Dimerization constant of SF6 and CF4 in cryosolutions

2011 ◽  
Vol 382 (1-3) ◽  
pp. 27-33 ◽  
Author(s):  
A.N. Dobrotvorskaia ◽  
D.N. Shchepkin ◽  
P.K. Sergeev ◽  
W.A. Herrebout ◽  
B.J. van der Veken
Keyword(s):  
Dimerization Constant

scholarly journals The association behaviour of β-lactamases. Sedimentation equilibrium studies in ammonium sulphate solutions

1986 ◽  
Vol 237 (2) ◽  
pp. 511-517 ◽  
Author(s):  
E H Braswell ◽  
J R Knox ◽  
J M Frère
Keyword(s):  
Equilibrium Constants ◽  
Solubility Limit ◽  
Sedimentation Equilibrium ◽  
Association Model ◽  
Sodium Cacodylate ◽  
Dimerization Constant ◽  
Equilibrium Studies ◽  
Crystal Forms ◽  
Beta Lactamases ◽  
Equilibrium Sedimentation

The beta-lactamases (EC 3.5.2.6) from TEM plasmid RP4, Bacillus licheniformis 749/C and Enterobacter cloacae P99 were studied in solution over a wide concentration range by equilibrium sedimentation. Though crystal symmetries indicate that all three enzymes are potentially dimeric in their crystal forms, in 50 mM-sodium cacodylate at pH 6.5 the enzymes show only a small tendency to associate, indicated by a weight-average Mr (Mw) at 3% (w/v) concentration about 9% greater than that of the monomer. Although the mode of association could not be determined, this extent of association corresponded to a dimerization constant of about 2 × 10(2) M-1. In 2.1 M-(NH4)2SO4 the B. licheniformis enzyme shows some association at concentrations over 1%, displaying an Mw value at 7% concentration about 60% more than the monomer. Under the same conditions Mw for the Entero. P99 enzyme is about 60% greater than the monomer near the solubility limit of about 2%. However, the Mw for the TEM enzyme is over twice that of the monomer at its solubility limit (3%) in 1.7 M-(NH4)2SO4. Fitting the sedimentation data of the TEM enzyme in 1.7 M-(NH4)2SO4 with a dimerization model and an indefinite-isodesmic-association model yielded equilibrium constants of 1.5 × 10(4) and 3.3 × 10(2) M-1 respectively, with the indefinite-isodesmic model giving the better fit. Fitting the data for the other two enzymes yielded values of 1.4 × 10(3) and 1.7 × 10(2) M-1 respectively for the Entero. P99 enzyme and 4.5 × 10(2) and 45 M-1 respectively for the B. licheniformis enzyme. It could not be determined which model was the better fit for these two enzymes. Since none of the beta-lactamases studied here showed strong evidence of the terminal aggregate being a dimer, we conclude that crystalline dimers, if they exist, will not be tightly associated or physiologically significant.

scholarly journals Study of the coordination of quinuclidine to a chiral zinc phthalocyanine dimer

2016 ◽  
Vol 20 (08n11) ◽  
pp. 1224-1232 ◽  
Author(s):  
Nelson Giménez-Agulló ◽  
Gemma Aragay ◽  
José Ramón Galán-Mascarós ◽  
Pablo Ballester
Keyword(s):  
Chemical Exchange ◽  
Variable Temperature ◽  
Exchange Process ◽  
Zinc Phthalocyanine ◽  
Hydrogen Atoms ◽  
Dimerization Constant ◽  
H Nmr ◽  
Dimerization Process ◽  
Nmr Titrations ◽  
Millimolar Concentration

We attempted the calculation of an accurate equilibrium constant for the dimerization process of enantiomerically pure Zn-1 using UV-vis dilution experiments. At millimolar concentration Zn-1 is involved in a chemical exchange process between its monomeric and dimeric state that is slow on the 1H NMR timescale. We performed variable-temperature 1H NMR experiments in CDCl3 solution to determine the dimerization constant value at different temperatures and performed a van’t Hoff plot to derive the thermodynamic parameters of the process. The calculated thermodynamic data revealed that the dimerization process is entropy-driven and enthalpically opposed. We also probed the coordination of quinuclidine, 1-azabicyclo[2.2.2]octane, 2, to the Zn-1 using UV-vis and 1H NMR titrations in CDCl3 solution. At micromolar concentration the Zn-1 exclusively exists in solution as a monomer and forms a simple 1:1, [Formula: see text], complex with quinuclidine having a stability constant of [Formula: see text]([Formula: see text]) [Formula: see text] 106 M[Formula: see text]. On the other hand, the 1H NMR titrations carried out at 298 K and at millimolar concentration showed that Zn-1 was present in solution as the dimer and formed 1:2, [Formula: see text], and 2:2, [Formula: see text] complexes by coordination to 2. In addition, the 1:1 complex, [Formula: see text] showed a reduced dimerization constant compared to the uncoordinated parent monomer Zn-1. At high quinuclidine concentration, the 1:1 complex, [Formula: see text], derived from the coordinated dimer dissociation was also detected. The 1H NMR spectra of the titrations displayed separate signals for some hydrogen atoms of the Zn-phthalocyanine in each one of the four species. Remarkably, the chemical exchange processes involving free and bound quinuclidine in the monomeric and dimeric complexes showed different kinetics on the NMR timescale.

Excess Gibbs energy for binary mixtures of acetonitrile with acetic acid, propionic acid, isobutyric acid, and trimethylacetic acid

1991 ◽  
Vol 69 (12) ◽  
pp. 2117-2121 ◽  
Author(s):  
T. S. Banipal ◽  
B. S. Lark ◽  
S. Singh
Keyword(s):  
Acetic Acid ◽  
Gibbs Energy ◽  
Carboxylic Acids ◽  
Propionic Acid ◽  
Binary Mixtures ◽  
Activity Coefficients ◽  
Excess Gibbs Energy ◽  
Composition Range ◽  
Isobutyric Acid ◽  
Dimerization Constant

Total vapour pressures for binary mixtures containing acetic acid, propionic acid, isobutyric acid, and trimethylacetic acid with acetonitrile have been measured for the entire composition range at 298.15 and 318.15 K using a static manometric method. All systems show positive deviations from Raoult's law, enhanced by both an increase in temperature and an increase in the methylation of acetic acid. Activity coefficients have been calculated by taking into consideration the dimerization of these carboxylic acids in the vapour phase. TSE values obtained from GE and earlier reported HE values are found to be negative for acetic acid, about zero for propionic and isobutyric acids, and positive for trimethylacetic acid for the whole composition range. The results have been interpreted in terms of various contributions such as depolymerization, heteromolecular dipole–dipole interactions, and the increasing dimerization constant and steric hindrance with increase of complexity of the acid. Key words: excess Gibbs energy, carboxylic acids, acetonitrile, activity coefficients

Study on the Effect of an Electrolyte on the Self-Aggregation and the Geometry of the Dye Aggregates of Methylene Blue in Aqueous Media

2016 ◽  
Vol 32 (1-2) ◽  
pp. 27
Author(s):  
Ng. Florence ◽  
H. Naorem
Keyword(s):  
Methylene Blue ◽  
Twist Angle ◽  
Aqueous Media ◽  
Least Square ◽  
The Self ◽  
Aggregation Process ◽  
Dimerization Constant ◽  
Sandwich Type ◽  
Linear Least Square ◽  
Self Aggregation

The self-aggregation of Methylene Blue (MB) dye in aqueous media has been investigated spectrophotometrically in presence of sodium chloride (NaCl) at 293.15, 303.15 and 313.15K. The dimerization constant (K<sub>D</sub>) of the MB dye in aqueous solution with or without the electrolyte has been computed using a non-linear least square regression technique. It is observed that presence of the electrolyte resulted into sharp increase in K<sub>D</sub> of MB indicating that presence of the electrolyte favours formation of dye aggregates. There is, however, a decrease in K<sub>D</sub> with increase in temperature. From the observed spectra of the dye, the twist (θ<sub>1</sub>) and the tilt (θ<sub>2</sub>) angles between the dipoles of MB molecules in the aggregates have been computed based on exciton model. Change in the monomeric fractions of the dye (α) in presence of the added electrolyte as a function of the dye concentration has also been computed. The results indicated that the dye aggregates formed is essentially of the sandwich type geometry (H-aggregates) with a slight deviation from an exact parallel stacking arrangement and reduced twist angle. The thermodynamic parameters of the aggregation process in presence of the electrolyte have been evaluated from the temperature dependence of K<sub>D</sub>. It is observed that the aggregation process is an enthalpy rather than entropy controlled one.

scholarly journals Role of dimerization in the control of the functioning of the human haemoglobin mutant haemoglobin Howick (β37 Trp→Gly)

1994 ◽  
Vol 300 (2) ◽  
pp. 553-556 ◽  
Author(s):  
T Brittain
Keyword(s):  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Oxygen Affinity ◽  
Amino Acid Side Chain ◽  
Oxygen Binding ◽  
Dimerization Constant ◽  
Equilibrium Studies ◽  
Human Haemoglobin ◽  
Dissociation Equilibrium ◽  
Wide Range

Haemoglobin Howick shows a high oxygen affinity (p50 = 1 mmHg) and a low co-operativity (n = 1.3). Equilibrium studies show the protein to be essentially totally dimeric in the oxygenated form. A wide range of rapid kinetic experiments indicate that the deoxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 3 microM. These kinetic data also indicate that the oxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 35 mM, and furthermore clearly identifies a large increase in the rate of the tetramer-to-dimer dissociation process as the origin of the vastly increased dissociation equilibrium constants. Simulations of the protein-concentration-dependence of the oxygen-binding properties of haemoglobin Howick, based on the measured equilibrium parameters, closely fits the experimental data. The change in dimerization constant for the deoxygenated form of the protein corresponds remarkably well to the free-energy change predicted for the simple transfer of the amino acid side chain at position beta 37 from a hydrophobic to a hydrophilic environment during the dimerization process.

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