Search results for "Protonation"
showing 10 items of 583 documents
How deprotonation changes molecular self-assembly – an AFM study in liquid environment
2013
We study the influence of Alizarin Red S deprotonation on molecular self-assembly at the solid-liquid interface of the natural cleavage plane of calcite immersed in aqueous solution. To elucidate the adsorption details, we perform pH dependent high-resolution atomic force microscopy measurements. When Alizarin Red S is deposited onto calcite(10.4) in a liquid environment at an acidic pH of 5, weakly bound, ordered islands with a (3 x 3) superstructure are observed. A sharp structural transition is revealed when increasing the pH above 8. Above this pH, stable needle-like structures oriented along the [01.0] direction form on the surface. Comparing these results with potentiometric titration…
Ferrocene containing chelating ligands 3. Synthesis, spectroscopic characterization, electrochemical behaviour and interaction with metal ions of new…
1995
Abstract Ferrocenecarboxaldehyde reacts with 2-amino-benzoic acid, 2-amino-5-methyl-benzoic acid or 3-amino-2-naphthoic acid to give the corresponding Schiff-base derivatives 2-ferrocenylmethylidenimino-benzoic acid (1), 2-ferrocenylmethylidenimino-5-methyl-benzoic acid (2) and 3-ferrocenylmethylidenimino-2-naphthoic acid (3). 1, 2 and 3 are stable in the solid state but easily hydrolyze in solution. This hydrolysis has been studied kinetically in a methanol-water medium. In order to increase the stability in solution to use these compounds as ligands, the imino group from 1, 2 and 3 was reduced by NaBH4 to give the amino derivatives 2-ferrocenylmethylamino-benzoic acid (4), 2-ferrocenylmet…
Synthesis, crystal and molecular structure of η3-allylundecacarbonylosmium tetrafluoroborate
1989
Abstract The η3-allylundecacarbonylosmium tetrafluoroborate has been synthesized in high yield by treatment of Os3(CO)11MeCN with allyl alcohol and subsequent protonation. It has been studied by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pna21 (no. 33) with a 17.933(2), b 11.440(2), c 11.797(2)A and Dc 2.76 g cm−3 for Z = 4. A final R value of 0.046 (Rw = 0.083) based on 2067 reflections was obtained. The presence of the positively charged allyl ligand in the triosmium cluster lengthens the Os1Os2 and Os2Os3 bonds (0.057A) and 0.074 A, respectively) relative to the OsOs bonds in Os3(CO)12.
Solubility of some calcium-carboxylic ligand complexes in aqueous solution
1994
Insoluble species were identified in the systems Ca(2+)-hemimellitate, Ca(2+)-1,2,3,4-butanetetracarboxylate and Ca(2+)-citrate, and their solubilities were determined in aqueous solution at T = 25 degrees C. Values of pK(s0) were obtained for the species CaLH (L = benzene-1,2,3-tricarboxylate or hemimellitate), Ca(2)L (L = 1,2,3,4-butanetetracarboxylate), CaLH and Ca(3)L(2) (L = citrate), together with their dependence on ionic strength. Solid compounds were also characterized by thermogravimetry. The complex formation in solution for the system Na(+) - and Ca(2+)-hemimellitate was studied too.
Atypical titration curves for GaAl12Keggin-ions explained by a joint experimental and simulation approach
2018
Although they have been widely used as models for oxide surfaces, the deprotonation behaviors of the Keggin-ions (MeAl127+) and typical oxide surfaces are very different. On Keggin-ions, the deprotonation occurs over a very narrow pH range at odds with the broad charging curve of larger oxide surfaces. Depending on the Me concentration, the deprotonation curve levels off sooner (high Me concentration) or later (for low Me concentration). The leveling off shows the onset of aggregation before which the Keggin-ions are present as individual units. We show that the atypical titration data previously observed for some GaAl12 solutions in comparison to the originally reported data can be explain…
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…
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…
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 …