Showing papers on "Equilibrium constant published in 1975"
TL;DR: Comparing biological activities of con jugated carbonyls their reactivity towards HS (k1) and the stability of the adducts must be considered and the equilibrium constants as well as the rate constants for forward and reverse reaction show an extreme variation depending on the carbonyl structure.
Abstract: 1. GSH reacts with conjugated carbonyls according to the equation: GSH+R-CH=CH-COR in equilibrium R-CH(SG)-CH2-COR. The forward reaction follows second order, the reverse reaction first order kinetics. It is assumed that this reaction reflects best the ability of conjugated carbonyls to inactivate SH groups in biological systems. 2. The rate of forward reaction increases with pH approx. parallel with alphaSH. Besides OH- ions also proton donors (e.g. buffers) increase the rate. The catalytic effect of pH and buffer is interpreted in view of the reaction mechanism. 3. The equilibrium constants as well as the rate constants for forward (k1) and reverse reaction show an extreme variation depending on the carbonyl structure. Acrolein and methyl vinyl ketone (k1 = 120 and 32 mol-1 sec-1, resp.) react more rapidly than any other carbonyl to give very stable adducts (half-lives for reverse reaction 4.6 and 60.7 days, resp). Somewhat less reactive are 4-hydroxy-2-alkenals and 4-ketopentenoic acid (k1 between 1 and 3 mol-1 sec-1), but they also form very stable adducts showing half-lives between 3.4 and 19 days. All other carbonyl studied react either very slowly (e.g. citral, ethly crotonate, mesityl oxide, acrylic acid) or form very labile adducts (crotonal, pentenal, hexenal, 3-methyl-butenone). Comparing biological activities of conjugated carbonyls their reactivity towards HS (k1) and the stability of the adducts must be considered.
240 citations
TL;DR: The cooperative formation of actin filaments from monomers was followed by light scattering and electron microscopy and a best fit of the model to the experimental data is achieved when the destruction of a dimer is much faster than the addition of a third protomer.
237 citations
TL;DR: The reaction product is proven to be a hydroxymethyl group and a reaction mechanism is proposed, and some implications of these results forpolynucleotide studies are discussed.
Abstract: A comprehensive description is given of both the equilibrium and the kinetic aspects of the reaction of formaldehyde with the exocyclic amino groups of derivatives of adenine, cytosine, and guanine; the results extend previous data in the literature to the point where formaldehyde can now be used as a quantitative probe of DNA structure and dynamic behavior. The main results are: (i) the reaction product is proven (by isolation followed by nuclear magnetic resonance (NMR) spectroscopy) to be a hydroxymethyl group; (ii) a dihydroxymethyl adduct is shown to exist at high formaldehyde concentrations; (iii) equilibrium constants at 25 degrees for forming the monoadduct with adenine and cytosine compounds are about 12 (M-1), while those for forming the dihydroxymethyl adduct are about 0.4 (M-1); (iv) the standard enthalpies for forming the monoadducts with adenine and cytosine compounds are about minus 4 to minus 6 kcal/mol; (v) indirect evidence is presented suggesting that a monohydroxymethyl group on adenine or cytosine derivatives exists preferentially as that rotational isomer which blocks Watson-Crick hydrogen bonding; (vi) in derivatives of guanine, it is shown that the N-1 endocyclic imino group can react with formaldehyde, as well as the amino group, the overall equilibrium constant being about 6 (M-1); (vii) all rate constants are reported, as well as their response to temperature, pH, and various solvent additives known to perturb DNA structure; (viii) using a series of substituted anilines, a linear free energy relation is obtained between the logarithm of both the forward and the reverse rate constant for the formaldehyde reaction and the amine pK, over a range of 10-8 change in amie basicity; (ix) using this relation, the pK's for protonating the nucleoside amino groups are estimated to lie in the range of minus 2 to minus 4; (x) a reaction mechanism is proposed; and (xi) some implications of these results forpolynucleotide studies are discussed.
212 citations
TL;DR: In this article, the equilibrium constants for hydrate-hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3
Abstract: Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3;...
158 citations
TL;DR: In this paper, the authors investigated the hydrolysis behavior of iron(III) in light and heavy water at 25°C and ionic strength 0·10, using ultraviolet spectrophotometry.
122 citations
TL;DR: Calculations presented in the Appendix indicate that the transition is better represented by a model in which terminal base-pair fraying and intermediate states are taken into account, and it is better to use a sloping rather than a flat low-temperature baseline to evaluate absorbance versus temperature profiles.
115 citations
TL;DR: This paper summarized results of many experimental investigations of the thermodynamics of ionization of H2O(liq.) from 0-300°C and from 1.0 atm to nearly 8000 atm.
Abstract: We have summarized results of many experimental investigations of the thermodynamics of ionization of H2O(liq.) from 0–300°C and from 1.0 atm to nearly 8000 atm. Results of these investigations (equilibrium constants, enthalpies of ionization, heat capacities, partial molal volumes, and compressibilities) have been used for a number of thermodynamic calculations. It is particularly noteworthy that it is possible to use thermal data from 0–145°C with an equilibrium constant for 25°C in calculating reasonably accurate equilibrium constants for temperatures as high as 300°C. Similarly, it is possible to use volumetric data that refer to 1.0 atm in calculating useful equilibrium constants that apply for pressures as high as 2000 atm.
103 citations
TL;DR: In this article, the authors give a chart mostly useful for heating and cooling Mn-Zn-ferrites with a constant oxidation degree, which has five different scales : a logarithmic one for PO 2 (arm), temperature (I/T), scales for Fe 2 O 3 and MnO contents (mole %), and another one for the oxidation degree.
Abstract: We give a chart mostly useful for heating and cooling Mn-Zn-ferrites with a constant oxidation degree. This chart has five different scales : a logarithmic one for PO 2 (arm), temperature (I/T), scales for Fe 2 O 3 and MnO contents (mole %) and another one for the oxidation degree. In the composition range given, with fixed values of PO 2 and T, the accuracy is better than an absolute error of ± 0.1 weight % Fe2+which corresponds to an absolute error of ± 0.002 for the parameter γ. We emphasize the care that must be taken to reach a real equilibrium due to the existence of a phase boundary and of metastable region. This chart has been calculated using two equilibrium constants derived from our experimental studies. Experimentally, the curves log PO 2 = f(1/T) are straight lines with the same slope whatever the composition. This slope corresponds to the enthalpy of transfer of one mole oxygen from the solid phase to the gas phase (ΔH= 66.5 Kcal.)
101 citations
TL;DR: Theory is presented in relation to sedimentation equilibrium results obtained with polymerizing systems, which permits evaluation of the activity of the monomer as a function of total weight concentration, which avoids errors inherent in differentiation and integration steps.
88 citations
85 citations
TL;DR: In this paper, the affinity of the neutral cyclic polyether dibenzo-18-crown-6 dissolved in various nitrobenzene-toluene mixtures has been studied.
TL;DR: The sensitivity is sufficient to permit determination of 13C and 15N isotope effects in favorable cases, and values of 1.031 for malic enzyme with 13CO2, and 1.047 for glutamate dehydrogenase with 15NH4+ have been determined.
Abstract: When malic enzyme is added to a mixture of malate-2-d, TPN, CO2, pyruvate, and TPNH at concentrations calculated to be at equilibrium, the TPNH level first drops and then increases slowly to its original level. This equilibrium perturbation is caused by slower cleavage of C-D than C-H bonds during hydride transfer as malate-2-d and TPNH are partly converted into TPND and malate-2-h in the process of establishing isotopic equilibrium. With malate-2-d, isotope effects for malic enzyme at pH 7.1 and malate dehydrogenase at pH 9.3 of 1.45 and 1.70-2.16 (depending on oxaloacetate level) were determined with this method, while the corresponding isotope effects on V/Kmalate and V for the chemical reactions were 1.5-1.8 and 1.0, and 1.9 and 1.5 for the two enzymes. The advantage of this method is its extreme sensitivity, and the lack of interference from various artifacts. The sensitivity is sufficient to permit determination of 13C and 15N isotope effects in favorable cases, and values of 1.031 for malic enzyme with 13CO2, and 1.047 for glutamate dehydrogenase with 15NH4+ have been determined. In the course of this work it was discovered that the equilibrium constants for oxidation by DPN, and oxidative decarboxylation by TPN are lower for malate-2-d than for malate-2-h by a factor of 0.76-0.82. Changes in Keq upon deuterium substitution, which are predicted by the calculations of Hartshorn and Shiner (1972), should be observed for many other reactions as well.
TL;DR: In this article, the drift tube-mass spectrometer apparatus was used to determine the equilibrium constant K and the forward rate coefficient k+ for the clustering reaction NO++N2+N2?NO+⋅N2 +N2.
Abstract: Drift tube–mass spectrometer apparatus have been used to determine the equilibrium constant K and the forward rate coefficient k+ for the clustering reaction NO++N2+N2?NO+⋅N2+N2. The values of K are 2×10−16, 1.5×10−18, and ?5×10−19 cm3 at 130, 180, and 220 K, respectively, with an estimated uncertainty of ∼50%. The values of k+ are 8×10−30 and ?10−30 cm6/sec at 130 and 220 K, respectively, with an estimated uncertainty of ∼30%. The energy of the NO+–N2 bond deduced from the equilibrium constant data is Eb=0.18±0.02 eV. These results are compared with other measurements, and implications for proposed D‐region reaction paths linking NO+ and H3O+⋅ (H2O)n ions are discussed.
TL;DR: In this article, the rate constants for electron transfer reactions of organic systems in aqueous solutions and their equilibrium constants are examined for possible correlation by the Marcus theory, if a reorganization parameter, λ, of 18 kcal/mole is used.
TL;DR: The concentration and temperature dependence of the self-association of ademosin-5'-triphosphate (ATP) in aqueous solution was studied by means of ultraviolet absorption spectroscopy and circular dichroism: it is interpreted as a first approximation within the framework of the exciton model.
TL;DR: That the same value of delta V, 90 ml/mol, was estimated from both the majority of the spindle BR data and data for the assembly of neural microtubules in vitro supports the possibility that spindlemicrotubules are assembled by a nucleated condensation mechanism.
Abstract: The present experiments were designed to test whether the simple equilibrium assembly model proposed by Inoue could predict variations in spindle microtubule assembly in response to changes in hydrostatic pressure as it does for changes in temperature. The results were also analyzed according to a model based on nucleated condensation polymerization since this recently appears to be the mechanism by which purified brain microtubules are assembled in vitro. Equilibrium birefringence (BR) of the meiotic metaphase-arrested spindle was measured in vivo as a function of hydrostatic pressure and temperature in Chaetopterus oocytes using a miniature microscope pressure chamber. Increasing pressure in steps to 3,000 psi at temperatures below 22 degrees C did produce decreases in spindle equilibrium BR predictable directly from the simple equilibrium model of spindle assembly. Thermodynamic analysis of the pressure data yielded a value of delta V congruent to 400 ml/mol of polymerizing unit. Theoretical curves based on the nucleated condensation model can also be made to fit the data, but semilog plots of the dependence of the equilibrium constant versus pressure and versus reciprocal temperature are biphasic, suggesting that either the size of the polymerizing unit changes or more than one equilibrium constant governs the assembly reaction. That the same value of delta V, 90 ml/mol, was estimated from both the majority of the spindle BR data and data for the assembly of neural microtubules in vitro supports the possibility that spindle microtubules are assembled by a nucleated condensation mechanism.
TL;DR: The equilibrium activities and concentrations of N chemical species in a multicomponent system may be calculated given M independent equilibrium constants relating these species and N -M mass balances as discussed by the authors, where initial concentration estimates are poor or the number of species large.
TL;DR: The chemical form of the potassium promoter on an iron-alumina catalyst during ammonia synthesis has been studied by two methods, viz, (i) the measurement of the equilibrium constant of the process KNH2 + H2 KH + NH3, and (ii) chemical analysis of the used catalyst.
TL;DR: In this article, the roles of excess vibrational energy in H3(+) ions and of equilibrium between forward and back reactions are discussed, and an equilibrium constant of 2.0 (plus or minus 0.4) at 298 K has been determined.
TL;DR: In this paper, the authors show that the equation mentioned above can also be applied to the system including salt, and they also show that it is possible to obtain the salt effect in the case of methanol-ethanol-water mixture.
Abstract: In a system accompanied by hypothetical chemical reaction vapor-liquid equilibrium ratio, Ki, of component i has been expressed by logKi=-Ai/T+Biwhere T is the absolute temperature, Ai is a constant determined by reaction system and component i, and Bi is a constant determined from vapor-liquid equilibrium data for the liquid composition at conversion 0 and/or 1. The object of this paper is to show that the equation mentioned above can also be applied to the system including salt. Following two systems are herein discussed: i-propanol-M-propanoI-calcium chloride methanol-ethanol-water-calcium chloride In these systems Ai implies the salt effect, but its behavior was not definitely observed.
TL;DR: In this article, equilibrium constants have been derived for reactions of the type M2++Cl−⇌MCl+ using aqueous solutions of the corresponding metal perchlorates as the reaction media (M=Mn, Co, Ni, and Zn).
Abstract: Equilibrium constants have been determined both potentiometrically and spectrophotometrically for reactions of the type M2++Cl−⇌MCl+ using aqueous solutions of the corresponding metal perchlorates as the reaction media (M=Mn, Co, Ni, and Zn). The variation in the quotient of the activity coefficients of these reactions with increasing molality of the reaction medium has been found to be approximately the same for the CuCl+ (previously studied), MnCl+, and ZnCl+ complexes, while a different dependence is observed for the CoCl+ and NiCl+ complexes. The results are interpreted as indicating equilibrium coexistence of the [MCl(OH2)5]+ and {[M(OH2)6]Cl}+ species in the latter two cases. Approximate values of the corresponding equilibrium constants are estimated in addition to the derived overall thermodynamic stability constants of the MCl+ formal complexes. The latter are found to follow a partly inverted Irving-Williams series, the fact being accountable in terms of the ligand field stabilization energy.
TL;DR: The forward and reverse rates of the reaction CO2 + e− CO2− were determined in tetramethylsilane, neopentane and 2,2,4-trimethylpentane as a function of temperature as mentioned in this paper.
TL;DR: The observed equilibrium constant (Kobs) for the reaction of choline acetyltransferase (EC 2.3.1.6) has been determined under physiological conditions and has been found to be insensitive to variations in ionic strength.
TL;DR: In this paper, the total pressure for the system of isopropanol and water was measured in a temperature range from 35 to 75°C by using a modified Othmer recirculation still.
Abstract: Total pressure for the system of isopropanol and water was measured in a temperature range from 35 to 75°C by using a modified Othmer recirculation still. The vapor-liquid equilibrium was calculated from the total pressure-composition data by using the numerical method of Barker. Simultaneous fitting of the excess Gibbs energy and the excess enthalpy data was successfully done by using the Wilson equation.
TL;DR: In this paper, the ADO theory appears to predict results which agree within 40% with experiments for proton transfer reactions to neutral molecules which have permanent dipole moments from zero to 2.
TL;DR: The kinetics of hydride transfer from NADH to aromatic aldehydes and from aromatic alcohols to NAD+ as a function of pH is investigated and is consistent with base-catalyzed removal of a proton from alcohol substrated and consequent acid catalysis of protonation of a zinc-alcoholate complex.
Abstract: New transient kinetic methods, which allow kinetics to be carried out under conditions of excess substrate, have been employed to investigate the kinetics of hydride transfer from NADH to aromatic aldehydes and from aromatic alcohols to NAD+ as a function of pH The hydride transfer rate from 4-deuterio-NADH to beta-naphthaldehyde is nearly pH independent from pH 60 to pH 99; the isotope effect is also pH independent with kappa-H/kappaD congruent to 23 Likewise, the rate of oxidation of benzyl alcohol by NAD+ changes little with pH between pH 875 and pH 59; the isotope effect for this process is between 30 and 44 Earlier substituent effect studies on the reduction of aromatic aldehydes were consistent with electrophilic catalysis by either zinc or a protonic acid The pH independence of hydride transfer is consistent with electrophilic catalysis by zinc since such catalysis by protonic acid (with a pK between 60 and 100) would show strong pH dependence However, protonic acid catalysis cannot be excluded if the pKa of the acid catalyst in the ternary NADH-E-RCOH complex were smaller than 60 or smaller than 100 The two kinetic parameters changing significantly with pH are the kinetic binding constant for ternary complex formation with aromatic alcohol and the rate of dissociation of aromatic alcohols from enzyme This is consistent with base-catalyzed removal of a proton from alcohol substrated and consequent acid catalysis of protonation of a zinc-alcoholate complex The equilibrium constant for hydride transfer from benzaldehyde to benzyl alcohol at pH 875 is K-eq equals kappa-H/kappa-H equals 42; this constant has important consequences concerning subunit interactions during liver alcohol dehydrogenase catalysis
TL;DR: In this article, Pappis and Kingery interpreted the conductivity measurements of iron-doped a-Al2O3 with a model in which ionic defects are the major defect species, leading to equilibrium constants for the establishment of non-stoichiornetry in Al2O 3 and for the oxidation-reduction of divalent to trivalent iron.
Abstract: Conductivity measurements of iron-doped a-Al2O3 by Pappis and Kingery are interpreted on the basis of a model in which ionic defects are the major defect species. The analysis leads to equilibrium constants for the establishment of non-stoichiornetry in Al2O3 and for the oxidation-reduction of divalent to trivalent iron, and to the position of the electronic level of Fe2+ (=FeA1′) in the gap at Er+ 3.66 eV.
TL;DR: Theoretical potential profiles for Ar, Kr, and Xe occluded in an idealized 5A zeolite are calculated and used to evaluate the Henry's law equilibrium constants for these species as mentioned in this paper.
Abstract: Theoretical potential profiles for Ar, Kr, and Xe occluded in an idealized 5A zeolite are calculated and used to evaluate the Henry's law equilibrium constants for these species. Calculations were ...
TL;DR: The kinetics of oxidation of oxymyoglobin by FeCDTA- were studied and the data are consistent with a mechanism where oxidation takes place entirely through the deoxy form.
Abstract: The reduction of metmyoglobin by the iron(II) complex of trans-1,2-diaminocyclohexane-N,N,N'N'-tetraacetate (FeCDTA2-) has been investigated. The equilibrium constant, measured spectrophotometrically, is 0.21 with a resulting reduction potential of 0.050 V for Mb0. The rate constant for the reduction is 28 M-1 sec-1 with a deltaH ++ of 13 kcal M-1 and deltaS ++ of -11 eu. Both CN- and OH- inhibit the reduction because of the relatively low reactivity of cyanometmyoglobin (Mb+CN-) and ionized metmyglobin (Mb+OH-). The rate constant for the reduction of Mb+CN- by FeCDTA2- is 4.0 X 10(-2) M-1 sec-1 and that for reduction of Mb+OH- is 4.8 M-1 sec-1. The nitric oxide complex of metmyoglobin is reduced with a rate constant of 10 M-1 sec-1. The kinetics of oxidation of oxymyoglobin by FeCDTA- were studied. The data are consistent with a mechanism where oxidation takes place entirely through the deoxy form. A rate constant of 1.45 X 10(2) M-1 sec-1 was calculated for the oxidation of deoxymyoglobin by FeCDTA-, in equilibrium constant and rate constant for reduction. The above data are discussed in terms of a simple outer-sphere reduction reaction.