Ion chromatographic analysis of hydronium ion using ODS modified with dodecylsulfate as the stationary phase

The hydronium ion (H3O+), the most essential species to every field of chemistry, was successfully separated from other cations. This major goal was achieved by a HPLC approach in which a reversed-phase ODS which had been initially modified with dodecylsulfate was used as the stationary phase and an aqueous KNO3 solution was used as the mobile phase. Of all tested monovalent cations (analyte ions), the hydronium ion (H3O+) showed the highest affinity towards the stationary phase, followed by NH4+, Na+, and then Li+. The hydronium ion, after the separation, was directly detected using conductivity and the detection signal (conductivity) was in linear proportion (linear range 7.8 x 10(-4)-0.45 M; injection volume, 100 microL) to the concentration of the acid species of the tested sample. This proposed HPLC method was applicable to separate/detect H3O+ from both strong and weak acidic samples.     

水合氢离子团簇从头算和ABEEM/MM的理论研究

应用高水平的从头计算方法和ABEEM/MM模型, 研究了水合氢离子团簇H3O＋(H2O)n (n＝1～6), 优化得到了低能构象, 探讨了其结合能和稳定性, 显示出H3O＋(H2O)3局域结构的优势存在．对H3O＋(H2O)6VIa团簇的ABEEM电荷分布进行分析, 表明第一水合层水分子与水合氢离子之间的氢键相互作用要明显强于与第二水层水分子的氢键相互作用. 研究结果表明, ABEEM/MM方法计算的结果和从头算得到的结果存在很好的一致性.     

Photodissociation of hydrogen halide molecules on free ice nanoparticles

Photodissociation of water clusters doped with HX(X=Br,Cl), molecules has been studied in a molecular beam experiment. The HX(H2O)n clusters are dissociated with 193 nm laser pulses, and the H fragments are ionized at 243.07 nm and their time-of-flight distributions are measured. Experiments with deuterated species DBr(H2O)n and HBr(D2O)n suggest that the photodissociation signal originates from the presence of the HX molecule on the water cluster, but does not come directly from a photolysis of the HX molecule. The H fragment is proposed to originate from the hydronium molecule H3O. Possible mechanisms of the H3O production are discussed. Experimental evidence suggests that acidic dissociation takes place in the cluster, but the H3O+ ion remains rather immobile.     

Novel CFCs-substitutes recommended by EPA (hydrofluorocarbon-245fa and hydrofluoroether-7100): Ion chemistry in air plasma and reactions with atmospheric ions

The ion chemistry of the title compounds, a nonafluorobutyl methyl ether and a hydrofluoropropane, is elucidated by a combination of studies using atmospheric pressure ionization mass spectrometry and triple quadrupole mass spectrometry. In the positive ion mode, the hydrofluoroether readily forms an [M - F]+ ion, attributable to hydronium ion induced dehydrofluorination, the product of which can be further hydrated to give a protonated hydrofluoroester. By contrast, the hydrofluoropropane does not react with the hydronium ion but rather gives hydrofluoroalkenylium cations via H atom and F atom abstraction by the dioxygen radical cation. In the negative ion mode, the fluorobutyl methyl ether undergoes dissociative electron capture with O2-*, O2-*(H2O), O3-*, and NO2- to generate the fluorobutoxy anion, which can dissociate by CF2[doublebond]O loss to give the perfluorocarbanion when the precursor ions are internally excited. The hydrofluoropropane reacts readily with common atmospheric anions to form molecular complexes with F-, O2-*, and O3-* and the strongly H-bonded species, O2-*(HF) and F-(HF). Interestingly, isomeric pentafluoropropanes form in the reaction with O2-*, either O2-*(HF) or F-(HF), depending on the specific pattern of the fluoro substitution.     

Special pair dance and partner selection: elementary steps in proton transport in liquid water

Conditional and time-dependent radial distribution functions reveal the details of the water structure surrounding the hydronium during the proton mobility process. Using this methodology for classical multistate empirical valence bond (MS-EVB) and ab initio molecular dynamics trajectories, as well as quantal MS-EVB trajectories, we supply statistical proof that proton hops in liquid water occur by a transition from the H3O+[3H2O] Eigen-complex, via the H5O2+ Zundel-complex, to a H3O+[3H2O] centered on a neighboring water molecule. In the "resting period" before a transition, there is a distorted hydronium with one of its water ligands at a shorter distance and another at a longer distance than average. The identity of this "special partner" interchanges rapidly within the three first-shell water ligands. This is coupled to cleavage of an acceptor-type hydrogen bond. Just before the transition, a partner is selected by an additional translation of the H3O+ moiety in its direction, possibly enabled by loosening of donor-type hydrogen bonds on the opposite side. We monitor the transition in real time, showing how the average structure is converted to a distorted H5O2+ cation constituting the transitional complex for proton hopping between water molecules.     

Behavior of the Eigen form of hydronium at the air/water interface

Surface affinity of hydro-nium was explored using umbrella sampling molecular dynamics simulations with a refined polarizable potential. The polarizable interaction potential of H(3)O(+) was reparametrized against accurate ab initio calculations for geometries including a water molecule approaching the Eigen cation from its oxygen side. Although there is no true hydrogen bonding with H(3)O(+) acting as an acceptor, respecting in the force field the very shallow ab initio minimum corresponding to this interaction leads to a decrease in surface propensity of hydronium compared to previous results. Qualitatively, the mild surface affinity and strong surface orientation of hydronium is, nevertheless, robustly predicted by various computational approaches, as well as by spectroscopic experiments.     

Computational studies of aqueous-phase photochemistry and the hydrated electron in finite-size clusters

A survey of recent ab initio calculations on excited electronic states of water clusters and various chromophore-water clusters is given. Electron and proton transfer processes in these systems have been characterized by the determination of electronic wave functions, minimum-energy reaction paths and potential-energy profiles. It is pointed out that the transfer of a neutral hydrogen atom (leading to biradicals) rather than the transfer of a proton (leading to ion pairs) is the generic excited-state reaction mechanism in these systems. The hydrated hydronium radical, (H3O)(aq), plays a central role in this scenario. The electronic and vibrational spectra of H3O(H2O)(n) clusters and the decay mechanism of these metastable species have been investigated in some detail. The results suggest that (H3O)(aq) could be the carrier of the characteristic spectroscopic properties of the hydrated electron in liquid water.     

Photochemistry of hydrogen halides on water clusters: simulations of electronic spectra and photodynamics, and comparison with photodissociation experiments

The photochemistry of small HX·(H(2)O)(n), n = 4 and 5 and X = F, Cl, and Br, clusters has been modeled by means of ab initio-based molecular simulations. The theoretical results were utilized to support our interpretation of photodissociation experiments with hydrogen halides on ice nanoparticles HX·(H(2)O)(n), n ≈ 10(2)-10(3). We have investigated the HX·(H(2)O)(n) photochemistry for three structural types: covalently bound structures (CBS) and acidically dissociated structures in a form of contact ion pair (CIP) and solvent separated pair (SSP). For all structures, we have modeled the electronic absorption spectra using the reflection principle combined with a path integral molecular dynamics (PIMD) estimate of the ground state density. In addition, we have investigated the solvent effect of water on the absorption spectra within the nonequilibrium polarizable continuum model (PCM) scheme. The major conclusion from these calculations is that the spectra for ionic structures CIP and SSP are significantly red-shifted with respect to the spectra of CBS structures. We have also studied the photodynamics of HX·(H(2)O)(n) clusters using the Full Multiple Spawning method. In the CBS structures, the excitation led to almost immediate release of the hydrogen atom with high kinetic energy. The light absorption in ionically dissociated species generates the hydronium radical (H(3)O) and halogen radical (X) within a charge-transfer-to-solvent (CTTS) excitation process. The hydronium radical ultimately decays into a water molecule and hydrogen atom with a characteristic kinetic energy irrespective of the hydrogen halide. We have also investigated the dynamics of an isolated and water-solvated H(3)O radical that we view as a central species in water radiation chemistry. The theoretical findings support the following picture of the HX photochemistry on ice nanoparticles investigated in our molecular beam experiments: HX is acidically dissociated in the ground state on ice nanoparticles, generating the CIP structure, which is then excited by the UV laser light into the CTTS states, followed by the H(3)O radical formation.     

New types of hybrid solids of tetravanadate polyanions and cucurbituril

Three inorganic-organic hybrid solids based on tetravanadate polyanions, {V(4)O(12)}(4-) and cucurbituril, Me(10)Q[5] and Q[5], namely (NH(4))(4)[(V(4)O(12))·(Me(10)Q[5]@0.5H(2)O)(2)]·～13H(2)O (1), Li(4)(H(2)O)(5)[(V(4)O(12))·(Me(10)Q[5]@H(2)O)(2)]·～20H(2)O (2), and Na(4)(H(2)O)(2)[(V(4)O(12))·(Q[5])(2)]·～15H(2)O (3), have been synthesized under hydrothermal conditions. In the structure of compound 1, two {Me(10)Q[5]@0.5H(2)O} moieties connect to one {V(4)O(12)}(4-) cluster through an NH(4)(+) counter-cation to form a trimer unit, which further forms a three-dimensional (3D) supramolecular architecture via extensive hydrogen bonds (H-bonds). Compound 2 contains a one-dimensional (1D) covalently bonded chain structure built by alternate {Me(10)Q[5]@H(2)O} moieties and {Li(2)O(4)(H(2)O)(3)}(2+) dimer units. The anionic {V(4)O(12)}(4-) units bond to every another {Li(2)O(4)(H(2)O)(3)}(2+) dimer unit sitting on the chain through multi-uncoordinated water molecules via H-bonds. Compound 3 is built from {V(4)O(12)}(4-) clusters, Q[5], and sodium cations into a two-dimensional (2D) covalent wavy structure, showing interesting connection between the building units, which is packed into 2D through plentiful H-bonds. It has been found that the cations dramatically affect the coordination of the tetravanadate polyanion and cucurbituril.     

The nature of the H3O+ hydronium ion in benzene and chlorinated hydrocarbon solvents. Conditions of existence and reinterpretation of infrared data

Salts of the C(3v) symmetric hydronium ion, H(3)O(+), have been obtained in the weakly basic solvents benzene, dichloromethane, and 1,2-dichloroethane. This is made possible by using carborane counterions of the type CHB(11)R(5)X(6)(-) (R = H, Me, Cl; X = Cl, Br, I) because they combine the three required properties of a suitable counterion: very low basicity, low polarizability, and high chemical stability. The existence of the H(3)O(+) ion requires the formation of three more-or-less equivalent, medium-to-strong H-bonds with solvent or anion bases. With the least basic anions such as CHB(11)Cl(11)(-), IR spectroscopy indicates that C(3v) symmetric trisolvates of formulation [H(3)O(+) .3Solv] are formed with chlorocarbon solvents and benzene, the latter with the formation of pi bonds. When the solvents and anions have comparable basicity, contact ion pairs of the type [H(3)O(+).nSolv.Carborane] are formed and close to C(3v) symmetry is retained. The conditions for the existence of the H(3)O(+) ion are much more exacting than previously appreciated. Outside of the range of solvent basicity bounded at the lower end by dichloromethane and the upper end by tributyl phosphate, and with anions that do not meet the stringent requirements of weak basicity, low polarizability of high chemical stability, lower symmetry species are formed. One H-bond from H(3)O(+) to the surrounding bases becomes stronger than the other two. The distortion from C(3v) symmetry is minor for bases weaker than dichloromethane. For bases stronger than tributyl phosphate, H(2)O-H(+)-B type species are formed that are more closely related to the H(5)O(2)(+) ion than to H(3)O(+). IR data allow criteria to be defined for the existence of the symmetric H(3)O(+) ion. This includes a linear dependence between the frequencies of nu(max)(OH) and delta(OH(3)) within the ranges 3010-2536 cm(-1) for nu(max)(OH) and 1597-1710 cm(-1) for delta(OH(3)). This provides a simple way to assess the correctness of the formulation of the proton state in monohydrated acids. In particular, the 30-year-old citation classic of the IR spectrum believed to arise from H(3)O(+) SbCl(6)(-) is re-interpreted in terms of (H(2)O)(x)().HSbCl(6) hydrates. The correctness of the hydronium ion formulation in crystalline H(3)O(+)A(-) salts (A(-) = Cl(-), NO(3)(-)) is confirmed, although, when A(-) is a fluoroanion, distortions from C(3)(v)() symmetry are suggested.     

A large protonated water cluster H+(H2O)27 in a 3D metal-organic framework

A large protonated water cluster, H+(H2O)27, has been trapped and stabilized within the well-modulated cavity of a 3D metal-organic framework formed by cobalt(II) and 4,4'-bipyridine-N,N'-dioxide with a globular Keggin structure [PW12O4]3- anion as template. The structurally characterized protonated water cluster might comprise a (H2O)26 shell with Oh symmetry and a monowater core within the center which is suggested to be a hydronium ion with the Eigen model.     

Photochemistry of HI on argon and water nanoparticles: hydronium radical generation in HI·(H2O)n

Photochemistry of HI molecules on large Ar(n) and (H(2)O)(n), n ～ 100-500, clusters was investigated after excitation with 243 nm and 193 nm laser radiation. The measured H-fragment kinetic energy distributions pointed to a completely different photodissociation mechanism of HI on water than on argon clusters. Distinct features corresponding to the fragment caging (slow fragments) and direct exit (fast fragments) were observed in the spectra from HI photodissociation on Ar(n) clusters. On the other hand, the fast fragments were entirely missing in the spectrum from HI·(H(2)O)(n) and the slow-fragment part of the spectrum had a different shape from HI·Ar(n). The HI·(H(2)O)(n) spectrum was interpreted in terms of the acidic dissociation of HI on (H(2)O)(n) in the ground state, and hydronium radical H(3)O formation following the UV excitation of the ionically dissociated species into states of a charge-transfer-to-solvent character. The H(3)O generation was proved by experiments with deuterated species DI and D(2)O. The experiment was complemented by ab initio calculations of structures and absorption spectra for small HI·(H(2)O)(n) clusters, n = 0-5, supporting the proposed model.     

Cucurbit[n]uril binding of platinum anticancer complexes

The encapsulation of cisplatin by cucurbit[7]uril (Q[7]) and multinuclear platinum complexes linked via a 4,4'-dipyrazolylmethane (dpzm) ligand by Q[7] and cucurbit[8]uril (Q[8]) has been studied by NMR spectroscopy and molecular modelling. The NMR studies suggest that some cisplatin binds in the cucurbituril cavity, while cis-[PtCl(NH3)2(H2O)]+ only binds at the portals. Alternatively, the dpzm-linked multinuclear platinum complexes are quantitatively encapsulated within the cavities of both Q[7] and Q[8]. Upon encapsulation, the non-exchangeable proton resonances of the multinuclear platinum complexes show significant upfield shifts in 1H NMR spectra. The H3/H3* resonances shift upfield by 0.08 to 0.55 ppm, the H5/H5* shift by 0.9 to 1.6 ppm, while the methylene resonances shift by 0.74 to 0.88 ppm. The size of the resonance shift is dependent on the cavity size of the encapsulating cucurbituril, with Q[7] encapsulation producing larger shifts than Q[8]. The upfield shifts of the dpzm resonances observed upon cucurbituril encapsulation indicate that the Q[7] or Q[8] is positioned directly over the dpzm linking ligand. The terminal platinum groups of trans-[{PtCl(NH3)2}2 mu-dpzm]2+ (di-Pt) and trans-[trans-{PtCl(NH3)2}2-trans-{Pt(dpzm)2(NH3)2}]4+ (tri-Pt) provide a barrier to the on and off movement of cucurbituril, resulting in binding kinetics that are slow on the NMR timescale for the metal complex. Although the dpzm ligand has relatively few rotamers, encapsulation by the larger Q[8] resulted in a more compact di-Pt conformation with each platinum centre retracted further into each Q[8] portal. Encapsulation of the hydrolysed forms of di-Pt and tri-Pt is considerably slower than for the corresponding Cl forms, presumably due to the high-energy cost of passing the +2 platinum centres through the cucurbituril portals. The results of this study suggest that cucurbiturils could be suitable hosts for the pharmacological delivery of multinuclear platinum complexes.     

Photochromic hybrid materials of cucurbituril and polyoxometalates as photocatalysts under visible light

Two isostructural organic-inorganic hybrid solid materials based on cucurbituril derivatives and polyoxometalates, {[K(2)(H(2)O)(2)Na(2)(H(2)O)(2)Na(2)(H(2)O)(6)](P(2)W(18)O(62))(Me(10)Q(5))(2)}·~7H(2)O (1) and {[Rb(2)(H(2)O)(2)Na(2)(H(2)O)Na(2)(H(2)O)(4)](P(2)W(18)O(62))(Me(10)Q(5))(2)}·~8H(2)O (2), which exhibit reversible photochromic properties as well as excellent photocatalytic activities toward the degradation of methyl orange (MO) and rhodamine-B (RB) under visible light irradiation, are reported.     

A new glance at HCl-monohydrate spectroscopy, using on-the-fly dynamics

On-the-fly dynamics is used to analyze the remarkably anharmonic infrared spectroscopy of crystalline HCl monohydrate, an ionic solid composed of H3O+ and Cl-. The dominant intense infrared feature is shown to originate from specific sections of the hydronium trajectory, in which one of the H-atoms interacts strongly with a neighboring Cl-.     

The oxidation of tyrosine and tryptophan studied by a molecular dynamics normal hydrogen electrode

The thermochemical constants for the oxidation of tyrosine and tryptophan through proton coupled electron transfer in aqueous solution have been computed applying a recently developed density functional theory (DFT) based molecular dynamics method for reversible elimination of protons and electrons. This method enables us to estimate the solvation free energy of a proton (H(+)) in a periodic model system from the free energy for the deprotonation of an aqueous hydronium ion (H(3)O(+)). Using the computed solvation free energy of H(+) as reference, the deprotonation and oxidation free energies of an aqueous species can be converted to pK(a) and normal hydrogen electrode (NHE) potentials. This conversion requires certain thermochemical corrections which were first presented in a similar study of the oxidation of hydrobenzoquinone [J. Cheng, M. Sulpizi, and M. Sprik, J. Chem. Phys. 131, 154504 (2009)]. Taking a different view of the thermodynamic status of the hydronium ion, these thermochemical corrections are revised in the present work. The key difference with the previous scheme is that the hydronium is now treated as an intermediate in the transfer of the proton from solution to the gas-phase. The accuracy of the method is assessed by a detailed comparison of the computed pK(a), NHE potentials and dehydrogenation free energies to experiment. As a further application of the technique, we have analyzed the role of the solvent in the oxidation of tyrosine by the tryptophan radical. The free energy change computed for this hydrogen atom transfer reaction is very similar to the gas-phase value, in agreement with experiment. The molecular dynamics results however, show that the minimal solvent effect on the reaction free energy is accompanied by a significant reorganization of the solvent.     

Ab initio QM/MM dynamics of H3O+ in water

A molecular dynamics (MD) simulation based on a combined ab initio quantum mechanics/molecular mechanics (QM/MM) method has been performed to investigate the solvation structure and dynamics of H3O+ in water. The QM region is a sphere around the central H3O+ ion, and contains about 6-8 water molecules. It is treated at the Hartree-Fock (HF) level, while the rest of the system is described by means of classical pair potentials. The Eigen complex (H9O4+) is found to be the most prevalent species in the aqueous solution, partly due to the selection scheme of the center of the QM region. The QM/MM results show that the Eigen complex frequently converts back and forth into the Zundel (H5O2+) structure. Besides the three nearest-neighbor water molecules directly hydrogen-bonded to H3O+, other neighbor waters, such as a fourth water molecule which interacts preferentially with the oxygen atom of the hydronium ion, are found occasionally near the ion. Analyses of the water exchange processes and the mean residence times of water molecules in the ion's hydration shell indicate that such next-nearest neighbor water molecules participate in the rearrangement of the hydrogen bond network during fluctuative formation of the Zundel ion and, thus, contribute to the Grotthuss transport of the proton.     

Synthesis of mono-, oligo- and polyamide-cucurbituril rotaxanes

Mono-, oligo- and polyamide rotaxanes with the macrocycle cucurbituril are synthesized easily with high yields by interfacial condensation. The complex of cucurbituril with 1,6-hexanediammonium ion is used as preorganized structure. With different acid and diacid chlorides a great variety of amiderotaxanes and polyrotaxanes can be synthesized. The characterization is difficult due to the low solubility of cucurbituril and rotaxanes. But with the methods of IR, DTA, ¹H NMR and elemental analyses, the existence of the rotaxanes is shown.     

Computational study on the interactions of mustard gas with cucurbituril macrocycles

The study on the absorption of toxic gases such as mustard gas by organic host is essential to the development of inexpensive detection and decontamination equipments. Using quantum chemical methods, we propose cucurbituril as an effective host to capture mustard gas. It was found that stable complexes are formed with the inclusion of the toxic gas molecules inside the cucurbituril cavity, compared with the lateral and exterior interactions. Oxygen mustard has a comparable binding energy with sulfur mustard and hence can be used during experimental investigation. Additionally, during the inclusion complex formation, the presence of heteroatoms helps the guest molecules to undergo a larger structural reorganization to get accommodated inside the cucurbituril macromolecule. Atoms‐in‐molecules analysis shows the existence of strong intermolecular CH…O bonding between the guest molecules and cucurbituril macromolecule. The presence of an intramolecular CH…Cl type of bonding accounts for the higher stabilization of sulfur mustard inside the cucurbituril macromolecule. © 2015 Wiley Periodicals, Inc.     

Why are water-hydrophobic interfaces charged?

We report ab initio molecular dynamics simulations of hydroxide and hydronium ions near a hydrophobic interface, indicating that both ions behave like amphiphilic surfactants that stick to a hydrophobic hydrocarbon surface with their hydrophobic side. We show that this behavior originates from the asymmetry of the molecular charge distribution which makes one end of the ions strongly hydrophobic while the other end is even more hydrophilic than the regular water (H2O) molecules. The effect is more pronounced for the hydroxide than for the hydronium. Our results are consistent with several experimental observations and explain why hydrophobic surfaces in contact with water acquire a net negative charge, a phenomenon that has important implications for biology and polymer science.