scholarly journals Acid dissociation constants of glycopeptides

1977 ◽  
Vol 163 (1) ◽  
pp. 31-38 ◽  
Author(s):  
B M Austen ◽  
R D Marshall
Keyword(s):  
Amino Acid ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Hydroxyl Group ◽  
Amino Acid Residues ◽  
Acid Base ◽  
Titration Curves ◽  
Pka Value ◽  
Hen’S Egg ◽  
Additional Amino Acid

Glycopeptides containing mainly four amino acid residues in the sequence Asn-Leu-Thr-Ser, with small amounts of additional amino acid residues, were isolated from enzymic hydrolysates of hen's-egg albumin. Heterogeneity of the carbohydrate moiety was confirmed. Acid-base titrations showed that the alpha-amino group has a pKa value of 6.43 at 25 degrees C. The standard free engery and entropy changes associated with the ionization at 25 degrees C were 37.2kJ-mol-1 and -0.014kJ-mol-1- K-1 respectively. The complications arising in the interpretation of titration curves of the glycopeptides, which are heterogeneous with respect to the peptide chain, were considered and discussed in the light of the earlier suggestion that the titration curve of the glycopeptide might be interpreted as being due in part to a structure in which the hydroxyl group of the threonine residue is hydrogen-bonded to the beta-aspartamido oxygen atom [Neuberger & Marshall (1968) in Symposium on Foods - Carbohydrates and their Roles (Schultz, H.W., Cain, R.F. & Wrolstad, R.W., eds.), pp. 115-132, Avi Publishing Co., Westport, CT]. It is concluded that either the glycopeptides do not contain a hydrogen bond of that type, or, if they do, that it cannot be recognized by acid-base-titration studies.

Nuclear magnetic resonance studies of the acid–base chemistry of amino acids and peptides. III. Determination of the microscopic and macroscopic acid dissociation constants of α,ω-diaminocarboxylic acids

1976 ◽  
Vol 54 (21) ◽  
pp. 3392-3400 ◽  
Author(s):  
Thomas L. Sayer ◽  
Dallas L. Rabenstein
Keyword(s):  
Chemical Shift ◽  
Dissociation Constants ◽  
Nonlinear Least Squares ◽  
Acid Dissociation ◽  
Acid Base ◽  
Acid Dissociation Constants ◽  
Ammonium Group ◽  
Titration Curves ◽  
Chemical Shift Titration ◽  
The Difference

The acid–base chemistry of 2,3-diaminopropionic acid (dap), 2,4-diaminobutyric acid (dab), ornithine (orn), and lysine (lys) has been studied by 13C and proton nmr spectroscopy. Macroscopic acid dissociation constants for titration of the two ammonium groups of each molecule have been calculated from the 13C chemical shift titration curves for the alkyl carbon atoms by nonlinear least squares curve fitting methods. Microscopic acid dissociation constants for the simultaneous titration of the two ammonium groups of protonated orn and lys have been obtained from their proton chemical shift titration curves and from the 13C titration curves for orn and dap. The results indicate that the α-ammonium group of each of these α,ω-diaminocarboxylic acids is more acidic than its ω-ammonium group, but that the difference decreases as the number of carbons separating the ammonium groups decreases so that the acidities of the two ammonium groups of dap are almost identical. Results of pmr studies of the acid–base chemistry of glycyl-L-lysine and L-lysylglycine also are reported.

scholarly journals ACID-BASE PROPERTIES OF -UNSATURATED KETONES OBTAINED FROM REACTION OF 5-FORMYL-8-HYDROXYQUINOLINE WITH P-SUBSTITUTED ACETOPHENONES

2019 ◽  
Vol 16 (31) ◽  
pp. 755-764
Author(s):  
Roberto FERNANDEZ-MAESTRE ◽  
Alonso J MARRUGO-GONZÁLEZ
Keyword(s):  
Electron Donor ◽  
Opposite Effect ◽  
Dissociation Constants ◽  
Phenyl Group ◽  
Hydroxyl Group ◽  
Ultraviolet Spectroscopy ◽  
Acid Base ◽  
Unsaturated Ketones ◽  
Ph Values ◽  
Phenyl Fragment

Chalcones (α,β-unsaturated ketones) containing aromatic or heterocyclic radicals are highly reactive, allowing the synthesis of novel organic compounds. In this study, the dissociation constants (pKa) of seven chalcones derived from 8-hydroxyquinoline were determined and the influence on dissociation of substituents in the phenyl group (-CH3, -OCH3, -N(CH3)2, -Cl, -Br, and -NO2) was analysed. pKa values are important because they determine the pH at which ligands are fully deprotonated -when they show their maximum chelating properties- and determine the ligands interactions at different pH values. The chalcones’ pKa’s were calculated by visible ultraviolet spectroscopy in a water-ethanol (1:1) mixture using the Henderson-Hasselbach equation. It was shown that the 8-hydroxyquinolinic fragment has a large electron donor effect on the π system of the chalcones. The introduction of substituents (R) in the phenyl fragment of the chalcones slightly affected the dissociation of the hydroxyl group and the protonation of the nitrogen in the hydroxyquinoline fragment. The acceptor substituents (Cl, Br, NO2) increased the polarity of OH- and its acidity. Nitrogen protonation decreased electron donor properties of this fragment, and deprotonation of the hydroxyl caused the opposite effect. Substituents introduction in the phenyl fragment slightly affected hydroxyl group dissociation and nitrogen protonation.

Chelating polymers. I. The synthesis and acid dissociation behavior of several N-(p-vinylbenzenesulfonyl)-substituted diaminopolyacetic acid monomers, monomeric analogues, and related intermediates

1970 ◽  
Vol 48 (1) ◽  
pp. 163-175 ◽  
Author(s):  
R. M. Genik-Sas-Berezowsky ◽  
I. H. Spinner
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Inductive Effects ◽  
Cyclic Amide ◽  
Amino Acid Analogues ◽  
Related Compounds ◽  
Chelating Polymers ◽  
Made In

Two new chelating monomers, N-(p-vinylbenzenesulfonyl)1,2-diaminoethane-N′,N′-diacetic (SS-EDDA) and -N,N′,N′-triacetic (SS-ED3A) acids, as well as several monomeric analogues and related intermediates have been prepared. In addition, 2-oxo-1-piperazine acetic (S-KP), 3-oxo-1-piperazine acetic (U-KP), and 2-oxo-1,4-piperazine diacetic (3-KP) acids have been synthesized and the interconvertibility between these cyclic amides and their unsubstituted linear amino acid analogues, ethylene-diamine-N,N′-diacetic (S-EDDA), -N,N-diacetic (U-EDDA), and -N,N,N′-triacetic (ED3A) acids respectively, was demonstrated.The acid dissociation constants of the various amino acids were determined potentiometrically at 25° and μ = 0.1 M(KNO3) and the results were compared with the hydrogen ion affinities of related compounds. Dissociation schemes were proposed for all the compounds based on these results. Rationalizations of the linear amino acid and the cyclic amide dissociation constants were made in terms of the effects of cyclization and the inductive effects of neighboring groups. These rationalizations were found to be helpful in clarifying the dissociation schemes previously proposed for several of the linear amino acids.

scholarly journals New Anti SARS-Cov-2 Targets for Quinoline Derivatives Chloroquine and Hydroxychloroquine

2020 ◽  
Vol 21 (16) ◽  
pp. 5856
Author(s):  
Davide Gentile ◽  
Virginia Fuochi ◽  
Antonio Rescifina ◽  
Pio Maria Furneri
Keyword(s):  
Hydrogen Bonding ◽  
Amino Acid ◽  
Hydroxyl Group ◽  
Simulation Methods ◽  
Quinoline Derivatives ◽  
Amino Acid Residues ◽  
Polar Amino Acid ◽  
Health Crisis ◽  
E Protein ◽  
Rapid Spread

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a severe global health crisis. In this paper, we used docking and simulation methods to identify potential targets and the mechanism of action of chloroquine (CQ) and hydroxychloroquine (HCQ) against SARS-CoV-2. Our results showed that both CQ and HCQ influenced the functionality of the envelope (E) protein, necessary in the maturation processes of the virus, due to interactions that modify the flexibility of the protein structure. Furthermore, CQ and HCQ also influenced the proofreading and capping of viral RNA in SARS-CoV-2, performed by nsp10/nsp14 and nsp10/nsp16. In particular, HCQ demonstrated a better energy binding with the examined targets compared to CQ, probably due to the hydrogen bonding of the hydroxyl group of HCQ with polar amino acid residues.

Acid-base and metal ion complex formation properties of polymers containing amino acid residues

1986 ◽  
Vol 19 (1) ◽  
pp. 37-42 ◽  
Author(s):  
Rolando Barbucci ◽  
Mario Casolaro ◽  
Mila Nocentini ◽  
Silvia Corezzi ◽  
Paolo Ferruti ◽  
...  
Keyword(s):  
Amino Acid ◽  
Complex Formation ◽  
Metal Ion ◽  
Amino Acid Residues ◽  
Acid Base ◽  
Polymers Containing Amino Acid ◽  
Metal Ion Complex
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