Values Of Kb Research Articles

Individual Prior Information in a Physiological Model of 2H8‐Toluene Kinetics: An Empirical Bayes Estimation Strategy

Physiologically‐based toxicokinetic (PBTK) models are widely used to quantify whole‐body kinetics of various substances. However, since they attempt to reproduce anatomical structures and physiological events, they have ahigh number of parameters. Their identification from kinetic data alone is often impossible, and other information about the parameters is needed to render the model identifiable. The most commonly used approach consists of independently measuring, or taking fom literature sources, some of the parameters, fixing them in the kinetic model, and then performing model identification on a reduced number of less certain parameters. This results in a substantial reduction of the degrees of freedom of the model. In this study, we show that this method results in final estimates of the free parameters whose precision is overestimated. We then compared this approach with an empirical Bayes approach, which takes into account not only the mean value, but also the error associated with the independently determined parameters. Blood and breath 2H8‐ toluene washout curves, obtained in17 subjects, were analyzed with a previously presented PBTK model suitable for person‐specific dosimetry. Model parameters with the greatest effect onpredicted levels were alveolar ventilation rate QPC, fat tissue fraction VFC, blood air partition coefficient Kb, fraction of cardiac output to fat Qa/co and rate of extrahepatic metabolismVmax.p. Differences in the measured and Bayesian‐fitted values of QPC, VFc and Kb were significant (p < 0.05), andthe precision of the fitted values Vmax.p and Qa/co went from 11 ± 5% to 75 ± 170% (NS) and from 8 ± 2% to 9 ± 2% (p < 0.05) respectively. The empirical Bayes approach did not result in less reliable parameter estimates: rather, it pointed out that the precision of parameter estimates can be overly optimistic when other parameters in the model, eitherdirectly measured or taken from literature sources, are treated as known without error. In conclusion, an empirical Bayes approach to parameter estimation resulted in a better model fit, different final parameter estimates, and more realistic parameter precisions.

Interaction of chlorpromazine and trifluoperazine with ionic micelles: electronic absorption spectroscopy studies

The characteristics of binding of two phenothiazine antipsychotic drugs, namely, chlorpromazine (CPZ) and trifluoperazine (TFP), to cationic cetyltrimethylammonium chloride (CTAC), zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS), neutral t-octylphenoxypolyethoxyethanol (TRITON X-100) and polyoxyethylene dodecyl ether (Brij-35) micelles were investigated using electronic absorption spectroscopy. Binding constants Kb and pKa values of drugs in micelles were estimated using the red shifts of the maximum absorption upon alkalization or in the presence of detergents. The pKa of TFP seems to be shifted by 2.5–4.1 units to lower values in the presence of different surfactants as compared to the experimental value of pKa obtained in buffer which is around 7.0. Consideration of the second pKa around 4.0 reported in the literature for TFP leads to a better rationalization of pKa changes for this compound. The changes in pKa contributed by electrostatic effects are all positive, small for CTAC (+0.2), and greater for HPS (+0.9). For CPZ the pKa shift due to its interaction with micelles is in the 0.7–2.3 range, the direction of the shift depending on the charge of the polar head. The electrostatic contribution for the shift is great for CTAC (−0.8) and smaller for HPS (+0.2). This result suggests a more polar localization in the micelle of CPZ as compared to TFP. The values of binding constants Kb for TFP and CPZ in different protonation states show that electrostatic interactions are essential in the affinity of the drugs to micelles bearing different charges on their headgroups (CTAC, HPS). Data for Brij-35 demonstrate that the additional charge on the TFP ring at pH 2.0 leads to a decrease of binding constant probably due to the repulsion of the phenothiazine ring from the protons accumulated at the polar head of the micelle at acidic pH values. For this micelle at pH 5.0 TFP has a Kb 3-fold greater than that for CPZ while at pH 2.0 Kb for TFP is 3-fold less than that for CPZ. So, for more hydrophobic TFP electrostatic interactions due to protonation of the ring are quite important even considering its deeper penetration into the micelle interior as compared to CPZ.

Scintillation response of organic and inorganic scintillators

A method to evaluate the scintillation response of organic and inorganic scintillators to different heavy ionizing particles is suggested. A function describing the rate of the energy consumed as fluorescence emission is derived, i.e., the differential response with respect to time. This function is then integrated for each ion and scintillator (anthracene, stilbene and CsI(Tl)) to determine scintillation response. The resulting scintillation responses are compared to the previously reported measured responses. Agreement to within 2.5% is observed when these data are normalized to each other. In addition, conclusions regarding the quenching parameter kB dependence on the type of the particle and the computed values of kB for certain ions are included.

Binding of Nitrodiphenylamines to Reverse Micelles of AOT inn-Hexane and Carbon Tetrachloride: Solvent and Substituent Effects

The absorption spectra ofN-[2-(trifluoromethyl)-4-nitrophenyl]-4-nitroaniline (1),N-[4-nitrophenyl]-4-nitroaniline (2), andN-[2-nitrophenyl]-4-nitroaniline (3) were analyzed in reversed micelles of AOT (sodium 1,4-bis (2-ethylhexyl sulfosuccinate) inn-hexane and carbon tetrachloride. For 1 and 2 the intensity of the band characteristic for the pure solvent decreases as the AOT concentration increases and a new band develops. This new band is attributed to the solute bound to the micelle. These changes allowed us to determine the binding constant (Kb) between these compounds and AOT. Kb atW0= [H2O]/[AOT] = 0 inn-hexane varies from 81 for 1 to 5092 for 2. Although similar trends are observed for carbon tetrachloride, the values of Kb are smaller than those forn-hexane. The possible solute–solvent interactions of these compounds were analyzed by means of Taft and Kamlet's solvatochromic comparison method. The strength of binding is interpreted considering their hydrogen-bond donor ability as well as their solubility in the pure solvents. For 1 Kb decreases asW0is increased, while for 2 no variation was observed. These effects are discussed in terms of nitrodiphenylamine–water competition for interfacial binding sites. Moreover, the effect of the solute size and the presence of the trifluoromethyl group in 1 are important factors to consider in explaining its binding behavior. The spectra of 3 change very little with AOT concentration and only a slight bathochromic shift is observed. Thus, 3 acts as nonhydrogen bond donor solute, merely sensing a slight change in the polarity of its microenvironment.

Aerodynamic Interference for Hypersonic Missiles at Low Angle of Attack

An Euler code is used to predict the e owe eld over a hypersonic missile and to determine the carryover factors KW(B), e n liftinthepresenceofthebody,and KB(W),liftproducedby thebody in thepresenceofthee ns. Themissile is assumed to have cruciform, delta e ns in the + orientation and an aspect ratio of 1.529. Results are presented as a function of e n span at Mach 6, 8, and 10, for a 2-deg angle of attack. Two ratios of specie c heats, 1.4 and 1.3, are considered to partially account for vibrational excitation effects. Both carryover factors have approximately the same variation with e n size as their slender body predictions. The values of KW(B) and KB(W) are 2 for a missile without e ns. Thevalue of KW(B) decreases toward 1 and KB(W) decreases toward 0.20 as thee n span becomeslarge. At a e xed e n size, KW(B) decreases and KB(W) increases as Mach number increases. At a e xed value of e n size and Mach number, both KW(B) and KB(W) increase slightly due to vibrational excitation effects. Nomenclature AF = wing-planform area formed by two e ns joined at their root chord, m 2 AR = aspect ratio of wing formed by joining two e ns at their rootchord CN = normal force coefe cient referenced to AF CNC = normal force coefe cient of entire missile CNF = normal force coefe cient of e n alone CNF;® = normal force curve slope, e n alone CNFB = forebody-alone normal force coefe cient CNFB;® = normal force curve slope, forebody alone KB.W/ = body‐e n interference factor KW.B/ = en‐body interference factor L B.W/ = body lift in presence of e n, N LC = entire missile cone guration lift, N L F = e n-alone lift, N LFB = forebody-alone lift, N LW.B/ = e n lift in presence of body, N M = freestream Mach number P = local pressure/(freestream pressure ) q = freestream dynamic pressure, N/m 2

Biodegradation: Selection of Suitable Model

Biodegradation of five herbicides, two acetanilides (propanil and propachlor), and three phenylureas (diuron, monuron, and fenuron) was analyzed in samples of river water during a period of 6–8 weeks. Concentrations of 0.2–5.0 mg/liter of the herbicides were used for biodegradation. Two types of river water samples with different numbers of microorganisms were collected from the Neris River: upstream and downstream of the city of Vilnius. The initial concentration of microorganisms varied from 4.7×105to 2.7×106cells/liter and from 1.4×108to 5.3×108cells/liter in water samples from the Neris River upstream and downstream of Vilnius, respectively. Chemical analysis was performed by the HPLC technique, using standards of herbicides and likely degradation products. Chemical parameters of different river water samples used in biodegradation experiments were analyzed. A second-order reaction rate model was used for the analysis of biodegradation data. Values of the first-order rate constants (Ka) revealed the following decrease in the biodegradation rate of herbicides: propanil⪢diuron≥monuron=propachlor>fenuron. This sequence was constant for all water samples analyzed. The set of decreasing value of second-order biodegradation rate constants (Kb) differed from the set of first-order constants (Ka) because the total number of bacteria in the water samples varied by up to two orders of magnitude, and this variation influenced the calculated values ofKb. Thus, different sets ofKbvalues were obtained for the water samples from the river upstream and downstream of the city. Schemes of a variety of biodegradation models are presented, and the suitability of the second-order reaction rate model for the description of biodegradation of xenobiotics is discussed.

Binding of nitroanilines to reverse micelles of AOT n-hexane

The electronic absorption spectra of a series of nitroanilines: p-nitroaniline (pNA); o-nitroaniline (oNA); 2,4-dinitroaniline (dNA) and N,N-dimethyl-p-nitroaniline (N,NpNA) have been measured in solutions of sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT) in n-hexane at different W=[H 2O]/[AOT]. On increasing AOT concentration, it is observed that the characteristic absorption band of pNA, oNA and dNA in n-hexane decreases in intensity, and a new band develops at higher wavelength. A net isosbestic point is detected in every case. The spectral changes are interpreted as a consequence of an equilibrium between nitroaniline free and bound to AOT in the micellar system. These changes allowed us to determine the binding constant (Kb) between the nitroanilines and AOT. The values of Kb vary from 73 M −1 for oNA to 3370M −1 for dNA at W = 0. For N,NpNA only a shift of the absorption band in n-hexane is observed. The magnitude of the possible solute-solvent interactions of these compounds was analyzed by means of the Taft and Kamlet's solvatochromic comparison method. Thus, taking into account our studies in pure solvents, the strength of binding is interpreted considering their polarity and hydrogen-bond donor ability as well as their solubility in n-hexane. The binding of oNA to AOT shows a decrease in Kb followed by a plateau value as W is increased. For pNA and dNA, which have large values of Kb, no variation is observed as W is increased. This effect is discussed in terms of a competition between the nitroaniline and water for interfacial binding sites. In addition the absorption maxima of the free nitroaniline tends toward that on hexane (hypsochromic shift) when increasing the water concentration and mainly for oNA, indicating that water competition for the hydrogen bond acceptor sites of AOT is greater for the weaker bounded nitroaniline. The absorption maxima of the bound nitroanilines shifts bathochromically on water addition as expected for the increasing polarity of the micellar interface.

Sensible heat flux and radiometric surface temperature over sparse Sahelian vegetation. I. An experimental analysis of the kB−1 parameter

Estimating the sensible heat flux H over sparse vegetation from thermal infrared temperature requires an estimate of the excess resistance r r to the aerodynamic resistance. This excess resistance has been commonly expressed as a function of the dimensionless parameter kB −1. Experimental analysis of this parameter over diverse sparse vegetation in semi-arid areas showed a large and unexpected range of variation. The flux and ground-based thermal infrared data of the East Central Site of HAPEX-Sahel were used in this paper to study the behaviour of the kB −1 parameter and to compare these results with the conclusions of previous studies. At first, the global accuracy of the estimation of H as a function of the kB −1 value was analysed; it was found that overestimating kB −1 has less serious consequences than underestimating it. Then, optimal values of kB −1, obtained for each site (one fallow savannah site and two millet sites), ranged from 5.1 to 10.2, with significantly different values for the two millet sites. The corresponding Root Mean Square Error (RMSE) between estimated and measured H ranged from 43 to 67 W m −2. Finally, the instantaneous values of kB −1 proved to be highly variable and the parameterization of kB −1 proposed by Kustas et al. (1989) as a function of u( T r − T a ) appeared valid only for high H values. For lower values, the slope of this relationship must be adjusted for each class of H. All the previous results confirmed that a constant value can neither be assumed for semi-arid areas nor for a given type of vegetation and that further studies are needed to understand its behaviour. Considering the difficulty in predicting the kB −1 values, a different approach based on the relationship observed between aerodynamic and radiometric temperatures was investigated. This approach gave more accurate estimate of H ( RMSE between 35 and 48 W m −2), but remains at this stage purely empirical. Further investigation is now needed to predict the parameterization of this approach.

A kinetic study of the reaction between boldine and singlet oxygen [O2(1ωg)

The sensitized photo-oxidation of boldine and its permethylated derivative, glaucine, has been studied in several solvents using steady-state kinetic methods. Values of kB, the total rate constant for the reaction between boldine and O2(1ωg), vary from 3.44 × 107M-1 s-1 in benzene to 150.00 × 107M-1 s-1 in water. For glaucine, similar values were determined. Quenching is faster in solvents with high capacity to stabilize a charge or dipole (higher π* parameter values). From these results, a charge-transfer quenching mechanism, to account for the interaction between boldine and O2(1Δg), is proposed. Rate constants for the chemical reaction are at least two orders of magnitude smaller than the total rate constants, which also show a large dependence on the π* parameter. This last result can be explained in terms of a more polar transition state leading to products.

USING CURVE NUMBERS TO DETERMINE BASELINE VALUES OF GREEN‐AMPT EFFECTIVE HYDRAULIC CONDUCTIVITIES1

ABSTRACT: Since the trend in infiltration modeling is currently toward process‐based approaches such as the Green‐Ampt equation, more emphasis is being placed on methods of determining appropriate parameters for this approach. The SCS curve number method is an accepted and commonly used empirical approach for estimating surface runoff, and is based on numerous data from a variety of sources. The time and expense of calibrating process‐based infiltration parameters to measured data are often prohibitive. This study uses curve number predictions of runoff to develop equations to estimate the “baseline” hydraulic conductivities (Kb) for use in the Green‐Ampt equation. Curve number predictions of runoff were made for 43 soils. Kb values in the Water Erosion Prediction Project (WEPP) model were then calibrated so that the annual runoff predicted by WEPP was equal to the curve number predictions. These calibrated values were used to derive an equation that estimated Kb based on the percent sand, percent clay, and cation exchange capacity of the soil. Estimated values of Kb from this equation compared favorably with measured values and values calibrated to measured natural runoff plot data. WEPP predictions of runoff using both optimized and estimated values of Kb were compared to curve number predictions of runoff and the measured values. The WEPP predictions using the optimized values of Kb were the best in terms of both average error and model efficiency. WEPP predictions using estimated values of Kb were shown to be superior to predictions obtained from the curve number method. The runoff predictions all tended to be biased high for small events and low for larger events when compared to the measured data. Confidence intervals for runoff predictions on both an annual and event basis were also developed for the WEPP model.

Ligand-induced biphasic thermal denaturation of RNAase A

DSC measurements have been accomplished in aqueous solutions of bovine pancreatic ribonuclease A (RNAase A) in the presence of subsaturating amounts of 3′ cytidine monophosphate (3′ CMP) and 2′ cytidine monophosphate (2′ CMP) atpH 5.0 and 5.5. In these conditions the experimental profiles do not conform to a one-step unfolding process. It can be emphasized, as a general phenomenon, that a strong linkage between the temperature-induced protein unfolding and the ligand binding, when the ligand is less than the saturation level, causes marked distortions from a two-state transition. A purely equilibrium thermodynamic analysis gives a correct account of this behaviour and allows to simulate calorimetric curves. It is thus possible to obtain, in an indirect manner, information about the thermodynamic parameters concerning the binding process, namely the association constant and the binding enthalpy. The values ofKb and ΔbH for 3′CMP and 2′CMP, so determined, are consistent with the literature data.

Modulation of PRM Activity by the Lambda PR Promoter in Both the Presence and Absence of Repressor

When the transcription startsites of the phage lambda promoters PRM and PR are separated by 82 bp (the wild-type spacing), mutating PR increases the rate of open complex formation at PRM at all RNA polymerase (RNAP) concentrations tested in vitro. This is reflected in a fourfold increase in kf (the rate constant for isomerization of closed to open complexes) and a threefold decrease in KB (the equilibrium constant for formation of closed complexes). These effects of mutating PR resemble qualitatively those we observed when the separation between the two promoters was decreased by a single base-pair, but are quantitatively less dramatic. Although mutating PR has the additional effect of uncovering a weak promoter, Pα , which overlaps both PRM and PR , the presence of Pα does not account for the effects of PR mutations on open complex formation at PRM.In fixed-time assays at a single RNAP concentration, repressor stimulated PRM approximately threefold on a P-R template, indicating that activation is mediated substantially by a direct interaction between repressor and RNAP. That is, activation of PRM is not merely an indirect consequence of repressing PR. Kinetic data confirm this conclusion. In a P-R genetic backgound, repressor increased kf six- to eightfold and decreased KB approximately twofold. Similar results were obtained when OR3 was mutated, indicating that the effect on KB is not due to repressor binding to OR3. Thus, repressor causes a significant increase in the rate of open complex formation at PRM even when PR is inactive.On a P+R template, 75 nM repressor stimulated PRM by increasing kf eightfold, with no effect on KB, which agrees with previous results. However, increased repressor concentrations stimulated kf by an additional factor of two to four, indicating that previous experiments underestimated the effect of repressor on kf. At the same time, increasing the repressor concentration decreased KB for PRM on a wild-type template. At the highest repressor concentration tested (275 nM), KB decreased 15-fold, presumably due to OR3-mediated repression of PRM . However, at an intermediate repressor concentration (170 nM) values of kf and KB for PRM on a P+R template were in close agreement with the corresponding parameters obtained on a P-R template. These data lead us to suggest that repressor causes a decrease in KB for PRM on both a P+R and a P-R template independent of its ability to bind to OR 3.

A voltammetric study of the kinetics of the hexacyanomanganate(III) disproportionation in acidic medium

The fast disproportionation of hexacyanomanganate(III) in acidic medium yields Mn(CN)62− and Mn(H2O)62+. The reaction has been studied by amperometry, with a rotating platinum-disk electrode, at a 1.0 V (vs. SCE) constant potential, in the acidity range 0.01–2.0 M and at temperatures between −5 and 15 °C. A reversible one-electron process takes place with a 0.85 V (vs. SCE) half-wave potential that is not dependent on acidity. The reaction kinetics is pseudo-first order in [Mn(CN)63−] and the rate constant depends on acidity according to the equation: kobs = ka + kb[H3O+] + kc[H3O+]2. At 5 °C and ionic strength 2.0, the determined values of ka, kb, and kc were (2.20 ± 0.08) × 10−3 s−1, (4.9 ± 0.2) × 10−3 s−1 M−1 and (1.40 ± 0.10) × 10−3 s−1 M−2, respectively. A mechanism is proposed where the three terms of kobs are assigned to pathways involving hexacyanomanganate(III) in three different states of protonation. From the effect of temperature the activation parameters, ΔH≠ and ΔS≠, for each pathway are also reported.Key words: hexacyanomanganate(IV), disproportionation, kinetics, amperometry, rotating platinum-disk electrode.

Slow upward drift of VO2 during constant-load cycling in untrained subjects.

The oxygen uptake kinetics during constant-load exercise when sitting on a bicycle ergometer were determined in 7 untrained subjects by measuring breath-by-breath VO2 during continuous exercise to volitional exhaustion (mean endurance time = 1160 +/- 172 s) at a pedal frequency of 70 revolutions.min-1. The power output, averaging 189.5 W, was set at 82.5% of that eliciting the individual VO2max during a 5 min incremental exercise test. Throughout the exercise period, the VO2 kinetics could be appropriately described by a two-component exponential equation of the form: VO2(t) = Ya[1 - exp(-kat)] + Yb[1 - exp(-kbt)] where VO2 is net oxygen consumption and t the time from work onset. VO2 measured at the end of exercise was close to VO2max (98% VO2max) and the mean values of Ya, ka, Yb and kb amounted to 1195 ml O2.min-1, 0.034 s-1, 1562 ml O2.min-1, and 0.005 s-1 respectively. The initial rate of increase in VO2 predicted from the above equation is slower than that calculated, for the same work intensity, on the basis of the data obtained by Morton (1985) in trained subjects. For t greater than 480 s, however, the two models yield substantially equal results.

ChemInform Abstract: Kinetics of the Reactions of NO3 Radicals with Cl and ClO.

AbstractThe kinetic behavior of NO3 (of interest in atmospheric chemistry) and ClO, observed in the modulated photolysis of Cl2‐ClONO2‐N2 mixtures at 1 atm pressure and in the temp. range 278‐338 K, is consistent with the occurrence of reactions A and B. The values of kA and kB are determined to be 5.5·10‐11 independent of temp. and 1.6·10‐12 exp(‐420/T) cm3 molecule‐1 s‐1 respectively.

Triazene drug metabolites. Part 6. The interaction of N-hydroxymethyl-triazenes with lanthanide-induced shift reagents

Paramagnetic induced chemical shifts were obtained for a series of 1-aryl-3-hydroxymethyl-3-methyltriazenes and related compounds by the addition of Pr(thd)3 or Eu(fod)3. Induced shifts were shown to be pseudo-contact in origin. Qualitative work using Pr(thd)3 inducated that the N–CH2–O proton resonances are shifted the most, followed by the N–Me resonances. Neither 1-aryl-3-methyl-nor 1-aryl-3,3-dimethyl-triazenes exhibit induced shifts of the N–Me resonances, which indicates that binding of the hydroxymethyltriazenes to the lanthanide ion occurs through the hydroxyl function. Quantitative work using Eu(fod)3 allowed values of ΔB, the paramagnetic shift of the bound hydroxymethyltriazene, and KB, the equilibrium binding constant, to be calculated. The data are consistent with 1 : 1 complex formation and values of KB, which lie between 10–60 l mol–1, are little affected by the aromatic substituent. Correlation of the pseudo-contact induced shifts, ΔB, with r3(where r is the distance between the resonating nucleus and the Eu3+ ion) occurs when the hydroxymethyltriazene is assumed to bind to Eu3+ through the hydroxyl oxygen atom. In contrast, 3-hydroxymethyl-3-methyl-1-(3′-pyridyl)triazene binds to both Pr3+ and Eu3+ through the pyridyl nitrogen atom.

A Study of the Flexural Rigidity of Annular Flanged Connections

In order to analyze the vibration of a structure whose elements are connected with bolts, it is necessary to estimate the flexural rigidity of bolted connections. But, although a few papers have reported studies of flexural rigidity, a calculation method to estimate the flexural rigidity has remained unestablished. This paper deals with a calculation method to estimate the flexural rigidity of bolted annular flange connections subjected to an external bending moment. In the analysis, models for estimating the flexural rigidity Kb of bolts, and Kf of annular flanges are proposed, taking account of the dispersiveness of bolt disposition. Thus, a calculation method for obtaining whole flexural rigidity of bolted flange connections is proposed, using the values of Kb and Kf. For verification, experiments are performed under several conditions. Calculated results are in a fairly good agreement with experimental ones.

A study of the flexural rigidity of annular flanged connections.

In order to analyze the vibration of a structure whose elements are connected with bolts, it is necessary to estimate the flexural rigidity of bolted connections : But, although a few papers have reported studies of flexural rigidity, it remains to establish a calculation method for flexural rigidity. This paper deals with a calculation method to estimate the flexural rigidity of bolted annular flanged connections subjected to an external bending moment. In the analysis, models for estimating the flexural rigidity Kb of bolts, and of annular flanges Kf are proposed, taking account of the dispersiveness of bolt disposition. Thus, a calculation method for obtaining whole flexural rigidity of bolted flanged connections is proposed, using the values of Kb and Kf For verification, experiments are performed under several conditions. Calculated results are in a fairly good agreement with experimental ones.

Kinetics and Equilibrium Studies on the Anation Reactions in Pentakis(dimethyl sulfoxide)dioxouranium(VI) and Tetrakis(hexamethylphosphoric triamide)dioxouranium(VI) Ions in Nonaqueous Media

Abstract The anation reactions in [UO2(dmso)5]2+ (dmso=dimethyl sulfoxide) and [UO2(hmpa)4]2+ (hmpa=hexamethylphosphoric triamide) ions by SCN− and N3−have been studied by the stopped-flow method in DMSO and acetonitrile. For the anation reactions of [UO2(dmso)5]2+ in DMSO as a medium, the pseudo-first order rate constant(kobsd) is expressed by kobsd={k−1+(k1+k−1)×Kos[X]}/(1+Kos[X]), where X=SCN− and [UO2(dmso)5]2+ for the anation reactions by SCN− and N3−, respectively. The values of k1, k−1, and Kos at 25 °C are 2.06×102 s−1, 62 s−1, 35 M−1 (M=mol dm−3), and 7.60×102 s−1, 0.0 s−1, and 41 M−1 for the SCN− and N3− anation reactions in [UO2(dmso)5]2+, respectively. For the anation reaction in [UO2(hmpa)4]2+ by SCN−, the pseudo-first order rate constant was found to be proportional to the concentrations of [UO2(hmpa)4]2+ and free HMPA: kobsd=kf[UO2(hmpa)42+]+kb[HMPA]free. The values of kf and kb at 25 °C are 9.70×103 M−1 s−1 and 9.05×102 M−1 s−1, respectively. The equilibrium constants for the titled reactions were also measured at 25 °C: K=85 M−1for the anation reaction of [UO2(dmso)5]2+ by SCN− in DMSO and K’=42.7 for the SCN− anation reaction in [UO2(hmpa)4]2+ in acetonitrile. The kinetic results suggest that the anation reactions in uranyl complexes proceed through an associative or an associative interchange mechanism.

Thermal Conductivity of Rare‐Earth Orthoferrites at Reorientation Phase Transitions

AbstractThe dependence of thermal conductivity on temperature is measured for the first time for three compositions of rare‐earth orthoferrites (REO): SmFeO3, Sm0.4Gd0.4FeO3, and Sm0.65Er0.15Tb0.2· ·FeO3 in the spin reorientation region (SRR). Characteristic anomalies are found on curves λ(T) at temperatures of reorientation phase transitions. Presence and form of the anomalies are associated with the summary effect of the changes of the specific heat, averaged free‐path length of phonons, and their averaged velocity of propagation. The behaviour of the averaged velocity of the phonon propagation at magnetic phase transitions is studied on the basis of the temperature dependence of the velocity of the shear sound wave. An interpretation is given by using the phenomenological model conformably to the case of REO. The values of the four‐fold anisotropy Kb = 7.97 × 103 J/m3 and magnetoelastic coupling B55 = 4.472 × 106 J/m3 constants are estimated for the compound Sm0.6Gd0.4FeO3. The temperature dependence of two‐fold anisotropy constant Ku(T) in the spin‐reorientation region and its ranges are calculated by way of example of a samarium–gadolinium orthoferrite.