Search results for "Proton"
showing 10 items of 5886 documents
Understanding the stereoselectivity in Brønsted acid catalysed Povarov reactions generating cis/trans CF3-substituted tetrahydroquinolines: a DFT stu…
2016
The Bronsted acid (BA) catalysed Povarov reactions of (E)-1-phenyl-N-(4-(trifluoromethyl)phenyl) methanimine with 1-vinylpyrrolidin-2-one (VPO) and with allyltrimethylsilane (ATMS), affording CF3-substituted cis/trans tetrahydroquinoline (THQ) derivatives, have theoretically been studied using the M06-2X functional together with the standard 6-31G(d) basis set. These BA catalysed Povarov reactions are multistep processes initialised by the nucleophilic attack of the non-substituted carbon atom of the nucleophilic ethylene on the imine carbon atom of the super-electrophilic protonated imine, yielding the corresponding cationic intermediate along the endo/exo stereoisomeric approach mode. Upo…
Hyperfine couplings ofN-alkoxy-N-polynitrophenylaminyl radicals determined by ENDOR and TRIPLE resonance spectroscopy
1995
Lead tetraacetate one-electron oxidation of nine different N-alkoxy-2,6-dinitroanilines substituted with trifluoromethyl, methyl and nitro groups in position 4 yielded aminyl radicals for which hyperfine couplings were measured by ENDOR and TRIPLE resonance spectroscopy. The optimum temperature range for proton ENDOR and general TRIPLE resonance measurements of aminyl radicals was 210–250 K and for nitrogen ENDOR 260 K in toluene. Further lowering for the temperature rapidly decreased the EPR intensity. The concentration of the sample and the amount of oxidant were optimized for obtaining ENDOR spectra. The relative signs of the hyperfine couplings of nitrogens, fluorines and protons were d…
Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
2009
The tris[oligo(1,4-phenylenevinylene)]carbinols 2a–f (n =1–4) and the tris(4-styrylphenyl)methanes 7a,b have been prepared by Wittig–Horner (3 + 4a–f 2a–f) and Siegristreactions (5 + 6a,b 7a,b). The Wittig–Horner reactions in these examples are accompanied by an autoxidation, whereas a reduction occurs in the Siegrist reactions. Compound 2a, the lowest member (n = 1) of the series 2a–d with terminal dialkylamino groups, generates first, on treatment with acids, the methylium dye 2′a, which absorbs far into the NIR region (λmax = 1100 nm). The higher members 2b,c (n = 2,3) of the carbinol series yield by acidic treatment only N-protonated methylium dyes 2″′b,c. The different behavior is due …
A Short Synthesis of Polysubstituted Pyrrolidines via α-(Alkylideneamino)nitriles
2004
α-(Alkylideneamino)nitriles can be deprotonated under mild conditions. Their conjugated anions react with enones in a 1,4-addition to yield δ-keto-α-(alkylideneamino)nitriles which in turn can be reduced to form pyrrolidines in a one-pot reaction sequence.
Protonation equilibria of some ortho-substituted and annelated aryl and thiophen-2-yl and -3-yl ketones
2001
For some phenyl- (1–8) and thiophen-2-yl (9–11) and thiophen-3-yl (12–14) ketones quantum-mechanical (PM3) calculations have been performed, and for compounds 2, 3, 5–8, 10–14 protonation equilibria have been determined. Phenyl ketones have similar values for the m* parameter and show good linear correlation between the proton affinities calculated in the gas phase and the measured pKBH+ values, which in turn parallel the trend for the calculated carbonyl–phenyl ring dihedral angle. It appears that the differences in basicity are governed essentially by “internal” factors (carbonyl–ring conjugation), while the base–conjugate acid differential solvation is not significantly affected by struc…
On the Deactivation Mechanisms of Adenine–Thymine Base Pair
2012
In this contribution, the multiconfigurational second-order perturbation theory method based on a complete active space reference wave function (CASSCF/CASPT2) is applied to study all possible single and double proton/hydrogen transfers between the nucleobases in the adenine-thymine (AT) base pair, analyzing the role of excited states with different nature [localized (LE) and charge transfer (CT)], and considering concerted as well as step-wise mechanisms. According to the findings, once the lowest excited states, localized in adenine, are populated during UV irradiation of the Watson-Crick base pair, the proton transfer in the N-O bridge does not require high energy in order to populate a …
3'-Untranslated regions of oxidative phosphorylation mRNAs function in vivo, as enhancers of translation
2000
Recent findings have indicated that the 3´-untranslated region (3´-UTR) of the mRNA encoding the β-catalytic subunit of the mitochondrial H+-ATP synthase has an in vitro translation-enhancing activity (TEA) [Izquierdo and Cuezva, Mol. Cell. Biol. (1997) 17, 5255–5268; Izquierdo and Cuezva, Biochem. J. (2000) 346, 849–855]. In the present work, we have expressed chimaeric plasmids that encode mRNA variants of green fluorescent protein in normal rat kidney and liver clone 9 cells to determine whether the 3´-UTRs of nuclear-encoded mRNAs involved in the biogenesis of mitochondria have an intrinsic TEA. TEA is found in the 3´-UTR of the mRNAs encoding the α- and β-subunits of the rat H+-ATP syn…
A theoretical study of the low-lying states of the anionic and protonated ionic forms of urocanic acid
2000
A multistate second-order perturbation theory (MS−CASPT2) study of the lowest lying states in the electronic spectra of urocanic acid in vacuo is presented. The anionic trans and cis isomers, as well as the biologically important trans protonated ionic structure, are considered. The vertical and 0−0 excitation spectra were computed for each system at the MS−CASPT2/ANO-L level, describing the lowest lying ππ* and nπ* singlet and triplet states. In all three systems, a weakly absorbing ππ* singlet state was observed at ∼4.0 eV in the vertical excitation spectrum, suggesting both a novel assignment and an alternative explanation for the previously described wavelength dependent photochemistry …
Inhibition by cellular vacuolar ATPase impairs human papillomavirus uncoating and infection.
2014
ABSTRACT Several viruses, including human papillomaviruses, depend on endosomal acidification for successful infection. Hence, the multisubunit enzyme vacuolar ATPase (V-ATPase), which is mainly responsible for endosome acidification in the cell, represents an attractive target for antiviral strategies. In the present study, we show that V-ATPase is required for human papillomavirus (HPV) infection and that uncoating/disassembly but not endocytosis is affected by V-ATPase inhibition. The infection inhibitory potencies of saliphenylhalamide, a proven V-ATPase inhibitor, and its derivatives, as well as those of other V-ATPase inhibitors, were analyzed on different HPV types in relevant cell l…
Targeting V-ATPase in primary human monocytes by archazolid potently represses the classical secretion of cytokines due to accumulation at the endopl…
2014
The macrolide archazolid inhibits vacuolar-type H(+)-ATPase (V-ATPase), a proton-translocating enzyme involved in protein transport and pH regulation of cell organelles, and potently suppresses cancer cell growth at low nanomolar concentrations. In view of the growing link between inflammation and cancer, we investigated whether inhibition of V-ATPase by archazolid may affect primary human monocytes that can promote cancer by sustaining inflammation through the release of tumor-promoting cytokines. Human primary monocytes express V-ATPase, and archazolid (10-100nM) increases the vesicular pH in these cells. Archazolid (10nM) markedly reduced the release of pro-inflammatory (TNF-α, interleuk…