36 research outputs found
Intramolecular Interactions versus Hydration Effects on <i>p</i>‑Guanidinoethyl-phenol Structure and p<i>K</i><sub>a</sub> Values
We analyze the structure, hydration, and p<i>K</i><sub>a</sub> values of <i>p</i>-guanidinoethyl-phenol through
a combined experimental and theoretical study. These issues are relevant
to understand the mechanism of action of the tetrameric form, the
antibacterial compound tetra-<i>p</i>-guanidinoethyl-calix[4]arene
(Cx1). The investigated system can also be useful to model other pharmaceutical
drugs bearing a guanidine function in the vicinity of an ionizable
group and the effect of arginine on the p<i>K</i><sub>a</sub> of vicinal ionizable residues (in particular tyrosine) in peptides.
The <i>p</i>-guanidinoethyl-phenol monomer (mCx1) has two
ionizable groups. One important particularity of this system is that
it exhibits high molecular flexibility that potentially leads to enhanced
stabilization in folded structures by direct, strong Coulombic interactions
between the ionizable groups. The first p<i>K</i><sub>a</sub> corresponding to ionization of the −OH group has experimentally
been shown to be only slightly different from usual values in substituted
phenols. However, because of short-range Coulombic interactions, the
role of intramolecular interactions and solvation effects on the acidities
of this compound is expected to be important and it has been analyzed
here on the basis of theoretical calculations. We use a discrete-continuum
solvation model together with quantum-mechanical calculations at the
B3LYP level of theory and the extended 6-311+G(2df,2p) basis set.
Both intra- and intermolecular effects are very large (∼70
kcal/mol) but exhibit an almost perfect compensation, thus explaining
that the actual p<i>K</i><sub>a</sub> of mCx1 is close to
free phenol. The same compensation of environmental effects applies
to the second p<i>K</i><sub>a</sub> that concerns the guanidinium
group. Such a p<i>K</i><sub>a</sub> could not be determined
experimentally with standard titration techniques and in fact the
theoretical study predicts a value of 14.2, that is, one unit above
the p<i>K</i><sub>a</sub> of the parent ethyl-guanidinium
molecule
Development and validation of a multi-residue method for pesticide determination in honey using on-column liquid-liquid extraction and liquid chromatography-tandem mass spectrometry
We report on the development and validation under ISO 17025 criteria of a multi-residue confirmatory method to identify and quantify 17 widely chemically different pesticides (insecticides: Carbofuran, Methiocarb, Pirimicarb, Dimethoate, Fipronil, Imidacloprid; herbicides: Amidosulfuron, Rimsulfuron, Atrazine, Simazine, Chloroturon, Linuron, Isoxaflutole, Metosulam; fungicides: Diethofencarb) and 2 metabolites (Methiocarb sulfoxide and 2-Hydroxytertbutylazine) in honey. This method is based on an on-column liquid liquid extraction (OCLLE) using diatomaceous earth as inert solid support and liquid chromatography (LC) coupled to mass spectrometry (MS) operating in tandem mode (MS/MS). Method specificity is ensured by checking retention time and theoretical ratio between two transitions from a single precursor ion. Linearity is demonstrated all along the range of concentration that was investigated, from 0.1 to 20 ng g(-1) raw honey, with correlation coefficients ranging from 0.921 to 0.999, depending on chemicals. Recovery rates obtained on home-made quality control samples are between 71 and 90%, well above the range defined by the EC/657/2002 document, but in the range we had fixed to ensure proper quantification, as levels found in real samples could not be corrected for recovery rates. Reproducibility is found to be between 8 and 27%. Calculated CC alpha and CC beta (0.0002-0.943 mg g(-1) for CC alpha, and 0.0002-1.232 ng g(-1) for CCP) show the good sensitivity attained by this rnulti-residue analytical method. The robustness of the method has been tested in analyzing more than 100 raw honey samples collected from different areas in Belgium, as well as some wax and bee samples, with a slightly adapted procedure. (C) 2007 Elsevier B.V. All rights reserved
LR12-peptide quantitation in whole blood by RP-HPLC and intrinsic fluorescence detection: Validation and pharmacokinetic study
International audienc
In vivo and in silico evaluation of a new nitric oxide donor, S,S′-dinitrosobucillamine
Purpose In a previous work, we have synthetized a new dinitrosothiol, i.e. S,S′-dinitrosobucillamine BUC(NO)2 combining S-nitroso-N-acetylpenicillamine (SNAP) and S-nitroso-N-acetylcysteine (NACNO) in its structure. When exposed to isolated aorta, we observed a 1.5-fold increase of •NO content and a more potent vasorelaxation (1 log higher pD2) compared to NACNO and SNAP alone or combined (Dahboul et al., 2014). In the present study, we analyzed the thermodynamics and kinetics for the release of •NO through computational modeling techniques and correlated it to plasma assays. Then BUC(NO)2 was administered in vivo to rats, assuming it will induce higher and/or longer hypotensive effects than its two constitutive S-mononitrosothiols. Methods Free energies for the release of •NO entities have been computed at the density functional theory level assuming an implicit model for the aqueous environment. Degradation products of BUC(NO)2 were evaluated in vitro under heating and oxidizing conditions using HPLC coupled with tandem mass spectrometry (MS/MS). Plasma from rats were spiked with RSNO and kinetics of RSNO degradation was measured using the classical Griess-Saville method. Blood pressure was measured in awake male Wistar rats using telemetry (n = 5, each as its own control, 48 h wash-out periods between subcutaneous injections under transient isoflurane anesthesia, random order: 7 mL/kg vehicle, 3.5, 7, 14 μmol/kg SNAP, NACNO, BUC(NO)2 and an equimolar mixture of SNAP + NACNO in order to mimic the number of •NO contained in BUC(NO)2). Variations of mean (ΔMAP, reflecting arterial dilation) and pulse arterial pressures (ΔPAP, indirectly reflecting venodilation, used to determine effect duration) vs. baseline were recorded for 4 h. Results Computational modeling highlights the fact that the release of the first •NO radical in BUC(NO)2 requires a free energy which is intermediate between the values obtained for SNAP and NACNO. However, the release of the second •NO radical is significantly favored by the concerted formation of an intramolecular disulfide bond. The corresponding oxidized compound was also characterized as related substance obtained under degradation conditions. The in vitro degradation rate of BUC(NO)2 was significantly greater than for the other RSNO. For equivalent low and medium •NO-load, BUC(NO)2 produced a hypotension identical to NACNO, SNAP and the equimolar mixture of SNAP + NACNO, but its effect was greater at higher doses (-62 ± 8 and -47 ± 14 mmHg, maximum ΔMAP for BUC(NO)2 and SNAP + NACNO, respectively). Its duration of effect on PAP (-50%) lasted from 35 to 95 min, i.e. shorter than for the other RSNO (from 90 to 135 min for the mixture SNAP + NACNO). Conclusion A faster metabolism explains the abilities of BUC(NO)2 to release higher amounts of •NO and to induce larger hypotension but shorter-lasting effects than those induced by the SNAP + NACNO mixture, despite an equivalent •NO-load