Spectroscopy Experiments Research Articles

Three new xanthones and other anti-inflammatory components from the aerial parts of Hypericum beanii.

Hypericum beanii, a traditional folk medicine plant, has been employed in treating various inflammation-related diseases. In this study, three new prenylated xanthones, named beanigenin A (1), beanigenin B (2), and beanigenin C (3), along with twenty-five known compounds (4-28), were isolated from the aerial parts of H. beanii. The new xanthones were elucidated based on modern spectroscopic experiments, including nuclear magnetic resonance spectroscopy (NMR) techniques, high-resolution electrospray ionization mass spectroscopy (HR-ESI-MS), and electronic circular dichroism (ECD). All the compounds were evaluated for their anti-inflammatory effects by measuring their inhibitory effect on nitric oxide (NO) production in LPS-stimulated RAW 264.7 macrophages. Our findings showed that compounds 1-10, 12, 14, 21-23, 26, and 28 displayed significant anti-inflammatory effects, with IC50 values ranging from 0.82 to 9.71μM. The MOE software was utilized to conduct an in silico evaluation of the potential inhibitory activity of the three new xanthones against inducible NO synthase (iNOS) and cyclooxygenase 2 (COX-2) proteins. The results indicated that the three new xanthones demonstrated a high binding affinity with both iNOS and COX-2 proteins.

Quantum-State Renormalization in Semiconductor Nanoparticles.

A single photoexcited electron-hole pair within a polar semiconductor nanocrystal (SNC) alters the charge screening and shielding within it. Perturbations of the crystal lattice and of the valence and conduction bands result, and the quantum-confinement states in a SNC shift uniquely with a dependence on the states occupied by the carriers. This shifting is termed quantum-state renormalization (QSR). This Perspective highlights QSR in semiconductor quantum wires and dots identified in time-resolved transient absorption and two-dimensional electronic spectroscopy experiments. Beyond the interest in understanding the principles of QSR and energy-coupling mechanisms, we pose the contributions of QSR in time-resolved spectroscopy data must be accounted for to accurately identify the time scales for intraband relaxation of the carriers within SNCs.

Cogwheel phase cycling in population-detected optical coherent multidimensional spectroscopy.

An integral procedure in every coherent multidimensional spectroscopy experiment is to suppress undesired background signals. For that purpose, one can employ a particular phase-matching geometry or phase cycling, a procedure that was adapted from nuclear magnetic resonance (NMR) spectroscopy. In optical multidimensional spectroscopy, phase cycling has been usually carried out in a "nested" fashion, where pulse phases are incremented sequentially with linearly spaced increments. Another phase-cycling approach that was developed for NMR spectroscopy is "cogwheel phase cycling," where all pulse phases are varied simultaneously in increments defined by so-called "winding numbers." Here we explore the concept of cogwheel phase cycling in the context of population-based coherent multidimensional spectroscopy. We derive selection rules for resolving and extracting fourth-order and higher-order nonlinear signals by cogwheel phase cycling and describe how to perform a numerical search for the winding numbers for various population-detected 2D spectroscopy experiments. We also provide an expression for a numerical search for nested phase-cycling schemes and predict the most economical schemes of both approaches for a wide range of nonlinear signals. The signal selectivity of the technique is demonstrated experimentally by acquiring rephasing and nonrephasing fourth-order signals of a laser dye by both phase-cycling approaches. We find that individual nonlinear signal contributions are, in most cases, captured with fewer steps by cogwheel phase cycling compared to nested phase cycling.

A Multifunctional Tb(III)-Based Metal-Organic Framework for Chemical Conversion of CO2, Fluorescence Sensing of Trace Water and Metamitron.

The utilization of metal-organic frameworks (MOFs) as fluorescent sensors for the detection of environmental and chemical reagent pollutants as well as heterogeneous catalysis for CO2 conversion represents a crucial avenue of research with significant implications for the protection of human health. In this work, a Tb(III)-based three-dimensional metal-organic framework, [Tb(L)·4DMF]n (Tb-MOF) (H3L = 5'-(4-carboxy-3-hydroxyphenyl)-3,3″-dihydroxy-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid), has been structurally conformed by single-crystal X-ray crystallography. It possesses a 1D rhombus channel along the [010] direction, featuring a pore size of 6.02 × 9.13 Å. Tb-MOF was proved to be a multifunctional material for a fluorescent sensor and CO2 cycloaddition heterogeneous catalyst material. Fluorescence sensing studies revealed that Tb-MOF demonstrates high sensitivity, selectivity, and favorable regeneration properties, making it an effective chemosensor for detecting the metamitron (MMT) pesticide and trace water in organic solvents. The mechanism of fluorescence quenching by MMT and water was elucidated by a combination of XRD, UV-vis absorption spectra, IR spectra, theoretical calculations, and fluorescence lifetimes. The material was also utilized for the sensing of MMT and water in paper strips. Additionally, the open Tb3+ site as Lewis acidic centers makes Tb-MOF achieve efficiently catalytic conversion for CO2 and epoxides to cyclic carbonates. Moreover, a possible catalytic mechanism for the conversion of carbon dioxide to cyclic carbonates was proposed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. It also exhibited recyclability for up to five cycles without noticing an appreciable loss in sensing or catalytic efficiency.

Simulating topological quantum gates in two-dimensional magnet-superconductor hybrid structures

The creation of topological quantum gates using Majorana zero modes—an outstanding problem in the field of topological quantum computing—relies on our ability to control the braiding process in time and space. Here, we propose two-dimensional magnet-superconductor hybrid structures as a new platform for the successful implementation of topologically protected σz-, σz- and σx-quantum gates using Majorana zero modes. Employing a novel theoretical formalism to compute the full time-dependent many-body wave-function and utilizing a braiding protocol motivated by recent advances in electron-spin-resonance techniques we simulate quantum gates in 2D systems up to 600 sites, on timescales from a few femto- to nanoseconds. We demonstrate that the braiding process can be visualized in time and space by computing the non-equilibrium local density of states, which is proportional to the time-dependent differential conductance measured in scanning tunneling spectroscopy experiments, allowing us to directly image Majorana world lines.

Cooperative Active Sites on Ag2Pt3TiS6 for Enhanced Low‐Temperature Ammonia Fuel Cell Electrocatalysis

AbstractAmmonia has attracted considerable interest as a hydrogen carrier that can help decarbonize global energy networks. Key to realizing this is the development of low temperature ammonia fuel cells for the on‐demand generation of electricity. However, the efficiency of such systems is significantly impaired by the sluggish ammonia oxidation reaction (AOR) and oxygen reduction reaction (ORR). Here, we report the design of a bifunctional Ag2Pt3TiS6 electrocatalyst that facilitates both reactions at mass activities exceeding that of commercial Pt/C. Through comprehensive density functional theory calculations, we identify that active site motifs composed of Pt and Ti atoms work cooperatively to catalyze ORR and AOR. Notably, in situ shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) experiments indicate a decreased propensity for *NOx formation and hence an increased resistance toward catalyst poisoning for AOR. Employing Ag2Pt3TiS6 as both the cathode and anode, we constructed a low temperature ammonia fuel cell with a high peak power density of 8.71 mW cm−2 and low Pt loading of 0.45 mg cm−2. Our findings demonstrate a pathway towards the rational design of effective electrocatalysts with multi‐element active sites that work cooperatively.

A New Polyvinyl Alcohol Lithium Chloride Hydrogel Electrolyte: High Ionic Conductivity and Wide Working Temperature Range

AbstractPolyvinyl alcohol/lithium chloride hydrogel (PVA/LiCl) is one of the most used electrolyte in supercapacitors. Increasing the ionic conductivity and operating temperature range of PVA/LiCl would greatly boost the electrochemical performance of supercapacitors and enhance the devices’ environmental adaptability. This is of great significance yet rarely concerned about in energy communities. In this work, SiO2 functionalized PVA/LiCl (PVA‐SiO2/LiCl) is experimentally realized with high ionic conductivity and wide operating temperature range. The spectroscopic and theoretical experiments prove that SiO2 significantly regulates cation solvation structure to promote cation‐anion pair dissociation and diminish coagulation of PVA chains, increasing ionic conductivity from 19.01 mS cm−1 of PVA/LiCl to 56.17 mS cm−1 of the new electrolyte. SiO2 can also prevent cation‐anion association as temperature decreases, and the abundant hydroxyl groups on the SiO2 and the stretched PVA chains tune hydrogen bonds among dipolar water molecules. They effectively expand the operating temperature range of PVA‐SiO2/LiCl. PVA‐SiO2/LiCl greatly boosts the electrochemical performance of MnO2‐based supercapacitor. The design concept developed here opens up a way toward high‐performance hydrogel electrolyte development.

TDS Simulator: A MATLAB App to model temperature-programmed hydrogen desorption

We present TDS Simulator, a new software tool aimed at modelling thermal desorption spectroscopy (TDS) experiments. TDS is a widely used technique for quantifying key characteristics of hydrogen-material interactions, such as diffusivity and trapping. However, interpreting the output of TDS experiments is non-trivial and requires appropriate post-processing tools. This work introduces the first software tool capable of simulating TDS curves for arbitrary choices of material parameters and hydrogen trap characteristics, using the primary hydrogen diffusion and trapping models (Oriani, McNabb-Foster). Moreover, TDS Simulator contains a specific functionality for loading experimental TDS data and conducting the inverse calibration of a selected transport model, providing automatic estimates of the density and binding energy of each hydrogen trap type in the material. In its first version, TDS Simulator is provided as a MATLAB App, which is made freely available to the community and provides a simple graphical user interface (GUI) to make use of TDS Simulator straightforward. As reported in the present manuscript, the outputs of TDS Simulator have been extensively validated against literature data. Demonstrations of automatic determination of trap characteristics from experimental data through the optimisation tool are also provided. The present work enables an efficient and straightforward characterisation of hydrogen-material characteristics relevant to multiple applications, from nuclear fusion to the development of hydrogen-compatible materials for the hydrogen economy. TDS Simulator can be downloaded from https://mechmat.web.ox.ac.uk/codes (To be uploaded immediately after the review process).

Temperature dependent human serum albumin Corona formation: A case study on gold nanorods and nanospheres.

Protein molecules interact with nanoparticles to form a protein layer on the surface called the protein corona. Corona formation can be affected by the temperature and shape of the nanoparticles thereby impacting the fate of the nanoparticles inside physiological systems. We have investigated the human serum albumin (HSA) corona formation and its interactions with gold nanospheres and nanorods at different temperatures (18-42 °C). UV-Vis, fluorescence, isothermal titration calorimetry (ITC), x-ray photoelectron spectroscopy (XPS) and circular dichroism (CD) experiments have been performed to determine the changes due to the shape and temperature. UV-Vis spectra show a greater propensity of corona induced aggregation in the nanorods compared to the nanospheres. The Stern-Volmer plot indicates that static quenching is predominant in the HSA-AuNP interactions with higher quenching efficiency for nanorods than nanospheres. ITC analyses show that HSA-nanorods are involved in more favorable interactions compared to HSA-nanospheres. XPS studies indicate a more electron rich environment on the AuNRs surface and higher AuS interactions in AuNSs. CD spectra show higher secondary structural changes with temperature in case of HSA-AuNR interactions compared to HSA-AuNS interactions. The changes in the protein corona due to nanoparticle shape and variable temperature have been investigated through protein adsorption and composition, types of interactions and protein conformation.

Large-Area Bright Emission of Plasmon-Coupled Dark Excitons at Room Temperature.

Brightening dark excitons in transition metal dichalcogenide monolayers (MLs) can provide large-area ultrathin devices for applications in quantum information science and optoelectronics. For practical applications of dark excitons, a robust and bright emission over a wide area at room temperature is desirable; however, no reliable approach has been demonstrated thus far. In this study, an efficient approach is presented for brightening dark excitons at room temperature over a large area of a WSe2 ML via coupling between plasmons and dark excitons. When a WSe2 ML is placed on gold micropillars (Au MPs), dark excitons are efficiently coupled to strongly localized surface plasmons at the edges of the Au MPs, along with a strong photoluminescence (PL) emission. Room-temperature dark exciton emission is confirmed via energy-, angle-, and time-resolved spectroscopy experiments, as well as confocal PL mapping. This study provides a generalizable method for the practical application of dark exciton.

Cooperative Active Sites on Ag2Pt3TiS6 for Enhanced Low-Temperature Ammonia Fuel Cell Electrocatalysis.

Ammonia has attracted considerable interest as a hydrogen carrier that can help decarbonize global energy networks. Key to realizing this is the development of low temperature ammonia fuel cells for the on-demand generation of electricity. However, the efficiency of such systems is significantly impaired by the sluggish ammonia oxidation reaction (AOR) and oxygen reduction reaction (ORR). Here, we report the design of a bifunctional Ag2Pt3TiS6 electrocatalyst that facilitates both reactions at mass activities exceeding that of commercial Pt/C. Through comprehensive density functional theory calculations, we identify that active site motifs composed of Pt and Ti atoms work cooperatively to catalyze ORR and AOR. Notably, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) experiments indicate a decreased propensity for *NOx formation and hence an increased resistance toward catalyst poisoning for AOR. Employing Ag2Pt3TiS6 as both the cathode and anode, we constructed a low temperature ammonia fuel cell with a high peak power density of 8.71 mW cm-2 and low Pt loading of 0.45 mg cm-2. Our findings demonstrate a pathway towards the rational design of effective electrocatalysts with multi-element active sites that work cooperatively.

Photodissociation Spectroscopy and Photofragment Imaging of the Mg+(Benzene) Complex

Photodissociation Spectroscopy and Photofragment Imaging of the Mg⁺(Benzene) Complex

Synthesis of Multisubstituted Cyclopentadiene Derivatives from 3,3-Disubstituted Cyclopropenes and Internal Alkynes Catalyzed by Low-Valent Niobium Complexes.

A low-valent niobium species generated from NbCl5 and 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (Si-Me-CHD) in combination with PPh3 catalyzed a [2+2+1]-cycloaddition reaction of 3,3-disubstituted cyclopropenes and 2 equiv of diaryl/dialkylalkynes, leading to isomeric mixtures of multisubstituted cyclopentadienes 3-5. The initial catalyst activation process was a one-electron reduction of NbCl5 with Si-Me-CHD to provide [NbCl3(μ-Cl) (L)]2 (L = PMe2Ph (6), L = PPh3 (7)) in the presence of phosphine ligands. An NMR spectroscopic time course experiment using complex 7 as the catalyst revealed an induction period for the product formation, corresponding to an additional one-electron reduction of 7 by the substrates to give catalytically active η2-alkyne complexes of NbCl3. A combined computational and experimental study clarified the mechanism of this unprecedented [2+2+1]-cyclopentadiene synthesis; a rate-determining 1,2-insertion of cyclopropene into η2-alkyne niobium species to form cyclopropane-fused metallacyclopentene followed by ring-opening β-C elimination provides a dienylalkylidene intermediate prior to incorporation of the second alkyne through carbene/alkyne metathesis. We also demonstrated the synthetic utility of the multisubstituted cyclopentadienes as the cyclopentadienyl ligands by derivatizing to the corresponding lithium cyclopentadienide, which is applicable for the synthesis of ferrocene 10.

Performance Descriptor of Subsurface Metal-Promoted Boron Catalysts for Low-Temperature Propane Oxidative Dehydrogenation to Propylene.

Boron-based catalysts have exhibited excellent olefin selectivity in the oxidative dehydrogenation of propane (ODHP) reaction. The substrate material should be a potential platform for performance modulation of boron catalysts in this reaction since the introduction of subsurface Ni promoters significantly improves the activity. In this study, we deciphered the substrate effect and identified a performance descriptor to comprehend the roles of subsurface materials in BOx/metal/BN ODHP catalysts by evaluating different metal promoters. Performance evaluation and transient infrared spectroscopic experiments demonstrate that the intrinsic activity and kinetic behaviors of the O-H bond dissociation/regeneration on the metal-promoted BOx overlayer are metal substrate-dependent. Combining density functional theory (DFT) calculations, it is found that the dissociation/regeneration inclination of the O-H bond in BOx(OH)3-x active species is controlled by the affinity of H for boron oxide species. The metal-O binding energy, which has been demonstrated to be linearly correlated with H affinity, can serve as a straightforward performance descriptor for both low-temperature radical initialization and ODHP reaction, revealing this reaction is controlled by the Sabatier principle, and moderate metal-O binding energy is essential for achieving remarkable performance in the BOx/M/BN catalysts. Following the guidance of a potential descriptor, Ni-Rh alloy substrates are investigated and the substrate with a Ni/Rh molar ratio of 15:1 significantly enhances the low-temperature intrinsic activity of the metal-modified BOx to 9.26 μmol/(m2·s), which reaches 105.9 times that of h-BN and is 18.3% larger than the monometallic BOx/Ni/BN catalysts.

Cu(II) Stability and UV-Induced Electron Transfer in a Metal-Organic Hybrid: An EPR, DFT, and Crystallographic Characterization of Copper-Doped Zinc Creatininium Sulfate.

Single-crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopic experiments, complemented by quantum chemical DFT calculations, were carried out on the copper-doped metal-organic hybrid and Tutton salt analogue zinc creatininium sulfate to determine its crystal structure, to characterize the electronic structure of the doped Cu(II) binding site, and to propose a pathway for an excited-state, proton-coupled electron transfer (PCET) process in UV-exposed crystals. The crystal structure is isomorphous to that of cadmium creatininium sulfate, which has the transition ion, not in direct coordination with the creatinine, but forming a hexahydrate complex, which is bridged to a creatininium through an intervening sulfate ion. The EPR g (2.446, 2.112, 2.082) and copper hyperfine (ACu: -327, -59.6, 10.8 MHz) tensor parameters are consistent with doped copper replacing host zinc in the metal-hexahydrate complex. These parameters are similar to those observed for copper hexahydrate in doped Tutton salt systems at low temperature, where the unpaired electron occupies mainly the copper 3dx2-y2 orbital. At room temperature in the Tutton systems, vibration couplings stemming from a dynamic Jahn-Teller effect cause tensor averaging which results in a reduction in their maximum g-tensor and hyperfine tensor values. However, like for the doped isomorphous Cd creatinine crystal, the Cu(II) EPR exhibits little, or no room temperature averaging compared to its low temperature pattern. Samples exposed to 254 nm UV light generate a carbon-centered free radical species, characterized by an isotropic g-tensor (g = 2.0029) and an alpha-proton hyperfine coupling (-24 -14 +4 G). These parameters identify it as a creatinine radical cation formed by the oxidative release of one of its C2 methylene hydrogens. DFT calculations confirm the unpaired electronic structures of both the Cu(II) site and free radical. The growth in radical concentration with an increase in the UV exposure time coincides with a decrease in the copper EPR signal, indicating a coupled light-induced oxidation reduction process. A comparison of the crystal structure with the EPR parameters and DFT results provides evidence for a UV-induced PCET.

New Insights into pH-dependent Complex Formation between Lignosulfonates and Anthocyanins: Impact on Color and Oxidative Stability.

Anthocyanins have limited application as natural colorants and antioxidants due to their color loss and instability under certain conditions. This research explores the formation of a complex between lignosulfonates (LS) and cyanidin-3-O-glucoside (C3G) using a multitechnique approach as well as the effect on C3G's red color, oxidative stability, and antioxidant activity in acidic mediums. All data revealed pH-dependent LS-C3G interactions. The thermodynamic parameters showed weak noncovalent interactions, mainly electrostatic interactions, hydrogen bonds, and hydrophobic effect, with a higher association constant determined at pH 3. Fourier-transform infrared spectroscopy and Zeta-potential experiments further corroborate evidence of these LS-C3G interactions. Fluorescence quenching and lifetime experiments revealed static and dynamic quenching at pH 1 and 3, respectively. UV-visible spectroscopy demonstrated a bathochromic shift upon complex formation and a hyperchromic effect at pH 3 and 4, as a consequence of the improved red color of C3G. Electrochemical results suggested that at pH 3 the LS enhances C3G stability by protecting its oxidizable moieties over time, as well as improving the antioxidant activity of the anthocyanin in the complex.

How Do the Morphology and Crystal Facet of CeO2 Determine the Catalytic Activity toward NO Removal?

Cerium oxide (CeO2) exhibits application potential for the selective catalytic reduction of nitrogen oxides (NOx) with NH3 (NH3-SCR). The crystal facets and morphology of CeO2 have a vital impact on the catalytic performance of NH3-SCR. However, the precise influence mechanisms on SCR activity remain elusive. In this work, CeO2 is successfully synthesized with three distinct crystal facets and nine diverse morphologies. This investigation involves a comprehensive blend of theoretical analysis and experiments, to gain profound insights into the underlying mechanisms governing the SCR catalytic activity concerning morphology and crystal facets. By closely integrating density functional theory (DFT) calculations, Ab initio thermodynamic analysis, SCR catalytic activity experiments, and X-ray photoelectron spectroscopy experiments, it is discovered that the concentration of surface-active oxygen (O*) plays a pivotal role in determining the catalytic activity of CeO2 in SCR reactions, as opposed to factors like specific surface area or oxygen defect concentration. This experimental-theoretical joint study provides design principles of CeO2 catalysts for NO removal.

Solid-State Electrochemical Carbon Dioxide Capture by Conductive Metal-Organic Framework Incorporating Nickel Bis(diimine) Units.

This paper presents the first implementation of electrically conductive metal-organic framework (MOF) Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) integrated with nickel bis(diimine) (Ni-BDI) units for efficient solid-state electrochemical carbon dioxide (CO2) capture. The electrochemical cell assembled using Ni3(HITP)2 as working electrodes can reversibly capture and release CO2 through potential control. A high-capacity utilization of 96% and a Faraday efficiency of 98% have been achieved. The material also exhibits excellent electrochemical stability with its capacity maintained during 50 capture-release cycles and resistance to general interferences, including O2, H2O, NO2, and SO2. Capacity utilization of up to 35% is obtained at CO2 concentrations as low as 1%. The capture of CO2 at concentrations ranging from 1% to 100% requires exceptionally low energy consumption of only 30.5-72.4 kJ mol-1. Studies combining spectroscopic experiments and computational approaches reveal that the CO2 capture and release mechanism involves reversible carbamate formation on the N atom of the Ni-BDI unit in the MOF upon its one-electron redox reaction.

Fluorine Labeling and 19F NMR Spectroscopy to Study Biological Molecules and Molecular Complexes.

High-resolution nuclear magnetic resonance (NMR) spectroscopy represents a key methodology for studying biomolecules and their interplay with other molecules. Recent developments in labeling strategies have made it possible to incorporate fluorine into proteins and peptides reliably, with manageable efforts and, importantly, in a highly site-specific manner. Paired with its excellent NMR spectroscopic properties and absence in most biological systems, fluorine has enabled scientists to investigate a rather wide range of scientific objectives, including protein folding, protein dynamics and drug discovery. Furthermore, NMR spectroscopic experiments can be conducted in complex environments, such as cell lysate or directly inside living cells. This review presents selected studies demonstrating how 19F NMR spectroscopic approaches enable to contribute to the understanding of biomolecular processes. Thereby the focus has been set to labeling strategies available and specific NMR experiments performed to answer the underlying scientific objective.

Fast Collective Hydrogen-Bond Dynamics in Hexafluoroisopropanol Related to its Chemical Activity.

Using fluorinated mono-alcohols, in particular hexafluoro-isopropanol (HFIP), as a solvent can enhance chemical reaction rates in a spectacular manner. Previous work has shown evidence that this enhancement is related to the hydrogen-bond structure of these liquids. Here, we investigate the hydrogen-bond dynamics of HFIP and compare it to that of its non-fluorinated analog, isopropanol. Ultrafast infrared spectroscopy experiments show that the dynamics of individual hydrogen-bonds is about twice as slow in HFIP as in isopropanol. Surprisingly, from dielectric spectroscopy we find the opposite behavior for the dynamics of hydrogen-bonded clusters: collective rearrangements are 3 times faster in HFIP than in isopropanol. This difference indicates that the hydrogen-bonded clusters in HFIP are smaller than in isopropanol. The differences in cluster size can be traced to changes in the hydrogen-bond donor and acceptor strengths upon fluorination. The smaller cluster size can boost reaction rates in HFIP by increasing the concentration of reactive, terminal OH-groups of the clusters, whereas the fast collective dynamics can increase the rate of formation of hydrogen-bonds with the reactants. The longer lifetime of the individual hydrogen-bonds in HFIP can enhance the stability of the hydrogen-bonded clusters, and so increase the probability of reactant-solvent hydrogen-bonding.