Structure-activity relations of (2-chloroethyl)nitrosoureas. 1. Deuterium isotope effects in the hydrolysis of 1-(2-chloroethyl)-1-nitrosoureas: evidence for the rate-limiting step

1987 ◽  
Vol 52 (4) ◽  
pp. 484-488 ◽  
Author(s):  
Neil Buckley
Keyword(s):  
Isotope Effects ◽  
Rate Limiting Step ◽  
Structure Activity ◽  
Limiting Step ◽  
Structure Activity Relations ◽  
Deuterium Isotope Effects ◽  
Rate Limiting ◽  
Hydrolysis Of

The Meyer Reaction of Phenylnitromethane in Acid. III. The Tautomerization to the aci-Form

1971 ◽  
Vol 49 (21) ◽  
pp. 3493-3501 ◽  
Author(s):  
J. T. Edward ◽  
P. H. Tremaine
Keyword(s):  
Rate Increase ◽  
Isotope Effects ◽  
Dilute Acid ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Deuterium Isotope Effects ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Competing Reactions

The rate-acidity profiles for the Meyer rearrangement–hydrolysis of phenylnitromethane in sulfuric, perchloric, and hydrochloric acid show a maximum near 3 M acid. Ring-substituted phenylnitromethanes also show a maximum in their rate profiles, at slightly different acid concentrations. These maxima arise because the slow formation of the aci-form is followed by two competing reactions: fast tautomerization back to the nitro-form, and fast rearrangement–hydrolysis to the Meyer products. The rearrangement is rate-limiting in dilute acid and is acid-catalyzed, causing the rate increase. In more concentrated acid, the rate-limiting step is the nitro to aci tautomerization, which is not acid-catalyzed, and which goes more slowly as the activity of water decreases.The tautomerization was studied by means of primary and solvent deuterium isotope effects, and was found to occur through proton abstraction by water, through a transition state closely resembling the products.

Biological treatability of a corn wet mill effluent

2002 ◽  
Vol 45 (12) ◽  
pp. 339-346 ◽  
Author(s):  
G. Eremektar ◽  
O. Karahan-Gul ◽  
F. Germirli-Babuna ◽  
S. Ovez ◽  
H. Uner ◽  
...  
Keyword(s):  
Biological Treatment ◽  
Rate Coefficient ◽  
Activated Sludge Process ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Metabolic Products ◽  
High Level ◽  
Biological Treatability ◽  
Rate Limiting ◽  
Hydrolysis Of

Corn wet mill effluents are studied in terms of their characteristics relevant for biological treatment. They have a high COD of mainly soluble and biodegradable nature, with practically no soluble inert components. They generate a relatively high level of soluble residual metabolic products, which affects the choice of the appropriate biological treatment and favors aerobic activated sludge process. Experimental assessment of process kinetics yields typical values. Hydrolysis of the slowly biodegradable COD, the rate limiting step for the utilization of substrate, is characterized by an overall rate coefficient, which is within the range commonly associated for the hydrolysis of starch.

scholarly journals The necessity of magnesium cation for acid assistance aglycone departure in catalysis by Escherichia coli (lacZ) β-galactosidase

1978 ◽  
Vol 175 (2) ◽  
pp. 539-546 ◽  
Author(s):  
M L Sinnott ◽  
S G Withers
Keyword(s):  
Escherichia Coli ◽  
Isotope Effects ◽  
Free Enzyme ◽  
Pyridinium Salts ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Magnesium Cation ◽  
Rate Of Hydrolysis ◽  
Rate Limiting ◽  
Hydrolysis Of

1. Removal of Mg2+ from Escherichia coli (lacZ) beta-galactosidase slightly increases the rate of hydrolysis of galactosyl pyridinium salts, but decreases the rate of hydrolysis of arylgalactosides. 2. Fair correlation of logkcat. and log (Km) with the pKa of aglycone is now observed for arglygalactosides, as well as for glycosyl pyridinium salts. 3. Degalactosylation of Mg2+-free enzyme is the rate-limiting step in the hydrolysis of 2,4-dinitrophenyl galactoside. 4. alpha-Deuterium kinetic isotope effects for both sets of substrates are consistent with the rate-determining generation of a glycosyl cation. 5. The pH-independent, SNl hydrolysis of 3,4-dinitrophenyl galactoside has been measured: it is as fast as that of the galactosyl 3-chloropyridinium ion. 6. Hydrolysis of these two substrates by Mg2+-free enzyme proceeds at very similar rates. 7. It is concluded that loss of both types of aglycone takes place, without acid catalysis, from the first ES complex of substrate and apoenzyme. 8. Data for galactosyl azide and thiopicrate confirm that neither charge nor change of atom is the cause of the differences in behavior between aryl galactosides and galactosylpyridinium salts.

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