scholarly journals pH Dependence of Acrylate-Derivative Polyelectrolyte Properties

2020 ◽  
Author(s):  
Thomas Swift
Keyword(s):  
Ph Dependence

Self-association of insulin. Its pH dependence and effect of plasma

Diabetes ◽  
1987 ◽  
Vol 36 (3) ◽  
pp. 261-264 ◽  
Author(s):  
E. Helmerhorst ◽  
G. B. Stokes
Keyword(s):  
Ph Dependence ◽  
Self Association

Rationalizing the pH-Activity Response for Escherichia Coli’s Glycinamide Ribonucleotidetransformylase Through Computational Methods

2019 ◽  
Author(s):  
Adrian Roitberg ◽  
Pancham Lal Gupta
Keyword(s):  
Transfer Reaction ◽  
Catalytic Mechanism ◽  
Ph Dependence ◽  
Ph Effects ◽  
Dependent Manner ◽  
E Coli ◽  
Gar Tfase ◽  
Activity Curve ◽  
Ph Dependent ◽  
Formyl Transfer

<div>Human Glycinamide ribonucleotide transformylase (GAR Tfase), a regulatory enzyme in the de novo purine biosynthesis pathway, has been established as an anti-cancer target. GAR Tfase catalyzes the formyl transfer reaction from the folate cofactor to the GAR ligand. In the present work, we study E. coli GAR Tfase, which has high sequence similarity with the human GAR Tfase with most functional residues conserved. E. coli GAR Tfase exhibits structural changes and the binding of ligands that varies with pH which leads to change the rate of the formyl transfer reaction in a pH-dependent manner. Thus, the inclusion of pH becomes essential for the study of its catalytic mechanism. Experimentally, the pH-dependence of the kinetic parameter kcat is measured to evaluate the pH-range of enzymatic activity. However, insufficient information about residues governing the pH-effects on the catalytic activity leads to ambiguous assignments of the general acid and base catalysts and consequently its catalytic mechanism. In the present work, we use pH-replica exchange molecular dynamics (pH-REMD) simulations to study the effects of pH on E. coli GAR Tfase enzyme. We identify the titratable residues governing the pH-dependent conformational changes in the system. Furthermore, we filter out the protonation states which are essential in maintaining the structural integrity, keeping the ligands bound and assisting the catalysis. We reproduce the experimental pH-activity curve by computing the population of key protonation states. Moreover, we provide a detailed description of residues governing the acidic and basic limbs of the pH-activity curve.</div>

pH Dependence of the polarographic limiting currents of α-keto acids

1961 ◽  
Vol 26 (1) ◽  
pp. 141-155 ◽  
Author(s):  
S. Ono ◽  
M. Takagi ◽  
T. Wasa
Keyword(s):  
Ph Dependence ◽  
Keto Acids

Photoreaction of 3,4-dimethoxy-1-nitrobenzene with butylamine. A pH dependence of regioselectivity

1986 ◽  
Vol 51 (8) ◽  
pp. 1665-1670 ◽  
Author(s):  
Petr Kuzmič ◽  
Libuše Pavlíčková ◽  
Jiří Velek ◽  
Milan Souček
Keyword(s):  
Ph Dependence ◽  
Molar Ratio

Irradiation of 3,4-dimethoxy-1-nitrobenzene in the presence of butylamine leads to the formation of both possible photosubstitution products, i.e., 2-methoxy-4-nitro-N-butylaniline and 2-methoxy-5-nitro-N-butylaniline with the predominance of the latter. Regioselectivity of the reaction as measured by molar ratio of the two isomeric products varies with pH of the solution, ranging from 3 : 1 at pH 10 to 12. The results are discussed in view of possible use of 3,4-dimethoxy-1-nitrobenzene moiety as a lysine-directed photoaffinity probe.

Electroanalytical chemistry of vanadium complexes: Electrochemical oxidation of [V(IV)O(nta)(H2O)]-

1989 ◽  
Vol 54 (1) ◽  
pp. 64-69 ◽  
Author(s):  
Roland Meier ◽  
Gerhard Werner ◽  
Matthias Otto
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Oxidation ◽  
Ph Dependence ◽  
Differential Pulse ◽  
Nitrilotriacetic Acid ◽  
Reduced Form ◽  
Vanadium Complexes ◽  
Differential Pulse Polarography ◽  
Electroanalytical Chemistry ◽  
Ph Range

Electrochemical oxidation of [V(IV)O(nta)(H2O)]- (H3nta nitrilotriacetic acid) was studied in aqueous solution by means of cyclic voltammetry, differential pulse polarography, and current sampled DC polarography on mercury as electrode material. In the pH-range under study (5.5-9.0) the corresponding V(V) complex is produced by one-electron oxidation of the parent V(IV) species. The oxidation product is stable within the time scale of cyclic voltammetry. The evaluation of the pH-dependence of the half-wave potentials leads to a pKa value for [V(IV)O(nta)(H2O)]- which is in a good agreement with previous determinations. The measured value for E1/2 is very close to the formal potential E0 calculated via the Nernst equation on the basis of known literature values for log Kox and log Kred, the complex stability constants for the oxidized and reduced form, respectively.

scholarly journals A Molecularly Imprinted Polymer for Selective Extraction of Phenolic Acids from Human Urine

2021 ◽  
Vol 11 (4) ◽  
pp. 1577
Author(s):  
Marco Mora-Granados ◽  
David González-Gómez ◽  
Jin Su Jeong ◽  
Alejandrina Gallego-Picó
Keyword(s):  
Phenolic Acids ◽  
Molecularly Imprinted Polymer ◽  
Human Urine ◽  
Limit Of Detection ◽  
Ph Dependence ◽  
Selective Extraction ◽  
Screening Methods ◽  
Specific Method ◽  
Imprinted Polymer ◽  
Molecularly Imprinted

Studies for monitoring the bioavailability of dietary flavonoid compounds generate great interest. Among them, low-molecular-weight phenolic acids, secondary metabolites present in colonic catabolism and urinary excretion, have been proposed as biomarkers of polyphenol intake. Using 4-hydroxyphenylacetic acid as a template, a molecularly imprinted polymer (MIP) was synthesized for selective extraction of these hydroxylated metabolites from human urine samples and posterior analysis in an HPLC-DAD-MS system. Polymers were characterized by Scanning electron microscopy (SEM), Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Brunauer-Emmett-Teller (BET) method, and binding experiments. MIP presents specific recognition ability for template and analogues molecules. This capacity of recognition and the pH dependence of the binding strength was also studied. The method was validated over a concentration range of 0.25–40 mg/L, r2 > 0.995. In the optimized conditions, the recovery value was 94% with RSD 1.2%. The Limit of Detection (LOD) and Limit of Quantification (LOQ) were 1.22 and 3.69 mg/L, respectively. In our knowledge, it is the first time that this methodology is applied to analyze urinary catabolites of the polyphenol compound and to provide a specific method and simple analysis alternative. The selective extraction of these metabolites improves the application and results obtained by other less sensitive analysis methods than the validation method. It also facilitates the development of new screening methods.

scholarly journals Electrochemical Response of Glucose Oxidase Adsorbed on Laser-Induced Graphene

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1893
Author(s):  
Sónia O. Pereira ◽  
Nuno F. Santos ◽  
Alexandre F. Carvalho ◽  
António J. S. Fernandes ◽  
Florinda M. Costa
Keyword(s):  
Electron Transfer ◽  
Glucose Oxidase ◽  
Ph Dependence ◽  
High Surface ◽  
High Surface Area ◽  
Cost Effective ◽  
Great Promise ◽  
Glucose Detection ◽  
Half Wave ◽  
Electrochemical Transducers

Carbon-based electrodes have demonstrated great promise as electrochemical transducers in the development of biosensors. More recently, laser-induced graphene (LIG), a graphene derivative, appears as a great candidate due to its superior electron transfer characteristics, high surface area and simplicity in its synthesis. The continuous interest in the development of cost-effective, more stable and reliable biosensors for glucose detection make them the most studied and explored within the academic and industry community. In this work, the electrochemistry of glucose oxidase (GOx) adsorbed on LIG electrodes is studied in detail. In addition to the well-known electroactivity of free flavin adenine dinucleotide (FAD), the cofactor of GOx, at the expected half-wave potential of −0.490 V vs. Ag/AgCl (1 M KCl), a new well-defined redox pair at 0.155 V is observed and shown to be related to LIG/GOx interaction. A systematic study was undertaken in order to understand the origin of this activity, including scan rate and pH dependence, along with glucose detection tests. Two protons and two electrons are involved in this reaction, which is shown to be sensitive to the concentration of glucose, restraining its origin to the electron transfer from FAD in the active site of GOx to the electrode via direct or mediated by quinone derivatives acting as mediators.

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