Metal Ion Promoted Hydrolysis of Polyphosphates

1993 ◽  
Vol 46 (7) ◽  
pp. 1021 ◽  
Author(s):  
RJ Geue ◽  
AM Sargeson ◽  
R Wijesekera
Keyword(s):  
Time Scale ◽  
Metal Ion ◽  
The Other ◽  
Phosphate Esters ◽  
Bond Rupture ◽  
Hydroxo Complexes ◽  
Leaving Group ◽  
Rapid Hydrolysis ◽  
Rate Limiting ◽  
Hydrolysis Of

Various CoIII amine aqua hydroxo complexes have been evaluated for their ability to hydrolyse pyrophosphate to phosphate rapidly. Two very effective reagents have emerged, [Co( trpn )(OH)(OH2)]2+ ( trpn = 3,3′,3″-nitrilotris(propan-1-amine)) and [Co( tamen )(OH)-OH2)]2+ ( tamen = 6-(4-amino-2-azabutyl)-6-methyl-1,4-diazacycloheptane), and the latter has been examined closely to assess details of the mechanistic path for hydrolysis. The study shows substitution of the reagent on the substrate is fast and not rate determining. Two moles of the reagent are required to bind to [(en)2Co(P2O7)]- (en = ethane-1,2-diamine) to effect rapid hydrolysis. One supplies the coordinated OH- nucleophile to cleave the phosphorus anhydride, and the other binds as a chelate to the leaving group to assist bond rupture. An unproductive side path, to form a symmetrical dichelate of the form [(en)2Co(P2O7)Co( tamen )]2+, becomes rate limiting. However, if this path can be reduced in significance or eliminated, the study implies that polyphosphates and phosphate esters should hydrolyse on the subsecond time scale.

scholarly journals Vanadium(III) binding strengths of small biomolecules

2005 ◽  
Vol 77 (9) ◽  
pp. 1583-1594 ◽  
Author(s):  
Péter Buglyó ◽  
Eszter Márta Nagy ◽  
Imre Sóvágó
Keyword(s):  
Aqueous Solution ◽  
Amino Acids ◽  
Ionic Strength ◽  
Metal Ion ◽  
Donor Ligands ◽  
Spectroscopic Techniques ◽  
Hydroxo Complexes ◽  
Similarities And Differences ◽  
Small Biomolecules ◽  
Hydrolysis Of

The hydrolysis of vanadium(III) and the complex formation reactions between V(III) and weakly coordinating [glycine (GLY), DL-aspartic acid (ASP), D-penicillamine (PEN), DL-histidine (HIS)] or strongly coordinating [N,O] donor [picolinic (PIC) or 6-methylpicolinic acid (MePIC)] and [O,O] donor [maltol (MALT), 1,2-dimethyl-3-hydroxy-4-(1H)-pyridinone (DHP), tiron (TIR)] ligands were studied at 25.0 °C and an ionic strength of 0.20 M (KCl) in aqueous solution using combined pH-potentiometric and UV-vis spectroscopic techniques. Although some interaction between the amino acids and V(III) was found, we could not obtain reliable models for these systems owing to the intensive hydrolysis of the metal ion and the formation of polynuclear hydroxo complexes. With pyridine carboxylates or [O,O] donor ligands 1:1, 1:2 (in the latter case, also 1:3 species) were found to be present as major complexes in solution. The similarities and differences in binding V(III) by these ligands are discussed.

scholarly journals The effect of methanol and dioxan on the rates of the β-galactosidase-catalysed hydrolyses of some β-d-galactopyranosides: rate-limiting degalactosylation. The pH-dependence of galactosylation and degalactosylation

1973 ◽  
Vol 133 (1) ◽  
pp. 81-87 ◽  
Author(s):  
Michael L. Sinnott ◽  
Odile M. Viratelle
Keyword(s):  
Steady State ◽  
Ph Dependence ◽  
Methanol Concentration ◽  
The Other ◽  
Fractional Rate ◽  
Rate Of Increase ◽  
Rate Limiting ◽  
Hydrolysis Of

1. The effect of methanol on the β-galactosidase-catalysed hydrolysis of some nitrophenyl β-d-galactopyranosides has been studied under steady-state conditions. 2. The initial fractional rate of increase of kcat. as a function of methanol concentration with 2,4- and 3,5-dinitrophenyl β-d-galactopyranosides, but not with the other substrates studied, indicated that degalactosylation of the enzyme was rate-limiting. 3. The decrease in kcat. at high methanol concentrations for these substrates is considered to arise from causes other than galactosylation becoming rate-limiting. 4. Both galactosylation and degalactosylation of the enzyme require protonation of a group of pKa approx. 9.

A mechanistic study of the [La2(OCH3)2]4+- and [(1,5,9-triazacyclodo-decane):Zn:(OCH3)]+-catalyzed methanolysis of carbonates: possible application for the recycling of bisphenol A polycarbonates

2013 ◽  
Vol 91 (11) ◽  
pp. 1139-1146 ◽  
Author(s):  
Alexei A. Neverov ◽  
Leanne D. Chen ◽  
Sean George ◽  
David Simon ◽  
Christopher I. Maxwell ◽  
...  
Keyword(s):  
Bisphenol A ◽  
Metal Ion ◽  
Catalytic Decomposition ◽  
Nucleophilic Attack ◽  
Alkyl Derivative ◽  
Mechanistic Study ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Leaving Group ◽  
Rate Limiting

The kinetics of the methanolysis of seven methyl aryl carbonates (3) and two methyl alkyl carbonates (4) promoted by [12[ane]N3:Zn:(OCH3)]+ and [La2(OCH3)2]4+ catalysts (1 and 2, respectively) have been studied at 25.0 °C. Brønsted plots of the [Formula: see text] values for methanolysis versus aryloxy and alkoxy leaving group (LG) [Formula: see text] or [Formula: see text] values (the pKa values of the parent ArOH or ROH in methanol) for substrates 3 and 4 show an apparent downward break at [Formula: see text] ∼16.6 and 15.2 with [12[ane]N3:Zn:(OCH3)]+ and [La2(OCH3)2]4+, respectively. The breakpoint is not due to a change in rate-limiting step in a two-step process involving metal ion delivery of a coordinated methoxide to a transiently associated substrate and the subsequent breakdown of a tetrahedral intermediate to form product. The more satisfactory explanation is that the break arises when one correlates the rate constants for two dissimilar sets of substrates, namely aryloxy- and alkoxy-substituted 3 and 4. DFT calculations for the 1-promoted reactions of methyl 4-nitrophenyl carbonate (3b), which has a good aryloxy leaving group, and methyl isopropyl carbonate (4b), which has a relatively poor alkyl one, indicate that the catalyzed processes involve two steps. Accordingly, the methanolysis of all 3 having [Formula: see text] values for the parent phenols ≤15.3 involves rate-limiting nucleophilic attack and fast breakdown. For the isopropyl alkyl derivative (4b) having a [Formula: see text] > 18.13, the rate-liming step is the metal ion promoted breakdown of a tetrahedral intermediate. The catalytic system employing 2 has utility for the catalytic decomposition of poly(bisphenol A carbonate). In a semi-optimized system where 1000 mg of poly(bisphenol A carbonate), treated at 100 °C for 30 min in 2 mL of 60:40 chloroform−methanol containing La(OTf)3:NaOMe (5:7.5 mmol L−1), the reaction gave an 84% yield of bisphenol A, corresponding to >300 turnovers per catalyst.

scholarly journals Purification and mechanistic properties of an extracellular α-l-arabinofuranosidase from Monilinia fructigena

1987 ◽  
Vol 245 (3) ◽  
pp. 843-849 ◽  
Author(s):  
M A Kelly ◽  
M L Sinnott ◽  
M Herrchen
Keyword(s):  
Ring Opening ◽  
Gel Filtration ◽  
Bond Breaking ◽  
Absolute Rate ◽  
Monilinia Fructigena ◽  
First Order ◽  
A Value ◽  
Leaving Group ◽  
Rate Limiting ◽  
Hydrolysis Of

1. The alpha-L-arabinofuranosidase isoenzyme designated AFIII [Laborda, Archer, Fielding & Byrde (1974) J. Gen. Microbiol. 81, 151-163] was purified by sequential isoelectric focusing, hydrophobic chromatography, gel filtration and chromatofocusing. 2. The enzyme is a monomer of Mr 40,000. 3. On inactivation of the enzyme with 3H-labelled 1-alpha-L-arabinofuranosylmethyl-3-p-nitrophenyltriazene, 0.64 mol of alpha-L-arabinofuranosylmethyl residues/mol of enzyme is estimated to become attached to protein. 5. Neither first-order nor second-order rate constants for hydrolyses of aryl alpha-L-arabinofuranosides are dependent upon leaving-group acidity [beta lg(V) = −0.16 +/− 0.11; Beta lg(V/K) = −0.11 +/- 0.07; n = 7; delta pKa = 4.5] 6. Bond-breaking is nonetheless rate-limiting, as is shown by a value of 18(V) of 1.030 +/− 0.007 for the hydrolysis of p-nitrophenyl arabinoside. 7. Proton-donation to the leaving group is thus far advanced at the rate-limiting transition state for this enzyme. 8. Four alpha-L-arabinofuranosyl pyridinium salts are substrates, and an approximate beta lg(V) value of −0.9 can be estimated. 9. The absolute rate enhancement with the 4-bromoisoquinolinium salt, 2.5 × 10(9), is comparable with that observed with pyranosidases. 10. Ring-opening mechanisms can therefore be dismissed, even though they are known in the acid-catalysed hydrolysis of arabinofuranosides.

A FACILE SYNTHESIS AND REACTIONS OF AMINO SELENOLO[2,3-b]PYRIDINE CARBOXYLATE

2015 ◽  
Vol 12 (1) ◽  
pp. 3910-3918 ◽  
Author(s):  
Dr Remon M Zaki ◽  
Prof Adel M. Kamal El-Dean ◽  
Dr Nermin A Marzouk ◽  
Prof Jehan A Micky ◽  
Mrs Rasha H Ahmed
Keyword(s):  
Biological Activity ◽  
Carbonyl Compounds ◽  
Mass Spectra ◽  
The Other ◽  
Pyridine Derivatives ◽  
Facile Synthesis ◽  
High Biological Activity ◽  
Basic Hydrolysis ◽  
Pyridine Carboxylate ◽  
Hydrolysis Of

 Incorporating selenium metal bonded to the pyridine nucleus was achieved by the reaction of selenium metal with 2-chloropyridine carbonitrile 1 in the presence of sodium borohydride as reducing agent. The resulting non isolated selanyl sodium salt was subjected to react with various α-halogenated carbonyl compounds to afford the selenyl pyridine derivatives 3a-f  which compounds 3a-d underwent Thorpe-Ziegler cyclization to give 1-amino-2-substitutedselenolo[2,3-b]pyridine compounds 4a-d, while the other compounds 3e,f failed to be cyclized. Basic hydrolysis of amino selenolo[2,3-b]pyridine carboxylate 4a followed by decarboxylation furnished the corresponding amino selenolopyridine compound 6 which was used as a versatile precursor for synthesis of other heterocyclic compound 7-16. All the newly synthesized compounds were established by elemental and spectral analysis (IR, 1H NMR) in addition to mass spectra for some of them hoping these compounds afforded high biological activity.

Sign in / Sign up

Export Citation Format

Share Document