Infrared Absorption Research Articles

Toward Hyphenated In Situ Infrared and Raman Spectroscopies in Interfacial Electrochemistry.

To address the pressing demand for hyphenated in situ characterization of the electrode-electrolyte interfaces at the molecular level, we report herein a technical note to demonstrate the hyphenation of in situ electrochemical surface-enhanced infrared absorption spectroscopy (SEIRAS) and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS). The core setup incorporates a top-down configured Raman optic fiber head loaded on a 3-dimension positioning module and a bottom-up configured attenuated total reflection infrared spectroscopy (ATR-IR) spectroelectrochemical cell accommodated in a custom-designed optical accessory. The feasibility of this integrated design is initially validated by the simultaneous measurement of two model systems, namely, potential dependent adsorption of pyridine on a Au film electrode and the CO2 reduction reaction on a Cu film electrode by in situ SEIRAS and SHINERS, yielding distinct and complementary spectral information.

Narrow-bandgap titanium sesquioxide with resonant metasurfaces for enhanced infrared absorption

We report on the structural, chemical, and optical properties of titanium sesquioxide Ti2O3 thin films on single-crystal sapphire substrates by pulsed laser deposition. The thin film of Ti2O3 on sapphire exhibits light absorption of around 25%–45% in the wavelength range of 2–10 μm. Here, we design an infrared photodetector structure based on Ti2O3, enhanced by a resonant metasurface, to improve its light absorption in mid-wave and long-wave infrared windows. We show that light absorption in the mid-wave infrared window (wavelength 3–5 μm) in the active Ti2O3 layer can be significantly enhanced from 30%–40% to more than 80% utilizing a thin resonant metasurface made of low-loss silicon, facilitating efficient scattering in the active layer. Furthermore, we compare the absorptance of the Ti2O3 layer with that of conventional semiconductors, such as InSb, InAs, and HgCdTe, operating in the infrared range with a wavelength of 2–10 μm and demonstrate that the absorption in the Ti2O3 film is significantly higher than in these conventional semiconductors due to the narrow-bandgap characteristics of Ti2O3. The proposed designs can be used to tailor the wavelengths of photodetection across the near- and mid-infrared ranges.

Enhancement of Sm3+ Luminescence in Sol-Gel Silica Matrix: Effect of Ligands Phenyl Phosphinic Acid and Trioctylphosphine Oxide.

Sol-gel silica matrices singly doped with Sm3+ and co-doped with ligands phenyl phosphinic acid (PPIA) and trioctylphosphine oxide (TOPO) were fabricated and studied for their structural and spectroscopic behaviour. Structural studies were done by x-ray diffraction (XRD) and Fourier transform infra-red (FTIR) absorption analysis whereas spectroscopic behaviour was studied by ultraviolet - visible (UV-Vis) absorption, photoluminescence (PL) excitation, emission and time-correlated decay analyses. XRD studies exhibit the amorphous nature of the samples and FTIR studies corroborate the presence of the ligands in the silica matrix. UV-Vis absorption and PL studies show significant enhancement in the radiative parameters in ligand co-doped samples compared to singly doped Sm3+ sample. Judd Ofelt parameters estimated from the absorption spectra possess higher values compared to popular hosts; revealing higher asymmetry and covalency around the active Sm3+ ions. An enhancement in PL intensity by 50.38 times and yield by 52.57 times with the co-doping of the ligands PPIA and TOPO is reported. These enhancement in the radiative output in ligand co-doped samples is attributed to the modification of the silica network with the incorporation of the ligands, energy transfer from ligands to nearby Sm3+ ions as well as due to the shielding of Sm3+ ions from the OH quenchers in the silica matrix. The improved PL behaviour especially corresponding to 4G5∕2→6H9∕2 transitions occurring at 643nm suggests the potential of PPIA and TOPO co-doped Sm3+ silica matrix for diverge optical applications.

Key Structure Parameters for Designing High-Performance Substrates of Surface-Enhanced Infrared Absorption Spectroelectrochemistry.

Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) plays a crucial role in understanding the interfacial reaction mechanisms at the molecular level, achieving an enhancement factor (EF) of up to 103. However, when this technique is integrated with electrochemistry (EC-ATR-SEIRAS), the EF is significantly reduced by ten- to hundred-fold. Thus, understanding of the key parameters that contribute to the EF is of great importance in designing high-performance substrates and extending the application for EC-SEIRAS. In this study, we propose that the structure of the substrate for EC-ATR-SEIRAS consists of an enhancement unit (EU) supported on a conductivity unit (CU). The CU will screen the incident IR light reaching and interacting with the EU, resulting in a smaller EF as the CU thickness increases. Then, we introduce a strategy to optimize the performance of the EC-SEIRAS substrate by assembling a plasmonic antenna array as the EU that is supported on IR-transparent and conductive monolayer graphene as the CU. The established plasmon-enhanced EC-SEIRAS substrate demonstrates much higher IR enhancement, repeatability, and stability.

Research on the influence of titanium addition on the structure and frictional performance of laser clad tin bronze coating

Cu has a high infrared light reflectivity, which leads to the easy formation of defects such as pores in copper alloys during the laser cladding process. The purpose of this research is to reduce the porosity of tin bronze coatings during laser cladding by adding titanium elements with high infrared absorption. The porosity of the coating was characterized using scanning electron microscopy, metallographic microscopy, energy-dispersive spectroscopy, and x-ray diffraction. The research results indicate that as the content of titanium element increases, the porosity within the coating first decreases and then increases. When the titanium addition was 2%, the minimum porosity of the coating was 0.034%. The microhardness of the samples was tested using a semiautomatic Vickers hardness tester, and the reciprocating dry friction performance at room temperature was tested using a UMT-3 friction tester. The incorporation of titanium significantly enhances the microhardness and frictional properties of the laser-clad tin bronze coating. Therefore, this study provides experimental data support for controlling the porosity and frictional properties of laser-clad tin bronze coatings through elemental composition.

Atomically precise (AgPd)27 nanoclusters for nitrate electroreduction to NH3: Modulating the metal core by a ligand induced strategy

Electrochemical nitrate reduction reaction (eNO3–RR) to synthesize NH3 is a sustainable method to convert environmental contaminants into valuables. Pd based bimetallic nanocatalysts have demonstrated great promise as efficient catalysts, yet modulating the composition and configuration to improve the catalytic performance and achieve comprehensive mechanistic understanding remains challenging. Herein, by employing two ligands with different electron functional groups, we successfully prepared two atomically precise (AgPd)27 bimetallic clusters of Ag18Pd9(C8H4F)24 (Ag18Pd9) and Ag22Pd5(C9H10O2)26 (Ag22Pd5). The two clusters possess markedly different metal core composition and configuration, where Ag18Pd9 has a sandwich metal core structure with 9 Pd atoms located in the middle layer and Ag22Pd5 has a rod-shaped metal core structure composed of the M13 configuration with 5 Pd atoms located at the center and vertices of the M13 configuration. Unexpectedly, Ag22Pd5 exhibited remarkably superior eNO−3RR performance than Ag18Pd9. Specifically, the highest Faradaic efficiency of NH3 (FENH3) and its yield rate can reach 94.42 ​% and 1.41 ​mmol ​h−1 ​mg−1 ​at −0.6 ​V vs. RHE for Ag22Pd5, but the largest FENH3 and NH3 yield rate is only 43.86 ​% and 0.41 ​mmol ​h−1 ​mg−1 ​at −0.5 ​V vs. RHE for Ag18Pd9. The in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) test provides the experimental evidence of the reaction intermediates hence revealing the reaction pathway, also shows that Ag22Pd5 has stronger capability for NO−3 adsorption and NH3 desorption than that of Ag18Pd9. Theoretical calculations indicate that the de-ligated clusters can expose the available AgPd bimetallic sites, synergistically serving as effective active sites and the different configurations result in significantly different catalytic activities, where the active sites in Ag22Pd5 are more favorable for NO−3 adsorption and NH3 desorption to accelerate the catalytic process.

In Situ Surface-Enhanced Infrared Absorption Spectroscopy to Explore the Stability of Electrolyte in Nonaqueous Lithium Oxygen Batteries

Tetraethylene glycol dimethyl ether (TEGDME) decomposition on the Au electrode surface is studied using in situ attenuated total reflectance surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). Due to the weak solvation of TEGDME, the superoxide intermediate (LiO2/O2−) of the discharge process rapidly gains electrons on the electrode surface to generate Li2O2. Furthermore, alkyl radical, formed by LiO2/O2− extracting hydrogen from ether, undergoes oxidative decomposition reactions to form by-products. During the charge process, amorphous film-like Li2O2 obtained from surface-phase mechanism oxidizes in the low potential range of 3–3.4 V, while the oxidation potential of large-sized crystal Li2O2 particles obtained from solution-phase mechanism is above 3.4 V. Besides, TEGDME is intrinsically unstable and can decompose at 3.8 V even the solution is saturated with argon, indicating that the degradation of ether-based electrolyte is inevitable during the cycling process. This work confirms the feasibility of ATR-SEIRAS in probing the reaction mechanism and electrolyte stability of lithium oxygen batteries, and provides direct spectroscopic evidence for subsequent optimization of electrolyte components.

External Cavity Quantum Cascade Laser Vibrational Circular Dichroism Spectroscopy for Fast and Sensitive Analysis of Proteins at Low Concentrations.

Proteins are characterized by their complex levels of structures, which in turn define their function. Understanding and evaluating these structures is therefore crucial to illuminating biological processes. One of the possible analytical methods is vibrational circular dichroism (VCD), which expands the structural sensitivity of classical infrared (IR) absorbance spectroscopy by the chiral sensitivity of circular dichroism. While this technique is powerful, it is plagued by low signal intensities and long measurement times. Here we present an optical setup leveraging the high brilliance of a quantum cascade laser to measure proteins in D2O at a path length of 204 μm. It was compared to classical Fourier-transform infrared spectroscopy (FT-IR) in terms of noise levels and in its applicability to secondary structure elucidation of proteins. Protein concentrations as low as 2 mg/mL were accessible by the laser-based system at a measurement time of 1 h. Further increase of the time resolution was possible by adapting the emission to cover only the amide I' band. This allowed for the collection of spectral data at a measurement time of 5 min without a loss of performance. With this high time resolution, we are confident that dynamic processes of protein can now be monitored by VCD, increasing our understanding of these reactions.

(Invited) Operando Spectroscopy-Inspired Design of Electrolyte-Electrode Interface

There has been a growing recognition that not only electrocatalysts but electrolytes influence the activity of surface electrocatalytic reactions. Therefore, understanding the electrolyte-electrode interface under realistic operating conditions is critical to designing active and stable electrochemical devices. The past few decades of research have focused on developing a range of spectroscopic and imagining tools to enable the study of the chemical and structural changes at the electrolyte-electrode interface. Here, we introduce operando surface-enhanced infrared absorption spectroscopy (SEIRAS), a promising lab-based tool for gaining a molecular-level understanding of interfacial electrochemical processes. This talk will bring the most recent understanding of the electrochemical interface during the operation of electrolysis applications, including electrochemical CO2 reduction reaction and water splitting, using operando SEIRAS. Furthermore, we demonstrate that the holistic information about the complex interaction in the electrochemical interface can alter the reaction energetics/kinetics in a way incapable of electrode-centered design strategy. We will highlight the significance of advanced operando techniques to accelerate the design of electrochemical interfaces by providing additional knobs to tune the reaction energetics/kinetics, leading further improvements in electrocatalytic activity for energy conversion and storage reactions.

(Invited) Protein Film Electrochemistry and Surface-Enhanced Infrared Absorption Spectroscopy of Transmembrane Metalloenzymes

Transmembrane metalloenzymes encapsulating transition metal complexes are involved in electron transfer and in material transformation in living organisms. Understanding their operating principles is not only important for identifying the origin of highly efficient enzymatic reactions but also for developing sensors and catalysts inspired by metalloenzymes [1]. Protein film electrochemistry (PFE) is a powerful technique to investigate the redox behavior and enzymatic activity of transmembrane metalloenzymes even with a submonolayer amount of the target protein (~10 pmol cm–2). The challenge of PFE of metalloenzymes is the interpretation of the results obtained in PFE: PFE provides current–potential curves like cyclic voltammograms and relatively large transmembrane metalloenzymes tend to have multiple redox active cofactors inside the protein, which makes the interpretation of cyclic voltammograms difficult.We are using PFE coupled with surface-enhanced infrared absorption (SEIRA) spectroscopy, which is a surface-sensitive vibrational spectroscopy, to understand enzymatic mechanisms and protein–lipid or protein–protein interactions of transmembrane metalloenzymes at the electrode surface. In this talk, we will discuss PFE–SEIRA spectroscopy results about the determination of redox potential using a vibrational probe of carbon monoxide for heme proteins [2], the mechanistic insights into nitric oxide reduction to nitrous oxide at cytochrome c-dependent nitric oxide reductase (cNOR) using in situ PFE-SEIRA spectroscopy, and protein–lipid and protein–protein interactions with cNOR [3] and cytochrome c oxidase (CcO) [4].References.[1] M. Kato, N. Fujibayashi, D. Abe, N. Matsubara, S. Yasuda, I. Yagi, ACS Catal., 11, 2356–2365 (2021).[2] M. Kato, S. Nakagawa, T. Tosha, Y. Shiro, Y. Masuda, K. Nakata, I. Yagi, J. Phys. Chem. Lett., 9, 5196 (2018).[3] M. Kato, Y. Masuda, N. Yoshida, T. Tosha, Y. Shiro, I. Yagi, Electrochim. Acta, 373, 137888 (2021).[4] M. Kato, R. Sano, N. Yoshida, M. Iwafuji, Y. Nishiyama, S. Oka, K. Shinzawa-Itoh, Y. Nishida, Y. Shintani, I. Yagi, J. Phys. Chem. Lett., 13, 9165-9170 (2022).

Temperature Effects on the Surface Dynamics of the CO2 Reduction Reaction over Copper

The electrochemical reduction of CO2 (CO2RR) has stood out as a pathway to mitigate carbon emissions and supply multi-carbon feedstocks to the chemical industry. While most CO2RR studies over copper are carried out at room temperature, heat transfer limitations in the electrolyte will result in temperature buildup near the electrode in industrial CO2 electrolyzers. Reaction temperature plays a key role in the reaction activity and product selectivity by controlling the distribution of species on the copper surface. In this study, we use surface enhanced infrared absorption spectroscopy (SEIRAS) and surface enhanced Raman spectroscopy (SERS) to investigate the effect of temperature on the dynamics of reactive intermediates in the reaction microenvironment (Fig. A).Using SEIRAS, we showed site-specific CO coverage is dependent on temperature, and how CO migration seems to directly impact product distribution at higher temperatures. We found that increasing temperature leads to decreased CO and increased alkyl groups coverage for a given potential (Fig. B). This suggests that temperature has a direct effect on the selection of mechanistic pathways in the conversion of CO to C1 and C2 products, beyond just controlling mass transport and local CO2 availability. Using SERS, we showed that the local pH is considerably higher than their bulk values, and that higher temperatures consistently led to higher local pH values (Fig. C). The significant depletion of local hydrogen with increasing temperature indicates that local pH plays a key role in driving reaction selectivity dependence on temperature. Understanding the effect of temperature on the CO2RR surface dynamics through surface sensitive techniques is a key step to rationalize product distribution and to design solutions for enhanced C2+ production in industrial CO2 electrolyzers. Figure 1

Multi-Shell Copper Catalysts for Selective Electroreduction of CO2 to Multicarbon Chemicals

Electrocatalytic CO2 reduction (CO2R) coupled with renewable electricity has been considered as a promising route for the sustainability transition of energy and chemical industries. However, the unsatisfactory yield of desired products, particularly multicarbon (C2+) products, has hindered the implementation of this technology. This work describes a strategy to enhance the yield of C2+ products formation in CO2R by utilizing spatial confinement effects. Our finite element simulation results suggest that increasing the number of shells in the catalyst will lead to a high local concentration of *CO and promote the formation of C2+ products. Inspired by this, we synthesize Cu nanoparticles with desired hollow multi-shell structures. The CO2 reduction results confirmed that as the number of shells increased, the hollow multi-shelled copper catalysts exhibited improved selectivity towards C2+ products. Specifically, Cu catalyst with 4.4-shell achieved a high selectivity of over 80% towards C2+ at a current density of 900 mA cm−2. Evidence from in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy unveils that multi-shelled Cu catalyst exhibits an enhanced *COatop coverage and the stronger interaction with *COatop compared to commercial Cu, confirming our simulation results. Overall, our work promises an effective approach for boosting CO2R selectivity towards value-added chemicals.

Tuning Hydrogen Evolution and Oxidation Electrocatalysis through Interfacial Hydrogen Bonds

Designing electrochemical water splitting and its reverse process is crucial for fuel cells to achieve high efficiency. Conventional design of catalysts has focused on tuning the surface electronic structures and binding strength of intermediates, while recent studies show that changing electrolyte compositions, such as cations and pH, can also significantly alter catalytic activity, highlighting new opportunities in tuning noncovalent interactions in the electrolytes to control activities. Yet, the mechanistic role of electrolytes and their structures at the electrochemical double-layer remain poorly understood. Challenges arise in characterizing the interface and understanding the reaction mechanisms under operando processes.In this talk, we tailor non-covalent hydrogen bonding interactions at the electrified interface to control electrochemical proton-coupled electron transfer reactions, and uncover the interfacial molecular mechanisms. We investigate hydrogen evolution and oxidation reactions (HER/HOR) by systematically confining water in organic matrixes. Tuning the hydrogen-bonding networks by changing the water concentration and altering the donor number of organic solvents shifted the onset potentials. High donor number solvents, such as DMSO, suppress HER more significantly due to its stabilization effect of isolated water, while the enhancement effect of HER with low donor number solvents, such as acetonitrile, is due to the promotion of interfacial hydrogen-bonded water. In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) measurements and molecular dynamics simulations provide further support to the changes in interfacial hydrogen bonding during the reactions. These findings provide design principles for electrolytes and open up immense opportunities for using non-covalent hydrogen bonding interactions at the electrified interface to control the kinetics. The understanding would also be impactful across other reactions involving proton-coupled electron transfer that are crucial for energy storage, such as CO2 reduction and aqueous batteries.

Operando FTIR Characterization of Interphases from Organosulfur Electrolytes in High Voltage Lithium-Ion Batteries

The widespread adoption of renewable energy storage technologies like electric vehicles and grid storage largely relies on the improvements of the energy density of the batteries inside those devices. Lithium-ion batteries (LIBs) are typically used for these applications due to their high energy density,[1] but the operating voltage of LIBs is limited by the electrochemical stability windows of the electrolyte. Resistive interphase layers form as a result of the breakdown of electrolyte molecules and limit LIB cycling stability. However, there is significant difficulty in the study and characterization of both the components and structure of the electrode-electrolyte interphases formed via electrolyte degradation.[2] Traditional characterization techniques provide information on what the interphase layers look like after cell disassembly, but sample preparations are difficult and destructive.[3] Therefore, it is crucial to develop in operando techniques to better understand the relationship between the interphase layers and battery performance.In this work, we develop a custom surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS) setup for in operando studies of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) in organosulfur electrolyte systems. Organosulfur molecules are potential components for high voltage LIBs due to their excellent performance.[4] We apply our custom ATR-SEIRAS setup to study ethyl methyl sulfone (EMS) containing electrolytes and propose possible reduction routes with the help of ex situ and postmortem characterization techniques. We study both SEI and CEI formed and correlate favorable interphase components with contributing molecules to identify important functional groups for novel molecular design. The work provides an opportunity to elevate our understanding of currently elusive electrochemical phenomena like the structure-reactivity relationships of SEI and CEI, and why certain sulfone systems outperform other formulations. Furthermore, it will provide molecular design principle for electrolyte systems in high performing and high voltage LIBs.References S. Chu, Y. Cui, and N. Liu, Nat. Mater., 16, 16–22 (2017).H. Wan, J. Xu, and C. Wang, Nat. Rev. Chem., 8, 30–44 (2024).A. Dopilka, Y. Gu, J. M. Larson, V. Zorba, and R. Kostecki, ACS Appl. Mater. Interfaces, 15, 6755–6767 (2023).M. A. Dato et al., Adv. Energy Mater., 2303794 (2024).

Direct Observation of Intermediates for Carbon Dioxide Reduction Reaction in Concentrated Electrolytes

There is a growing need to utilize CO2 and realize a carbon-neutral society from the perspective of environmental problems caused by CO2 from fossil fuel-based processes. In this trend, electrochemical carbon dioxide reduction reaction (CO2RR), which converts CO2 to valuable fuels and chemicals with renewable energy, is attracting attention[1]. However, CO2RR has many challenges, including its low product selectivity. In particular, the hydrogen evolution reaction (HER), which occurs at the potential close to the standard electrode potential of CO2RR, reduces the selectivity of CO2RR, especially in aqueous electrolytes such as KHCO3 [2] [3]. Therefore, we focus on a concentrated electrolyte, which is used as a means of HER suppression in water-based Li-ion batteries[4], to improve the selectivity of CO2RR. A concentrated electrolyte is an electrolyte with a high salt concentration, which can improve the electrochemical stability of water by creating a specific water environment[5]. Furthermore, due to its high salt concentration, the effect of anions and/or cations may become significant[6][7]. However, there has been no detailed understanding of how the electrolyte concentration affects the complex reaction pathway of CO2RR.Here, we report the effect of concentrated electrolytes on the reaction process of CO2RR by directly observing reaction intermediates in situ while applying the potential. The product selectivity of CO2RR in 22.2, 42.0, and 61.7 mol kg– 1 of concentrated electrolyte was evaluated. Gas chromatography (GC) analysis confirms the suppression of HER in the series of concentrated electrolytes compared to 0.1 M KHCO3, a common aqueous electrolyte. In addition, an increase in the Faradaic efficiency of C2H4 was observed in ~ 42.0 mol kg– 1, implying a concentration-dependent change in the CO2RR reaction pathway (Fig.1). To elucidate the cause of the high C2H4 selectivity, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), which allows direct observation of the reaction intermediates, was performed. The results showed that as the electrolyte concentration was increased, the peaks at 1400 to 1500 cm– 1 region became more pronounced at low potential. We also observed the difference in the potential dependency for the intensity of CO adsorbates peak at 2100 cm–1 by electrolyte concentration. We will then discuss the effect of electrolyte concentration on the intermediates, unraveling the concentration-dependent change of the C2H4 selectivity. The work highlights the use of concentrated electrolytes to open up additional knobs for tuning the product selectivity of CO2RR, simply by designing an electrolyte component.[1] De Luna, P. et al, Science. 2019 364, 350.[2] Pan, F.; Yang, Y. Energy Environ. Sci. 2020, 13, 2275–2309.[3] Hori, Y. et al, Electrochim. Acta. 1994 39, 1833–1839.[4] Han, J. et al, Energy Environ. Sci. 2023 16, 1480.[5] Ko, S. et al, Electrochem. Commun. 2020 116, 106764.[6] Shin, S. J. et al, Nat. Commun. 2022 13, 5482.[7] Varela, A. S. et al, ACS Catal. 2016 6, 2136-2144. Figure 1

Probing CO2 Reduction Chemistry Under Operando Condition

Noble-metal and transition-metal based materials have been demonstrated as promising catalysts for selective electrochemical CO2 reduction reaction (CO2RR), however, neither the detailed structures of catalytic intermediates nor the key surface species have been unambiguously identified. In this work, a series of single transition-metal atom catalysts with well-defined structures were developed as model systems to explore the electrochemical CO2RR chemistry. Employing a combination of operando X-ray absorption spectroscopy, attenuated total reflectance surface enhanced infrared absorption spectroscopy, Raman spectroscopy and Mössbauer spectroscopy, we successfully captured the dynamic evolution of the catalytic centers during the CO2RR process.

Effect of Acetonitrile on the Conformation of Bovine Serum Albumin.

The use of organic solvents in drug delivery systems (DDSs) either to produce albumin nanoparticles or to manipulate the binding of target molecules to albumin, a promising nanocarrier material, presents challenges due to the conformational changes induced in the protein. In this study, we investigated the alterations in the conformation of bovine serum albumin (BSA) caused by acetonitrile (ACN) in aqueous solution by using a combination of spectroscopic analysis and molecular dynamics (MD) simulations. Ultraviolet (UV) absorption, fluorescence, and infrared (IR) absorption spectroscopy were used to analyze the BSA conformation in the solutions containing 0-60 vol % ACN. Additionally, MD simulations were conducted to elucidate the interactions between BSA and solvent components, focusing on the structural changes in the hydrophobic pocket with Trp residues of the albumin. Increasing the ACN concentration leads to significant changes in the BSA conformation, as evidenced by shifts in UV fluorescence wavelength, decreased intensity, and alterations in IR absorption bands. Furthermore, the formation of protein aggregates was observed at high ACN concentration (30 vol % ACN), shown by increased hydrodynamic diameter distribution. MD simulations further demonstrate that the presence of ACN molecules near the hydrophobic pocket with the Trp-213 residue increases the fluctuations in the positions of amino acids observed near the hydrophobic pocket with Trp-213. Moreover, the intrusion of water molecules into the hydrophobic pocket under 60% ACN conditions with highly decreased solvent polarity was correlated with the changes in the BSA secondary structure. These findings enhance our understanding of how solvent polarity affects the albumin conformation, which is crucial for optimizing albumin-based DDS applications.

Operando Spectroscopic Investigation of the Re2O7.2H2O Adduct obtained by Controlled Hydration of Re2O7.

We provide here a comprehensive investigation spectroscopic of the controlled hydration of Re2O7 using Raman, Fourier-Transform Infrared (FTIR) and X-Rays Absorption (XAS) techniques in complement with ab initio modelling for confirming the spectral assignments. Hence, the Raman signature of Re2O7.2H2O was obtained, and the evolution kinetics was investigated to provide a detailed description of the hydration process.

Excited State Dynamics of Geometrical Evolution of α-Substituted Dibenzoylmethanatoboron Difluoride Complex with Aggregation-Induced Emission Property.

Organic molecules with an aggregation-induced emission (AIE) property have been attracting much attention from the viewpoint of application to solid state emissive materials. For the AIE mechanism, quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model with the contribution of the conical intersection (CI) and deduced the importance of the restricted access to a conical intersection (RACI) in the potential energy surface (PES). Although these theoretical studies have contributed to the elucidation of AIE phenomena, direct detection of the reaction dynamics is indispensable to clarify the actual PES and the deactivation mechanism. Along this line, we investigated excited state dynamics of the AIE molecule with dibenzoylmethanatoboron difluoride complexes using time-resolved absorption spectroscopies in both visible and infrared (IR) regions. While the reference system of 1,3-bis(4-methoxyphenyl)methanatoboron difluoride (2aBF2) showed strong emission in solution, the methyl-substituted derivative at the α-position of the dioxaborine ring (2amBF2) led to the very weak fluorescence in solution but strong emission in the solid state. Time-resolved visible absorption measurements revealed a peak shift and broadening of the stimulated emission in the solution of 2amBF2, owing to the rapid change of the molecular geometry. With the temporal evolution of time-resolved IR absorption signals and density functional theory (DFT) calculation of these systems, it was deduced that 2amBF2 has two stable geometries, namely, planar and bending, in the S1 state and the bending geometry in the S1 state led to rapid conversion to the S0 state. These results support the RACI model in the aggregated states, leading to the AIE properties.

The Electrode/Electrolyte Interface Study during the Electrochemical CO2 Reduction in Acidic Electrolytes.

Electrochemical CO2 Reduction (CO2R) in acidic electrolytes has gained significant attention owing to higher carbon efficiency and stability than in alkaline counterparts. However, the proton source and the role of alkali cations for CO2R are still under debate. By using rotating ring disk electrode and surface-enhanced infrared absorption spectroscopy, we find that a neutral/alkaline environment at the interface is necessary for CO2R even in acidic electrolytes. We also confirm that water molecules, rather than protons serve as the proton source for CO2R. Alkali cations in the outer Helmholtz plane activate H2O and promote the desorption of adsorbed carbon monoxide. Additionally, the solvated CO2, or CO2(aq), is the actual reactant for CO2R. This study provides a deeper understanding of the electrode/electrolyte interface during CO2R in acidic electrolytes and sheds light on further performance improvement of this system.