scholarly journals Unreliability of rate constants derived from a linear transformation of kinetic data, with special reference to cholesterol equilibration between phospholipid vesicles

1992 ◽  
Vol 283 (2) ◽  
pp. 537-539 ◽  
Author(s):  
N Gains
Keyword(s):  
Linear Regression ◽  
Special Reference ◽  
Correlation Coefficient ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Data ◽  
Time Dependent ◽  
Phospholipid Vesicles ◽  
Zero Time ◽  
Made In

In the time-dependent transfer of a lipid from a donor to an acceptor vesicle population a(t) is the amount transferred to the acceptor vesicles at time t, a infinity is the equilibrium transfer value and a0 is the value at zero time. In order to plot kinetic data (a(t) as ln[(a infinity - a(t))/(a infinity - a(t))] against time and to fit these with a linear regression, it is necessary to know the equilibrium value, a infinity, or to choose one. Here it is shown that even if a very larger error is made in the choice of a infinity, the resulting plot can still be acceptably linear and the correlation coefficient of the regression acceptably high. When a infinity is overestimated the rate constant derived from the slope of such a plot is underestimated. In extreme cases a 10-fold error can occur.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2021 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

Spectroscopic studies of the interaction of cobalt(II) N,N',N″,N‴-tetramethyltetra-3,4-pyridinoporphyrazine with amino acids and nitrogen oxides

2001 ◽  
Vol 05 (12) ◽  
pp. 839-845 ◽  
Author(s):  
MAMOTHIBE A. THAMAE ◽  
TEBELLO NYOKONG
Keyword(s):  
Nitric Oxide ◽  
Amino Acids ◽  
Nitrogen Oxides ◽  
Equilibrium Constant ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Data ◽  
Spectroscopic Studies

The interaction of histidine, cysteine, NO and nitrite with cobalt(II) N,N',N″,N‴-tetramethyltetra-3,4-tetrapyridinoporphyrazine ([ Co II tmtppa ]4+) is reported. Metal-based autoreduction of [ Co II tmtppa ]4+ occurs with the formation of the [ Co I tmtppa (-2)]3+ species in the presence of histidine and cysteine. Kinetic data for the auto reduction of [ Co II tmtppa ]4+ in the presence of these amino acids gave the rate constants k f = 2.1 × 101 and 2.8 dm3 mol-1 s-1, for cysteine and histidine, respectively. One molecule of NO or nitrite was found to coordinate to the [ Co II tmtppa ]4+ species. The equilibrium and rate constants for the coordination of the nitric oxide were K = 2.3 × 104 dm 3 mol -1 and k f = 7.5 dm 3 mol -1 s -1, respectively. The coordination of nitrite to [ Co II tmtppa ]4+ occurred with an equilibrium constant of K = 2.0 × 102 dm 3 mol -1 and a rate constant of k f = 4.0 × 10-3 dm 3 mol -1 s -1. There was no evidence for the coordination of two molecules of nitrite to the [ Co II tmtppa ]4+ species.

Flame structure and flame reaction kinetics - V. Investigation of reaction mechanism in a rich hydrogen+nitrogen+oxygen flame by solution of conservation equations

1970 ◽  
Vol 317 (1529) ◽  
pp. 235-263 ◽  
Keyword(s):  
Reaction Mechanism ◽  
Hydrogen Atom ◽  
Reaction Zone ◽  
Rate Constant ◽  
Rate Constants ◽  
Time Dependent ◽  
Flame Velocity ◽  
Atom Concentration ◽  
Comparison With Experiment ◽  
Oxygen Flame

A powerful combination of two computational methods has been used to investigate the reaction mechanism in a fuel-rich hydrogen+nitrogen+oxygen flame. The first of these involves the solution of the time-dependent heat conduction and diffusion equations by finite difference methods. It allows a preliminary assessment of reaction mechanisms and rate constants which must be used to reproduce the observed flame velocity. However, the transport fluxes are only represented approximately in this time-dependent model, so that a precise calculation of flame profiles cannot be made. The second computational method uses a Runge–Kutta procedure to calculate the steady-state flame profiles, and is an extension of the methods discussed by Dixon-Lewis (1968). It incorporates detailed transport property calculations, and thus allows computation of detailed flame profiles for comparison with experiment. Application of the methods to the rich hydrogen+nitrogen+oxygen flame and subsequent comparison with experiment has established the participation of hydroperoxyl in the flame mechanism, and has shown the principal reactions in the flame to be: OH + H 2 = H 2 O + H, (i) H + O 2 =OH + O, (ii) O + H 2 =OH + H, (iii) H + O 2 + M = HO 2 + M, (iv) H + HO 2 = OH + OH, (vii) H + HO 2 = H 2 + O 2 , (xii) H+ H + M = H 2 + M. (xv) It was found that the interplay between these reactions is such that it is impossible to use the atmospheric pressure flame for an independent, precise determination of the hydrogenoxygen chain branching-rate constant k 2 . Another property of the mechanism is that the hydrogen atom concentration profile in the flame is not very dependent on the precise rate constants employed, so that the profile itself can be computed probably to better than ±10%. The reaction zone of the very rich flame commences at about 550 K, the maximum overall reaction rate is at about 900 K, and the maximum hydrogen atom concentration is at 1030 to 1040 K. The rate constant ratio k 7 / k 12 is found to lie in the range 5±1, assumed independent of temperature over the reaction zone. Assuming equal efficiencies of all the molecules in the flame as third bodies in the hydrogen atom recombination, the rate constant k 15 is estimated to lie in the range 4.5±1.5 x 10 15 cm 6 mol -2 s -1 .

Enzyme-induced coagulation of casein micelles: a number of different kinetic models

1993 ◽  
Vol 60 (4) ◽  
pp. 517-533 ◽  
Author(s):  
Douglas B. Hyslop
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Energy Barrier ◽  
Time Dependent ◽  
Series Expansions ◽  
Simple Relationship ◽  
Casein Micelles ◽  
Functional Sites ◽  
The Third ◽  
Flocculation Rate

SummarySeveral mathematical models are presented in an attempt to describe the kinetics of the enzyme-induced coagulation of casein micelles. In each model the primary phase of the clotting reaction is assumed to follow first order kinetics. The only differences amongst the various models centre on the definition of the flocculation rate constant, which is defined in seven different ways. The rate constants are defined and discussed in terms of activation energy and functionality theory. The first model is such that the number of functional sites is two. The second is such that the number is much larger. The third and fourth are such that there is an exponential energy barrier, one which has a magnitude proportional to the extent of proteolysis caused by the clotting enzyme. These two definitions differ only in the pre-exponent. In one case the pre-exponent is a constant, whereas in the other it is dependent on the size of clotting particles. The fifth and sixth definitions are also energy barrier rate constants, but the energy barrier changes in an arbitrary fashion with respect to time during proteolysis. The seventh definition assumes a large number of functional sites, but such that the number increases with extent of proteolysis. In the Payens nomenclature (Payens, 1989), all models could be considered to be ‘source’ models, and all are derived using the Drake moment equation (Drake, 1972). Only the first model has a truly constant flocculation rate parameter, and only this model has a relatively simple analytical solution. All other models yield analytical solutions only by way of infinite series expansions. Thus, all models are presented in terms of power series expansions, and only through the first five time-dependent coefficients. This confines all models to the early stages of coagulation. In all cases the first three coefficients are virtually the same. The first two coefficients involve only proteolysis, and the third includes initial flocculation information. Time-dependent changes in the flocculation rate constant begin to take effect in the fourth coefficient. When the fourth coefficients of the third and seventh models are compared, a simple relationship is suggested between free energy barrier removal and functional site generation, but only assuming that the number of functionalities is large.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2020 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

scholarly journals Collision Energy Dependence of the Overall Rate Constant for the Reaction NH(a1Δ ) + HN3

1995 ◽  
Vol 15 (2-4) ◽  
pp. 183-194 ◽  
Author(s):  
Akihiro Watanabe ◽  
Katsuyoshi Yamasaki ◽  
Ikuo Tokue
Keyword(s):  
Long Range ◽  
Rate Constant ◽  
Rate Constants ◽  
Collision Energy ◽  
Time Dependent ◽  
Intermolecular Potential ◽  
Potential Approximation ◽  
Initial Stage ◽  
Vibrational Levels ◽  
Hydrogen Azide

The overall rate constant for the reaction NH(a1Δ ) + HN3 has been determined by the laser photolysis of hydrogen azide (HN3) at 266 nm and 193nm. The visible emission from vibronically excited NH2(A˜2A1) was dispersed and its time-dependent profiles were measured at several wavelengths. The rate constants are dependent not only on the photolysis wavelengths but also on the vibrational levels of the NH2(A˜2A1) produced in the reaction. The intermolecular potential between NH(a1Δ) and HN3 was determined to be the form V(R) = –C/Rs (2 < s < 4, C: constant) from the analysis with a long-range potential approximation. The interaction between NH(a1Δ ) and HN3 is mainly governed by the dipoledipole interaction in the initial stage of the reaction.

Rate of addition of bromine atoms to ethylene

1970 ◽  
Vol 48 (15) ◽  
pp. 2426-2429 ◽  
Author(s):  
K. T. Wong ◽  
D. A. Armstrong
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Data ◽  
Addition Reactions

The rate of combination of bromine atoms in the photosensitized hydrobromination of ethylene has been determined by the rotating sector technique. From this and kinetic data reported previously the rate constant for the addition of bromine atoms to ethylene in the presence of 380 Torr of propane as deactivating gas has been calculated to be 1.5 ± 0.3 × 10−14 cm3 molecule−1 s−1, independent of temperature in the range 15 to 35 °C. This result is discussed and compared with rate constants for other addition reactions to ethylene.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2020 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

Pengaruh Penghargaan Terhadap Kinerja Karyawan pada CV. Dino Manunggal Karsa Bogor

2019 ◽  
Vol 4 (2) ◽  
pp. 17
Author(s):  
Dedy Mulyadi ◽  
Didik Purwanto
Keyword(s):  
Linear Regression ◽  
Performance Assessment ◽  
Correlation Coefficient ◽  
Linear Regression Analysis ◽  
Strong Relationship ◽  
Simple Linear Regression ◽  
New Employees ◽  
Company Policy ◽  
Effective Manner ◽  
Relationship Of

The question of compensation in addition to sensitive to be driving someone to worl due to an effect on morale and discipline employees. Therefore , any  agency or any organization should be able to provide compensation equal to the workload  to create a workforce that efficient and effective manner can be realized. Amaore than that, the company’s goal to improve performance. Performance assessment is a subjective process that involves human judgments. Thus, performance assessment is very likely wrong and very easily influonced by sources that are not actual, so it must be taken into account and considered reasinable. Frformance appraisals are considered  to meet the target if it has a good impact on new employees who rated their performance. Simple linear regression analysis using SPSS version 12:00 data processing obtained tegression equation Y = 0,487 X 74 + with an explanation of X = award, 74 = constant, 0.487 = coefficient awards, and Y = performance based on simple linear regression equation in case of increase of one unit of the  performance award will be increased 0.487 units. If company policy negates the performance award will remain at a constant rate (74) units . (A) Test results obtained thitung significant constants of (12.574) > t table for (1.960 then reject Ho constanta significant meaning. (B) significant Test award coefficient t count the results obtained by (2.164)> t table foe (1.96) then reject Ho the mean coeffent of appreciation affect the performance . (C) correlation coefficient analysis is done by calculating the product moment corration (pearson)  to test  whether or not a strong  relationship between the variables X  dan Y , based on the results of cakculations with SPSS  table valuse obtained by calculating the  correlation coefficient r (0.3100> r on the table for a = 0,05 (0.291) then reject Ho, which means there is a relationship of respect for performance. When we enter these valuse in the table shows the interpretation of the correlation coefficient between the interval from 0.20 to 0.399 which has a low relationship

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