Ultrafast Solvation Dynamics Research Articles

Mapping solvation dynamics at the function site of flavodoxin in three redox states.

Flavoproteins are unique redox coenzymes, and the dynamic solvation at their function sites is critical to the understanding of their electron-transfer properties. Here, we report our complete characterization of the function-site solvation of holoflavodoxin in three redox states and of the binding-site solvation of apoflavodoxin. Using intrinsic flavin cofactor and tryptophan residue as the local optical probes with two site-specific mutations, we observed distinct ultrafast solvation dynamics at the function site in the three states and at the related recognition site of the cofactor, ranging from a few to hundreds of picoseconds. The initial ultrafast motion in 1-2.6 ps reflects the local water-network relaxation around the shallow, solvent-exposed function site. The second relaxation in 20-40 ps results from the coupled local water-protein fluctuation. The third dynamics in hundreds of picoseconds is from the intrinsic fluctuation of the loose loops flanking the cofactor at the function site. These solvation dynamics with different amplitudes well correlate with the redox states from the oxidized form, to the more rigid semiquinone and to the much looser hydroquinone. This observation of the redox control of local protein conformation plasticity and water network flexibility is significant, and such an intimate relationship is essential to the biological function of interprotein electron transfer.

Ultrafast solvation and anisotropy dynamics in a tri-branched molecule based on a triphenylamine core

The steady-state spectra and the isotropic and anisotropic fluorescence dynamics of a tri-branched molecule comprising a triphenylamine core and 2,3-di(2-thienyl)acrylonitrile branches were studied in solution and solid film in the femtosecond regime. Isotropic fluorescence dynamics revealed an ultrafast decay component (ranging from 0.3 ps to 6.7 ps depending on solvent and emission wavelength) that was observed only in solution and was attributed to solvation; a slow decay component (∼1 ns), attributed to radiative population decay, was also observed. The solvation process was studied in three different solvents of different polarities and viscosities. The solvation efficiency increased with increasing solvent polarity whilst solvation time was greatest in the solvent of highest viscosity. Anisotropy dynamics showed an ultrafast decay in the fs regime indicating strong intramolecular interactions among the branches.

Ultrafast solvation dynamics at binding and active sites of photolyases

Dynamic solvation at binding and active sites is critical to protein recognition and enzyme catalysis. We report here the complete characterization of ultrafast solvation dynamics at the recognition site of photoantenna molecule and at the active site of cofactor/substrate in enzyme photolyase by examining femtosecond-resolved fluorescence dynamics and the entire emission spectra. With direct use of intrinsic antenna and cofactor chromophores, we observed the local environment relaxation on the time scales from a few picoseconds to nearly a nanosecond. Unlike conventional solvation where the Stokes shift is apparent, we observed obvious spectral shape changes with the minor, small, and large spectral shifts in three function sites. These emission profile changes directly reflect the modulation of chromophore's excited states by locally constrained protein and trapped-water collective motions. Such heterogeneous dynamics continuously tune local configurations to optimize photolyase's function through resonance energy transfer from the antenna to the cofactor for energy efficiency and then electron transfer between the cofactor and the substrate for repair of damaged DNA. Such unusual solvation and synergetic dynamics should be general in function sites of proteins.

Ultrafast solvation dynamics at binding and active sites of photolyases

Ultrafast solvation dynamics at binding and active sites of photolyases

Ultrafast Solvation Dynamics of Flavin Mononucleotide in the Reductase Component of p-Hydroxyphenylacetate Hydroxylase

The reductase unit of p-hydroxyphenylacetate hydroxylase contains flavin mononucleotide (FMN) as a cofactor. Fluorescence decay curves measured by fluorescence up-conversion method were remarkably dependent on monitored emission wavelength. The fluorescence lifetime was shorter at the shorter emission wavelengths and longer at the longer wavelengths. Spectral shift correlation function of p-coumaric acid in water and FMN in C1 protein in buffer solution were expressed by two-exponential functions. Correlation times, phi1 and phi2, of p-coumaric acid were 0.053 and 0.650 ps, respectively, which was similar to previous works. phi1 and phi2 of C1 were 0.455 and 250 ps, respectively. The Stokes shift from t=0 to t=infinity was 2200 cm(-1), while it is 500 cm(-1) in the static Stokes shift obtained by the solvent effect of the fluorescence spectrum under static excitation. This suggests that the isoalloxazine ring of FMN in C1 is exposed in hydrophilic environment. Such large Stokes shift was unusual among flavoproteins. The biphasic decay of the spectral correlation function in C1 was discussed and compared to the biphasic decay of tryptophan in proteins.

Absorption and emission lineshapes and ultrafast solvation dynamics of NO in parahydrogen

We perform a theoretical study on the electronic spectroscopy of dilute NO impurity embedded in parahydrogen (p-H(2)). Absorption and emission lineshapes for the A (2)Sigma(+)<--X (2)Pi Rydberg transition of NO in parahydrogen have been previously measured and simulated, which yielded results for the NO/p-H(2) ground and excited state pair potentials [L. Bonacina et al., J. Chem. Phys. 125, 054507 (2006)]. Using these potentials, we performed molecular dynamics simulation, theoretical statistical mechanical calculations of absorption and emission lineshapes, and both equilibrium and nonequilibrium solvation correlation functions for NO chromophore in parahydrogen. Theory was shown to be in good agreement with simulation. Linear response treatment of solvation dynamics was shown to break down due to a dramatic change in the solute-solvent microstructure upon solute excitation to the Rydberg state and the concomitant increase of the solute size.

A surface science approach to ultrafast electron transfer and solvation dynamics at interfaces

Excess electrons in polar media, such as water or ice, are screened by reorientation of the surrounding molecular dipoles. This process of electron solvation is of vital importance for various fields of physical chemistry and biology as, for instance, in electrochemistry or photosynthesis. Generation of such excess electrons in bulk water involves either photoionization of solvent molecules or doping with e.g. alkali atoms, involving possibly perturbing interactions of the system with the parent-cation. Such effects are avoided when using a surface science approach to electron solvation: in the case of polar adsorbate layers on metal surfaces, the substrate acts as an electron source from where photoexcited carriers are injected into the adlayer. Besides the investigation of electron solvation at such interfaces, this approach allows for the investigation of heterogeneous electron transfer, as the excited solvated electron population continuously decays back to the metal substrate. In this manner, electron transfer and solvation processes are intimately connected at any polar adsorbate-metal interface. In this tutorial review, we discuss recent experiments on the ultrafast dynamics of photoinduced electron transfer and solvation processes at amorphous ice-metal interfaces. Femtosecond time-resolved two-photon photoelectron spectroscopy is employed as a direct probe of the electron dynamics, which enables the analysis of all elementary processes: the charge injection across the interface, the subsequent electron localization and solvation, and the dynamics of electron transfer back to the substrate. Using surface science techniques to grow and characterize various well-defined ice structures, we gain detailed insight into the correlation between adsorbate structure and electron solvation dynamics, the location (bulk versus surface) of the solvation site, and the role of the electronic structure of the underlying metal substrate on the electron transfer rate.

Echo-peak shift fails to resolve the liquid–glass phase transition

The echo-peak shift (EPS) technique, frequently used to study ultrafast solvation dynamics, can be remarkably insensitive to changes in systems’ dynamical properties. This is illustrated by comparing the results of EPS and time-resolved photon echo experiments on temperature-dependent optical dephasing in a glass-forming liquid. The observed failure of the EPS technique appears to be a fundamental problem for systems with strong inhomogeneous contribution to the line broadening.

Towards biosensing of arteriosclerotic nanoplaque formation using femtosecond spectroscopy

The ultrafast dynamics of proteoheparan sulfate (HS-PG) in Krebs blood substitute solution was measured using femtosecond transient absorption spectroscopy after UV excitation. Interacting with blood lipoproteins and Ca 2+ ions, the proteoglycan HS-PG is the key component of the so-called nanoplaque, the earliest stage in atherogenesis. Since tryptophan (Trp) residues are the main optically active parts of HS-PG, analogous measurements were performed on bare Trp in Krebs solution. The comparison reveals distinct differences to main characteristics of the HS-PG broadband absorption spectra. Analyzing the Trp spectra, we show that the results from transient absorption spectroscopy resemble the time constants of the chromophore ultrafast solvation dynamics that have been found by another group using fluorescence up-conversion techniques. Yet, the broadband transient absorption provides more details about the molecular dynamics, including stimulated emission, excited state absorption and resonant energy transfer. Furthermore, the absorption long time dynamics upon adding Ca 2+ to the HS-PG probe were investigated by transient absorption spectroscopy and by surface force and ellipsometry investigations. Notably, a Ca 2+-induced conformational change responsible for arteriosclerotic nanoplaque formation was detected. Slight differences, which are only visible as broad spectral features in the sub-picosecond time scale, provide a first insight into the molecular formation of nanoplaques in blood vessels, which may yield a better understanding of the genesis of arteriosclerosis.

On the non-adiabatic dynamics of solvation: A molecular hydrodynamic formulation

An extended hydrodynamic formulation is developed to describe non-adiabatic solvation dynamics for coupled electronic states. Starting from a hybrid quantum–classical kinetic equation, coupled equations for the solvent local density and momentum density are derived which feature the characteristic population/coherence coupling of the non-adiabatic quantum evolution. These equations have the same formal structure as the non-adiabatic quantum hydrodynamic equations described in [I. Burghardt, L.S. Cederbaum, J. Chem. Phys. 115 (2001) 10312]. In accordance with the molecular hydrodynamics approach, a generalized free energy functional is introduced, adapted to the hybrid quantum–classical setting. A microscopic Marcus-type functional for polar solvation is considered as a special case. The present formulation is particularly appropriate to describe ultrafast solvation dynamics coupled with charge transfer, for example in photochemical charge transfer processes. By the explicit consideration of quantum coherence, the details of the population transfer and its susceptibility to decoherence effects, become amenable to direct investigation.

Ultrafast Solvation Dynamics of Human Serum Albumin: Correlations with Conformational Transitions and Site-Selected Recognition

Human serum albumin, the most abundant protein found in blood plasma, transports a great variety of ligands in the circulatory system and undergoes reversible conformational transitions over a wide range of pH values. We report here our systematic studies of solvation dynamics and local rigidity in these conformations using a single intrinsic tryptophan (W214) residue as a local molecular probe. With femtosecond resolution, we observed a robust bimodal distribution of time scales for all conformational isomers. The initial solvation occurs in several picoseconds, representing the local librational/rotational motions, followed by the dynamics, in the tens to hundreds of picoseconds, which result from the more bonded water in the tryptophan crevice. Under the physiological condition of neutral pH, we measured approximately 100 ps for the decay of the solvation correlation function and observed a large wobbling motion at the binding site that is deeply buried in a crevice, revealing the softness of the binding pocket and the large plasticity of the native structure. At acidic pH, the albumin molecule transforms to an extended conformation with a large charge distribution at the surface, and a similar temporal behavior was observed. However, at the basic pH, the protein opens the crevice and tightens its globular structure, and we observed significantly faster dynamics, 25-45 ps. These changes in the solvation dynamics are correlated with the conformational transitions and related to their structural integrity.

Ultrafast Infrared Mechanistic Studies of the Interaction of 1-Hexyne with Group 6 Hexacarbonyl Complexes

The ultrafast solvation and rearrangement dynamics following the photolysis of M(CO)6 (M = Cr, Mo, W) in terminal alkyne solutions have been investigated. Upon photoinitiated loss of a ligand from the parent metal hexacarbonyl, coordination to an alkyne solvent molecule is followed by rearrangement to a complex that is bound to the terminal alkyne site in a π-bonded fashion. This rearrangement occurs on a time scale that is anticorrelated with the metal−ligand binding energy. A dissociative rearrangement is ruled out for this process in favor of an associative or interchange mechanism. Previous theoretical and experimental studies are examined, and we conclude that the ultimate rearrangement to a vinylidene species is energetically inaccessible at ambient temperatures on the femtosecond to millisecond time scale.

Ultrafast surface solvation dynamics and functionality of an enzyme α-chymotrypsin upon interfacial binding to a cationic micelle

In this contribution we report studies on enzymatic activity of α-chymotrypsin (CHT) upon complexation with cationic cetyltrimethylammonium bromide (CTAB) micelle. With picosecond time resolution, we examined solvation dynamics at the interface of CHT–micelle complex, and rigidity of the binding. We have used 5-(dimethyl amino) naphthalene-1-sulfonyl chloride (dansyl chloride; DC) that is covalently attached to the enzyme at the surface sites. The solvation processes at the surface of CHT in buffer solution are found to be mostly in the sub-50 ps time scale. However, at the interface the solvation correlation function decays with time constant 150 ps (65%) and 500 ps (35%), which is significantly different from those found at the enzyme and micellar surfaces. The binding structure of the enzyme–micelle complex was examined by local orientational motion of the probe DC and compared with the case without micelle. The orientational dynamics of the probe DC in the complex reveals a structural perturbation at the surface sites of CHT upon complexation, consistent with other reported structural studies. We also found possible entanglement of charge transfer dynamics of the probe DC on the measured solvation processes by using time-resolved area normalized emission spectroscopic technique. The interfacial solvation process and complex rigidity elucidate the strong recognition mechanism between CHT and the micelle, which is important to understand the biological function of CHT upon complexation with the micelle.

The Ultrafast Relaxation Dynamics of a Viscosity Probe Molecule in an AOT-Reversed Micelle: Contribution of the Specific Interactions with the Local Environment

The ultrafast relaxation dynamics of a widely used viscosity probe molecule, auramine O (AuO), was investigated in water and a water/aerosol-OT (AOT)/n-heptane reversed micelle. We discussed the contribution of specific interactions between AuO and the local environment to the relaxation dynamics. The transient absorption spectra of AuO showed that the nonradiative relaxation process of the photoexcited AuO in the AOT-reversed micelle was approximately 1 order slower than that in bulk water and the relaxation rate decreased with a decrease of the size of the reversed micelle. The slowing down of the relaxation was attributed to a depletion of the ultrafast solvation dynamics of water molecules in the interfacial area of the reversed micelle as well as an increase of viscosity, which strongly suggested that the viscosity of the reversed micelle determined from the fluorescence yield of AuO was somewhat overestimated. In addition, it was observed that the absorption coefficient of the twisted intramolecular charge transfer-like (TICT-like) intermediate state of the AuO in the reversed micelle was about half as large as that in bulk water. A decrease of the refractive index of the TICT-like state was also observed in the reversed micelle by the ultrafast transient lens measurements. The reduction of both the absorption coefficient and the refractive index of the TICT-like state indicated a considerable change of the molecular structure or the charge distribution of the TICT-like state. Such a change of the TICT-like state suggested the existence of strong interactions between AuO and AOT. These interactions would also affect the relaxation dynamics and the fluorescence yield of the AuO in the reversed micelle.

Ultrafast Solvation Dynamics: A View from the Solvent's Prospective Using a Novel Resonant-Pump, Nonresonant-Probe Technique

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionUltrafast Solvation Dynamics: A View from the Solvent's Prospective Using a Novel Resonant-Pump, Nonresonant-Probe TechniqueDavid F. Underwood and David A. BlankCite this: J. Phys. Chem. A 2003, 107, 45, 9736Publication Date (Web):October 16, 2003Publication History Published online16 October 2003Published inissue 1 November 2003https://doi.org/10.1021/jp031015xCopyright © 2003 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views285Altmetric-Citations7LEARN 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 (41 KB) Get e-Alerts Get e-Alerts

Ultrafast Solvation Dynamics at Silica/Liquid Interfaces Probed by Time-Resolved Second Harmonic Generation.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionUltrafast Solvation Dynamics at Silica/Liquid Interfaces Probed by Time-Resolved Second Harmonic Generation.Xiaoming Shang, Alexander V. Benderskii, and Kenneth B. EisenthalCite this: J. Phys. Chem. B 2001, 105, 47, 11928Publication Date (Web):November 2, 2001Publication History Published online2 November 2001Published inissue 1 November 2001https://doi.org/10.1021/jp0135196Copyright © 2001 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views199Altmetric-Citations2LEARN 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 (9 KB) Get e-Alerts Get e-Alerts

Ultrafast Solvation Dynamics at Silica/Liquid Interfaces Probed by Time-Resolved Second Harmonic Generation

The static absorption and ultrafast solvation dynamics of a tricarbocyanine dye IR144 at the silica/acetonitrile and the silica/butanol interfaces were investigated by using steady-state second harmonic generation (SHG) spectroscopy and pump-probe time-resolved SHG (TRSHG) experiments. At both interfaces, the peak wavelength for the S0 f S1 transition of adsorbed IR144 is significantly red-shifted with respect to the maximum absorption wavelength in the corresponding bulk solvent. Because IR144 is negatively solvatochromic, this shift is indicative of a smaller polarity at the interface. A theoretical model of TRSHG is discussed which allows extraction of the solvation dynamics correlation function from the time dependence of the TRSHG signal measured in the pump-probe experiment at a chosen probe wavelength. The time constant for the diffusive component of solvation at the silica/acetonitrile interface was found to be 1.05 ( 0.14 ps. It is somewhat shorter, although of the same order of magnitude, than the time constant for the diffusive solvation in bulk acetonitrile, 2.23 ps. At the silica/butanol interface, a time constant of 1.20 ( 0.15 ps was extracted, whereas in the bulk butanol, the corresponding diffusive solvation is biexponential with times of 3.5 and 33 ps.

Temperature dependent relaxation and recombination dynamics of the hydrated electron

The ultrafast solvation and recombination dynamics of the hydrated electron generated by two-photon ionization of water at 4.65 eV is studied by transient absorption spectroscopy as a function of temperature in the range from 277 K to 355 K. The part of the spectral blue shift which is observed in the absorption spectrum of the hydrated electron after 1 ps is purely continuous and is accurately described by the well known analytical expression for the temperature dependent absorption spectrum of the ground state hydrated electron. This indicates that thermal relaxation or more likely solvation of the hydrated electron predominantly causes the blue shift. The survival probability of the hydrated electron shows a strong temperature dependence, which is satisfactory explained by the temperature dependent mobility and reaction rates of the species involved in the recombination. This implies that the average initial separation between the hydrated electron and the ionization site of 〈r0〉=1.0±0.1 nm does not depend significantly on the bulk water temperature.

Ultrafast Solvation Processes in Polar Liquids Probed with Large Organic Molecules

Several optical techniques are used to characterize the ultrafast solvation dynamics of two structurally different molecules, LD690 and LDS750. Linear absorption, fluorescence, resonance Raman, and time-resolved four-wave mixing experiments have been performed on both molecules in a variety of solvents. The combination of different experiments is necessary to characterize the femtosecond dynamics. We find that both molecules exhibit very fast dephasing, due to sub-100 fs decays of the solvation correlation function M(t). The LD690 data is analyzed in depth, using a multimode oscillator model to treat both intramolecular vibrations and the solvent coordinates. The dynamics are solvent-dependent, but this dependence cannot be explained in a straightforward manner using quantities such as inertial solvent rotational motion or a simple dielectric continuum response. Various aspects of the spectroscopy, both linear and nonlinear, provide clues that the dynamics are influenced by molecular-level interactions th...

Effect of Solute Orientation on Solvation Dynamics at the Air/Water Interface

The ultrafast solvation dynamics of courmarin 314 (C314) molecules at the air/water interface has been shown to depend on their orientation with respect to the plane of the interface. A pump/second harmonic probe method using femtosecond laser pulses were used to measure the interface solvation dynamics. The pump light was S polarized, i.e., in the interface plane, or P polarized, i.e., in the plane perpendicular to the plane of the interface. The S pumped C314 molecules yielded a solvation time of 820 ± 60 fs, whereas P pumped yielded a solvation time of 1215 ± 90 fs. The interface inhomogeneous broadening on the solvation time scale is due to the differing orientations of C314 at the air/water interface.