Hydrolysis of two acyl activated esters in water-rich 2-butoxyethanol-water mixtures. Effects of hydrophobic interactions on enthalpies, entropies, and heat capacities of activation

1980 ◽  
Vol 102 (12) ◽  
pp. 4256-4257 ◽  
Author(s):  
Herman A. J. Holterman ◽  
Jan B. F. N. Engberts
Keyword(s):  
Hydrophobic Interactions ◽  
Heat Capacities ◽  
Activated Esters ◽  
Hydrolysis Of

Synthesis of conjugates of 1-(carboxymethyl)cytosine and 1-(5-O-carboxymethyl-β-D-arabinofuranosyl)cytosine with proteins

1979 ◽  
Vol 44 (10) ◽  
pp. 3023-3032 ◽  
Author(s):  
Helmut Pischel ◽  
Antonín Holý ◽  
Günther Wagner
Keyword(s):  
Human Serum Albumin ◽  
Acetic Anhydride ◽  
Serum Albumin ◽  
Human Serum ◽  
Activated Esters ◽  
Hydrolysis Of

1-(Carboxymethyl)cytosine (Ia), 1-(5-O-carboxymethyl-β-D-arabinofuranosyl)cytosine (IIa) and 5'-O-carboxylmethylcytidine (IIIa) were transformed by treatment with acetic anhydride and 4-dimethylaminopyridine to the peracetyl derivatives Ib-IIIb. These products reacted with p-nitrophenol in the presence of N, N'-dicyclohexylcarbodiimide to give the activated esters Ic-IIIc which on reaction with ammonia, dimethylamine or 2-aminoethanol afforded the corresponding carboxamides Id-IIId, IIe,f. Reactions of Ic and IIc with human serum albumin and bovine γ-globulin at pH 9.2, followed by hydrolysis of the N- or O-acetyl groups at pH 9.5, gave 50% up to 64% yields of the respective conjugates Ig, IIg and Ih, IIh.

The heat capacities and volumes of some low molecular weight amides, ketones, esters, and ethers in water over the whole solubility range

1978 ◽  
Vol 56 (22) ◽  
pp. 2808-2814 ◽  
Author(s):  
Geneviève Roux ◽  
Gérald Perron ◽  
Jacques E. Desnoyers
Keyword(s):  
Hydrophobic Interactions ◽  
Heat Capacities ◽  
Initial Slope ◽  
Pure Liquid ◽  
Factors Affecting ◽  
Solubility Range ◽  
Low Concentrations ◽  
Hydrophobic Solutes ◽  
Molal Volumes ◽  
Apparent Molal Heat Capacities

The densities and heat capacities per unit volume of aqueous solutions of propionamide, methylacetate, ethylacetate, methylethylketone and diethylketone, and bis(2-ethoxyethyl)ether were measured over the whole solubility range with a flow densimeter and a flow microcalorimeter. Most systems were studied at 10, 25, and 40 °C. Properties of the pure liquids were also measured whenever possible. The derived apparent molal volumes [Formula: see text] all decrease with concentration in the water-rich region, except with ethyl acetate which increases at high temperature. In general the more hydrophobic the solute the more negative the initial slope. All apparent molal heat capacities [Formula: see text] decrease as a function of concentration and the decrease is more important for more hydrophobic solutes. The apparent molal expansibilities [Formula: see text] are obtained from [Formula: see text]. They are positive for all solutes but, at low concentrations, they are smaller than the corresponding molar value of the pure liquid. Various factors affecting hydrophobic interactions are examined.

An Examination of the Heat Capacity of Activation for the Hydrolysis of t-Butyl Chloride in Water

1972 ◽  
Vol 50 (2) ◽  
pp. 167-175 ◽  
Author(s):  
J. M. W. Scott ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Alternative Hypothesis ◽  
Ion Pairs ◽  
Heat Capacities ◽  
Butyl Chloride ◽  
Methyl Halides ◽  
Displacement Reactions ◽  
Arrhenius Temperature Dependence ◽  
Hydrolysis Of ◽  
Arrhenius Temperature

The influence of ion-pair intermediates on solvolytic displacement reactions is considered for cases where the observed rate constant is complex.Such complex and composite rate constants under certain conditions may show deviations from the Arrhenius temperature dependence law. The deviations will manifest themselves as "spurious" positive and/or negative heat capacities of activation, superimposed on the real heat capacity terms.The hypothesis of Albery and Robinson (1) which proposes that the heat capacity of activation for t-butyl chloride is entirely "spurious" in the sense outlined above, is critically evaluated and rejected. An alternative hypothesis that considers the heat capacity to be a manifestation of solvation effects is retained.The mechanism of the hydrolysis of both the methyl and t-butyl halides in water is discussed and the kinetic laws appropriate to each are shown to be consistent with real heat capacities of activation. The mechanism proposed differs from the classical SN1–SN2 description. Both series of substrates are considered to give rise to intimate-ion-pairs but in the case of the methyl halides these react further by a path which involves the nucleophilicity of the solvent in a kinetically significant way. In the cases of the tertiary compounds, solvent separation of ion-pairs becomes kinetically significant. The nucleophilic component which characterizes the destruction of the solvent-separated ion-pairs for the tertiary compounds is kinetically insignificant.

Large hydrophobic interactions with clearly defined geometry. A dimeric steroid with catalytic properties

1982 ◽  
Vol 60 (6) ◽  
pp. 747-764 ◽  
Author(s):  
J. Peter Guthrie ◽  
Patricia A. Cullimore ◽  
Robert S. McDonald ◽  
Stella O'Leary
Keyword(s):  
Design Parameter ◽  
Reductive Amination ◽  
Catalytic Properties ◽  
Hydrophobic Interactions ◽  
Artificial Enzymes ◽  
Sodium Cyanoborohydride ◽  
Rate Enhancement ◽  
Nitrobenzoic Acid ◽  
Transition State Geometry ◽  
Hydrolysis Of

The steroid dimer α,α′-bis(17β-(4'-imidazolyl)-11-keto-5α- androstan-3β-amino)-p-xylene, 3, has been synthesized by reductive animation of 17β-(4′-imidazolyl)-5α- androstane-3,11-dione by p-xylenediamine in the presence of sodium cyanoborohydride, and by reductive amination of terephthalaidehyde by 3β-amino-17β-(4′-imidazolyl)-5α- androstan-11-one. The second method is stereochemically unambiguous; the first is not. Compound 3 acts as a catalyst for the hydrolysis of 3-arylpropionate esters of 3-hydroxy-4-nitrobenzoic acid. For the phenanthryl propionate the rate enhancement relative to imidazole is 200-fold, and the rate enhancement relative to the hypothetical rate for the propionate reacting with the steroid by the same transition state geometry is 3000-fold. The slope of a plot of log kcorr vs. π for the reaction of 3b with aryl propionate esters was 0.83; the corresponding slope for 12 was 0.39. This provides a design parameter for the construction of artificial enzymes.

Volumes and heat capacities of transfer of ammonium salts from water to aqueous octyldimethylamine oxide at 25 °C

1988 ◽  
Vol 66 (4) ◽  
pp. 767-773 ◽  
Author(s):  
Daniel Hétu ◽  
Jacques E. Desnoyers
Keyword(s):  
Aqueous Solutions ◽  
Thermodynamic Functions ◽  
Transfer Functions ◽  
Hydrophobic Interactions ◽  
Critical Micellar Concentration ◽  
Heat Capacities ◽  
Ammonium Salts ◽  
Salting Out ◽  
Ionic Systems ◽  
Micellization Process

The effect of an additive on a water–surfactant system can be studied through thermodynamic functions of transfer of the additive from water to aqueous solutions of the surfactant. These thermodynamic functions often go through extrema in the region of the critical micellar concentration (cmc) of the surfactant. As it can be shown with a simple chemical equilibrium model, the general shape of the transfer functions is primarily related to the pair-wise hydrophobic interactions between the additive and the surfactant monomers, to a shift in the monomer–micelle equilibrium and to the distribution of the additive between the aqueous phase and the micelles. Medium and electrostatic effects are also possible, especially with ionic systems. To separate these effects and identify the salts which distribute themselves in the micelles, the volumes and heat capacities of transfer of hydrophobic ammonium salts from water to aqueous solutions of dimethyloctylamine oxide have been investigated. The short chain salts have only a small effect on monomer–micelle equilibrium by salting out the monomers, whereas the more hydrophobic ones participate also to the micellization process, shifting more strongly the surfactant monomer–micelle equilibrium.

Sign in / Sign up

Export Citation Format

Share Document