo-dynamics of the OCP from Synechocystis PCC 6803, carried out using Visible-NIR femtosecond time-resolved absorption spectroscopy as a function of the excitation pulse power and wavelength. We found that a carotenoid radical cation can form even at relatively low excitation power, obscuring the determination of photo-activation yields for P1. Moreover, the comparison of green (540 nm) and blue (470 nm) excitations revealed the existence of an hitherto uncharacterized excited state, denoted as S~, living a few tens of picoseconds and formed only upon 470 nm excitation. Since neither the P1 quantum yield nor the photo-activation speed over hundreds of seconds vary under green and blue continuous irradiation, this S~ species is unlikely to be involved in the photo-activation mechanism leading to OCPR. We also addressed the effect of His-tagging at the N- or C-termini on excited state photo-physical properties. Differences in spectral signatures and lifetimes of the different excited states were observed, at variance with the usual assumption that His-tagging hardly influences protein dynamics and function. Altogether our results advocate for careful consideration of the excitation power and His-tag position when comparing the photo-activation of different OCP variants, and beg to revisit the notion that S* is the precursor of photoactivated OCPR.

Download Full-text

Ground- and excited-state characteristics in photovoltaic polymer N2200

RSC Advances ◽

10.1039/d1ra01474a ◽

2021 ◽

Author(s):

Guanzhao Wen ◽

Xianshao Zou ◽

Rong Hu ◽

Jun Peng ◽

Zhifeng Chen ◽

...

Keyword(s):

Density Functional Theory ◽

Excited State ◽

Steady State ◽

Excited States ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Time Dependent ◽

Functional Theory ◽

Time Resolved ◽

Dependent Density

Ground- and excited-states properties of N2200 have been studied by steady-state and time-resolved spectroscopies as well as time-dependent density functional theory calculations.

Download Full-text

Ten-Nanosecond Step-Scan FT-IR Absorption Difference Time-Resolved Spectroscopy: Applications to Excited States of Transition Metal Complexes

Applied Spectroscopy ◽

10.1366/0003702971940648 ◽

1997 ◽

Vol 51 (4) ◽

pp. 580-583 ◽

Cited By ~ 23

Author(s):

Pingyun Chen ◽

Richard A. Palmer

Keyword(s):

Excited State ◽

Excited States ◽

Signal To Noise Ratio ◽

Ir Absorption ◽

Decay Kinetics ◽

Time Resolved ◽

Ligand Charge Transfer ◽

Ft Ir ◽

Good Signal ◽

Nanosecond Time Resolution

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy (S2FT-IR Δ A TRS) and demonstrated by measuring Δ A spectra of fac-[Re(bpy)(CO)3Cl] and cis-[Os(bpy)2(CO)(4,4′-bpy)]2+ (bpy = 2,2′-bipyridine; 4,4′-bpy=4,4′-bipyridine) in CH3CN solution, following 355-nm laser excitation. In both complexes, the large shifts in (CO) to higher energy are consistent with the assignment that the lowest-energy excited states are metal-to-ligand charge transfer in nature. For [Os(bpy)2(CO)(4,4′-bpy)]2+, it is also possible to measure the excited-state decay kinetics, again with 10-ns resolution. In addition, Δ A bands are observed that are related to excited-state vibrations of the bipyridine ligands. Δ A spectra of good signal-to-noise ratio can be obtained for complexes with lifetimes as short as 10 ns.

Download Full-text

Time-Resolved Resonance Raman Spectroscopy of Excited-State Porphyrins

Laser Chemistry ◽

10.1155/1999/82824 ◽

1999 ◽

Vol 19 (1-4) ◽

pp. 271-274 ◽

Cited By ~ 4

Author(s):

S. E. J. Bell ◽

J. H. Rice ◽

J. J. McGarvey ◽

R. E. Hester ◽

J. N. Moore ◽

...

Keyword(s):

Excited State ◽

Excited States ◽

Laser Excitation ◽

Resonance Raman Spectroscopy ◽

Resonance Raman ◽

Laser Pulses ◽

Significant Shift ◽

Time Resolved ◽

Two Component ◽

Absorbance Difference

Time-resolved resonance Raman (TR3) and absorbance difference studies of the excited states of Cu(TPP) (TPP=5,10,15,20-tetraphenylporphyrin) have been carried out with < 10 ps times resolution in THF and pyridine solvents. In THF the distinctive transient Raman bands in the ν2 and ν4 regions, previously observed with ns laser pulses, grow in the first 55 ps before decaying in 100's of ps. The ∆A spectra also show biphasic decay. This behaviour is associated with attack by solvent on the 4-coordinate excited state to form the longer lived species observed in TR3 experiments.In pyridine two component decay is also observed but it is the shorter-lived species which gives the transient Raman bands seen previously with ns laser excitation. This state is different from that seen in THF. At 5 ps delay ν4 is broader than in the ground state and, more importantly, there is a significant shift in the two pyridine bands at ca. 1000 cm-1. This implies a significant involvement of the pyridine-based orbitals in the excited state.

Download Full-text

Excited States and Intermediates by Time-Resolved Infrared Spectroscopy

Laser Chemistry ◽

10.1155/1999/31863 ◽

1999 ◽

Vol 19 (1-4) ◽

pp. 245-251 ◽

Cited By ~ 4

Author(s):

J. J. Turner ◽

M. W. George ◽

I. P. Clark ◽

I. G. Virrels

Keyword(s):

Infrared Spectroscopy ◽

Excited State ◽

Charge Transfer ◽

Excited States ◽

Fast Time ◽

Time Resolved ◽

Excited Species ◽

Charge Transfer Transitions ◽

Time Resolved Infrared Spectroscopy ◽

Kinetics Of

For coordination compounds containing CO or CN groups, fast time-resolved infrared spectroscopy (TRIR) provides a convenient method of probing excited states and intermediates. TRIR has proved particularly powerful for probing the structure and kinetics of organometallic intermediates. The interpretation is particularly straightforward when combined with IR data from matrix isolation experiments, although there can be some subtle differences. In excited state studies, shifts in ν(CO) and ν(CN) frequencies, from ground to excited state, are sensitive to the changes in electron distribution on excitation, thus allowing the distinction between charge-transfer and non-charge-transfer transitions. Subtle effects on excited state ν(CO) band positions occur with change from fluid to rigid solvent-“infrared rigidochromism”. There is often a change in ν(CO) band width on excitation; this can be interpreted in terms of specific interactions between the excited species and the solvent. This paper presents some of our recent work in this area.

Download Full-text

Drug-biomolecule interactions in the excited states

Pure and Applied Chemistry ◽

10.1351/pac200678122277 ◽

2006 ◽

Vol 78 (12) ◽

pp. 2277-2286 ◽

Cited By ~ 9

Author(s):

Virginie Lhiaubet-Vallet ◽

Miguel Angel Miranda

Keyword(s):

Amino Acids ◽

Excited State ◽

Excited States ◽

Binding Sites ◽

Photophysical Properties ◽

Building Blocks ◽

Point Of View ◽

Time Resolved ◽

Specific Antibodies ◽

Chemical Mechanisms

Drug-biomolecule interactions in the excited state are relevant from a photobiological point of view as they can be correlated with a number of photosensitization disorders such as photocarcinogenicity, photoallergy, phototoxicity, etc. Nonsteroidal anti-inflammatory 2-arylpropionic acids and antibacterial fluoroquinolones have been selected as typical examples of photoactive drugs. Protein photosensitization has revealed photoadduct formation; the major amino acids involved are Tyr, Trp, and His. Generation of specific antibodies has allowed us to identify relevant structures of the drug epitopes. Then, drugs have been submitted to systematic steady-state and time-resolved studies on their photophysical properties, alone and in the presence of biomolecules: proteins, DNA, and their simple building blocks. The results are discussed in the framework of the chemical mechanisms underlying photosensitization by drugs and also in connection with the potential of drug excited states as (chiral) reporters for the binding sites of biomolecules.

Download Full-text

Determination of the Lowest Excited State of Metal Complexes of Dipyrido[3, 2-a:2′,3′-c]Phenazine

Laser Chemistry ◽

10.1155/1999/48354 ◽

1999 ◽

Vol 19 (1-4) ◽

pp. 287-289

Author(s):

Mark R. Waterland ◽

Keith C. Gordon

Keyword(s):

Raman Spectroscopy ◽

Excited State ◽

Metal Complexes ◽

Excited States ◽

Copper Complexes ◽

Resonance Raman Spectroscopy ◽

Resonance Raman ◽

Time Resolved ◽

State Data

The nature of the lowest excited state of rhenium and copper complexes of dipyrido[3,2- a:2′ ,3′-c]phenazine (Dppz) has been determined using Resonance Raman, Time- Resolved Resonance Raman Spectroscopy and Spectroelectrochemistry. Comparison of spectroelectrochemical data and excited state data show that for the complexes studied no reduced ligand bands are observed in the excited state spectra thus the lowest excited states are all Ligand Centred in nature. The use of substituents at the 11 and/or 12 position of the ligand has no effect on the excited state ordering.

Download Full-text

Sequestration Effect on the Open-Cyclic Switchable Property of Warfarin by Cyclodextrin: Ultrafast Dynamical Study

10.20944/preprints201707.0059.v1 ◽

2017 ◽

Author(s):

Naji Al-Dubaili ◽

Na'il Saleh

Keyword(s):

Excited State ◽

Excited States ◽

Time Resolved Fluorescence ◽

Excited State Lifetime ◽

Deprotonated Form ◽

Dynamical Study ◽

Visible Absorption ◽

Time Resolved ◽

Pka Values ◽

Fluorescence Measurements

The excited-state lifetimes of the anticoagulant drug warfarin (W) in water and in the absence and presence of methyl-β-cyclodextrins (Me-β-CD) were recorded using time-resolved fluorescence measurements. Selective excitation of the open and cyclic protonated isomers of W were acquired with laser emitting diodes (LED) producing 320 and 280 nm excitation pulses, respectively. Formation of the inclusion complex was checked by UV–visible absorption spectroscopy, and the values of binding constants (2.9 × 103 M–1 and 4.2 × 102 M–1 for protonated and deprotonated forms, respectively) were extracted from the spectrophotometric data. Both absorption and time-resolved fluorescence results established that the interior of the macromolecular host binds preferentially the open protonated form, red shifts the maximum of its absorption of light at ~305 nm, extends its excited-state lifetime, and decreases its emission quantum yield (ФF). Collectively, sequestration of the open guest molecules decreases markedly their radiative rate constants (kr), likely due to formation of hydrogen-bonded complexes in both the ground and excited states. Due to lack of interactions, no change was observed in the excited-state lifetime of the cyclic form in the presence of Me-β-CD. The host also increases the excited-state lifetime and ФF of the drug deprotonated form (W¯). These later findings could be attributed to the increased rigidity inside the cavity of Me-β-CD. The pKa values extracted from the variations of the UV–visible absorption spectra of W versus the pH of aqueous solution showed that the open isomer is more acidic in both ground and excited states. The positive shifts in pKa values induced by three derivatives of cyclodextrins: HE-β-CD, Ac-β-CD, and Me-β-CD supported the preferential binding of these hosts to open isomers over cyclic.

Download Full-text