Complexation of Benzoic, 4-Methylbenzoic, and (R)- and (S)-2-Phenylpropanoic Acids and Their Conjugate Bases by 3A-Amino-3A-deoxy-(2AS,3AS)-β-cyclodextrin in Aqueous Solution

1995 ◽  
Vol 48 (6) ◽  
pp. 1117 ◽  
Author(s):  
R Dhillon ◽  
CJ Easton ◽  
SF Lincoln ◽  
J Papageorgiou
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Amino Group ◽  
Complexation Constants ◽  
Charged Species ◽  
Singly Charged ◽  
Conjugate Bases ◽  
Titration Study

A potentiometric titration study of the complexation of benzoic, 4-methylbenzoic, and (R)- and (S)-2-phenylpropanoic acids and their conjugate bases by 3A-amino-3A-deoxy-(2AS,3AS)-β- cyclodextrin, βCD3NH2, in which the amino group may be protonated to produce a singly charged species, βCD3NH3+, is reported. In aqueous solution at 298.2K and I = 0.10 mol dm-3 ( KCl ), the complexation constants for the complexes indicated have the values (in dm3 mol-1) shown in parentheses: benzoic acid.βCD3NH3+ (KHA = 110�10); benzoate.βCD3NH3+ (KA = 19�2); 4-methylbenzoic acid.βCD3NH3+ (KHA = 210�10); 4-methylbenzoate.βCD3NH3+ (KA = 21�3); (R)- and (S)-2-phenylpropanoic acid.βCD3NH3+ (KRHA = 64�8, KSHA = 57�5); (R)- and (S)-2-phenylpropanoate.βCD3NH3+ (KRA = 51�6, KSA = 32�6); and (R)- and (S)-2-phenylpropanoate.βCD3NH2 (KRA′ = 13�7; KSA′ is too small to quantify reliably). These complexation constants are substantially less than those for the host-guest complexes formed by the isomeric 6A-amino-6A-deoxy-β-cyclodextrin and also for those formed by β-cyclodextrin. The origins of these differences are discussed.

Cyclodextrin and Termethylated Cyclodextrin Complexation of Aromatic Carboxylic Acids and Their Conjugate Bases in Aqueous Solution: the Effect of Size, Hydrophobicity and Charge

1995 ◽  
Vol 48 (6) ◽  
pp. 1125 ◽  
Author(s):  
K Hendrickson ◽  
CJ Easton ◽  
SF Lincoln
Keyword(s):  
Aqueous Solution ◽  
Carboxylic Acids ◽  
Potentiometric Titration ◽  
Complexation Constants ◽  
Cyclodextrin Complexes ◽  
Aromatic Carboxylic Acids ◽  
Factors Influencing ◽  
Cyclodextrin Complexation ◽  
Binary Complexes ◽  
Conjugate Bases

For α- cyclodextrin ( αCD ), the complexation constants (K) for the formation of binary host-guest complexes ( HA.αCD ) are 750�60, 1070�60, 27�3 and 17�4 dm3 mol-1 when the guests (HA) are benzoic, 4-methylbenzoic and (R)- and (S)-2-phenylpropanoic acids, respectively, as determined by potentiometric titration in aqueous solution at 298.2 K and I = 0.10 mol dm-3 ( KCl ). For the analogous hexakis (2,3,6-tri-O-methyl)-α- cyclodextrin complexes ( HA.TMαCD ), K = 1580�150, 2890�130, 220�10 and 207�8 dm3 mol-1, and for the heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin complexes ( HA.TMαCD ), K = 200�20, 340�30, 129�5 and 170�10 dm3 mol-1. The binary complexes formed by the corresponding carboxylates (A-) are much less stable. Ternary host-guest α- cyclodextrin complexes (HA.αCD2) are also formed. These data, together with literature data for β- cyclodextrin, are discussed in terms of the factors influencing complexation.

Reaction of metallic nitrilotriacetates with histamine

1969 ◽  
Vol 47 (8) ◽  
pp. 1269-1273 ◽  
Author(s):  
A. L. Beauchamp ◽  
J. Israeli ◽  
H. Saulnier
Keyword(s):  
Potentiometric Titration ◽  
Formation Constants ◽  
Amino Group ◽  
Mixed Complex ◽  
Ph Values ◽  
Titration Curves ◽  
Terminal Amino ◽  
Complex Ion

Cu(II), Ni(II), Co(II), and Zn(II) nitrilotriacetates (MeX−) react with histamine nitrate (LH+) to form a protonated mixed complex MeXLH where the metal appears to be bound only to the tertiary imidazolic nitrogen of histaminium ion. At higher pH values the proton dissociates to yield a mixed complex ion MeXL− in which both the imidazolic nitrogen and the terminal amino group are coordinated. The formation constants of these species were calculated from the potentiometric titration curves.

A study of the decomposition behaviour of 12-tungstophosphate heteropolyacid in solution

2003 ◽  
Vol 81 (10) ◽  
pp. 1044-1050 ◽  
Author(s):  
Zhirong Zhu ◽  
Ruan Tain ◽  
Colin Rhodes
Keyword(s):  
Aqueous Solution ◽  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
Potentiometric Titration ◽  
Inductively Coupled Plasma ◽  
High Performance ◽  
Atomic Emission ◽  
Inductively Coupled ◽  
Vis Spectroscopy ◽  
Decomposition Behaviour

In this paper, the decomposition of H3PW12O40 in aqueous solution or in mixed solutions of water–ethanol or water–acetone is investigated by potentiometric titration and 31P NMR. Identification of the products from H3PW12O40 decomposition over a pH range of 1–12 was achieved using preparation high performance liquid chromatography (Pre-HPLC) combined with IR, UV–vis spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP). It is found that H3PW12O40 in aqueous solution decomposes in a stepwise fashion with increasing pH, with the following solution compositions: [PW12O40]3– (at pH ~ 1) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– (at pH 2.2) [Formula: see text] [PW12O40]3– + [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– + [P2W19O67]10– (at pH 3.5) [Formula: see text] [P2W21O71]6– + [PW11O39]7– + [P2W18O62]6– (at pH 5.4) [Formula: see text] [PW9O34]9– (at pH 7.3) [Formula: see text] PO43– + WO42– (pH > 8.3). In the first stages at pH < 8, H3PW12O40 decomposes partially with removal of W=O units. In the second stage at pH > 8, tungstophosphoric completely decomposes to PO43–. In contrast, the decomposition of H3PW12O40 is reduced, or the stability of the [PW12O40]3– anion is enhanced, in ethanol–water or acetone solution at pH < 8. Key words: 12-tungstophosphate heteropolyacid, decomposition behaviour, potentiometric titration, 31P NMR, preparation high performance liquid chromatography.

Kinetics, stoicheiometry, and mechanism in the bromination of aromatic heterocycles. I. Aqueous bromination of pyrazole, 1-methylpyrazole, and 3,5-dimethylpyrazole

1971 ◽  
Vol 24 (7) ◽  
pp. 1413 ◽  
Author(s):  
BE Boulton ◽  
BAW Coller
Keyword(s):  
Aqueous Solution ◽  
Potentiometric Titration ◽  
Electrode Potential ◽  
Rate Coefficients ◽  
Molecular Bromine ◽  
Aromatic Heterocycles ◽  
Dilute Aqueous Solution ◽  
Direct Attack ◽  
Rate Behaviour ◽  
Bromide Solutions

A procedure is described for monitoring the reactivity of a substrate towards bromine in aqueous bromide solutions, as a function of extent of reaction, by following the changes of electrode potential with time in the intervals between successive periods of electrolysis. ��� The title compounds show 1 : 1 stoicheiometry with substitution in the 4-position. The observed rate behaviour may be understood in terms of direct attack by molecular bromine on the neutral substrate molecules, rate coefficients for dilute aqueous solution at 25�C being: ����� k20(Br2+pyrazole) = 3.8x105 dm3 mol-1 s-1, kH/kD = 1.39;����� k20(Br2+1.methylpyrazole) = 8.0x105 dm3 mol-1 s-1;����� k20(Br2+3,5-dimethylpyrazole) = 1.4x109 dm3 mol-1 s-1, kH/kD = 1.08 Values of pKa(pyrazole-H+) = 2.58 and pKa(3,5-dimethylpyrazole-H+) = 4.11 were determined by potentiometric titration methods.

Gerüstumlagerungen bei einem Yliddiylphosphan-Tetrameren

1998 ◽  
Vol 53 (11) ◽  
pp. 1285-1293 ◽  
Author(s):  
Skeletal Rearrangements ◽  
Ylidediylphosphane Tetramer ◽  
Hans-Peter Schrödel ◽  
Alfred Schmidpeter ◽  
Heinrich Nöth
Keyword(s):  
Spin System ◽  
Nmr Spectra ◽  
Amino Group ◽  
Counter Ion ◽  
Singly Charged

Condensation of the bis(trimethylsilyl)ylide Ph3PC(SiMe3)2 with PX3 (X = Cl, Br) yields the ionic tetramers 4a,b of ylidediyl-halophosphanes. Their cations (Ph3PC)4P4X3+ possess a tetraphosphabicyclo[2.2.2]octane (or tetraphospha-barrelane) skeleton ([AC]3BD spin system in 31P NMR spectra). Reaction of 4a with AlCl3 or GaCl3 converts the singly charged cation into the tetracation (Ph3PC)4P44+ having a cubane structure ([AB]4 spin system in the 31P NMR spectum). SbCl5 oxidizes 4a to give the dication (Ph3PC)4P4Cl42+ (counter ion: SbCl52-) with the barrelane skeleton either preserved (7) or rearranged into a tetraphospha-bicylco[3.3.0]- octane structure 8. In the latter case the dication contains a central diphosphanedionium bridge. Replacement of a chloro-substituent in 4a by an amino group also gives rise to a further dissociation and a concomitant rearrangement. The resulting dications (Ph3PC)4P4NR2Cl2+ possess a tetraphospha-bicyclo-[3.2.1]octane structure (with eight nonequivalent phosphorus atoms).

Sign in / Sign up

Export Citation Format

Share Document