Transient Grating Method Research Articles

Photodecarboxylation of ketoprofen studied by transient absorption spectroscopy and transient grating method: Estimation of the partial molar volume of carbon dioxide

The photoreaction of ketoprofen, a widely used nonsteroidal anti-inflammatory drug (NSAID), was intensively investigated in methanol by transient absorption spectroscopy and transient grating (TG) method. From quantitative analyses of the transient absorption and of the TG signal due to CO2, we successfully determined the partial molar volume of CO2 to be 46 ± 2 cm3 mol−1. With the partial molar volume of CO2 obtained in this work, the reaction quantum yield of photodecarboxylation of other NSAIDs can be estimated from only the TG signal. The approach with the TG method would be a new tool for evaluating photoreactivity of NSAIDs.

Development of charge carrier-selective heterodyne transient grating spectroscopic technique and its application in the distinction of surface trap states in hematite.

We developed a new spectroscopic technique, which is named the charge carrier-selective heterodyne transient grating (CS-HD-TG) method, for the distinction of surface trap states existing in photocatalysts and photovoltaic materials by employing a burn laser inducing depletion of the number of surface trapped charge carriers. In addition, as a case study, we measured the heterodyne transient grating responses of hematite under bias conditions with and without the burn laser and revealed that two distinct trap states co-exist at the surface of the hematite film and only one of them could act as the reaction intermediate for the oxygen evolution reaction (OER), which is consistent with former studies.

Using deep learning to identify the depth of metal surface defects with narrowband SAW signals

An effective nondestructive testing technique that enables the detection and quantification of surface and subsurface defects is highly demanded for assuring the safety and reliability of materials. In this paper, we classified and regressed defects with different depths. A transient thermal grating (TTG) method induced by a pulsed laser is used to characterize the properties of surface defects. Based on thermo-elasticity theory, a theoretical model with different types of surface defects is established with the finite element method (FEM). Surface acoustic waves (SAWs) excited by the TTG method propagate at the surface of a sample with defects at different penetration depths and are measured by a vibrometer.By combining the simulation and experimental results, the time–frequency scalograms of 8200 images were obtained by wavelet transform analysis. 70 % of the images are randomly selected to train the residual network (Resnet) model, and the remaining data (2460 images), as well as 10 scalograms in an independent experiment, are used as previously unknown experimental signals to test the robustness of the Resnet model. The results indicate that the Resnet with scalograms via wavelet transform achieves a 96.21 % classification accuracy on the validation set, with a prediction accuracy of 90.00 % for the 10 scalograms. Moreover, compared with three widely used machine learning algorithms, VGG16, back propagation (BP), and support vector machine (SVM), this method achieves the highest classification accuracy. Finally, 500 data selected randomly from the previously trained experimental database and 10 data in an independent experiment are used for regression prediction. The result shows that the data are well located along or close to a straight line with a slope of 1. The statistical results suggest that 80.6 % (66.0 %) of the residuals of the experimental data fell within the size range ±10 μm (±5 μm). This work proves the feasibility and reliability of the combination of the Resnet model with wavelet transform and numerical simulation to identify the depth of surface defects using laser ultrasonics.

Revealing protein reactions using transient grating method: Photo-induced heating, volume change, and diffusion change

The transient grating (TG) method, which is one of the photothermal techniques, can enable sensitive detection of thermal energy with high temporal resolution based on changes in the refractive index of a material. In addition to thermal energy, the TG method can also detect any changes that affect the refractive index, such as changes in the partial molar volume and in the absorption spectrum far from the probe wavelength. In this Perspective, recent studies on chemical reaction dynamics of proteins using the TG method are reviewed and discussed. To reveal the reaction schemes of proteins, it is particularly important to detect dynamics that cannot be detected by optical spectroscopy (spectrally silent dynamics), such as enthalpy changes, conformational changes, and changes in intermolecular interactions (protein–water, protein–protein, protein–lipids, and protein–DNA). The TG method is appropriate and powerful for such applications. Spectrally silent dynamics have clearly been observed by monitoring time-resolved diffusion and volume changes. Furthermore, the impact of the structural fluctuation of proteins on their reactivity has been successfully demonstrated by monitoring the thermal expansion and compressibility changes of short-lived intermediates. For expansion of the TG application to non-photochemical reactions, one attempt using the stopped flow-TG technique is described. Future possible applications of the TG method are suggested.

Applications of Time-Resolved Thermodynamics for Studies on Protein Reactions

Thermodynamics and kinetics are two important scientific fields when studying chemical reactions. Thermodynamics characterize the nature of the material. Kinetics, mostly based on spectroscopy, have been used to determine reaction schemes and identify intermediate species. They are certainly important fields, but they are almost independent. In this review, our attempts to elucidate protein reaction kinetics and mechanisms by monitoring thermodynamic properties, including diffusion in the time domain, are described. The time resolved measurements are performed mostly using the time resolved transient grating (TG) method. The results demonstrate the usefulness and powerfulness of time resolved studies on protein reactions. The advantages and limitations of this TG method are also discussed.

Molecular diffusion and aggregate formation of photoproducts from ketoprofen in aqueous solutions

We investigated photochemical reaction of deprotonated ketoprofen (KP−) in aqueous solutions at neutral pH by transient grating (TG) method. At low excitation fluences or KP− concentrations, the TG signal showed molecular diffusion of KP− and its photoproducts such as hydrogen carbonate and 3-ethylbenzophenone (3-EBP). On the other hand, at high fluences or high KP− concentrations, the aggregation dynamics of 3-EBP was observed. The hydrodynamic radii of the formed aggregates reached beyond 5 nm, and their formation was driven in water-rich solutions.

Origin of photoelastic phenomena in Ge-Se network glasses

The elastic properties of a series of Ge-Se glasses are measured during irradiation with sub-band-gap light using a laser-induced transient grating method. The elastic modulus is found to decrease prominently with increasing irradiation intensity. The process is found to be less prominent in glasses of high average coordination $\ensuremath{\langle}r\ensuremath{\rangle}$. Measured kinetics in the millisecond range are found to be too slow for a photoinduced electronic process and instead suggest a thermal origin. Infrared thermography is performed during irradiation to monitor temperature changes during photodarkening, photoexpansion, and photoelastic measurements. It is found that in the conditions of irradiation where photoelasticity is observed, all photostructural changes are directly associated with a change in temperature. comsol modeling of thermal flow through the sample closely reproduces the kinetics of photodarkening. Transient grating measurements as a function of temperature confirm that the change in elasticity during irradiation is essentially a thermally induced process. Currently available experimental evidence indicates that the photoelastic phenomena are not an optoelectronic process but rather the result of laser heating.

Photoreaction of photoactivated adenylate cyclase from cyanobacterium Microcoleus chthonoplastes.

The photochemical reaction of photoactivated adenylate cyclase from cyanobacterium Microcoleus chthonoplastes PCC 7420 (mPAC), which consists of a Per-Arnt-Sim (PAS), a light‑oxygene-voltage (LOV), and an adenylate cyclase (AC) domain, was investigated mainly using the time-resolved transient grating method. An absorption spectral change associated with an adduct formation between its chromophore (flavin mononucleotide) and a cysteine residue was observed with a time constant of 0.66μs. After this reaction, a significant diffusion coefficient (D)-change was observed with a time constant of 38ms. The determined D-value was concentration-dependent indicating a rapid equilibrium between the dimer and tetramer. Combining the results of size exclusion chromatography and CD spectroscopy, we concluded that the photoinduced D-change was mainly attributed to the equilibrium shift from the dimer rich to the tetramer rich states upon light exposure. Since the reaction rate does not depend on concentration, the rate determining step of the tetramer formation is not the collision of proteins by diffusion, but a conformation change. The roles of the PAS and AC domains as well as the N- and C-terminal flanking helices of the LOV domain (A'α- and Jα-helices) were investigated using various truncated mutants. The PAS domain was found to be a strong dimerization site and is related to efficient signal transduction. It was found that simultaneous existence of the A'α- and Jα-helices in mPAC is important for the light-induced conformation change to lead the conformation change which induces the tetramer formation. The results suggest that the angle changes of the coiled-coil structures in the A'α and Jα-helices are essential for this conformation change. The reaction scheme of mPAC is proposed.

Size evaluation of gold nanoparticles using transient grating method with deep-UV excitation pulses

Transient grating (TG) method was applied for evaluating the size of gold nanoparticles (AuNPs) in aqueous solution. Using nanosecond deep-UV pulses for excitation, AuNPs were reduced to smaller particles, making it feasible to determine their diffusion coefficients and hydrodynamic diameters. The diffusion signals of AuNPs were enhanced significantly by probing at the plasmon resonant wavelength, enabling the data acquisition within a few seconds. The determined hydrodynamic diameters were in agreement with those by other experimental techniques, indicating that the TG method is applicable for size evaluation of these nanoparticles in solution at short time.

Spectrally Silent Protein Reaction Dynamics Revealed by Time-Resolved Thermodynamics and Diffusion Techniques.

Biological functions essentially consist of a series of chemical reactions, including intermolecular interactions, and also involve the cooperation of a number of biological molecules performing these reactions. To understand this function at the molecular level, all steps of the reactions must be elucidated. However, since the biosystems including the surrounding environment are notably large, the reactions have to be elucidated from several different approaches. A variety of techniques have been developed to obtain structural information, and the knowledge of the three-dimensional structure of biomolecules has increased dramatically. Contrarily, the current information on reaction dynamics, which is essential for understanding reactions, is still not enough. Although frequently used techniques, such as spectroscopy, have revealed several important processes of reactions, there are various hidden dynamics that are not detected by these methods (silent dynamics). For example, although water molecules are essential for bioreactions, dynamics of the protein-water interaction are very difficult to trace and spectrally silent. Transient association/dissociations of proteins with partner proteins are difficult to observe. Another important property to understand the reaction of proteins is fluctuations, which are random movements that do not change the average structure and energy. The importance of fluctuations has been pointed out in order to explain enzymatic activity; however, it is extremely difficult to detect changes in fluctuation during a reaction. In this Account, unique time-resolved methods, time-resolved thermodynamics, and time-resolved diffusion methods, both of which are able to detect silent dynamics in solution at physiological temperature, are described.Thermodynamic properties are important for characterizing materials, in particular, macromolecules such as biomolecules. Therefore, the data available regarding these properties, for several stable proteins, is abundant. However, it is almost impossible to characterize short-lived intermediate species in irreversible reactions using traditional thermodynamic techniques. Similarly, although the translational diffusion coefficient is a useful property to determine the protein size and intermolecular interactions, there have been no reports revealing reaction dynamics. The transient grating (TG) method enables us to measure these quantities in a time-resolved manner for a variety of irreversible reactions. With this method, it is now possible to study biomolecule reactions from the viewpoint of thermodynamic properties and diffusion, and to elucidate reaction dynamics that cannot be detected by other spectroscopic methods.Here, the principles of the methodologies used, their characteristic advantages, and their applications to protein reactions are described. The TG measurements of octopus rhodopsin revealed a spectrally hidden intermediate and determined an energetic profile along the reaction coordinate. This emphasizes that the measurement in solution, not for trapped intermediates, is important to characterize the reaction intermediates. The application of these methods to a blue light sensor PixD revealed many spectrally silent dynamics as well as the importance of fluctuation for the reaction. As an example of the time-resolved heat capacity change and transient thermal expansion measurements, the reaction of PYP was briefly described. The reaction scheme of another blue light sensor protein, phototropins, and a spectrally silent DNA binding process of EL222 were fully elucidated by the time-resolved diffusion method.

Diffusion process in photoreaction of ketoprofen probed by transient grating method

Translational diffusion dynamics in photoreaction of ketoprofen (KP), one of the most popular nonsteroidal anti−inflammatory drugs, with and without triethylamine (TEA) in methanol was studied by transient grating method coupled with transient absorption spectroscopy. We successfully determined diffusion coefficients of neutral, carboxylate anion, ketyl radical of KP as well as ketyl biradical complex with TEA in methanol for the first time. The diffusion coefficients for the ketyl radical (6.9 × 10−10 m2 s−1), the carboxylate anion (8.1 × 10−10 m2 s−1), and the complex (5.6 × 10−10 m2 s−1) were found to be smaller than that for neutral KP (9.8 × 10−10 m2 s−1). The molecular volume, the viscosity of the solvent, and/or a specific attractive interaction with solvent molecules would contribute to the diffusion process of these species. These new findings on the diffusion property and the interaction of each species with surrounding molecules are essential for understanding the photoreaction of KP with various biomolecules in vivo.

A Transient Grating Method to Measure the Dispersion of Elastic Waves in Nanostructures

We describe the so-called “Transient Grating Method” which is a non-invasive experimental technique well suited to measure the dispersion properties of ordered or disordered nanostructures and thin films, at frequencies up to a few GHz. This pump-and-probe technique involves the interference pattern produced by two in-coming IR optical pulses to set a standing elastic wave on the surface of the sample through photoelastic processes. The wave vector of this elastic wave can be easily tuned by adjusting the angle between the two incident beams. Two continuous visible laser beams in a heterodyne detection scheme are used to detect the vibrations on the surface and in turn the dispersion of the related elastic modes. The achievements of the technique are illustrated by the measurement of the dispersion of surface acoustic waves in piezogenerators consisting of GaN nanowires embedded into a dielectric matrix (HSQ). We then report on the analysis of the experimental data that allowed extracting the elastic parameters of this composite medium.

Photoreaction Dynamics of Full-Length Phototropin from Chlamydomonas reinhardtii.

Phototropin (phot) is a blue light sensor involved in the light responses of several species from green algae to higher plants. Phot consists of two photoreceptive domains (LOV1 and LOV2) and a Ser/Thr kinase domain. These domains are connected by a hinge and a linker domain. So far, studies on the photochemical reaction dynamics of phot have been limited to short fragments, and the reactions of intact phot have not been well elucidated. Here, the photoreactions of full-length phot and of several mutants from Chlamydomonas reinhardtii (Cr) were investigated by the transient grating and circular dichroism (CD) methods. Full-length Cr phot is in monomeric form in both dark and light states and shows conformational changes upon photoexcitation. When LOV1 is excited, the hinge helix unfolds with a time constant of 77 ms. Upon excitation of LOV2, the linker helix unfolds initially followed by a tertiary structural change of the kinase domain with a time constant of 91 ms. The quantum yield of conformational change after adduct formation of LOV2 is much smaller than that of LOV1, indicating that reactive and nonreactive forms exist. The conformational changes associated with the excitations of LOV1 and LOV2 occur independently and additively, even when they are excited simultaneously. Hence, the role of LOV1 is not to enhance the kinase activity in addition to LOV2 function; we suggest LOV1 has different functions such as regulation of intermolecular interactions.

Spiropyran labeling for sensitive probing of protein diffusion by the transient grating method

The pulsed laser induced transient grating method is a powerful technique for measuring the diffusion coefficient (D) sensitively with a high time-resolution. For expanding the applicability of this method, a labeling method with a spiropyran derivate is demonstrated. The signals upon photoexcitation of the labeled proteins were strong and it was simple to determine D accurately. D and the circular dichroism spectra at various concentrations of a denaturant were measured and it was found that D changes before the circular dichroism spectrum change at a low concentration region, indicating that D is a sensitive probe for monitoring protein conformation.

Time-Resolved Diffusion Detection with Microstopped Flow System

The transient grating (TG) method is a powerful technique for monitoring the time dependence of the diffusion coefficient during photochemical reactions. However, the applications of this technique have been limited to photochemical reactions. Here, a microstopped flow (μ-SF) system is developed to expand the technique's applicability. The constructed μ-SF system can be used for a solution with a total volume as small as 3 μL, and mixing times for absorption and diffusion measurements were determined to be 400 μs and 100 ms, respectively. To demonstrate this system with the TG method, an acid-induced denaturation of a photosensor protein, phototropin LOV2 domain with a linker, was studied from the viewpoint of the reactivity. This system can be used not only for time-resolved diffusion measurement but also for conventional absorption or fluorescence detection methods. In particular, this system has a great advantage for a target solution in that only a very small amount is needed.

Time-Resolved Study of Interprotein Signaling Process of a Blue Light Sensor PapB-PapA Complex.

PapB is a short BLUF protein from the purple bacterium Rhodopseudomonas palustris, and it has the function of regulating the phosphodiesterase activity of its partner protein PapA. Because PapA is an enzymatic protein containing an EAL domain, which hydrolyzes a cyclic-dimeric-GMP, the PapB-PapA complex regulates, for example, biofilm formation in a light-dependent manner. The reaction dynamics of PapB, as well as dynamics of signal transduction in the PapB-PapA complex, were studied mostly by time-resolved transient grating and CD methods. It was found that although PapB exists as a monomer in both dark and light states, the diffusion coefficient slightly increases and partial molar volume changes upon light irradiation with time constants of 80 μs, 3.2 ms, and 24 ms. The last conformational change leads to a signaling state that is attributed to the α-helix unfolding in the C-terminal region of the BLUF domain. Interestingly, when PapA is added to a PapB solution to form a PapB-PapA complex, the diffusion coefficient decreases significantly, with a time constant of 26 ms, which is similar to the rate of the last conformational change of PapB. It was found that this change is due to the conformational change of PapA, and the light signal from PapB is transmitted through the conformational change of PapB. Compared with another BLUF protein, BlrP1, which possesses the EAL effector domain and requires photoexcitation of two monomer units of the dimer for a major conformational change, the conformational change of the PapB-PapA complex is induced by excitation of one monomer PapB among the heterotetramer.

Characterization of Texture Evolution during Recrystallization by Laser-Induced Transient Thermal Grating Method

The analyses of texture evolution of cold rolled interstitial free (IF) steel sheets during annealing and recrystallization are presented, in which the dispersion curves of surface acoustic waves (SAW) excited by laser-induced transient thermal grating method are measured. The results show that the angular anisotropy of the SAW velocity changes due to the texture changes at different stages of recrystallization. The theoretically simulated angular dispersion of SAW velocity within individual crystal revealed that the change of SAW velocity is closely related to recrystallization texture evolution. A model for the angular dependence of the SAW velocity in textured polycrystalline IF steel with different oriented crystals is presented and the simulations are yielded, which show that the results agree with those of experiments.

The Photoreaction Dynamics and Its Diversity of Phototropin Studied by the Transient Grating Method

The Photoreaction Dynamics and Its Diversity of Phototropin Studied by the Transient Grating Method

Evaluation of Effective Elastic Properties of Nitride NWs/Polymer Composite Materials Using Laser-Generated Surface Acoustic Waves

In this paper we demonstrate a high potential of transient grating method to study the behavior of surface acoustic waves in nanowires-based composite structures. The investigation of dispersion curves is done by adjusting the calculated dispersion curves to the experimental results. The wave propagation is simulated using the explicit integral and asymptotic representations for laser-generated surface acoustic waves in layered anisotropic waveguides. The analysis of the behavior permits to determine all elastic constants and effective elastic moduli of constituent materials, which is important both for technological applications of these materials and for basic scientific studies of their physical properties.

Probing elastic properties of nanowire-based structures

We report the analysis of elastic properties of a composite medium consisting of GaN nanowires embedded into a dielectric matrix, which constitutes the active material of nanowire-based piezogenerators. A non-invasive technique, Transient Grating Method, is used to generate and analyze the propagation of acoustic waves in the frequency range from a few tens of MHz to several GHz. The wave propagation is simulated using the time-efficient computer model based on the explicit integral and asymptotic representations for laser-generated surface acoustic waves in layered anisotropic waveguides. Effective parameters of the multilayered model are obtained via the minimization of the discrepancy between the measured and calculated wave characteristics. A comparison with a reference composed of a dielectric matrix without nanowires shows that the mechanical behavior is strongly influenced by the presence of the nanostructures.