Infrared spectroscopic studies on hydrogen-bonded water networks in gas phase clusters

Network Models of BACE-1 Inhibitors: Exploring Structural and Biochemical Relationships

This study investigates the clustering patterns of human β-secretase 1 (BACE-1) inhibitors using complex network methodologies based on various distance functions, including Euclidean, Tanimoto, Hamming, and Levenshtein distances. Molecular descriptor vectors such as molecular mass, Merck Molecular Force Field (MMFF) energy, Crippen partition coefficient (ClogP), Crippen molar refractivity (MR), eccentricity, Kappa indices, Synthetic Accessibility Score, Topological Polar Surface Area (TPSA), and 2D/3D autocorrelation entropies are employed to capture the diverse properties of these inhibitors. The Euclidean distance network demonstrates the most reliable clustering results, with strong agreement metrics and minimal information loss, indicating its robustness in capturing essential structural and physicochemical properties. Tanimoto and Hamming distance networks yield valuable clustering outcomes, albeit with moderate performance, while the Levenshtein distance network shows significant discrepancies. The analysis of eigenvector centrality across different networks identifies key inhibitors acting as hubs, which are likely critical in biochemical pathways. Community detection results highlight distinct clustering patterns, with well-defined communities providing insights into the functional and structural groupings of BACE-1 inhibitors. The study also conducts non-parametric tests, revealing significant differences in molecular descriptors, validating the clustering methodology. Despite its limitations, including reliance on specific descriptors and computational complexity, this study offers a comprehensive framework for understanding molecular interactions and guiding therapeutic interventions. Future research could integrate additional descriptors, advanced machine learning techniques, and dynamic network analysis to enhance clustering accuracy and applicability.

Spectroscopic and Theoretical Identifications of Two Structural Motifs of (H2O)10 Cluster

Precise characterization of archetypal systems of aqueous hydrogen-bonding networks is essential for developing accurate potential functions and universal models of water. The structures of water clusters (H2O)n (n = 2-9) have been verified recently through size-specific infrared spectroscopy with a vacuum ultraviolet free electron laser (VUV-FEL) and quantum chemical studies. For (H2O)10, the pentagonal prism and butterfly motifs were proposed to be important building blocks and were observed in previous experiments. Here we report the size-specific infrared spectra of (H2O)10 via a joint experimental and theoretical study. Well-resolved spectra provide a unique signature for the coexistence of pentagonal prism and butterfly motifs. These (H2O)10 motifs develop from the dominant structures of (H2O)n (n = 8, 9) clusters. This work provides an intriguing prelude to the diverse structure of liquid water and opens avenues for size-dependent measurement of larger systems to understand the stepwise formation mechanism of hydrogen-bonding networks.

Vascular Bundle for Exceptional Water Confinement, Transport, and Evaporation

Nature, through billions of years of evolution, has constructed extremely efficient biosystems for transporting, confining, and vaporizing water. Mankind's ability to master water, however, is far from impeccable, and a sustainable supply of clean fresh water remains a global challenge. Here, we learn from Nature and prepare papyrus carbon (PC) from Egyptian papyrus paper as a sustainable solar desalination material. By taking advantage of the capillary pores from vascular bundles that are inherently built for transporting water in plants, PC achieves an evaporation rate of 4.1 kg m-2 h-1 in a passive single-stage device. Raman spectroscopy and thermal calorimetry show that the capillary pores pose a confinement effect to generate loosely hydrogen-bonded intermediate water, which substantially reduces the enthalpy of vaporization, allowing for exceptionally high energy efficiencies. The understanding is applicable to all nature-designed vascular plants and man-made separation and purification systems.

Insight into the Binding of Argon to Cyclic Water Clusters from Symmetry-Adapted Perturbation Theory

This work systematically examines the interactions between a single argon atom and the edges and faces of cyclic H2O clusters containing three-five water molecules (Ar(H2O)n=3-5). Full geometry optimizations and subsequent harmonic vibrational frequency computations were performed using MP2 with a triple-ζ correlation consistent basis set augmented with diffuse functions on the heavy atoms (cc-pVTZ for H and aug-cc-pVTZ for O and Ar; denoted as haTZ). Optimized structures and harmonic vibrational frequencies were also obtained with the two-body-many-body (2b:Mb) and three-body-many-body (3b:Mb) techniques; here, high-level CCSD(T) computations capture up through the two-body or three-body contributions from the many-body expansion, respectively, while less demanding MP2 computations recover all higher-order contributions. Five unique stationary points have been identified in which Ar binds to the cyclic water trimer, along with four for (H2O)4 and three for (H2O)5. To the best of our knowledge, eleven of these twelve structures have been characterized here for the first time. Ar consistently binds more strongly to the faces than the edges of the cyclic (H2O)n clusters, by as much as a factor of two. The 3b:Mb electronic energies computed with the haTZ basis set indicate that Ar binds to the faces of the water clusters by at least 3 kJ mol-1 and by nearly 6 kJ mol-1 for one Ar(H2O)5 complex. An analysis of the interaction energies for the different binding motifs based on symmetry-adapted perturbation theory (SAPT) indicates that dispersion interactions are primarily responsible for the observed trends. The binding of a single Ar atom to a face of these cyclic water clusters can induce perturbations to the harmonic vibrational frequencies on the order of 5 cm-1 for some hydrogen-bonded OH stretching frequencies.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

Isotope Effects in the Zundel-Eigen Isomerization of H+(H2O)6

The isomerization pathway between the energetically low-lying Zundel and Eigen isomers of the protonated water hexamer was investigated using high-level ab initio calculations including a treatment of zero-point corrections. On the basis of these calculations, the Zundel-Eigen isomerization was found to proceed through a stable intermediate isomer, which consists of a four-membered ring with two single acceptor water molecules. The inclusion of vibrational zero-point energy is shown to be important for accurately establishing the relative energies of the three relevant isomers involved in the Zundel-Eigen isomerization. Diffusion Monte Carlo calculations including anharmonic vibrational effects show that all three isomers of H⁺(H₂O)₆ and D⁺(D₂O)₆ have well-defined structures. The energetic ordering of the three isomers changes upon deuteration. The implications of these results for the vibrational spectra of H⁺(H₂O)₆ and D⁺(D₂O)₆ are also discussed.

Microhydration of the Pyrrole Cation (Py+) Revealed by IR Spectroscopy: Ionization-Induced Rearrangement of the Hydrogen-Bonded Network of Py+(H2O)2

Microhydration of heterocyclic aromatic molecules can be an appropriate fundamental model to shed light on intermolecular interactions and functions of macromolecules and biomolecules. We characterize herein the microhydration process of the pyrrole cation (Py⁺) by infrared photodissociation (IRPD) spectroscopy and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). Analysis of IRPD spectra of mass-selected Py⁺(H₂O)₂ and its cold Ar-tagged cluster in the NH and OH stretch range combined with geometric parameters of intermolecular structures, binding energies, and natural atomic charge distribution provides a clear picture of the growth of the hydration shell and cooperativity effects. Py⁺(H₂O)₂ is formed by stepwise hydration of the acidic NH group of Py⁺ by a hydrogen-bonded (H₂O)₂ chain with NH···OH···OH configuration. In this linear H-bonded hydration chain, strong cooperativity, mainly arising from the positive charge, strengthens both the NH···O and OH···O H-bonds with respect to those of Py⁺H₂O and (H₂O)₂, respectively. The linear chain structure of the Py⁺(H₂O)₂ cation is discussed in terms of the ionization-induced rearrangement of the hydration shell of the neutral Py(H₂O)₂ global minimum characterized by the so-called "σ-π bridge structure" featuring a cyclic NH···OH···OH···π H-bonded network. Emission of the π electron from Py by ionization generates a repulsive interaction between the positive π site of Py⁺ and the π-bonded OH hydrogen of (H₂O)₂, thereby breaking this OH···π hydrogen bond and driving the hydration structure toward the linear chain motif of the global minimum on the cation potential.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg²⁺) has become a severe issue for human beings. Herein, a 3D-MoS₂ sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS₂ sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m^-2 h^-1 under sunlight irradiation and produces freshwater with Hg²⁺ under the WHO drinking water standard at 0.001 mg L^-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Towards complete assignment of the infrared spectrum of the protonated water cluster H+(H2O)21

The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H⁺(H₂O)_n extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H⁺(H₂O)₂₁ cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster.

Protonated water species have been the subject of numerous experimental and computational studies. Here the authors provide a nearly complete assignment of the experimental IR spectrum of the H⁺(H₂O)₂₁ water cluster based on high-level wavefunction theory and anharmonic vibrational quasi-degenerate perturbation theory.

Temperature evolution in IR action spectroscopy experiments with sodium doped water clusters

The combination of supersonic expansions with IR action spectroscopy techniques is the basis of many successful approaches to study cluster structure and dynamics. The effects of temperature and temperature evolution are important with regard to both the cluster synthesis and the cluster dynamics upon IR excitation. In the past the combination of the sodium doping technique with IR excitation enhanced near threshold photoionization has been successfully applied to study neutral, especially water clusters. In this work we follow an overall examination approach for inspecting the interplay of cluster temperature and cluster structure in the initial cooling process and in the IR excitation induced heating of the clusters. In molecular simulations, we study the temperature dependent photoionization spectra of the sodium doped clusters and the evaporative cooling process by water molecule ejection at the cluster surface. We present a comprehensive analysis that provides constraints for the temperature evolution from the nozzle to cluster detection in the mass spectrometer. We attribute the IR action effect to the strong temperature dependence of sodium solvation in the IR excited clusters and we discuss the effects of geometry changes during the IR multi-photon absorption process with regard to application prospects of the method.

Vibrational Signature of Dynamic Coupling of a Strong Hydrogen Bond

Elucidating the dynamic couplings of hydrogen bonds remains an important and challenging goal for spectroscopic studies of bulk systems, because their vibrational signatures are masked by the collective effects of the fluctuation of many hydrogen bonds. Here we utilize size-selected infrared spectroscopy based on a tunable vacuum ultraviolet free electron laser to unmask the vibrational signatures for the dynamic couplings in neutral trimethylamine-water and trimethylamine-methanol complexes, as microscopic models with only one single hydrogen bond holding two molecules. Surprisingly broad progression of OH stretching peaks with distinct intensity modulation over ∼700 cm^-1 is observed for trimethylamine-water, while the dramatic reduction of this progression in the trimethylamine-methanol spectrum offers direct experimental evidence for the dynamic couplings. State-of-the-art quantum mechanical calculations reveal that such dynamic couplings are originated from strong Fermi resonance between the stretches of hydrogen-bonded OH and several motions of the solvent water/methanol, such as translation, rocking, and bending, which are significant in various solvated complexes commonly found in atmospheric and biological systems.

A comprehensive infrared spectroscopic and theoretical study on phenol-ethyldimethylsilane dihydrogen-bonded clusters in the S0 and S1 states

To investigate microscopic characters of Si-H⋯H-O type dihydrogen bonds, we observed OH and SiH stretch bands in both the S₀ and S₁ states of phenol-ethyldimethylsilane (PhOH-EDMS) clusters by infrared (IR)-ultraviolet (UV) and UV-IR double resonance spectroscopies. Density functional theory (DFT) calculations and energy decomposition analysis were also performed. Structures of two isomers identified were unambiguously determined through the analysis of IR spectra and DFT calculations. To discuss the strength of dihydrogen bond in various systems, we performed theoretical calculations on clusters of EDMS with several acidic molecules in addition to PhOH. It was revealed that charge-transfer interaction energies from a bonding σ orbital of SiH bond to an anti-bonding σ^* orbital of OH bond well reflect strengths of dihydrogen bonds. Additionally, it was found that the red shift of SiH stretch frequencies can be used as a crude measure of the strength of dihydrogen bonds. Relationship between the red shifts of OH/SiH stretch frequencies and various electrostatic components of the interaction energy was examined. In the S₁ state, large increases in red shifts were observed for both the OH and SiH stretch frequencies. Since the EDMS moiety is not associated with the electronic excitation in a cluster, the strength of dihydrogen bonds in the S₁ and S₀ states was able to be directly compared based on the red shifts of the SiH stretch bands. A significant increase in the red shift of SiH stretch frequency indicates a strengthening of the dihydrogen bonds during the electronic excitation of the PhOH moiety.

Analytic intermolecular potential energy surface and first-principles prediction of the rotational profiles for a symmetric top ion-atom complex: A case study of H3O+-Ar

We presented the first three-dimensional (3D) ab initio intermolecular potential energy surface (PES) for the H₃O⁺-Ar complex. The electronic structure computations were carried out at the explicitly correlated coupled cluster theory-F12 with an augmented correlation-consistent triple zeta basis set. Analytic 3D PES was obtained by least-squares fitting the multi-dimensional Morse/Long-Range (mdMLR) potential model to interaction energies, where the mdMLR function form was applied to the nonlinear ion-atom case for the first time. The 3D PES fitting to 1708 points has root-mean-square deviations of 0.19 cm^-1 with only 108 parameters for interaction energies less than 500 cm^-1. With the 3D PES of the H₃O⁺-Ar complex, we employed the combined radial discrete variable representation/angular finite basis representation method and Lanczos algorithm to calculate rovibrational energy levels. The rotational profiles of the O-H anti-stretching vibrational bands of v₃ ⁺(S)←0⁺ and v₃ ^-(A)←0^- for the H₃O⁺-Ar complex were predicted and were in good agreement with the experimental results.

An effective Hamiltonian analysis of a Franck-Condon-like pattern in the IR spectra of phenol-alkylsilane dihydrogen-bonded clusters in the S1 state

Infrared (IR) spectra in a region of the OH stretch band of phenol (PhOH)-ethyldimethylsilane (EDMS), phenol (PhOH)-triethylsilane (TES), and phenol (PhOH)-t-butyldimethylsilane (BDMS) dihydrogen-bonded clusters in the S₁ state were observed. All of the species exhibited unconventional band patterns in which many combination bands appeared with comparable intensities to those of allowed bands. Such a behavior is sometimes called a Franck-Condon-like pattern. In the case of the PhOH-BDMS, one intermolecular vibrational mode is involved in this behavior. The observed IR spectra were well reproduced based on the concept of the Franck-Condon-like behavior. As an alternative treatment, we analyzed the band patterns on the concept of intensity borrowing due to the vibrational anharmonic interaction. The analysis was based on an effective Hamiltonian involving an anharmonic interaction between the OH stretch and intermolecular vibrational modes. Two treatments provided the same results. Thus, it was confirmed that the Franck-Condon-like behavior originates from vibrational anharmonic interactions. In the cases of the PhOH-EDMS and PhOH-TES, we carried out a two-dimensional Franck-Condon and an effective Hamiltonian analysis to interpret the Franck-Condon-like patterns. We examined vibrational wave functions obtained by the latter analysis. Shapes of the wave functions suggest that a recombination of the intermolecular vibrational modes occurs during the excitation of OH stretch mode in these clusters, which is a similar behavior to the Duschinsky effect in the electronic transition.

Vibrational spectroscopy of protonated amine–water clusters: tuning Fermi resonance and lighting up dark states

The H-bonded NH stretching fundamentals of protonated amine–water clusters pass through the “Fermi resonance window” formed by bending overtones, generating split bands due to anharmonic couplings.

Size-Dependent Formation of an Ion Pair in HSO4-(H2O) n: A Molecular Model for Probing the Microsolvation of Acid Dissociation

With a p K_a of 2.0, HSO₄^- is not a strong acid as its dissociation percentage is only ∼10% in a solution of 1 M. However, our ab initio molecular dynamics and density functional theory calculations show that acid dissociation in the hydrate clusters, HSO₄^-(H₂O) _n, is quite facile at moderate sizes. It starts at around n = 12 and is completed by n = 16 when the energetics becomes very favorable. The dissociation explains the significant broadening at n = 16 in the S═O stretching region of the previously reported infrared photodissociation spectra for HSO₄^-(H₂O) _n as the solvation shell is tightened around the sulfate dianion and the proton. More importantly, HSO₄^-(H₂O) _n should provide an ideal model to probe the molecular details involved in an acid dissociation process.

Infrared photodissociation spectroscopy of ion-radical networks in cationic dimethylamine complexes

Infrared photodissociation spectroscopy was employed to establish the general trends in the stepwise growth motif of cationic dimethylamine (DMA)n+ (n = 4-13) complexes. Electronic structure calculations were performed to identify the structure of the low-lying isomers and to assign the observed spectral features. The results showed the preference of the formation of the proton-transferred (CH3)2NH2+ ion core. The (CH3)2NH2+-[(CH3)2N] ion-radical pair contact and the ion-radical separated pair could coexist at n = 4. The [(CH3)2N] radical is separated from the (CH3)2NH2+ ion core by one DMA molecule at n = 4-6 and by two or more DMA molecules in the larger clusters. This suggests that the (CH3)2NH2+-[(CH3)2N] ion-radical contact pair is not stable in the subsequent radiation-induced processes of DMA, and the [(CH3)2N] radical is released from the charged site in the cationic DMA networks.

Nature-Inspired, 3D Origami Solar Steam Generator toward Near Full Utilization of Solar Energy

Solar steam generation, due to its capability of producing clean water directly by solar energy, is emerging as a promising eco-friendly and energy-efficient technology to address global challenges of water crisis and energy shortage. Although diverse materials and architectures have been explored to improve solar energy utilization, high efficiency in solar steam generation could be accomplished only with external optical and thermal management. For the first time, we report a deployable, three-dimensional (3D) origami-based solar steam generator capable of near full utilization of solar energy. This auxetic platform is designed based on Miura-ori tessellation and is able to efficiently recover radiative and convective heat loss as well as to trap solar energy via its periodic concavity pattern. The 3D solar steam generator device with a nanocarbon composite of graphene oxide and carbon nanotubes being photothermal component in this work shows a very strong dependence between its solar energy efficiency and surface areal density. The device yields an extraordinary solar energy efficiency close to 100% under 1 sun illumination at a highly folded configuration. The 3D origami device can withstand a great number of folding and unfolding cycles and shows unimpaired solar steam generation performances. The unique structural feature of the 3D origami structure offers a new insight into the future development of highly efficient and easily deployable solar steam generator.

Highly efficient solar vapour generation via hierarchically nanostructured gels

Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m^-2 h^-1 via 94% solar energy from 1 sun irradiation, and 18-23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight.

Infrared photodissociation spectroscopy of cold cationic trimethylamine complexes

Infrared spectroscopic studies reveal the general trends in the stepwise growth motif of trimethylamine (TMA)_n⁺ complexes.

Hydrogen bond network structures of protonated short-chain alcohol clusters

Protonated alcohol clusters enable extraction of the physical essence of the nature of hydrogen bond networks.

Infrared spectroscopy of O˙- and OH- in water clusters: evidence for fast interconversion between O˙- and OH˙OH. Phys Chem Chem Phys 2017;19:25346-25351. [PMID: 28891582 PMCID: PMC7100789 DOI: 10.1039/c7cp04577h]

We present infrared multiple photon dissociation (IRMPD) spectra of (H2O)nO˙- and (H2O)nOH- cluster ensembles for n[combining macron] ≈ 8 and 47 in the range of 2400-4000 cm-1. Both hydrated ions exhibit the same spectral features, in good agreement with theoretical calculations. Decomposition of the calculated spectra shows that bands originating from H2OO˙- and H2OOH- interactions span almost the whole spectral region of interest. Experimentally, evaporation of OH˙ is observed to a small extent, which requires interconversion of (H2O)nO˙- into (H2O)n-1OH˙OH-, with subsequent H2O evaporation preferred over OH˙ evaporation. The modeling shows that (H2O)nO˙- and (H2O)n-1OH˙OH- cannot be distinguished by IRMPD spectroscopy.

Quantitative Temperature Dependence of the Microscopic Hydration Structures Investigated by Ultraviolet Photodissociation Spectroscopy of Hydrated Phenol Cations

To discuss the temperature effect on microscopic hydration structures in clusters, relative populations of the isomers having different hydration structures at well-defined temperatures are quite important. In the present study, we measured ultraviolet photodissociation spectra of the temperature-controlled hydrated phenol cation [PhOH(H₂O)₅]⁺ trapped in the 22-pole ion trap. Two isomers having a distinct hydration motif with each other are identified in the spectra, and a clear change in the relative populations is observed in the temperature range from 30 to 150 K. This behavior is quantitatively interpreted by statistical mechanical estimation based on density functional theory calculations. A ring with tail-type hydration motif is dominant in cold conditions, whereas a chain-like motif is dominant in hot conditions. The present study provides very quantitative information about the temperature effect on the microscopic hydration structures.

Communication: Trapping a proton in argon: Spectroscopy and theory of the proton-bound argon dimer and its solvation

Ion-molecule complexes of the form H⁺Ar_n are produced in pulsed-discharge supersonic expansions containing hydrogen and argon. These ions are analyzed and mass-selected in a reflectron spectrometer and studied with infrared laser photodissociation spectroscopy. Infrared spectra for the n = 3-7 complexes are characterized by a series of strong bands in the 900-2200 cm^-1 region. Computational studies at the MP2/aug-cc-pVTZ level examine the structures, binding energies, and infrared spectra for these systems. The core ion responsible for the infrared bands is the proton-bound argon dimer, Ar-H⁺-Ar, which is progressively solvated by the excess argon. Anharmonic vibrational theory is able to reproduce the vibrational structure, identifying it as arising from the asymmetric proton stretch in combination with multiple quanta of the symmetric argon stretch. Successive addition of argon shifts the proton vibration to lower frequencies, as the charge is delocalized over more ligands. The Ar-H⁺-Ar core ion has a first solvation sphere of five argons.

Deciphering environment effects in peptide bond solvation dynamics by experiment and theory

Probing solvation dynamics at the molecular level: different water migration pathways around a peptide bond.

Probing the microhydration of metal carbonyls: a photoelectron velocity-map imaging spectroscopic and theoretical study of Ni(CO)3(H2O)n. Phys Chem Chem Phys 2016;18:26719-26724. [PMID: 27711570 DOI: 10.1039/c6cp05035b]

A series of microhydrated nickel carbonyls, Ni(CO)₃(H₂O)_n^- (n = 0-4), are prepared via a laser vaporization supersonic cluster source in the gas phase and identified by mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations. Vertical detachment energies for the n = 1-4 anions are measured from the photoelectron spectra to be 1.429 ± 0.103, 1.698 ± 0.090, 1.887 ± 0.080, and 2.023 ± 0.074 eV, respectively. The C-O stretching vibrational frequencies in the corresponding neutral clusters are determined to be 1968, 1950, 1945, and 1940 cm^-1 for n = 1-4, respectively, which are characteristic of terminal CO. It is determined that the hydrogen atom of the first water molecule is bound to the nickel center. Addition of a second water molecule prefers solvation at the carbonyl terminal. Spectroscopy combined with theory suggests that the solvation of nickel tricarbonyl is dominated by a water-ring network. The present findings would have important implications for the fundamental understanding of the multifaceted mechanisms of the multibody interaction of water and carbon monoxide with transition metals.

Tuning the vibrational coupling of H3O+ by changing its solvation environment

This study demonstrates how the intermode coupling in the hydronium ion (H₃O⁺) is modulated by the composition of the first solvation shell.

Disentangling the Contribution of Multiple Isomers to the Infrared Spectrum of the Protonated Water Heptamer

We use infrared/infrared double-resonance population labeling (IR(2)MS(2)) spectroscopy in the spectral region of the free and hydrogen-bonded OH stretching fundamentals (2880-3850 cm(-1)) to identify the number and to isolate the vibrational signatures of individual isomers contributing to the gas-phase IR spectra of the cryogenically cooled protonated water clusters H(+)(H2O)n·H2/D2 with n = 7-10. For n = 7, four isomers are identified and assigned. Surprisingly, the IR(2)MS(2) spectra of the protonated water octa-, nona-, and decamer show no evidence for multiple isomers. The present spectra support the prediction that the quasi-2D to 3D structural transition occurs in between n = 8 and 9 in the cold cluster regime. However, the same models have difficulty explaining the remarkable size dependence of the isomer population reported here.

Hydrogen-bonded ring closing and opening of protonated methanol clusters H+(CH3OH)n (n = 4–8) with the inert gas tagging

Temperature dependence of hydrogen bond network structures of protonated methanol clusters is explored by IR spectroscopy and DFT simulations.