Laser-induced Temperature-jump Research Articles

Measuring Double Layer Charging Via Droplet Approach Technique

The potential of zero-charge (PZC) is an important property of the electrochemical double layer (EDL) that has been shown to correlate with changes in the activities of several important reactions such as the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER)1. This property was historically measured on droplet mercury electrodes (DME) where surface tension was measured vs potential, an experiment difficult to perform with other metal electrodes. Electrochemical impedance spectroscopy, cyclic voltammetry and galvanic discharge have been widely used to elucidate double layer capacitance but make several assumptions about the ideality of the double layer, measurement system, physical model employed, and have suffered from irreproducibility. The potential of maximum entropy (PME), where the solvent molecules are most disordered, has been measured via the laser induced temperature jump (LITJ) technique which works well when there is no specific adsorption2. A multiple approach mode of scanning electrochemical cell microscopy (SECCM) has also been used to measure local PZCs of polycrystalline3 and high-entropy alloy electrodes4. The SECCM approach is similar to an older immersion method that is not often used5. In this work we create a simple droplet type cell with a pneumatic sample stage to enable a simplified and less expensive version of the SECCM approach/immersion experiments and compare the results to those obtained via the LITJ method.

Temperature Jump Methods for Measuring the Pme of RuO2

The potential of maximum entropy (PME) is used to understand the structure and charging of the electrochemical double layer. Closely related to the potential of zero charge (PZC), the PME occurs when disorder of the solvent molecules at the surface reaches a maximum. Using a laser induced temperature jump (LITJ) to measure the PME has been shown to be a convenient method for metal electrodes. We present experiments using LITJ to investigate a metal oxide thin film and film thickness. The PME of these thin films appears to change with thickness, correlating with surface strain where a thinner film shifts the PME closer to OER potentials in turn reducing the overpotentials required. Our experiments are shown to be reproducible and independent of sweep rate or the vertex potentials selected. Interestingly we observe a hysteresis with scan direction, of 100-250 mV which we nominally attribute to surface adsorbates. Our results highlight the link between excess surface charge and catalytic activity and how this may be tuned via surface strain. Figure 1

Effect of the interfacial electric field on the HER on Pt(111) modified with iron adatoms in alkaline media

The study of the hydrogen evolution reaction (HER) aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy. In previous works, laser-induced temperature jump (LITJ) experiments on Pt(111) modified with Ni(OH)2 in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER. It was hypothesised that small amounts of Ni(OH)2 cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution. In this work, to test the validity of this hypothesis, the study has been extended to Pt(111) surfaces modified with Fe(OH)2. The modified surfaces have been studied voltammetrically, and the voltammetric charges have been analysed. The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II) to Fe(0). In agreement with the coulometric analysis, the voltammetric features in the OH adsorption region would be related with the oxidation to the +3 valence state. The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules, shifting the potential of maximum entropy away from the onset of the HER. Hence, the most catalytic surface is the one with the lowest Fe coverage.

Fast-Folding Kinetics Using Nanosecond Laser-Induced Temperature-Jump Methods.

The development of ultrafast kinetic methods is one of the factors that allowed the research on protein folding to flourish over the last 20years. The introduction of new optical triggering techniques enabled to experimentally investigate the protein dynamics at the nanosecond to millisecond timescale, allowing researchers to test theoretical predictions and providing experimental benchmarks for computer simulations. In this work, the details of how to perform kinetic experiments by the laser-induced temperature-jump technique, using the two most commonly used probing techniques (namely infrared absorption and fluorescence spectroscopy) are given, with a strong emphasis on the practical details.

Elucidating the Structure of the Cu-Alkaline Electrochemical Interface with the Laser-Induced Temperature Jump Method

A detailed description of the Cu–electrolyte interface is vital to understand the electrocatalytic properties of Cu surfaces. Herein, we combine cyclic voltammetry and the laser-induced temperature...

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

We present work detailing the destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) via rapid laser heating under atmospheric conditions. Following Nd:YAG laser ablation of l...

Interfacial Study of Nickel-Modified Pt(111) Surfaces in Phosphate-Containing Solutions: Effect on the Hydrogen Evolution Reaction.

The surface modification of electrodes attracts great interest in electrocatalysis. It has often been observed that deposition of foreign adatoms on the surface of an electrode can originate a significant enhancement in the catalytic activity. For example, it has been reported that nickel deposits on Pt surfaces improve the rate of the hydrogen evolution reaction (HER, Nature Energy 2017, 2, 17031). During the deposition process of such metal adlayers, the pH and the nature of the ions in the electrolyte play an important role. Phosphate species are typically used to prepare buffer solutions in a wide range of pH. Therefore, electrolytes containing phosphate species are used in a large number of applications. However, the effect of phosphate on platinum surface modification with nickel deposits has not been studied yet. In this work, new data about the interaction of phosphate with nickel adatoms deposited on Pt(111) at pH 5 is investigated using cyclic voltammetry and infrared spectroscopy. The results show that, when nickel is in solution, the phosphate ions are adsorbed at lower potentials than in the absence of nickel. In addition, Laser-Induced Temperature Jump Technique demonstrates that nickel facilitates the adsorption of phosphate because of a shift of the potential of zero charge (pzc) toward negative potentials. This increases the magnitude of the positive electric field on the electrode surface, at a given potential E>pzc, facilitating the adsorption of anions. CO displacement technique has been also employed to obtain additional information about co-adsorbed phosphate on nickel adlayers. Finally, the HER has been studied at pH 5 in the presence of nickel, with and without phosphate in the bulk solution.

Investigating the M(hkl)| ionic liquid interface by using laser induced temperature jump technique

The interface between several Room Temperature Ionic Liquids (RTILs) in contact with both Au(hkl) basal planes and Pt(111) was studied by using cyclic voltammetry and Laser Induced Temperature Jump Technique (LITJT). Three RTILs, based on the imidazolium cation and the [Tf2N] anion were investigated: [Emmim][Tf2N], [Emim][Tf2N] and [Bmmim][Tf2N]. These three RTILs were selected with the aim to analyse how the balance between the different ion-ion interactions influences the interfacial properties of the M(hkl)|RTIL interface. It was found that the voltammetric response of the Au(hkl)|[Emmim][Tf2N] was highly sensitive to the geometry of the active surface sites, displaying sharp spikes superimposed to a capacitive voltammetric current. Conversely, these sharp spikes disappeared when [Bmmim][Tf2N] replaced [Emmim][Tf2N], although the capacitive voltammetric current profile was essentially maintained. This result is most likely related to the increase of the van der Waals interactions in the [Bmmim][Tf2N]. When [Emim][Tf2N] was analysed, the increase of the hydrogen bond interactions due to the hydrogenation of C2 (second carbon at the imidazolium ring) resulted also in the disappearance of the voltammetric spikes. The laser measurements showed that the highest values of the potential of maximum entropy (pme) in RTIL media correspond to the atomically closest packet surface structures, following the order: Au(111)>Au(100)>Au(110), in agreement with work function values. The measurement with Pt(111) revealed that the voltammetric profiles for this surface are featureless in all cases. However, the laser experiments showed that solvent restructuration, as a function of both value and direction of the applied potential, is dependent on the type of cation.Finally, the interface Au(hkl)|Choline chloride:urea Deep Eutectic Solvent (DES) was also investigated by using cyclic voltammetry and LITJT. The voltammetric response of DES was also sensitive to the orientation of the Au single crystal, and the cyclic voltammograms displayed distinct sharp and characteristic features. Nevertheless, the laser response could not provide a value of the pme for the Au(hkl)|DES interface, likely due to the complex chemical structure of the DES which, in addition, strongly adsorbs on Au(hkl).

レーザー温度ジャンプ型過渡透過光計測法による温度応答性高分子水溶液の相分離ダイナミクスの研究

レーザー温度ジャンプ型過渡透過光計測法による温度応答性高分子水溶液の相分離ダイナミクスの研究

Impact ofβ-Turn Sequence onβ-Hairpin Dynamics Studied with Infrared-Detected Temperature Jump

Folding dynamics forβ-structure loss and disordered structure gain were studied in a modelβ-hairpin peptide based on Cochran’s tryptophan zipper peptide Trpzip2, but with an altered Thr-Gly (TG) turn sequence, that is, SWTWETGKWTWK, using laser-induced temperature-jump (T-jump) kinetics with IR detection. As has been shown previously, the TG turn sequence reduces the thermodynamicβ-hairpin stability as compared to the Asn-Gly sequence used in Trpzip2 (TZ2-NG). In this study, we found that the TG-turn slows down the overall relaxation dynamics as compared to TZ2-NG, which were studied at higher temperatures where the time constants show little difference between relaxation of theβ-strand and the disordered conformation. These time constants become equivalent at lower temperatures for TZ2-TG than was seen for TZ2-NG. The correlation of thermodynamic stability and rates of relaxation suggests that the change from NG to TG turn results in a slowing of folding, lowerkf, with less change of the unfolding rate,ku, assuming two state behavior at higher temperatures.

Anion Adsorption and Adsorption/Desorption Kinetics onto/from Au(111) Electrodes Studied Using the Indirect Laser-Induced Temperature Jump Technique

We demonstrate that the potential dependence of the initial change (A/ΔTeq) in the open-circuit potential of Au(111) | (nonelectroactive) electrolyte solution interfaces (effected by the temperature perturbation (ΔTeq) induced by the indirect laser-induced temperature jump (ILIT) technique) is sensitive to the presence of the anion components of the electrolyte adsorbed onto the electrode surfaces for a wide variety of anions. Analysis of the potential dependence of A/ΔTeq for the ClO4− and SO42− anions, therefore, is used to ascertain (for ClO4−) or estimate (for SO42−) the temperature derivative of the dipole potential (i.e., (dVD)/(dT)) associated with the relevant Au(111) | electrolyte solution interface. The value and any potential dependence of (dVD)/(dT) are suitable probes of the structure of the pertinent electrode | electrolyte interface. The negative value determined here for the (dVD)/(dT) associated with a complete (saturated) layer of ClO4− ions adsorbed onto a Au(111) electrode surface (i.e...

Rapid Thermal Tuning of Chromophore Structure in Membrane Protein

We show that the configuration and the optical property of the retinal chromophore in bacteriorhodopsin (bR) can be tuned dynamically from the all-trans configuration to the 13-cis by using a nanosecond laser-induced temperature-jump. The rapid bleach in the visible absorption optical density of retinal has an apparent formation time of ca. 170 ns, whereas the relaxation process finishes within tens of ms. The dynamical transition of retinal from the all-trans to 13-cis species is believed to occur as a result of rapid protein conformational change especially in the vicinity of retinal binding site. Our study reveals the intrinsic dynamical aspect of the retinal chromophore with respect to the protein structure.

Probing the folding intermediate of Rd‐apocyt b562 by protein engineering and infrared T‐jump

Small proteins often fold in an apparent two-state manner with the absence of detectable early-folding intermediates. Recently, using native-state hydrogen exchange, intermediates that exist after the rate-limiting transition state have been identified for several proteins. However, little is known about the folding kinetics from these post-transition intermediates to their corresponding native states. Herein, we have used protein engineering and a laser-induced temperature-jump (T-jump) technique to investigate this issue and have applied it to Rd-apocyt b(562) , a four-helix bundle protein. Previously, it has been shown that Rd-apocyt b(562) folds via an on-pathway hidden intermediate, which has only the N-terminal helix unfolded. In the present study, a double mutation (V16G/I17A) in the N-terminal helix of Rd-apocyt b(562) was made to further increase the relative population of this intermediate state at high temperature by selectively destabilizing the native state. In the circular dichroism thermal melting experiment, this mutant showed apparent two-state folding behavior. However, in the T-jump experiment, two kinetic phases were observed. Therefore, these results are in agreement with the idea that a folding intermediate is populated on the folding pathway of Rd-apocyt b(562) . Moreover, it was found that the exponential growth rate of the native state from this intermediate state is roughly (25 microsec)(-1) at 65 degrees C.

Nanosecond-time-resolved infrared spectroscopic study of fast relaxation kinetics of protein folding by means of laser-induced temperature-jump

Elucidating the initial kinetics of folding pathways is critical to the understanding of the protein folding mechanism. Transient infrared spectroscopy has proved a powerful tool to probe the folding kinetics. Herein we report the construction of a nanosecond laser-induced temperature-jump (T-jump) technique coupled to a nanosecond time-resolved transient mid-infrared (mid-IR) spectrometer system capable of investigating the protein folding kinetics with a temporal resolution of 50 ns after deconvolution of the instrumental response function. The mid-IR source is a liquid N2 cooled CO laser covering a spectral range of 5.0?m (2000 cm?1)~ 6.5?m (1540 cm?1). The heating pulse was generated by a high pressure H2 Raman shifter at wavelength of 1.9?m. The maximum temperature-jump could reach as high as 26?1?C. The fast folding/unfolding dynamics of cytochrome C was investigated by the constructed system, providing an example.

Experimental resolution of early steps in protein folding: testing molecular dynamics simulations.

Time-resolved Tyr fluorescence spectroscopy coupled with a laser-induced temperature-jump (T-jump) was employed to follow the folding relaxation dynamics of the B-domain of Staphylococcal protein A. The single Tyr is located in helix 1 (H1) and is a sensitive probe of the structure of this helix and the overall helical bundle structure. The results from this study were compared to those from a complementary infrared T-jump study on this protein [Vu, D. M.; Myers, J. K.; Oas, T. G.; Dyer, R. B. Biochemistry 2004, 43, 3582]. Both methods detect a microsecond process that follows the cooperative relaxation of the helical bundle core. However, a fast process (10-7 s) that follows the relaxation of the individual helices was observed only with the infrared probe. Thus, fast formation of H1 is not observed, but rather H1 forms in the microsecond phase, concomitantly with the docking to (and stabilization by) the other two helices to form the helical bundle structure. This observation validates the results of several previous molecular dynamics simulations that predict H1 formation only in the final assembly of the helix bundle.

Infrared study of the stability and folding kinetics of a 15-residue beta-hairpin.

The thermal stability and folding kinetics of a 15-residue beta-hairpin (SESYINPDGTWTVTE) have been studied by using infrared (IR) spectroscopy coupled with laser-induced temperature-jump (T-jump) technique for rapid folding-unfolding initiation. An alternative method based on analyzing IR difference spectra was also introduced to obtain thermodynamic properties of beta-sheets, which complements the commonly used circular dichroism (CD) and fluorescence techniques. Equilibrium IR measurements indicate that the thermal unfolding of this beta-hairpin is fairly broad. However, it can be described by a two-state transition with a thermal melting temperature of approximately 29 degrees C. Time-resolved IR measurements following a T-jump, probed at 1634 cm(-1), indicate that the folding of this beta-hairpin follows first-order kinetics and is amazingly fast. At 300 K, the folding time is approximately 0.8 micros, which is only 2-3 times slower than that of alpha-helix formation. Additionally, the energetic barrier for folding is small (approximately 2 kcal mol(-1)). These results, in conjunction with results from other studies, support a view that the details of native contacts play a dominant role in the kinetics of beta-hairpin folding.

Laser-induced temperature jump electrochemistry on gold nanoparticle-coated electrodes.

Laser-induced temperature jumps (LITJs) at gold nanoparticle-coated indium tin oxide (ITO) electrodes in contact with electrolyte solutions have been measured using temperature-sensitive redox probes and an infrared charge-coupled device. Upon irradiation with 532 nm light, interfacial temperature changes of ca. 20 degrees C were recorded for particle coverages of ca. 1 x 1010 cm-2. In the presence of a redox molecule, LITJ yields open-circuit photovoltages and photocurrents that are proportional to the number of particles on the surface. When ssDNA was used to chemisorb nanoparticles to the ITO surface, solution concentrations as low as 100 fM of target ssDNA-modified nanoparticles could be detected at the electrode surface.

Indirect Laser-Induced Temperature Jump Study of the Chain-Length Dependence of the pKa's of ω-Mercaptoalkanoic Acid Monolayers Self-Assembled on Gold

The indirect laser-induced temperature-jump (ILIT) technique is used to measure the pKa's of self-assembled monolayers (SAMs on gold electrodes) composed of dibutanoic acid disulfide (DBAD) and 6-mercaptohexanoic acid (MHA) in contact with 1.00 M ionic strength NaClO4 electrolyte solutions. The ILIT technique may be used to determine the pKa of a surface-attached acid because the size of the ILIT response is related to the potential drop across the electrode/electrolyte interface that is, in turn, related to the extent of ionization of the acid. The pertinent data are the potentials of zero ILIT response (Epzr) versus pH. It is found that the measured Epzr versus pH data set for the DBAD monolayers is (within experimental error) the same as that measured for the MHA monolayers. Additionally, an analysis of the combined DBAD/MHA data set gives a pKa (4.5 ± 0.2) and a total concentration (ΓT) of either DBAD or MHA comprising the SAM (ΓT = (5.4 ± 0.3) × 10-10 mol/cm2) that (again within experimental error) a...

Site-Hopping of Adsorbed CO in c(4×2)-CO/Ni(111) by Laser-Induced Temperature Jump: Time-Resolved Sum-Frequency Generation Observation

The c(4×2)-CO/Ni(111) surface under pulsed near-infrared irradiation is examined by time-resolved sum-frequency generation (SFG) spectroscopy. At a surface coverage of 0.5, the surface is confirmed to consist almost exclusively of hollow CO molecules, as evidenced by a sole SFG peak at 1904 cm-1. Under pulsed irradiation, this peak weakened, followed by the emergence of a new peak attributable to atop CO. This represents a direct observation of site-hopping of adsorbed CO. The hopping phenomenon was found to be entirely transient, with the surface returning to the pre-excited state within a few hundred picoseconds without desorption. The dynamics of the process are also discussed.

Helix–coil kinetics of two 14-residue peptides

The helix–coil transition kinetics of two 14-residue helical peptides of different stability were studied by time-resolved infrared (IR) spectroscopy coupled with laser-induced temperature-jump (T-jump) technique. The T-jump induced relaxation kinetics of both peptides show strong dependence on the final temperature, implying the existence of an enthalpic barrier for the nucleation process. In addition, the peptide with end-capping groups, which is more stable, folds faster. Together, these results suggest that the overall helical stability plays an important role in controlling the kinetics of the helix–coil transition, in agreement with results of early theoretical studies.