1956-07-6Relevant academic research and scientific papers
Covalent Catalysis by Cross β Amyloid Nanotubes
Chatterjee, Ayan,Das, Dibyendu,Sarkhel, Baishakhi
supporting information, p. 4098 - 4103 (2020/08/19)
The binding pockets of extant enzymes feature precise positioning of amino acid residues that facilitate multiple complex transformations exploiting covalent and non-covalent interactions. Reversible covalent anchoring is extensively used as an efficient tool by Nature for activating modern enzymes such as esterases and dehydratases and also for proteins like opsins for the complex process of visual phototransduction. Here we construct paracrystalline amyloid surfaces through the self-propagation of short peptides which offer binding pockets exposed with arrays of imidazoles and lysines. As covalent catalysis is utilized by modern-day enzymes, these homogeneous amyloid nanotubes exploit Schiff imine formation via the exposed lysines to efficiently hydrolyze both activated and inactivated esters. Controls where lysines were mutated with charged residues accessed similar morphologies but did not augment the rate. The designed amyloid microphases thus foreshadow the generation of binding pockets of advanced proteins and have the potential to contribute to the development of functional materials.
Rhodium-Catalyzed Carbonylative Coupling of Alkyl Halides with Phenols under Low CO Pressure
Ai, Han-Jun,Li, Chong-Liang,Wang, Hai,Wu, Xiao-Feng
, p. 5147 - 5152 (2020/05/27)
A rhodium-catalyzed carbonylative transformation of alkyl halides under low pressure of CO has been developed. This robust catalyst system allows using phenols as the carbonylative coupling partner and, meanwhile, exhibits high functional group tolerance and good chemoselectivity. Substrates even with a large steric hindrance group or multiple reaction sites can be selectively converted into the desired products in good to excellent yields. A gram-scale experiment was performed and delivered an almost quantitative amount of the product. Control experiments were performed as well, and a possible reaction mechanism is proposed.
An invesigation of activities and paraoxon sensitivities of hepatic aliesterases in β-naphthoflavone-treated rats
Watson, Angela M.,Chambers, Howard,Chambers, Janice E.
, p. 217 - 226 (2007/10/03)
Aliesterases (carboxylesterases, EC 3.1.1.1) are serine esterases which may protect acetylcholinesterase during organophosphorus insecticide intoxication by providing alternative phosphorylation sites. Levels of hepatic aliesterase activity were investigated after the intraperitoneal administration of β-naphthoflavone (BNF) to female rats using nine 4-nitrophenyl esters as substrates (including straight and branched chain aliphatic and aromatic esters) and 1-naphthyl acetate. In addition, the in vitro sensitivities of aliesterases to inhibition by paraoxon, the active metabolite of the common insecticide parathion, were studied. Hepatic aliesterases from BNF-treated rats displayed lower activities than those from controls with all substrates except 4-nitrophenyl phenylbutyrate and isovalerate. The aliesterases from BNF-treated rats were more sensitive to paraoxon inhibition with 4-nitrophenyl phenylbutyrate, valerate, and butyrate. Esterases hydrolyzing 4-nitrophenyl butyrate, valerate, and branched chain esters were most sensitive to paraoxon inhibition while those hydrolyzing 4-nitrophenyl hexanoate and aromatic esters were least sensitive. The results suggested that BNF-induced changes in hepatic aliesterases could alter responses to organophosphates. Keywords: Aliesterases; β-Naphthoflavone; Paraoxon; Organophosphate
Inhibition of the Hydrolysis of p-Nitrophenyl Esters by Association with an Erythromycin A Derivative
Barra, Monica,Rossi, Rita H. de
, p. 1758 - 1772 (2007/10/02)
The alkaline hydrolysis of p-nitrophenyl esters (1) of an homologous series of straight chain acids and derivatives of naphthoic acids was studied in the presence of the antibiotic erythromycin A (E) and its hydrolysis product (Z).While (E) does not affect the hydrolysis of 1, (Z) inhibits this reaction.The observed pseudo-first-order rate constants decrease as the Z concentration increases and they tend to a minimum value.This inhibition is ascribed to the formation of a host-guest complex between Z and 1.It is suggested that the attack of an external HO- at the carbonyl ester group is hindered by steric and electrostatic effects.The association constants and the second-order rate constants for the complexed esters were calculated.The inhibition tends to be complete for esters of alkyl chains with an add number of carbon atoms.Such a trend is probably related to the geometric requirements of inclusion.
Parallel Behavior in Kinetic and NMR Effects: Secondary Deuterium Isotope Effects on the Alkaline Hydrolysis of Esters
Matta, Michael S.,Broadway, Dale E.,Stroot, Michele K.
, p. 4916 - 4918 (2007/10/02)
β-Deuterium secondary kinetic isotope effects (β-D KIEs) on the alkaline hydrolysis of the p-nitrophenyl esters of acetic, propanoic, butanoic, and pentanoic acids in pH 10.70, 0.20 M carbonate buffer at 25 deg C tend to increase with increasing chain length of the esters up to the pentanoate.The β-D KIEs are respectively 0.975 +/- 0.004, 0.960 +/- 0.002, 0.940 +/- 0.001, and 0.948 +/- 0.004.The activation energies of the esterolyses of the isotopically light esters follow a similar pattern, as do the 13C NMR nuclear shieldings in CDCl3 of the isotopically light parent carboxylic acids (20.9, 27.4, 35.9, and 33.8 (ppm)) and 13C NMR one-bond isotope shifts produced by disubstitution of deuterium for hydrogen at the α-carbons of the acids (0.45, 0.55, 0.60, and 0.59 (ppm)).Correlation of nuclear shieldings and isotope shifts is known from previous work.The possibility is considered that all of the kinetics-based and NMR relationships are linked through the operation of a common ground-state feature of the ester and acid alkyl chains.
