Chemical Reactions In Solution Research Articles

Li/Na Ion Storage Performance of a FeOF Nano Rod with Controllable Morphology

Although the conversion material iron oxyfluoride (FeOF) possesses a high theoretical specific capacity as a cathode material for Li/Na ion batteries, its poor rate and cycling performances, caused mainly by sluggish (Li+/Na+) reaction kinetics, restrict its practical application. Herein, FeOF with high purity, a fusiform nanorod shape and high crystallinity is prepared through a facile chemical solution reaction. The electrochemical measurements show that the present FeOF exhibits high capacity and good cycling stability as a cathode material for Li-ion batteries. Capacities of 301, 274, 249, 222, and 194 mAh/g at stepwise current densities of 20, 50, 100, 200, and 400 mA/g are achieved, respectively. Additionally, the capacity at 100 mA/g retains 123 mAh/g after 140 cycles. Meanwhile, as a cathode material for Na ion battery, it delivers discharge capacities of 185, 167, 151, 134 and 115 mAh/g at stepwise current densities of 20, 50, 100, 200, and 400 mA/g, respectively. A discharge capacity of 83 mAh/g at 100 mA/g is achieved after 140 cycles. The excellent lithium/sodium-storage performance of the present FeOF material is ascribed to its unique nanostructure.

Likelihood-based non-Markovian models from molecular dynamics

SignificanceThe analysis of complex systems with many degrees of freedom generally involves the definition of low-dimensional collective variables more amenable to physical understanding. Their dynamics can be modeled by generalized Langevin equations, whose coefficients have to be estimated from simulations of the initial high-dimensional system. These equations feature a memory kernel describing the mutual influence of the low-dimensional variables and their environment. We introduce and implement an approach where the generalized Langevin equation is designed to maximize the statistical likelihood of the observed data. This provides an efficient way to generate reduced models to study dynamical properties of complex processes such as chemical reactions in solution, conformational changes in biomolecules, or phase transitions in condensed matter systems.

Bifunctional biohybrid magnetically propelled microswimmer

Inspired by the intrinsic helical structures of vessels in banana leaves, a novel bifunctional biohybrid magnetic microswimmer with both environment remediation and biomedical application was synthesized by a simple chemical method. Here, spiral vessels isolated from banana leaves were used as biological templates, where nickel layers with magnetic properties and Fe3+-TA (tannic acid, TA) films with pH-dependent degradation capabilities were modified on their surfaces by simple chemical reactions in solution at room temperature. The obtained magnetic helical (Helix/Ni/Fe3+-TA) microswimmers can be efficiently propelled in either pollutant solution (rhodamine B, RhB) or biofluid solution (DMEM culture medium and fetal bovine serum) in the presence of a magnetic field. The developed Helix/Ni/Fe3+-TA microswimmers can be used to efficiently degrade organic pollutant RhB due to the Fe3+-TA films which can produce reactive oxygen species under the action of hydrogen peroxide (H2O2). Moreover, due to the specific chemical interaction between the microswimmers and the surface of cancer cells, the microswimmers can precisely capture cancer cells and then produce heat under light irradiation to kill those cells. These novel helical microswimmers with simple and economic fabrication, efficient magnetic propulsion and diverse functionality show great potential in future environmental and biological applications.

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Development of Range-Corrected Deep Learning Potentials for Fast, Accurate Quantum Mechanical/Molecular Mechanical Simulations of Chemical Reactions in Solution.

We develop a new deep potential─range correction (DPRc) machine learning potential for combined quantum mechanical/molecular mechanical (QM/MM) simulations of chemical reactions in the condensed phase. The new range correction enables short-ranged QM/MM interactions to be tuned for higher accuracy, and the correction smoothly vanishes within a specified cutoff. We further develop an active learning procedure for robust neural network training. We test the DPRc model and training procedure against a series of six nonenzymatic phosphoryl transfer reactions in solution that are important in mechanistic studies of RNA-cleaving enzymes. Specifically, we apply DPRc corrections to a base QM model and test its ability to reproduce free-energy profiles generated from a target QM model. We perform these comparisons using the MNDO/d and DFTB2 semiempirical models because they differ in the way they treat orbital orthogonalization and electrostatics and produce free-energy profiles which differ significantly from each other, thereby providing us a rigorous stress test for the DPRc model and training procedure. The comparisons show that accurate reproduction of the free-energy profiles requires correction of the QM/MM interactions out to 6 Å. We further find that the model's initial training benefits from generating data from temperature replica exchange simulations and including high-temperature configurations into the fitting procedure, so the resulting models are trained to properly avoid high-energy regions. A single DPRc model was trained to reproduce four different reactions and yielded good agreement with the free-energy profiles made from the target QM/MM simulations. The DPRc model was further demonstrated to be transferable to 2D free-energy surfaces and 1D free-energy profiles that were not explicitly considered in the training. Examination of the computational performance of the DPRc model showed that it was fairly slow when run on CPUs but was sped up almost 100-fold when using NVIDIA V100 GPUs, resulting in almost negligible overhead. The new DPRc model and training procedure provide a potentially powerful new tool for the creation of next-generation QM/MM potentials for a wide spectrum of free-energy applications ranging from drug discovery to enzyme design.

Synthesis of composite of graphene and UO3 composite via one-step solution chemical reaction and its application to UO2-based accident tolerant fuel

In this paper, two kinds of composites constructed by UO3 nanoflakes (which is UO3·yNH3·xH2O, precisely) and different graphene oxide (GO) nanosheets (homemade GO, GO-h, and commercial GO, GO-c) were prepared via solution chemical reaction. The two kinds of GO share similar morphology and possess the same species of functional groups. Nevertheless, GO-h possesses higher oxidization degree and thus could adsorb more uranyl ions, and the corresponding composite shows a much more regular shape: UO3 nanoflakes and GO nanosheets cross each other, which would help overcome the disadvantage of graphene aggregation. As a result, homemade reduced graphene oxide (RGO-h) sheets inside the final UO2 pellets (named as UO2/GO-h) could construct a well-bulit thermally conductive network to enhance its thermal conductivity. However, similar RGO-c network cannot be observed in the UO2/GO-c pellest originated from GO-c. Therefore, only the thermal conductivity of UO2/GO-h pellet acquires a dramatic increase, 37.30% relative to UO2 pellet at 1200 °C, showing that UO2/GO-h possesses great potential for the development of novel UO2-based ATF fuels.

Fabrication of C@Si@G for flexible lithium-ion batteries

The commercial application of silicon is still impeded by poor conductivity and significant volume change. In this work, a C@Si@G composite was synthesized by a facile chemical solution reaction and carbonization procedure with cocoon silk as a natural carbon source. This composite has a sandwich structure, where Si nanoparticles as a sandwich middle layer and graphene (G) as an out layer. And it possesses the advantages of flexible, nitrogen-doped and is environmentally friendly. The optimized C@Si@G-15 composite is used as a self-supporting anode without a current collector, and it shows a reversible discharge capacity of 972 mAh g−1after 120 cycles at 1 A g−1 and a relatively high capacity of 1070 mAh g−1 after 300 cycles at 200 mA g−1, demonstrating the effect of coating the N-doped carbonized silk and the graphene synergistically to improve electrical connectivity and to constrain the pulverization of Si nanoparticles. Hence, it delivers great potential for application on wearable devices.

Imaging‐Guided Targeted Drug Delivery using Stimuli‐Sensitive Theranostic Nanoparticles: Characterization and In Vivo Trafficking Patterns

Purpose : In type 1 diabetes (T1D), the existing delivery systems for insulin all suffer from the inability to regulate insulin without patient intervention. A major unmet medical need is to develop innovative strategy, which would increase the efficacy of immune therapeutics but also, reduce their toxicity. Targeted drug carriers using polymeric nanoparticles (NP) holds particular promise to enhance the delivery of immunoregulatory agents to treat T1D. The aim of this study was to synthesize and characterize the in vivo trafficking patterns of stimuli-responsive, thermosensitive, immunoregulatory-carriers for potential use in image-guided targeted delivery and on site controlled release. Methods : A number of metal nanoparticles with hyperthermia magnetic (HMNs) properties made out of Gd-Zn-Fe were fabricated that intrinsically have the ability to self-regulate their heating level to the desired therapeutic range, Curie temperature (Tc). Production of particles of uniform size and shape was ensured by constant reaction kinetics and efficient physical and chemical reactions in solution. The particles morphology was examined using electron microscopy. The size distribution was evaluated using Malvern Nanosizer device. Magnetic resonance imaging (MRI) relaxivities of HMNs were measured over a range of 25-45°C. Non-targeted and MECA79-targeted HMNs were engineered using self-assembly nanoprecipitation method. Targeted trafficking of MECA79-HMNs in skin transplanted NOD mice with distinctive lymphatic draining to the draining lymph nodes (DLN) was evaluated. To be able to image the particles, particles were coated with IRDye 800CW. Using iBox, live fluorescence imaging was carried out 8 days post transplantation (24 hours post IV administration). Results : The temperature of HMN (with Tc 38-40°C) rose only up to the Tc when the particles were subjected to an oscillating magnetic field, and further increasing the intensity of the field did not increase heating beyond their Tc. Increasing Gd ratio modulated Tc linearly with amount of Gd-substituted Zn Ferrite particles (Figure 1A). NPs TEM micrograph showed a dispersion of spherical particles with a narrow size distribution (Figure 1B). MRI relaxivities, R1 and R2, showed linear increase of the relaxation rate. Twenty-four hours post IV administration, there was a significant increase in the trafficking of MECA79 conjugated particles as compared to the non-targeted NPs to the DLN in the skin transplanted NOD mice (Figure 2). Conclusion : Nanomedicine's application of ITS to T1D remains to be developed. While there are a number of delivery approaches that target the LN, virtually all of them rely on passive lymphatic absorption (i.e., intradermal injection). Data presented here represent major achievements to establish for the first time systemic delivery of particles to specific sites in diabetic mice. These experiments serve the basis for developing more of multifunctional NPs.

Machine learning meets mechanistic modelling for accurate prediction of experimental activation energies.

Accurate prediction of chemical reactions in solution is challenging for current state-of-the-art approaches based on transition state modelling with density functional theory. Models based on machine learning have emerged as a promising alternative to address these problems, but these models currently lack the precision to give crucial information on the magnitude of barrier heights, influence of solvents and catalysts and extent of regio- and chemoselectivity. Here, we construct hybrid models which combine the traditional transition state modelling and machine learning to accurately predict reaction barriers. We train a Gaussian Process Regression model to reproduce high-quality experimental kinetic data for the nucleophilic aromatic substitution reaction and use it to predict barriers with a mean absolute error of 0.77 kcal mol−1 for an external test set. The model was further validated on regio- and chemoselectivity prediction on patent reaction data and achieved a competitive top-1 accuracy of 86%, despite not being trained explicitly for this task. Importantly, the model gives error bars for its predictions that can be used for risk assessment by the end user. Hybrid models emerge as the preferred alternative for accurate reaction prediction in the very common low-data situation where only 100–150 rate constants are available for a reaction class. With recent advances in deep learning for quickly predicting barriers and transition state geometries from density functional theory, we envision that hybrid models will soon become a standard alternative to complement current machine learning approaches based on ground-state physical organic descriptors or structural information such as molecular graphs or fingerprints.

Direct structural and mechanistic insights into fast bimolecular chemical reactions in solution through a coupled XAS/UV-Vis multivariate statistical analysis.

In this work, we obtain detailed mechanistic and structural information on bimolecular chemical reactions occurring in solution on the second to millisecond time scales through the combination of a statistical, multivariate and theoretical analysis of time-resolved coupled X-ray Absorption Spectroscopy (XAS) and UV-Vis data. We apply this innovative method to investigate the sulfoxidation of p-cyanothioanisole and p-methoxythioanisole by the nonheme FeIV oxo complex [N4Py·FeIV(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) in acetonitrile at room temperature. By employing statistical and multivariate techniques we determine the number of key chemical species involved along the reaction paths and derive spectral and concentration profiles for the reaction intermediates. From the quantitative analysis of the XAS spectra we obtain accurate structural information for all reaction intermediates and provide the first structural characterization in solution of complex [N4Py·FeIII(OH)]2+. The employed strategy is promising for the spectroscopic characterization of transient species formed in redox reactions.

Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion.

Chemical reactions in confined environments are important in areas as diverse as heterogenous catalysis, environmental chemistry and biochemistry, yet they are much less well understood than the equivalent reactions in either the gas phase or in free solution. The understanding of chemical reactions in solution was greatly enhanced by real time studies of model reactions, through ultrafast spectroscopy (especially when supported by molecular dynamics simulation). Here we review some of the efforts that have been made to adapt this approach to the investigation of reactions in confined media. Specifically, we review the application of ultrafast fluorescence spectroscopy to measure reaction dynamics in the nanoconfined water phase of reverse micelles, as a function of the droplet radius and the charge on the interface. Methods of measurement and modelling of the reactions are outlined. In all of the cases studied (which are focused on ultrafast intramolecular reactions) the effect of confinement was to suppress the reaction. Even in the largest micelles the result in the bulk aqueous phase was not usually recovered, suggesting an important role for specific interactions between reactant and environment, for example at the interface. There was no simple one-to-one correspondence with direct measures of the dynamics of the confined phase. Thus, understanding the effect of confinement on reaction rate appears to require not only knowledge of the dynamics of the reaction in solutions and the effect of confinement on the medium, but also of the interaction between reactant and confining medium.

Introduction to Femtochemistry: Excited-State Proton Transfer from Pyranine to Water Studied by Femtosecond Transient Absorption

In order to introduce students to the fascinating field of femtochemistry, we propose here a practical laboratory training course conceived for second-year master’s students in chemistry. We describe the use of a broadband femtosecond transient absorption (pump–probe) experiment for monitoring a fast light-triggered chemical reaction in solution. The experiments are performed on the pyranine photoacid, which upon photoexcitation at 390 nm undergoes a proton transfer to the solvent in about 90 ps. While this practical course involves advanced equipment and techniques, the measured transient absorption data allow easy analysis and interpretation. The transient absorption spectra at a few selected delay times can be analyzed qualitatively in terms of bleach, induced absorption, and stimulated emission. Likewise, the transient absorption signals at a few chosen wavelengths can be quantitatively analyzed and explained with simple kinetic models to determine the time constant of the proton-transfer reaction. This training aims at giving the students the opportunity to face some of the current challenges in contemporary chemistry by learning the basics of ultrafast spectroscopy.

Nature of the bond, reduction potential, and solvation properties of ruthenium nitrosyl complexes of the type trans‐[Ru(NH3)4(L)(NO)]2+/3+ and [Ru(salen)(L)(NO)]2+/3+ in different charge and spin states

AbstractIn this work, we present a systematic study of the nature of the RuNO bond, reduction potential, and behavior in the solution of several ruthenium nitrosyl complexes of the type trans‐[Ru(NH3)4(L)(NO)]2+/3+ (L = Cl, H2O, NH3, OH, py = pyridine, POEt3 = triethylphosphite, TVP = trivinyl phosphite) and [Ru(salen)(L)(NO)]2+/3+ (L = Cl, H2O) in different charge and spin states. We employed density functional theory, complete active space self‐consistent field, the quantum theory of atoms in molecules, charge decomposition analysis, and Monte Carlo statistical simulation in aqueous solution to investigate how the different ligands on the coordination sphere of the ruthenium atom can affect the nature of the RuNO bond and, therefore, its reactivity, reduction potential, and solvation properties. The nature of the RuNO bond varies significantly between the singlet, doublet, and triplet electronic states of these complexes, in part due to the change in the coordination mode of the NO ligand and also due to the electron correlation effects along the RuNO bond that changes drastically. For all complexes studied, the RuNO bond shows some intriguing characteristics, such as large kinetic energy density and considerable amount of electron localization between the atoms, besides high multiconfigurational character, with a significant contribution from the RuIIINO0 configuration. In addition, for all the complexes investigated, the NO ligand does not interact with the solvent through hydrogen bonds, making this group accessible for chemical reactions in solution. Another important finding was that some of the RuIIINO compounds can be reduced by biological reducing agents in the singlet ground state, while all of them have high reduction potentials in the triplet excited state, making them suitable candidates for the photorelease of nitric oxide.

Synthesis and Luminescence Properties of Rare Earth (Eu, Tb) Complexes of Octanoylphenylalanine

Tb (oct-phe)3·H2O and Eu (oct-phe)3·H2O were prepared by chemical reaction in solution. The molecular formula of the complex was determined by elemental analysis and FT-IR. The optical properties of rare earth complexes were further tested by ultraviolet-visible-infrared absorption measurements. The results show that the optical absorption performance is better in the wavelength range of 200-300 nm. The luminescent properties of the rare earth complexes in the wavelength range of 450-750 nm were tested. It was found that the rare earth (Eu, Tb) complexes of octylphenylalanine have good luminescent properties.

Synthesis and luminescent properties of novel red-emitting Eu(III) complexes based on alanine aliphatic derivatives with different optical rotation

A series of novel luminescent amino acid-rare earth complexes (denoted as Eu(L/D-SA)3-Phen) have been successfully synthesized. Using stearoyl alanine (denoted as SA) with different optical rotations as the first ligand and 1,10-phenanthroline (Phen) as the second ligand, the products were prepared by solution chemical reaction. Fourier transform infrared spectrometer (FT-IR), nuclear magnetic resonance spectroscopy (1H NMR), x-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet and visible spectrum (UV) and photoluminescence spectroscopy were used to characterize the properties of Eu(L/D-SA)3-Phen. FT-IR, 1H NMR and XRD indicate that ligand SA and Phen were prepared and successfully combined with Eu3+ ions. SEM analysis shows relatively uniform morphological structure. Eu(L/D-SA)3-Phen exhibit a typical luminescence emission peak at 614 nm. In addition, the lifetimes of Eu(L/D-SA)3-Phen are in scale of millisecond. The relationship between fluorescence intensity of Eu(L/D-SA)3-Phen and the optical rotation of ligand SA has been studied and discussed. Based on the results, Eu(L/D-SA)3-Phen have excellent luminescent performance and possess potential application as luminescent materials.

Solvent effects on a derivative of 1,3,4-oxadiazole tautomerization reaction in water: A reaction density functional theory study

In this work, we investigate the simple and water assisted tautomerization reaction in a derivative of 1,3,4-oxadiazole by means of the proposed multiscale reaction density functional theory (RxDFT). The complete scheme and reaction pathways among four different tautomers are investigated, and the free energy profiles of four corresponding tautomerization reactions in the absence and presence of 1–3 water molecules are calculated. The results show that the presence of liquid water considerably reduces the free energy barriers of the tautomerization reactions, but imposes negligible impact on the reaction free energies. The solvent effects are ascribed primarily to the assistance of water molecules, and then to the difference in solvation free energy. The satisfactory accuracy and low computational cost of RxDFT highlight its great potential for studying solvent effect on chemical reactions in solution compared with ab initio or QM/MM method.

Preparation and Electrochemical Properties of Multi-Walled Carbon Nanotube/Dextran/Nano-Gold Composites

Multi-walled carbon nanotube (MWCNT)/dextran/nano-gold composite was prepared by chemical solution reaction. The average diameter of gold nanoparticles was around 15 nm. MWCNT/dextran/nano-gold composites were uniformly dispersed in aqueous solution as electrode materials. MWCNT/dextran/nano-gold composites exhibited excellent electrochemical property in [Fe(CN)6]3– /4– solution. Experimental results showed that the MWCNT/dextran/nano-gold composites with 50% MWCNTs presented obvious redox peak and low impedance and had good electrochemical response to Cu2+. The redox peak currents were linear while the concentration of copper ions ranged from 1× 10–2 to 1 × 10–4 M. The relationship between oxidation peak currents I (A) and Cu2+ concentration C (M) was: ipk (A) = 2.6207 × 10–6 + 43.91572 × 10–4 × C (M), and the limit of determination (LOD) of Cu2+ was 0.63 × 10–6 M, and linear coefficient was 0.9923.

(Invited) Novel Fuel Production Based on Sonochemistry and Sonoelectrochemistry

Power ultrasoundhas been used in many applications such as the chemical and processing industries where it is employed to improve both catalytic and synthetic processes and to produce new chemicals. This technology area has been termed sonochemistry, which mainly focusses on chemical reactions in solutions yielding an increase in erosion of catalytic surfaces, reaction kinetics, and product yield [1,2]. Sonoelectrochemistryis the study of the combination of ultrasound and electrochemical processes and its applications [2-4]. This area of research covers various studies from organic syntheses, polymeric materials syntheses, production of nanomaterials, environmental (soil and water) treatments, water disinfection, corrosion of metals, analytical procedures, film and membrane preparations to the elucidation of electrochemical mechanisms in various ‘exotic’ solvents. In the ongoing energy transition from a fossil based energy economy to a renewable energy economy, most of the energy input will change from readily storable carbons and hydrocarbons into intermittent electricity. [5] This means that we need to both process electricity efficiently and intensively into forms that are storable and portable. Such a mix is likely to be presented by chargeable batteries, hydrogen systems and biofuels. Power ultrasound is a tool that can allow for more intensive and more efficient ways for the energy conversion required in the coming generation and here we look particularly on efforts within production of hydrogen and biofuels. Hydrogen is an attractive fuel source due to its rather high specific energy compared to other conventional fuel. There are various methods available to produce hydrogen. However, most of the methods are not environmentally friendly, since they release large amount of fossile CO2(ca. 7.05 kg of CO2per kg of H2production). Power ultrasoundcould be an attractive alternative since ultrasonication of water produces clean hydrogen. Power ultrasound breakdowns water molecules into OH• and H• radicals, where the recombination of these radicals produces hydrogen. It is crucial to characterize the amount of radicals formed by ultrasonication in order to understand and further developing the hydrogen production process using ultrasonication [4]. Global biogas production has been growing significantly in recent years. A new generation of feedstocks, potentially allowing extensive increases in yields, is currently under development based on lignocellulosic-containing residues. However, lignocellulose presents a bottleneck due to its’ rigid and obstinate structure. Pre-treatment of feedstocks can be achieved in a variety of ways including enzymatic hydrolysis [6,7] and steam explosion [8]. In this research, a new method has been applied using power ultrasound coupled to Fenton reagents to assess its ability to improve the yield of biogas from steam exploded birch wood. In our conditions, an increase in the yield of 5% and an increase in the rate of production of 7% of biogas has been observed. [1] B.G. Pollet, M. Ashokkumar, Introduction to Ultrasound, Sonochemistry and Sonoelectrochemistry, B.G. Pollet, M. Ashokkumar, Eds.; SpringerBriefs: Berlin, Germany, 2019; in press. [2] B.G. Pollet (Ed), Power ultrasound in electrochemistry: from versatile laboratory tool to engineering solution, John Wiley & Sons (2012) ISBN: 978-0-470-97424-7. [3] B.G. Pollet, A short introduction to Sonoelectrochemistry. Electrochem. Soc. Interface 2018, 27, 41–42. [4] Md.H. Islam, O.S. Burheim, B.G. Pollet, Sono(electro)chemical Production of Hydrogen, Ultras. Sonochem. 51 (2019) 533-555. [5] O.S. Burheim, “Engineering Energy Storage”, Academic press, ISBN: 9780128141007, 2017. [6] J.J. Lamb, S. Sarker, D.R. Hjelme, K.M. Lien, Fermentative bioethanol production using enzymatically hydrolysed saccharina latissima. Adv. Microbiol. 2018; 8(05) [7] J.J. Lamb, D.R. Hjelme, K.M. Lien, Biomethane potential from enzymatically hydrolysed Saccharina latissima. Adv. Microbiol. 2019; 9(04).

Atomistic structures and dynamics of prenucleation clusters in MOF-2 and MOF-5 syntheses

Chemical reactions in solution almost always take place via a series of minute intermediates that are often in rapid equilibrium with each other, and hence hardly characterizable at the level of atomistic molecular structures. We found that single-molecule atomic-resolution real-time electron microscopic (SMART-EM) video imaging provides a unique methodology for capturing and analyzing the minute reaction intermediates, as illustrated here for single prenucleation clusters (PNCs) in the reaction mixture of metal–organic frameworks (MOFs). Specifically, we found two different types of PNCs are involved in the formation of MOF-2 and MOF-5 from a mixture of zinc nitrate and benzene dicarboxylates at 95 °C and 120 °C, respectively. SMART-EM identified a small amount of 1-nm-sized cube and cube-like PNCs in the MOF-5 synthesis, but not in the MOF-2 synthesis. In the latter, we instead found only linear and square PNCs, suggesting that the MOF-2/-5 bifurcation takes place at the PNC stage.

Relation between Anharmonicity of Free-Energy Profile and Spectroscopy in Solvation Dynamics: Differences in Spectral Broadening and Peak Shift in Transient Hole-Burning Spectroscopy Studied by Equilibrium Molecular Dynamics Simulation

Solvation dynamics is used to monitor the time-dependent fluctuation of solvents, which plays an essential role in chemical reactions in solution. Transient hole-burning spectroscopy, in which a ground-state depletion (hole) formed by a laser pulse is observed, can be used to monitor solvation dynamics. Previous experiments demonstrated that the hole bandwidth relaxes an order of magnitude slower than the hole peak shift in organic solute-solvent systems. However, the detailed mechanisms behind this are still unclear. In this study, we developed a methodology to calculate transient hole spectra using equilibrium molecular dynamics simulation, in which a series of time-dependent system ensembles is accumulated to derive the appropriate dynamic properties. The simulated transient hole spectra adequately reproduced previous spectroscopic results. The different hole bandwidth and peak shift dynamics are ascribed to a non-Gaussian property or anharmonicity of the free energy profile with respect to the solvation coordinate.