Role of trinuclear Zn(II) complexes in promoting the hydrolysis of 4-nitrophenyl acetate

2004 ◽  
Vol 82 (3) ◽  
pp. 409-417 ◽  
Author(s):  
Qing-Chun Ge ◽  
Yan-He Guo ◽  
Hai Lin ◽  
Dong-Zhao Gao ◽  
Hua-Kuan Lin ◽  
...  
Keyword(s):  
Rate Constants ◽  
Volume Fraction ◽  
Bound Water ◽  
Catalytic Efficiency ◽  
Active Species ◽  
Nucleophilic Attack ◽  
Carboxyl Oxygen Atom ◽  
Ph Range ◽  
Hydrolysis Of

Potentiometric determination shows that trinuclear Zn(II) complexes of the four tripods 1,3,5-tri(2′,5′-diazahexyl)benzene (L1), 1,3,5-tri(2′,5′-diazaheptyl)benzene (L2), 1,3,5-tri(2′,5′-diazaoctyl)benzene (L3), and 1,3,5-tri(2′,5′-diazanonyl)benzene (L4) could be potential hydrolytic catalysts. CH3CN solutions containing [3Zn:L]T (0.5~2 × 10–3 mol·dm–3) with I = 0.10 mol·dm–3 of KNO3 and Good's buffer (10% volume fraction) were studied for the catalyzing hydrolysis of p-nitrophenyl acetate (NA, 0.5~2 × 10–3 mol·dm–3), at 298 K, in the 6.5–8.2 pH range. The observed rate constants, kobs, fit the equilibrium equation kobs = kcom [3Zn:L]T + kOH[OH–] + k0. The sigmoid pH~kcom profiles for NA hydrolysis suggest that either the Zn(II)-bound hydroxyl or the Zn(II)-bound water forms of the catalysts can be the active species. The observed second-order rate constants are 0.0082, 0.011, 0.0059, and 0.0019 mol–1·dm3·s–1 for the four Zn3L–H2O complexes (kA) and 0.342, 0.257, 0.382, and 0.091 mol–1·dm3·s–1 for the four Zn3L–OH- groups (kB), respectively. However, under the condition that [NA] = 0.5 × 10–3 mol·dm–3 and [3Zn:L1]T = 2~4 × 10–2 mol·dm–3 at pH 7.6, the observed rate constants, kobs, obey the equilibrium kobs = kcom[3Zn:L]T/(1/K′ + [3Zn:L]T). This indicates that the 3:1 complex (or its deprotonated hydroxide form) mediates NA hydrolysis by nucleophilic attack of the carboxyl center with the pre-formation of a coordination bond between the carboxyl oxygen atom and the Zn(II) ion. Comparison with other models was made, and the reasons for the high catalytic efficiency of the tripodal complexes were given.Key words: tripod, Zn(II), catalysis, NA hydrolysis, polynuclear.

Stability of the Nerve Gas Antidote BIS (4-Hydroxyiminomethyl-1-Pyridinomethyl) Ether Dichloride (Toxogonin®)

1968 ◽  
Vol 2 (9) ◽  
pp. 234-243 ◽  
Author(s):  
Inga Christenson
Keyword(s):  
Aqueous Solution ◽  
Hydrochloric Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Kinetics Of Hydrolysis ◽  
Dilute Aqueous Solution ◽  
Nerve Gas ◽  
Ph Range ◽  
Kinetics Of ◽  
Hydrolysis Of

The products and kinetics of hydrolysis of the nerve gas antidote bis(4-hydroxyiminomethyl - 1 - pyridinemethyl) ether dichloride (Toxogonin ®) have been investigated. A survey of these studies is given: The hydrolytic reactions were studied in the pH range 1 M hydrochloric acid to 1 M sodium hydroxide at 25, 45, 75 and 85° C. Rate constants were determined in dilute aqueous solution, generally with an initial Toxogonin concentration of 0.01 mg per ml. In addition, a report is given concerning two-year storage of 25 percent (w/v) Toxogonin solutions at pH 2.5, 3.0 and 3.5. The solutions were stored in glass or polypropylene ampuls at 5, 15, 25 and 45°C. At 5 and 15C° decomposition was negligible, at 25 and 45 °C average decomposition was 1.5 percent and 3.3 percent, respectively.

Isothiazole chemistry. IV. Cyanide cleavage of the S-N bond in 3-hydroxyisothiazole

1967 ◽  
Vol 20 (12) ◽  
pp. 2729 ◽  
Author(s):  
WD Crow ◽  
I Gosney
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Nucleophilic Attack ◽  
Effect Of Temperature ◽  
Cyanide Ion ◽  
Equilibrium Studies ◽  
Conjugate Acid ◽  
Ph Range ◽  
Rate Profile ◽  
Direct Attack

Nucleophilic attack on 3-hydroxyisothiazole by cyanide ion, yielding cis-3-thiocyanoacrylamide, has been investigated over the pH range 0.00-5.50. Rate constants have been measured both for direct attack by cyanide ion and from the effect of cyanide ion in retarding the cyclization of the thiocyanoacrylamide; in both cases the derived rate constants agree. The pH-rate profile of the reaction reveals the existence of two kinetically discrete mechanisms. Within the range 5.50-4.00 the dominating mechanism is one involving a slow direct attack on 3-hydroxyisothiazole itself, while at pH less than 3.50 the conjugate acid of this molecule is subjected to a much faster attack. Equilibrium studies have been made for the system, and the effect of temperature on the equilibrium constant has been used to derive thermodynamic parameters.

The Study of the Hydrolysis of the Phosphate Diester Catalyzed by an Anion Metallomicelle of Ce3+-Diethylenetriamine

2012 ◽  
Vol 554-556 ◽  
pp. 353-356
Author(s):  
Shu Lan Cai ◽  
Fa Mei Feng ◽  
Tao Wang ◽  
Xiu Lan Zhang
Keyword(s):  
Critical Micelle Concentration ◽  
High Activity ◽  
Catalytic Efficiency ◽  
Active Species ◽  
Phosphate Ester ◽  
Catalytic Hydrolysis ◽  
Phosphate Diester ◽  
Nitrophenyl Phosphate ◽  
Hydrolysis Of ◽  
Lauroyl Sarcosinate

The catalytic hydrolysis of Bis(p-nitrophenyl) phosphate ester (BNPP) in the metallomicelle made up of Ce3+-diethylenetriamine and LSS (N-lauroyl sarcosinate) was investigated by UV/VIS method. The effect of the catalytic efficiency and stability of the system was studied under the different conditions. The results indicated that the catalytic system exhibited high activity, stability and reproducibility in the BNPP catalytic hydrolysis under proper proportion of Ce3+ion and diethylenetriamine, pH and temperature when the concentration of LSS is higher than its CMC (critical micelle concentration). The results also showed that the active species is the complex made up of Ce3+ion and diethylenetriamine.

An ATP-inhibited soluble 5'-nucleotidase of rat kidney

1988 ◽  
Vol 254 (2) ◽  
pp. F191-F195
Author(s):  
M. Le Hir ◽  
U. C. Dubach
Keyword(s):  
High Speed ◽  
Catalytic Properties ◽  
Divalent Cations ◽  
Rat Kidney ◽  
Maximal Activity ◽  
Rate Of Hydrolysis ◽  
Membrane Bound ◽  
Ph Range ◽  
Hydrolysis Of

Hydrolysis of 5'-AMP by 5'-nucleotidase is a possible source of adenosine in the kidney. A renal membrane-bound ecto-5'-nucleotidase has been previously described. The present study deals with the catalytic properties of a 5'-AMP phosphohydrolase partially purified from high-speed supernatants of rat kidney homogenates. It exhibits phosphatase activity toward 5'-AMP, 5'-IMP, and 5'-GMP, but not toward 2'- and 3'-AMP and corresponds therefore to a 5'-nucleotidase. The hydrolysis of 5'-AMP by the soluble 5'-nucleotidase requires divalent cations. Maximal activity is reached with 10 microM of either Mn2+ or Co2+, whereas half-maximal activity is obtained with approximately 400 microM Mg2+. The soluble 5'-nucleotidase exhibits Michaelis-Menten kinetics with a Km of 9.5 microM for 5'-AMP. In the presence of 1 mM of free Mg2+, physiological concentrations of ATP provoke an increase of the Km for 5'-AMP and a decrease of Vmax. An increase of the pH of 0.4 units in the pH range 6.4-7.4 roughly doubles the rate of hydrolysis of 5'-AMP. The effects of ATP and of the pH are compatible with a role of the renal soluble 5'-nucleotidase in the hydrolysis of 5'-AMP and in the production of adenosine during hypoxia.

The uncatalysed, and the imidazole and o-mercaptobenzoic acid catalysed, hydrolysis of p-nitrophenyl N-benzyloxycarbonylglycinate

1969 ◽  
Vol 22 (1) ◽  
pp. 109 ◽  
Author(s):  
RW Hay ◽  
RJ Trethewey
Keyword(s):  
Active Species ◽  
Ion Concentration ◽  
Nucleophilic Catalysis ◽  
First Order ◽  
Catalysed Reaction ◽  
Catalytically Active ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The uncatalysed hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate has been studied in 40% (v/v) ethanol-water over the pH range 7.6-8.5. The reaction shows a first-order dependence on the hydroxide ion concentration. The quite rapid hydrolysis (k = (4.4�0.4) x 104 1. mole-1 min-1 at 20�) may possibly indicate the formation of a 2-benzyloxyoxazoline-5-one intermediate. ��� Unlike the hydrolysis of the p-nitrophenyl esters of α-amino acids, the hydrolysis of the N-protected derivatives is not catalysed by carbon dioxide. The hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate is, however, catalysed by imidazole in 40% v/v ethanol-water. Unprotonated imidazole (Im) is the catalytically active species. N-Benzyloxycarbonylaminoacetylimidazole has been detected spectrophotometrically as an intermediate in the reaction, indicating nucleophilic catalysis by the base. o-Mercaptobenzoic acid was also found to catalyse the hydrolysis of p-nitrophenyl N- benzyloxycarbonylglycinate. pH-rate profile studies indicate that the dianion of o-mercaptobenzoic acid is the catalytically active species, the substrate presumably hydrolysing via the thioester intermediate Z- NHCH2COSC6H4COO-, although efforts to detect such an intermediate have been unsuccessful. Some evidence for a thioester intermediate in the L- cysteine-catalysed reaction has been obtained.

The hydrolysis of some N-benzoylamino acids in dilute mineral acid

1967 ◽  
Vol 45 (17) ◽  
pp. 1921-1924 ◽  
Author(s):  
J. B. Capindale ◽  
H. S. Fan
Keyword(s):  
Carboxylic Acid ◽  
Hydrochloric Acid ◽  
Glutamic Acid ◽  
Rate Constants ◽  
Mineral Acid ◽  
Dilute Solution ◽  
Acid Catalyzed ◽  
Ph Range ◽  
Hydrolysis Of ◽  
Derivatives Of

The behavior of N-benzoylaspartic acid and N-benzoylglutamic acid has been investigated at 100° in dilute solution in water and aqueous hydrochloric acid within the pH range 3.1–0.5. Some data are presented concerning the hydrolysis of the N-benzoyl derivatives of alanine, β-alanine, leucine, glycine, serine, and β-ethanolamine in water, 0.1 N hydrochloric acid, and 2 N hydrochloric acid. Benzoylglutamic acid undergoes a pH-independent conversion into pyrrolid-2-one-5-carboxylic acid, which then hydrolyses in mineral acid to glutamic acid; however, N-benzoylaspartic acid, under similar conditions, hydrolyses much more rapidly by a route which does not involve the corresponding lactam as an intermediate. In anhydrous alcohols the solvolysis of N-benzoylaspartic acid gives mixtures of aspartic acid and the β ester.First-order rate constants have been obtained for the acid-catalyzed hydrolysis of pyrrolid-2-one-5-carboxylic acid (I) and azetidin-2-one-4-carboxylic acid (II) in water over this pH range.

scholarly journals Role of Asp104 in the SHV β-Lactamase

2006 ◽  
Vol 50 (12) ◽  
pp. 4124-4131 ◽  
Author(s):  
Christopher R. Bethel ◽  
Andrea M. Hujer ◽  
Kristine M. Hujer ◽  
Jodi M. Thomson ◽  
Mark W. Ruszczycky ◽  
...  
Keyword(s):  
Amino Acid ◽  
Catalytic Efficiency ◽  
Saturation Mutagenesis ◽  
Amino Acid Residues ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Threefold Increase ◽  
Rate Limiting ◽  
Hydrolysis Of

ABSTRACT Among the TEM-type extended-spectrum β-lactamases (ESBLs), an amino acid change at Ambler position 104 (Glu to Lys) results in increased resistance to ceftazidime and cefotaxime when found with other substitutions (e.g., Gly238Ser and Arg164Ser). To examine the role of Asp104 in SHV β-lactamases, site saturation mutagenesis was performed. Our goal was to investigate the properties of amino acid residues at this position that affect resistance to penicillins and oxyimino-cephalosporins. Unexpectedly, 58% of amino acid variants at position 104 in SHV expressed in Escherichia coli DH10B resulted in β-lactamases with lowered resistance to ampicillin. In contrast, increased resistance to cefotaxime was demonstrated only for the Asp104Arg and Asp104Lys β-lactamases. When all 19 substitutions were introduced into the SHV-2 (Gly238Ser) ESBL, the most significant increases in cefotaxime and ceftazidime resistance were noted for both the doubly substituted Asp104Lys Gly238Ser and the doubly substituted Asp104Arg Gly238Ser β-lactamases. Correspondingly, the overall catalytic efficiency (k cat/Km ) of hydrolysis for cefotaxime was increased from 0.60 ± 0.07 μM−1 s−1 (mean ± standard deviation) for Gly238Ser to 1.70 ± 0.01 μM−1 s−1 for the Asp104Lys and Gly238Ser β-lactamase (threefold increase). We also showed that (i) k 3 was the rate-limiting step for the hydrolysis of cefotaxime by Asp104Lys, (ii) the Km for cefotaxime of the doubly substituted Asp104Lys Gly238Ser variant approached that of the Gly238Ser β-lactamase as pH increased, and (iii) Lys at position 104 functions in an energetically additive manner with the Gly238Ser substitution to enhance catalysis of cephalothin. Based on this analysis, we propose that the amino acid at Ambler position 104 in SHV-1 β-lactamase plays a major role in substrate binding and recognition of oxyimino-cephalosporins and influences the interactions of Tyr105 with penicillins.

scholarly journals Phe-140 Determines the Catalytic Efficiency of Arylacetonitrilase from Alcaligenes faecalis

2020 ◽  
Vol 21 (21) ◽  
pp. 7859
Author(s):  
Jung-Soo Kim ◽  
Sanjay K. S. Patel ◽  
Manish K. Tiwari ◽  
Chunfen Lai ◽  
Anurag Kumar ◽  
...  
Keyword(s):  
Amino Acids ◽  
Catalytic Efficiency ◽  
Thiol Group ◽  
Alcaligenes Faecalis ◽  
Nucleophilic Attack ◽  
Charged Amino Acids ◽  
Molecular Determinant ◽  
Systematic Strategy

Arylacetonitrilase from Alcaligenes faecalis ATCC8750 (NitAF) hydrolyzes various arylacetonitriles to the corresponding carboxylic acids. A systematic strategy of amino acid residue screening through sequence alignment, followed by homology modeling and biochemical confirmation was employed to elucidate the determinant of NitAF catalytic efficiency. Substituting Phe-140 in NitAF (wild-type) to Trp did not change the catalytic efficiency toward phenylacetonitrile, an arylacetonitrile. The mutants with nonpolar aliphatic amino acids (Ala, Gly, Leu, or Val) at location 140 had lower activity, and those with charged amino acids (Asp, Glu, or Arg) exhibited nearly no activity for phenylacetonitrile. Molecular modeling showed that the hydrophobic benzene ring at position 140 supports a mechanism in which the thiol group of Cys-163 carries out a nucleophilic attack on a cyanocarbon of the substrate. Characterization of the role of the Phe-140 residue demonstrated the molecular determinant for the efficient formation of arylcarboxylic acids.

Kinetic and Mechanistic Studies of the Acid-Catalysed Hydrolysis of Ditert.-butyl Malonate in Dioxane-Water Media

1986 ◽  
Vol 41 (11) ◽  
pp. 1330-1334
Author(s):  
Fayez Y. Khalil ◽  
Morcos T. Hanna ◽  
Adel N. Asaad
Keyword(s):  
Dielectric Constant ◽  
Organic Solvent ◽  
Rate Constants ◽  
Maximum Concentration ◽  
Steric Effects ◽  
Kinetic Investigation ◽  
Mechanistic Studies ◽  
Water Media ◽  
Hydrolysis Of

A kinetic investigation of the consecutive acid-catalysed hydrolysis of ditert.-butyl malonate in dioxane-water mixtures is given. The rate constants of the first and second hydrolysis steps decrease by addition of the organic solvent, and both steps proceed concurrently by AA11 and AAc2 mechanisms. The kinetic ratio kI/kII depends on the solvent composition. The results are compared with those obtained previously for ditert.-butyl succinate in many aspects such as rate, percentage AA11 fission and the role of the inductive as well as steric effects. The maximum concentration of the intermediate, halfester, decreases with decrease in the ionising power of the solvent and has nearly the same value for malonate and succinate in isocomposition media. The effect of the dielectric constant on the rate constant and the activation thermodynamic parameters are discussed.

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