Search results for "Protonation"
showing 10 items of 583 documents
Acidochromism of the luminescence of bis(4-pyridylethenyl)arenes
2004
Abstract A series of C 2 -symmetrical bis[( E )-2-(4-pyridyl)ethenyl]arenes has been synthesised via two-fold PO-activated olefinations. 1,4-Benzene, 1,4-naphthalene, 9,10-anthracene and 2,2′-diphenyl were used as central units. These fluorescent compounds were freely soluble in common solvents. The absorption and the emission were sensitive towards solvent polarity and acid, in solution as well as in the solid state. Depending on the concentration of acid, protonation of the ground state and/or the excited state caused reductions of the fluorescence efficiencies, accompanied by bathochromic shifts of the absorption and the emission spectra of some chromophores. The title compounds, except …
XAFS study of gadolinium and samarium bisporphyrinate complexes.
2001
The comparative X-ray absorption spectroscopy study of gadolinium and samarium bisporphyrinate complexes represented by the formulas Gd(III)H(oep)(tpp), Gd(III)(oep)(2), Gd(III)H(tpp)(2) and Sm(III)H(oep)(tpp), Sm(III)(oep)(2), Sm(III)H(tpp)(2) is reported. The XAFS spectra are recorded on the LURE-DCI storage ring (Orsay, France) in transmission mode on the microcrystalline samples at the Gd and Sm L(3) edges. The local environment for Ln(3+) ions has been reconstructed applying one-shell and two-shell XAFS analysis procedures. The protonated and nonprotonated bisporphyrinate complexes present different XAFS features. After our analysis on the title derivatives, the gadolinium ion (at 80 K…
Protonation of the Biliverdin IXα Chromophore in the Red and Far-Red Photoactive States of a Bacteriophytochrome
2019
The tetrapyrrole chromophore biliverdin IXα (BV) in the bacteriophytochrome from Deinococcus radiodurans (DrBphP) is usually assumed to be fully protonated, but this assumption has not been systematically validated by experiments or extensive computations. Here, we use force field molecular dynamics simulations and quantum mechanics/molecular mechanics calculations with density functional theory and XMCQDPT2 methods to investigate the effect of the five most probable protonation forms of BV on structural stability, binding pocket interactions, and absorption spectra in the two photochromic states of DrBphP. While agreement with X-ray structural data and measured UV/vis spectra suggest that …
Synthesis, Characterization, and Electrochemistry of Open-Chain Pentapyrroles and Sapphyrins with Highly Electron-Withdrawing meso -Tetraaryl Substit…
2017
International audience; A series of open-chain pentapyrroles and sapphyrins with highly electron-withdrawing substituents (i.e., CN, CF3 , or CO2 Me) on the meso-phenyl rings was synthesized and characterized as to the spectral properties, protonation reactions, and electrochemistry in non-aqueous media. The investigated compounds are represented as (Ar)4 PPyH3 and (Ar)4 SapH3 where PPy and Sap correspond to the tri-anion of the open-chain pentapyrrole and sapphyrin, respectively, and Ar=p-CNPh, p-CF3 Ph, or p-CO2 MePh. UV/Vis and 1 H NMR spectroscopy as well as mass spectrometry data are given for the confirmation of the structures for the newly synthesized compounds. An X-ray structure fo…
A molecular dynamics study on the role of the protonation state in the biosynthesis of R-PAC by AHAS
2019
Abstract The effect of the protonation state of the hydroxyl-ethylthiamin diphosphate intermediate, HEThDP, on the enzyme-substrate interactions and their consequences on the biosynthesis of R-phenylacetylcarbinol, R-PAC, by the acetohydroxy acid synthase, AHAS, is addressed by molecular dynamics simulations. It is found that the form of HEThDP, which favors the formation of R-PAC, is that having the 4-aminopyrimidine ring with the N1′ atom protonated and the N4′ atom as aminopyrimidinium ion. Under this form both active sites of AHAS have the ability to perform the catalysis, unlike that observed for the other possible protonation states of N1′ and N4′ atoms.
Polycarboxylic acids in sea water: acid–base properties, solubilities, activity coefficients, and complex formation constants at different salinities
2016
This paper reports the results of the investigations carried out in synthetic sea water at different salinities for different classes of polycarboxylic acids. The investigations can be summarized as follows: (a) Determination of the protonation constants in such multicomponent solution in a salinity range 15 ≤ S ≤ 45, at t = 25 °C, for the linear dicarboxylic acids HOOC-(CH2) n –COOH (0 ≤ n ≤ 8), and aromatic polycarboxylic acids (o-phthalic and 1,2,4-benzenetricarboxylic acids). For malonic, succinic, 1,2,3-benzenetricarboxylic, and 1,2,3,4-benzenetetracarboxylic acids, investigations were also carried out at t = 10 and 37 °C; (b) Determination of the total and intrinsic solubility (S T an…
Modeling S-carboxymethyl-L-cysteine protonation and activity coefficients in sodium and tetramethylammonium chloride aqueous solutions by SIT and Pit…
2007
Solubility and acid–base properties of S-carboxymethyl-l-cysteine (carbocysteine, ccys) in NaClaq and tetramethylammonium chloride, (CH3)4NClaq ,a tt =2 5 ◦ C and at different ionic strengths were investigated. Solubility was studied at 1.0 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 1.0 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq, while potentiometric measurements (by ISE-H + , glass electrode) were performed at 0.1 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 0.5 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq. Solubility data allowed us to determine Setschenow constants and activity coefficients of neutral carbocysteine (H2ccys). Dependence on ionic strength and ionic medium of protonation constants and activity coeff…
Solubility and acid-base properties and activity coefficients of chitosan in different ionic media and at different ionic strengths, at T=25°C
2009
Studies on the acid-base properties and solubility of a polyammonium polyelectrolyte (chitosan) with different molecular weights (MW 310 and 50 kDa), were performed at T=25 °C, in the pH range 2.5–7. The protonation of chitosan was investigated by potentiometry ([H+]-glass electrode) in NaCl, NaNO3 and mixed NaNO3+Na2SO4 ionic media, at different ionic strengths. Protonation constants were calculated as a function of dissociation degree α by means of two different models, namely, a simple linear model and the modified Henderson–Hasselbalch equation. Experimental data were also fitted using a model independent of α (Diprotic-like model), according to which the acid-base properties can be sim…
Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations.
2006
Abstract The acid–base properties of Adenosine 5′-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0 I / mol L − 1 ≤ 5 for NaCl aq , 0 I / mol L − 1 ≤ 3 for KCl aq ) and at t = 25 °C were investigated. A selection of literature data on ATP protonation constants and on activity isopiestic coefficients was performed, together with new potentiometric measurements (by ISE-H + , glass electrode). Both literature and new experimental data were used to model the dependence on ionic strength and ionic medium of ATP protonation by SIT (Specific ion Interaction Theory) and Pitzer equations. In addition to values of first and second ATP protonation constants in…
A quantum mechanics/molecular mechanics study of the acylation reaction of TEM1 β-lactamase and penicillanate
2000
The acylation step in β-lactamase catalyzed hydrolysis of β-lactams has been explored by means of a quantum mechanics/molecular mechanics approach (AM1/CHARMM). The TEM1 enzyme, a class A β-lactamase, and the penicillanate constitute the system employed in our study. The entire molecular system is divided into a quantum and a classical region: the quantum part is composed by the substrate, the serine Ser70 and the essential moieties of key active site residues, Lys73, Ser130 and Glu166, as well as a water molecule present in the active site region, while the classical part is formed by the remaining residues and structural waters of the enzyme. In particular, the sequence of steps proposed …