The partitioning of tetrahedral intermediates of the hydrolysis of benzimidatonium ions in acid solutions

1980 ◽  
Vol 58 (22) ◽  
pp. 2318-2325 ◽  
Author(s):  
Robert A. McClelland ◽  
Janet P. Potter
Keyword(s):  
Strong Acid ◽  
Major Product ◽  
Dilute Acid ◽  
Acid Product ◽  
Aromatic Substituent ◽  
Tetrahedral Intermediate ◽  
Zwitterionic Form ◽  
Hydrolysis Of ◽  
Ester Product ◽  
Amide Acetals

The products (a benzoate ester or an N,N-dimethylbenzamide) have been accurately determined for the hydrolysis of the O-ethyl-N,N-dimethylbenzimidatonium ion (1) and its 4-nitro derivative (2) in dilute and moderately concentrated H2SO4 solutions. In dilute acid the ratio of amide:ester is very small (0.0005–0.001). It is proposed that the ester product arises from the zwitterionic form of the tetrahedral intermediate of the hydrolysis. The small amount of amide is due to an SN2 hydrolysis reaction and to the non-catalyzed breakdown of the neutral form of the tetrahedral intermediate, the relative contributions of the two being unknown. Although ester remains the major product throughout, at some intermediate acid concentration (20% H2SO4 for 1 and 35% H2SO4 for 2) a sharp increase in the amide:ester ratio is observed, followed by a levelling-off. This change is shown to be associated with tetrahedral intermediate partitioning, and not the SN2 reaction. It is argued that the strong acid product ratio represents the breakdown of the tetrahedral intermediate via cationic transition States. Two kinetically equivalent reactions are involved, the breakdown of the N-protonated tetrahedral intermediate producing a protonated ester and amine and the H+-catalyzed breakdown of the neutral tetrahedral intermediate producing a protonated amide and alcohol. Analogous pathways are also observed for the decomposition in acid of the amide acetals ArC(OMe)2NMe2, and the two systems are compared. A similar effect of the aromatic substituent on the partitioning ratio is noted, but the tetrahedral intermediate exhibits a greater tendency for amine expulsion. A kinetic analysis produces the estimate of 1011 s−1 for the rate constant for the breakdown of the zwitterionic form of the tetrahedral intermediate. This very large rate explains why its decomposition remains important even in concentrated acids, where the amount of tetrahedral intermediate which actually exists as zwitterion must be extremely low.

Dilute Acid Hydrolysis of Wheat Straw Oligosaccharides

2008 ◽  
Vol 153 (1-3) ◽  
pp. 116-126 ◽  
Author(s):  
Luís C. Duarte ◽  
Talita Silva-Fernandes ◽  
Florbela Carvalheiro ◽  
Francisco M. Gírio
Keyword(s):  
Acid Hydrolysis ◽  
Wheat Straw ◽  
Dilute Acid ◽  
Dilute Acid Hydrolysis ◽  
Hydrolysis Of

Dilute Acid Hydrolysis of Softwoods

1999 ◽  
pp. 133-142 ◽  
Author(s):  
Quang A. Nguyen ◽  
Melvin P. Tucker ◽  
Fred A. Keller ◽  
Delicia A. Beaty ◽  
Kevin M. Connors ◽  
...  
Keyword(s):  
Acid Hydrolysis ◽  
Dilute Acid ◽  
Dilute Acid Hydrolysis ◽  
Hydrolysis Of

PHOTOSYNTHESIS AND METABOLISM IN MARINE ALGAE: VII. PRODUCTS OF PHOTOSYNTHESIS IN FRONDS OF FUCUS VESICULOSUS AND THEIR USE IN RESPIRATION

1967 ◽  
Vol 45 (9) ◽  
pp. 1557-1565 ◽  
Author(s):  
R. G. S. Bidwell
Keyword(s):  
Sodium Carbonate ◽  
Marine Algae ◽  
Fucus Vesiculosus ◽  
Complex Compounds ◽  
Major Product ◽  
Dilute Acid ◽  
Active Metabolites

Samples of Fucus vesiculcsus fronds were permitted to assimilate 14CO2 for 5 h and were then maintained in alternating periods of light and darkness for 3 days. Samples were collected at intervals, and the radioactivity of various simple and complex compounds was measured. The major product of photosynthesis was mannitol; relatively small amounts of 14C entered other compounds. From its behavior, it appears that mannitol is the major substrate of respiration in these plants; there may be secondary substrates among the complex polysaccharides. The complex polysaccharides are not formed directly from mannitol in light, but from some common precursors, or else from a small isolated pool of mannitol which is separated from the main cellular supplies. In darkness, the complex polysaccharides appear to be derived from stored mannitol. One of the more active metabolites, judged from its behavior, is a component of the residue left after dilute acid and sodium carbonate extraction. This component undergoes turnover, i.e. breakdown and resynthesis from newly-acquired photosynthate in the light, and is formed from stored photosynthate in the darkness.

scholarly journals Novel activity of angiotensin-converting enzyme. Hydrolysis of cholecystokinin and gastrin analogues with release of the amidated C-terminal dipeptide

1989 ◽  
Vol 262 (1) ◽  
pp. 125-130 ◽  
Author(s):  
P Dubreuil ◽  
P Fulcrand ◽  
M Rodriguez ◽  
H Fulcrand ◽  
J Laur ◽  
...  
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Chloride Ion ◽  
Peptide Bond ◽  
Major Product ◽  
Enzyme Hydrolysis ◽  
Ion Concentration ◽  
Converting Enzyme ◽  
Rabbit Lung ◽  
Hydrolysis Of

ACE (angiotensin-converting enzyme; peptidyl dipeptidase A; EC 3.4.15.1), cleaves C-terminal dipeptides from active peptides containing a free C-terminus. We investigated the hydrolysis of cholecystokinin-8 [CCK-8; Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2] and of various gastrin analogues by purified rabbit lung ACE. Although these peptides are amidated at their C-terminal end, they were metabolized by ACE to several peptide fragments. These fragments were analysed by h.p.l.c., isolated and identified by comparison with synthetic fragments, and by amino acid analysis. The initial and major site of hydrolysis was the penultimate peptide bond, which generated a major product, the C-terminal amidated dipeptide Asp-Phe-NH2. As a secondary cleavage, ACE subsequently released di- or tri-peptides from the C-terminal end of the remaining N-terminal fragments. The cleavage of CCK-8 and gastrin analogues was inhibited by ACE inhibitors (Captopril and EDTA), but not by other enzyme inhibitors (phosphoramidon, thiorphan, bestatin etc.). Hydrolysis of [Leu15]gastrin-(14-17)-peptide [Boc (t-butoxycarbonyl)-Trp-Leu-Asp-Phe-NH2] in the presence of ACE was found to be dependent on the chloride-ion concentration. Km values for the hydrolysis of CCK-8, [Leu15]gastrin-(11-17)-peptide and Boc-[Leu15]gastrin-(14-17)-peptide at an NaCl concentration of 300 mM were respectively 115, 420 and 3280 microM, and the catalytic constants were about 33, 115 and 885 min-1. The kcat/Km for the reactions at 37 degrees C was approx. 0.28 microM-1.min-1, which is approx. 35 times less than that reported for the cleavage of angiotensin I. These results suggest that ACE might be involved in the metabolism in vivo of CCK and gastrin short fragments.

scholarly journals Investigation of interaction between cellulase and residual lignin fractions in acid-pretreated bamboo residues and their effect on enzymatic digestibility

2021 ◽  
Author(s):  
Wenqian Lin ◽  
Jinlai Yang ◽  
Yayue Zheng ◽  
Caoxing Huang ◽  
Qiang Yong
Keyword(s):  
Enzymatic Hydrolysis ◽  
Negative Impact ◽  
Interaction Mechanism ◽  
Dilute Acid Pretreatment ◽  
Affinity Constant ◽  
Residual Lignin ◽  
Dilute Acid ◽  
Enzymatic Digestibility ◽  
Acid Pretreatment ◽  
Hydrolysis Of

Abstract Background: During dilute acid pretreatment, pseudo lignin and lignin form droplets which deposit on the surface of lignocellulose, and further inhibit its enzymatic hydrolysis. However, how this lignin interacts with cellulase enzymes and then affects enzymatic hydrolysis is still unknown. In this work, different fractions of surface lignin (SL) obtained from dilute acid pretreated bamboo residues (DAP-BR) were extracted by various organic reagents and the residual lignin in extracted DAP-BR was obtained by milled wood lignin (MWL) method. All the obtained lignin fractions from DAP-BR were used to investigate the interaction mechanism between lignin and cellulase using surface plasmon resonance (SPR) technology in order to understand how they affect enzymatic hydrolysisResults: Results showed that removing surface lignin significantly decrease the enzymatic hydrolysis of DAP-BR from 36.5% to 18.6%. The addition of MWL samples to Avicel decreased enzymatic hydrolysis of Avicel, while different SL samples showed a slight increase to its enzymatic digestibility. Due to the higher molecular weight and hydrophobicity of MWL samples versus the SL samples, stronger affinity for MWL (KD = 6.8-24.7 nM) was found versus that of SL (KD = 39.4-52.6 nM) by SPR analysis. The affinity constant of all tested lignin had good correlations (R2>0.6) with their effects on enzymatic digestibility of extracted DAP-BR and Avicel.Conclusions: This work reveals that the surface lignin on DAP-BR is necessary towards maintaining enzyme digestibility levels, and its removal has a negative impact on the substrate’s digestibility.

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