Molar Volume Change Research Articles

Time resolved calorimetry of photo-induced folding in horse heart cytochrome c at high pH

Here the molar volume and enthalpy changes associated with the early events in the folding of ferrocytochrome c (Cc) at high pH have been examined using time resolved photoacoustic calorimetry (PAC). The data reveal an overall volume change of 1.3 ± 0.3 mL mol−1 and an enthalpy change of 13 ± 7 kcal mol −1 occurring subsequent to photodissociation of the unfolded CO bound Cc species in <∼20 ns. Two additional kinetic phases are observed that are associated with non-native His binding (ΔH and ΔV of 2 ± 4 kcal mol−1 and -0.5 mL mol−1, τ ∼ 2.5 μs ) and Met binding (ΔH and ΔV -0.4 ± 2 kcal mol−1 and -0.1 ± 0.1 mL mol−1, τ∼ 660 ns). Considering only protein conformational changes (excluding volume and enthalpies associated with heme ligation events) the initial conformational event exhibits a ΔH and ΔV of 6 ± 3 kcal mol−1 and -3±0.1 mL mol−1, respectively, that are attributed to a small contraction of the unfolded protein. The corresponding enthalpy associated with both native and non-native ligand binding are found to be −5±4 kcal mol−1 (Fe-Met) and +20 ± 4 kcal mol−1 (Fe-His) with the change in volume for both phases being essential negligible. This would indicate that non-native ligand binding likely occurs from an already collapsed conformation.

Water film rupture in blocked oil recovery by gas injection: Experimental and modeling study

Water shielding phenomenon generally occurs after waterflooding in water-wet rocks, and impedes direct contact between the oil and the injected gas in tertiary gas injection processes. In this work, a set of visualization experiments were performed on micromodel patterns including designed dead-end pores with a film of water on the surface of pore bodies, which is a more realistic representation of porous media. The experiments were conducted at different miscibility conditions, and the required time for water to be displaced from the throat by the swelling of oil was measured for first contact miscible (n-C5/CO2) and immiscible (n-C10/CO2) systems. In the next step, a model was proposed to simulate the results of the experiments, based on the work of Bijeljic et al. (2003). As the impact of non-ideal mixing in this process has not been previously discussed in the available literature, the new model was developed by taking into account the changes in the partial molar volumes of oil and gas components using the PR and the SRK equations of state, and also by considering the mass transfer from the surrounding water on the pore body into the shielded oil. The rupture times predicted by the model were compared with the measured experimental data, as well as those reported by Campbell and Orr (1985). It was found that inclusion of partial molar volumes of components improves the accuracy of the model. The results also revealed the significant role of the water film on the pore body surfaces in mass transfer rate between the phases in water-wet media. The close agreement between the results of the model proposed in this study and the experimental data shows that it can be helpful for developing more accurate multiphase compositional models.

The Nature of Electrochemical Delithiation of Li-Mg Alloy Electrodes: Neutron Computed Tomography and Analytical Modeling of Li Diffusion and Delithiation Phenomenon

Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain the delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. Following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes.

Photoacoustic calorimetry studies of CO photo-dissociation from chloramine-T modified horse heart cytochrome-c

Treatment of horse heart Cytochrome-c (Cc) with N-chloro-4-toluosulfonamide (Chloramine-t, CT) results in the oxidation of methionine (Met) residues to the corresponding sulfoxide including the distal heme ligand, Met80. The resulting Fe-sulfoxide coordination is sufficiently labile in the ferrous form to be displaced by gaseous ligands, including CO. Photolysis of the CO-CT-Cc complex provides an opportunity to examine ligand binding dynamics that are associated with a relatively rigid distal heme pocket. In this work, photoacoustic calorimetry (PAC) was utilized to obtain the kinetics as well as enthalpy and molar volume changes subsequent to CO photo-dissociation from CO-CT-Cc. Previous photolysis studies of CO-CT-Cc have led to a proposed model for ligand recombination in which the Met80-sulfoxide and CO recombine with the heme on relatively slow timescales (50 μs and ∼500 μs, respectively). The PAC data presented here reveals two additional kinetic phases with lifetimes of <20 ns and 534 ± 75 ns. The fast phase (<20 ns) is associated with an ΔH of 44 ± 5 kcal mol−1 and ΔV of −0.5 ± 0.5 mL mol−1, whereas the slower phase (534 ns) is associated with a small ΔH of 2 ± 3 kcal mol−1 and ΔV of 1 ± 0.5 mL mol−1.

A New Finding About Conditions for More Than One Kirkendall Marker Plane in Binary Single Phase Diffusion Couples

It is now well known that there are experimental results of bifurcate, trifurcate or more Kirkendall marker planes (K-plane) in a multiple phase diffusion couple (M-couple). In the case of Au-Zn binary alloy system, for example, even in a β’/β’ single phase diffusion couple (S-couple) there is a possibility of the bifurcate K-planes because the ratio R = DZn/DAu of the intrinsic diffusion coefficients in the β’ phase is smaller than 1 in the Au rich side and larger than 1 in the Zn rich side. It has been reported that the positions of the K-planes in a diffusion zone can be found graphically as intersections between the plot of marker moving distance \(2t\upsilon_{\text{k}}^{\text{D}}\) versus Xk and the plot of a straight line \(2t\upsilon_{\text{k}}^{\text{EX}}\) versus Xk. Here, \(\upsilon_{\text{k}}^{\text{D}}\) is the marker velocity with respect to the volume fixed frame of reference (V-frame) defined by, $$\upsilon_{\text{k}}^{\text{D}} = \upsilon_{\text{k}} - \upsilon_{\text{V}} = V_{\text{B}} \left( {D_{\text{B}}^{\text{V}} - D_{\text{A}}^{\text{V}} } \right)\left( {\frac{{\partial C_{\text{B}} }}{\partial X}} \right),$$ and \(\upsilon_{\text{k}}^{\text{Ex}}\) is that determined experimentally by the following equation, $$\upsilon_{\text{k}}^{\text{Ex}} = \upsilon_{\text{k}} - \upsilon_{0} = \frac{{X_{k} - X_{0} }}{2t}.$$ In this work, we studied the alignments of multiple markers (M-Ms) after diffusion anneal embedded in a S-couple for widely different constant values of ratio of intrinsic diffusion coefficients, R = DB/DA, with respect to the mole fixed frame of reference (N-frame) by our numerical technique taking the change in molar volume into account. For this purpose, new two plots to know the K-plane(s) for the N-flame were derived. A possibility was indicated that Kirkendall markers can locate not only at the intersection(s) between these new two plots but also at an unexpected place where the intersection cannot be found.

A fundamental study of the impact of pressure on the adsorption mechanism in reversed-phase liquid chromatography

A fundamental investigation of the pressure effect on individual adsorption sites was undertaken based on adsorption energy distribution and adsorption isotherm measurements. For this purpose, we measured adsorption equilibrium data at pressures ranging from 100 to 1000bar at constant flow and over a wide concentration range for three low-molecular-weight solutes, antipyrine, sodium 2-naphthalenesulfonate, and benzyltriethylammonium chloride, on an Eternity C18 stationary phase. The adsorption energy distribution was bimodal for all solutes, remaining clearly so at all pressures. The bi-Langmuir model best described the adsorption in these systems and two types of adsorption sites were identified, one with a low and another with a high energy of interaction. Evidence exists that the low-energy interactions occur at the interface between the mobile and stationary phases and that the high-energy interactions occur nearer the silica surface, deeper in the C18 layer. The contribution of each type of adsorption site to the retention factor was calculated and the change in solute molar volume from the mobile to stationary phase during the adsorption process was estimated for each type of site. The change in solute molar volume was 2⿿4 times larger at the high-energy site, likely because of the greater loss of solute solvation layer when penetrating deeper into the C18 layer. The association equilibrium constant increased with increasing pressure while the saturation capacity of the low-energy site remained almost unchanged. The observed increase in saturation capacity for the high-energy site did not affect the column loading capacity, which was almost identical at 50- and 950-bar pressure drops over the column.

In-Situ Monitoring of Stress Development and Electrochemical Behaviour of Metallic Thin Film Anode Materials for Li-Ion Batteries

Due to their high specific capacities and higher (safer) operating potentials, metallic materials such as Sn and Al are among the promising alternatives to graphitic carbon as anode materials for Li-ion batteries. However, the metallic anode materials undergo huge volumetric changes during lithiation/delithiation which leads to the development of stresses that result in severe mechanical degradation and concomitant drastic capacity fade. Furthermore, the stresses affect the thermodynamics of the lithiation/delithiation ‘reactions’ and exert influences on the various electrochemical behaviour. In order to develop better understanding of the origins, magnitudes and resulting effects of such stress developments, in correlation with the initial stress states, crystallographic orientations, stages of lithiation/delithiation, associated phase transformations and surface reactions, we have monitored the stress developments in-situ during lithiation/delithiation. Sn and Al have been selected for the present studies, with the concerned electrodes possessing simple thin film architectures, without binder/additive/porosity. The active electrode films of ~100 nm in thickness have been deposited via e-beam deposition on different current collector films (~100 nm thick), such as Cu (for both Sn and Al), Ni (for Sn) or Ti (for Sn) on thicker (~0.5 mm) quartz substrates (stiff substrate) for allowing monitoring of the in-plane stress developments via substrate curvature technique using multi-beam optical stress sensor (MOSS) in-situ during electrochemical cycling against Li metal in custom-made electrochemical cell [1]. In addition to the expected developments of compressive stresses during lithiation and reverse during delithiation, we focus on some of the finer features of the stress developments, which involves the stress evolution during the first order phase transformations that take place during the Li-alloying reactions (i.e. formation of the various Li-Sn and Li-Al intermetallic) [2]. To develop better understanding, attempt has also been made to mathematically model the observed in-plane stress developments at the different stages (single and two-phase regimes). As will be demonstrated, our observations suggest occurrences of mechanical degradation mainly during the phase transformations, with the electrode materials being fairly stable during the single phase (solid solution) regimes. In order to explore a possible route towards improving the mechanical integrity and cyclic stability upon lithiation/delithiation, the effects of inducing pre-cycling residual stresses via simple annealing treatments have been investigated. Carefully planned experiments with films possessing different residual stress states, aided with in-situ monitoring of the stress developments during lithiation/delithiation, have highlighted the importance of such initial conditions on aspects related to cyclic stability and overpotentials. The use of Sn and Al based electrodes, where the molar volume change associated with the phase transformations are considerably higher compared to other electrode materials, have further strengthened the understanding. On a different note, the influences of different current collectors (Cu, Ni and Ti) on the crystallographic orientations, and concomitantly on the various electrochemical behaviour and stress developments will also be highlighted. Our in-situ observations also suggest the development of stresses due to SEI formation, similar to the case of graphitic carbon [3]. It is believed that the understandings developed as part of the present work will contribute towards successful developments of electrode materials based on alloying reactions. Keywords: anode materials, Sn, Al, stress development

Volumetric and phase behaviour of mixtures of tetracyanoborate-based ionic liquids with high pressure carbon dioxide

The high-pressure solubility of carbon dioxide in ionic liquids based on tetracyanoborate anion, 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][B(CN)4]) and 1-hexyl-3-methylimidazolium tetracyanoborate ([hmim][B(CN)4]), was determined experimentally at the temperature of 313.15K and pressures up to 19MPa. Additionally, measurements of volume expansion of a liquid phase, based on a change in total or molar volume of a liquid upon carbon dioxide addition, are reported. The obtained results show that CO2 has a high solubility in tetracyanoborate-based ionic liquids, comparable, or even slightly higher, to the CO2 solubility in fluorinated CO2-philic ionic liquids. Approximately 60% CO2-induced volume expansion of the liquid was observed at the highest pressures, an unprecedented result for ionic liquid+ CO2 systems.

Thermal behavior and the properties of BaO–B2O3–P2O5 glasses

Borophosphate glasses of the BaO–B2O3–P2O5 ternary system were prepared and studied within the large glass-forming region of the system. Fourteen investigated glass samples of barium borophosphate glasses were discussed for a comparison of the compositional trends in their properties in four compositional series such as A: (100 − x)Ba(PO3)2–xB2O3, B: 40BaO–yB2O3–(60 − y)P2O5, C: (50 − z)BaO–zB2O3–50P2O5, and D: (60 − w)BaO–wB2O3–40P2O5. Changes in glass density and molar volume primarily depend on the BaO content in the glasses. The thermal properties were studied with a differential thermal analysis, hot-stage microscopy, and dilatometry. Glass transition temperature increases with a rising B2O3 content most rapidly in the glass series A and B. It reaches its maximum in these series for the glasses containing 20–30 mol%, where the glass network represents a 3D structure interlinked with P–O–B, P–O–P, and B–O–B bridges. The thermal expansion coefficient decreases, in contrast, with the increasing B2O3 content in these ternary glasses as well as their chemical durability. The crystallization of these glasses, in the samples with a low B2O3 content, results in the formation of barium metaphosphate BaP2O6. Certain crystallized samples also contain a small amount of BPO4, and diffraction lines of ternary compounds BaBPO5 and Ba3B(PO4)3 were revealed in a number of samples. A new compound of the composition Ba5B2P8O28 was identified in the crystallized glass 50BaO–10B2O3–40P2O5.

Sodium-free mixed alkali bioactive glasses

AbstractTwo sodium-free mixed alkali series of bioactive glasses based on compositions Bioglass 45S5 and ICIE1, containing lithium and/or potassium as alkali ions, were prepared by a melt-quench route. Thermal properties showed the well-known mixed alkali effect, with glass transition and crystallisation temperatures and the coefficient of thermal expansion going either through a minimum or a maximum for the mixed alkali composition, resulting in a wider processing window. Ion release, by contrast, was controlled by the modifier ionic radius, with ion release rates in dynamic and static dissolution studies increasing for potassium-substituted glasses compared to the composition containing lithium as the only alkali ion. This was caused by pronounced changes in oxygen packing density and molar volume of the glasses owing to the differences in ionic radii (76 pm for Li+ and 138 pm for K+). Partially substituting one alkali for another therefore helps to improve high temperature processing of bioactive glasses and can also be used to control or tailor ion release.

Pressure Effect on the Folding of G-Quadruplex DNA Modified with Hexaethylene Glycol

Objective: Pressure can influence the folding of nucleic acids, and the effect of pressure depends on the volumetric difference between folded and unfolded states. In this study, we investigated how modification with hexaethylene glycol affected the folding of a guanine-rich DNA oligonucleotide. Results: The stability of the G-quadruplex formed by the thrombin binding aptamer (TBA), 5’-GGTTGGTGTGGTTGG-3’ (loop regions underlined) modified with hexaethylene glycol (HEG) at the 5’-terminus decreased more significantly as pressure increased than did the G-quadruplex formed by the unmodified TBA. The change of partial molar volume, ΔV, of 5-HEG TBA folding was 101 cm3 mol-1, where as that of TBA was 54.6 cm3 mol-1. The HEG at 5’ terminus of TBA increased volume of the folded structure due to induction of dehydration. In contrast, replacement of the 5’-most loop of the TBA G-quadruplex with HEG resulted in a ΔV value of 62.8 cm3 mol-1, whereas replacement of the second loop resulted in a ΔV value of 82.8 cm3 mol-1. It has been suggested that bases of the nucleotides in the second loop form stacking interaction with G-quartet but those in the first loop do not. Conclusion: These results indicate that a 5’ covalently linked HEG disrupts the stacked structure of the second loop on the G-quartet; this stacking accompanied dehydration during the quadruplex formation. Thus, modification with poly(ethylene glycol) units enhances the effect of pressure on the folding of G-quadruplex DNA.

Ultrasonic speeds, refractive indices, and densities of dimethoxymethane + aliphatic alcohols (C1–C4) at (298.15 and 303.15) K with COSMO-RS and ERAS analyses

The ultrasonic speeds, refractive indices, and densities of binary mixtures dimethoxymethane+aliphatic alcohols (C1–C4) were determined. The excess quantities for the binary mixtures are fitted to the Redlich–Kister polynomials. The observed excess molar volumes are rationalized in terms of the intermolecular force and geometry contributions of the constituent molecules. The intermolecular forces are discussed using accepted theories and the more recent conductor-like screening model (COSMO). The extended real associating solution (ERAS) model is also utilized in the analysis of excess molar volumes. The σ-profile of dimethoxymethane and alcohols are computed with COSMO-RS and interpreted to be not supportive of earlier interpretations of hydrogen bonds in the energetics. Sign changes in excess molar volume and excess isentropic compressibility are discussed and rationalized in detail quantitatively. Sellmeier's equation is used to quantitatively rationalize the measured refractive indices and a consistency with regard to sign and sign changes of the other measured excess quantities can be deduced.

The Energetics of a Three‐State Protein Folding System Probed by High‐Pressure Relaxation Dispersion NMR Spectroscopy

AbstractThe energetic and volumetric properties of a three‐state protein folding system, comprising a metastable triple mutant of the Fyn SH3 domain, have been investigated using pressure‐dependent 15N‐relaxation dispersion NMR from 1 to 2500 bar. Changes in partial molar volumes (ΔV) and isothermal compressibilities (ΔκT) between all the states along the folding pathway have been determined to reasonable accuracy. The partial volume and isothermal compressibility of the folded state are 100 mL mol−1 and 40 μL mol−1 bar−1, respectively, higher than those of the unfolded ensemble. Of particular interest are the findings related to the energetic and volumetric properties of the on‐pathway folding intermediate. While the latter is energetically close to the unfolded state, its volumetric properties are similar to those of the folded protein. The compressibility of the intermediate is larger than that of the folded state reflecting the less rigid nature of the former relative to the latter.

The energetics of a three-state protein folding system probed by high-pressure relaxation dispersion NMR spectroscopy.

The energetic and volumetric properties of a three-state protein folding system, comprising a metastable triple mutant of the Fyn SH3 domain, have been investigated using pressure-dependent (15) N-relaxation dispersion NMR from 1 to 2500 bar. Changes in partial molar volumes (ΔV) and isothermal compressibilities (ΔκT ) between all the states along the folding pathway have been determined to reasonable accuracy. The partial volume and isothermal compressibility of the folded state are 100 mL mol(-1) and 40 μL mol(-1) bar(-1) , respectively, higher than those of the unfolded ensemble. Of particular interest are the findings related to the energetic and volumetric properties of the on-pathway folding intermediate. While the latter is energetically close to the unfolded state, its volumetric properties are similar to those of the folded protein. The compressibility of the intermediate is larger than that of the folded state reflecting the less rigid nature of the former relative to the latter.

Osmotic Pressure Effects Reveal a Specific Dehydration-Induced Hydrophobic Electron Transfer Structure Comprising Cytochrome C and Cytochrome C Oxidase

In the mitochondrial respiratory chain, Cytochrome c oxidase (CcO) accepts electrons from Cytochrome c (Cyt c) to reduce molecular oxygen. Previous studies showed that the complex formation of Cyt c with CcO is characterized by the positive entropy change, suggesting the dehydration from hydrophobic residues, but no experimental evidence of such dehydration has been reported. To confirm the dehydration during the complex formation between Cyt c and CcO, we focused on the partial molar volume change of protein (ΔV W) for the complex formation, which reflects the volume of dehydrated water molecules. ΔV W is correlated with the osmotic pressure (π) dependence of the K d. Osmotic pressure was increased by addition of sugars or polyols having no specific interactions with proteins and K d was estimated by the Michaelis-Menten analysis of the steady state kinetics for the electron transfer from Cyt c to CcO. As Figure 1 shows, the K d value is decreased with increasing the osmotic pressure, corresponding to the negative ΔV W of – 300 ± 78 mL mol-1. Assuming that the partial molar volume change of one hydrated water molecule around hydrophobic residues would be－17.5 mL mol-1, the volume change we obtained here corresponds to the dehydration of 17 ± 4 water molecules. Considering that the entropy change from the dehydration (dehydΔS) of one water molecule was estimated to be 5.5 JK-1mol-1, dehydΔS of 17 water molecules corresponds to ~90 JK-1mol-1, which is about 75% of total entropy change for the Cyt c-CcO complex formation. The dehydration is, therefore, one of the major factors to increase the entropy for the complex formation. To identify the dehydration sites from hydrophobic residues in the interaction site for CcO on Cyt c, we mutated Ile11 or Ile81, hydrophobic amino acid residues in the interaction site for CcO [1], to Ala, an amino acid residue having a smaller side chain and less number of the hydrated water molecules. As clearly illustrated in Figure 1, the slope of the osmotic pressure dependence of K d for the Ile mutant is less steep than that for the wild type protein. The estimated numbers of the dehydrated water molecules were reduced to 13 ± 3 and 8 ± 2 for the Ile11 and Ile81 mutants, respectively. The reduced numbers of the dehydrated water molecules in these Ile mutants indicate that the hydrated water molecules around Ile11 and Ile81 were expelled to the solvent in the complex formation between Cyt c and CcO. In conclusion, we successfully identified that about 17 water molecules are dehydrated in the Cyt c-CcO complex formation and the primary dehydration sites are Ile11 and Ile81. Such dehydration from the hydrophobic residues can be a major factor to increase the entropy, facilitating the complex formation and the electron transfer from Cyt c to CcO.

A look at the effect of sequence complexity on pressure destabilisation of DNA polymers

Our previous studies on the helix–coil transition of double-stranded DNA polymers have demonstrated that molar volume change (ΔV) accompanying the thermally-induced transition can be positive or negative depending on the experimental conditions, that the pressure-induced transition is more cooperative than the heat-induced transition [Rayan and Macgregor, J Phys Chem B2005, 109, 15558–15565], and that the pressure-induced transition does not occur in the absence of water [Rayan and Macgregor, Biophys Chem, 2009, 144, 62–66]. Additionally, we have shown that ΔV values obtained by pressure-dependent techniques differ from those obtained by ambient pressure techniques such as PPC [Rayan et al. J Phys Chem B2009, 113, 1738–1742] thus shedding light on the effects of pressure on DNA polymers. Herein, we examine the effect of sequence complexity, and hence cooperativity on pressure destabilisation of DNA polymers. Working with Clostridium perfringes DNA under conditions such that the estimated ΔV of the helix–coil transition corresponds to −1.78mL/mol (base pair) at atmospheric pressure, we do not observe the pressure-induced helix–coil transition of this DNA polymer, whereas synthetic copolymers poly[d(A-T)] and poly[d(I-C)] undergo cooperative pressure-induced transitions at similar ΔV values. We hypothesise that the reason for the lack of pressure-induced helix–coil transition of C. perfringens DNA under these experimental conditions lies in its sequence complexity.

Negative thermal expansibility change for dissociation of lysozyme variant amyloid protofibril.

A disulfide-deficient variant of hen lysozyme, 0SS, is known to form an amyloid protofibril spontaneously, and to dissociate into monomers at high hydrostatic pressure. We carried out native PAGE at various temperatures (20-35°C) and pressures (0.1-200 MPa), to characterize the dissociation equilibrium of disulfide-deficient variant of hen lysozyme amyloid protofibril. Based on the density profiles, the partial molar volume and thermal expansibility changes for dissociation, ΔvD and ΔeD , were obtained to be -74 cm(3) /mol at 25°C and -2.3 cm(3) mol(-1) K(-1) , respectively. The dissociation of amyloid fibril destroys the cross β-structure, and such conformational destruction in native protein fold rarely accompanies negative thermal expansibility change. We discussed the negative thermal expansibility change in terms of hydration and structural packing of the amyloid protofibril.

Physical, Optical absorption and EPR studies on fluoro- bismuthate glasses

Glasses of the xLiF-(50-x)Li2O-20SrO-30Bi2O3 system, with 0 ≤ x ≤ 20 mole % were studied by EPR and Optical measurements. The changes in both density and molar volume indicate structural modifications occur due to addition of LiF. The glass transition temperatures are observed to decrease with an increase in LiF content in the compositions. The local structure around Cu2+ ions has been examined by means of electron paramagnetic resonance and optical absorption measurements. It is observed that the spin-Hamiltonian parameters calculated from the EPR spectra are influenced by the glass composition. The Cu2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu2+ is and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d-d transition bands of Cu2+ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated.

High-pressure phase behaviors of ZnTiO3: ilmenite–perovskite transition, decomposition of perovskite into constituent oxides, and perovskite–lithium niobate transition

High-pressure high-temperature phase transitions of ZnTiO3 ilmenite were examined using multianvil apparatus up to 25.5 GPa and 1,500 °C and diamond anvil cell to 26.5 GPa and about 2,000 °C. Combined results of the multianvil quench experiments and in situ diamond anvil cell experiments indicated that at about 10 GPa and 1,200 °C ZnTiO3 ilmenite transforms to orthorhombic perovskite which is converted to lithium niobate phase on release of pressure. The boundary of the ilmenite–provskite transition is expressed by P(GPa) = 15.9 − 0.005T (°C). The high-pressure experiments also indicated that at 20–24 GPa and 1,000–1,400 °C ZnTiO3 orthorhombic perovskite dissociates into rocksalt-type ZnO + baddeleyite-type TiO2 which are recovered, respectively, as wurtzite-type ZnO and α-PbO2-type TiO2 at 1 atm. The boundary of the perovskite dissociation is expressed by P(GPa) = 8.7 + 0.011T (°C). Molar volume changes of ZnTiO3 at ambient conditions were estimated as −4.7 % for the ilmenite–perovskite transition and −3.5 % for the perovskite decomposition into the oxides. The absence of CaIrO3-type postperovskite in ZnTiO3 is consistent with that dissociation of ZnTiO3 perovskite into the oxides has the larger molar volume change than −1 to −2 % of the perovskite–postperovskite transition in various ABO3 compounds and with previous data that ABO3 perovskites with relatively ionic B–O bonds do not transform to the postperovskite. The transition behaviors of ZnTiO3 are similar to those of MnTiO3 and FeTiO3, but ZnTiO3 perovskite dissociates into the constituent oxides.

Photoacoustic Calorimetry Studies of Ferric Cytochrome-C Folding using an No Photo-Trigger

In this study, NO is utilized as a photo-trigger together with photoacoustic calorimetry to probe the kinetics, enthalpy and molar volume changes associated with the earliest folding events in ferric Cytochrome-c (Cc3+). The ferric heme protein was examined under different denaturing conditions including guanidine hydrochloride (2.8M GdnHCl) and Sodium dodecyl sulfate (SDS 0.4mM) (both in 50 mM Hepes buffer, pH ∼7.5) along with NO resulting in the disruption of the axial heme Methionine-80 heme bond, triggering the partial unfolding of the complex. Under these conditions photo-dissociation of NO leaves the protein in a conformational state that favors refolding of the protein. The PAC data reveals three kinetic phases taking place subsequent to photolysis regardless of the denaturant environment. Specifically, in the presence of 2.8 M GdnHCl photolysis gave rise to kinetic events with lifetimes of <20 ns, ∼860 ns, and ∼6 μs that were associated with ΔH/ΔV = −25 kcal mol-1/-9 mL mol-1, 26 kcal mol-1/15mL mol-1, and 9 kcal mol-1/-26 mL mol-1, respectively. In the presence of 0.4 mM SDS, kinetic events were observed with lifetimes of <20 ns, ∼640 ns, and ∼8 μs with corresponding ΔH/ΔV of −11 kcal mol-1/-1 mL mol-1, 5 kcal mol-1/3 mL mol-1, and 30 kcal mol-1/-9 mL mol-1, respectively. The data suggests a uniform mechanism for the early folding events occurring in the folding of Cc3+ complex subsequent to NO photo-dissociation which are attributed to NO dissociation from the heme, followed by reorganization of the distal pocket (i.e hydrogen bond formation/breakage, NO solvation, etc.) and potentially a intermolecular binding of Methionine (80 or 65) or Histidine (23 or 33) to the heme iron upon folding.