Real-Time Observation of Bimodal Proton Transfer in Acid-Base Pairs in Water

Rini, Matteo; Magnes, Ben‐Zion; Pines, Ehud; Nibbering, Erik T. J.

doi:10.1126/science.1085762

Cited by 444 publications

(531 citation statements)

References 19 publications

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“…The visible absorption spectrum of [Fe(tren(py) 3 )] 2+ in CH 3 CN solution is plotted in Figure 3. The intense feature having λ max = 560 nm is due to a spin-allowed metal-to-ligand chargetransfer (MLCT) transition (i.e., 1 A 1 → 1 MLCT); in terms of an orbital description, this absorption corresponds roughly to a (t 2g ) 6 (π*) 0 → (t 2g ) 5 (π*) 1 transition, where the π* orbital is associated with the pyridyl rings of the tren(py) 3 ligand.…”

Section: Resultsmentioning

confidence: 99%

Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

et al. 2010

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Solution-phase photo-induced low-spin to high-spin conversion in the Fe II polypyridyl complex [Fe(tren(py) 3 )] 2+ (where tren(py) 3 is tris(2-pyridylmethylimino-ethyl)amine) has been studied via picosecond soft x-ray spectroscopy. Following 1 A 1 → 1 MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L 2 and L 3 edges were observed concomitant with formation of the transient high-spin 5 T 2 state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of ~1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 Å increase in Fe-N bond length upon formation of the high-spin state. The overall occupancy of the Fe 3d-orbitals remains constant upon spin-crossover, suggesting that the reduction in σ-donation is compensated by significant attenuation of π-back-bonding in the metal-ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft x-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations.

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Section: Resultsmentioning

confidence: 99%

Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

et al. 2010

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“…However, since a transition from photoacid to photobase due to proton transfer is accompanied by a change in the electronic charge distribution, the vibrational transitions due to modes with CÀO stretching content will change in the frequency position and absorption cross-section. [50,51] This is most pronounced when comparing the IR spectra of the groundstate HPTS photoacid and photobase in the frequency range between 1450-1600 cm À1 .…”

Section: Methodsmentioning

confidence: 99%

“…As a result, the transient bands of the HPTS photoacid change their magnitude not only because of rotational diffusion, but also because it converts into the conjugate photobase, as indicated by an ingrowth of photobase bands. We have reported in a previous acid-base neutralization study [50] how changes of the transient spectrum of HPTS in the range around 1500 cm À1 , where the strongest bands of the excited state photoacid and photobase species occur for the upper half of the fingerprint region, indicate the transition from the photoacid to the photobase, when a deuteron transfer to an accepting base takes place.…”

Section: Transient Vibrational Dynamics Of Mpts and Hpts Photoacids Amentioning

confidence: 99%

Solvent‐Dependent Photoacidity State of Pyranine Monitored by Transient Mid‐Infrared Spectroscopy

et al. 2005

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We investigate with femtosecond mid‐infrared spectroscopy the vibrational‐mode characteristics of the electronic states involved in the excited‐state dynamics of pyranine (HPTS) that ultimately lead to efficient proton (deuteron) transfer in H2O (D2O). We also study the methoxy derivative of pyranine (MPTS), which is similar in electronic structure but does not have the photoacidity property. We compare the observed vibrational band patterns of MPTS and HPTS after electronic excitation in the solvents: deuterated dimethylsulfoxide, deuterated methanol and H2O/D2O, from which we conclude that for MPTS and HPTS photoacids the first excited singlet state appears to have charge‐transfer (CT) properties in water within our time resolution (150 fs), whereas in aprotic dimethylsulfoxide the photoacid appears to be in a nonpolar electronic excited state, and in methanol (less polar and less acidic than water) the behaviour is intermediate between these two extremes. For the fingerprint vibrations we do not observe dynamics on a time scale of a few picoseconds, and with our results obtained on the OH stretching vibration we argue that the dynamic behaviour observed in previous UV/Vis pump–probe studies is likely to be related to solvation dynamics.

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“…S3) reveals that initial energy dissipation takes on multiple yet less directional pathways. The coherent low-frequency modes originate from vibronic coupling and are likely ubiquitous in photoexcited environments (22,(39)(40)(41), similar to the case of photoacid pyranine in various solvents (31,(42)(43)(44)(45). Pyranine undergoes ESPT in water following photoexcitation (45), but ESPT is blocked in methanol and multiple low-frequency modes are observed (31).…”

Section: Structural Dynamics In the Chromophore Local Environment Formentioning

confidence: 99%

Excited-state structural dynamics of a dual-emission calmodulin-green fluorescent protein sensor for calcium ion imaging

Oscar

Liu

Zhao

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

191

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Fluorescent proteins (FPs) have played a pivotal role in bioimaging and advancing biomedicine. The versatile fluorescence from engineered, genetically encodable FP variants greatly enhances cellular imaging capabilities, which are dictated by excited-state structural dynamics of the embedded chromophore inside the protein pocket. Visualization of the molecular choreography of the photoexcited chromophore requires a spectroscopic technique capable of resolving atomic motions on the intrinsic timescale of femtosecond to picosecond. We use femtosecond stimulated Raman spectroscopy to study the excited-state conformational dynamics of a recently developed FP-calmodulin biosensor, GEM-GECO1, for calcium ion (Ca 2+ ) sensing. This study reveals that, in the absence of Ca 2+ , the dominant skeletal motion is a ∼170 cm −1 phenol-ring in-plane rocking that facilitates excited-state proton transfer (ESPT) with a time constant of ∼30 ps (6 times slower than wild-type GFP) to reach the green fluorescent state. The functional relevance of the motion is corroborated by molecular dynamics simulations. Upon Ca 2+ binding, this in-plane rocking motion diminishes, and blue emission from a trapped photoexcited neutral chromophore dominates because ESPT is inhibited. Fluorescence properties of site-specific protein mutants lend further support to functional roles of key residues including proline 377 in modulating the H-bonding network and fluorescence outcome. These crucial structural dynamics insights will aid rational design in bioengineering to generate versatile, robust, and more sensitive optical sensors to detect Ca 2+ in physiologically relevant environments.calcium-sensing fluorescent protein | femtosecond Raman spectroscopy | fluorescence modulation mechanism | molecular movie G reen fluorescent protein (GFP) first emerged as a revolutionary tool for bioimaging and molecular and cellular biology about 20 years ago (1-3), and the quest to discover and engineer biosensors with improved and expanded functionality has yielded exciting advances. Recently, the color palette of genetically encoded Ca 2+ sensors for optical imaging (the GECO series) has been expanded to include blue, improved green, red intensiometric, and emission ratiometric sensors (4-7). The GECO proteins belong to the GCaMP family of Ca 2+ sensors that are chimeras of a circularly permutated (cp)GFP, calmodulin (CaM), and a peptide derived from myosin light chain kinase (M13) (8). The CaM unit undergoes large-scale structural changes upon Ca 2+ binding as it wraps around M13. These changes, especially at the interfacial region where CaM interacts with cpGFP, allosterically alter the local environment of the tyrosine-derived chromophore and lead to dramatic fluorescence change in the presence of Ca 2+ (9, 10). Because GCaMP and GECO proteins are genetically encodable, show sensitivity to physiologically relevant Ca 2+ concentrations, and respond to Ca 2+ concentration changes rapidly, they have gained increasing popularity for in vivo imaging of Ca 2+ in neur...

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Real-Time Observation of Bimodal Proton Transfer in Acid-Base Pairs in Water

Cited by 444 publications

References 19 publications

Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

Solvent‐Dependent Photoacidity State of Pyranine Monitored by Transient Mid‐Infrared Spectroscopy

Excited-state structural dynamics of a dual-emission calmodulin-green fluorescent protein sensor for calcium ion imaging

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