scholarly journals The relative values of the turnover number and the dissociation rate constant determine the definition of the Michaelis-constant

2016 ◽  
Author(s):  
Gassan Nazzal
Keyword(s):  
Partition Function ◽  
Ground State ◽  
Effective Diffusion ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Dissociation Rate ◽  
Saturation Curve ◽  
Kinetics Parameters ◽  
Km Value ◽  
Definition Of

Abstract.In this work, we attempt to determine the assumptions of each case of the QSSA. We came to the conclusion that for an enzyme with average kinetics parameters the REA is a good approximation to derive the rate equation and the Km value tends to equal the dissociation constant Kd. The active site classifies the population of the substrate into two energy states, the ground state, and the transition state. The ratio Km/Kd is equal to the partition function of the assumed two-state-system. For the average enzyme, the partition function of the transition tends to equal 1 thus the majority of the substrate molecules are in the ground state and the assumption kcat << k−1 is valid hence Km ≈ Kd. In contrast, when the enzyme is diffusion controlled, the Km value is equal to the productive dissociation rate kcat/k1. We have also redefined the Km value as the equivalence point of the reaction rates, namely, the effective diffusion rate and the maximal catalytic rate, which reflects more clearly the transition from the bimolecular reaction to the unimolecular reaction in the saturation curve.

scholarly journals Kinetic Study of the Reaction of Rh(a4F9/2) with N2O, O2 and NO

1998 ◽  
Vol 17 (4) ◽  
pp. 219-237 ◽  
Author(s):  
Mark L. Campbell
Keyword(s):  
Gas Phase ◽  
Excited States ◽  
Ground State ◽  
Rate Constants ◽  
Room Temperature ◽  
Reaction Rate ◽  
Removal Rate ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Temperature Rate

The gas phase reactivity of Rh(a4F9/2) with N2O, O2 and NO is reported. Removal rate constants for the excited states of rhodium below 13,000cm-1 are also reported. The reaction rate of Rh(a4F9/2) with N2O is relatively temperature insensitive. The rate constants for the bimolecular reaction are described in Arrhenius form by (1.3±0.3)×10−12exp⁡(−1.3±0.8KJ/mol/RT)cm3s−1 The reaction rates of the a4F9/2 state with O2 and NO are pressure dependent. For O2, the limiting low-pressure thirdorder, K0, and limiting high-pressure second-order, K∞, room temperature rate constants in argon buffer are (6.6±0.6)×10−30cm6s−1 and (2.1±0.2)×10−11cm3s−1, respectively. For NO, K2 and K∞ are (1.3±0.2×10−30cm6s−1) and (2.1±0.4)×10−11cm3s−1, respectively. The removal rates of the excited states are faster than the ground state by a factor of 2 or more.

Validation of Pin-Resolved Reaction Rates, Kinetics Parameters, and Linear Source MOC in MPACT

2020 ◽  
Vol 195 (1) ◽  
pp. 50-68
Author(s):  
Yuxuan Liu ◽  
Kyle Vaughn ◽  
Brendan Kochunas ◽  
Thomas Downar
Keyword(s):  
Reaction Rates ◽  
Linear Source ◽  
Kinetics Parameters

The Reaction and Microscopic Electron Properties from Dynamic Evolutions of Condensed-Phase RDX Under Shock Loading

2020 ◽  
Vol 75 (4) ◽  
pp. 285-291
Author(s):  
Jiao-Nan Yuan ◽  
Hai-Chao Ren ◽  
Yong-Kai Wei ◽  
Wei-Sen Xu ◽  
Guang-Fu Ji ◽  
...  
Keyword(s):  
Shock Wave ◽  
Ground State ◽  
Shock Loading ◽  
Reaction Rates ◽  
Reaction Products ◽  
Decomposition Rates ◽  
Multi Scale ◽  
Wave Velocities ◽  
Wide Gap ◽  
Reaction Initiation

AbstractMicroscopic electron properties of α-hexahydro-1,3,5-trinitro-1,3,5-triazine (α-RDX) with different shock wave velocities have been investigated based on molecular dynamics together with multi-scale shock technique. The studied shock wave velocities are 8, 9 and 10 km ⋅ s−1. It has been said that the shock sensitivity and reaction initiation of explosives are closely relevant with their microscopic electron properties. The reactions, including the reaction products, which are counted from the trajectory during the simulations are analysed first. The results showed that the number of the products strictly rely on shock wave velocities. The reaction rates and decomposition rates are also studied, which showed the differences between the different shock velocities. The results of electron properties show that α-RDX is a wide-gap insulator in the ground state and the metallisation conditions of shocked RDX are determined, which are lower than under-static high pressure.

scholarly journals mTORC1 controls phase-separation and the biophysical properties of the cytoplasm by tuning crowding

2017 ◽  
Author(s):  
M. Delarue ◽  
G.P. Brittingham ◽  
S. Pfeffer ◽  
I.V. Surovtsev ◽  
S. Ping-lay ◽  
...  
Keyword(s):  
Phase Separation ◽  
Fluorescent Protein ◽  
Effective Diffusion ◽  
Reaction Rates ◽  
Biophysical Properties ◽  
Cell Interior ◽  
Profound Impact ◽  
Mtorc1 Pathway

Summary (Abstract)Macromolecular crowding has a profound impact on reaction rates and the physical properties of the cell interior, but the mechanisms that regulate crowding are poorly understood. We developed Genetically Encoded Multimeric nanoparticles (GEMs) to dissect these mechanisms. GEMs are homomultimeric scaffolds fused to a fluorescent protein. GEMs self-assemble into bright, stable fluorescent particles of defined size and shape. By combining tracking of GEMs with genetic and pharmacological approaches, we discovered that the mTORC1 pathway can tune the effective diffusion coefficient of macromolecules ≥15 nm in diameter more than 2-fold without any discernable effect on the motion of molecules ≥5 nm. These mTORCI-dependent changes in crowding and rheology affect phase-separation both in vitro and in vivo. Together, these results establish a role for mTORCI in controlling both the biophysical properties of the cytoplasm and the phase-separation of biopolymers.

On the Kinetics and Mechanism of Spontaneous Intramolecular Reduction of the Central Metal Ion in K2[Mn(IV)-2-α-hydroxyethyl isochlorin e4] Acetate in Aqueous Alkaline Solutions and its Relation to the Binding Sites of Manganese in Photosynthesis

1975 ◽  
Vol 30 (5-6) ◽  
pp. 327-332 ◽  
Author(s):  
Gerhard Vierke ◽  
Manfred Müller
Keyword(s):  
Electron Transfer ◽  
Metal Ion ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Reduction Reaction ◽  
Alkaline Solutions ◽  
Central Metal ◽  
Pseudo First Order Reaction ◽  
Spontaneous Reduction ◽  
Acid Base Equilibrium

Abstract Spectrophotometric investigation of the kinetics of the spontaneous reduction of the central metal ion in K2[Mn (IV)-2-α-hydroxyethyl-isochlorine e4] acetate in aqueous alkaline solution in the absence of any reducing agent reveals that it is a pseudo-first order reaction which is specifically hydroxide ion catalyzed. The pKα-value of the acid-base equilibrium has been estimated to be 14.4. Electron transfer to the central metal ion is the rate limiting step. The measurements of its temperature dependence yields an activation enthalpy of ∆H‡ = 12 kcal/mol and an entropy of activation ∆S‡ = - 30 e.u. thus indicating that the electron transfer step is a bimolecular reaction. The most likely reactant is water. The reduction reaction does not take place with appreciable reaction rates at physiological pH. Thus, when bound to a suitable ligand of the chlorin type, Mn (IV)-compounds are sufficiently stable with respect to autoxidation to play some role in biological redox reactions as postulated recently for the photoreactivation process of the water splitting system in photosynthesis.

On the Role of the Pauli Antisymmetry Principle in Pericyclic Reactions

1997 ◽  
Vol 52 (10) ◽  
pp. 727-738
Author(s):  
Michael C. Böhm ◽  
Johannes Schütt
Keyword(s):  
Wave Function ◽  
Ground State ◽  
Statistical Difference ◽  
Pericyclic Reactions ◽  
Electron Systems ◽  
Electronic Wave Function ◽  
Quantum Statistical ◽  
Definition Of ◽  
Electronic Ground

Abstract In the present work we discuss the role of the Pauli antisymmetry principle (PAP) in synchronous pericyclic reactions. These reactions are allowed in the electronic ground state whenever the PAP does not act as a quantum constraint in the transition state. The possible suppression of the influence of the PAP is a peculiarity of π electron systems. The PAP is a hidden (= deactivated) variable in the π electron subspace of polyenes and (4n + 2) annulenes (n = 0, 1, 2,...). In 4n annulenes (n = 1, 2, 3,...) it leads to minority signs in the kinetic hopping matrix of the π electronic wave function and thus to an energetic destabilization. The quantum statistical difference between the above families of π systems renders possible a microscopical definition of the quantities “aromaticity” and “antiaromaticity”. The sign behaviour of the kinetic hopping elements is used in the discussion of pericyclic reactions. The present quantum statistical description of these reactions is related to the Dewar-Zimmermann and Woodward-Hoffmann rules.

scholarly journals Comments on open string with ‘massive’ boundary term

2020 ◽  
Vol 476 (2236) ◽  
pp. 20190748
Author(s):  
Arkady A. Tseytlin
Keyword(s):  
Scattering Amplitudes ◽  
Partition Function ◽  
Gauge Field ◽  
Path Integral ◽  
Open String ◽  
One Dimensional ◽  
Conformally Invariant ◽  
Additional Constant ◽  
The One ◽  
Definition Of

We discuss possible definition of open string path integral in the presence of additional boundary couplings corresponding to the presence of masses at the ends of the string. These couplings are not conformally invariant implying that as in a non-critical string case one is to integrate over the one-dimensional metric or reparametrizations of the boundary. We compute the partition function on the disc in the presence of an additional constant gauge field background and comment on the structure of the corresponding scattering amplitudes.

SIGNATURES OF AN EMERGENT GRAVITY FROM BLACK HOLE ENTROPY

2009 ◽  
Vol 18 (14) ◽  
pp. 2323-2327
Author(s):  
CENALO VAZ
Keyword(s):  
Phase Transition ◽  
Black Hole ◽  
Mass Spectrum ◽  
Partition Function ◽  
Ground State ◽  
Degrees Of Freedom ◽  
Thermodynamic Description ◽  
Black Hole Entropy ◽  
Fundamental Particle ◽  
Horizon Radius

The existence of a thermodynamic description of horizons indicates that space–time has a microstructure. While the "fundamental" degrees of freedom remain elusive, quantizing Einstein's gravity provides some clues about their properties. A quantum AdS black hole possesses an equispaced mass spectrum, independent of Newton's constant, G, when its horizon radius is large compared to the AdS length. Moreover, the black hole's thermodynamics in this limit is inextricably connected with its thermodynamics in the opposite (Schwarzschild) limit by a duality of the Bose partition function. G, absent in the mass spectrum, re-emerges in the thermodynamic description through the Schwarzschild limit, which should be viewed as a natural "ground state." It seems that the Hawking–Page phase transition separates fundamental, "particle-like" degrees of freedom from effective, "geometric" ones.

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