Mechanistic Information on the Aquations of Complexes of the Pentaamminecobalt(III) Series from Kinetic Studies at High Pressures

1972 ◽  
Vol 50 (17) ◽  
pp. 2739-2746 ◽  
Author(s):  
W. E. Jones ◽  
L. R. Carey ◽  
T. W. Swaddle
Keyword(s):  
High Pressures ◽  
Rate Coefficient ◽  
Kinetic Studies ◽  
Quadratic Equation ◽  
Water Molecules ◽  
First Order ◽  
Unit Slope ◽  
Straight Line ◽  
The Mean ◽  
The Stability

The logarithm of the pseudo-first-order rate coefficient k for the aquation of Co(NH3)5X(3–n)+ can be represented by a quadratic equation in the pressure P, or, better, by[Formula: see text]where P is in kbar, [Formula: see text] is the volume of activation at P = 0, and x is the increase in the number of water molecules solvating the complex as it goes to the transition state. For [Formula: see text]Cl−, Br−,[Formula: see text] and [Formula: see text] at 25° [Formula: see text] and ionic strength I = 0.1 M LiClO4/HClO4, [Formula: see text] −10.6, −9.2, −6.3, and +16.8 cm3 mol−1, and x = 8.0, 4.1, 3.9, 1.9, and −4.2; for Xn− = NCS−, the mean ΔV* from P = 0.001 to 2.5 kbar at 88° is −4 cm3 mol−1. Detailed consideration of these data, especially their correlation with the molar volume of reaction by a straight line of unit slope for [Formula: see text] Cl−, Br−, NO3−, and H2O, provides strong evidence for a dissociative interchange mechanism. For [Formula: see text] the separating entity is probably HN3 rather than [Formula: see text] For Xn− = NCS−, aquation is incomplete, at practical complex concentrations; at 88.0°, 1 bar, and I = 0.1 M LiClO4/HClO4, k = 3.3 × 10−6 s−1 and the stability constant of Co(NH3)5NCS2+ is 490 M−1.

scholarly journals The thermal decomposition of acetaldehyde and the existence of different activated states

1933 ◽  
Vol 141 (843) ◽  
pp. 41-55 ◽  
Keyword(s):  
High Pressures ◽  
Initial Pressure ◽  
Bimolecular Reaction ◽  
Bimolecular Reactions ◽  
First Order ◽  
Straight Line ◽  
Gas Reactions ◽  
Pass Through ◽  
Low Pressures ◽  
Kinetics Of

Homogeneous thermal gas reactions were at one time tacitly assumed to possess a definite order, unimolecular and bimolecular reactions, for example, being sharply distinguished. The kinetics of the decomposition of acetalde­ hyde, CH 3 CHO = CH 4 + CO, over the pressure range of 100 to 400 mm. were found to satisfy the criterion of a bimolecular reaction, namely, that the reciprocal of the time for half change (1/ t 1/2 ) )plotted against the initial pressure ( p 0 ) gave a straight line inclined to the axes. The line, however, did not pass through the origin, as may be seen in fig. 1 of the present paper. This indicated the presence of some first order reaction, the nature of which was not determined. Subsequently, in accordance with the collision theory of activation and deactivation, it was shown that certain reactions, sometimes called quasiummolecular, change their order from the second at low pressures to the first at high pressures. This apparently was the reverse of the behaviour shown by acetaldehyde.

Mathematical model of acetylcholine kinetics in neuroeffector junctions

1994 ◽  
Vol 266 (1) ◽  
pp. H298-H309 ◽  
Author(s):  
F. Dexter ◽  
Y. Rudy ◽  
G. M. Saidel
Keyword(s):  
Mathematical Model ◽  
Heart Rate ◽  
Rate Coefficient ◽  
Sinus Node ◽  
Vagal Activity ◽  
Pacemaker Cells ◽  
Order Linear ◽  
First Order ◽  
Linear Kinetics ◽  
The Mean

Acetylcholine (ACh) kinetics in neuroeffector junctions (NEJ) of the sinus node plays a key role in vagal control of heart rate. Prior studies have shown that the concentration of ACh ([ACh]) in NEJ appears to follow first-order linear kinetics. To find out the reason why, we examine mathematically diffusion, degradation, and receptor binding of ACh in NEJ. We identify seven conditions that potentially influence ACh kinetics. Because these conditions are satisfied for NEJ in the sinus node, 1) the nonlinearity of ACh binding to muscarinic receptors has little effect on [ACh]; 2) [ACh] does not depend on the distribution of acetylcholinesterase between the interstitial space and the pacemaker cells; 3) the interval from trough to subsequent peak [ACh] at the pacemaker cells is negligible; 4) the mean [ACh] at the pacemaker cells is proportional to the frequency of vagal activity multiplied by the amount of ACh released per vagal stimulus and divided by the rate coefficient of ACh degradation; and 5) [ACh] at pacemaker cells nearly follows first-order linear kinetics but does not at other sites in the NEJ. We conclude that earlier studies showed that [ACh] follows first-order linear kinetics, because they predicted [ACh] only at pacemaker cells. ACh kinetics at other sites in the NEJ, such as at nerve endings, is different.

Mercury-photosensitized decomposition of dimethyl ether. Part II. The thermal decomposition of the methoxymethyl radical

1967 ◽  
Vol 45 (22) ◽  
pp. 2767-2773 ◽  
Author(s):  
Leon F. Loucks ◽  
Keith J. Laidler
Keyword(s):  
Carbon Dioxide ◽  
Dimethyl Ether ◽  
Pressure Range ◽  
High Pressures ◽  
Rate Coefficient ◽  
Rate Coefficients ◽  
Methyl Radical ◽  
Lower Efficiency ◽  
First Order ◽  
Order Rate

The decomposition of the methoxymethyl radical, generated in the mercury-photosensitized decomposition of dimethyl ether, has been investigated over the temperature range 200 to 300 °C and the pressure range 3 to 600 mm Hg. The radical decomposes to give a formaldehyde molecule and a methyl radical. The effects of pressure and temperature on the first-order rate coefficient for the decomposition of the methoxymethyl radical have been examined in detail. The rate coefficient shows a pressure dependence over the full pressure range studied. The order of the decomposition is about 1.4 at the middle of the pressure range studied, with a lower order at higher pressures and a higher order at lower pressures. At 100 mm Hg the observed activation energy for the decomposition of the methoxymethyl radical is 24.8 kcal/mole.The first-order and second-order rate coefficients, k∞ and k0, corresponding to the limiting conditions of high pressures and low pressures respectively, have been evaluated as [Formula: see text]Kassel integrations have been carried out for the methoxymethyl radical and have been fitted to the experimental data. It is concluded that 8 or 9 normal modes contribute to the energization of the radical. The rate coefficient is increased by the presence of carbon dioxide, but carbon dioxide has a lower efficiency than dimethyl ether for the transfer of energy in the energization process.

scholarly journals Dynamical interactions in the planetary system GJ4276

2019 ◽  
Vol 490 (2) ◽  
pp. 2732-2739
Author(s):  
Fergus Horrobin ◽  
Hanno Rein
Keyword(s):  
Planetary System ◽  
Stable Region ◽  
Mean Motion Resonances ◽  
Orbital Parameters ◽  
First Order ◽  
Mean Motion ◽  
The Mean ◽  
The Stability ◽  
The One ◽  
Mean Motion Resonance

ABSTRACT GJ4276 is an M4.0 dwarf star with an inferred Neptune mass planet from radial velocity (RV) observations. We re-analyse the RV data for this system and focus on the possibility of a second, super-Earth mass, planet. We compute the time-scale for fast resonant librations in the eccentricity to be $\sim \!2000 \, \mathrm{d}$. Given that the observations were taken over $700\, \mathrm{d}$, we expect to see the effect of these librations in the observations. We perform a fully dynamical fit to test this hypothesis. Similar to previous results, we determine that the data could be fit by two planets in a 2:1 mean motion resonance. However, we also find solutions near the 5:4 mean motion resonance that are not present when planet–planet interactions are ignored. Using the mean exponential growth of nearby orbits indicator, we analyse the stability of the system and find that our solutions lie in a stable region of parameter space. We also find that though out-of-resonance solutions are possible, the system favours a configuration that is in a first-order mean motion resonance. The existence of mean motion resonances has important implications in many planet formation theories. Although we do not attempt to distinguish between the one- and two-planet models in this work, in either case, the predicted orbital parameters are interesting enough to merit further study. Future observations should be able to distinguish between the different scenarios within the next 5 yr.

Injuries to the Coronoid Process of the Ulna with Involvement of the Lesser Sigmoid Notch

2020 ◽  
Author(s):  
Valentin Rausch ◽  
Sina Neugebauer ◽  
Tim Leschinger ◽  
Lars Müller ◽  
Kilian Wegmann ◽  
...  
Keyword(s):  
Fragment Size ◽  
Coronoid Process ◽  
Annular Ligament ◽  
Concomitant Injuries ◽  
Proximal Ulna ◽  
Sigmoid Notch ◽  
Coronoid Fractures ◽  
The Mean ◽  
The Stability ◽  
Arthritic Changes

Abstract Introduction This study aimed to describe the involvement of the lesser sigmoid notch in fractures to the coronoid process. We hypothesized that injuries to the lateral aspect of the coronoid process regularly involve the annular ligament insertion at the anterior lesser sigmoid notch. Material and Methods Patients treated for a coronoid process fracture at our institution between 06/2011 and 07/2018 were included. We excluded patients < 18 years, patients with arthritic changes or previous operative treatment to the elbow, and patients with concomitant injuries to the proximal ulna. In patients with involvement of the lesser sigmoid notch, the coronoid height and fragment size (anteroposterior, mediolateral, and craniocaudal) were measured. Results Seventy-two patients (mean age: 47 years ± 17.6) could be included in the study. Twenty-one patients (29.2%) had a fracture involving the lateral sigmoid notch. The mean anteroposterior fragment length was 7 ± 1.6 mm. The fragment affected a mean of 43 ± 10.8% of the coronoid height. The mean mediolateral size of the fragment was 10 ± 5.0 mm, and the mean cranio-caudal size was 7 ± 2.7 mm. Conclusion Coronoid fractures regularly include the lesser sigmoid notch. These injuries possibly affect the anterior annular ligament insertion which is important for the stability of the proximal radioulnar joint and varus stability of the elbow.

Instant 99mTc-Labelled Glucoheptonate Kit for Kidney Imaging

1983 ◽  
Vol 22 (05) ◽  
pp. 246-250 ◽  
Author(s):  
M. Al-Hilli ◽  
H. M. A. Karim ◽  
M. H. S. Al-Hissoni ◽  
M. N. Jassim ◽  
N. H. Agha
Keyword(s):  
Sodium Hydroxide Solution ◽  
Normal Subjects ◽  
Organ Distribution ◽  
Stable Complex ◽  
Scintillation Camera ◽  
Ph Adjustment ◽  
The Mean ◽  
The Stability ◽  
Kidney Imaging ◽  
Mean Concentration

Gelchromatography column scanning has been used to study the fractions of reduced hydrolyzed 99mTc, 99mTc-pertechnetate and 99mTc-chelate in a 99mTc-glucoheptonate (GH) preparation. A stable high labelling yield of 99mTc-GH complex in the radiopharmaceutical has been obtained with a concentration of 40-50 mg of glucoheptonic acid-calcium salt and not less than 0.45 mg of SnCl2 2 H2O at an optimal pH between 6.5 and 7.0. The stability of the complex has been found significantly affected when sodium hydroxide solution was used for the pH adjustment. However, an alternative procedure for final pH adjustment of the preparation has been investigated providing a stable complex for the usual period of time prior to the injection. The organ distribution and the blood clearance data of 99mTc-GH in rabbits were relatively similar to those reported earlier. The mean concentration of the radiopharmaceutical in both kidneys has been studied in normal subjects for one hour with a scintillation camera and the results were satisfactory.

First passage time for the state of exact chemical equilibrium

1980 ◽  
Vol 45 (3) ◽  
pp. 777-782 ◽  
Author(s):  
Milan Šolc
Keyword(s):  
Chemical Equilibrium ◽  
First Passage Time ◽  
Passage Time ◽  
The State ◽  
Recurrence Time ◽  
First Passage ◽  
First Order ◽  
The Mean ◽  
Passage Times ◽  
Number Of Particles

The establishment of chemical equilibrium in a system with a reversible first order reaction is characterized in terms of the distribution of first passage times for the state of exact chemical equilibrium. The mean first passage time of this state is a linear function of the logarithm of the total number of particles in the system. The equilibrium fluctuations of composition in the system are characterized by the distribution of the recurrence times for the state of exact chemical equilibrium. The mean recurrence time is inversely proportional to the square root of the total number of particles in the system.

The Structure and Photochromism of 2,4,4,6-Tetraphenyl-4H-thiopyran

1992 ◽  
Vol 57 (6) ◽  
pp. 1326-1334 ◽  
Author(s):  
Jaroslav Vojtěchovský ◽  
Jindřich Hašek ◽  
Stanislav Nešpůrek ◽  
Mojmír Adamec
Keyword(s):  
Solid State ◽  
Uv Light ◽  
Order Reaction ◽  
Boat Conformation ◽  
X Rays ◽  
Exponential Time ◽  
First Order ◽  
Double Plane ◽  
The Mean ◽  
Independent Molecules

2,4,4,6-Tetraphenyl-4H-thiopyran, C29H22S, orthorhombic, Pna21, a = 17.980(4), b = 6.956(2), c = 34.562(11) Å, V = 4323(2) Å3, Z = 8, Dx = 1.237 g cm-3, F(000) = 1696, λ(CuKα) = 1.54184 A, μ = 1.372 mm-2, T = 294 K. The final R was 0.050 for the unique set of 3103 observed reflections. The central 4H-thiopyran ring forms a boat conformation for both symmetrically independent molecules with average boat angles 4.4(3) and 6.8(3)° at S and C(sp3), respectively. The mean planes of phenyls at the position 2 and 6 are turned from the double plane of 4H-thiopyran by 42.5(5) and 35.8(3)°, respectively. The investigated material undergoes a photochromic change in the solid state after irradiation with UV light or X-rays. The maximum of the new absorption band is situated at 564 nm. The non-exponential time dependence of photochromic bleaching is analysed in terms of a dispersive first-order reaction.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

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