Intramolecular catalysis. Part 9.1 The hydrolysis of p-nitrophenyl acetate catalysed by imidazoles having proximate carboxylate groups

1997 ◽  
pp. 219-222 ◽  
Author(s):  
Keith Bowden ◽  
Andrew Brownhill
Keyword(s):  
Intramolecular Catalysis ◽  
Carboxylate Groups ◽  
Hydrolysis Of

scholarly journals Tetrakis(μ-2-phenylacetato-κ2O:O′) bis{(DMSO κO′)]copper(II)}(Cu-Cu)]

2014 ◽  
Vol 70 (a1) ◽  
pp. C1709-C1709
Author(s):  
Meriem Benslimane ◽  
Yasmine Kheira Redjel ◽  
Georges Denes ◽  
Hocine Merazig
Keyword(s):  
Transition Metals ◽  
Bond Length ◽  
Phenylacetic Acid ◽  
Inversion Center ◽  
Polymeric Complex ◽  
Dimeric Complex ◽  
Bridging Ligands ◽  
Carboxylate Groups ◽  
Distorted Octahedral ◽  
Hydrolysis Of

Carboxylate groups may interact as bridging ligands with divalent transition metals present in biological environments, thereby altering the bioavailability of drugs. Moreover, it is well known that many complexes of divalent transition metals are capable of catalyzing the hydrolysis of RNA (Stem et al., 1990; Kimura, 1994). The coordination chemistry of Cu2+ complexes bridged by phenylacetate has been reported. We have found only two reports of a dinuclear Co2+ complexes, namely tetrakis (phenylacetato)bis[(quinoline-N)-cobalt(II)](Cui et al.,1999),μ-aqua-κ2O:O-di-μ-phenylacetato-κ4O:O′-bis[(1,10-phenanthroline-κ2N,N′) (phenyl acetato-κO)cobalt(II)](Kong et al., 2005) and dinuclear Cu2+ complex, namely tetrakis (phenylacetato)bis-[(N,N-dimethylformamide)copper(II)], in which all phenylacetate groups are in bidendate bridging modes. In this presentation, the crystal structure of a new dimeric complex obtained by reaction of phenylacetic acid with copper(II) acetate is described. Each Cu(II) atom is six-coordinated by five O atoms from carboxylate groups of the phenylacetate and DMSO ligands and is completed by a Cu-Cu bond in a strongly distorted octahedral coordination, in which an inversion center is located at the mid-point of the Cu-Cu bond with a Cu...Cu distance of 2.6321(4) Å. This is longer than the 2.251(2)Å distance found in the polymeric complex [Cu2(C8H7O2)4]n. However, it is similar to the 2.6414(8) Å and 2.6261(8)Å distances found in the complex [Cu2(C8H7O2)4(C3H7NO)2] (Kong et al., 2005). The Cu-O phenylacetate bond length lies in the range 1.9644(14) to 1.9734 (14) Å and the Cu-ODMSO bond length is 2.1319(13) Å.

scholarly journals Role of Aspartic and Polyaspartic Acid on the Synthesis and Hydrolysis of Brushite.

2019 ◽  
Vol 10 (1) ◽  
pp. 11 ◽  
Author(s):  
Katia Rubini ◽  
Elisa Boanini ◽  
Adriana Bigi
Keyword(s):  
Aspartic Acid ◽  
Octacalcium Phosphate ◽  
Physiological Solution ◽  
Cooperative Action ◽  
Phosphate Dihydrate ◽  
Mineral Phases ◽  
Carboxylate Groups ◽  
Hydrolysis Of ◽  
Thermal Stability Of

Dicalcium phosphate dihydrate (DCPD) is one of the mineral phases indicated as possible precursors of biological apatites and it is widely employed in the preparation of calcium phosphate bone cements. Herein, we investigated the possibility to functionalize DCPD with aspartic acid (ASP) and poly-aspartic acid (PASP), as models of the acidic macromolecules of biomineralized tissues, and studied their influence on DCPD hydrolysis. To this aim, the synthesis of DCPD was performed in aqueous solution in the presence of increasing concentrations of PASP and ASP, whereas the hydrolysis reaction was carried out in physiological solution up to three days. The results indicate that it is possible to prepare DCPD functionalized with PASP up to a polyelectrolyte content of about 2.3 wt%. The increase of PASP content induces crystal aggregation, reduction of the yield of the reaction and of the thermal stability of the synthesized DCPD. Moreover, DCPD samples functionalized with PASP display a slower hydrolysis than pure DCPD. On the other hand, in the explored range of concentrations (up to 10 mM) ASP is not incorporated into DCPD and does not influence its crystallization nor its hydrolysis. At variance, when present in the hydrolysis solution, ASP, and even more PASP, delays the conversion into the more stable phases, octacalcium phosphate and/or hydroxyapatite. The greater influence of PASP on the synthesis and hydrolysis of DCPD can be ascribed to the cooperative action of the carboxylate groups and to its good fit with DCPD structure.

Intramolecular Catalysis of the Hydrolysis of N-Dimethylaminomaleamic Acid

Science ◽  
1963 ◽  
Vol 140 (3566) ◽  
pp. 485-486 ◽  
Author(s):  
G. Dahlgren ◽  
N. L. Simmerman
Keyword(s):  
Intramolecular Catalysis ◽  
Hydrolysis Of

Hydrolysis of aryl hydrogen maleate esters mediated by cyclodextrins — Effect on the intramolecular catalysis

2005 ◽  
Vol 83 (9) ◽  
pp. 1281-1286 ◽  
Author(s):  
Gabriel O Andrés ◽  
O Fernando Silva ◽  
Rita H de Rossi
Keyword(s):  
Maleic Anhydride ◽  
Transition State ◽  
Rate Constant ◽  
Association Constant ◽  
Kinetic Studies ◽  
Association Constants ◽  
Bulk Solution ◽  
Intramolecular Catalysis ◽  
Hydrolysis Of ◽  
Nonlinear Fashion

Kinetic studies of the hydrolysis of Z-aryl hydrogen maleates (Z = H, p-CH3, m-CH3, p-Cl, m-Cl) were carried out in the presence and absence of hydroxypropyl-β-cyclodextrin (HPCD) at variable pH from 1.00 to 3.00. The reaction involves the formation of maleic anhydride as an intermediate and the rate of its formation is strongly dependent on the pH. This is because the neighboring carboxylate group is a better catalyst than the carboxylic group. The rate constant for the formation of maleic anhydride decreases as the HPCD concentration increases in a nonlinear fashion. The results were interpreted in terms of the formation of a 1:1 inclusion complex of the esters with HPCD. The neutral (HA) and anionic (A) species of the substrate have different association constants (K[Formula: see text] and K[Formula: see text]). In all cases studied, K[Formula: see text] is higher than K[Formula: see text] for the same substrate. This difference is responsible for a decrease in the amount of the anionic substrate (reactive species) in the presence of HPCD, which results in a diminution of the observed rate constant. Besides, the rate constant for the reaction of the complexed substrate is smaller than that in the bulk solution indicating that the transition state of the cyclodextrin mediated reaction is less stabilized than the anionic substrate. The values of ΔΔG‡ are almost independent of the substituent on the aryl ring and range within 0.48 and 1.05 kcal mol–1 (1 cal = 4.184 J). There is no correlation between KTS and the association constant of the substrate indicating that the factors stabilizing the transition state are different from those that stabilize the substrate. Key words: cyclodextrins, intramolecular catalysis, hydrolysis, inhibition.

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