Nucleophilic Attack by Oxyanions on a Phosphate Monoester Dianion:  The Positive Effect of a Cationic General Acid

Kirby, Anthony J.; Lima, Marcelo F.; Silva, Davi Da; Nome, Faruk

doi:10.1021/ja038428w

Cited by 28 publications

(19 citation statements)

References 16 publications

(20 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, significant differences have emerged [54]. However, significant differences have emerged [54].…”

Section: Scheme 223mentioning

confidence: 99%

General Acid–Base Catalysis in Model Systems

Kirby

2006

Hydrogen‐Transfer Reactions

Self Cite

View full text Add to dashboard Cite

IntroductionProton transfer is the most common reaction in living systems, in which reactions have to be strictly controlled, and most are catalyzed by enzymes. The great majority of enzyme catalyzed reactions are ionic, involving heterolytic bond making and breaking, and thus the creation or neutralization of charge. Under conditions of constant pH this requires the transfer of protons (Eq. (2.1)). ð2:1ÞGeneral acid and general base catalysis are terms commonly used to describe two different characteristics of reactions, the (observable) form of the rate law or a (hypothetical) reaction mechanism proposed to account for it. It is important to be aware of (and for authors to make clear) which is meant in a particular case.General acid-base catalysis provides mechanisms for bringing about the necessary proton transfers without involving hydrogen or hydroxide ions, which are present in water at concentrations of only about 10 À7 M under physiological conditions. At pHs near neutrality relatively weak acids and bases can compete with lyonium or lyate species because they can be present in much higher concentrations. 2.1.1 KineticsThe basics of general acid and general base catalysis are described clearly and in detail in Chapter 8 of Maskill [1]. Acid-base catalysis is termed specific if the rate of the reaction concerned depends only on the acidity (pH, etc.) of the medium. This is the case if the reaction involves the conjugate acid or base of the reactant preformed in a rapid equilibrium process -normal behavior if the reactant is weakly basic or acidic. The conjugate acid or base is then, by definition, a strong 975 acid or base, and the reverse proton transfer to solvent is thus rapid, probably diffusion-controlled -and certainly faster than a competing forward reaction involving the making or breaking of covalent bonds. This forward reaction of the conjugate acid or base of the reactant is therefore rate determining, and the rate expression -for example for the hydrolysis of an unreactive ester (Scheme 2.1)contains only a single term in (lyonium) acid concentration:General acid-base catalysis is defined experimentally by the appearance in the rate law of acids and/or bases other than lyonium or lyate ions. For example, the hydrolysis of enol ethers 1.2 (Scheme 2.2) is general acid-catalyzed. In strong acid the rate expression will be the same as in Scheme 2.1, but near neutral pH the rate is found to depend also on the concentration of the buffer ðHA þ A À Þ used to maintain the pH. Measurements at different buffer ratios show that the catalytic species is the acid HA. (If more than one acid is present there will be an additional term k HAi ½HA i ½1:2 for each.)If in these experiments the measurements at different buffer ratios showed that the catalytic species was the conjugate base A À the reaction would be kinetically general base catalyzed. In which case HA and A À would probably subsequently be referred to as BH þ and B. Thus the enolisation of ketones is general base catalysed (Scheme 2.3). Àd½1:3=dt ¼ k...

show abstract

“…However, significant differences have emerged [54]. However, significant differences have emerged [54].…”

Section: Scheme 223mentioning

confidence: 99%

General Acid–Base Catalysis in Model Systems

Kirby

2006

Hydrogen‐Transfer Reactions

Self Cite

View full text Add to dashboard Cite

show abstract

“…[10][11][12] The development of such stable and highly reactive nucleophiles has a wide range of applications in chemical detoxification, e.g., where quantitative phosphate bond cleavage is the target. 13 Some researchers in this field have noted that α-nucleophiles, such as hydroxylamine, represent a new perspective, but a better understanding of the attacking nucleophilic atom is still to be gained and this has prompted extensive mechanistic studies of the reactions of α-nucleophiles with activated acyl derivatives [14][15][16][17][18][19][20] , phosphate esters [21][22][23][24][25][26][27][28][29] and amides [30][31][32][33] . Hydroxylamine is a single α-nucleophile, the neutral and anionic forms of which ensure high rates of acyl transfer over a wide pH range and no other known α-nucleophile can beat it on its very strong nucleophilicity.…”

Section: Introductionmentioning

confidence: 99%

On the mechanism of the reaction between aryl acetates and hydroxylamine

Mazera¹,

Gesser²,

Pliego³

2007

Arkivoc

View full text Add to dashboard Cite

The reaction of aryl acetates and hydroxylamine produces O-acylhydroxylamine and Nacylhydroxylamine, the latter being essentially observed for good leaving group esters and the former for poor leaving esters. For both acylation reactions, kinetics studies suggested a tetrahedral intermediate intervention for nucleofuges in a pKa range of 1 to 9. Esters having leaving groups with a pKa value less than 7 react by a rate-determining step inferred to be the tetrahedral intermediate formation, while for esters having leaving groups with a pKa value equal to or higher than 7, the rate-limiting step has been proposed to be the tetrahedral intermediate decomposition. General bifunctional acid-base catalysis by a second hydroxylamine molecule was identified as one of the components of the reaction for the intermediate collapse to products in the poor leaving group ester

show abstract

“…[1] These species are extremely inert under laboratory conditions, but under enzymatic conditions the rate enhancements of their reactions are among the largest established to date. [2] The proficiency of enzymes catalyzing phosphate ester processes have constantly encouraged a huge number of experimental [3][4][5][6][7][8] and theoretical [9][10][11][12][13][14][15] studies aimed at explaining how this catalysis is achieved. However, despite the great deal of information obtained, there are still unresolved issues.…”

Section: Introductionmentioning

confidence: 99%

“…After thermalization with Ar introduced into the cell through a pulsed valve, the ions were re-isolated by "single shots" and allowed to react with reagents in the cell. The pressure of the neutral reactants ranged from 10 À8 to 10 À7 mbar and was measured by a Bayard-Alpert ionization gauge, whose readings were calibrated using, as a reference, the known rate coefficient of the CH 4 + CH 4 + !CH 5 + + CH 3 C reaction. The readings were corrected for the relative sensitivity to the various gases used according to a standard method.…”

mentioning

confidence: 99%

Gas‐Phase Chemistry of Diphosphate Anions as a Tool To Investigate the Intrinsic Requirements of Phosphate Ester Enzymatic Reactions: The [M¹M²HP₂O₇]⁻ Ions

Pepi

Barone

Cimino

et al. 2007

Chemistry A European J

View full text Add to dashboard Cite

Experimental studies on gaseous inorganic phosphate ions are practically nonexistent, yet they can prove helpful for a better understanding of the mechanisms of phosphate ester enzymatic processes. The present contribution extends our previous investigations on the gas-phase ion chemistry of diphosphate species to the [M(1)M(2)HP(2)O(7)](-) ions where M(1) and M(2) are the same or different and correspond to the Li, Na, K, Cs, and Rb cations. The diphosphate ions are formed by electrospray ionization of 10(-4) M solutions of Na(5)P(3)O(10) in CH(3)CN/H(2)O (1/1) and MOH bases or M salts as a source of M(+) cations. The joint application of mass spectrometric techniques and quantum-mechanical calculations makes it possible to characterize the gaseous [M(1)M(2)HP(2)O(7)](-) ions as a mixed ionic population formed by two isomeric species: linear diphosphate anion coordinated to two M(+) cations (group I) and [PO(3)M(1)M(2)HPO(4)](-) clusters (group II). The relative gas-phase stabilities and activation barriers for the isomerization I-->II, which depend on the nature of the M(+) cations, highlight the electronic susceptibility of P-O-P bond breaking in the active site of enzymes. The previously unexplored gas-phase reactivity of [M(1)M(2)HP(2)O(7)](-) ions towards alcohols of different acidity was investigated by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). The reaction proceeds by addition of the alcohol molecule followed by elimination of a water molecule.

show abstract

Nucleophilic Attack by Oxyanions on a Phosphate Monoester Dianion: The Positive Effect of a Cationic General Acid

Cited by 28 publications

References 16 publications

General Acid–Base Catalysis in Model Systems

General Acid–Base Catalysis in Model Systems

On the mechanism of the reaction between aryl acetates and hydroxylamine

Gas‐Phase Chemistry of Diphosphate Anions as a Tool To Investigate the Intrinsic Requirements of Phosphate Ester Enzymatic Reactions: The [M¹M²HP₂O₇]⁻ Ions

Contact Info

Product

Resources

About

Nucleophilic Attack by Oxyanions on a Phosphate Monoester Dianion: The Positive Effect of a Cationic General Acid

Cited by 28 publications

References 16 publications

General Acid–Base Catalysis in Model Systems

General Acid–Base Catalysis in Model Systems

On the mechanism of the reaction between aryl acetates and hydroxylamine

Gas‐Phase Chemistry of Diphosphate Anions as a Tool To Investigate the Intrinsic Requirements of Phosphate Ester Enzymatic Reactions: The [M1M2HP2O7]− Ions

Contact Info

Product

Resources

About

Gas‐Phase Chemistry of Diphosphate Anions as a Tool To Investigate the Intrinsic Requirements of Phosphate Ester Enzymatic Reactions: The [M¹M²HP₂O₇]⁻ Ions