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1. Observation of the fastest chemical processes in the radiolysis of water

   Loh, Z.-H.; Doumy, G.; Arnold, C.; Kjellsson, L.; Southworth, S. H.; Al Haddad, A.; Kumagai, Y. Tu; Ho, P. J; March, A. M.; Schaller, R. D.; et al (January 2020, Science)

   Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. Although numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, remains elusive. We used tunable femtosecond soft x-ray pulses from an x-ray free electron laser to reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The isolated resonance associated with the valence hole (H2O+/OH) enabled straightforward detection. Molecular dynamics simulations revealed that the x-ray spectra are sensitive to structural dynamics at the ionization site. We found signatures of hydrated-electron dynamics in the x-ray spectrum. 

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2. The role of charge in microdroplet redox chemistry

   https://doi.org/10.1038/s41467-024-47879-0  

   Heindel, Joseph_P; LaCour, R_Allen; Head-Gordon, Teresa (April 2024, Nature Communications)

   Abstract In charged water microdroplets, which occur in nature or in the lab upon ultrasonication or in electrospray processes, the thermodynamics for reactive chemistry can be dramatically altered relative to the bulk phase. Here, we provide a theoretical basis for the observation of accelerated chemistry by simulating water droplets of increasing charge imbalance to create redox agents such as hydroxyl and hydrogen radicals and solvated electrons. We compute the hydration enthalpy of OH⁻and H⁺that controls the electron transfer process, and the corresponding changes in vertical ionization energy and vertical electron affinity of the ions, to create OH^•and H^•reactive species. We find that at ~ 20 − 50% of the Rayleigh limit of droplet charge the hydration enthalpy of both OH⁻and H⁺have decreased by >50 kcal/mol such that electron transfer becomes thermodynamically favorable, in correspondence with the more favorable vertical electron affinity of H⁺and the lowered vertical ionization energy of OH⁻. We provide scaling arguments that show that the nanoscale calculations and conclusions extend to the experimental microdroplet length scale. The relevance of the droplet charge for chemical reactivity is illustrated for the formation of H₂O₂, and has clear implications for other redox reactions observed to occur with enhanced rates in microdroplets. 

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3. Vibrational predissociation of the phenol–water dimer: a view from the water

   https://doi.org/10.1039/C8CP06581K  

   Kwasniewski, Daniel; Butler, Mitchell; Reisler, Hanna (January 2019, Physical Chemistry Chemical Physics)

   The vibrational predissociation (VP) dynamics of the phenol–water (PhOH–H 2 O) dimer were studied by detecting H 2 O fragments and using velocity map imaging (VMI) to infer the internal energy distributions of PhOH cofragments, pair-correlated with selected rotational levels of the H 2 O fragments. Following infrared (IR) laser excitation of the hydrogen-bonded OH stretch fundamental of PhOH (Pathway 1) or the asymmetric OH stretch localized on H 2 O (Pathway 2), dissociation to H 2 O + PhOH was observed. H 2 O fragments were monitored state-selectively by using 2+1 Resonance-Enhanced Multiphoton Ionization (REMPI) combined with time-of-flight mass spectrometry (TOF-MS). VMI of H 2 O in selected rotational levels was used to derive center-of-mass (c.m.) translational energy ( E T ) distributions. The pair-correlated internal energy distributions of the PhOH cofragments derived via Pathway 1 were well described by a statistical prior distribution. On the other hand, the corresponding distributions obtained via Pathway 2 show a propensity to populate higher-energy rovibrational levels of PhOH than expected from a statistical distribution and agree better with an energy-gap model. The REMPI spectra of the H 2 O fragments from both pathways could be fit by Boltzmann plots truncated at the maximum allowed energy, with a higher temperature for Pathway 2 than that for Pathway 1. We conclude that the VP dynamics depends on the OH stretch level initially excited. 

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4. Chromate Incarceration by Nanojars and Its Removal from Water by Liquid–Liquid Extraction

   https://doi.org/10.1021/acs.inorgchem.3c00262  

   Al Isawi, Wisam A.; Hartman, Christian K.; Singh, Pooja; Zeller, Matthias; Mezei, Gellert (April 2023, Inorganic Chemistry)

   The unprecedented liquid–liquid extraction of the dinegative chromate ion (CrO42–) from neutral aqueous solutions into aliphatic hydrocarbon solvents using nanojars as extraction agents is demonstrated. Transferring chromate from water into an organic solvent is extremely challenging due to its large hydration energy (ΔGh° = −950 kJ/mol) and strong oxidizing ability. Owing to their highly hydrophilic anion binding pockets lined by a multitude of hydrogen bond donor OH groups, neutral nanojars of the formula [cis-CuII(μ-OH)(μ-4-Rpz)]n (n = 27–33; pz = pyrazolate anion; R = H or n-octyl) strongly bind the CrO42– ion and efficiently transfer it from water into n-heptane or C11 – C13 isoalkanes (when R = n-octyl). The extracted chromate can easily be recovered from the organic layer by stripping with an aqueous acid solution. Electrospray ionization mass spectrometric, UV–vis and paramagnetic 1H NMR spectroscopic, X-ray crystallographic, and thermal stability studies in solution and chemical stability studies toward NH3, methanol, and Ba2+ ions are employed to explore the binding of the CrO42– ion by nanojars. Titration of carbonate nanojars [CO3 ⊂ {Cu(OH)(pz)}n]2– with H2CrO4 leads to anion exchange and the formation of chromate nanojars [CrO4 ⊂ {Cu(OH)(pz)}n]2–. Details of chromate binding by H-bonding based on single-crystal structures of (Bu4N)2[CrO4 ⊂ {Cu(OH)(pz)}28], four pseudopolymorphs of (Bu4N)2[CrO4 ⊂ {Cu(OH)(pz)}31], and also the methoxy-substituted derivative (Bu4N)2[CrO4 ⊂ {Cu31(OH)30(OCH3)(pz)31}] are presented. 

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5. Insights into how the aqueous environment influences the kinetics and mechanisms of heterogeneously-catalyzed COH* and CH ₃ OH* dehydrogenation reactions on Pt(111)

   https://doi.org/10.1039/C9CP00824A  

   Bodenschatz, Cameron J.; Xie, Tianjun; Zhang, Xiaohong; Getman, Rachel B. (May 2019, Physical Chemistry Chemical Physics)

   Water influences catalytic reactions in multiple ways, including energetic and mechanistic effects. While simulations have provided significant insight into the roles that H 2 O molecules play in aqueous-phase heterogeneous catalysis, questions still remain as to the extent to which H 2 O structures influence catalytic mechanisms. Specifically, influences of the configurational variability in the water structures at the catalyst interface are yet to be understood. Configurational variability is challenging to capture, as it requires multiscale approaches. Herein, we apply a multiscale sampling approach to calculate reaction thermodynamics and kinetics for COH* dehydrogenation to CO* and CH 3 OH* dehydrogenation to CH 2 OH* on Pt(111) catalysts under liquid H 2 O. We explore various pathways for these dehydrogenation reactions that could influence the overall mechanism of methanol decomposition by including participation of H 2 O structures both energetically and mechanistically. We find that the liquid H 2 O environment significantly influences the mechanism of COH* dehydrogenation to CO* but leaves the mechanism of CH 3 OH* dehydrogenation to CH 2 OH* largely unaltered. 

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