Determination of the Tacticity of Poly(methyl methacrylate) by Hydrolysis Rate Measurements

1992 ◽  
Vol 57 (2) ◽  
pp. 349-356 ◽  
Author(s):  
František Mikeš ◽  
Jan Pecka
Keyword(s):  
Methyl Methacrylate ◽  
Ester Group ◽  
Hydrolysis Rate ◽  
Nucleophilic Attack ◽  
Carbonyl Carbon Atom ◽  
Poly Methyl Methacrylate ◽  
Carboxylic Groups ◽  
Simple Kinetic Model ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The rate of hydrolysis of poly(methyl methacrylate) increases with the content of meso(isotactic) diads in the polymer. The increase in the rate of hydrolysis of isotactic polymers is due to an intramolecular nucleophilic attack by the adjacent carboxylic ion on the carbonyl carbon atom in the ester group. An analysis of the content of sequences of variously arranged ester and carboxylic groups shows that the hydrolysis of s-poly(methyl methacrylate) is a random process, while i-poly(methyl methacrylate) is hydrolyzed gradually (by zip mechanism), starting from the carboxylate group formed by an external attack by hydroxylic ions. The kinetic data thus obtained cannot be interpreted in terms of a simple kinetic model. The tacticity of poly(methyl methacrylate) may be estimated from the dependence of the rate of hydrolysis on the content of meso diads determinated by NMR spectrometry. The rate of hydrolysis depends not only on the tacticity of the polymer, but probably also on its configurational sequence statistics.

Reactions of macroions with ester and carboxylic groups of polymers

1987 ◽  
Vol 52 (9) ◽  
pp. 2194-2203
Author(s):  
Miloslav Kučera ◽  
Dušan Kimmer ◽  
Karla Majerová ◽  
Josef Majer
Keyword(s):  
Maleic Anhydride ◽  
Acrylic Acid ◽  
Methyl Methacrylate ◽  
Bond Formation ◽  
Covalent Bond ◽  
The Other ◽  
Poly Methyl Methacrylate ◽  
Other Hand ◽  
Carboxylic Groups ◽  
Poly Acrylic Acid

In the reaction of dianions with poly(methyl methacrylate), only an insignificant amount of insoluble crosslinked product is obtained. If, however, the concentration of grafting dianions approaches that of ester groups, the amount of poly(methyl methacrylate) which may thus be crosslinked becomes quite significant. Dications, too, can bring about crosslinking of only an insignificant number of poly(methyl methacrylate) chains. Carboxylic groups in poly(acrylic acid) react with dianions and dications in an anhydrous medium similarly to ester groups. On the other hand, in the presence of a cocatalytic amount of water dications are more readily bound to carboxylic groups, forming a covalent bond. The relatively highest efficiency was observed in the bond formation between dication and the poly[styrene-alt-(maleic anhydride)], both in an anhydrous medium and in the presence of H2O.

scholarly journals Stability of unimolecular films of 32P-labelled lecithin

1967 ◽  
Vol 105 (1) ◽  
pp. 401-407 ◽  
Author(s):  
H. Hauser ◽  
R. M. C. Dawson
Keyword(s):  
Pressure Change ◽  
Ion Concentration ◽  
Hydrolysis Rate ◽  
Ion Distribution ◽  
Rapid Perfusion ◽  
Poisson Boltzmann ◽  
Rate Of Hydrolysis ◽  
Poisson Boltzmann Equation ◽  
The Stability ◽  
Hydrolysis Of

1. The stability of monolayers of a highly unsaturated yeast lecithin labelled with 32P has been investigated by a surface radioactivity technique. 2. Lecithin films on distilled water at all surface pressures between 6 and 48dynes/cm. were completely stable on rapid perfusion of the subphase and on addition of ionic amphipathic substances to the film. 3. Ultrasonically treated lecithin added to the subphase caused a slow loss of surface radioactivity but little pressure change. 4. The addition of proteins to the subphase caused negligible changes in the film even when conditions were favourable for electrostatic heterocoagulation and penetration. 5. Lecithin films were not hydrolysed by a strongly acid subphase at room temperature. The very low rate of hydrolysis produced by alkali was proportional to the subphase OH−ion concentration: the apparent activation energy and temperature coefficient (Q10) of the reaction were 14250 cal. and 2·37 respectively. 6. Alkaline hydrolysis of lecithin monolayers was markedly stimulated by adding methanol (10–20%, v/v) to the subphase. The addition of ionic amphipaths to the monolayer had the expected type of effect on the hydrolysis rate, but its magnitude was far less than that suggested by an application of the Poisson–Boltzmann equation for ion distribution at a charged interface (Davies & Rideal, 1963).

scholarly journals Genetic control of the hydrolysis of aromatic esters by sheep plasma A-esterase

1966 ◽  
Vol 7 (3) ◽  
pp. 373-382 ◽  
Author(s):  
R. M. Lee
Keyword(s):  
Esterase Activity ◽  
Phosphate Esters ◽  
Hydrolysis Rate ◽  
Aromatic Esters ◽  
Hydrolysis Rates ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Naphthyl Acetate ◽  
Genetic Marking ◽  
Genetic Hypothesis

1. The rate of hydrolysis by sheep plasma of some carboxylic and phosphate esters has been determined for a random flock, and for a flock previously selected for its ability to hydrolyse di-(2-chloroethyl) aryl phosphates.2. A discontinuous variation in hydrolysis rate was found with all substrates tested and, using combinations of substrates, six types of plasma could be distinguished, each type having a different pattern of esterase activity.3. The most useful substrates for distinguishing between phenotypes were 1-naphthyl acetate and 4-ethoxycarbonylcoumarin-7-yl acetate. Three rates of hydrolysis were possible for each of these esters, and the highest rate for one was invariably combined with the lowest rate for the other, although the converse did not apply.4. To explain these results, and those of Lee (1964), it has been postulated that the quantitative production of esterase hydrolysing 1-naphthyl acetate is governed by the presence of an allele, termed Esa, at a particular gene locus. Similarly, the production of esterase hydrolysing 4-ethoxycarbonylcoumarin-7-yl acetate is determined by allele Esb, and where neither substrate is attacked the presence of a third allele, Esc, is proposed.5. The hydrolysis rates of haloxon, 1-naphthyl butyrate and 4-nitrophenyl butyrate varied in the same way as that of 1-naphthyl acetate, whereas the hydrolysis of indophenyl acetate followed the same pattern as that of 4-ethoxycarbonylcoumarin-7-yl acetate. The variation in hydrolysis rate of Coroxon could be explained by assuming that Esa and Esb are equal in this respect.6. A mating experiment produced results which were in accordance with the genetic hypothesis, but were too few in number to provide confirmation.7. The genetic marking of six types of sheep is possible, utilizing the variation in plasma A-esterase activity.

scholarly journals Hydrolysis of GTP by Sec4 protein plays an important role in vesicular transport and is stimulated by a GTPase-activating protein in Saccharomyces cerevisiae.

1992 ◽  
Vol 12 (5) ◽  
pp. 2017-2028 ◽  
Author(s):  
N C Walworth ◽  
P Brennwald ◽  
A K Kabcenell ◽  
M Garrett ◽  
P Novick
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Synthetic Lethality ◽  
Vesicular Transport ◽  
Yeast Cells ◽  
Hydrolysis Rate ◽  
Phosphoryl Group ◽  
Absolute Level ◽  
Yeast Saccharomyces Cerevisiae ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

Sec4, a GTP-binding protein of the ras superfamily, is required for exocytosis in the budding yeast Saccharomyces cerevisiae. To test the role of GTP hydrolysis in Sec4 function, we constructed a mutation, Q-79----L, analogous to the oncogenic mutation of Q-61----L in Ras, in a region of Sec4 predicted to interact with the phosphoryl group of GTP. The sec4-leu79 mutation lowers the intrinsic hydrolysis rate to unmeasurable levels. A component of a yeast lysate specifically stimulates the hydrolysis of GTP by Sec4, while the rate of hydrolysis of GTP by Sec4-Leu79 can be stimulated by this GAP activity to only 30% of the stimulated hydrolysis rate of the wild-type protein. The decreased rate of hydrolysis results in the accumulation of the Sec4-Leu79 protein in its GTP-bound form in an overproducing yeast strain. The sec4-leu79 allele can function as the sole copy of sec4 in yeast cells. However, it causes recessive, cold-sensitive growth, a slowing of invertase secretion, and accumulation of secretory vesicles and displays synthetic lethality with a subset of other secretory mutants, indicative of a partial loss of Sec4 function. While the level of Ras function reflects the absolute level of GTP-bound protein, our results suggest that the ability of Sec4 to cycle between its GTP and GDP bound forms is important for its function in vesicular transport, supporting a mechanism for Sec4 function which is distinct from that of the Ras protein.

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