Ln Kd Research Articles

Single-crystal thermometric calibration of Fe-Mg order-disorder in pigeonites

The single-crystal X-ray technique was used to calibrate a new intracrystalline geothermometer based on equilibrium Mg-Fe* fractionation (Fe* = Fe2+ + Mn2+) between M1 and M2 sites of natural P21/c pigeonite. Suitable crystals free of exsolution textures and sharp diffraction maxima were selected by careful TEM and XRD investigations from a large number of samples. Two single crystals, PCA82506-3 (Wo6En76Fs18) from the Pecora Escarpment 82506 Antarctic ureilite, and BTS308- 2 (Wo10En47Fs43) from the BTS308 Paranà rhyodacite, were annealed at temperatures ranging from 600 to 1000 °C. The TEM investigation, carried out on fragments of selected single crystals both before and after thermal treatment, shows heating-induced texture modifications preliminary to spinodal decomposition in both crystals and a size increase in antiphase domains in BTS308-2. The two geothermometric equations calculated by linear regression of ln KD* vs. 1/T are:

The Linear Dependence of Log(kcat/Km) for Reduction of NAD+ by PhCH2OH on the Distance between Reactants when Catalyzed by Horse Liver Alcohol Dehydrogenase and 203 Single Point Mutants

Like most dehydrogenases, with horse liver alcohol dehydrogenase (LADH), a bulky amino acid residue (Val 203) is positioned at the face of NAD+ distal to substrate alcohol in order to restrict the separation of reactants and to control the stereochemistry. Molecular dynamics simulations of native (Val203) and single-point mutants (Leu203, Ala203, and Gly203) of LADH·PhCH2OH·NAD+ provide the close contact distances (CCD) between PhCH2OH and NAD+ reactants. It is found that log(kcat/Km) is linearly dependent upon CCD. This linear dependence of log(kcat/Km) upon CCD is expected if hydride transfer is the rate-determining step. Since log(kcat/Km) has been found to be a linear function of tunneling, ln(kH/kT)/ln(kD/ kT), it follows that tunneling in LADH has a linear dependence upon CCD.

Adsorption Studies of CuII from Aqueous/Acidic Solutions on to Bentonite

The ability of bentonite to remove CuII from aqueous and acidic solutions at different pH values has been studied for different adsorbate concentrations by varying the amount of adsorbent, temperature and shaking time. The maximum (85%) adsorption of CuII was achieved from aqueous solution at pH 3.8. The influence of different anions and cations in the 0–1000 μg/ml concentration range on the adsorption of copper under optimized conditions has been examined. A flame atomic absorption spectrometer was used for measuring the copper concentration before and after adsorption. Isotherm analysis of the adsorption data obtained at 25°C, 30°C, 40°C and 50°C showed that the adsorption of copper(II) on bentonite could be described by both the Langmuir and the Freundlich isotherms. Values of ΔH0 and ΔS0 were calculated from the slope and intercept of the ln KD versus l/T plots.

Characterizing the heterogeneity and correlation of perchloroethene sorption and hydraulic conductivity using a facies‐based approach

A facies‐based approach was used to delineate both geochemical and physical aquifer property heterogeneity. Specifically, the parameters considered were the sorption coefficient (Kd) for a model organic contaminant and hydraulic conductivity (K) inferred from the particle size distribution. Subfacies‐sized samples were analyzed for both tetrachloroethene Kd and K in a vertical core of the Borden aquifer. Both parameters were correlated with the six sedimentary facies identified within the vertical core. As a consequence of their relations to sedimentary facies, significant positive correlations between ln K and ln Kd which were different from the core‐scale correlation and different from each other were identified for some facies. Fades‐specific correlations generally resulted in improved statistics (i.e., higher correlation coefficients and reduced confidence intervals) compared to the core‐scale correlation. The results suggest that a facies‐based approach can be useful in characterizing the heterogeneity of the transport properties of sedimentary aquifers.

Kinetic mechanism of a partial folding reaction. 1. Properties Of the reaction and effects of denaturants.

The bimolecular association rate constant (kon) and dissociation rate constant (koff) of the complex between fluorescein-labeled S-peptide analogues and folded S-protein are reported. This is the first kinetic study of a protein folding reaction in which most of the starting material is already folded and only a small part (one additional helix) becomes ordered; it provides a folding landscape with a small conformational entropy barrier, and one in which kinetic traps are unlikely. Refolding and unfolding are measured under identical strongly native conditions, and the reaction is found to be two-state at low reactant concentrations. The dissociation constant (Kd) of the complex and the properties of the transition state may be calculated from the rate constants without extrapolation. The folded complex is formed fast (kon = 1.8 x 10(7) M-1 s-1) and is very stable (Kd = 6 pM) at 10 degrees C, 10 mM MOPS, pH 6.7. Charge interactions stabilize the complex by 1.4 kcal mol-1. The charge effect enters in the refolding reaction: increasing the salt concentration reduces kon dramatically and has little effect on koff. Urea and GdmCl destabilize the complex by decreasing kon and increasing koff. The slopes (m-values) of plots of ln Kd vs [cosolvent] are 0.75 +/- 0.04 and 2.8 +/- 0.3 kcal mol-1 M-1 for urea and GdmCl, respectively. The ratio mon/(mon + moff) is 0.54 +/- 0.04 for urea and 0.57 +/- 0.1 for GdmCl, where mon is the m-value for kon and moff is the m-value for koff, indicating that more than half of the sites for interaction with either cosolvent are buried in the ensemble of structures present at the transition state.

Radionuclide partitioning coefficients in the Sava River ecosystem

The radionuclides54Mn,60Co,90Sr,95Nb,95Zr,103Ru,106Ru,125Sb,131I,134Cs,137Cs,140Ba,144Ce,226Ra and228Ac have been studied in the Sava River environment since the Chernobyl accident in 1986. The measured periphyton concentration ratios (CR) for each radionuclide were correlated with the measured sediment distribution coefficients (Kd) for that radionuclide. The Kd-CR relationships obtained were defined by the equation ln Kd=−0.5 ln CR +7.4. These Kd-CR relationships were assumed to be referable to the Sava River ecosystem and were used to predict the missing soil Kd values and/or the missing CR values for the wide range of radionuclides, respectively. Moreover, the Kd-CR relationship characteristic for the Sava River ecosystem was compared with the Kd-CR relationship proposed by Baes1 and by Shepard2. The characterization of the partition coefficients in the Sava River environment and understanding of the mechanisms affecting radionuclide retardation and bioaccumulation are required for the planning of radioactive waste depositories in the area.

Selective adsorption of thorium on activated charcoal from electrolytic aqueous solution

The adsorption of thorium on activated charcoal has been studied as a function of shaking time, amount of adsorbent, pH, concentration of adsorbate and temperature. Adsorption of thorium obeys the Langmuir isotherm. ΔH0 and ΔS0 were calculated from the slope and intercept of ln KD vs. 1/T plots. The influence of different anions and cations on thorium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under specified conditions to check its selectivity. Consequently, thorium was removed from Cs, Co, Ba, Cr, Sr, Cd, Cu, Mn and Zn. More than 98% adsorbed thorium on activated charcoal can be recovered with 55 ml 3M HNO3 solution. Wavelength dispersive X-rays fluorescence spectrometer was used for measuring thorium concentration.

Selective Adsorption of Uranium on Activated Charcoal from Electrolytic Aqueous Solutions

Abstract Adsorption of uranium on activated charcoal has been studied as a function of shaking time, amount of adsorbent, pH, concentration of adsorbate, and temperature. Uranium adsorption obeys the Langmuir isotherm. ΔHΔ and ΔSΔ were calculated from the slope and intercept of plots of ln KD vs 1/T. The influence of different anions and cations on uranium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under specified conditions to check its selectivity; consequently, uranium was removed from Cs, Ba, Zn, and Co. More than 98% adsorbed uranium on activated charcoal can be recovered with 65 mL of 3 M HNO3 solution. A wavelength dispersive x-ray fluorescence spectrometer was used for measuring uranium concentration.

Selective Adsorption of Strontium on Activated Charcoal from Electrolytic Aqueous Solutions

The adsorption of strontium on activated charcoal has been studied as a function of shaking time, pH, concentration of adsorbate and temperature. Wavelength dispersive X-ray fluorescence spectrometer was used for measuring strontium concentration. The adsorption of strontium obeys Freundlich and Langmuir isotherms. Quantities ∆H0 and ∆S0 were calculated from the slope and intercept of plot ln KD vs 1/T. The influence of different cations and anions on strontium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under specific conditions to check its selectivity. Consequently, strontium was removed from Rh, Pr, Rb and Cs. More than 95% adsorbed strontium on activated charcoal can be recovered with 65 ml 3M HNO3 solution.

Spatial Variability of Strontium Distribution Coefficients and Their Correlation With Hydraulic Conductivity in the Canadian Forces Base Borden Aquifer

Distribution coefficients (Kd), defined as the ratio of the concentration of solute associated with the solids to the concentration in solution, are widely used in the prediction of reactive solute transport. With the advent of stochastic approaches to describe solute transport, there is a need to examine the spatial distribution of Kd, and its correlation with the hydraulic conductivity (K). Distribution coefficients were measured in triplicates for strontium on 1279 subsamples of cores from Canadian Forces Base Borden for which K measurements were available. The Kd values ranged from 4.4 to 29.8 mL/g, with a mean of 9.9 and standard deviation of 2.89 mL/g. The standard error on the triplicate means was 0.95 mL/g or approximately 10% of the mean. The spatial behavior of Kd and K (expressed as In (Kd) and ln (K)) was examined in three directions: horizontally along two orthogonal transects and vertically. The two variables each behaved nearly identically in the two horizontal directions, suggesting horizontal isotropy. Horizontally, ln (Kd) appeared as “white noise” suggesting that the horizontal spacing between cores (1 m) was too large to detect any self‐correlation. The distribution coefficient displayed increasing power spectral density with increasing scale in the vertical direction, while In (K) showed these trends in all directions. Depending on the model used, the, correlation lengths obtained by least squares fits of the power spectra varied from 1 to 7.5 m horizontally and from 10 to 30 cm vertically for ln (K); and from 30 cm to 2 m horizontally and from 30 to 70 cm vertically for ln (Kd). The ln (Kd) values showed a significant but very weak negative overall correlation with ln (K) at the 99.95% confidence level. The cross‐spectral and coherency analysis showed that the sign and degree of correlation between ln (Kd) and ln (K) depended on the scale and direction considered. The correlations in all directions and at all scales were weak, and could not always be declared significantly different than zero at the 95% confidence level.

Solvent effect on radiative and non-radiative transitions in all-trans-1,6-diphenylhexatriene

The spectral and luminescent properties of all-rans-1,6-diphenyl-1,3,5-hexatriene (DPH) were studied at room temperature in solvents with various refractive indices (1.33 < n < 1.63) and dielectric constants (1.9 < ϵ < 37.4). The maximum fluorescence quantum yield of DPH (φo = 0.85) was measured in quinoline, and the lowest quantum yield was observed in acetonitrile (φo = 0.17). The experimentally determined values of the fluorescence and non-radiative deactivation probabilities (kf1 and kd) of the lowest singlet excited state S1 are 2.9 × 108 s−1 (quinoline) and 2.0 × 108 s−1 (acetonitrile). The fluorescence from the S1(21A*g) state (the transition to which from the ground state S0(11Ag) is symmetry forbidden) is due to vibronic mixing with a higher S2(11B*u) state, which participates in the strongly allowed electron transition S2 ← S0. The matrix element of the vibronic interaction between the S1 and S2 states (V12) is 840 cm−1.Non-radiative transitions from the S1 state are essentially dependent on the solvent polarity. There is a linear dependence of ln kd on the empirical parameter ET(30), which characterizes the solvent polarity. The polar solvent quenches the fluorescence of DPH by inducing non-radiative transitions through intermediate twisted structures possessing dipole moments of a few debyes.

Internally-consistent geothermometry and H2O barometry in metamorphic rocks: The example garnet-chlorite-quartz

Temperature and H2O activity can be determined with high precision using metamorphic mineral assemblages that define both a dehydration equilibrium and a temperature-sensitive cation-exchange equilibrium. Such determinations are obtained by applying the Gibbs method and then integrating two resulting differential equations, as illustrated here for the assemblage garnet-chlorite-quartz. The first equation, a geothermometer that monitors temperature based upon Fe−Mg exchange between garnet and chlorite, was calibrated using rocks at Pecos Baldy, New Mexico: 0=0.05 P(bars)−19.02 T(K)+4607 ln K D+24,156 with errors of ±8°C based upon analytical precision. The second equation monitors differences in the activity of water between specimens (1) and (2): 0=(0.1 X Mg−chl, 1 − 2.05)(P 2 − P 1) +[−33.02+5.96 ln(X Fe−chl, 1/X alm, 1)][T 2−T 1 −2.67 RT 1ln[a(H2O)2/a(H2O)1] +5.96 T 1ln(X Fe−chl, 2 X alm, 1/X Fe−chl, 1 X alm, 2). For samples equilibrated at the same pressure and temperature, microprobe analytical errors of 1% limit precision to ±0.01 a(H2O). For samples equilibrated at the same pressure but variable temperature, uncertainty of ±8°C limits precision to ±0.06 a(H2O). Extreme presure sensitivity requires that the H2O-barometer be applied only to rocks where pressure gradients are absent or well-constrained. The geothermometer gives temperatures in agreement with two other garnet-chlorite geothermometers (Dickenson and Hewitt 1986; Ghent et al. 1987) and with garnet-biotite geothermometry (ferry and Spear 1978) over the temperature range 350–520°C. Application of the relative H2O barometer shows variations in the activity of water approaching 0.30 in several study areas. Either pelitic schists commonly equilibrate with a fluid that is not pure H2O, or some pelitic rocks undergo metamorphism in the absence of a free fluid phase.

Biotite and garnet compositional variation and mineral equilibria in Grenville gneisses of the Otter Lake area, Quebec

Garnet‐biotite gneisses, some of which contain sillimanite or hornblende, are widespread within the Otter Lake terrain, a portion of the Grenville Province of the Canadian Shield. The metamorphic grade is upper amphibolite to, locally, lower granulite facies.The atomic ratio Fe2+/(Fe2++ Fe3+) in biotite ranges from 0.79 to 0.89 (ferrous iron determinations in 10 highly pure separates), with a mean of 0.86. Mg and Fe2+ atoms occupy 67–78% of the octahedral sites, the remainder are occupied by Fe3+, Ti, and Al, and some are vacant. Mg/(Mg + Fe2+), denoted X, in the analysed samples ranges from 0.32 to 0.65. Garnet contains 1–24% grossular, 1–12% spessartine and X ranges from 0.07 to 0.34.Compositional variation in biotite and garnet is examined in relation to three mineral equilibria:(I) biotite + sillimanite + quartz = garnet + K‐feldspar + H2O;(II) pyrope + annite = almandine + phlogopite;(III) anorthite = grossular + sillimanite + quartz.Measurements of X (biotite) and X (garnet) are used to construct an illustrative model for equilibrium (I) which relates the observed variation in X to a temperature range of 70°C or a range in H2O activity of 0.6; the latter interpretation is preferred.In sillimanite‐free gneisses, the distribution of Mg and Fe2+ between garnet (low in Ca and Mn) and biotite is adequately described by a distribution coefficient (KD) of 4.1 (equilibrium II). The observed increase in the distribution coefficient with increasing Ca in garnet is ln KD= 1.3 + 2.5 × 10−2 [Ca]where [Ca] = 100 Ca/(Mg + Fe2++ Mn + Ca). The distribution coefficient is apparently unaffected by the presence of up to 12% spessartine in garnet.In several specimens of garnet‐sillimanite‐plagioclase gneiss, the Ca contents of garnet and of plagioclase increase in unison, as required by equilibrium (III). The mean pressure calculated from these data (n= 17) is 5.9 kbar, and the 95% confidence limits are ±0.5 kbar.

Base metal exchange between magnetite and a chloride-rich hydrothermal fluid

Base metal exchange reactions between magnetite and a supercritical aqueous chloride solution have been experimentally calibrated at T = 600 to 800°C, P = 2 kb, and total chloride = 2.06 M. The results are expressed as the distribution coefficients Kd MFe= (X MX Fe ) fl (X MX Fe ) s , where fl and s represent the fluid and the solid solution, respectively, and X M= m M (m M + m Fe total (m M + m Fe total ) are the mole fractions of the metal of interest and of total Fe, respectively. The experimentally determined distribution coefficients are Kd MnFe = 64, 33, and 18, and Kd ZnFe=161, 87, and 53, at T=600, 700, and 800°C, respectively. Linear regression yields the best fit equations: ln Kd ZnFe = 5198/ T(K) − 0.872 ( r 2 = 0.9999) and ln Kd MnFe = 5941/ T(K) − 2.63 ( r 2 = 0.9995). Kd values were independent of composition over the range of concentrations investigated. Clearly, both Mn and Zn are strongly fractionated into the fluid with respect to Fe. A combination of Kd MnFe and Kd ZnFe yields Kd ZnMn = 2.54, 2.67, and 2.94 at 600, 700, and 800°C, where Kd = (X Zn X Mn ) fl / (X Zn X Fe ) s . The partitioning and temperature dependence described by Kd ZnMn are significantly weaker than those shown by Kd MnFe and Kd ZnFe. Results for the CdFe and CuFe exchange reactions indicate that both Cd and Cu are extremely partitioned into the fluid with respect to Fe and very strongly partitioned into the fluid with respect to Zn and Mn. The experimental results suggest that even minor to trace concentrations of these base metals in natural magnetites indicate strong enrichment of Zn, Mn, Cu, and Cd relative to Fe in chloride-rich hydrothermal fluids. In particular, Kd MnFe was applied to magnetites from skarn deposits. Calculations at 360 to 420°C suggest that skarn fluids in equilibrium with magnetites containing only minor concentrations of Mn can have Mn/Fe ratios greater than 1.

Studies on freshness of trawl catches. V. The influence of habitat water temperature on the relative thermostability of myofibrillar Ca2+-ATPase in fishes collected in the waters from tropical to frigid zones.

The first order rate constants, KD, of thermal inactivation of myofibrillar Ca2+-ATPase were determined for a total of 79 fishes of 50 families caught from six waters covering from the tropical waters, 28°C in a bottom water temperature, to the cold waters, 2°C. The mean value of KD for fishes from a certain fishing ground tended to be lower with a higher habitat temperature; the value was lowest for the fishes from the Gulf of Thailand (28°C in the habitat temperature), followed by fishes from northern waters in the order of the adjacent waters of Amami-Oshima (25°C), Sakishima Islands (28°C), the East China Sea (17°C), the Yollow Sea (9°C), and off Kushiro (2°C). A significant, negative, logarithmic functional correlation was seen between the bottom water temperature of a fishing ground (t) and the mean value of KD for fishes inhabiting there (-KD); their rela-tion is formulated as below. ln KD=-0.1013t+5.611 Similar influences of habitat temperatures on KD were also seen for a fish from two areas of different habitat temperatures, though the degree of the influence was somewhat variable by fish species. Fishes with higher values of ΔK32, the increasing rate of K value, tended to show higher values of KD.

Lipid-protein interaction at solid-water interface. Adsorption of human apo-high density lipoprotein to amphiphilic interfaces.

Hydrophobic glass beads with well characterized physical properties were used as a model system to study at the amphiphilic interface the properties of apolipoproteins A-I and A-II from human serum high density lipoproteins. In this study, spherical glass beads with known diameter were coated covalently with a film of silicone to varying surface density. The decrease in surface tension induced by coating was directly related to the increase in silicone film density and likely to the hydrophobicity of the glass surface. The adsorption of apo-A-I and apo-A-II to the hydrophobic glass bead surface was determined by following the decrease of 1) the radioactivity of preparations of 125I-iodinated proteins from the solution, 2) the UV absorbance of the solution at 206 nm, and 3) the fluorescence emitted by the complex formed between free protein and Fluram II in solution. All of the three measurements gave identical results. Both proteins adsorbed rapidly and reversibly to the hydrophobic glass surface. The adsorption isotherms followed the Langmuir equation with apo-A-II showing a higher surface affinity; delta Gaff = RT ln Kd has a value of -9.1 kcal/mol and -10.5 kcal/mol for apo A-I and apo A-II, respectively. The addition of canine serum high density lipoprotein (HDL) to the above system caused a rapid desorption of apolipoproteins from the beads into the aqueous phase and adsorption onto the HDL surface with no detectable structural changes of this lipoprotein. The results indicate that apo-A-I and apo-A-II can reversibly be adsorbed at a solid hydrophobic surface and that these apoproteins are capable of moving into a HDL particle if added to the system via a solution phase. The data suggest that the rate limiting aspect of the desorption-adsorption processes is the concentration of the apoproteins in solution.

Impurity-limited mobility of semiconducting thin wire

Sakaki [Jpn. J. Appl. Phys. 19, L735 (1980)] has investigated the mobility of semiconducting thin wire structures when the mobility of the wire is limited by scattering from ionized impurities which are located a fixed distance outside the wire. We have used a similar model to theoretically calculate the impurity-limited mobility of such semiconducting thin wires for the cases where the impurities are either in the wire itself (background impurities) or are distributed outside the wire (remote impurities) or are distributed uniformly both inside and outside the wire. For the case of scattering from the background impurities, we find that the mobility decreases with decreasing wire radius d as [ln (kd)]−2 where k is either the thermal or Fermi wave vector of the carriers. For the case of scattering from remote impurities, the size dependence of the impurity-limited mobility depends upon how the remote impurities are distributed outside the wire. When the distribution of ionized impurities outside the wire is uniform, the mobility is independent of the wire radius while, if the ionized impurities are separated from the wire by a fixed distance, we recover the results previously obtained by Sakaki. When the impurities are distributed uniformly both inside and outside the wire, the mobility again is size independent.

Effect of pH on the adsorption of trace radioactive cesium by sediments

The adsorption of trace radioactive cesium by sediments from the Savannah River Plant area follows a theoretically expected linear relationship between ln Kd* and the pH of the equilibrium solution, where Kd* is the equilibrium distribution coefficient: Cs adsorbed (meq g−1)/Cs+ in solution (meq ml−1). Theoretically, the slope of these plots is proportional to the fraction of surface area occupied by pH dependent charges. Experimentally, the slope becomes zero after removal of hydroxy Al interlayers with citrate pretreatment. Hydroxy Al interlayers are thus the main source for the pH dependent charges making Cs+ adsorption pH dependent.

Effect of temperature and hydroxy aluminum interlayers on the adsorption of trace radioactive cesium by sediments near water‐cooled nuclear reactors

The adsorption of 137Cs by sediments from the Savannah River Plant follows a theoretically expected linear relationship between ln Kd* and l/T where Kd* and T are the equilibrium distribution coefficient (Cs adsorbed, meg g−1/Cs+ in solution, meq ml−1) and the temperature in kelvins, respectively. The slope of these plots decreases after removal of hydroxy Al interlayers with citrate pretreatment. Hydroxy Al interlayers thus make Cs+ adsorption more temperature dependent. This thermal effect of hydroxy Al interlayers becomes more significant in sediments containing a nonswelling 2:1–2:2 intergrade clay mineral than in those containing a swelling 2:1–2:2 intergrade clay mineral. The phenomenon is explained by considering hydroxy Al interlayers as a source of hydronium ions H3O+ which compete with Cs+ for exchange positions in wedge zones. An increase in temperature favors an increase in H3O+ ions, which in turn favors less adsorption of Cs+. Aside from their thermal effect the positively charged hydroxy aluminum polymeric groups drastically decrease the cation exchange capacity and consequently the adsorption of cesium.