The role of heterogeneity in the kinetics of a surface reactionIII. Distributions in activation enthalpy and entropy

1976 ◽  
Vol 43 (1-3) ◽  
pp. 181-191 ◽  
Author(s):  
J VANBOKHOVEN ◽  
A KUIPER ◽  
J MEDEMA
Keyword(s):  
Activation Enthalpy ◽  
Enthalpy And Entropy ◽  
Kinetics Of

Physical Chemistry of Crosslinking

1976 ◽  
Vol 46 (5) ◽  
pp. 329-342 ◽  
Author(s):  
G. L. Madan ◽  
S. B. Patel ◽  
N. T. Baddi ◽  
P. C. Mehta
Keyword(s):  
Physical Chemistry ◽  
Crosslinking Agent ◽  
Crosslinking Reaction ◽  
Solution Properties ◽  
Urea Derivatives ◽  
Structure Solution ◽  
Catalyst Temperature ◽  
Enthalpy And Entropy ◽  
Kinetics Of

Crosslinked cotton fabrics suffer significant losses in strength and abrasion resistance. In order to understand why these losses occur and also to reduce them, the physical chemistry of the process of crosslinking and the role of adsorption in the crosslinking reaction were studied. An attempt is made to relate adsorption and reactivity of different cyclic urea derivatives (DMEU, DMPU, DHEU, and DMDHEU) to the molecular structure, solution properties, pH, nature and concentration of catalyst, temperature, and time of reaction. Solution properties of crosslinking compounds were determined from measurements of electrical conductivity and the depression of the freezing points of aqueous solutions of the crosslinking compounds. A study on chemisorption with different cyclic urea derivatives showed that the maximum chemisorption takes place at pH 2.5 with DMEU and DMPU, and at 0.8 and zero pH with DHEU and DMDHEU, respectively. The kinetics of chemisorption in these crosslinking compounds revealed that the amount of DMEU and DMPU chemisorbed increases initially with time and then decreases and finally reaches an equilibrium value. The chemisorption of DHEU and DMDHEU increase with time and finally reach an equilibrium value. The data show that the chemisorption of these crosslinking compounds are pseudo first-order reactions with respect to the concentration of the crosslinking agent. Equilibrium physical and chemisorption for all the four crosslinking compounds were studied and found to be of the Langmuir type. The thermodynamic parameters such as affinity, enthalpy, and entropy of chemisorption were calculated. The saturation value for different crosslinking compounds are found to be in the order DMEU > DMPU > DHEU > DMDHEU.

The Kinetics of the Insertion Reaction of Tin(II) Chloride with Hexacarbonylbis(triphenylphosphite)dicobalt

1974 ◽  
Vol 52 (22) ◽  
pp. 3773-3777 ◽  
Author(s):  
Peter Fowler Barrett
Keyword(s):  
Electron Acceptor ◽  
Activation Enthalpy ◽  
Visible Spectrum ◽  
Insertion Reaction ◽  
Two Stage ◽  
Temperature Range ◽  
Metal Metal ◽  
Enthalpy And Entropy ◽  
Kinetics Of

The kinetics of the thermal insertion reaction of SnCl2 with the metal–metal bonded complex [P(OC6H5)3Co(CO)3]2 have been studied by following the change in the visible spectrum in THF over the temperature range 35.0 to 55.0 °C. The activation enthalpy and entropy for the reaction are 24.7 ± 0.4 kcal/mol and 2.4 ± 1.3 cal mol−l deg−1 respectively. The data are consistent with a two-stage mechanism identical to that proposed for the corresponding reaction with [P(n-C4H9)3Co(CO)3]2 and from a comparison of the two reactions it is concluded that the cobalt–cobalt bond is slightly weakened when tributylphosphine is replaced by the better π-electron acceptor triphenylphosphite. The insertion products [LCo(CO)3]2SnCl2 are shown to undergo further reaction with [LCo(CO)3]2 to form [LCo(CO)3]3SnCl (L = CO, P(n-C4H9)3, P(OC6H5)3).

Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures

1993 ◽  
Vol 58 (5) ◽  
pp. 1001-1006 ◽  
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Transfer Functions ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Oxidation Of Co ◽  
Kinetics Of Oxidation ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Alcohol Mixtures ◽  
Kinetics Of

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.

scholarly journals Association between perinatal factors, genetic susceptibility to obesity and age at adiposity rebound in children of the EDEN mother–child cohort

2021 ◽  
Author(s):  
Aminata Hallimat Cissé ◽  
Sandrine Lioret ◽  
Blandine de Lauzon-Guillain ◽  
Anne Forhan ◽  
Ken K. Ong ◽  
...  
Keyword(s):  
Weight Gain ◽  
Genetic Susceptibility ◽  
Gestational Weight Gain ◽  
Gestational Age ◽  
Obesity Risk ◽  
Perinatal Factors ◽  
Gestational Weight ◽  
Adiposity Rebound ◽  
Kinetics Of

Abstract Background Early adiposity rebound (AR) has been associated with increased risk of overweight or obesity in adulthood. However, little is known about early predictors of age at AR. We aimed to study the role of perinatal factors and genetic susceptibility to obesity in the kinetics of AR. Methods Body mass index (BMI) curves were modelled by using mixed-effects cubic models, and age at AR was estimated for 1415 children of the EDEN mother–child cohort study. A combined obesity risk-allele score was calculated from genotypes for 27 variants identified by genome-wide association studies of adult BMI. Perinatal factors of interest were maternal age at delivery, parental education, parental BMI, gestational weight gain, maternal smoking during pregnancy, and newborn characteristics (sex, prematurity, and birth weight). We used a hierarchical level approach with multivariable linear regression model to investigate the association between these factors, obesity risk-allele score, and age at AR. Results A higher genetic susceptibility to obesity score was associated with an earlier age at AR. At the most distal level of the hierarchical model, maternal and paternal educational levels were positively associated with age at AR. Children born to parents with higher BMI were more likely to exhibit earlier age at AR. In addition, higher gestational weight gain was related to earlier age at AR. For children born small for gestational age, the average age at AR was 88 [±39] days lower than for children born appropriate for gestational age and 91 [±56] days lower than for children born large for gestational age. Conclusion The timing of AR seems to be an early childhood manifestation of the genetic susceptibility to adult obesity. We further identified low birth weight and gestational weight gain as novel predictors of early AR, highlighting the role of the intrauterine environment in the kinetics of adiposity.

scholarly journals Phosphorylation of GAPVD1 Is Regulated by the PER Complex and Linked to GAPVD1 Degradation

2021 ◽  
Vol 22 (7) ◽  
pp. 3787
Author(s):  
Hussam Ibrahim ◽  
Philipp Reus ◽  
Anna Katharina Mundorf ◽  
Anna-Lena Grothoff ◽  
Valerie Rudenko ◽  
...  
Keyword(s):  
Circadian Clock ◽  
Transcriptional Repression ◽  
Small Gtpase ◽  
Main Role ◽  
Interacting Proteins ◽  
Casein Kinase 1 ◽  
Bona Fide ◽  
Kinetics Of

Repressor protein period (PER) complexes play a central role in the molecular oscillator mechanism of the mammalian circadian clock. While the main role of nuclear PER complexes is transcriptional repression, much less is known about the functions of cytoplasmic PER complexes. We found with a biochemical screen for PER2-interacting proteins that the small GTPase regulator GTPase-activating protein and VPS9 domain-containing protein 1 (GAPVD1), which has been identified previously as a component of cytoplasmic PER complexes in mice, is also a bona fide component of human PER complexes. We show that in situ GAPVD1 is closely associated with casein kinase 1 delta (CSNK1D), a kinase that regulates PER2 levels through a phosphoswitch mechanism, and that CSNK1D regulates the phosphorylation of GAPVD1. Moreover, phosphorylation determines the kinetics of GAPVD1 degradation and is controlled by PER2 and a C-terminal autoinhibitory domain in CSNK1D, indicating that the regulation of GAPVD1 phosphorylation is a novel function of cytoplasmic PER complexes and might be part of the oscillator mechanism or an output function of the circadian clock.

scholarly journals Halloysite nanotubes filled with salicylic acid and sodium diclofenac: effects of vacuum pumping on loading and release properties

2021 ◽  
Author(s):  
Lorenzo Lisuzzo ◽  
Giuseppe Cavallaro ◽  
Stefana Milioto ◽  
Giuseppe Lazzara
Keyword(s):  
Salicylic Acid ◽  
Release Kinetics ◽  
Halloysite Nanotubes ◽  
Drug Molecules ◽  
Sodium Diclofenac ◽  
Tunable Release ◽  
Feature Based ◽  
Kinetics Of ◽  
Filling Mechanism

AbstractIn this work, we investigated the effects of the vacuum pumping on both the loading efficiencies and the release kinetics of halloysite nanotubes filled with drug molecules dissolved in ethanol. As model drugs, salicylic acid and sodium diclofenac were selected. For comparison, the loading of the drug molecules was conducted on platy kaolinite to explore the key role of the hollow tubular morphology on the filling mechanism of halloysite. The effects of the pressure conditions used in the loading protocol were interpreted and discussed on the basis of the thermodynamic results provided by Knudsen thermogravimetry, which demonstrated the ethanol confinement inside the halloysite cavity. Several techniques (TEM, FTIR spectroscopy, DLS and $$\zeta$$ ζ -potential experiments) were employed to characterize the drug filled nanoclays. Besides, release kinetics of the drugs were studied and interpreted according to the loading mechanism. This work represents a further step for the development of nanotubular carriers with tunable release feature based on the loading protocol and drug localization into the carrier. Graphic abstract The filling efficiency of halloysite nanotubes is enhanced by the reduction of the pressure conditions used in the loading protocol.

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