Prediction of a phase transition to a hydrogen bond ordered form of ice VI

Ice VI is a hydrogen bond disordered crystal over its known region of stability. In this work, we predict that ice VI will transform into a hydrogen bond ordered phase near 108 K, and have identified the likely low-temperature phase as ferroelectric (space group Cc) with an antiferroelectric structure (space group P2(1)2(1)2(1)) close by in energy. Electronic density functional theory calculations provide input to our calculations, which are extended to cells large enough for statistical simulations by using graph invariants. A significant decrease in the configurational entropy is predicted as hydrogen bonds exhibit partial order above the transition, provided that the hydrogen bonds can equilibrate on an experimental time scale. Conversely, partial disorder is predicted at temperatures below the transition. Although some evidence for ordering of ice VI has been observed in experiments, a low-temperature proton ordered phase has not been identified experimentally.     

A high pressure spectroscopic study on the ice III — ice IX. Disordered — ordered transition

The only published data on the disordered-to-ordered ice III to ice IX transition refers to measurements of di-electric constant. Raman spectra of ice III and ice IX were recorded under a pressure of 0.3 GPa for temperatures in the range 250 to 130 K. They clearly show a transition that is predominantly of the disordered-ordered type. Raman spectra in the frequency range 15–4000 cm^?1 will be shown but special attention will be given to two translational lattice modes at about 190 cm^?1 and 65.5 cm^?1 which show somewhat unusual behaviour. Small discontinuities in the frequency versus temperature plots suggest that there is a small discontinuous decrease in the volume during the ice III to ice IX transition.     

A calorimetric study on the low temperature dynamics of doped ice V and its reversible phase transition to hydrogen ordered ice XIII

Doped ice V samples made from solutions containing 0.01 M HCl (DCl), HF (DF), or KOH (KOD) in H(2)O (D(2)O) were slow-cooled from 250 to 77 K at 0.5 GPa. The effect of the dopant on the hydrogen disorder --> order transition and formation of hydrogen ordered ice XIII was studied by differential scanning calorimetry (DSC) with samples recovered at 77 K. DSC scans of acid-doped samples are consistent with a reversible ice XIII <--> ice V phase transition at ambient pressure, showing an endothermic peak on heating due to the hydrogen ordered ice XIII --> disordered ice V phase transition, and an exothermic peak on subsequent cooling due to the ice V --> ice XIII phase transition. The equilibrium temperature (T(o)) for the ice V <--> ice XIII phase transition is 112 K for both HCl doped H(2)O and DCl doped D(2)O. From the maximal enthalpy change of 250 J mol(-1) on the ice XIII --> ice V phase transition and T(o) of 112 K, the change in configurational entropy for the ice XIII --> ice V transition is calculated as 2.23 J mol(-1) K(-1) which is 66% of the Pauling entropy. For HCl, the most effective dopant, the influence of HCl concentration on the formation of ice XIII was determined: on decreasing the concentration of HCl from 0.01 to 0.001 M, its effectiveness is only slightly lowered. However, further HCl decrease to 0.0001 M drastically lowered its effectiveness. HF (DF) doping is less effective in inducing formation of ice XIII than HCl (DCl) doping. On heating at a rate of 5 K min(-1), kinetic unfreezing starts in pure ice V at approximately 132 K, whereas in acid doped ice XIII it starts at about 105 K due to acceleration of reorientation of water molecules. KOH doping does not lead to formation of hydrogen ordered ice XIII, a result which is consistent with our powder neutron diffraction study (C. G. Salzmann, P. G. Radaelli, A. Hallbrucker, E. Mayer, J. L. Finney, Science, 2006, 311, 1758). We further conjecture whether or not ice XIII has a stable region in the water/ice phase diagram, and on a metastable triple point where ice XIII, ice V and ice II are in equilibrium.     

Raman spectroscopic study of hydrogen ordered ice XIII and of its reversible phase transition to disordered ice V

Raman spectra of recovered ordered H(2)O (D(2)O) ice XIII doped with 0.01 M HCl (DCl) recorded in vacuo at 80 K are reported in the range 3600-200 cm(-1). The bands are assigned to the various types of modes on the basis of isotope ratios. On thermal cycling between 80 and 120 K, the reversible phase transition to disordered ice V is observed. The remarkable effect of HCl (DCl) on orientational ordering in ice V and its phase transition to ordered ice XIII, first reported in a powder neutron diffraction study of DCl doped D(2)O ice V (C. G. Salzmann, P. G. Radaelli, A. Hallbrucker, E. Mayer, J. L. Finney, Science, 2006, 311, 1758), is demonstrated by Raman spectroscopy and discussed. The dopants KOH and HF have only a minor effect on hydrogen ordering in ice V, as shown by the Raman spectra.     

Thermosonimetry of the phase II/III transition of hexachloroethane

A thermosonimetric study has shown that the Phase II/III polymorphic transition of hexachloroethane emits acoustic signals. This solid-solid phase transition is known to occur by a nucleation-growth process during which a nucleus of the new phase, once formed, grows at the expense of the mother phase to form a complete crystal without fracture. Acoustic emissions from a conditioned multi-crystal sample have been used to study the transition. Acoustic activity correlated well with dilatometric measurements. Frequency analysis on waveforms of many hundreds of individual acoustic emissions revealed marked differences between individual signals. Principal-components analysis on 24 signal features revealed a single dispersed cluster with a highly non-uniform distribution of signals. These experiments provided highly reproducible average power spectra. Time-resolved acoustic power spectra were also generated. These additional types of information cannot be obtained by other techniques.     

A molecular "phase ordering" phase transition leading to a modulated aperiodic composite in n-heptane/urea

n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (T(c1) = 145 K) is a ferroelastic phase transition that generates superstructure reflections for the host while leaving the guest with 1D order. The second (T(c2) = 130 K) is a "phase ordering" transition to a four-dimensional structure (P2(1)11(0βγ)) with pronounced host-guest intermodulation and a temperature dependent phase shift between guests in adjacent channels.     

Phase transition in hydrazinium hydrogen oxalate. A calorimetric study of the short hydrogen bond system

The heat capacity of hydrazinium hydrogen oxalate crystal has been measured between 14 and 300 K. A first-order phase transition was found at 217.6 K. Total transition enthalpy and entropy are 1.09 kJ mol⁻¹ and 4.18 J K⁻¹ mol⁻¹, respectively. The high temperature phase supercooled to 165−170 K. The heat capacity of the supercooled high temperature phase was significantly larger than that of the low temperature phase. By fitting a Schottky heat capacity function to the heat capacity difference, a Schottky energy level was found at (135 ± 4) cm⁻¹ above the ground state and related to the tunneling splitting of the energy levels of the short acidic hydrogen bond. A thermodynamic model of the first-order transition is proposed in which the Schottky anomaly plays the main role. Far-infrared spectra of hydrazinium hydrogen oxalate are reported for the frequency range 400–30 cm⁻¹ at temperatures of 295 and 90 K.     

D and Cs NMR study of the hydrogen bond network and antiferroelectric phase transition of cesium trihydrogen selenite

The ²D and ¹³³Cs NMR spectra of deuterated and protiated single crystals of antiferroelectric cesium trihydrogen selenite have been studied in the high- and low-temperature phases. The number of chemically nonequivalent hydrogen bonds, their lengths, and directions in the unit cell were determined from deuteron electric field gradient tensors. The deuterons of centered hydrogen bonds have been found disordered in the paraelectric phase over two equivalent sites on either side of a center of symmetry. The antiferroelectric phase transition is accompanied by order-disorder phenomena of the H system and displacive behavior of the heavy-ion system.     

Intermolecular proton transport along the hydrogen bond and the dielectric properties of ice crystals

Conclusion We have attempted here to explain some of the dielectric properties of ice crystals by a concept involving the activated transport of a proton along the hydrogen bond. The choice of the almost symmetrical curve with two minima for a proton in the hydrogen bridge and the rejection of tunnel transport of a proton makes it possible to suggest a theory which explains adequately the dependence of the low frequency dielectric constant on temperature and the phenomenon of the dielectric relaxation of ice. The electrical polarization of an ice crystal according to our model is produced by the defect structure of the ice, the ion pairs, which arises when the proton moves between two neutral water molecules.This particular model does not involve orientation or Bjerrum defects in the ice structure and raises a doubt as to the necessity of introducing them into explanations of the dielectric properties of ice.Moscow Physicotechnical Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 11, No. 3, pp. 415–420, May–June, 1970.     

2D and 133Cs NMR study of the hydrogen bond network and antiferroelectric phase transition of cesium trihydrogen selenite

The ²D and ¹³³Cs NMR spectra of deuterated and protiated single crystals of antiferroelectric cesium trihydrogen selenite have been studied in the high- and low-temperature phases. The number of chemically nonequivalent hydrogen bonds, their lengths, and directions in the unit cell were determined from deuteron electric field gradient tensors. The deuterons of centered hydrogen bonds have been found disordered in the paraelectric phase over two equivalent sites on either side of a center of symmetry. The antiferroelectric phase transition is accompanied by order-disorder phenomena of the H system and displacive behavior of the heavy-ion system.     

The role of orbital ordering in the tetragonal-to-cubic phase transition in CuCr2O4

Copper(II) chromite (CuCr₂O₄) undergoes a first-order structural transition from a tetragonal distorted spinel structure in space group (I4₁/amd) to a cubic spinel structure in Fd3¯m, near 600 °C. The transition has been followed using synchrotron X-ray powder diffraction between room temperature and 750 °C. The structure changes as a consequence of a transition from an orbitally ordered to orbital disordered state associated with a Jahn-Teller-type distortion of the CuO₄ tetrahedron. The orbital melting results in a small increase in cell volume.     

Relaxation study of strong hydrogen bond lifetime in gas phase

Laser temperature jump and shock tube techniques have been used to measure the monomer-dimer relaxation time in the gas phase. With the former method, the lifetime of the cyclic dimer of acetic acid is found to increase from 3 μs at 315 K to 16 μs at 285 K. The activation energy has been determined to be 11.4 ± 0.8 kcal mol^?1. A step-wise mechanism of dissociation is discussed.     

Assessment of density functional theory to calculate the phase transition pressure of ice

To assess the accuracy of density functional theory (DFT) methods in describing hydrogen bonding in condensed phases, we benchmarked their performance in describing phase transitions among different phases of ice. We performed DFT calculations of ice for phases Ih, II, III, VI and VII using BLYP, PW91, PBE, PBE-D, PBEsol, B3LYP, PBE0, and PBE0-D, and compared the calculated phase transition pressures between Ih-II, Ih-III, II-VI, and VI-VII with the 0 K experimental values of Whalley [J. Chem. Phys., 1984, 81, 4087]. From the geometry optimization of many different candidates, we found that the most stable proton orientation as well as the phase transition pressure does not show much functional dependence for the generalized gradient approximation and hybrid functionals. Although all these methods overestimated the phase transition pressure, the addition of van der Waals (vdW) correction using PBE-D and PBE0-D reduced the transition pressure and improved the agreement for Ih-II. On the other hand, energy ordering between VI and VII reversed and gave an unphysical negative transition pressure. Binding energy profiles of a few conformations of water dimers were calculated to understand the improvement for certain transitions and failures for others with the vdW correction. We conclude that vdW dispersion forces must be considered to accurately describe the hydrogen bond in many different phases of ice, but the simple addition of the R(-6) term with a small basis set tends to over stabilize certain geometries giving unphysical ordering in the high density phases.     

Fluorescence detection of guanine-adenine transition by a hydrogen bond forming small compound

In combination with abasic site-containing oligodeoxynucleotides, 2-amino-4-oxopteridine (pterin) can selectively recognize guanine base over other nucleobases accompanied by fluorescence quenching, which allows clear detection of a guanine-adenine transition with the naked eye.     

The hydrogen bond in ice probed by soft x-ray spectroscopy and density functional theory

We combine photoelectron and x-ray absorption spectroscopy with density functional theory to derive a molecular orbital picture of the hydrogen bond in ice. We find that the hydrogen bond involves donation and back-donation of charge between the oxygen lone pair and the O-H antibonding orbitals on neighboring molecules. Together with internal s-p rehybridization this minimizes the repulsive charge overlap of the connecting oxygen and hydrogen atoms, which is essential for a strong attractive electrostatic interaction. Our joint experimental and theoretical results demonstrate that an electrostatic model based on only charge induction from the surrounding medium fails to properly describe the internal charge redistributions upon hydrogen bonding.     

On the gas phase hydrogen bond complexes between formic acid and hydroperoxyl radical. A theoretical study

We present a systematic study on the gas-phase hydrogen-bonded complexes formed between formic acid and hydroperoxyl radical, which has been carried out by using B3LYP and CCSD(T) theoretical approaches in connection with the 6-311+G(2df,2p) basis set. For all complexes we have employed the AIM theory by Bader and the NBO partition scheme by Weinhold to analyze the bonding features. We have found 17 stationary points, and 11 of them present a cyclic structure. Their computed stabilities vary from 0.3 to 11.3 kcal/mol, depending on several factors, such as involvement in the hydrogen bond interaction, the geometrical constraints, and the possible concurrence of further effects such as resonance-assisted hydrogen bonds or inductive effects. In addition, three stationary points correspond to transition structures involving a double proton-transfer process whose features are also analyzed.     

Selective stabilization of the chorismate mutase transition state by a positively charged hydrogen bond donor

Citrulline was incorporated via chemical semisynthesis at position 90 in the active site of the AroH chorismate mutase from Bacillus subtilis. The wild-type arginine at this position makes hydrogen-bonding interactions with the ether oxygen of chorismate. Replacement of the positively charged guanidinium group with the isosteric but neutral urea has a dramatic effect on the ability of the enzyme to convert chorismate into prephenate. The Arg90Cit variant exhibits a >104-fold decrease in the catalytic rate constant kcat with a 2.7-fold increase in the Michaelis constant Km. In contrast, its affinity for a conformationally constrained inhibitor molecule that effectively mimics the geometry but not the dissociative character of the transition state is only reduced by a factor of approximately 6. These results show that an active site merely complementary to the reactive conformation of chorismate is insufficient for catalysis of the mutase reaction. Instead, electrostatic stabilization of the polarized transition state by provision of a cationic hydrogen bond donor proximal to the oxygen in the breaking C-O bond is essential for high catalytic efficiency.     

Defining the bond energy of a strong hydrogen bond

Based on a recent definition of hydrogen-bond energy the hydrogen bond in [HCOO…H…F]^? is weaker than that in [F…H…F]^?, although the former still ranks as a very strong hydrogen bond.