Anions titration

Active matter Hyamine titration Cationic/anionic titration... 

Assignment of the isotropically shifted signals observed for the CuNiSOD example discussed in the previous paragraph has been achieved by means of anion titrations (not discussed here) and nuclear Overhauser enhancement spectroscopy (NOESY), to be discussed next. In Figure 3.24B the CuNiSOD active site is depicted with histidine nitrogens and protons identified for the discussion of the NOESY results. The copper(II) ion is coordinated to the N ligand atoms of his46... 

Proton nmr halide anion titrations reveal that the ethyl- [79], propyl-[80] and butyl- [81] linked derivatives (Fig. 43) form complexes of 1 1 stoichiometry in acetonitrile solution. Stability constant determinations suggest that the ethyl derivative [79] exhibits selectivity for the chloride anion in preference to bromide or iodide. As the chain length increases, so the selectivity for chloride decreases and also the magnitude of the stability constant which is evidence for an anionic chelate effect with the chloride anion. Receptors containing larger aryl [81], [83], [84] and alkylamino spacers [85] (Fig. 43) form complexes of 2 1 halide anion receptor stoichiometry. 

Initial ll NMR titration data performed in DMS0-c/ /5%H20 revealed that whilst all other anions (chloride, bromide, hydrogen sulphate and benzoate) could be fitted to a 1 1 binding model, association constants could not be reliably calculated for fluoride and dihydrogen phosphate due to the sharp curve obtained. Consequently for these anions, titrations were repeated in a more competitive solvent mix of DMS0/25%H20, providing stability constants with 19 of 114 and 234 M 1 and with 20 11 and 20 M"1 respectively. 

Marks and co-workers provided a most valuable examination of absolute bond disruption enthalpies of various relevant metalorganic ligands X in Cp 2Sm-X. The data were obtained by anionic titration calorimetry in toluene (Fig. 4) [41 ]. Although the Ln-X bonds seem to be thermodynamically very stable, they usually display kinetic lability due to high ligand exchange ability, chelating and solubility effects. 

Carboxylates with weakly basic cationics. As for quats. Results of acid-base titration must be interpreted bearing in mind the degree of protonation or deprotonation in the product acid titration measures free bases plus carboxylate anions, titration with alkali measures free acids plus protonated amine cations. If only weak acids and bases are present, acid titration measures the bases and alkali titration the acids. 

Selection and Standardization of Titrants EDTA is a versatile titrant that can be used for the analysis of virtually all metal ions. Although EDTA is the most commonly employed titrant for complexation titrations involving metal ions, it cannot be used for the direct analysis of anions or neutral ligands. In the latter case, standard solutions of Ag+ or Hg + are used as the titrant. 

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

Analysis. The abiUty of silver ion to form sparingly soluble precipitates with many anions has been appHed to their quantitative deterrnination. Bromide, chloride, iodide, thiocyanate, and borate are determined by the titration of solutions containing these anions using standardized silver nitrate solutions in the presence of a suitable indicator. These titrations use fluorescein, tartrazine, rhodamine 6-G, and phenosafranine as indicators (50). 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the stmcture and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxyUc acids, and such solutions maybe titrated using strong base to a sharp phenolphthalein end point. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. EquiUbria of the type ... 

Thus quaternized thiazoles (170) consume two equivalents of OH on titration because the pseudo bases (171) ring open to (172), which form anions (173). Quaternized oxazoles (174) are readily attacked by hydroxide to give open-chain products such as (175) (74AHC(17)99), and quaternized 1,3,4-oxadiazoles behave similarly. Quaternary isothiazoles (e.g. 176) are cleaved by hydroxide (72AHC(l4)l), as are 1,2,4-thiadiazolium salts (177 178). 

In the present work the acid-base surface properties of three Al O samples for a chromatography are investigated acidic (I), basic (II) and neutral (III) ones with the using of heterogeneous titration of their suspensions by HCl and NaOH solutions. To establish the correlations between the acid-base and adsoi ption properties studied Al O the representatives of cationic dyes -diamond green (DG), fuchsine (F) and anionic dyes - eriochrom black T and chromic dark blue have been used. 

Choline chloride [67-48-1] M 139.6, m 302-305 (dec). Extremely deliquescent. Purity checked by AgN03 titration or by titration of free base after passage through an anion-exchange column. Crystd from absolute EtOH, or EtOH-diethyl ether, dried under vacuum and stored in a vacuum desiccator over P2O5 or Mg(C104)2. 

If a sample contains groups that can take up or lose a proton, (N//, COO//), then one must expect the pH and the concentration to affect the chemical shift when the experiment is carried out in an acidic or alkaline medium to facilitate dissolution. The pH may affect the chemical shift of more distant, nonpolar groups, as shown by the amino acid alanine (38) in neutral (betaine form 38a) or alkaline solution (anion 38b). The dependence of shift on pH follows the path of titration curves it is possible to read off the pK value of the equilibrium from the point of inflection... 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

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